Micromagnetic Characterization of Spot Welds: Optimizing Calibration for Steel Plates of Varying Thickness

This study demonstrates the robustness of the 3MA (Micromagnetic Multiparameter Microstructure and stress Analysis) non-destructive technique for determining the nugget size and quality of resistance spot welds. The 3MA system combines four electromagnetic methods: Eddy Current, Incremental Permeability, Barkhausen Noise, and Harmonic Analysis of the Tangential Magnetic Field. Investigations were conducted on SPFC590 high-tensile steel plates. To ensure good target quality, a large database was developed covering various scenarios, including different plate thicknesses and nugget diameters, which enabled the development of a successful predictive model. Results show that measurements taken from the plate side with a fixed thickness yield a high degree of accuracy in predicting nugget diameter. In contrast, measurements from the side with variable thickness were unreliable and produced significant prediction errors. This study concludes that fixing the measurement-side plate thickness is a critical guideline for robust calibration. This approach minimizes the influence of the opposing plate's thickness and probe lift-off variations, significantly reducing calibration effort and making the technique more efficient for industrial applications.