SPOT WELDING AND ITS PROCESS

Spot Welding is employed to join overlapping strips and sheets or plates of metal at small areas. The pieces are assembled and placed between two electrodes, which must possess high electrical and thermal conductivity and retain the required strength at high temperatures. So they are made of pure copper for a limited amount of service , and of alloys of copper or tungsten, or copper and chromium for continuous working. When the current is turned on, the pieces are heated at their areas of contact to a welding temperature, and with the aid of mechanical pressure the electrodes are forced against the metal to be welded. the pressure may be developed by a foot lever or by air pressure or by hydraulic cylinders. This may be used to weld steel and other metal parts up to a total thickness to 12 mm.

Practically all combination of ductile metals and alloys can be spot welded. The spot welding method is used for fabricating all types of sheet metal structures where mechanical strength rather than water or air tightness is required. This may be applied to all types of boxes, cans, enclosing cases, etc. Spot welding machines are made in capacities from 10 to 150 KVA.

To obtain a good welds, the sheet metal should be free of foreign matter and scale. Films of any type have a tendency to cause variations in surface resistance and also increase the heating effect of the metal in contact with the electrodes.

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Mechinopedia For Mechanical Engineers

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