| A comprehensive dynamic model that predicts the dynamic micro-end mill vibrations at very high spindle speeds (80K--500K rpm) in the presence of alignment errors at the spindle/shank and manufacturing errors at the cutting edges has been developed. The model considers the micro-end mill as a rotating Timoshenko beam to allow considerations of rotary inertia, shear deformation, and gyroscopic moments. It also considers additional dynamics due to the faults or errors at the cutting edges introduced by the design of micro-end mills with features of a large shank, taper, and reduced diameter at the cutting edges. Further, due to the minimum chip thickness effect, no chip is formed when the chip thickness is below the minimum chip thickness, and part of the work material plastically deforms under the edge of the tool and the rest elastically recovers. Thus, a force model that includes the influences of the dead metal cap and the effects of minimum chip thickness, elastic recovery, and elastic-plastic nature of the ploughing/rubbing has been developed.; Experimental and analytical methods have been developed to estimate the values of the faults in micro-end milling. Experimental validation of the model has been performed, and the model is shown to predict cutting forces and micro-end mill deflections within an average of 15%. Effects of process faults on micro-end mill vibrations have been studied varying feedrates for which the cutting mechanisms vary from ploughing-dominated to shearing-dominated. The stability characteristics based on the regenerative effect that are unique in the micro-end mill have also been studied. Vibration contour maps have been generated to investigate the dynamic behavior of micro-end mills under different cutting mechanisms. The results show that the stability lobes from the second mode, which are generally neglected in macro-scale end milling, affect the micro-end mill stability significantly. The contour maps show that the minimum chip thickness effect has significant effect on the micro-end mill dynamic behavior at low feedrates where the process is ploughing-dominated. The model has also been applied and validated for a high-speed end milling process. |
