MT MODULE 2.pptx

MANUFACTURING
TECHNOLOGY
MODULE 2
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE
OF POLYTECHNICS

DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS

DEPARTMENT OF MECHANICAL ENGINEERING, SCMS
COLLEGE OF POLYTECHNICS

PREVEIW
• What is Metal casting ?
• It is the industry of pouring
liquid metal
into a mold to achieve a desired
shape.

INTRODUCTION
(Contd)
Almost all metals can be cast.
• The challenge in casting is to produce
products (casts) that are of
the desired composition, free from
defects, and meet
requirements for strength, dimensional
accuracy and surface finish.

Metal Casting
• Combustion used to melt material
• Electricity used to melt material
Create liquid metal - Melting
• Permanent mold casting
• Semi Permanent mold casting
• Consumable mold casting
Create solid shape - Casting

TYPES OF
CASTING
PROCESSES
• The principle of casting consists of introducing
the molten metal in to a cavity known as mould
and allow it to solidify, the shape of the object is
determined by the shape of the mould cavity
• Important casting processes are
1. Sand mould casting
2. Permanent mould casting
3. Special casting process
a) Die casting
b) Slush casting
c) Centrifugal casting
d) Plaster mould casting
e) Shell mould casting
f) Investment casting

SAND MOULD CASTING
• In this process sand aggregates are
used to make the mould
• Whenever the molten metal is
poured into sand mould and allowed
to solidify the product may be called
as sand casting

DIE CASTING
• Die casting is a process, in which the molten
metal is injected into the mold cavity.
• The reusable steel mold used in the die
casting process is called a die.
• Die casting is a highly productive method of
casting parts with low dimensions tolerance
and high surface quality.
The following parts are manufactured by die
casting method: automotive connecting rods,
pistons, cylinder beds, electronic enclosures,
toys, plumbing fittings.
The molten metal injection is carried out by a
machine called die casting machine.
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GRAVITY DIE CASTING
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PERMENANT MOULD CASTING OR GAVITY DIE
CASTING
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• A casting produced by pouring molten metal in
metallic mould is known as permanent mould
casting
• The moulds made of metals are called metal moulds
• These moulds are also known as permanent moulds
or dies. They can be reused many times
• Usually, they are made of gray cast iron or steel and
sometimes bronze, anodized aluminium etc. Are
used
• Pouring in permanent mould is done simply due to
gravity(without any external pressure) hence it is
called gravity die casting
• A metal mould or permanent mould is made in two
halves and an ejector pin mechanism is also
provided for the easy removal of casting
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The mould is first pre heated and given a refractory
coating
Mould halves are closed properly and liquid metal is
poured into it under gravity
Castings are ejected from the mould after they are
solidified
This process is generally used for non ferrous metals
and their alloys such as aluminium, zinc, magnesium
etc.
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GOOSE NECK TYPE
(SUBMERGED
PLUNGER TYPE) HOT
CHAMBER DIE
CASTING MACHINE
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• The hot chamber die casting machine has the metal melting unit as its integral
part
• Hot chamber die casting machines are used for casting zinc, lead and other
low melting alloys
• A submerged plunger type of hot chamber die casting machine is operated by
a pneumatically operated plunger
• When the plunger is in up position the molten metal enters inside the cylinder
through the port shown in the figure
• As the plunger moves down the port gets closed and the molten metal is
forced into the die at a pressure of 70 to 140 bar
• When the metal solidifies die is opened and the casting is ejected
• The die is then closed, the plunger is drawn back to upward position and the
cyAcle is repeated
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DIRECT INJECTION
TYPE OR AIR
INJECTION TYPE HOT
CHAMBER DIE
CASTING MACHINE
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In this type of die casting machine the molten metal from the
container is forced into the die by direct air pressure
In the beginning of the cycle the goose neck is submerged in the
molten metal and is filled by gravity
It is then raised and the injector is brought in contact with the die
opening
Compressed air forces the metal into the die and the pressure is
maintained till the solidification
After solidification the casting is removed and the goose neck
container is lowered to fill the molten metal and the cycle repeats
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COLD CHAMBER DIE CASTING
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In cold chamber die casting machine the melting unit is separate
Molten metal from the melting unit is transformed to the die casting machine by
means of ladles
After closing the die a measured quantity of molten metal is poured into the cold
chamber cylinder using ladles
This molten metal is then forced into the die at a very high pressure using
hydraulically operated plunger
After solidification the die is opened and the casting is removed and the cycle
repeats
The cold chamber machine is used for die casting of copper and other high melting
alloys
Castings produced will have more density and accuracy than hot chamber process
but the production rate is low
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ADVANTAGES
AND
DISADVANTAGES
OF DIE CASTING
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SLUSH CASTING

SLUSH CASTING
Slush casting is a process used for making hollow casting without the use of cores
In this process the molten metal is poured into a metallic mould
The metal is retained in the mould for long enough for the outer skin to solidify
Finally the mould is inverted to remove metal that is still in liquid state, this results
in a thin walled casting
The thickness of the mould depends upon the time for which the molten metal
allowed to remain in the mould
This method is used for making toys, ornaments etc. With non ferrous alloys such
as gold, tin, lead etc DEPARTMENT OF MECHANICAL ENGINEERING, SCMS

• Advantages of Slush Casting
1. Slush Casting method is cheaper as compared to other casting methods.
2. The main advantage of slush casting is that it produces hollow castings which are light in
weight.
3. Use of molten metal is also less as the components are hollow.
4. The die used in slush casting process is simple and of low cost.
5. Accurate outer geometry can be obtained on the casted components by using this
process.
6. Good surface finish is also obtained.
• Disadvantages of Slush Casting
1. Slush casting process is suitable for metals which have lower melting temperatures.
2. In order to pour out the molten metals, the mechanical turning mechanism is required.
3. Slush casting is suitable for manufacturing the small quantity of castings.
4. Strength and other mechanical properties of the casting components are difficult to
control in this process.
5. The internal geometry of the casting cannot be controlled by using slush casting process.
• Applications of Slush Casting
1. Slush casting process is used for manufacturing the components which are hollow (for
example, toys, lamp bases, statues, etc)
2. Slush process is also used for making some decorative coatings to improve the

CENTRIFUGAL CASTING

Centrifugal casting is a process in which molten metal is poured and allowed to
solidify while the mould is kept revolving
The process is also known as liquid forging
The mould is made of metal and lined with refractory materials
The mould is rotated at very high speed and the molten metal is poured into the
cavity by ladle
The centrifugal force directs the fluid metal to the inner surface of the mould with
considerable pressure, where solidification occurs and forms hollow casting
The thickness of the mould is controlled by the amount of metal poured

ADVANTAGES
• It is quick and economical
• It eliminates the use of gates, risers
and cores
• Ferrous and non ferrous metals can be
casted
• Castings are free from shrinkage
• APPLICATIONS
• Centrifugal castings are used for
casting particles of symmetrical shape
eg. Pipes, gears, flywheels, cylinders,
piston etc.

VACUUM CASTING
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RECRYSTALLISATION
During the plastic deformation of metal, the existing grains or crystals
are distorted or broken out
The refining of metal is done by heating the metal
It will lead to the formation of new grains with undistorted space
lattice and this is called recrystallisation
The temperature at which re crystallisation take place.ie. New grains
are formed in the crystal is called recrystallisation temperature
This temperature is different for different metals

COLD WORKING OF METALS
• The mechanical working of metals below its
recrystallisation temperature is called cold
working
• Cold working normally done at room
temperature
• Cold working produces following effects on
metals
i. It distorts the grain structure
ii. It introduce strain hardening or work
hardening
iii. Residual stresses will setup during cold
working
iv. It will decrease the ductility of the material
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Advantages:
Accurate dimensional control can be obtained
No surface oxidation results in the process
Better surface finish is obtained
Strength and hardness of the metal increases
Disadvantages
High pressure and heavier equipments are needed
Only small sized components can be easily cold worked
Only ductile material can be shaped easily
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COLD WORKING
OPERATIONS
1. DRAWING
2. BENDING
3. SQUEEZING
4. SHEARING
5. EXTRUSION
6. SHOT PEENING
7. HOBBING
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DRAWING
• It is the process of producing various cross sections by forcing the metal
through a die by means of a tensile force
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1.1. Wire drawing
This process consist of forcing a large diameter rod
through a die there by reducing the cross-sectional
area of the rod
The rod is first cleaned to remove scale and rust
Some lubricants are coated to avoid corrosion and
oxidation
The wire is drawn by pulling the rod through several
dies of decreasing diameter
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2. Tube Drawing
The tubes produced through hot working are
cold drawn for providing good surface finish
and better dimensional accuracy
The tube is pulled through the die over a fixed
mandrel
The outside diameter of the tube is controlled
by the opening of the die
The inside diameter is controlled by the
mandrel
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3. Deep
Drawing
•This process
involves the
production of a
dish or cup from a
flat sheet metal by
the action of a
punch
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4. Metal
Spinning
• It is the operation of shaping a sheet metal by
pressing against a form while it is rotating
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BENDING
•The bars, rods,
structural shapes,
sheet metals can
be bent to many
shapes in cold
conditions through
dies
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SQUEEZING
•In squeezing metal is made to
flow with in the cavity of die and
punch to attain desired shape
•This process requires great
amount of pressure and is
usually performed in hydraulic
press
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Cold Rolling
•The metal is passed
through a number of
rollers there by
reduction in area until
the required thickness is
obtained
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2.
Upsetting
• It is a squeezing operation
in which the metal is
subjected to reduction in
height or length with a
corresponding increase in
cross-sectional area
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3. Coining
• Coins, medals and other similar
articles are produced by this
process
• This operation is carried out in
dies in which the metal is
confined and restricted its flow
in lateral direction DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE
OF POLYTECHNICS

4. Embossing
5. Cold Heading
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6. Hobbing
• It is the process of producing cavities in softer metals
by forcing a hardened steel form or Hob
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SHEARING
• This is the process of cutting the metal using punch
and die
a)Trimming
• It consist of removal of excess material left around the
parting lines
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b)Punching/ Piercing
It is an operation of cutting holes in a sheet metal using
punch and die
c)Blanking
It is an operation of cutting flat sheet to the desired
shape
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COLD EXTRUSION
• The process of extrusion involves the flow of metal in its
plastic state through a shaped die under pressure
Impact Extrusion
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HOT
WORKING OF
METALS
It improves the mechanical properties
such as ductility, toughness, elongation
percentage, resistance to shock and
vibrations
Mechanical working of metals above its
recrystallisation temperature is known
as hot working
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HOT ROLLING
• Rolling is the most economical and rapid method of converting
large section into desired shape
• The forming of bars, plates, sheets, I beams and other structural
sections are made by rolling
• The process of rolling consist of passing the hot billets through at
least two rolls rotating in opposite direction
• The space between the rolls is adjusted to obtain the desired
thickness
• The rolls thus squeeze the passing billets to reduce its cross-
section and to increase its length
• When there is only top, and bottom rolls the mill is called two high
mill
• If three rolls are mounted, it is called three high mill
• Four high mills consists of four rolls, two of which are working rolls
and the other two are backing up rolls
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HOT PIERCING
• It is the process to produce
seamless tubes
• In this process cylindrical
billets are passed between
two conical shaped rolls
rotating in the same
direction
• The fixed mandrel assists in
piercing and controls the
size of the hole
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HOT DRAWING
•It is mostly used
for the
production of
seamless tubes
and cylinders
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HOT EXTRUSION
• It is the process of
pushing a heated
billet of metal
through an
opening in the die,
thus forming an
elongated part of
uniform cross-
section
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Direct or Forward Extrusion
Heated billet is placed in the die chamber and the pressure is applied through ram
The metal is extruded through the die opening in the forward direction i.e. the same direction of the ram
movement
2. Indirect or Backward Extrusion
The extruded metal is forced through the hollow ram
3. Tube Extrusion
Mandrel attached to the ram is pushed through the centre of the heated billet and the die
Pressure is applied on the billet by advancing the ram
The metal flows through the opening between the die and the mandrel
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HOT SPINNING
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Powder Metallurgy (PM)
• Metal processing technology in which parts are produced from metallic
powders
• Usual PM production sequence:
1. Pressing - powders are compressed into desired shape to produce
green compact
• Accomplished in press using punch-and-die
2. Sintering – green compacts are heated to bond the particles into a
hard, rigid mass
• Temperatures are below melting point
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Why Powder Metallurgy is Important
PM parts can be mass produced to net shape or near net shape,
eliminating or reducing the need for subsequent machining
PM process wastes very little material - ~ 97% of starting powders
are converted to product
PM parts can be made with a specified level of porosity, to
produce porous metal parts
• Filters, oil-impregnated bearings and gears
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More Reasons Why PM is Important
Certain metals that are difficult to fabricate by other methods can be shaped by
powder metallurgy
• Tungsten filaments for incandescent lamp bulbs are made by PM
Certain alloy combinations and cermets made by PM cannot be produced in other
ways
PM compares favorably to most casting processes in dimensional control
PM production methods can be automated for economical production
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Limitations and Disadvantages
• High tooling and equipment costs
• Metallic powders are expensive
• Problems in storing and handling metal powders
• Degradation over time, fire hazards with certain metals
• Limitations on part geometry because metal powders do not readily
flow laterally in the die during pressing
• Variations in density throughout part may be a problem, especially for
complex geometries
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PM Work
Materials
Largest tonnage of metals are
alloys of iron, steel, and aluminum
Other PM metals include copper,
nickel, and refractory metals such
as molybdenum and tungsten
Metallic carbides such as tungsten
carbide are often included within
the scope of powder metallurgy
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PM part-making sequence
 Conventional PM part-making sequence consists of:
1. Blending and mixing of powders
2. Compaction - pressing into desired shape
3. Sintering - heating to temperature below melting point to cause
solid-state bonding of particles and strengthening of part
 In addition, secondary operations are sometimes performed to
improve dimensional accuracy, increase density, and for other
reasons

Conventional PM Production Sequence
 (1) Blending, (2) compacting, and (3) sintering

Blending and Mixing of Powders
 For successful results in compaction and sintering, the starting powders
must be homogenized
 Blending - powders of the same chemistry but possibly different
particle sizes are intermingled
 Different particle sizes are often blended to reduce porosity
 Mixing - powders of different chemistries are combined

Compaction
 Application of high pressure to the powders to form them into the required
shape
 Conventional compaction method is pressing, in which opposing
punches squeeze the powders contained in a die
 Work part after pressing is called a green compact, the word green
meaning not fully processed
 The green strength of the part when pressed is okay for handling but
far less than after sintering

Conventional Pressing in PM
 Pressing in PM: (1)
filling die cavity with
powder by automatic
feeder; (2) initial and
(3) final positions of
upper and lower
punches during
pressing, (4) part
ejection

Sintering
 Heat treatment to bond the metallic particles, thereby increasing strength
and hardness
 Usually carried out at 70% to 90% of the metal's melting point
(absolute scale)
 Generally agreed among researchers that the primary driving force
for sintering is reduction of surface energy
 Part shrinkage occurs during sintering due to pore size reduction

Densification and Sizing
 Secondary operations are performed on sintered part to
increase density, improve accuracy, or accomplish
additional shaping
 Repressing - pressing in closed die to increase
density and improve properties
 Sizing - pressing to improve dimensional accuracy
 Coining - pressing details into its surface
 Machining - for geometric features that cannot be
formed by pressing, such as threads and side holes

PM Materials –
Elemental Powders
 A pure metal in particulate form
 Common elemental powders:
 Iron
 Aluminum
 Copper
 Elemental powders can be mixed with other metal
powders to produce alloys that are difficult to
formulate by conventional methods
 Example: tool steels

PM Materials –
Pre-Alloyed Powders
 Each particle is an alloy comprised of the desired chemical composition
 Common pre-alloyed powders:
 Stainless steels
 Certain copper alloys
 High speed steel

PM Products
 Gears, bearings, sprockets, fasteners, electrical
contacts, cutting tools, and various machinery parts
 Advantage of PM: parts can be made to near net
shape or net shape
 When produced in large quantities, gears and bearings
are ideal for PM because:
 Their geometries are defined in two dimensions
 There is a need for porosity in the part to serve as
a reservoir for lubricant

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