Friction stir welding is a solid-state joining process that uses a rotating tool to join two facing workpieces without melting them. Frictional heat is generated between the shoulder and pin of the tool and the material to create a weld. It was invented in 1991 and has since been adopted by 28 organizations worldwide. Key benefits over fusion welding include improved mechanical properties, reduced distortion and defects, and the ability to weld previously unweldable materials. It can weld in all positions and creates straight or complex welds.