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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.

The welding heat is generated by the electric current, which is transferred to the workpiece through copper alloy electrodes. Copper is used for the electrodes as it has a high thermal conductivity and low electrical resistance compared to most other metals, ensuring that the heat is generated preferentially in the work pieces rather than the electrodes. The amount of heat depends on the thermal conductivity and electrical resistance of the metal as well as the amount of time the current is applied. Other materials commonly spot welded include stainless steels (in particular austenitic and ferritic grades), nickel alloys and titanium. Read extra info at Spot Welder.

Portable spot welders are compact, lightweight and handy for difficult-to-access joints. As such, they are most commonly used in coachbuilding. They have an average welding capacity of 2 + 2mm and are relatively inefficient due to the fact that the electrodes aren’t cooled between cycles. Automatic adjustment makes it easier to adjust the spot parameters according to the thickness of sheet and welding head used.