TWI Industrial Member Report Summary 195/1982
By S A Westgate and R M Rivett
There has been a gradual increase in the interest in, and application of, resistance spot welding for thick section mild steel. Only limited work has previously been carried out and there are conflicting data in current IIW and British Standard recommended conditions. This report principally covers work done to assess the effect of welding schedule on the weldability of 3, 5 and 7mm low carbon steel. Both a single phase a.c. and a three-phase secondary rectified d.c. power supply were used to enable comparison of the two types to be made. In addition, a study was made of the effect of specimen dimensions on the weld strength when static shear or, cross-tension testing material from 3 to 12mm thickness.
It was found that, in terms of weldability alone, similar results were obtained for both a.c. and d.c. power supplies, indicating that similar schedules could be recommended for both types of supply. There is also evidence to suggest that the pulsed conditions normally recommended by IIW and BSI are often unnecessary as continuous current schedules were found to give generally equal or better weldability than the recommended conditions.
IIW recommended full size static shear test specimen widths were found to be suitable but reduced width sample sizes could give misleading results in that a substantially different estimation of the full weld strength was often obtained.