Investigation of Post Processing and Robust Insulation of High-Performance Additively Manufactured Al-Fe-Zr Electrical Machine Windings

Metal Additive Manufacturing (AM), in which feedstock is selectively bonded in a succession of 2D layers to incrementally form a 3D part, offers unparalleled design freedom in realising high-performance windings for electrical machines. AM allows unconventional combinations of conductor profiles and topology, intended to minimise frequency dependent losses, and enables embedding of thermal management features such as fluid cooling channels. The resulting conductors are inherently produced in the wound state allowing use of novel electrical insulation formulations that can exhibit superior thermal performance (> 200 oC) and dielectric strength at the cost of reduced mechanical properties. The resulting as-built windings are often heat treated to improve both electrical conductivity and mechanical properties and typically exhibit a level of surface roughness that requires post-processing to facilitate insulation coating. This study focuses on a commercial aluminium alloy (Al-Fe-Zr), for mass-critical applications such as aerospace, paired with a commercially available dielectric resin. The type and extent of surface post-processing in terms of heat treatment and surface polishing required to achieve robust high-voltage insulation coating of AM windings is explored. Firstly, batches of AM windings are produced, subject to varying heat treatment and then characterised in terms of electrical conductivity, surface roughness, and light microscopy. Results obtained elucidate the evolution of the microstructure with heat treatment and its influence on the electrical conductivity. The second part of the study involves applying an insulation coating on the windings. Preliminary studies have identified surface roughness as a parameter that impacts the homogeneity of the insulation coating thickness. The samples are subject to varying levels of electrochemical polishing to reduce the surface roughness. The prepared samples are coated with resin in a controlled process and the resulting layer inspected for thickness and homogeneity. Finally, breakdown voltages of the coatings are established. The dataset is used to establish the post-processing requirements for robust electrical insulation coatings on AM parts and underpins future steps in applying novel, high-performance coatings that are ideally suited to the pre-formed winding geometry arising from AM.