10 | LEARNING TO WELD | 10 |
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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 inch (10 to 12 mm) long.
The easiest way to tell whether the CTWD is the correct length is by listening to its sound. The cor- rect 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
Contact Tip
Wire Electrode
CTWD
4.The Correct Welding Speed
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 weld- ing speed. The ridge should be approximately 3/8” (10 mm) behind the wire electrode.
Most beginners tend to weld too fast, resulting in a thin, uneven, “wormy” looking bead. They are not watching the molten metal.
FIGURE 19
Molten puddle
Weld metal ridge
Base metal
Helpful Hints
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
Practice
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 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 inch (10 to 12 mm) and the gun is at proper angle.
Push Technique
