Unlike Spot and Projection welding which is static welding, Seam welding is welding through motion. One or two wheels rotate to make a series of overlapping spot welds on sheet components to achieve air or liquid proof on the welded part. There are Roll Spot and Seam in seam welding. Roll spot are an interchange between a spot or a series of spot welds and a period of cool time but without opening the electrode during the welding process. Roll spot is well depicted in the brake shoe seam welding process where the embossments on the rim are roll spot welded. Seam in seam welding separates into continuous seam and pulse seam. Continuous seam is overlap of spot welds without cool time while pulse seam is overlap of spot welds with cool time but so short that the spots are still connected together. Both continuous seam and pulse seam sometimes can run on same machine. The selection between continuous seam and pulse seam can be decided based on the sheet component material and the weld appearance. The seam welding machine also has Internal and External cooling on the electrode wheels. Selection between Internal and External cooling on seam welding vary among sheet component material, weld strength to be achieved and application of the weld part.