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1 Introduction
New Product Design concept starts with conceptualization of ‘Product Idea’. The product
idea typically takes into consideration of customer requirements.
Design for manufacture (DFM) has evolved over the past decade or so from a general
awareness of the need to consider more thoroughly the ease and economics of manufacture
into a set of structured strategies, methodologies, and tools for evaluating a strategies,
methodologies, and tools for evaluating a design for its manufacturability. Spiraling costs and
the emergence of global competition have put an emphasis on design-to-cost strategies,
where cost is elevated to the same level of concern as performance and function, from the
moment the new product is conceived. 1 Design-to cost strategies require cost estimates at
each stage in the product development process. However, the average engineering designer
knows little about the cost of materials and processes implied and specified through the
design drawings. Manufacturing options even for simple parts are numerous, and the effects
on both recurring costs (piece-part costs) and nonrecurring costs (tooling costs) are dramatic.
Rapid cost estimating systems are necessary to enable product designers and product
development teams to make sound decisions early in the conceptual design phase and not, as
is often the case, provide fodder for later value-analysis teams) The conscientious design
engineer is interested in the existence of any design tradeoffs that can be made to help
converge on the most economical approach. Many product manufacturers outsource much of
their primary manufacturing. In some cases, they will only carry out the final assembly
process or even just final distribution and marketing. The product with designing the highest
quality product for the lowest cost manufacture by local, national, or offshore lowest cost
manufacture by local, national, or offshore contractors. Access and understanding of cost
even at the conceptual design stage of the product development process is key to the
realization of competitive world-class products.
A manufacturing system is composed of a large number of distinct processes which all
influence product cost, product quality and productivity of the system. The interactions
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between these various facets of a manufacturing system are complex, and decisions made
concerning one aspect have ramifications which extend to the others.
A product is usually created by design engineers who may not be familiar with
manufacturing and assembly processes of the product. With insufficient communication with
other engineers and manufacturing functions, design engineers may design a product that will
lead to severe problems during manufacturing and assembly operations. These problems
include failures of meeting dimensions and tolerance requirements, or difficulty in producing
the product in a cost effective way.
Contrary to the traditional sequential approach to design, the distinct processes in a
concurrent product development environment are accomplished simultaneously. Concurrent
design involves the simultaneous consideration and integration of various engineering
activities throughout the product life cycle. By bringing downstream expertise of processes to
the design stage, concurrent engineering will result in fewer design changes and hence lower
cycle time and production cost. According to the experience of Ford Motors Co.,
approximately 70% of the manufacturing cost is dictated by decisions made at the design
stage, although design only accounts for 5% of the total product development expenses
(Plastics World, 1988). This clearly indicates the need of an increased effort on design by
considering the products’ requirements of manufacturing and assembly processes. To avoid
the drawbacks of the conventional product development approach and to take advantage of
the concurrent engineering approach, a framework of concurrent engineering, which models
the engineering design procedure, is developed. The framework consists of four design steps:
design formation, product modeling and representation, Design for Assembly and
Manufacture (DFA and DFM) critique and evaluation, and design optimization. Feature-
based design provides the advantage of using features, which are high level entities closely
related to their manufacturing and assembly operations, for representing products.
The principles of design for manufacturability (DFM) and its application are not really new.
Awareness of the importance of designing products for easy manufacture has existed in
clever design and manufacturing engineers since product design and manufacturing activities
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originated. However, use of the term design for manufacturability, recognition of it as a
worthwhile engineering approach, and development of an organized DFM methodology are
more recent. The following are some highlights from the history of designing products for
easier manufacture. It is entirely possible for a design engineer, aware of the advantages of
designing for manufacturability to work independently in optimizing the product design for
ease of manufacture. However, most current DFM specialists advocate a team approach in
applying DFM. Essentially, this means that the design and manufacturing people work
together to gain the benefits of manufacturing knowledge and experience that the designer
may not have and to ensure that the product is both functional and manufacturable.
DFM is not a fixed system. This system is continually being developed, both in
university research projects and by a number of consultants and within companies. The
objectives of almost all developments are to make guidelines more accessible to designers
and more easily applied. Additionally, and more important, evaluations are put on each
guideline so that the designer can determine how much cost gain can be achieved if the
guideline is incorporated. All these advances depend on the use of computers.
Computerization is the developing movement in DFM.
The following principles, applicable to virtually all manufacturing processes, will aid
designers in specifying components and products that can be manufactured at minimum cost.
1. Simplicity. Other factors being equal, the product with the fewest parts, the least
intricate shape, the fewest precision adjustments, and the shortest manufacturing
sequence will be the least costly to produce. Additionally, it usually will be the most
reliable and the easiest to service.
2. Standard materials and components. Use of widely available materials and off-the-
shelf parts enables the benefits of mass production to be realized by even low-
unitquantity products. Use of such standard components also simplifies inventory
management, eases purchasing, avoids tooling and equipment investments, and speeds
the manufacturing cycle.
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3. Standardized design of the product itself. When several similar products are to be
produced, specify the same materials, parts, and subassemblies for each as much as
possible. This procedure will provide economies of scale for component production,
simplify process control and operator training, and reduce the investment required for
tooling and equipment.
4. Liberal tolerances. Although the extra cost of producing too tight tolerances has
been well documented, this fact is often not appreciated well enough by product
designers. The higher costs of tight tolerances stem from factors such as (a) extra
operations such as grinding, honing, or lapping after primary machining operations,
(b) higher tooling costs from the greater precision needed initially when the tools are
made and the more frequent and more careful maintenance needed as they wear, (c)
longer operating cycles, (d) higher scrap and rework costs, (e) the need for more
skilled and highly trained workers, (f) higher materials costs, and (g) more sizable
investments for precision equipment.
5. Use of the most processible materials. Use the most processible materials available
as long as their functional characteristics and cost are suitable. There are often
significant differences in processibility (cycle time, optimal cutting speed, flow
ability, etc.) between conventional material grades and those developed for easy
processibility. However, in the long run, the most economical material is the one with
the lowest combined cost of materials, processing, and warranty and service charges
over the designed life of the product.
6. Teamwork with manufacturing personnel. The most producible designs are
provided when the designer and manufacturing personnel, particularly manufacturing
engineers, work closely together as a team or otherwise collaborate from the outset.
7. Avoidance of secondary operations. Consider the cost of operations, and design in
order to eliminate or simplify them whenever possible. Such operations as deburring,
inspection, plating and painting, heat treating, material handling, and others may
prove to be as expensive as the primary manufacturing operation and should be
considered as the design is developed. For example, firm, nonambiguous gauging
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points should be provided; shapes that require special protective trays for handling
should be avoided.
8. Design appropriate to the expected level of production. The design should be
suitable for a production method that is economical for the quantity forecast. For
example, a product should not be designed to utilize a thin-walled die casting if
anticipated production quantities are so low that the cost of the die cannot be
amortized. Conversely, it also may be incorrect to specify a sand-mold aluminum
casting for a mass-produced part because this may fail to take advantage of the labor
and materials savings possible with die castings.
9. Utilizing special process characteristics. Wise designers will learn the special
capabilities of the manufacturing processes that are applicable to their products and
take advantage of them. For example, they will know that injection-molded plastic
parts can have color and surface texture incorporated in them as they come from the
mold, that some plastics can provide “living hinges,” that powder-metal parts
normally have a porous nature that allows lubrication retention and obviates the need
for separate bushing inserts, etc. Utilizing these special capabilities can eliminate
many operations and the need for separate, costly components.
10. Avoiding process restrictiveness. On parts drawings, specify only the final
characteristics needed; do not specify the process to be used. Allow manufacturing
engineers as much latitude as possible in choosing a process that produces the needed
dimensions, surface finish, or other characteristics required.
The advantages of DFM are included:
a) Reduce Time to Market
b) Reduce manufacturing time
c) Reduce rework
d) Improve design efficiency
e) Helps in Rapid Prototyping
f) Better cost control
g) Less time in product testing
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2 Product Specification
The product that has been chosen for this study is Toaster. The function of this product is to
Toast breads by transport the heat to the breads with the heated element made from Tungsten
to change the electricity energy to the heat.
Toaster is typically a small Mechanic-electric kitchen appliance designed to toast multiple
types of Bread products. A typical modern two-slice toaster draws from 600 to 1200 Watts
and makes toast in 1 to 3 minutes. There are also non-electrical toasters that can be used to
toast bread products over an open fire or flame.
Figure 2.0: Isometric view from New Designed Toaster
Specification:
• Metallic body
• Plastic bottom cover
• Environment protective
• Overall parts = 32 parts
• Different parts = 23 parts
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2.1 Illustration the main parts of product in an exploded/disassembly view
As it is obvious in the figure 2.0, the main components of Toaster has been exhibited.
Figure 2.1: Exploded view of toaster and illustration of main components.
The detailed and some fasteners has been omitted.
2.2 Objectives
In this project we intend to first, detect the best material and process for five components of
our product. By Appling the Boothroyd-Dewhurst DFM methodology; Determine what type
of materials are used in the new design of the product and the cause of that. How they are
made and why those particular manufacturing processes are used, by which the parts can be
made economically. The goal of selection materials are to minimize the cost of
manufacturing and materials and also to minimize waste in manufacturing furthermore to
maximize the performance of the part and safety of the product and also to maximize in the
product life cycle.
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2.3 Selection of product’s components
2.3.1 Total number of parts
The Toaster contains of 23 different parts which is introduced in the table below.
Table 3.1: Introduction of Toaster Components
PartIDNO.
picture
Nameofpart
1 Front plate
2 Small Fire proof plate
3 Cylindrical Guide
4 Spring
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PartIDNO.
picture
Nameofpart
5 moving system
6 U shape
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Plastic part of U plate
female
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Plastic part of U plate
male
10
PartIDNO.
picture
Nameofpart
9
Heater board left
(Standard Part)
10
Heater board middle
(Standard Part)
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Heater board right
(Standard Part)
12 Back plate
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PartIDNO.
picture
Nameofpart
13 connector
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Electrical kit
(Standard Part)
15 Timer regulator
16 Stopper switch
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PartIDNO.
picture
Nameofpart
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Switch
(Standard part)
18 wire of plug
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Electrical connection
snap-fit
20 Bottom cover
13
PartIDNO.
picture
Nameofpart
21 Top Cover
22 Handling plastic part
23 Holder of wire
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2.3.2 Introduction of redesigned parts
Based on product chosen in our Design for Assembly (DFA) assignment we need to select 5
different parts from the product and illustrate them in a detail manner:
1. Front plate
2. Moving system
3. Electrical connection snap-fit
4. Bottom cover
5. Top Cover
Front plate
Easy to manipulate.
Thickness = 10 mm
Size = 120 mm
Justification: The process of this part
has been changed and it has combined
two functions with each other. Before the
changes this part just guided the moving
system. Also it had 3 more punching
processes which is eliminated in this
new design.
Function: Main role of front plate is
Holding the heater board and moving
system. The other role is to guide the
moving system and cover the inner side
of toaster.
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Moving system
Easy to manipulate.
Thickness = 100 mm
Size = 150 mm
Justification: this part have been
contained from 4 deferent part but same
material, in new design all the parts have
been design by bending process with just
one sheet metal.
Function: Holding the handling plate,
Magnet, Bread’s Holder. Also sliding
movement to move the breads down and
return it up after toasting Operation.
Electrical connection snap-fit
Easy to manipulate.
Thickness = 4 mm
Size = 12 mm
Justification: The previous process for
this part was soldering the wire to the
switch, by designing the snap fit
connector and manufacturing it. It would
be beneficial in cost and time wastage.
Function: Fastening the wire of plug to
the switch.
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Bottom cover
Easy to manipulate.
Thickness = 15 mm
Size = 250 mm
Justification: The bottom cover in new
design, has some snap fits instead of
using screws for fastening, also its
material has been changed from metallic
to the plastic to improve the time and
cost of manufacturing by improving the
time of manufacturing
Function: To cover and maintain all
assembled parts and the main cover
Top Cover
Easy to manipulate.
Thickness = 300 mm
Size = 250 mm
Justification: The Top cover also has
been changed from the premier design
by changing the material and design
also. This part changed from
combination of plastic and metallic of 4
parts to one plastic part.
Function: Covering all Sub assembly
parts.
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3 Suitable materials for each par
3.1 Type of material
3.1.1 Cast Iron:
Cast irons represent the largest quantity of all metals cast, and they can be cast easily into
intricate shapes. They generally possess several desirable properties, such as wear resistance,
high hardness, and good machinability.
3.1.2 Carbon Steels
Improvement hardening, strength, hardness, and wear resistance; it reduces ductility, ability
to weld, and toughness.
• Low Carbon Steels (Mild Steel):
Mild steel (<0.25% carbon) is the most commonly used, readily welded construction
material, and has the following typical mechanical properties (Grade 43A in BS4360; ability
to weld structural steel):
• Tensile strength, 430 N/mrn2
• Yield strength, 230 N/m2
• Elongation, 20%
• Tensile modulus, 210 KN/mm2
• Hardness, 130 DPN
None steel exceeds the tensile modulus of mild steel. Therefore, in applications in which
rigidity is a limiting factor for design (e.g., for storage tanks and distillation columns), high-
strength steels have no advantage over mild steel. Stress concentrations in mild steel
structures are relieved by plastic flow and are not as critical in other, less-ductile steels. Low-
carbon plate and sheet are made in three qualities: fully killed with silicon and aluminum,
semikilled (or balanced), and rimmed steel. Fully killed steels are used for pressure vessels.
Most general-purpose structural mild steels are semikilled steels. Rimming steels have
minimum amounts of deoxidation and are used mainly as thin sheet for consumer
applications.
The strength of mild steel can be improved by adding small amounts (not exceeding 0.1 %)
of niobium, which permits the manufacture of semikilled steels with yield points up to 280
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N/mm. By increasing the manganese content to about 1.5% the yield point can be increased
up to 400 N/mm2. Thus provides better retention of strength at elevated temperatures and
better toughness at low temperatures.
• Corrosion Resistance:
Equipment from mild steel usually is suitable for handling organic solvents, with the
exception of those that are chlorinated, cold alkaline solutions (even when concentrated),
sulfuric acid at concentrations greater than 88% and nitric acid at concentrations greater than
65% at ambient temperatures.
Mild steels are rapidly corroded by mineral acids even when they are very dilute (pH less
than 5). However, it is often more economical to use mild
steel and include a considerable corrosion allowance on the thickness of the apparatus. Mild
steel is not acceptable in situations in which metallic contamination of the product is not
permissible.
• Heat Resistance:
The maximum temperature at which mild steel can be usedis 550°C. Above this temperature
the formation of iron oxides and rapid scaling makes the use of mild steels uneconomical. For
equipment subjected to high loadings at elevated temperatures, it is not economical to use
carbon steel in cases above 450°C because of its poor creep strength. (Creep strength is time-
dependent, with strain occurring under stress.)
• Low Temperatures
At temperatures below 10°C the mild steels may lose ductility, causing failure by brittle
fracture at points of stress concentrations (especially at welds) [8,9]. The temperatures at
which the transition occurs from ductile to
brittle fraction depends not only on the steel composition, but also on thickness.
Stress relieving at 600-7OO'C for steels decreases operation at temperatures some 20°C
lower. Unfortunately, suitable furnaces generally are not available, and local stress relieving
of welds, etc., is often not successful because further stresses develop on cooling.
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3.1.3 High-Carbon Steels
High carbon steels containing more than 0.3% are difficult to weld, and nearly all production
of this steel is as bar and forgings for such items as shafts, bolts, etc Theseitems can be
fabricated without welding.
• Low-Temperature Ductility:
Nickel is the alloying element used for improving low-temperature ductility. The addition of
1 .5% nickel to 0.25% Cr/0.25% Mo steels provides satisfactory application for moderately
low temperatures down to about -50°C.
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Heat treatment by quenching and tempering improves the low temperature ductility of steels
such as 0.5 Cr, 0.5% Mo, 1% Ni Type V. For lower- temperature application (below -
196"C), up to 9% nickel is used as the sole alloying element.
3.1.4 High-Carbon, Low-Alloy Steels:
High-carbon (about 0.4%), low-alloy steels that are not weldable usually are produced as
bars and forging for such items as shafting, high-temperature bolts and gears and ball bearing
components. These steels can be less drastically quenched and tempered to obtain tensile
strengths of at least 1500 N/mm2, thus minimizing the danger of cracking.
• Properties of High-Alloy Steels:
Stainless and heat-resisting steels containing at least 18% by weight chromium and 8%
nickel are in widespread use in industry. The structure of these steels is changed from
magnetic body centered cubic or ferritic crystal structure to a nonmagnetic, facecentered
cubic or austenitic crystal structure. 3.5.1 Chromium Steels (400 Series), Low-Carbon
Ferritic (Type 405): 12-13% Chromium. The main use of this type steel is for situations in
which the process material may not be corrosive to mild steel, yet contamination due to
rusting is not tolerable and temperatures or conditions are unsuitable for aluminum. However,
prolonged use of these steels in the temperature range of 450 to 550°C causes low-
temperature embrittlement of most ferritic steels with more than 12% chromium.
3.1.5 Alloy Steel
Steel classification is important in understanding what types are used in certain
applications and which are used for others. For example, most commercial steels are
classified into one of three groups: plain carbon, low-alloy, and high-alloy. Steel
classification systems are set up and updated frequently for this type of information.
Generally, carbon is the most important commercial steel alloy. Increasing carbon
content increases hardness and strength andimproves hardenability. But carbon also increases
brittleness and reduces weldability because of its tendency to form martensite. This means
carbon content can be both a blessing and a curse when it comes to commercial steel.
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And while there are steels that have up to 2 percent carbon content, they are the exception.
Most steel contains less than 0.35 percent carbon. To put this in perspective, keep in mind
that’s 35/100 of 1 percent.
Now, any steel in the 0.35 to 1.86 percent carbon content range can be hardened using a heat-
quench-temper cycle. Most commercial steels are classified into one of three groups:
• Plain carbon steels
• Low-alloy steels
• High-alloy steels
3.1.6 Low-alloy Steels
When these steels are designed for welded applications, their carbon content is usually below
0.25 percent and often below 0.15 percent. Typical alloys include nickel, chromium,
molybdenum, manganese, and silicon, which add strength at room temperatures and increase
low-temperature notch toughness.
These alloys can, in the right combination, improve corrosion resistance and influence
the steel’s response to heat treatment. But the alloys added can also negatively influence
crack susceptibility, so it’s a good idea to use low-hydrogen welding processes with them.
Preheating might also prove necessary. This can be determined by using the carbon
equivalent formula, which we’ll cover in a later issue.
3.1.7 High-alloy Steels
For the most part, we’re talking about stainless steel here, the most important commercial
high-alloy steel. Stainless steels are at least 12 percent chromium and many have high nickel
contents. The three basic types of stainless are:
• Austenitic
• Ferritic
• Martensitic
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Martensitic stainless steels make up the cutlery grades. They have the least amount of
chromium, offer high hardenability, and require both pre- and postheating when welding to
prevent cracking in the heat-affected zone (HAZ).
Ferritic stainless steels have 12 to 27 percent chromium with small amounts of austenite-
forming alloys.
Austenitic stainless steels offer excellent weldability, but austenite isn’t stable at room
temperature. Consequently, specific alloys must be added to stabilize austenite. The most
important austenite stabilizer is nickel, and others include carbon, manganese, and nitrogen.
3.1.8 Stainless Steels
They primarily are characterised by their corrosion resistance, high strength and
ductility, and high chromium content. They are called stainless because, in the presence of
oxygen (air), they develop a thin, hard, adherent film of chromium oxide that protects the
metal from corrosion. This protective film builds up again in the event that the surface is
scratched.
3.1.9 Tool and Die Steels
Tool and die steels are specially alloyed steels designed for high strength, impact
toughness, and wear resistance at room and elevated temperature. They commonly are used
in the forming and machining of metals.
Aluminum and its’ alloys
Aluminum is the world’s most abundant metal and does the third most common
element comprise 8% of the earth’s crust. The versatility of aluminum makes it the most
widely used metal after steel.
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Aluminum is derived from the mineral bauxite. Bauxite is converted to aluminum oxide
(alumina) via the Bayer Process. The alumina is then converted to aluminum metal using
electrolytic cells and the Hall-Heroult Process.
Pure aluminum is soft, ductile, and corrosion resistant and has a high electrical
conductivity. It is widely used for foil and conductor cables, but alloying with other elements
is necessary to provide the higher strengths needed for other applications. Aluminum is one
of the lightest engineering metals, having strength to weight ratio superior to steel. By
utilizing various combinations of its advantageous properties such as strength, lightness,
corrosion resistance, recyclability and formability, aluminum is being employed in an ever-
increasing number of applications. This array of products ranges from structural materials
through to thin packaging foils.
Aluminum is most commonly alloyed with copper, zinc, magnesium, silicon,
manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and
nickel are also made and iron is invariably present in small quantities.
There are over 300 wrought alloys with 50 in common use. They are normally
identified by a four figure system which originated in the USA and is now universally
accepted.
Aluminum has a density around one third that of steel or copper making it one of the
lightest commercially available metals. The resultant high strength to weight ratio makes it an
important structural material allowing increased payloads or fuel savings for transport
industries in particular.
Pure aluminum doesn’t have a high tensile strength. However, the addition of alloying
elements like manganese, silicon, copper and magnesium can increase the strength properties
of aluminum and produce an alloy with properties tailored to particular applications.
Aluminum is well suited to cold environments. It has the advantage over steel in that
its’ tensile strength increases with decreasing temperature while retaining its toughness. Steel
on the other hand becomes brittle at low temperatures
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When exposed to air, a layer of aluminum oxide forms almost instantaneously on the
surface of aluminum. This layer has excellent resistance to corrosion. It is fairly resistant to
most acids but less resistant to alkalis.
The thermal conductivity of aluminum is about three times greater than that of steel.
This makes aluminum an important material for both cooling and heating applications such as
heat-exchangers. Combined with it being non-toxic this property means aluminum is used
extensively in cooking utensils and kitchenware.
Along with copper, aluminums has an electrical conductivity high enough for use as an
electrical conductor. Although the conductivity of the commonly used conducting alloy
(1350) is only around 62% of annealed copper, it is only one third the weights and can
therefore conduct twice as much electricity when compared with copper of the same weight.
From UV to infra-red, aluminums is an excellent reflector of radiant energy. Visible
light reflectivity of around 80% means it is widely used in light fixtures. The same properties
of reflectivity makes aluminums ideal as an insulating material to protect against the sun’s
rays in summer, while insulating against heat loss in winter.
Aluminum can be severely deformed without failure. This allows aluminums to be
formed by rolling, extruding, drawing, machining and other mechanical processes. It can also
be cast to a high tolerance.
Alloying, cold working and heat-treating can all be utilised to tailor the properties of
aluminum.
The tensile strength of pure aluminum is around 90 MPa but this can be increased to
over 690 MPa for some heat-treatable alloys
3.1.10 Copper and its’ alloys:
Copper is an excellent electrical conductor. Most of its uses are based on this property
or the fact that it is also a good thermal conductor. However, many of its applications also
rely on one or more of its other properties. For example, it wouldn't make very good water
and gas pipes if it were highly reactive. On this page, we look at these other properties:
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• a good electrical conductor
• a good thermal conductor
• corrosion resistant
• antibacterial
• easily joined
• ductile
• tough
• non magnetic
• attractive colour
• easy to alloy
• recyclable
• catalytic
Copper is low in the reactivity series. This means that it doesn't tend to corrode. Again,
this is important for its use for pipes, electrical cables, saucepans and radiators. However, it
also means that it is well suited to decorative use. Jewellery, statues and parts of buildings
can be made from copper, brass or bronze and remain attractive for thousands of years.
Copper is a ductile metal. This means that it can easily be shaped into pipes and drawn
into wires. Copper pipes are lightweight because they can have thin walls. They don't corrode
and they can be bent to fit around corners. The pipes can be joined by soldering and they are
safe in fires because they don't burn or support combustion.
Copper and copper alloys are tough. This means that they were well suited to being
used for tools and weapons. Imagine the joy of ancient man when he discovered that his
carefully formed arrowheads no longer shattered on impact. The property of toughness is
vital for copper and copper alloys in the modern world. They do not shatter when they are
dropped or become brittle when cooled below 0 °C.
Copper can be recycled without any loss of quality. 40% of the world's demand is met
by recycled copper.
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3.1.11 Zinc and Alloys:
Zinc is a metal that is fourth most utilized industrially, after iron, aluminum, and copper. It
uses for galvanizing iron, steel sheet, and wire. And also it applies as a material in casting.
Zinc based alloys are used extensively in die casting for making such products as fuel pumps
and grills for automobiles, components for household appliances such as vacuum cleaners
and washing machines, kitchen equipment, various machinery parts, and photoengraving
equipment. Another use for zinc is in superplastic alloys that can be formed by methods used
for forming plastics or metals.
3.1.12 Magnesium Alloys:
Controls the shape of inclusions and improves toughness in high strength, low-alloy steels; it
deoxidizes steels. And it has the same effects as Cerium.
3.1.13 Titanium and its’ Alloys
Titanium does not occur free in Nature. However, when combined with other
elements, it is quite abundant, occurring in small amounts in most of the
volcanic,sedimentary and metamorphic rocks. Its more important minerals are ilmenite,
rutile, arizonite (iron titanate), brookite, anatase, leucochene (titanium dioxide), perovskite
(calcium titanate), and others. The first two have commercial importance, and can be found
in deposits spread all over the world. There are important rutile and limonite deposits in
Australia, Argentina, USA, Central Africa, Brazil, Canada, Egypt, India and Norway. The
largest well-known deposits of rutile are located in Australia.
Titanium and its alloys are relatively new engineering metals since they have been in use
only since about 1952. They are extremely attractive materials for engineers because they
have a high strength to weight ratio, high elevated temperature properties to about 550o
C,
and excellent corrosion resistance particularly in oxidising acids and chloride media. This
metal is being increasingly used for marine applications. Its resistance to seawater attack
combined with its mechanical properties make it a prime choice for equipment operating
within the sea or transferring seawater.
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Titanium is not an 'exotic' metal; it is the fourth most abundant structural metal in
the earth's crust, and the ninth industrial metal. This metal has become the prime selection
for a wide range of critical and demanding applications.
Titanium Alloys are generally divided into three groups (Alpha, Alpha-Beta and
Beta). The Alpha group contain most importantly aluminum and tin. They can also contain
molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon. Alpha alloys
are not suitable for heat treatment. Alpha alloys are used for aircraft parts and cryogenic
equipment. The Alpha-Beta group can be strengthened by heat treatment. The alloys are used
in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware. The
Beta Alloys have good hardenability. Beta alloys are slightly more dense than other titanium
alloys, having densities ranging from 4800 to 5050 kg/m3
. They are the least creep resistant
alloys, they are weldable, and can have yield strengths up to 1345 x 106
Pa.(Solution treated
and age hardened) Beta alloys are the smallest group. They are used for heavier duty
purposes on aircraft.
3.1.14 Nickel Alloys
Improves strength, toughness, corrosion resistance and hardenability. Nickel alloys
are used in high temperature applications (such as jet engine components, rockets, and
nuclear power plants), in coins, and in marine applications.
3.1.15 Refractory Alloys
There are four refractory metals: Molybdenum, Niobium, Tungsten, and Tantalum.
These metals are called refractory because of their high melting points. More than most other
metals and alloys, the refractory metals maintain their strength at elevated temperatures.
Therefore, they are of great importance in rocket engines, gas turbines, and various other
aerospace applications; in the electronic, nuclear-power, and chemical industries; and as tool
and die materials.
28
3.1.16 Thermoplastics
Thermoplastics soften when heated and harden again to their original state when
cooled. This allows them to be molded to complex shapes. Most accept coloring
agents and fillers, and many can be blended to give a wide range of physical, visual
and tactile effects. Their sensitivity to sunlight is decreased by adding UV filters, and
their flammability is decreased by adding flame retardants. The common
thermoplastics are listed in the adjacent table. They include polyolefin (polyethylene,
polypropylene), PVCS, polystyrenes, acrylics and certain polyesters (PET and PBT).
Some are crystalline, some amorphous, some a mixture of both. The properties of
thermoplastics can be controlled by chain length (measured by molecular weight), by
degree of crystallinity and by blending and plasticizing. As the molecular weight
increases, the resin becomes stiffer, tougher, and more resistant to chemicals, but it is
more difficult to mold to thin-wall sections. For thin-walls, choose a low molecular
weight resin; for higher performance, choose one with higher molecular weight.
Crystalline polymers tend to have better chemical resistance, greater stability at high
temperature and better creep resistance than those that are amorphous. For
transparency the polymer must be amorphous; partial crystallinity gives translucency.
The most transparent polymers are Acrylics, PC, PS and PET.
Some polymers crystallize faster than others: polyethylene crystallizes quickly
but polyesters do so more slowly – they remain amorphous under normal cooling
rates. Crystalline polymers have a more or less sharp melting point, which must be
exceeded for molding. Amorphous polymers do not; instead they progressively soften
and become more fluid as temperature increases above the glass transition
temperature; they must be heated above this temperature for extrusion and injection
molding. The processing force required to generate flow decreases slowly as
temperature rises above the glass transition temperature. Amorphous polymers have
greater impact strength and relatively low mold shrinkage. Semi-crystalline polymers
have higher shrinkage because of the volume change on crystallization.
29
Holes and ribs reduce the effect of shrinkage in a thermoplastic part. Areas near
the filling gate tend to shrink less than areas farther away. Shrinkage increases with
wall thickness and decreases with higher molding pressures. Fiber filled polymers
shrink less in the direction of flow because the fibers line up in this direction; the
shrinkage in the cross-flow direction is 2–3 times more than in the flow direction.
High service temperatures can cause shrinking in some semi-crystalline materials.
Fillers, or additives, are used to tailor certain properties of the composite such as
density, colour, flame/smoke retardance, moisture resistance and dimensional
stability. Most thermoplastics can be recycled.
3.1.17 Thermosets
If you are a do-it-yourself type, you have Araldite in your toolbox – two tubes,
one a sticky resin, the other an even stickier hardener. Mix and warm them so they
react to give a stiff, strong, durable polymer, stuck to whatever it was put on. Araldite
typifies thermosets – resins that polymerize when catalyzed and heated; when
reheated they do not melt – they degrade. The common thermosets are listed in the
table here. The first commercial thermoset was Bakelite, a trade-name for a phenolic
resin. Polyurethane thermosets are produced in the highest volume; polyesters come
second; phenolics, epoxies and silicones follow, and – not surprisingly – the cost rises
in the same order. Epoxies are two-part system that – when mixed – undergo a mildly
exothermic reaction that produces cross-linking. Phenolics are cross-linked by the
application of heat or heat and pressure. Vulcanization of rubber, catalyzed by the
addition of sulfur, can change the soft rubber of a latex glove to the rigid solid of
ebonite, depending on the level of cross-linking. Once shaped, thermosets cannot be
reshaped.
Thermosets have greater dimensional stability than thermoplastics; they are
used where there is a requirement for high temperature resistance and little or no
creep. Most are hard and rigid, but they can be soft and flexible (like natural and
synthetic rubber, as described above). Phenolics are most used where close-tolerance
30
applications are necessary, polyesters (often combined with glass fibers) where high
strength with low shrinkage is wanted.
Thermosets are shaped by compression molding, resin transfer molding,
injection molding, pultrusion and casting. They duplicate the mold finish and are
relatively free from flow lines and sink marks, depending on the mold design – high
gloss, satin or sand-blasted finishes are possible, and raised lettering can be molded in.
Molding can be adapted to low volume production by using low cost molds; but
higher production volumes, up to a million or greater, are economical only with
expensive molds that allow fast heating, cooling and extraction. Phenolics can only be
molded in black or brown; urea, melamine, alkyd and polyester compounds are
available in a wider range of colors. The fluidity of some thermosets before molding
allows them to take up fine detail, and to penetrate between fibers to create
composites. Most high-performance polymer composites have thermosetting matrix
materials. Dough and sheet molding compounds (dmc and smc) use polyesters;
filament-wound carbon or glass use epoxies as the matrix to give the highest
performance of all. Thermosets cannot be recycled.
3.1.18 Elastomers
Elastomers were originally called “rubbers” because they could rub out pencil
marks – but that is the least of their many remarkable and useful properties. Unlike
any other class of solid, elastomers remember their shape when they are stretched –
some, to five or more times their original length – and return to it when released. This
allows conformability – hence their use for seals and gaskets. High damping
elastomers recover slowly; those with low damping snap back, returning the energy it
took to stretch them – hence their use for springs, catapults, and bouncy things.
Conformability gives elastomers high friction on rough surfaces, part of the reason
(along with comfort) that they are used for pneumatic tires and footwear. Elastomers
are easy to foam, giving them the comfort of cushions, and increasing even further
their ability to conform to whatever shape is pressed against them.
31
Almost all engineering solids have elastic moduli (measuring their stiffness)
between 1 and 1000 Gpa. Elastomers are much less stiff – between 0.0001 and 1 Gpa.
This low stiffness, their ability to stretch and to remember their original shape all
derive from their structure. The molecules in an elastomer are long chains of linked
carbon (or, in silicones, silicon-oxygen chains), with hydrogen, nitrogen, chlorine or
fluorine attached to the sides. The carbon atoms that link to form the chain are
strongly bonded to each other, but the side-branches of one molecule are only weakly
attracted to those of another – indeed, at room temperature these molecule-to-
molecule bonds in an elastomer have melted. In this state the elastomer is a very
viscous liquid, its molecules tangled like a plate of cooked spaghetti, and it can be
molded. It is then cured; the curing creates occasional strong links between molecules,
freezing the tangle in its molded shape. Most of the length of any one molecule can
still slither over its neighbors, allowing stretch, but when released, the widely spaced
attachment points pull the tangle back to its original shape. In the case of natural
rubber, curing is achieved by heating with sulphur (“vulcanization”); in synthetic
rubbers the curing process is more complex but the effect is the same. This means that
elastomers are thermosets – once cured, you can’t remold them, or reshape or recycle
them, a major problem with car tires. Tires are the single biggest use of elastomers;
the second is footwear, followed by industrial rollers, belts, cushions, clothes and
sports-equipment. Elastomers are processed by casting, calendaring, extrusion, and
foaming.
3.1.19 A.B.S.
Acrylonitrile, butadiene, and styrene combine to form this common plastic often used to
make housings or other mechanical parts.
3.1.20 ACETATE
Acetates have good electrical insulating properties and is the material used to make movie
and microfilm.
32
3.1.21 ACRYLIC
Lucite and Plexiglass are trade names for acrylic which has widespread use where toughness
and transparency are required. Solvent cement is quite effective for welding pieces together.
3.1.22 BERYLLIUM OXIDE
A hard white ceramic-like material used as an electrical insulator where high thermal
conductivity is required. Beryllium oxide is highly toxic in powder form and should never be
filed or sanded and consequently has fallen out of common use. Power semiconductor heat
sinks can still be found with beryllium oxide spacers for electrical insulation.
3.1.23 CERAMIC
Ceramics are used to fabricate insulators, components, and circuit boards. The good
electrical insulating properties are complemented by the high thermal conductivity.
3.1.24 DELRIN
This Dupont acetal resin is made from polymerized formaldehyde and finds uses similar to
nylon. The material is rigid and has excellent mechanical and electrical properties making its
use common in appliances and electronics.
3.1.25 EPOXY/FIBERGLASS
This laminate is quite common due to its superior strength and excellent electrical properties
even in humid environment. Most modern circuit boards are made from a grade of
epoxy/fiberglass. (Grades include G10/FR4 and G11/FR5 extended temperature grade.)
3.1.26 GLASS
Glass insulation comes in a wide variety of forms including solid glass, fiber tapes, fiberglass
sheets and mats, woven tubing and cloth, and various composites. High temperature
operation is a key feature.
33
3.1.27 KAPTON
Polyimide film has exceptionally good heat resistance and superb mechanical and electrical
properties. Kapton tapes are fairly expensive but often indispensable.
3.1.28 KYNAR
As is Teflon, Kynar is a floropolymer with excellent chemical and abrasion resistance. It is
readily machined and welded.
3.1.29 LEXAN and MERLON
These polycarbonates have excellent electrical insulating properties. Optical grades are
available and the material is so tough that it meets U.L. requirements for burglary-resistance.
Non-transparent grades are machined to make strong insulators, rollers, and other mechanical
parts.
3.1.30 MELAMINE
Melamine laminated with woven glass makes a very hard laminate with good dimensional
stability and arc resistance. (Grades G5 is the mechanical grade and G9 is the electrical
grade.)
3.1.31 MICA
Mica sheets or "stove mica" is used for electrical insulation where high temperatures are
encountered. Thermal conductivity is high so mica insulators are useful for heat sinking
transistors or other components with electrically conductive cases. Puncture resistance is
good but the edges of the mica should be flush against a flat surface to prevent flaking. Mica
finds uses in composite tapes and sheets which are useful to 600 degrees centigrade with
excellent corona resistance. Sheets and rods of mica bonded with glass can tolerate extreme
temperatures, radiation, high voltage, and moisture. This rather expensive laminate may be
machined and it will not burn or outgas.
34
3.1.32 NEOPRENE
Neoprene rubber is the material used for most wet suits. This black rubber is commonly used
for gaskets, shock absorbers, grommets, and foams.
3.1.33 NOMEX
Nomex is a Dupont aromatic polyamide with an operating temperature range over 220
degrees centigrade and with superb high voltage breakdown. It is an excellent choice for
standardization since it outperforms many other materials.
3.1.34 NYLON
Nylon has good resistance to abrasion, chemicals, and high voltages and is often used to
fashion electro-mechanical components. Nylon is extruded and cast and is filled with a
variety of other materials to improve weathering, impact resistance, coefficient of friction,
and stiffness.
3.1.35 P.E.T.
Polyethylene terephthalate is a highly dimensionally stable thermoplastic with good
immunity to moisture. This excellent insulator has a low coefficient of friction and is
excellent for guides and other moving parts.
3.1.36 P.E.T.G.
A clear, tough copolyester commonly used for durable "bubble-packs" or food containers.
3.1.37 PHENOLICS
Phenolic laminated sheets are usually brown or black and have excellent mechanical
properties. Phenolics are commonly used in the manufacture of switches and similar
components because it is easily machined and provides excellent insulation. Phenolic
laminates are widely used for terminal boards, connectors, boxes, and components. (Grades
x, xx, xxx are paper/phenolic and grades c, ce, l, le are cotton/phenolic which is not the best
35
choice for insulation. Grade N-1 is nylon/phenolic and has good electrical properties even in
high humidity but exhibits some cold flow.)
3.1.38 POLYESTER (MYLAR)
A strong material often used in film sheets and tapes for graphic arts and electronics. Those
shiny balloons and "space blankets" are usually made from metalized Mylar. Mylar is also
used as a dielectric in capacitors.
3.1.39 POLYOLEFINS
Polyethylene is the white Teflon-like material used for food cutting board. Different densities
are available with the ultra-high molecular weight grade at the top offering toughness
outlasting steel in some applications. Polypropylene is another widely used polyolefin.
3.1.40 POLYSTYRENE
A clear insulator with superb dielectric properties. Polystyrene capacitors exhibit little
dielectric adsorption and virtually no leakage. Liquid polystyrene or Q-dope is a low-loss coil
dope used to secure windings and other components in RF circuits.
3.1.41 POLYURETHANE
Polyurethane is another common polymer which features abrasion and tear resistance along
with a host of desirable characteristics. Degrading little over time or temperature,
polyurethane is popular in both commercial and consumer applications.
3.1.42 PVC
Poly vinyl Cloride or PVC is perhaps the most common insulating material. Most wiring is
insulated with PVC including house wiring. Irradiated PVC has superior strength and
resistance to heat. PVC tapes and tubing are also quite common. Electrical and electronic
housings are commonly molded from PVC.
36
3.1.43 SILICONE/FIBERGLASS
Glass cloth impregnated with a silicone resin binder makes an excellent laminate with good
dielectric loss when dry. (Grades include G7.)
3.1.44 SILICONE RUBBER
A variety of silicone foam rubbers are available for insulating and cushioning electronic
assemblies. Silicone rubbers exhibit a wish list of characteristics including superb chemical
resistance, high temperature performance, good thermal and electrical resistance, long-term
resiliency, and easy fabrication. Liquid silicone rubbers are available in electrical grades for
conformal coating, potting, and gluing. Silicone rubbers found in the hardware store should
be avoided in electronic assemblies because they produce acetic acid. Silicone rubbers filled
with aluminum oxide are available for applications requiring thermal conductivity.
3.1.45 TFE (TEFLON)
Teflon is an excellent high temperature insulation with superb electrical properties. Teflon
tubing and wire insulation comes in a variety of colors and typically feels slippery. The
insulation is impervious to the heat and chemicals normally encountered in electronics
manufacturing but the material will "cold flow" so Teflon insulation is avoided where sharp
corners or points are encountered. Laminated TFE circuit boards take advantage of Teflon's
excellent microwave characteristics. Teflon emits a dangerous gas when exposed to extreme
heat. White Teflon terminals are commonly used where extremely good insulation is
required. The slick surface repels water so the insulation properties are fantastic even in high
humidity. High quality I.C. sockets are made from Teflon to reduce leakage currents. Teflon
and Teflon composite tapes with adhesive are available. FEP is a lower temperature Teflon.
37
3.2 Material Selection
Front plate
Function: Main role of front plate is Holding
the heater board and moving system. The
other role is to guide the moving system and
cover the inner side of toaster.
Material Properties:High Ductility, High
Melting point, Low Cost, Mettalic.
Material Selected: According to the material properties, Carbon steel, Alloy steel and
Stainless steel can be chosen from table 2.2 (in the appendix)
38
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
Not applicable Less applicable Normal applicable
39
Moving system
Function: Holding the handling plate,
Magnet, Bread’s Holder. Also sliding
movement to move the breads down and
return it up after toasting Operation.
Material Properties: High Ductility, High
Melting point, Low Cost, metallic
Material Selected: According to the material properties, Carbon steel, Alloy steel and
Stainless steel can be chosen from table 2.2 (in the appendix)
40
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
Not applicable Less applicable Normal applicable
41
Electrical connection snap-fit
Function: Fastening the wire of plug to the
switch.
Material Properties: High Ductility, High
conductivity, metallic
Material Selected: According to the material properties, Copper and alloys can be chosen
from table 2.2 (in the appendix)
42
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
43
Bottom cover
Function: To cover and maintain all
assembled parts and the main cover
Material Properties: Heat resistance, good
insulator, approximately high melting point.
Low cost, non-metalic
Material Selected: According to the material properties, Thermoplastic and Thermosets can
be chosen from table 2.2 (in the appendix)
44
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
45
Top Cover
Function: Covering all Sub assembly parts.
Material Properties: Heat resistance, good
insulator, approximately high melting point.
Low cost, non-metallic
Material Selected: According to the material properties, Thermoplastic and Thermosets can
be chosen from table 2.2 (in the appendix)
46
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
47
4 Suitable process for each part
4.1 Shape attributes
4.1.1 Depressions (Depress)
The ability to form recesses or grooves in the surfaces of the part. The first column
entry refers to the possibility of forming depressions in a single direction, while the second
entry refers to the possibility of forming depressions in more than one direction. These two
entries refer to depressions in the direction of tooling motion and those in other directions.
The following are some examples of tooling motion directions. Processes with split moulds—
the direction of mold opening. Processes that generate continuous profiles-normal to the
direction of extrusion or normal to the axis of the cutting medium. Forging (impact)
processes—the direction of impact of the tooling onto the part.
Uniform wall (UniWall):
Uniform wall thickness. Any no uniformity arising from the natural tendency of the
process, such as material stretching or build-up behind projections in centrifugal processes is
ignored, and the wall is still considered uniform.
Uniform cross section (UniSect):
Parts where any cross sections normal to a part axis are identical, excluding draft.
Axis of rotation (AxisRot):
Parts whose shape can be generated by rotation about a single axis: a solid of
revolution.
48
Regular cross section (RegXSec):
Cross sections normal to the part's axis contain a regular pattern (e.g., a hexagonal or
splined shaft). Changes in shape that maintain a regular pattern are permissible (e.g., splined
shaft with a hexagonal head).
Captured cavities (CaptCav):
The ability is needed to form cavities with reentrant surfaces (e.g., a bottle).
Enclosed (Enclosed):
Parts are hollow and completely enclosed.
Draft-free surfaces (NoDraft):
The capability of producing constant cross sections in the direction of tooling motion.
Many processes can approach this capability when less than ideal draft allowances are
specified, but this designation is reserved for processes where this capability is a basic
characteristic and no draft can be obtained without cost penalty.
49
The sample of shape attributes
1 Depression YES/NO
2 Uniform wall YES/NO
3 Uniform cross section YES/NO
4 Axis Rotation YES/NO
5 Regular Cross section YES/NO
6 Capture Cavity YES/NO
7 Enclosed Cavity YES/NO
8 No Draft YES/NO
From this figure we find the attribute of each part’s shape and it can help us to choose
primary process of materials. So with next table that illustrate the primary process selection.
In primary process selection if YES or NO from attribute table under attributes. After that
from the vertical columns, all the processes that which have, N below YES in table and M
below NO are eliminating. The sample of table for primary process selection is shown in
table 2.2 in the appendix, at first some information about process can be useful.
50
Front plate
1 Depression YES
2 Uniform wall YES
3 Uniform cross section NO
4 Axis Rotation NO
5 Regular Cross section NO
6 Capture Cavity NO
7 Enclosed Cavity NO
8 No Draft NO
According to shape attributes and referring to table 2.2, the items with Yes will eliminate
process that are not capable producing these features which are shown in the table with N and
those futures with No answer will eliminate process which are only capable of producing
parts with present features which are shown with M in table 2.2.
In the following table the result for 8 shape attributes have been summarized. The Black color
is shown the process which eliminated.
51
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
52
Moving System
1 Depression YES
2 Uniform wall YES
3
Uniform cross
section
NO
4 Axis Rotation NO
5
Regular Cross
section
NO
6 Capture Cavity NO
7 Enclosed Cavity NO
8 No Draft NO
According to shape attributes and referring to table 2.2, the items with Yes will eliminate
process that are not capable producing these features which are shown in the table with N and
those futures with No answer will eliminate process which are only capable of producing
parts with present features which are shown with M in table 2.2.
In the following table the result for 8 shape attributes have been summarized. The Black color
is shown the process which eliminated.
53
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
54
1 Depression YES
2 Uniform wall YES
3
Uniform cross
section
NO
4 Axis Rotation NO
5
Regular Cross
section
NO
6 Capture Cavity NO
7 Enclosed Cavity NO
8 No Draft NO
According to shape attributes and referring to table 2.2, the items with Yes will eliminate
process that are not capable producing these features which are shown in the table with N and
those futures with No answer will eliminate process which are only capable of producing
parts with present features which are shown with M in table 2.2.
In the following table the result for 8 shape attributes have been summarized. The Black color
is shown the process which eliminated.
55
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
56
1 Depression YES
2 Uniform wall NO
3
Uniform cross
section
NO
4 Axis Rotation NO
5
Regular Cross
section
NO
6 Capture Cavity NO
7 Enclosed Cavity NO
8 No Draft NO
According to shape attributes and referring to table 2.2, the items with Yes will eliminate
process that are not capable producing these features which are shown in the table with N and
those futures with No answer will eliminate process which are only capable of producing
parts with present features which are shown with M in table 2.2.
In the following table the result for 8 shape attributes have been summarized. The Black color
is shown the process which eliminated.
57
NO Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
58
1 Depression YES
2 Uniform wall YES
3
Uniform cross
section
NO
4 Axis Rotation NO
5
Regular Cross
section
NO
6 Capture Cavity NO
7 Enclosed Cavity NO
8 No Draft NO
According to shape attributes and referring to table 2.2, the items with Yes will eliminate
process that are not capable producing these features which are shown in the table with N and
those futures with No answer will eliminate process which are only capable of producing
parts with present features which are shown with M in table 2.2.
In the following table the result for 8 shape attributes have been summarized. The Black color
is shown the process which eliminated.
59
N
O
Process
CastIron
CarbonSteel
AlloySteel
StainlessSteel
AluminumandAlloys
CopperandAlloys
ZincandAlloys
MagnesiumandAlloys
TitaniumandAlloys
NickelandAlloys
RefractionMetals
Thermoplastics
Thermosets
1 Sand Casting
2 Investment Casting
3 Die Casting
4 Injection Moulding
5 Structural Form Moulding
6 Blow Molding (Ext.)
7 Blow Molding (Inj.)
8 Rotational Molding
9 Impact Extrusion
10 Cold Heading
11 Closed Die Forging
12 Powder Metal Parts
13 Hot Extrusion
14 Rotary Swaging
15 Machining (From Stock)
16 ECM
17 EDM
18 Wire EDM
19 Sheet Metal (Stamp/bend)
20 Thermoforming
21 Metal Spinning
60
4.2 Appropriate Manufacturing Processes
4.2.1 Sand Casting:
The traditional method of casting metals is in sand molds and has been used for millennia.
Sand casting is still the most prevalent form of casting. Typical applications of sand casting
include machine bases, large turbine impellers, propellers, plumbing fixtures, and a wide
variety of other products and components (Figure 8.).
Basically, sand casting consists of (a) placing a pattern (having the shape of the desired
casting) in sand to make an imprint, (b) incorporating a gating system, (c) removing the
pattern and filling the mold cavity with molten metal, (d) allowing the metal to cool until it
solidifies, (e) breaking away the sand mold, and (f) removing the casting.
Figure 8. Schematic illustration of a sand casting, showing various features.
61
Process Part
Size
Tolerances Surface
Finish
Shape Produced
Competitively
Process
Limitation
Materials
Sand
Casting
Weight
: 0.2 lb
-450
ton
Min
Wall:
0.125
in
General : +-
0.02 ( 1 in ) +-
0.1 ( 24 in )
For dimensions
across parting
line add +-0.03
( 50 Sq in ) +-
0.04 ( 200 Sq in
)
500-1000
micro
inches
Large parts with
walls and internal
passages of complex
geometry requiring
good vibration
damping
characteristics
Secondary
machining
usually required
production rates
often lower than
that for other
casting processes
Tolerances,
Surface finish
Coarser than
other casting
processes
1.Cast Iron,
2.Carbon
Steel
3.Alloy Steel
4.Stailnless
steel
5.Alluminium
6.Copper
7.Zinc
8.Magnesium
12.Nickel
4.2.2 Investment Casting:
The investment casting process, also called the lost wax process, was first used during the
period from 4000 to 3000 B.C. Typical parts made are components for office equipment, as
well as mechanical components such as gears, cams, valves, and ratchets. Parts up to 1.5 m in
diameter and weighting as much as 1140 Kg have been cast successfully by this process. The
pattern is made of wax, or of a plastic such as polystyrene, by molding or rapid-prototype
techniques. The pattern is then dipped into a slurry of refractory material such as very fine
silica and binders, including water, ethyl silicate, and acids. After this initial coating has
dried, the pattern is coated repeatedly to increase its thickness for better surface finish in the
casting; subsequent layers use larger particles and are intended to build coating thickness
quickly (Figure 9.)The term investment derives from the fact that the pattern is invested
(surrounded) with the refractory materials. Wax patterns require careful handling because
they are not strong enough to withstand the forces encountered during mold making;
however, unlike plastic pattern, wax can be recovered and reused.
62
Process Part Size Tolerances
Surface
Finish
Shape
Produced
Competitively
Process
Limitation
Materials
Investment
Casting
Weight : 1
Oz-110 lb ,
Major
Dimension:
to 50 lb ,
Min Wall :
0.025 (
Ferrous ) ,
0.060
Nonferrous)
General :
+- 0.002 (
1 in )
+- 0.004
(6in)
63-25
Micro
inches
Small
intricate parts
requiring
good surface
finish, good
dimensional
control, and
high strength
Most
investment
casting are
less than 12
in,
Long and
less than 10
lbs,
L/D ratio of
though or
blind holes
less than
4:1 and 1:1
respectively
Tooling
cost and
lead time
generally
greater than
for
othercasting
processes
except die
casting
2.Carbon
Steel
3.Alloy Steel
4.Stailnless
steel
5.Alluminium
6.Copper
12.Nickel
Figure 9. Schematic illustration of the investment casting (lost wax) process.
4.2.3 Die Casting:
In pressure die casting, the metal is injected into the mold at high
primarily used for high-volume production of zinc, aluminum, and magnesium alloys,
although ferrous and copper-base alloys may also be cast. The process is capable of high
production rates. Production rates are related to the siz
complex as automotive engine blocks and transmission housings are routinely made by die
casting.
Die Casting Processes. There are two major types of die casting machines: hot
chamber and cold chamber. In the hot cham
gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into
the mold. This method avoids one metal transfer operation, and it is used primarily for zinc
and magnesium. In the cold chamber process (
poured or metered into the shot sleeve. The piston is then activated to force the metal into the
mold. Cold chamber machines are used for aluminum, because the process minimizes the
amount of time that the molten alloy is in contact with the die casting machine.
Fig. 19 Schematic showing the principal components of a hot chamber die casting machine
In pressure die casting, the metal is injected into the mold at high pressures. The process is
volume production of zinc, aluminum, and magnesium alloys,
base alloys may also be cast. The process is capable of high
production rates. Production rates are related to the size and complexity of the part. Parts as
complex as automotive engine blocks and transmission housings are routinely made by die
Die Casting Processes. There are two major types of die casting machines: hot
chamber and cold chamber. In the hot chamber machine (Fig 19) ,the injection chamber is a
gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into
the mold. This method avoids one metal transfer operation, and it is used primarily for zinc
the cold chamber process (Fig20) the metal is melted separately and
poured or metered into the shot sleeve. The piston is then activated to force the metal into the
mold. Cold chamber machines are used for aluminum, because the process minimizes the
of time that the molten alloy is in contact with the die casting machine.
Fig. 19 Schematic showing the principal components of a hot chamber die casting machine
63
pressures. The process is
volume production of zinc, aluminum, and magnesium alloys,
base alloys may also be cast. The process is capable of high
e and complexity of the part. Parts as
complex as automotive engine blocks and transmission housings are routinely made by die
Die Casting Processes. There are two major types of die casting machines: hot
the injection chamber is a
gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into
the mold. This method avoids one metal transfer operation, and it is used primarily for zinc
the metal is melted separately and
poured or metered into the shot sleeve. The piston is then activated to force the metal into the
mold. Cold chamber machines are used for aluminum, because the process minimizes the
Fig. 19 Schematic showing the principal components of a hot chamber die casting machine
Fig. 20 Schematic showing the principal components of a cold chamber die casting
Dies. The die consists of at least two parts, the cover half and the ejector half (
dies are made of heat-resistant tool steels. The metal enters the die through the nozzle or shot
sleeve, which is located in the cover half. The cover
pins, which are activated when the ejector half retracts after the casting is solid, are located in
the ejector half of the die. The gating is also generally placed in the ejector half of the die.
Undercuts in the casting may be formed by metal slides or retractable cores in the die, which
can enter the die space from each side as well as the top and bottom. Ceramic cores may be
placed in the die to make configurations that cannot be made any other way; the cores
removed chemically after the casting is solid.
Fig. 21 Components of a single-cavity die casting die for use in a hot chamber machine
The die also contains vents and overflow areas where excess metal flows during
injection. In addition, most dies
permanent molding, proper placement of the water lines is critical to obtaining good quality
castings, especially for multiple-cavity dies.
Processing sequence: The sequence of the die casting proc
open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution.
This spray coats the die with a thin layer of mold release, and the water evaporates, cooling
the die surface. The die is closed, and m
ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first
stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal
Fig. 20 Schematic showing the principal components of a cold chamber die casting
Dies. The die consists of at least two parts, the cover half and the ejector half (
resistant tool steels. The metal enters the die through the nozzle or shot
sleeve, which is located in the cover half. The cover half is stationary during casting. Ejector
pins, which are activated when the ejector half retracts after the casting is solid, are located in
the ejector half of the die. The gating is also generally placed in the ejector half of the die.
e casting may be formed by metal slides or retractable cores in the die, which
can enter the die space from each side as well as the top and bottom. Ceramic cores may be
placed in the die to make configurations that cannot be made any other way; the cores
removed chemically after the casting is solid.
cavity die casting die for use in a hot chamber machine
The die also contains vents and overflow areas where excess metal flows during
injection. In addition, most dies contain water cooling lines to control die heating. As in
permanent molding, proper placement of the water lines is critical to obtaining good quality
cavity dies.
The sequence of the die casting process begins when the die is
open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution.
This spray coats the die with a thin layer of mold release, and the water evaporates, cooling
the die surface. The die is closed, and metal is either injected into the die (hot chamber) or
ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first
stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal
64
Fig. 20 Schematic showing the principal components of a cold chamber die casting machine
Dies. The die consists of at least two parts, the cover half and the ejector half (Fig 21 ). The
resistant tool steels. The metal enters the die through the nozzle or shot
half is stationary during casting. Ejector
pins, which are activated when the ejector half retracts after the casting is solid, are located in
the ejector half of the die. The gating is also generally placed in the ejector half of the die.
e casting may be formed by metal slides or retractable cores in the die, which
can enter the die space from each side as well as the top and bottom. Ceramic cores may be
placed in the die to make configurations that cannot be made any other way; the cores are
cavity die casting die for use in a hot chamber machine
The die also contains vents and overflow areas where excess metal flows during
contain water cooling lines to control die heating. As in
permanent molding, proper placement of the water lines is critical to obtaining good quality
ess begins when the die is
open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution.
This spray coats the die with a thin layer of mold release, and the water evaporates, cooling
etal is either injected into the die (hot chamber) or
ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first
stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal
65
before injection begins. In the second stage, the piston moves very quickly, forcing the metal
into the mold cavity. The dies are filled in less than 0.15 s. Pressure builds up on the metal
during this phase. In the third stage, pressure is intensified to minimize the formation of
porosity. The high pressures (up to 70 MPa, or 5 tsi) require elaborate locking mechanisms to
keep the dies closed during the cycle; locking forces of up to 45,000 kN (5000 tonf) are used
in the largest machines.
After the casting is solid, the dies open, and the casting and its runner system are removed
from the die. Slides and cores are usually retracted first, and then the dies open. The gates are
trimmed off on a separate trim press. High production die casting operations are highly
automated, with the cycle controlled by computer and robots handling the metering of metal
into the shot sleeve and removing the casting and gating from the die. After the casting is
removed, the die is sprayed again, and the cycle is repeated.Risers are rarely used in die
casting because the metal freezes so quickly that feeding does not have time to occur. The
gating system is designed to fill the mold as quickly and efficiently as possible. The area
where the shot plunger comes to rest in the gating system is called the "biscuit."Molten metal
may be transferred to the shot sleeve by means of hand ladling, automated ladling, or by
being pumped from the melting furnace to the shot sleeve, using pumps made of ceramics, or
using electromagnetic force.Die casting machines are complex. They must be capable of
rapid, repetitive motion. The dies must maintain alignment during operation to avoid being
damaged, and the cycle of the machine must be controlled accurately. Die failure is usually
by thermal shock (heat checking). Iron is often added to aluminum alloys used in die casting
to prevent soldering of the alloy to the die. The amount of iron must be controlled, as excess
iron (above 0.8%) forms a sludge in the alloy, which, if carried over into the casting as
inclusions, will lower casting properties and casting machinability.
Air Entrapment: The rapid injection of metal into the die cavity inevitably traps air in
the casting. This air expands during heat treatment, forming blisters on the surface of the
casting. For this reason, most conventional die castings are not heat treated. However, there
are a number of methods that may be used to minimize the entrapment of air in the die cavity.
In one, the air in the cavity is evacuated prior to making the shot. In another method used for
aluminum alloys, the die cavity is filled with oxygen before the shot. During the shot, the
oxygen reacts with the aluminum alloy, forming tiny particles of aluminum oxide, which are
dispersed in the casting. Because all of the gas in the c
no gas to form gas bubbles in the casting.Because of the limitations of conventional die
casting, a variation on the process has been developed to substantially reduce air entrapment.
In this method, called "vertical squeezecasting," the shot sleeve is located beneath the die
cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The
metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are
larger than those used in conventional die casting to assure that mold filling is even and free
of turbulence, which causes air entrapment. Production rates are slightly lower using vertical
squeeze casting, but casting quality is improved. Vertical squeez
confused with another process known as squeeze casting, in which liquid is ladled into the
bottom half of a metal die, and the die is closed, similar to a forging press. This process
eliminates porosity.
dispersed in the casting. Because all of the gas in the cavity is used in this reaction, there is
no gas to form gas bubbles in the casting.Because of the limitations of conventional die
casting, a variation on the process has been developed to substantially reduce air entrapment.
l squeezecasting," the shot sleeve is located beneath the die
cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The
metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are
larger than those used in conventional die casting to assure that mold filling is even and free
of turbulence, which causes air entrapment. Production rates are slightly lower using vertical
squeeze casting, but casting quality is improved. Vertical squeeze casting is not to be
confused with another process known as squeeze casting, in which liquid is ladled into the
bottom half of a metal die, and the die is closed, similar to a forging press. This process
66
avity is used in this reaction, there is
no gas to form gas bubbles in the casting.Because of the limitations of conventional die
casting, a variation on the process has been developed to substantially reduce air entrapment.
l squeezecasting," the shot sleeve is located beneath the die
cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The
metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are
larger than those used in conventional die casting to assure that mold filling is even and free
of turbulence, which causes air entrapment. Production rates are slightly lower using vertical
e casting is not to be
confused with another process known as squeeze casting, in which liquid is ladled into the
bottom half of a metal die, and the die is closed, similar to a forging press. This process
67
Process Part
Size
Tolerances Surface
Finish
Shape
Prodeuced
Competitively
Process
Limitation
Materials
Die
Casting
Min
Wall (
in ) :
0.025
Min
Hole
dia:
0.04-
0.08 in
Max
Weight
: 35
(Zn) ,
20 (Al)
, 10
(Mg)
General :
+-0.0002 (
1in ), Zinc
+-0.003 (1
in) .(
Allum &
Mg) Add
+- 0.004
across
parting
line or
moving
core
32-85
Micro
inches
Small to
minimum
sized parts
with intricate
detail and
good surface
finish
Triming
operations
required for
flash and
overflow
removal
porosity can
be present ,
Die life
limited to
approximately
200 K shots
in Al or Mg
or 1 million
Zn.
5.Alluminium
6.Copper
7.Zinc
8.Magnesium
4.2.4 Injection molding:
The largest quantity of plastic parts is made by injection molding. Plastic compound is
fed in powdered or granular form from a hopper through metering and melting stages and
then injected into a mold. After a brief cooling period, the mold is opened and the solidified
part is ejected is a manufacturing process for both thermoplastic and thermosetting
plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity
where it cools and hardens to the configuration of the mold cavity. After a product is
designed, usually by an industrial designer or an engineer molds are made by
a MoldMaker (or toolmaker) from metal, usually either steel or aluminum, and precision-
machined to form the features of the desired part. Injection molding is widely used for
manufacturing a variety of parts, from the smallest component to entire body panelsof cars.
68
Effects on the material properties:
The mechanical properties of a part are usually little affected. Some parts can have
internal stresses in them. This is one of the reasons why it's good to have uniform wall
thickness when molding. One of the physical property changes is shrinkage. A permanent
chemical property change is the material thermoset, which can't be remelted to be injected
again.
Tool materials:
Tool steel or beryllium-copper are often used. Mild steel, aluminum, nickel or epoxy
are suitable only for prototype or very short production runs. Modern hard aluminum (7075
and 2024 alloys) with proper mold design, can easily make molds capable of 100,000 or more
part life.[Citation needed]
Geometrical Possibilities:
The most commonly used plastic molding process, injection molding, is used to create
a large variety of products with different shapes and sizes. Most importantly, they can create
products with complex geometry that many other processes cannot. There are a few
precautions when designing something that will be made using this process to reduce the risk
of weak spots. First, streamline your product or keep the thickness relatively uniform.
Second, try and keep your product between 2 to 20 inches.
69
The size of a part will depend on a number of factors (material, wall thickness, shape,process
etc.). The initial raw material required may be measured in the form of granules, pellets or
powders. Here are some ranges of the sizes.
Method Raw materials
Maximum
size
Minimum size
Injection molding (thermo-
plastic)
Granules, pellets,
powders
700 oz.
Less than 1
oz.
Injection molding (thermo-
setting)
Granules, pellets,
powders
200 oz.
Less than 1
oz.
Machining of Mold:
Molds are built through two main methods: standard machining and EDM.
Standard Machining, in its conventional form, has historically been the method of building
injection molds. With technological development, CNC machining became the predominant
means of making more complex molds with more accurate mold details in less time than
traditional methods.
The electrical discharge machining (EDM) or spark erosion process has become
widely used in mold making. As well as allowing the formation of shapes that are difficult to
machine, the process allows pre-hardened molds to be shaped so that no heat treatment is
required. Changes to a hardened mold by conventional drilling and milling normally require
annealing to soften the mold, followed by heat treatment to harden it again. EDM is a simple
process in which a shaped electrode, usually made of copper or graphite, is very slowly
lowered onto the mold surface (over a period of many hours), which is immersed in paraffin
oil. A voltage applied between tool and mold causes spark erosion of the mold surface in the
inverse shape of the electrode.
70
The Cost:
The cost of manufacturing molds depends on a very large set of factors ranging from
number of cavities, size of the parts (and therefore the mold), complexity of the pieces,
expected tool longevity, surface finishes and many others. The initial cost is great, however
the piece part cost is low, so with greater quantities the overall price decreases.
Injection molding cycle:
The sequence of events during the injection mold of a plastic part is called the injection
molding cycle. The cycle begins when the mold closes, followed by the injection of the
polymer into the mold cavity. Once the cavity is filled, a holding pressure is maintained to
compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to
the front screw. This causes the screw to retract as the next shot is prepared. Once the part is
sufficiently cool, the mold opens and the part is ejected.
The time it takes to make a product using injection molding can be calculated by adding:
Twice the Mold Open/Close Time (2M)+Injection Time (T)+Cooling Time (C)+Ejection
Time(E), Where T is found by dividing:Mold Size (S) / Flow Rate (F)
Total time = 2M + T + C + E ; T = V/R ; [V = Mold cavity size (in3), R = Material flow, rate
(in3/min)]
4.2.5 Blow Molding (Ext.):
In extrusion blow molding, a tube or perform (usually oriented so that it is vertical) is
first extruded. It is then clamped into a mold with a cavity much larger than the tube diameter
and blown outward to fill the mold cavity. (Figure 3.) Depending on the material, the blow
ratio may be as high as 7:1. Blowing usually is done with a hot air blast at a pressure ranging
from 350 to 700 kPa. Drums with a volume as large as 2000 liters can be made by this
process. Typical die material are steel, aluminum, and beryllium copper.
71
In some operations, the extrusion is continuous and the molds move with the tubing. The
molds close around the tubing, sealing off one end, breaking the long tube into individual
sections, and moving away as air is injected into the tubular piece. The part is then cooled
and ejected from the mold. Corrugated-plastic pipe and tubing are made by continuous blow
molding in which the pipe or tubing is extruded horizontally and blown into moving molds.
4.2.6 Blow Molding (Inj.):
In injection blow molding, a short tubular piece (parison) is injection molded (Figure
4.) into cool dies. (Parisons may be made and stored for later use.) The dies then open, and
the parison is transferred to a blow molding die by an indexing mechanism. Hot air is injected
into the parison, expanding it do the walls of the mold cavity. Typical products made are
plastic beverage bottles (typically made of polyethylene or polyetheretherketone, PEEK) and
small, hollow containers.
72
4.2.7 Impact Extrusion:
Impact extrusion is similar to indirect extrusion, and the process often is included in
the cold extrusion category. The punch descends rapidly on the blank (slug), which is
extruded backwards (Figure 5.). Because of volume constancy, the thickness of the tubular
extruded section is a function of the clearance between the punch and the die cavity. Some
products made by impact extrusion are collapsible tubes (similar to those used for
toothpaste), light fixture, automotive parts, and small pressure vessels. Most nonferrous
metals can be impact extruded in vertical presses and at production rates as high as two parts
per second.
The maximum diameter of the parts made is about 150 mm. The impact extrusion process can
produce thin-walled tubular sections having thickness to diameter ratios as small as 0.005.
Consequently, the symmetry of the part and the concentricity of the punch and the blank are
important.
73
4.2.8 Cold Heading:
In cold heading or upsetting, force applied by one or more blows of a tool displaces metal in
a portion or all of a slug, wire, or rod blank. This plastic flow produces a section or part of
different contour, larger in cross section than the original material. Force is generally applied
by a moving punch to form that portion of the blank protruding from a stationary die. As seen
in
Fig. 3.7.1, some parts are upset in the punch, some in the die, some in both punch and die,
and others between the punch and the die.
Related Processes: Upsetting is often combined with forward or backward extrusion,
particularly in cold-forming large-headed, small-shanked parts. Warm heading is applied for
processing difficult-to-head metals such as medium-to high-carbon steels, austenitic stainless
steels, and other materials that work-harden rapidly. In this compromise between cold and hot
heading, the metal is preheated to between 150 and 540°C (300 and 1000°F) or more
(depending on the particular metal, but below its recrystallization temperature) to increase its
plasticity and reduce the force required for heading.
74
Rotary forging is a related process in which deformation is induced progressively rather than
by a single direct squeeze. The workpiece is subjected to a combined rolling and squeezing
action to produce progressive upsetting. This method is particularly suitable for thin, intricate
flange sections.
Secondary Operations Many secondary operations are performed on cold-upset parts,
depending on th design and application of the part. These include grooving, shaving,
pointing, flattening, bending, piercing, drilling, tapping, threading (often done with a thread-
rolling machine made an integral part of the header), heat treating, and plating.
Cold-Heading Machines:
Most cold-heading machines used in high production are fed coil stock. A machinemay
include a straightener, draw die, feed rolls, and shear. Sheared slugs are automatically
transferred to a stationary die, and the projecting end of each slug is struck axially by the
upsetting tool (punch). In some cases, as in nail making, the stock can be upset first and then
sheared to length. Multistation and progressive headers, as well as bolt-making machines, are
equipped with automatic-transfer mechanisms to move parts to successive stations and may
have trimming, pointing, and thread-rolling stations.
Headers and forming machines are available in a wide variety of sizes and types. They are
frequently rated by maximum-diameter-cutoff capacity and feed lengths (generally up to 14
times rated diameter, but this capacity can vary).
Suitable Materials:
Any material that is malleable when cold can be cold-formed. Materials having the lowest
yield strength and the greatest range between yield and ultimate strengths are the most
malleable. Since strain or work hardening during cold working decreases formability, the rate
of strain hardening of the material is an important consideration. Hardness of the material is
also critical, since too hard a material is impracticable to cold-work.
Prior operations, sometimes required to prepare material for upsetting, can include
heat treating, drawing, descaling, and lubricating. The upsetting properties of most steels are
improved by annealing or spheroidizing.
Whenever possible, the designer should avoid specifying exact material analyses, since this
limits the upsetter’s flexibility and may increase production costs. Several different analyses
75
of a basic material often can satisfy service requirements, but they may vary in upsettability,
availability, and cost.
• Steels: Low-carbon steels , Medium high-carbon steels , High-carbon steels , Alloy
steels , Rimmed steels ,
• Stainless Steels
• Nickel Alloys
• Aluminum Alloys
• Copper and Copper Alloys
• Other Materials: Titanium, beryllium, and refractory metals are less formable at
room temperatures, and they are likely to crack when cold-headed. As a result, they
are often processed warm.
Dimensions: As wide a tolerance as possible should be allowed on lugs, fins, tapers and
projections because metal-flow behavior is sometimes unpredictable in forming these shapes.
Radii generally can be formed to tolerances of 0.13 mm (0.005 in).
Geometry: Concentricity variations of 0.025 to 0.08 mm (0.001 to 0.003 in) TIR are not
uncommon in blank sizes up to 6 mm in) in diameter if the difference between the two
referenced diameters is not too great. Greater concentricity tolerance is generally needed for
larger-size parts and larger differences in diameters. If closer tolerances are needed,
secondary operations such as machining, shaving, or grinding are generally required.
Straightness of cold-upset parts can generally be held to about 0.4 percent of length.
Surface Finishes: A finish of 0.4 to 0.8m (16 to 32 in) usually can be obtained
economically.
Upsetting of heads, however, sometimes can decrease the quality of surface finish unless high
pressures are exerted on the sidewalls of the containing die. High-quality finishes generally
also require the use of high-quality clean wire.
Surface finish also can vary among different parts or different areas of the same part,
depending on the surface of the wire or bar being headed, the amount of cold working
performed in various areas, the lubricant used, and the condition of the tools. The best finish
on any part is usually achieved when direct contact has been made with the tools.
76
4.2.9 Powder Metal Parts
Powder metallurgy is used for manufacturing products or articles from powdered metals by
placing these powders in molds and are compacting the same using heavy compressive force.
Typical examples of such article or products are grinding wheels, filament wire, magnets,
welding rods, tungsten carbide cutting tools, self-lubricating bearings electrical contacts and
turbines blades having high temperature strength. The manufacture of parts by powder
metallurgy process involves the manufacture of powders, blending, compacting, profiteering,
sintering and a number of secondary operations such as sizing, coining, machining,
impregnation, infiltration, plating, and heat treatment. The compressed articles are then
heated to temperatures much below their melting points to bind the particles together and
improve their strength and other properties. Few non-metallic materials can also be added to
the metallic powders to provide adequate bond or impart some the needed properties. The
products made through this process are very costly on account of the high cost of metal
powders as well as of the dies used. The powders of almost all metals and a large quantity of
alloys, and nonmetals may be used. The application of powder metallurgy process is
economically feasible only for high mass production. Parts made by powder metallurgy
process exhibit properties, which cannot be produced by conventional methods. Simple
shaped parts can be made to size with high precision without waste, and completely or almost
ready for installation.
Powder Metallurgy Process:
The powder metallurgy process consists of the following basic steps: 1. Formation of
metallic powders. 2. Mixing or blending of the metallic powders in required proportions. 3.
Compressing and compacting the powders into desired shapes and sizes in form of
articles. 4. Sintering the compacted articles in a controlled furnace atmosphere. 5. Subjecting
the sintered articles to secondary processing if needed so.
77
Particle shape:
There are various shapes of metal powders namely spherical, sub-rounded, rounded,angular,
sub-angular, flakes etc. Particles shape influences the packing and flow characteristics of the
powders.
Chemical Composition:
Chemical composition of metallic powder implies the type and percentage of
alloyingelements and impurities. It usually determines the particle hardness and
compressibility. The chemical composition of a powder can be determined by chemical
analysis methods.
Particle microstructure:
Particle microstructure reveals various phases, inclusions and internal porosity.
Apparent density:
Apparent density is defined as the weight, of a loosely heated quantity of powder necessaryto
fill a given die cavity completely.
Flow characteristics:
Flow-ability of metal powders is most important in cases where moulds have to be filled
quickly. Metal powders with good flow characteristics fill a mould cavity uniformly.
78
Secondary Operations:
Some powder metal parts may be used in the sintered condition while in some other cases
additional secondary operations have to be performed to get the desired surface finish, close
tolerance etc. The secondary operations may be of following types:
1. Annealing.
2. Repressing for greater density or closer dimensional control.
3. Machining.
4. Polishing.
5. Rolling, forging or drawing.
6. Surface treatments to protect against corrosion.
7. In some cases infiltration is needed to provide increased strength, hardness,
densityobtainable by straight sintering.
8. The procedures for plating powdered metal parts are quite different from those usedfor
wrought or cast metal parts. In powdered metal parts, porosity must be eliminated before the
part is plated. After the porosity has been eliminated regular plating procedures can be used.
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
Design For Manufacturing, (DFM)
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Design For Manufacturing, (DFM)

  • 1. 1 1 Introduction New Product Design concept starts with conceptualization of ‘Product Idea’. The product idea typically takes into consideration of customer requirements. Design for manufacture (DFM) has evolved over the past decade or so from a general awareness of the need to consider more thoroughly the ease and economics of manufacture into a set of structured strategies, methodologies, and tools for evaluating a strategies, methodologies, and tools for evaluating a design for its manufacturability. Spiraling costs and the emergence of global competition have put an emphasis on design-to-cost strategies, where cost is elevated to the same level of concern as performance and function, from the moment the new product is conceived. 1 Design-to cost strategies require cost estimates at each stage in the product development process. However, the average engineering designer knows little about the cost of materials and processes implied and specified through the design drawings. Manufacturing options even for simple parts are numerous, and the effects on both recurring costs (piece-part costs) and nonrecurring costs (tooling costs) are dramatic. Rapid cost estimating systems are necessary to enable product designers and product development teams to make sound decisions early in the conceptual design phase and not, as is often the case, provide fodder for later value-analysis teams) The conscientious design engineer is interested in the existence of any design tradeoffs that can be made to help converge on the most economical approach. Many product manufacturers outsource much of their primary manufacturing. In some cases, they will only carry out the final assembly process or even just final distribution and marketing. The product with designing the highest quality product for the lowest cost manufacture by local, national, or offshore lowest cost manufacture by local, national, or offshore contractors. Access and understanding of cost even at the conceptual design stage of the product development process is key to the realization of competitive world-class products. A manufacturing system is composed of a large number of distinct processes which all influence product cost, product quality and productivity of the system. The interactions
  • 2. 2 between these various facets of a manufacturing system are complex, and decisions made concerning one aspect have ramifications which extend to the others. A product is usually created by design engineers who may not be familiar with manufacturing and assembly processes of the product. With insufficient communication with other engineers and manufacturing functions, design engineers may design a product that will lead to severe problems during manufacturing and assembly operations. These problems include failures of meeting dimensions and tolerance requirements, or difficulty in producing the product in a cost effective way. Contrary to the traditional sequential approach to design, the distinct processes in a concurrent product development environment are accomplished simultaneously. Concurrent design involves the simultaneous consideration and integration of various engineering activities throughout the product life cycle. By bringing downstream expertise of processes to the design stage, concurrent engineering will result in fewer design changes and hence lower cycle time and production cost. According to the experience of Ford Motors Co., approximately 70% of the manufacturing cost is dictated by decisions made at the design stage, although design only accounts for 5% of the total product development expenses (Plastics World, 1988). This clearly indicates the need of an increased effort on design by considering the products’ requirements of manufacturing and assembly processes. To avoid the drawbacks of the conventional product development approach and to take advantage of the concurrent engineering approach, a framework of concurrent engineering, which models the engineering design procedure, is developed. The framework consists of four design steps: design formation, product modeling and representation, Design for Assembly and Manufacture (DFA and DFM) critique and evaluation, and design optimization. Feature- based design provides the advantage of using features, which are high level entities closely related to their manufacturing and assembly operations, for representing products. The principles of design for manufacturability (DFM) and its application are not really new. Awareness of the importance of designing products for easy manufacture has existed in clever design and manufacturing engineers since product design and manufacturing activities
  • 3. 3 originated. However, use of the term design for manufacturability, recognition of it as a worthwhile engineering approach, and development of an organized DFM methodology are more recent. The following are some highlights from the history of designing products for easier manufacture. It is entirely possible for a design engineer, aware of the advantages of designing for manufacturability to work independently in optimizing the product design for ease of manufacture. However, most current DFM specialists advocate a team approach in applying DFM. Essentially, this means that the design and manufacturing people work together to gain the benefits of manufacturing knowledge and experience that the designer may not have and to ensure that the product is both functional and manufacturable. DFM is not a fixed system. This system is continually being developed, both in university research projects and by a number of consultants and within companies. The objectives of almost all developments are to make guidelines more accessible to designers and more easily applied. Additionally, and more important, evaluations are put on each guideline so that the designer can determine how much cost gain can be achieved if the guideline is incorporated. All these advances depend on the use of computers. Computerization is the developing movement in DFM. The following principles, applicable to virtually all manufacturing processes, will aid designers in specifying components and products that can be manufactured at minimum cost. 1. Simplicity. Other factors being equal, the product with the fewest parts, the least intricate shape, the fewest precision adjustments, and the shortest manufacturing sequence will be the least costly to produce. Additionally, it usually will be the most reliable and the easiest to service. 2. Standard materials and components. Use of widely available materials and off-the- shelf parts enables the benefits of mass production to be realized by even low- unitquantity products. Use of such standard components also simplifies inventory management, eases purchasing, avoids tooling and equipment investments, and speeds the manufacturing cycle.
  • 4. 4 3. Standardized design of the product itself. When several similar products are to be produced, specify the same materials, parts, and subassemblies for each as much as possible. This procedure will provide economies of scale for component production, simplify process control and operator training, and reduce the investment required for tooling and equipment. 4. Liberal tolerances. Although the extra cost of producing too tight tolerances has been well documented, this fact is often not appreciated well enough by product designers. The higher costs of tight tolerances stem from factors such as (a) extra operations such as grinding, honing, or lapping after primary machining operations, (b) higher tooling costs from the greater precision needed initially when the tools are made and the more frequent and more careful maintenance needed as they wear, (c) longer operating cycles, (d) higher scrap and rework costs, (e) the need for more skilled and highly trained workers, (f) higher materials costs, and (g) more sizable investments for precision equipment. 5. Use of the most processible materials. Use the most processible materials available as long as their functional characteristics and cost are suitable. There are often significant differences in processibility (cycle time, optimal cutting speed, flow ability, etc.) between conventional material grades and those developed for easy processibility. However, in the long run, the most economical material is the one with the lowest combined cost of materials, processing, and warranty and service charges over the designed life of the product. 6. Teamwork with manufacturing personnel. The most producible designs are provided when the designer and manufacturing personnel, particularly manufacturing engineers, work closely together as a team or otherwise collaborate from the outset. 7. Avoidance of secondary operations. Consider the cost of operations, and design in order to eliminate or simplify them whenever possible. Such operations as deburring, inspection, plating and painting, heat treating, material handling, and others may prove to be as expensive as the primary manufacturing operation and should be considered as the design is developed. For example, firm, nonambiguous gauging
  • 5. 5 points should be provided; shapes that require special protective trays for handling should be avoided. 8. Design appropriate to the expected level of production. The design should be suitable for a production method that is economical for the quantity forecast. For example, a product should not be designed to utilize a thin-walled die casting if anticipated production quantities are so low that the cost of the die cannot be amortized. Conversely, it also may be incorrect to specify a sand-mold aluminum casting for a mass-produced part because this may fail to take advantage of the labor and materials savings possible with die castings. 9. Utilizing special process characteristics. Wise designers will learn the special capabilities of the manufacturing processes that are applicable to their products and take advantage of them. For example, they will know that injection-molded plastic parts can have color and surface texture incorporated in them as they come from the mold, that some plastics can provide “living hinges,” that powder-metal parts normally have a porous nature that allows lubrication retention and obviates the need for separate bushing inserts, etc. Utilizing these special capabilities can eliminate many operations and the need for separate, costly components. 10. Avoiding process restrictiveness. On parts drawings, specify only the final characteristics needed; do not specify the process to be used. Allow manufacturing engineers as much latitude as possible in choosing a process that produces the needed dimensions, surface finish, or other characteristics required. The advantages of DFM are included: a) Reduce Time to Market b) Reduce manufacturing time c) Reduce rework d) Improve design efficiency e) Helps in Rapid Prototyping f) Better cost control g) Less time in product testing
  • 6. 6 2 Product Specification The product that has been chosen for this study is Toaster. The function of this product is to Toast breads by transport the heat to the breads with the heated element made from Tungsten to change the electricity energy to the heat. Toaster is typically a small Mechanic-electric kitchen appliance designed to toast multiple types of Bread products. A typical modern two-slice toaster draws from 600 to 1200 Watts and makes toast in 1 to 3 minutes. There are also non-electrical toasters that can be used to toast bread products over an open fire or flame. Figure 2.0: Isometric view from New Designed Toaster Specification: • Metallic body • Plastic bottom cover • Environment protective • Overall parts = 32 parts • Different parts = 23 parts
  • 7. 7 2.1 Illustration the main parts of product in an exploded/disassembly view As it is obvious in the figure 2.0, the main components of Toaster has been exhibited. Figure 2.1: Exploded view of toaster and illustration of main components. The detailed and some fasteners has been omitted. 2.2 Objectives In this project we intend to first, detect the best material and process for five components of our product. By Appling the Boothroyd-Dewhurst DFM methodology; Determine what type of materials are used in the new design of the product and the cause of that. How they are made and why those particular manufacturing processes are used, by which the parts can be made economically. The goal of selection materials are to minimize the cost of manufacturing and materials and also to minimize waste in manufacturing furthermore to maximize the performance of the part and safety of the product and also to maximize in the product life cycle.
  • 8. 8 2.3 Selection of product’s components 2.3.1 Total number of parts The Toaster contains of 23 different parts which is introduced in the table below. Table 3.1: Introduction of Toaster Components PartIDNO. picture Nameofpart 1 Front plate 2 Small Fire proof plate 3 Cylindrical Guide 4 Spring
  • 9. 9 PartIDNO. picture Nameofpart 5 moving system 6 U shape 7 Plastic part of U plate female 8 Plastic part of U plate male
  • 10. 10 PartIDNO. picture Nameofpart 9 Heater board left (Standard Part) 10 Heater board middle (Standard Part) 11 Heater board right (Standard Part) 12 Back plate
  • 12. 12 PartIDNO. picture Nameofpart 17 Switch (Standard part) 18 wire of plug 19 Electrical connection snap-fit 20 Bottom cover
  • 13. 13 PartIDNO. picture Nameofpart 21 Top Cover 22 Handling plastic part 23 Holder of wire
  • 14. 14 2.3.2 Introduction of redesigned parts Based on product chosen in our Design for Assembly (DFA) assignment we need to select 5 different parts from the product and illustrate them in a detail manner: 1. Front plate 2. Moving system 3. Electrical connection snap-fit 4. Bottom cover 5. Top Cover Front plate Easy to manipulate. Thickness = 10 mm Size = 120 mm Justification: The process of this part has been changed and it has combined two functions with each other. Before the changes this part just guided the moving system. Also it had 3 more punching processes which is eliminated in this new design. Function: Main role of front plate is Holding the heater board and moving system. The other role is to guide the moving system and cover the inner side of toaster.
  • 15. 15 Moving system Easy to manipulate. Thickness = 100 mm Size = 150 mm Justification: this part have been contained from 4 deferent part but same material, in new design all the parts have been design by bending process with just one sheet metal. Function: Holding the handling plate, Magnet, Bread’s Holder. Also sliding movement to move the breads down and return it up after toasting Operation. Electrical connection snap-fit Easy to manipulate. Thickness = 4 mm Size = 12 mm Justification: The previous process for this part was soldering the wire to the switch, by designing the snap fit connector and manufacturing it. It would be beneficial in cost and time wastage. Function: Fastening the wire of plug to the switch.
  • 16. 16 Bottom cover Easy to manipulate. Thickness = 15 mm Size = 250 mm Justification: The bottom cover in new design, has some snap fits instead of using screws for fastening, also its material has been changed from metallic to the plastic to improve the time and cost of manufacturing by improving the time of manufacturing Function: To cover and maintain all assembled parts and the main cover Top Cover Easy to manipulate. Thickness = 300 mm Size = 250 mm Justification: The Top cover also has been changed from the premier design by changing the material and design also. This part changed from combination of plastic and metallic of 4 parts to one plastic part. Function: Covering all Sub assembly parts.
  • 17. 17 3 Suitable materials for each par 3.1 Type of material 3.1.1 Cast Iron: Cast irons represent the largest quantity of all metals cast, and they can be cast easily into intricate shapes. They generally possess several desirable properties, such as wear resistance, high hardness, and good machinability. 3.1.2 Carbon Steels Improvement hardening, strength, hardness, and wear resistance; it reduces ductility, ability to weld, and toughness. • Low Carbon Steels (Mild Steel): Mild steel (<0.25% carbon) is the most commonly used, readily welded construction material, and has the following typical mechanical properties (Grade 43A in BS4360; ability to weld structural steel): • Tensile strength, 430 N/mrn2 • Yield strength, 230 N/m2 • Elongation, 20% • Tensile modulus, 210 KN/mm2 • Hardness, 130 DPN None steel exceeds the tensile modulus of mild steel. Therefore, in applications in which rigidity is a limiting factor for design (e.g., for storage tanks and distillation columns), high- strength steels have no advantage over mild steel. Stress concentrations in mild steel structures are relieved by plastic flow and are not as critical in other, less-ductile steels. Low- carbon plate and sheet are made in three qualities: fully killed with silicon and aluminum, semikilled (or balanced), and rimmed steel. Fully killed steels are used for pressure vessels. Most general-purpose structural mild steels are semikilled steels. Rimming steels have minimum amounts of deoxidation and are used mainly as thin sheet for consumer applications. The strength of mild steel can be improved by adding small amounts (not exceeding 0.1 %) of niobium, which permits the manufacture of semikilled steels with yield points up to 280
  • 18. 18 N/mm. By increasing the manganese content to about 1.5% the yield point can be increased up to 400 N/mm2. Thus provides better retention of strength at elevated temperatures and better toughness at low temperatures. • Corrosion Resistance: Equipment from mild steel usually is suitable for handling organic solvents, with the exception of those that are chlorinated, cold alkaline solutions (even when concentrated), sulfuric acid at concentrations greater than 88% and nitric acid at concentrations greater than 65% at ambient temperatures. Mild steels are rapidly corroded by mineral acids even when they are very dilute (pH less than 5). However, it is often more economical to use mild steel and include a considerable corrosion allowance on the thickness of the apparatus. Mild steel is not acceptable in situations in which metallic contamination of the product is not permissible. • Heat Resistance: The maximum temperature at which mild steel can be usedis 550°C. Above this temperature the formation of iron oxides and rapid scaling makes the use of mild steels uneconomical. For equipment subjected to high loadings at elevated temperatures, it is not economical to use carbon steel in cases above 450°C because of its poor creep strength. (Creep strength is time- dependent, with strain occurring under stress.) • Low Temperatures At temperatures below 10°C the mild steels may lose ductility, causing failure by brittle fracture at points of stress concentrations (especially at welds) [8,9]. The temperatures at which the transition occurs from ductile to brittle fraction depends not only on the steel composition, but also on thickness. Stress relieving at 600-7OO'C for steels decreases operation at temperatures some 20°C lower. Unfortunately, suitable furnaces generally are not available, and local stress relieving of welds, etc., is often not successful because further stresses develop on cooling.
  • 19. 19 3.1.3 High-Carbon Steels High carbon steels containing more than 0.3% are difficult to weld, and nearly all production of this steel is as bar and forgings for such items as shafts, bolts, etc Theseitems can be fabricated without welding. • Low-Temperature Ductility: Nickel is the alloying element used for improving low-temperature ductility. The addition of 1 .5% nickel to 0.25% Cr/0.25% Mo steels provides satisfactory application for moderately low temperatures down to about -50°C.
  • 20. 20 Heat treatment by quenching and tempering improves the low temperature ductility of steels such as 0.5 Cr, 0.5% Mo, 1% Ni Type V. For lower- temperature application (below - 196"C), up to 9% nickel is used as the sole alloying element. 3.1.4 High-Carbon, Low-Alloy Steels: High-carbon (about 0.4%), low-alloy steels that are not weldable usually are produced as bars and forging for such items as shafting, high-temperature bolts and gears and ball bearing components. These steels can be less drastically quenched and tempered to obtain tensile strengths of at least 1500 N/mm2, thus minimizing the danger of cracking. • Properties of High-Alloy Steels: Stainless and heat-resisting steels containing at least 18% by weight chromium and 8% nickel are in widespread use in industry. The structure of these steels is changed from magnetic body centered cubic or ferritic crystal structure to a nonmagnetic, facecentered cubic or austenitic crystal structure. 3.5.1 Chromium Steels (400 Series), Low-Carbon Ferritic (Type 405): 12-13% Chromium. The main use of this type steel is for situations in which the process material may not be corrosive to mild steel, yet contamination due to rusting is not tolerable and temperatures or conditions are unsuitable for aluminum. However, prolonged use of these steels in the temperature range of 450 to 550°C causes low- temperature embrittlement of most ferritic steels with more than 12% chromium. 3.1.5 Alloy Steel Steel classification is important in understanding what types are used in certain applications and which are used for others. For example, most commercial steels are classified into one of three groups: plain carbon, low-alloy, and high-alloy. Steel classification systems are set up and updated frequently for this type of information. Generally, carbon is the most important commercial steel alloy. Increasing carbon content increases hardness and strength andimproves hardenability. But carbon also increases brittleness and reduces weldability because of its tendency to form martensite. This means carbon content can be both a blessing and a curse when it comes to commercial steel.
  • 21. 21 And while there are steels that have up to 2 percent carbon content, they are the exception. Most steel contains less than 0.35 percent carbon. To put this in perspective, keep in mind that’s 35/100 of 1 percent. Now, any steel in the 0.35 to 1.86 percent carbon content range can be hardened using a heat- quench-temper cycle. Most commercial steels are classified into one of three groups: • Plain carbon steels • Low-alloy steels • High-alloy steels 3.1.6 Low-alloy Steels When these steels are designed for welded applications, their carbon content is usually below 0.25 percent and often below 0.15 percent. Typical alloys include nickel, chromium, molybdenum, manganese, and silicon, which add strength at room temperatures and increase low-temperature notch toughness. These alloys can, in the right combination, improve corrosion resistance and influence the steel’s response to heat treatment. But the alloys added can also negatively influence crack susceptibility, so it’s a good idea to use low-hydrogen welding processes with them. Preheating might also prove necessary. This can be determined by using the carbon equivalent formula, which we’ll cover in a later issue. 3.1.7 High-alloy Steels For the most part, we’re talking about stainless steel here, the most important commercial high-alloy steel. Stainless steels are at least 12 percent chromium and many have high nickel contents. The three basic types of stainless are: • Austenitic • Ferritic • Martensitic
  • 22. 22 Martensitic stainless steels make up the cutlery grades. They have the least amount of chromium, offer high hardenability, and require both pre- and postheating when welding to prevent cracking in the heat-affected zone (HAZ). Ferritic stainless steels have 12 to 27 percent chromium with small amounts of austenite- forming alloys. Austenitic stainless steels offer excellent weldability, but austenite isn’t stable at room temperature. Consequently, specific alloys must be added to stabilize austenite. The most important austenite stabilizer is nickel, and others include carbon, manganese, and nitrogen. 3.1.8 Stainless Steels They primarily are characterised by their corrosion resistance, high strength and ductility, and high chromium content. They are called stainless because, in the presence of oxygen (air), they develop a thin, hard, adherent film of chromium oxide that protects the metal from corrosion. This protective film builds up again in the event that the surface is scratched. 3.1.9 Tool and Die Steels Tool and die steels are specially alloyed steels designed for high strength, impact toughness, and wear resistance at room and elevated temperature. They commonly are used in the forming and machining of metals. Aluminum and its’ alloys Aluminum is the world’s most abundant metal and does the third most common element comprise 8% of the earth’s crust. The versatility of aluminum makes it the most widely used metal after steel.
  • 23. 23 Aluminum is derived from the mineral bauxite. Bauxite is converted to aluminum oxide (alumina) via the Bayer Process. The alumina is then converted to aluminum metal using electrolytic cells and the Hall-Heroult Process. Pure aluminum is soft, ductile, and corrosion resistant and has a high electrical conductivity. It is widely used for foil and conductor cables, but alloying with other elements is necessary to provide the higher strengths needed for other applications. Aluminum is one of the lightest engineering metals, having strength to weight ratio superior to steel. By utilizing various combinations of its advantageous properties such as strength, lightness, corrosion resistance, recyclability and formability, aluminum is being employed in an ever- increasing number of applications. This array of products ranges from structural materials through to thin packaging foils. Aluminum is most commonly alloyed with copper, zinc, magnesium, silicon, manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities. There are over 300 wrought alloys with 50 in common use. They are normally identified by a four figure system which originated in the USA and is now universally accepted. Aluminum has a density around one third that of steel or copper making it one of the lightest commercially available metals. The resultant high strength to weight ratio makes it an important structural material allowing increased payloads or fuel savings for transport industries in particular. Pure aluminum doesn’t have a high tensile strength. However, the addition of alloying elements like manganese, silicon, copper and magnesium can increase the strength properties of aluminum and produce an alloy with properties tailored to particular applications. Aluminum is well suited to cold environments. It has the advantage over steel in that its’ tensile strength increases with decreasing temperature while retaining its toughness. Steel on the other hand becomes brittle at low temperatures
  • 24. 24 When exposed to air, a layer of aluminum oxide forms almost instantaneously on the surface of aluminum. This layer has excellent resistance to corrosion. It is fairly resistant to most acids but less resistant to alkalis. The thermal conductivity of aluminum is about three times greater than that of steel. This makes aluminum an important material for both cooling and heating applications such as heat-exchangers. Combined with it being non-toxic this property means aluminum is used extensively in cooking utensils and kitchenware. Along with copper, aluminums has an electrical conductivity high enough for use as an electrical conductor. Although the conductivity of the commonly used conducting alloy (1350) is only around 62% of annealed copper, it is only one third the weights and can therefore conduct twice as much electricity when compared with copper of the same weight. From UV to infra-red, aluminums is an excellent reflector of radiant energy. Visible light reflectivity of around 80% means it is widely used in light fixtures. The same properties of reflectivity makes aluminums ideal as an insulating material to protect against the sun’s rays in summer, while insulating against heat loss in winter. Aluminum can be severely deformed without failure. This allows aluminums to be formed by rolling, extruding, drawing, machining and other mechanical processes. It can also be cast to a high tolerance. Alloying, cold working and heat-treating can all be utilised to tailor the properties of aluminum. The tensile strength of pure aluminum is around 90 MPa but this can be increased to over 690 MPa for some heat-treatable alloys 3.1.10 Copper and its’ alloys: Copper is an excellent electrical conductor. Most of its uses are based on this property or the fact that it is also a good thermal conductor. However, many of its applications also rely on one or more of its other properties. For example, it wouldn't make very good water and gas pipes if it were highly reactive. On this page, we look at these other properties:
  • 25. 25 • a good electrical conductor • a good thermal conductor • corrosion resistant • antibacterial • easily joined • ductile • tough • non magnetic • attractive colour • easy to alloy • recyclable • catalytic Copper is low in the reactivity series. This means that it doesn't tend to corrode. Again, this is important for its use for pipes, electrical cables, saucepans and radiators. However, it also means that it is well suited to decorative use. Jewellery, statues and parts of buildings can be made from copper, brass or bronze and remain attractive for thousands of years. Copper is a ductile metal. This means that it can easily be shaped into pipes and drawn into wires. Copper pipes are lightweight because they can have thin walls. They don't corrode and they can be bent to fit around corners. The pipes can be joined by soldering and they are safe in fires because they don't burn or support combustion. Copper and copper alloys are tough. This means that they were well suited to being used for tools and weapons. Imagine the joy of ancient man when he discovered that his carefully formed arrowheads no longer shattered on impact. The property of toughness is vital for copper and copper alloys in the modern world. They do not shatter when they are dropped or become brittle when cooled below 0 °C. Copper can be recycled without any loss of quality. 40% of the world's demand is met by recycled copper.
  • 26. 26 3.1.11 Zinc and Alloys: Zinc is a metal that is fourth most utilized industrially, after iron, aluminum, and copper. It uses for galvanizing iron, steel sheet, and wire. And also it applies as a material in casting. Zinc based alloys are used extensively in die casting for making such products as fuel pumps and grills for automobiles, components for household appliances such as vacuum cleaners and washing machines, kitchen equipment, various machinery parts, and photoengraving equipment. Another use for zinc is in superplastic alloys that can be formed by methods used for forming plastics or metals. 3.1.12 Magnesium Alloys: Controls the shape of inclusions and improves toughness in high strength, low-alloy steels; it deoxidizes steels. And it has the same effects as Cerium. 3.1.13 Titanium and its’ Alloys Titanium does not occur free in Nature. However, when combined with other elements, it is quite abundant, occurring in small amounts in most of the volcanic,sedimentary and metamorphic rocks. Its more important minerals are ilmenite, rutile, arizonite (iron titanate), brookite, anatase, leucochene (titanium dioxide), perovskite (calcium titanate), and others. The first two have commercial importance, and can be found in deposits spread all over the world. There are important rutile and limonite deposits in Australia, Argentina, USA, Central Africa, Brazil, Canada, Egypt, India and Norway. The largest well-known deposits of rutile are located in Australia. Titanium and its alloys are relatively new engineering metals since they have been in use only since about 1952. They are extremely attractive materials for engineers because they have a high strength to weight ratio, high elevated temperature properties to about 550o C, and excellent corrosion resistance particularly in oxidising acids and chloride media. This metal is being increasingly used for marine applications. Its resistance to seawater attack combined with its mechanical properties make it a prime choice for equipment operating within the sea or transferring seawater.
  • 27. 27 Titanium is not an 'exotic' metal; it is the fourth most abundant structural metal in the earth's crust, and the ninth industrial metal. This metal has become the prime selection for a wide range of critical and demanding applications. Titanium Alloys are generally divided into three groups (Alpha, Alpha-Beta and Beta). The Alpha group contain most importantly aluminum and tin. They can also contain molybdenum, zirconium, nitrogen, vanadium, columbium, tantalum, and silicon. Alpha alloys are not suitable for heat treatment. Alpha alloys are used for aircraft parts and cryogenic equipment. The Alpha-Beta group can be strengthened by heat treatment. The alloys are used in aircraft and aircraft turbine parts, chemical processing equipment, marine hardware. The Beta Alloys have good hardenability. Beta alloys are slightly more dense than other titanium alloys, having densities ranging from 4800 to 5050 kg/m3 . They are the least creep resistant alloys, they are weldable, and can have yield strengths up to 1345 x 106 Pa.(Solution treated and age hardened) Beta alloys are the smallest group. They are used for heavier duty purposes on aircraft. 3.1.14 Nickel Alloys Improves strength, toughness, corrosion resistance and hardenability. Nickel alloys are used in high temperature applications (such as jet engine components, rockets, and nuclear power plants), in coins, and in marine applications. 3.1.15 Refractory Alloys There are four refractory metals: Molybdenum, Niobium, Tungsten, and Tantalum. These metals are called refractory because of their high melting points. More than most other metals and alloys, the refractory metals maintain their strength at elevated temperatures. Therefore, they are of great importance in rocket engines, gas turbines, and various other aerospace applications; in the electronic, nuclear-power, and chemical industries; and as tool and die materials.
  • 28. 28 3.1.16 Thermoplastics Thermoplastics soften when heated and harden again to their original state when cooled. This allows them to be molded to complex shapes. Most accept coloring agents and fillers, and many can be blended to give a wide range of physical, visual and tactile effects. Their sensitivity to sunlight is decreased by adding UV filters, and their flammability is decreased by adding flame retardants. The common thermoplastics are listed in the adjacent table. They include polyolefin (polyethylene, polypropylene), PVCS, polystyrenes, acrylics and certain polyesters (PET and PBT). Some are crystalline, some amorphous, some a mixture of both. The properties of thermoplastics can be controlled by chain length (measured by molecular weight), by degree of crystallinity and by blending and plasticizing. As the molecular weight increases, the resin becomes stiffer, tougher, and more resistant to chemicals, but it is more difficult to mold to thin-wall sections. For thin-walls, choose a low molecular weight resin; for higher performance, choose one with higher molecular weight. Crystalline polymers tend to have better chemical resistance, greater stability at high temperature and better creep resistance than those that are amorphous. For transparency the polymer must be amorphous; partial crystallinity gives translucency. The most transparent polymers are Acrylics, PC, PS and PET. Some polymers crystallize faster than others: polyethylene crystallizes quickly but polyesters do so more slowly – they remain amorphous under normal cooling rates. Crystalline polymers have a more or less sharp melting point, which must be exceeded for molding. Amorphous polymers do not; instead they progressively soften and become more fluid as temperature increases above the glass transition temperature; they must be heated above this temperature for extrusion and injection molding. The processing force required to generate flow decreases slowly as temperature rises above the glass transition temperature. Amorphous polymers have greater impact strength and relatively low mold shrinkage. Semi-crystalline polymers have higher shrinkage because of the volume change on crystallization.
  • 29. 29 Holes and ribs reduce the effect of shrinkage in a thermoplastic part. Areas near the filling gate tend to shrink less than areas farther away. Shrinkage increases with wall thickness and decreases with higher molding pressures. Fiber filled polymers shrink less in the direction of flow because the fibers line up in this direction; the shrinkage in the cross-flow direction is 2–3 times more than in the flow direction. High service temperatures can cause shrinking in some semi-crystalline materials. Fillers, or additives, are used to tailor certain properties of the composite such as density, colour, flame/smoke retardance, moisture resistance and dimensional stability. Most thermoplastics can be recycled. 3.1.17 Thermosets If you are a do-it-yourself type, you have Araldite in your toolbox – two tubes, one a sticky resin, the other an even stickier hardener. Mix and warm them so they react to give a stiff, strong, durable polymer, stuck to whatever it was put on. Araldite typifies thermosets – resins that polymerize when catalyzed and heated; when reheated they do not melt – they degrade. The common thermosets are listed in the table here. The first commercial thermoset was Bakelite, a trade-name for a phenolic resin. Polyurethane thermosets are produced in the highest volume; polyesters come second; phenolics, epoxies and silicones follow, and – not surprisingly – the cost rises in the same order. Epoxies are two-part system that – when mixed – undergo a mildly exothermic reaction that produces cross-linking. Phenolics are cross-linked by the application of heat or heat and pressure. Vulcanization of rubber, catalyzed by the addition of sulfur, can change the soft rubber of a latex glove to the rigid solid of ebonite, depending on the level of cross-linking. Once shaped, thermosets cannot be reshaped. Thermosets have greater dimensional stability than thermoplastics; they are used where there is a requirement for high temperature resistance and little or no creep. Most are hard and rigid, but they can be soft and flexible (like natural and synthetic rubber, as described above). Phenolics are most used where close-tolerance
  • 30. 30 applications are necessary, polyesters (often combined with glass fibers) where high strength with low shrinkage is wanted. Thermosets are shaped by compression molding, resin transfer molding, injection molding, pultrusion and casting. They duplicate the mold finish and are relatively free from flow lines and sink marks, depending on the mold design – high gloss, satin or sand-blasted finishes are possible, and raised lettering can be molded in. Molding can be adapted to low volume production by using low cost molds; but higher production volumes, up to a million or greater, are economical only with expensive molds that allow fast heating, cooling and extraction. Phenolics can only be molded in black or brown; urea, melamine, alkyd and polyester compounds are available in a wider range of colors. The fluidity of some thermosets before molding allows them to take up fine detail, and to penetrate between fibers to create composites. Most high-performance polymer composites have thermosetting matrix materials. Dough and sheet molding compounds (dmc and smc) use polyesters; filament-wound carbon or glass use epoxies as the matrix to give the highest performance of all. Thermosets cannot be recycled. 3.1.18 Elastomers Elastomers were originally called “rubbers” because they could rub out pencil marks – but that is the least of their many remarkable and useful properties. Unlike any other class of solid, elastomers remember their shape when they are stretched – some, to five or more times their original length – and return to it when released. This allows conformability – hence their use for seals and gaskets. High damping elastomers recover slowly; those with low damping snap back, returning the energy it took to stretch them – hence their use for springs, catapults, and bouncy things. Conformability gives elastomers high friction on rough surfaces, part of the reason (along with comfort) that they are used for pneumatic tires and footwear. Elastomers are easy to foam, giving them the comfort of cushions, and increasing even further their ability to conform to whatever shape is pressed against them.
  • 31. 31 Almost all engineering solids have elastic moduli (measuring their stiffness) between 1 and 1000 Gpa. Elastomers are much less stiff – between 0.0001 and 1 Gpa. This low stiffness, their ability to stretch and to remember their original shape all derive from their structure. The molecules in an elastomer are long chains of linked carbon (or, in silicones, silicon-oxygen chains), with hydrogen, nitrogen, chlorine or fluorine attached to the sides. The carbon atoms that link to form the chain are strongly bonded to each other, but the side-branches of one molecule are only weakly attracted to those of another – indeed, at room temperature these molecule-to- molecule bonds in an elastomer have melted. In this state the elastomer is a very viscous liquid, its molecules tangled like a plate of cooked spaghetti, and it can be molded. It is then cured; the curing creates occasional strong links between molecules, freezing the tangle in its molded shape. Most of the length of any one molecule can still slither over its neighbors, allowing stretch, but when released, the widely spaced attachment points pull the tangle back to its original shape. In the case of natural rubber, curing is achieved by heating with sulphur (“vulcanization”); in synthetic rubbers the curing process is more complex but the effect is the same. This means that elastomers are thermosets – once cured, you can’t remold them, or reshape or recycle them, a major problem with car tires. Tires are the single biggest use of elastomers; the second is footwear, followed by industrial rollers, belts, cushions, clothes and sports-equipment. Elastomers are processed by casting, calendaring, extrusion, and foaming. 3.1.19 A.B.S. Acrylonitrile, butadiene, and styrene combine to form this common plastic often used to make housings or other mechanical parts. 3.1.20 ACETATE Acetates have good electrical insulating properties and is the material used to make movie and microfilm.
  • 32. 32 3.1.21 ACRYLIC Lucite and Plexiglass are trade names for acrylic which has widespread use where toughness and transparency are required. Solvent cement is quite effective for welding pieces together. 3.1.22 BERYLLIUM OXIDE A hard white ceramic-like material used as an electrical insulator where high thermal conductivity is required. Beryllium oxide is highly toxic in powder form and should never be filed or sanded and consequently has fallen out of common use. Power semiconductor heat sinks can still be found with beryllium oxide spacers for electrical insulation. 3.1.23 CERAMIC Ceramics are used to fabricate insulators, components, and circuit boards. The good electrical insulating properties are complemented by the high thermal conductivity. 3.1.24 DELRIN This Dupont acetal resin is made from polymerized formaldehyde and finds uses similar to nylon. The material is rigid and has excellent mechanical and electrical properties making its use common in appliances and electronics. 3.1.25 EPOXY/FIBERGLASS This laminate is quite common due to its superior strength and excellent electrical properties even in humid environment. Most modern circuit boards are made from a grade of epoxy/fiberglass. (Grades include G10/FR4 and G11/FR5 extended temperature grade.) 3.1.26 GLASS Glass insulation comes in a wide variety of forms including solid glass, fiber tapes, fiberglass sheets and mats, woven tubing and cloth, and various composites. High temperature operation is a key feature.
  • 33. 33 3.1.27 KAPTON Polyimide film has exceptionally good heat resistance and superb mechanical and electrical properties. Kapton tapes are fairly expensive but often indispensable. 3.1.28 KYNAR As is Teflon, Kynar is a floropolymer with excellent chemical and abrasion resistance. It is readily machined and welded. 3.1.29 LEXAN and MERLON These polycarbonates have excellent electrical insulating properties. Optical grades are available and the material is so tough that it meets U.L. requirements for burglary-resistance. Non-transparent grades are machined to make strong insulators, rollers, and other mechanical parts. 3.1.30 MELAMINE Melamine laminated with woven glass makes a very hard laminate with good dimensional stability and arc resistance. (Grades G5 is the mechanical grade and G9 is the electrical grade.) 3.1.31 MICA Mica sheets or "stove mica" is used for electrical insulation where high temperatures are encountered. Thermal conductivity is high so mica insulators are useful for heat sinking transistors or other components with electrically conductive cases. Puncture resistance is good but the edges of the mica should be flush against a flat surface to prevent flaking. Mica finds uses in composite tapes and sheets which are useful to 600 degrees centigrade with excellent corona resistance. Sheets and rods of mica bonded with glass can tolerate extreme temperatures, radiation, high voltage, and moisture. This rather expensive laminate may be machined and it will not burn or outgas.
  • 34. 34 3.1.32 NEOPRENE Neoprene rubber is the material used for most wet suits. This black rubber is commonly used for gaskets, shock absorbers, grommets, and foams. 3.1.33 NOMEX Nomex is a Dupont aromatic polyamide with an operating temperature range over 220 degrees centigrade and with superb high voltage breakdown. It is an excellent choice for standardization since it outperforms many other materials. 3.1.34 NYLON Nylon has good resistance to abrasion, chemicals, and high voltages and is often used to fashion electro-mechanical components. Nylon is extruded and cast and is filled with a variety of other materials to improve weathering, impact resistance, coefficient of friction, and stiffness. 3.1.35 P.E.T. Polyethylene terephthalate is a highly dimensionally stable thermoplastic with good immunity to moisture. This excellent insulator has a low coefficient of friction and is excellent for guides and other moving parts. 3.1.36 P.E.T.G. A clear, tough copolyester commonly used for durable "bubble-packs" or food containers. 3.1.37 PHENOLICS Phenolic laminated sheets are usually brown or black and have excellent mechanical properties. Phenolics are commonly used in the manufacture of switches and similar components because it is easily machined and provides excellent insulation. Phenolic laminates are widely used for terminal boards, connectors, boxes, and components. (Grades x, xx, xxx are paper/phenolic and grades c, ce, l, le are cotton/phenolic which is not the best
  • 35. 35 choice for insulation. Grade N-1 is nylon/phenolic and has good electrical properties even in high humidity but exhibits some cold flow.) 3.1.38 POLYESTER (MYLAR) A strong material often used in film sheets and tapes for graphic arts and electronics. Those shiny balloons and "space blankets" are usually made from metalized Mylar. Mylar is also used as a dielectric in capacitors. 3.1.39 POLYOLEFINS Polyethylene is the white Teflon-like material used for food cutting board. Different densities are available with the ultra-high molecular weight grade at the top offering toughness outlasting steel in some applications. Polypropylene is another widely used polyolefin. 3.1.40 POLYSTYRENE A clear insulator with superb dielectric properties. Polystyrene capacitors exhibit little dielectric adsorption and virtually no leakage. Liquid polystyrene or Q-dope is a low-loss coil dope used to secure windings and other components in RF circuits. 3.1.41 POLYURETHANE Polyurethane is another common polymer which features abrasion and tear resistance along with a host of desirable characteristics. Degrading little over time or temperature, polyurethane is popular in both commercial and consumer applications. 3.1.42 PVC Poly vinyl Cloride or PVC is perhaps the most common insulating material. Most wiring is insulated with PVC including house wiring. Irradiated PVC has superior strength and resistance to heat. PVC tapes and tubing are also quite common. Electrical and electronic housings are commonly molded from PVC.
  • 36. 36 3.1.43 SILICONE/FIBERGLASS Glass cloth impregnated with a silicone resin binder makes an excellent laminate with good dielectric loss when dry. (Grades include G7.) 3.1.44 SILICONE RUBBER A variety of silicone foam rubbers are available for insulating and cushioning electronic assemblies. Silicone rubbers exhibit a wish list of characteristics including superb chemical resistance, high temperature performance, good thermal and electrical resistance, long-term resiliency, and easy fabrication. Liquid silicone rubbers are available in electrical grades for conformal coating, potting, and gluing. Silicone rubbers found in the hardware store should be avoided in electronic assemblies because they produce acetic acid. Silicone rubbers filled with aluminum oxide are available for applications requiring thermal conductivity. 3.1.45 TFE (TEFLON) Teflon is an excellent high temperature insulation with superb electrical properties. Teflon tubing and wire insulation comes in a variety of colors and typically feels slippery. The insulation is impervious to the heat and chemicals normally encountered in electronics manufacturing but the material will "cold flow" so Teflon insulation is avoided where sharp corners or points are encountered. Laminated TFE circuit boards take advantage of Teflon's excellent microwave characteristics. Teflon emits a dangerous gas when exposed to extreme heat. White Teflon terminals are commonly used where extremely good insulation is required. The slick surface repels water so the insulation properties are fantastic even in high humidity. High quality I.C. sockets are made from Teflon to reduce leakage currents. Teflon and Teflon composite tapes with adhesive are available. FEP is a lower temperature Teflon.
  • 37. 37 3.2 Material Selection Front plate Function: Main role of front plate is Holding the heater board and moving system. The other role is to guide the moving system and cover the inner side of toaster. Material Properties:High Ductility, High Melting point, Low Cost, Mettalic. Material Selected: According to the material properties, Carbon steel, Alloy steel and Stainless steel can be chosen from table 2.2 (in the appendix)
  • 38. 38 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning Not applicable Less applicable Normal applicable
  • 39. 39 Moving system Function: Holding the handling plate, Magnet, Bread’s Holder. Also sliding movement to move the breads down and return it up after toasting Operation. Material Properties: High Ductility, High Melting point, Low Cost, metallic Material Selected: According to the material properties, Carbon steel, Alloy steel and Stainless steel can be chosen from table 2.2 (in the appendix)
  • 40. 40 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning Not applicable Less applicable Normal applicable
  • 41. 41 Electrical connection snap-fit Function: Fastening the wire of plug to the switch. Material Properties: High Ductility, High conductivity, metallic Material Selected: According to the material properties, Copper and alloys can be chosen from table 2.2 (in the appendix)
  • 42. 42 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 43. 43 Bottom cover Function: To cover and maintain all assembled parts and the main cover Material Properties: Heat resistance, good insulator, approximately high melting point. Low cost, non-metalic Material Selected: According to the material properties, Thermoplastic and Thermosets can be chosen from table 2.2 (in the appendix)
  • 44. 44 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 45. 45 Top Cover Function: Covering all Sub assembly parts. Material Properties: Heat resistance, good insulator, approximately high melting point. Low cost, non-metallic Material Selected: According to the material properties, Thermoplastic and Thermosets can be chosen from table 2.2 (in the appendix)
  • 46. 46 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 47. 47 4 Suitable process for each part 4.1 Shape attributes 4.1.1 Depressions (Depress) The ability to form recesses or grooves in the surfaces of the part. The first column entry refers to the possibility of forming depressions in a single direction, while the second entry refers to the possibility of forming depressions in more than one direction. These two entries refer to depressions in the direction of tooling motion and those in other directions. The following are some examples of tooling motion directions. Processes with split moulds— the direction of mold opening. Processes that generate continuous profiles-normal to the direction of extrusion or normal to the axis of the cutting medium. Forging (impact) processes—the direction of impact of the tooling onto the part. Uniform wall (UniWall): Uniform wall thickness. Any no uniformity arising from the natural tendency of the process, such as material stretching or build-up behind projections in centrifugal processes is ignored, and the wall is still considered uniform. Uniform cross section (UniSect): Parts where any cross sections normal to a part axis are identical, excluding draft. Axis of rotation (AxisRot): Parts whose shape can be generated by rotation about a single axis: a solid of revolution.
  • 48. 48 Regular cross section (RegXSec): Cross sections normal to the part's axis contain a regular pattern (e.g., a hexagonal or splined shaft). Changes in shape that maintain a regular pattern are permissible (e.g., splined shaft with a hexagonal head). Captured cavities (CaptCav): The ability is needed to form cavities with reentrant surfaces (e.g., a bottle). Enclosed (Enclosed): Parts are hollow and completely enclosed. Draft-free surfaces (NoDraft): The capability of producing constant cross sections in the direction of tooling motion. Many processes can approach this capability when less than ideal draft allowances are specified, but this designation is reserved for processes where this capability is a basic characteristic and no draft can be obtained without cost penalty.
  • 49. 49 The sample of shape attributes 1 Depression YES/NO 2 Uniform wall YES/NO 3 Uniform cross section YES/NO 4 Axis Rotation YES/NO 5 Regular Cross section YES/NO 6 Capture Cavity YES/NO 7 Enclosed Cavity YES/NO 8 No Draft YES/NO From this figure we find the attribute of each part’s shape and it can help us to choose primary process of materials. So with next table that illustrate the primary process selection. In primary process selection if YES or NO from attribute table under attributes. After that from the vertical columns, all the processes that which have, N below YES in table and M below NO are eliminating. The sample of table for primary process selection is shown in table 2.2 in the appendix, at first some information about process can be useful.
  • 50. 50 Front plate 1 Depression YES 2 Uniform wall YES 3 Uniform cross section NO 4 Axis Rotation NO 5 Regular Cross section NO 6 Capture Cavity NO 7 Enclosed Cavity NO 8 No Draft NO According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2. In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.
  • 51. 51 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 52. 52 Moving System 1 Depression YES 2 Uniform wall YES 3 Uniform cross section NO 4 Axis Rotation NO 5 Regular Cross section NO 6 Capture Cavity NO 7 Enclosed Cavity NO 8 No Draft NO According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2. In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.
  • 53. 53 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 54. 54 1 Depression YES 2 Uniform wall YES 3 Uniform cross section NO 4 Axis Rotation NO 5 Regular Cross section NO 6 Capture Cavity NO 7 Enclosed Cavity NO 8 No Draft NO According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2. In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.
  • 55. 55 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 56. 56 1 Depression YES 2 Uniform wall NO 3 Uniform cross section NO 4 Axis Rotation NO 5 Regular Cross section NO 6 Capture Cavity NO 7 Enclosed Cavity NO 8 No Draft NO According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2. In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.
  • 57. 57 NO Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 58. 58 1 Depression YES 2 Uniform wall YES 3 Uniform cross section NO 4 Axis Rotation NO 5 Regular Cross section NO 6 Capture Cavity NO 7 Enclosed Cavity NO 8 No Draft NO According to shape attributes and referring to table 2.2, the items with Yes will eliminate process that are not capable producing these features which are shown in the table with N and those futures with No answer will eliminate process which are only capable of producing parts with present features which are shown with M in table 2.2. In the following table the result for 8 shape attributes have been summarized. The Black color is shown the process which eliminated.
  • 59. 59 N O Process CastIron CarbonSteel AlloySteel StainlessSteel AluminumandAlloys CopperandAlloys ZincandAlloys MagnesiumandAlloys TitaniumandAlloys NickelandAlloys RefractionMetals Thermoplastics Thermosets 1 Sand Casting 2 Investment Casting 3 Die Casting 4 Injection Moulding 5 Structural Form Moulding 6 Blow Molding (Ext.) 7 Blow Molding (Inj.) 8 Rotational Molding 9 Impact Extrusion 10 Cold Heading 11 Closed Die Forging 12 Powder Metal Parts 13 Hot Extrusion 14 Rotary Swaging 15 Machining (From Stock) 16 ECM 17 EDM 18 Wire EDM 19 Sheet Metal (Stamp/bend) 20 Thermoforming 21 Metal Spinning
  • 60. 60 4.2 Appropriate Manufacturing Processes 4.2.1 Sand Casting: The traditional method of casting metals is in sand molds and has been used for millennia. Sand casting is still the most prevalent form of casting. Typical applications of sand casting include machine bases, large turbine impellers, propellers, plumbing fixtures, and a wide variety of other products and components (Figure 8.). Basically, sand casting consists of (a) placing a pattern (having the shape of the desired casting) in sand to make an imprint, (b) incorporating a gating system, (c) removing the pattern and filling the mold cavity with molten metal, (d) allowing the metal to cool until it solidifies, (e) breaking away the sand mold, and (f) removing the casting. Figure 8. Schematic illustration of a sand casting, showing various features.
  • 61. 61 Process Part Size Tolerances Surface Finish Shape Produced Competitively Process Limitation Materials Sand Casting Weight : 0.2 lb -450 ton Min Wall: 0.125 in General : +- 0.02 ( 1 in ) +- 0.1 ( 24 in ) For dimensions across parting line add +-0.03 ( 50 Sq in ) +- 0.04 ( 200 Sq in ) 500-1000 micro inches Large parts with walls and internal passages of complex geometry requiring good vibration damping characteristics Secondary machining usually required production rates often lower than that for other casting processes Tolerances, Surface finish Coarser than other casting processes 1.Cast Iron, 2.Carbon Steel 3.Alloy Steel 4.Stailnless steel 5.Alluminium 6.Copper 7.Zinc 8.Magnesium 12.Nickel 4.2.2 Investment Casting: The investment casting process, also called the lost wax process, was first used during the period from 4000 to 3000 B.C. Typical parts made are components for office equipment, as well as mechanical components such as gears, cams, valves, and ratchets. Parts up to 1.5 m in diameter and weighting as much as 1140 Kg have been cast successfully by this process. The pattern is made of wax, or of a plastic such as polystyrene, by molding or rapid-prototype techniques. The pattern is then dipped into a slurry of refractory material such as very fine silica and binders, including water, ethyl silicate, and acids. After this initial coating has dried, the pattern is coated repeatedly to increase its thickness for better surface finish in the casting; subsequent layers use larger particles and are intended to build coating thickness quickly (Figure 9.)The term investment derives from the fact that the pattern is invested (surrounded) with the refractory materials. Wax patterns require careful handling because they are not strong enough to withstand the forces encountered during mold making; however, unlike plastic pattern, wax can be recovered and reused.
  • 62. 62 Process Part Size Tolerances Surface Finish Shape Produced Competitively Process Limitation Materials Investment Casting Weight : 1 Oz-110 lb , Major Dimension: to 50 lb , Min Wall : 0.025 ( Ferrous ) , 0.060 Nonferrous) General : +- 0.002 ( 1 in ) +- 0.004 (6in) 63-25 Micro inches Small intricate parts requiring good surface finish, good dimensional control, and high strength Most investment casting are less than 12 in, Long and less than 10 lbs, L/D ratio of though or blind holes less than 4:1 and 1:1 respectively Tooling cost and lead time generally greater than for othercasting processes except die casting 2.Carbon Steel 3.Alloy Steel 4.Stailnless steel 5.Alluminium 6.Copper 12.Nickel Figure 9. Schematic illustration of the investment casting (lost wax) process.
  • 63. 4.2.3 Die Casting: In pressure die casting, the metal is injected into the mold at high primarily used for high-volume production of zinc, aluminum, and magnesium alloys, although ferrous and copper-base alloys may also be cast. The process is capable of high production rates. Production rates are related to the siz complex as automotive engine blocks and transmission housings are routinely made by die casting. Die Casting Processes. There are two major types of die casting machines: hot chamber and cold chamber. In the hot cham gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into the mold. This method avoids one metal transfer operation, and it is used primarily for zinc and magnesium. In the cold chamber process ( poured or metered into the shot sleeve. The piston is then activated to force the metal into the mold. Cold chamber machines are used for aluminum, because the process minimizes the amount of time that the molten alloy is in contact with the die casting machine. Fig. 19 Schematic showing the principal components of a hot chamber die casting machine In pressure die casting, the metal is injected into the mold at high pressures. The process is volume production of zinc, aluminum, and magnesium alloys, base alloys may also be cast. The process is capable of high production rates. Production rates are related to the size and complexity of the part. Parts as complex as automotive engine blocks and transmission housings are routinely made by die Die Casting Processes. There are two major types of die casting machines: hot chamber and cold chamber. In the hot chamber machine (Fig 19) ,the injection chamber is a gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into the mold. This method avoids one metal transfer operation, and it is used primarily for zinc the cold chamber process (Fig20) the metal is melted separately and poured or metered into the shot sleeve. The piston is then activated to force the metal into the mold. Cold chamber machines are used for aluminum, because the process minimizes the of time that the molten alloy is in contact with the die casting machine. Fig. 19 Schematic showing the principal components of a hot chamber die casting machine 63 pressures. The process is volume production of zinc, aluminum, and magnesium alloys, base alloys may also be cast. The process is capable of high e and complexity of the part. Parts as complex as automotive engine blocks and transmission housings are routinely made by die Die Casting Processes. There are two major types of die casting machines: hot the injection chamber is a gooseneck inserted in the melt. Pressure is applied to the melt to force some of the metal into the mold. This method avoids one metal transfer operation, and it is used primarily for zinc the metal is melted separately and poured or metered into the shot sleeve. The piston is then activated to force the metal into the mold. Cold chamber machines are used for aluminum, because the process minimizes the Fig. 19 Schematic showing the principal components of a hot chamber die casting machine
  • 64. Fig. 20 Schematic showing the principal components of a cold chamber die casting Dies. The die consists of at least two parts, the cover half and the ejector half ( dies are made of heat-resistant tool steels. The metal enters the die through the nozzle or shot sleeve, which is located in the cover half. The cover pins, which are activated when the ejector half retracts after the casting is solid, are located in the ejector half of the die. The gating is also generally placed in the ejector half of the die. Undercuts in the casting may be formed by metal slides or retractable cores in the die, which can enter the die space from each side as well as the top and bottom. Ceramic cores may be placed in the die to make configurations that cannot be made any other way; the cores removed chemically after the casting is solid. Fig. 21 Components of a single-cavity die casting die for use in a hot chamber machine The die also contains vents and overflow areas where excess metal flows during injection. In addition, most dies permanent molding, proper placement of the water lines is critical to obtaining good quality castings, especially for multiple-cavity dies. Processing sequence: The sequence of the die casting proc open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution. This spray coats the die with a thin layer of mold release, and the water evaporates, cooling the die surface. The die is closed, and m ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal Fig. 20 Schematic showing the principal components of a cold chamber die casting Dies. The die consists of at least two parts, the cover half and the ejector half ( resistant tool steels. The metal enters the die through the nozzle or shot sleeve, which is located in the cover half. The cover half is stationary during casting. Ejector pins, which are activated when the ejector half retracts after the casting is solid, are located in the ejector half of the die. The gating is also generally placed in the ejector half of the die. e casting may be formed by metal slides or retractable cores in the die, which can enter the die space from each side as well as the top and bottom. Ceramic cores may be placed in the die to make configurations that cannot be made any other way; the cores removed chemically after the casting is solid. cavity die casting die for use in a hot chamber machine The die also contains vents and overflow areas where excess metal flows during injection. In addition, most dies contain water cooling lines to control die heating. As in permanent molding, proper placement of the water lines is critical to obtaining good quality cavity dies. The sequence of the die casting process begins when the die is open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution. This spray coats the die with a thin layer of mold release, and the water evaporates, cooling the die surface. The die is closed, and metal is either injected into the die (hot chamber) or ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal 64 Fig. 20 Schematic showing the principal components of a cold chamber die casting machine Dies. The die consists of at least two parts, the cover half and the ejector half (Fig 21 ). The resistant tool steels. The metal enters the die through the nozzle or shot half is stationary during casting. Ejector pins, which are activated when the ejector half retracts after the casting is solid, are located in the ejector half of the die. The gating is also generally placed in the ejector half of the die. e casting may be formed by metal slides or retractable cores in the die, which can enter the die space from each side as well as the top and bottom. Ceramic cores may be placed in the die to make configurations that cannot be made any other way; the cores are cavity die casting die for use in a hot chamber machine The die also contains vents and overflow areas where excess metal flows during contain water cooling lines to control die heating. As in permanent molding, proper placement of the water lines is critical to obtaining good quality ess begins when the die is open before the shot. The die is first sprayed with a lubricant, usually an aqueous solution. This spray coats the die with a thin layer of mold release, and the water evaporates, cooling etal is either injected into the die (hot chamber) or ladled into the shot sleeve (cold chamber). The shot proceeds in three stages. In the first stage, the piston moves slowly, to fill the shot sleeve so that air is not entrapped in the metal
  • 65. 65 before injection begins. In the second stage, the piston moves very quickly, forcing the metal into the mold cavity. The dies are filled in less than 0.15 s. Pressure builds up on the metal during this phase. In the third stage, pressure is intensified to minimize the formation of porosity. The high pressures (up to 70 MPa, or 5 tsi) require elaborate locking mechanisms to keep the dies closed during the cycle; locking forces of up to 45,000 kN (5000 tonf) are used in the largest machines. After the casting is solid, the dies open, and the casting and its runner system are removed from the die. Slides and cores are usually retracted first, and then the dies open. The gates are trimmed off on a separate trim press. High production die casting operations are highly automated, with the cycle controlled by computer and robots handling the metering of metal into the shot sleeve and removing the casting and gating from the die. After the casting is removed, the die is sprayed again, and the cycle is repeated.Risers are rarely used in die casting because the metal freezes so quickly that feeding does not have time to occur. The gating system is designed to fill the mold as quickly and efficiently as possible. The area where the shot plunger comes to rest in the gating system is called the "biscuit."Molten metal may be transferred to the shot sleeve by means of hand ladling, automated ladling, or by being pumped from the melting furnace to the shot sleeve, using pumps made of ceramics, or using electromagnetic force.Die casting machines are complex. They must be capable of rapid, repetitive motion. The dies must maintain alignment during operation to avoid being damaged, and the cycle of the machine must be controlled accurately. Die failure is usually by thermal shock (heat checking). Iron is often added to aluminum alloys used in die casting to prevent soldering of the alloy to the die. The amount of iron must be controlled, as excess iron (above 0.8%) forms a sludge in the alloy, which, if carried over into the casting as inclusions, will lower casting properties and casting machinability. Air Entrapment: The rapid injection of metal into the die cavity inevitably traps air in the casting. This air expands during heat treatment, forming blisters on the surface of the casting. For this reason, most conventional die castings are not heat treated. However, there are a number of methods that may be used to minimize the entrapment of air in the die cavity. In one, the air in the cavity is evacuated prior to making the shot. In another method used for aluminum alloys, the die cavity is filled with oxygen before the shot. During the shot, the oxygen reacts with the aluminum alloy, forming tiny particles of aluminum oxide, which are
  • 66. dispersed in the casting. Because all of the gas in the c no gas to form gas bubbles in the casting.Because of the limitations of conventional die casting, a variation on the process has been developed to substantially reduce air entrapment. In this method, called "vertical squeezecasting," the shot sleeve is located beneath the die cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are larger than those used in conventional die casting to assure that mold filling is even and free of turbulence, which causes air entrapment. Production rates are slightly lower using vertical squeeze casting, but casting quality is improved. Vertical squeez confused with another process known as squeeze casting, in which liquid is ladled into the bottom half of a metal die, and the die is closed, similar to a forging press. This process eliminates porosity. dispersed in the casting. Because all of the gas in the cavity is used in this reaction, there is no gas to form gas bubbles in the casting.Because of the limitations of conventional die casting, a variation on the process has been developed to substantially reduce air entrapment. l squeezecasting," the shot sleeve is located beneath the die cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are larger than those used in conventional die casting to assure that mold filling is even and free of turbulence, which causes air entrapment. Production rates are slightly lower using vertical squeeze casting, but casting quality is improved. Vertical squeeze casting is not to be confused with another process known as squeeze casting, in which liquid is ladled into the bottom half of a metal die, and the die is closed, similar to a forging press. This process 66 avity is used in this reaction, there is no gas to form gas bubbles in the casting.Because of the limitations of conventional die casting, a variation on the process has been developed to substantially reduce air entrapment. l squeezecasting," the shot sleeve is located beneath the die cavity fig22. The shot sleeve tilts to be filled, then it returns to the injection position. The metal fills the mold at a much slower rate, expelling the gas in the mold ahead of it. Gates are larger than those used in conventional die casting to assure that mold filling is even and free of turbulence, which causes air entrapment. Production rates are slightly lower using vertical e casting is not to be confused with another process known as squeeze casting, in which liquid is ladled into the bottom half of a metal die, and the die is closed, similar to a forging press. This process
  • 67. 67 Process Part Size Tolerances Surface Finish Shape Prodeuced Competitively Process Limitation Materials Die Casting Min Wall ( in ) : 0.025 Min Hole dia: 0.04- 0.08 in Max Weight : 35 (Zn) , 20 (Al) , 10 (Mg) General : +-0.0002 ( 1in ), Zinc +-0.003 (1 in) .( Allum & Mg) Add +- 0.004 across parting line or moving core 32-85 Micro inches Small to minimum sized parts with intricate detail and good surface finish Triming operations required for flash and overflow removal porosity can be present , Die life limited to approximately 200 K shots in Al or Mg or 1 million Zn. 5.Alluminium 6.Copper 7.Zinc 8.Magnesium 4.2.4 Injection molding: The largest quantity of plastic parts is made by injection molding. Plastic compound is fed in powdered or granular form from a hopper through metering and melting stages and then injected into a mold. After a brief cooling period, the mold is opened and the solidified part is ejected is a manufacturing process for both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the mold cavity. After a product is designed, usually by an industrial designer or an engineer molds are made by a MoldMaker (or toolmaker) from metal, usually either steel or aluminum, and precision- machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panelsof cars.
  • 68. 68 Effects on the material properties: The mechanical properties of a part are usually little affected. Some parts can have internal stresses in them. This is one of the reasons why it's good to have uniform wall thickness when molding. One of the physical property changes is shrinkage. A permanent chemical property change is the material thermoset, which can't be remelted to be injected again. Tool materials: Tool steel or beryllium-copper are often used. Mild steel, aluminum, nickel or epoxy are suitable only for prototype or very short production runs. Modern hard aluminum (7075 and 2024 alloys) with proper mold design, can easily make molds capable of 100,000 or more part life.[Citation needed] Geometrical Possibilities: The most commonly used plastic molding process, injection molding, is used to create a large variety of products with different shapes and sizes. Most importantly, they can create products with complex geometry that many other processes cannot. There are a few precautions when designing something that will be made using this process to reduce the risk of weak spots. First, streamline your product or keep the thickness relatively uniform. Second, try and keep your product between 2 to 20 inches.
  • 69. 69 The size of a part will depend on a number of factors (material, wall thickness, shape,process etc.). The initial raw material required may be measured in the form of granules, pellets or powders. Here are some ranges of the sizes. Method Raw materials Maximum size Minimum size Injection molding (thermo- plastic) Granules, pellets, powders 700 oz. Less than 1 oz. Injection molding (thermo- setting) Granules, pellets, powders 200 oz. Less than 1 oz. Machining of Mold: Molds are built through two main methods: standard machining and EDM. Standard Machining, in its conventional form, has historically been the method of building injection molds. With technological development, CNC machining became the predominant means of making more complex molds with more accurate mold details in less time than traditional methods. The electrical discharge machining (EDM) or spark erosion process has become widely used in mold making. As well as allowing the formation of shapes that are difficult to machine, the process allows pre-hardened molds to be shaped so that no heat treatment is required. Changes to a hardened mold by conventional drilling and milling normally require annealing to soften the mold, followed by heat treatment to harden it again. EDM is a simple process in which a shaped electrode, usually made of copper or graphite, is very slowly lowered onto the mold surface (over a period of many hours), which is immersed in paraffin oil. A voltage applied between tool and mold causes spark erosion of the mold surface in the inverse shape of the electrode.
  • 70. 70 The Cost: The cost of manufacturing molds depends on a very large set of factors ranging from number of cavities, size of the parts (and therefore the mold), complexity of the pieces, expected tool longevity, surface finishes and many others. The initial cost is great, however the piece part cost is low, so with greater quantities the overall price decreases. Injection molding cycle: The sequence of events during the injection mold of a plastic part is called the injection molding cycle. The cycle begins when the mold closes, followed by the injection of the polymer into the mold cavity. Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the part is sufficiently cool, the mold opens and the part is ejected. The time it takes to make a product using injection molding can be calculated by adding: Twice the Mold Open/Close Time (2M)+Injection Time (T)+Cooling Time (C)+Ejection Time(E), Where T is found by dividing:Mold Size (S) / Flow Rate (F) Total time = 2M + T + C + E ; T = V/R ; [V = Mold cavity size (in3), R = Material flow, rate (in3/min)] 4.2.5 Blow Molding (Ext.): In extrusion blow molding, a tube or perform (usually oriented so that it is vertical) is first extruded. It is then clamped into a mold with a cavity much larger than the tube diameter and blown outward to fill the mold cavity. (Figure 3.) Depending on the material, the blow ratio may be as high as 7:1. Blowing usually is done with a hot air blast at a pressure ranging from 350 to 700 kPa. Drums with a volume as large as 2000 liters can be made by this process. Typical die material are steel, aluminum, and beryllium copper.
  • 71. 71 In some operations, the extrusion is continuous and the molds move with the tubing. The molds close around the tubing, sealing off one end, breaking the long tube into individual sections, and moving away as air is injected into the tubular piece. The part is then cooled and ejected from the mold. Corrugated-plastic pipe and tubing are made by continuous blow molding in which the pipe or tubing is extruded horizontally and blown into moving molds. 4.2.6 Blow Molding (Inj.): In injection blow molding, a short tubular piece (parison) is injection molded (Figure 4.) into cool dies. (Parisons may be made and stored for later use.) The dies then open, and the parison is transferred to a blow molding die by an indexing mechanism. Hot air is injected into the parison, expanding it do the walls of the mold cavity. Typical products made are plastic beverage bottles (typically made of polyethylene or polyetheretherketone, PEEK) and small, hollow containers.
  • 72. 72 4.2.7 Impact Extrusion: Impact extrusion is similar to indirect extrusion, and the process often is included in the cold extrusion category. The punch descends rapidly on the blank (slug), which is extruded backwards (Figure 5.). Because of volume constancy, the thickness of the tubular extruded section is a function of the clearance between the punch and the die cavity. Some products made by impact extrusion are collapsible tubes (similar to those used for toothpaste), light fixture, automotive parts, and small pressure vessels. Most nonferrous metals can be impact extruded in vertical presses and at production rates as high as two parts per second. The maximum diameter of the parts made is about 150 mm. The impact extrusion process can produce thin-walled tubular sections having thickness to diameter ratios as small as 0.005. Consequently, the symmetry of the part and the concentricity of the punch and the blank are important.
  • 73. 73 4.2.8 Cold Heading: In cold heading or upsetting, force applied by one or more blows of a tool displaces metal in a portion or all of a slug, wire, or rod blank. This plastic flow produces a section or part of different contour, larger in cross section than the original material. Force is generally applied by a moving punch to form that portion of the blank protruding from a stationary die. As seen in Fig. 3.7.1, some parts are upset in the punch, some in the die, some in both punch and die, and others between the punch and the die. Related Processes: Upsetting is often combined with forward or backward extrusion, particularly in cold-forming large-headed, small-shanked parts. Warm heading is applied for processing difficult-to-head metals such as medium-to high-carbon steels, austenitic stainless steels, and other materials that work-harden rapidly. In this compromise between cold and hot heading, the metal is preheated to between 150 and 540°C (300 and 1000°F) or more (depending on the particular metal, but below its recrystallization temperature) to increase its plasticity and reduce the force required for heading.
  • 74. 74 Rotary forging is a related process in which deformation is induced progressively rather than by a single direct squeeze. The workpiece is subjected to a combined rolling and squeezing action to produce progressive upsetting. This method is particularly suitable for thin, intricate flange sections. Secondary Operations Many secondary operations are performed on cold-upset parts, depending on th design and application of the part. These include grooving, shaving, pointing, flattening, bending, piercing, drilling, tapping, threading (often done with a thread- rolling machine made an integral part of the header), heat treating, and plating. Cold-Heading Machines: Most cold-heading machines used in high production are fed coil stock. A machinemay include a straightener, draw die, feed rolls, and shear. Sheared slugs are automatically transferred to a stationary die, and the projecting end of each slug is struck axially by the upsetting tool (punch). In some cases, as in nail making, the stock can be upset first and then sheared to length. Multistation and progressive headers, as well as bolt-making machines, are equipped with automatic-transfer mechanisms to move parts to successive stations and may have trimming, pointing, and thread-rolling stations. Headers and forming machines are available in a wide variety of sizes and types. They are frequently rated by maximum-diameter-cutoff capacity and feed lengths (generally up to 14 times rated diameter, but this capacity can vary). Suitable Materials: Any material that is malleable when cold can be cold-formed. Materials having the lowest yield strength and the greatest range between yield and ultimate strengths are the most malleable. Since strain or work hardening during cold working decreases formability, the rate of strain hardening of the material is an important consideration. Hardness of the material is also critical, since too hard a material is impracticable to cold-work. Prior operations, sometimes required to prepare material for upsetting, can include heat treating, drawing, descaling, and lubricating. The upsetting properties of most steels are improved by annealing or spheroidizing. Whenever possible, the designer should avoid specifying exact material analyses, since this limits the upsetter’s flexibility and may increase production costs. Several different analyses
  • 75. 75 of a basic material often can satisfy service requirements, but they may vary in upsettability, availability, and cost. • Steels: Low-carbon steels , Medium high-carbon steels , High-carbon steels , Alloy steels , Rimmed steels , • Stainless Steels • Nickel Alloys • Aluminum Alloys • Copper and Copper Alloys • Other Materials: Titanium, beryllium, and refractory metals are less formable at room temperatures, and they are likely to crack when cold-headed. As a result, they are often processed warm. Dimensions: As wide a tolerance as possible should be allowed on lugs, fins, tapers and projections because metal-flow behavior is sometimes unpredictable in forming these shapes. Radii generally can be formed to tolerances of 0.13 mm (0.005 in). Geometry: Concentricity variations of 0.025 to 0.08 mm (0.001 to 0.003 in) TIR are not uncommon in blank sizes up to 6 mm in) in diameter if the difference between the two referenced diameters is not too great. Greater concentricity tolerance is generally needed for larger-size parts and larger differences in diameters. If closer tolerances are needed, secondary operations such as machining, shaving, or grinding are generally required. Straightness of cold-upset parts can generally be held to about 0.4 percent of length. Surface Finishes: A finish of 0.4 to 0.8m (16 to 32 in) usually can be obtained economically. Upsetting of heads, however, sometimes can decrease the quality of surface finish unless high pressures are exerted on the sidewalls of the containing die. High-quality finishes generally also require the use of high-quality clean wire. Surface finish also can vary among different parts or different areas of the same part, depending on the surface of the wire or bar being headed, the amount of cold working performed in various areas, the lubricant used, and the condition of the tools. The best finish on any part is usually achieved when direct contact has been made with the tools.
  • 76. 76 4.2.9 Powder Metal Parts Powder metallurgy is used for manufacturing products or articles from powdered metals by placing these powders in molds and are compacting the same using heavy compressive force. Typical examples of such article or products are grinding wheels, filament wire, magnets, welding rods, tungsten carbide cutting tools, self-lubricating bearings electrical contacts and turbines blades having high temperature strength. The manufacture of parts by powder metallurgy process involves the manufacture of powders, blending, compacting, profiteering, sintering and a number of secondary operations such as sizing, coining, machining, impregnation, infiltration, plating, and heat treatment. The compressed articles are then heated to temperatures much below their melting points to bind the particles together and improve their strength and other properties. Few non-metallic materials can also be added to the metallic powders to provide adequate bond or impart some the needed properties. The products made through this process are very costly on account of the high cost of metal powders as well as of the dies used. The powders of almost all metals and a large quantity of alloys, and nonmetals may be used. The application of powder metallurgy process is economically feasible only for high mass production. Parts made by powder metallurgy process exhibit properties, which cannot be produced by conventional methods. Simple shaped parts can be made to size with high precision without waste, and completely or almost ready for installation. Powder Metallurgy Process: The powder metallurgy process consists of the following basic steps: 1. Formation of metallic powders. 2. Mixing or blending of the metallic powders in required proportions. 3. Compressing and compacting the powders into desired shapes and sizes in form of articles. 4. Sintering the compacted articles in a controlled furnace atmosphere. 5. Subjecting the sintered articles to secondary processing if needed so.
  • 77. 77 Particle shape: There are various shapes of metal powders namely spherical, sub-rounded, rounded,angular, sub-angular, flakes etc. Particles shape influences the packing and flow characteristics of the powders. Chemical Composition: Chemical composition of metallic powder implies the type and percentage of alloyingelements and impurities. It usually determines the particle hardness and compressibility. The chemical composition of a powder can be determined by chemical analysis methods. Particle microstructure: Particle microstructure reveals various phases, inclusions and internal porosity. Apparent density: Apparent density is defined as the weight, of a loosely heated quantity of powder necessaryto fill a given die cavity completely. Flow characteristics: Flow-ability of metal powders is most important in cases where moulds have to be filled quickly. Metal powders with good flow characteristics fill a mould cavity uniformly.
  • 78. 78 Secondary Operations: Some powder metal parts may be used in the sintered condition while in some other cases additional secondary operations have to be performed to get the desired surface finish, close tolerance etc. The secondary operations may be of following types: 1. Annealing. 2. Repressing for greater density or closer dimensional control. 3. Machining. 4. Polishing. 5. Rolling, forging or drawing. 6. Surface treatments to protect against corrosion. 7. In some cases infiltration is needed to provide increased strength, hardness, densityobtainable by straight sintering. 8. The procedures for plating powdered metal parts are quite different from those usedfor wrought or cast metal parts. In powdered metal parts, porosity must be eliminated before the part is plated. After the porosity has been eliminated regular plating procedures can be used.