Fully 3D-Printed, Monolithic, Mini Magnetic Actuators for Low-Cost, Compact Systems

We report the design, fabrication, and experimental characterization of the first fully 3D-printed, multi-material miniature magnetic actuators for compact systems in the literature. The actuator design integrates a bonded hard magnet made of NdFeB microparticles embedded in a Nylon 12 matrix (55% by volume) with structural and support elements made of pure Nylon 12. The device is a 10 mm-diameter, 1.2 mm wall-thick, and 9 mm tall cylindrical frame that mounts on an off-the-shelf solenoid and a 10 mm diameter, 100 \mu \text{m} -thick, leak-tight membrane connected at its center to a 4 mm diameter, 4.95 mm tall hard magnet. The actuators are monolithically printed in layers as thin as 100~\mu \text{m} using 600~\mu \text{m} -wide strokes via fused filament fabrication (FFF) -a low-cost 3D printing technology capable of processing high-performance thermoplastics to create monolithic objects made of a plurality of distinctive feedstock. The average surface roughness, Young's modulus, and hardness of the FFF-printable hard-magnetic filament were estimated at 58.55~\mu \text{m} , 3.59 GPa, and Shore D 71.5, respectively, while the average surface roughness, Young's modulus, and yield strength of FFF-printed magnetic material were estimated at 5.79~\mu \text{m} , 2.02 GPa, and 55.99 MPa ± 4.59 MPa, respectively. Magnetic characterization of the FFF-printed NdFeB-embedded Nylon 12 feedstock demonstrates the fabrication of isotropic hard magnets with an intrinsic coercivity of ~700 kA/m, remanence of ~395 mT, and a maximum energy product of 27 kJ/ \text{m}^{3} . Simulations of the stray magnetic field produced by a printed sample made of NdFeB-embedded Nylon 12 were validated using a scanning Hall probe. The vertical displacement of a miniature 3D-printed magnetic actuator was characterized with a solenoid for various coil bias voltages; a maximum displacement equal to 50 \mu \text{m} was obtained with 3.1 V DC applied to the driving coil. Finite element simulations of