On-line tool condition monitoring is essential for optimizing modern machining systems especially in the case of precession and unmanned machining. Knowledge of the condition and the expected life of the cutting tool are very important inputs for determining the optimal machining parameters. Previous efforts have indicated that ultrasonic gauging methods can be used to directly measure, in-process, gradual tool wear during turning operations. Good correlation was shown to exist between the level of gradual wear and the ultrasonic signals. However, the correlation was tool dependent and was mainly attributed to variations in the tool materials and other mechanical factors.; This work describes a robust method for on-line gradual wear monitoring using normalized ultrasonic signals. A consistent calibration mark, cut in the lower corner of the tool nose, is used to generate a calibration echo. The calibration echo is affected by the same variations as that of the gradual wear and is used to normalize the nose and flank echoes. Experiments under various cutting conditions showed that the gradual wear measurements can be made tool independent by normalizing the measurements by a calibration mark. In addition, the variations in the signals which were previously reported are also eliminated.
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