Welding is a process in which metals or thermoplastics are joined together through coalescence; usually welding is done by melting the materials that are being worked with and adding a third, filler material (the welding rods) to create a pool of molten material that hardens together and creates a strong, sturdy joint once it cools down. Welding differs from soldering and brazing in that soldering and brazing melt a material with a low melting point and uses this to join the work pieces together, while welding melts all the work pieces along with the filler to join them together. Sometimes pressure is used along with the heat to weld the materials together.
Originally the only welding method available was forge welding, which is the kind of welding so often seen in medieval-type movies where the work pieces are heated and then joined together by hammering; next came the introduction of arc welding, oxy-fuel welding, and then resistance welding. Following the World Wars more modern welding techniques were introduced such as shielded metal arc welding, gas metal arc welding, submerged arc welding, flux-cored arc welding, and electroslag welding; toward the latter part of the century laser beam welding, electron beam welding and robot welding were added to the list and as technology advances, it is likely that newer welding techniques will be introduced as well.
The machines used for welding are as numerous and varies as the welding methods that are available; welding machines use several different energy sources including a gas flame, an electric arc, and a laser.
In gas welding, the equipment needed is a welding gun, a wire feed unit, a shielding gas supply, a power supply, and an electrode wire; gas welding produces very high temperatures that can rust or oxidize molten metal in moments if it is exposed to the open air, so the welded material must be kept away from oxygen while it cools. To achieve this, a steady stream of gas is blown out of the nozzle of the welding gun which displaces the air around the area that is being welded and allows it to harden properly. Gas welders are manufactured by companies such as MIG, Hobart, and Campbell Hausfeld.
In electric/arc welding the equipment that is used are a power supply and an electrode; electric welding works by creating a continuous electric arc between the electrode and the base material at the welding point. Electric arcs can use either DC or AC current, and consumable or non-consumable electrodes; manufacturers of the electric welder include Lincoln, Syncrowave, and Miller.
In laser welding powerful, highly focused beams are used which can make deep welds while minimizing the size of the weld area; the main disadvantage is that laser welding equipment is very costly while being prone to thermal cracking. Laser welding machines use a beam of very concentrated light to heat the work pieces and melt them to create a weld; to two types of lasers most often used in laser welding are the Nd:YAG and CO2 lasers. Manufacturers of laser welding machines include LaserStar Technologies and Sigma Laser.