Ultraprecision grinding of tungsten carbide for spherical mirrors

This paper reports the ultraprecision grinding of tungsten carbide for spherical mirrors with nanometre surface roughness and submicron form accuracy. Spherical grinding was conducted with a computer numerical control grinding machine using a metal-bond diamond tool with grit size of 15 (mu)m. Form accuracy and surface roughness were investigated as functions of the grinding conditions. Ground tungsten carbide with concave and convex spherical surfaces was obtained with form accuracy in terms of peak-to-valley values of 0.13-0.165 wave (83-104 nm) and surface roughness values smaller than Ra = 5 nm. These surfaces were also characterized with fracture-free morphology. The analyses of microscopic topography of the applied diamond tool showed that self-sharpening of diamond abrasives occurred in grinding. The results show that ultraprecision grinding can be applied to the direct fabrication of spherical mirrors made of tungsten carbide without additional lapping and polishing processes.