Additive manufacturing allows for the production of complex parts with minimum material waste, offering an effective technique for fabricating permanent magnets which frequently involve critical rare earth elements. In this report, we demonstrate a novel method - Big Area Additive Manufacturing (BAAM) - to fabricate isotropic near-net-shape NdFeB bonded magnets with magnetic and mechanical properties comparable or better than those of traditional injection molded magnets. The starting polymer magnet composite pellets consist of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12). The density of the final BAAM magnet product reached 4.8 g/cm3, and the room temperature magnetic properties are: intrinsic coercivity Hci = 688.4 kA/m, remanence Br = 0.51 T, and energy product (BH)max = 43.49 kJ/m3 (5.47 MGOe). In addition, tensile tests performed on four dog-bone shaped specimens yielded an average ultimate tensile strength of 6.60 MPa and an average failure strain of 4.18%. Scanning electron microscopy images of the fracture surfaces indicate that the failure is primarily related to the debonding of the magnetic particles from the polymer binder. The present method significantly simplifies manufacturing of near-net-shape bonded magnets, enables efficient use of rare earth elements thus contributing towards enriching the supply of critical materials.

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Extrusion based additive manufacturing of polymer composite magnets can increase the solid loading volume fraction with greater mechanical force through the printing nozzle as compared to traditional injection molding process. About 63 vol% of isotropic NdFeB magnet powders were compounded with 37 vol% of polyphenylene sulfide and bonded permanent magnets were fabricated while using Big Area Additive Manufacturing without any degradation in magnetic properties. The polyphenylene sulfide bonded magnets have a tensile stress of 20 MPa, almost double than that of nylon bonded permanent magnets. Additively manufactured and surface-protective-resin coated bonded magnets meet the industrial stability criterion of up to 175 °C with a flux-loss of 2.35% over 1000 h. They also exhibit better corrosion resistance behavior when exposed to acidic (pH = 1.35) solution for 24 h and also annealed at 80 °C over 100 h (at 95% relative humidity) over without coated magnets. Thus, polyphenylene sulfide bonded, additively manufactured, protective resin coated bonded permanent magnets provide better thermal, mechanical, and magnetic properties.

Isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are fabricated via an extrusion-based additive manufacturing, or 3D printing system that enables rapid production of large parts for the first time. The density of the printed magnet is 5.15 g/cm 3 . The room temperature magnetic properties are: intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58 Tesla), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m 3 ). The as-printed magnets are then coated with two types of polymers, both of which improve the thermal stability at 127 °C as revealed by flux aging loss measurements. Tensile tests performed at 25 °C and 100 °C show that the ultimate tensile stress (UTS) increases with increasing loading fraction of the magnet powder, and decreases with increasing temperature. AC magnetic susceptibility and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets exhibit extremely 2 low eddy current loss and high resistivity. Finally, we show that through back electromotive force measurements that motors installed with 3D printed Nd-Fe-B magnets exhibit similar performance as compared to those installed with sintered ferrites.

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Permanent magnets (PMs) produce magnetic fields and maintain the field even in the presence of an opposing magnetic field. Electrical machines using permanent magnets are more efficient than those without. Currently, all known strong magnets contain rare earth (RE) elements, and they are core components of a wide range of applications including electric vehicles and wind turbines. RE elements such as Nd and Dy have become critical materials due to the growing demand and constrained supply. Improving the manufacturing process is effective in mitigating the RE criticality issue by reducing waste and improving parts consistency. In this article, the state of the industry for PM is reviewed in detail considering both the technical and economic drivers. The importance of RE elements is discussed along with their economic importance to green energy. The conventional sintering and casting manufacturing processes for commercial magnets, including Nd-Fe-B, Sm-Co, Alnico, and ferrite, are described in detail.

This study presents the effects of substitution of Zn 2+ for Co2+ at low concentrations and the effects of temperature variations on the structural, magnetic, and magnetostrictive properties ofcobalt ferrite. Although the Zn-substituted cobalt ferrite samples, Co1−x Zn xFe2O4 (x = 0.02, 0.04, 0.06, 0.09, and 0.17) did not show observable changes in crystal structure, the magnetic and magnetostrictive properties were strongly affected. The variation in magnetic susceptibilitywith composition can be related to the variations in magnetization, coercive field and magnetocrystalline anisotropy. The changes in coercive field were found to be primarily due to the variations in the magnetocrystalline anisotropy. The effect of magnetocrystalline anisotropyon magnetization was stronger at lower cation concentration than at higher concentrations. The decrease in magnetization around 150 K is attributed to the high magnetocrystalline anisotropyat low temperatures which prevented the maximum applied field of 4 MA/m from causing the saturation of magnetization in the samples. Because the magnetocrystalline anisotropy was determined with the magnetization data using the Law of Approach to saturation magnetization, the reliability of the result was found to decrease with decrease in temperature. Peak-to-peakmagnetostriction amplitude and the strain sensitivity decreased with increase in Znsubstitution. KeywordsAmes Laboratory, Zinc, Magnetic anisotropy, Ferrites, Cobalt, Magnetic fields Disciplines Electromagnetics and Photonics CommentsThe following article appeared in Journal of Applied Physics 113 (2013) This study presents the effects of substitution of Zn 2þ for Co 2þ at low concentrations and the effects of temperature variations on the structural, magnetic, and magnetostrictive properties of cobalt ferrite. Although the Zn-substituted cobalt ferrite samples, Co 1Àx Zn x Fe 2 O 4 (x ¼ 0.02, 0.04, 0.06, 0.09, and 0.17) did not show observable changes in crystal structure, the magnetic and magnetostrictive properties were strongly affected. The variation in magnetic susceptibility with composition can be related to the variations in magnetization, coercive field and magnetocrystalline anisotropy. The changes in coercive field were found to be primarily due to the variations in the magnetocrystalline anisotropy. The effect of magnetocrystalline anisotropy on magnetization was stronger at lower cation concentration than at higher concentrations. The decrease in magnetization around 150 K is attributed to the high magnetocrystalline anisotropy at low temperatures which prevented the maximum applied field of 4 MA/m from causing the saturation of magnetization in the samples. Because the magnetocrystalline anisotropy was determined with the magnetization data using the Law of Approach to saturation magnetization, the reliability of the result was found to decrease with decrease in temperature. Peak-to-peak magnetostriction amplitude and the strain sensitivity decreased with increase in Zn substitution. V C 2013 AIP Publ...