Prediction of birefringence in plastic moldings

This article deals with prediction of birefringence and changes in refractive index in polymer optical parts due to the injection molding process using finite element analysis. The simulation includes analysis of mold filling, packing and cooling as well as post-molding deformations (warpage). The geometry of a part and runner systems is represented by a 3D tetrahedral mesh. The material model includes non-linear viscoelasticity in the liquid (molten) and solid (frozen) domains. The simulation predicts the distribution of birefringence and refractive index over the part as well as integral retardance for light coming from an arbitrary direction. Verification experiments for PMMA and COP moldings show reasonable agreement with the numerical results.