Subsurface damage mechanisms at high-speed ductile machining of optical glasses

The production of new transparent glass surfaces by ductile removal of viscoplastic glass layers has been investigated up to 100 m/s cutting speeds using monocrystalline diamond cutting tools. It has been found that the factors which limit the surface quality are micro-shear bands and micro ripple pattern, subsurface residual stresses and different types of micro-cracks, which are influenced by the type of glass, the cutting speeds, the micro-geometry of the cutting edge, the depth of the cut, and environmental conditions. At elevated cutting speeds the heat generated in the cutting zone due to adiabatic micro shearing gives rise to continuous chip formation, smooth surfaces and annealing of residual stresses, however, may also change the glass properties in the processing zone (glass ceramics e.g.). These different surface quality controlling effects involved in the ductile machining of glass and other brittle materials will be discussed