Classification of Processes:

Welding procedure may be classified according to the way in which the four fundamental requirements - particularly the first three - are satisfied as explined in Section 11.2. The energy for welding is almost supplied as heat so that divisions might be made according to the methods by which the heat is produced locally. These methods might be defined and grouped as follows :

Mechanical

Heat produced by impact or friction or liberated by the elastic or plastic deformation of the metal.

Thermochemical

Exothermic reactions, flames and arc plasmas. It is essential to explain why plasmas must be put in the same class as oxyfuel gas flames. Though chemical reactions might not occur in a plasma the method of heat transfer to the work is the similar as for processes employing an envelope of burning gas. This holds for all procedures in which the work does not form part of the arc circuit. The so-called non-transferred arc generated a plasma flame, while the transferred arc is a constricted arc and falls in the arc-process category.