welding

The main welding techniques - gas welding and arc welding - are first documented at the end of the 19th century. The oxyacetylene process was in use by World War I, and since then, welding techniques have remained essentially the same. Later developments were concerned mainly with equipment and safety.

Shielded metal arc welding, or stick welding, is one of the most commonly used welding processes. The metal to be joined is heated by means of an electric arc created between the welding tool's coated electrode and the metal.

Joining pieces of metal (or non-metal) at faces rendered plastic or liquid by heat or pressure (or both). The principal processes today are gas and arc welding, in which the heat from a gas flame or an electric arc melts the faces to be joined. Additional ‘filler metal’ is usually added to the joint.

Forge (or hammer) welding, employed by blacksmiths since early times, was the only method available until the late 19th century. Resistance welding is another electric method in which the weld is formed by a combination of pressure and resistance heating from an electric current. Recent developments include electric-slag, electron-beam, high-energy laser, and the still experimental radio-wave energy-beam welding processes.