It takes a long time to develop an electric drive device for an electric vehicle, usually as long as three years. During this period, new requirements may arise: for example, different power supply voltages, changes in installation space. Most of the development process can be completed with the aid of simulation, but it takes time to map in the hardware. Most importantly, the development of electric motor stator windings for electric vehicles is usually a well-known bottleneck, and 3D printing can avoid this development barrier with almost no molds.
Since traditional production involves complicated bending and welding processes, the time savings brought by 3D printing are especially rewarded with so-called hairpin windings. Usually the waiting time for new windings is sometimes six months or longer. The latest market development trend is to shorten the time to several weeks. In this issue, let’s learn about the cutting-edge development and application trends of 3D printing in motor stator windings.
According to Baidu Encyclopedia, the motor stator is an important part of motors such as generators and starters, and the stator is an important part of the motor. The stator consists of three parts: a stator core, a stator winding and a base. The main function of the stator is to generate a rotating magnetic field, while the main function of the rotor is to be cut by the lines of magnetic force in the rotating magnetic field to generate (output) current. my country’s current motor parts and accessories market is distributed in the southeast coast and the Yangtze River Delta. The stator winding refers to the winding installed on the stator, that is, the copper wire wound on the stator. Winding is a collective term for a phase or the entire electromagnetic circuit composed of multiple coils or coil groups. Most of the current AC motor stators use distributed windings.
According to different machine types, models and process conditions of coil embedding, the motors are designed with different winding types and specifications. The stator winding forms the relationship between the actual number of magnetic poles according to the number of magnetic poles of the motor and the distribution of the windings. It can be divided into two types: explicit pole and implicit pole. In the market, the German Additive Drives company uses 3D printing to additively manufacture motor stator windings and is expected to significantly improve the performance of parts. The maximum output power of the motor is limited due to its preheating, for example due to the allowable winding temperature. There are usually two levers to increase the power limit: first, to reduce losses with the same power, and second, to improve heat dissipation. The design of the winding plays a major role here because it is the main heat source.
The classic round wire winding has many limitations: copper conductors, winding technology and slot geometry must match. The conductors entangled with each other form a strong pattern. In addition, the round wire (the classic conductor shape) does not fit well with the trapezoidal groove in terms of geometry. As a result, each groove is half filled with copper, thereby forming a void. The relatively small conductor cross-section can ensure a large electrical heating loss.
The German Additive Drives company has achieved a higher degree of freedom through 3D printing. Through the powder bed-based SLM selective metal 3D printing process, the copper content in the groove is greater. Physically, this means the largest cross-section of the turns and a smaller resistance. The variable shape achieved by 3D printing is also good for heat dissipation, because each wire is in thermal contact with the so-called laminated core of the coil, so there are no hot spots.
Of course, in this process, the most important thing is how to reduce or avoid copper laser reflection?
Due to the excellent thermal conductivity and reflectivity of copper, this makes it difficult to handle copper metal inside the 3D printer. Although the current selective laser melting (SLM) 3D printing technology can be used to manufacture copper metal powder materials. However, in the process of laser melting, the absorption rate of copper metal is low, and it is difficult for the laser to continuously melt the copper metal powder, which leads to problems such as low forming efficiency and difficult control of metallurgical quality. In addition, the high ductility of copper makes post-processing tasks such as removing excess powder more difficult.
Fraunhofer ILT, one of the R&D members of ACAM, Aachen Additive Manufacturing Center, has launched the “SLM Green” solution. The laser used in the current powder bed laser melting technology is usually in the infrared spectrum of light. This is why the low absorption rate of copper occurs, and the energy of light cannot effectively melt the copper metal. Pure copper absorbs 80% of the energy from the electron beam melting process, while only 2% of the energy is absorbed in the red laser beam. The laser has become a breakthrough point for copper metal printing.
Unleashing the potential of 3D printing copper applications, a particularly important trend is the development of blue direct diode lasers for welding and 3D printing of copper materials. In 2019, Laserline launched a 1 kW product. Blue lasers process metals faster and more efficiently, and these metals have a poor ability to absorb the 1 micron infrared radiation produced by most industrial laser systems.
Shimadzu Corporation (Japan) has commercialized its BLUE IMPACT blue impact diode laser, which can generate 100 watts of power at high brightness. This product was developed by Shimadzu Corporation in cooperation with Osaka University, Japan, and is part of a Japanese national project.
The BLUE IMPACT laser incorporates many gallium nitride (GaN) blue laser diodes from Nichia Chemical Corporation (Japan). Since 2006, the efficiency has doubled and the output power has increased by an order of magnitude. A key application of Shimadzu’s 450nm blue diode laser is the 3D printing of copper materials.
With the development of lasers, the application of 3D printed copper has moved towards a benign development trend. According to the market observation of 3D Science Valley, in the 3D printing of stator windings, as winding tools are saved, up to 500 can be economically produced through 3D printing. Small batch motor stator windings below the station. Lower wire harness resistance, less loss, and shorter winding heads, all of which increase the value of the motor.
The current limit that 3D printed motor stator windings can withstand is about 1 megawatt, but for commercial prospects, it is more appropriate to focus on the power range of about 100 kW, because this is common in automotive traction motors.