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 μm-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 μm using 600 μm-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 μm, 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 μm, 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/m3. 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 μm was obtained with 3.1 V DC applied to the driving coil. Finite element simulations of the actuator design estimate at 2.38 MPa the maximum stress on the membrane at 50 μm actuation (i.e., below the fatigue limit of Nylon 12), and at 592.61 Hz the natural frequency of the device, which was corroborated via experiment.