Friction stir welding (FSW) is a patented joining process, which was invented at TWI ten years ago. A wear resistant rotating tool is used to join sheet and plate materials such as aluminium, copper and lead. In laboratory experiments, aluminium based metal matrix composites, magnesium alloys, zinc, titanium alloys and steels have also been friction stir welded. The welds are made below the melting point in the solid phase. The excellent mechanical properties and low distortion are attributed to the low heat input and the absence of melting. As it is a solid phase process, FSW permits joining of materials that cannot be welded with conventional fusion welding processes.In the aerospace industry, large tanks for launch vehicles are being produced by FSW from high-strength aluminium alloys, and a Delta II rocket with a friction stir welded Interstage Module has successfully been launched in August 1999. In the shipbuilding and rolling stock industry several companies now exploit the process, e.g. for the production of large prefabricated aluminium panels, which are made from extrusions. The automotive industry uses FSW in the high-volume production of components (light alloy wheels and hollow aluminium extrusions). Research and production FSW machines are commercially available and include installations for welding up to16m lengths.
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