While magnetic materials are pretty important when it comes to creating and implementing novel technologies, like 3D printing, it’s not easy to integrate or tune them in complicated designs, because of constraints in conventional manufacturing methods. A team of researchers from ETH Zurich, the Universitat Autònoma de Barcelona, and ETH Zurich spin-off company Magnes AG published a paper, titled “3D Printing of Thermoplastic-bonded Soft-and Hard-Magnetic Composites: Magnetically Tuneable Architectures and Functional Devices,” that explains their investigation into creating polymer composites – using a customized FDM 3D printer – that possess magnetic properties and tailored geometries.
“Recently, there has been an interest in printing hard magnets, owing to the significance of these materials in a wide range of applications. Hard-magnetic components are ubiquitous in industrial equipment and consumer goods. However, the processability and integration of these materials has hampered further development of advanced magnetic technologies, which are crucial in the fields of robotics, renewable energy, aeronautics or automotive engineering,” the researchers explained.
“Current manufacturing methods for these materials such as injection molding and sintering face several obstacles, particularly in the production of complex geometries.”
By using 3D printing, it’s possible to make high-performance, composite magnets that are patterned in “arbitrary shapes and architectures” and made specifically for certain applications, which helps keep costs down.
“In this work, we investigate the manufacturing of 3DP thermoplastic–bonded magnetic composites (TBMC), with both tailored geometries and magnetic properties, using a customized fused deposition modeling (FDM) 3D printer,” the researchers wrote. “The composites are made of polyamide and contain magnetic particles of different sizes and magnetic behavior.”
The team created and tested a total of three TBMC filaments, each with a different magnetic property. The next step was showing how the feedstock magnetic materials’ specific properties were preserved in the final structure, and then the researchers explained how to adjust its magnetic behavior by using a double nozzle setup to 3D print parts with varying “magnetic attributes.”
“To demonstrate the versatility of our double–nozzle customized FDM printer, we also fabricated 3D structures made of non-magnetic and magnetic parts,” the researchers explained. “To this end, we print planetary magnetic gearboxes with different configurations, and we demonstrate their potential applicability as magnetic rotary encoders (MRE).”
MREs, which position and control the motion of industrial robotic tools, are made up of a magnetic ring, or disc, where “a magnetic pattern of alternating poles is written.” Additional sensor components aren’t necessary when the magnetic material is 3D printed directly onto the rotary shaft, and more materials can be used.
The researchers used three commercially available polyamide (PA)-based magnetic composite pellets for their experiments, and optimized the extrusion parameters when producing each one: Nd2Fe14B (NFB/PA12), Fe6.72Si1.27Al (FSA)/PA12, and SrFe12O19/PA12 (SFO/PA12). The composites, and the final structures, were tested for features like surface morphology, magnetic properties, adhesion, and thermal energy, among others.
“A powerful feature that can be exploited using a dual nozzle process is illustrated in Figure 3a, which shows 3D printed structures made of magnetically dissimilar TBMC parts,” the researchers wrote. “By combining TBMCs with different magnetic properties, the overall magnetic behavior can be customized. For example, it is possible to adjust the coercivity, the saturation magnetization, or the remanence of the final printed structure.”
Using this approach, the team 3D printed a disc with a soft-magnetic TBMC top layer and hard-magnetic TBMC bottom layer, and a crisscross patterned cuboid with alternating hard-magnetic and soft-magnetic TBMC stripes.
“By combining two different TBMCs, a semi-hard magnetic material with a slightly constricted-type hysteresis loop is obtained, suggesting an influence of interparticle magnetic dipolar interactions,” the researchers explained. “Note that structures made of the same composite but with different shapes can exhibit differences in their magnetization loops mainly due to shape anisotropy.”
A dual nozzle extruder also makes it possible to 3D print self-contained mechanisms, with several moving parts, without having to assemble them separately – a major application in the field of gear technology. The researchers used their custom 3D printer to fabricate a magnetic gear system out of both magnetic and nonmagnetic material. They performed Finite Element Method simulations on the system in order to analyze its magnetization behavior.
“For our experiment, the maximal applied rotational frequency (cut-off frequency) was measured at 28 Hz. Above this frequency, the gearbox starts to stutter and the motion changes from a revolving to a shaking motion. The cut-off frequency and the shaking motion are related to the interplay between rotational drag and the alignment of the magnetization of the gear with the external magnetic field. Above 28 Hz, the drag generated by the gears is sufficient to make the magnetic gear lag back. The induced lag allows the external magnetic field to overtake the gear itself, causing the torque on the magnetic gear to switch direction back-and-forth, producing the rocking motion of the gearbox,” the researchers explained.
Because 3D printing offers such high complexity, the researchers were able to achieve multiple TBMC complex shapes and tunable customized magnetic properties. Their work showed that their TBMC materials can transfer magnetic properties to the 3D printed structure without any deterioration.
“The use of 3DP for magnetic applications represents a leap towards on-site versatile fabrication of complex magnetic devices, which would otherwise be unfeasible with conventional manufacturing techniques,” they concluded.
Co-authors of the paper were George Chatzipirpiridis, Simone Gervasoni, Cedric Fischer, Olgaç Ergeneman, Eva M. Pellicer, Bradley J. Nelson, and Salvador Pané.
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