Mechanism analysis and modelling of surface roughness for CeO2 slurry assisted grinding of BK7 optics considering both particle size and mass fraction

Abstract

Prolonged polishing deteriorates the shape accuracy of an optical element and reduces production efficiency simultaneously. In order to reduce the amount of polishing and polishing time, even obtain polish-free fine surfaces, a cerium oxide (CeO2) slurry assisted grinding (SAG) is investigated. A novel theoretical model was established to predict the surface roughness of the workpiece processed by CeO2 SAG. The modelling considered the effects of the protrusion height of active grains in the grinding wheel and the sizes and mass fractions of CeO2 particles in the grinding zone on undeformed chip thickness (UCT). Then, the mechanism of CeO2 SAG was investigated through nanoindentation method. Indentation hardness and energy spectrum of the surface were estimated to verify the softened layer. The results showed that the model of surface roughness was well consistent with the experiment. The CeO2 particle size significantly influenced on the surface roughness than the mass fraction. The load-bearing effect of larger CeO2 particle size reduced the protruding height of the grinding wheel grains and reduced the UCT to a greater extent in grinding process. The chemical reaction between CeO2 slurry and BK7 glass results in a softening layer which enhances the critical load and critical depth of ductile-brittle transition of grinding. Finally, the optimized parameters were used for CeO2 SAG of an ellipsoid BK7 optics.