Three-dimensional thermo-viscoplastic analysis of compression molding of sheet molding compounds with fiber volume fraction prediction

Abstract

SMC (Sheet Molding Compounds) is a thermosetting material which consists of unsaturated polyester resin and other additives reinforced with randomly distributed chopped fiberglass strands. While the incorporation of chopped short fiberglass strands into the thermosetting SMC resin has added strength and stiffness to molded parts, a better understanding of overall effects of SMC resin components, mold geometries and processing variables on flow characteristics and mechanical performance of the molded parts is complicated. Thus, a three-dimensional rigid thermo-viscoplastic finite element program including chemical reaction and fiber volume fraction prediction was developed in the present study and applied to the analysis of compression molding of SMC charge. The rheological characteristics of the SMC charge were modeled by a power law as a function of strain rate and temperature based on compression test data. To investigate the effects of dwelling time, mold closing speed, friction, and mold temperature on mold filling and curing, series of three-dimensional molding simulations of the SMC charge block were carried out using various molding parameters such as mold closing speeds of 45 mm/min and 250 mm/min, mold temperatures of 130 degrees C and 150 degrees C, and constant shear frictional factors of 0.1 and 0.8. The calculated fiber volume fraction distribution for plane strain condition was compared to the experimental result obtained from scanning electron microscope available in the literature. From this study, it was found that the currently developed three-dimensional finite element program coupled with heat transfer and chemical reaction can provide valuable information in understanding flow characteristics, fiber volume fraction distribution, and the curing behavior of SMC compression molding in detail.