Cyclostationarity analysis of instantaneous angular speeds for monitoring chatter in high speed milling

The detection of chatter is crucial in machining process and its monitoring is a key issue, so as to insure a better surface quality, to increase productivity and to protect both the machine and the workpiece. An investigation of chatter monitoring in high speed machining process on the basis of cyclostationary analysis of the instantaneous angular speeds is presented in this paper. Experimental cutting tests were carried out on slot milling operations of aluminum alloy. Our experimental set-up allows for the measurement of instantaneous angular speed by using the signal delivered by the standard encoder mounted on the spindle motors. Monitoring chatter in high speed milling, made particularly call to the cyclostationary character of instantaneous angular speeds signals. The cyclostationarity appears on average properties (first order) of signals and on the energetic properties (second order). We show the importance of the utilization of these two kinds of cyclostationarity, particularly to distinguish between stable and unstable machining conditions. The results show that stable machining generates only very few cyclostationary components of second order. The appearance of the chatter, which is characterized by unstable, chaotic motion of the tool and by a strong anomalous fluctuations of cutting forces, makes growing strongly the level of cyclostationary components of second order.