Laser welding components for electric vehicles with a high-power blue laser system

Welding copper to itself and other metals is challenging using conventional welding techniques. The process window for welding copper with an infrared (IR) laser, resistance welder, or an ultrasonic welder is very narrow. In the case of the infrared laser, the high reflectivity at these wavelengths makes it difficult to couple the power into the material and control the temperature of the weld puddle. In the case of ultrasonic and resistive welding, the high thermal conductivity of the material and the tendency to create particles cause less than ideal welds. These fundamental problems can be overcome by using a laser with a wavelength that is highly absorbed by these materials. This paper will present recent welding results using a fiber coupled 500-W blue laser system coupled to a welding head to deliver a 215 mu m spot size and an average power density of 1.6 MW/cm(2). These results will be compared with the authors' previous results from a free space delivered laser system that was the prototype for the 500-W fiber coupled laser. The fiber coupled laser system performance exceeded the free space performance because of two factors: (1) the welding was able to be performed at normal incidence (90 degrees) to the surface allowing for greater power coupling into the copper and (2) a smaller spot size with a higher power density was used (1.6 MW/cm(2) vs 398 kW/cm(2)). Tests on welding battery components, including stacks of foils, buss bars, hairpins (for motors), and other components, with no porosity and no spatter will be covered. Both copper and mixed metals welding results will be presented. Tests have also been performed with 1 kW of laser power from a processing head with a 400 mu m spot size and an average power density of 800 kW/cm(2). Both systems have enough power density to initiate the keyhole welding process in copper, stainless steel, and aluminum. The difference in welding speeds for these two systems will be compared in this paper.