Experimental Investigation of Subsurface Damages Made by Cup Grinding and Lapping Process of Optical Glass BK7 in Ductile Mode

Conventional material removal of BK7 optical glass will normally result in brittle fracture at the surface, generating severe subsurface damage and poor surface finish. Subsurface damages induced by grinding strongly influence the mechanical strength and optical quality of optical glasses. However, through ductile mode grinding it is possible to reduce the surface and subsurface cracks. It is meaningful to evaluate the depth of subsurface cracking through the measurement of surface roughness under different grinding parameters. In this research, the surface and subsurface damages during micro cup grinding and lapping process of optical glass BK7 are being investigated. In order to invest the subsurface damages, cross section polishing method is being used and the cross sections are inspected through SEM microscope. The results indicate that number of subsurface median cracks after lapping process are strongly decreased and surface lateral cracks are extended all over the sample's ground surface.