Practical guidelines for predicting steady state cure time during sheet molding compound (SMC) compression molding

Abstract The longest part of the molding cycle during SMC compression molding is the curing stage. Thus it is extremely important to be able to predict its duration to estimate the cost of manufacturing a new part. During an SMC molding cycle, the mold surface temperature drops suddenly when it contacts the cold charge. The surface temperature then gradually recovers as heat is conducted from the interior of the mold and the resin releases heat during curing. In general, this exchange of heat remains locally unbalanced, causing a gradual decrease in the local surface temperature. To avoid blistering, the cure time must be increased with consecutive moldings until a steady state value is achieved (t_css). In this paper, we present a series of charts that can be used to estimate the steady state cure time for new parts. These values can then be used to estimate the manufacturing cost.