Presentation Information
[P1-43]Advantages of Manufacturing Radially Oriented Ring Magnets through Hot Forming and the Impact on Electrical Machines
*Martin Krengel1, Stefan Schmülling1, Lukas Schäfer2, Semih Ener2, Burçak Ekitli2, Oliver Gutfleisch2 (1. WILO SE (Germany), 2. TU Darmstadt / Functional Materials (Germany))
Keywords:
NdFeB ring magnets,Hotforming,Synchronous Motor,Cogging torque
This paper examines the innovative manufacturing process of hot pressing and hot forming in detail. The focus is on the unique features of this process, which arise from the fact that the anisotropy or orientation of the magnetic materials is not achieved through an external magnetic field in a press, as is conventionally done. Instead, a thermo-mechanical orientation is applied, which can be varied through a specially chosen pressing direction. Instead of the usual forward or backward extrusion, this paper employs transverse pressing relative to the cylinder axis. Figure 1 illustrates this setup.
This distinctive approach allows the creation of magnet geometries that are oriented in such a way, through the selection of punch geometry that they induce extraordinary effects in air gap induction (Examples of punches in Figure 2). These effects are particularly advantageous for use in high-performance electrical machines, as they can significantly enhance the efficiency and performance of these devices.
Figure 3 shows the two-dimensional cross section of a small electric motor with a rated power of 90W for heating applications. The stator has 6 slots and 3 phases. It is equipped with a tooth coil winding providing a fundamental 4-pole flux distribution. The rotor consists of an anisotropic ring magnet and back iron, pressed onto a stainless-steel shaft. The radially oriented ring provides a rectangular flux distribution within the airgap region. The advantage of those magnets is a higher power density compared to injection moulded or compression moulded isotropic solutions. Due to the rectangular flux density cogging torque and noise often becomes a problem. A common measure to reduce noise and vibration is skewing. Skewing allows to reduce harmonics but also effects the peak torque and efficiency of a motor.
Figure 4 shows the same motor with a special shaped anisotropic ring. This ring can be manufactured by transverse hot forming (c.f. Fig. 1 and Fig. 2). The stator shows no major difference in flux distribution. Nevertheless, the airgap induction becomes more sinusoidal without loss of performance. While keeping the motor performance constant, the shape provides significant reduction in cogging torque and vibration. While the overall torque is reduced by 3% from 400 mNm to 388 mNm, cogging torque is reduced by 163%.
Transverse hot forming offers many possibilities to affect the properties of magnets directly. On possibilities is to improve the motor behaviour regarding noise and vibration by improving the shape of a ring magnet.
This distinctive approach allows the creation of magnet geometries that are oriented in such a way, through the selection of punch geometry that they induce extraordinary effects in air gap induction (Examples of punches in Figure 2). These effects are particularly advantageous for use in high-performance electrical machines, as they can significantly enhance the efficiency and performance of these devices.
Figure 3 shows the two-dimensional cross section of a small electric motor with a rated power of 90W for heating applications. The stator has 6 slots and 3 phases. It is equipped with a tooth coil winding providing a fundamental 4-pole flux distribution. The rotor consists of an anisotropic ring magnet and back iron, pressed onto a stainless-steel shaft. The radially oriented ring provides a rectangular flux distribution within the airgap region. The advantage of those magnets is a higher power density compared to injection moulded or compression moulded isotropic solutions. Due to the rectangular flux density cogging torque and noise often becomes a problem. A common measure to reduce noise and vibration is skewing. Skewing allows to reduce harmonics but also effects the peak torque and efficiency of a motor.
Figure 4 shows the same motor with a special shaped anisotropic ring. This ring can be manufactured by transverse hot forming (c.f. Fig. 1 and Fig. 2). The stator shows no major difference in flux distribution. Nevertheless, the airgap induction becomes more sinusoidal without loss of performance. While keeping the motor performance constant, the shape provides significant reduction in cogging torque and vibration. While the overall torque is reduced by 3% from 400 mNm to 388 mNm, cogging torque is reduced by 163%.
Transverse hot forming offers many possibilities to affect the properties of magnets directly. On possibilities is to improve the motor behaviour regarding noise and vibration by improving the shape of a ring magnet.
