The influence of fine blanking on the magnetic properties of soft magnetic steel

The magnet yokes for most of the Hadron Electron Ring Accelerator magnets are made from 5-mm thick fine-blanked laminations. Differences in the measured and calculated field distributions using the specified values for the relative permeability are explained by distortions of the magnet steel caused by cold deformation in the cutting edge zones during the fine blanking. A comparison of fine-blanked, laser-cut and lathe-turned annular samples made from the same starting material shows that a reduction of the relative permeability and an increase of the coercive force depend strongly on the volume of the areas distorted in the fabrication process. Better agreement between calculated and measured field distribution was achieved by using properly chosen permeability curves taking into account the cold deformation from the lamination production. The influence of the production process on the magnetic properties of laminations can be reduced and even completely mitigated by additional heat treatment.