HD Manual Arc Welders
©2000 CIGWELD All rights reserved
26
12.2 Overcoming Distortion Effects
There are several methods of minimising distortion effects.
a) Peening:
This is done by hammering the weld while it is still hot. The weld metal is flattened
slightly and because of this the tensile stresses are reduced a little. The effect of peening is
relatively shallow, and is not advisable on the last layer.
b) Distribution of Stresses:
Distortion may be reduced by selecting a welding sequence which will distribute the
stresses suitably so that they tend to cancel each other out. See Figure 24 to
Figure 27 for various weld sequences. Choice of a suitable weld sequence is probably the
most effective method of overcoming distortion, although an unsuitable sequence may
exaggerate it. Simultaneous welding of both sides of a joint by two welders is often
successful in eliminating distortion.
c) Restraint of Parts:
Forcible restraint of the components being welded is often used to prevent distortion. Jigs,
positions, and tack welds are methods employed with this in view.
d) Presetting:
It is possible in some cases to tell from past experience or to find by trial and error (or less
frequently, to calculate) how much distortion will take place in a given welded structure.
By correct pre-setting of the components to be welded, constructional stresses can be made
to pull the parts into correct alignment. A simple example is shown in Figure 21.
e) Preheating:
Suitable preheating of parts of the structure other than the area to be welded can be
sometimes used to reduce distortion. Figure 22 shows a simple application. By removing
the heating source from
b
and
c
as soon as welding is completed, the sections
b
and
c
will
contract at a similar rate, thus reducing distortion.
Figure 21 - Principle of presetting
Figure 22 - Reduction of distortion by
preheating
a
c
b
