Optimum design of process conditions to minimize residual stresses and birefringence in injection-molded parts

In this paper, a theoretical study has been made to reduce the residual stresses and birefringence in the injection-molded parts. An optimization program has been used to minimize the residual stresses and birefringence calculated from a simulation program. The thermally induced stress has been calculated using a linear viscoelasticity model. The flow stress and birefringence has been calculated using the Leonov's viscoelasticity model. This has been applied to the injection molding of a circular disc and a plate. The optimization has been done either by changing process variables while maintaining the mold temperature constant or by varying the mold-wall temperature with time. This study shows that significant reduction in residual stress and birefringence is possible through the optimization of processing conditions.