Key Manufacturing Processes for Automatic Assembly of Magnets in Permanent Magnet Motors

Permanent magnet motors are widely used in many fields due to their high power factor and high efficiency. Permanent magnet motors generally install magnets on the rotor to ensure the reliability of the stator electrical connection. Its structural types are:

Embedded magnets - the rotor punching is punched with magnet slots, and the magnets are installed in the slots. The symmetry of the magnet slots is fully guaranteed during the manufacturing of the punching, thereby ensuring the symmetry of the magnetic circuit;

Bonded magnets - the magnets are bonded to the yoke with a special adhesive; the process ensures that the magnets are uniform so that the magnetic circuit is symmetrical; the bonding is firm so that they will not come apart at a high linear speed.

In recent years, most of the series of products developed in the field of permanent magnet motors belong to the embedded magnet structure. In addition to general manufacturing processes (such as mechanical, thermal, and electric clamp processes), there are several key processes in the manufacture of permanent magnet motors:

(1) Due to the extremely strong adsorption force of the magnets, they are easily adsorbed when close to ferromagnetic materials (such as iron cores, shafts, etc.). During rotor assembly, the gap between the magnet and the rotor magnet slot is only about 0.1 mm. When the magnet approaches the rotor core, the extremely strong adsorption force directly adsorbs the magnet on the core and it is difficult to install it into the slot; once adsorbed, it is difficult to separate, which makes assembly extremely difficult and dangerous.

(2) If the rotor is not guided strongly and accurately during assembly, the stator and rotor will be adsorbed and locked by strong magnetic force, making it difficult to separate, resulting in assembly failure.

1 Rotor magnet assembly process

1. 1 Key points of the process

When assembling the magnet, efforts should be made to overcome the strong magnetic attraction of the magnet to the rotor core to ensure smooth assembly and correct polarity of the magnet to ensure symmetry of the magnetic circuit. For this purpose, detailed process tests were carried out, the process plan for magnet assembly was determined, the magnet assembly tooling and guide fixture were designed, and the polarity of the assembled magnet was qualitatively analyzed by reasonable means. The relative magnetic flux values of each slot magnet are close, that is, the magnetic circuit is symmetrical, so as to ensure the quality of magnet assembly.

1.2 Process

(1) To ensure accurate assembly, design fixtures;

(2) Separate the magnetic steel, check the polarity identification, and check the relative value of the magnetic flux to ensure that the magnetic flux of each pole is equal after assembly. At the same time, perform an appearance inspection to see if there is any damage. Although various brands of permanent magnetic materials have national standards to guarantee their basic performance, the enterprise standards of each factory are different. Moreover, the same brand of permanent magnetic materials, even if produced in the same factory, have different processes, which will cause performance deviations of permanent magnetic materials of different dates or different furnace numbers. Therefore, the above inspection work is very important. A motor should be equipped with magnetic steel of the same batch number to ensure the electromagnetic performance of the motor.

(3) Preparation of the work site: The rotor assembly work site is surrounded by non-magnetic guardrails and clear warnings are placed in conspicuous locations; the work site is cleaned and all corners of the site are cleaned with high-pressure air. No ferromagnetic waste such as iron filings and welding slag is allowed; non-magnetic fixtures, stainless steel non-magnetic wrenches, partitions, wooden supports, copper hammers, 3240 glass cloth boards, etc. are prepared.

(4) The stacked and punched rotor is blown clean with high-pressure air and wrapped with white cloth to prevent other impurities and waste from being carried during transportation; the rotor is supported (to make the rotor horizontal), and the magnetic steel slots on the rotor are checked again with a sample, and then the protective fixture is fixed to the rotor to prepare for the installation of the magnets.

(5) Each two magnets are separated by a non-magnetic plate with a thickness of about 15 mm, and the "N" and "S" polarities are marked on the two large surfaces (working surfaces) of each magnet, and the relative values of the magnetic flux are clearly marked. Magnets with the same values are basically placed together for easy assembly. Use your hands to separate the magnets on the wooden support. Note: Please do not operate with two magnets. Once they are adsorbed together, they cannot be separated. In addition, the adsorption process of the two magnets is very likely to injure people, which is very dangerous. The operator is required to assemble the magnets one by one during the operation. Keep the magnets away from ferromagnetic materials, and then install them into the magnet guide tooling, aligning them with the magnet slots on the rotor. At this time, pay attention to the "N" and "S" assembly polarities of the magnets and the relative values of the magnet flux. When assembling, do not fill all the magnets in a rotor slot. Instead, first install one magnet in each of the rotor magnet slots in sequence until the entire assembly is completed. During assembly, if a magnet is not assembled in place, you can use a copper rod or a non-magnetic hard rod to push the magnet into place. Note: Do not use too much force to avoid knocking and damaging the magnet.

(6) Use a compass to align the rotor outer circle slots to check the magnet polarity. After the polarity is qualified, assemble other fixing parts; finally, wrap the rotor as a whole with white cloth and prepare to flow into the next process.

2 Assembly process

2.1 Key points of the process

The rotor with magnetic steel has a strong overall adsorption force. The air gap between the stator and the rotor is small. During assembly, it is easy to cause collision between the stator and the rotor due to the strong gravitational force, which may cause the stator and the rotor to be adsorbed together and difficult to separate, or even scrapped, and easily cause personal injury. The traditional vertical or horizontal assembly process can no longer meet the requirements. Therefore, the key to the process is to ensure that the stator and the rotor are absolutely concentric before assembly.

2.2 Process

(1) Design a non-magnetic dummy rotor and use it to calibrate the base;

(2) Install the end cover and permanent magnet rotor;

(3) Assembly.

3. Process improvement

Combined with permanent magnet motor manufacturing, the process technology level can be improved in the following aspects:

(1) Considering rotor aluminum casting and magnetic steel assembly at the same time: When developing the UT series permanent magnet synchronous submersible motor, due to the complex rotor magnetic steel slot shape and the only 1 mm interval with the cast aluminum guide bar, the deformation of the magnetic steel slot after aluminum casting is difficult to control, and the scrap rate is high during motor manufacturing. For this reason, a rotor magnetic steel slot positioning guarantee plan is formulated in the process, and aluminum casting and magnetic steel assembly are considered at the same time. A series of devices such as slot trimming and magnetic steel assembly guide are configured to make it easy to assemble the magnetic steel in place, and the dynamic balance of the rotor is not affected, so as to meet the design accuracy requirements.

(2) "Layered" assembly of magnets: Since the structure of the punching sheet is more complex, each rotor is equipped with 80 magnets, and the magnets have strong adsorption and repulsion forces. Therefore, a "layered" assembly scheme is adopted in the process, and a precise guiding non-standard device is configured to enable the magnets to overcome the adsorption and repulsion forces and enter the slot smoothly. The assembly design position avoids the damage of the magnets, and at the same time improves the assembly efficiency of the magnets by one third, ensuring the correct polarity.

(3) Use of dummy rotor positioning assembly: Since the conventional assembly process causes the stator and rotor to be adsorbed and stuck during assembly and cannot be assembled, the stator and rotor are assembled in place through the combination of dummy rotor, stator assembly mechanism and lathe.

Ningbo Nide Mechanical Equipment Co., Ltd., was established in 2010, committing to provide customers with highly automated, intelligent, and flexible motor manufacturing solutions, and focusing on the production line of stator, rotor and final assembly of various motors.

We provide customers with a variety of electric motor manufacturing solutions, including BLDC motor assembly lines, DC motor manufacturing line, AC motor manufacturing line, permanent magnet motor manufacturing equipment, brushless motor manufacturing equipment, etc., which are mainly used in Automobiles, aviation machinery, industrial equipment, household appliances, etc. We can also customize complete brushless motor manufacturing solutions according to customer needs. If you need, please feel free to contact us.