Chapter 17 GMAW and FCAW: Flat Welding Position 249 Copyright Goodheart-Willcox Co., Inc. desirable. Too much preheating results in shallow penetration. Proper electrode extension is different for GMAW than for FCAW, Figure 17-4. Self-shielded FCAW requires a long electrode extension. An electrode extension from 3/4″ to 3 3/4″ is necessary. The actual extension is based on the diameter and the particular electrode being used. Larger diameters of self-shielded electrodes require a longer extension to preheat the wire. Review electrode manufacturers’ specification (spec) sheets for electrode extension recommendations. Manufacturers’ spec sheets also list recommended voltages, wire feed speed, polarity, and other useful information. The contact tube usually cannot be seen when welding because it is inside the nozzle. Therefore, the welder uses the nozzle-to-work distance to control the contact tube-to-work distance or electrode extension. Nozzle-to-work distance is the distance from the end of the nozzle to the base metal. Hold the nozzle off the base metal to obtain the correct electrode extension. Recommended Shielding Gas and Flow Rates Metal Thickness Shielding Gas Flow Rate in mm cfm L/min Mild Steel 1/16 1.6 90% Ar—10% CO2 75% Ar—25% CO2 100% CO2 25 12 1/8–3/16 3.2–4.8 30 15 1/4–1/2 6.4–12.7 35 15 Stainless Steel 1/16 1.6 98% Ar—2% O2 30 15 1/8–3/16 3.2–4.8 35 15 1/4–1/2 6.4–12.7 40 20 Aluminum Alloys 1/16 1.6 Argon 30 15 1/8–3/16 3.2–4.8 35 15 1/4 6.4 40 20 3/8 9.5 50 25 Nickel Alloys Up to 3/8 Up to 9.5 Argon 30 15 Magnesium Alloys .025–3/16 0.6–4.8 Argon 50 25 1/4–1/2 6.4–12.7 60 30 Process Method Electrode Extension GMAW Short circuiting 1/4″–1/2″ (6 mm–13 mm) GMAW Spray transfer 1/2″–1″ (13 mm–25 mm) FCAW Gas-shielding 3/4″–1 1/2″ (19 mm–38 mm) FCAW Self-shielding 3/4″–3 3/4″ (19 mm–95 mm) Nozzle Contact tube Electrode extension distance Contact tube– to-work distance Electrode wire Nozzle- to-work distance Arc length Base metal Goodheart-Willcox Publisher Figure 17-2. Recommended shielding gases and flow rates for various base metals. Increase flow rates 10% when welding out of position. The overhead position may require even higher flow rates. FCAW is only used to weld mild steel and stainless steel. Goodheart-Willcox Publisher Figure 17-3. Note the various distances associated with GMAW and FCAW, including the electrode extension distance. Goodheart-Willcox Publisher Figure 17-4. These are the proper electrode extensions for the different metal transfer methods for GMAW and FCAW.