Spot Welding

Spot welding is a method of resistance welding in which the joining of two metal surfaces is done by the heat obtained from resistance. to the flow of electric current.

In spot welding both the work pieces to be joined are held together between copper or copper alloy electrodes. The electrode tips were spaced
at suitable intervals of space and the welding current is made to pass through a small spot and the sheets are clamp together. A heavy current ranging from 1000 A to 10000 A at a very low voltage usually less than 2V is passed through the spot which will melt the metal and form weld. So to get high current and low voltage a step down transformer is being used. The amount of heat energy delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current as given by the following equation.

H=I²Rt

A good weld can be obtained by applying either low current for longer duration or high current for a short period of time.

The joint formed by the spot welding will provide better mechanical strength but do not provide air or water tight welding. To form such a weld the welding current should be localized and a sufficient pressure should be applied on the sheets to be welded.

Effect of Spot welding

The generation of heat at junction between the electrode and the metal will cause electrode sticking and melt through holes. To prevent this electrode sticking the electrodes should either be made of high electrical and thermal conductivity or water cooled by circulating cold water continuously.

Applications of Spot welding

Spot welding is used in welding of wire mesh, fabricating sheet metal, automobile manufacturing industry. Spot welding is also used in manufacturing of nickel–cadmium and nickel–metal hydride cells to make batteries.