Short Notes: Metal Casting Processes | Short Notes for Mechanical Engineering PDF Download

 Page 1


Metal Casting Processes  
Casting is basically melting a solid material, heating to a special temperature, and 
pouring the molten material into a cavity or mould, which is in proper shape. In 
casting, we can make most intricate of shapes, both external and internal. Casting 
process can be shown in a flow chart as
Pattern making
i
Core making
i
Moulding
i
Melting and pouring
i
Cooling and solidification
i
Cleaning
The process can be applied on metals and plastics The process can be applied on 
metals and plastics.
The term The term casting is commonly used for metals and the is commonly used 
for metals and the term molding is used for plastics.
The typical mold for a sand casting is shown in the picture:
Page 2


Metal Casting Processes  
Casting is basically melting a solid material, heating to a special temperature, and 
pouring the molten material into a cavity or mould, which is in proper shape. In 
casting, we can make most intricate of shapes, both external and internal. Casting 
process can be shown in a flow chart as
Pattern making
i
Core making
i
Moulding
i
Melting and pouring
i
Cooling and solidification
i
Cleaning
The process can be applied on metals and plastics The process can be applied on 
metals and plastics.
The term The term casting is commonly used for metals and the is commonly used 
for metals and the term molding is used for plastics.
The typical mold for a sand casting is shown in the picture:
idler roll
Ring rolling used to reduce the wall thickness and increase the diameter of a ring
• The set of channels through which a molten metal flows to the mould cavity is 
called gating system.
• Typical gating system consists of a pouring cup and a sprue receiving the 
poured melt, runner - a channel through which the melt is supplied to the 
gates through which the molten metal enters the mould cavity.
• A gating system may include a riser (feed head) - a cavity connected to the 
gating system feeding the casting when it is shrinking.
• Air within the mould cavity and gases formed when a molten metal contacts 
the mould surface are removed through the vents.
• The interior cavities of a casting are formed by separate inserts called cores. 
Cores are usually made of sand and baked.
Pattern Making: First of all, pattern is a replica or facsimile model of desired 
casting which produces a cavity. Molten metal solidifies in this cavity. The process 
of making such cavity by using pattern is known as pattern making.
Pattern materials are:
1. Wood
2. Plastic
3. Plaster of Paris
4. Wax
Core Making: Cores are used to produce the internal features of part such as hole 
or any opening. Cores are placed in the cavity produced by pattern.
Molding: Moulding is the process to prepare a mould for receiving mould metal.
Cores are mold parts used to shape internal holes and cavities. They are also 
fortification parts of molds where wearing occurs. These parts are made of sand 
and organic-inorganic bonders such as cereal meals, dextrin, sodium silicate, 
cement etc. Some properties of cores must have are the followings:
1. High-Temperature Resistivity
2. Metal Erosion Resistivity
3. Easiness of Deformation After Casting
4. Gas Insertion Ability
5. Smooth Surfaces
6. Saving Physical Properties During Storage
Melting and Pouring: Melting is used to melt the metal, so that it can flow inside 
mould cavity. Molten metal is poured in pouring cup. This is known as sprue and 
horizontal portion of this cup and is known as runner. The points through which 
metal enters into cavity are known as gate.
Cooling and Solidification: We know, density of solid is more than liquid. Hence, 
when molten metal solidifies, the size of solid is less in comparison of molten 
metal. This process is known as shrinkage.
Page 3


Metal Casting Processes  
Casting is basically melting a solid material, heating to a special temperature, and 
pouring the molten material into a cavity or mould, which is in proper shape. In 
casting, we can make most intricate of shapes, both external and internal. Casting 
process can be shown in a flow chart as
Pattern making
i
Core making
i
Moulding
i
Melting and pouring
i
Cooling and solidification
i
Cleaning
The process can be applied on metals and plastics The process can be applied on 
metals and plastics.
The term The term casting is commonly used for metals and the is commonly used 
for metals and the term molding is used for plastics.
The typical mold for a sand casting is shown in the picture:
idler roll
Ring rolling used to reduce the wall thickness and increase the diameter of a ring
• The set of channels through which a molten metal flows to the mould cavity is 
called gating system.
• Typical gating system consists of a pouring cup and a sprue receiving the 
poured melt, runner - a channel through which the melt is supplied to the 
gates through which the molten metal enters the mould cavity.
• A gating system may include a riser (feed head) - a cavity connected to the 
gating system feeding the casting when it is shrinking.
• Air within the mould cavity and gases formed when a molten metal contacts 
the mould surface are removed through the vents.
• The interior cavities of a casting are formed by separate inserts called cores. 
Cores are usually made of sand and baked.
Pattern Making: First of all, pattern is a replica or facsimile model of desired 
casting which produces a cavity. Molten metal solidifies in this cavity. The process 
of making such cavity by using pattern is known as pattern making.
Pattern materials are:
1. Wood
2. Plastic
3. Plaster of Paris
4. Wax
Core Making: Cores are used to produce the internal features of part such as hole 
or any opening. Cores are placed in the cavity produced by pattern.
Molding: Moulding is the process to prepare a mould for receiving mould metal.
Cores are mold parts used to shape internal holes and cavities. They are also 
fortification parts of molds where wearing occurs. These parts are made of sand 
and organic-inorganic bonders such as cereal meals, dextrin, sodium silicate, 
cement etc. Some properties of cores must have are the followings:
1. High-Temperature Resistivity
2. Metal Erosion Resistivity
3. Easiness of Deformation After Casting
4. Gas Insertion Ability
5. Smooth Surfaces
6. Saving Physical Properties During Storage
Melting and Pouring: Melting is used to melt the metal, so that it can flow inside 
mould cavity. Molten metal is poured in pouring cup. This is known as sprue and 
horizontal portion of this cup and is known as runner. The points through which 
metal enters into cavity are known as gate.
Cooling and Solidification: We know, density of solid is more than liquid. Hence, 
when molten metal solidifies, the size of solid is less in comparison of molten 
metal. This process is known as shrinkage.
Cleaning: When metal is cooled and solidified, we withdraw it. Cleaning is done to 
remove the dust or other particles of moulding sand.
Design of Gating System: Bernoulli's theorem plays an important role in regulating 
the flow of metal in gating system. According to Bernoulli's theorem, 'the total 
energy head remains constant at any system'. It is given by
pg
v
2a
-f h
= constant
where, p = Pressure (in N/m2 or Pa) 
v = Velocity of the liquid (in m/s) 
h = Potential head (in m) 
p = Density of the liquid (in kg/m3 ) 
g = 9.8 m/s2 = Acceleration due to gravity
According to continuity law, 'mass of the metal flowing at any section in the would 
is constant'.
m = P 1 A1 V 1 = p2 A2v2
But density remain constant.
So, Pt = p2 
A1 V 1 = A2 v2 
Q = A -|V -| = A2 v2
Where, Q = Rate of flow of the metal (in m3 /s)
A = Area of cross-section of that section, where metal is flowing (in m2) 
v = Velocity of the metal (in m/s)
Design of Risers: The purpose of riser is to provide liquid metal to compensate 
liquid and shrinkage during phase change. The secondary purpose of riser is to 
show that whether casting is full or not. So, a riser is designed in such a way that it 
stays molten longer than the casting.
The solidification time both for casting and riser given as
t — k
(Chvorinovi rule)
t = Solidification time (in second) 
SA = Surface area (in m2 )
V = Volume (in m3) 
k = Mould constant
• The freezing ratio x of a mould is defined as the ratio of cooling 
characteristics of casting to the riser.
SA
V
SA
V mar
Page 4


Metal Casting Processes  
Casting is basically melting a solid material, heating to a special temperature, and 
pouring the molten material into a cavity or mould, which is in proper shape. In 
casting, we can make most intricate of shapes, both external and internal. Casting 
process can be shown in a flow chart as
Pattern making
i
Core making
i
Moulding
i
Melting and pouring
i
Cooling and solidification
i
Cleaning
The process can be applied on metals and plastics The process can be applied on 
metals and plastics.
The term The term casting is commonly used for metals and the is commonly used 
for metals and the term molding is used for plastics.
The typical mold for a sand casting is shown in the picture:
idler roll
Ring rolling used to reduce the wall thickness and increase the diameter of a ring
• The set of channels through which a molten metal flows to the mould cavity is 
called gating system.
• Typical gating system consists of a pouring cup and a sprue receiving the 
poured melt, runner - a channel through which the melt is supplied to the 
gates through which the molten metal enters the mould cavity.
• A gating system may include a riser (feed head) - a cavity connected to the 
gating system feeding the casting when it is shrinking.
• Air within the mould cavity and gases formed when a molten metal contacts 
the mould surface are removed through the vents.
• The interior cavities of a casting are formed by separate inserts called cores. 
Cores are usually made of sand and baked.
Pattern Making: First of all, pattern is a replica or facsimile model of desired 
casting which produces a cavity. Molten metal solidifies in this cavity. The process 
of making such cavity by using pattern is known as pattern making.
Pattern materials are:
1. Wood
2. Plastic
3. Plaster of Paris
4. Wax
Core Making: Cores are used to produce the internal features of part such as hole 
or any opening. Cores are placed in the cavity produced by pattern.
Molding: Moulding is the process to prepare a mould for receiving mould metal.
Cores are mold parts used to shape internal holes and cavities. They are also 
fortification parts of molds where wearing occurs. These parts are made of sand 
and organic-inorganic bonders such as cereal meals, dextrin, sodium silicate, 
cement etc. Some properties of cores must have are the followings:
1. High-Temperature Resistivity
2. Metal Erosion Resistivity
3. Easiness of Deformation After Casting
4. Gas Insertion Ability
5. Smooth Surfaces
6. Saving Physical Properties During Storage
Melting and Pouring: Melting is used to melt the metal, so that it can flow inside 
mould cavity. Molten metal is poured in pouring cup. This is known as sprue and 
horizontal portion of this cup and is known as runner. The points through which 
metal enters into cavity are known as gate.
Cooling and Solidification: We know, density of solid is more than liquid. Hence, 
when molten metal solidifies, the size of solid is less in comparison of molten 
metal. This process is known as shrinkage.
Cleaning: When metal is cooled and solidified, we withdraw it. Cleaning is done to 
remove the dust or other particles of moulding sand.
Design of Gating System: Bernoulli's theorem plays an important role in regulating 
the flow of metal in gating system. According to Bernoulli's theorem, 'the total 
energy head remains constant at any system'. It is given by
pg
v
2a
-f h
= constant
where, p = Pressure (in N/m2 or Pa) 
v = Velocity of the liquid (in m/s) 
h = Potential head (in m) 
p = Density of the liquid (in kg/m3 ) 
g = 9.8 m/s2 = Acceleration due to gravity
According to continuity law, 'mass of the metal flowing at any section in the would 
is constant'.
m = P 1 A1 V 1 = p2 A2v2
But density remain constant.
So, Pt = p2 
A1 V 1 = A2 v2 
Q = A -|V -| = A2 v2
Where, Q = Rate of flow of the metal (in m3 /s)
A = Area of cross-section of that section, where metal is flowing (in m2) 
v = Velocity of the metal (in m/s)
Design of Risers: The purpose of riser is to provide liquid metal to compensate 
liquid and shrinkage during phase change. The secondary purpose of riser is to 
show that whether casting is full or not. So, a riser is designed in such a way that it 
stays molten longer than the casting.
The solidification time both for casting and riser given as
t — k
(Chvorinovi rule)
t = Solidification time (in second) 
SA = Surface area (in m2 )
V = Volume (in m3) 
k = Mould constant
• The freezing ratio x of a mould is defined as the ratio of cooling 
characteristics of casting to the riser.
SA
V
SA
V mar
• In order to be able to feed the casting, the riser should solidify last and hence 
its freezing should be greater than unity.
So, we can write it as
SA
>
SA
I V
c a s tin g
V
• Based on the Chvorinovi's rule, Caine developed a relationship empirically for 
the freezing ratio of steel casting. The equation is
0.10
x ---------------- hi
y — 0.03
where,
Riser volume
y = ----------------------
Casting volume 
For aluminium casting,
0.10
x = ------------+ 1.08
y — 0.06
y-x graph
Sphere have a minimum ratio of surface area to the volume. But it is not used as a 
riser for casting because hottest metal being at the center of the sphere and it is 
difficult to use for feeding the casting.
Generally, cylindrically shaped risers are used for casting purpose.
Design of Castings: When designing casting the most important consideration is 
the effect of shrinkage during cooling. Other important factors include metal flow 
and porosity. Some general rules are given in the following: •
• Avoid sharp corners - they can lead to hot tearing during cooling
• Use fillets cautiously - they lead to stresses as they shrink a radius of 1/8" to 
1" are acceptable.
• Avoid large masses - they will cool more slowly, and can lead to pores and 
cavities in the final part. Cores can be used to hollow out these large volumes. 
Metal padding 'chills' can also be placed inside the mold near large masses to 
help increase cooling rates.
• Use uniform cross sections -this will keep the cooling rate relatively uniform 
and avoid stresses.
• Avoid large flats - large flat areas tend to warp.
• Allow some give as the part cools - by allowing the shrinkage of one part to 
deform another slightly, the internal stresses will be reduced. Figures of 1-2% 
shrinkage are common.
Page 5


Metal Casting Processes  
Casting is basically melting a solid material, heating to a special temperature, and 
pouring the molten material into a cavity or mould, which is in proper shape. In 
casting, we can make most intricate of shapes, both external and internal. Casting 
process can be shown in a flow chart as
Pattern making
i
Core making
i
Moulding
i
Melting and pouring
i
Cooling and solidification
i
Cleaning
The process can be applied on metals and plastics The process can be applied on 
metals and plastics.
The term The term casting is commonly used for metals and the is commonly used 
for metals and the term molding is used for plastics.
The typical mold for a sand casting is shown in the picture:
idler roll
Ring rolling used to reduce the wall thickness and increase the diameter of a ring
• The set of channels through which a molten metal flows to the mould cavity is 
called gating system.
• Typical gating system consists of a pouring cup and a sprue receiving the 
poured melt, runner - a channel through which the melt is supplied to the 
gates through which the molten metal enters the mould cavity.
• A gating system may include a riser (feed head) - a cavity connected to the 
gating system feeding the casting when it is shrinking.
• Air within the mould cavity and gases formed when a molten metal contacts 
the mould surface are removed through the vents.
• The interior cavities of a casting are formed by separate inserts called cores. 
Cores are usually made of sand and baked.
Pattern Making: First of all, pattern is a replica or facsimile model of desired 
casting which produces a cavity. Molten metal solidifies in this cavity. The process 
of making such cavity by using pattern is known as pattern making.
Pattern materials are:
1. Wood
2. Plastic
3. Plaster of Paris
4. Wax
Core Making: Cores are used to produce the internal features of part such as hole 
or any opening. Cores are placed in the cavity produced by pattern.
Molding: Moulding is the process to prepare a mould for receiving mould metal.
Cores are mold parts used to shape internal holes and cavities. They are also 
fortification parts of molds where wearing occurs. These parts are made of sand 
and organic-inorganic bonders such as cereal meals, dextrin, sodium silicate, 
cement etc. Some properties of cores must have are the followings:
1. High-Temperature Resistivity
2. Metal Erosion Resistivity
3. Easiness of Deformation After Casting
4. Gas Insertion Ability
5. Smooth Surfaces
6. Saving Physical Properties During Storage
Melting and Pouring: Melting is used to melt the metal, so that it can flow inside 
mould cavity. Molten metal is poured in pouring cup. This is known as sprue and 
horizontal portion of this cup and is known as runner. The points through which 
metal enters into cavity are known as gate.
Cooling and Solidification: We know, density of solid is more than liquid. Hence, 
when molten metal solidifies, the size of solid is less in comparison of molten 
metal. This process is known as shrinkage.
Cleaning: When metal is cooled and solidified, we withdraw it. Cleaning is done to 
remove the dust or other particles of moulding sand.
Design of Gating System: Bernoulli's theorem plays an important role in regulating 
the flow of metal in gating system. According to Bernoulli's theorem, 'the total 
energy head remains constant at any system'. It is given by
pg
v
2a
-f h
= constant
where, p = Pressure (in N/m2 or Pa) 
v = Velocity of the liquid (in m/s) 
h = Potential head (in m) 
p = Density of the liquid (in kg/m3 ) 
g = 9.8 m/s2 = Acceleration due to gravity
According to continuity law, 'mass of the metal flowing at any section in the would 
is constant'.
m = P 1 A1 V 1 = p2 A2v2
But density remain constant.
So, Pt = p2 
A1 V 1 = A2 v2 
Q = A -|V -| = A2 v2
Where, Q = Rate of flow of the metal (in m3 /s)
A = Area of cross-section of that section, where metal is flowing (in m2) 
v = Velocity of the metal (in m/s)
Design of Risers: The purpose of riser is to provide liquid metal to compensate 
liquid and shrinkage during phase change. The secondary purpose of riser is to 
show that whether casting is full or not. So, a riser is designed in such a way that it 
stays molten longer than the casting.
The solidification time both for casting and riser given as
t — k
(Chvorinovi rule)
t = Solidification time (in second) 
SA = Surface area (in m2 )
V = Volume (in m3) 
k = Mould constant
• The freezing ratio x of a mould is defined as the ratio of cooling 
characteristics of casting to the riser.
SA
V
SA
V mar
• In order to be able to feed the casting, the riser should solidify last and hence 
its freezing should be greater than unity.
So, we can write it as
SA
>
SA
I V
c a s tin g
V
• Based on the Chvorinovi's rule, Caine developed a relationship empirically for 
the freezing ratio of steel casting. The equation is
0.10
x ---------------- hi
y — 0.03
where,
Riser volume
y = ----------------------
Casting volume 
For aluminium casting,
0.10
x = ------------+ 1.08
y — 0.06
y-x graph
Sphere have a minimum ratio of surface area to the volume. But it is not used as a 
riser for casting because hottest metal being at the center of the sphere and it is 
difficult to use for feeding the casting.
Generally, cylindrically shaped risers are used for casting purpose.
Design of Castings: When designing casting the most important consideration is 
the effect of shrinkage during cooling. Other important factors include metal flow 
and porosity. Some general rules are given in the following: •
• Avoid sharp corners - they can lead to hot tearing during cooling
• Use fillets cautiously - they lead to stresses as they shrink a radius of 1/8" to 
1" are acceptable.
• Avoid large masses - they will cool more slowly, and can lead to pores and 
cavities in the final part. Cores can be used to hollow out these large volumes. 
Metal padding 'chills' can also be placed inside the mold near large masses to 
help increase cooling rates.
• Use uniform cross sections -this will keep the cooling rate relatively uniform 
and avoid stresses.
• Avoid large flats - large flat areas tend to warp.
• Allow some give as the part cools - by allowing the shrinkage of one part to 
deform another slightly, the internal stresses will be reduced. Figures of 1-2% 
shrinkage are common.
• Put parting lines near corners - this will hide the flash.
• Straight Parting Lines - where possible a straight parting line will allow easier 
mold making.
• Use a Draft angle - A small angle of 0.5-2° on the vertical walls will make the 
pattern easier to remove.
• Machining Allowances - allow excess material for later machining of critical 
dimensions
• Wide Tolerances - because shrinkage occurs as the part cools it will be very 
hard to keep tight tolerances.
• Stress Relieve When Needed - Stress relief can reduce the effects of non- 
uniform cooling.
• Avoid thin sections - These will be very hard to fill, and will tend to harden 
quickly.
• Avoid internal features - These will require extra steps in mold making, and 
may create metal flow problems.
Advantages of casting:
• Casting can produce very complex geometry parts with internal cavities parts 
with internal cavities.
• It can be used to make small (few hundred grams) to very large size parts 
(thousands of kilograms)
• It is economical, with very little wastage: the extra metal in each casting is re­
melted and re-used used.
• Cast metal is isotropic. It has the same physical and mechanical properties 
along any direction .