There are many ways in which welding processes may be grouped and different countries have adopted various classification schemes based on the application of heat, whether external pressure is applied, the type of energy involved (mechanical, electrothermic, thermochemical), etc. The American Welding Society (AWS) groups welding processes based primarily on the mode of energy transfer, and secondarily on the influence of capillary action in effecting distribution of filler metal in the joint (as in brazing and soldering).
AWS defines welding as “a joining process that produces coalescence (i.e. growing together) of materials by heating them to the welding temperature, with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material”. In the AWS approach, welding processes are grouped into the following major categories:
- arc welding (AW) g soldering (S)
- solid state welding (SSW) g brazing (B)
- resistance welding (RW) g other welding
- oxyfuel gas welding (OFW) g allied processes (such as cutting, thermal spraying)
Arc welding processes are, by far, the most commonly used in the welding industry and are, therefore, the main focus in this book. However, arc welding involves melting and most metals, when melted in air, become contaminated with oxides and nitrides through contact with the oxygen and nitrogen in the air. This contamination may result in a poor quality weld. Most arc welding processes have some means of shielding (protecting) the molten metal from the air or some other means of removing the
harmful effects of oxygen and nitrogen. The two main methods of arc shielding are:
- flux shielding
- gas shielding
Most of the arc welding processes are distinguished principally by the method of shielding or the way in which it is applied.
The exact selection of an arc welding process for a particular application involves several considerations including:
- Is the process suitable for welding the metal or alloy involved? In the required thickness and position?
- Would the welded joint have the required quality and physical (mechanical, corrosion) properties?
- Is it the most economical of the available choices?
- Are the equipment and skilled welders available for the chosen process?