Editing Welding (section)

===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" />