Resistance seam welding (RSEW) is similar to spot welding except that rotating wheel electrodes are used. The process is used when leak-tight welds or long strings of spot welds are required. Three forms of seam welding exist: standard seam, mash seam, and roll spot welding.
In standard seam welding, a series of overlapping weld nuggets are formed by rotating the wheel electrodes along the workpieces and firing a continuous series of current pulses. This action forms a continuous, leak-tight joint.
In mash seam welding (RSEW-MS), there is a small overlap of sheets, typically about one to two times the sheet thickness. Sheets are then mashed together while current applied, making a solid state joint. The resulting welded joint is generally 110-150% of the original sheet thickness. This final joint thickness can be reduced by post-weld planishing.
In roll spot welding, the current pulses as wheels traverse the workpieces to form a line of separate spot welds (not a leak-tight joint).