Welding is a method of permanently joining two pieces of a material (or materials) owing to the formation of bonds between atoms. Welding is applicable to metals and non-metals, such a glass, plastics, graphite, and some rocks. All existing welding processes used in engineering industries may be divided into two broad systems: fusion welding and pressure welding. In fusion welding, the two pieces to be joined are heated to a melting point at the joint, a filter metal is added, the weld pool is stirred,and a weld is allowed to form on cooling. In some fusion welding processes, no filler metal is used. In pressure welding, the workpiece is raised at the joint to a temperature below the melting point of the material, and a weld is formed by applying pressure.

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