An investigation of residual stresses in micro-end-milling considering sequential cuts effect

The distribution of machining-induced residual stresses has significant effects on the fatigue life, corrosion resistance, and precision durability of parts. An analytical model is presented to reveal the evolution regularity of residual stresses in workpiece for micro-end-milling. Considering the characteristics of tool rotation and interrupted cutting, the process of cutting entry and exit of each flute is treated as one cut, and sequential cuts effect is taken into account in the proposed model. The stress state caused by the previous cut is taken as the initial condition for the current cut. In order to improve the prediction efficiency, a new methodology which supposes the tool makes reverse movement is developed to determine the initial cutter position for residual stress calculation. The theoretical model is validated by machining NAK80 steel under different flank wear widths on a 3-axis ultra-precision micro-milling machine. Residual stresses are tested by means of X-ray diffraction. The computed results show that residual stresses are compressive and present a hook-shaped distribution, which is consistent with experimental results. Moreover, the effects of feed rate and radial depth of cut on residual stresses are theoretically investigated. This work can be further applied to optimize cutting conditions to achieve better surface integrity.