Process to prepare a pattern for metal castings

Abstract

A plastic model pattern indicative of the desired completed pattern having prescribed dimensional tolerances and surface finish characteristics is encased within a Type I material which may be a soluble wax or low melting point material, and subsequently leached from the Type I material to define a cavity corresponding to the dimensional characteristics of the plastic model pattern. A Type II material, such as an insoluble wax or high melting point material, may then be injected into the cavity to recreate the plastic model pattern without the use of any plastics materials, to avoid potentially mold deteriorating expansion of such plastics materials. The mold form of Type I material may then be removed by leaching, melting or the like to reveal the completed expendable pattern usable in a lost wax mold forming process. An injection apparatus and die structure is advantageously utilized in conjunction with the process to achieve high production quality and insure proper formation of the expendable pattern. The process and apparatus allows for the advantageous use of plastic models, while eliminating the deficiencies thereof in a cost effective and novel process.