64 May/June 2025 | E-Mobility Engineering Peter Donaldson parses the wisdom of industry experts in motor materials Making a material difference Materials are as fundamental to e-motors as they are to every other engineered artifact, and selecting the right material for each application is crucial in any motor development project. Powering a broad range of vehicles with diverse duty cycles and operating environments, presents multifaceted challenges and material trade-offs. Prominent among those challenges are the needs for high power density and high specific power to enable high performance without adding too much weight or bulk. Simultaneously, efficiency is pursued to maximise vehicle range/endurance and minimise energy consumption. These core performance requirements mandate careful consideration of the materials employed throughout the motor. Harsh work E-motors must withstand harsh operating conditions, including extreme temperatures, vibrations and environmental stressors such as corrosion-promoting salty/humid conditions. Coatings and surface treatments can improve corrosion resistance, for example, but they add cost and complexity associated with the extra steps required in the manufacturing process. Temperature stability is also critical, and materials must maintain their properties over a wide temperature range, which can be a particular challenge with respect to magnets and insulation materials. Vibration induces high-frequency stress reversals that can cause cracking in many materials. Therefore, robust mechanical design and resilient materials are equally crucial, and work must be done to improve the reliability and durability of insulation materials. High rpm and centrifugal force Power is a product of torque and rotational speed, and high power output often means a motor spinning very fast, which generates large centrifugal forces that, in turn, necessitate highstrength alloys that can withstand such forces without deformation or failure, although these might add weight. Lamination stacks can also be subjected to large stresses at high rotational speeds, meaning that strong bonding techniques and high-quality insulation materials are essential. Rotational speed also affects the selection of bearing materials because increased outward force can affect bearing lifespan and efficiency; thus, bearing materials must minimise friction and consequent wear. Advanced ceramic bearings, for example, offer low friction and high durability, but are more expensive than traditional steel bearings, more on which later. Taking the heat Motors with higher power density inevitably generate more heat, meaning that the tasks of cooling and, more broadly, thermal management become increasingly important. Engineers, therefore, are faced with selecting materials for heat sinks, cooling channels and thermal interfaces that require thermal conductivity to be balanced against weight and cost. Effective thermal design, such as employing thermally conductive potting compounds or implementing actively cooled stators, can help mitigate the peak temperatures experienced by motor components, thereby preserving efficiency and extending lifespan. The higher thermal conductivities of self-bonding varnishes (Backlack for example) on electrical steel, compared Typical radial flux motor showing laminated electrical steel stator core, copper windings and magnets held in place with Henkel’s Loctite EA 9536 epoxy-based, tolerance compensating bonding tape (Image courtesy of Henkel)
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