Piece of steel showing a friction stir weld join, 2000.
© Science Museum / Science & Society Picture Library
Friction stir welding (FSW) was invented by Wayne Thomas of the Welding Institute in 1991. It is actually a solid-state joining proces that is a combination of extruding and forging rather than a true welding proces. FSW occurs at a temperature below the melting point of the material being worked on, unlike fusion welding, in which the material has to be melted before pieces can be joined together. Frictional heat is generated between a rotating welding tool and two pieces of sheet or plate material, which are butted together. The heat causes the material to soften without reaching its melting point and allows the tool to traverse the weld line, making a solid phase bond between the two pieces. FSW is a safer and more energy efficient proces than conventional welding.