Machinery's Handbook, 31st Edition
Gas Metal Arc Welding 1577 content such as the E70S-3. For welding low-carbon and low-alloy steels with conventional argon mixture shielding gases, there is little difference between the E70S-3 and E70S-6. Electrode Diameters.— One of the most important welding decisions is selecting the op- timum GMAW electrode diameter, which should be based on the material thickness, as shown for carbon and stainless steels in Table 1, the compatibility of the electrode current requirements with the material thickness, the mode of weld metal transfer, and the depo- sition rate potential shown in Table 2. The two most popular GMAW electrode sizes are 0.035 inch (1.0 mm) and 0.045 inch (1.2 mm). Diameters of electrodes used for GMAW exert a strong influence on cost of welding. Table 2 also shows how the weld deposition rate varies in short-circuit and spray transfer modes in welding carbon and stainless steels. Table 1. GMAW Electrode Sizes for Welding Carbon and Stainless Steels
Electrode Diameter
0.030 inch (0.8 mm)
0.035 inch (1.0 mm)
0.045 inch (1.2 mm)
0.062 inch (1.6 mm)
Material Thickness
25 to 21 gage (0.020 to 0.032 inch)
yes
… … …
… yes
… …
20 gage to 1 ∕
4 inch (0.036 to 0.25 inch)
… … yes
…
16 to
7 ∕ 16 inch flat and horizontal
3 ∕
1 ∕ 2 inch and up … … … yes The table is based on suitability of the electrode size to mode of weld transfer, material thickness, and cost-effectiveness. If a smaller electrode size is selected, the lower deposition rates could increase welding costs by 20 to 60 percent. Table 2. Typical Maximum GMAW Deposition Rates for Carbon and Stainless Steels. Constant-Voltage 450-amp Power Source and Standard Wire Feeder
Electrode Diameter
Weld transfer mode Short circuit
0.030 inch (0.8 mm) (2.3 kg/h) 9 lb/h (4 kg/h) 5 lb/h
0.035 inch (1.0 mm) (3.2 kg/h) 11 lb/h (5 kg/h) 7 lb/h
0.045 inch (1.2 mm) 9 lb/h (4 kg/h) 19 lb/h (8.6 kg/h)
0.062 inch (1.6 mm)
…
Spray transfer
21 lb/h
(9.5 kg/h) For the lowest-cost welds with GMAW electrodes larger than 0.030 inch in diameter, the power source should provide a minimum of 350 amps. The compatibility of the optimum current range of the 0.035-inch (1.0-mm) electrode and its deposition potential make it the first choice for welding of 20 gage to 1 ∕ 4 inch (0.88 to 6.4 mm) thicknesses. For welding thinner sheet metals of 25 to 21 gage, the optimum electrode diameter is 0.030 inch (0.8 mm). The 0.045-inch (1.2-mm) electrode is the most practical choice for spray transfer applications on materials over 1 ∕ 4 inch (6.4 mm) thick and thicker. As an example, when welding 1 ∕ 4 -in. (6.4-mm) thick steel, with 100 percent arc-on time and a labor cost of $15/h, the deposition rate with a 0.035-in. (0.9-mm) electrode is approx imately 11 lb/h (5 kg/h). The labor cost per lb at $15/h ÷ 11 lb/h = $1.36/lb ($3.00/kg). If an electrode of 0.045-in. (1.2-mm) diameter is used for the same application, the deposition rate is 16 lb/h (7.2 kg/h) and at a $15/h labor rate, the cost of weld metal deposited = $15/h ÷ 16 lb/h = $0.93/lb ($2.00/kg). The 0.045-in. diameter electrode would also cost less per pound than a smaller wire, and the weld time with the 0.045-in. electrode would be reduced, so less shielding gas also would be consumed. GMAW Welding of Sheet Steel.— In GMAW, the short-circuit transfer mode is used to weld carbon steel, low-alloy steel, and stainless steel sheet of 24 gage (0.023 in., or 0.6 mm) to 11 gage (0.12 in., or 3 mm). The most common gage sizes welded with short-circuit transfer are 20 gage to 11 gage (0.88 to 3 mm) and the best GMAW electrode for these thin, sheet
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