Adaptive control of back bead in V groove welding without backing plate

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 thus employed the switch back welding method for welding V groove joints without using backing plates. Moreorer, in the field work, there is misalignment of both metal plates during set-up. The suitability of the welding conditions for each root gap and the misalignment were verified by observation of the arc, molten pool and external appearance of back beads. Welding conditions, namely, welding current, wire feedrate, weaving width forward/backward stroke of switch back motion and welding speed, were controlled continuously according to root gap variations. Stable back beady were obtained for root gaps between 4.9 and 2.3 mm and and misalignments between 0.1 and 2.8 mm.