With the development of new energy vehicle industry year by year, the explosive growth of electric vehicle production and sales, the demand for high-performance motors is also increasing, flat wire winding with its unique advantages over round wire winding has gained rapid development, become the hot direction of new energy vehicle motor research and development.
Drive motor is one of the core components of new energy vehicles, Hairpin motor, as the name implies, is a "hairpin" motor; when the drive motor from the traditional round enameled wire structure into a flat copper wire structure, the shape of the stator winding also changed, becoming like a hairpin. In the manufacture of the stator, the winding is shaped like a hairpin, then threaded into the stator slot and out the other end, and the end of the hairpin is soldered together.
Hairpin motor with its small size, high slot full rate, high power density, good NVH performance, heat conduction and heat dissipation performance and other performance advantages, as well as the economic advantage of reduced cost of consumables, the application in new energy vehicles is increasing, and the penetration rate of flat wire motors in China is expected to reach 70%-80% in 2025. (Data from the network)
Existing welding methods are mainly laser welding or argon arc welding, both of which are used to form a welded joint by melting copper through instant high temperature, thus realizing the electrical connection of the winding. There are also other companies that use CMT cold welding or other welding methods.
Comparison of HairPin welding methods
Advantages of laser welding: Concentrated beam energy density, high heating efficiency, fast welding speed, so the deformation of the base material is small, the metal in the non-melting zone is less affected by heat, and the welding strength is high, which can meet the requirements of various motor indicators.
Laser-Copper Interaction
The interaction between laser and copper material can be roughly divided into three stages: the first stage, the material absorption rate of the laser is low, for the heating stage; the second stage, as the temperature of the material increases, the absorption rate of the laser increases, for the melting stage of the material; the third stage, the temperature of the material continues to rise, the absorption rate of the laser continues to rise, to achieve the establishment and expansion of the melt pool effect, this stage directly affects the welding seam width and depth of the weld, which affects the strength of the weld.
Flat copper wire material for copper, copper in laser welding is a relatively difficult material to weld, in the solid state on the 1μm wavelength of the initial absorption rate of the laser is only 5%, after reaching the melting point absorption rate instantly becomes about 15%, as the absorption rate becomes higher heat input into the molten pool also increases, the internal reaction of the molten pool, welding spatter also increases.
The welding difficulties of Hairpin: 1, brittle phase 2, porosity
Both brittle phase and porosity are welding defects that can cause Hairpin to fail the tensile test after welding.
Methods to reduce or avoid defects:
- The use of small core warp or spot ring spot laser, vibration lens focus / collimation ratio as small as possible, so that the spot at the energy density is higher, reducing the generation of welding defects.
- Reasonable optimization of the trajectory of welding and laser energy control, remelting will be more likely to produce brittle phase.
- Can properly add protective gas to reduce the oxidation of copper welding process, copper oxides and copper impurities in the form of oxides are mostly in the weld in the form of brittle phase.
Laser welding points
- Hairpin assembly requirements are high, the terminals must be neat and consistent, splicing against the tight, if necessary, using the cutting process to repair neat.
- Choose the right light source and oscillator optical ratio to reduce the generation of welding defects.
- Control the size of the mushroom head, the mushroom head is too large and easy to cause the welding process melt pool down, the mushroom head is too small to carry the area is not enough, resulting in substandard tension test.
- The use of air knife protection to reduce the loss of lenses.
- Adopt special jig to position the hairpin.
- The gap between the two pin angles should not be too large, otherwise the laser will ablate the insulation layer of the lower end of the hairpin.
Technical features of products
1. Two external control modes of the laser are convenient for customer applications:
- Dual analog voltage control laser "point" and "ring" part of the output power, you can work in the process of real-time power changes.
- Internal preset "point" "ring" energy ratio, a single analog voltage control of the overall output power.
2. Laser models are available in a wide variety of styles and flexible options.
① laser has 4kW, 6kW, 12kW, 20kW four power band a total of 9 typical configuration laser
② Laser output mode "point", "ring" and "point-ring symbiosis" three modes
3. Support EtherCAT bus, low latency and high fidelity transmission
4. Optical and electrical separation design, compact, safe and reliable
5. Self-developed high-efficiency signal combiner and spot homogenizing device, stable output energy and power, uniform distribution
6. For the beginning and end of the welding track "slow rise and slow fall" processing, to solve the problem of closing arc pit
7. Different welding process parameters and waveforms can be stored, up to 256 groups
