AWS WHC-3.06:2008

Friction Welding
Scope : Friction welding (FRW) is a solid-state process that produces a weld when two or more workpieces, rotating or moving relative to one another, are brought into contact under pressure to produce heat and plastically displace material from the faying surface (weld interface).1,2 Although friction welding is a solid-state welding process, under certain circumstances a molten film may form at the weld interface during the heating stage. Localized melting is seldom a problem, however, because this layer is extruded during the extensive hot working that takes place during the final stage of the process. Filler metal, flux, and shielding gas are not required with this process. The two main variations of friction welding are direct drive friction welding (FRW-DD) and inertia friction welding (FRW-I). In direct drive friction welding, the energy required to make the weld is supplied by the welding machine through a direct motor connection for a preset period of the welding cycle. The energy required to make an inertia friction weld is supplied primarily by the stored rotational kinetic energy of the welding machine. Friction stir welding (FSW) is classified by the American Welding Society as a variation of friction welding, but is not included in this chapter because of the substantial differences in the mechanics of the processes. Friction stir welding is discussed in detail in Chapter 7. Friction welding and its variations are used in nearly all industries for many different applications. The processes are used for high-volume production applications, when solid-state joining is a preference or a necessity, or when the geometries of the workpieces (the components) are such that other welding processes are not applicable. Friction welding can be used to weld nearly all combinations of metals and their alloys, including many dissimilar material combinations. The processes are important to fabricators who serve the aerospace, automotive, defense, transportation, agricultural, chemical, construction, and other industries. The photograph on the title page of this chapter shows an example of a common application: a threaded steel joint being welded to the end of a steel drill pipe used in the oil industry. The equipment is a direct drive friction welding machine with a 300-ton forge force. The fundamentals of friction welding, variations of the process, and modes of operation are covered in this chapter. Other topics include the advantages and limitations of friction welding, applications, equipment, weldability of various materials, weld quality, inspection, and economics. Important information on safe practices is presented in the last section of the chapter. The supplementary reading list provides sources of additional technical information.