The estimation of the critical current (Ic) and AC losses of high--temperature superconductor (HTS) devices through modeling and simulation requires the knowledge of the critical current density (Jc) of the superconducting material. This Jc is in general not constant and depends both on the magnitude (Bloc) and the direction (θ, relative to the tape) of the local magnetic flux density. In principle, Jc(Bloc θ) can be obtained from the experimentally measured critical current Ic(Ba,θ), where Ba is the magnitude of the applied magnetic field. However, for applications where the superconducting materials experience a local field that is close to the self--field of an isolated conductor, obtaining Jc(Bloc, θ) form Ic(Ba, θ) is not a trivial task. It is necessary to solve an inverse problem to correct for the contribution derived from the self--field. The methods presented in the literature comprise a series of approaches dealing with different degrees of mathematical regularization, such as the use of brute force or optimization methods to fit the parameters of preconceived non--linear formulas. In this contribution, we present a parameter--free method that provides excellent reproduction of experimental data and requires no human interaction or preconception of the Jc dependence with respect to the magnetic field. In particular, it allows going from the experimental data to a ready--to--run Jc(Bloc, θ) model in a few minutes.

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The paper is focused on the control of resistance projection welding process applied in joining of thin-walled metal elements. The motion of electrode is generated by electric servo actuator that controls the force exerted on electrode or alternatively, just travel itself of electrode. The projection welding has been discussed for welding of 1.5 mm thick DX53 steel sheets where one sheet contains an embossed projection. Apart of electric servo actuator, another source of force has been described, i.e. pneumatic actuator (classical one), for the reason of comparison. The solution where the electric servo operates together with appropriate algorithm makes the new solution that is alternative for classical, pneumatic one. Optimized motion of electrode due to new proposed source of electrode force or/and travel, based on relevant algorithm yields improved quality of joints.

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