These slides were presented at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

As the transportation industry increasingly adopts electrification, efforts to enhance the power density of electric motors have gained importance. This focus stems from the need for more compact, efficient systems. Advances in electromagnetics, including innovative materials and refined designs, have significantly improved power density. Technologies such as high-performance magnets, reluctance-effect materials, advanced winding methods, and ultra-thin laminates enable engineers to achieve greater output in smaller motors. While these advancements enhance electromagnetic performance, they simultaneously increase the need for robust mechanical power transmission. A critical factor is the shaft-hub connection within the rotor assembly, which governs torque transmission, particularly at high rotational speeds. Rotors are typically assembled using interference fits, which ensure precise alignment, balance, and gap-free assembly, resulting in smooth, vibration-free operation with minimal energy losses. However, at high rotational speeds, this method suffers from reduced torque transmission due to centrifugal forces and thermal strain. To address these limitations, friction fitting with higher interference levels has been proposed, increasing joint pressure between the rotor core and the shaft. Extensive research has been conducted to evaluate the feasibility of shaft-hub connections with substantial interference. However, most studies focus on solid shafts and hubs, failing to account for the geometric complexities of modern electric motors with laminated rotor cores. The iron cores of contemporary rotor assemblies are not solid but consist of individual, electrically insulated laminations designed to minimize eddy currents'?circular currents induced in conductive materials by changing magnetic fields. These laminations, typically coated with an insulating layer, interrupt the flow of eddy currents, significantly reducing energy losses and heat generation, thereby improving motor efficiency. Lamination stacks are composed of extremely thin electrical steel strips, typically ranging from 0.1 to 1 mm in thickness. One common manufacturing technique for producing laminated cores is interlocking, a cost-effective and efficient process. This method involves punching thin sheets of electrical steel into precise shapes and bundling them into stacks, where embossed areas on the laminations are pressed together under axial force to form an interference fit between the laminations. Interlocking offers high production speeds, reduced material waste, and consistent mechanical and electromagnetic performance. However, experimental and numerical investigations revealed that interlocked laminated cores are not ideal for high-interference applications. Under such conditions, these cores exhibit nonlinear deformation, or buckling, due to elevated joint pressures. This elastic buckling leads to delamination of the rotor core, negatively affecting its electromagnetic properties and increasing rotor shaft imbalance. Furthermore, the buckling deformation significantly alters the joint pressure distribution at higher interference levels, reducing the mechanical performance and torque transmission capacity of the connection. To address these challenges, a robust and precise numerical framework was developed based on experimental results and material tests. Numerical simulations were conducted to analyse the deformation behaviour of laminated cores under high interference conditions and to identify the key parameters influencing buckling. The results revealed critical factors governing the buckling behaviour of laminated cores. Using these insights, the geometry of the electrical steel laminations was numerically optimized to enhance their buckling resistance under high joint pressures. These optimized designs enable the rotor cores to withstand higher interference pressures, facilitating the transmission of greater torque. These optimizations represent a significant step toward improving the mechanical stability of laminated rotor cores in high-interference-fit applications, supporting higher torque transmission and overall performance. Future research could focus on experimentally validating the improved stability and torque transmissibility of the numerically optimized rotor core geometry under dynamic operating conditions, in order to assess the practical feasibility and effectiveness of the proposed optimizations.