welding, process for joining separate pieces of metal in a continuous metallic bond. Cold-pressure welding is accomplished by the application of high pressure at room temperature; forge welding (forging) is done by means of hammering, with the addition of heat. In most processes in common use, the metal at the points to be joined is melted; additional molten metal is added as a filler, and the bond is allowed to cool. In the Thomson process, resistance to an electric current, passed through the sections to be joined, causes them to melt. Other notable methods include the thermite process, oxyacetylene, electric arc, oxyhydrogen, and the atomic hydrogen flame. In this last-named method, molecules of hydrogen gas passing through an electric arc are broken up into atoms of hydrogen by absorbing energy; when outside the arc, the atoms reunite into molecules, yielding in the process enough heat to weld the material. Another process, the argon-arc method, is widely used with metals such as stainless steel, aluminum, magnesium, and titanium, which require an inert atmosphere for successful welding. The use of argon prevents slag from forming in the weld and greatly increases the speed of the welding.

See A. C. Davies, The Science and Practice of Welding (6th ed. 1972); J. E. Brumbaugh, Welder's Guide (3d ed. 1983).

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