Abstract
The time-varying contact stiffness at the spindle-holder-tool joint in a magnetic levitation milling spindle significantly affects system dynamics during high-speed machining. To address this issue, a dynamic model of the rotor system is developed by integrating Timoshenko beam theory, rotor dynamics, and joint contact theory. The joint interface is modeled using distributed spring-damping elements, and the influence of centrifugal expansion on contact stiffness degradation is analyzed. The model incorporates the effects of magnetic bearing support stiffness, gyroscopic moments, and milling force excitation. The dynamic response is obtained using time-domain numerical integration. Results indicate that increasing rotational speed reduces joint contact stiffness, alters mode shapes, and amplifies tool tip vibration amplitudes, thereby diminishing the system’s vibration resistance and increasing the risk of instability. This study provides a theoretical foundation for improving the stability and dynamic performance of high-speed magnetic levitation spindles.
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