Spot welding is one of the oldest welding processes. It can be used on very thin foils or thick sections but it is rarely used above about 6mm thickness. It is used in a wide range of industries but notably for the assembly of sheet steel vehicle bodies. High quality welds can also be made in steel, stainless steels, and titanium for aerospace application.
Spot welding is one of a group of resistance welding processes that involve the joining of two or more metal parts together in a localised area by the application of heat and pressure. The heat is generated within the material being joined by the resistance to the passage of a high current through the metal parts, which are held under a pre-set pressure. The process is used for joining sheet materials anduses shaped copper alloy electrodes to apply pressure and convey the electrical current through the workieces. Heat is developed mainly at the interface between two sheets, eventually causing the material being welded to melt, forming a molten pool, the weld nugget. The molten pool is contained by the pressure applied by the electrode tip and the surrounding solid metal.
Spot welding is the most commonly used form of resistance welding. Usually used on sheet metal and in applications having some type of overlapping joint design, resistance spot welds are made from electrodes on both sides of the joint (unlike TIG and MIG spots, which are made from one side only). No filler metal is used.