ESTIMATION OF SINK MARK DEPTH IN COMPRESSION MOLDED SMC PARTS WITH SUBSTRUCTURES

Sink mark, a surface defect along the centerline over a substructure i s observed when compression molding of SMC (Sheet Molding Compounds) a pplies in fabrication of a thin plate with substructures. The magnitud e of sink mark formed depends on process parameters used in manufactur ing process. The surface quality of the external panels in automotive industry is so critical that this kind of defect should be eliminated during manufacturing stages. Thus, the effect of process parameters on sink mark depth formed in the compression molded thin plate with subs tructures was experimentally investigated in the present study. In ord er to estimate the effect of the process parameters such as molding te mperature, mold closing speed, depth of the rib, corner radius of the rib, and final molded part thickness of flat portion on the magnitude of sink mark depth under the given experimental conditions, the non-di mensionalized molding parameters were determined based on physical rel evances among various parameters. Then, the non-dimensionalized depth of sink mark was determined through dimensional analysis based on the experimental data. It was further tested by comparing the estimated va lues of sink mark depth with the experimental data. According to this comparison, reasonably accurate prediction was obtained. Compared to t he previous study in the literature, the sink mark depths were quantit atively determined according to the various processing parameters and the non-dimensional equation to predict the sink mark level was derive d in the present investigation. In addition, the orientation and distr ibution of fiberglass which directly affect the formation and magnitud e of the depth of sink mark were investigated by taking the photograph s of the cross-sectional area of the compression molded specimen by SE M (Scanning Electron Microscope). The non-dimensionalized equation for prediction of sink mark depth proposed in the present investigation w ill be useful in estimating the magnitude of sink mark depth in compre ssion molded SMC plates with substructures and the experimental observ ations were useful in understanding the formation of sink mark during compression molding.