The document provides an overview of the casting process, including: 1. Casting involves pouring molten metal into a mold to solidify into the shape of the mold cavity. It can be used to create complex internal and external geometries. 2. There are two main categories of casting processes - expendable mold processes using materials like sand, and permanent mold processes using reusable metal molds. 3. Key steps in casting include preparing the mold, pouring the molten metal, solidification as it cools and shrinks, and removing the finished casting from the mold. Proper design of gating, risers, and directional solidification is important to prevent defects.

1. Lecture# 03
Hafiz Zahid Nabi
Dr. Ghulam Moeen uddin
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2. Introduction
 Casting is a process in which molten metal flows by
gravity or other force into a mold where it solidifies
in the shape of the mold cavity.
 Done for both
 Ingots
 Shape Casting(CASTING)
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3.  Casting can be used to create complex part geometries,
including both external and internal shapes.
 Poor dimensional control, porosity, hardness
 Net Shape products (no finishing),
 Near Net Shape (finishing)
 Can be for Very large parts upto 100 tons
 On any metal that can be heated to the liquid state.
 Some casting methods are quite suited to mass
production.
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4. Classification of solidification processes

5. History of casting
Casting of metals can be traced back 4000 B.C.
Gold was first metal to be discovered and used by the
early civilization.
Copper that gave rise to the need for casting. Shapes
much more complicated made by casting than by
hammering.
Alloys Copper, Tin and aluminum based
 in 1340 - cast iron
 in 1826 - malleable iron
 in 1948 - nodular cast iron
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6. Bronze France, 1500–1300 BC.
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7. Bronze
China, 1600–1046 BC
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8. Bronze
National
Museum of
Korea
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9. Examples of Cast Parts
Crank handle formed by casting; some areas
were machined and assembled after casting
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10. Examples of Cast Parts
C-clamps formed by casting (left) and machining (right)
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11. Examples of Cast Parts
Complex part formed by casting
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12. Overview of Casting Technology
 Casting is usually performed in a foundry
 Foundry is a factory equipped for making molds,
melting and handling molten metal, performing the
casting process, and cleaning the finished casting
 Workers are called Foundry men
 Mold contains a cavity whose geometry determines
part shape
 PATTERN is a dummy part to build cavity in sand
castings
 Cavity must be slightly oversized to allow for
shrinkage of metal
 Types of Casting processes based on type of Molds 12

13. Open Molds and Closed Molds
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14. Two Categories of Casting Processes
Expendable mold processes - mold is sacrificed to
remove part. Uses an expendable mold which must
be destroyed to remove casting.
Mold materials: sand, plaster, and similar materials, plus
binders
 Advantage: more complex shapes possible
 Disadvantage: production rates often limited by time
to make mold rather than casting itself
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15. Permanent mold processes - mold is made of
metal and can be used to make many castings .Uses a
permanent mold which can be used over and over to
produce many castings.
Mold materials :Made of metal (or, less commonly, a
ceramic refractory material)
 Advantage: higher production rates
 Disadvantage: geometries limited by need to open
mold
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16. Sand Casting Mold
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Container
• Sprues, runner, riser, pouring cup constitute Gating System
• Escape of trapped air either to the sand in sand casting or special escape routes
Compensate for shrinkage
To control splashing
Core
For internal features

17. Sand Casting Molded Part Out
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Container
• Sprues, runner, riser, pouring cup constitute Gating System
• Escape of trapped air either to the sand in sand casting or special escape routes
Compensate for shrinkage
To control splashing
Core
For internal features

18. Construction of Mold Cavity
 Mold cavity is formed by packing sand around a
pattern, which has the shape of the part
 When the pattern is removed, the remaining cavity of
the packed sand has desired shape of cast part
 The pattern is usually oversized to allow for shrinkage
of metal during solidification and cooling
 Sand for the mold is moist and contains a binder
to maintain its shape
 Ladle: A long-handled spoon with a deep bowl for
serving liquids.
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19. Use of a Core in the Mold Cavity`
 The mold cavity provides the external surfaces of the
cast part
 In addition, a casting may have internal surfaces,
determined by a core, placed inside the mold cavity to
define the interior geometry of part
 Core Print a region used to support the core
 In sand casting, cores are generally made of sand
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20. 20
Ladle material can be steel, iron
, stainless steel& refractory
material.

21. Preparation of casting
Preparation of liquid metal
 Get all materials ready
 Make suitable composition
 Melt materials (Combustion or Electricity)
 Liquid metal protection
Preparation of casting
 Store and transfer liquid – ladle
 Moulds
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22. Heating the Metal
 The heat required is the sum of:
 Heat to raise temperature to melting point
 Heat of fusion to convert from solid to liquid
 Heat to raise molten metal to desired temperature for
pouring
H = ρV{Cs (Tm-T0)+ Hf + Cl( Tp-Tm)}
H = total heat required to raise the temp of the metal to the pouring temperature, J (Btu);
ρ = density; g=cm3 lbm/ in3;
Cs = weight specific heat for the solid metal, J/g-C (Btu/lbm-F);
Tm = melting temperature of the metal, C (F);
To = starting temperature—usually ambient, C (F);
Hf = heat of fusion, J/g (Btu/lbm);
Cl = weight specific heat of the liquidmetal, J/g-C (Btu/lbm-F);
Tp = pouring temperature, (F); and
V = volume of metal being heated, cm3 (in3).
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23. Heating the Metal
 The heat required is the sum of:
 Heat to raise temperature to melting point
 Heat of fusion to convert from solid to liquid
 Heat to raise molten metal to desired temperature for
pouring
H = ρV{Cs (Tm-T0)+ Hf + Cl( Tp-Tm)}
H = total heat required to raise the temp of the metal to the pouring temperature, J (Btu);
ρ = density; g=cm3 lbm/ in3;
Cs = weight specific heat for the solid metal, J/g-C (Btu/lbm-F);
Tm = melting temperature of the metal, C (F);
To = starting temperature—usually ambient, C (F);
Hf = heat of fusion, J/g (Btu/lbm);
Cl = weight specific heat of the liquidmetal, J/g-C (Btu/lbm-F);
Tp = pouring temperature, (F); and
V = volume of metal being heated, cm3 (in3).
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Example
10.1 self do

24. Pouring the Molten Metal
 For this step to be successful, metal must flow into all
regions of the mold, most importantly the main cavity,
before solidifying
 Factors that determine success
 Pouring temperature
 Pouring rate
 Turbulence
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25.  Pouring temperature should be sufficiently high in order
to prevent the molten metal to start solidifying on its way
to the cavity.
 Pouring rate should neither be high (may stuck at the
runner – should match viscosity of the metal) nor very
low that may start solidifying on its way to the cavity.
 Turbulence should be kept to a minimum in order to
allow smooth flow and to avoid mold damage and
entrapment of foreign materials.
 Mold Erosion: the gradual wearing away of the mold
surfaces due to impact of the flowing molten metal.
Molten metals are more chemically reactive than at room
temperature.
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26. Engineering Analysis of Pouring
Bernoulli’s Theorem which states sum of energies at any
two points in a flowing liquids are equal.
h1+P1/ρ+V1
2 /2g +F1=h2+P2/ρ+V2
2 /2g+F2
 H=head, cm (in), p=pressure on the liquid, N=cm2 lb/ in2; ρ = density; g/cm3 (lbm/in3); v = flowvelocity; cm/s
ðin/secÞ; g = gravitational acceleration constant, 981 cm/s/s (32.212= 386 in/sec/sec); and F= head losses due to
friction, cm (in). Subscripts 1 and 2 indicate any two locations in the liquid flow
assume F=0 P= atmospheric pressure = 1
h1+ V1
2 /2g = h2+V2
2 /2g
Now point 1 is top of sprue and 2 is the bottom point
Then h2 =0 & V1 =0 which further simplifies
h1= V2
2 /2g
Can be solved for velocity
Continuity law: volume rate of flow stays constant
Q=V1A1=V2A2 Q=volume flow rate=cm3/sec
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27. Engineering Analysis of Pouring
Based on that the time required to fill the mold cavity
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Example 10.2 self do

28. Fluidity of Molten Metal
Fluidity
The capability of a molten metal to fill mold cavities
Viscosity
Higher viscosity decreases fluidity
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29. Factors Fluidity of Molten Metal
Surface tension
Decreases fluidity; often caused by oxide film. Low surface tension causes
better filling of the mold cavity
Impurity
Insoluble particles can increase viscosity, reducing fluidity
Mold design
The design and size of the sprue, runners, and risers affect fluidity
Mold material and surface
Thermal conductivity and roughness decrease fluidity
Superheating
The temperature increment above the melting point increases fluidity
Pouring
Lower pouring rates decrease fluidity because of faster cooling
Heat transfer
Coefficient of thermal conductivity
Heat of fusion
The amount of heat required to be lost to solidify the metal from liquid
state. A higher heat of fusion tends to increase the measured fluidity in
casting 29
Very Important to Understand

30. Solidification of Metals
It is the transformation of molten metal back into solid
state
Solidification differs depending on whether the metal is
 A pure element or
 An alloy
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31.  A pure metal solidifies at a constant temperature equal
to its freezing point (same as melting point).
 Chilling action of mold wall, a thin skin of solid metal is
formed at the interface immediately after pouring.
 Rate of freezing depends on heat transfer into mold, as
well as thermal properties of the metal.
 Most alloys freeze over a temperature range rather than
at a single temperature.
 Solidification takes time.
 Layers, consisting of different compositions of the alloy
are formed around the wall of mold.
 It depends upon the melting point and densities of
different constituents in the alloy.
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32. Pure Metal
Local solidification Time
“The actual freezing takes time called the local
solidification time in casting during which the metal’s
latent heat of fusion is released into the surrounding
mold.”
Total solidification Time
“It is time taken b/w pouring and complete
solidification. After the casting has completely
solidified, cooling continuous at a rate indicated by the
downward slope of the cooling curve.”
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33. 33

34. Cooling Rate
 Rapid cooling at mold walls produces equiaxed
(roughly round) grains
 Slow cooling towards the interior forms long
columnar grains that grow towards the center
 Nucleating Agent: Nucleating agents are additives
that provide sites for crystal formation in the polymer
melt. Chemical substances which when incorporated in
plastics form nuclei for the growth of crystals in the
polymer melt.
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35. Metal Solidification
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Dentritic Growth
oriented towards the center
Equiaxed grains
(roughly round) grains

36. Effect of Nucleating Agent on
Metal Solidification
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A nucleating agent
(inoculants) is a
substance that
induces grains to
nucleate and form at
the same time
throughout the
structure.

37. Solidification of Alloys
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Most alloys freeze over a temperature range rather than a single
temperature and the range depends upon the properties of the
constituent metals
Liquidus: The minimum temperature at which all components of a mixture, such
as an alloy, can be in a liquid state.
Solidus: The minimum temperature at which all components of a mixture, such as
an alloy, can be in a solid state.

38. Solidification of Alloys
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Most alloys freeze over a temperature range rather than a single
temperature and the range depends upon the properties of the
constituent metals

39. Effect of Cooling Rate
Dendrites
Tree-like structures that form during the solidification of
alloys
 Slow cooling rates produce dendrites with larger branch
spacing;
 Faster cooling rates produce finer spacing;
 Very fast cooling rates produce no dendrites or grains
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40. Effect of Composition
 Composition of the dendrites as they start to form favors
the metal with the higher melting point
 This imbalance keeps on growing as the solidification
progresses
 Ends up segregating the metals in the alloy
 Variation in chemical composition within single grains
of the casting
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41. Eutectic Alloys
 Eutectic alloy is a particular composition in an alloy system
for which the solidus and liquidus are at the same
temperature.
 Any alloy in theory can be made Eutactic but there has to
be a
 Eutectic Composition
 Eutectic Temperature
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42.  An empirical relationship known as Chvorinov’s
rule, which states:
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Solidification Time
TTS = total solidification time, min;
V = volume of the casting, cm3 (in3);
A = surface area of the casting, cm2 (in2);
n is an exponent usually taken to have a value = 2;
Cm is the mold constant

43. Metals shrink (contract) during solidification. Shrinkage,
causes dimensional changes - and sometimes cracking.
Three kinds are:
 Contraction of the molten metal as it cools prior to its
solidification;
 Contraction of the metal during phase change from
liquid to solid (latent heat of fusion);
 Contraction of the solidified metal (the casting) as its
temperature drops to ambient temperature
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Shrinkage

44. Volumetric contraction for different
casting metals
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45. (0) starting level of molten metal immediately after pouring;
(1) reduction in level caused by liquid contraction during cooling
(dimensional reductions are exaggerated for clarity).
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Shrinkage in Solidification and Cooling

46. Shrinkage in Solidification and Cooling
(2) reduction in height and formation of shrinkage cavity caused by
solidification shrinkage; (3) further reduction in height and diameter due
to thermal contraction during cooling of solid metal (dimensional
reductions are exaggerated for clarity).
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47.  The cavity (containing liquid metal) remains at upper
level because liquid metal has low density as
compared to solid metal. But it is not at the top because
the layer of the metal has already solidified at the top
due to rapid cooling there.
 The shrinkage cavity is called a pipe by foundaryman.
 The amount by which the mold must be made larger
relative to final casting size is called the pattern
shrinkage allowance.
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Shrinkage Cavity

48. Solidification Shrinkage
 Exception: cast iron with high C content
 Graphitization during final stages of freezing
causes expansion that counteracts volumetric decrease
associated with phase change
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49. Shrinkage Allowance
 Pattern makers account for solidification shrinkage
and thermal contraction by making mold cavity
oversized
 Amount by which mold is made larger relative to final
casting size is called pattern shrinkage allowance
 Casting dimensions are expressed linearly rather
than volumetrically, so allowances are applied
accordingly
 A pattern is a replica of the object to be cast, used to
prepare the cavity into which molten material will be
poured during the casting process.
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50. Directional Solidification
It is desirable for the regions of the
casting most distant from the liquid
metal supply to freeze first and for
solidification to progress from these
remote regions toward the riser(s)
Locating sections of the casting with lower
V/A ratios away from the riser, freezing
will occur first in these regions
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51. Directional Solidification
 Another way to encourage directional solidification is to use
Chills.
 Internal chills: small metals parts placed inside the cavity
before pouring so that the molten metal solidify first around
these parts.
 External chills: metal inserts in the walls of the mold cavity
that can remove heat from the molten metal more rapidly
than the surrounding sand in order to permote solidification.
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52. Riser Design
 Riser must stay liquid as long as all the metal is solidified.
 Riser is waste metal that is separated from the casting and
remelted to make more castings
 To minimize waste in the unit operation, it is desirable for the
volume of metal in the riser to be a minimum
 Since the geometry of the riser is normally selected to maximize
the V/A ratio, this allows riser volume to be reduced to the
minimum possible value
 V/A -> Body volume per unit surface area. Spherical shape has
the maximum value of V/A. If the surface area is going to
increase more material is wasted because of interacting with
surroundings
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53.  Side Riser
It is attached to the side of casting by means of small
channel.
 Top Riser
It is one that is connected to the top surface of the
casting.
 Open Riser
It is exposed to the outside at the top surface of the
cope.
 Blind Riser
It is entirely closed in the mold.
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54. 54
Sample Problem 10.3
DIY

55. The risers in the mold serve as reservoirs to feed molten metal into the casting to prevent
porosity forming in isolated sections during solidification.
Proper design (location, number, and size) of the risers is critical to prevent porosity caused
by solidification shrinkage.
the risers should provide metal feed into the heavy sections of the casting which are the last
to solidify.
-- But the risers must be placed so that they can be cut off without leaving undesirable
grinding marks.
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