The disposable pattern is usually made by injecting wax into a metal (usually aluminum) die that was previously machined and having a negative impression of the part you wish to produce. 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.
These disposable wax patterns have the geometry replicating 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 is typically designed to have one or more gates which are usually located at the heaviest casting section.
The gate has several 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
- to ensure a sound part by feeding the casting during solidification.