OPTIMUM DESIGN OF PROCESS CONDITIONS TO MINIMIZE RESIDUAL-STRESSES ININJECTION-MOLDED PARTS

An Inverse design method has been developed to obtain an optimum mold- wall-temperature history that produces an injection-molded part with m inimum residual-stress distribution. Optimization has been formulated within the framework of nonlinear least squares and a modified Gauss-N ewton method with a zeroth-order regularization technique. The transie nt temperature field has been generated based upon a purely viscous fo rmulation of the filling and post-filling stages, and the cooling-indu ced residual stresses have been calculated employing a thermo-rheologi cally simple, linear viscoelastic model. The present study shows that, with an optimum cooling history, maximum residual-stress levels can b e reduced significantly for both unconstrained and constrained vitrifi cation with holding pressure.