Polishing of spherical lenses using spherical tool on a 3-axis computer numerical control machine

Polishing is considered as the last and most important step in the manufacturing of optical component. Computer control polishing (CCP) methods are usually used to polish complex surfaces. In this method, material removal is controlled at each point, depending on error at that point. In contact polishing mechanism, tool feed rate is often controlled to eliminate local errors. It means that the higher tool feed rate, the lower material removal would be and vice versa. Tool influence function (TIF) which is defined as the instantaneous material removal under the polishing tool for a given tool motion, is the most important parameter in CCP and its predictability during the polishing process leads to reliable result. In this study, a new spherical tool which can polish complex surfaces by using a 3- axis CNC machine is presented. Because of spherical geometry of both tool and workpiece, tool material removal rate is variable because of changing the angle between tool axis and surface normal vector that leads to variation of relative speed. Tool influence function which depends on tool engagement’s angle was modeled based on Pereston equation. Moreover, the simulation is modeled based on discretization of tool path. To evaluate the methodology, some polishing experimental testes were performed. The experimental results show that a 130 mm spherical convex lens with initial surface roughness of 1.114 micrometer for PV was decreased to 395 nm for PV using the CCP method developed in this study.