Design and manufacturing of permanent magnet bearing rings for high speed applications

We provide an overview of the challenges for the design of magnet rings for high-speed permanent magnet bearings focusing on manufacturing aspects. We analyze an assembly of a NdFeB magnet ring with a hub and a bandage, both made of Ti-6Al-4V (titanium grade 5). Thereby, we consider bandage thicknesses, tolerances and assembling processes. This is supported by simulations using Finite Element Method (FEM) analysis in ANSYS workbench 2020. We analyze the stresses during a press-fit joining process between the magnet and the bandage and subsequent consequences for the stresses on the system for rotation speeds up to 120,000 RPM. Finally, we consider safety aspects by implementing a cracking of the magnet at high rotation speed. The results of the simulations show that the stresses on the magnet are the limiting factor of the rotation speed in all cases analyzed here. For an idealized system, mainly the bandage thickness and the required rotation speed define suitable tolerancesfor the fitting of the bandages and magnets. For a real system, residual stresses of the joining process and ovalization effects of the bandage decrease either the allowable speed or the allowable tolerances, thereby considerably influencing the required manufacturing precision. A safety analysis shows that the hub-magnet-bandage assemblies analyzed here are safe with respect to magnet cracking even at high speed.