In the tandem MIG/MAG process (sometimes referred to as 'twin-wire' or double wire welding), two wires are continuously fed through a special welding torch and are consumed to form a single molten pool. In current systems, the wires are electrically isolated from each other within the contact tip. Systems normally comprise two separate wire feed units and two power sources, so the wires can be operated independently i.e. with different wire diameters, current levels or operating modes (continuous or pulsed). In pulsed mode, the current in each wire is pulsed alternately to avoid magnetic interactions between the two arcs. Welding commonly takes place with the two wires in line along the joint line, although the torch can be rotated across the joint to give a wider weld bead.
Twin-wire GMAW systems have only recently become commercially available since 1996. The process offers high deposition rates - up to 24 kg/h at a travel speed of 0.8m/min has been claimed (1) - and travel speeds more than twice that of conventional GMAW have been reported (up to 5m/minute for a 2mm lap joint). At increased travel speeds, heat input is reduced and less distortion occurs. It is also claimed that tandem MIG/MAG reduces porosity because the elongated weld pool extends the degasification time. Metal- or flux-cored wires can also be used to further increase deposition rates.
However, this technology can only be used for mechanised or robotic welding because of the precision required in positioning the bulky torch. Joint accessibility is also restricted because of the torch size.
The tandem MIG/MAG process has been applied in the automotive industry, and in the shipbuilding, construction equipment, railway vehicle, and boiler construction fields for welding aluminium alloys, steels and other materials. Weld overlays have also been deposited using this technique.
1. Platz J: 'Two-wire technique increases the speed in MAG welding (Dvojdrotova technika...)'. Zvaranie/Svarovani vol.45, no.6, June 1996. pp.124-126. (English translation of text and captions pp.4-5).