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Casting Processes
ver. 2
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Types of Parts Made
Engine blocks
Pipes
Jewelry
Fire hydrants
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Complex, 3-D shapes
Near net shape
Low scrap
Relatively quick process
Intricate shapes
Large hollow shapes
No limit to size Reasonable to good surface finish
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Processes
Sand
Shell
Plaster
Ceramic Investment
Lost foam
Pressure Vacuum
Die Centrifugal
Squeeze
Semi-solid Single crystal
Directional
solidification Slush
Continuous
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Metals processed by casting
Sand casting60%
Investment casting7%
Die casting9%
Permanent mold casting11%
Centrifugal casting7%
Shell mold casting6%
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Breakdown of Castings
Ingots for bulk deformation processing -
85%
Cast to near net shape - 15%
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Ingots
Iron or steel molds
Water-cooled molds
Continuous casting
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Shapes
Expendable Molds
sand
shell slurry
investment
lost wax
lost foam
Permanent mold
(cavity)
die casting hot chamber
cold chamber
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Shapes
Centrifugal
pipes
spinning
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Capabilities
Dimensions
sand casting - as large as you like
small - 1 mm or so
Tolerances
0.005 in to 0.1 in
Surface finish
die casting 8-16 micro-inches (1-3 mm)
sand casting - 500 micro-inches (10-25 mm)
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Casting Stepsquick route from raw material to finished
product
Melt metals
Pour / force liquid into hollow cavity
(mold)
Cool / Solidify
Remove
Finish
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Melting
Raw material (charge)
scrap, alloying materials
Atmosphere
Air (oxygen), vacuum, inert gas (argon)
Heating
External - electric, gas, oil
Internal - induction, mix fuel with charge
steel making in blast furnace -mix coke with iron
Furnace material
refractory ceramics
Heat
Raw materials
Furnace
Atmosphere
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Furnaces
Blast furnace Basic Oxygen Furnace
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Furnaces
Electric Arc Furnace
Oxygen-Fuel,
Oxygen Lance Furnace
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Furnaces
Induction Furnace Electric Furnace
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Sand Casting
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Sand Casting
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Sand Casting
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Sand Casting Steps
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Sand Cast Parts
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Permanent Mold Casting
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Low Pressure Casting
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Die Casting (high pressure)
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Die Casting Machine
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Die Casting
Cold chamber
Hot chamber
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Direct Squeeze Casting
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Die Casting Part Example
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Continuous Casting
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InvestmentCasting
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Vacuum Casting
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Investment (top) and Conventional
Castings
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Lost Foam Casting
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Lost Foam Castings
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Centrifugal Casting
verticalsand-lined mold
casting
horizontal
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Centrifugal Casting
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Pipe CastingProcess
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Directional Solidification
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Casting CharacteristicsTable 5.6
Typical Weig ht (kg)
Typical
surface
Section
thickness (mm)
Process
materials
cast Minimum Maximum
finish
(micron,
Ra) Porosity*
Shape
complexity
*
Dimensional
accuracy* Minimum Maximum
Sand All 0.05 No limit 5-25 4 1-2 3 3 No limit
Shell All 0.05 100+ 1-3 4 2-3 2 2 --
Expendable
mold
pattern All 0.05 No limit 5-20 4 1 2 2 No limit
Plaster
mold
Nonferrou
s (Al, Mg,
Zn, Cu) 0.05 50+ 1-2 3 1-2 2 1 --
Investment
All
(High melting
pt.) 0.005 100+ 1-3 3 1 1 1 75
Permanent
mold All 0.5 300 2-3 2-3 3-4 1 2 50
Die
Nonferrou
s (Al, Mg,Zn, Cu)
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Microstructure
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Microstructure - Dendrites
Finer structure at
walls
Grains / dendrites
grow to center
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Grains on Willie Bs head
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Microstructure - Dendrites
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Fluidity
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Casting Defects - Porosity
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Casting Defects
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Shrinkage
TABLE 5.1
Metal or alloy
Volumetric
solidification
contraction (%) Metal or alloy
Volumetric
solidification
contraction (%)
Aluminum 6.6 70%Cu30%Zn 4.5
Al4.5%Cu 6.3 90%Cu10%Al 4
Al12%Si 3.8 Gray iron Expansion to 2.5
Carbon steel 2.53 Magnesium 4.2
1% carbon steel 4 White iron 45.5
Copper 4.9 Zinc 6.5
Source: After R. A. Flinn.
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Differential Cooling
Transition between thicker and thinner
sections can lead to porosity
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Pipe Defect
Due to shrinkage giving rise to
a funnel-like cavity
Solutions insulate top (glass wool)
heat top (exothermic mixture -
thermit)
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Defects - Hot Tears
Chills
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Chills
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Car Rims
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Stamped Cast
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Casting Defects - Porosity
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Design Rules Summary
Uniform wall thickness Flat parting lines
Gradual thickness
transitions
Draft for removal
tapers: 0.5 to 2 degrees
Surface of mold gives
surface of part
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Sand Casting Rules
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Casting costs
TABLE 5.10Cost*
Process Die Equipment Labor Productionrate (Pc/hr)
Sand L L LM
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Process economics
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