Method of making precision casting using thixotropic materials

Abstract

Precision castings such as brake calipers and other cast metal parts requiring a fine finish and having complex internal geometries can be produced by casting a shot of a semi-solid thixotropic metal alloy in a die having one or more inserts that have a lower melting point than the solid-to-semi-solid transition temperature of the thixotropic alloy. A core of the same or similar material may also be placed in the die between the inserts. Then, after the shot solidifies to form a casting, the inserts and core (if present) are melted from the casting. The process dramatically reduces or even eliminates machining requirements for cast metal parts because the surfaces of the casting are of extremely low porosity and meet stringent tolerance requirements and because the melt-away inserts and/or core can be formed with protrusions, indentations, and other structures that can be removed by melting but that prevent mechanical removal of the inserts and/or core from the part and that form undercuts, threads, bores, passages, etc. in the part.