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ORNL team shows 3D-printed permanent magnets outperform conventional versions, conserve rare materials

Researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) and colleagues have demonstrated that permanent magnets produced by additive manufacturing can outperform bonded magnets made using traditional techniques while conserving critical materials. NdFeB magnets are used in a range of applications from computer hard drives and headphones to clean energy technologies such as electric vehicles and wind turbines.

The team fabricated isotropic, near-net-shape, neodymium-iron-boron (NdFeB) bonded magnets at DOE’s Manufacturing Demonstration Facility at ORNL using the Big Area Additive Manufacturing (BAAM) machine. The result, published in an open-access paper in Scientific Reports, was a product with comparable or better magnetic, mechanical, and microstructural properties than bonded magnets made using traditional injection molding with the same composition.

IMG_0327
This isotropic, neodymium-iron-boron bonded permanent magnet was 3D-printed at DOE’s Manufacturing Demonstration Facility at Oak Ridge National Laboratory. Click to enlarge.

The additive manufacturing process began with composite pellets consisting of 65 vol% isotropic NdFeB powder and 35 vol% polyamide (Nylon-12) manufactured by Magnet Applications, Inc. The pellets were melted, compounded, and extruded layer-by-layer by BAAM into desired forms.

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.

NdFeB permanent magnets generally are sintered or bonded magnets. Sintered magnets retain full density and offer high energy product; bonded magnets, on the other hand, offer a high degree of net-shape formability but with an intermediate energy product.

Bonded permanent magnets are fabricated by blending magnetic powders with a polymer as binder; this mixture is then molded into desired shapes utilizing several commercial processing methods. Bonded permanent magnets feature intricate shapes, low weight and cost, superior mechanical properties and corrosion resistance. As a result, industrial interest in them is increasing.

… developing better NdFeB bonded magnets has been heavily researched. Magnet powder properties, processing temperature, loading factor, magnet density and degree of orientation are critical process variables for improving magnetic and mechanical properties of NdFeB bonded magnets.

Nevertheless, the conventional techniques used for bonded magnets fabrication have several drawbacks such as specific tooling requirement for each design and limitations in shape flexibility and complexity. Additive Manufacturing (AM) is an emerging technology that builds three dimensional objects from computer-aided design (CAD) models by adding layer-by-layer of material. It has attracted tremendous attention from both the research and industrial communities.

… Since permanent magnets are frequently composed of rare earth elements, most of which are defined as critical materials, AM could potentially offer an effective way to reduce the usage of critical materials during bonded magnets fabrication.

—Li et al.

While conventional sintered magnet manufacturing may result in material waste of as much as 30 to 50%, additive manufacturing will simply capture and reuse those materials with nearly zero waste, said Parans Paranthaman, principal investigator and a group leader in ORNL’s Chemical Sciences Division.

The project was funded by DOE’s Critical Materials Institute (CMI). Using a process that conserves material is especially important in the manufacture of permanent magnets made with neodymium, dysprosium—rare earth elements that are mined and separated outside the United States.

The printing process not only conserves materials but also produces complex shapes, requires no tooling and is faster than traditional injection methods, potentially resulting in a much more economic manufacturing process, Paranthaman said.

Future work will explore the printing of anisotropic, or directional, bonded magnets, which are stronger than isotropic magnets that have no preferred magnetization direction. Researchers will also examine the effect of binder type, the loading fraction of magnetic powder, and processing temperature on the magnetic and mechanical properties of printed magnets.

The ability to print high-strength magnets in complex shapes is a game changer for the design of efficient electric motors and generators. It removes many of the restrictions imposed by today’s manufacturing methods.

—Alex King, Director of the Critical Materials Institute

Contributing to the project were Ling Li, Angelica Tirado, Orlando Rios, Brian Post, Vlastimil Kunc, R. R. Lowden, Edgar Lara-Curzio at ORNL, as well as researchers I. C. Nlebedim and Thomas Lograsso working with CMI at Ames Laboratory. Robert Fredette and John Ormerod from Magnet Applications Inc. (MAI) contributed to the project through an MDF technology collaboration. The DOE’s Advanced Manufacturing Office provides support for ORNL’s Manufacturing Demonstration Facility, a public-private partnership to engage industry with national labs.

Resources

  • Ling Li, Angelica Tirado, I. C. Nlebedim, Orlando Rios, Brian Post, Vlastimil Kunc, R. R. Lowden, Edgar Lara-Curzio, Robert Fredette, John Ormerod, Thomas A. Lograsso & M. Parans Paranthaman (2016) “Big Area Additive Manufacturing of High Performance Bonded NdFeB Magnets” Scientific Reports 6, Article number: 36212 doi: 10.1038/srep36212

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