Surface Integrity Of 316L Stainless Steel In Vertical Milling Based On Tool-paths

This paper is sponsored by the National Natural Science Foundation of China Project under the No.51175339,as the core parts of nuclear main pump, impeller need to work long time and safety in the conditions of high temperature, high pressure and radiation, so it must have good mechanical performance and hydraulic characteristics. AISI-316 L stainless steel with acid resistance, wear resistance, high toughness, good weldability and strong corrosion resistance, are widely used in nuclear main pump impeller. However, its cutting performance is also poor, and it is one of difficult-to-cut metal materials. Therefore, the research on surface integrity of AISI-316 L stainless steel is important to the impeller, it has great significance for the improvement of mechanical performance, hydraulic characteristics, working life and the decrease of stress corrosion crack.In order to research the vertical milled surface integrity of AISI-316 L stainless steel, the methods of finite element simulation and experimental analys is are used. The effect on machined surface integrity of tool-paths, milling parameters and the overlap between adjacent tool-paths are analyzed, with the measurement of surface residual stress, surface hardness and surface roughness.Firstly, a three-dimensional thermal and mechanical couple vertical milling FEM is built based on Abaqus software, it simulates the milling process in the conditions of four different tool-paths with Abaqus/Explicit calculation, this model consider the effect of both cutting force and cutting heat, and it meet the actual milling process. Based on this model, the distribution of machined surface residual stress and plastic strain are simulated. At the same time, the effect on residual stress and plastic strain of milling parameters are also predicted.Secondly, milling experiments of AISI-316 L stainless steel are conducted by CNC milling machine, and the machined surface residual stress, micro hardness, roughness, surface profile are measured. The comparisons of simulated and measured results of surface residual stress show that the predict errors are less than27%, which validates the accuracy of this FE model. Meanwhile, the effect on surface micro hardness and roughness of four tool-paths and milling parameters are analyzed, the measures about selecting tool-path and milling parameters that can improve the machined surface integrity are proposed.Finally, in the milling process,as the space between adjacent cutter paths is less than the cutter diameter, so that there is overlap region among the adjacent cutter paths, and it will appear two or more repeat cutting phenomenon in these regions. In order to analyze the influence of this phenomenon on the machined surface integrity, the two factors of overlap ratio K and overlap direction are researched. It will provide reference for the choice of space and tool-path.