The nature of the undercuts formation

The electromagnetic nature of the undercuts formation has been established. As welding speed increases, the diameter of active spots decreases, heat input to the side edges of the bath reduces, the electrical resistance of the side edges decreasing. As a result, the amount of current flo wing through the bath side edges increases as well as increase of the field induction, electromagnetic force and the magnetic pressure, under which the liquid metal flows down from the bath edges, which leads to the undercuts formation. The regularity of the electrode shape influence and the metal thickness on the formation of welded joints and the undercuts formation is established, according to which, with a decrease of the metal thickness, the tendency to undercutting decreases as a result of a decrease in the ferromagnetic mass directed downward in the region of the bath side edges of the electromagnetic forces and magnetic pressure, what provides the qualitative welds formation and confirms the electromagnetic nature of the undercuts formation. A method has been developed for high-speed one-side welding with a composite electrode. This process provides a heat input increase to the side edges of the bath, electrical resistance increase, current decrease, electromagnetic forces and magnetic pressure, directed downward in the regions of the bath side edges decrease, high-quality seams without undercuts, the reverse roller on the flux cushion, the microstructure grinding and an increase in the toughness of welded joints