ARC WELDING METHOD

PURPOSE:To execute a follow-up of a weld line by providing an alternating magnetic field, vibrating an arc in the left and right directions being orthogonal to the weld line, detecting and comparing an arc current or voltage of the left and right of the vibration, and controlling a torch position so that its deviation becomes zero. CONSTITUTION:AC is impressed to an iron core coil 38 through an amplifier 42 from a generating circuit 40, an alternating magnetic field is formed in the direction of a weld line in the vicinity of an arc 22, and the arc 22 is vibrated in the direction orthogonal to the weld line. Subsequently, in accordance with an integration instruction and a storage instruction in a half period of an arc vibration which is outputted by a logic generating circuit 44 by an AC signal of the circuit 40, a detecting signal of an arc current by a shunt 26 is inputted alternately to storing circuits 30, 32, is integrated and stored, it is subtracted by a differential amplifier 34, and a signal corresponding to a shift of the vibration center is obtained. As a result, a direction of the shift is discriminated by a motor controlling circuit 36, and a motor 4 is controlled so that the shift becomes zero. In this way, the automatic follow-up of the weld line of a torch can be executed.