Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
9.3.1 GTAW
Cold wire GTAW
The GTAW process is easily adapted for narrow-gap operation since compact
welding torches are available and, in thinner sections, it is only necessary to
extend the distance by which the electrode projects from a conventional gas
shroud (Fig. 9.3). Some provision must also be made for feeding a filler wire
into the weld pool, but, again, conventional equipment is often suitable for
thicknesses up to 12 mm. For thicker sections a special torch design is
required to ensure adequate gas cover and reliable wire positioning. Torches
specifically designed for narrow-gap GTAW are usually elongated as shown
in Fig. 9.4, the shielding gas is delivered to rectangular slots either side of
the electrode and, in addition, gas may be supplied through holes in the side
of the blade.
Whilst the design is, in principle, fairly straightforward, it has been found
that the achievement of adequate gas cover without entrainment of air from
the surroundings is quite difficult. [183] Telescopic gas shrouds and flexible
surface baffles are often added to supplement the gas shroud as shown in
Fig. 9.5.
The process has been used for welding thicknesses of up to 200 mm,
particularly for circumferential welds and pipe-work.
Hot wire GTAW
The hot wire GTAW process described in Chapter 6 is particularly suitable
for narrow-gap welding, since it allows the deposition rate of the process to
Gas cup
Gas lens
Electrode
9.3 Narrow-gap welding with a conventional GTAW torch. (Note that
some auxiliary shielding may be needed.)