Critical Nugget Diameter of Resistance Spot Welded Stiffened Thin Plate Structure

Abstract

Stiffened thin plate structure which is mostly applied to the car body structures consists of frame and sheet. It is a low cost method to reach a high-performance vehicle structure because of requirement low volume materials. Frame is thicker than sheet, so it acts as the reinforcement of this structure. The resistance spot welding (RSW) is generally used to join it. In this study failure modes of resistance spot welded thin plate structure, pullout and interfacial failure modes, were investigated based on thickness of joined plates and load secondary voltage to determine the critical nugget diameter. Three pairs of joined plates thickness of 1-1, 2-1 and 3-1 mm were spot welded using varied voltage in a range of 1.6 V to 2.3 V. The spot weld nugget of the stiffened thin plate structure joint were asymmetric form. Increasing welding voltage made the shear load bearing capacity of RSW joint increase. In the pullout failure, the bearing capacity increased if the thickness of joined materials increased. The experimental critical nugget diameter to guarantee pullout failure mode in the unequal sheet thickness joint of the stiffened thin plate structure decreased if the sheet thickness of joined materials increased. It was higher than nugget diameter obtained by AWS formula. AWS formula should be used carefully in the dissimilar sheet thickness joint of the stiffened thin plate structure.