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1. Manufacturing Technology II
(ME-202)
Overview of
Casting
Processes
Dr. Chaitanya Sharma
PhD. IIT Roorkee

2. Title of slide
Lesson Objectives
In this chapter we shall discuss the following:
Learning Activities
1. Look up
Keywords
2. View Slides;
3. Read Notes,
4. Listen to
lecture
Keywords:

3. ©2007 John Wiley &
Sons, Inc. M P
Shell Molding
Casting process in which the mold is
a thin shell of sand held together
by thermosetting resin binder
Figure 11.5 Steps in shell-molding: (1) a match-plate or
cope-and-drag metal pattern is heated and placed over

4. ©2007 John Wiley &
Sons, Inc. M P
Shell Molding
Figure 11.5 Steps in shell-molding: (2) box is inverted so that sand
and resin fall onto the hot pattern, causing a layer of the
mixture to partially cure on the surface to form a hard shell; (3)
box is repositioned so that loose uncured particles drop away;

5. ©2007 John Wiley &
Sons, Inc. M P
Shell Molding
Figure 11.5 Steps in shell-molding: (4) sand shell is heated in oven
for several minutes to complete curing; (5) shell mold is stripped
from the pattern;

6. ©2007 John Wiley &
Sons, Inc. M P
Shell Molding
Figure 11.5 Steps in shell-molding: (6) two halves of the shell mold
are assembled, supported by sand or metal shot in a box, and
pouring is accomplished; (7) the finished casting with sprue
removed.
From www.janfa.com

7. ©2007 John Wiley &
Sons, Inc. M P
Advantages and
Disadvantages
• Advantages of shell molding:
– Smoother cavity surface permits easier
flow of molten metal and better surface
finish
– Good dimensional accuracy - machining
often not required
– Mold collapsibility minimizes cracks in
casting
– Can be mechanized for mass production
• Disadvantages:
– More expensive metal pattern
– Difficult to justify for small quantities

8. ©2007 John Wiley &
Sons, Inc. M P
Expanded Polystyrene
Process
Figure 11.7 Expanded polystyrene casting process: pattern of
polystyrene is coated with refractory compound;
Uses a mold of sand packed around a polystyrene foam pattern
which vaporizes when molten metal is poured into mold
 Other names: lost-foam process, lost pattern process,
evaporative-foam process, and full-mold process
 Polystyrene foam pattern includes sprue, risers, gating system,
and internal cores (if needed)
 Mold does not have to be opened into cope and drag sections
From www.wtec.org/loyola/casting/fh05_20.jpg

9. ©2007 John Wiley &
Sons, Inc. M P
Expanded Polystyrene
Process
Figure 11.7 Expanded
polystyrene casting process:
(2) foam pattern is placed in
mold box, and sand is
compacted around the
pattern;
Figure 11.7 Expanded polystyrene
casting process: (3) molten metal is
poured into the portion of the pattern
that forms the pouring cup and sprue.
As the metal enters the mold, the
polystyrene foam is vaporized ahead
of the advancing liquid, thus the
resulting mold cavity is filled.

10. ©2007 John Wiley &
Sons, Inc. M P
Advantages and
Disadvantages
• Advantages of expanded polystyrene
process:
– Pattern need not be removed from the mold
– Simplifies and speeds mold-making, because two
mold halves are not required as in a conventional
green-sand mold
• Disadvantages:
– A new pattern is needed for every casting
– Economic justification of the process is highly
dependent on cost of producing patterns

11. ©2007 John Wiley &
Sons, Inc. M P
Expanded Polystyrene
Process
• Applications:
– Mass production of castings for automobile
engines
– Automated and integrated manufacturing systems
are used to
1. Mold the polystyrene foam patterns and then
2. Feed them to the downstream casting operation

12. ©2007 John Wiley &
Sons, Inc. M P
Investment Casting (Lost
Wax Process)
A pattern made of wax is coated with a
refractory material to make mold, after
which wax is melted away prior to
pouring molten metal
• "Investment" comes from a less familiar
definition of "invest" - "to cover
completely," which refers to coating of
refractory material around wax pattern
• It is a precision casting process -
capable of producing castings of high

13. ©2007 John Wiley &
Sons, Inc. M P
Investment Casting
Figure 11.8 Steps in investment casting: (1) wax patterns are
produced, (2) several patterns are attached to a sprue to
form a pattern tree

14. ©2007 John Wiley &
Sons, Inc. M P
Investment Casting
Figure 11.8 Steps in investment casting: (3) the pattern tree is
coated with a thin layer of refractory material, (4) the full
mold is formed by covering the coated tree with sufficient
refractory material to make it rigid

15. ©2007 John Wiley &
Sons, Inc. M P
Investment Casting
Figure 11.8 Steps in investment casting: (5) the mold is held in an
inverted position and heated to melt the wax and permit it to
drip out of the cavity, (6) the mold is preheated to a high
temperature, the molten metal is poured, and it solidifies

16. ©2007 John Wiley &
Sons, Inc. M P
Investment Casting
Figure 11.8 Steps in investment casting: (7) the mold is
broken away from the finished casting and the parts
are separated from the sprue

17. ©2007 John Wiley &
Sons, Inc. M P
Investment Casting
Figure 11 9 A one-piece compressor stator with 108
separate airfoils made by investment casting (photo
courtesy of Howmet Corp.).

18. ©2007 John Wiley &
Sons, Inc. M P
Advantages and
Disadvantages
• Advantages of investment casting:
– Parts of great complexity and intricacy can be cast
– Close dimensional control and good surface finish
– Wax can usually be recovered for reuse
– Additional machining is not normally required - this
is a net shape process
• Disadvantages
– Many processing steps are required
– Relatively expensive process

19. ©2007 John Wiley &
Sons, Inc. M P
Plaster Mold Casting
Similar to sand casting except mold is
made of plaster of Paris
(gypsum - CaSO4-2H2O)
• In mold-making, plaster and water
mixture is poured over plastic or metal
pattern and allowed to set
– Wood patterns not generally used due to extended
contact with water
• Plaster mixture readily flows around
pattern, capturing its fine details and

20. ©2007 John Wiley &
Sons, Inc. M P
Advantages and
Disadvantages
• Advantages of plaster mold
casting:
– Good accuracy and surface finish
– Capability to make thin cross-sections
• Disadvantages:
– Mold must be baked to remove
moisture, which can cause problems in
casting
– Mold strength is lost if over-baked
– Plaster molds cannot stand high
temperatures, so limited to lower
melting point alloys

21. ©2007 John Wiley &
Sons, Inc. M P
Ceramic Mold Casting
Similar to plaster mold casting except
that mold is made of refractory ceramic
material that can withstand higher
temperatures than plaster
• Can be used to cast steels, cast irons,
and other high-temperature alloys
• Applications similar to those of plaster
mold casting except for the metals cast
• Advantages (good accuracy and finish)
also similar

22. ©2007 John Wiley &
Sons, Inc. M P
Permanent Mold Casting
Processes
• Economic disadvantage of expendable
mold casting: a new mold is required for
every casting
• In permanent mold casting, the mold is
reused many times
• The processes include:
– Basic permanent mold casting
– Die casting
– Centrifugal casting

23. ©2007 John Wiley &
Sons, Inc. M P
The Basic Permanent Mold
Process
Uses a metal mold constructed of two
sections designed for easy, precise
opening and closing
• Molds used for casting lower melting
point alloys are commonly made of steel
or cast iron
• Molds used for casting steel must be
made of refractory material, due to the
very high pouring temperatures

24. ©2007 John Wiley &
Sons, Inc. M P
Permanent Mold Casting
Figure 11.10 Steps in permanent mold casting: (1) mold is preheated
and coated

25. ©2007 John Wiley &
Sons, Inc. M P
Permanent Mold Casting
Figure 11.10 Steps in permanent mold casting: (2) cores (if used)
are inserted and mold is closed, (3) molten metal is poured into
the mold, where it solidifies.

26. ©2007 John Wiley &
Sons, Inc. M P
Advantages and
Limitations
• Advantages of permanent mold
casting:
– Good dimensional control and surface
finish
– More rapid solidification caused by the
cold metal mold results in a finer grain
structure, so castings are stronger
• Limitations:
– Generally limited to metals of lower
melting point
– Simpler part geometries compared to
sand casting because of need to open the

27. ©2007 John Wiley &
Sons, Inc. M P
Applications of Permanent
Mold Casting
• Due to high mold cost, process is best
suited to high volume production and can
be automated accordingly
• Typical parts: automotive pistons, pump
bodies, and certain castings for aircraft
and missiles
• Metals commonly cast: aluminum,
magnesium, copper-base alloys, and cast
iron

28. ©2007 John Wiley &
Sons, Inc. M P
Die Casting
A permanent mold casting process in which
molten metal is injected into mold cavity
under high pressure
• Pressure is maintained during
solidification, then mold is opened and
part is removed
• Molds in this casting operation are
called dies; hence the name die casting
• Use of high pressure to force metal into
die cavity is what distinguishes this

29. ©2007 John Wiley &
Sons, Inc. M P
Die Casting Machines
• Designed to hold and accurately close
two mold halves and keep them closed
while liquid metal is forced into cavity
• Two main types:
1. Hot-chamber machine
2. Cold-chamber machine

30. ©2007 John Wiley &
Sons, Inc. M P
Hot-Chamber Die Casting
Metal is melted in a container, and a
piston injects liquid metal under high
pressure into the die
• High production rates - 500 parts per
hour not uncommon
• Applications limited to low melting-point
metals that do not chemically attack
plunger and other mechanical
components
• Casting metals: zinc, tin, lead, and

31. ©2007 John Wiley &
Sons, Inc. M P
Hot-Chamber Die Casting
Figure 11.13 Cycle in hot-chamber casting: (1) with die closed
and plunger withdrawn, molten metal flows into the chamber
(2) plunger forces metal in chamber to flow into die,
maintaining pressure during cooling and solidification.

32. ©2007 John Wiley &
Sons, Inc. M P
Cold-Chamber Die Casting
Machine
Molten metal is poured into
unheated chamber from external
melting container, and a piston
injects metal under high pressure
into die cavity
• High production but not usually as
fast as hot-chamber machines
because of pouring step
• Casting metals: aluminum, brass,
and magnesium alloys

33. ©2007 John Wiley &
Sons, Inc. M P
Cold-Chamber Die Casting
Figure 11.14 Cycle in cold-chamber casting: (1) with die
closed and ram withdrawn, molten metal is poured
into the chamber

34. ©2007 John Wiley &
Sons, Inc. M P
Cold-Chamber Die Casting
Figure 11.14 Cycle in cold-chamber casting: (2) ram forces metal to
flow into die, maintaining pressure during cooling and
solidification.

35. ©2007 John Wiley &
Sons, Inc. M P
Molds for Die Casting
• Usually made of tool steel, mold steel, or
maraging steel
• Tungsten and molybdenum (good
refractory qualities) used to die cast
steel and cast iron
• Ejector pins required to remove part
from die when it opens
• Lubricants must be sprayed into cavities
to prevent sticking

36. ©2007 John Wiley &
Sons, Inc. M P
Advantages and
Limitations
• Advantages of die casting:
– Economical for large production quantities
– Good accuracy and surface finish
– Thin sections are possible
– Rapid cooling provides small grain size and
good strength to casting
• Disadvantages:
– Generally limited to metals with low metal
points
– Part geometry must allow removal from
die

37. ©2007 John Wiley &
Sons, Inc. M P
Centrifugal Casting
A family of casting processes in which the
mold is rotated at high speed so
centrifugal force distributes molten
metal to outer regions of die cavity
• The group includes:
– True centrifugal casting
– Semicentrifugal casting
– Centrifuge casting

38. ©2007 John Wiley &
Sons, Inc. M P
True Centrifugal Casting
Molten metal is poured into rotating mold
to produce a tubular part
• In some operations, mold rotation
commences after pouring rather than
before
• Parts: pipes, tubes, bushings, and rings
• Outside shape of casting can be round,
octagonal, hexagonal, etc , but inside
shape is (theoretically) perfectly round,
due to radially symmetric forces

39. ©2007 John Wiley &
Sons, Inc. M P
True Centrifugal Casting
Figure 11.15 Setup for true centrifugal casting.

40. ©2007 John Wiley &
Sons, Inc. M P
Semicentrifugal Casting
Centrifugal force is used to produce solid
castings rather than tubular parts
• Molds are designed with risers at center
to supply feed metal
• Density of metal in final casting is
greater in outer sections than at center
of rotation
• Often used on parts in which center of
casting is machined away, thus
eliminating the portion where quality is

41. ©2007 John Wiley &
Sons, Inc. M P
Centrifuge Casting
Mold is designed with part cavities located
away from axis of rotation, so that
molten metal poured into mold is
distributed to these cavities by
centrifugal force
• Used for smaller parts
• Radial symmetry of part is not required
as in other centrifugal casting methods

42. ©2007 John Wiley &
Sons, Inc. M P
Furnaces for Casting
Processes
• Furnaces most commonly used in
foundries:
– Cupolas
– Direct fuel-fired furnaces
– Crucible furnaces
– Electric-arc furnaces
– Induction furnaces

43. ©2007 John Wiley &
Sons, Inc. M P
Cupolas
Vertical cylindrical furnace equipped with
tapping spout near base
• Used only for cast irons
– Although other furnaces are also used, the largest
tonnage of cast iron is melted in cupolas
• The "charge," consisting of iron, coke,
flux, and possible alloying elements, is
loaded through a charging door located
less than halfway up height of cupola

44. ©2007 John Wiley &
Sons, Inc. M P
Direct Fuel-Fired Furnaces
Small open-hearth in which charge is
heated by natural gas fuel burners
located on side of furnace
• Furnace roof assists heating action by
reflecting flame down against charge
• At bottom of hearth is a tap hole to
release molten metal
• Generally used for nonferrous metals
such as copper-base alloys and aluminum

45. ©2007 John Wiley &
Sons, Inc. M P
Crucible Furnaces
Metal is melted without direct contact
with burning fuel mixture
• Sometimes called indirect fuel-fired
furnaces
• Container (crucible) is made of
refractory material or
high-temperature steel alloy
• Used for nonferrous metals such as
bronze, brass, and alloys of zinc and
aluminum

46. ©2007 John Wiley &
Sons, Inc. M P
Crucible Furnaces
Figure 11.19 Three types of crucible furnaces: (a) lift-out crucible,
(b) stationary pot, from which molten metal must be ladled, and
(c) tilting-pot furnace.

47. ©2007 John Wiley &
Sons, Inc. M P
Electric-Arc Furnaces
Charge is melted by heat generated from an electric arc
• High power consumption, but electric-arc furnaces can be
designed for high melting capacity
• Used primarily for melting steel

48. ©2007 John Wiley &
Sons, Inc. M P
Induction Furnaces
Uses alternating current passing through a coil to develop
magnetic field in metal
• Induced current causes rapid heating and melting
• Electromagnetic force field also causes mixing action in liquid
metal
• Since metal does not contact heating elements, environment can
be closely controlled to produce molten metals of high quality
and purity
• Melting steel, cast iron, and aluminum alloys are common
applications in foundry work

49. ©2007 John Wiley &
Sons, Inc. M P
Ladles
• Moving molten metal from
melting furnace to mold is
sometimes done using crucibles
• More often, transfer is
accomplished by ladles

50. Selecting the Right Metal
Casting Process
 For any Metal Casting Process, selection of right alloy, size,
shape, thickness, tolerance, texture, and weight, is very vital.
 Special requirements such as, magnetism, corrosion, stress
distribution also influence the choice of the Metal Casting
Process.
 Views of the Tooling Designer; Foundry / Machine House needs,
customer's exact product requirements, and secondary
operations like painting, must be taken care of before selecting
the appropriate Metal Casting Process.
 Tool cost.
 Economics of machining versus process costs.
 Adequate protection / packaging, shipping constraints,
regulations of the final components, weights and shelf life of
protective coatings also play their part in the Metal Casting
process.

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

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

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

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

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

57. • SAND CASTING

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Sacks and Bohnart
Expandable mold
permanent pattern
LOST FOAM CASTING
INVESTMENT CASTING Lost foam casting (LFC) is a
type of investment casting
process that uses foam
patterns as a mold. The
method takes advantage of
the properties of foam to
simply and inexpensively
create castings that would
be difficult to achieve using
other casting techniques.

59. Lost foam casting

60. • Lost foam, is similar to Investment or
Lost wax, in that the medium, or pattern
device, is Expendable, they melt or
evaporate away, leaving the cast part.
• They both have advantages, for the type
of function they were designed. One
Process's advantage, could be the other
Process's weak area.
• These points are brought up in the text
portion of Education Section.

61. PERMANENT MOLD
DIE CASTING
Liquid metal injected into reusable steel mold, or die,
very quickly with high pressures .
Die casting is a process in which the molten metal is
injected into the mold cavity at an increased
pressure
The mold used in the die casting process is called a
die.

63. • In a cold chamber process, the molten metal is ladled
into the cold chamber for each shot. There is less time
exposure of the melt to the plunger walls or the plunger.
This is particularly useful for metals such as Aluminum,
and Copper (and its alloys) that alloy easily with Iron at
the higher temperatures.
PERMANENT MOLD
DIE CASTING
COLD CHAMBER

64. • In a hot chamber process the pressure chamber is connected to the
die cavity is immersed permanently in the molten metal. The inlet port
of the pressurizing cylinder is uncovered as the plunger moves to the
open (unpressurized) position. This allows a new charge of molten metal
to fill the cavity and thus can fill the cavity faster than the cold
chamber process. The hot chamber process is used for metals of low
melting point and high fluidity such as tin, zinc, and lead that tend not
to alloy easily with steel at their melt temperatures.
PERMANENT MOLD
DIE CASTING
HOT CHAMBER