Fabrication of large-diameter single-crystal silicon aspheric lens by straight-line enveloping diamond-turning method

The conventional method for aspheric surface diamond turning is the arc-enveloping method. In the present study, a new method termed the straight-line enveloping method is proposed, in which the aspheric surface is generated using a straight-nosed diamond tool on a three-axis simultaneous control ultraprecision machine tool. This method is preferable to the conventional method for the machining of convex aspheric surfaces on hard brittle materials since it significantly improves efficiency and lowers tool wear. The experimental setup configuration and the tool setting method are described and the formation of form error is analyzed. An aspheric lens having 1.36μm form error and 78nmR_y surface roughness was obtained on a 120mm diameter single-crystal silicon substrate at a tool feed rate of 20μm/rev. by applying the proposed method.