Machining, Measurement, and Control Laboratory

2 0 0 0    J o u r n a l    P a p e r

High speed, high productive tapping by intelligent machine tools (1st report)
--Automatic detection of tool failure and chip jamming--
Yoshinori Yamaoka (YAMAZAKI MAZAK Corp.)
Yoshiaki Kakino (Kyoto University)
Yasuhiko Suzuki (YAMAZAKI MAZAK Corp.)
Akimitsu Nagae (YAMAZAKI MAZAK Corp.)
Toshiyuki Muraki (YAMAZAKI MAZAK Corp.)

High speed, high productive tapping is studied by using newly developed intelligent machine tools. Intelligent machine tools have three levels of feedback loop, which controls cutting forces and torque during tapping processes and determine cutting conditions, in addition to conventional feedback loops of the position, velocity of the table and the current of spindle and servo motors.

The cutting force and torque are estimated by using internal sensors. Experimental tests show that the estimated cutting force and torque coincide well with those measured by a tool dynamometer. By using the signal from internal sensors, the monitoring of cutting forces and torque is proved to be possible through experiments, when M4 taps or larger ones are used for tapping of steel, cast iron and aluminum alloys. In a successive tapping process of multiple workpieces, the increase of cutting forces and torque is monitored by the internal sensors. The cutting forces and torque increase as the tool wears, and thus the tool life can be estimated by monitoring the increase of cutting forces or torque. Furthermore, the monitoring of the chip jamming in a tapping process is also proved to be possible.

Several researches have been reported in the literature about on-line adaptive control of cutting conditions in various machining processes, such as drilling, end-milling, and face- milling processes. In a tapping process, however, it is not sufficient to control only cutting conditions. In this paper, we propose an adaptive control scheme to update servo parameters in tapping processes. By using the proposed adaptive control, the productivity of tapping processes is greatly improved.

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