PREDICTING MOLDING FORCES IN SMC COMPRESSION MOLDING

A model relating molding force, compression speed, and part thickness, to material properties, part size, and processing conditions (mold and charge temperature) is necessary, to determine the ranges of closing speed feasible, when molding a predetermined part with a press of given capacity (tonnage). The faster we can close, in principle, the faster reacting systems we can run in a given press. A model has been developed to predict the force required for compression molding of SMC under non-isothermal conditions. The model requires two material rheological parameters, namely, the material resistance to extension eta and a friction coefficient lambda. A method has been developed to measure these coefficients. Preheating the charge is an attractive way of decreasing the molding force required. Also higher molding temperatures would give lower friction and thus lower molding force.