casting processes
DESCRIPTION
Casting Processes. Tim Goldmann – General Overview Caleb Hanson – Molten Metal Phillip Pinsonneault – Mold Design Rey Jordan – Solidification and Inspection. History of Casting. Complex forms, low cost Certain shapes cannot be machined One piece parts vs. multiple piece parts - PowerPoint PPT PresentationTRANSCRIPT
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Casting ProcessesTim Goldmann – General Overview
Caleb Hanson – Molten MetalPhillip 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
• 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
• 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
• 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, Goodheart-
Wilcox Company, Inc., 1990• Lindbeck, John R., Product Design and Manufacture, Prentice-
Hall, 1995 • Kalpakjian & Schmid, Manufacturing Engineering and
Technology, Prentice-Hall, Fifth Ed.