New technology for measuring dynamic resistance and estimating strength inresistance spot welding

Because welded structures such as automotive bodies have become smaller and lighter, a strong emphasis is being placed on the quality of the welds. Ov er the years many quality estimation systems have been developed by several researchers in order to ensure that welds are of high quality. The dynamic resistance signal, which is closely related to the nugget formation of the weld, has been used very effectively for this purpose, together with the e lectrode displacement signal. However, in previous research, the dynamic re sistance was calculated using process parameters that were measured in the secondary circuit of the welding machine, causing many in-process problems. In this study, the process variables, which were monitored in the primary circuit of the welding machine, are used to obtain the variation of the dyn amic resistance across electrodes. This allows the dynamic resistance monit oring system to be applied to the in-process system without any extra monit oring devices in the secondary circuit. Also, in order to test the reliabil ity of such a system, an artificial intelligence algorithm to estimate the weld quality using the primary dynamic resistance is proposed.