Chapter 8 Gas Metal and Flux Cored Arc Welding 211 Copyright Goodheart-Willcox Co., Inc. GMAW Short Circuiting Transfer — Suggested Gases Metal Shielding gas Advantages Aluminum, copper, magnesium, nickel, and their alloys argon and argon-helium Argon satisfactory on sheet metal argon-helium preferred on thicker sheet metal. Steel, carbon argon-20%–25% CO2 argon-50% CO2 CO2* Suitable for metal less than 1/8″ (3 mm) thick high welding speeds without melt-through minimum distortion and spatter good penetration. Suitable for metal greater than 1/8″ (3 mm) thick minimum spatter clean weld appearances good weld pool control in vertical and overhead positions. Deeper penetration faster welding speeds minimum cost. Steel, low-alloy 60%–70% helium-25%–35% argon-4%–5% CO2 argon-20%–25% CO2 Minimum reactivity good toughness excellent arc stability, wetting characteristics, and bead contour little spatter. Fair toughness excellent arc stability wetting characteristics, and bead contour little spatter. Steel, stainless 90% helium-7.5% argon- 2.5% CO2 No effect on corrosion resistance small heat-affected zone no undercutting minimum distortion good arc stability. * - CO2 is used with globular transfer also. Goodheart-Willcox Publisher Figure 8-32. Suggested gases and gas mixtures for GMAW short circuiting transfer. GMAW Spray Transfer — Suggested Gases Metal Shielding gas Advantages Aluminum argon 75% helium- 25% argon 90% helium- 10% argon Suitable for metal 0.1″–1″ (0.25 mm–25 mm) thick best metal transfer and arc stability least spatter. Suitable for metal 1″–3″ (25 mm–76 mm) thick higher heat input than argon. Suitable for metal up to 3″ (76 mm) thick highest heat input minimizes porosity. Copper, nickel, and their alloys argon helium-argon Provides good wetting good control of weld pool for thickness up to 1/8″ (3 mm). Higher heat inputs of 50% and 75% helium mixtures offset high heat conductivity of thicker base metals. Magnesium argon Excellent cleaning action. Reactive metals (titanium, zirconium, tantalum) argon Good arc stability minimum weld contamination. Inert gas backing is required to prevent air contamination on back of weld area. Steel, carbon argon- 2%–5% oxygen Good arc stability produces a more fluid and controllable weld pool good coalescence and bead contour, minimizes undercutting permits higher speeds, compared with argon. Steel, low-alloy argon- 2% oxygen Minimizes undercutting provides good toughness. Steel, stainless argon- 1% oxygen argon- 2% oxygen Good arc stability produces a more fluid and controllable weld pool, good coalescence and bead contour, minimizes undercutting on heavier stainless steels. Provides better arc stability, coalescence, and welding speed than 1% oxygen mixture for thinner stainless steel materials. Goodheart-Willcox Publisher Figure 8-33. Suggested gases and gas mixtures for GMAW spray transfer.