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 toot with grit size of 15 mum. 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 R-a = 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

Influence of microstructure on ultraprecision grinding of cemented carbides

The influence of microstructure on the ultraprecision grinding response of a series of cemented carbides for spherical mirrors was characterized by means of optical and laser interferometry, atomic force microscopy, scanning electron microscopy and Xray diffraction. Surface roughness, form accuracy, grinding-induced residual stress and material removal behaviors were studied as a function of tungsten carbide (WC) grain size. In connection with the removal mechanisms in ultraprecision grinding, microindentations performed on each material showed similar deformation patterns, all in the plastic regime. The microstructure of WC-Co materials was found to have little influence on the nanometre surface roughness and submicron form accuracy. However, the X-ray stress measurements indicated that the microstructure of carbide materials had a significant influence on the grinding-induced residual stresses; i.e. an increase in grinding-induced residual compressive stress with an decrease in WC grain size. No grinding-induced cracks were observed in the ground cemented carbide surfaces. The material removal in ultraprecision grinding was considered to occur within the ductile regime. The formation of microgrooves and plastic flow regions via slip bands of WC grains along the cobalt binder without visible resultant microfracturing of WC grains were the dominant removal mechanisms. (C) 2003 Elsevier Ltd. All rights reserved