Effect of tool geometry and cutting parameters on surface quality and chip morphology of amorphous electroless nickel-phosphorus alloy in ultra-precision turning

The high surface quality of the machined nickel-phosphorus (Ni–P) alloy has an important influence on the performance of optical molds. However, the ultra-precision turning properties of amorphous electroless Ni–P alloys are not known at present. In this study, single-point diamond turning (SPDT) experiments of electroless Ni–P alloy were conducted with different tool geometries and cutting parameters in the orthogonal experiment and the single factor design. Subsequently, we measured the cutting forces and the machined surface roughness, and analyzed the chip morphology. The results show that the cutting forces reduce, and the surface quality improved with the increased cutting speed in the turning experiments. The large depth of cut and feed rate affected the increased variation of cutting forces, while feed rate significantly affected machined surface roughness. The predicted values and the linear regression analysis for the surface roughness also illustrated these results. In addition, machining by the tool with a large tool nose radius and a negative rake angle caused high cutting forces, but improved surface quality during the cutting process. The lamellar chip morphology showed that the individual chip segment deformation involved the formation of primary shear zones and secondary shear bands. The plastic flow of primary shear zone was found to be responsible for chip lamellar, and the secondary shear bands were related to enhancing the material plasticity. This study provides reasonable cutting parameters to obtain excellent cutting performance in order to achieve a high surface quality of Ni–P alloy. Meanwhile, it proposes a solution to the problem of the continuous variation of rake angles of the tools during ultra-precision turning of a free-form surface.