19casting - 2.008 Metal Casting Outline Introduction...

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Unformatted text preview: 2.008 Metal Casting Outline Introduction Process Constraints Green Sand Casting Other Processes Some Facts First casting: 5000-3000 BC Bronze, iron age, light metal age? Versatility Many types of metals Rapid production Wide range of shapes and sizes Complex parts as an integral unit Example Sand Casting Example Die Casting Example Investment Casting Casting Process Physics and Constraints Phase Change Density Solubility Diffusion rates High melting temperature Chemical activity High latent heat Handling Analysis of Casting Processes Fluid mechanics for mold filling Heat transfer for solidification Thermodynamics, mass transfer and heat transfer for nucleation and growth Materials behavior for structure-property relationships Mold Filling . 2 2 const g v g P h = + + 4 10 5 Re = vD m/s 5 . 1 2 gh v Bernoullis equation Reynolds number Turbulence Injection Molding : Re ~ 10-4 h Cooling for Sand Mold T T METAL - MOLD INTERFACE MOLD - AIR INTERFACE DISTANCE T T w TEMPERATUR E MOLD AIR SOLID LIQUID Conductivity / Diffusivity Sand Casting sand < metal Die Casting tool metal > polymer Injection Molding tool metal ~ metal Conductivity (W/mK) Cu ~ 400, Al ~ 200 Sand ~ 0.5, PMMA ~ 0.2 Solidification Time : Sand Casting Transient 1-D heat transfer 2 2 x T t T s = t x erf T T T T s M o M 2 = Solution 2 = A V C t s Solidification time Chvorinovs rule Solidification Time : Die Casting Transient 1-D heat transfer ) ( o p T T Ah t T mC = + = mold eject mold sp inject p T T T T T Ah mC t ln Solution 1 = A V C t s Solidification time Comparison: Sand Mold vs Metal Mold Sand Mold Sand casting t s ~ (V/A) 2 Metal Mold Die casting t s ~ (V/A) 1 Microstructure Formation Schematic illustration of three basic types of cast structures (a) Columnar dendritic (b) equiaxed dendritic (c) equiaxed nondendritic Formation of Dendrites Temperature Alloying element Solid Liquid T S T L Solid Solid Liquid Liquid L+S S + L Mushy zone Dendrites Mold wall S o l id u s L iq u id u s Constitutional Supercooling...
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This note was uploaded on 02/23/2012 for the course MECHANICAL 2.008 taught by Professor Jung-hoonchun during the Spring '04 term at MIT.

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19casting - 2.008 Metal Casting Outline Introduction...

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