Holistic analysis of the influence of oxygen and other gas compositions on laser beam welding in a vacuum (OxiMeta)

• Applicant: Dr.-Ing. Simon Olschok
• Subject Area: Joining and Separation Technology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 572834102

Since the 1980s, laser beam welding in a vacuum has established itself as a promising process for overcoming the challenges of welding with CO2 lasers. The reduced working pressure not only suppresses the disruptive plasma, but also significantly increases the welding depth. Since then, studies have investigated the influence of the vacuum on the geometric characteristics of the weld seams, but have neglected the exact composition of the residual atmosphere in the vacuum chamber. However, the latest findings show that variations in the O2 and N2 content within the vacuum chamber can have a significant impact on the weld seam quality. The aim of this research is therefore to gain a deeper understanding of the influence of gas compositions and partial pressures in a vacuum on the quality of weld seams. A central element of the project is the investigation of the interactions between the O2 content at varying vacuums and the formation of flows in the melt. These flows are crucial for heat transfer and thus for the depth and quality of the welds. The results obtained so far indicate that an increased O2 content influences the surface tension of the melt, causing a reversal of the flow direction and achieving greater weld penetration. However, the underlying mechanism is not yet fully understood, as the addition of sulphur, which also increases the surface gradient, does not cause a reversal of the flow direction. Rather, it is postulated that the additional oxidation energy increases the vapor pressure in the capillary, which in turn leads to a change in the capillary geometry and consequently to melt pool flows. On the other hand, increased O2 content causes particles to form in the metal vapor plume, which scatter the laser beam more strongly, resulting in reduced intensity on the component, which inhibits the formation of capillaries or causes them to fluctuate. The project comprises several interlinked work steps in which the influencing factors of O2 and other gases on the weld seam quality are systematically determined by varying the partial pressures at varying working pressures. The dynamics of the molten pool are analyzed and their relationship to surface tension is investigated. The effect of the reaction enthalpies of gases on temperature conditions in the molten pool and, consequently, on surface tension is also taken into account. Finally, the project aims to apply the knowledge gained directly through an innovative approach with dynamic beam profiles. The working hypothesis is that the influence of the O2 content and other gases during laser beam welding can be determined separately for the weld metal and their effect on the geometric characteristics and chemical composition of the weld seam can be analyzed.

• DFG Programme: Research Grants