AWS WHC-3.02:2008

Projection Welding
Scope : Projection welding (PW) is an electric resistance welding process that produces welds by the heat obtained from the resistance to the flow of the welding current. The resulting welds are localized at predetermined points by projections, embossments, or intersections.1,2 Force is always applied before, during, and after the application of current to confine the weld contact area at the faying surfaces and, in some applications, to forge the weld metal during postheating. The localization of heating is obtained by a projection or embossment on one or both of the workpieces. Projection welding is primarily used to join a stamped, forged, or machined component to another component. One or more projections are produced on the workpiece during the forming operations or other prior operations. A common application of projection welding is the use of specially designed nuts that have projections on the portion of the workpiece to be welded to the assembly. Fasteners or mounting devices, such as bolts, nuts, pins, brackets, and handles, can be welded to sheet metal, providing a variety of design options for countless applications. Projection welding generally is used for section thicknesses ranging from 0.5 millimeters (mm) to 3.2 mm (0.02 inch [in.] to 0.125 in.). The process is used to join various carbon steels, alloy steels, and some nickel alloys in a large variety of applications, from auto- motive mounting brackets to the cross-wire welding of grocery carts. Projection welding is easily automated for the high-speed welding of multiple projections. This chapter presents the fundamentals of the projection welding process, its advantages, limitations, and applications. Topics include the equipment and materials associated with the process, welding variables, welding schedules and weld quality. A discussion of a variation of projection welding, cross wire welding, is presented. The chapter continues with a brief discussion of the economics of projection welding, and concludes with a section on safe practices.