Since its invention in 1991 by The Welding Institute (TWI), Friction Stir Welding (FSW) has been predominantly used for welding aluminum alloys and other soft metals; however significant research over the past decade has enabled the FSW of high melting temperature materials such as steel, titanium, and nickel alloys. FSW is considered a green process as it does not generate any hazardous welding fumes and is energy efficient. Because this process is solid-state, the heat input is lower as compared to other welding processes which results in lower post weld distortion and the elimination of solidification defects. FSW can be applied to almost any type of geometric configuration including butt, lap, corner, fillet, circumferential girth, and T-joints. FSW has been proven on a wide range of materials including aluminum, copper, magnesium, steel, titanium, and nickel based alloys. Currently, single pass welds can be made on aluminum alloys up to 75 mm thick, steel up to 19 mm thick, and titanium up to 25 mm thick.
FSW joins materials through the use of a non-consumable rotating tool. A typical FSW tool is comprised of two main components: the shoulder and the pin (Figure 1). The rotating tool is plunged at the start of the joint until it is at the appropriate depth; where the shoulder contacts the material. The tool then traverses along the weld joint while continuing to rotate. After traveling the desired length, the tool is retracted. 
During welding, the material is heated by a combination of frictional and adiabatic heating, plasticizing the base material. This plasticized material is rotated around the tool and consolidated due to compressive forces from the tool. Due to the rotation rate and compressive forces applied by the tool, the base material experiences a high strain rate which promotes dynamic recrystallization. This phenomenon leads to a very fine grain microstructure.
Two variations of this process have emerged taking advantage of the microstructural modification caused by FSW. Friction Stir Spot Welding (FSSW) utilizes the benefits of FSW, but in a spot weld configuration similar to Resistance Spot Welding. Friction Stir Processing (FSP) can modify large areas of a base material in order to vary the through thickness properties of a monolithic plate. FSP can also be used to refurbish worn parts, heal cracks, and enhance traditional arc welds. For these reasons and others, FSW and its process variations, have seen acceptance across a broad range of industries including aerospace, automotive, defense, oil and gas, transportation, and consumer products.
If you would like to learn more about FSW and how this process could benefit your organization, please consider attending EWI’s Introduction to Friction Stir Welding and Process Fundamentals course on December 6th. This one-day course will introduce attendees to the Friction Stir Welding (FSW) process and its derivatives; Friction Stir Spot Welding (FSSW) and Friction Stir Processing (FSP). It will provide a solid background on the issues that influence the FSW process and reviews current industry applications. This course is for those who are new to the FSW process or need to become more proficient in FSW terminology, equipment, procedures development, and capabilities. For more information on how to register, please click on the link below.