PLANE-STRAIN COMPRESSION MOLDING ANALYSIS OF SHEET MOLDING COMPOUNDS IN FLAT AND CROSS-SECTIONAL T-SHAPE MOLDS

Sheet molding compounds (SMC) made of unsaturated polyester resin and other additives, reinforced with randomly distributed chopped fibergla ss strands, have emerged recently as a substitute for steel automotive outer body panels because of their low weight, high stiffness, and no n-corrosiveness per unit mass. During the mold filling and curing stag es of the compression molding of SMC, the process is non-isothermal si nce the molding temperature is usually about 150 degrees C. Thus, an u nderstanding of heat transfer and flow characteristics during the fabr ication of SMC under various molding conditions is of importance. In t he present study, an experimental sep-up was designed and used for pla ne-strain molding experiments of class-B and A SMC in flat and cross-s ectional T-shape molds in order to investigate the effect of molding p arameters such as the mold geometry, the thickness of initial charge d imension, three different mold closing speeds of 15, 45, and 50 mm min (-1), and two different molding temperatures of 130 and 150 degrees C on the flow characteristics. Experiments with different colored SMC la yers were used in capturing the flow patterns at various compression s tages. A one-dimensional finite-difference solution in the thickness d irection was obtained and compared to the measure temperature data obt ained from molding experiments at two locations in the SMC charge. For determination of the machine capacity for practical use, approximate solutions were obtained by applying the slab method under various cons tant shear frictional conditions. The calculated pressure distribution s at the center of the top mold, and the load requirements for flat an d cross-sectional T-shape moldings obtained from slab analyses, were c ompared with the measure data. The predicted values of temperature, pr essure, and load were found to compare reasonably well with the measur ed data. The experimental observations obtained from the present inves tigation will be useful for mold design and process control of compres sion molding of SMC in practice.