Comparison in surface integrity and fatigue performance for hardened steel ball-end milled with different milling speeds

Abstract

This paper aims at comparing the surface integrity and fatigue performance of hardened AISI D2 steel ball-end milled with different milling speeds. Results show that the milling speed has a significant effect on surface topography, surface roughness, microhardness and residual stress. The fatigue life for samples with hard milled surface was raised at least 83% compared with that of polished samples. This is ascribed to the high surface residual compressive stress and the enhanced microhardness induced by the hard milling process. The maximum difference in fatigue life is about 12.2% for samples milled with spindle speed N ranging from 3000 r/min to 8000 r/min. Samples milled with a low or high spindle speed have a longer fatigue life than those samples milled with a middle spindle speed condition (N=6000 r/min). Moreover, excessive surface strain hardening will increase surface brittleness which is detrimental to fatigue resistance. The increase of spindle speed can decrease the degree of strain hardening to some extent. Based on this, selecting a relatively high spindle speed can obtain a satisfying combination of surface residual stress and microhardness during the ball-end milling process of hardened AISI D2 steel, which is feasible and prospective from high fatigue performance of ball-end milled surface and the machining efficiency point of view.