Connection of two surfaces in the electric resistance welding (ERW) is done by simultaneous heating and compressing. Due to having electrical resistance, metals are heated by electric current and may even reach their melting phase. Applying electric current with high density in short duration causes the considered component to become soft (before melting), and applying pressure before and during the passage of electric current guaranteed the connection, leading to forging the welding area at the time when the piece is heated. The compression continues after disconnection of electricity, helping the forging stage and cooling the welding area. The max temperature that is available in these processes is usually higher than the melting point of the base metal.
There is one or more arc(s) between the metal electrode or electrodes (solid welding filler wire) and the weld pool in arc welding process. The arc and the molten metal are protected by welding powder or lubricating granules on the working piece. The process does not apply pressure and the filler metal is provided by electrodes (filler wire) or sometimes an extra source (filler wire, metal granules or lubricant). Since the electric arc is hidden in this process under the welding powder, this process is also sometimes called hidden arc welding. in the submerged welding, one end of the filler wire is placed in the accumulated lubricating substance that covers the welding area or the connection area. Arc is produced by the impact of electrode and the surface of the working piece. The filler wires, except the stainless steel filler wires have copper coating. Copper coating is to ensure appropriate transmission of electricity, reducing the erosion of nozzles and preventing corrosion of the filler wires, especially during storage. The used filler wires in the submerged arc welding should have clean surface without any pollutants. Anyhow, some filler wires with small diameters are covered by hydrogen-free grease to have easy movement from inside the nozzles and their moving routes.