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The effect of punching on electrical machine
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Punching electrical steels drastically alters their magnetic properties near the cutting edges, which should be accounted for when designing machines. A simple magneto-mechanical coupled finite element analysis, suitable for fully processed grades, is proposed in order to model the consequences of this local degradation of the material on the global behavior of a machine. The model is used to study the effective section of the teeth of a punched stator; calculated results are compared with experimental data and a good agreement is found
The authors deal with the problem of estimating the zone width of damaged material, which is the result of industrial processes in relation to the magnetic sheet. The authors propose two approaches: the former uses the 3D FEM model, while the latter proposes an analytical formula. Both approaches use the results of measurements performed on toroidal samples. The final result of the study is the comparison between the width of the damaged zone computed with the two proposed approaches and the comparison between the calculated and measured power losses.
Mechanical punching of electrical steels causes a degradation of their magnetic characteristics which can extend several millimeters from the cut edge. So, in the field of industrial applications, particularly that of small electrical machines, the stator core made of rigid and thin 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 electrical machines used in on board applications (aircraft power generators, automotive, etc). Two SiFe alloys and a CoFe alloy have been investigated. First, different rectangular 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 kHz and from 0.3 T to near saturation. Both rolling and transverse directions have been considered. Finally, a first 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.
The effect of rolling and annealing on the crystallographic texture and the magnetic properties of Fe-2.6% Si non-oriented electric steel during 90% cold rolling and different annealing temperature at (600 °C, 700 °C, 900 °C and 1100 °C) for 60 min and 20 min was analyzed. The 97% hot rolled as received material shows development of alpha and gamma fiber texture affecting on the magnetic properties at rolling and transverse direction. 90% cold rolling with moderate annealing temperature (up to 700 °C) and 60 min annealing time leads to better textures and improved magnetic properties. Due to coarse grained microstructure after annealing, neutron diffractions is an efficient tool for the analysis of Bulk texture of polycrystalline materials, well known for sufficient grain statistics and bulk texture measurement.
Measurements of the bulk magnetic properties of four non-oriented electrical steels after guillotine cutting with varying clearances are reported. A heterogeneous state of deformation is observed at the sheared edge. The deformation-affected zone extends to several millimeters away from the cut edge and possibly occupies the entire sample volume. An obvious correlation was established between the clearance of the guillotine cut and the general deterioration of the magnetic properties such as the total core losses (at 50Hz), the coercive field, the relative permeability and the remanent induction. The existence of a transition zone was demonstrated in the range of applied clearances for which the magnetic properties were severely deteriorated. This clearance transition zone corresponds with the drastic change of one shearing parameter: the knife displacement at fracture. The observed effects are discussed in terms of the strain heterogeneities that are introduced in the sample by the guillotine cutting process.