Laser welding process for flat wire motor stator manufacturing

Flat wire motor manufacturing was initially suitable for high-power motors and high-power generator sets in the industrial field, and later extended to the vehicle field. Many application functions on vehicles use flat wire motors, such as automotive generators, starters, EPS motors, main drive motors, P2 hybrid motors, etc. Automobile starter rotor, automobile generator stator, flat wire winding, high current density and high overload capacity.

Due to the growth in demand for electric vehicles, motor manufacturers are seeking more productive processes for high-capacity, high-quality welding. The realization of a higher degree of automation is the fundamental guarantee for high-capacity demand. As a result, flat-wire stators largely prevailed: manufacturers began using compressed air to insert rectangular copper wires (called "flat wires" because of their shape) throughout the stator slots, instead of in the Round copper wire is wrapped around a single stator slot. Typical edge lengths for rectangular cross-sections of flat copper wires are between 2 and 4 mm. The process enables higher production speeds and can be easily automated. Because flat copper wire is stiffer than round wire, the alignment of the flat copper wire in the motor can be better controlled. The larger the fill factor, the higher the thermal load capacity and the greater the motor power. The copper wire is coated with an insulating layer and requires local ablation (paint removal of the flat copper wire) at both ends to achieve contact, here processed using a pulsed laser. Laser processing offers an 80% increase in productivity compared to mechanical processing such as planing and milling.

Flat Wire Motor Stator Welding process

After the pin insertion process, the raised ends of the flat copper wires on the stator must be welded together one by one to achieve optimal physical contact. In preparation for welding, the wire cutter cuts and separates the flat copper wire, forming a sheared smooth surface at the copper wire port, which is then twisted together or fixed in place. There are considerable positional tolerances here, and the flat copper wires cannot always be perfectly aligned with each other. Tolerances involving height offsets and gap widths can have a negative impact on the welding process, since excessive tolerances will reduce the effective joint surface. On the other hand, the welding process has very strict requirements on weld tolerances. This challenge must be addressed during the welding process.

In order to optimize the flat copper wire welding process and obtain better solder joints, the swing path of the laser welding beam needs to be optimized. Here, if the flat copper wires are to be connected on their short sides, a linear wobble welding trace is particularly recommended; on the other hand, if the flat copper wires are to be connected on their long sides, a circular or oval wobble welding trace is to be selected. Through this process, high-speed welding can be achieved while minimizing the formation of spatter and pores. The achieved welds have high tensile strength and good penetration, allowing the flat copper wire to obtain optimal conductivity. In addition, the almost zero overhang of the laser welding joint makes it possible for the core groove and the flat copper wire to be positioned closer together. This means that a more compact motor design can be achieved when the installation space of the motor is fixed.

The existing welding methods mainly include laser welding or argon arc welding. Both methods melt copper through instant high temperature to form solder joints, thereby realizing the electrical connection of windings.

However, laser welding or argon arc welding technology has two main disadvantages:

First, laser welding and argon arc welding require an instantaneous high temperature to melt the copper, which can easily damage the enameled wire film around the welding point and reduce the insulation reliability;

Second, there are a large number of hairpin coils or single-sided coils that constitute the stator winding of the flat wire motor, which requires a large number of solder joints. Laser welding or argon arc welding generally welds the solder joints one by one, which seriously affects the production efficiency of the flat wire stator.

In the flat copper wire welding process, the combination of disk laser, high-speed optical galvanometer and image capture system simultaneously meets the high quality (low spatter and pores) and high productivity requirements of motor flat copper wire welding. In addition, optical galvanometers also provide extremely flexible solutions for various weld shapes of target components.