Copyright Goodheart-Willcox Co., Inc. Chapter 7 Gas Metal Arc Welding Procedures and Techniques 71 welding, the welder controls this variable. The welder must adapt the speed to changing shapes, improper fi tup, gaps, and other variables as the weld continues. fi The welder’s skill is important to the quality of the weld. Direction of Travel The GMAW operation can be done with the welding gun pointing back at the weld and the weld progressing in the opposite direction. This is called backhand welding or g pull welding. See g g Figure 7-4. Advantages of backhand welding include a more stable arc, less spatter, and deeper penetration. The other method of gun manipulation is to point the gun forward in the direction of travel. This method is called forehand welding or g push welding. g g This is the recommended direction for aluminum and when the spray transfer or pulsed-spray transfer mode of deposition is used. See Figure 7-5. In compar- ison to backhand welding, forehand welding results in more spatter, less penetration, and better visibility of the weld seam. This technique provides increased cleaning action of the base metal, which is why it is used for welding aluminum. Gun Angle Gun angles are defi in either longitudinal fined (along the weld) or transverse (across the weld) angle dimensions. The longitudinal angle is referred to as the travel angle. Longitudinal angles generally range between 10° and 25° off perpendicular. The transverse angle is referred to as the work angle. See Figure 7-6. Transverse angles range from 0° to 45°, depending on ° the welding position and joint type. Gun angle affects weld penetration, bead form, and fi nal weld bead appearance. As the weld fi progresses, changes in gun angle may be required to maintain good weld pool control and weld bead shape. Figure 7-7 shows the transverse gun angles (for initial welding setup only) and bead placement for fl at multi-pass groove welds. Longitudinal angles fl are 10°–15° from the vertical position. Each variation in groove angle or thickness dimension affects the required gun angle. Remember, the molten weld pool must fl ow into the previous pass and the side walls of fl Travel direction Completed weld Goodheart-Willcox Publisher Figure 7-4. The backhand (pull welding) technique requires more skill on the part of the welder than the forehand technique, since the weld joint is difficult to see because of the position of the gas nozzle. Travel direction Completed weld Goodheart-Willcox Publisher Figure 7-5. The forehand or push welding technique is easy to use because the weld joint is directly in front of the electrode. Compared to backhand welding, there will be less penetration into the joint and spatter will increase. A B Goodheart-Willcox Publisher Figure 7-6. Gun angles. A—Travel angle. B—Work angle.