Improvements in investment casting with stereolithography patterns

Abstract

The use of investment casting to gain functional metal parts from stereolithography (SL) models is well documented. However, despite the thousands of metal castings produced, the original stereolithography build structures that were designed for investment casting have only been partly successful in combating the effects of the thermal expansion SL resins. Investment casting foundries still have to alter their existing techniques and, significantly, are dewaxing shells containing SL models in the flash furnace rather than the steam autoclave. This paper describes how a greater understanding has been established of why SL investment casting patterns are causing the shells to crack. Theoretical and practical stress analysis, utilizing finite element analysis and strain gauge techniques, has given a much clearer picture of the failure modes of the ceramic shells and SL models. This has led to a set of criteria for the design of build structures that allows the successful autoclaving and subsequent casting of stereolithography models. Details of the background research, stress analysis and design criteria are presented along with a new design of internal build structure that allows the successful autoclaving and casting of stereolithography models.