Why are holes drilled in the corners of some embedded rotor magnet slots?

In the application of permanent magnets, some embedded rotor magnet slots feature small holes at the corners. What is the purpose and benefit of this design?

The primary benefit of the small holes at the corners of the magnet slots is to improve magnetic saturation. Under certain operating conditions, the sharp corners of the magnet slots may cause uneven magnetic field distribution, thereby affecting the magnetic saturation of the magnets. By drilling holes at the corners, the issue of magnetic field non-uniformity caused by sharp corners can be effectively mitigated, reducing magnetic saturation. Circular or curved holes allow for a more uniform magnetic field, helping to improve the motor’s efficiency and stability.

In embedded rotors, the corners of the magnets are typically areas where stress concentration is particularly pronounced. Sharp corners can easily cause excessive localised stress, leading to fractures or damage in the more brittle parts of the material. By incorporating small holes at these corners, stress can be distributed more evenly, preventing stress concentration and enhancing the overall mechanical strength of the rotor. This design not only extends the service life of the rotor but also reduces mechanical failures caused by excessive stress.

Magnetic steel is typically made of brittle materials and is susceptible to damage during processing. Particularly in high-speed, high-temperature environments, magnetic steel may develop cracks or sustain damage due to excessive mechanical stress or temperature fluctuations. The design of small holes at the corners effectively reduces the brittleness of the edge areas, protecting the magnetic steel from direct impact by external pressure.

In addition to addressing magnetic and mechanical issues, the corner holes serve as vent holes, facilitating the smooth drainage of excess adhesive. The above outlines some of the benefits of incorporating corner holes in the magnet slots of embedded rotors; we hope this information proves useful to you.