Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
Current
150
100
50
0
–50
–100
–150
Electrode positive
Cleaning
Heating
Time (ms)
Electrode negative
6.4 The effect of square wave AC operation on GTAW.
output to be obtained. It is reported [34] that a unit of this type is capable of
reversing the polarity of the output within 100 ms and gives effective cathodic
cleaning on aluminium alloys with 20 ms electrode negative polarity and
4 ms positive (i.e. a pulse frequency of 41.66 Hz).
6.3.4 Cold- and hot-wire feed additions in GTAW
A useful feature of the GTAW process is the ability to control weld pool
temperature and size by means of independent cold-wire addition. This is
used in manual welding operations to control the weld profile and penetration,
particularly in positional work. Mechanized wire addition by means of a
separate hand-held wire dispenser or a torch-mounted feed system are available
for manual operation, but, although these can increase the operating efficiency
of the process, they tend to be restricted to simple weld geometry and joints
with good access.
In automated GTAW, the wire is normally fed at a set constant rate and the
element of control exerted by the welder is lost. A mechanized wire-feed
addition system, called ‘Dabber TIG’ 2 , which feeds the wire with a
reciprocating motion similar to that used by manual welders, has been
introduced. [92] The frequency of wire addition may be set between 2 and 10
Hz. A controlled low heat input deposit may be achieved and the technique
2 Dabber TIG is a trade name of the Hobart Company Ltd.