Risk reduction in the manufacturing of interference fits for laminated rotating cores of electrical machines

Abstract

Electric drive systems are becoming increasingly popular in all areas from personal automobiles to naval ships. Electric motors and generators are being pushed to higher power and energy densities. The increase in power and energy results in increased rotor speeds, placing more importance on the interference fit between the rotor core and its shaft. Traditional manufacturing methods for rotor cores, such as thermal fits or keying, typically fall short of the interference fit requirements of the rotor or present undesirable manufacturing conditions. The more common methods used for motors are also inherently risky operations that are irreversible. This thesis examines how a hydraulic expansion fit provides a solution to the traditional manufacturing problems of interference fits for laminated rotating cores of electrical machines. Hydraulic expansion fits have been implemented successfully in the coupling industry for several years; however, their application to rotating cores of electrical machines is a novel approach that is beneficial in many respects. The hydraulic expansion fit is a robust manufacturing technique capable of large interference fit pressures. It can be controlled and monitored during installation, thereby reducing manufacturing risks. Additionally, the rotor can be removed after installation using the hydraulic expansion methods. The paper outlines traditional methods and details the design issues associated with a hydraulic expansion fit for a laminated motor core. In addition, the installation method is implemented on a prototype induction motor rotor core and documented measurements from an installation are presented.