Casting Processes

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

Casting Processes

ver. 1

Types of Parts Made

• Engine blocks• Pipes• Jewelry• Fire hydrants

Casting Steps quick route from raw material to finished

product

• Melt metals• Pour / force liquid into hollow cavity

(mold)• Cool / Solidify• Remove• Finish

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

Raw materials

Furnace

Atmosphere

Furnaces

Blast furnace Basic Oxygen Furnace

Furnaces

Electric Arc FurnaceOxygen-Fuel,

Oxygen Lance Furnace

Furnaces

Induction Furnace Electric Furnace

Breakdown of Castings

• Ingots for bulk deformation processing -85%

• Cast to near net shape - 15%

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

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)

Processes• Sand• Shell• Plaster• Ceramic• Investment• Lost foam• Pressure• Vacuum

• Die• Centrifugal• Squeeze• Semi-solid• Single crystal• Directional

solidification• Slush• Continuous

Metals processed by casting

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

Sand Casting

Sand Casting Steps

Sand Cast Parts

Permanent Mold Casting

Low Pressure Casting

Die Casting (high pressure)

Die Casting Machine

Die Casting

Cold chamber

Hot chamber

Die Casting Part Example

Continuous Casting

Investment Casting

Investment (top) and Conventional Castings

Lost Foam Casting

Lost Foam Castings

Centrifugal Casting

verticalsand-lined moldcasting

horizontal

Centrifugal Casting

Pipe CastingProcess

Squeeze Casting

Directional Solidification

Vacuum Casting

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

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.

Microstructure

Microstructure - Dendrites

• Finer structure at walls

• Grains / dendrites grow to center

Grains on Willie B’s head

Microstructure - Dendrites

Fluidity

Casting Defects - Porosity

Casting Defects

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.

Differential Cooling

• Transition between thicker and thinner sections can lead to porosity

Pipe Defect

• Due to shrinkage giving rise to a funnel-like cavity

• Solutions– insulate top (glass wool)– heat top (exothermic mixture -

thermit)

Defects - Hot Tears

Chills

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

Sand Casting Rules

Casting costsTABLE 5.10

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.

Process economics

Casting Processes

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