Resistance spot welding is a type of manufacturing process that uses electrical current to internally fuse two sheets of metal together. The resistance of the metal, to the electrical current, causes heat to build up at the site where the current is applied. When two sheets are clamped together and current is passed through them for a certain amount of time, a weld or spot fastening, can be formed.
The process of resistance spot welding usually involves the use of a machine equipped with copper electrode tips, through which the electrical current passes. As the metal sheets, which are clamped together by the electrode tips and sometimes other positioning devices, receive the current, an interior weld nugget begins to be formed by the melting metal. This is different than arc welding, which forms the weld from the outside of the metal at that spot.
Care must be taken to apply just the right amount of current for the type of metal used in resistance spot welding — along with a certain amount of pressure, and for a precise time. The kind of metal that is to be joined, along with its thickness determines the appropriate values of current, pressure, and time. The most commonly used metals — steel, nickel alloys, titanium, or aluminum — typically vary in size from 0.008 inches (0.2 mm) to 1.25 inches (31.75 mm) in this process. If these variables are too high for the metal being welded, the pieces can melt too much or form a hole. Values that are too low may produce an ineffective, weak joint.
Resistance spot welding is often utilized in the automobile and aerospace industries. It is also used in orthodontics, in the creation of bands, or braces, that go around teeth. Manufacturers generally like to use this process because it takes very little time to complete. Also, robots can often be used in repetitive welds of this kind, and this can help to eliminate some of the safety hazards that welding can present to people.
Unlike arc welding, resistance spot welding does not emit harmful ultraviolet light rays. Care must be taken, however, to protect the eyes — and other body parts — from molten metal and sparks that may fly as the weld is created. Some other hazards to humans can include having fingers or hands crushed by clamps, or inhaling fumes caused by heating coated metals. Proper safety precautions should be observed when a person is operating a resistance spot welder.