The motor developed in the MODULED project is twice more compact than a state-of-the art motor thanks to the increased rotating speed. This allows to diminish the amount of necessary NdFeB magnets and therefore decreases the dependence on critical rare-earth metal supply.
To further decrease the critical element content, injected magnets have been proposed as a substitution to sintered magnets as they do not contain any heavy rare earth nor Gallium. The advantages and drawbacks of injected magnets compared to sintered magnets are summarized in the following table 1.
|Only simple shapes allowed||(almost) total freedom in shape|
|Magnets need to be inserted and fixed/glued||Magnets fill the perfect shape of the cavities|
|Contains Dy/Tb and Ga||No Heavy rare-earths, no Ga|
|High electrical conductivity Eddy losses||Low electrical conductivity almost no Eddy losses|
|High remanence (1.2T)||Lower remanence (0.74T)|
|Price/kg x needed amount is lower with today’s prices on RE||Price x needed amount is higher today due to more complex production process of the powder and lower overall volumes|
|Standard process||Not standard yet|
Table 1: Comparison of injected magnets vs sintered NdFeB magnets
Both sintered and injected magnet motors have been designed during the ModulED project. The critical element content of both ModulED motors is shown in table 2.
|Total rare earth metal [g]||391||488|
|Heavy rare earth metal [g]||32||2|
Table 2: Comparison of the critical material content of both MODULED motors (BPMM1 is the sintered magnet motor, and BPMM2 is the injected magnet motor)
The injected magnets’ lack of performances in terms of cost and process standardisation is due to the early maturity of this cutting-edge technology. The aim of ModulED’s development is to accelerate product maturity by proposing a new efficient solution to replace sintered magnets.
Design and realization of the injected Mold
The design of the injection mold had to comply with numerous requirements, including mechanical features (maintain of the rotor, force management), injection specifics (simultaneous and complete filling, minimalization of the sprue), thermal management, and generation of a six-pole magnetic field. Details of the design steps and feasibility studies have been provided in the former deliverables. A schematic view of the mold design is shown on the Figure 1. Once all the details have been fixed, the mold has been manufactured and released in January 2020. A view of the interior of the mold is shown on the Figure 2.
The first injection experiments were performed with fake rotor pieces to fix all the process parameters without wasting the prototype laminations from the motorist of the project: four complete sets of rotors had been provided by BRUSA, and it was necessary to provide two complete injected sets for the motor tests and the integration tasks. This led to some small modifications on the mold (tooling to extract the rotors, alignment pins…) and allowed to successfully inject the two required rotor sets for the project.
Figure 3: Injected ModulED rotors
Characterization of the injected rotors
Each rotor was thoroughly characterized before being sent back to the motorist BRUSA for further processing. The magnetic characterization was performed with a Hall probe mounted on a 3-axis motorized system as shown on the Figure 4.
Figure 4: Magnetic characterization of the rotors
Two aspects of the magnetic consistence of the rotors were mainly checked with this characterization:
- Repeatability of the magnetic signal over the rotor thickness: the magnetic field was measured at different levels of the lateral surface of the rotor (corresponding to the 5 slices indicated on the Figure 4) and almost no difference were observed as shown on the Figure 5. This confirms the homogeneity of the injected magnets.
- Repeatability of the measurements over the 12 rotor stacks (Figure 6) showed almost no difference between the rotors, proving the process stability and repeatability. Moreover, the measured curves were compared to the simulated curves assuming the nominal remanence of the injected magnets (0.74T). Theperfect correspondence of the simulated curves with the measured ones shows that the injected magnets are properly aligned and magnetized and confirms the validity of the mold design.
Measurement of the mass difference allowed to ensure all the cavities were densely filled with magnetic material. The aspect of the rotor was checked to ensure no deformation was caused by the injection process and confirming the proper maintain of the rotor stacks in the mold.
Towards latest CEA’s development on injected rotor, the consortium has validated the following performances:
- The magnetic field is homogeneous;
- The rotor injection is reproductible;
- Remanence of the injected magnets is close to nominal.
Thus, the injected magnets’ lack of performances in terms of process standardisation has been tackled by consortium’s developments. The ModulED project's acquired knowledge is now enriched by the validation of an efficient production process for injected rotors. During the further spin, assembly and insertion tests into the BPMM2 motors, the ModulED’s motor will be able to display the expected power and torque.