Effect of cutting speed on the surface integrity of single point diamond turned (100)Ge

The surface integrity of single crystal (100)Ge machined by on-axis single point diamond turning was investigated. The specimen was machined with a -25◦ rake angle single crystal diamond tool, with a depth of cut of 10 µm and a feedrate of 4 µm/rev. Six circular bands were machined on the specimen at different cutting speeds, ranging from 0.2 m/s to 10 m/s, while keeping all other machining and geometrical parameters constant. The surface topography was measured by atomic force microscopy and the near surface lattice disorder was investigated by Raman spectroscopy. The cutting and thrust forces were measured during machining, and their frequency domain was analyzed. Machining resulted in four lobes with four-fold symmetry, with differing amounts of surface fracture at each cutting speed. It was found that increasing the cutting speed generates surfaces with less or no brittle fracture for all cutting directions, causing some lobes to be undistinguishable. As the speed increased, the cutting and thrust force decreased monotonically. The frequency content of the force changed accordingly with the appearance of the surface, with a shift from 8 oscillations per revolution to 4 oscillations per revolution.