In the tandem pulsed gas metal arc welding, the occurrence of arc interruption by the electromagnetic interaction between the two adjacent arcs becomes a problem. In order to clarify this problem, effects of interwire distance and Ar-CO 2 gas mixture ratio on an abnormal arc voltage and arc interruption are investigated. The abnormal arc voltage and the arc interruption frequently occur with pulse peak currents which are supplied alternately to two wires. In addition, both phenomena occur in trailing arc which is located on molten pool at base current duration remarkably. There is most number of abnormal arc voltage and arc interruption times in trailing when the interwire distance is 10 mm, because a deflected length of trailing arc by the electromagnetic interaction becomes the longest. Moreover, the CO 2 mixture ratio in shielded gas affects the occurrence of abnormal arc voltage and arc interruption. The abnormal arc voltage and arc interruption do not occur when CO 2 gas mixture ratio is equal to or less than 5%. However, number of abnormal arc voltage and arc interruption times increase rapidly with increasing CO 2 gas mixture ratio when CO 2 gas mixture ratio is over 10%.

Undercut and humping bead are the common defects that limit the maximum welding speed of tandem pulsed gas metal arc (GMA) welding. In order to increase the maximum welding speed, effects of the inclination angle, interwire distance and welding current ratio between the leading wire and trailing wire on bead formation in high speed welding are investigated. The undercut and humping bead is attributed to the irregular flow of molten metal towards the rear part of the weld pool. This irregular flow can be prevented by the trailing wire with a push angle from 5° to 13°, which provides an appropriate component of arc force in the welding direction. The irregular flow is also related to the distance between the leading wire and the trailing wire, and the flow becomes regular when the distance is in the range 9–12 mm. Moreover, the stabilisation of the bulge of the weld pool between the two wires, the presence of enough molten metal below the trailing arc, and the reduced velocity of molten metal flow towards the rear part of the weld pool, are essential to increase the maximum welding speed. These conditions can be obtained by adjusting the ratio of the leading arc current to the trailing arc current. A maximum welding speed as high as 4–4·5 m min−1 is achieved by setting the current ratio to a value ranging from 0·31 to 0·5.

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