a chance to cool. Reducing current or using a pulsed arc keeps the weld pool smaller than the pool used for fl at welding. Shielding gas fl ow rates must be higher for overhead welding. Argon gas is heavier than air. Therefore, it easily covers the weld area when welding is performed in the fl at position. Refer to Figure 19-13. However, when welding is performed overhead, the gas will fall away from the welding area and not give good protection. To compensate, fl ow rates are increased by 3–5 cfh (2-3 Lpm) for thin metals. On metals 3/16″ (5 mm) or thicker, an additional 5 cfh (3 Lpm) or more is used. If you get porosity when welding overhead, check to make sure you are keeping the correct arc length. If your arc length is correct and you are still getting porosity, increase the shielding gas fl ow. The angles used to weld fi llet or butt welds overhead are the same as those used in other positions. Filler metal is added to the leading edge on a fi llet weld. Figure 22-12 shows a welder making a fi llet weld in the overhead welding position. Figure 22-13 shows a butt weld being made in the overhead welding position. Exercise 22-6 Making an Overhead Fillet Weld on a T-Joint 1. Obtain two pieces of carbon steel measuring 3/16″ × 3″ × 6″ (5 mm × 75 mm × 150 mm). 2. Clean one long edge on one piece and one face on the other piece. 3. Set up the welding station for welding carbon steel. Use 85A–90A current. Use 18 cfh–20 cfh (8 Lpm–9 Lpm) argon shielding. 4. Tack weld the two pieces together to form a T-joint. Clamp the tack welded pieces in the overhead position. 5. Weld both sides of the T-joint. Keep the molten weld pool small so the metal does not fall or sag. Inspection: The completed weld should be of the same quality as a weld made in the flat position. Examine the completed weld for evidence of porosity. Also, look for any metal sagging that might cause underfill or overlap. Goodheart-Willcox Publishing Figure 22-13. A bead being laid in a butt joint in the overhead welding position. Goodheart-Willcox Publishing Figure 22-12. A fillet weld being made on a lap joint in the overhead position. The angles of the electrode and welding rod are the same as those used in the flat position. 330 Section 4 Gas Tungsten Arc Welding Copyright Goodheart-Willcox Co., Inc.