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In this study, an incrementally coupled finite element analysis procedure is used to analyze the electrical, thermal, and mechanical interaction during resistance spot welding processes. The results of the finite element analysis are validated by experimental measurements of the weld nugget sizes and dynamic resistance. The temperature results from the thermo-electric analysis are used as the input for the prediction of the microstructure evolution in the resistance spot welds of high strength steels. Consequently such welding parameters as welding current, electrode force, electrode designs, cooling water temperature and flow rate, and electrode holding time can be linked with the weld nugget size, microstructure and mechanical properties in spot welds, and eventually the residual stresses and performance of spot welded structures.

Resistance welding control systems utilizing secondary current feedback receive widespread utilization both in Europe and Japan. However, these types of control systems are only beginning to be used in any extended basis in this country. Currently, two variants of these systems are available; so called “self-teaching” systems, and “learning curve” systems. Either system has been shown to be capable of providing a stable secondary resistance welding current within two cycles. Recent work has indicated, however, that the self-teaching type control systems may be adversely affected by non-optimum set-up conditions, particularly poor fit-up and the introduction of organics (sealers or adhesives) at the faying surface. This work examines the performance of learning curve type constant current control systems under these adverse set-up conditions. Six conditions were selected for study; three degrees of progressively poorer fit-up, with and without an organic sealer.

This study examined the effect of primers containing a conductive pigment on the resistance spot weldability of hot-dip galvanized steel. The pigment used was ferrophos, essentially Di-iron phosphide. Basically, two types of tests were used in this work. Current range tests were used to establish the effect these primers have on the effective ranges of weldability. Limited electrode life tests were used to infer the long term performance of the hot-dip galvanized steels with and without this paint. It was found that the addition of the Ferrophos bearing paints had pronounced effects on weldability. Typically, required current levels were reduced by several thousand amps, and effective current ranges were increased by 50 to 100 percent. During electrode life testing significant reductions were also noted both in the rates of electrode face diameter increase, and the degree of electrode pitting.