Reaction injection molding : analyzing the filling stage of a complex product with a highly viscous thermoset Reaction Injection Molding: Analyzing the Filling Stage of a Complex Product With a Highly Viscous Thermoset*

Although numerical simulation has proved to be a useful tool to predict the filling behavior of injection molding products, few applications in reaction injection molding (RIM) have been reported. This is mainly due to the lack of appropriate descriptions of the material behavior, and to the lack of accurate material data. The analysis of the filling stage of the RIM process requires the determination of the cure kinetics and the rheological, PUT, and thermal behavior of the material, which in this study is a highly filled copolymer of ethylene and vinyl-acetate (EVA). Since this copolymer yields some viscosity anomalies, due to the amount of filler, the rheology of a similar EVA compound with low filler content was also investigated. The viscosity of this compound can be described by a Carreau model at low conversions levels (< 1 %I, whereas a conversion-dependent Power-Law model proves appropriate for higher conversion. Moreover, the viscosity behavior of both compositions is similar in the processing range. The combined Carreau/ Power Law viscosity model is used for the numerical simulations of a complex product. The simulation results agree well with experimental molding results. The analysis shows that a combination of material characterization and modeling, numerical simulation, and experimental verification is necessary to make simulation programs a useful design tool for RIM products and molds