Design For Disassembly: A Novel Magnet Fixation Approach in PM Rotors Using Hygroscopic Thermoplastic Interlayers for Enhanced Recyclability

Permanent Magnet (PM) synchronous machines play a critical role in electrified transportation due to their high-power density, efficiency, and compactness. These machines typically use rare earth (RE) magnets, which are almost exclusively sourced from PR China due to its market dominance of the entire production process chain. To counteract this dependency, new legislation is constantly being drafted, such as the European Critical Raw Materials Act, which among other goals promotes the recycling of RE materials. To achieve this, design for recycling and design for disassembly approaches are of particular interest. However, the fixation of RE magnets within the rotor structure of electric traction drives poses significant challenges in terms of recyclability and end-of-life disassembly. Conventional fixation techniques, such as adhesives or mechanical press fits, often create irreversible assemblies that hinder the recovery of critical raw materials like neodymium and dysprosium. To address these limitations, this study explores the use of thermoplastic interlayers as an innovative and reversible fixation method for magnets in PM rotors. Hygroscopic thermoplastics demonstrate controlled swelling behavior in response to moisture and temperature. This study investigates whether this property can be utilized for a passive, press-fit-like fixation of the magnets, eliminating the need for mechanical fasteners or chemical adhesives. Furthermore, the possibility of controlled disassembly is analyzed by reheating the hygroscopic interlayers above their specific drying temperature, which causes the plastic to shrink again. The study evaluates suitable hygroscopic thermoplastics, focusing on their thermal stability, swelling characteristics, fixation strength, and ease of fixation reversibility. Simulations investigate the feasibility of using swelling-based interlayer fixation with different geometries as a sustainable alternative to conventional magnet fixation in rotors. The results demonstrate the method’s potential to support circular economy objectives by enabling efficient recovery of RE magnets from future electric drive systems designed and engineered for recycling and reuse.