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LEARNING TO WELD
3.
The Contact Tip to Work Distance (CTWD)
The Contact Tip to Work Distance (CTWD) is the distance from the end
of the contact tip to the work. See Figure 18.
Once the arc has been established, maintaining the correct CTWD
becomes extremely important. The CTWD should be approximately
3/8" to 1/2" (10 to 12 mm) long.
The easiest way to tell whether the CTWD is the correct length is by
listening to its sound. The correct CTWD has a distinctive "crackling"
sound, very much like eggs frying in a pan. A long CTWD has a
hollow, blowing or hissing sound. If the CTWD is too short, you may
stick the contact tip or nozzle to the weld puddle and/or fuse the wire
to the contact tip.
FIGURE 18
4.
The Correct Welding Speed
Contact Tip
Wire Electrode
The important thing to watch while welding is the puddle of molten
metal right behind the arc. See Figure 19. Do not watch the arc itself.
It is the appearance of the puddle and the ridge where the molten
Puddle solidifies that indicates correct welding speed. The ridge
should be approximately 3/8" (10 mm) behind the wire electrode.
Welding too fast is a common problem. Pay attention to the molten
bead that forms as you weld. If you notice that your bead is thin,
uneven, and wormy looking, reduce your travel speed.
Figure 19
Weld metal ridge
Push Technique
1.
For general welding, it is not necessary to weave the
arc, neither forward or backward nor sideways. Weld
along at a steady pace. You will find it easier.
2.
When welding on thin plate, you will find that you will
have to increase the welding speed or else burn
through, whereas when welding on heavy plate, it is
necessary to go more slowly in order to get good
penetration.
3.
When welding sheet metal 16 gauge (1.5 mm) and
lighter, heat buildup may cause part warpage and burn
through. One way to eliminate these problems is to use
the back-stepping method illustrated in Figure 15.
The best way of getting practice in the four skills that enable you to
maintain:
1.
Correct welding position.
2.
Correct way to strike an arc.
3.
Correct Contact Tip to Work Distance.
4.
Correct welding speed is to perform the following
exercise. Refer to Figure 16. Use PROCESS
GUIDELINES in the Instruction Manual and Application
Guide on the inside of wire feed section door for
selection of welding wire, shielding gas, wire feed
CTWD
speed, voltage, and for range of metal thicknesses that
can be welded.
1.
Position face shield to protect face and eyes.
2.
Learn to strike an arc by positioning the gun over the
joint and touching the wire to the work.
3.
Press gun trigger, hold gun so contact tip to work
distance Is about 3/8" to 1/2" (10 to 12 mm) and the gun
is at proper angle.
Molten puddle
Base metal
1
HELPFUL HINTS
PRACTICE
Capítulos
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