What does FSW mean in welding?

FSW stands for Friction Stir Welding.
Invented in 1991 by The Welding Institute (TWI), the FSW process is based on the assembly of two parts by heating the materials. The pasty state is obtained thanks to the friction of a rotating tool coupled with a kneading that generates the plastic deformation.
The major advantage of friction stir welding is its ability to join two parts without reaching fusion temperature. This is called cold welding. Thus, the material does not undergo cracks, deformations or loss of resistance as during a traditional fusion welding.