Modeling and experiment of surface error for large-aperture aspheric SiC mirror based on residual height and wheel wear

Abstract

In the grinding process of large-aperture aspheric silicon carbide mirror, the wear of grinding wheel affects the surface accuracy seriously due to high hardness of silicon carbide and large diameter of aspheric mirror. Therefore, establishing surface error model of large-aperture aspheric silicon carbide mirror taking the wear of grinding wheel into account is of great significance to improve the processing quality and the imaging quality of aspheric mirror. The spiral grinding method is chosen to grind large-aperture aspheric SiC mirror in this work. The surface error of large-aperture aspheric silicon carbide mirror is established based on residual height and radial wear of grinding wheel using the grinding ratio as a bridge. The influence of grinding parameters on surface error is analyzed based on theoretical model. The results show that surface error increases with the increase of the rotation radius of workpiece and feed velocity of wheel, while it decreases with the increase of rotation velocity of workpiece and arc radius of wheel. The influence of the rotation velocity of workpiece and feed velocity of wheel is greater than that of the rotation radius of workpiece and arc radius of wheel. The regression equation of grinding ratio is established through grinding experiment, and the correlation coefficient is 0.9774 which verifies the reliability of the regression equation. Furthermore, the complete formula of surface error is acquired based on regression equation of grinding ratio. Finally, the grinding experiment of large-aperture aspheric silicon carbide mirror is carried out on the five-axis NC milling and grinding machine tool of HZ-091 type, and the error between measured value of grinding experiment and prediction value of theoretical model is less than 20%, which indicates that the theoretical model is reliable.