Conformal polishing of Fresnel microstructured surfaces

The success of injection molding is restricted by the poor surface finish of the mold especially the poor finish of the structured edges significantly limits the performance of injection molded parts. To address this challenge, a non-contact polishing method was developed to achieve conformal polishing and experimentally applied to study the finishing of Fresnel microstructured molds. A complementary finite element simulation model involving non-Newtonian fluid was also developed to elucidate the mechanism of shape evolution during the polishing process. The findings revealed built up of stress intensity at sharp corners of the Fresnel microstructured surface due to the dynamic pressure from the polishing fluid which differs in distribution significantly from other areas such as the bottom and sides of the microstructures. This leads to inconsistent material removal from a microstructured surface which needs careful
consideration. Using the proposed polishing method, it has been experimentally shown that the pre-existing defects on the Fresnel microstructured surface can successfully be removed without introducing new damage and a smooth surface with Sa of 1.6 nm and form error of less than 0.6 μm can be obtained.