The present work monitors on line the drilling torques of microdrills. To carry out the drilling experiment, 50 microdrills of 0.34 mm diameter were used, and the drilling torques were measured when the microdrills broke. The distribution of the drilling torques was found by curve fitting the measurement data. Then, from reliability theory, the torques with respect to different reliabilities at which microdrills do not break can be obtained using the distribution. Finally, the threshold value for the on-line monitoring is determined from the reliability to prevent microdrills from breaking and to increase microdrill availability.
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