9412 Other Arc Welding Processes

Stud welding (SW) is a process used to attach studs to a part. Two methods are used for aluminum: arc stud welding, which uses a conventional welding arc over a timed interval, and capacitor discharge stud welding, which uses an energy discharge from a capacitor. Arc stud welding is used to attach studs ranging from | in. (6 mm) to \ in. (13 mm) in diameter, while capacitor discharge stud welding uses studs ^ in. (1.6 mm) to \ in. (6 mm) in diameter. Capacitor discharge stud welding is very effective for thin sheet [as thin as 0.040 in. (1.0 mm)], because it uses much less heat than arc stud welding and does not mar the appearance of the sheet on the opposite side from the stud. Studs are inspected using bend, torque, or tension tests. Stud alloys are the common filler alloys. Stud welding requirements are included in AWS D1.2 [21].

Plasma arc welding with variable polarity (PAW-VP) [also called variable polarity plasma arc (VPPA) welding] is an outgrowth of TIG welding and uses a direct current between a tungsten electrode and either the workpiece or the gas nozzle. Polarity is constantly switched from welding to oxide cleaning modes at intervals tailored to the joint being welded. Two gases, a plasma gas and a shielding gas, are provided to the arc. Welding speed is slower than MIG welding, but often fewer passes are needed, single pass welds in metal up to | in. (16 mm) thick having been made. The main disadvantage is the cost of the required equipment.

Plasma-MIG welding is a combination of plasma arc and MIG welding, by which the MIG electrode is fed through the plasma coaxially, superimposing the arcs of each process. Higher deposition rates are possible, but equipment costs are also higher than for conventional MIG welding.

Arc spot welding uses a stationary MIG arc on a thin sheet held against a part below, fusing the sheet to the part. The advantage over resistance welding (discussed below) is that access to both sides of the work is unnecessary.

Problems with gaps between the parts, overpenetration, annular cracking, and distortion have limited the application of this method. It has been used to fuse aluminum to other metals such as copper, aluminized steel, and titanium for electrical connections.

Shielded metal arc welding (SMAW) is an outdated, manual process that uses a flux-coated filler rod, the flux taking the place of the shielding gas in removing oxide. Its only advantage is that it can be performed with commonly used shielded metal arc steel welding equipment. Shielded metal arc welding is slow, prone to porosity [especially in metal less than | in. (10 mm) thick], susceptible to corrosion if the slightest flux residue is not removed, and produces spatter (especially if rods are exposed to moisture) and requires preheating for metal 0.10 in. thick and thicker. Only 1100, 3003, and 4043 filler alloys are available for this process; see AWS A5.3, Specification for Aluminum and Aluminum Alloy Electrodes for Shielded Metal Arc Welding [18] for more information. For these reasons, gas-shielded arc welding is preferred.

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