A Study of Investment Casting with Plastic Patterns

This article presents a study of plastic pattern used in investment casting as expendable material. Numerical analyses of transient heat transfer coupled with structural mechanics were conducted in order to study the thermal stresses inside a ceramic shell under both dewaxing (180 degrees C) and burnout temperatures (1120 degrees C). Moreover, the sensitivity of thermal stresses to the nonlinear thermal and mechanical properties of plastic patterns are reviewed and discussed. It was found that the thermal stress is most sensitive to the glass transition temperature, followed by the coefficient of thermal expansion of plastic patterns. Not only are the results valuable for plastic rapid prototyping (RP) patterns, but they will serve as guidelines for introducing plastic patterns from injection molding to investment casting, due to the wide range of plastics available. Therefore, these results will make the investment casting process more versatile and successful, providing high-temperature metal and metal alloy parts with more precision, more repeatability, lower production costs, and labor in high volume production for small or mini metal parts.