Tool path selection for high-speed ball-end milling process of hardened AISI D2 steel based on fatigue resistance

This paper aims at revealing how tool paths influence the fatigue resistance of high-speed ball-end hard milled surfaces and proposing corresponding tool path selection methods. Three kinds of tool paths (tool paths A, B, and C with angles relative to the length direction of cuboid workpiece 0 degrees, 90 degrees, and 45 degrees, respectively) were utilized during high-speed milling process of hardened AISI D2 steel. The fatigue resistance of samples for different tool paths was evaluated through three-point bending fatigue tests. Results shows that tool paths have significant effect on fatigue resistance, and the maximum discrepancy in fatigue life can reach about 37.6% for different tool paths. Samples for tool path C shows the longest fatigue life when radial depth of cuta(e) = 0.1 mm. However, with the further increase ofa(e), samples for tool path A have the best fatigue resistance, followed by tool path C and B. Microscopic stress concentration and effective residual stress are the main ways by which tool paths influence the fatigue resistance. Changing tool paths leads to the difference in surface topography orientation and then in degree of microscopic stress concentration. Moreover, the effective residual stress (residual stress component in direction parallel to cyclic tensile stress) is also directly determined by tool paths. Tool path selection methods are put forward based on the aforementioned influence mechanisms. This study indicates that improving the fatigue resistance of high-speed ball-end hard milled surfaces suffering given cyclic tensile stress is feasible by choosing appropriate tool paths.