9415 Resistance Welding

Resistance welding is a group of processes that use the electrical resistance of an assembly of parts for the heat required to weld them together. Resistance welding includes both fusion and solid-state welding, but it's useful to consider the resistance welding methods as their own group. Because aluminum's electrical conductivity is higher than steel's, it takes more current to produce enough heat to fuse aluminum by resistance welding than for steel.

Resistance spot welding (RSW) produces a spot weld between two or more parts that are held tightly together by briefly passing a current between them. It is useful for joining aluminum sheet and can be used on almost every aluminum alloy, although annealed tempers may suffer from excessive indentation due to their softness. Its advantages are that it is fast, automatic, uniform in appearance, not dependent on operator skill, strong, and minimizes distortion of the parts. Its disadvantages are that it only applies to lap joints, is limited to parts no thicker than | in. (3 mm), requires access to both sides of the work, and the equipment is costly and not readily portable. Tables are available that provide the minimum weld diameter, minimum spacing, minimum edge distance, minimum overlap, and shear strengths as a function of the thickness of the parts joined. Proper cleaning of the surface by etching or degreasing and mechanical cleaning is needed for uniform quality.

Weld bonding is a variation on resistance spot welding in which adhesive is added at the weld to increase the bond strength.

Resistance roll spot welding is similar to resistance spot welding except that the electrodes are replaced by rotating wheel electrodes. Intermittent seam welding has spaced welds; seam welding has overlapped welds and is used to make liquid or vapor-tight joints.

Flash welding (FW) is a two-step process: Heat is generated by arcing between two parts and then the parts are abruptly forced together. The process is automatically performed in special-purpose machines, producing very narrow welds. It has been used to make miter and butt joints in extrusions used for architectural applications and to join aluminum to copper in electrical components.

High-frequency resistance welding uses high-frequency welding current to concentrate welding heat at the desired location and for aluminum is used for longitudinal butt joints in tubular products. The current is supplied by induction for small-diameter aluminum tubing and through contacts for larger tubes.

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