Advanced Welding Processes: Technologies and Process Control

Advanced gas tungsten arc welding 91
of the local magnetic fields (Fig. 6.12) techniques such as high-frequency
pulsing, dual-shield and magnetic stabilization are used.
6.3.9 A-TIG welding
The Paton Institute in the Ukraine has developed a novel technique for
extending the operating range of GTAW by the use of surface pastes. These
pastes are applied to the weld joint before welding either by brush or aerosol.
They have been shown to radically alter the weld profile; increasing depthto-width
ratio and eliminating the ‘cast-to-cast problem’. When these activating
pastes or fluxes are employed the process is referred to as A-TIG (Activated
TIG) welding or PA-TIG (Paton Activated TIG) welding. [101] The composition
of the fluxes varies depending on the material and application; in some cases
halide salts are used whilst in others simple oxides such as TiO 2 and SiO 2
have been shown to be effective. The exact mechanism by which the process
improvements are achieved is not fully resolved but it has been proposed
that surface active salts may influence the surface tension of the molten
material or release ionic species, which promote arc constriction, into the
arc.
6.3.10 Buried arc GTAW
The buried arc GTAW process was first developed in the USA, but has been
further developed in the Ukraine and Australia. The arc is initiated on the
plate surface, then, using the plasma force to depress the molten pool, the
electrode is lowered until it is below the level of the workpiece surface. The
arc then operates in a cavity as shown in Fig. 6.14.
This mode of operation enhances the thermal efficiency of the arc and
enables higher travel speeds to be used. It is normally only possible at very
high currents with mechanised systems.
6.3.11 High current GTAW
Further increases in current allow the GTAW arc to develop sufficient arc
pressure to form a keyhole and torches with capacities of up to 1000 A have
been developed. In this mode, the process offers a high travel speed alternative
to plasma techniques.
6.4 Control of GTAW and related processes
GTAW and related processes are capable of producing very high quality
welds but, for consistent results, the influence of the welding parameters on
weld geometry and quality must be identified and controlled.