Soft Magnetic Composite Materials (SMCs) adopt powder metallurgy technology, which has many advantages compared with traditional silicon steel sheets widely used in electromagnetic devices, and has been well developed in the past ten years. It has been applied and has become another optional material in addition to silicon steel sheets in magnetic materials. SMCs are molded by mixing high-purity iron powder and organic materials. The surface of the iron powder particles is covered with an insulating layer and an organic material for bonding, so the material has high resistivity, magnetic properties and thermal properties are isotropic. The electromagnetic device based on the three-dimensional magnetic circuit structure is more flexible in design and processing, and can realize the use of traditional laminations.
The magnetic circuit structure, which is difficult to achieve with a chip, also improves the heat dissipation effect. Unlike silicon steel sheets, compression-molded SMCs can be directly made into finished products or finished products close to their final shape and size, and are smooth at structural corners (such as the tooth grooves of motors), which can reduce insulation thickness and improve slot utilization. With careful design, devices using SMCs can outperform traditional two-dimensional magnetic circuit structures using silicon steel sheets.
However, SMCs also have their obvious disadvantages. Because they contain non-ferromagnetic materials, their magnetic permeability is lower than that of ordinary silicon steel sheets, and the better ones are only about 500-700, so this material is suitable for permanent magnet motors. In addition, the hysteresis loss of SMCs is relatively high, and the saturation flux density and mechanical strength are lower than those of silicon steel sheets. Due to the obvious differences in magnetic, thermal and mechanical properties between SMCs and silicon steel sheets, it is impossible to simply replace the silicon steel sheets in existing motors with SMCs.
In order to explore the application prospects of SMCs in motors, many foreign institutions have carried out active development and research in this field, and have achieved a lot of experience and results. These institutions include Newcastle University in the UK, Sheffield University in the UK, Laval in Canada University , Aachen University in Germany etc.
The idea of applying SMCs to electric motors dates back to the 19th century, but it was not taken seriously until the 1980s. In 1990, Kordecki and Weglinski introduced several soft magnetic powder composite materials and raised some problems in their application. In 1992, Jansson reported the processing and characteristics of SMCs applied to AC magnetic circuits. Since then, the development of SMCs and its application in motors has gradually become a hot topic, and many research results have been achieved. In addition, the improvement of SMCs material properties and processing technology, and the market Demand and other factors also promote the development of SMCs.
Generally speaking, it is quite difficult or even impossible to use laminated iron cores in small and complex magnetic circuit structures, and the use of whole steel structures will encounter the problem of large eddy current losses. While the one-shot molding of SMCs, the isotropic nature of magnetic and thermal properties allows designers to overcome many of the constraints encountered with laminated cores. At present, micro-motors and small-power motors are widely used in automobiles, robots, office and home automation equipment, and the annual demand is large, and the application of SMCs in these fields may generate huge economic benefits.
Soft magnetic composites adopt metallurgical powder molding processing technology, and the processing process contains three important steps: First, mixing pure iron powder and organic materials; Second, using molds to mold the composite material; Third, heat treatment after molding. Parameters such as material ratio, pressure, and temperature in these three processes have a great influence on the iron loss, resistivity, and mechanical strength of SMCs materials. Applying SMCs in the motor, the iron core processing can be molded at one time, the processing process is easy to control, and parts with quite complex shapes can be processed, the cutting amount is small, the metal loss is small, and the process flow is short. After processing, the dimensional stability of SMCs means Dressing and assembly will be easier, and mass production can reduce processing costs. For larger motors, the method of molding parts first and then assembling can be used.
The SMCs used in the motor are pre-mixed high-purity iron powder with an electrical insulating layer and organic insulating materials, and then molded. After the iron powder particles are molded, there is still a thin layer of insulation on the surface, which can greatly reduce the vibration in all directions. Eddy current loss, the total iron loss of SMCs is much higher than that of silicon steel sheets at low frequencies, and relatively low at medium and high frequencies of 400Hz and above, suitable for medium and high frequency applications.
Many efforts have been made in the development of SMCs motors abroad, and some results have been achieved. The earliest attempt was in the 1980s, but due to various reasons, the performance of the prototype is far from satisfactory. Since 1995, the research group of Newcastle University in the United Kingdom has cooperated with Höganäs AB in Sweden to study several SMCs motors with different structures and uses, including axial field motors, transverse field motors, claw pole motors, permanent magnet servo motors, and shaft motors. Radial hybrid flux motors and AC-DC dual-purpose motors, etc.; Sheffield University in the UK studied the prospect of SMCs for high-speed brushless permanent magnet DC motors; 1997-1998, Zhang Z and Profumo F in Turin, Italy, used Höganäs AB company to provide two axial flux permanent magnet brushless DC motors; in 2000, the Henneber research group of Aachen University in Germany developed a transverse magnetic field SMCs motor, which is a three-dimensional magnetic field and can make full use of the advantages of SMCs; Cros and others from Laval University in Canada have cooperated with Quebec Metal Powders to study SMCs motors since 1998. By 2001, they reported the development of two brushless DC permanent magnet motors and one AC and DC dual-purpose SMCs motor. The stator adopts a claw pole structure, and both the stator and the rotor use SMCs; in 2002, Cvetkovski of Napier University in the United Kingdom reported a SMCs permanent disk motor developed by them. This motor has axial flux, double stators, and a permanent magnet in the middle. Magnetic rotor; University of Technology Sydney, Australia, has been working with Höganäs AB since 1998
To study SMCs motors, based on its advanced magnetic material measurement and analysis technology, combined with magnetic field numerical calculation and optimization technology, the research group has successively designed and processed two claw pole permanent magnet SMCs motors and one transverse magnetic field SMCs motor, one of which is 500W The claw pole motor has an efficiency of 81% at a rated speed of 1800r/min.
Since now, Soft magnetic composites have been successfully used in many commercial applications. In terms of motor application, the Norwegian University of Norway and SMART Motor Company in Trondheim, Norway have started the application research of SMCs in electric vehicle drive motors since 1997; Electric motors are used in the braking system of vehicles; in the same year, Phase Motion Control, a servo motor manufacturer in Italy company, started mass production of the "Ultract T" series of brushless servo motors based on SMCs technology, which have a high slot-fill rate and a compact structure, and also achieve high torque density.
To sum up, in order to successfully apply SMCs to motors, the influence of its high shape freedom, high dimensional precision and low relative permeability on the performance of the motor must be fully considered. In addition, further research work must be carried out from the following aspects, summarized as following:
(1) Further research is needed on the three-dimensional magnetic field characteristics of SMCs in order to better design three-dimensional magnetic field motors; how to get the best match between the magnetic and mechanical properties of SMCs requires optimizing the composition of SMCs.
(2) In order to take advantage of the three-dimensional magnetic field characteristics of the material, the structure of the SMCs motor is generally complex, but its winding is simple, and the simplicity of the circuit can reduce the cost of the drive. Therefore, it is necessary to study the control method and design of the drive to maximize the performance of the motor.
(3) Improve the mechanical processing technology of SMCs and further reduce the processing cost to obtain commercial applications with good economic benefits.
(4) The motor structure suitable for the application of SMCs needs to be studied in order to achieve a good cost performance.
(5) In terms of motor design, advanced analysis methods should be used, such as accurate iron loss analysis, magnetic field numerical calculation, optimal design, etc.
