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Welding:

Welding is a fabrication or sculptural process that joinsmaterials, usually metals or thermoplastics, by causingcoalescence. This is often done by melting the work piecesand adding a filler material to form a pool of molten material(the weld pool) that cools to become a strong joint, withpressure sometimes used in conjunction with heat, or byitself, to produce the weld. This is in contrast with solderingand brazing, which involve melting a lower-melting-pointmaterial between the work pieces to form a bond betweenthem, without melting the work pieces.

Many different energy sources can be used forwelding, including a gas flame, an electric arc, a laser, anelectron beam, friction, and ultrasound. While often anindustrial process, welding can be done in many differentenvironments, including open air, under water and in outerspace. Regardless of location, however, welding remainsdangerous, and precautions are taken to avoid burns, electric

shock, eye damage, poisonous fumes, and overexposure toultraviolet light.

Until the end of the 19th century, the only weldingprocess was forge welding, which blacksmiths had used forcenturies to join iron and steel by heating and hammeringthem. Arc welding and oxyfuel welding were among the firstprocesses to develop late in the century, and resistancewelding followed soon after. Welding technology advancedquickly during the early 20th century as World War I andWorld War II drove the demand for reliable and inexpensive

joining methods. Following the wars, several modern weldingtechniques were developed, including manual methods like

shielded metal arc welding, now one of the most popularwelding methods, as well as semi-automatic and automaticprocesses such as gas metal arc welding, submerged arcwelding, flux-cored arc welding and electroslag welding.Developments continued with the invention of laser beamwelding and electron beam welding in the latter half of thecentury. Today, the science continues to advance. Robotwelding is becoming more commonplace in industrial settings,and researchers continue to develop new welding methodsand gain greater understanding of weld quality andproperties.

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Oxy-Fuel Gas Welding:

Oxy-fuel welding (commonly called oxyacetylenewelding, oxy welding, or gas welding in the U.S.) and oxy-fuelcutting are processes that use fuel gases and oxygen to weldand cut metals, respectively. French engineers EdmondFouche and Charles Picard became the first to develop anoxygen-acetylene welding set-up in 1903. Pure oxygen,instead of air (20 % oxygen / 80 % nitrogen), is used toincrease the flame temperature to allow localized melting ofthe work piece material (e.g. steel) in a room environment. Acommon propane/air flame burns at about 2, 000 C, apropane/oxygen flame burns at about 2, 500 C, and anacetylene/oxygen flame burns at about 3, 500 C. Since ironmelts at about 1, 500 C (high carbon steel at about 1,150 C), air flames can achieve melting only in a specializedinsulated furnace. Small, high-flow, oxygen flames provideenough heat flow to locally exceed the melting point in a largework piece (e.g., sheet).

Oxy-fuel is one of the oldest welding processes, thoughin recent years it has become less popular in industrialapplications. However, it is still widely used for welding pipesand tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metal-basedartwork. In oxy-fuel welding, a welding torch is used to weldmetals. Welding metal results when two pieces are heated toa temperature that produces a shared pool of molten metal.

The molten pool is generally supplied with additional metalcalled filler. Filler material depends upon the metals to bewelded.

SMAW:

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Shielded metal arc welding (SMAW), also known asmanual metal arc (MMA) welding or informally as stickwelding, is a manual arc welding process that uses aconsumable electrode coated in flux to lay the weld.

An electric current, in the form of either alternatingcurrent or direct current from a welding power supply, is usedto form an electric arc between the electrode and the metalsto be joined. As the weld is laid, the flux coating of theelectrode disintegrates, giving off vapors that serve as ashielding gas and providing a layer of slag, both of whichprotect the weld area from atmospheric contamination.

Because of the versatility of the process and thesimplicity of its equipment and operation, shielded metal arcwelding is one of the world's most popular welding processes.It dominates other welding processes in the maintenance andrepair industry, and though flux-cored arc welding is growingin popularity, SMAW continues to be used extensively in theconstruction of steel structures and in industrial fabrication.

The process is used primarily to weld iron and steels(including stainless steel) but aluminium, nickel and copperalloys can also be welded with this method.

Shielded metal arc welding is one of the world's mostpopular welding processes, accounting for over half of allwelding in some countries. Because of its versatility andsimplicity, it is particularly dominant in the maintenance andrepair industry, and is heavily used in the construction of steelstructures and in industrial fabrication.

In recent years its use has declined as flux-cored arcwelding has expanded in the construction industry and gas

metal arc welding has become more popular in industrialenvironments. However, because of the low equipment costand wide applicability, the process will likely remain popular,especially among amateurs and small businesses wherespecialized welding processes are uneconomical andunnecessary.

SMAW is often used to weld carbon steel, low and highalloy steel, stainless steel, cast iron, and ductile iron. Whileless popular for nonferrous materials, it can be used on nickeland copper and their alloys and, in rare cases, on aluminium.

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The thickness of the material being welded is bounded on thelow end primarily by the skill of the welder, but rarely does itdrop below 0.05 in (1.5 mm). No upper bound exists: withproper joint preparation and use of multiple passes, materialsof virtually unlimited thicknesses can be joined. Furthermore,depending on the electrode used and the skill of the welder,

SMAW can be used in any position.