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

An inverse design method has been developed to obtain an optimum mold-wall-temperature history that produces an injection-molded part with minimum residual-stress distribution. Optimization has been formulated within the framework of nonlinear least squares and a modified Gauss-Newton method with a zeroth-order regularization technique. The transient temperature field has been generated based upon a purely viscous formulation of the filling and post-filling stages, and the cooling-induced residual stresses have been calculated employing a thermo-rheologically simple, linear viscoelastic model. The present study shows that, with an optimum cooling history, maximum residual-stress levels can be reduced significantly for both unconstrained and constrained vitrification with holding pressure.