Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
Pre-weld sensing with optical sensors has been applied to large aluminium
structures fabricated by GMAW, [241] where, due to the complexity of the
component, a significant tolerance build up may occur. In this case, a laser
vision system (see ‘Structured light/vision sensors’ below) was used to track
and correct the weld path before welding.
Through-arc sensors. Through-arc sensing techniques utilize the change
in one or more of the electrical parameters of the arc during oscillation of the
torch tip to locate the joint position. These techniques are usually employed
in fillet, heavy-section V butt and narrow-gap welding situations. If the
welding head or the arc is oscillated laterally across the seam, the arc length
or electrode-to-workpiece distance will decrease as the joint edges are reached
(Fig. 10.14). In GTAW with a constant-current power source, the voltage
will decrease at the outer edges of the weld, whereas when a constantvoltage
power source is used for GMAW or SAW the current will increase.
The limit of torch travel may be controlled by the change in parameters such
that the centre of oscillation is always maintained on the joint axis. In GTAW
and plasma welding, the arc may be oscillated magnetically to provide the
joint scanning required for through-arc seam tracking. [242]
These through-arc tracking systems are now commonly available on welding
robots and have also been applied to the orbital GTAW of pipelines. [243]
12
10
8
6
4
2
0
Through-arc sensing
Voltage fluctuation across joint
(fixed torch height & constant
current supply).
Arc voltage
Distance across joint
10.14 Through-arc sensing.
Distance
along joint