Material Removal Uniformity in Water Dissolution Ultraprecision Continuous Polishing for Large-Size Water-Soluble Crystals

Abstract

Abstract Water dissolution ultraprecision continuous polishing is a nontraditional machining method specifically designed for water-soluble crystals. The aim of this study is primarily to reduce the surface roughness for small sizes from an experimental standpoint. A trajectory uniformity simulation analysis is carried out for a consistent material removal. A material removal model is developed based on the water dissolution principle and kinematic analysis. Numerical simulations of single- and multiple-water-core polishing trajectories are performed to explore the influences of the processing parameters such as movement form, number of water cores, speed ratio, polishing time, and period ratio on the material removal uniformity. The material removal rate is calculated according to the Preston equation. The trajectory density nonuniformity is utilized to evaluate the global uniformity of the trajectory distributions and optimize the processing parameters for a better material removal uniformity. Verification experiments are conducted on a large-size ultraprecision continuous polisher using a typical potassium dihydrogen phosphate (KDP) crystal with a water-soluble structure. The edge collapse is improved from 51.499 μm to 1.477 μm by trajectory uniformity optimization. The changing trends of line profile variations in the validation experiment and simulation are similar. An ultrasmooth surface of a 180 mm × 180 mm KDP crystal with a surface roughness root mean square of 1.718 nm is obtained after water dissolution ultraprecision continuous polishing. This study provides a comprehensive method for evaluation of material removal uniformity, which is valuable for the realization of high-quality machining for water-soluble crystals.

Keywords

• Water-soluble crystals
• Material removal
• Trajectory density nonuniformity
• Surface quality