Tandem-MAG welding is an advanced development of conventional MIG/MAG welding and is used where high production rate is required as very fast travel speeds in welding is easily achieved. Although, the two wires work in same weld pool, the electrodes are insulated from each other in separate contact tube and the welding parameters for each are different and set independently but share common welding torch and gas nozzle. The penetration is controlled by the lead arc whereas the trail arc is responsible for bead. In order to straighten the wires, two wire feeders are required for unwinding from the drum coils and spools. Irrespective of the two electrodes, feeders, different parameters, the possibility is made to use just one arc and single wire for welding.
The advantage of Tandem-MAG welding is that in such hi-tech welding, the distortion rate of the work piece is relatively very low. But the ultra high speed lap welding and high deposition fillet welding in Tandem-MAG comes at a high cost which is a disadvantage thereby making the initial investment on the project higher and does not find economically suitable for small production units whereas conventional MIG/MAG can be incorporated in any production line at much lower cost than Tandem-MAG system and this is the reason, Tandem-MAG welding machines are more seen in European countries such as England, France, Germany and Italy but not many installations are found in all other countries.
In Tandem-MAG welding, the synchronized pulse current controls virtually the spatter and potential arc blow problems. Further, the high deposition rate for thin and thick plates is made possible and complex shape can be welded at high speed welding. For these reasons, this process is suitable for robotic welding.
The Tandem-MAG welding equipment works on GMAW automated process. The parameters for power are controlled independently and the synchronized wire feeders are installed separately. The two arcs are generated by two different electrodes in one single gas nozzle.
There are two variants of Tandem-MAG welding which are discussed below in detail.
Synchronized pulsed welding
The synchronized pulsed welding process involves of so many parameters making the application trials become time consuming. The problems of arc interactions and process stability have to be taken care of and for controlling the process and for preventive measures, synchronized pulsed welding is chosen. In this case, lead arc is synchronized pulsed and the trailing arc is constant voltage for achieving desired maximum welding speed and gap bridging.
For short inter-distance of electrode, the synchronization of arc may be either between the power pulse peaks (phase-displacement) for each arc or the arcs working in-phase or anti-phase in the peak current timing and the type of synchronization for optimal performance is decided by welding engineer/programmer.
An advantage of choosing synchronized pulsed welding is the chance of operating on different weld currents and types of arcs which are helpful in optimizing the penetration and geometry of welding and good joint properties are achieved.
The constraints in synchronized pulsed welding may be productivity, difficulty in feeding wires when traveling at high speed as the material takes adequate time to melt for each current pulse and the pulses starts overlapping resulting in increased spatter and instability. The lengthy time for preparation of weld data and arc deflections are added limitations.
Non-synchronized welding (standard pulsed)
The non-synchronized welding is preferred with the combination of larger inter-distance between the electrodes to avoid arc interferences. In this welding process, stability is evident, spatter and arc deflections problems are substantially reduced. We can achieve better penetration too with larger inter-distance of electrodes and with short arc welding can be applied with optimal results on thin sheet material.
Tandem-MAG welding without synchronization is best suited for the electrodes distance maintained at approximately 20 mm making the process feasible and flexible where all arc types in combinations can be made to work. As the inter-distance between two electrodes goes on increasing, adverse effects will follow. The weld pool will start solidifying which is undesired between the arcs and the beneficial aspect of penetration is not seen.
The Benefits and Advantages of Tandem-MAG welding are:
1. The productivity can be doubled or more using this welding process.
2. Penetration is better.
3. Deposition is higher.
4. Process is independent
5. Robots can easily handle this welding process as the tracking can be done in any direction with either of the wire – leading or trailing for more flexibility in programming.
6. Higher speed in welding
7. Heat input is controlled and reduced
8. Reduced cycle time
9. Convenience of using both solid and cored wires of diverse diameters at the same time or independently.
Joakim Hedegard, Mathias Lundin – Tandem-MAG welding