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1. Manufacturing Technology II
(ME-202)
Special
Moulding
Processes
Dr. Chaitanya Sharma
PhD. IIT Roorkee

2. Title of slide
Lesson Objectives
In this chapter we shall discuss the following:
1. Carbon dioxide molding process
2. Investment casting process
3. Shell molding process
4. Die casting process
5. Full molding process
6. Vacuum-Sealed casting process.
Learning Activities
1. Look up
Keywords
2. View Slides;
3. Read Notes,
4. Listen to
lecture
5. http://www.custom
partnet.com/wu/Sa
ndCasting
Keywords: Carbon dioxide molding process, Investment casting
process, Die casting process, Shell molding process, Full molding
process, Vacuum-Sealed casting process

3. Other Expendable Mold
Processes
• Shell Molding
• Vacuum Molding
• Expanded Polystyrene Process
• Investment Casting
• Plaster Mold and Ceramic Mold Casting
Here is a good reference web site:
http://www.custompartnet.com/wu/SandCasting

4. Carbon Dioxide Moulding
• Carbon dioxide moulding is a sand casting process that
employs a moulding mixture of sand and liquid silicate
binder such as sodium silicate (Na2SiO3).
• Moulding mixture is hardened by blowing CO2 gas through
it.
• In this process, the CO2 gas forms a weak acid which
hydrolyzes the sodium silicate, thus forming an
amorphous silica that becomes the bond.
• There is also a bonding action from the sodium silicate
itself. The use of CO2 gives an almost instantaneous set.
• Mold is fully hardened before pattern is drawn from mold
sections.

5. Advantages & Disadvantages
Advantages:
• Good dimensional tolerances through strong core & mould
• Increased accuracy & Excellent casting surface finish
• Accommodates wide range of core and mould sizes
• Co2 core making can be automated for large production.
• Reduced production time, fuel cost and no of mould boxes
• All sands can be used as base aggregate for silicate sand
mixture.
Disadvantages
• More alkaline the binder, longer it takes to gas and the greater
the tendency for the core to remain rubbery instead of firm.
Application:
• Ideal for casting application where speed and flexibility is

6. Shell Mould Casting
• Shell mould casting is similar to sand casting, where in molten
metal is poured into an expendable mould.
• The mould is a thin-walled shell created from applying a
sand-resin mixture around a pattern.
• Shell mould casting requires the use of a metal pattern, oven,
sand-resin mixture, dump box, and molten metal.
• A reusable pattern allows for higher production rates, while
disposable moulds enable complex geometries to be cast.
• Shell mould casting allows the use of both ferrous and non-
ferrous metals, most commonly using cast iron, carbon steel,
alloy steel, stainless steel, aluminum alloys, and copper alloys.
• Typical parts are small-to-medium in size and require high
accuracy, such as gear housings, cylinder heads, connecting
rods, and lever arms.

7. Steps In Shell Moldings
• Casting process in which the mold is a thin shell of sand
held together by thermosetting resin binder.
1. Heating of (a match-plate or cope-and-drag) metal
pattern which is placed over a box containing sand mixed
with thermosetting resin.
2. Inverting of the box: x 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. Repositioning of the box so that loose uncured particles
drop away;
4. Curing of sand shell, shell is heated in oven for several
minutes to complete curing;
5. Shell mold is stripped from the pattern;

8. Shell Molding Steps
1. Pattern heating
2. Inverting Box
3. Repositioning of box

9. Shell Molding Steps
4. Curing sand shell
5. Shell mold stripping from pattern;
6. Assembling of shell mold halves &
pouring
7. Finished casting after sprue etc.

10. Steps In Shell Moulding
• The shell mold casting process consists of the following steps:
• Pattern creation - A two-piece metal pattern is created in the shape of the desired
part, typically from iron or steel, aluminum or graphite for casting reactive materials.
• Mold creation - First, each pattern half is heated to 175-370°C and coated with a
lubricant to facilitate removal. Next, the heated pattern is clamped to a dump box,
which contains a mixture of sand and a resin binder. The dump box is inverted, allowing
this sand-resin mixture to coat the pattern. The heated pattern partially cures the
mixture, which now forms a shell around the pattern. Each pattern half and
surrounding shell is cured to completion in an oven and then the shell is ejected from
the pattern.
• Mold assembly - The two shell halves are joined together and securely clamped to
form the complete shell mold. If any cores are required, they are inserted prior to
closing the mold. The shell mold is then placed into a flask and supported by a backing
material.
• Pouring - The mold is securely clamped together while the molten metal is poured from
a ladle into the gating system and fills the mold cavity.
• Cooling - After the mold has been filled, the molten metal is allowed to cool and
solidify into the shape of the final casting.
• Casting removal - After the molten metal has cooled, the mold can be broken and the
casting removed. Trimming and cleaning processes are required to remove any excess
metal from the feed system and any sand from the mold.

11. Advantages & 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
• Applications:
• Cylinder heads, connecting rods

12. Full-Mould Process
• When only a few casting are required the expense of
making a pattern can be an important factor.
• In this process the pattern is made of polystyrene
around which the sand mold is formed.
• The sand may be bonded or unbounded. Then, without
removing the pattern, the molten metal is poured into
the mold, this immediately vaporizes the polystyrene
thus forming the mold cavity.
• Complex casting of various sizes can be made
economically by this process.

13. 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 .
• This process is beneficial for casting metals with high
melting temperatures that can not be molded in
plaster or metal such as turbine blades or firearm
components., parts for the automotive, aircraft, and
military industries.

14. • The mold is formed by using a wax pattern - a disposable piece in the
shape of the desired part.
• The pattern is surrounded, or "invested", into ceramic slurry that
hardens into the mold.
• Investment casting is often referred to as "lost-wax casting" because
the wax pattern is melted out of the mold after it has been formed.
• Lox-wax processes are one-to-one (one pattern creates one part), which
increases production time and costs relative to other casting processes.
• However, since the mold is destroyed during the process, parts with
complex geometries and intricate details can be created.
• Investment casting can make use of most metals, most commonly using
aluminum alloys, bronze alloys, magnesium alloys, cast iron, stainless
steel, and tool steel.
• Investment casting requires the use of a metal die, wax, ceramic slurry,
furnace, molten metal, and any machines needed for sandblasting,
cutting, or grinding

15. Steps In Investment Casting
Fig:
1. Wax patterns are produced,
2. Several patterns are attached to a sprue to form a pattern tree
3. 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

16. Steps In Investment Casting
Fig:
5. Inverting and heating the mold to melt the wax and permit it to
drip out of the cavity,
6. Mold preheating (high temperature), pouring and solidification,
7. the mold is broken away from the finished casting and the parts are
separated from the sprue

17. Application of Investment
Casting
Fig: A one-piece compressor
stator with 108 separate
airfoils made by investment
casting (photo courtesy of
Howmet Corp.).

18. 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. 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

20. 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. 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

22. 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

23. Steps In Permanent Mold Casting
Fig:
1. Mold is preheated and coated
2. Cores (if used) are inserted & mold is closed,
3. Pouring of molten metal & solidification

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. 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. ©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.

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. ©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

32. 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.

33. 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

34. Expanded Polystyrene Process
Fig: 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

35. Expanded Polystyrene Process
Fig 1: Expanded
polystyrene casting
process: (2) foam pattern
is placed in mold box, and
sand is compacted around
the pattern;
Fig 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.

36. 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

37. Vacuum Sealed Moulding Process
• Vacuum sealed moulding process (VSMP) was developed in Japan in
1971 & used to produce dimensionally accurate and smooth castings.
• In VSMP moulds are made utilizing dry sand, plastic film and a
physical means of binding using negative pressure or vacuum.
• In VSMP, a vacuum, of the order of 250 – 450 mm hg, is imposed to
bind the dry free flowing sand encapsulated in b/w two plastic films.
• Mold cavity is formed by vacuum forming of a plastic film over the
pattern, backed by unbounded sand, which is compacted by vibration
and held rigidly in place by applying vacuum.
• When the metal is poured into the molds, the plastic film first melts
and then gets sucked just inside the sand voids due to imposed
vacuum where it condenses and forms a shell-like layer.
• The vacuum must be maintained until the metal solidifies, after
which the vacuum is released allowing the sand to drop away leaving a
casting with a smooth surface.
• No shakeout equipment is required and the same sand can be cooled

38. ©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

39. 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