Seam welding

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Resistance Seam Welding is a resistance welding process that produces a weld at the faying surfaces of overlapped parts along a length of a joint. The weld may be made by overlapping weld nuggets, a continuous weld nugget or by forging the joint as it is heated to the welding temperature by resistance to the flow of welding current. Instead of using two cylindrical electrodes as in case of spot welding, here two circular disks are used as electrodes. The workpiece is passed through the space between the two discs, and under pressure applied by the discs and current flowing through them, a continuous weld is formed.

With seam welding the material passes between two rotating wheels or welding rollers. The welding rollers perform three tasks:

• Weld current transmission
• Welding pressure
• Feed motion transmission

The high electrical A/C current (low voltage) is supplied from a transformer.

The overlap of the work piece with its comparatively high electrical resistance is intensely heated by the current. With each positive or negative current half-wave the parts are heated to a semi-molten condition, especially at the current peaks. The semi-molten overlap surfaces are pressed together by the welding pressure which causes them to bond together into an uniforming welded structure after cooling. Most seam welded technologies use water cooling through the weld roller assemblies due to the intense heat generated.