Advances in polishing of optical freeform surfaces: A review

Ultra-precision polishing is one of the main machining processes for components with high surface finish requirements, such as optical molds. Typical optical mold materials include mold steel, silicon carbide and tungsten carbide, which have many excellent properties like strong corrosion resistance, low thermal expansion coefficient, strong oxidation resistance, low density, and high hardness. To ensure that the replicated parts meet high precision form and finish specifications, the molds made in hard and brittle materials must be machined to obtain a high-quality part surface. Therefore, polishing has evolved into ultra-precision polishing, which has a critical impact on the mold service life as well as the precision optical component quality. This paper presents the basic concepts and classification of ultra-precision polishing, introduces typical polishing processes, discusses polishing mechanisms and characteristics, and finally indicates the directions for future development of ultra-precision polishing processes.