Cutting the electrical steel sheets to form the shape of the stator and the rotor affects the magnetic properties of the sheets. The increase of the magnetic losses as well as the drop of the magnetic permeability can impact on the design of electrical devices. This paper investigates this deterioration effect on the optimal design of the stator of a high-speed permanent magnet synchronous motor. The deterioration due to punching is phenomenologically analyzed based on measurement of strips of steel sheets with various widths on an enlarged Epstein frame. The losses are computed with a Bertotti model whose coefficients depend on the width of the sheets. The optimization of a synchronous machine is then carried out with this magnetic losses model.