Metal Casting II
Manufacturing
Processes
Outline
Sand Casting
Shell Mold Casting
Composite Molds
Expendable Pattern Casting
Plaster Mold Casting
Ceramic Mold Casting
Investment Casting
Pressure Casting
Vacuum Casting
Die Casting
Centrifugal Casting
Squeeze Casting and Semisolid Metal
Forming
Casting Single Crystals
Rapid Solidification
Melting
Design Considerations
Examples of Cast Parts
Examples of Cast Parts
Typical Casting Metals
Aluminum
Aluminum-silicon alloy
Aluminum-copper
Brass
Gray cast iron
Copper
Lead
Steel
Casting Processes
Sand Casting
Uses a mold made of compressed
sand; after the metal solidifies, the
sand is broken away
Sand Casting
Pattern
Full sized model of the part
Core
Full sized model of the interior
surfaces of the part
Sand Silica (SiO2)
90% sand
3% water
7% clay
Sand Casting
Sand Casting
Example of a Sand
Casting Mold
Sand Casting
Advantages:
Almost no limit on size, shape,
weight or complexity; low cost;
almost any metal
Limitations:
Relatively poor tolerances and
surface finish; machining often
required; low production rate
Common metals:
Cast irons, steel, stainless steel,
casting alloys of aluminum and
copper, magnesium and nickel
Sand Casting
Size limits:
1 oz – 6000 lb
Thickness limits:
As thin as 3/32 in, no maximum
Tolerances:
1/32 in for the first 6 in, .003 in for each
additional inch; additional increment
across the parting line
Draft allowance:
1 - 3°
Surface finish:
100 -1000 µin
Shell Casting
Casting process in which the mold is
a thin shell (typically 3/8 inch) made
of sand held together by a
thermosetting binder
Shell Casting
Shell Casting
Advantages:
Higher production rate than sand
casting; high dimensional accuracy
and smooth finish
Limitations:
Requires expensive metal patterns;
resin adds to cost; part size is
limited
Common metals:
Cast irons, casting alloys of
aluminum and copper
Shell Casting
Size limits:
1 oz minimum; usually less than 25 lb;
mold area usually less than 500 in2
Thickness limits:
1/16 – ¼ in depending on material
Tolerances:
.005 in/in
Draft allowance:
¼ - ½°
Surface finish:
50 – 150 µin
Composite Molds
Made from 2 or more different
materials
Good for complex shapes such as
turbine blades
Expendable Pattern
Casting
Polystyrene pattern vaporizes on
contact with molten metal
Foam Pattern of an
Engine Block
Plaster Mold Casting
Uses a mold made of plaster
(gypsum) with talc and silica,
which is broken away after the
metal solidifies
The mold has a relatively low
thermal conductivity; a
somewhat uniform grain
structure can be produced
Plaster Mold Casting
Advantages:
High dimensional accuracy and
smooth finish; can make net- or
near-net-shaped parts
Limitations:
Lower temperature nonferrous
metals only; long molding time;
mold material is not reusable;
maximum size limited
Common metals:
Primarily aluminum and copper
Plaster Mold Casting
Size limits:
1 oz – 15 lb
Thickness limits:
As thin as .025 in
Tolerances:
.005 in on the first 2 in; .002 in per
additional inch
Draft allowance:
½ - 1°
Surface finish:
50-125 µin
Ceramic Mold Casting
Uses a mold made of refractory
ceramic materials which can be
used for high-temperature
applications
Ceramic Mold Casting
Ceramic Mold Casting
Advantages:
Intricate detail, close tolerances,
smooth finish
Limitations:
Mold material is expensive and not
reusable
Common metals:
Ferrous and high-temperature
nonferrous metals are most
common; can be used with alloys of
aluminum, copper, magnesium,
titanium and zinc
Ceramic Mold Casting
Size limits:
Several ounces to several tons
Thickness limits:
As thin as .05 in, no maximum
Tolerances:
.005 in on the first inch; .003 in per
additional inch
Draft allowance:
1°
Surface finish:
75-150 µin
Investment Casting
Uses a wax pattern which is
coated with refractory materials
to form a mold; the wax is then
melted out and the mold cavity
is filled with metal
Can be used for high precision
complex shapes from high
melting point metals that are
not readily machinable
Investment Casting
Example of a Wax
Injection Mold
Example of a Wax
Pattern
Example of a Coated
Pattern
Example of Finished
Castings
Investment Casting
Advantages:
Excellent surface finish; high
dimensional accuracy; nearly
unlimited intricacy; almost any
metal; no flash or parting line
Limitations:
Expensive patterns and molds; high
labor costs; limited size
Common metals:
Mainly aluminum, copper and steel;
also used with stainless steel,
nickel, magnesium and precious
metals
Investment Casting
Size limits:
As small as 1/10 oz; usually less than 10
lb
Thickness limits:
As thin as .025 in, less than 3 in
Tolerances:
.005 in on the first inch; .002 in per
additional inch
Draft allowance:
none required
Surface finish:
50-125 µin
Pressure Casting
Pressure casting forces the metal up
into the mold chamber by applying
a small amount of pressure
Vacuum Casting
Permanent Mold Casting
(Pressure/Vacuum)
Advantages:
Good surface finish and dimensional
accuracy; metal mold causes rapid
cooling and fine grain structure; molds
can be used up to 25 000 times
Limitations:
High initial mold cost; shape, size and
complexity are limited; mold life is very
limited with metals with high melting
points
Common metals:
Alloys of aluminum, magnesium and
copper most common; iron and steel can
be used in graphite molds; alloys of lead,
tin and zinc also used
Permanent Mold Casting
(Pressure/Vacuum)
Size limits:
Several ounces to about 150 lb
Thickness limits:
Minimum depends on material but generally
thicker than 1/8 in; maximum about 2 in
Tolerances:
.015 in for the first inch and .002 in for each
additional inch; .01 in added across the
parting line
Draft allowance:
2 - 3°
Surface finish:
100 - 250 µin
Die Casting
Another form of permanent mold
casting; molten metal is forced
into the mold cavity at
pressures ranging from .7 MPa
- 700 MPa
Die Casting
Die Casting
Example of a Die
Casting Mold
Centrifugal Casting
Uses a rotating mold to form hollow
cylindrical parts such as pipes, gun
barrels and lamp posts
Vertical Centrifugal
Casting
Centrifugal Casting
Advantages:
Can produce a wide range of
cylindrical parts; good dimensional
accuracy and cleanliness
Limitations:
Limited shape; spinning equipment
may be expensive
Common metals:
Iron, steel, stainless steel, alloys of
aluminum, copper and nickel
Centrifugal Casting
Size limits:
Up to 10 ft in diameter and 50 ft in length
Thickness limits:
Wall thickness .1 – 5 in
Tolerances:
Outer diameter within .1 in; inner
diameter within about .15 in
Draft allowance:
1/8 in / ft
Surface finish:
40 - 100 µin
Semicentrifugal Casting
Uses a rotating mold to form parts
with radial symmetry, such as
wheels with spokes
Squeeze Casting
A combination of casting and forging;
a die applies pressure as the metal
solidifies
Casting Single Crystals
Uses a slow crystal-growth
solidification procedure to
produce parts made of a single
crystal with no grain
boundaries
A helical constriction only allows
one crystal of favorable
orientation to grow into and fill
the mold chamber
Casting Single Crystals
Rapid Solidification
Cools metal rapidly at rates as high
as 106 K/s so that it cannot
crystallize and instead forms an
amorphous glasslike structure
Melting Furnaces
Cupola
Crucible Furnace
Induction Furnace
Melting Furnaces
Cupola
A vertical cylindrical furnace used
for melting cast iron
Melting Furnaces
Crucible furnace
Melts metal without direct contact
with a burning fuel mixture
Melting Furnaces
Induction furnace
Uses an alternating magnetic field
to heat the metal
Design Considerations
Design Considerations
Design Considerations
Design Considerations
Casting Alloys
Summary
A variety of casting processes
are available for different
applications
Design considerations must be
taken to prevent casting
defects