Flow Characteristics of Sheet Molding Compound in Panels with Integrated Ribs

Abstract

A series of experiments was conducted using two different formulations of sheet molding compound (SMC) materials in an instrumented ribbed mold with outside dimensions of 750 x 600 x 410 mm. The experiments showed that the flow of the material into the ribs (side flow) takes place long before the completion of the flow parallel to the flat surfaces of the mold (radial flow). This observation is in contrast to the general belief that the side flow starts after the completion of the radial flow. Also, the analysis of the data from the thermocouples showed that the rib filling takes place through a "bridging and looping" mechanism as well as "concurrent flow." The above findings were verified using short-shot moldings under various conditions. In these short-shot experiments the plaques were solidified at different stages of the flow and, hence, provided informative evidence with regard to the nature of the flow during the compression molding of SMC. The data from the pressure transducers showed that while the radial flow is in progress, the internal pressure in the material increases to a level high enough to cause the side flow into the ribs. It was then concluded that if the pressure in the vicinity of the radial flow front is artificially increased it will promote the "concurrent flow." This type of flow is im portant because our previous studies have shown that it would lead to a reduction in rib readout.