Molecular dynamics simulation has become a major theoretical analysis method for ultra precision machining of various materials. Large Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is used to construct a molecular dynamics model for cutting polycrystalline Fe-Cr-W alloy with CBN tool. The geometric parameters of the tool model are: the rake angle is −10°, the clearance angle is 7°, and the tool tip radius is 1.5 nm, including 8570 atoms. The size of the workpiece model is 24 nm × 10 nm × 10 nm, including 203,893 atoms. Ovito is used to visually analyze the influence of cutting parameters on the machinability of workpieces. The results show that the extrusion of the tool on the workpiece makes the atoms of the workpiece move and become chips and machined surfaces. Excessive cutting speed and depth will produce large hydrostatic stress, large cutting force, high cutting temperature and deteriorate the machined surface.

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The surface topography of the workpiece directly affects its service performance. In this study, CLSM and SEM are used to analyze the effects of turning speed, turning feed, and turning depth on the three dimensional topography and surface defects of the machined surface. Amplitude parameters are used to characterize the machined surface topography of hard turning. Twelve groups of single factor experiments are used to analyze the influence of turning parameters on surface topography. Based on analysis of variance (ANOVA) and 15 groups of Box-Behnken Design (BBD), whether cutting parameters have significant influence on arithmetic mean deviation ( Sa) is analyzed. A mathematical statistical model of Sa is established by Response Surface Methodology, and the effectiveness of the model is verified by 10 groups of experiments. By analyzing the research results, it can be concluded that: (1) The consistency of the surface topography of hard turning is good; (2) In the turning feed direction, the surface defects of the machined surface by hard turning include turning grooves, material side flow, adhering chips, and material surface tearing; (3) In hard turning, the most significant factor affecting the three dimensional roughness ( Sa) is the turning feed.