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What you need to know about Friction Welding Processes

July 24, 2012

Friction has been used to weld parts for both new make and for repair for many decades. The friction welding family of processes encompasses many different variants, including rotary friction welding (inertia, direct-drive, and radial), linear friction welding, and more recently, friction stir welding (FSW). In each case, friction heats the material to a plastic state in conjunction with an applied force to create the weld. Since no melting occurs, these processes are classified as solid-state welding. Solid-state welding often produces welds with mechanical properties approaching or superior to that of the base materials. The resulting weldment often has less distortion than is typical for fusion welding methods (such as arc, laser, etc.) Also, since the bonding mechanism is solid-state, dissimilar material combinations can be welded that are not possible with fusion welding processes.

Friction welding of dissimilar metals accounts for nearly half of the welds made by the process. Shown in Figure 1 is a cross-section of a typical aluminum-to-steel friction weld. Dissimilar welds such as aluminum-to-steel have often been made on smaller diameter parts (< 1-in. [25 mm]) but have are now possible for larger structural type joints (> 3-in. [75 mm] outside diameter and 0.5-in. [12.5 mm] wall thicknesses). Friction welding is also viable for some cast materials, such as shown in Figure 2.

While most rotary friction welding is used on round, symmetrical parts, linear friction welding and FSW allow for solid state welds to be made on a wider range of part geometries. Figure 3 is a linear friction weld between two rectangular cross-section parts. Alternatively, one of the parts can be of a different shape (e.g. a square cross-section attachment welded to a flat plate surface).

FSW allows for solid-state welding on many different types of joint geometries, however it is most common for making long linear welds. FSW has been used to weld many softer materials (aluminum, copper, magnesium, etc.) for over a decade, and has more recently shown promise for welding harder metal alloys (steels, titanium, and nickel). Shown in Figure 4 is a typical friction stir weld made on ¾-in. (19-mm) thick high-strength steel. Research is currently underway to evaluate tool life and weld properties for FSW of steel.

EWI has been working to advance the friction welding processes for nearly 25 years. Our activities span nearly every market segment to effectively apply friction process variants for a wide range of applications. These technologies offer manufacturers opportunities to join many different materials and material combinations with a fast, environmentally friendly and highly-controlled process.

Questions/comments? Contact Tim Stotler, EWI’s Friction Welding Technology Leader, at [email protected] or 614.688.5221.