Effects of Prepulse Resistance Spot Welding Schedules on the Weldability Characteristics of Galvanized Steel

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. Conventional resistance spot welding schedules (with no prepulse) should perform relatively satisfactorily in most applications. It should be noted however, that welding with prepulse schedules may be beneficial in solving production problems related to metal fitup and electrode sticking.