Investigation of the correlation between dynamic electrode force signals and nugget diameter in resistance spot welding

As a process signal in resistance spot welding, dynamic electrode force more prominently reflects the nugget formation process. To quantify the correlation between dynamic electrode force and nugget diameter, a non-destructive measurement method based on dynamic electrode force is proposed. In this systematic study, a pin-type force sensor, installed between the servo actuator and the welding gun arm, was used to monitor dynamic electrode force signals during DP340 welding experiments. Based on the welding formation mechanism, 25 features were extracted from the dynamic force signals, including 4 features related to expulsion. Regression analysis quantified the relationship between these features and welding parameters, and analysis of variance was used to identify key features. Results showed that t α , k 1 , and D 1 had no significant correlation with the welding parameters. Further analysis examined correlations between expulsion features and welding parameters, as well as between expulsion features and the selected key features, to explore how expulsion behavior is reflected in the dynamic force signals. Based on the selected features, correlations with nugget diameter were analyzed. Seven features showed high correlation, with f e and D 2 providing the best fitting performance. A support vector regression model was built using these features to predict nugget diameter, achieving an R 2 of 0.925 and an average relative error of 2.119%. Studies have shown that dynamic electrode force signals and their features can effectively serve as basis for weld quality evaluation.