Two methods of mold modification for injection molding specialty plastic parts wereexplored in three projects: First, The effect of an in-mold static mixer on orientation of fiber-reinforced polypropylene (PP) was explored within the injection molding process. Several mold geometries and helical mixer designs were assessed via simulation to identify the mixing ability and the potential effect on fiber orientation. It was found that the static mixers within the runner segment could successfully mix the polymer and randomize the fibers but that the fiber alignment reduction was quickly recovered. Injection molding experiments were carried out to verify these simulations using one geometry case. Fiber orientation at different mold locations were measured using micro-CT (µCT) scans and the degree of fiber orientation was quantified by “goodness of fit” to a normal Gaussian function approach. The experimental fiber orientation results showed good agreement with the simulations. These experiments indicated that the use of a static mixer within the runner system of a mold could be used for mixing the polymer melt after the plasticizing unit of the injection molding machine. However, its effect on changing the overall alignment of the fibers within injection molded parts could be offset by the melt flow downstream of the static mixer, suggesting the importance of mixer location with respect to the part cavity. In a related project, the effect of an in-mold static mixer on optical properties of polystyrene (PS) parts was explored within the injection molding process. Several helical mixer designs were assessed via simulation and molding trials to identify the mixing ability and the potential effect on optical properties including retardation and birefringence. It was found that the static mixers within the runner segment could successfully mix the polymer and disrupt property distributions such as temperature but that there was only slight improvement in retardation with some of the mixer cases. The experiments and simulations showed relatively good correlation in results although there were slight differences in the trends that could be due to the experimental retardation measurement resolution or unaccounted-for variables between the experiments and simulations. The retardation was experimentally measured using a custom-made polariscope using photography and image processing. These experiments indicated that the use of a static mixer within the runner system of a mold could be used for homogenizing the polymer melt after the plasticizing unit of the injection molding machine. However, its effect on improving the optical performance of injection molded parts could be offset by the melt flow downstream of ii the static mixer and potential increase of residual stresses due to flow restriction, suggesting the importance of mixer location and geometry. Last, the use of a sacrificial reservoir as part of an injection mold with optical polycarbonate (PC) materials was explored with simulations. Three different methods of reservoir designs were considered. The first method was using engineering intuition to determine the geometry, the second method used a combination of mass and momentum balance equations to determine the geometry, the third method used the mass balance equation to determine the geometry. Using these three methods eight reservoirs were designed and simulated and compared to two noreservoir cases. 27 runs varying three levels of injection flow rate, V/P switch, and packing pressure were simulated for each of the 10 geometry cases. Considering the quality parameters of flow and thermally induced retardation and the average and standard deviation of volumetric shrinkage the benefit of using a reservoir for manufacturing lens parts was considered. For each of the quality parameters the minimum, best, case occurred with one of the reservoirs. Thus, this study offers a proof of concept that reservoirs could offer a method to improve both the retardation and warpage defects in injection molded optical parts.