Electric Resistance:
Heat produced by either the passage of a current introduced directly to the metal to be joined or by a current induced within the parent metal.
Radiant Energy:
This category is recommended to cover the new procedure such as laser and electron- beam welding and others, which might yet to be developed. The necessary feature of a radiant-energy procedure is that energy is focused on the workpiece and heat is produced only where the focused beam is intercepted.