The annealing influence onto the magnetic and energetic properties in soft magnetic material after punching process

The paper presents a method to determine the deterioration effects due to the punching process on soft magnetic materials used in electrical machines. Furthermore the possibility to recovery the magnetic and energetic original properties by mean of subsequent annealing treatments is reported too. The proposed methodology is based on a full experimental approach. Five toroidal cores, with the same geometrical dimensions, have been assembled overlapping a different number of laminations shaped as concentric rings. The rings have been obtained by means of a punching process: in this way the five cores have consistent differences in terms of punched edge length. The comparison between the magnetic and energetic properties on the five cores has put in evidence in qualitative and quantitative ways the punching process effects. In order to quantify the recovery of the magnetic and magnetic properties of the magnetic material, an annealing process has been applied on five other cores, twins with the first five. In addition, the cores have been tested at several frequencies in the range of 10 Hz to 100 Hz and the separation between eddy current and hysteresis losses has been obtained. The experimental test on the annealed cores has highlighted a heavy recovery of the hysteresis loss increase due to the punch process and a reduction of the global specific iron losses. The annealing process allows recovery of the specific losses with a reduction of about 40%, due to a hysteresis contribution reduction. On the base of the results obtained on the cores two twin 11 kW induction motor have been assembled. The first one with a standard stator core, the second one with an annealed stator core. The comparison between the iron losses measured on the two motors has shown that a 20% reduction of the motor iron losses can be obtained.