Transcript
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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
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