Optical injection molded parts are used in many different industries including electronics, consumer, medical and
automotive due to their cost and performance advantages compared to alternative materials such as glass. The injection
molding process, however, induces elastic (residual stress) and viscoelastic (flow orientation stress) deformation into the
molded article which alters the material’s refractive index to be anisotropic in different directions. Being able to predict
and correct optical performance issues associated with birefringence early in the design phase is a huge competitive
advantage. This paper reviews how to apply simulation analysis of the entire molding process to optimize
manufacturability and part performance.
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.
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