welding

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.

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

welding Technique for joining metal parts, usually by controlled melting. Several welding processes are used. In fusion welding, the parts to be joined are heated together until the metal starts to melt. On cooling, the molten metal solidifies to form a permanent bond between the parts. Such welds are usually strengthened with filler metal from a welding rod or wire. In arc welding, an electric arc heats the work and filler metal. In oxyacetylene welding, heat is provided by burning ethyne gas in oxygen. In resistance or spot welding, the heat is generated by passing an electric current through the joint. In brazing and soldering, the temperature used is sufficient to melt the filler metal, but not the parts that it joins.