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Abstracts Twin-wire metal inert gas/metal active gas (MIG/ MAG) arc welding is one typical type of the high-efficient welding technologies. In order to further improve the welding efficiency without increasing the welding heat input, a novel welding technology entitled twin-arc integrated cold wire hybrid welding was developed. The addition of cold wire not only increased the welding deposition rate but also improved the welding stability. In this paper, the influential mechanism of cold wire on welding stability was studied by the highspeed photography and electrical signal acquisition. It was found that the cathode spot could be stabilized on the surface of the weld pool by increasing the cold wire feed speed, which significantly improved the welding stability. The main reasons are as follows: the addition of cold wire significantly decreased the temperature of the liquid weld pool metal around the cold wire. This led to increasing the electron emission difficulty and reducing the gradient distribution of surface tension. Therefore, the cathode spot would be more likely to stabilize in the high temperature zone instead of drifting with the rear flow of the liquid weld pool metal. Besides, the cathode spot could also be stabilized because of the less dramatic fluid flow of the liquid metal. Finally, the welding stability was evaluated by a mathematical statistic method, which further verified that the welding stability could be improved with the increase of cold wire feed speed to a proper range.

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The metal transfer behaviour of self-shielded flux cored wire and the resultant welding spatter were investigated by using a high speed camera. Three modes of metal transfer were found, i.e. bridging transfer without arc interruption in explosive form or by surface tension, globular repelled transfer and droplet transfer, while the former two modes played a key role in the weld metal transfer. Correspondingly, the bridge explosion, discontinuous globular repelled process and the misalignment of droplets transfer were the main factors causing the welding spatter.