A high-efficient precision grinding for fabricating moderately thick plane mirror (MTPM)

Plane mirrors have been widely used in various optical systems. The performance of optical systems relies heavily on the surface quality and flatness of plane mirror which are achieved by grinding or lapping followed by polishing or figuring. It is widely acknowledged that grinding is a high efficient method to machine plane mirrors with appropriate dimensional accuracy before polishing. However, the deformation of mirror induced by the mounting or clamping force will influence the final surface shape accuracy especially for the plane mirror with a feature of moderate thickness. In this paper, a new method is proposed for machining a moderately thick plane mirror (MTPM) employing the rotational grinding technique and the deformation compensation method. An accurate plane mirror can be machined efficiently relying on measuring the elastic deformation of the mirror in the clamping process and the mathematic relationship between the posture angles of grinding wheel spindle and surface profile of the plane mirror. A Φ100 mm × 6 mm silicon mirror (Si mirror) is machined based on the proposed method. The experiment results show that the Si mirror is totally removed 15 μm in thickness with feed rate of 15 μm/min and the peak and valley (PV) value of the Si mirror surface is reduced from 4.80 to 1.32 μm. The average value of the surface roughness Ra 9.6 nm is measured by means of the atom force microscope (AFM). The research indicates that the proposed method is excellent in machining MTPM with high quality and flatness.