A rotor assembly for an electric motor includes a plurality of laminations disposed in a stack, a tension rod extending axially through the rotor lamination stack, and end clamps disposed at each end of the rotor lamination stack and secured to the tension rod for compressing the stack to hold the laminations...http://www.google.es/patents/US4993290?utm_source=gb-gplus-sharePatente US4993290 - Method of stamping rotor and stator laminations
