Laser welding zinc-coated steels is of major importance in automotive engineering and other industries to ensure cost-effective corrosion resistance of assemblies without requiring post-weld rework. However, the low evaporation temperature of zinc is causing welding defects, in particular melt ejections and spatter. In this work, in-situ experiments of laser beam welding were performed using high-speed synchrotron Xray imaging (up to 40,000 images/second) to determine the dynamics in the keyhole and in the weld pool and to provide detailed explanations for the formation of weld defects. A simplified sample geometry made it possible to weld zinc-coated steel sheets (DX51D Z275) in a lap joint (sheet thickness 1.25 mm each) with a fiber laser (COHERENT HighLight FL-ARM 8000) to describe fundamental phenomena. The high spatial and temporal resolution of the radiography allowed describing the acting mechanisms and their effect on keyhole and melt pool. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)

Laser welding of copper is of great importance for industrial applications, e.g., for manufacturing of electrical components such as hairpins. Solid state lasers are widely used due to the high power and beam brilliance, but the implementation can be challenging in terms of process instabilities and resulting weld defects, i.e., spatter and pore formation. In order to understand the formation thus avoid these defects, the development of the understanding of the keyhole and its interaction with the surrounding melt pool is required. In this paper, high-speed synchrotron X-ray imaging (frame rate: 20,000 Hz) demonstrated its capability to study the keyhole geometry to quantify and describe the dynamic behavior inside the workpiece. Thus, novel insights into fundamental processes are provided and a new methodic approach was introduced to describe the time-dependent behavior of the keyhole and its interaction with the melt pool during laser beam deep welding of copper (Cu-ETP/CW004A).

High processing speeds enormously enlarge the number of possible fields of application for laser processes. For example, material removal for sheet cutting using multiple passes or precise mass corrections can be achieved by means of spatter formation. For a better understanding of spatter formation at processing speeds of several hundred meters per minute, characterizations of the processing zone are required. For this purpose, a 400 W single-mode fiber laser was used in this study to process stainless steel AISI 304 (1.4301/X5CrNi18-10) with speeds of up to 600 m/min. A setup was developed that enabled a lateral high-speed observation of the processing zone by means of a glass plate flanking. This approach allowed for the measurement of several dimensions, such as the penetration depth, spatter formation, and especially, the inclination angle of the absorption front. It was shown that the loss of mass started to significantly increase when the absorption front was inclined at about 60°. In combination with precise weighings, metallographic examinations, and further external process observations, these findings provided an illustration of four empirical process models for different processing speeds.

Balancing processes require highly precise mass corrections especially in case of high-speed turning rotors. Material removal by means of cw-mode laser radiation represents a novel approach for industrial balancing applications in order to achieve sufficient removal rates. Thereby, spatter formation was identified as primary removal mechanism. In this study, the effect of reduced ambient pressures and atmospheres with varying concentrations of argon, nitrogen and oxygen on spatter formation and loss of mass were investigated for AISI304 (1.4301, X5CrNi18-10) and EN AW-2618 (DIN 3.1924) under the use of a 400W single mode-fiber laser.

Ultrasonic metal welding represents a well-suited technology for various applications, especially regarding joining of dissimilar materials or sensitive components. For electrical applications, joining stranded wire to contact elements represents a particular challenge, as both the compaction of the strand and the bond towards the terminal have to be realised by the ultrasonic process. This investigation focusses on the influence of local preheating on the joint quality of EN AW 1070 stranded wire to NiP plated EN CW004A terminals, especially regarding strand compaction and bond formation at the interface. The objective of locally preheating the work piece on the sonotrode averted side is to adjust the heat input gradient over the strand cross section and therefore facilitate the deformation of the wires close to the interface. Thus, the compaction process of the strand can be accelerated, vibration damping losses throughout the strand can be reduced and more welding power/energy is available for the bond formation at the interface. The results show a significant increase in failure load, accompanied by a reduced scattering of the values. Moreover, the compaction of the strand and the contact area towards the terminal could also be enhanced by the applied strategy.