In the construction sites of chemical and electric power plants etc., many pipes are welded with conventional MIG/TIG arc welding methods in these days. Nevertheless, much time should be necessary to weld thick pipes with these welding methods because of their slow welding speed and multiple paths welding to fill up their joints. On the other hand, laser welding which can weld thick plate with low distortion at high speed needs small tolerance of gap. From these backgrounds, the development of a new welding process with a YAG laser where the accurate adjustment of a joint before welding is not necessary has been expected.
In this research, therefore, we developed an all position filler addition YAG laser welding process for stainless steel butt joint with large gap. As a result of the observation of the droplets from the filler wire during welding and the compositional analysis of the distribution of the filler wire in the welded bead, it was revealed that the droplets were scattered to the opposite direction of an irradiated laser beam and transported to the back side of the work piece due to the melted metal flow along a keyhole by evaporation recoil force of plasma/plume even if the welding was performed in overhead position.
As the result of applying this welding process to a SUS304 stainless steel pipe joint, which was 267.4 mm in diameter and 5 mm in thickness and 1 mm in gap tolerance, class 1 weld was attained in the radiographic test of JIS.
