Effects of aging on epoxy-based rapid tooling materials

This study shows the effects of aging on epoxy-based rapid tooling materials. Two epoxy-acrylate resins used for stereolithography and one aluminum powder-filled epoxy used for the high-speed machining of plastic injection molds were selected to investigate their aging behavior in different environments. Four different conditions, each characterized by a specific relative humidity, were used to perform a seven week long aging study. Temperature was kept a constant at 30degreesC. Both the stereolithographic resins showed a drop in mechanical properties and in their glass transition temperatures in wet environments, whereas aging time showed little influence on these properties after an initial induction phase. Moisture uptake is mainly responsible for this drop and the coefficients of water diffusion were determined in this process. On the other hand, the aluminum powder-filled epoxy showed little humidity-dependent drop in mechanical properties and in its glass transition temperature during aging. A simple empirical model that only takes into account the moisture uptake was developed.