Unpredictable tool life and premature tool failure are major problems in micromachining. In this study, the failure mechanism of micro-end-mills was studied during the machining of aluminum workpieces. The machining operations were performed at low cutting speeds, to identify the fatigue and extensive stress related failure mechanisms easily, by monitoring the cutting force variation since, the visual inspection (even with microscope) of the broken shaft of the micro-end-mills with 0.015 inches diameter is extremely difficult and unreliable. The existence of a relationship was demonstrated between the utilization related changes (wear), and the outcomes (increasing cutting force and raising stress on the tiny shaft). This relationship was called Wear Induced Stress (WIS). Inspection of the cutting force variation patterns of the large number of micro-end-mills indicated that tool failure occurs in addition to chip clogging with fatigue or excessive stress, depending on the magnitude and trend of the WIS. The study indicated that tool life can be extended by carefully selecting tool material, geometry and continuously cleaning the cutting edges of the tool. A breakage prediction method was developed by considering the WIS mechanism from the wavelet transformation coefficients.
