A resistance seam welding process variation that makes a lap joint primarily by high-temperature plastic working and diffusion as opposed to melting and solidification. The joint thickness after welding is less than the original assembled thickness.
Mash seam welding requires high electrode force, continuous welding current, and accurate control of force, current, welding speed, overlap and joint thickness to obtain consistent welding characteristics. Overlap is maintained to close tolerances by clamping or tack-welding the workpieces.
This seam welding process requires considerably less overlap than a conventional lap joint. With proper welding procedures, the overlap is about 1 to 1.5times the sheet thickness. Wide, flat-faced wheel electrodes that completely cover the overlap are used.
Mash seam welding produces continuous seams that have good appearance and are free of crevices. Crevice-free joints are necessary in many applications with strict contamination or cleanliness requirements, such as joints in food containers or refrigeration liners. To obtain acceptable welds, the materials to be mash seam welded must have wide plastic temperature ranges. Low-carbon steel and stainless steel can be mash seam welded in certain applications.