© 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





Lesson 1
The Basics of Arc Welding
Lesson 2
Common Electric
Arc Welding Processes
Lesson 3
Covered Electrodes for Welding
Mild Steels
Lesson 4
Covered Electrodes for Welding Low Alloy Steels
Lesson 5
Welding Filler Metals for Stainless Steels
Lesson 6
Carbon & Low Alloy
Steel Filler Metals -
GMAW,GTAW,SAW
Lesson 7
Flux Cored Arc Electrodes Carbon Low Alloy Steels
Lesson 8
Hardsurfacing Electrodes
Lesson 9
Estimating & Comparing Weld Metal Costs
Lesson 10
Reliability of Welding Filler Metals
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