Effect of Strain by Mechanical Punching on Nonoriented Si–Fe Electrical Sheets for a Nine-Slot Motor Core

Domain observation has been done to investigate the effect of strain due to a punching process on the magnetization process of a nine-slot core for 12-pole small brushless dc motor by using the Kerr microscopy technique. Stripe domain structures oriented to a transverse direction are observed at the edge of a tooth of the core without stress relief annealing. Due to the domain configuration, permeability near the punched edge of the motor core is reduced. A stress relief annealing at 700degC for 2 h can relive the punching stress