Novel ways of using Nd:YAG laser for welding thick section austenitic stainless steel: Dissertation

Autogenous laser welding has shown many advantages over traditional welding methods in numerous applications. Still the process has disadvantages, which are impeding the applicability for the wider industrial use, e.g. tight tolerances in groove manufacturing, fixturing of the pieces against distortions and limited area of thicknesses. Owing to these limiting factors, a great deal of research work has been carried out to overcome these disadvantages by different ways. In many studies it has been pointed out that by using filler metal with laser welding, it is possible to reduce the above-mentioned limitations. The gap bridging ability is then increased strongly and the filler wire plays an important role also when welding thicker sections by using a narrow gap joint configuration and multi pass technique. Recently so-called hybrid welding, which is a combination of the laser beam and arc welding process, has been a target of great interest. A hybrid process seems to be very effective in overcoming the reductions of autogenous laser welding. Not only for the reason of filler wire addition, but also for the extra heat coming from the arc to make the process more effective by increasing the welding speed. In this study filler wire and an arc were used with an Nd:YAG laser in the way of a multi pass technique to weld thick austenitic stainless steel sections. To reduce the welding time and distortions, very narrow grooves were used. The applicability of the laser welding with filler wire was shown, up to a thickness of 20 mm using a 3 kW Nd:YAG laser. Hybrid welding was introduced to the narrow groove by the help of stabilizing, guiding and the contraction effect of the laser beam to the arc discharged. The applicability was shown for a groove angle of 10o and thickness of up to 30 mm.