Casting

From DDL Wiki

When manufacturing shapes that are too complex or costly to simply cut, a casting process can be used. Casting is the process whereby a solid is obtained from a molten material, such as metal or plastic, poured into a mold.

Castings will often shrink when they cool due to solidification and temperature differences. Different materials have different shrinkage rates. Shrinkage can sometimes cause problems because it weakens the cast by leaving cavities. One way of dealing with this problem is to oversize the pattern by 1-6%. Another solution is to include risers, often called feeders, are included in the cast. Risers pump additional material into the cast as it solidifies.