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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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