System for the additive manufacture of an anisotropic bonded magnet and associated manufacturing methods

Abstract

The invention relates to a system for the additive manufacture of an anisotropic bonded magnet from an initial material formed of a binder matrix and particles of anisotropic magnetic material, the system comprising an extruder body, a nozzle intended to eject a filament of initial material in viscous form, and an alignment system (30) surrounding the nozzle and generating a vertical magnetic induction (B) capable of aligning the magnetic material particles such that their easy magnetisation axis is oriented in the direction of magnetic alignment in the filament before it is ejected. The alignment system (30) consists of a first ring (31) made of permanent magnet material having radial magnetisation, a second ring (32) made of permanent magnet material having axial magnetisation, a yoke (34) made of magnetic material and an adapter (33) made of non-magnetic material. The invention also relates to manufacturing methods based on this system.

Description

EQUIPMENT FOR THE ADDITIVE MANUFACTURING OF AN ANISOTROPIC BOUND MAGNET AND ASSOCIATED MANUFACTURING METHODS FIELD OF THE INVENTION

[0001] The present invention relates to the field of additive manufacturing of bonded permanent magnets. In particular, it relates to equipment for the additive manufacturing of anisotropic bonded magnets and to particular manufacturing methods based on this equipment. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Additive manufacturing (also known as 3D printing) is a very attractive technique for rapid prototyping and the development of objects, potentially with complex shapes. In addition, 3D printing techniques do not require the manufacture of molds, they limit or even eliminate finishing machining steps (unlike traditional molding techniques), they reduce material waste and are more energy efficient: they are therefore economically attractive solutions.

[0003] Additive manufacturing is therefore also developing in the field of permanent magnets. In the case of the manufacture of bonded magnets, the initial material used includes particles of magnetic material and a polymer binder matrix. This initial material is melted in an extruder then ejected through a nozzle: the filament of molten material is deposited on a receiving surface and will solidify; the movement of the nozzle makes it possible to arrange the filament in such a way as to form the different layers which will give rise to the targeted magnet.

[0004] While it is easy to apply 3D printing to the development of isotropic bonded magnets, the manufacture of anisotropic bonded magnets requires overcoming several challenges to be competitive and efficient. To achieve magnetic anisotropy, it is necessary to use, during the development of the part, a magnetic source to orient the magnetic material particles contained in the molten filament, either during the construction of the layers or before solidification. This magnetic field source must be located near the tip of the nozzle from which the molten filament emerges: it is a hot environment and space is restricted, which makes its implementation difficult.

[0005] Documents US2012323072 and EP3711949 propose alignment systems either electromagnetic to generate a pulsed magnetic field, or based on a permanent magnet of the Halbach cylinder type. SUBJECT OF THE INVENTION

[0006] The present invention proposes an alternative, simpler and more efficient solution. It relates to equipment for the additive manufacturing of anisotropic bonded magnets which comprises a high-performance magnetic alignment system that withstands the environmental constraints of the nozzle. The invention further relates to a manufacturing method based on this equipment and to a layer construction strategy favorable to obtaining bonded magnets having a very good degree of alignment. Finally, it relates to a method for manufacturing a composite material wire, also based on the aforementioned equipment. BRIEF DESCRIPTION OF THE INVENTION

[0007] The invention relates to equipment for the additive manufacturing of an anisotropic bonded magnet from an initial material formed of a bonding matrix and particles of anisotropic magnetic material each having an axis of easy magnetization, the equipment comprising:

[0008] - an extruder body, intended to receive the initial material in solid form and to introduce it into a nozzle in viscous form by melting the binding matrix,

[0009] - the nozzle, intended to eject a filament of initial material in viscous form, said nozzle defining a channel extending along a main axis and ending in an ejection orifice, and

[0010] - an alignment system, surrounding the nozzle and generating a magnetic induction capable of aligning the particles of magnetic material so that their axis of easy magnetization is located in a direction of magnetic orientation, in the filament, before its ejection.

[0011] The equipment is remarkable in that the alignment system consists of a stack of generally annular shape, centered on the main axis, said stack comprising:

[0012] - a first permanent magnet ring with radial magnetization, normal to the main axis,

[0013] - a second permanent magnet ring having axial magnetization, parallel to the main axis, the second ring being arranged under the first ring,

[0014] - a yoke made of magnetic material, having an annular part arranged under the second ring and a cylindrical part surrounding a periphery of the first and second rings, the annular part being located on the side of the ejection orifice,

[0015] - an adapter made of non-magnetic material, secured on the one hand to the extruder body or the nozzle, and on the other hand to the first ring and / or the cylinder head.

[0016] The magnetic induction generated by the alignment system is parallel to the main axis and maximum in a region of interest of the channel, located upstream of the ejection orifice.

[0017] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination: the nozzle is made of amagnetic material, for example brass, stainless steel or ceramic, with one end made of a material whose hardness is greater than that of the particles of the initial material or resistant to abrasion by said particles, for example ruby, diamond or zirconia; the permanent magnet of the first and second rings is formed of SmCo and / or NdFeB; the permanent magnet of the first ring is composed of several angular portions, in particular six, eight or twelve; the material of the yoke is soft ferromagnetic, such as iron, steel, an FeCo or FeSi alloy; the material of the adapter is chosen from aluminum, brass, copper, a ceramic or a polymer resistant to a maximum temperature implemented on the equipment;the permanent magnet of the first ring and the permanent magnet of the second ring have a remanence greater than or equal to 0.7 T, or even preferably greater than or equal to 0.9 T, at a temperature of 230°C;

[0018] According to an advantageous embodiment of the equipment, the extruder body comprises: a cylinder having an internal space intended to accommodate the solid initial material at an upstream end and having a downstream end secured to the nozzle, a piston capable of moving in the cylinder to push the initial material towards the downstream end, a heating block arranged near the downstream end of the cylinder, capable of providing a temperature greater than or equal to a melting temperature of the binder matrix to give its viscous form to the initial material, a cooling block arranged near the upstream end of the cylinder, a feed hopper connected to the cylinder near its upstream end, for introducing granules of initial material, when the piston is in an initial position, the most upstream position in the cylinder;

[0019] According to another embodiment of the equipment, the extruder body comprises: a cylinder whose internal space is intended to receive the solid initial material at an upstream end and whose downstream end is integral with the nozzle, a worm screw arranged in the cylinder to push the initial material towards the downstream end, a heating block arranged near the downstream end of the cylinder, capable of providing a temperature greater than or equal to a melting temperature of the binding matrix to give its viscous form to the initial material, a cooling block arranged near the upstream end of the cylinder, a feed hopper connected to the cylinder near its upstream end, to introduce granules of initial material.

[0020] The invention also relates to a method for additive manufacturing of an anisotropic bonded magnet, using the aforementioned equipment, comprising the following steps:

[0021] a) the definition of the object, anisotropic bonded magnet, to be printed, said object being capable of being made up of one or more region(s) each with a given direction of magnetization,

[0022] b) the ejection by the nozzle of the filament of initial material in viscous form whose magnetic particles have their easy magnetization axis aligned with the axis of the filament, the ejection being made according to a unidirectional trajectory and an orientation, in a plane normal to the main axis, the easy magnetization axis of the particles being parallel to the unidirectional trajectory,

[0023] c) the progressive development of the object, while maintaining the same unidirectional trajectory and ejection orientation, to form the same region of the object with parallel cords of a solidified material whose magnetic particles have their axis of easy magnetization aligned along the axis of said cords which constitutes the direction of magnetization of the region.

[0024] Optionally, the method further comprises a step d) after step c), corresponding to the application of a magnetic field to each region to magnetize said region.

[0025] Finally, the invention relates to a method for manufacturing a composite material thread, using the aforementioned equipment, comprising a step of ejecting, through the nozzle, the filament of initial material in viscous form, the magnetic particles of which have their easy magnetization axis aligned along the axis of the filament, said filament, upon solidifying, forming the composite material thread. BRIEF DESCRIPTION OF THE FIGURES

[0026] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures:

[0027] This is a table of characteristics of three examples of initial material which can be used in equipment in accordance with the invention;

[0028] The present invention provides equipment for the additive manufacturing of an anisotropic bonded magnet in accordance with the present invention;

[0029] The present two examples (i) (ii) of nozzle for equipment for the additive manufacturing of an anisotropic bonded magnet according to the present invention;

[0030]

[0031]

[0032] Figures 4a, 4b, 4c show examples of alignment systems for an equipment for additive manufacturing of an anisotropic bonded magnet according to the present invention; it should be noted that only half of the alignment system is illustrated, taking into account the axial symmetry (along the main axis z) of said system;

[0033] The present invention presents different constructions of the first ring included in the alignment system for additive manufacturing equipment according to the present invention;

[0034] Lapresents a straight line connecting the intensity of the magnetic induction (B RI ) in the region of interest and the remanence of the permanent magnets constituting the two rings of the alignment system for additive manufacturing equipment according to the present invention;

[0035] Two examples of an alignment system for additive manufacturing equipment according to the invention are presented; depending on the construction of the alignment system, more or less significant magnetic induction intensities can be obtained, the materials constituting the alignment system being otherwise identical;

[0036] The present invention is a table detailing printing parameters for three initial materials of the present invention, in equipment and according to a method in accordance with the present invention;

[0037] The present two examples of objects (Halbach network (i) and cylinder (ii)) capable of being printed in equipment and according to a method in accordance with the invention;

[0038]

[0039] Figures 10a and 10b show portions of hysteresis cycles carried out on two test pieces (A and B) produced in equipment and according to a method according to the invention, on an extruded filament produced in equipment and according to a method according to the invention, and on a magnetically isotropic reference sample; compares all the samples with each other according to their alignment direction while compares the magnetization according to the alignment direction with a normal direction for each sample. DETAILED DESCRIPTION OF THE INVENTION

[0040] The invention relates to equipment for the additive manufacturing of anisotropic bonded magnets.

[0041] The initial material, intended to be introduced at the inlet of the equipment, is preferably in the form of granules with a size between 1mm and 5mm, preferably between 2mm and 4mm. It is formed from a thermoplastic binder matrix and particles of anisotropic magnetic material; each particle has an axis of easy magnetization.

[0042] The anisotropic magnetic material is preferably based on rare earths and transition metals, and can in particular be chosen from NdFeB, SmFeN, SmCo. These materials can come from mining and be produced by wheel quenching ("Melt Spun" according to the English terminology), by powder metallurgy, by the HDDR process ("hydrogenation-disproportionation-desorption-recombination") or come from the recycling of Waste Electrical and Electronic Equipment (WEEE) by hydriding (HD) for example.

[0043] The magnetic material can alternatively be chosen from ferrites or other materials for permanent magnets.

[0044] The particle size of magnetic material particles typically corresponds to a d 0.5 between 1 µm and 500 µm. As a reminder, a d 0.5 100 µm means that 50% of the particles have a size (Sauter equivalent diameter) less than or equal to 100 µm.

[0045] The volume fraction of magnetic material particles in the initial material is between 3% and 80%, preferably between 50% and 70%, so as to maximize the amount of magnetic material while having enough polymer to obtain good flow during printing.

[0046] The binder matrix may be chosen from a polyamide (PA12, PA11, PA6), a thermoplastic polyurethane (TPU), a polyethylene (PE), or a polylactic acid (PLA), or a combination of thermoplastic materials having a melting temperature, typically less than 300°C.

[0047] Using pellets as the starting material eliminates the costs and difficulties associated with producing a winding wire. In addition, pellets can be highly charged (e.g. 60-70% vol.) unlike wire, which loses flexibility and becomes difficult to process when the charge rate is high.

[0048] The table below shows the characteristics of three examples of starting material. Other magnetic materials can of course be printed, provided that their charge rate and particle size correspond to the above specifications.

[0049] The initial material MI1 consists of NdFeB particles produced by HDDR, spheroidal in shape and whose d 0.5 is equal to 105 µm. The remanence of the MI1 material is 0.84 T, and its coercivity is 1030 kA / m. The powder is formulated in PA12 at 63% vol. The initial material MI2 is produced from the same type of magnetic powder as MI1 but the latter has been ground to a d 0.5 of 76 µm. It has a charge rate of 52% vol. The initial material MI3 is a mixture of SmFeN particles, spherical in shape, with a d 0.5 3 µm, at 60% vol in a PA12 binder matrix.

[0050] The equipment 100 for additive manufacturing of anisotropic bonded magnets according to the invention is illustrated in the. It basically comprises an extruder body 10, a nozzle 20 and an alignment system 30. The extruder body 10 / nozzle 20 / alignment system 30 assembly (similar to a 3D printing head) typically has a dimension of between 150mm and 250mm along the vertical axis z, and a dimension, along the y axis, of between 20mm and 50mm.

[0051] The extruder body 10 is configured to receive the initial material previously described, in solid form, and to introduce it into the nozzle 20 in viscous form by melting the binding matrix.

[0052] According to an advantageous embodiment, the extruder body 10 comprises a cylinder 11, an internal space of which is intended to receive the solid initial material at an upstream end (upper zone along the main vertical axis z, on the). The downstream end (lower zone) of the cylinder 11 is integral with the nozzle 20. The extruder body 10 also comprises a piston 12 capable of moving in the cylinder 11 to push the initial material towards the downstream end. The piston 12 can be actuated by conventional mechanical means, for example by a linear stepper motor 17 with a worm screw, or a pneumatic or hydraulic device. The extruder body 10 comprises a heating block 13 arranged near the downstream end of the cylinder 11, capable of providing a temperature greater than or equal to a melting temperature of the binder matrix, to give its viscous form to the initial material.A cooling block 14 (for example with fins) is also provided, near the upstream end of the cylinder 11. Finally, a feed hopper 15 is connected to the cylinder 11 near its upstream end: it is at this point that the granules of initial material are introduced, when the piston 12 is in an initial position, the most upstream position in the cylinder 11. In the example of the, the piston 12 has a stroke of approximately 38 mm.

[0053] It is advantageous for an upstream portion of the cylinder 11, including the upstream end, to be maintained at a temperature less than or equal to 80°C and for a downstream portion, including the downstream end, to be maintained at a temperature greater than or equal to 200°C, the temperature required to melt the thermoplastic binder matrix of the initial material. Advantageously, the temperature in the downstream portion is aimed at 30°C-40°C above the melting temperature of the binder matrix.

[0054] The significant thermal gradient (of the order of 40°C / cm) between the upstream and downstream ends is ensured by the presence of the heating block 13 and the cooling block 14. This gradient makes it possible to achieve melting of the binder matrix over a short distance, thus promoting the compactness of the equipment 100. In addition, it prevents the piston 12 from being in contact with the initial material in viscous form, as this would risk blocking the opening provided in the piston 12 to balance the pressure on both sides of said piston, or inducing suction of the viscous material when the piston 12 is raised to transfer the initial material from the feed hopper 15 into the cylinder 11. The stroke of the piston 12 therefore stops before reaching the downstream part.

[0055] According to an alternative embodiment (not shown), the extruder body 10 comprises, instead of the piston 12, an endless screw which allows the initial material to be conveyed to the nozzle 20. It is then composed of the following elements:

[0056] - a cylinder with an internal space intended to accommodate the initial solid material at an upstream end and a downstream end of which is secured to the nozzle,

[0057] - a worm screw arranged in the cylinder to push the initial material towards the downstream end,

[0058] - a heating block arranged near the downstream end of the cylinder, capable of providing a temperature greater than or equal to a melting temperature of the binding matrix to give its viscous form to the initial material,

[0059] - a cooling block located near the upstream end of the cylinder,

[0060] - a feed hopper connected to the cylinder near its upstream end, to introduce granules of initial material.

[0061] In this alternative embodiment, a temperature gradient can also be applied, to promote the compactness of the equipment and to limit the mechanical resistance linked to the friction of the viscous material against the cylinder and the screw.

[0062] The embodiment of the extruder body 10 comprising the piston 12 is particularly interesting because it makes it possible to develop significant thrust forces, using a reasonable electrical power, namely less than or equal to 40 W. It should be remembered that the extruder body 10 must convey the initial material in viscous form towards the ejection orifice of the nozzle 20 and must for this overcome friction forces of the viscous material against the internal walls of the cylinder 11 and of the channel 21 as well as forces, linked to the magnetic induction B produced by the alignment system (which will be described later), opposing the flow of the material. For example, a thrust force greater than or equal to 100 N, 250 N and 450 N is necessary, respectively when the alignment system 30 generates a magnetic induction of 300 mT, 600 mT and 1000 mT.

[0063] The extruder body 10 may also comprise an axial fan 19a and a radial fan 19b, to manage the temperature of the cylinder 11, and more generally of the extruder body 10. A level sensor 18 may also be useful for controlling the arrangement of the filament on the printing plate (where the anisotropic bonded magnet type object will be formed) during its ejection from the orifice 22. Finally, a frame 16 conventionally makes it possible to support and mechanically move the various constituent elements of the extruder body 10. During the additive manufacturing of the magnet object, the frame 16 and / or the plate receiving the filament are moved according to the shape of said object.

[0064] In the equipment 100, the nozzle 20 makes it possible to eject a filament of initial material in viscous form onto the printing plate receiving the anisotropic bonded magnet type object. The nozzle 20 defines a channel 21 extending along a main axis z and which narrows in the extreme part, to end with an ejection orifice 22 (). The channel 21 has a diameter of the order of a few millimeters, preferably less than or equal to 2 mm, or even 1.5 mm. This diameter must not be too large so that the particles do not undergo the radial magnetic force gradient: indeed, as will be described later, the alignment system 30 of the equipment 100 is configured to develop a magnetic induction as homogeneous as possible in this channel 21, so as to effectively and uniformly align the particles of the initial material in viscous form.The thickness of the wall of the nozzle 20 must be sufficient to ensure heat transfer but not too great so that the aligner system 30 is as close as possible to the particles so that they see the most homogeneous and intense magnetic induction possible. Ideally, the wall of the nozzle 20, at least around the channel 21 in the region of interest RI (region of the channel 21 in which the initial material in viscous form will be influenced by the magnetic induction) has a thickness of 1 mm.

[0065] The ejection orifice 22 has a diameter less than or equal to 0.8 mm, 0.6 mm, or even less than or equal to 0.4 mm. The diameter of the ejection orifice 22 must be at least twice, preferably four times, greater than the dimension of the largest particles of the initial material, to avoid possible obstruction.

[0066] The nozzle 20 is made of a non-magnetic material, for example brass or stainless steel or ceramic, preferably with an end made of a material whose hardness is greater than that of the particles of the initial material or resistant to abrasion by said particles, for example ruby, diamond or zirconia.

[0067] The nozzle 20 may be directly secured to the downstream end of the extruder body 10, for example by screwing. Alternatively, a connector may be used to extend the body of the nozzle 20 and adjust its position at the heart of the alignment system 30; if used, this connector is made of a non-magnetic material, like the nozzle 20.

[0068] In the equipment 100, the alignment system 30 surrounds the nozzle 20 and generates a magnetic induction B capable of aligning the particles of magnetic material, so that their axis of easy magnetization is located according to the direction of magnetic orientation (defined by the induction B), in the filament, before its ejection.

[0069] The alignment system 30 consists of a stack of generally annular shape, centered on the main axis z (). The stack comprises a first ring 31 made of a permanent magnet having a radial magnetization, normal to the main axis z, and a second ring 32 made of a permanent magnet having an axial magnetization, parallel to the main axis z, arranged under the first ring 31. The stack further comprises a yoke 34 made of magnetic material. The yoke 34 has an annular portion arranged under the second ring 32 and a cylindrical portion surrounding a periphery of the first 31 and second 32 rings; the annular portion of the yoke 34 is located on the side of the ejection orifice 22. Finally, the stack comprises an adapter 33 made of a non-magnetic material, which allows the mechanical maintenance of the alignment system 30 around the nozzle 20.The adapter 33 is secured on the one hand to the extruder body 10 or the nozzle 20, and on the other hand to the first ring 31 and / or the cylinder head 34.

[0070] The magnetic induction B generated by the alignment system 30 is deployed vertically, parallel to the main axis z, and is maximum in a region of interest RI, which region encompasses the channel 21 of the nozzle 20 and is located upstream of the ejection orifice 22. In the particular example of the, the Hall probe characterization of the alignment system 30 (such as that of the) shows an excellent correspondence with the numerical simulation under COMSOL; the two rings 31 are made of Sm2Co 17and have a thickness (along the z axis) of 4 mm, an internal radius of 4 mm, an external radius of 15.8 mm (first ring 31) and 15 mm (second ring 32); the adapter 33 is made of aluminum; the yoke 34 is made of iron and has a thickness (along the z axis) of 2 mm, an internal radius of 4 mm, an external radius of 17 mm; an induction of between 200 mT and 600 mT prevails in the region of interest RI.

[0071] The particles of magnetic material composing the initial material will undergo this magnetic induction B during their passage in the channel 21, at the region of interest RI, and will orient themselves in the viscous matrix, so that their axis of easy magnetization is aligned according to the direction of magnetic orientation defined by the magnetic induction B. The filament of viscous initial material, when it is ejected by the orifice 22 of the nozzle 20, therefore has its particles of magnetic material oriented in the direction of magnetic orientation, which gives it a magnetic anisotropy. This direction of magnetic orientation is parallel to the longitudinal axis of the filament.

[0072] In the example of the, the magnetic induction B is deployed vertically and is oriented downwards. This is obtained by implementing a first magnet 31 with centripetal radial magnetization and a second magnet 32 ​​with axial magnetization, oriented upwards.

[0073] In another configuration of the alignment system 30, the induction B could be oriented upwards, by implementing a first magnet 31 with centrifugal radial magnetization and a second magnet 32 ​​with axial magnetization, oriented downwards.

[0074] The permanent magnet constituting the first ring 31 and the second ring 32 may be formed from SmCo or NdFeB, since these materials have high remanence and coercivity, and good temperature resistance. Generally, the nature of the permanent magnet of the two rings 31, 32 may be chosen so as to provide the required magnetic induction (at the operating temperature, typically greater than 200°C) to induce a degree of magnetic alignment greater than or equal to 0.1, greater than or equal to 0.2, or even greater than or equal to 0.4 in the filament after its passage through the region of interest RI. It should be recalled that the degree of magnetic alignment (DOA) is defined as:

[0075] DOA = [M r_para - M r_perp ] / [M r_para + M r_perp ], with M r_para the remanence according to the direction of magnetic orientation, and M r_perp remanence along an axis normal to the direction of magnetic orientation.

[0076] Each ring 31, 32 is produced in one piece or by assembling portions.

[0077] Advantageously, to facilitate its construction, the first magnet 31 is composed of several angular portions 31a, 31b ((2)), for example four, six, eight or twelve. Each portion may have a radial magnetization or only parallel to the surface plane ((3)). In the latter case, the greater the number of angular portions, the closer we will get to the scale of the first ring 31 of a continuously radial magnetization. It should be noted that the angular portions may have their internal 31i and / or external 31e edges flat or rounded ((4)) depending on the ease of manufacturing or cutting the portions.

[0078] The second ring 32, for its part, can be composed of two portions symmetrical along the main axis z. In portions or in a single piece, the second ring 32 preferably has an external diameter substantially smaller than the diameter of the yoke 3, typically 10% smaller; this prevents part of its magnetic flux from being short-circuited by looping back to a peripheral contact interface between the ring 32 and the yoke 34.

[0079] Even though only two rings 31,32 have been described, it is of course conceivable that a larger number of permanent magnet rings are stacked in the alignment system 30. In this case the orientation of the additional rings is adjusted so that their contribution to the central magnetic flux is vertical and adds to the fluxes of the other rings.

[0080] The material of the yoke 34 may be soft ferromagnetic, chosen for example from iron, steel, an FeCo or FeSi alloy, or be a soft ferrite. The role of the yoke 34 is multiple: firstly, its outer cylindrical part makes it possible to loop back the external magnetic flux; secondly, its annular part (under the second ring 32) concentrates the magnetic flux lines towards the region of interest RI as close as possible to the nozzle, to maximize the induction there while protecting from this induction the already printed object, located below, on the printing plate.

[0081] The material of the adapter 33 is preferably chosen from aluminum, brass, copper, a ceramic or a polymer resistant to a maximum temperature implemented on the equipment, typically of the order of 300°C (such as for example PEEK or PEI).

[0082] According to an advantageous embodiment, the permanent magnet of the first ring 31 and the permanent magnet of the second ring 32 have a remanence greater than or equal to 0.7 T, preferably greater than or equal to 0.9 T, or even more preferably greater than or equal to 1 T, at a temperature of 230°C, allowing, in the latter case, the alignment system 30 to generate a magnetic induction of the order of 600 mT in the region of interest RI (for a construction such as on the). This configuration is particularly favorable in the case of an initial material whose magnetic particles are made of NdFeB, such as the materials MI1 and MI2 previously mentioned (); it makes it possible to achieve a degree of magnetic alignment greater than or equal to 0.2, or even 0.4, in the ejected filament and at least under certain printing conditions.

[0083] This presents the relationship between the intensity of magnetic induction B RIin the region of interest RI and the remanence of the permanent magnets constituting the two rings 31, 32 of the alignment system 30, for a construction as illustrated on the and described with reference to the previously.

[0084] Lamontre two different constructions of alignment system 30. The materials constituting the two rings 31, 32, the yoke 34 and the adapter 33 being identical in both cases, it is observed that the proximity between the alignment system 30 and the region of interest RI makes it possible to significantly increase the magnetic induction (from 600 mT to 950 mT). To optimize the magnetic induction, it is therefore important to adjust the design of the nozzle 20 (in particular its external diameter) in synergy with the alignment system 30. It is also possible to vary the thickness of the rings 31, 32 to affect the vertical extent of the region of interest RI as well as the homogeneity and intensity of the magnetic induction in this region.

[0085] The present invention also relates to a method for additive manufacturing of an anisotropic bonded magnet, capable of implementing the equipment described above. The method comprises a first step a) corresponding to the definition of the object, anisotropic bonded magnet, to be printed. The targeted object may consist of one or more region(s) each with a given magnetization direction. The digital model of the object is designed with software such as “SolidWork” and is then sliced ​​with software such as “Cura” to generate a .GCODE file containing all the trajectories of the equipment 100 and / or the printing plate, as well as the quantity of material to be extruded for each bead.

[0086] The second step b) of the method corresponds to the ejection by the nozzle 20 of the filament of initial material in viscous form, with magnetic particles whose axis of easy magnetization during ejection is aligned with the central axis of the filament. The ejection is made according to a unidirectional trajectory and a defined orientation, in the plane of the printing plate (plane normal to the main axis z). The axis of easy magnetization of the particles is found to be substantially parallel to the unidirectional trajectory.

[0087] Printing parameters (temperature, speed and extrusion factor) are given, as an example, for the three initial materials MI1, MI2, MI3 previously mentioned, in the table. The printing temperature must be at least 40°C above the melting temperature of the binder matrix but can be adjusted during calibration. The extrusion factor (steps / mm) controls the speed of advance of the piston 12 (advantageous embodiment of the extruder body 10) and therefore the extrusion flow rate at the nozzle 20. The higher this value, the more the piston 12 will advance per mm of material to be extruded. The printing speed controls the speed at which the print head moves relative to the plate. The higher this speed, the more the flow rate of extruded material must be increased in order to deposit good quality beads.Before printing any anisotropic bonded magnet, it is necessary to calibrate these three parameters, knowing that they can vary from one initial material to another.

[0088] The third step c) corresponds to the progressive development of the object. For each region, defined by a particular magnetization direction, the relative movement of the nozzle 20 and the plate is carried out while maintaining the same unidirectional trajectory and the same ejection orientation. This makes it possible to form the same region of the object with parallel cords of a solidified material whose magnetic particles have their easy magnetization axis aligned along the axis of said cords. This also promotes homogeneous pre-magnetization of the cords in each region and can, in certain cases, avoid or limit the application of a magnetic field to magnetize the relevant region of the object, after its printing. For example, as indicated in the table of the, the printed layer height (height of the cords) is 0.2 mm.

[0089] If we consider an object to be printed comprising two distinct regions, expected to have different magnetizations, steps b) and c) are carried out with a first unidirectional direction and a first orientation for the first region, and are carried out with a second unidirectional direction and a second orientation for the second region. This may for example be the case for the development of a linear Halbach network ((i)) or a Halbach cylinder ((ii)). These objects respectively comprise five regions and eight distinct regions, at least adjacent two by two, and each requiring a particular direction and sense of magnetization (illustrated by the black arrows). The method according to the invention makes it possible to produce such objects, simply and with a good level of performance.

[0090] The figure shows a portion of the hysteresis cycle of two specimens A, B (objects) printed from the initial material MI3 (SmFeN / PA12), with equipment and a method in accordance with the present invention. This figure also shows a portion of the hysteresis cycle of an isotropic reference specimen and that of a filament ejected by the nozzle 20 but not deposited in the form of a bead on the printing plate.

[0091] The shows the portions of the hysteresis cycles (measurement of the magnetization provided by the printed magnet as a function of the external magnetic field applied to it) respectively of the filament extruded but not deposited in the form of a bead, of the test piece A and of the test piece B. The graphs include the measurements following the alignment direction and the normal directions respectively.

[0092] It is from the value of the remanent magnetization along the alignment direction (para) and a normal direction (perp) that it is possible to determine the degree of alignment (DOA) of the bonded magnet.

[0093] The isotropic reference logically has an alignment degree of 0. The two printed specimens A and B have alignment degrees of 0.14 and 0.29 respectively. The extruded but not deposited filament has an alignment degree of 0.4, higher than that of the printed specimens.

[0094] If we now compare two methodologies for printing the object (specimens A and B), the degree of alignment is lower in specimen A (DOA = 0.14) than in specimen B (DOA = 0.29). Thus, for the same part geometry, a unidirectional printing path parallel to the largest dimension of the object seems to give a higher degree of alignment.

[0095] Advantageously, when one of the dimensions of the object to be printed is larger than the others, the unidirectional ejection trajectory is therefore chosen parallel to this dimension of the object.

[0096] According to certain embodiments, the method comprises a fourth step d), after step c), consisting of applying a magnetic field to each region of the object to magnetize said region according to the magnetization direction defined during printing and advantageously according to the direction (orientation) defined during printing.

[0097] The present invention also relates to a method for manufacturing a composite material wire, using the additive manufacturing equipment described above. This method comprises a step of ejecting, via the nozzle 20, the filament of initial material in viscous form, the magnetic particles of which have their easy magnetization axis aligned along the axis of the filament. The filament is not deposited or substantially crushed on the printing plate as is the case with cords; it is only ejected via the nozzle 20 and then recovered in a solidified state. In this solid state, it forms a composite material wire (binding matrix + aligned particles of magnetic material), which can be used as a raw material for manufacturing anisotropic bonded magnets.

[0098] As illustrated in Figures 10a and 10b, the composite yarn (extruded filament) exhibits an excellent degree of alignment.

[0099] Of course, the invention is not limited to the embodiments and examples described, and variant embodiments may be made without departing from the scope of the invention as defined by the claims.

Claims

Equipment (100) for the additive manufacturing of an anisotropic bonded magnet from an initial material formed of a binder matrix and particles of anisotropic magnetic material each having an axis of easy magnetization, the equipment (100) comprising:- an extruder body (10), intended to receive the initial material in solid form and to introduce it into a nozzle (20) in viscous form by melting the binder matrix,- the nozzle (20), intended to eject a filament of initial material in viscous form, said nozzle (20) defining a channel (21) extending along a main axis (z) and ending in an ejection orifice (22), and- an alignment system (30), surrounding the nozzle (20) and generating a magnetic induction (B) capable of aligning the particles of magnetic material so that their axis of easy magnetization is located in a direction of magnetic orientation, in the filament, before its ejection,the equipment (100) being characterized in that the alignment system (30) consists of a stack of generally annular shape, centered on the main axis (z), said stack comprising: - a first ring (31) of permanent magnet having a radial magnetization, normal to the main axis (z), - a second ring (32) of permanent magnet having an axial magnetization, parallel to the main axis (z), the second ring (32) being arranged under the first ring (31), - a yoke (34) of magnetic material, having an annular part arranged under the second ring (32) and a cylindrical part surrounding a periphery of the first (31) and second (32) rings, the annular part being on the side of the ejection orifice (22), - an adapter (33) of non-magnetic material, integral on the one hand, with the extruder body (10) or the nozzle (20), and on the other hand, with the first ring (31) and / or the cylinder head (32),the magnetic induction (B) generated by the alignment system (30) being parallel to the main axis (z) and maximum in a region of interest (RI) of the channel (21), located upstream of the ejection orifice (22)., Equipment (100) according to the preceding claim, in which the nozzle (20) is made of non-magnetic material, for example brass, stainless steel or ceramic, with an end made of a material whose hardness is greater than that of the particles of the initial material or resistant to abrasion by said particles, for example ruby, diamond or zirconia. Equipment (100) according to one of the preceding claims, wherein the permanent magnet of the first (31) and second (32) rings is formed from SmCo and / or NdFeB. Equipment (100) according to one of the preceding claims, wherein the permanent magnet of the first ring (31) is composed of several angular portions, in particular six, eight or twelve. Equipment (100) according to one of the preceding claims, wherein the material of the yoke (34) is soft ferromagnetic, such as iron, steel, an FeCo or FeSi alloy. Equipment (100) according to one of the preceding claims, wherein the material of the adapter (33) is chosen from aluminum, brass, copper, a ceramic or a polymer resistant to a maximum temperature implemented on the equipment (100). Equipment (100) according to one of the preceding claims, in which the permanent magnet of the first ring (31) and the permanent magnet of the second ring (32) have a remanence greater than or equal to 0.7 T, or even preferably greater than or equal to 0.9 T, at a temperature of 230°C. Equipment (100) according to one of the preceding claims, in which the extruder body (10) comprises: - a cylinder (11) having an internal space intended to receive the solid initial material at an upstream end and having a downstream end secured to the nozzle (20), - a piston (12) capable of moving in the cylinder (11) to push the initial material towards the downstream end, - a heating block (13) arranged near the downstream end of the cylinder (11), capable of providing a temperature greater than or equal to a melting temperature of the binder matrix to give its viscous form to the initial material, - a cooling block (14) arranged near the upstream end of the cylinder (11), - a feed hopper (15) connected to the cylinder (11) near its upstream end, for introducing granules of initial material, when the piston (12) is in an initial position, the most upstream position in the cylinder (11). Equipment (100) according to one of claims 1 to 7, in which the extruder body (10) comprises: - a cylinder (11) whose internal space is intended to receive the solid initial material at an upstream end and whose downstream end is integral with the nozzle (20), - a worm screw arranged in the cylinder (11) to push the initial material towards the downstream end, - a heating block (13) arranged near the downstream end of the cylinder (11), capable of providing a temperature greater than or equal to a melting temperature of the binder matrix to give its viscous form to the initial material, - a cooling block (14) arranged near the upstream end of the cylinder (11), - a feed hopper (15) connected to the cylinder (11) near its upstream end, to introduce granules of initial material. A method of additive manufacturing an anisotropic bonded magnet, implementing the equipment (100) according to one of the preceding claims, comprising the following steps: a) defining the object, anisotropic bonded magnet, to be printed, said object being capable of being made up of one or more region(s) each with a given magnetization direction, b) ejecting by the nozzle (20) the filament of initial material in viscous form whose magnetic particles have their easy magnetization axis aligned along the axis of the filament, the ejection being made along a unidirectional trajectory and an orientation, in a plane normal to the main axis, the easy magnetization axis of the particles being parallel to the unidirectional trajectory, c) progressively developing the object, while maintaining the same unidirectional trajectory and ejection orientation,to form the same region of the object with parallel cords of a solidified material whose magnetic particles have their axis of easy magnetization aligned along the axis of said cords which constitutes the direction of magnetization of the region., Additive manufacturing method according to the preceding claim, further comprising a step d) after step c), corresponding to the application of a magnetic field to each region to magnetize said region. Method for manufacturing a composite material thread, using the equipment (100) according to one of claims 1 to 9, comprising a step of ejecting by the nozzle (20) the filament of initial material in viscous form whose magnetic particles have their easy magnetization axis aligned along the axis of the filament, said filament, upon solidifying, forming the composite material thread.

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