Welded structures are composed of a large amount of the horizontal fillet joint whereby high speed fillet welding significantly influences on improvement of productivity. The "Tandem Arc MAG Process" here referred to is a newly developed process which realizes high speed horizontal fillet welding without any undercut by means of holding a stagnant molten metal formed between two electrodes. The authors have prepared the model of a molten metal pool, and researched relations among the displacement of molten metal and solidification point along a toe of weld metal. This research has been accompanied by studies on a distance between electrodes where stagnant molten metal is stably maintained as well as on current distribution to the leading and trailing electrodes. At the same time, a welding wire has been developed, that has excellent blowhole resistance in high speed welding. As a result, high quality welds have been obtained in a welding speed about 3 times as high as that of the conventional process.
The system is being applied to field work and proved that a process capability is improved to a great extent, thus the system is contributing greatly to productivity.