Investigations in instable process conditions during laser beam microwelding of copper

主要目的是揭示在薄铜箔激光微焊接过程中使用NIR和混合NIR/维斯激光脉冲的基本效应。从实验观察以及从文献中已知，铜的激光焊接表现出非常低的再现性，此外，该过程非常不稳定。在该项目中，应验证工作假设，即这些不稳定性是（1）由于特定材料数量（如吸收和热扩散系数）的温度依赖性引起的正反馈回路，以及（2）表面形貌的修改和由此产生的吸收机制可能是这种行为的起源。因此，与NIR/维斯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。基于实验和理论研究的工艺窗口将位于铜箔之间可以实现可靠的接头。使用适当的传感器和闭环控制，该过程基本上也可以用单个NIR波长激光器来稳定。在中期时间尺度上，必须实现稳定和可重复的铝铜混合接头，因为电动汽车应用的需求不断增长。

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.