This document discusses casting manufacturing technology. It describes sand casting, the most common type of casting, where molten metal is poured into a sand mold. The key steps in sand casting are pattern making, core making, mold making using green sand composed of silica, clay and water, gating system design, melting and pouring, solidification, and cleaning. The document discusses the advantages and disadvantages of sand casting and provides details on molding sand properties, types of patterns, mold testing methods, and core making process.

1. Manufacturing Technology
CASTING
AKHIL NARAYANAN

2. Casting
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•Involves pouring molten metal into a mold cavity where
upon solidification, it takes the shape of cavity
•Can be used to produce a range of sizes from a fraction of
an ounce to hundreds of tons.

3. Casting
• Capable of large sizes
• Capable of producing complex
parts
• Internal cavities or hollow
parts can be produced.
• Useful for metals with low
ductility
• Most economical type of
fabrication
• Minimal waste
• Empty spaces can weaken
metal
• Poor surface finish
• Small parts hard to remove
• Additional hardening usually
needed
Advantages Disadvantages

4. Sand Casting
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5. Sand casting
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•Sand is the mold material
•Inexpensive
•Resistant to elevated temperature

6. Sand Casting
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7. Sand Casting
• Two-piece casting flask
– top is cope, bottom is drag
• Sand packed around
pattern of intended shape
• Gating system for metal
flow and escape
– trimming necessary
• Often used with
automotive parts
– Iron, steel, bronze,
aluminum, lead, tin, zinc

8. Sand Casting
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9. Steps in sand casting process
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•Pattern making
•Core making
•Sand mould making
•Gating system
•Melting and pouring
•Solidification
•Shake out and cleaning

10. Moulding sand composition
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•What is the composition in moulding sand
•Silica grains (SiO2)
•Clay
•Used as binding agents to provide strength
•Water
•It activate clay to provide necessary plasticity and
strength
•Additives
•Add in small quantities to improve properties

11. Desirable properties of molding sand
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Strength
The ability of sand mixture to withstand mechanical
pressure imposed during sand casting process
Permeability
The ability of sand mould to permit the escape of air, gases
and steam during the sand casting process
Collapsibility
Ability of sand mixture to collapse under force. Collapsibility
allow the sand mould to shrink freely during the
solidification phase of the process

12. Desirable properties of moulding sand
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Refractory strength
Ability to withstand high temperature
Flowability
The ability of sand mixture to flow over and fill the sand
casting pattern during the impression making phase of the
sand moulding process
Reusability
The ability of sand mixture to be reused.

13. Types of moulding sand
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Natural sand
Sand available in river beds. It contains clay and can be
used directly
Synthetic sand
Washed silica sand with selected binders
Facing sand
The sand used next to pattern to obtain cleaner and
smoother casting surfaces

14. Types of moulding sand
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Parting sand
Sand which is sprinkled on the pattern and to the parting
surfaces of the mould halves
Core sand
Used to make cores. Contains special binders and
additives.
Loam sand
For heavy and large casting. Clay content is high

15. Pattern
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Pattern is the replica of the component to be
manufactured
Pattern dimension is different from casting because
of two reasons
Pattern allowances
Provision of core prints

16. Pattern Allowances
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•Shrinkage or contraction allowances
•Draft or taper allowances
•Machining or finish allowances
•Distortion or camber allowances
•Rapping allowances

17. Shrinkage Allowance
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•Types of shrinkage of metals
•Liquid contraction
•Reduction of volume during temperature drop from
pouring temperature to melting temperature
•Reduction of volume during phase change from liquid to
solid at melting temperature
•Compensated by riser
•Solid contraction
•Reduction of volume of solid during temperature drop
from melting temperature to room temperature
•Compensated by providing allowances in pattern
•Can shrinkage allowance be same for all
metals?

18. Draft Allowance
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19. Machining Allowance
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•To improve the surface finish

20. Distortion Allowance
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Distortion of casting during solidification due to internal
stresses or non-uniform cooling
Can be avoided by providing sufficient distortion
allowance

21. Rapping Allowance
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•Negative allowance to adjust the increase of cavity size
during withdrawal of pattern.

22. Pattern Materials
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•Wood
•Cheap, poor surface finish, poor dimensional accuracy
•Metals and alloys
•Good surface finish, expensive, chance of corrosion
•Wax
•Good surface finish, Only one time use
•Plastics
•Plaster of paris
•Good surface finish and dimensional accuracy,
expensive

23. Types of pattern
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•Single piece pattern
•Split piece pattern
•Match plate pattern
•Gated pattern
•Sweep pattern
•Loose piece pattern
•Skelton pattern
•Cope and drag pattern

24. Single piece pattern
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•Used when the casting is simple
•Molded in drag box

25. Split piece pattern
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•Used for making intricate casting
•It is split along the parting surfaces
•One half of the pattern is molded in drag box and other
half in cope

26. Match plate pattern
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•Two pieces of a split pattern are attached to opposite
sides of a metal or wooden plate
•A number of different sized and shaped patterns may be
mounted on one match plate

27. Gated pattern
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•Sections connecting different patterns serves as runner
and gates.
•Employed for producing small castings of large
numbers

28. Sweep pattern
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•Here 2D pattern is used
• Casting is three dimensional symmetrical shape
•Employed for producing large castings with axi-
symmetrical shape

29. Loose piece pattern
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•Certain patterns cannot be withdrawn once they are
embedded in the molding sand. Such patterns are made
with one or two loose piece for removal from the molding
box .

30. Skelton pattern
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•Used for making huge castings
•Hollow pattern

31. Cope and drag pattern
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•Used for making huge castings
•Provision of molding runner and gates

32. Follow board pattern
• When the use of solid or split patterns becomes
difficult, a contour corresponding to the exact shape
of one half of the pattern is made in a wooden
board, which is called a follow board and it acts as a
molding board for the first molding operation as
shown in Fig.

33. Segmental or part pattern
• Patterns of this type are generally used for circular castings,
for example wheel rim, gear blank etc. Such patterns are
sections of a pattern so arranged as to form a complete mould
by being moved to form each section of the mould.
• The movement of segmental pattern is guided by the use of a
central pivot. A segment pattern for a wheel rim is shown in
Fig

34. Kinds of Molding Sand
Green sand
• Green sand is also known as tempered or natural sand.
• silica sand with 18 to 30 percent clay, having moisture content
from 6 to 8%.
• fine, soft, light, and porous.
• Commonly employed for production of ferrous and non-
ferrous castings.
Dry sand
• Silica sand + Clay+ Sodium Silicate
• Green sand or Dry Sand with 50% clay – Loam sand

35. Additives in sand
• For improving the moulding sand properties
1. Corn flour and Dextrin
• Belongs to carbohydrates
• Used increase the collapsibility
• Get Volatilized on heating , there by leaving space
there for easily can be break the mould
2. Coal dust
• Mainly used to obtain reducing atmosphere.
• So that tendency to form scales get reduces
• Mainly for ferrous materials

36. Sea coal and Pitch
• Generally uses around 0.02-0.2%.
• When heated it changes to coke which fills the
pores and prevent free movement.
Wood Flour
• Generally long thin fibres are used
• 0.05-2% in mould as well as core sand
• Increase the collapsibility
Silica Flour
• Added up to 3%
• Increases the hot strength of mould

37. Sand Testing
• For obtaining the higher surface finish and
dimensional accuracy.
• Often allows the use of less expensive local sand
• Ensure the determination of optimum mixture.
• If variation from standard mixture found, we can
adjust the mixture to obtain given properties.
• Choices for desired finish
• Optimum choice reduces the defects in casting.

38. Moisture Content Test
• Drying a 20-50gm moulding sand up to 100 C
• It is cooled to room temp. and reweighed.
• Loss of weight shows the moisture content.
• Also obtained by moisture teller .
• Based on the reaction between CaC2 sand
water.
• The amount of acetylene gas produced is
measured which is proportional to moisture
content.
O

39. Clay content Test
• Take 50gm of dry sand and transferred to wash
bottle.
• Add 475 cc distilled water + 25cc of 35% NaoH
• Stir it for 10 min
• Fill the water bottle up to mark, allow settle
down.
• Clay get dissolved in water ( Repeat it for 7 times)
• Remove water , dry the sand and reweigh it.
• Weight of clay = 50- Reweighed sand weight

40. Grain Fineness Test
• Used to determine grain size, distribution and
fineness.
• Take dry sand of 50gm
• Pass it through a series of Standard sieves ( in a
stack)
• The topmost is coarser and bottom most is finer.
• The above set up is vibrated for 15 minutes,
• Weigh the sand left on each sieve
• Find the percentage distribution

41. Refractoriness Test
• Observe the sand particle under microscope.
• Heating the sand specimen to high temperatures.
• Then cool it to room temp. Examine under
microscope for surface characteristics.
• A good refractory sand retains the shape, But
generally up to 7% expansion is allowed.
• Less refractory specimen will shrink and distort.

42. Flow ability Test
• Flowability is the ability to sand to take the
desired shape.
• It must be capable of transmitting the blows.
• A standard sand specimen is prepared.
• Ram plunger is dropped on specimen for 5
times.
• The movement sand drop for measured
between 4th and 5th and calibration for the given
sand.

44. Shatter index test
• Based on AFS standards.
• Generally used to determine the shatter index of
green sand
• A standard specimen of 50mm dia and 50mm height
is allowed to fall from a height of 1.83metres.
• The weight of sand retained on the sieve is weighed
and calculating the shattered index.

46. Strength test
• Green strength and dry strength are the measure of holding
power of various constituents.
• Most commonly used test is the compression test.
• The test set up is as shown below;
• The specimen having a dimensions of 50mm dia and 50mm
height.
• The specimen is placed between the grips.
• The load is applied on the specimen using the hand wheel.
• The dial indicator measures the deformation of the specimen.
• Machine consist of two indicators – Low strength and High
strength.
• Gradually increasing the load.
• As soon as the specimen breaks compression strength is measured
by the manometer.

48. Mould Hardness Test
• It is based on the Brinell hardness testing machine.
• According to the AFS standard hardness tester a half
inch dia steel hemi spherical ball is loaded with spring
load of 980gm.
• This ball is allowed to penetrate into mould sand
sample.
• The dial is calibrated to read the readings directly.

50. Permeability Test
• Permeability is also known as porosity.
• Specimen having a dimension of 50.8mm dia and
50.8 height.
• The test conducted by permeability meter.
• The apparatus consist of two concentric cylinders
one inside the other.
• The space between them is filled with water.
• The bell is placed above the water level.
• Standard specimen is placed together with ram
tube as shown in figure.

52. • In this way air stream from bell to nozzle.
• Permeability is the volume of air (1cc) passing through
a sand specimen of area ( 1cm*1cm)and 1 cm height at
a pressure difference of 1 gm/cm2.
• It is expressed as;

53. CORES
• Cores are compact mass of core sand placed mould
cavity at predetermined location, usually for
producing hollow casting.
• Generally core has to withstand severe action of hot
metal which completely surround it.
• Core sand special kind moulding sand mainly pure
silica sand and a binder.
• The main purpose of binder is to hold the grains
together
• The binder should produces minimum amount of
gases when it comes contact with molten metal.
• Organic binders are most preferred.

54. Selection criteria for core sand
• High refractoriness
• High permeability
• Preferable to non reactive constituents
• Optimum collapsibility.
Binders for core sand
a) Ceral binders: develops green strength, baking strength.
b)Protein binders : for collapsibility
c) Sulphite binders : usually uses with clay - Green strength.
d) Dextrin: for collapsibility
e) Pitch: For hot strength
f) Molasses : To increase the hardness during baking
g) Thermosetting Resins : High strength, commonly uses phenol
formaldehyde and urea formaldehyde
h) Core oil : increases the cohesive property

55. Core Making
• Involves five stages
A) Core Sand Preparation
• Mixture depends on the required properties,
• Preferred to have homogenous mixture,
• Mixing usually done with roller mill,
B) Core Making Process
• Small shapes are usually hand rammed,
• Core making machines – Core blowing, Core extrusion
and core ramming.
• Core ramming – Squeezing , jolting and slinging.

56. C) Core Baking
• Usually performed using the baking ovens or furnaces.
• Removing the moisture and strengthen the core.
• Generally baked up to 380 C.
• Binders get activated and form bond between the
particles.
• Core ovens and dielectric bakers
• Core oven are of two types;
1) Continuous type: Core carrying conveyors or chains
move continuously through oven. Baking time is
controlled by speed of conveyor. Commonly used for
mass production
o

57. 2) Batch type ovens : Baking variety of cores in batches.
Cores are placed commonly in drawers or racks and put in
a ovens.
Dielectric bakers
• Based on dielectric heating.
• Placed in between the dielectric medium
• During breakdown large voltage and current develops.
• This energy is utilized for heating the cores.

58. d) Core Finishing
• The fins, projections, sand particles from the surface of
the core is removed by filing or rubbing.
• A sound casting require dimensionally accurate core.
• Cores are coated with protective materials using
brushing, dipping or spraying.
f) Setting of Cores
• Positioning of core in the mould.
• It must be accurately positioned.
• Small cores are set by hand and large by cranes.
• Some times use of chaplets required for additional
support.
• They are made of same material as that of core.

59. Sand Moulding Machines
• Moulding machines are used to obtain ramming force
required for making sand moulds.
• It is also used for inverting the mould, rapping of pattern
or breaking of mould.
• Most of the moulding machines performs combination
these functions.
• It is classified as;
a) Squeeze machine
b) Jolting Machine
c) Jolt-Squeezer machine
d) Slinging machine

60. Squeezer machine
• The machines are either hand operated or power
operated.
• The pattern is placed over machine table followed by
the moulding box.
• The table is lifted towards squeezer plate.
• The sand get squeezed in the moulding box.

62. Jolting Machine
• Known as jar machine which comprises of air operated
piston and cylinder.
• The air is allowed to enter the bottom side.
• And raises the piston to certain height.
• The table is attached to the top of the piston which carries
the pattern and mould box with sand
• Air below the piston is suddenly released and the table
drops down suddenly.
• This cause sand to pack evenly around the pattern.
• This process repeated several times.

64. JOLT AND SQUEEZER MACHINE
• It uses the principle of both jolt and squeezer machines in
which complete mould is produced.
• The cope and drag are assembled together.
• Initially the drag is filled with sand followed ramming by
jolting action of table.
• After levelling of the sand on the upper side of drag box.
• The upper part has cope box, which filled with sand and
rammed by squeezing.

65. Slinging Machines
• Also known as sand slingers.
• The consolidation and ramming is obtained by impact of
sand which falls at very high velocity on mould box.
• A typical sand slinger consist of heavy base, bin or hopper to
carry sand, a bucket elevator to which a number of buckets
are attached
• A swinging arm which carries a belt conveyor and sand
impeller head.
• The head revolves at a very high speed, as result of sand
throws into moulding box at high velocity.
• Sometimes extra ramming is provide to get the additional
strength.

67. GATING SYSTEM
• It is the assembly of channels that’s facilitates the flow of
molten into the cavity.

68. Any gating system designed should aim at providing a defect free
casting. This can be achieved by considering following requirements:
• A gating system should avoid sudden or right angle changes in
direction.
• A gating system should fill the mould cavity before freezing.
• The metal should flow smoothly into the mould without any
turbulence. A turbulence metal flow tends to form dross in the
mould.
• Unwanted materials such as slag, dross and other mould
materials should not be allowed to enter the mould cavity.
• The metal entry into the mould cavity should be properly
controlled in such a way that aspiration of the atmospheric air is
prevented.

69. • Metal flow should be maintained in such a way that no
gating or mould erosion takes place.
• The gating system should ensure that enough molten metal
reaches the mould cavity.
• It should be economical and easy to implement and remove
after casting solidification.

71. • The gating system is composed of
 Pouring basin
 Sprue or down gate
 Runner or cross gate
 Gates or Ingates
 Risers
Gating ratio : Sprue area: runner area: ingate area

72. • Classification of gating system:
1. Based on pressure above molten metal in pouring basin
A) Non-pressurized gating system
• If the pressure above molten metal in gating system is equal
to atmospheric pressure.
• Most common system sprue base act as the choke.
• Optimum gating ratio- 1:2:2, 1:4:4
• Suitable for non-reactive metals.
B) Pressurized gating system
• If the pressure above the molten metal above the pouring
basin greater than atmospheric pressure.
• A back pressure is maintained.
• Mostly ingates serve as choke.
• Typical gating ratio- 4:3:2,1:2:1

74. TOP GATING SYSTEM
• If the molten metal enters into the cavity from top side.
• Generally produces favourable temperature gradient.

75. Advantages of top gating system
• Easy to construct
• The velocity of molten metal.
• Pouring time is found to be minimum.
• Removal top gating system is easier
• The chances of sand erosion are quiet high.
• Chance of high turbulent flow
Disadvantages of top gating system

76. BOTTOM GATING SYSTEM
• A bottom gate is made in the drag portion of the mould.
• In a bottom gate the liquid metal fills rapidly the bottom portion of
the mould cavity and rises steadily and gently up the mould walls.
• As comparison to top gate, bottom gate involves little turbulence
and sand erosion.
• Bottom gate produces good casting surfaces

77. PARTING GATING SYSTEM
• Middle or side or parting gating systems combine the
characteristics of top and bottom gating systems.
• In this technique gate is provided along the parting line such
that some portion of the mould cavity will be below the
parting line and some portion will be above the parting line.
• The cavity below the parting line will be filled by assuming top
gating and the cavity above the parting line will be filled by
assuming bottom gating

78. STEP GATING SYSTEM
• Molten metal enters into the cavity from various locations .
• Time required for filling the mould is reduced.
• Suitable for large casting.

79. RISER
• Also known as feeder head.
• It provides visual checking to ensure that cavity filled.
• Provide extra metal during shrinkage of molten metal.
• Permits escape of gases in the mould cavity.
• Two types of risers based on construction
A) Open riser
B) Blind riser
• Two type risers based on position
A) Top riser
B) Side riser

83. RISER SHAPE
• The metal should remain in molten state than the cavity.
• So heat loss should minimum from the riser.
• In order to achieve it volume to surface area ratio should
high.
• Base on study spherical shape is mostly fulfilling the above
condition.
• But due to difficulty in construction, nowadays uses
cylindrical risers.
• Height of cylindrical riser = 1.5 times diameter.

84. • Chvorinovs rule
• Caines method

85. SPECIAL CASTING PROCESS

86. • Greater dimensional accuracy.
• High production rate.
• Ability to cast extremely thin sections
• Better surface finish.
• Higher mechanical properties ( denser and finer grain size)

87. GRAVITY MOULD CASTING
• It is having a permanent mould.
• It mould can be used several times.
• The molten metal is poured into the mould under gravity.
• This permanent mould are made of dense fine grained heat
resistant materials like cast iron, bronze etc
• Generally it have two halves.
• Sprue, gate and riser are made in the mould itself.
• Used for production of carburetor bodies, hydraulic break
cylinders, automotive pistons, aircraft engine coverings.
• Casting involves 3 steps

91. DIE CASTING
• Die casting is a permanent mold casting
process.
• 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.
• The molten metal injection is carried out by a
machine called die casting machine.

92. • Pressure is maintained during solidification, then mold is
opened and part is removed
• Use of high pressure to force metal into die cavity is what
distinguishes this from other permanent mold processes.
Die Casting Machines
• Designed to hold and accurately close two mould halves
and keep them closed while liquid metal is forced into
cavity
Two main types:
• 1. Hot-chamber machine
• 2. Cold-chamber machine

93. 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 – 50 parts per hour or more
• Applications limited to low melting-point metals that do
not chemically attack plunger and other mechanical
components
• Casting metals: zinc, tin, lead, and magnesium

95. • The setup is known as gooseneck or air injection type or
submerged plunger type – air blown.
• Parts : frame, source of molten metal, molten metal transferring
mechanism, die casting dies, injection mechanism.
• Air pressure required in the range of 30 to 45 bars.

96. Cold-Chamber Die Casting
• Molten metal is poured into unheated chamber from external
melting container, and a piston injects metal under high
pressure into die cavity.
• The pouring temperature is lower than that of hot chamber die
casting.
• 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 favour its use on low
melting-point alloys (zinc, tin, lead).

99. SHELL MOULD CASTING
• Casting process in which the mould is a thin shell of sand held
together by thermosetting resin binder.
• In this process a two piece pattern or match plate pattern is heated
around 400 C.
• Each half of the pattern is then covered with mixture of sand and
thermosetting resin. Binder helps to form a layer above the
pattern.
• The patterns are removed and two half of the shells joined. And
molten metal poured to it.
• After solidification the shell is broken to get the part.
0

105. Advantages
• Suitable for thin castings.
• Good dimensional accuracy
• Often machining not required.
• It can mechanized for mass production
• Smoother cavity surface permits easier flow of molten metal.
Disadvantages
• Not suitable for small scale production
• Not suitable large components
• Mould is not reusable
Applications
• Rocker arms, valve bodies, small pipes, bearing caps, small
gears.

106. Investment Casting(Lost Wax Process)
• A pattern made of wax is coated with a refractory material to
make mould, after which wax is melted away prior to pouring
molten metal.
• "Investment" comes from one of the less familiar definitions
of "invest" - "to cover completely," which refers to coating of
refractory material around wax pattern.
• It is a precision casting process - capable of castings of high
accuracy and intricate detail

112. Centrifugal Casting
• A group of casting processes in which the mould is rotated at
high speed so centrifugal force distributes molten metal to
outer regions of die cavity
• The group includes:
1.True centrifugal casting
2.Semicentrifugal casting
3.Centrifuge casting

113. True Centrifugal Casting
• Molten metal is poured into rotating mould to
produce a tubular part
• In some operations, mould rotation commences after
pouring rather than before
• Applications: 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.

115. Merits
• Lighter impurities within the metal floats near the centre which
can be easily removed.
• Dense and fine grained castings
• Proper directional solidification( outside to inside)
• Central core or gating system is not required.
Demerits
• Limited to certain shapes
• Cost is high
• Skilled workers is required.

116. Semi-centrifugal Casting
• Centrifugal force is used to produce solid castings rather than
tubular parts
• Moulds 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 lowest
• Examples: wheels and pulleys

118. Centrifuge Casting
• Parts are not symmetrical about the axis.
• A group of mould is arranged as shown, which is having a
common sprue.
• The axis mould does not coincide with axis of rotation.
• Metal distributed into the cavity by the action of centrifugal
force.
• The mould is designed in such part cavities located away from
the axis rotation.
• Suitable for smaller parts.

120. Vacuum Casting
• This is called counter-gravity casting.
• In this process the material is sucked upwards into the mould
by a vacuum pump.
• It is inverted position.
• By realising the pressure a short time after the mould is filled,
unsolidified metal back into the flask.
• So allows us to create hollow casting.
• Suitable thin sectioned parts.

122. Slip Casting( Ceramic mould casting)

123. • It uses a suspension of ceramic powder in water called slip.
• Slip contains 25% to 40% water.
• Slip is poured into a porous plaster of paris mould.
• Plaster of paris has a tendency to absorb water.
• Two types
A) Drain casting : mould is inverted to drain excess slip after
required thickness is produced. Producing hollow object.
B) Solid casting : Here mould is not drained.

124. Slush Casting
• It is limited to tin-zinc or lead based alloys.
• Molten metal is filled the cavity, not allowed to
completely solidify it.
• When desired thickness is obtained , remaining
molten metal drained out.
• Hollow casting are produced.
• Open die halves and coated
• Assemble the dies and molten metal is poured to it.
• Usually a hole is provided at the bottom of the object
to drain the excess metal.

126. DEFECTS IN CASTING

135. INCLUSIONS
• Any undesirable foreign particle present within the metal of a
casting is called as inclusions.
• It may be oxides, sand, slag, dirt etc., which enters the mould
cavity with the molten metal during pouring & weakens the
casting & also spoils the surface of the casting.

136. HOT TEARS
• Hot tears are ragged irregular internal or external cracks
occurring immediately after the metal have solidified.
• Causes : Lack of collapsibility of core & mould, Hard ramming
of mould, Faulty casting design.
• Remedies :Providing softer ramming, Improve casting design,
Improve collapsibility of core, mould.