Improvements in the Simulation of Orientation in Injection Molding of Short Fiber Thermoplastic Composites

The mechanical properties of injection molded short-fiber reinforced thermoplastic composite parts are highly dependent on the orientation distribution of the fibers. A simulation tool capable of predicting fiber orientation accurately as a function of mold design and processing conditions is required as the predicted fiber orientation capabilities in commercial software show large discrepancies when compared with experimentally measured orientation. In this work a two dimensional coupled Hele-Shaw approximation for predicting the flow-induced orientation of glass fibers in injection molded composite parts is presented. In addition to coupling the stresses to fiber orientation for a highly concentrated short glass fiber PBT suspension, the model considers the slowdown of the evolution of orientation due to fiber interaction. Material parameters in the model are determined from basic rheometry rather than using data from injection molding experiments. The equation of motion coupled with stress equations are discretized using the discontinuous Galerkin Finite Element Method. Flow simulations are performed using a measured orientation profile at the gate instead of random orientation assumed in previous studies. Finally, the evolution of fiber orientation in the cavity is determined experimentally using a modified version of the method of ellipses and results are compared against the predicted values of orientation. The fiber orientation predicted in the entry region and the core layer structure at the end of fill region are now in closer agreement with the experimental values, but there are still some discrepancies.