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How Arc Welding Works
At the most basic level, arc welding with any kind of welding machine – MIG, TIG, stick, and so on – is based around completing an electrical circuit through the metal that is being welded together. Although most people think of all types of welding as involving flame, the fact of the matter is that only oxyacetylene welding makes use of an actual flaming gas. The rest of the world's welding is accomplished using the heat generated by electrical resistance.
The main body of the welder, or converter as it is often known, is the place where electricity enters the system from the power grid or, alternatively, from a generator of some kind. The controls are also located here, although some welders feature remote controls such as an amperage switch on the welding gun or as a foot pedal so that the amps can be changed during welding.
Electricity flows through the gun cable and into the welding gun itself, from which it is discharged into the metal. The electricity then passes through the metal itself, and back out through a work clamp – a magnetic clamp attached to the metal's surface near the work site, and linked back to the main body of the welder by another cable. Thus, the arc welder forms a complete circuit for the electricity to flow through. It is this flowing which produces the welding results that are used to assemble everything from computer circuit boards and bicycles to jet fighter aircraft and industrial holding tanks.
Resistance and welding
Although there is no actual flame involved in arc welding, there is ferocious heat – enough to melt the metal at the point where the welding arc flows into it, creating what is known as a “welding pool”. Filler metal is also usually added, either as a continuously fed wire that doubles as the electrode, a “stick”, or a rod that is moved into the arc by hand. This, too, must melt to add extra volume to the welding pool.
The heat is generated by resistance. Metal resists electricity to some extent, and as a result, some welding is carried out with the electrode actually touching the surface of the metal. This is only done when the electrode is also the filler metal wire, and generally only with thin sheets of steel.
Air resistance is the more common form of resistance used to generate welding heat. In this scenario, the electrode is slightly separated from the workpiece, creating an air gap between the electrode and the substrate. The electricity jumps across this space, but air is a poor conductor of electricity. As a result, a lot of the electricity is lost, and ends up being radiated as heat instead. This heat is so intense that it can melt steel, gold, copper, iron, aluminum, and any other weldable metal.
Welding, then, is the process of creating a continuous strong current which is interrupted at one point so that some of the electricity will dissipate as heat. That point is the welding arc where the action takes place and the heat is intense enough to melt two pieces of metal so that they flow together and join into one.