The Effect of Electrode Geometry and Pre-heating Treatment on Resistance Spot Welding Strength

Abstract

Resistance spot welding (RSW) is one of the most significant and common metal joining methods used in industries. The present paper discusses the comparative performance of resistance spot welding electrodes of nontraditional design with the traditional one of 8 mm contact diameter in welding a 1.5 mm thick low carbon steel sheet used in automobile structural bodies and bridges. The modified electrode tip surface center was machined to have three different holes of 2, 3, and 4 mm depth and three different diameters of 2, 4, and 6 mm producing nine different hollow electrode dimensions. As well as the influence of pre-heating temperature on the mechanical properties of the weld joint was investigated by considering the other main parameters of welding time, current, and force are constant. The shear tensile test and torsion test examinations are carried out to investigate the mechanical properties. Also, to interrupt the results, a macrograph examination was conducted to determine the nugget size formation. The results show that the increase or decrease in the strength of the weld joint is greatly influenced by the proper selection of the modified electrode geometries. Also, the results indicated that the maximum improvement in shear tensile strength and torsional strength is about 140% and 150% compared to the traditional one. Furthermore, pre-heating processes helped decrease the contact resistance at the faying surfaces and improve the weld tensile strength and torsional strength to about 141% and 171% at 200 oC. Moreover, improvement may be achieved by slightly increasing pre-heating temperatures