The motor core is a key component in the motor, usually made of electromagnetic steel plates through specific processing and assembly. In the production process of the motor, the electromagnetic steel plate will go through a series of processes such as punching, laminating, and connecting. These processes have a decisive effect on the final performance of the motor core. In the manufacturing process of motor core, stress relief annealing is a very important step. The heat treatment process removes residual stress inside the motor core by heating it, thereby restoring and improving its magnetic properties, which is essential for achieving high efficiency and miniaturization of the motor. However, the traditional stress relieving annealing has some limitations, such as the use of large electric furnace and long heating time, which pushes up the operating cost.

Japanese researchers Kai Kai Yuichiro and others proposed a new heat treatment process, that is, the use of induced current to heat the motor core. In this method, a wire heating device is inserted in the motor core slot, and the induced current generated in the motor core is used as the heat source to achieve uniform heating of the core. Compared with the traditional heat treatment method without large equipment, even the complex shape of the core can be uniformly heated, and the heating time is short, the temperature distribution is uniform, with low cost and high performance advantages.

It is found that the motor core can be heated more evenly and the surface temperature difference can be reduced by inserting the heating wire into the core groove compared with the traditional heating wire configuration. By inserting two heating wires into each slot of the motor core, a uniform distribution of temperature can be achieved. This heating process can increase the heat treatment temperature of the motor laminated core to 600°C, allowing for more efficient stress annealing. The heating wire configuration not only improves the heating efficiency, but also shortens the temperature rise time.

Compared with the conventional heating wire configuration method, the magnetic properties of the motor core are significantly improved after stress relief annealing, especially in the middle part of the core, but the improvement is relatively small in the upper part, which may be related to the relatively low temperature in the upper part.

The researchers propose that future research directions will include further research into the magnetic characteristics of the back and teeth of the motor core to further optimize the configuration of the heating wire and reduce the magnetic characteristics differences.