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Transcript of Casting Processes
ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton
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Casting Processes
ver. 1
ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton
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Types of Parts Made
• Engine blocks• Pipes• Jewelry• Fire hydrants
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Casting Steps quick route from raw material to finished
product
• Melt metals• Pour / force liquid into hollow cavity
(mold)• Cool / Solidify• Remove• Finish
ME 4210: Manufacturing Processes and Engineering Prof. J.S. Colton
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Melting
• Raw material (charge)– scrap, alloying materials
• Atmosphere– Air (oxygen), vacuum, inert gas (argon)
• Heating– External - electric, gas, oil– Internal - induction, mix fuel with charge
• steel making in blast furnace -mix coke with iron
• Furnace material – refractory ceramics
Heat
Raw materials
Furnace
Atmosphere
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Furnaces
Blast furnace Basic Oxygen Furnace
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Furnaces
Electric Arc FurnaceOxygen-Fuel,
Oxygen Lance Furnace
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Furnaces
Induction Furnace Electric Furnace
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Breakdown of Castings
• Ingots for bulk deformation processing -85%
• Cast to near net shape - 15%
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Complex, 3-D shapes
• Near net shape• Low scrap• Relatively quick process• Intricate shapes• Large hollow shapes• No limit to size• Reasonable to good surface finish
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Capabilities
• Dimensions– sand casting - as large as you like– small - 1 mm or so
• Tolerances– 0.005 in to 0.1 in
• Surface finish– die casting 8-16 micro-inches (1-3 μm)– sand casting - 500 micro-inches (10-25 μm)
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Processes• Sand• Shell• Plaster• Ceramic• Investment• Lost foam• Pressure• Vacuum
• Die• Centrifugal• Squeeze• Semi-solid• Single crystal• Directional
solidification• Slush• Continuous
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Metals processed by casting
• Sand casting – 60%• Investment casting – 7%• Die casting – 9%• Permanent mold casting – 11%• Centrifugal casting – 7%• Shell mold casting – 6%
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Sand Casting
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Sand Casting
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Sand Casting
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Sand Casting Steps
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Sand Cast Parts
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Permanent Mold Casting
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Low Pressure Casting
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Die Casting (high pressure)
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Die Casting Machine
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Die Casting
Cold chamber
Hot chamber
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Die Casting Part Example
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Continuous Casting
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Investment Casting
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Investment (top) and Conventional Castings
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Lost Foam Casting
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Lost Foam Castings
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Centrifugal Casting
verticalsand-lined moldcasting
horizontal
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Centrifugal Casting
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Pipe CastingProcess
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Squeeze Casting
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Directional Solidification
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Vacuum Casting
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Casting CharacteristicsTable 5.6
Typical Weig ht (kg)Typical surface
Section thickness (mm)
Processmaterials
cast Minimum Maximum
finish (micron,
Ra) Porosity*
Shape complexity
*Dimensional
accuracy* Minimum MaximumSand All 0.05 No limit 5-25 4 1-2 3 3 No limitShell All 0.05 100+ 1-3 4 2-3 2 2 --
Expendable mold pattern All 0.05 No limit 5-20 4 1 2 2 No limit
Plaster mold
Nonferrous (Al, Mg,
Zn, Cu) 0.05 50+ 1-2 3 1-2 2 1 --
Investment
All (High melting
pt.) 0.005 100+ 1-3 3 1 1 1 75Permanent mold All 0.5 300 2-3 2-3 3-4 1 2 50
Die
Nonferrous (Al, Mg,
Zn, Cu) <0.05 50 1-2 1-2 3-4 1 0.5 12Centrifugal All -- 5000+ 2-10 1-2 3-4 3 2 100*Relative rating: 1 best, 5 worst.Note : These ratings are only general; significant variations can occur, depending on the methods used.
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Microstructure
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Microstructure - Dendrites
• Finer structure at walls
• Grains / dendrites grow to center
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Grains on Willie B’s head
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Microstructure - Dendrites
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Fluidity
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Casting Defects - Porosity
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Casting Defects
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Shrinkage
TABLE 5.1
Metal or alloy
Volumetricsolidification
contraction (%) Metal or alloy
Volumetricsolidification
contraction (%)Aluminum 6.6 70%Cu–30%Zn 4.5Al–4.5%Cu 6.3 90%Cu–10%Al 4Al–12%Si 3.8 Gray iron Expansion to 2.5Carbon steel 2.5–3 Magnesium 4.21% carbon steel 4 White iron 4–5.5Copper 4.9 Zinc 6.5Source: After R. A. Flinn.
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Differential Cooling
• Transition between thicker and thinner sections can lead to porosity
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Pipe Defect
• Due to shrinkage giving rise to a funnel-like cavity
• Solutions– insulate top (glass wool)– heat top (exothermic mixture -
thermit)
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Defects - Hot Tears
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Chills
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Design Rules Summary
• Uniform wall thickness• Flat parting lines• Gradual thickness
transitions• Draft for removal
– tapers: 0.5 to 2 degrees• Surface of mold gives
surface of part
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Sand Casting Rules
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Casting costsTABLE 5.10
Cost*
Process Die Equipment LaborProductionrate (Pc/hr)
Sand L L L–M <20Shell-mold L–M M-H L–M <50Plaster L–M M M–H <10Investment M–H L-M H <1000Permanent mold M M L–M <60Die H H L–M <200Centrifugal M H L–M <50* L, low; M, medium; H, high.
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Process economics
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