Effects of locally adjusted intensity distributions on the mechanisms leading to spatter formation in deep penetration laser welding at high welding speeds

• Applicants: Professor Dr.-Ing. Jean Pierre Bergmann; Professor Dr. Thomas Graf
• Subject Area: Joining and Separation Technology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 503306266

Spatter formation is a major challenge in welding of steel with solid-state lasers. In particular, this phenomenon occurs at welding speeds between 8 m/min and 20 m/min. To reduce spatter formation, there are currently various approaches being examined. Based on investigations on partial penetration welding, the use of locally adjusted intensity distributions has proven to be a very promising approach for the reduction of spatter formation. By using multicore fiber systems as well as superimposed laser beams, a significant reduction of spatter formation could be observed even at high welding speeds. However, the effect of the locally adjusted intensity distributions on the reduced spatter formation has only been proven empirically so far. Therefore, it is not known in which way the thermo- and fluiddynamics in the melt pool and the keyhole are effected by the locally-adjusted energy input, nor which of these mechanism do actually contribute to spatter formation (spatter mechanisms). In addition, it is not known which specifications for the intensity distributions are required to achieve a spatter reduction, since the relevant and influencing spatter mechanisms are not yet sufficiently understood and known. Therefore, in a first funding period the project aims to quantify the interactions of locally adjusted intensity distributions regarding the effects on the thermo- and fluiddynamics in the melt pool and the keyhole to identify the relevant mechanism of spatter formation. For this purpose, the investigations are focused on the determination of resulting temperature fields and gradients, geometry and fluctuations of the melt pool and the keyhole as well as on the determination of resulting flow patterns of the melt pool and the escaping metal gas flow. Moreover, the spatter formation will be described by appropriate quantities. Using an empirical correlation between the measured effects and the correlating spatter formation with an adjusted weighting for each of the measured quantities, the relevant mechanisms for spatter formation are to be determined. Within a second funding period, it is planned to derive optimized locally adjusted intensity distributions to achieve a maximum spatter reduction. Finally, it should be possible to quantify the overall interactions of locally adjusted intensity distributions in order to reduce spatter formation.

• DFG Programme: Research Grants