Prediction of Self-excited Machine Tool Chatter

Theoretical and experimental investigations were carried out to identify the dynamics of a machine tool structure during cutting and to predict the borderline of stability against the self-excited regenerative chatter. The validity of theoretical analysis in calculating the stability limit for conventional machining was confirmed by cutting experiments employing a structural model on an engine lathe. The model dynamics were identified during cutting under stable (non-chattering) cutting conditions by applying a technique of system identification based on the time series analysis of the small random cutting force variations measured by a specially designed tool dynamometer and the corresponding minute vibrations. The identified natural frequency of the model during cutting was found to be identical with that obtained by a harmonic excitation test when the machine was not running. The dynamic compliance, on the other hand, varied depending on the cutting conditions, especially the depth of cut. The experimentally obtained borderline of stability had a fairly good agreement with that calculated from the identified dynamics of the structure and the cutting dynamics, the latter being estimated from the static cutting data based on the so-called shear plane model. Both experiment and prediction showed high stability at low cutting speeds.