Additive manufacturing: The future of permanent magnets production

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Permanent magnets are used in numerous everyday and industrial applications, for example door locks and motors and generators. Permanent magnet production, however, relies on the use of critical rare earth elements, which are scarce. To reduce waste and labour associated with permanent magnet fabrication, Dr Mariappan Parans Paranthaman, a corporate fellow at Oak Ridge National Laboratory, developed a bonded magnet fabrication method using additive manufacturing, also known as 3D printing. His work shows that additive manufacturing can be used successfully for bonded permanent magnet fabrication, leading to products with high thermal stability and corrosion resistance.

All of us have made use of magnets at one time or another. From decorative fridge magnets and door closing systems, to magnets used in electronics, motors and generators, magnets have a very large market, which has been expanding with the development of environmentally friendlier technologies.

There are three main categories of magnets, namely soft (temporary), permanent, and electromagnets. Their difference arises from their magnetism (magnetic ability), which can be temporarily induced upon exposure near a magnetic field (soft magnets), permanent and unaffected due to constantly aligned atomic structure or caused by electricity passing through a coil (electromagnets).

There are several types of permanent magnets, such as rare earth magnets, samarium cobalt magnets, alnico magnets (based on an alloy of Aluminium, Nickel, and Cobalt), ceramic magnets, magnets produced via injection moulding, and magnets of flexible structure. Each type has distinct advantages and disadvantages, which affect the popularity for different applications. Rare earth magnets are the strongest among permanent magnets, consisting of alloys containing rare earth elements, such as Neodymium (Nd), and Dysprosium (Dy). Some of the critical properties of magnets for certain applications are corrosion resistance, mechanical strength, thermal stability, ability to be shaped on request, coercive force, and of course, cost.

“3D printing bonded permanent magnets could reduce the use of scarce rare earth elements, reduce energy and labour requirements, and explore endless capabilities of magnet shapes. “

3D printing magnets

Rare earth magnets might be the strongest permanent magnets, but they rely on the availability of rare earth elements, and this supply is currently in crisis, leading to high costs of raw materials. Conventional manufacturing methods for permanent magnet production are considered inefficient, as they can generate a sizeable waste when magnets are shaped to the required shapes and sizes through cutting and slicing. Furthermore, recovering rare earth elements from waste scraps is not an easy task, especially considering the rapid oxidation of such elements.

BAAM printed NdFeB polyphenylene sulphide bonded magnets. Magnet surfaces were polished and clear coated.

In recent years, research efforts have been focused on the production of magnets that do not require a large concentration of rare earth elements, in order to deal with the scarcity of such elements, as well as on methods to produce magnets that lead to minimised waste. One such method that has been gaining attention for magnet production is additive manufacturing. In contrast to “regular” (or subtract) manufacturing, additive manufacturing offers the ability to create a three-dimensional (3D) structure using a layer-by-layer, or additive, mode of construction. In this way, complex structures can be created easily without the need for added machining and manual labour to form the required shapes. In addition, waste and energy requirements are vitally minimised.

Additive manufacturing, commercially also known as 3D printing, operates via computer-aided design (CAD), which means that once the design is created in the computer, it can be produced in real life without the expensive moulds. Recently, additive manufacturing was explored outside the usual remit of structural materials, to produce permanent magnets. 3D printing bonded permanent magnets could reduce the use of scarce rare earth elements, but also reduce energy and labour requirements, and explore the endless capabilities of magnet shapes.

Permanent magnet production

Producing permanent magnets through 3D printing can be tricky and not straightforward. Using a CAD model and knowing the optimal concentration of raw materials (in this case rare earth powders and mixing polymer agents) are two essential factors. Dr Mariappan Parans Paranthaman and his research group have been conducting research in the area of bonded permanent magnet production through additive manufacturing, focusing on both isotropic and anisotropic NdFeB (Neodymium, Iron, Boron) permanent magnets.

3D printing bonded permanent magnets could reduce the use of scarce rare earth elements, but also reduce energy and labour requirements, and explore the endless capabilities of magnet shapes.

Dr Paranthaman is a materials chemist and distinguished corporate fellow at Oak Ridge National Laboratory. In his most recent publication, Dr Paranthaman and his colleagues explored the production of isotropic NdFeB permanent magnets using polyphenylene sulfide (PPS) as a bond (mixing agent to hold the rare earth powders together). Building upon previous research which explored the potential of Big Area Additive Manufacturing (BAAM) and its advantages compared to traditional permanent magnet production processes, in his recent work Dr Paranthaman focused on the optimisation of the properties of 3D-printed permanent magnets. Using the BAAM principles of fast production of large-scale items as close to ideal shape as possible, Dr Paranthaman combined NdFeB magnet powders with PPS to create an optimal mixture that could be 3D-printed and produce isotropic permanent magnets with enhanced properties.

Critical materials research: NdFeB magnets

With years of research experience in the area of critical materials such as rare earth elements, Dr Paranthaman identified the opportunity to use BAAM for the production of bonded NdFeB permanent magnets, moving away from traditional methods. Such methods include injection bonding using a thermoplastic binder and compression bonding using a thermoset binder. In the first method, magnet powder and thermoplastic binder are mixed and injected under heat into complex shapes, whereas in the second, magnet powder and thermoset binder are pressed under heat into a mould of usually simple geometries.

BAAM printed NdFeB nylon bonded magnets. Magnet surfaces were polished and clear coated.

Compared to the traditional techniques, 3D-printing allows for better properties of the final product. A comparison between magnets produced via additive manufacturing and injection bonding showed that the former had a higher density of magnetic powder, despite starting with the same proportion of magnetic powder to binder. This led to improved magnetic attributes, such as intrinsic coercivity (the ability to resist demagnetisation), remanence (residue magnetisation upon magnetic field removal), and energy product (the maximum magnetostatic energy stored).

NdFeB bonded magnets: One step forward

According to research literature, the volume percentage of magnetic powder required to produce a bonded permanent magnet has been anywhere between 60% and 80%, the rest being the binder. After successfully producing NdFeB bonded permanent magnets through additive manufacturing using 70% magnetic powders (the rest being nylon), Dr Paranthaman explored the possibility of increasing the percentage of magnetic powder required with much improved properties of the final product without the need for mould and no wastage. In this way the rare earth elements will be efficiently used, adding to the overall effort for sustainable magnet production, without compromising the need for adequate magnets in industrially important applications such as in motors and generators.

“Dr Paranthaman explored the possibility of increasing the percentage of magnetic powder in polymer binders, with improvement in magnetic properties of the final product.”

Dr Paranthaman and his team managed to increase the percentage of magnetic powder to 63% (the rest being PPS), fabricating magnets that showed no degradation in magnetic properties compared to those with a higher percentage of magnetic powder. Upon exploration of post-printing treatment using different coatings, Dr Paranthaman found that thermal stability, magnetic flux loss over prolonged use in high temperatures, and corrosion resistance – all very important properties for rare earth magnets used in motors and generators – could be massively enhanced.

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The future of rare earth magnets

Throughout his many contributions to critical material research, Dr Paranthaman has managed to move several steps forward with the fabrication of permanent magnets that do not disrespect the need to minimise material waste and labour. His work has shown that additive manufacturing can be successfully used for the production of rare earth bonded permanent magnets, without any limitations regarding shape requirements.

There is more work to be done before 3D printing is explored for magnet fabrication for industrial applications. According to Dr Paranthaman, some challenges pending resolution are the optimisation of the nozzle and temperature during extrusion, the optimisation of residual stress and microstructure of magnets fabricated via 3D printing, and the ability to transform magnetic powder from isotropic to anisotropic during magnet fabrication. Furthermore, a technoeconomic analysis will be needed to explore the feasibility of additive manufacturing to be used for magnet fabrication for industrial applications.

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Do you think that additive manufacturing superseded existing methods for permanent magnet fabrication?

Yes. The additive manufacturing method has already passed the injection molding process by increasing the loading of magnetic particles in a polymer binder. AM magnets have outperformed injection molded magnets.

 

References

DOI
10.26904/RF-137-1595082832

Research Objectives

Dr Mariappan Parans Paranthaman is working to produce permanent magnets using additive manufacturing, thereby heightening performance and reducing waste.

Funding

This research was supported by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office.

Research on printing soft magnets and critical rare earth free magnets were supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Wind Energy Technologies Office Program.

Collaborators

Dr Paranthaman would like to thank Dr Ikenna C. Nlebedim and his team from Ames Laboratory, Critical Materials Institute and Dr Brian Post and his team from Oak Ridge National Laboratory.

Bio

Dr Mariappan Parans Paranthaman is a materials chemist. Dr Paranthaman received his Ph.D. from Indian Institute of Technology, Madras. He worked with Nobel Prize winner Professor John Goodenough at the University of Texas at Austin and University of Colorado, Boulder before joining Oak Ridge National Laboratory, where he is currently a corporate fellow. He is a fellow of several societies including National Academy of Inventors. He has authored or co-authored more than 440 journal publications with an “h-index” of 69 (Google scholar citation) and issued 53 U.S. Patents and he has commercialised and licensed his technologies to six companies. His current research focuses on the development of additive manufacturing of soft and hard magnets for motors and generators, lithium separation from geothermal brine, recovery of carbon from recycled tires for clean energy applications, and development of electrode materials for energy storage applications.

Dr Mariappan Parans Paranthaman

Contact
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6100, USA

E: paranthamanm@ornl.gov
T: +1 (865) 574-5045
W: https://www.ornl.gov/staff-profile/m-paranthaman
W: https://scholar.google.com/citations?user=4vFTn_UAAAAJ&hl=en
W: https://bit.ly/3hx3LMl

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