Ultranarrow GMAW process with newly developed wire melting control system

An ultranarrow gap GMA welding (UNGW) process with less than 5 mm gap width has been developed in which the arc pole is strongly oscillated over the groove wall in the thickness direction. A simulation model for wire melting tip behaviour with dc pulse current has been proposed and verified by observation of the tip motion in the UNGW groove. This simulation can define the optimum welding conditions to avoid welding defects. A synchronised control system consisting of a pulsed arc current waveform with cyclical variation of wire feed rate has been successfully developed on the base of the computer simulation. The newly developed UNGW system makes it possible to reduce arc heat input density sufficiently to produce an excellent weld joint with a narrow (1–2 mm) HAZ. Penetration shape control can also be achieved by this control method.