High-speed milling is often used in industry to maximize productivity of the manufacturing of high-technology components, such as aeronautical components, mold, and dies. The occurrence of chatter highly limits the efficiency and accuracy of high-speed milling operations. In this paper, two control strategies are presented that guarantee a chatter-free high-speed milling operation by automatic adaptation of spindle speed and feed. Moreover, the proposed strategies are robust for changing process conditions (e.g., due to heating of the spindle or tool wear). An important part of the control strategy is the detection of chatter. A novel chatter detection algorithm is presented that automatically detects chatter in an online fashion and in a premature phase such that no visible marks on the workpiece are present. Experiments on a state-of-the-art high-speed milling machine underline the effectiveness of the proposed detection and control strategies.
SUMMARYChatter is an instability phenomenon in high-speed milling that limits machining productivity by the induction of tool vibrations, inferior machining accuracy, noise, and wear of machine components. In this paper, a fixed-structure active chatter control design methodology is proposed, which enables dedicated shaping of the chatter stability boundary such that working points of higher machining productivity become feasible while avoiding chatter. The control design problem is cast into a nonsmooth optimization problem, which is solved using bundle methods. Using this approach, fixed-structure dynamic (delayed) output feedback controllers can be synthesized. Distinct benefits of this approach are the a priori fixing of the controller order, the limitation of the control action, and the fact that no finite-dimensional model approximations and online chatter estimation techniques are required. All these benefits are important in milling practice. Representative examples illustrate the power of the proposed methodology in terms of increasing the chatter-free depth of cut, thereby enabling significant increases in machining productivity.
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