Friction Stir Welding (FSW) is a state of the art process of welding metal together.  Conventional welding melted the metal together and added material, which adversely changes the properties the original metal.  Friction stir welding maintains more of its original  properties, which creates a stronger joint.  FSW done by butting two pieces of metal together then driving a tool that is rotating at high rpm, between the metals. 

                                  Cross Section of Weld