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1. Other Expendable Mold Processes
 Shell Molding
 Expanded Polystyrene Process
 Investment Casting
 Plaster Mold
 Ceramic Mold Casting

2. FUNDAMENTAL OF CASTING
PROCESSES
BY MR RAJAT A. BAGADE
(DEPARTMENT OF MECHANICAL
ENGINEERING)
MAHARASHTRA INSTITUTE OF
POLYECHNIC BETALA
4/18/2023

3. 1. Shell Molding
Casting process in which the mold is a thin shell of sand
held together by thermosetting resin binder
Figure 1 Steps in shell-molding: (1) a match-plate or
cope-and-drag metal pattern is heated and placed
over a box containing sand mixed with thermosetting
resin.

4. Shell Molding
Figure 1 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. 1.Shell Molding
Figure 1 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. 1.Shell Molding
Figure 1 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. 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. 2.Expanded Polystyrene Process
Figure 2 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. 2.Expanded Polystyrene Process
Figure 2 Expanded polystyrene
casting process: (2) foam
pattern is placed in mold box,
and sand is compacted around
the pattern;
Figure 2 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. 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. 3.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 accuracy and intricate
detail

12. 3.Investment Casting
Figure 3 Steps in investment casting: (1) wax
patterns are produced, (2) several patterns are
attached to a sprue to form a pattern tree

13. 3.Investment Casting
Figure 3 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

14. 3.Investment Casting
Figure 3 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

15. 3.Investment Casting
Figure 3 Steps in investment casting: (7) the
mold is broken away from the finished
casting and the parts are separated from the
sprue

16. 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

17. 4.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 good surface finish

18. 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

19. 5.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

20. 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

21. 1.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

22. Permanent Mold Casting
Figure 1 Steps in permanent mold casting: (1) mold
is preheated and coated

23. Permanent Mold Casting
Figure 1 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.

24. 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 mold
 High cost of mold

25. 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

26. 2.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 from other
permanent mold processes

27. 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

28. 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 magnesium

29. Hot-Chamber Die Casting
Figure 2.1 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.

30. 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
 Advantages of hot-chamber process favor its use on
low melting-point alloys (zinc, tin, lead)

31. Cold-Chamber Die Casting
Figure 2.2 Cycle in cold-chamber casting: (1)
with die closed and ram withdrawn, molten
metal is poured into the chamber

32. Cold-Chamber Die Casting
Figure 2.2 Cycle in cold-chamber casting: (2) ram
forces metal to flow into die, maintaining
pressure during cooling and solidification.

33. 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

34. 3.Centrifugal Casting
• For centrifugal casting, molten metal is
introduced into a mould that is rotated during
solidification.
• The centrifugal force improves the feed and
filling consistency achieving surface detail.
• This method has been specifically adapted to the
production of cylindrical parts and eliminates the
need for gates, risers and cores.
• The process is typically unsuitable for
geometries that do not allow a linear flow-
through of metal.
4/18/2023

35. Centrifugal Casting
Fig.3 Setup for true centrifugal casting
4/18/2023

36. Advantages:
• Centrifugal casting improves homogeneity and
accuracy in special circumstances.
• High surface finish.
• Eliminates the need for gating systems.
• High production rate.
Limitations:
• The process imposes limitations on the shape of
castings, and is normally restricted to the
production of cylindrical geometric shapes.
• Expensive set-up.
4/18/2023

37. Furnaces for Casting Processes
 Furnaces most commonly used in foundries:
 Cupolas
 Direct fuel-fired furnaces
 Crucible furnaces
 Electric-arc furnaces
 Induction furnaces

38. CASTING QUALIT Y
 General Defects: Some defects are common to any and
all casting processes.
a) Misruns, which are castings that solidify before
completely filling the mold cavity. Typical causes include
(1) fluidity of the molten metal is insufficient,
(2) pouring temperature is too low,
(3) pouring is done too slowly, and/or
(4) cross-section of the mold cavity is too thin.
4/18/2023

39. CASTING DEFECTS
b)Cold Shuts, which occur when two portions of the metal
flow together but there is a lack of fusion between them
due to premature freezing. Its causes are similar to misrun.
c) Cold shots, This defect is caused by a small amount of
molten metal entering the gating system or mold cavity
and solidifying in the form of a small ball, can’t dissolve or
fuse with the molten metal entering the mold.
4/18/2023

40. CASTING DEFECTS
d) Shrinkage cavity, is a cavity caused by contraction of
the molten metal caused by solidification shrinkage
that restricts amount of molten metal available in last
region to freeze. The problem can often be solved by
proper riser design.
4/18/2023

41. CASTING DEFECTS
Sand Casting Defects:
a) Sand blow, is a defect consisting of a balloon-shaped
gas cavity caused by release of mold gases during
pouring. It occurs at or below the casting surface near
the top of the casting. Low permeability, poor venting,
and high moisture content of the sand mold are the
usual causes.
4/18/2023

42. CASTING DEFECTS
b) Pinholes, also caused by release of gases during
pouring, consist of many small gas cavities formed at
or slightly below the surface of the casting.
c) Sand wash, which is an irregularity in the surface of
the casting that results from erosion of the sand mold
during pouring, and the contour of the erosion is
formed in the surface of the final cast part.
4/18/2023

43. CASTING DEFECTS
c) Mold shift, refers to a defect caused by a sidewise
displacement of the mold cope relative to the drag, the result
of which is a step in the cast product at the parting line.
d) Mold crack, occurs when mold strength is insufficient, and a
crack develops, into which liquid metal can seep to form a
‘‘fin ’’ on the final casting.
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44. TESTING METHODS
 DESTRUCTIVE TESTING
 NON DESTRUCTIVE TESTING
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INSPECTION OF CASTING

45. DESTRUCTIVE TESTING
 This test is done causing harm to the
casting i.e. by destroying it.
 Various tests include fatigue tests,
compression tests, creep tests etc.
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46. NON DESTRUCTIVE TESTING
 Here parts to be tested are inspected for internal
defects and surface defects without destroying the
component.
 Various methods available are:
visual inspection
Liquid penetrate test LPI
Magnetic particle inspection MPI
X – Ray radiography XRR
Ultrasonic testing UT
4/18/2023

47. VISUAL INSPECTION
 Simplest and most fastest inspectional
methods.
 Most commonly employed.
 Usually good to check surface
defects.
 Fails to identify internal defects.
4/18/2023

48. Liquid penetrant test
 Surface preparation
 Penetrant application
 Penetrant dwell
 Excess Penetrant removal
 Developer application
 Indication development
 Inspection
 Clean surface.
4/18/2023

49. Magnetic Particle Inspection -
MPI
 Most satisfactory method Used to
find surface and sub surface defects.
 It is quick, cheap, very sensitive
 Can only be applied to ferrous
metals like steel, cast iron etc
4/18/2023

50. Principle - MPI
 When a metal placed in magnetic field,
magnetic flux are intersected by the
defect – magnetic poles are induced on
either side of discontinuity.
 Abrupt change in path of flux – local
leakage
 This can detected when magnetic
particles are attracted towards
defective region.
 Magnetic particles piles up in defective
region.
4/18/2023

51. Magnetization
 To induce magnetic lines – two methods –
permanent magnet – electromagnet.
 Electromagnet is proffered as it has capability to
produce stronger magnetic field.
 Magnetization – two types – longitudinal or for
parallel defects – circular or for perpendicular
defects.
 For a defect to be detected flux lined should pass
perpendicular line.
4/18/2023

52. Application of magnetic
particles
 Magnetic particles are applied uniformly so
that they move on the surface freely.
 The particles must be as fine as possible.
 Generally pulverized iron oxide, carbonyl
iron powder are used.
4/18/2023

53. Inspection of
defect
 Generally carried out in good light.
 If no defects then regular pattern, if presence
of defects then flux lines distorted.
 Magnetic particles spreads out at the point of
defects indicating presence of defect.
4/18/2023

54. X – ray radiography
 X – Rays are produced when high energy
electrons collide with the nucleus of an
atom .
 The x – ray equipment ---which produces
incandescent light, placed near a highly
charged cathode, causing the electrons to
flow from the cathode which is attributed by
the anode or target.
 The intensity of x – rays produced is
directly proportional to the number of
electrons produced at the filament.
 The pattern of the x – ray so produced
depends on the shape of the target.
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55. Ultrasonic Testing
 Ultrasonic Testing (UT) uses high frequency sound
energy to conduct examinations and make
measurements.
 Ultrasonic testing is based on piezoelectric effect
which converts electrical energy to mechanical
energy thus generating ultrasonic waves
 Ultrasonic waves are generated when a high
frequency alternating current of about a million times
per second is impressed across the forces of
piezoelectric materials like quartz crystal.
 The crystal expands in full half of the cycle and
contracts when the electric field is increased, thus
producing mechanical vibrations.
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56. 4/18/2023

57. Ultrasonic Testing
 When there is a discontinuity (such as a crack) in the
wave path, part of the energy will be reflected back
from the flaw surface
 The reflected wave signal is transformed into an
electrical signal by the transducer and is displayed on
a screen
 In the applet below, the reflected signal strength is
displayed versus the time from signal generation to
when an echo was received. Signal travel time can be
directly related to the distance that the signal traveled
 From the signal, information about the reflector
location, size, orientation and other features can
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