Characteristics of cutting force and surface finish in diamond turning of polycrystalline copper achieved by friction stir processing (FSP)

Cutting force and surface finish are two critical characteristic parameters for diamond turned polycrystalline copper components. In this work, polycrystalline copper with different grain sizes achieved by friction stir processing (FSP) was machined by single point diamond turning. To accurately predict cutting force in diamond turning, a theoretical prediction model considering grain size of copper, Hall-Petch effect, and stress distribution on a diamond tool was developed. Three-direction cutting forces, i.e., principal cutting force, thrust force, and feed force, in the diamond turning process were calculated, respectively. To analyse the material microstructure and mechanical property, Electron Back Scattered Diffraction (EBSD), X-Ray Diffraction (XRD) and nano-indentation analysis were successively performed on the work material. Combing theoretical model and experimental results, the relationship between principal cutting force and thrust force on various processing parameters was successfully revealed. Furthermore, surface roughness of the copper work material processed by FSP is smaller than that without treatment. According to material analysis results, the combination of misorientation angle and Hall-Petch effect reduces the step height on diamond turned surface, which further contributes to a flatter diamond turned surface. Therefore, the combination of friction stir processing and single point diamond turning has the application potential to achieve a super-smooth surface finish in industry.