Investigation on the ultra-precision diamond turning of ZnSe aspheric surfaces using straight-nosed cutting tools

Theoretical and experimental investigations on the machining performance and mechanisms in single-point diamond turning (SPDT) of ZnSe aspheric surfaces using straight-nosed cutting tools have been carried out. Analyses of the chip formation process have shown that using straight-nosed cutting tools can significantly reduce the cut thickness by about 60 % compared with using round-nosed cutting tools for facilitating the ductile-mode material removal and reducing surface damages. The analyses have also shown that the height of residual feed marks can be reduced by using the straight-nosed cutting tools by about 80 %, which can further improve the machined surface integrity. Experiments on the machining performance of using straight-nosed and round-nosed cutting tools were conducted to verify the analytical deductions. It has been shown that nano-scale surface finish with surface roughness Ra -1.5 nm can be achieved by using straight-nosed cutting tools, which is significantly improved comparing with that by the round-nosed cutting tools (Ra -7.8 nm) and is consistent with the analytical results. Needle-like chip with periodical layered structure was collected from the SPDT processes using straight-nosed cutting tools, indicating a relatively continuous chip formation process under the ductile-mode material removal. Raman spectroscopy has shown increased metallization of ZnSe occurred during the machining with straight-nosed cutting tools, which is considered to reduce the brittle fractures along with the chip formation process. It has been further found that the straight-nosed cutting tool can reduce work adhesion and micro-edge chipping of cutting tools for extending the cutting tool life.