ZNS sub-nano roughness manufacturing process based on tool mark suppression

ZnS crystals are critical infrared optical materials for national defense development. However, their soft-brittle and polycrystalline nature poses significant challenges to achieving sub-nanometer precision machining. To address this issue, a hybrid process combining single-point diamond turning (SPDT) and vibration-assisted magnetorheological finishing (V-MRF) is proposed. SPDT enables rapid shaping but generates periodic tool marks, while V-MRF disturbs the polishing trajectory to eliminate these tool marks, ultimately realizing sub-nanometer precision polishing of ZnS. In this study, process parameters were optimized to suppress tool marks during both the SPDT and MRF stages. Under the optimal parameters, the SPDT-processed surface achieved a roughness of 1.327 nm RMS with a tool mark amplitude of < 2 nm, and V-MRF further improved the surface quality to a roughness of 0.887 nm RMS with a tool mark amplitude of < 0.9 nm. After V-MRF processing, the surface roughness of the turned surface and the amplitude of the tool marks were reduced by 33.15% and 55%, respectively, proving the correctness of this combined process.