Welding
Welding is an operation in which two or more parts or metals (similar or dis-similar) are united by means of pressure in such a way that there is continuity in the nature of the material (metal) between these parts. A filler metal, whose melting temperature is of the same order as that of the parent material, may or may not be used.
(welding)
Classification of Welding:

Fig. 1.1 classification of welding processes

Friction stir welding
Introduction: Friction stir welding is a solid state welding. It is the process of joining of metallic components of similar or dis-similar material with the help of a cylindrical rotating tool. After the tool put into the rotation, due to friction between tool and workpiece, heat is generated which softens the material around the tool probe. The localized plastic deformation process occurring in the workpiece due to friction. The plastic deformation occurs at higher temperature, but lower than the melting point temperature of the workpiece. The tool softens both the components around the interface and mixes the softened material from both the components around the interface to provide bonding. On cooling a solid phase bond is created between the workpiece.

Fig. 1.2 friction stir welding

Principle of friction stir welding:
At first, the sheets or plates are abutted along edge to be welded and the rotating pin is sunken into the sheets/plates until the tool shoulder is in full contact with the sheets or plates surface.