Abstract
The electrification of the automobile industry leads to an increasing demand for high-performance energy storage systems. The more complex the battery pack, the more complex the electronic components will become. Very high currents have to be transported in a short time and very fast electrical switching processes have to be made possible. These requirements have an effect on the required quality of the electrical connection. Furthermore, a joining process is required that offers short cycle times and a high degree of automation. Laser micro welding with fibre lasers (1070 nm) meets the requirements placed on joining technology. Due to the high beam quality, very small spot diameters and thus very high intensities can be achieved. Copper materials of high purity are used to achieve the high conductivity of the electrical connection. This material, in turn, poses a great challenge to the welding process, since the reflectance for the beam sources mentioned is above 95%.This paper presents a way of significantly reducing the reflectance for copper connectors and thus making the joining process more efficient. For this purpose, the copper connectors are first pre-processed with an ultrashort pulse laser process, which significantly increases the surface area. In a second step, bead-on-plate welds are carried out on the structured surfaces and the absorption coefficient is determined during the welding process with the aid of a double integrating sphere assembly in comparison to a bare copper sample.
Highlights
Nitrogen oxide pollution represents a health risk in the modern world
This paper presents a way of significantly reducing the reflectance for copper connectors and making the joining process more efficient
This work investigates the possibility of increasing the efficiency of a laser beam micro welding process by using surface structures
Summary
Nitrogen oxide pollution represents a health risk in the modern world. According to statistics from the Federal Environment Agency in Germany, the level of nitrogen oxide pollution has tended to decline over the past 15 years, but the limit values set by the EU Directive 2008/50/EC are still exceeded at more than half of the traffic-related measuring stations [1]. Cells based on lithium ion are used for this purpose These individual cells are in turn connected to form modules and several of these modules form a battery pack. In addition to the battery pack, many other electrical and electronic components are required, such as a battery management system (BMS). Due to their electrical conductivity, copper connectors are used as electrical connecting elements between the cells, modules and peripheral electronics. This results in a large number of joints that have to withstand thermal, mechanical and electrical loads. Laser beam welding of copper is difficult due to material-specific properties [3, 4]
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