Defect Assessment of Spot Welding

Abstract

Spot welding is the welding method that uses the heat generated by the resistance of the material to the electrical current together with the gripping pressure simultaneously. There is no extra external heat source. Heat is produced only on the parts to be welded and pressure is applied by the rocker arms or electrode arms. The high current density is provided by the transformations and the pressure is provided by the hydraulic and pneumatic equipment’s. It is the most common form of electric resistance welding as its method is very easy, practical and easeful. Although it is seemed to be very basic, its process is very complex and requires the continuous control of specified parameters. The method may be used for joining sheet to sheet, sheets to rolled sections or extrusions, wire to wire, for sundry special applications using combinations of the above. By far the widest application in industry is the spot welding together of sheet-metal parts, as in the hollow-ware industry (handles to kettles and saucepans) or the automotive industry. For example, the typical car body contains about 5000 spot welds joining a mixture of sheet metal material types and thicknesses. This welding method is very advantageous corresponding to its high speed of operation, hence its adaptability to mass production, its cleanliness, no need for welding rods, and its high degree of control possible by electrical means (i.e., reducing the necessity for a degree of operational skill). The process spot welding involves the joining of two or more pieces of sheet metal in localized areas (spots) where the melting and coalescence of a small volume of material occurs from heating caused by resistance to passage of an electric current. The electric current is carried to the sheets via electrodes that are also used to clamp the work pieces together.