Advanced Welding Processes: Technologies and Process Control

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Advanced welding processes
Cross-sectional area (mm 2 )
6000
5000
4000
3000
2000
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10 mm parallel gap
20 mm parallel gap
60 degree V
0
10 20 30 40 50 60 70 80 90 100
Thickness (mm)
9.1 The principle of narrow-gap welding – the effect of joint
preparation on weld cross-sectional area.
more uniform joint properties. It has been reported by several investigators
[181] that the mechanical properties of narrow-gap joints are better than
those achieved with conventional V butt configurations. This is probably due
to the progressive refinement of the weld bead by subsequent runs and the
relatively low heat input. One practical problem that may arise on thicker
sections is the difficulty of post-weld inspection and repair. This leads to the
requirement for consistent welding performance and adequate in-process
control and monitoring.
9.3 Narrow-gap welding processes
The narrow-gap welding processes have certain common features:
∑ they use a special joint configuration;
∑ they often require a special welding head/equipment;
∑ they usually require arc length control/seam tracking;
∑ they may require modified consumables.
The simplest joint configuration is the straight, parallel-sided gap with a
backing strip, but there are a number of variants of preparation based on the
process and the nature of the application. Some typical preparations [182]
are shown in Fig. 9.2. The gap width also varies depending on the process
and the equipment; from around 8 mm for GTAW up to 20 mm with SAW.
It is possible to use standard automatic welding equipment with some processes,
but with thicker sections (over 100 mm) 1 it is necessary to use purpose-
1 The limiting thickness for changing from conventional to special-purpose narrow-gap
equipment is not fixed but depends on the application and the process economics.