An arc welder fuses metal to metal by means of heating the materials to their melting point. The heat source is an electrical discharge arc produced by an electrical current that is passed across an air gap between an electrode and the metal work pieces.
As the electrode also melts, it adds more metal to the weld seam to fill any empty space and reinforce the joint. The electric current can be varied by a manually controlled transformer; the usual range is between 30 and 250 amps.
A typical arc welder consist of a portable box containing the transformer and controls, connected to two welding cables, a ground cable terminating in a ground clamp, and a live cable terminating in the welding electrode and it’s holder.
A flux coating covers the electrode’s outside. Some of this coating burns off in the welding process, and this forms a gas which protects the melting metal from oxidization. The material which remains behind combines with any impurities that in the molten metal’s surface and form a slag coating that breaks off when the weld cools to a certain point.
In Gas Metal Arc Welding (GMAW), an inert or semi-inert shielding gas is flowed around the electrode wire to prevent the weld site from contamination. Constant voltage, direct current is the most commonly used power source with GMAW, but constant current alternating current is used as well. This form of arc welding is used mostly in industrial settings, such as automobile manufacturing.
The brightness of the arc weld area can leads to a condition called Arc Eye, in which ultraviolet light causes inflammation of the eye’s cornea and can burn the retina. For this reason, when using an arc welder, specialized dark glass goggles or a welder’s face mask must be worn; they also protect against the showers of sparks given off. Heavy duty gloves that have gauntlets are recommended, as is a leather apron to protect clothing from sparks.
The workbench should be covered with a fireguard sheet of ¼ inch thickness steel. Ensure the space immediately surrounding work area is free of any flammable materials and containers.
The welder’s ground cable clamp should be connected to the work piece, or, if the work is on a metal work bench and in contact with it, to the work bench. Some welding machines that use a high frequency AC current component can affect pacemaker operation when within 2 meters of the power unit and 1 meter of the weld site, although arc welders up to 225 Amps were found in one study not to have an effect on pacemakers.