Die Cast Aluminum Coils for Efficient Electric Motors
Whether pedelecs, e-scooters or drones - all these forms of mobility use an electric motor to drive them. In order to make the motors more efficient, researchers at Fraunhofer IFAM have developed a casting process that can be used to produce lightweight windings from aluminum and a higher groove filling factor.
After having already succeeded in manufacturing aluminum coils by investment casting in recent years, it was an obvious goal of the "Foundry Technology and Lightweight Construction" department at the Fraunhofer Institute for Manufacturing Engineering and Applied Materials Research IFAM to manufacture the coils for series production also by die casting. A study has now shown that aluminium coils increase the continuous output of electrical machines compared to copper windings, reduce the operating temperature and at the same time save weight and raw material costs.
Casted coils are characterized by a flat conductor arrangement, which leads to a higher groove filling factor and thus to a better utilization of the available installation space. Although the casted aluminum coils have a higher electrical resistance in relation to the material than the wound copper coils, the larger cross-section results in a lower resistance in relation to the entire coil. Due to the better connection to the laminated core and the more favourable utilisation of the installation space, the thermal and electromagnetic behaviour is significantly better. For this reason, it is possible to replace wound copper coils with casted aluminum coils with improved performance and lower material costs. In order to ensure direct comparison, commercially available 250 Watt pedelec motors were used for the study. The converted motors with different sheet metal packages and coil combinations were then tested on a test bench.
Improved Efficiency due to Aluminum Coils
Following the conversion of the pedelec engine, the groove filling factor was increased from 32 to 60 %. At the same time, weight savings of 10 % were achieved. The torque increased by 30 %. Due to the improved thermal behavior of the coils, the continuous output at operating temperature increased by almost 20 %. The aluminum coil is better able to dissipate the heat generated to the laminated core and thus to the environment. This results in improved continuous performance, since the coils only reach the permissible continuous operating temperature at higher currents.
Even more advantageous were the measurement results for a sheet metal package optimized for the casted coils with another modified pedelec motor. With a lower weight, the torque increased by almost 80 % and the continuous output by 25 % compared to the original motor. Design changes can further improve the performance of motors with aluminum coils.
Diverse Potential for Electric Motors
Due to many years of development work on casted coils at Fraunhofer IFAM, it is now possible to cover a wide range of application scenarios. Coils made of copper of the highest quality can be produced by investment casting for use in high-performance machines. The die casting process is particularly suitable for applications in series production, such as those required in the manufacture of steering motors or refrigeration and air conditioning systems. In order to optimize die cast production and further reduce production costs, the next development step is automated post-processing of the casted coils. Large quantities in short cycle times can then be produced in any die casting foundry.
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