The present invention relates to casting processes for the manufacture of metal and alloy structures, and more particularly, to systems, methods and materials associated with fugitive patterns used for casting operations.
Investment casting, which is also commonly known as the lost wax process, is one of the oldest known techniques utilized for forming metal. In practice, a wax substance is patterned, such as by injecting melted wax into a die. When the wax cools, it solidifies in a pattern that corresponds to the component to be cast in metal. The molded wax pattern then is invested in a ceramic shell mold, such as by repeatedly dipping the wax pattern in a ceramic slurry until a desired thickness of ceramic material is built-up on the wax pattern. The shell mold is initially heated to remove the molded wax pattern and is then fired at an elevated temperature to develop appropriate mold strength for casting a molten metal or alloy.
There are several major limitations and potential problems with using wax to manufacture investment castings, especially when it comes to certain components, such as highly complex castings, large castings and/or castings with relatively thin cross-sections. For example, the dimensional accuracy of a part manufactured using a conventional investment casting process is limited due to the inherent distortion of the pattern that occurs in the processing of wax. Moreover, wax must be handled at room temperature or lower to prevent undesired wax characteristics and/or defects, such as shape distortion, fingerprints, creep, etc. Still further, conventional wax costs are relatively high due to the requirement of initial melt cycle(s) necessary to melt the wax prior to injecting the wax into a corresponding die. Cost is further increased due to the relatively high scrap rates, which typically result due to metal leakage from shell mold cracks caused by wax expansion. Cost is also increased due to defects that lead to inclusions in the molten metal caused by ash content from wax reacting with the shell material.