Editing Welding (section)

==Processes==
[[File:MIG welding.webm|thumb|thumbtime=2|[[Gas metal arc welding]] (GMAW) filmed through a shaded lens<ref>{{cite web |last=MacDonald |first=Chris |date=16 July 2020 |url=https://www.youtube.com/watch?v=tDcR9tHguIA&t=109s |title=Hey! Trying to Film Some Welding Here!|work=Just1Guy Metalworks |time=1:49}}</ref>]]

Welding joins two pieces of metal using heat, pressure, or both. The most common modern welding methods use heat sufficient to melt the base metals to be joined and the filler metal.<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|p=48}}</ref> This includes [[gas welding]] and all forms of [[arc welding]].<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|pp=35-57}}</ref> The area where the base and filler metals melt is called the [[weld pool]] or puddle.<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|p=48}}</ref> The weld pool must be protected from oxygen in the air that will oxidize with the molten metal and from other gases that could contaminate the weld.<ref>{{harvnb|Weman|2003|p=12}}</ref> Most welding methods involve pushing the puddle along a [[welding joint|joint]] to create a weld bead.<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|p=96}}</ref> Overlapping pieces of metal can be joined by forming the weld pool within a hole made in the topmost piece of base metal to form a plug weld.<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|pp=118, 120}}</ref> 

Solid-state welding processes join two pieces of metal using pressure.<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|p=542}}</ref> [[Electric resistance welding]] is a common industrial process that combines heat and pressure to join overlapping base metals without any filler material.<ref>{{harvnb|Bowditch|Bowditch|Bowditch|2017|pp=39, 486}}</ref>  

===Gas welding===
{{main|Oxy-fuel welding and cutting}}
[[File:Oxyfuel gas welding operation-no.svg|thumb|right|alt=diagram|Diagram of oxyfuel welding:
{{image key
|list type=ordered
|Torch tip
|Filler rod
|Flame (outer envelope)
|Fusion
|Base metal
|Weld metal
}}]]

Gas welding, also known as oxyacetylene welding, uses an open flame to generate heat and shield the weld. Compared to arc welding, the flame is less concentrated and lower in temperature, about 3100&nbsp;°C (5600&nbsp;°F) near the torch tip. This causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. The diffuse outer envelope of the flame consumes oxygen before it can reach the molten weld pool.<ref name="Weman26" /> When working with easily oxidized metals, such as stainless steel, flux can be brushed onto the base metals.<ref>{{harvnb|Weman|2003|p=30}}</ref>

The equipment is relatively inexpensive and simple, consisting of a torch, hoses, pressure regulators, a tank of [[oxygen]], and a tank of fuel (usually [[acetylene]]).<ref>{{harvnb|Weman|2003|pp=26-29}}</ref> It is one of the oldest and most versatile welding processes, but it has become less popular in industrial applications. It is still widely used for welding pipes and tubes, as well as repair work.<ref name="Weman26" /> A similar process, generally called oxyfuel cutting, is used to cut metals. Oxyfuel equipment can also be used to heat metal before bending or straightening.<ref>{{harvnb|Weman|2003|pp=26-29}}</ref>

===Arc welding===
{{Main|Arc welding|Shielded metal arc welding| Gas tungsten arc welding| Gas metal arc welding| Flux-cored arc welding| Submerged arc welding| Electroslag welding}}
[[File:Weld puddle, also known as a weld pool or welding pool.png|thumb|upright=1.3|Welding seen from a welder's perspective through a shaded lens (left) and from the side without a shaded lens (right)<ref>From video by Jose Bueno: {{cite web |last=Bueno |first=Jose |date=2023 |url=https://www.youtube.com/watch?v=KHb5lU1k_OI&t=857s  |title=SMAW - Single Bevel 2G Welding Project |work=Bueno's Handyworks |time=15:10 |archive-url=https://web.archive.org/web/20230512052647/https://www.youtube.com/watch?v=KHb5lU1k_OI |archive-date=12 May 2023}}</ref>]]

All arc welding processes use a [[welding power supply]] to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use [[alternating current]] (AC) or [[direct current]] (DC). For DC welding, the electrode can be connected to the machine's positive terminal (DCEP) or negative terminal (DCEN), changing the current's direction. The process and type of electrode used will typically determine the current.<ref>{{cite web |title=How Polarity Affects Electrode Performance in Arc Welding |url=https://www.kobelco-welding.jp/education-center/abc/ABC_2002-02.html |website=Kobelco |access-date=3 February 2025}}</ref><ref>{{cite book |last1=Hughes |first1=S. E. |title=A Quick Guide to Welding and Weld Inspection |date=20 October 2009 |publisher=Elsevier |isbn=978-1-84569-767-9 |url=https://www.google.com/books/edition/A_Quick_Guide_to_Welding_and_Weld_Inspec/OamjAgAAQBAJ |language=en}}</ref> 

[[Shielding gas]] prevents oxygen in the atmosphere from entering the molten weld pool. In some processes, the shielding gas is delivered from [[gas cylinder]]s containing inert or semi-[[inert gas]]. In others, a flux coating on a consumable electrode disintegrates to create the gas.<ref>{{Cite journal |last=Thomas |first=Daniel J. |date=2018-04-01 |title=Analyzing the Failure of Welded Steel Components in Construction Systems |journal=Journal of Failure Analysis and Prevention |language=en |volume=18 |issue=2 |pages=304–314 |doi=10.1007/s11668-018-0392-x |s2cid=139797543 |issn=1864-1245|doi-access=free }}</ref><ref>{{cite web |last1=Molyneaux |first1=Justin |title=Flux-Cored Arc Welding Shielding Gas Basics |url=https://www.canadianmetalworking.com/canadianfabricatingandwelding/blog/welding/flux-cored-arc-welding-shielding-gas-basics |website=Canadian Metalworking |publisher=FMA Communications Canada |date=March 1, 2024}}</ref> Filler material is typically added to the molten weld pool and is necessary for processes that use a consumable electrode.<ref>{{cite web |title=Difference between Filler Metal and Electrode |url=https://aqcinspection.com/difference-between-filler-metal-and-electrode/ |website=AQC Inspection |access-date=3 February 2025 |date=21 November 2022}}</ref>

====Arc welding processes====
[[Image:SMAW area diagram.svg|thumb|right|Diagram of arc and weld area, in shielded metal arc welding:
{{image key
|list type=ordered
|Flux coating
|Core wire
|Shield gas
|Fusion
|Base metal
|Weld metal
|Solidified slag
}}]]

One of the most common types of arc welding is [[shielded metal arc welding]] (SMAW);<ref name="Weman63">{{harvnb|Weman|2003|p=63}}</ref> it is also known as manual metal arc welding (MMAW) or stick welding. Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of filler material (typical steel) and is covered with a flux that protects the weld area from [[redox|oxidation]] and contamination by producing [[carbon dioxide]] (CO<sub>2</sub>) gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary.<ref name="Weman63" />

The process is versatile and can be performed with relatively inexpensive equipment, making it well suited to shop jobs and field work.<ref name="Weman63" /><ref name="Cary103">{{harvnb|Cary|Helzer|2005|p=103}}</ref> An operator can become reasonably proficient with a modest amount of training and can achieve mastery with experience. Weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding.<ref name="Weman63" /> Furthermore, the process is generally limited to welding ferrous materials, though special electrodes have made possible the welding of [[cast iron]], stainless steel, aluminum, and other metals.<ref name="Cary103" />

[[File:GMAW weld area.svg|thumb|alt=diagram|Gas metal arc welding:{{image key|list type=ordered
|Travel
|Contact tube
|Electrode
|Shielding gas
|Fusion
|Weld metal
|Base metal}}
]]

[[Gas metal arc welding]] (GMAW), also known as metal inert gas or MIG welding, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and an inert or semi-inert gas mixture to protect the weld from contamination. Since the electrode is continuous, welding speeds are greater for GMAW than for SMAW.<ref name="LE5.43">{{harvnb|Lincoln Electric|1994|p=5.4-3}}</ref>

[[File:FCAW diagram.svg|thumb|alt=diagram|Flux-cored arc welding: {{image key|list type=ordered
|Flux core
|Tubular electrode
|Shield Gas
|Fusion
|Base metal
|Weld metal
|Solidified slag}}]]

A related process, [[flux-cored arc welding]] (FCAW), uses similar equipment but uses wire consisting of a tubular steel electrode surrounding a powder fill material. This cored wire is more expensive than the standard solid wire and can generate fumes and/or slag, but it permits even higher welding speed and greater metal penetration.<ref>{{harvnb|Weman|2003|p=53}}</ref> As the electrode is consumed, the flux disintegrates to create shielding gas and a protective layer of slag similar to stick welding. Some flux-cored machines have a nozzle that uses a shielding gas to supplement the protection from the flux. This is called dual shield welding, and uses a specialized gas shielded flux-core wire.<ref>{{Cite web |title=Solid Wire Versus Flux Cored Wire: When to Use Them and Why |url=http://www.millerwelds.com/education/articles/article62.html |archive-url=https://web.archive.org/web/20061015112618/http://www.millerwelds.com/education/articles/article62.html |archive-date=15 October 2006 |website=Miller}}</ref>

[[File:GTAW.svg|Gas tungsten arc welding|thumb|alt=diagram]]
[[Gas tungsten arc welding]] (GTAW), or tungsten inert gas (TIG) welding, is a manual welding process that uses a non-consumable [[tungsten]] electrode, an inert or semi-inert gas mixture, and a separate filler material.<ref name="Weman31">{{harvnb|Weman|2003|p=31}}</ref> Especially useful for welding thin materials, this method is characterized by a stable arc and high-quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds.<ref name="Weman31" />

GTAW can be used on nearly all weldable metals, though it is most often applied to [[stainless steel]] and light metals. It is often used when quality welds are extremely important, such as in [[bicycle]], aircraft and naval applications.<ref name="Weman31" /> A related process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process. Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process and it is much faster. It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is one important application of the process. A variation of the process is [[plasma cutting]], an efficient steel cutting process.<ref>{{harvnb|Weman|2003|pp=37–38}}</ref>

[[Submerged arc welding]] (SAW) is a high-productivity welding method in which the arc is struck beneath a covering layer of flux. This increases arc quality since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself, and combined with the use of a continuous wire feed, the weld deposition rate is high. Working conditions are much improved over other arc welding processes, since the flux hides the arc and almost no smoke is produced. The process is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels.<ref>{{harvnb|Weman|2003|p=68}}</ref> Other arc welding processes include [[atomic hydrogen welding]], [[electroslag welding]] (ESW), [[electrogas welding]], and [[stud arc welding]].<ref>{{harvnb|Weman|2003|pp=93–94}}</ref> ESW is a highly productive, single-pass welding process for thicker materials between 1 inch (25&nbsp;mm) and 12 inches (300&nbsp;mm) in a vertical or close to vertical position.

====Arc welding power supplies====
To supply the electrical power necessary for arc welding processes, a variety of different power supplies can be used. The most common welding power supplies are constant [[electrical current|current]] power supplies and constant [[voltage]] power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux-cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.<ref>{{harvnb|Cary|Helzer|2005|pp=246–249}}</ref>

The type of current used plays an important role in arc welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged [[anode]] will have a greater heat concentration, and as a result, changing the polarity of the electrode affects weld properties. If the electrode is positively charged, the base metal will be hotter, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds.<ref>{{harvnb|Kalpakjian|Schmid|2001|p=780}}</ref> Non-consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current, as well as alternating current. However, with direct current, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds.<ref>{{harvnb|Lincoln Electric|1994|p=5.4–5}}</ref> Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossings, has been addressed with the invention of special power units that produce a [[Square wave (waveform)|square wave]] pattern instead of the normal [[sine wave]], making rapid zero crossings possible and minimizing the effects of the problem.<ref>{{harvnb|Weman|2003|p=16}}</ref>

===Resistance welding===
{{Main|Resistance welding}}

Resistance welding generates heat from [[electrical resistance]] in the base metals. Two electrodes are simultaneously used to press the metal sheets together and to pass current through the sheets. The electrodes are made from highly conductive material, usually copper. The higher resistance in the base metals causes small pools of molten metal to form at the weld area as high current (1,000–100,000 [[Ampere|A]]) is passed through.<ref name="Weman8084">{{harvnb|Weman|2003|pp=80–84}}</ref> 

[[Image:Spot welder.miller.triddle.jpg|thumb|Spot welder]]
Resistance [[spot welding]] is a popular method used to join overlapping metal sheets of up to 3&nbsp;mm thick. The advantages of the method include [[efficient energy use]], limited workpiece deformation, high production rates, easy automation, and no required filler materials. Weld strength is significantly lower than with other welding methods, making the process suitable for only certain applications. It is used extensively in the automotive industry—ordinary cars can have several thousand spot welds made by [[industrial robot]]s. In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the equipment cost can be high. A specialized process called [[shot welding]], can be used to spot weld stainless steel.<ref name="Weman8084" />

[[Seam welding]] also relies on two electrodes to apply pressure and current to join metal sheets. However, instead of pointed electrodes, wheel-shaped electrodes roll along and often feed the workpiece, making it possible to make long continuous welds. In the past, this process was used in the manufacture of beverage cans, but now its uses are more limited.<ref name="Weman8084" /> Other resistance welding methods include [[butt welding]],<ref>{{Cite book|author = John Jernberg| title = Forging| page = [https://archive.org/details/forgingmanualpr00jerngoog/page/n38 26]| publisher = American Technical society| year = 1919| url = https://archive.org/details/forgingmanualpr00jerngoog}}</ref> [[flash welding]], [[projection welding]], and [[upset welding]].<ref name="Weman8084" />

===Energy beam welding===
Energy beam welding methods, namely [[laser beam welding]] and [[electron beam welding]], are relatively new processes that have become quite popular in high production applications.<!--Reference is at the end of the paragraph--> The two processes are quite similar, differing most notably in their source of power. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses an electron beam. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area. Both processes are extremely fast, and are easily automated, making them highly productive. The primary disadvantages are their very high equipment costs (though these are decreasing) and a susceptibility to thermal cracking.<!--Reference at the end of the paragraph--> Developments in this area include [[laser-hybrid welding]], which uses principles from both laser beam welding and arc welding for even better weld properties, [[cladding (metalworking)|laser cladding]], and [[x-ray welding]].<ref>{{harvnb|Weman|2003|pp=95–101}}</ref>

===Solid-state welding===
[[File:Solid-state welding processes - AWS A3.0 2001.svg|thumb|300px|Solid-state welding processes [[classification chart]]<ref>AWS A3.0:2001, Standard Welding Terms and Definitions Including Terms for Adhesive Bonding, Brazing, Soldering, Thermal Cutting, and Thermal Spraying, American Welding Society (2001), p. 117. {{ISBN|0-87171-624-0}}</ref>]]

Like [[forge welding]] (the earliest welding process discovered), some modern welding methods do not involve the melting of the materials being joined. One of the most popular, [[ultrasonic welding]], is used to connect thin sheets or wires made of metal or thermoplastic by vibrating them at high frequency and under high pressure.<ref name="Weman8990">{{harvnb|Weman|2003|pp=89–90}}</ref> The equipment and methods involved are similar to that of resistance welding, but instead of electric current, vibration provides energy input.  When welding metals, the vibrations are introduced horizontally, and the materials are not melted; with plastics, which should have similar melting temperatures, vertically. Ultrasonic welding is commonly used for making electrical connections out of aluminum or copper, and it is also a very common polymer welding process.<ref name="Weman8990" />

Another common process, [[explosion welding]], involves the joining of materials by pushing them together under extremely high pressure. The energy from the impact plasticizes the materials, forming a weld, even though only a limited amount of heat is generated. The process is commonly used for welding dissimilar materials, including bonding aluminum to carbon steel in ship hulls and stainless steel or titanium to carbon steel in petrochemical pressure vessels.<ref name="Weman8990" />

Other solid-state welding processes include [[friction welding]] (including [[friction stir welding]] and [[friction stir spot welding]]),<ref name="NZ">
Stephan Kallee (August 2006) [https://www.twi-global.com/technical-knowledge/published-papers/nz-fabricators-begin-to-use-friction-stir-welding-to-produce-aluminium-components-and-panels-august-2006 "NZ Fabricators begin to use Friction Stir Welding to produce aluminium components and panels"]. ''New Zealand Engineering News''.</ref> [[magnetic pulse welding]],<ref name="EMPT">Stephan Kallee et al. (2010) ''[http://www.msm.cam.ac.uk/phase-trans/2010/IPM.pdf Industrialisation of Electromagnetic Pulse Technology (EMPT) in India]'' 38th Anniversary Issue of PURCHASE India.</ref> co-extrusion welding, [[cold welding]], [[diffusion bonding]], [[exothermic welding]], [[Radio-frequency welding|high frequency welding]], hot pressure welding, [[induction welding]], and [[roll bonding]].<ref name="Weman8990" />