Welding

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool causing fusion. Welding is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal. In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material (the weld pool) that cools to form a joint that, based on weld configuration (butt, full penetration, fillet, etc.), can be stronger than the base material (parent metal). Pressure may also be used in conjunction with heat, or by itself, to produce a weld. Welding also requires a form of shield to protect the filler metals or melted metals from being contaminated or oxidized. Many different energy sources can be used for welding, including a gas flame (chemical), an electric arc (electrical), a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding may be performed in many different environments, including in open air, under water, and in outer space. Welding is a hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation. Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for millennia to join iron and steel by heating and hammering. Arc welding and oxy-fuel welding were among the first processes to develop late in the century, and electric resistance welding followed soon after. Welding technology advanced quickly during the early 20th century as the world wars drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. Developments continued with the invention of laser beam welding, electron beam welding, magnetic pulse welding, and friction stir welding in the latter half of the century. Today, the science continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality. The term 'weld' is of English origin, with roots from Scandinavia. It is often confused with the Old English word, weald, meaning 'a forested area', but this word eventually morphed into the modern version, 'wild'. The Old English word for welding iron was samod (to bring together) or samodwellung (to bring together hot, with 'hot' more relating to red-hot or a swelling rage; in contrast to samodfæst, 'to bind together with rope or fasteners'). The term 'weld' is derived from the Middle English verb 'well' (wæll; plural/present tense: wælle) or 'welling' (wællen), meaning: 'to heat' (to the maximum temperature possible); 'to bring to a boil'. The modern word was likely derived from the past-tense participle, 'welled' (wællende), with the addition of 'd' for this purpose being common in the Germanic languages of the Angles and Saxons. It was first recorded in English in 1590, from a version of the Christian Bible that was originally translated into English by John Wycliffe in the fourteenth century. The original version, from Isaiah 2:4, reads, '...thei shul bete togidere their swerdes into shares...' (they shall beat together their swords into plowshares), while the 1590 version was changed to, '...thei shullen welle togidere her swerdes in-to scharris...' (they shall weld together their swords into plowshares), suggesting this particular use of the word likely became popular in English sometime between these periods. The word is derived from the Old Swedish word valla, meaning 'to boil'. Sweden was a large exporter of iron during the Middle Ages, and many other European languages used different words but with the same meaning to refer to welding iron, such as the Illyrian (Greek) variti (to boil), Turkish kaynamak (to boil), Grison (Swiss) bulgir (to boil), or the Lettish (Latvian) sawdrit (to weld or solder, derived from wdrit, to boil). In Swedish, however, the word only referred to joining metals when combined with the word for iron (jarn), as in valla jarn (literally: to boil iron). The word possibly entered English from the Swedish iron trade, or possibly was imported with the thousands of Viking settlements that arrived in England before and during the Viking Age, as more than half of the most common English words in everyday use are Scandinavian in origin. The history of joining metals goes back several millennia. The earliest examples of this come from the Bronze and Iron Ages in Europe and the Middle East. The ancient Greek historian Herodotus states in The Histories of the 5th century BC that Glaucus of Chios 'was the man who single-handedly invented iron welding'. Welding was used in the construction of the Iron pillar of Delhi, erected in Delhi, India about 310 AD and weighing 5.4 metric tons. The Middle Ages brought advances in forge welding, in which blacksmiths pounded heated metal repeatedly until bonding occurred. In 1540, Vannoccio Biringuccio published De la pirotechnia, which includes descriptions of the forging operation. Renaissance craftsmen were skilled in the process, and the industry continued to grow during the following centuries.