Relative tool sharpness (RTS) is identified as the ratio of undeformed chip thickness to tool cutting edge radius. This paper studies the effects of RTS on the surface generation mechanism of precision turning of electroless nickel-phosphorus (Ni-P) coating. An R-shaped tungsten carbide (WC) tool was adopted for the face turning experiment. The cutting edge radius was 1.84 μm measured by a laser scanning confocal microscope (LSCM). The chip formation behavior, cutting forces and surface morphology were investigated under different RTS values. Results showed that the chip changes from continuous to discontinuous as RTS decreases from 0.54 to 0.27, indicating the transition of the material removal mechanism. The periodical fluctuations with small amplitudes on the machined surface are associated with the high-frequency tool-tip vibration. The low-frequency fluctuations of the cutting forces are related to the material swelling and recovery. The optimal machined surface roughness was obtained at the RTS of 0.38.
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