Firepower MST 180i Operating Manual page 69

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 4-31.
E. Preheating
Suitable preheating of parts of the structure other than the area to be welded can be sometimes used to reduce distortion.
Figure 4-32 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 4-31: Principle of Presetting
B
Preheat
Dotted lines show effect if no preheat is used
Figure 4-32: Reduction of Distortion by Preheating
Figure 4-33: Examples of Distortion
1
Art # A-07710_AB
Figure 4-34: Welding Sequence
Manual 0-5339
Art # A-07707
Art # A-07708
C
Preheat
Weld
Art # A-07709
3
2
Block Sequence.
The spaces between the welds are
filled in when the welds are cool.
4
Art # A-07711_AB
Figure 4-35: Step back Sequence
Figure 4-36: Chain Intermittent Welding
Art # A-07713_AB
Figure 4-37: Staggered Intermittent Welding
4-15
Firepower MST 180i
1
2
3
Art # A-07428_AB
BASIC WELDING GUIDE