Friction stir welding, a process invented at Cambridge, involves the joining of metals without fusion or filler materials. It is used already in routine, as well as critical applications, for the joining of structural components made of aluminium and its alloys. Indeed, it has been convincingly demonstrated that the process results in strong and ductile joints, sometimes in systems which have proved difficult using conventional welding techniques. The process is most suitable for components which are flat and long (plates and sheets) but can be adapted for pipes, hollow sections and positional welding. The welds are created by the combined action of frictional heating and mechanical deformation due to a rotating tool. The maximum temperature reached is of the order of 0.8 of the melting temperature.
It's a manufacturing process welding type that really shows potential for things like building cars and other production items.
Wikipedia calls it the "Frictional heat is generated between the wear resistant welding tool shoulder and nib, and the material of the work-pieces. This heat, along with the heat generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without reaching the melting point (hence cited a solid-state process), allowing the traversing of the tool along the weld line in a a plasticised tubular shaft of metal. As the pin is moved in the direction of welding the leading face of the pin, assisted by a special pin profile, forces plasticised material to the back of the pin whilst applying a substantial forging force to consolidate the weld metal. The welding of the material is facilitated by severe plastic deformation in the solid state involving dynamic recrystallization of the base material."
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