It is a joining process that is used in large pieces of metals, particularly on aluminum. At each instance, the joint is formed in a solid state and the metal characteristics remain unchanged as far as possible. This process is more advantageous than the conventional welding process by the following features such as, it has good mechanical properties with improved safety, requires no consumables and operated in all positions and it emits no radiation, welding fumes and spattering, fully automated process with little maintenance. Tool rotation, traverse speeds, tool tilt, plunge depth and tool design are its important welding parameters. This process is suitable to materials such as copper, lead, titanium, magnesium, zinc, plastic and nickel and it is used to recover the temper characteristics. It was invented by Wayne Thomas and its colleagues in 1991.