To produce good welds, the tungsten electrode
must be shaped correctly. The general practice is to use
a pointed electrode with dc welding, and a spherical
end with ac welding. It is also important that the
electrode be straight, otherwise the gas flow will be
off-center from the arc.
SHIELDING GASES.--Shielding gas for gas
tungsten-arc welding can be argon, helium, or a
mixture of argon and helium. Argon is the most popular
shielding gas used in the gas tungsten-arc process.
Helium is rarely used because of its higher cost as
compared to argon. In addition, since argon is heavier
Figure 6-45.--Starting the arc.
than air, it provides a better blanket over the weld. A
mixture of argon and helium is sometimes used in
made rapidly to provide the maximum amount of gas
welding metals that require a higher heat input.
protection to the weld zone.
Welding Procedures
If a dc machine is used, hold the torch in the same
position; but in this case, the electrode can touch the
Before you begin the welding process, be sure to
plate to start the arc. When the arc is struck, withdraw
observe the following preliminary steps:
the electrode so it is about 1/8 inch above the work
1. Check all electrical circuit connections to make
piece.
sure they are tight.
STOPPING THE ARC.--To stop an arc on the ac
2. Check for proper diameter electrode and cup
or dc machine, swing the electrode back to the
size.
horizontal position, as shown in figure 6-46. Make this
movement rapidly to avoid marring or damaging the
3. Adjust the electrode so that it extends the
weld surface.
appropriate distance beyond the edge of the gas cup for
the particular joint being welded.
Some machines are equipped with a foot pedal to
permit a gradual decrease of current. With such control,
4. Check the electrode to be certain that it is
it is easier to fill the crater completely and prevent
firmly held in the collet. If the electrode moves in the
crater cracks.
nozzle, tighten the collet holder or gas cup. Be careful
not to over tighten the gas cup because this will strip the
threads.
5. Set the machine for the correct welding
amperage.
6. If a water-cooled torch is to be used, turn on the
water.
7. Turn on the inert gas and set it to the correct
flow.
STARTING THE ARC.--If you are using an ac
machine, the electrode should not touch the metal to
start the arc. To strike the arc, first turn on the welding
current and hold the torch in a horizontal position about
2 inches above the work. Angle the end of the torch
toward the work piece so the end of the electrode is 1/8
inch above the plate. Figure 6-45 shows the procedure
for starting the arc. The high-frequency current will
jump the gap between the electrode and the plate,
establishing the arc. Be sure the downward motion is
Figure 6-46.--Breaking the arc.
6-31
