Monitoring of the cutting process is one of the most crucial and difficult problems in unmanned machining technology. In this paper, the effects to the thrust and the torque in drilling by some abnormal cutting states have been investigated. Experiments show that the dynamic components of the thrust and the torque provide useful information for identifying different tool failures. Reasonable explanations have been given for the phenomena from physical mechanisms. A mathematical model for the dynamic cutting process was proposed and some problems about the estimation of the time series AR(n) model were also discussed. After having compared several defined monitoring parameters, a new inprocess signal processing method, `adaptive variance-residual recursive algorithm,' based on least squares theory has been suggested with which signal signatures of cutting states can be extracted effectively. It bears the advantages of rapid response, less amount of calculation, and easy to set deterministic thresholds. The in-process monitoring system developed shows a bright prospect in practical application.
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