Thermoset-bonded injection-molded magnets with defined structure of magnetization
Final Report Abstract
The aim of the project was to establish a fundamental understanding of the properties of injection-molded, thermoset-bonded magnets in processing and application. The project was initially based on extensive material characterization. Epoxy resin (EP) and phenolic resin (PF) were considered as matrix materials. In addition to anisotropic SrFeO, an isotropic and an anisotropic type of neodymium-iron-boron (NdFeB) were analyzed. The filler content was varied between 40 and 70 vol.%. With regard to material characterization, the reaction kinetics and crosslink density were determined relative to temperature and time using differential scanning calorimetry (DSC) measurements. Furthermore, the rheological behavior was determined by rotational viscometry measurements as a function of temperature and time. To evaluate the wetting and adhesion between the filler and the matrix, the surface energy was defined as an application test, and the fracture surface was analyzed after the mechanical tests using a scanning electron microscope. The mechanical behavior could be attributed to four factors with close interaction. These are the polymer network structure, the crosslink density, and the wetting and adhesion potential. Based on the material characterization, a model for network theory and an overview of the processing window could be defined. Network theory in particular plays a decisive role in understanding material behavior, also with regard to the properties in the component. For the experimental tests with multipolar rings in the injection molding process, an injection molding tool with an integrated magnetic field was designed using FE methods. After the multipolar ring test specimens were manufactured, they were analyzed in terms of their magnetic properties, differentiating between the properties resulting from orientation and partial magnetization and those resulting from complete magnetization and thus the full exploitation of the material's potential. This shows that subsequent magnetization is essential in the case of thermoset-based plastic-bonded permanent magnets, as the increased mold temperatures prevent saturation magnetization in the mold. At the same time, the outer magnetic field can already be reproduced in the outer diameter without the formation of a rapidly solidified edge layer or a deflection of the orientation. However, the orientation is limited towards the center of the component depending on the component thickness and the strength of the external magnetic field, as the strength of the external magnetic field decreases. Taking into account the material characterization and the process understanding gained, design guidelines for plastic-bonded permanent magnets based on thermosets could be defined. Here, a PF with an SrFeO with a high filler content of at least 55 vol.% should be aimed for in the matrix material. Within the tool concept, a high number of poles in the outer magnetic field was to be selected, along with low permeability of the cavity wall material, low sample thickness, and a double point gate with a center gate position. Due to the cross-linking reaction of the matrix materials, only a limited number of parameters can be varied during process control, whereby a high holding pressure combined with a short heating time is recommended. The project has laid important foundations that can be transferred to applications with more complex geometries, such as in the field of drive technology.
Publications
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Correlation between the Flow and Curing Behavior of Hard Magnetic Fillers in Thermosets and the Magnetic Properties. Magnetism, 1(1), 37-57.
Rösel, Uta & Drummer, Dietmar
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Simulationsgestützte Auslegung eines Spritzgießwerkzeugs zur Herstellung von kunststoffgebundenen Dauermagneten auf Duroplast Basis, Werkstoffe in der Fertigung, 2 (2022), S. 18-22.
Rösel, U. & Drummer, D.
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Understanding the Effect of Material Parameters on the Processability of Injection-Molded Thermoset-Based Bonded Magnets. Magnetism, 2(3), 211-228.
Rösel, Uta & Drummer, Dietmar
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Correlation between the Material System and the Magnetic Properties in Thermoset-Based Multipolar Ring Magnets. Magnetism, 3(3), 226-244.
Rösel, Uta & Drummer, Dietmar
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Extension of the Application Range of Multipolar Bonded Ring Magnets by Thermosets in Comparison to Thermoplastics. Magnetism, 3(1), 71-89.
Rösel, Uta & Drummer, Dietmar
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Zum Spritzgießen multipolarer kunststoffgebundener Dauermagnete auf Duroplast-Basis Dissertation, Friedrich-Alexander-Universität Erlangen-Nürnberg, 2023.
Rösel, U.
