Chapter 8 Gas Metal and Flux Cored Arc Welding 221 Copyright Goodheart-Willcox Co., Inc. The backhand method produces the best penetra- tion. A 25° drag travel angle, with the gun forward of perpendicular, produces the best penetration in the fl at welding position. For the best control of the weld pool, a travel angle of 15°–25° forward of perpendicu- lar is preferred for most positions. Before beginning to weld, check the welding station for safety. Check all electrical, gas, and water connections for tightness. Weldments should be tack welded or secured in fi xtures prior to welding. Back- ing may be needed when complete joint penetration is required. Backing refers to a plate, ring, strip, or other device placed on the root side of the joint to control penetration of the weld. To start welding, tip the top of the gun 15°–25° in the direction of travel to create a drag travel angle. Hold the gun and electrode wire directly over the spot where the weld is to begin. Use an autodarkening hel- met or fl ip the non-autodarkening helmet down over your eyes. Squeeze the trigger on the gun to start the welding current, the wire feeder, and the gas fl ow. When the wire contacts the base metal, it quickly melts, initiating the arc. No striking or up-and-down motion is required to start the arc, as is required with SMAW. GMAW and FCAW are fast welding processes, especially with spray transfer. You need to start mov- ing almost immediately after starting the arc. Con- tinue to move the gun along the joint, watching the width of the weld pool to maintain a uniform size. Continue at a steady forward speed until the end of the joint is reached. Weld beads can be stringer beads or weave beads. A weave bead is made with some side-to-side motion, which creates a wider weld bead. The end of the weld may have a crater (depres- sion). This depression can be fi lled by moving the electrode to the end of the weld and then back over the completed bead about 1/2″ (13 mm). At the end of this reverse travel, release the trigger switch. Properly fi lling the crater is a skill to practice. To shield the end of the weld, hold the gun in position to allow the gas postfl ow to protect the weld until it cools. Postfl ow is the fl ow of shielding gas after the arc has extinguished. More than one pass may be required to fi ll a weld groove or produce the required fi llet weld size. Each pass should be cleaned before the next pass is laid. This is generally done with a wire brush or wire wheel. The glass-like coating on some gas metal arc welds is eas- ily removed. The slag layer on a fl ux cored arc weld is heavier and requires more effort to remove. A chip- ping hammer and a wire brush or wire wheel may be needed to clean an FCAW bead. 8.8 Running a Bead Initial training involves running a weld bead in the fl at position. A few hours of practice will develop skill in manipulating the welding gun. You will learn to observe (read) the weld pool and make nec- essary corrections. This training will allow you to learn the proper distance to hold the torch above the workpiece and develop proper travel speed and travel angle. Follow the procedure in section 8.4 to set up the GMAW or FCAW welding equipment. Select either .035″ (0.9 mm) or .045″ (1.2 mm) carbon steel electrode wire. Obtain some 1/8″ (3.2 mm) or thicker carbon steel. Set the appropriate short circuiting voltage and wire feed speed (amperage) on the welding machine. Make sure you are wearing all required safety equip- ment and the correct welding lens shade. Initial practice will be done with about a 15° drag travel angle. A right-handed welder will move from left to right on the base metal. A left-handed welder will travel from right to left. Pull the gun trigger for one second while holding the gun in the air to cause electrode wire to feed. Use your welding pliers to cut the wire so about 1/2″ (13 mm) is sticking out beyond the nozzle. Position the welding gun over the area where you will strike the arc. Flip down your helmet if not using an autodarkening lens. Pull the gun trigger. The electrode wire will feed and the arc will start. Work to keep the arc close to the front of the weld pool. The arc must stay in the weld pool. Do not let the arc stray toward the center of the weld pool or your travel speed will be too slow. Do not let the arc get in front of the weld pool or your travel speed will be too fast. Observe your weld bead. Make additional weld beads. Work to keep the edges of the bead straight and the nozzle a constant distance from the base metal. Maintain a consistent travel angle. Compare your weld to the welds shown in Figure 8-46. A weld bead made with a travel speed that is too fast is nar- row and does not melt in and fl ow with the base metal. A weld bead made with a travel speed that is too slow is too wide. Adjust your travel speed to pro- duce a bead that melts into the base metal at the toes of the weld and has the proper width. Modify your techniques as necessary to produce a quality stringer weld bead on plate. The next step is to add a small weaving motion, which is commonly used in GMAW and FCAW weld- ing. Two common weaves in the fl at, horizontal, and overhead positions are the oval weave and W-weave.