45 E-Mobility Engineering | July/August 2026 E-motor production technology | Deep insight Steel “Depending on the motor design, different requirements are placed on the electrical steel used,” say Roman Sonnleitner, product manager electrical steel at voestalpine Steel Division and Ronald Fluch, lead engineer at voestalpine new business incubator. Key components of an electric motor are the electrical steel laminate stacks in the stator and rotor. These are constructed from stacked electrical steel laminations where the magnetic and mechanical properties of the material are crucial. Reducing the thickness minimises eddy current losses at high frequencies. It is also important to reduce electrical conductivity by adding elements such as silicon or aluminium, which also minimise eddy current losses. This increases the motor’s efficiency. In turn, this means lower power consumption and thus greater range with the same battery capacity. The sheet thicknesses used for e-mobility traction motors are generally ≤0.35 mm, most often ≤0.3 mm. At the same time, amplifying the magnetic field is a core function of the electrical steel used. Magnetic parameters for this amplification include permeability and polarisation, which can be improved through optimal grain orientation and adjustment of the alloying elements. However, an excessively Nick Flaherty gets up to speed on the challenges of e-motor production Manufacturing an EV powertrain with a permanent magnet synchronous motor or an induction motor requires fusion of precise metallurgy, high-speed automation and stringent thermal-electrical isolation. Optimising this process is a balancing act between maximising power density, ensuring noise, vibration and harshness (NVH) suppression and maintaining structural integrity under extreme centrifugal forces. Electric motors are reducing in size and increasing in speed, which puts increasing pressure on both the manufacturing process and the cooling. “Designs that focus on electrically excited synchronous motors [EESMs] to avoid the use of rare earth materials are getting close to the efficiencies of permanent magnets,” says Gerhard Meister, group vice president for the Electrification Business Unit at AVL. “An e-motor speed of 30,000 rpm allows you to downsize a 120 kW e-machine to the size of a drinks can and a beer case would accommodate such a unit that would weigh just 30 kg. So, we are looking at the cost – we have developed an e-axle where we can use the same stator with industrial, EESM or permanent magnet motors with the same electronics. “There is a trade-off in materials – whether the magnets or the copper – and the benefits of the savings from downsizing are much higher than the investment in the manufacturing, The tolerances of the bearings are tight but the material cost reductions outweigh the additional production cost,” he says. The production workflow is broadly divided into three core stages: stator fabrication, rotor assembly and final integration. An e-axle showing the e-motor (Image: AVL) Stator fabrication and hairpin winding The stator core is constructed from ultrathin (typically) electrical steel laminations, coated with an insulating oxide layer to minimise eddy current losses. These sheets are progressively stamped and stacked using interlocking or welding techniques to form the stator core. Modern EV OEMs heavily favour hairpin winding technology over traditional continuous wire winding owing to its superior slot fill factor – often exceeding 70% compared to 45% for round wire. See the focus on page 32 of this issue for more details on hairpin windings. In the forming process, solid, rectangular copper wires are stripped of their enamel insulation at the tips, CNCbent into a precise ‘U’ or hairpin shape and then automatically inserted into the lined stator slots. The open ends of the hairpins are mechanically twisted to create the correct phase architecture. Laser welding (usually via high-power fibreoptic laser) fuses the tips with CNC precision, maintaining strict control over the heat-affected zone to protect the surrounding enamel.
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