Welding force as a variable in resistance spot welding control

This paper presents research about the possible usage of welding force for the estimation of the weld strength. Other signals like welding current or electrode displacement are commonly used for this purpose. Our previous research has however shown that welding force is a very good indicator of expulsion occurrence. In this paper we presented the relationship between time needed for expulsion occurrence and weld strength. The results are better than in the case of welding current. In order not to limit this approach only to welds with expulsion, another variable is calculated from the welding force signal. The welding force variation is the sum of square differences of welding force and mean welding force. Although slightly less accurate than time needed for expulsion variable, it is not limited to expulsion welds.