Casting Processes ver. 2 1
Types of Parts Made Engine blocks Pipes Jewelry Fire hydrants 2
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 3
Processes Sand Shell Plaster Ceramic Investment Lost foam Pressure Vacuum Die Centrifugal Squeeze Semi-solid Single crystal Directional solidification Slush Continuous 4
Metals processed by casting Sand casting 60% Investment casting 7% Die casting 9% Permanent mold casting 11% Centrifugal casting 7% Shell mold casting 6% 5
Breakdown of Castings Ingots for bulk deformation processing - 85% Cast to near net shape - 15% 6
Ingots Iron or steel molds Water-cooled molds Continuous casting 7
Shapes Permanent mold (cavity) die casting hot chamber cold chamber Expendable Molds sand shell slurry investment lost wax lost foam 8
Shapes Centrifugal pipes spinning 9
Dimensions Capabilities 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 mm) sand casting - 500 micro-inches (10-25 mm) 10
Casting Steps quick route from raw material to finished product Melt metals Pour / force liquid into hollow cavity (mold) Cool / Solidify Remove Finish 11
Melting Heat Furnace Atmosphere Raw material (charge) scrap, alloying materials Atmosphere Raw materials 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 12
Furnaces Blast furnace Basic Oxygen Furnace 13
Furnaces Electric Arc Furnace Oxygen-Fuel, Oxygen Lance Furnace 14
Furnaces Induction Furnace Electric Furnace 15
Sand Casting 16
Sand Casting 17
Sand Casting 18
Sand Casting Steps 19
20
Sand Cast Parts 21
Permanent Mold Casting 22
Low Pressure Casting 23
Die Casting (high pressure) 24
Die Casting Machine 25
Die Casting Cold chamber Hot chamber 26
Direct Squeeze Casting 27
Die Casting Part Example 28
Continuous Casting 29
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Investment Casting 33
Vacuum Casting 34
Investment (top) and Conventional Castings 35
Lost Foam Casting 36
Lost Foam Castings 37
Centrifugal Casting horizontal sand-lined mold casting vertical 38
Centrifugal Casting 39
Pipe Casting Process 40
Directional Solidification 41
Casting Characteristics Table 5.6 Process Typical Weig ht (kg) materials cast Minimum Maximum Typical surface finish (micron, Ra) Porosity* Shape complexity * Section thickness (mm) Dimensional accuracy* Minimum Maximum Sand All 0.05 No limit 5-25 4 1-2 3 3 No limit Shell 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 Nonferrou Plaster s (Al, Mg, mold 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 75 Permanent mold All 0.5 300 2-3 2-3 3-4 1 2 50 Nonferrou s (Al, Mg, Die Zn, Cu) <0.05 50 1-2 1-2 3-4 1 0.5 12 Centrifugal 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 use d. 42
Microstructure 43
Microstructure - Dendrites Finer structure at walls Grains / dendrites grow to center 44
Grains on Willie B s head 45
Microstructure - Dendrites 46
Fluidity 47
Casting Defects - Porosity 48
Casting Defects 49
Shrinkage TABLE 5.1 Volumetric solidification contraction (%) Volumetric solidification contraction (%) Metal or alloy Metal or alloy Aluminum 6.6 70%Cu 30%Zn 4.5 Al 4.5%Cu 6.3 90%Cu 10%Al 4 Al 12%Si 3.8 Gray iron Expansion to 2.5 Carbon steel 2.5 3 Magnesium 4.2 1% carbon steel 4 White iron 4 5.5 Copper 4.9 Zinc 6.5 Source: After R. A. Flinn. 50
Differential Cooling Transition between thicker and thinner sections can lead to porosity 51
Pipe Defect Due to shrinkage giving rise to a funnel-like cavity Solutions insulate top (glass wool) heat top (exothermic mixture - thermit) 52
Defects - Hot Tears 53
Chills 54
Car Rims Stamped Cast 55
Casting Defects - Porosity 56
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 57
Sand Casting Rules 58
Casting costs TABLE 5.10 Cost* Process Die Equipment Labor Production rate (Pc/hr) Sand L L L M <20 Shell-mold L M M-H L M <50 Plaster L M M M H <10 Investment M H L-M H <1000 Permanent mold M M L M <60 Die H H L M <200 Centrifugal M H L M <50 * L, low; M, medium; H, high. 59
Process economics 60
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