New methods of resistance spot welding using reference waveforms of welding power

The use of high strength steels in car bodies has increased gradually in recent years, contributing to lighter weight vehicles. In general, the resistance spot weldability of high strength steels is poor when compared to that of low-carbon steels due to a number of factors including narrow welding range (weld lobe), irregular occurrence of expulsion, high resistivity of base metals, and zinc coating. To improve the weldability of high strength steels, technologies such as adaptive resistance spot welding and optimization of welding conditions have been developed and applied within the automotive industry. This study focuses on developing two methods of resistance spot welding with the aim of improving the weldability of high strength steels. The first method is reference welding, which uses the reference power waveforms obtained from preliminary welding. The second is modified reference welding, which uses modified power waveform from the reference welding method. The features and effects of these welding methods were evaluated through a tensile shear test, analysis of welding signals, and an investigation into the frequency of expulsion. Both welding methods showed high tensile shear strength results and reductions in expulsion over a wide variety of different steel types including GI coated steels.