1. Fundamentals of Casting
Casting, one of the oldest manufacturing processes, dates
back to 4000 B.C. when copper arrowheads were made.
Casting processes basically involve the introduction of a
molten metal into a mold cavity, where upon solidification,
the metal takes on the shape of the mold cavity.
Simple and complicated shapes can be made from any
metal that can be melted.
Example of cast parts: frames, structural parts, machine
components, engine blocks, valves, pipes, statues,
ornamental artifacts…..
Casting sizes range form few mm (teeth of a zipper) to
10 m (propellers of ocean liners).
Ken Youssefi
Mechanical Engineering Dept., SJSU
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2. Casting Processes
• Preparing a mold cavity of the desired shape with
proper allowance for shrinkage.
• Melting the metal with acceptable quality and
temp.
• Pouring the metal into the cavity and providing
means for the escape of air or gases.
• Solidification process, must be properly designed
and controlled to avoid defects.
• Mold removal.
• Finishing, cleaning and inspection operations.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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5. Solidification Time
Solidification time = C(volume/surface area)2
Where C is a constant that depends on mold
material and thickness, metal characteristics and
temperature.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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7. Casting Defects
Hot tearing – hot tearing, cracking, occurs if casting is
restrained from shrinking, during solidification.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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8. Casting Defects
These defects can be
eliminated by proper mold
preparation, casting design
and pouring process.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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9. Casting Defects
Hot spots – thick sections cool slower than other sections
causing abnormal shrinkage. Defects such as voids, cracks
and porosity are created.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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10. Casting Defects and Design Consideration
Ken Youssefi
Mechanical Engineering Dept., SJSU
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12. Die Casting
Hot chamber, low-melting
alloys; tin, zinc, lead.
Cold chamber, high-melting
alloys; aluminum, copper.
Higher pressure needed
High production rates, good strength, good dimensional
accuracy and surface finish, and good quality parts.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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14. Squeeze Casting
Cast parts have good mechanical properties, good dimensional
accuracy, fine microstructure, good surface finish.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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15. Precision Casting
Plaster Molding
Plaster of Paris (gypsum) is used as the mold material, other
components are added to improve the strength and reduce the
setting time. The pattern is dried at 400 oF and the two halves
are assembled and molten metal is poured into the cavity.
The process produces fine detail with good dimensional
accuracy and surface finish. Used to cast aluminum, zinc and
copper-based alloys (low-melting temp.)
Ceramic Molding
Similar to plaster molding, except it uses ceramic as a mold
which is suitable for high temp. applications. Mixture of
zircon (ZrSiO4), aluminum oxide (Al2O3), silica (SiO2) and
other bounding agents.
Ken Youssefi
Mechanical Engineering Dept., SJSU
15
18. Design Considerations
• Wall thickness should be kept uniform if possible.
Non uniform wall thickness could lead to warpage
and dimensional variations.
Minimum recommended; .025 in or .65 mm, up
to .125 for large parts.
• Round interior and exterior corners to .01-.015 in
radius (min.), prevents an edge from chipping.
Ken Youssefi
Mechanical Engineering Dept., SJSU
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