The process begins with production of a one-piece heat-disposable pattern. This pattern is usually made by injecting wax or plastic into a metal die. These dies may range from a simple, hand-operated single cavity tool to a fully automated multi-cavity tool, depending on production quantities and complexity of the part.
A heat-disposable pattern is required for each casting. These disposable patterns have the exact geometry of the required finished part with allowances made to compensate for volumetric shrinkage (a) in the pattern production stage and (b) during the solidification in the ceramic mold.
The pattern carries one or more gates which are usually located at the heaviest casting section. The gate has three functions: to attach patterns to the spruce of runner, forming a cluster; to provide a passage for draining out pattern material as it melts upon heating; to guide molten metal entering the mold by cavity in the casting operation; and to ensure a sound part by feeding the casting during solidification.