Investigations in instable process conditions during laser beam microwelding of copper

主要目的是揭示近红外和近红外/可见光混合激光脉冲激光微细焊接薄铜箔过程中的基本效应。从实验观察和文献中都知道，铜的激光焊接重复性很低，而且焊接过程非常不稳定。在项目中，这些不稳定性的工作假设应该得到验证：(1)由于特定材料数(如吸收系数和热扩散系数)的温度依赖而产生的正反馈回路，以及(2)表面形貌和由此产生的吸收机制的修改可能是这种行为的根源。因此，与近红外/可见光脉冲激光器以及铝箔的比较研究有望提供有关工艺行为的更多细节。实验将伴随着动态有限元模拟。在实验和理论研究的基础上，确定了实现铜箔可靠连接的工艺窗口。使用足够的传感器和闭环控制，单台近红外波长激光器也可以基本稳定这一过程。在中期内，由于电动汽车应用的需求不断增长，必须实现稳定和可重复的铝-铜-混合接头。

The main objective is to reveal the fundamental effects during laser microwelding of thin copper foils using NIR and mixed NIR/VIS laser pulses. From experimental observation as well as from literature it is known that laser welding of copper exhibits a very low reproducibility and, moreover, the process is quite unstable. Within the project the working hypothesis should be verified that these instabilities are (1) due to a positive feedback loop originating from the temperature dependence of specific material numbers like absorption and heat diffusion coefficient, and (2) modifications of the surface topography and the resulting absorption mechanisms can be the origin of this behavior. Therefore, comparative studies with NIR/VIS pulsed lasers as well as with aluminum foils are expected to deliver more details about the process behavior. The experiments will be accompanied by dynamic FE simulations. Based on the experimental and theoretical investigations a process window will be located where reliable joints between copper foils can be realized. Using adequate sensors and closed-loop control the process can basically be stabilized also with single NIR wavelength lasers. In the midterm timescale stable and reproducible aluminum-copper-hybrid joints have to be realized because there is a growing demand in electromobile applications.