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Weld nuts and weld studs are commonly used to provide a means for subsequent fastening of additional components and assemblies, or for periodic removal of service parts for maintenance and repair. When specifying welded fasteners, care should be taken not to tightly tolerance concentricity or perpendicularity to a datum plane, since this drastically increases cost. Weld fasteners located by holes punched by prior stamping operations are an accurate and generally preferred location method. For maximum cost-effectiveness, select weld nuts and studs of one size that will be used throughout the assembly. This helps to keep set-ups to a minimum and increases manufacturing throughput. Nuts located by holes are typically within ±0.006 (0.15 mm) of the original hole location. Studs can be located to ±0.020 (0.51 mm) with simple fixturing. Closer tolerances require more sophisticated and costly fixtures.

Position the welding torch with the wire in the center of the hole contacting the back sheet of metal. It is important to arc against this back sheet rather than on the edge of the hole, otherwise the weld might not penetrate into the back sheet. The torch should ideally be pointing directly into the hole rather than at the angle in the photograph. Start welding in this position and don’t move the welder until the hole is almost full of weld. Then move the welder outwards in ever increasing circles until the weld is completed.

Where is Spot Welding Used? Spot welding has applications in a number of industries, including automotive, aerospace, rail, white goods, metal furniture, electronics, medical building and construction. Given the ease with which spot welding can be automated when combined with robots and manipulation systems, it is the most common joining process in high volume manufacturing lines and has in particular been the main joining process in the construction of steel cars for over 100 years. See extra info at Auto Body Spot Welder.

What type of sheets can be welded? Rust-free, non-painted sheets of the same or different metals can be welded provided they are compatible alloys with a very similar melting point. Metals such as stainless steel, aluminium, steel alloys and galvanized steels can be spot welded, subject to operating adjustments (current, welding time, intensity of compression). Note that the coating on galvanized metals tends to clog the electrodes – which must be cleaned regularly!