Casting Processes

ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton

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Casting Processes

ver. 1


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Types of Parts Made

• Engine blocks• Pipes• Jewelry• Fire hydrants


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Casting Steps quick 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 FurnaceOxygen-Fuel,

Oxygen Lance Furnace


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Furnaces

Induction Furnace Electric Furnace


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Breakdown of Castings

• Ingots for bulk deformation processing -85%

• Cast to near net shape - 15%


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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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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 μm)– sand casting - 500 micro-inches (10-25 μm)


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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 casting – 60%• Investment casting – 7%• Die casting – 9%• Permanent mold casting – 11%• Centrifugal casting – 7%• Shell mold casting – 6%


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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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Die Casting Part Example


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Continuous Casting


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Investment 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 moldcasting

horizontal


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Centrifugal Casting


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Pipe CastingProcess


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Squeeze Casting


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Directional Solidification


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Vacuum Casting


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Casting CharacteristicsTable 5.6

Typical Weig ht (kg)Typical surface

Section thickness (mm)

Processmaterials

cast Minimum Maximum

finish (micron,

Ra) Porosity*

Shape complexity

*Dimensional

accuracy* Minimum MaximumSand All 0.05 No limit 5-25 4 1-2 3 3 No limitShell 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

Nonferrous (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 75Permanent mold All 0.5 300 2-3 2-3 3-4 1 2 50

Die

Nonferrous (Al, Mg,

Zn, Cu) <0.05 50 1-2 1-2 3-4 1 0.5 12Centrifugal All -- 5000+ 2-10 1-2 3-4 3 2 100*Relative rating: 1 best, 5 worst.Note : These ratings are only general; significant variations can occur, depending on the methods used.


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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 B’s 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

Volumetricsolidification

contraction (%) Metal or alloy

Volumetricsolidification

contraction (%)Aluminum 6.6 70%Cu–30%Zn 4.5Al–4.5%Cu 6.3 90%Cu–10%Al 4Al–12%Si 3.8 Gray iron Expansion to 2.5Carbon steel 2.5–3 Magnesium 4.21% carbon steel 4 White iron 4–5.5Copper 4.9 Zinc 6.5Source: 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


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Chills


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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 costsTABLE 5.10

Cost*

Process Die Equipment LaborProductionrate (Pc/hr)

Sand L L L–M <20Shell-mold L–M M-H L–M <50Plaster L–M M M–H <10Investment M–H L-M H <1000Permanent mold M M L–M <60Die H H L–M <200Centrifugal M H L–M <50* L, low; M, medium; H, high.


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Process economics


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Documents

Casting Processes