Optimization of axial magnetic bearing for application of vibration assisted drilling

Abstract:
Thrust magnetic bearing characteristics are frequency dependent due to the eddy-currents inducted inside magnetic parts that oppose any change of magnetic flux in the inner parts. When used as linear actuator for vibration assisted drilling in industrial production, eddy-currents limit the maximum achievable stroke and vibration frequency with active thrust bearing. This reduces tool-feed rate or shortens tool average useful life. After introducing the problem, material properties and shape optimization are evaluated and compared in the frequency range of interest for vibration assisted drilling. While material properties are determinant, mechanical constraints often limit the selection to materials with significant electrical conductivity. Eddy-current effect can only be partially mitigated with shape optimization.