Advanced Welding Processes: Technologies and Process Control

Welding automation and robotics 221
was able to produce consistent high-quality joints in a time scale which
would have been impossible to meet using manual welding. A similar system
was used [264] in the fabrication of 96 m of butt welds in a 24.4 m diameter
crane tub in 35 mm thick BS 4360 50D material. It was estimated in this
application that the cost saving was some £30000 compared with vertical
welding using the manual metal arc process.
These tractor-based systems are very adaptable and with a little ingenuity
may be configured to suit a wide range of applications. An example of the
use of a standard tractor system for a novel application is shown in Fig. 11.3.
The application required the stainless-steel nut insert to be welded at intervals
into large carbon-steel plates. A leak-proof fillet weld was required and
skilled GTAW welders were not available. GMAW welding with a smalldiameter
stainless-steel filler wire and a helium/argon/CO 2 shielding gas
was found to give acceptable bead profile, but access and the high welding
speed made it difficult to achieve consistent quality using manual techniques.
The tractor and track system were therefore adapted as shown; a GMAW
torch was substituted for the normal oxy-fuel cutting system, and an insulated
peg was used to locate the assembly in the insert (and protect the thread from
spatter damage). The total cost of the mechanization system was under $2000
and a large number of high-quality joints were produced with an average
welding time of 20 s. This example illustrates that, although these systems
are usually most suitable for long weld seams with simple geometry they
may also be applied to much smaller joints. They are also more easily applied
with the consumable electrode processes (GMAW, FCAW, SAW) but special
systems for GTAW and plasma welding are also available. This type of
automation still requires constant supervision by a welder, but the welder is
removed from the immediate vicinity of the heat source and the exposure to
fumes is reduced; the fatigue factor is also reduced.
Tractor drive
Track
Central location pin and
spatter guard
Gas
shield
11.3 Fender nut welding system.
Nut insert
GMAW torch