Advances in small-scale resistance spot welding of the Ni-15 %Fe-4 %Mo-1 %Mn permalloy in the production of low-noise ring cores for fluxgate magnetometers

Abstract

The aim of this study was to assess the possibility of improving control of small-scale resistance spot welding (SSRSW) of the Ni-15 %Fe-4 %Mo-1 %Mn permalloy in the production of low-noise ring cores for fluxgate magnetometers. It was found that the range of the optimal current–time parameters (weld lobe) was within current amplitudes of 1–2 kA and pulse durations of 6–14 ms, which allowed to form sound nuggets with sufficient diameters but without expulsions in most cases. A preheating stage (a pulse with an amplitude of about 1 kA and a duration of 3–4 ms) had a positive effect on the stability of both dimensions and mechanical characteristics of the investigated nuggets. A decrease in the solidification rate slightly improved the stability of tensile shear strength values of the SSRSW joints despite the absence of fundamental differences in the microstructure and phase composition of the weld metals. To determine the reliability of predicting the quality of the SSRSW joints by assessing dynamic resistances measured during the formation of nuggets, a comparative statistical analysis of their diameters and the tensile shear strength values was carried out. The obtained results did not reveal any strong correlation between these parameters.