High Frequency Magnetic Characterization of SiFe and CoFe Sheets: Punching Impact Evaluation and Modeling
Résumé
Mechanical punching of electrical steels causes a degradation of their magnetic characteristics,
which can extend several millimeters from the edge. So, in the field of industrial applications,
particularly that of small electrical machines, the stator core made of rigid and fine teeth would be
subject to more losses. Thus, this topic of the effect of punching has to be submitted to further deep
characterization and development in order to give some insight into the different mechanisms. In
this framework, this paper evaluates the combined effect of punching and frequency on the
magnetization curve and iron losses in thin SiFe and CoFe soft magnetic sheets. These alloys are
typically suitable for the manufacture of high-speed machines used in embedded applications
(aircraft generators, automotive, etc). Two SiFe alloys and a CoFe alloy have been investigated.
First, different rectangular core samples of variable width (15, 10, 5, 3 mm) have been industrially
punched. Then, a dedicated magnetic characterization has been made, using basically a mini-
Epstein frame. Measurements have been performed from 50 Hz to 1∼1.5 kHz and from 0.3 T to
near saturation. Both rolling and transverse directions have been considered. Finally, a 1st attempt to
predict the degradation due to the punching is presented. A useful description of the magnetic
permeability as a function of B and f is given and the degradation parameters are estimated based on
the knowledge of the reference permeability.