Influence of the metal vapour on the beam properties and the capillary during laser beam welding by investigations at ambient pressure and in vacuum

• Applicants: Professor Dr. Thomas Graf; Professor Dr.-Ing. Uwe Reisgen
• Subject Area: Joining and Separation Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 463452146

In deep penetration laser welding, the welding process is strongly influenced by the process atmosphere and the ambient pressure. This is particularly evident in the formation of the capillary and the welding depth. The vapor capillary and its stability is a key element in the deep penetration laser welding process and the formation of the capillary has a significant influence on the occurring processes during the welding process as well as on the resulting weld seam. The formation of the capillary is determined by both the ambient pressure and the incident intensity distribution, which in turn is influenced by the process emissions in the beam path.Depending on the ambient pressure and oxygen content in the process zone, the generated metal vapour partly condensates and solidifies into metallic particles of different sizes or reacts with the available supply of oxygen to form metal oxides. Depending on the size and type of the emissions, a mixture of the mechanisms absorption, scattering, thermal defocusing and beam deflection occurs. A quantification of the influence of the individual effects on the resulting beam profile and the welding process, the capillary formation, and finally the weld seam has not been performed so far. Nor have the effects of process emissions and the purely ambient pressure-dependent effects on the capillary geometry been separated from each other.The aim of the proposed project is therefore to separate the influence of the individual interaction mechanisms on the laser beam by the targeted influencing of the process emissions by adjusting the ambient atmosphere and the ambient pressure and to quantify their effect on the intensity distribution and the capillary formation.To achieve this, the first step is to quantitatively and qualitatively determine the composition of the process emissions under regular welding conditions and the influence of the reduction of the ambient pressure of a controlled atmosphere on the process emissions. Furthermore, the effect of process emissions with different compositions on the beam properties will be investigated. For this purpose, beam measurements of a test laser beam, which propagates coaxially to the working laser beam through the process emissions, are combined with ray-tracing in order to separate the influencing factors of the process emissions on the beam properties. Furthermore, the purely ambient pressure-dependent effects on the formation of the capillary geometry are investigated, as well as the effects of the beam properties, influenced by the process emissions, on the formation of the capillary geometry. Finally, this should allow to separate and quantify the effects of the different influencing factors on the beam, the capillary formation and the welding result.

• DFG Programme: Research Grants
• Major Instrumentation: Bearbeitungsoptik für koaxiale Überlagerung von Arbeits- und Messstrahl
• Instrumentation Group: 5980 Faseroptische Bauelemente