Casting is a process where liquid material is poured into a mold and allowed to solidify. The solidified part that is formed is known as a casting. Casting dates back thousands of years, with early humans casting materials like gold, silver, and copper. The basic casting process of melting material, using patterns to form molds, and allowing the material to solidify has remained the same, though furnace technology, mold materials, and allowed alloys have advanced over time.

2.  Casting is a manufacturing process by which a liquid
material is usually poured into a mould, which contains a
hollow cavity of the desired shape, and then allowed to
solidify. The solidified part is also known as a casting, which
is ejected or broken out of the mold to complete the
process.

3.  Since the evolution of mankind, man has used
his intelligence and creative instinct to develop
things that will reduce his labor.
 He shaped bowls, tools and weapons out of
stones and wood which was naturally found in
nature. With the passage of time he discovered
other element in nature like gold, silver and
copper. He melted and shaped these metal
according to his desires.

4.  Different Ages of Casting: According to Biblical records casting technology can
be traced back to 5000 BC
 Copper Age (7700-3300BC): Stone age is followed by copper age in the
prehistoric times. Mankind found copper in the fires from copper-bearing ore
that he lined his fire pits. Copper found an instant liking with man because it can
be melted and molded into any desired form
 The Bronze Age: (3300-1200 BC): Eventually, he learned that tin could be mixed
with copper to produce a stronger, durable and attractive metal which was called
bronze.
 Iron Age (1200 BC onwards): Iron age brought the systematic production of
metals. The advent of this age in every culture was coincidental in changes in
agricultural practice, religious beliefs and cultural beliefs
 Industrial Age (18th Century Onwards): Also known as the age of technical
revolution this age saw rapid increased in the demand for casted products. Mass
production was made possible by the invention of new machines in this age

5.  Metal casting origin dates back to the period around 3000
BC. It is possible that metal casting technology, using
moulds originated in the Middle East. However, there are
suggestions that this process may have been developed in
India and China.

6.  The melting ovens of the early Iron Age can
partly be traced back to ceramic burning ovens.
 The model and mould building was mastered
very well from the beginning.
 Lost moulds made of loam and clay, wax
models, single piece-work as well as permanent
moulds made of stone and metal for the serial
production of casting parts were already used.

7.  During World War II, with urgent military demands
overtaxing the machine tool industry, the art of
investment casting provided a shortcut for producing
near net shape precision parts and allowed the use of
specialized alloys which could not be readily shaped
by alternative methods.
 The Investment Casting process was found practical for
many wartime needs--and during the postwar period
it expanded into many commercial and industrial
applications where complex metal parts were needed.

8.  Evolution of casting process: Gold, silver, copper, iron, lead, mercury and tin are
known as the 'magnificent metals' since they were known to man from ancient
times. The basic process of melting of metals in furnace, using patterns and
solidifying the metal in mould has remained the same.
 Furnace: The earliest furnace were simple and easy to operate, with bee wax
used for patterns and bellows for blowing air into the furnace. In the iron age
probably ceramic ovens were used to melt the metals.
 Molds: Different types of mold made from clay, wax and loam were known from
the early times. The lost form technique was also prevalently used from the early
times.
 Patterns: The first patterns of casting were made probably 4000 years from bee
wax. A frog casted in copper is the oldest living proof of intricate patterns used as
early as 3200 B.C.

9.  In metalworking, casting involves
pouring liquid metal into a mould, which
contains a hollow cavity of the desired
shape, and then allowing it to cool and
solidify.
 The solidified part is also known as a
casting, which is ejected or broken out of
the mould to complete the process.
Casting is most often used for making
complex shapes that would be difficult to
make by other methods.

10.  Casting is a solidification process, which
means the solidification phenomenon
controls most of the properties of the casting.
 Solidification occurs in two steps: nucleation
and crystal growth.

11.  In the Nucleation Stage solid particles form
within the liquid.
 When these particles form their internal
energy is lower than the surrounded liquid,
which is followed by the crystal growth stage

12.  All of the nucleation's represent a crystal, which grows
as the heat of fusion is extracted from the liquid until
there is no liquid left.
 The direction, rate, and type of growth can be
controlled to maximize the properties of the casting.
 Directional solidification is when the material solidifies
at one end and proceeds to solidify to the other end;
this is the most ideal type of grain growth because it
allows liquid material to compensate for shrinkage.

13.  Area of the casting which is cooled quickly
will have a fine grain structure and an area
which cools slowly will have a coarse grain
structure.
 Cooling curve for pure metal & eutectic alloy.

14.  Most castings are of alloys, which have a
cooling curve shaped as shown below.
 There is no longer a Thermal arrest, instead
there is a freezing range. The freezing range
corresponds directly to the liquidus and
solidus found on the phase diagram for the
specific alloy.

16. Chvorinov's Rule:
 The local solidification time can be calculated using
Chvorinov's rule, which is:
 Where t is the solidification time, V is the volume of the
casting, A is the surface area of the casting that contacts
the mold, n is a constant, and B is the mould constant. It is
most useful in determining if a riser will solidify before the
casting, because if the riser does solidify first then it is
worthless.

17.  Mould Architecture :

18.  The gating system:
 The gating system serves many purposes, the most
important being conveying the liquid material to the
mold, but also controlling shrinkage, the speed of the
liquid, turbulence, and trapping dross.
 In especially large castings multiple gates or runners
may be required to introduce metal to more than one
point in the mold cavity.

19.  The speed of the material is important because if
the material is traveling too slowly it can cool
before completely filling, leading to misruns and
cold shuts.
 If the material is moving too fast then the liquid
material can erode the mold and contaminate the
final casting.
 The shape and length of the gating system can
also control how quickly the material cools.

20.  Shrinkage
 There are three types of shrinkage:
 Shrinkage of the liquid,
 Solidification shrinkage
 Patternmaker's shrinkage.
 The shrinkage of the liquid is rarely a problem because more
material is flowing into the mold behind it.
 Solidification shrinkage occurs because metals are less dense as a
liquid than a solid, so during solidification the metal density
dramatically increases.
 Patternmaker's shrinkage refers shrinkage that occurs when the
material is cooled from the solidification temperature to room
temperature, which occurs due to thermal contraction.

21.  Risers and riser aids
 Risers, also known as feeders, are the most
common way of providing directional
solidification. It supplies liquid metal to the
solidifying casting to compensate for
solidification shrinkage.

22.  For a riser to work properly the riser must
solidify after the casting, otherwise it cannot
supply liquid metal to shrinkage within the
casting.
 Risers add cost to the casting because it
lowers the yield of each casting; i.e. more
metal is lost as scrap for each casting.

23.  Risers are classified by three criteria. The first is if the riser
is open to the atmosphere, if it is then its called
an open riser, otherwise its known as a blind type.
 The second criterion is where the riser is located; if it is
located on the casting then it is known as a top riser and if
it is located next to the casting it is known as a side riser.
 Finally, if riser is located on the gating system so that it
fills after the molding cavity, it is known as a live
riser or hot riser, but if the riser fills with materials that's
already flowed through the molding cavity it is known as
a dead riser or cold riser.

24.  Contraction allowances: The pattern needs to
incorporate suitable allowances for shrinkage; these
are called contraction allowances, and their exact
values depend on the alloy being cast and the exact
sand casting method being used.
 Draft allowance-When the pattern is to be removed
from the sand mold, there is a possibility that any
leading edges may break off, or get damaged in the
process. To avoid this, a taper is provided on the
pattern, so as to facilitate easy removal of the pattern
from the mold, and hence reduce damage to edges.

25.  Finishing allowance: The surface finish obtained in sand
castings is generally poor (dimensionally inaccurate), and
hence in many cases, the cast product is subjected
to machining processes like turning , grinding in order to
improve the surface finish. During machining processes,
some metal is removed from the piece. To compensate for
this, a machining allowance should be given in the casting.
 Shake allowance: Usually during removal of the pattern
from the mold cavity, the pattern is rapped all around the
faces, in order to facilitate easy removal. In this process,
the final cavity is enlarged. To compensate for this, the
pattern dimensions need to be reduced.

26.  Distortion allowance :
During cooling of the mold, stresses developed in
the solid metal may induce distortions in the cast. This
is more evident when the mold is thinner in width as
compared to its length. This can be eliminated by
initially distorting the pattern in the opposite
direction.

27.  Fluid Life
 Solidification Shrinkage
 Slag and/or Dross Formation
Tendency
 Pouring Temperature

28.  Fluid Life-A molten metal's fluid life is more than its
ability to fill the mould cavity. The fluid life also
determines how easily and how long the metal flows
through narrow channels to form thin sections, and
how readily it conforms to fine surface detail.
 Fluid life will affect the design characteristics of a
casting. By understanding the nature of an alloy's fluid
life, the designer will recognize several important
design criteria. Some of these are:
 Minimum section thickness that can be attained;
 The maximum length of a thin section;
 The fineness of cosmetic detail that is possible;

29.  Solidification Shrinkage
 There are three distinct stages of shrinkage as molten
metal alloys solidify:
 Liquid shrinkage
 Liquid-to-solid shrinkage
 Solid shrinkage

30.  Liquid Shrinkage is the contraction of the liquid before
solidification begins. While important to metal casters, it is
not an important design consideration.
 Liquid-to-Solid Shrinkage is the shrinkage of the metal as
it goes from the liquid's disconnected atoms and
molecules to the formation of crystals of atoms and
chemical compounds, the building blocks of solid metal.
Liquid-to-Solid shrinkage is an extremely important
consideration for the design engineer. In some alloys,
disregard for this type of shrinkage results in voids in the
casting. Both the design and foundry engineer have the
tools to combat this problem, but the designer has the
most cost-effective tool, that is geometry.

31.  Solid Shrinkage (often called patternmaker's shrink)
occurs after the metal has completely solidified and is
cooling to ambient temperature. Solid shrinkage
changes the dimension of the casting from those in
the mould to those dictated by the rate of solid
shrinkage for the alloy.
 In other words, as the solid casting shrinks away from
the mould walls, it assumes final dimensions that
must be predicted by the patternmaker. This
variability of patternmaker's shrink is a very important
design consideration.

32.  Slag / Dross Formation
 Slag is usually is associated with the higher
melting point metals (ferrous metals) and is
composed of liquid non-metallic compounds ,
products of alloying and products of oxidation in
air. Dross, on the other hand, usually is associated
with lower melting point metals (non-ferrous
alloys) and often means the non-metallic
compounds produced primarily by the molten
metal reacting with air.

33.  Pouring Temperature
 Metal castings are produced in moulds that must
withstand the extremely high temperature of liquid
metals. Interestingly, there really are not many
choices of refractors to do the job. As a result, high
molten metal temperatures are very important to
casting geometry as well as what casting process
should be used.
 The following is a summary of common foundry alloys
and their pouring temperatures:

34.  For practical purposes, sand and ceramic materials with
their refractory limits of 3,000 - 3,330°F (1650-1820°C) are
the most common mould materials used today.
 As the temperature of the molten metal alloy increases,
design consideration must be given to heat transfer
problems and thermal abuse of the mould itself.
 Metal moulds, such as those used in die-casting and
permanent moulding, also have temperature limitations.
In fact, most of the alloys on the list are beyond the
refractory capability of metal moulds (except for special
thin geometry designs, alloys from the copper-base group
and up require sand or ceramic moulds).

35.  The chill zone is named so because it occurs at the walls of the mold
where the wall chills the material. Here is where the nucleation
phase of the solidification process takes place.
 As more heat is removed the grains grow towards the center of the
casting. These are thin, long columns that are perpendicular to the
casting surface, which are undesirable because they
have anisotropic properties.
 Finally, the center zone contains spherical, randomly oriented
crystals. These are desirable because they have isotropic properties.
The creation of this zone can be promoted by using a low pouring
temperature, alloy inclusions, or inoculants

37.  Expendable mold casting is a generic classification
that includes sand, plastic, shell, plaster, and
investment (lost-wax technique) moldings. This
method of mold casting involves the use of
temporary, non-reusable moulds.
 Non-expendable mold casting differs from
expendable processes in that the mold need not be
reformed after each production cycle. This technique
includes at least four different methods: permanent,
die, centrifugal, and continuous casting.

38.  Sand casting is one of the most popular and simplest
types of casting that has been used for centuries.
 The most widely used casting process, utilizes
expendable sand molds to form complex metal parts.
Because the sand mold must be destroyed in order to
remove the part, called the casting.

39.  Sand casting typically has a low production rate.
 he 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.

41.  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.
 Disadvantages:
 Poor material strength.
 High porosity possible.
 Poor surface finish and tolerance.
 Secondary machining often required.
 Low production rate.
 High labor cost.
 Applications: Engine blocks and manifolds, machine bases, gears, pulleys

42.  Mould-making - The first step in the sand casting process is to create the mold for the
casting. In an expendable mold process, this step must be performed for each casting. A
sand mold is formed by packing sand into each half of the mold.
 Clamping - Once the mold has been made, it must be prepared for the molten metal to be
poured, the cores are positioned and the mold halves are closed and securely clamped
together.
 Pouring - The molten metal is maintained at a set temperature in a furnace. After the mold
has been clamped, the molten metal can be ladled from its holding container in the furnace
and poured into the mold.
 Cooling - The molten metal that is poured into the mold will begin to cool and solidify once
it enters the cavity. When the entire cavity is filled and the molten metal solidifies, the final
shape of the casting is formed.
 Removal - After the predetermined solidification time has passed, the sand mold can
simply be broken, and the casting removed. This step, sometimes called shakeout, is
typically performed by a vibrating machine that shakes the sand and casting out of the
flask.
 Trimming - During cooling, the material from the channels in the mold solidifies attached
to the part. This excess must be trimmed from the casting either manually via cutting.

43.  The quality of the sand that is used also greatly affects the quality of
the casting and is usually described by the following five 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.

44.  Investment casting is one of the oldest manufacturing processes,
dating back thousands of years, in which molten metal is poured
into an expendable ceramic mold.
 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.
 Lost -wax processes are one-to-one (one pattern 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

46.  Pattern creation - The wax patterns are typically injection
molded into a metal die and are formed as one piece. Cores
may be used to form any internal features on the pattern.
 Mold creation - This "pattern tree" is dipped into a slurry of fine
ceramic particles, coated with more coarse particles, and then
dried to form a ceramic shell around the patterns and gating
system. This process is repeated until the shell is thick enough
to withstand the molten metal it will encounter.
 Pouring - The mold is preheated in a furnace to approximately
1000°C (1832°F) and the molten metal is poured from a ladle
into the gating system of the mold, filling the mold cavity.

47.  Cooling - After the mold has been filled, the molten metal
is allowed to cool and solidify into the shape of the final
casting. Cooling time depends on the thickness of the
part, thickness of the mold, and the material used.
 Casting removal - After the molten metal has cooled, the
mold can be broken and the casting removed. The ceramic
mold is typically broken using water jets, but several other
methods exist
 Finishing - Often times, finishing operations such as
grinding or sandblasting are used to smooth the part at
the gates. Heat treatment is also sometimes used to
harden the final part.

48.  Advantages:
 Can form complex shapes and fine details
 Many material options
 High strength parts
 Very good surface finish and accuracy
 Little need for secondary machining
 Disadvantages: Time-
 Consuming process
 High labor cost
 High tooling cost
 Long lead time possible
 Applications: Turbine blades, pipe fittings, lock parts, hand tools,
jewelry.

49.  Shell Mould casting is a metal casting process similar to sand
casting, in that molten metal is poured into an expendable mold.
 However, in shell mold casting, the mold is a thin-walled shell
created from applying a sand-resin mixture around a pattern.
 The pattern, a metal piece in the shape of the desired part, is
reused to form multiple shell molds.
 A reusable pattern allows for higher production rates, while the
disposable molds enable complex geometries to be cast. Shell
mold casting requires the use of a metal pattern, oven, sand-resin
mixture, dump box, and molten metal.

51.  Pattern creation - A two-piece metal pattern is created in
the shape of the desired part, typically from iron or steel.
Other materials are sometimes used, such as aluminum for
low volume production or graphite for casting reactive
materials.
 Mold creation - First, each pattern half is heated to 175-
370°C (350-700°F) 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.

52.  Pattern creation - A two-piece metal pattern is created in
the shape of the desired part, typically from iron or steel.
Other materials are sometimes used, such as aluminum for
low volume production or graphite for casting reactive
materials.
 Mould creation - First, each pattern half is heated to 175-
370°C (350-700°F) 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.

53.  Mould 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.

54.  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.

55.  Advantages:
 Can form complex shapes and fine details
 Very good surface finish
 High production rate
 Low labor cost
 Low tooling cost
 Little scrap generated
 Disadvantages: High equipment cost
 Applications: Cylinder heads, connecting rods

56.  Centrifugal casting, sometimes called rotocasting, is a
metal casting process that uses centrifugal force to
form cylindrical parts.
 This differs from most metal casting processes, which
use gravity or pressure to fill the mold.
 In centrifugal casting, a permanent mould made from
steel, cast iron, or graphite is typically used. However,
the use of expendable sand molds is also possible. The
casting process is usually performed on a horizontal
centrifugal casting machine vertical machines are
also available.

58.  Mould preparation - The walls of a cylindrical mold are
first coated with a refractory ceramic coating, which
involves a few steps (application, rotation, drying, and
baking).
 Pouring - Molten metal is poured directly into the
rotating mold, without the use of runners or a gating
system. The centrifugal force drives the material
towards the mold walls as the mold fills

59.  Cooling - With all of the molten metal in the mold, the
mold remains spinning as the metal cools. Cooling
begins quickly at the mold walls and proceeds inwards.
 Casting removal - After the casting has cooled and
solidified, the rotation is stopped and the casting can
be removed.
 Finishing - While the centrifugal force drives the dense
metal to the mold walls, any less dense impurities or
bubbles flow to the inner surface of the casting. As a
result, secondary processes such as machining,
grinding, or sand-blasting, are required to clean and
smooth the inner diameter of the part.

60.  Advantages:
 Can form very large parts.
 Good mechanical properties.
 Good surface finish and accuracy.
 Low equipment cost.
 Low labor cost.
 Little scrap generated.
 Disadvantages:
 Limited to cylindrical parts.
 Secondary machining is often required for inner diameter.
 Long lead time possible.
 Applications :Pipes, wheels, pulleys, nozzles

61.  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).
 In both machines, after the molten metal is injected into the dies, it
rapidly cools and solidifies into the final part, called the casting.

62.  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
 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.

63.  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.
 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

64.  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.

65.  Two types of die casting machines are :-
 Hot chamber die casting machines
 Cold chamber die casting machines

66.  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 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. 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.

68.  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.

69.  Cold chamber die casting machine 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.

70.  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
e hot chamber machine.

72.  Advantages:
 Can produce large parts.
 Can form complex shapes.
 High strength parts.
 Very good surface finish and accuracy.
 High production rate.
 Low labor cost.
 Scrap can be recycled.
 Disadvantages:
 Trimming is required.
 High tooling and equipment cost.
 Limited die life.
 Long lead time
 Applications: Engine components, pump components, appliance
housing.

73.  Permanent mold casting is a metal casting process that shares
similarities to both sand casting and die casting.
 As in sand casting, molten metal is poured into a mold which is
clamped shut until the material cools and solidifies into the desired
part shape.
 However, sand casting uses an expendable mold which is destroyed
after each cycle. Permanent mold casting, like die casting, uses a
metal mold (die) that is typically made from steel or cast iron and can
be reused for several thousand cycles.
 Because the molten metal is poured into the die and not forcibly
injected, permanent mold casting is often referred to as gravity die
casting.

75.  Mould preparation - First, the mould is pre-heated to
around 300-500°F (150-260°C) to allow better metal
flow and reduce defects.
 Mould assembly - The mould consists of at least two
parts - the two mold halves and any cores used to
form complex features. Such cores are typically made
from iron or steel, but expendable sand cores are
sometimes used. In this step, the cores are inserted
and the mold halves are clamped together

76.  Pouring - The molten metal is poured at a slow rate from a
ladle into the mold through a sprue at the top of the mold.
The metal flows through a runner system and enters the
mold cavity.
 Cooling - The molten metal is allowed to cool and solidify
in the mould.
 Mold opening - After the metal has solidified, the two
mold halves are opened and the casting is removed.
 Trimming - During cooling, the metal in the runner system
and sprue solidify attached to the casting. This excess
material is now cut away.

77.  Advantages:
 Can form complex shapes.
 Good mechanical properties.
 Many material options.
 Low porosity.
 Low labor cost
 Scrap can be recycled.
 Disadvantages:
 High tooling cost.
 Long lead time possible.
 Applications: Gears, wheels, housings, engine
components.

78.  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.

79.  Shrinkage defects
 Shrinkage defects occur when feed metal is not available to compensate
for shrinkage as the metal solidifies. Shrinkage defects can be split into two
different types: open shrinkage defects and closed shrinkage defects. Open
shrinkage defects are open to the atmosphere , therefore as the shrinkage cavity
forms air compensates. There are two types of open air defects: pipes and caved
surfaces. Pipes form at the surface of the casting and burrow into the casting,
while caved surfaces are shallow cavities that form across the surface of the
casting.
 Closed shrinkage defects, also known as shrinkage porosity, are defects that form
within the casting. Isolated pools of liquid form inside solidified metal, which are
called hot spots. The shrinkage defect usually forms at the top of the hot spots.
They require a nucleation point, so impurities and dissolved gas can induce
closed shrinkage defects. The defects are broken up into macro porosity and micro
porosity (or micro shrinkage), where macro porosity can be seen by the naked eye
and micro porosity cannot.[4][5]

80.  Gas porosity
 Gas porosity is the formation of bubbles within the casting after it
has cooled. This occurs because most liquid materials can hold a
large amount of dissolved gas, but the solid form of the same
material cannot, so the gas forms bubbles within the material as it
cools.
 Gas porosity may present itself on the surface of the casting as
porosity or the pore may be trapped inside the metal,[which
reduces strength in that vicinity.
 Nitrogen, oxygen and hydrogen are the most encountered gases in
cases of gas porosity.
 In aluminum castings, hydrogen is the only gas that dissolves in
significant quantity, which can result in hydrogen gas porosity.

81.  Pouring Metal defects
 Pouring metal defects include misruns, cold shuts, and inclusions.
 A misrun occurs when the liquid metal does not completely fill the mold
cavity, leaving an unfilled portion.
 Cold shuts occur when two fronts of liquid metal do not fuse properly
in the mold cavity, leaving a weak spot.
 Both are caused by either a lack of fluidity in the molten metal or
cross-sections that are too narrow.
 The fluidity can be increased by changing the chemical composition
of the metal or by increasing the pouring temperature. Another
possible cause is back pressure from improperly vented mold cavities

82.  Metallurgical defects
 There are two defects in this category: hot tears and hot
spots. Hot tears, also known as hot cracking, are failures in
the casting that occur as the casting cools. This happens
because the metal is weak when it is hot and the residual
stresses in the material can cause the casting to fail as it
cools. Proper mold design prevents this type of defect.
 Hot spots are areas on the surface of casting that become
very hard because they cooled more quickly than the
surrounding material. This type of defect can be avoided
by proper cooling practices or by changing the chemical
composition of the metal.