Magnetic actuator for active damping and stabilization of an air bearing spindle for micro machining

• Applicant: Professor Dr.-Ing. Jan C. Aurich
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491400446

Micro machining processes are characterized by the high degree of achievable geometry complexity, the wide range of machinable materials, short process chains, and short production times. Due to their advantages, mainly air bearing machine tool spindles are used for micro machining. They allow very high rotational speeds (> 300,000 rpm) and low tool run-out which cannot be achieved by any other bearing principle. Despite the variety of advantages, these air bearing spindles application is still limited due to the purely passive operating principle of said air bearings. As such, the achievable rotational speed is limited by self-excited vibrations within the air bearings. Further, changes of the spindle’s rotational speed due to changes of the feed rate lead to vibrations and thus to undesirable shape deviations of the machining result. Additionally, the spindle’s rotor balancing must be carried out extremely thorough in order to minimize disturbing unbalance forces.To achieve higher rotational speed, lower tool run-out, and free-of-unbalanced-forces operation, it is necessary to add an active component to the otherwise passive air bearings. The use of an active component allows to compensate both for speed-independent disturbing forces caused by environmental influences and for speed-dependent influences such as centrifugal forces, thermal loads and cutting forces by an active machine control. Furthermore, it is possible to actively assist the spindle rotor balancing and thus enable free-of-unbalanced-forces spindle operation.In the proposed research project, a magnetic actuator is to be developed for the active damping and stabilization of an air bearing machine tool spindle for micro machining. The research project also includes the design of the corresponding control loop as well as the model-based design and programming of the controller. Furthermore, an air bearing spindle is to be modified to allow integration of the developed magnetic actuator. A functional model of this modified air bearing spindle, including the magnetic actuator and controller, is to be manufactured in order to validate the model-based design of the magnetic actuator and its control accuracy. Afterwards, milling tests are carried out with the modified air bearing spindle with integrated magnetic actuator in order to evaluate the magnetic actuator’s ability to compensate vibrations due to changes of the feed rate. In addition, milling tests are carried out to evaluate the machining results during free-of-unbalance-forces operation at rated spindle speed. After completion of the project, it will be possible to achieve rotational speeds adapted to the optimum feed rate when milling. Furthermore, unbalances are actively compensated by the magnetic actuator, enabling free-of-unbalanced-forces micro milling at a specified nominal speed.

• DFG Programme: Research Grants