SUBSURFACE DAMAGE MECHANISMS AT HIGH-SPEED DUCTILE MACHINING OF OPTICAL-GLASSES

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