Selective laser sintering of bonded magnets from flake and spherical powders

Mapley, Martin; Pauls, Jo P.; Tansley, Geoff; Busch, Andrew; Gregory, Shaun D.

doi:10.1016/j.scriptamat.2019.07.029

Cited by 16 publications

(17 citation statements)

References 5 publications

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“…4b-c). Such a mechanism may be present in powder compacts with a wide particle size distribution [12,13,38,[81][82][83], where local arrangements may produce triangular required geometry (Fig. 1d).…”

Section: Discussion: Implications and Limitationsmentioning

confidence: 99%

“…These influences will couple with the microstructural elements and micromechanics of sintering (as indicated in [42]), and result in a rather complex process. Such complexity behavior will arise for powders with wide size distribution and shape variations, i.e., spherical and flat surfaces, [37,38], where the inter-particle contacts can be locally represented using a combination of case-I, II, III, IV V and V (Fig. 1).…”

Section: Discussion: Implications and Limitationsmentioning

confidence: 99%

“…These scaling laws predict a smooth neck evolution, but do not allow us to view temporal change in microstructure near the neck region, i.e., they are ''static'' models. The description of such microstructural evolution is necessary, because technologically important powder materials increasingly contain extreme variations in size distribution, e.g., nanocomposites [14][15][16][17]19] and shape (this category will be discussed later) [36][37][38].…”

Section: Introductionmentioning

confidence: 99%

“…Consideration of curvature effects is now even more important because of two technical applications. First, powder particles of vastly different shapes are increasingly used for sintering applications, e.g., particles of spherical and plate-like shapes are mixed together to form a green-compact [36][37][38]. Second, in recent years, selective laser melting is extensively used to produce porous structures [55][56][57][58][59].…”

Section: Introductionmentioning

confidence: 99%

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Particle curvature effects on microstructural evolution during solid-state sintering: phenomenological insights from phase-field simulations

Choudhuri

Blake

2021

J Mater Sci

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Local curvatures have a profound influence on sintered microstructure. Here, using phase-field simulations, particle curvature effects were phenomenologically investigated by using geometrical configurations of two, three, and four particles, and by systematically varying particle curvatures. Some geometries, involving two, three and four particles, exhibited the expected smooth necklength evolution, where the maximum neck length was determined by grain boundary (GB) energy (c GB ) rather than surface energy (c S ). In contrast, triangular arrangement of particles with unequal radii manifested a secondary necking event in form of a step during neck evolution. The secondary necking event coincided with internal pore collapse, and only specific range of particle radius ratios manifested such a mechanism. c S played a dominant role in triggering the secondary necking event, while c GB determined the remnant microstructure. Broadly, the geometries employed here allow us to computationally examine the sintering of particles that display wide variation in shapes and size distributions.

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Section: Discussion: Implications and Limitationsmentioning

confidence: 99%

Section: Discussion: Implications and Limitationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Particle curvature effects on microstructural evolution during solid-state sintering: phenomenological insights from phase-field simulations

Choudhuri

Blake

2021

J Mater Sci

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“…Previously, bonded PMs have been produced by our group using an AM technique known as selective laser sintering (SLS) where a mechanically alloyed mixture of isotropic NdFeB flakes or spheres and polyamide-12 were selectively sintered in layers by a high-powered laser (Mapley et al, 2019;Wendhausen et al, 2017). This method has many similarities to SLM; however, by the introduction of a binder, much lower processing temperatures can be used.…”

Section: Introductionmentioning

confidence: 99%

Selective laser sintering of bonded anisotropic permanent magnets using an in situ alignment fixture

Mapley

Tansley

Pauls

et al. 2021

RPJ

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Purpose Additive manufacturing (AM) techniques have been developed to rapidly produce custom designs from a multitude of materials. Bonded permanent magnets (PMs) have been produced via several AM techniques to allow for rapid manufacture of complex geometries. These magnets, however, tend to suffer from lower residual induction than the industry standard of injection moulding primarily due to the lower packing density of the magnetic particles and secondly due to the feedstock consisting of neodymium-iron-boron (Nd-Fe-B) powder with isotropic magnetic properties. As there is no compaction during most AM processes, increasing the packing density is very difficult and therefore the purpose of this study was to increase the magnetic properties of the PMs without increasing the part density. Design/methodology/approach Accordingly, this research investigates the use of anisotropic NdFeB feedstock coupled with an in-situ alignment fixture into an AM process known as selective laser sintering (SLS) to increase the magnetic properties of AM magnets. A Helmholtz coil array was added to an SLS machine and used to expose each powder layer during part fabrication to a near-uniform magnetic field of 20.4 mT prior to consolidation by the laser. Findings Permeagraph measurements of the parts showed that the alignment field introduced residual induction anisotropy of up to 46.4 ± 2.2% when measured in directions parallel and perpendicular to the alignment field. X-ray diffraction measurements also demonstrated a convergence of the orientation of the crystals when the magnets were processed in the presence of the alignment field. Originality/value A novel active alignment fixture for SLS was introduced and was experimentally shown to induce anisotropy in bonded PMs. Thus demonstrating a new method for the enhancement in energy density of PMs produced via AM methods.

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