AZL consortium starts building CFRP rotor sleeve variants and the rigs to test them

An industry consortium coordinated by AZL Aachen is putting a systematic benchmark for carbon-fiber-reinforced plastic (CFRP) rotor sleeves into practical implementation, comparing press-fit and direct-winding concepts along with several manufacturing routes and material systems. The group is also developing and validating the characterization methods it will use to evaluate mechanical, thermal and long-term loading.

CFRP sleeves are fitted over high-speed motor rotors to hold the magnets in place against centrifugal loading, and they are pre-stressed so they stay tight as the rotor expands in service.

The comparison will use two design strategies—press-fit sleeves and direct winding onto the rotor—and three manufacturing routes—wet filament winding, towpreg winding and thermoplastic tape winding. A single reference rotor with a surface speed of around 200 m/s will prevent differences between materials and processes from being obscured by inconsistent design assumptions.

The material side of the program compares high-end solutions to industrial cost-performance materials. High-end grades are often chosen as the technically safe option because reliable comparative data on the added performance per added cost is missing, according to the company. The carbon fiber spectrum runs from economical industrial grades to high-performance fibers at different stiffness and strength levels and correspondingly different prices. On the matrix side, the consortium is investigating epoxy resins and several thermoplastic polymers, whose mechanical properties, particularly close to the allowable temperature limits, affect not only strength, pre-stress retention and long-term behavior, but also processing windows, cycle times, production capacity and total cost.

The consortium is developing an adapted split-disk test, pre-stress measurement, a non-rotating radial-load test rig and high-temperature and long-duration testing. Each method is being built, analyzed, optimized and validated inside the project, which AZL says creates one evaluation chain covering different material types, temperature levels and load cases.

The project also evaluates production capacities, process chains and costs, and the economic assessment covers the route from raw material to the finished sleeved rotor. Achievable material utilization gets particular attention because it affects wall thickness, rotor expansion, air gap and ultimately overall motor performance.

Partners in the Joint Partner Project receive a benchmarking matrix, computer-aided engineering (CAE)-to-test correlations, cost comparisons, a process-cost assessment, material-selection criteria, recommendations by motor type and a validated test methodology. Specific values, rankings and material- or process-specific conclusions stay inside the consortium, and new partners can still influence the remaining test campaigns and the characterization methods.

“The Joint Partner Project is designed as a shared decision platform: it connects electric-motor users, manufacturers and developers with the composites industry and creates a robust basis for assessing materials, designs and manufacturing technologies from both technical and economic perspectives,” said Philipp Fröhlig, AZL’s Head of Industrial Services.

Source: AZL Aachen