Wheel normal grinding of hard and brittle materials

Abstract

Microaspherical and freeform optics of hard and brittle materials have been more and more widely used in aerospace, optical system, and digital products with the rapid development of science and technology. The wheel normal grinding has an important practical significance for the manufacture of these microaspherical and freeform optical surfaces because not only the interference between grinding wheel and microsurface can be overcome but also the tool geometry errors can be avoided to transfer into the ground surface. In this paper, the kinematics and surface formation in wheel normal grinding process were presented firstly. Then, for hard and brittle materials, the maximum uncut chip thickness and ductile/brittle regime have been addressed by analysis of grinding mode and calculation of ductile/brittle transition critical depths. Special attention has been given to the condition for generating a ductile mode response on the ground surface in wheel normal grinding process. Finally, the aspherical surfaces of BK7, ZERODUR, and binderless WC were ground by wheel normal grinding. The surface roughness Ra was 8.5, 6.6, and 7.4 nm, respectively, and the form error (PV) of BK7 and binderless WC was less than 0.3 μm, while that of ZERODUR was less than 0.5 μm.