cast iron design

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Casting Design

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Design Considerations

Developed over many years Established though practical experience

Analytical methods

Process modeling CAD

Manufacturing techniques

Improving productivity

Cost savings

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Design for expandable-Mold Casting

Corners, angles, and section thickness Flat areas

Shrinkage

Parting line

Draft

Dimensional tolerances Machining allowance

Residual stresses

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Casting design modifications

Fig : Suggested design

modifications to avoid

defects in castings.

Note that sharp corners

are avoided to reduce

stress concentrations.

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Design guideline for expandable-Mold CastingCont

Fig : Examples of designs showing the importance of maintaining uniform cross-sections

in castings to avoid hot spots and shrinkage cavities

(a) avoid sharp corners(b) use fillets to blend section changes smoothly

(c1) avoid rapid changes in cross-section areas

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Design guideline cont.(c1) avoid rapid changes in cross-section areas

(c2) if unavoidable, design mold to ensure- easy metal flow

- uniform, rapid cooling (use chills, fluid-cooled tubes)

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(d) avoid large, flat areas

- warpage due to residual stresses (why?)

Design guideline cont.

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(e) provide drafts and tapers- easy removal, avoid damage

- along what direction should we taper ?

Design guideline cont.

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Avoiding shrinkage cavities

Fig : Examples of design modifications to avoid shrinkage cavities in castings.

(f) account for shrinkage

- geometry

- shrinkage cavities

Design guideline cont.

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(g) proper design of parting line: flattest parting line is best for

reducing of defects

Design guideline cont.

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Chills

Fig : The use of metal

padding (chills) to

increase the rate of

cooling in thick regionsin a casting to avoid

shrinkage cavities.

Design guideline cont.

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Normal Shrinkage Allowance for some Metals Cast in

Sand Molds

Metal Percent

Grey Cast Iron 0.83 1.3

White Cast Iron 2.1

Malleable cast Iron 0.78 1.0Aluminum alloys 1.3

Magnesium alloys 1.3

Yellow Brass 1.3 1.6

Phosphor bronze 1.0 1.6

Aluminum bronze 2.1

High-manganese steel 2.6

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Solidification Contraction of various Cast

Metals

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Casting Design Modifications

Special consideration

Draft angle

Galling

Eamples of casting designmodifications.

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Desirable and Undesirable Die-Casting Practices

Examples of undesirable and

desirable design practicesfor die-cast parts. Note thatsection-thickness uniformityis maintained throughout thepart.

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Nonferrous Casting Alloys

Aluminum-based alloys

Magnesium-based alloys

Copper-based alloys

Zinc-based alloys

High-temperature alloys

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Ferrous Casting Alloys

Cast Irons Gray cast iron

Ductile iron

White cast iron

Malleable iron

Compacted graphite iron

Cast steels

Cast stainless steels

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The Economics of Castings Casting Processes

Some involve more labor than others

Some take a more time than others

Some more time to produce Cost of a product

Materials

Labor

Tooling

Equipment

Cost of casting process

Sand casting little cost

Die-casting

Materials

Machining

Preparation

Melting and pouring of molten metal

Cost for furnaces Related machinery

Cost of finishing the casting

Heat treating

Cleaning

Inspecting

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THE END