QUALITY OF SILICON CONVEX LENSES FABRICATED BY ULTRA-HIGH PRECISION DIAMOND MACHINING

Infra-red optical components are made mainly from hard and brittle materials such as germanium and silicon. Silicon machining is characterised by some difficulties when ultra-high precision machined by mono-crystalline single-point diamond. Accelerated tool wear and machined-surface deterioration may take place if the machining parameters are not properly selected. In this study, we conducted a machining test on an ultra-high precision machine tool, using ductile regime cutting conditions when fabricating a convex surface on a silicon lens of aperture of 60 mm diameter, and using a mono-crystalline diamond. It was found that the cutting conditions for shaping a convex surface of 500 mm radius resulted in good form accuracy. However, more attention should be paid to optimising the holding force of the vacuum chuck employed.