48 A fundamental distinction is made between processes integrated into the stamping process (interlocking, face or spot bonding) and those performed after the stamping process (welding, clamping, conventional bonding). The joining method is selected based on the specific application, the design of the electric machine and economic considerations. A wide range of new electrical steel grades has been developed and launched by voestalpine. In addition to magnetic and mechanical properties, the development process also takes into account the key factor of processability. In high-speed machines, electrical steel with low losses at high frequencies is used in the stator. High strength is required in the rapidly rotating rotor to keep the air gap between the rotor and stator as small as possible and to position any permanent magnets used as far outward as possible in the rotor. For the optimal design of the rotor and stator, two different grades of electrical steel with properties optimised for the respective component should ideally be used. To achieve optimal material utilisation in the stator, it is possible to segment it; however, this entails a complex manufacturing process. Alternatively, the use of post-annealable electrical steel is recommended, which offers high strength in its as-delivered state, combined with good polarisation and moderate losses. Post-annealable electrical steel is also suitable for use in the stator, particularly when followed by heat treatment of the stator laminations after the stamping process. This heat treatment results in optimal magnetic properties, and additionally eliminates all stresses and deformations introduced into the material during the stamping process. An interesting alternative is to focus on grades with high polarisations. This allows the same torque to be achieved with a lower magnetic field and reduces conduction losses in the copper windings. For dot bonding to join steel laminations, voestalpine has developed a wet-embossed structure on an electrical steel insulation varnish (Type C5). This is applied with a structured roller directly after the insulation step. The textured and functional surface modification prevents the adhesive from running and ensures controlled flow, resulting in a more homogeneous fracture pattern and significantly improved adhesive strength. Even the best electrical steel and the copper in the coils cause the rotor and stator to heat up during motor operation, which must be dissipated by cooling systems. A core element for cooling is the optimisation of self-bonding technology (Backlack). The toptyte Backlack process developed by voestalpine is a dynamic process optimised through targeted control of temperature, time and pressure, resulting in complete surface bonding while effectively preventing the Backlack from being squeezed out, which leads to increased process stability. The hot embossed Backlack process is particularly relevant for rotor applications with direct magnetic cooling, where minimal seal widths are required. Insulation Insulating the various parts of the motor is key, from the hairpins to the magnetic wire. Slot liner film such as Ajedium from Sysenqo is used to insulate the stator slots, replacing traditional paper and polyimide laminates. This polyphenylsulfone material has high heat resistance up to 180 C and a glass transition at over 230 C, allowing for thinner insulation, better thermal conductivity and increased copper fill to improve overall motor efficiency. For the magnet wire insulation, a polyetheretherketone material such as KetaSpire is used to coat magnet wires, providing superior electrical, thermal and mechanical performance required for high-voltage (800 V+) motors. High-performance polymers such as Torlon PAI, Amodel PPA and Ryton PPS are moulded into stator end caps, rotor parts and drivetrain bearings to withstand aggressive e-fluids and extreme temperatures. The process chain is characterised by tool-bound manufacturing steps that can only be adapted to varying design features with great effort and at high cost. July/August 2026 | E-Mobility Engineering The Speedformer line for hairpin bending (Image: Wafios)
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