Hot forming processes, such as die-casting, investment casting, plaster casting, and sand casting, each provide their own unique manufacturing benefits. Comparing both the advantages and disadvantages of the common types of casting processes can help in selecting the method best suited for a given production run.

1. Introduction
• Metal Casting is one of the oldest materials shaping
methods known. Casting means pouring molten metal into
a mold with a cavity of the shape to be made, and allowing
it to solidify.
• When solidified, the desired metal object is taken out from
the mold either by breaking the mold or taking the mold
apart.
• The solidified object is called the casting. By this process,
intricate parts can be given strength and rigidity frequently
not obtainable by any other manufacturing process. The
mold, into which the metal is poured, is made of some heat
resisting material. Sand is most often used as it resists the
high temperature of the molten metal. Permanent molds of
metal can also be used to cast products

2. Process in which molten metal flows by gravity
or other force into a mold where it solidifies in
the shape of the mold cavity
• The term casting also applies to the part made in
the process
• Steps in casting seem simple:
1. Melt the metal
2. Pour it into a mold
3. Let it freeze

3. The Mold in Casting
• Mold is a container with cavity whose
geometry determines part shape
– Actual size and shape of cavity must be slightly oversized
to allow for shrinkage of metal during solidification and
cooling
– Molds are made of a variety of materials, including sand,
plaster, ceramic, and metal

4. Open Molds and Closed Molds
Two forms of mold: (a) open mold, simply a container in the shape of the
desired part; and (b) closed mold, in which the mold geometry is more
complex and requires a gating system (passageway) leading into the cavity.

5. Two Categories of Casting Processes
1. Expendable mold processes – uses an
expendable mold which must be destroyed
to remove casting
– Mold materials: sand, plaster, and similar materials,
plus binders
2. Permanent mold processes – uses a
permanent mold which can be used over
and over to produce many castings
– Made of metal (or, less commonly, a ceramic refractory
material)

6. Moulds
Expendable Mould
• Can only make one metal casting
• Made of sand, or other similar materials
• Binders used to support material hold its shape
• Mould that metal hardens in should be damaged
to wipe out casting
• More complex geometries are feasible for casting

7. Mould
Long-lasting Mould
• Can create many metal castings
• Generally made of metals or often a refractory
ceramic
• It has parts that can close or open, permitting
eradication of the casting
• Have to open mould limitations part designs

8. Sand Casting Mold

9. Sand Casting Mold Terms
• Mold consists of two halves:
– Cope = upper half of mold
– Drag = bottom half
• Mold halves are contained in a box, called a
flask
• The two halves separate at the parting line

10. Solidification Processes
We consider starting work material is either a
liquid or is in a highly plastic condition, and a
part is created through solidification of the
material
• Solidification processes can be classified
according to engineering material processed:
– Metals
– Ceramics, specifically glasses
– Polymers and polymer matrix composites (PMCs)

11. Classification of solidification processes.

12. Metal solidification process
• Casting is a common metal solidification
process which utilized the melting and re-
solidification of a metal or alloy within a mold
to produce a final desired product.
• Casting is often used to create complex shapes
that would be complicated or expensive to
manufacture using other methods. Here is a
step-by-step explanation of the solidification
of metals and alloys in castings.

13. Solidification Process
• Melting
• Degassing
• Pouring
• Freezing
• Solidification
• Casting

14. 1. MELTING
• The casting process starts by heating a metal alloy in a crucible until
it melts. When a metal is heated above its freezing point, it
becomes liquid. This is also known as its melting point.
• The melting point of metal depends upon the type of metal or alloy
being used. For instance, our zinc alloys melt around 900 degrees F,
whereas some of the bronze alloys we pour melt above 2000
degrees F (hotter than lava). In addition, pure metals melt at the
same constant temperature.
• Conversely, metal alloys will melt within a range of temperatures
depending on the composition of the materials. In its molten state,
a metal contains a high amount of energy. The alloy is heated above
its melting point to allow for enough time for the metal to cool
during the pouring process

15. DEGASSING/MODIFICATION
• When we pour zinc alloys or aluminium alloys, they must
be degassed prior to pouring. This is accomplished by
inserting a graphite lance into the melt. The lance spins very
fast and argon is injected through the lance dispersing it
through the melted alloy. The argon moves dissolved
hydrogen and other contaminants to the surface of the melt.
This contamination is then removed from the crucible prior
to pouring.
• Many alloys require modification prior to pouring. These
modifications increase metal flow ability, improve grain
structure, remove contaminants, etc. Some of the materials
we use to accomplish this are titanium-boron, copper-
phosphorous, strontium, manganese, etc

16. 3. POURING
• After degassing and/or modification, the metal is
tested to ensure it is approximately 50 degrees
(Fahrenheit) above its desired pouring temperature.
This allows enough time for the metal to cool during
the pouring process.
• The crucible is transported via an overhead rail to the
pouring lines. The liquid metal is then poured into a
sand mold. Inside the hollow cavity of the sand mold is
the shape of the desired end product. Sometimes this
cavity is only one part and sometimes it is several
individual parts. It is imperative to keep the lip of the
crucible as close to the sand mold as possible to reduce
the velocity the metal enters the mold cavity

17. 4. FREEZING
• Once the molten liquid has been poured into
the mold it cools rapidly. When the
temperature of the liquid metal changes below
the melting point of that particular metal or
alloy, the solidification process begins. This
usually takes less than a few minutes

18. 5. SOLIDIFICATION
• As the temperature drops further, the molten metal loses
energy and crystals begin to form. This process starts near
the mold walls where it cools first. These crystals eventually
become grains within the final structure. If the metal
solidifies slowly, the grains are longer. If it cools quickly, the
grains are visibly shorter. The crystals (or dendrites)
continue to form and harden until the entire melt is
solidified. During the solidification process, the metal is
shrinking. It is important to feed this shrinking to ensure
the castings are free of voids and shrink defects. This is
accomplished by the use of risers.

19. 6. CASTING
• Once hardened, the cooled metal is removed or
broken from the sand mold to complete the
solidification process. This finished piece is
also called a casting or castings. The casting(s)
are then trimmed, finished and polished based
on the specifications of its final application

20. Products/Parts Made by Casting
• Big parts
– Engine blocks and heads for automotive vehicles, wood
burning stoves, machine frames, railway wheels, pipes,
bells, pump housings
• Small parts
– Dental crowns, jewelry, small statues, frying pans
• All varieties of metals can be cast - ferrous and
nonferrous

21. Overview
• Casting is usually performed in a foundry
Foundry = factory equipped for
• making molds
• melting and handling molten metal
• performing the casting process
• cleaning the finished casting
• Workers who perform casting are called
foundrymen

22. Capabilities and Advantages of
Casting
• Can create complex part geometries that can not be
made by any other process
• Can create both external and internal shapes
• Some casting processes are net shape; others are near
net shape
• Can produce very large parts (with weight more than
100 tons), like m/c bed
• Casting can be applied to shape any metal that can
melt
• Some casting methods are suited to mass production
• Can also be applied on polymers and ceramics

23. Disadvantages of Casting
• Different disadvantages for different casting
processes:
– Limitations on mechanical properties
– Poor dimensional accuracy and surface finish for some
processes; e.g., sand casting
– Safety hazards to workers due to hot molten metals
– Environmental problems

24. Different types of casting process
The Metal Casting or just Casting process may be
divided into two groups
• Hot Forming Process
• Cold Forming Process

25. Hot Forming Process
• Examples of Hot Forming Process are
Centrifugal casting, Extrusion, Forging, Full
mold casting, Investment casting, Permanent
or Gravity Die casting, Plaster mold casting,
Sand Casting, Shell Mold casting. The method
to be used depends upon the nature of the
products to be cast.

26. Cold Forming Process
• Examples of Cold Forming Process are Squeeze
casting, Pressure die casting, Gravity die
casting, Burnishing, Coining, Cold forging,
Hubbing, Impact Extrusion, Peening, Sizing,
Thread rolling.

27. Sand casting process
contents
• Capabilities
• Process Cycle
• Equipment
• Tooling
• Materials
• Possible Defects
• Design Rules
• Cost Drivers

28. • Sand casting, the most widely used casting process, utilizes expendable sand
molds to form complex metal parts that can be made of nearly any alloy. Because
the sand mold must be destroyed in order to remove the part, called the casting,
sand casting typically has a low production rate.
• The sand casting process involves the use of a furnace, metal, pattern, and sand
mold. The metal is melted in the furnace and then ladled and poured into the
cavity of the sand mold, which is formed by the pattern. The sand mold separates
along a parting line and the solidified casting can be removed. The steps in this
process are described in greater detail in the next section
• Sand casting is used to produce a wide variety of metal components with complex
geometries. These parts can vary greatly in size and weight, ranging from a couple
ounces to several tons. Some smaller sand cast parts include components as gears,
pulleys, crankshafts, connecting rods, and propellers. Larger applications include
housings for large equipment and heavy machine bases. Sand casting is also
common in producing automobile components, such as engine blocks, engine
manifolds, cylinder heads, and transmission cases.

30. Capabilities
Typical Feasible
Shapes: Thin-walled: Complex
Solid: Cylindrical
Solid: Cubic
Solid: Complex
Flat
Thin-walled: Cylindrical
Thin-walled: Cubic
Part size: Weight: 1 oz - 450 ton
Materials: Metals
Alloy Steel
Carbon Steel
Cast Iron
Stainless Steel
Aluminum
Copper
Magnesium
Nickel
Lead
Tin
Titanium
Zin

31. Surface finish
- Ra:
300 - 600 μin 125 - 2000
μin
Tolerance: ± 0.03 in. ± 0.015 in
Max wall
thickness:
0.125 - 5 in. 0.09 - 40 in
Quantity: 1 - 1000 1 - 1000000
Lead time: Days Hours
Lead time is the total time
required to manufacture an order
of parts, from the time the order
is received until the parts are
shipped. The lead time depends
on several factors including the
design and manufacturing time of
any required tooling, the
equipment setup time, and the
production rate of the process.
Processes with minimal setup and
standard tooling can have lead
times of only a few hours, while
more complex processes may
require several months
The roughness of a part's surface resulting
from a manufacturing process. Surface
roughness is typically measured as the
arithmetic average (Ra) or root mean square
(RMS) of the surface variations, measured in
microinches or micrometers. A typical
primary manufacturing process results in an
Ra surface roughness of 32-250 microinches
and finishing operations can lower the
roughness to 1-32 microinches.

32. process cycle for sand casting
•
Mold-making
Clamping
Pouring
Cooling
Removal
Trimming

33. Sand
• The sand that is used to create the molds is typically
silica sand (SiO2) that is mixed with a type of binder to
help maintain the shape of the mold cavity.
• Using sand as the mold material offers several benefits
to the casting process. Sand is very inexpensive and is
resistant to high temperatures, allowing many metals to
be cast that have high melting temperatures.
• There are different preparations of the sand for the
mold, which characterize the following four unique
types of sand molds.

34. Types of sand mould
• Greensand mold - Greensand molds use a mixture of sand, water, and a
clay or binder. Typical composition of the mixture is 90% sand, 3% water,
and 7% clay or binder. Greensand molds are the least expensive and most
widely used.
• Skin-dried mold - A skin-dried mold begins like a greensand mold, but
additional bonding materials are added and the cavity surface is dried by a
torch or heating lamp to increase mold strength. Doing so also improves the
dimensional accuracy and surface finish, but will lower the
collapsibility. Dry skin molds are more expensive and require more time,
thus lowering the production rate.
• Dry sand mold - In a dry sand mold, sometimes called a cold box mold, the
sand is mixed only with an organic binder. The mold is strengthened by
baking it in an oven. The resulting mold has high dimensional accuracy, but
is expensive and results in a lower production rate.
• No-bake mold - The sand in a no-bake mold is mixed with a liquid resin
and hardens at room temperature

35. The quality of the sand measures
• Strength - Ability of the sand to maintain its shape.
• Permeability - Ability to allow venting of trapped gases through the
sand. A higher permeability can reduce the porosity of the mold, but
a lower permeability can result in a better surface finish.
Permeability is determined by the size and shape of the sand grains.
• Thermal stability - Ability to resist damage, such as cracking, from
the heat of the molten metal.
• Collapsibility - Ability of the sand to collapse, or more accurately
compress, during solidification of the casting. If the sand can not
compress, then the casting will not be able to shrink freely in the
mold and can result in cracking.
• Reusability - Ability of the sand to be reused for future sand molds.

36. Packing equipment
• There exists many ways to pack the sand into the mold.There are
several types of equipment that provide more effective and efficient
packing of the sand
• One such machine is called a sandslinger and fills the flask with
sand by propelling it under high pressure
• A jolt-squeeze machine is a common piece of equipment which
rapidly jolts the flask to distribute the sand and then uses hydraulic
pressure to compact it in the flask
• impact molding, uses a controlled explosion to drive and compact
the sand into the flask. In what can be considered an opposite
approach, vacuum molding packs the sand by removing the air
between the flask and a thin sheet of plastic that covers the pattern.
• The packing of the sand is also automated in a process known as
flask-less molding

37. Tooling
• The main tooling for sand casting is the pattern that is used to create the
mold cavity. The pattern is a full size model of the part that makes an
impression in the sand mold. However, some internal surfaces may not be
included in the pattern, as they will be created by separate cores.
• The pattern is actually made to be slightly larger than the part because the
casting will shrink inside the mold cavity. Also, several identical patterns
may be used to create multiple impressions in the sand mold, thus creating
multiple cavities that will produce as many parts in one casting.
• Several different materials can be used to fabricate a pattern, including
wood, plastic, and metal. Wood is very common because it is easy to shape
and is inexpensive, however it can warp and deform easily.
• Wood also will wear quicker from the sand. Metal, on the other hand, is
more expensive, but will last longer and has higher tolerances. The pattern
can be reused to create the cavity for many molds of the same part.

38. Types of pattern
• a pattern that lasts longer will reduce tooling
costs. A pattern for a part can be made many
different ways, which are classified into the
following four types
• Solid pattern
• Split pattern
• Match-plate pattern
• Cope and drag pattern

39. Solid pattern
• - A solid pattern is a model of
the part as a single piece. It is
the easiest to fabricate, but can
cause some difficulties in
making the mold. The parting
line and runner system must be
determined separately. Solid
patterns are typically used for
geometrically simple parts that
are produced in low quantities.

40. Split pattern
• A split pattern models the part as
two separate pieces that meet along
the parting line of the mold. Using
two separate pieces allows the mold
cavities in the cope and drag to be
made separately and the parting line
is already determined. Split patterns
are typically used for parts that are
geometrically complex and are
produced in moderate quantities.

41. Match-plate pattern
• A match-plate pattern is similar to a split
pattern, except that each half of the
pattern is attached to opposite sides of a
single plate. The plate is usually made
from wood or metal. This pattern design
ensures proper alignment of the mold
cavities in the cope and drag and the
runner system can be included on the
match plate. Match-plate patterns are
used for larger production quantities and
are often used when the process is
automated.

42. Cope and drag pattern
• - A cope and drag pattern is similar to a
match plate pattern, except that each half of
the pattern is attached to a separate plate and
the mold halves are made independently. Just
as with a match plate pattern, the plates
ensure proper alignment of the mold cavities
in the cope and drag and the runner system
can be included on the plates. Cope and drag
patterns are often desirable for larger
castings, where a match-plate pattern would
be too heavy and cumbersome. They are also
used for larger production quantities and are
often used when the process is automated

43. Materials
• Sand casting is able to make use of almost any
alloy. An advantage of sand casting is the
ability to cast materials with high melting
temperatures, including steel, nickel, and
titanium.
• The four most common materials that are used
in sand casting are shown below, along with
their melting temperatures.

44. Materials
Materials Melting temperature
Aluminum alloys 1220 °F (660 °C)
Brass alloys 1980 °F (1082 °C)
Cast iron 1990-2300 °F (1088-1260 °C)
Cast steel 2500 °F (1371 °C)

45. Possible Defects
Defect Causes
Unfilled sections •Insufficient material
•Low pouring temperature
Porosity •Melt temperature is too high
•Non-uniform cooling rate
•Sand has low permeability
Hot tearing •Non-uniform cooling rate
Surface projections •Erosion of sand mold interior
•A crack in the sand mold
•Mold halves shift

46. Cost Drivers
• Material cost
• Production cost
• Tooling cost

47. Material cost
• The material cost for sand casting includes the cost of the
metal, melting the metal, the mold sand, and the core
sand. The cost of the metal is determined by the weight of
the part, calculated from part volume and material density,
as well the unit price of the material. The melting cost will
also be greater for a larger part weight and is influenced by
the material, as some materials are more costly to melt.
However, the melting cost in typically insignificant
compared to the metal cost. The amount of mold sand that
is used, and hence the cost, is also proportional to the
weight of the part. Lastly, the cost of the core sand is
determined by the quantity and size of the cores used to
cast the part

48. Production cost
The production cost includes a variety of operations used
to cast the part, including core-making, mold-making,
pouring, and cleaning. The cost of making the cores
depends on the volume of the cores and the quantity used
to cast the part. The cost of the mold-making is not
greatly influenced by the part geometry when automated
equipment is being used. However, the inclusion of cores
will slightly slow the process and therefore increase the
cost. Lastly, the cost of pouring the metal and cleaning the
final casting are both driven by the weight of the part. It
will take longer to pour and to clean a larger and heavier
casting.

49. Tooling cost
• The tooling cost has two main components - the pattern and the
core-boxes. The pattern cost is primarily controlled by the size of
the part (both the envelope and the projected area) as well as the
part's complexity. The cost of the core-boxes first depends on their
size, a result of the quantity and size of the cores that are used to
cast the part. Much like the pattern, the complexity of the cores will
affect the time to manufacture this part of the tooling (in addition to
the core size), and hence the cost.
The quantity of parts that are cast will also impact the tooling cost. A
larger production quantity will require the use of a tooling material,
for both the pattern and core-boxes, that will not wear under the
required number of cycles. The use or a stronger, more durable,
tooling material will significantly increase the cost.

50. Advantages
• Can produce very large parts
• Can form complex shapes
• Many material options
• Low tooling and equipment cost
• Scrap can be recycled
• Short lead time possible

51. Disadvantages
• Poor material strength
• High porosity possible
• Poor surface finish and tolerance
• Secondary machining often required
• Low production rate
• High labor cost

52. Applications
• Engine blocks
• machine bases,
• gears,
• pulleys

53. Sand Casting
Advantages Disadvantages
Recommended
Application
Least Expensive in small
quantities (less than 100)
Dimensional accuracy
inferior to other
processes, requires larger
tolerances
Use when
strength/weight ratio
permits
Ferrous and non - ferrous
metals may be cast
Castings usually exceed
calculated weight
Tolerances, surface finish
and low machining cost
does not warrant a more
expensive process
Possible to cast very large
parts
Surface finish of ferrous
castings usually exceeds
125 RMS
• Least expensive
tooling

54. Histroy of investment castin
• Originally developed by ancient Chinese and
Egyptian culture to create artwork •
• Primarily used for art until development of the
jet turbine engine at the end of World War II

55. Investment casting process
• Creating a Wax Pattern
• Wax Tree Assembly
• Shell Building
• Dewax / Burnout
• Metal Pouring
• Shell Knock Off
• Cut Off
• Individual Castings

56. Creating a Wax Pattern
• In today’s manufacturing world, wax patterns are
typically made by injecting wax into a metal tool
or “die” •
• With the evolution of Additive Manufacturing,
patterns can be printed •
• In the art community, one of a kind pieces are
carved by the artist from wax blocks •
• For multiple castings, a silicon tool is usually
made from the artist’s sculpture and wax is
injected or poured into the resulting cavity

57. Wax Tree Assembly
• It is typically uneconomical to make small parts one at
a time, so wax patterns are typically attached to a wax
“sprue”
• The sprue serves two purposes
1. Provides a mounting surface to assemble multiple
patterns into a single mold, which will be later filled
with alloy
2. Provides a flow path for the molten alloy into the
void created by the wax pattern(s)
• The wax between the pattern(s) and the sprue are
called “Gates”, because they throttle the direction and
flow of the alloy into the void made by the pattern

59. Shell Building
• The next step in the process is to build a ceramic shell
around the wax tree
• This shell will eventually become the mold that metal is
poured into
• To build the shell, the tree is dipped into a ceramic bath
or “slurry”
• After dipping, fine sand or “stucco” is applied to the wet
surface
• The mold is allowed to dry, and the process is repeated
a number of times until a layered (or laminated)
ceramic mold, capable to undergo the stresses of the
casting process, has been built

60. Dewax / Burnout
• Before pouring metal into the mold, the wax is
removed
• This is typically done using a steam-dewax autoclave,
which is like a large, industrial pressure cooker
• Another method is the use of a flash fire oven, which
melts and burns off the wax
• Many foundries use both methods in concert
• Autoclave removes the majority of the wax, which can
be reconditioned and reused
• Flash fire burns off residual wax and cures the shell,
readying it for casting

61. Metal Pouring
• Before the metal is poured into the ceramic mold or “shell”,
the mold is preheated to a specific temperature to prevent
the molten alloy from solidifying or “freezing off” before
the entire mold is filled
• Alloy is melted in a ceramic cup (called a crucible) using a
process known as induction melting
• A high frequency electric current creates a magnetic field
around the alloy, generating electric fields inside the metal
(eddy currents)
• The eddy currents heat the alloy due to the material’s
electrical resistance
• When the alloy reaches its specified temperature, it is
poured into the mold, and the mold is allowed to cool

62. Shell Knock Off
• Once cool, the shell material is removed from the
metal
• This is typically done via mechanical means
• Hammer
• High Pressure Water Blast
• Vibratory Table
• Shell removal can also be accomplished chemically,
using a heated caustic solution of either potassium
hydroxide or sodium hydroxide, but this approach is
being phased out due to environmental and health
concerns

63. Cut Off
• Once the shell material has been removed, the
parts are cut off the sprue and the gates are
ground off
• Part cut off can be done manually
• Chop saw
• Torch
• Laser (limited applications)
• Parts can also be cut off using automation, that is,
the mold can be secured using a fixture on a
programmable cut off saw

64. Individual Castings
• Once the parts are removed from the sprue, and the
gates removed, the surface can be finished via a
number of means
• Vibratory/Media finishing
• Belting or hand grinding
• Polishing
• Finishing can be done by hand, but in many cases it is
automated
• • Parts are then inspected, marked (if required),
packaged and shipped • Depending on the application,
the parts can be used in their “net shape” or undergo
machining for precision mating surfaces

67. Benefits of Investment Casting
• Superior surface finish
• Wide range of alloys
• Complex, near net geometries
• Fine detail

68. Application of investment casting
• Aerospace and Defense
• Power Generation
• Automotive
• Oil and Gas
• Space Exploration
• Medical / Orthopedics
• Agriculture
• Construction
• Commercial and Consumer products

69. Investment Cast
Advantages Disadvantages Recommended Application
Close dimensional
tolerance
Costs are higher than
Sand, Permanent Mold or
Plaster process Castings
Use when Complexity
precludes use of Sand or
Permanent Mold Castings
Complex shape, fine
detail, intricate core
sections and thin walls are
possible
The process cost is justified
through savings in
machining or brazing
Ferrous and non-ferrous
metals may be cast
Weight savings justifies
increased cost
As-Cast" finish (64 - 125
RMS)

70. Permanent mold casting process
• The Permanent Mold Casting Process (also referred to
as Gravity Die Casting) is a molding method that
incorporates gravity-induced pressure with rapid
solidification to produce both aesthetically pleasing and
fully functional castings.
• The Permanent Mold Casting Process consists of pouring
molten metal into a permanent mold, usually created from
iron or steel (as opposed to molds made of sand for the
sand casting process).
• The molten metal enters the mould cavity under gravity
pressure, flowing into the small crevices of the mold, and
remains there until solidification to produce intricate and
fully formed castings. This process is cost competitive with
medium to large volumes of production

71. • Metal inserts can be used to produce various features
during the casting process which will not need to be
machined afterward, thus yielding some cost reduction.
• Sand cores (chemically bonded sand used to generate a
desired shape inside a casting ) can also be used to hollow
out the inner sections of a casting or to produce an area
with undercuts – this variant is called Semi-Permanent
Mold castings.Powercast manufactures its own sand cores.
• Typical casting sizes range from 50 g to 70 kg (1.5 ounces to
150 lb).
• Typical materials used with this process include aluminium,
magnesium and brass alloys. Powercast typically pours
various aluminium alloys.

72. Permanent mold vs Other process
• When selecting a casting process, the permanent mold process is
often compared to two others – namely the sand casting and pressure
die casting processes. While each process has its advantages and
disadvantages,
• The permanent mold process offers a middle-ground
alternative: affordable tooling and the possibility of
using cores (like sand castings), with excellent part accuracy and
surface finish (similarly to pressure die casting parts).
• The fact that these castings use gravity as pressure ensures that they
can achieve high levels of quality (as opposed to pressure that is
forced – which may entrap air inside the casting). Moreover, due to
the rapid heat transfer from the molten metal to the mold itself,
permanent mold castings have finer grain structures and better
strength properties than casts made by sand casting method. Bottom
line: permanent mold castings often yield the optimal
combination of high quality and competitive cost

73. Pouring Permanent Mold casting
• The type of furnaces used to melt aluminium varies per foundry;
some prefer crucibles, other refractory-type, etc., and they all vary
in sizes, depending on the foundry’s operations and plant layout.
Some are gas-fired, while others are electric. Various aluminium
alloys are poured, such as 319, 356, A356, 413, etc., depending on
customer requirements. Alloys must be heated to the right
temperature, with the right gas level.
• Before and during the casting process, the molds are usually
sprayed with one or more coatings: for instance one type is
generally graphite-based and acts as a die-release agent, while
another is silica-based and is used as a heat-preserving layer. The
molds required to be pre-heated at the right temperature before
the metal is poured into the cavity.

74. • Permanent mold castings are generally either poured using a Static
Pour or a Tilt Pour system. The Static Pour is the more traditional method
of pouring – the aluminium is poured directly into the mold cavity, and the
casting is removed after solidification. The molds are closed and set into
the vertical position for pouring; thus, the parting line is in the vertical
position. It is a flexible method of pouring and can accommodate various
shapes and sizes of castings. The tilt Pour process involves closing and
placing the mold in the horizontal position at which point molten metal is
poured into a cup(s) attached to the mold. The mold is then tilted to the
vertical position, allowing the molten metal to flow out of the cup(s) into
the mold cavity. The tilt time is predetermined and programmed; hence
part of the production process is automated. This partial automation helps
control the metal flow into the mold cavity, thereby minimizing
turbulence. Lesser turbulence generates better castings. Semi-Permanent
Mold castings can be poured using either of the aforementioned pouring
methods.

75. Post Casting Operation
• Once the castings are poured, one can improve their
mechanical properties by having them go through a Heat
Treating process. This process consists of using a
combination of heating, quenching and cooling in order to
artificially age the castings quickly, thereby improving their
hardness, conductivity, and strength. Once the parts are
heat treated, they are also easier to machine. Powercast
conducts its own heat treating. Permanent mold aluminium
castings can be machined, anodized, painted, etc., and
Powercast can take care of these additional operations for
you. Most aluminium castings are used as is, while other
are anodized or painted, depending on their functionality.

76. Applications
• Permanent mold casting process is used to cast
products from iron, aluminum, magnesium, and
copper based alloys.
• Typical permanent mold casting components
include gears, splines, wheels, gear housings,
pipe fittings, fuel injection housings, and
automotive engine pistons, timing gears,
impellers, compressors, pump parts, marine
hardware, valve bodies, aircraft parts and missile
components.

77. Advantages
• Suitable for high volume casting ceramic
• Quality of heavier casting improves with
better use of tooling's and equipment
• Casted products have better tensile strength
and elongation than sand castings
• Mass productions can be done is a single
production run, which reduces the
manufacturing cost
• Products have excellent mechanical properties

78. Permanent and Semi-permanent
Mold Casting
Advantages Disadvantages
Recommended
Application
Less expensive than
Investment or Die
Castings
Only non-ferrous metals
may be cast by this
process
Use when process
recommended for parts
subjected to hydrostatic
pressure
Dimensional Tolerances
closer than Sand Castings
Less competitive with
Sand Cast process when
three or more sand cores
are required
Ideal for parts having low
profile, no cores and
quantities in excess of 300
Castings are dense and
pressure tight
Higher tooling cost than
Sand Cast

79. Plaster Cast
Advantages Disadvantages Recommended Application
Smooth "As Cast" finish
(25 RMS)
More costly than Sand or
Permanent Mold-Casting
Use when parts require
smooth "As Cast" surface
finish and closer tolerances
than possible with Sand or
Permanent Mold Processes
Closer dimensional
tolerance than Sand Cast
Limited number of
sources
• Intricate shapes
and fine details including
thinner "As Cast" walls are
possible
Requires minimum of 1
deg. draft
• Large parts cost
less to cast than by
Investment proce

80. • Die casting is a manufacturing process that can produce geometrically
complex metal parts through the use of reusable molds, called dies.
• The die casting process involves the use of a furnace, metal, die casting
machine, and die.
• The metal, typically a non-ferrous alloy such as aluminum or zinc, is
melted in the furnace and then injected into the dies in the die casting
machine. There are two main types of die casting machines - hot chamber
machines (used for alloys with low melting temperatures, such as zinc)
and cold chamber machines (used for alloys with high melting
temperatures, such as aluminum).
• The differences between these machines will be detailed in the sections
on equipment and tooling. However, in both machines, after the molten
metal is injected into the dies, it rapidly cools and solidifies into the final
part, called the casting. The steps in this process are described in greater
detail in the next section

81. • The castings that are created in this process can vary
greatly in size and weight, ranging from a couple
ounces to 100 pounds.
• One common application of die cast parts are housings
- thin-walled enclosures, often requiring
many ribs and bosses on the interior.
• Metal housings for a variety of appliances and
equipment are often die cast. Several automobile
components are also manufactured using die casting,
including pistons, cylinder heads, and engine blocks.
Other common die cast parts include propellers, gears,
bushings, pumps, and valves.

82. Process Cycle
Clamping
• - The first step is the preparation and clamping of the two halves of the
die.
• Each die half is first cleaned from the previous injection and then
lubricated to facilitate the ejection of the next part. The lubrication time
increases with part size, as well as the number of cavities and side-cores.
Also, lubrication may not be required after each cycle, but after 2 or 3
cycles, depending upon the material.
• After lubrication, the two die halves, which are attached inside the die
casting machine, are closed and securely clamped together. Sufficient
force must be applied to the die to keep it securely closed while the metal
is injected. The time required to close and clamp the die is dependent
upon the machine - larger machines (those with greater clamping forces)
will require more time. This time can be estimated from the dry cycle
time of the machine.

83. Injection
• The molten metal, which is maintained at a set temperature in the furnace, is next
transferred into a chamber where it can be injected into the die.
• The method of transferring the molten metal is dependent upon the type of die
casting machine, whether a hot chamber or cold chamber machine is being used.
The difference in this equipment will be detailed in the next section.
• Once transferred, the molten metal is injected at high pressures into the die.
Typical injection pressure ranges from 1,000 to 20,000 psi. This pressure holds the
molten metal in the dies during solidification.
• The amount of metal that is injected into the die is referred to as the shot. The
injection time is the time required for the molten metal to fill all of the channels
and cavities in the die.
• This time is very short, typically less than 0.1 seconds, in order to prevent early
solidification of any one part of the metal. The proper injection time can be
determined by the thermodynamic properties of the material, as well as the wall
thickness of the casting. A greater wall thickness will require a longer injection
time. In the case where a cold chamber die casting machine is being used, the
injection time must also include the time to manually ladle the molten metal into
the shot chamber.

84. • Cooling
• - The molten metal that is injected into the die will begin to
cool and solidify once it enters the die cavity. When the
entire cavity is filled and the molten metal solidifies, the
final shape of the casting is formed. The die can not be
opened until the cooling time has elapsed and the casting is
solidified. The cooling time can be estimated from several
thermodynamic properties of the metal, the maximum wall
thickness of the casting, and the complexity of the die. A
greater wall thickness will require a longer cooling time.
The geometric complexity of the die also requires a longer
cooling time because the additional resistance to the flow
of heat.

85. • Ejection
• - After the predetermined cooling time has passed, the
die halves can be opened and an ejection mechanism
can push the casting out of the die cavity. The time to
open the die can be estimated from the dry cycle time
of the machine and the ejection time is determined by
the size of the casting's envelope and should include
time for the casting to fall free of the die. The ejection
mechanism must apply some force to eject the part
because during cooling the part shrinks and adheres to
the die. Once the casting is ejected, the die can be
clamped shut for the next injection.

86. • Trimming
• - During cooling, the material in the channels of the die will
solidify attached to the casting. This excess material, along
with any flash that has occurred, must be trimmed from
the casting either manually via cutting or sawing, or using a
trimming press. The time required to trim the excess
material can be estimated from the size of the casting's
envelope. The scrap material that results from this
trimming is either discarded or can be reused in the die
casting process. Recycled material may need to be
reconditioned to the proper chemical composition before it
can be combined with non-recycled metal and reused in
the die casting process.

88. Equipment
• The two types of die casting machines are a
hot chamber machine and cold chamber
machine.
• Hot chamber die casting machine
• Cold chamber die casting machine

89. Hot chamber die casting machine
– Hot chamber machines are used for alloys with low melting
temperatures, such as zinc, tin, and lead. The temperatures
required to melt other alloys would damage the pump, which is
in direct contact with the molten metal.
– The metal is contained in an open holding pot which is placed
into a furnace, where it is melted to the necessary temperature.
The molten metal then flows into a shot chamber through an
inlet and a plunger, powered by hydraulic pressure, forces the
molten metal through a gooseneck channel and into the die.
– Typical injection pressures for a hot chamber die casting
machine are between 1000 and 5000 psi. After the molten
metal has been injected into the die cavity, the plunger remains
down, holding the pressure while the casting solidifies.

90. • After solidification, the hydraulic system retracts the plunger and the part
can be ejected by the clamping unit. Prior to the injection of the molten
metal, this unit closes and clamps the two halves of the die. When the die
is attached to the die casting machine, each half is fixed to a large plate,
called a platen..
• The front half of the die, called the cover die, is mounted to a
stationary platen and aligns with the gooseneck channel. The rear
half of the die, called the ejector die, is mounted to a movable
platen, which slides along the tie bars.
• The hydraulically powered clamping unit actuates clamping bars
that push this platen towards the cover die and exert enough
pressure to keep it closed while the molten metal is injected.
Following the solidification of the metal inside the die cavity, the
clamping unit releases the die halves and simultaneously causes the
ejection system to push the casting out of the open cavity. The die
can then be closed for the next injection

91. Die casting hot chamber machine
overview

92. Cold chamber die casting machine
• Cold chamber machines are used for alloys with high melting temperatures that
can not be cast in hot chamber machines because they would damage the
pumping system. Such alloys include aluminum, brass, and magnesium.
• The molten metal is still contained in an open holding pot which is placed into a
furnace, where it is melted to the necessary temperature. However, this holding
pot is kept separate from the die casting machine and the molten metal is ladled
from the pot for each casting, rather than being pumped.
• The metal is poured from the ladle into the shot chamber through a pouring hole.
The injection system in a cold chamber machine functions similarly to that of a hot
chamber machine, however it is usually oriented horizontally and does not include
a gooseneck channel. A plunger, powered by hydraulic pressure, forces the molten
metal through the shot chamber and into the injection sleeve in the die.
• The typical injection pressures for a cold chamber die casting machine are
between 2000 and 20000 psi. After the molten metal has been injected into the
die cavity, the plunger remains forward, holding the pressure while the casting
solidifies. After solidification, the hydraulic system retracts the plunger and the
part can be ejected by the clamping unit. The clamping unit and mounting of the
dies is identical to the hot chamber machine. See the above paragraph for details.

93. Die casting cold chamber machine
overview

94. Die Casting
Advantages Disadvantages Recommended Application
Good dimensional
tolerances are possible
Economical only in very
large quantities due to
high tool cost
Use when quantity of parts
justifies the high tooling cost
Excellent part-part
dimensional consistency
Not recommended for
hydrostatic pressure
applications
Parts are not structural and
are subjected to hydrostatic
pressure
Parts require a minimal
post machining
For Castings where
penetrant (die) or
radiographic inspection are
not required.
Difficult to guarantee
minimum mechanical
properties