Investigation On Process Geometry And Surface Topography For Multi-axis Ball End Milling Of Mold Steel

Due to the characteristics of high efficiency, high flexibility, and high machining accuracy, high-speed ball-end milling technology was widely used in the machining field of aeronautics and astronautics, resourses and power, and mold and dies. Based on the tool-workpiece action zone in high-speed ball-end milling of mold steel, the effects of tool path, workpiece surface inclination angle and cutting parameters on chip formation, cutting forces, cutting temperature and machined surface topography were investigated, which could provide theoretical basis and technical guidance for the multi-axis ball end milling process.Geometric analysis method was applied to built the tool-workpiece action zone geometric model. For the purpose of avoiding tool tip engaging in cutting process, ranges of workpiece surface inclination angle were analyzed for varying tool paths. Combining the structure features of the ball-end mill, the relationship between the maximum effective cutting speed and workpiece surface inclination angle was investigated for various tool paths. The evolution of tool-workpiece contact length and cross-section area with rotation angle was analyzed resorting to3D-CAD technology.Finite element simulation of ball-end milling process was performed to study the chip formation process. The effects of tool path and workpiece surface inclination angle on chip morphology were distinguished by means of FEM modelling and experimental analysis. It was found that sphere-like chip formed on the chip tip because of high temperature induced by high effective cutting speed under special cutting conditon.Based on the analysis of tool-workpiece action zone, both finite element simulation and milling experiments were applied to reveal the effects of tool path, workpiece surface inclination angle and cutting parameters on the cutting forces. The results show that the variation trends of both the cutting forces and chip cross-section area with the increment of tool rotation angle are identical with each other. The influence of tool path on the temperatures of workpiece and chip was investigated, and the results show that both the workpiece and chip temperatures were relatively low when up-ramping in up-cutting was used.Experimental analysis was conducted to investigate the effects of tool path, workpiece surface inclination angle and cutting parameters on the machined surface topography. It could be concluded that surface topography became betterwhen the workpiece surface inclination angle increase. The surface roughness increases with the increment of radial depth of cut and feed per tooth. However, the experimental results show that higher spindle speed leads to relatively smaller surface roughness value. It was found that the best surface roughness could be acquired when up-ramping in down-cutting process was used to machine the workpiece with surface inclination angle32°.