Extension of gap tolerance in square butt joint welding with Nd:YAG laser

Abstract

A feasibility of combined heat sources, which provide wide heat source distribution, was investigated to improve the weldability of a square butt-joint with a wide gap. Two welding methods were examined in this study : one was welding with twin YAG laser beams and a filler wire, and the other was welding with YAG laser -TIG arc hybrid welding and a filler wire. In twin beam welding of 5 mm thick Type 304 stainless steel, two 2 kW Nd : YAG lasers were used and arranged in tandem or parallel to the weld line. Without a filler wire, the gap tolerance to obtain a sound weld bead was approximately 0.7 mm and 1.6 mm with tandem and parallel arrangement, respectively. With Type 308 filler wire, the gap width of 2.2 mm was successfully welded with tandem arrangement, but lack of fusion occurred at the bottom part of the weld bead at the gap width of 1.9 mm. In the parallel arrangement welding with filler wire, however, good welding was achieved up to 2.2 mm by optimizing the distance of two spots. As for porosity, it was found that the number of porosity detected by the X-ray inspection test was different according to the beams arrangements. More porosity was generated near the fusion boundary in welding with the parallel arrangement. However, there was little porosity in the weld bead produced with the tandem arrangement. Welding with a 4 kW YAG laser combined with TIG arc with a filler wire was successfully performed in 8 mm thick stainless steel with the gap of up to 3.7 mm. Such YAG laser-TIG arc hybrid welding was found to be extremely effective to the improvement of gap tolerance. In this method, the number of porosity in the weld beads was much smaller than that in the welding with a single laser beam.