Welding Fundamentals, 5th Edition Page 251 (271 of 656)

Chapter 17 GMAW and FCAW: Flat Welding Position 251 Copyright Goodheart-Willcox Co., Inc. weld pool is fi lled, release the switch. The electrode wire will stop feeding, and the welding arc will also stop. Hold the gun in the same position until the shielding gas stops fl owing. For the same diameter electrode, more metal is deposited using spray transfer than globular or short circuiting transfer. The welder must move the welding gun much faster when using spray transfer than with the other two transfer methods. Regardless of the transfer method, watch the weld pool size. It determines the travel speed. If the pool gets too large, move the gun faster. If you are Direction of travel 20°–25° drag travel angle A–Backhand Direction of travel Direction of travel 0° travel angle 20°–25° push travel angle C–Forehand B–Perpendicular 20°–25° Vertical line Shielding gas Electrode wire Direction of motion Penetration Arc Weld pool Centerline of crater Base metal surface Goodheart-Willcox Publisher Figure 17-7. The welder is ready to strike the arc. Note that the torch is held at 20°–25° from vertical. This weld will be made in the backhand position. Goodheart-Willcox Publisher Figure 17-6. Notice the effects of travel angle on the completed weld. A—The backhand method produces a narrower weld bead with deep penetration. B—The perpendicular position produces a medium-width weld bead and medium penetration. C—The forehand welding position produces a wide weld bead with less penetration. Goodheart-Willcox Publisher Figure 17-8. Penetration is determined by the depth of the weld pool. Note that the electrode wire is kept ahead of the centerline of the weld crater.

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Chapter 17 GMAW and FCAW: Flat Welding Position 251 Copyright Goodheart-Willcox Co., Inc. weld pool is fi lled, release the switch. The electrode wire will stop feeding, and the welding arc will also stop. Hold the gun in the same position until the shielding gas stops fl owing. For the same diameter electrode, more metal is deposited using spray transfer than globular or short circuiting transfer. The welder must move the welding gun much faster when using spray transfer than with the other two transfer methods. Regardless of the transfer method, watch the weld pool size. It determines the travel speed. If the pool gets too large, move the gun faster. If you are Direction of travel 20°–25° drag travel angle A–Backhand Direction of travel Direction of travel 0° travel angle 20°–25° push travel angle C–Forehand B–Perpendicular 20°–25° Vertical line Shielding gas Electrode wire Direction of motion Penetration Arc Weld pool Centerline of crater Base metal surface Goodheart-Willcox Publisher Figure 17-7. The welder is ready to strike the arc. Note that the torch is held at 20°–25° from vertical. This weld will be made in the backhand position. Goodheart-Willcox Publisher Figure 17-6. Notice the effects of travel angle on the completed weld. A—The backhand method produces a narrower weld bead with deep penetration. B—The perpendicular position produces a medium-width weld bead and medium penetration. C—The forehand welding position produces a wide weld bead with less penetration. Goodheart-Willcox Publisher Figure 17-8. Penetration is determined by the depth of the weld pool. Note that the electrode wire is kept ahead of the centerline of the weld crater.

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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.

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250 Section 3 Gas Metal and Flux Cored Arc Welding Copyright Goodheart-Willcox Co., Inc. Holding the Welding Gun Pick up the welding gun. Use a grip that is comfortable, so you can weld for long periods of time without fatigue. Hold the gun so your fi nger or thumb (depending on the type of gun) is on the switch. Find a position that is comfortable. You may want to place the cable across your arm. See Figure 17-5. Press the inch switch on the wire feeder or press the trigger on the welding gun until the electrode sticks out about 2″. Using a pair of welpers or wire cutters, cut the electrode wire to obtain the proper electrode extension. Warning Place one hand over the electrode wire as it is cut to prevent the excess piece from flying through the air. The piece of electrode wire could hit someone in the eye, resulting in injury. Laying a Weld Bead Gas metal arc welding is performed using a backhand or forehand welding method or with the gun held vertically. Flux cored arc welding is performed primarily using the backhand method or with the gun nearly vertical. The backhand welding method pulls or drags the weld pool along the weld axis. The tip of the electrode points opposite the direction of travel. Backhand welding uses a travel angle of about 25°. A backhand travel angle is called a drag angle. See Figure 17-6A. The electrode can be held perpendicular to the workpiece. In such instances, the travel angle is 0°. See Figure 17-6B. The forehand welding method pushes the weld pool, as seen in Figure 17-6C. The tip of the electrode points in the direction of travel. The forehand welding travel angle is called a push angle. The electrode and gun form a push travel angle of about 25°. In all these situations, a work angle of 0° is used. The backhand welding method is used to obtain better penetration than forehand or vertical. It also has a more stable arc and produces less spatter than the other two methods. Position the gun over the area where you will begin welding. Tilt the gun to obtain the desired travel angle. For a drag travel angle, this is about 20°–25° in the backhand position. Touch the electrode wire to the base metal, but do not press the switch. Raise the gun 1/16″ (1.6 mm) or less. Lower your helmet and press the switch. See Figure 17-7. A welding arc will then form. The arc rapidly, almost immediately, melts the base metal and forms a weld pool (depression). The depth of this weld pool is the amount of penetration of the weld. Figure 17-8 shows that penetration is determined by the depth of the weld pool. Begin moving the welding gun in the direction of travel. Metal from the electrode will constantly be added to the pool. The weld pool shape is round to oval. A wider weld bead is obtained by moving the welding gun from side to side. The electrode should be in front of the centerline of the pool. See Figure 17-8. Continue moving the arc and pool until you reach the end of the weld. Keep the nozzle-to- work distance and the angle of the welding gun as constant as possible. The weld pool must be fi lled at the end of the joint or when you are ready to stop. Move the gun backward over the weld pool 1/4″–1/2″ (6 mm–13 mm). This will fi ll the weld pool. Once the Goodheart-Willcox Publisher Figure 17-5. Looping the electrode cable over the arm reduces the weight of the gun and makes it more comfortable to hold the gun.

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Page 2Section 1 Introduction to Welding click to expand contents

Page 126Section 2 Shielded Metal Arc Welding click to expand contents

Page 208Section 3 Gas Metal and Flux Cored Arc Welding click to expand contents

Page 276Section 4 Gas Tungsten Arc Welding click to expand contents

Page 334Section 5 Plasma Arc Cutting click to expand contents

Page 350Section 6 Oxyfuel Gas Processes click to expand contents

Page 478Section 7 Resistance Welding click to expand contents

Page 502Section 8 Welding in Industry click to expand contents

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