special casting processes

Squeeze Casting - This interesting process aims to improve product quality by solidifying the casting under a metallostatic pressure head sufficient to (a) prevent the formation of shrinkage defects and (b) retain dissolved gases in solution until freezing is complete. This method was originally developed in Russia and has undergone considerable improvement in the U.S. It is carded out in metal molds resembling, the punch and die sets used in sheet metal forming.

After introducing a carefully metered charge of molten metal, the upper die assembly is lowered into place, forming a fight seal. The "punch" portion of the upper die is then forced into the cavity, displacing the molten metal under pressure until it fills the annular space between the die halves.

Proponents of squeeze casting claim that it produces very low gas entrapment and that castings exhibit shrinkage volumes approximately one half those seen in sand castings. Very high production rates, comparable to die casting but with considerably lower die costs, are also claimed. The process produces the high quality surfaces typical of metal mold casting, with good reproduction of detail. Rapid solidification results in a fine grain size, which in mm improves mechanical properties. It is claimed that squeeze casting can be applied to many of the copper alloys, although die and permanent mold casting alloys should be favored.