Plasma hybrid welding with an integrated laser and sensor equipment

The objective of the "PiLS" research project carried out by iLAS and INP was to refine the plasma welding process in the current range up to 200 A without any filler material for steel sheets with sheet thicknesses between 2 mm and 5 mm. The aims were a substantially higher process speed, a raised weld quality as well as lower component distortions at system costs which are well below the costs of laser beam or laser beam hybrid processes. The arc attachment was to be influenced by the targeted and controlled utilisation of a low-power laser beam with certain focusing. However, contrary to the original assumption, it was not possible to spectroscopically prove any interactions of the laser beam with the plasma gas or the shielding gas (argon) or any interactions of the laser radiation with the metal constituents (material: S235), i.e. essentially iron. Instead of this, high-speed photographs served to reveal that the addition of the laser beam gives rise to an inversion of the flow in the molten pool which contributes to the formation of the keyhole. As a result of the investigations, it was possible to confirm the positive effect on the welding process exerted by the support of a low-power laser beam (less than 500 W). The welding speed as well as the process stability and the gap-bridging capacity were increased considerably with an added laser. Even difficult geometries and welding paths with corners and curves did not constitute any problems and the welding could be carried out reliably without any intervention in the process