Design of Spot Welds for Optimal Strength of Structure

Resistance Spot Welding (RSW) is particularly employed for high volume and rapid welding applications in automotive assembly process for joining multiple metal sheets and parts. For that reason, the strength and mechanical behavior of spot welds play a vital role in durability of automobiles and associated safety considerations under different fatigue loading conditions and impact. It is also imperative to study the factors and parameters which effect the strength of these spot weld joints. Failure of Spot weld is linked to several factors such as, weld nugget size, thickness of the sheets, edge distance, spacing between spot welds, welding parameters, material properties of Heat Affected Zone (HAZ), residual stresses, thickness and material inhomogeneity. Finite Element Analysis (FEA) of multiple spot welded joints under tensile-shear loads are investigated to attain optimum strength and desired factor of safety. The analysis was carried out by employing ANSYS software. The results indicate that the spacing between adjacent spot welds, edge distance and thickness of the sheets are primary factors affecting the strength of the joints for a given material. The optimal edge distance increases the spot weld strength by providing adequate clearance from plate edge without compromising the load bearing effect. Moreover, the stress field imposition of adjacent spot welds and the load bearing effect places a narrow margin for the optimal spacing between the spot welds. The variation of sheet thickness has an impact on the spot welds strength and the optimal edge distance varies with the sheet thickness. For asymmetric thickness of sheets, strength is defined by thinner sheet. Optimal edge distance, optimal spacing and thickness of the sheets for a given material are presented in this article.