TOOL CONDITION MONITORING IN DRILLING USING VIBRATION SIGNATURE ANALYSIS

This paper presents a study on monitoring tool wear and failure in dri lling using vibration signature analysis techniques. Discriminant feat ures, which are sensitive to drill wear and breakage, were developed i n both time and frequency domains. These features were found to be rel atively insensitive to cutting conditions, and sensor location. In the time domain, a monitoring feature based on calculating the kurtosis v alue of both the transverse and thrust vibrations, was found to be rat her effective for on-line detection of drill breakage. On the other ha nd, in the frequency domain, a cepstrum ratio, derived from the spectr a of the vibrations monitored in both directions, was also found effec tive in detecting breakage events. The effect of different types of we ar on the vibration power spectra, in both the transverse and the thru st directions, was also investigated. A signature feature, namely the instantaneous ratio of the absolute mean value (RAMV(i)), was develope d in this study and used as a threshold for controlled capture of the vibration signal. The ability of the monitoring features to detect dri ll wear and breakage was verified experimentally. The drilling tests w ere performed using 3 and 6 mm diameter high speed steel twist drills, and cast iron workpieces. The results confirmed tile effectiveness an d robustness of the proposed monitoring features. Copyright (C) 1996 E lsevier Science Ltd