Effect of Sheet Thickness on Weld Nugget Growth Behavior during Three-Sheet Resistance Spot Welding

One of the most important issues in three sheet resistance spot welding is the insufficient growth of the weld nugget in the sheet/sheet interface, where it is most needed. This reduces the mechanical properties of the joint and increases the tendency to fail in the interfacial failure mode. In this paper the effect of sheet thickness on the pattern of weld nugget development during resistance spot welding of three low carbon steel sheets of equal thickness is studied. Results showed that there is a critical sheet thickness at which the fusion zone size at the sheet/sheet interface is nearly equal to its size at the geometrical center of the joint. When sheet thickness is lower than the critical value, an elliptical nugget is formed in which the weld nugget growth in the geometrical center of the joint is higher than the sheet/sheet interface. While, increasing the sheet thickness above the critical size causes the formation of a non-elliptical nugget in which the weld nugget growth mostly occurs in the sheet/sheet interfaces.