Study on fabrication of butt welded joints of thick plates by laserarc hybrid welding in horizontal position

Laser-arc hybrid welding (LAHW) is an advanced welding process that combines arc and laser welding as one molten pool. Compared with conventional arc welding, LAHW can be performed higher welding speeds with narrower grooves, and weld deformation can be significantly reduced. When LAHW is applied to construction of structural members, the welding is generally performed in a flat position because it is automatic welding system is applied from the viewpoint of safety in the work environment. / Flat position (PA), it is expected to be applied to many welds of large steel structures by applying LAHW to horizontal position. However, the application of LAHW in the construction of large structures is expected by expanding the applicable welding position. / In this study, butt joints with a plate thickness of 20 mm were fabricated in the horizontal position (PC) as a target of welding position in LAHW. By trial and error, referring to the welding conditions in the flat position, the welding conditions that produced a sound weld bead appearance were derived. However, molten metal was sagging at some of lower weld bead edge of the front bead. A sliding jig was designed to prevent the front bead sagging. As a result, the sagging was prevented and it was expected that the jig was effective in relaxing the shape of the weld toe for improving the fatigue strength of the joint. / In the construction stages of large structures, it is difficult to maintain a constant root gap over the entire length of the weld line, so it is desirable to extend the allowable range of the initial gap. Therefore, we attempted to process with an initial root gap of 1.5 mm. However, we were unable to find welding conditions that would avoid undercutting and melting-in, and confirmed that the applicable limit of the initial root gap is 1.0 mm for the construction method studied in this study.