Development and Application of the 3-Electrode MAG High-Speed Horizontal Fillet Welding Process

In the shipbuilding industry, welding efficiency without deteriorating weld quality has been desired to, as a consequence of the recent increase in the amount of shipbuilding and the size of ship hulls. Especially, an innovation in the welding efficiency and weld quality in horizontal fillet welding is a more important issue, because the amount of horizontal fillet welding work generally accounts for 70 percent or higher of the total welding work for ship hulls. One of high-speed horizontal fillet welding processes known as “Twin Tandem One Pool process” has been used in actual fabrication. However, the maximum welding speed of the twin tandem one pool process is approximately 1.5 m/min. In order to increase welding speed and welding quality of the twin tandem one pool process, the authors have employed an additional filler wire positioned between the two wires of the twin tandem one pool process. The additional wire carries DC-EN currents, opposite to DC-EP currents for the main welding wires, thereby reducing arc interference and arc blow at high currents. With this new technique, the authors have improved the stability of the weld pool formation at high currents. Consequently, horizontal fillet welding at a speed of 2.0 m/min on primer-coated steel plates has been achieved with excellent bead appearance, shape, and porosity resistance. Recently, this new process has just been installed in actual shipbuilding and it is confirmed that it truly contributes to improve welding efficiency and minimize repair time.