©
COPYRIGHT 1998 THE ESAB GROUP, INC. LESSON
II 2.3.2
Power
Sources - Both AC and
DC power sources are used in gas tungsten arc welding.
They are the constant current type with a drooping volt-ampere curve. This
type of power
source produces very slight changes in the arc current when the arc length (voltage)
is varied. Refer
to Lesson I, Section 1.9. 2.3.2.1
The choice between an AC or DC welder
depends on the type and thickness of the metal
to be welded. Distinct differences exist between AC and DC arc characteristics,
and if DC is chosen,
the polarity also becomes an important factor. The effects of polarity in
GTAW are directly
opposite the effects of polarity in SMAW as described in paragraphs 2.2.2.3
through 2.2.2.5. In SMAW,
the distribution of heat between the electrode and work, which
determines the penetration and weld
bead width, is controlled mainly by the ingredients in the
flux coating on the electrode. In
GTAW where no flux coating exists, heat distribution between
the electrode and the work is controlled
solely by the polarity. The choice of the proper welding
current will be better understood by
analyzing each type separately. The chart in Figure 7 lists
current recommendations.
FIGURE 7 Material
& Thickness
DCEN DCEP
AC High
Freq. Argon
Helium Ar/He
Aluminum Under
1/8" Over 1/8"
2 2
& 3 1
1 1
1 2
3 2
Magnesium Under
1/16" Over 1/16"
2 1
1 1
1 2
Carbon Steel Under
1/8" Over 1/8"
1 1
1 1
2 3
Stainless Steel
Under 1/8" Over
1/8" 1
1 1
1 2
2 Copper
Under 1/8" Over
1/8" 1
1 1
1 Nickel
Alloys Under
1/8" Over 1/8"
1 1
1 3
2 2
1 Titanium
Under 1/8" Over
1/8" 1
1 2
2 1
WELDING CURRENT
SHIELDING GAS
1. Preferred
Choice - Manual Welding 2.
Preferred Choice - Automatic Welding
3. Second
Choice - Automatic Welding CURRENT/SHIELDING
GAS SELECTION, TUNGSTEN GAS ARC WELDING
