Brief Paper: Model-Free Adaptive Spindle Speed Regulation for Mitigation of Machining Vibrations

This paper presents novel adaptive spindle speed control strategies to minimize machining vibrations. Machining processes suffer from forced and chatter vibrations that deteriorate surface finish, reduce tool life and can damage the machine components. Model-based process planning strategies are used to minimize the effect of these unwanted vibrations. These approaches require conducting modal (tap) testing to be performed on the machine tool and developing machining process model to determine the forced vibration levels and to generate stability lobe diagrams for chatter-free cutting conditions. Although such model-based strategies are effective in process planning and determining optimal spindle speed and depth-of-cut pairs, these model-guided strategies suffer from key bottlenecks; namely, 1) they require expert knowledge that is not widely available in small-to-medium sized enterprises and 2) their effectiveness depends on the accuracy of the employed models. Thus, the majority of machining industries utilize know-how-based process planning to mitigate vibrations in machining. This paper proposes practical and model-free self-optimizing (adaptive) spindle-speed regulation strategies that minimize machining vibrations through in-situ vibration (acceleration) measurements. Two approaches are presented aimed at mitigating the effect of both forced and chatter vibrations by monitoring the acceleration levels during machining. Strategy-I utilizes a dither signal to determine the best spindle speed to minimize overall machining vibrations, whereas strategy-II is a dither-free approach and utilizes least squares fitting to seek the optimal spindle speed. Both approaches can determine chatter-free cutting conditions and also minimize forced vibration levels for a better surface finish. Simulation studies are presented in this brief paper to showcase their effectiveness.