Research On The Failure Mode Of Micro-Ball-End Cutter In Micro-Milling Process And Its Influence On Machining Accuracy

Due to the ability to machine three-dimensional (3D) complex shapes on a variety of materials and process flexibility, micro milling has gained a wide range of applications in the fields of biomedical, microelectronics and energy, et al. However, due to the small-size and fragile cutter, the major problems that hinder the development of micro milling are unpredictable tool life and premature tool failure in micro milling process. In addition, as in micro milling process the ratio of run-out to tool diameter are tens times of that in conventional milling process, the damages of runout to machining accuracy are much worse in micro milling operation. Recently, the researches of micro milling focused on the on-line detection of micro-milling process and the developments of cutting force model, lack the investigations of the influence of cutter run-out and cutting process parameters on the failure of micro milling tools and the machining accuracy. Therefore, this article has decided to study the influence of run-out and cutting parameters on micro milling cutter failures and machining accuracy.This article has taken finite element method (FEM) to create the micro milling model, which has considered the cutter deflection and tool run-out; kinematic analysis is used to study the trajectory of tool tip and study the influence of run-out on the failure of single-precision ball milling cutter; based on the FEM model, simulation is conducted for the micro milling process under different run-outs and cutting parameters; the method of the transient dynamics is taken to simulate the tool tip trajectory and amplification effect of cutter run-out in the process of micro milling with installation errors and study the influence of tool inclination angle, eccentricity, tool overhang length and spindle speed on the run-out amplification; experiments are conducted to study the influence of process parameters on the machining accuracy of micro milling.The results of Kinematic analysis has shown that when run-out angles are 0 or 180°, the influence of run-out on machining accuracy is largest; when run-out angles are 90°or 270°, run-out has no influence on machining accuracy; when run-out angles are 0 or 270°, the run-out will enlarge the cutter deflection; when run-out angles are 90°or 180°, run-out will diminish cutter deflection; run-out has little influence on cutting forces and cutter deflection brought by cutting forces, which is consistent with the results of the kinematic analysis; the cutting forces and cutter deflections under different cutting parameters are solved, which increase with cutting depth and feed per revolution and decrease with spindle speed; the breakage of the new cutter mostly occur at the point of highest speed, the profanity of shank fracture is very low and tool failure probability increases with cutting parameters; run-out amplification increases with installation errors, tool overhang length and spindle speed, while the ratio of run-out amplification decreases with installation errors and increases with tool overhang length and spindle speed; in addition, experiments are conducted under different cutting depths, feed per tooth and spindle speeds and the size of the slots are measured and the variation of machining accuracies with process parameters is consistent with the simulated results.