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ARC WELDING

Arc welding is a process that uses an electric arc to join the metals being welded. A distinct advantage of arc welding over gas welding is the concentration of heat. In gas welding the flame spreads over a large area, sometimes causing heat distortion. The concentration of heat, characteristic of arc welding, is an advantage be­cause less heat spread reduces buckling and warping. This heat concentration also increases the depth of pene­tration and speeds up the welding operation; therefore, you will find that arc welding is often more practical and economical than gas welding.

All arc-welding processes have three things in com­mon: a heat source, filler metal, and shielding. The source of heat in arc welding is produced by the arcing of an electrical current between two contacts. The power

MASTER CHART OF WELDING AND ALLIED PROCESSES ARC WELDING (AW)

Figure Figure 3-1.-Welding processes.

Figure 3-2.-Oxyfuel gas welding (OFW).

source is called a welding machine or simply, a welder. This should not be confined with the same term that is also used to describe the person who is performing the welding operation. The welder (welding machine) is either electric- or motor-powered. In the Naval Con­struction Force (NCF), there are two main types of arc-welding processes with which you should become familiar. They are shielded metal arc welding and gas shielded arc welding.

Shielded Metal Are Welding (SHAW)

Shielded metal arc welding (fig. 3-3) is performed by striking an arc between a coated-metal electrode and the base metal. Once the arc has been established, the molten metal from the tip of the electrode flows together with the molten metal from the edges of the base metal to forma sound joint. This process is known as fusion. The coating from the electrode forms a covering over the weld deposit, shielding it from contamination;

Figure 3-3.-Shielded metal arc welding (SHAW).

therefore the process is called shielded metal are welding. The main advantages of shielded metal arc welding are that high-quality welds are made rapidly at a low cost. You will learn more about shielded metal arc welding in chapter 7.

Gas Shielded Arc Welding

The primary difference between shielded metal arc welding and gas shielded arc welding is the type of shielding used. In gas shielded arc welding, both the arc and the molten puddle are covered by a shield of inert gas. The shield of inert gas prevents atmospheric con­tamination, thereby producing a better weld. The pri­mary gases used for this process are helium, argon, or carbon dioxide. In some instances, a mixture of these gases is used. The processes used in gas shielded arc welding are known as gas tungsten are welding

Figure 3-4.-Gas tungsten arc welding (GTAW).

(GTAW) (fig. 3-4) and gas metal arc welding (GNAW) (fig. 3-5). You will also hear these called "TIG" and "MIG." Gas shielded arc welding is extremely useful because it can be used to weld all types of ferrous and nonferrous metals of all thicknesses.

Now that we have discussed a few of the welding processes available, which one should you choose? There are no hard-and-fast rules. In general, the control­ling factors are the types of metal you are joining, cost involved, nature of the products you are fabricating, and the techniques you use to fabricate them. Because of its flexibility and mobility, gas welding is widely used for maintenance and repair work in the field. On the other hand, you should probably choose gas shielded metal arc welding to repair a critical piece of equipment made from aluminum or stainless steel.

No matter what welding process you use, there is some basic information you need to know. The remain­der of this chapter is devoted to this type of information. Study this information carefully because it allows you to follow welding instructions, read welding symbols, and weld various types of joints using the proper weld­ing techniques.

Figure 3-5.-Gas metal arc welding (GNAW).

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