Modified magnetic properties due to roller leveling of electrical steel

Abstract

When processing stator and rotor cores from electrical steel strip material, different processing steps induce additional mechanical stress resulting in deteriorated magnetic properties. They can originate from heating process induced thermal strains or plastic deformation process induced mechanical strains. Due to its impact on magnetic material properties, such process-related deteriorations must be considered when developing an electrical machine. With regards to blanking, a high-volume production process, different manufacturing steps, i.e. punching, blanking, forming and interlocking, can induce plastic deformation. One process often neglected is roller leveling. This process sometimes is necessary to enable complex lamination geometries for rotor, stator or both to be cut from an electrical steel strip. Especially, for magnetic cores that get bigger in diameter and therefore stamping tools that increase in length, using roller leveling to produce flat parts becomes inevitable. Within the presented study electrical steels varying in its manufacturer, its batch and its thickness are roller leveled to different levels of plastic deformation. The increasing mechanical stress' impact on magnetic properties like specific iron loss is discussed regarding different frequencies and polarizations. Overall, the study proves that roller leveling is a process one might consider twice before using it to produce top-notch electrical machines.