Effects of pad characteristics on surface quality of soft-brittle crystals in water dissolution continuous polishing

Water dissolution continuous polishing is essential for fabricating large-sized soft-brittle crystals to achieve global planarity and smooth surfaces. The pad, as a core component, directly affects polishing efficiency and quality. In this study, the effects of pad characteristics, including polyurethane, damping, and nonwoven materials on surface quality are extensively examined. Material properties such as surface roughness, asperity distribution, and porosity are studied to achieve high-quality surfaces. Based on the direct contact model between the pad and the workpiece, three pad surface shapes are proposed to optimize pad performance. Through a combination of trajectory uniformity simulation and experimental verification, the influence of the pad surface shape on the workpiece surface quality is systematically analyzed. The results demonstrate that the pad characteristic is a critical determinant of polishing quality. The polyurethane pads with convexity surfaces perform well in water dissolution continuous polishing due to their high hardness and low compressibility. A 200 mm × 200 mm × 10 mm KDP crystal with a surface roughness of 1.694 nm and PV of 0.153 λ is successfully obtained, significantly improving surface control efficiency and accuracy.