A novel method for determination of the subsurface damage depth in diamond turning of brittle materials

Micro-structured surfaces on brittle materials, e.g. ceramic and glass, are gaining increasing industrial applications such as optics, semiconductor and biomedical. However, these materials tend to be damaged with brittle fracture in machining. To generate crack-free surfaces, ductile-regime machining should be maintained for the entire micro-structured surface. In ductile-regime machining the material is removed by both plastic deformation and brittle fracture, but the cracks produced are prevented from extending into the finished surface. In this paper, a machining model has been developed for fast tool servo (FTS) diamond turning of micro-structured surfaces on brittle materials. Based on the model, a damaged region analysis method (DRAM) is proposed to determine the subsurface damage depth (C_m) by analyzing the surface damaged region of a machined micro-structured surface with sinusoidal wave along radial direction. Only one micro-structured surface is required to be machined to obtain C_m, which greatly reduces the effort for determination of C_m. With C_m, the maximum feedrate for machining a crack-free micro-structured surface can be determined. Machining experiments have verified the validity of DRAM.