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For aluminum castings, sand casting represents about 12% of the total tonnage by weight (surpassed only by die casting at 57%, and semi-permanent and permanent mold at 19%; based on 2006 shipments). The exact process and pattern equipment is always determined by the order quantities and the casting design.
Shrinkage allowance: Depends on shrinkage property of material core and cavity size; Cooling circuit: In order to reduce the cycle time, water circulates through holes drilled in both the core and cavity plates. Ejection gap: The gap between the ejector plate face and core back plate face should hold dimension within the core.
an allowance is a planned deviation from the nominal or theoretical dimension. In other words, it is an intended difference between the maximum material conditions of mating parts. [ 1 ]
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The machining allowance varies drastically from one process to another. Sand castings generally have a rough surface finish, therefore need a greater machining allowance, whereas die casting has a very fine surface finish, which may not need any machining tolerance. Also, the draft may provide enough of a machining allowance to begin with. [28]
Closed shrinkage defects, also known as shrinkage porosity, are defects that form within the casting. Isolated pools of liquid form inside solidified metal, which are called hot spots. The shrinkage defect usually forms at the top of the hot spots. They require a nucleation point, so impurities and dissolved gas can induce closed shrinkage defects.
The tightness of fit is controlled by amount of interference; the allowance (planned difference from nominal size). Formulas exist [2] to compute allowance that will result in various strengths of fit such as loose fit, light interference fit, and interference fit. The value of the allowance depends on which material is being used, how big the ...
Alcoa produces 900,000 metric tons of aluminum in Canada, with a majority going to the US. Aluminum is an important component in auto parts such as suspension and engine castings, as well as in ...