Analytical process design for chemo-mechanical polishing of glass aspheres

This work deals with the chemo-mechanical sub-aperture polishing of glass lenses using spiral tool path and pressure-inflated membrane tools. Current trends in manufacturing precision optics in Europe go to smaller lot sizes and an increasing ratio of custom specific lens design. This requires deterministic processes as well as methods for an analytical process set-up without empirical try-outs. Chemo-mechanical polishing is typically applied for pre-polishing step, which aims for smoothing the surface with moderate shape correction. But due to kinematic effects the spiral-polishing process often shows changes in the radius of curvature, which are right now corrected by empirical try-outs and iterative corrections. This paper suggests an analytical tool for the compensation of these effects and contributes doing so to an efficient pre-polishing of aspheres. A mathematical model calculates the local distribution of material removal. It is based on Preston's equation and takes into account the influence of the major input parameters, such as feed rate, spindle revolutions and spot size. The given results show a significant reduction in shape deviation applying this methods compared to a polishing process without any compensation