Optimization Of Aspheric Grinding Process For Large Aperture SiC Mirror

With the development of space exploration, the imaging performance of the observation equipment is getting higher and higher. The reactive bonded silicon carbide(RB- Si C) ceramics has been the preferred material for the primary mirror based on its good physical properties. The shape and the size of the silicon carbide mirror determines the imaging quality of the observation equipment. Therefore, it is an important way to improve the imaging quality by manufacturing large aperture Si C aspheric mirror and improving the shape accuracy of mirror. The surface accuracy of the aspheric surface is poor, and the surface of the mirror is seriously damaged for the low grinding efficiency of the large aperture mirror and the serious wear of grinding wheel. So, it is of important significance to improve the surface accuracy of aspheric surface, reduce the sub surface damage of aspheric surface and improve the efficiency of grinding process.In this paper, the grinding process of large aperture Si C aspheric surface is optimized to improve the surface shape, reduce the damage and improve the efficiency. When the arc grinding wheel processed the aspheric workpiece with spiral trajectory, the residual height model considering the radial wear of grinding wheel was established in the direction of the generatrix. The residual height of surface shape error formula was derived, the influence of the parameters on profile error was analyzed and the experiment of arc grinding wheel grinding the aspheric mirror was carried out to verify the correctness of the surface shape error model. The correction factor was used to modify the model. In order to derive radial wear of the grinding wheel, the experiment of grinding ratio G was carried out and regression equation of grinding ratio G was established. The establishment of surface profile error model provides a theoretical basis for the process optimization of grinding strategy.In order to research the sub surface damage of RB-Si C ceramics, the surface grinding experiment was carried out. The damage depth of sub surface, damage depth of broken layer and the material removal mechanism under different parameters were studied. The surface quality under different parameters were analyzed. And the influence laws of parameters on damage depth of sub surface, damage depth of broken layer and surface roughness were analyzed. The grinding parameters was optimized and the best optimization value was obtained. The study of sub surface damage and the optimization of process parameters lay the theoretical foundation for the selection of grinding parameters.Process optimization strategy of grinding process parameters includes the analysis and selection of grinding strategy, analysis and selection of the trajectory of the grinding wheel, establishment of surface shape error compensation model based on grinding wheel wear, the common residual high optimization based on changing the feed rate, analysis and selection of grinding layer thickness, and analysis and calculation of the grinding efficiency. The grinding process and grinding parameters were collaboratively optimized for large aperture Si C mirror using the process optimization strategy. The surface profile error and grinding efficiency after being optimized were compared with that in the normal process, which improved the surface profile accuracy, reduced the damage depth of sub surface, and improve the processing efficiency. And the optimization strategy which is suitable for grinding large aperture mirror of Si C ceramics is finally obtained.