Arc welding is a general term for a handful of various welding processes that make use of an electric arc to generate heat and create the molten puddle.
The controllable electric arc was discovered in 1800. It was essentially a battery-powered bolt of lightening sparking between two solid carbon rods. By 1850, electric arcs replaced whale oil in street lamps. Carbon-arc welding came about in 1880, but was limited due to the carbon's causing impurities and brittleness in welds. Metal-arc welding happened at about the same time and had greater development potential. The first metal-arc process to be discovered that is still widely used was Shielded Metal Arc Welding (SMAW).
Unlike carbon-arc welding, in metal-arc welding, the metal rod became a part of the electrical circuit, carried the heat required to melt the base metal, and also melted to become a part of the weld.
Early metal-arc processes resulted in welds that were porous, brittle and weak. For a while, it was a mystery why corroded (iron oxide covered) metal rods actually performed better than non-corroded ones, but it subsequently was learned that the iron oxide provided some shielding from atmospheric gasses; the importance of shielding was learned.
Gas Tungsten Arc Welding (GTAW) became widely used during World War II in the production of aircraft. GTAW uses a rod (electrode) made of tungsten that does not get consumed. The first shielding gas used with GTAW was helium, so GTAW was sometimes called heliarc welding.
In 1948, a hybrid between SMAW and GTAW was invented. Like SMAW, it had a consumable metal, and like GTAW, it used gas for shielding. It also introduced something new: instead of a rod, it had a spool of wire continuously fed by motor. It was called wirefeed welding, but is correctly known today as Gas Metal Arc Welding (GMAW). The initial shielding gas used with GMAW was argon, which was expensive and later replaced with carbon dioxide.
