Tweco 175 TE Arcmaster - Manual (Page 40)

arc master 175 te oPeration
Operation 4-12 Manual 0-5116
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
4-25 through 4-28 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 4-22.
E. Preheating
Suitable preheating of parts of the structure other
than the area to be welded can be sometimes used
to reduce distortion. Figure 4-23 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 4-22: Principle of presetting
Art # A-07708
B
Preheat Preheat
Dotted lines show effect if no preheat is used
Weld
C
Figure 4-23: Reduction of distortion by preheating
Art # A-07709
Figure 4-24: 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 4-25: Welding sequence
Art # A-07711_AB
4
3
2
1
Figure 4-26: Step back sequence
Art # A-07712
Figure 4-27: Chain intermittent welding
Art # A-07713_AB
Figure 4-28: Staggered intermittent welding