Progress in laser-MAG hybrid welding of high-strength steels up to 30mm thickness

Within the European project HYBLAS, funded by the Research Fund for Coal and Steel (RFCS), significant progress has been achieved in laser-MAG hybrid welding of thick high-strength steel plates up to 30 mm. Results are presented in this paper. Fraunhofer ILT as leader of the HYBLAS work package "Process development and production of welds", has performed extensive investigations with CO2 lasers up to 20 kW and Nd:YAG lasers up to 7.2 kW in order to expand the hitherto existing state-of-the art regarding e.g. weldable thickness, bridgeable gaps, hot crack prevention and fatigue properties. The work resulted in qualified process rules for parameter settings like focal position, laser-arc orientation and laser-arc distance as well as characteristics for adaptation of laser power, welding speed and wire feed rate depending on thickness and gap width. A simple physical model of the gap situation during single pass hybrid welding has been derived, which explains the process l imits and reveals the crucial parameters for welding thick sections without drop-through. Hybrid welded large scale demonstrators show excellent mechanical properties. Moreover, new hybrid techniques for very deep welds and for special seam shaping capabilities have been developed and demonstrate even further potential for applications in shipbuilding, earth-moving equipment and steel construction.