Indicators for monitoring chatter in milling based on instantaneous angular speeds
Résumé
The detection of chatter is crucial in the machining process and its monitoring is a key issue to ensure a better surface quality, to increase productivity and to protect both the machine and the workpiece. An investigation of chatter monitoring in the high speed machining process on the basis of the analysis of cutting forces and instantaneous angular speeds (IAS) in the angular domain is presented in this paper. Experimental cutting tests were carried out on slot milling operation of aluminum alloy. Our experimental set-up allows for, on the one hand, the acquisition of the angular cutting force and, on the other hand, the measurement of IAS. The latter is computed from the signal delivered by the standard encoder mounted on the spindle motors. The same signal is used as a base for synchronous angular sampling. The acquisition methodology is described and discussed in this paper. Data analysis confirms the relevance of cutting forces for chatter monitoring and the good correlation between cutting forces and IAS of the spindle. Two chatter indicators are developed in the angular domain from the periodic and residual parts of angular speed and cutting force signals. They are used successfully for the detection of the chatter phenomenon. The indicator based on IAS is very convenient because it does not require additional sensors and can be realized without increasing the cost of the manufacturing system.