The word weld once meant to boil, and slipped into Isaiah
Weld grew out of an old verb meaning to well up or boil, with a stray d tacked on. The shift shows up in English Bibles: John Wycliffe's 14th-century translation has people beating swords into ploughshares, but a 1590 version has them welding the swords together instead.
The root is Scandinavian, akin to Swedish välla, which could mean to boil, bubble over or melt; the Swedish term for the raw material of wrought iron literally means boiling iron. Old English called joining iron samodwellung. By Middle English, weld had become a variant of well, to spring up like a fountain, and came to mean heating metal fiercely or hammering it hot. The first English record dates from 1590.
Joining metal is far older than the word. In the Bronze Age, gold was soft enough to press together with little or no heat, and archaeologists have found small boxes made from overlapping gold sheets. Iron Age smiths developed forge welding, heating metal until it was malleable and hammering pieces together; a dagger buried with Tutankhamun was forged from meteoric iron below 950 degrees Celsius. Herodotus credited Glaucus of Chios with inventing iron welding, citing an iron stand he made at Delphi to hold a silver bowl. Greek and Roman sculptors did true fusion welding, pouring molten bronze into the seams between separately cast sections of large statues. Forge welding also produced the 5.4-tonne Iron Pillar of Delhi around 310 AD.
Electricity transformed the craft. Humphry Davy found a short-pulsed electric arc in 1800, and in 1802 the Russian scientist Vasily Petrov produced a continuous arc and suggested it could melt metals. In 1881 Auguste de Méritens used an arc to join lead battery plates, and his pupil Nikolai Benardos, with Stanisław Olszewski, devised carbon arc welding. Until the late 19th century, forge welding had been the only method.
Demand during the world wars accelerated development, and afterwards came shielded metal arc welding, now among the most common techniques, along with automated processes. Modern welders melt the base metal, usually add filler to form a weld pool that can end up stronger than the surrounding material, and shield it from oxidation. Heat may come from a gas flame, an arc, a laser, an electron beam, friction or ultrasound, and the work is done underwater and even in space.
Source: Welding
