Tweco 200DC Inverter Arc Welding Machine - Manual (Page 45)

WELDSKILL 200 AC/DC INVERTER
Manual 0-5207 4-9 BASIC WELDING GUIDE
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