7.12 The GMAW/FCAW Welding Gun
The primary function of the welding gun used in GMAW and FCAW is to direct the welding electrode to the weld. Additional connections on the gun provide electrical connections, connections for shielding gas if used, and for water cooling if used. There are similarities and differences between a gun used for GMAW and one used for FCAW. 7.12.1 GMAW Welding Gun A typical gas-cooled gas metal arc welding gun and its electrode lead and gas hose are shown in Figure 7-42. The gas hose, the electrode lead, and the electrode wire carrier, called a liner, are all built into one large cable. The gun has a fully insulated handle, a trigger switch, a current contact tube, and a nozzle. The trigger switch turns on the current and wire feeder and starts the shielding gas flowing. Figure 7-43 shows the main parts of a gas-cooled GMAW gun. Gas metal arc welding guns are usually gas-cooled. Gas flowing through the gun and air on the outside of the welding gun keep the gun from overheating. Carbon dioxide GMAW guns can be used for intermittent duty up to 600A. Figure 7-44 shows a gas-cooled GMAW gun. Gas metal arc welding performed with a gas-cooled gun and argon or helium shielding gas must be done at much lower currents than are possible with carbon dioxide. Continuous welding or welding at amperages above 300A with argon or helium shielding gases requires the use of water-cooled guns. Torches used with CO2 above 600A, or for continuous duty, are also water-cooled. Figure 7-45 shows a water-cooled GMAW gun. In addition to an electrical lead and a shielding gas hose, a water-cooled gun must have a hose to carry water to the gun. The water returns to the water cooler through the combination power cable and water tube.A GMAW gun can be used for gas-shielded flux cored arc welding. |
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Gas metal arc welding guns that have self-contained wire drive units are available. See Figure 7-46. These guns are commonly referred to as spool guns. They have an electric motor and drive rolls to drive the electrode wire enclosed in the gun. A small spool of electrode wire mounts directly on the gun. An advantage of a spool gun is it eliminates the need to push the electrode wire through a long cable. This way the gun can be used a long distance from the power supply. Electrical cables and shielding gas are still required. Two disadvantages of a spool gun are they hold a limited amount of electrode wire and are considerably heavier than a standard gun.
Another type of gun that is used is called a pull-type welding gun. When welding long distances from the wire feeder or when welding using aluminum wire (especially smaller diameter aluminum wire), a pull-type welding gun is used. See Figure 7-47.
A pull-type gun has a motor and drive rolls in it, which pull the electrode wire. Attempting to feed aluminum wire by pushing it through the cable to the gun will cause it to kink or bend. Aluminum electrode wire is not rigid enough to be pushed. Kinking can also happen when feeding steel or stainless steel electrode wire a long distance, because there is a lot of friction on the wire. To prevent kinking the wire, a pull gun is used. Pull guns are usually used in combination with a traditional wire feeder, in an arrangement known as a push-pull system. The pull-type gun pulls the wire while the regular wire drive unit pushes the wire. Figure 7-48 shows a push-pull system that includes a power source with a wire feeder and a pull-type welding gun. Welding can be done 50″ (16m) from the wire feeder using this push-pull method.
Welding guns used for automatic GMAW often have a straight body and nozzle. They do not have a handle. They are firmly attached to a carriage, robot, or other mechanism for welding, as shown in Figure 7-49. Since automatic welding is often done almost continuously, many guns used for automatic welding are water-cooled. Gas-cooled guns are only for welding with low amperages that will not overheat them. For automatic welding, electrode wire and shielding gas is fed through the gun body to the arc area in the same manner as shown in Figure 7-43.
A new GMAW system has been developed for performing emergency or quick repairs. The system is highly portable and relatively light in weight. The power source is two 12-volt long-life batteries, which provide 24-volt power. The welding gun contains a small wire spool, wire drive rolls, wire speed controls, and an on-board computer. See Figure 7-50.
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