Laser welding of copper is being used with increasing demand for contacting applications in electric components such as batteries, power electronics, and electric drives. With its local, non-contact energy input and high automation capability enabling reproducible weld quality, this joining technology represents a key enabler of future mobility systems. However, a major challenge in process design is the combination of energy efficiency and precise process guidance in terms of weld seam depth and defect prevention (i.e., spatter and melt ejections) due to the high electrical and thermal conductivity of copper. High-power lasers in the near infrared wavelength range (𝜆 ≈ 1 μm) and excellent beam quality provide an established joining solution for this purpose; nevertheless, the low absorptivity (≤5%) advocates novel beam sources at visible wavelengths due to altered absorptivity (40% at 515 nm) characteristics as an improved tool. In order to understand the influence of laser wavelength and process parameters on the vapor capillary geometry, in situ synchrotron investigations on Cu-ETP with 515 nm and 1030 nm laser sources with the same spot diameter are compared. The material phase contrast analysis was successfully used to distinguish keyhole and melt pool phase boundaries during the welding process. A significantly different sensitivity of the keyhole depth in relation to the feed rate was found, which is increased for the infrared laser. This behavior could be attributed to the increased effect of multiple reflections at 1030 nm.

Full-penetration laser beam welding is characterized by a weld seam whose depth equals the material thickness. It is associated with a stable capillary and is therefore widely used for welding of sheet metal components. The realization of lightweight concepts in car body production requires the application of high-strength aluminum alloys that contain magnesium as an alloying element, which significantly influences the evaporation temperature and pressure. This change of the evaporation processes influences the geometry of the capillary and therefore its absorptance. In order to quantify the influence of magnesium on the capillary, their geometries were captured by means of high-speed synchrotron X-ray imaging during the welding process of the aluminum alloys AA1050A (Al99.5), AA5754 (AlMg3) and AA6016 (AlSi1.2Mg0.4). The 3D-geometries of the capillaries were reconstructed from the intensity distribution in the recorded X-ray images and their absorptance of the incident laser beam was determined by the analysis of the reconstructed 3D-geometry with a raytracing algorithm. The results presented in this paper capture for the first time the influence of the magnesium content in high-strength aluminum alloys on the aspect ratio of the capillary, which explains the reduced absorptance in case of full-penetration laser beam welding of aluminum alloys with a high content of volatile elements. In order to improve the absorptance in full-penetration welding, these findings provide the information required for the deduction of new optimization approaches.

For joining metallic materials for battery applications such as copper and stainless steel, laser beam micro welding with beam sources in the near-infrared range has become established in recent years. In laser beam micro welding, spatial power modulation describes the superposition of the linear feed motion with an oscillating motion. This modulation method serves to widen the cross-section of the weld seam as well as to increase the process stability. Temporal power modulation refers to the controlled modulation of the laser power over time during the welding process. In this paper, the superposition of both temporal and spatial power modulation methods is presented, which enables a variable control of the weld penetration depth. Three weld geometries transverse to the feed direction are part of this investigation: the compensation of the weld penetration depth due to the asymmetric path movement during spatial power modulation only, a W-shaped weld profile, and a V-shaped. The weld geometries are investigated by the bed on plate weld tests with CuSn6. Furthermore, the use of combined power modulation for welding tests in butt joint configuration between CuSn6 and stainless steel 1.4301 with different material properties is investigated. The study shows the possibility of precise control of the welding depth by this methodology. Depending on the material combination, the desired regions with maximum and minimum welding depth can be achieved by the control of local and temporal power modulation on the material surface.

In the recent years, laser beam welding has become an established joining process, especially for components in the electrical powertrain (copper applications). However, laser beam welding of copper is generally considered to be difficult, particularly due to its high heat conductivity and due to its low absorptivity using laser sources with a wavelength of 1 μm. The resulting welds show numerous weld defects, such as pores and spatters. Using “blue” lasers with a wavelength of 450 nm promises a smoother welding process with less spatters. Therefore, a blue diode laser with increased absorptivity in copper materials was developed by Laserline and used for welding copper. In this contribution, the results of welding copper using blue lasers with respect to the penetration depth and the resulting weld quality are discussed. In addition, investigations by Bosch at the electron-synchrotron DESY with a blue diode laser enabled us to have a look into the material during welding. Consequently, melt pool dynamics and capillary dynamics were analyzed with respect to the formation of weld defects and will be discussed as well. Furthermore, it is demonstrated that it can be beneficial to use a so-called spot-in-spot beam shaping tool to further improve the melt pool dynamics and, therefore, the resulting weld quality.