Investment casting patterns created using an additive manufacturing or 3D printing process have become very popular and are now used by nearly all industrial investment foundries. The most common cause of failure remains shell cracking in the autoclave as the result of thermal expansion of the pattern. Thin wall castings have been particularly troublesome and have been very difficult for most foundries to process. Foundries often resort to skipping the autoclave step altogether and go right to burnout which introduces other issues.

This study attempted to compare the autoclave performance of thin wall patterns for leading additive manufacturing technologies. Thin wall patterns were created in four different wall thicknesses by three different additive manufacturing technology. The patterns were assembled onto sprues, and the assemblies were then shelled and autoclaved. The shells were then examined for cracks.

In addition, the study attempted to determine the minimum shell thickness required to survive the autoclave cycle. Patterns were created by the same three additive manufacturing technologies and a number of identical assemblies built. The assemblies were all shelled but with decreasing number of layers. All assemblies were autoclaved together and then examined for failure. The results of this investigation will allow foundries to better evaluate the choice of pattern for thin wall applications and to understand how strong their shell must be to survive the autoclave cycle.