252 Section 3 Gas Metal and Flux Cored Arc Welding Copyright Goodheart-Willcox Co., Inc. moving the arc in front of the pool, slow down the travel speed. Keep the electrode wire directly in front of the center of the pool. A good weld bead should have evenly spaced ripples. The edges of the weld should be the same width. There should be about 1/16″–1/8″ (1.6 mm–3.2 mm) of reinforcement. Figure 17-9 shows an example of a good fi llet weld bead on a T-joint. Practice moving the gun at a constant speed to obtain evenly spaced ripples in the completed weld. If the edges are not the same width along the entire weld, practice holding the gun steady. Avoid moving the gun from side to side. Exercise 17-1 Laying a Weld Bead on a Plate 1. Obtain a piece of mild steel measuring 3/16″ × 3″ × 6″ (4.8 mm × 75 mm × 150 mm). 2. Clean both surfaces with a wire brush. 3. Using a ruler and a piece of soapstone, mark out five straight lines. You will lay your weld beads along those lines. 4. Refer to Figure 16-18 and select the electrode wire diameter, wire feed speed, and voltage for GMAW with short circuiting transfer. Set the values on the welding machine. Refer to Chapter 16 for details. 5. Select the appropriate shielding gas and set the flowmeter. Figures 16-11 and 17-2 list the correct gases and flow rates. 6. Use the backhand method. Figure 17-7 shows the correct angle between the welding gun and the plate. This angle is the same for most GMAW and FCAW operations in any position. 7. Watch the metal as the welding arc starts. A molten weld pool develops quickly. Move the arc toward the forward edge of the pool. Note the width of the pool and the amount of penetration. Keep the same width and penetration as the weld progresses. 8. Fill the weld pool at the end of the weld bead. 9. Examine the weld bead. Change the voltage, wire feed speed, travel speed, or shielding gas flow rate as required. 10. Weld beads on the other four lines on the plate. Inspection: Each weld bead should be straight with evenly spaced ripples and continuous reinforcement. The crater at the end of the weld should be filled. No evidence of porosity should be seen. Turn the plate over and repeat this exercise. Set the welding machine for spray transfer. Change the shielding gas to argon with carbon dioxide or argon with oxygen. See Figures 16-12 and 16-18. Adjusting a Weld Bead Multiple variables affect the quality of a GMAW or FCAW bead. These variables include: • Voltage. • Wire feed speed (amperage). • Travel speed. • Contact tube-to-work distance. • Gun angle. Increasing the voltage produces a wider, fl atter weld pool. Setting the voltage too high causes porosity. Setting the voltage too low can cause the electrode to short to the weld pool. Increasing the wire feed speed adds more electrode wire to the weld pool. This increases the amount of metal deposited and increases penetration. A high wire feed speed can cause a convex bead, which has excess reinforcement. This is a waste of electrode wire. Goodheart-Willcox Publisher Figure 17-9. This is a well-formed fillet weld on a T-joint. Note that the weld bead is slightly convex.