In recent years, laser processes have taken an ever-increasing market share in the manufacture of components. The development of new, improved beam sources with corresponding systems technology and the decreasing investment costs of the beam sources are important keys to this success. Particularly, high frequency beam oscillation has great potential in laser beam welding and cutting. The main obstacle for the widespread breakthrough of high frequency (HF) beam oscillation is the still insufficient understanding of the underlying physical mechanisms. Gaining a deeper insight is essential for process optimization. The in situ observation with x rays enables the visualization and analysis of these highly dynamic processes inside the workpiece. The goal of the performed experiment described in this paper was to in situ analyze the structural evolution of and defect generation in laser welding beads of different aluminum alloys. A fiber laser (max. 600 W, cw output power) including a beam scanner control system for rapid beam guidance was used. Of general interest was the comparison between static and oscillated beam guidance and the effects on the joining procedure. This paper shows the initial results of the analysis of the melt pool behavior and seam formation as well as the formation of seam irregularities during the laser process. In the simplest case, radiographs were taken, i.e., 2D projections of the x-ray absorption coefficient distribution within a material. Thereby, recordings from 10 000 up to 40 000 fps could be generated. Furthermore, tomoscopies—the continuous acquisition of tomographic (3D) images, up to 100 tomograms per second—could be generated with proven equipment, whose main components are a high-speed rotation stage and a camera system. The findings will help to get a better understanding of keyhole phenomena as well as effects of turbulent melt flow such as pore formation and guide to solutions for preventing them. Hence, initial results of high frequency beam oscillation processes including melt pool degassing and porosity reduction will be shown and discussed.

中文翻译：

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用X射线观察铝基合金激光束焊接工艺的初步探索

近年来，激光加工在零件制造中占据了越来越大的市场份额。利用相应的系统技术开发新的，经过改进的光束源以及降低光束源的投资成本是取得成功的重要关键。特别地，高频光束振荡在激光束焊接和切割中具有很大的潜力。高频（HF）光束振荡的广泛突破的主要障碍是对底层物理机制的了解仍然不够。获得更深刻的见解对于流程优化至关重要。在原位观察X射线能够在工件内部，这些高动态过程的可视化和分析。本文所述的进行实验的目的是原位分析了不同铝合金的激光焊珠的结构演变和缺陷产生。使用了包括光束扫描仪控制系统以进行快速光束引导的光纤激光器（最大600 W，CW输出功率）。普遍感兴趣的是静态和振荡波束引导之间的比较以及对连接过程的影响。本文显示了分析熔池行为和接缝形成以及激光过程中接缝不规则形成的初步结果。在最简单的情况下，将进行射线照相，即材料内X射线吸收系数分布的2D投影。因此，可以生成从10000到40,000 fps的记录。此外，X线断层扫描-连续获取断层（3D）图像，经验证的设备可以产生高达每秒100层的X线断层图，其主要部件是高速旋转台和摄像头系统。这些发现将有助于更好地了解锁孔现象以及湍流熔体流动（例如孔的形成）的影响，并为防止这些现象的解决方案提供指南。因此，将显示和讨论高频光束振荡过程的初步结果，包括熔池脱气和孔隙率降低。