202 AC/DC INVERTER BASIC WELDING
BASIC WELDING GUIDE
4-8
Manual 0-5239
Art # A-07706_AB
Weld
Permanent Upset
Contraction
with tension
Figure 4-20: Parent Metal Contraction
Overcoming Distortion Effects
There are several methods of minimizing 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 Figures 4-20 through 4-23 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 4-21.
E. Preheating
Suitable preheating of parts of the structure other
than the area to be welded can be sometimes used
to reduce distortion. Figure 4-22 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.
Art # A-07707
Figure 4-21: Principle of Presetting
Art # A-07708
B
Preheat
Preheat
Dotted lines show effect if no preheat is used
Weld
C
Figure 4-22: Reduction of Distortion by Preheating
Art # A-07709
Figure 4-23: Examples of Distortion
Art # A-07710_AB
1
Block Sequence.
The spaces between the welds are
filled in when the welds are cool.
2
3
Figure 4-24: Welding Sequence
Art # A-07711_AB
4
3
2
1
Figure 4-25: Step back Sequence
