Tool condition monitoring in drilling using vibration signature analysis

This paper presents a study on monitoring tool wear and failure in drilling using vibration signature analysis techniques. Discriminant features, which are sensitive to drill wear and breakage, were developed in both time and frequency domains. These features were found to be relatively insensitive to cutting conditions, and sensor location. In the time domain, a monitoring feature based on calculating the kurtosis value of both the transverse and thrust vibrations, was found to be rather effective for on-line detection of drill breakage. On the other hand, in the frequency domain, a cepstrum ratio, derived from the spectra of the vibrations monitored in both directions, was also found effective in detecting breakage events. The effect of different types of wear on the vibration power spectra, in both the transverse and the thrust directions, was also investigated. A signature feature, namely the instantaneous ratio of the absolute mean value (RAMVi), was developed in this study and used as a threshold for controlled capture of the vibration signal. The ability of the monitoring features to detect drill wear and breakage was verified experimentally. The drilling tests were performed using 3 and 6 mm diameter high speed steel twist drills, and cast iron workpieces. The results confirmed the effectiveness and robustness of the proposed monitoring features.