FR3142367A1 - Process for manufacturing a part comprising at least one magnet by additive manufacturing - Google Patents

Abstract

Method for manufacturing a part comprising at least one unit magnet (1a) placed in an insulating material (1b) by additive manufacturing, comprising the steps consisting of: - defining (11) first zones corresponding to each unit magnet (1a) to be made in a first material, - define the pixelation of said first zones according to a predefined pattern, - deposit (12) the first material in said first zones determined by additive manufacturing while respecting the pixelation, and deposit (14) a second electrical insulating material in second zones of the room distinct from the first zones. Figure for abstract: Fig 3

Description

Process for manufacturing a part comprising at least one magnet by additive manufacturing

The technical field of the invention is the manufacture of permanent magnets, and more particularly, the manufacture of such magnets for electrical rotating machines.

Previous techniques

Electric rotating machines require magnets, particularly permanent magnets in their rotor.

The permanent magnet manufacturing process involves producing a powder of magnetic material, pressing this powder into shape and then sintering to obtain the final part. The material obtained is then gradually cut into smaller pieces in order to form permanent magnets. A final step, called pixelization, involves cutting the magnets into blocks of 2 to 3 mm, called pixels, in order to reduce eddy current losses during operation of the machine.

In order to optimize the magnetic field generated and the associated performances, the magnets must have particular shapes, sometimes complex and expensive to produce with conventional production means.

In order to hold the magnets thus formed in place, an insulator must be poured around them. This step limits the shape of the final object obtained and is a source of problems if defects are present in the insulation.

Recently, new axial flow machines such as those manufactured by Whylot have appeared. These machines require the production of blocks of magnets composed of a mosaic of unit magnets separated by a thin wall of insulator. Although it is possible to make these block magnets with conventional manufacturing processes, manufacturing can be long and complex.

From the state of the prior art, we know the document KR101718591 describing a 3D printing process for manufacturing a permanent magnet.

Document CN103854844 describes a process for preparing bonded magnets with complex shapes using 3D printing.

Document EP2920796 describes a process for manufacturing a permanent magnet as well as a permanent magnet made from bonded magnets.

However, none of these processes makes it possible to prepare a mosaic of individual pixelated permanent magnets, in particular those intended for the rotor of axial flux machines.

The technical problem to solve is therefore how to create a mosaic of individual pixelated permanent magnets.

The subject of the invention is a method of manufacturing a part comprising at least one magnet, by additive manufacturing by powder sintering, comprising the steps consisting of:
- define first zones of the part corresponding to each magnet to be made in a first material,
- determine the pixelation of said first zones to be produced in the first material, the pixelation being chosen according to a predefined pattern,
- deposit the first material in said first zones by additive manufacturing, and deposit a second electrical insulating material in second zones of the part distinct from the first zones.

The method may further include steps consisting of depositing the first material layer by layer, then performing sintering.

The method may further comprise steps consisting of depositing the second material layer by layer, then carrying out sintering.

The method may further include steps consisting of depositing the first material layer by layer, depositing the second material layer by layer, and then simultaneously sintering the two materials.

The composition of the first material can be varied in at least one of the layers deposited.

The first material can be deposited under a magnetic field.

The first material can be sintered under a magnetic field.

A layer of heavy rare earth is deposited and annealed.

The part is subjected to a pressing treatment under temperature.

The part is subjected to a magnetization step by application of a magnetic field.

the pixelation is carried out with a predefined parallelepiped pattern, preferably chosen from a square, honeycomb, hexagonal, circular, ring or ellipsoidal pattern.

The first material is chosen from rare earth magnets, in particular NdFeB and SmCo, soft magnetic composite materials, ferrites, and the second material is chosen from thermoplastic polymers, filled or not, such as PES (acronym for "polyethersufone"), PPS (acronym for "polyphenylene sulfide"), PTE (acronym for "polyethylene terephthalate"), PVdF (acronym for "polyvinylidene fluoride"), PA (acronym for "polyamide"), PEEK (acronym for “polyetheretherketone”), PEKK (acronym for “polyetherketoneketone”), thermosetting polymers, filled or not, PI (acronym for “polyimide”), Epoxy, PU (acronym for “polyurethane”, MS polymer (English acronym for “modified”) silicon” or “modified silicone” in French), silicones, rubbers, ceramic materials such as silica or alumina.

The additive manufacturing method is the metal binder jetting process MBJ (English acronym for “metal binder jetting (MBJ)”) or by any other metal additive manufacturing process in combination with MBJ.

The additive manufacturing method, particularly for the second material, is cold spraying.

Another object of the invention is a rotor sector of a rotating electric machine, comprising a plurality of magnets produced by the manufacturing process as described above.

A guide rail can be provided on each side of the sector, different from an arc, so as to facilitate assembly.

The manufacturing process has the advantage of no loss of material (deposit just as necessary), no cutting of the magnet, mastery of the geometry of the part, no need for void of material between the magnets due to poor injection of the insulation, better mechanical behavior of the magnet block and total control of the force and configuration of the magnet block.

Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

- the figure illustrates a rotor sector comprising a plurality of unit magnets produced by the manufacturing process according to the invention,

- the figure illustrates the pixelation of a unit magnet of a sector,

- the figure illustrates the main stages of a manufacturing process according to a first embodiment,

- the figure illustrates the main stages of a manufacturing process according to a second embodiment,

- the figure illustrates the main stages of a manufacturing process according to a third embodiment,

- the figure illustrates the main stages of a manufacturing process according to a fourth embodiment,

- the figure illustrates a rotor sector arranged in a rotor,

- the figure illustrates the main stages of a manufacturing process according to a fifth embodiment,

- the figures has illustrate an exemplary embodiment obtained using the manufacturing process according to the invention.

detailed description

The figure illustrates a rotor sector 1 comprising a plurality of unit magnets 1a arranged in an insulating material 1b. Several sectors 1 are assembled to form an axial flux machine rotor.

The manufacturing process according to the invention makes it possible to manufacture such sectors 1 using an additive manufacturing technique by powder sintering with or without a binder. We can cite the combination of MBJ with other technologies such as metal photolithography (“Metal photolithography” in English), directed energy deposition DED (English acronym for “Directed Energy Deposition”), bed fusion of PBF powder (English acronym for “Powder Bed Fusion”) either by laser or electron beam, cold spraying (“Cold Spray” in English), material projection (“Material Jetting” in English) or direct writing processes (“Direct Write Processes” in English).

A first material having magnetic properties is deposited by additive manufacturing. Depending on the implementation modes, a second material having insulating properties and resistant to the operating temperature of the machine is also deposited by an additive manufacturing technique, simultaneously or subsequently to the production of the magnets or by conventional deposition, such as 'in molding or injection. Finally, in certain embodiments, all of the magnets and the insulator are encapsulated in a third material.

In a first embodiment illustrated by the figure , the manufacturing process begins with a first step 11 during which the shape of a part to be produced and the location of at least one zone to be produced with the first material are determined, as well as the pixelation of the zone to be produced. made in the first material. The part to be produced can be the rotor sector described above.

By determining the shape to be made, we mean the shape itself, as well as the size and arrangement of the contours of the shape to be made.

Likewise, by determining the location of at least one zone to be produced in the first material, we mean the arrangement of each zone in relation to the shape to be produced, and the size and arrangement of the contours of each zone. We thus indirectly define the thicknesses of the walls between the magnets, which can vary from a few tens to several hundred microns.

Pixelation is obtained by cutting each area to be produced in the first material into small parallelepipeds of 1mm to 10mm side and 2mm to 20mm thickness. The figure illustrates the pixelation of a magnet 1a into parallelepipeds 1c, separated in this case by parts 1b which will be filled with the second material. The parallelepipeds 1c are separated by providing spacings of 0.1µm to 5mm on the surface, extending totally or partially in the thickness of the magnet. Other pixelation patterns can be used, such as honeycomb, hexagonal, circular, ring or ellipsoidal. Such pixelation makes it possible to avoid mechanical or laser cutting of the magnets.

The determination of the shape, the zones to be produced in the first material and the pixelation of each zone must take into account the effects of densification following sintering. During sintering, a reduction in the void space between the powder particles is observed leading to a reduction in the total volume of the sintered part. Depending on the extent of densification of the first material, the areas to be made with the first material must be enlarged so that after densification, the desired size is obtained.

During a second step 12, a layer of the first material is deposited in each location to be produced in the first material during a first sub-step 12a. During a second sub-step 12b, the first sub-step 12a is repeated until the desired height is obtained.

The first material is chosen from rare earth magnets, notably NdFeB and SmCo, soft magnetism composite materials, ferrites.

The shape of the areas to be made with the first material is not limited due to the use of additive manufacturing so that any desired shape can be achieved. These include a square, rectangular, hexagonal, trapezoidal, rhomboidal, triangular, arc-shaped, or oval shape.

During a third step 13, it is sintered in an oven. If a binder has been used, it is removed before sintering. The temperature increase must be as low as possible to avoid temperature variations inside the volumes made in the first material, so as to avoid deformation and cracking. The temperature ramp depends on the first material used and the geometry of the volumes.

The sintering temperature is generally high but must be lower than the melting temperature of the first material.

Once reached, the sintering temperature is maintained for a predetermined duration depending on the first material chosen and the shape of the zones made in the first material.

As with the temperature increase, the cooling must have the lowest possible temperature ramp to avoid temperature variations inside the volumes made in the first material, so as to avoid deformation and cracking.

• protéger mécaniquement les aimants lors des étapes suivantes de fabrication des machines électriques,
• protéger mécaniquement les aimants durant le fonctionnement du rotor en fonction de la conception de la machine électrique et des conditions de fonctionnement, et
• offrir une protection contre la corrosion, notamment pour les aimants NdFeB.

In one mode of implementation, the process continues with a fourth step 14 during which all of the magnets are molded in a second material or a layer of the second material is deposited. This deposit allows you to achieve at least one of the following effects:

• mechanically protect the magnets during the following stages of manufacturing electrical machines,
• mechanically protect the magnets during rotor operation depending on the design of the electrical machine and operating conditions, and
• provide protection against corrosion, particularly for NdFeB magnets.

The second material is chosen from thermoplastic polymers, filled or not, such as PES (“polyethersulfone”), PPS (“polyphenylene sulphide”), PTE (“polyethylene terephthalate”), PVdF (“polyvinylidene fluoride”), PA (“polyamide”), PEEK (“polyetheretherketone”), PEKK (“polyetherketoneketone”), thermosetting polymers, filled or not, PI (“polyimide”), Epoxy, PU (“polyurethane), MS polymer (English acronym for “modified silicon” or “modified silicone”), silicones, rubbers, ceramic materials such as silica or alumina. In a particular embodiment, the order of deposition of the first material and the second material is reversed.

In a second embodiment, the fourth step 14 is avoided by depositing the second material in additive manufacturing like the first material.

When the two materials are deposited by additive manufacturing, particular care must be taken in sequencing with regard to the sintering step.

In an embodiment illustrated by the figure , the two materials are deposited simultaneously and then sintered simultaneously. The steps common with the previous embodiment bear common references. The process includes a second step 121 during which the two materials are deposited. The second step 121 comprises a sub-step 12c of depositing the insulation carried out between the first sub-step 12a and the second sub-step 12b. The two materials are sintered simultaneously during a step 13a.

In another embodiment illustrated by the figure , the two materials are deposited sequentially, notably by MBJ or by a combination of MBJ and other technologies, but sintered simultaneously.

During a first step 11, the shape of a part to be produced and the location of at least one zone to be produced with the first material are determined, as well as the pixelation of the zone to be produced in the first material.

During a second step 122, a layer of the first material is deposited in each location to be produced in the first material during a first sub-step 12a. During a second sub-step 12b, the first sub-step 12a is repeated until the desired height is obtained.

During another sub-step 12c, a layer of the second material is then deposited in all the locations of the part which are not to be made in the first material. During a sub-step 12f, sub-step 12c is repeated until the desired height is obtained.

The process continues with a step 13a of sintering the first and second material in an oven.

In these two cases, the materials must be chosen so that their sintering temperatures are close in order to be able to choose an intermediate temperature which is not unfavorable to one of the two materials.

In another embodiment illustrated by the figure , the two materials are deposited (steps 12,123) and sintered (steps 13,13b) one after the other. It is then necessary to ensure that the second material deposited has a sintering temperature lower than the melting temperature of the first material deposited, preferably lower than the sintering temperature of the first material deposited.

During a first step 11, the shape of a part to be produced and the location of at least one zone to be produced with the first material are determined, as well as the pixelation of the zone to be produced in the first material.

During a second step 12, a layer of the first material is deposited in each location to be produced in the first material during a first sub-step 12a. During a second sub-step 12b, the first sub-step 12a is repeated until the desired height is obtained.

During a third step 13, the first material is sintered.

The process continues with a step 123, during which a layer of the second material is then deposited in all the locations of the part which are not to be made in the first material, during a sub-step 12c. It should be noted that the part may include recesses which are free of the first material and the second material. In this sense, the recesses are not part of the part and are therefore not filled by either the first material or the second material. During a sub-step 12f, sub-step 12c is repeated until the desired height is obtained.

The process continues with a step 13b of sintering the second material in an oven.

As explained in the first embodiment, the effects of densification during sintering must be taken into account in the dimensioning of the zones to be produced in each material. This is particularly obtained when using HIP treatment (acronym for “Hot Isostatic Pressing” also known by the French acronym CIC for “Compression Isostatic à Chaud”), described later in this presentation.

Alternatively, the second material can be deposited by additive manufacturing after sintering of the first material, in particular by cold spray deposition (“Cold Spray” in English) so as to fill all the interstices. Also, the second material can be formed separately then glued in contact with the first material.

In a specific embodiment, the first material varies in composition in at least one of the layers deposited, in particular by combining a material rich in rare earth and a material poor in rare earth or without rare earth. This makes it possible to adjust the intrinsic coercive field H _cj of the manufactured magnet. For example, the first material may be dysprosium, the concentration of which is higher at the surface than at depth.

In a particular mode of implementation, the deposition of the first material is carried out under a magnetic field. In the case of manufacturing by MBJ, the magnetic field is applied during the deposition of the powder before printing the binder. The powder thickness must then be between 10µm and 100µm. Such deposition under a field makes it possible to align the magnetic domains, generates a magnetocrystalline anisotropy and improves the properties of the magnet obtained, in particular the remanent field Br and the coercivity.

In a particular mode of implementation, the sintering of the first material is also carried out under a magnetic field. As for the deposition, this step makes it possible to align the magnetic domains, generates a magnetocrystalline anisotropy and improves the properties of the magnet obtained, in particular the remanent field Br and the coercivity.

In another mode of implementation, a layer of heavy rare earth material (HREE acronym for “Heavy Rare Earth Element”), such as Terbium Tb, Dysprosium Dy or Holmium Ho, is deposited by any means on the surface of the magnets obtained after sintering. After deposition, the assembly is subjected to annealing at a temperature higher than the melting temperature of the heavy rare earth material. Such annealing makes it possible to diffuse the neodymium in the magnet in order to improve its coercivity.

In yet another mode of implementation, a fifth step is added to the process, during which the finished part undergoes a pressing treatment under HIP temperature in order to increase its density. HIP treatment is known to those skilled in the art of powder metallurgy. It is produced under pressures of 50MPa to 100MPa and at temperatures between 400°C and 1400°C depending on the metal powders used.

In all cases, it is possible to deposit a layer of anti-corrosion material on the finished magnets.

Likewise, the finished part can be subjected to a magnetization step in order to give it the magnetic properties required for the intended use.

In the case of an application to the manufacture of sectors of a rotor for an electric machine, in particular an axial flux electric machine, guide rails 1d can be provided on the sides of a sector during manufacturing. These rails then facilitate the installation and alignment of a sector 1 during assembly of the rotor by cooperating with corresponding grooves 2a provided in the rotor 2. Figure illustrates such an arrangement.

In the embodiments described above, several additive manufacturing techniques with sintering can be used, such as L-PBF (English acronym for “laser-Powder Bed Fusion”) also called SLM (English acronym for “Selective Laser Melting”). ") or selective laser sintering DSLS (English acronym for "Direct Selective Laser Sintering") or MBJ. However, we will prefer the MBJ technique which allows the magnetic structure of the first material to be preserved due to heating below the melting temperature.

In an embodiment illustrated by the figure , the shape of the part to be produced and the location of at least one zone to be produced in the first material are determined, in a manner similar to the first embodiment, during a first step 11.

A layer of the first material is then deposited in each location to be made in the first material and a layer of the second material in the entire shape excluding the locations to be made in the first material during a second step 124. Deposition of the first material and the deposition of the second material are carried out simultaneously via a double print head, that is to say a print head allowing two different materials to be printed simultaneously, in particular by MBJ, during a sub-stage 12g. During a second sub-step 12h, the first sub-step 12g is repeated until the desired height is obtained. The two materials are sintered simultaneously during a step 13a.

By way of example, the manufacturing process described above, in any of its embodiments, can be applied to the manufacture of magnets of particular shape as illustrated in the figure . Comb-shaped magnets 90a, 90b, complementary to each other are manufactured. Such combs 90a, 90b comprise a back and teeth each extending from the back, the teeth being spaced relative to each other. Each comb tooth 91a, 91b has a prismatic shape along a transverse cutting plane, as illustrated in the figure .

At the end of sintering, the combs 90a, 90b are glued with a binder then brought into contact. The whole is then pressed and the binder crosslinked.

After crosslinking of the binder, the back of each of the combs 90a, 90b is cut. We then obtain a generally parallelepiped element comprising the nested and glued teeth 91a, 91b. Such a parallelepiped is illustrated by the figure and presents according to its edge an alternation of imbricated prismatic structures as illustrated by the figure .

The object obtained has a particular structure which cannot be easily obtained without using the manufacturing process described above.

Claims (15)

Method of manufacturing a part comprising at least one unit magnet (1a) placed in an insulating material (1b), by additive manufacturing by sintering, comprising the steps consisting of:
- define (11) first zones corresponding to each unit magnet (1a), to be made in a first material,
- define the pixelation of said first zones according to a predefined pattern,
- deposit (12) the first material in said first zones by additive manufacturing while respecting the pixelation, and deposit (14) a second electrical insulating material in second zones of the part distinct from the first zones. A manufacturing method according to claim 1, further comprising the steps of:
- deposit (12, 122) the first material layer by layer, and
- carry out (13, 13a) sintering. Manufacturing method according to one of claims 1 or 2, further comprising the steps consisting of:
- deposit (122, 123) the second material layer by layer, and
- carry out (13b) sintering. A manufacturing method according to claim 1, further comprising the steps of:

• deposit (12a) the first material layer by layer,
• deposit (12b) the second material layer by layer,
• simultaneously sinter (13a) the two materials.

Manufacturing method according to any one of the preceding claims, in which the composition of the first material varies in at least one of the layers deposited. Manufacturing process according to any one of the preceding claims, in which the deposition of the first material is carried out under a magnetic field. Manufacturing method according to any one of the preceding claims, in which the sintering of the first material is carried out under a magnetic field. A manufacturing method according to any one of the preceding claims, in which a layer of heavy rare earth is deposited and annealed. Manufacturing method according to any one of the preceding claims, in which the part is subjected to a pressing treatment under temperature. Manufacturing method according to any one of the preceding claims, in which the part is subjected to a magnetization step by application of a magnetic field. Manufacturing method according to any one of the preceding claims, in which the pixelation is carried out with a predefined parallelepiped pattern, preferably chosen from a square, honeycomb, hexagonal, circular, ring or ellipsoidal pattern. Manufacturing method according to any one of the preceding claims, in which the first material is chosen from magnets based on rare earths, in particular NdFeB and SmCo, composite materials with soft magnetism, ferrites, and the second material is chosen from thermoplastic polymers, filled or not, such as PES (“polyethersufone”), PPS (“polyphenylene sulfide”), PTE (“polyethylene terephthalate”), PVdF (“polyvinylidene fluoride”), PA (“polyamide”), PEEK (“polyetheretherketone”), PEKK (“polyetherketoneketone”), thermosetting polymers, filled or not, PI (“polyimide”), Epoxy, PU (“polyurethane), MS polymer (English acronym for “modified silicon” or “silicone”) modified"), silicones, rubbers, ceramic materials such as silica or alumina. Manufacturing process according to any one of the preceding claims, in which the additive manufacturing method is the binder jet metal manufacturing process. Manufacturing process according to any one of claims 1 to 12, in which the additive manufacturing method, in particular for the second material, is cold spraying. Rotating electrical machine rotor sector (1), comprising a plurality of unit magnets (12a) produced by the manufacturing process according to any one of claims 1 to 14.