Sheet molding compound compression‐molding flow

Abstract

Abstract Most available descriptions of sheet molding compound (SMC) flow are based on a generalized Hele‐Shaw type model. These analyses have several deficiencies. SMC slip at the wall is neglected, and unrealistic rheological models are used. Consequently, molding pressures are incorrectly predicted but, nonetheless, the fill patterns for thin, large area charges typical of exterior automotive body panels are reasonably well predicted as is shown here by comparison with experiment. Recently, a model has been developed that allows for slip at the wall and assumes extensional resistance controls in the interior of the SMC. The model contains the Hele‐Shaw approximation as an extreme case. The predicted molding forces during fill are compared with experiment for some commercial moldings. A dimensionless group to predict when the Hele‐Shaw type models fail in predicting the charge shape is developed and its applicability demonstrated.