Grinding of single crystal sapphire: workpiece roughness correlations

Abstract

Experiments were performed on single crystal sapphire with a selection of bound abrasive cup tools to produce fine ground surfaces with rms roughness on the order of 1 μm. Both workpiece roughness and the ease of material removal (as quantified by Preston's coefficient or the specific grinding energy) were found to decrease with decreasing chip thickness. However, great variability was observed even for a fixed chip thickness as a result of differences in tool performance. A strong correlation was also found between Preston's coefficient and the workpiece roughness. Data for all tool bond types (resin, metal, and vitrified), abrasive sizes (2–80 μm diamond), surface conditions (as-dressed and glazed), and tool geometries fell on the same curve. This behavior has important practical effects during infeed controlled grinding. Only above a certain ‘critical roughness’, which depended on the workpiece size, was grinding able to remove the programmed infeed depth.