Fronius CMT Twin provides solution to high speed optimum energy input welding of light gauge sheet
2 mins read
Fronius International's CMT Twin tandem welding process allows users to exploit two cold metal transfer (CMT) processes, or combine a CMT process with a GMA pulsed-arc welding process. This solution is particularly well suited to welding light gauge sheets at high speed, and for positional welding with high deposition rates yet without exceeding optimum thermal input.
To do this, the Fronius CMT Twin comes with two digital power sources that work independently of each other. This allows each weld process to be individually adjusted to suit the application and also means that – within the given physical limitations – any wire-feeder can be selected. Widely diverging wire feed speeds can be set and it permits great flexibility in terms of which weld processes are used. Users are able to control the thermal input and deposition rate very precisely to deliver optimum welding speed and seam quality with virtually any welding position and combination of materials, explains Fronius.
CMT Twin complements the existing TimeTwin high performance twin-wire weld process. TimeTwin uses two arcs (one leading, the other trailing, which may be pulsed if necessary), synchronised in 180° phase opposition. This means that there is relatively limited scope for diverging the wire feed speeds. Consequently, TimeTwin is the right choice when the priority is to raise the welding speeds and/or deposition rate. However, on welds requiring a large seam cross-section, there is a risk that excessive heat input may cause problems – as on fillet-welds where the seam will 'sag' if the weld-pool becomes too liquid. These cases call for a process in which the thermal input is lower and can be precisely adjusted.
The CMT Twin uses the CMT process in which the electrode is moved back and forward in a controlled manner during welding to manually assist droplet detachment. This inputs considerably less heat than a conventional dip-transfer arc. Other advantages of CMT are that hardly any spattering occurs, and the process is even more stable as the arc length is unaffected by the surface of the workpiece or the welding speed. As a result, it is possible to achieve high welding speeds; in the case of a fillet weld welded at the lap joint of two 2 mm steel sheets, these can be as fast as 4 m/min.
The question of which combination of processes is right for CMT Twin will depend on the requirements of each specific welding task, in terms of welding speed, deposition rate, gap-bridging and frequency of spattering.
For difficult fillet welds, for example, it is best to combine a pulsed arc (lead) with the CMT process (trail). While the leading electrode is fed at a high wire feed speed to achieve the desired deep penetration, the trailing electrode fills the seam at a low wire feed speed and with minimised thermal input. This combination, says Fronius, allows welders to achieve perfect results, even when welding a6 fillet welds in the horizontal-vertical (PB) position.
To ensure a perfect weld using the CMT Twin, the trail electrode does not start work until the lead electrode process has stabilised and the power source for the trail electrode has received a start-up signal.
