Analysis of ceramic shell cracking in stereolithography-based rapid casting of turbine blade

Rapid casting (RC) of freeform-surface parts can be realized via replacing wax patterns by stereolithography (SL) patterns to overcome the disadvantage of time-and-cost consuming in traditional investment casting. It has a promising application prospect in single and small batch production. But ceramic shell cracking during the pyrolyzing of SL patterns limits the application and popularization of RC. In this paper, a simplified thermo-mechanical model was first built and the distribution rule of circumferential stress on the contact boundary between SL patterns and ceramic shell was theoretically derived using displacement method to predict dangerous area of freeform-surface parts. Subsequently, the variation rule of circumferential stress at the predicted dangerous area with changing temperature was revealed by applying transient thermo-mechanical finite element analysis (FEA) on a turbine blade cross section. The comparison of theoretical and FEA results indicated that the circumferential stress was enlarged by the freeform shape of turbine blade instead of being relieved due to the softening of resin. Dangerous temperature range was then determined, so polyimide was added to increase strength under corresponding temperature to prevent shell cracking. An experimental validation was offered to verify our point.