Evaluation of grinding parameters on the surface and sub-surface characteristics of flat optical elements by cup wheel

Abstract

Optical glass BK7 is an amorphous crown glass widely used in the aviation industry and high-power laser equipment due to its mechanical and optical properties. With the hard surface and brittle nature, the grinding process is one of the standard machining methods of BK7. Fracture is a dominant mechanism in removing brittle materials, which causes surface and sub-surface defects in the workpiece. Prediction of the depth of sub-surface damage (SSD) that has occurred allows the optimal reduction or even elimination of sub-surface defects in the finish grinding stage. This research aimed to comprehensively investigate the multifaceted influence of seven pertinent parameters on the depth of sub-surface damage (SSD) and surface roughness (SR) resulting from the grinding process. More specifically, it delved into the effects of the grinding wheel's movement direction under varying contact conditions, including angular grinding, vertical grinding, and face grinding, focusing on three critical aspects: the maximum undeformed chip thickness, depth of sub-surface damage, and resulting surface roughness. The contact conditions between the grinding wheel and the workpiece were systematically classified into four groups based on predetermined input parameters to facilitate in-depth analysis. Subsequently, the resulting outputs were evaluated and compared across these diverse contact conditions. The comparative examination between theoretical equations and experimental findings unveiled a maximum deviation of 10 % in SSD depths and 15.61 % in SR estimations. Furthermore, this study's experimental assessments identified nonlinear and monotonic relationships between the depth of SSD, surface roughness, and the maximum undeformed chip thickness (hm). The experimental relationships and the measured results notably highlighted observed discrepancies of 4.27 %, 10 %, and 10 % for the respective parameters (SSD, surface roughness, and hm).