2007 Volume 25 Issue 1 Pages 86-94
The formation of stable back beads in the first layer weld during one side multilayer welding is important to achieve high quality welded metal joints. The authors employed the switch back welding method for V groove joints without backing plates. In this welding method, the torch is moved backward and forward like switch back. First, the torch is moved forward and backward with high speed to discharge the arc to the root edges of the base metal. Next, the torch is moved forward with slow speed to form the weld bead. The mentioned torch motion is repeated. The authors tried to apply the switch back welding method to the butt welding to joint the disc with the flat metal plate without the backing plates. The tip of the electrode wire is changing due to a curve of its wire extension in accordance with a rotation of the torch axis. Even if the teaching is achieved before the welding, the weaving center is shifted from the gap center. The controller of the seam tracking was designed to prevent steady state error by using the B spline function to estimate the variation of the welding line. The burn through takes places during the welding. In order to investigate temperature distribution, the numerical simulation of the switch back welding was carried out. From its result, the gap was changed due to the heat distortion.
During the welding, the authors propose a method to detect the gap by processing the weld pool image taken with a CCD camera. In the robotic welding system, the switch back welding is carried out by using giving the gap and the weaving center at the beginning of the welding. The performance of this welding method was verified by carrying out the welding experiments.
