One of the key challenges in Automating GTAW is the
consistency of fit up and ovality of the work piece / joint. As when
the torch is fixed and the job is rotating any change in the
tungsten to work piece will result in a change in voltage. As the
distance reduces the voltage reduces and if the distance
increases so does the voltage. Any change in voltage can result in
inconsistence weld penetration.
Automatic Voltage Corrector is a motorized slide controller which
helps maintain the same voltage by altering the arc gap. This
ensures constant voltage, constant arc gap during welding. So
when the work piece moves closer to the tungsten, the arc voltage
reduces from the set level, the motorized slide moves upwards
away from the work piece to maintain the same arc voltage.
Similarly when the work piece gets away from the tungsten, the voltage increases from the set
level, the motorized slide starts moving back towards the work piece to maintain the set voltage
level. The speed at which this correction happens can be adjusted to suite the welding speed
and avoid unwanted movement of the torch.
Weaving or oscillating the torch setup can help cover a larger area. This can help take care of
slight fit up mismatches and capping runs as well.
Using AVC Slides we can do root welds in Automated GTAW. This can be coupled with
Weavers, Oscillators to get wider weld beads along with Cold / Hot Wire feeding. This can bring
up welding speeds and deposition rates for GTAW process. For example in Figure 1 we can
see a 300mm dia. pipe to pipe joint made for Auxiliary piping of power plant skids. The 8mm
thick pipes were welded together to get X-Ray quality welds using AVC based automation
system. The joint was welded in 2 pass, root with filler and capping pass. This system replaced
the existing practice of welding root with GTAW and then fill-up with GMAW.
This AutoTig Head consisting of AVC, Weaving , Cold Wire Feeder can be added on to any
existing Column / Boom Setup to make a complete automated GTAW welding.
This can speed up the welding speeds upto 150mm/min to 200mm/min. With repeatable results
on quality and productivity.