Welding is a fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperatures to melt the parts together and allow them to cool, causing fusion. Common alternative methods include solvent welding (of thermoplastics) using chemicals to melt materials being bonded without heat, and solid-state welding processes which bond without melting, such as pressure, cold welding, and diffusion bonding. Metal welding is distinct from lower-temperature bonding techniques such as brazing and soldering, which do not melt the base metal (parent metal) and instead require flowing a filler metal to solidify their bonds. In addition to melting the base metal in welding, 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 can be stronger than the base material. Welding processes use some form of shielding to protect the melting 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 the open air, underwater, 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 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, as 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.
Etymology The term weld is derived from a Scandinavian word and is possibly related to the Swedish välla (to well) or Danish vælde (to well up or overflow). In the 8th century AD, a period known as the Viking Age began, and Scandinavians settled across England, resulting in loan words, shifts in word meaning, and grammatical changes. In many languages, the terms for welding are related to those for boiling or bubbling. In Old Swedish, välla can mean to boil, to bubble up, to overflow, to boil over, or to melt. The Swedish word for the raw material used to make wrought iron is välljärn, literally meaning "boiling iron". The Old English word for welding iron together was samodwellung. Derived from the Old English weallan, weld entered usage in Middle English as an alternative form of the verb well (wæll), meaning 'to spring up' (as if from a fountain) or 'to boil'. The added 'd' was excrescent, a consonant added without etymological rationale. It came to mean to boil, to heat to a high degree, or to beat iron after heating. The word was first recorded in English in 1590. A 14th-century translation of the Christian Bible into English by John Wycliffe translated Isaiah 2:4 as "...thei shul bete togidere their swerdes into shares..." (they shall beat together their swords into plowshares). In a 1590 version, this was changed to "...thei shullen welle togidere her swerdes in-to scharris..." (they shall weld together their swords into plowshares), suggesting that this use of the word became popular in English sometime between these periods.
History
The history of joining metals goes back several millennia. Fusion welding processes that join metals by melting them were not widely used in pre-industrial welding. Early welding techniques used pressure to join the metals, often with heat not sufficient to fully melt the base metals. One notable exception was a technique to join sections of large statues. In Greek and Roman lost-wax casting, the statues were cast as smaller pieces and molten bronze was poured into the joints with temperatures sufficient to create fusion welds. The earliest known welding dates to the Bronze Age. Gold is soft enough to be pressure welded with little to no heat, and archaeologists have found small boxes made by pressure welding overlapping sheets of gold. In the Iron Age, Mediterranean societies developed forge welding. In forge welding, metal is heated to the point that it becomes soft enough for a blacksmith to hammer separate pieces together. Very early examples include the iron objects found with Tutankhamun including an iron headrest and dagger. The dagger was forged from meteoric iron at temperatures below 950 °C (1,740 °F). Iron metallurgy was independently developed at least twice: in Anatolia by 1800 BC and in China by around 900 BC. Typically, wrought iron is forged at around 1,350 °C (2,460 °F). The ancient Greek historian Herodotus credits Glaucus of Chios with discovering "iron welding". Glaucus is known for an iron pedestal welded to hold a silver krater at Delphi. By the 7th century BCE, blast furnaces were developed in China, but the technology traveled westward only during the Islamic Golden Age. By the time they arrived in Europe, blast furnaces were being independently developed in modern-day Germany.
… excerpt ends here. Continue reading the full article.
