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Many automotive production plants are using various prepulse schedules for resistance spot welding thin gauge galvanized steel. The claimed reasons are that wider current range and longer electrode life are obtainable in comparison to the conventional schedule. However, data to support this are not available. The objective of this program was to determine the effect of prepulsation on spot weldability of galvanized steel. In this work, several prepulse resistance spot welding schedules were evaluated in two full factorial experiments. The effect of the number of prepulse cycles, the prepulse heat level and the effect of cool time were studied in detail. Weldability was evaluated using an electrode life test procedure in which the current range was periodically examined over the life of the electrodes. Generally, the results indicate that prepulsation has a negative effect on the resistance spot weldability of thin gauge galvanized steel.

The influence of coating weight on the weldability lobe and electrode life performance of a zinc-coated steel was studied. Variations in substrate chemistry, coating weight and welding process were minimized. Statistically quantified weldability lobes were generated for each material. The size and shape of these lobes were found to be relatively invariant to coating weight over the range of coating weights studied. However, the degree of scatter in the data increased with coating weight. Surprisingly, decrease in coating weight did not result in longer electrode life. The intermediate coating weight G60* showed the longest electrode life. Even though material and process variables were substantially minimized, a significant level of scatter in the weldability data was measured. The irregular electrode wear during weld testing is thought to be a major source of this variability.

Conductive heat resistance seam welding (CHRSEW) is a new process developed at Edison Welding Institute for creating butt joints on aluminum sheet. The process uses conventional resistance seam welding equipment, and takes advantage of steel cover sheets on either side of the intended joint. Resulting joints are fusion in character, and can be manufactured at very high welding speeds (∼ 3 to 4 m/min). In this study, the conductive heat resistance seam welding process was extended to some new applications. These included joining a 7075-T6 alloy, and a dissimilar thickness 1- to 2-mm 5754 configuration. The former is generally considered unweldable by fusion methods, and is of considerable interest for aerospace applications. The latter is representative of a tailor welded blank for automotive applications. Resulting welds were evaluated using metallurgical examinations and mechanical testing.