Evaluation of grinding-induced subsurface damage in optical glass BK7

Optical glass BK7 is widely used in optical industries but the grinding process of it with aggressive machining parameters (e.g., fast infeed rate, big depth of cut) easily leads to subsurface damage (SSD). Many methods have been proposed to evaluate SSD but they unavoidably changed or even destroyed the ground BK7 surfaces, required expensive equipment and operator skills, or needed tedious preparation works. In this paper, an explicit relation between SSD and Rz in the BK7 grinding process is established based on the analytical calculation of the classic brittle material crack system and the grinding kinematics. To validate the relation, the SSD values evaluated by the proposed relation are compared with the values obtained in both the experiments and other previous studies. The results indicate that the proposed relation can nondestructively and conveniently evaluate grinding-induced SSD, in situ and ex situ, by using a simple handheld profilometer. Furthermore, the proposed relation is transformed into another two forms, relating SSD with grinding process parameters (such as undeformed chip thickness, wheel and workpiece speed and wheel depth of cut). The two transformed relations indicate that the proposed relation can not only evaluate SSD after the grinding process but also optimize process parameters to control SSD during the grinding process. The study of this paper is expected to be meaningful in the SSD measurement and design, manufacture and application of optical glass BK7.