Quantitative Phase Contrast Imaging of Microinjection Molded Parts Using Computational Shear Interferometry

Microinjection molding is an effective mass production technology to replicate microcomponents. However, compared with conventional injection molding, microinjection molding requires an adapted processing due to larger surface-area-to-volume ratios, as well as higher shear and cooling rates. Since the functionality of the final parts depends on their defect-free fabrication, a fast, robust, and reliable quality inspection of the final part is mandatory. Here, we demonstrate the applicability of computational shear interferometry (CoSI) for the quality inspection of microinjection molding parts. An analytic model based on the Jones matrix is developed to predict what information of the light field generated behind the inspected part is measured using CoSI technique. A microinjection molding part having spiral shape is inspected indicating areas with manufacturing defects, such as air bubbles, scratches, and internal stresses.