Casting Processes
Tim Goldmann – General Overview
Caleb Hanson – Molten Metal
Phillip Pinsonneault – Mold Design
Rey Jordan – Solidification and Inspection
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History of Casting
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Advantages
• Complex forms, low cost
• Certain shapes cannot be
machined
• One piece parts vs. multiple
piece parts
• Design changes are easily
incorporated
• High volume, low skilled labor
• Large, heavy parts can be made
easily
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Disadvantages
• Problems with internal
porosity
• Dimensional variations due
to shrinkage
• Trapped impurities, solids
and gasses
• High-tolerance, smooth
surfaces not possible
• More costly than stamping
or extruding in some cases
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Expendable Molds
• Green Sand
• Dry Sand
• Shell
• Investment
• Plaster
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Expendable Molds
• Pattern must be produced
• New mold for every cycle
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Permanent Molds
• Die
• Centrifugal
• Pressure
• Injection
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Permanent Molds
• Made of durable material
• Multiple use
• Built-in Alignment
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Cupola Furnaces
Five Zones
• Stack
• Charging Zone
• Melting Zone
• Tuyers (Air Intake)
• Crucible or Hearth
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Induction Furnaces
• Magnetic field
• Rapid melting rate
• Low pollution
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Foundries
• Pattern and Mold Making
– Computer Aided
Design
– Manufacturing
– Rapid Prototyping
• The Casting Process
– Metal Melting
– Metal Compositions
– Impurities
– Pouring into molds
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Foundries
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Foundry Automation
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Pouring into Molds
Cleaning
Heat Treatment
Inspection
Automated Guided
Vehicles
– Automatic Storage
– Moving Cores and
patterns
– Etc.
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Reasons For Automation
• Increased Manufacturing
Efficiency
• Reducing Costs
• Reliability in Harsh
Environments
• Release of Skilled Man
Power
• Maximize Space
• Improved Quality
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Why Fluid Flow?
• When Heated Metal
Becomes Liquid
• Important in Cast Design
- Sprue
- Well
- Runner
- Gate
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Fluidity of Metals
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Viscosity
Surface Tension
Inclusions
Mold Design
Degree of Super Heat
Mold Material
- Thermal Conductivity
- Surface Roughness
• Heat Transfer
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Tests for Fluidity
• There are several
different fluidity tests
• All use the same principle
• Useful in simulating how
metal will react
• See how far the metal will
travel before solidification
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Heat Transfer
• Heat transfer is important
in many aspects of
casting
- Pouring
- Solidification
- Cooling rate
- Rate is a function
of Volume and
surface area
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Design, Materials and Economics
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Design Considerations in Casting
• Design of the part
• Casting process and
material
• Locate parting line
• Locate design gates
• Locate mold features
such as sprue, screens
and risers
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Design Consideration of Cast
Parts
Corners, angles,
section thickness
– Avoid sharp corners
angles and fillets
– Stress raisers,
cracking, and tearing
– Sections should be
blended smoothly
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Design Consideration of Cast Parts
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Design Consideration of Cast Parts
• Flat Areas
– Large flat areas may
warp during cooling
– Poor surface finish from
uneven flow in pouring
– Resolve with ribs, and
serrations
• Circles and Rounds
– Lower cooling rate in
circles induces hot spots
– Shrinkage cavities and
porosity
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Design Consideration of Cast Parts
• Shrinkage
– to avoid cracking during
the cooling process
there should be
shrinkage allowance
– Staggered ribs, change
the intersection
geometry
• Patternmaker’s Shrinkage
Allowance
– 10-20 mm/m
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Design Consideration of Cast Parts
• Draft
– Used to enable easy
removal of pattern
without damage to mold
– Range from 5 to
15mm/m
– Angles of 0.5° to 2°
• Dimensional Tolerances
– As wide as possible
within limits of good
performance
– Letters and markings
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Locating the Part Line
• Part line
– separates upper and
lower mold
– Flat plane, along
corners or edges
– This will avoid flash
at the parting lines
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Locating and Designing Gates
• Gates
– Connections between
runners and the part
– Multiple gates preferred
– Feed into thick sections
of the castings
• Runners
– Distribution channel for
molten metal from the
sprue into the gates
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Casting Alloys
• Nonferrous Alloys
– Aluminum, magnesium,
copper, zinc, tin, lead
– Good electrical
conductivity and
resistant to corrosion
– Most of these alloys
share characteristics of
good machinability and
can all be welded
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Casting Alloys
• Ferrous alloys
– Cast irons
• Largest quantity of all
metals cast
• Good wear
resistance, hardness
and machinability
– Cast Steels
• Material used under
extreme heat
conditions
• Railroad, mining and
construction
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Casting Economics
• Cost
– Depends on materials,
equipment, and labor
– Preparations require raw
materials, time and effort
– Melting, pouring, heating,
cleaning, inspections
– Equipment cost lowers
with large # of castings
– Solutions to alleviate
unneeded cost are being
looked into
• Rapid prototyping
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Molten Metal Pour
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Solidification
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Solidification Temperatures
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Dimensional Change
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Pinholes
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Blowhole
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Scab
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Pinholes
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Rough Surface
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References
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ABB, Automation Solutions, 2005, 10/01/2005, www.abb.com
Brown Jerry, Primary Metals, 10/01/2005, www.p2pays.org
ECO BRASS workability, 10/01/2005, www.ecobrass.com
2.008 Casting, 10/01/2005, www.ocw.mit.edu
Wright, Thomas, Processes of Manufacturing, GoodheartWilcox Company, Inc., 1990
• Lindbeck, John R., Product Design and Manufacture, PrenticeHall, 1995
• Kalpakjian & Schmid, Manufacturing Engineering and
Technology, Prentice-Hall, Fifth Ed.
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