METHOD FOR MANUFACTURING A MULTIPOLAR FLUX-ORIENTED MAGNET

Abstract

The invention relates to a method for manufacturing a rotor magnet for an electrical machine, said method comprising a first phase (P1) of producing a magnet blank including a step (ET4) of pressing powders under a magnetic field in a magnet mold by subjecting them to a magnetic field generated by a first magnetization tool, a step (ET6) of densifying the resulting magnet blank, and a second phase (P2) of finishing the magnet blank including at least one final magnetization step of the magnet blank, to obtain a magnet, characterized in that the mold is disposed in a densification chamber, and in that the densification step (ET6) is carried out by SPS flash sintering in said densification chamber. Figure 13 for the abstract.

Description

Title of the invention: METHOD FOR MANUFACTURING A MULTIPOLAR FLUX-ORIENTED MAGNET Technical field of the invention

[0001] The invention relates to a method for manufacturing a magnet, and in particular a multipolar magnet with oriented flux for a rotor of an electrical machine such as an electric motor, generator or sensor, and a tooling enabling the implementation of this method. Technical background

[0002] There are two types of magnets, unidirectional magnets, which have a unidirectional orientation between their two North and South poles, and variable orientation magnets, which have a continuously variable orientation between their two North and South poles.

[0003] These have asymmetrical field lines on either side of the magnet, and are therefore called oriented flux magnets because the fields they generate are of higher intensity on one side of the magnet than on the other with respect to the North / South orientation.

[0004] This property is particularly useful in the manufacture of multipole ring magnets. These magnets help to limit magnetic leakage when used in electrical machines.

[0005] Thus, a multipolar ring magnet with oriented flux constitutes a network of so-called Halbach magnets which has the advantage of increasing the magnetic field on one side of the magnet while almost totally eliminating the magnetic field on the other side.

[0006] When such a magnet is used in the rotor of an electric machine, this configuration results in field lines oriented predominantly outwards from the rotor, i.e., towards its stator, with an overall higher magnetic field strength, and virtually no field lines towards the inside of the rotor. Consequently, this allows for electric machines with better efficiency than those equipped with traditional magnets.

[0007] The magnetization of such magnets is widely known from the prior art and is notably documented by document WO-97 / 37362-A1

[0008] In the context of manufacturing an electric machine rotor, such a magnet also has the advantage of being a single piece. Indeed, in a conventional design using unidirectional magnets, it is necessary to glue a large number of these magnets onto an annular support. Such an operation is not very advantageous in terms of manufacturing time and cost, while a design implementing a monobloc magnet reduces manufacturing times.

[0009] Document EP-3637060-A2 describes a method for manufacturing such a magnet. Conventionally, such a method includes a first step in which materials are selected to provide metal powders for magnets. These materials are melted in an induction furnace, and the resulting ingots undergo a first grinding phase to obtain grains of approximately 500 µm in size. These grains are then pulverized by ball milling or pressurized gas jet milling to achieve a size of approximately 10 µm.

[0010] Then, a second step follows in which these powders are mixed, a third step in which the powders are placed in a mold, and a fourth step in which the powders are pressed at room temperature while being subjected to a magnetic field generated by a first magnetizing tool.

[0011] Then, in a fifth step, the magnetic field generated by the first magnetizing tool is stopped, and in a sixth step, the resulting magnet blank is densified by a conventional sintering process. This blank can then be machined in a seventh step, and finally magnetized in an eighth final magnetization step.

[0012] This process has several disadvantages.

[0013] Firstly, this method is limited to obtaining simple shapes that are easy to demold.

[0014] Secondly, the pressing at room temperature, densification, and final magnetization steps are separated and generally carried out in independent tooling, which increases the complexity of the production process and results in long manufacturing times. This also introduces a problem of repositioning the magnet blank to be magnetized between the different steps in order to strengthen the final magnetic field of the magnet, since during the eighth final magnetization step, the blank must be oriented in the same position as during the fourth step. This point is all the more critical for Shaped Field magnets, for which the angular difference between the cold magnetization step and the densification step must be minimized.

[0015] Thirdly, the densification step is often carried out without the blank being held under pressure, in so-called "free" sintering, which requires, in order to achieve high densification levels above 90%, significant densification times and temperatures.

[0016] Finally, the cold magnetization steps require a lot of energy to saturate the material, and therefore high-capacity magnetization tools, which is limiting in the case of the creation of a rotating field because the total energy consumed is distributed over a wide range of angular domains of the field, resulting in a reduction of the amplitude of the field for each orientation.

[0017] There is therefore a real need for a manufacturing process that makes it possible to manufacture a flux-oriented multipolar magnet in a reduced number of steps. Summary of the invention

[0018] The invention remedies these drawbacks by proposing a new manufacturing process in which the pressing at ambient temperature and densification steps are carried out in the same tooling and in which the densification step is carried out by SPS flash sintering, (Anglo-Saxon acronym for Spark Plasma Sintering), or arc plasma sintering.

[0019] To this end, the invention proposes a method for manufacturing a rotor magnet for an electrical machine, said method comprising a first phase of producing a blank magnet comprising:

[0020] - a first step in which metal powders and / or ce are supplied Ramics for magnet

[0021] - a second step in which said powders are mixed,

[0022] - a third step in which said powders are placed in a mold and a first magnetization tool is placed around said mold,

[0023] - a fourth pressing step under a magnetic field during which one the said powders are pressed at room temperature to obtain the initial magnet blank, and they are simultaneously subjected to a magnetic field generated by the first magnetization tool,

[0024] - a fifth step in which the magnetic field generated by is stopped the first magnetization tool, and

[0025] - a sixth step in which the magnet blank is densified,

[0026] said method further comprising a second finishing phase of the magnet blank including at least one machining step of the magnet blank and a final magnetization step of the magnet blank, to obtain the magnet,

[0027] characterized in that, during the third step, the mold is placed in a densification chamber, in that the sixth step is carried out by SPS flash sintering in said densification chamber.

[0028] Thus, the process of the invention makes it possible to carry out the pressing at ambient temperature and the densification steps in the same tooling, thereby eliminating transfer times from one tooling to another and angular positioning errors. Furthermore, conducting the densification step by SPS flash sintering substantially reduces the duration of this step because it is no longer necessary to proceed with a long temperature increase of the enclosure in which the densification is carried out.

[0029] According to another feature of the process, the second finishing phase of the magnet blank comprises, according to a first variant:

[0030] - a seventh step during which the magnet blank is allowed to cool up to a Curie temperature of the magnet,

[0031] - an eighth step forming the final magnetization step during which subjects the blank magnet again to a magnetic field generated by the first magnetizing tool, and

[0032] - a ninth machining step of the magnet blank out of the mold, at the end of from which the magnet is obtained.

[0033] In this first variant, the pressing at ambient temperature, densification and magnetization steps are advantageously all carried out in the same tooling, which allows for a substantial time saving and a reduction in the number of tools involved.

[0034] The eighth densification step, which is carried out while the magnet blank is cooling while still at a temperature close to its Curie temperature, also makes it possible to strongly magnetize the material while limiting the energy consumed by the first magnetization tooling, because the orientation of the magnetic domains or Weiss domains in the material is easier to achieve and less energy-intensive at a temperature close to the Curie temperature.

[0035] According to another feature of the process, the second finishing phase of the magnet blank comprises, according to a second variant:

[0036] - a seventh machining step of the magnet blank out of the mold,

[0037] - an eighth step in which the magnet blank is placed in a a second magnetization tool independent of the mold, with an orientation analogous to the position occupied by the magnet blank in the first magnetization tool at the end of the fourth step, and

[0038] - a ninth step forming the final magnetization step during which one subjects the blank magnet again to a magnetic field generated by the second magnetization tool independent of the mold.

[0039] In this second variant, the pressing at ambient temperature and the densification steps are advantageously carried out in the same tooling, resulting in substantial time savings and a reduction in the number of tools required. The magnetization step, on the other hand, is performed in a separate magnetization tooling independent of the mold. This frees up the mold to prepare another magnet.

[0040] According to another feature of the process, in the second finishing phase of the magnet blank, according to a third variant, the ninth magnetization step This can also be carried out in a second magnetization tool independent of the mold, consisting of a stator of an electrical machine designed to receive the magnet. This ninth step (ET'9) of magnetization is therefore an in-situ magnetization.

[0041] The invention also relates to a device for implementing the manufacturing process of the type described above, which comprises at least:

[0042] - a metal mold comprising a fixed matrix delimiting a cavity and at least a punch which is complementary to a section of the cavity, and which is moved by a hydraulic press between a position outside the cavity and a position in which it seals the cavity and enters said cavity according to a determined stroke,

[0043] - an SPS flash sintering tool comprising at least one current generator pulsed, current-conducting means arranged in said die and said punch, and an enclosure containing the mold capable of being selectively evacuated or filled with a neutral gas, and

[0044] - a first magnetization tool, comprising an annular magnetic circuit housed within the enclosure and surrounding the mold.

[0045] According to other features of the device:

[0046] - the device further comprises an annular thermal screen interposed between the mold and magnetic circuit,

[0047] - the device further comprises an annular cooling exchanger arranged around the magnetic circuit inside the enclosure,

[0048] - the device is configured for manufacturing a multipolar ring magnet at X-axis oriented flux, and:

[0049] • the mold cavity is annular with axis X, • the annular magnetic circuit of the first magnetization tool comprises a substantially annular magnetic core crossed along axis X by a plurality of magnetic coils with axes parallel to the axis X and distributed angularly in a regular manner around said axis X.

[0050] The invention also relates to an installation for manufacturing a multipolar ring magnet with X-axis oriented flux according to the second and third variants of the manufacturing process described above, characterized in that it comprises a manufacturing device and a second external magnetizing tooling, said manufacturing device and of similar configuration to the first magnetizing tooling, suitable for surrounding the magnet blank.

[0051] According to another feature of this manufacturing installation, the second magnetizing tool is a stator of an electrical machine whose rotor is intended to receive the flux-oriented magnet. Brief description of the figures

[0052] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which:

[0053] [Fig-1] [Fig.1] is a schematic cross-sectional view of the principle of a single magnet rectionnel;

[0054] [Fig.2] [Fig.2] is a schematic cross-sectional view of the principle of a magnet variable orientation or directed flow;

[0055] [Fig.3] [Fig.3] is a perspective view of a conventional rotor ring electrical machine incorporating unidirectional magnets;

[0056] [Fig.4] [Fig.4] is a perspective view of a machine rotor ring electric according to the invention comprising multipolar magnets with oriented flux;

[0057] [Fig. 5] [Fig. 5] is a schematic view of the steps of a conventional process of manufacturing a magnet;

[0058] [Fig. 6] [Fig. 6] is a schematic view of a manufacturing device according to the invention;

[0059] [Fig.7] [Fig.7] is a half-axial sectional view of a first fa device construction according to the invention;

[0060] [Fig.8] [Fig.8] is a perspective view of part of the first device of the [Fig.7];

[0061] [Fig.9] [Fig.9] is a perspective view with the first part removed device of the [Fig.7];

[0062] [Fig. 10] [Fig. 10] is a cross-sectional view of a second manufacturing device according to the invention;

[0063] [Fig. 11] [Fig. 11] is a developed view of the magnetic circuit of a first variant of the device of [Fig. 10];

[0064] [Fig. 12] [Fig. 12] is a developed view of the magnetic circuit of a second variant of the device of [Fig. 10];

[0065] [Fig. 13] [Fig. 13] is a block diagram illustrating the steps of a first variant of the manufacturing process of the invention;

[0066] [Fig. 14] [Fig. 14] is a block diagram illustrating the steps of the second or third variants of the manufacturing process of the invention. Detailed description of the invention

[0067] Fig. 1 schematically illustrates a unidirectional rectilinear magnet 10 known per se from the prior art.

[0068] As illustrated by the arrow in [Fig. 1], such a magnet has a unidirectional orientation of its magnetic field B between its two poles North N and South S, and the field lines 12 generated by the magnet are distributed substantially symmetrically on either side of a North-South axis 14 of the magnet 10.

[0069] Magnets with variable orientation, such as for example magnet 16 which was shown in [Fig.2], have a variable orientation of their magnetic field which is thus likely to follow several directions assimilable to magnetic fields B1, B2, B3, B4, B5, etc., between their two North N and South S poles, and this continuously between their two North N and South S poles.

[0070] The consequence for this type of magnet is that the field lines are not distributed symmetrically on both sides of the magnet 16. Thus on one side of the North-South axis 14, the field lines 18 are very close together, a sign of a strong magnetic field, while on the other side of the North-South axis 14, the field lines 18 are more spaced out, a sign of a weaker magnetic field.

[0071] This property is of particular interest in the context of manufacturing a ring magnet intended for use in an electric motor. With such a magnet, during its manufacture and especially its magnetization, it is possible to maximize the magnetic field inside or outside the magnet, so as to conversely minimize the magnetic field, and therefore the magnetic losses, on the opposite side of the ring magnet, i.e., conversely, outside or inside the ring magnet.

[0072] The invention relates more particularly to the manufacture of a ring magnet for an electric machine rotor, for which the aim is to maximize the magnetic field outside the magnet in order to maximize the magnetic fields between the rotor and the stator of the electric machine surrounding the rotor. This makes it possible to improve the efficiency of the electric machine incorporating such a ring magnet.

[0073] Figure 3 shows an annular rotor 22 comprising a plurality of unidirectional magnets 12. Such a rotor 22 has an annular support 24 onto which unidirectional magnets 12 are bonded. For example, slightly fewer than 400 magnets 12 must be bonded to the support 24. This is an extremely time-consuming operation and does not allow for obtaining a rotor 22 with optimal efficiency. Furthermore, there is always a risk of the magnets detaching, which could cause irreversible damage to the electric motor.

[0074] Indeed, another advantage of multipolar ring magnets with oriented flux, besides the efficiency they allow the electrical machine to achieve, is their monobloc configuration. Figure 4 shows a rotor 26 comprising eight multipolar ring magnets 20 with oriented flux. This configuration eliminates the need for a support such as the support 24 described previously and considerably reduces the number of magnets to be assembled.

[0075] Figure 5 illustrates the steps of a conventional process for obtaining a magnet 20. The process mainly comprises a first phase PI of producing a a magnet blank, and a second phase P2 for finishing the magnet blank

[0076] The first phase PI for making the magnet blank includes a first step ET1 during which metal powders for magnets are supplied. This first step ET1 includes a substep SET1 during which raw materials 28 such as Samarium Sm, Cobalt Co, Iron Fe, Copper Cu, and Zirconium Zr are collected. Then the first step ET1 includes a substep SET2 in which the raw materials 28 are melted in an induction furnace 30, then a substep SET3 in which they are ground in a mill 32 until particles of size less than 500 sqm are obtained and a substep SET4 in which they are pulverized in a ball mill or pressurized gas jet mill 34 until particles of size less than 10 pm are obtained.

[0077] Then, in a second step ET2, the said powders are mixed, and in a third step ET3, the powders 36 are placed in a mold 38 and a first magnetizing tool 40 is placed around this mold

[0078] Then, in a fourth step ET4 of pressing under a magnetic field, the powders 36 are pressed at room temperature to obtain a blank magnet 42, and are simultaneously subjected to a magnetic field B generated by the first magnetizing tool 36. This operation aims, while compacting them, to orient the powder grains along a preferred direction in which subsequent final magnetization will be established more easily than in other directions. A blank magnet 42 is obtained.

[0079] Then, in a fifth step ET5, the magnetic field generated by the first magnetizing tool is stopped, and in a sixth step ET6, the blank magnet 42 is densified by a conventional sintering process such as a furnace 44.

[0080] Following this first phase PI of making the blank magnet, the second phase P2 of finishing the blank magnet 42 takes place. This second phase P2 includes at least one machining step ET7 of the blank magnet in a machining machine 46 and a final magnetization step ET8 of the blank magnet in a magnetization tool 48, to obtain the final magnet 20.

[0081] As previously seen, in this process, the steps of pressing at ambient temperature ET4, densification ET6 and final magnetization ET8 are separated and carried out in independent tooling, which increases the complexity of the production range and results in long manufacturing times in order to obtain a magnet 20.

[0082] The densification step is conventionally carried out in a high-temperature heated chamber such as the furnace 44. Introducing the magnet blanks 42 into the furnace 44 requires that it initially be at a temperature close to ambient temperature before its temperature is raised, which, given the fact that the densification itself is a long operation requiring several hours induces a total immobilization time of the magnet blank 42 in the furnace which is particularly high.

[0083] The invention remedies this drawback by proposing a method in which, during the third step ET3, the mold 38 is placed in a densification chamber, this chamber being a special chamber allowing, during the sixth step ET6, to carry out a flash SPS sintering in this densification chamber.

[0084] Spark Plasma Sintering (SPS) is a pressure sintering process based on the use of the Joule effect to heat and densify powder particles. The powder to be sintered is placed in a matrix made of graphite, steel, or tungsten carbide, between two conductive electrodes, which also subject it to uniaxial pressure. A very high-intensity direct current, with successive pulses and a defined frequency, passes through the matrix, the electrodes, and the powder, allowing for a very rapid temperature rise and complete sintering in a few minutes.

[0085] In practice, the steps ET3 to ET6 previously mentioned as occurring on the one hand in the mold 38 and on the other hand in the furnace 44, according to the process of the invention, take place in a single device 50, the principle of which has been schematically represented in [Fig. 6]. This device 50 allows the formation of a blank of a cylindrical magnet 42.

[0086] According to the invention, the device 50 comprises at least one metal mold 38 including a fixed die 52 defining a cavity 54 and at least one punch 56. The punch 56 is complementary to a section of the cavity 54, and it is moved by a cylinder 57 of a hydraulic press between a position outside the cavity 54 and a position in which it closes the cavity and enters said cavity 54 along a predetermined stroke. Here, the device 50 has been shown as comprising two opposing punches 56, but this configuration is not limiting to the invention.

[0087] The device 50 further comprises SPS flash sintering tooling including at least one pulsed current generator 58, current-conducting means 60 arranged in the die 52, and punches 56. Typically, these current-conducting means are graphite-based conductors. The tooling also includes a densification chamber 64 containing the mold 38, which is capable of being selectively evacuated or filled with an inert gas.

[0088] The device 50 includes a first magnetization tool 66, comprising an annular magnetic circuit 68 housed in the enclosure 64 and surrounding the mold 38.

[0089] With the device 50, powders with a particle size <10 pm (Samarium-Cobalt SmCo, Neodymium NdFeB, Ferrites or others) used during step ET3 to design a magnet can therefore be placed in the mold 38 in graphite or WC (tungsten carbides) or MAX phase ceramic (ternary carbides), having the shape of the part to be produced with punches 56 closing the cavity 54 of the mold. The magnetizing tooling 66 is positioned around the mold 38 and the assembly is placed in the densification chamber 64.

[0090] Then, during step ET4, the densification chamber 64 is evacuated and the magnetic field produced by the first magnetization tool 66 is then applied. An increasing pressure of less than 100 MPa is then applied, without heating, by the punches 56 on the mold until the movement of the cylinders 57 stops.

[0091] Once this state is reached, the magnetic field is switched off following step ET5 and the atmosphere in the densification chamber 64 is adapted by injecting a suitable atmosphere such as a neutral gas in place of the vacuum.

[0092] During step ET6, a pulsed current is supplied by the generator 58 to the mold 38 in order to rapidly raise its temperature to between 900 and 1200°C and thus densify the powder. The force exerted by the cylinders 57 can be controlled during this step, reducing it to 0 MPa and then increasing it again in different increments, independently. In any case, the applied pressure remains below 100 MPa. Then, a temperature plateau is applied for a period of 5 to 40 minutes until the powders are completely densified. The magnet blank 42 is then obtained.

[0093] As illustrated in Figures 11 and 12, after this first phase PI of making the blank magnet 42 there is a second phase P2 of finishing the blank magnet 42 comprising at least one machining step of the blank magnet 42 and a final magnetization step of the blank magnet 42, to obtain the magnet.

[0094] This second phase P2 can occur partly within device 50 or outside device 50.

[0095] According to a first embodiment of the invention, as shown in [Fig. 13], the second finishing phase P2 of the magnet blank 42 first comprises a seventh step ET7 during which the pressure exerted by the punches 56 is removed, the heating is switched off, and the magnet blank 42 is allowed to cool to a Curie temperature of the magnet. The cooling temperature is, for example, controlled by means of a thermocouple inserted in the mold.

[0096] The Curie temperature depends on the nature of the powders 36 used. For example, it is 400 to 500°C for ferrite Fe powders, 700 to 900°C for Samarium-Cobalt SmCo powders and 300 to 400°C for neodymium NdFeB powders.

[0097] In this first variant, the second finishing phase P2 of the magnet blank 42 then comprises an eighth step ET8 forming the final magnetization step during which the magnet blank 42 is again subjected to a magnetic field. genetic generated by the first magnetization tool 66.

[0098] This configuration is particularly advantageous because it allows the final magnetization of the magnet blank 42 to be carried out in the device 50 using the same initial magnetization tool 66 previously employed. The magnet blank 42 therefore emerges from the device 50 practically ready for use, and it is thus only necessary to complete its finishing during a ninth machining step ET9 of the magnet blank 42 outside the mold 38, at the end of which the magnet 20 is obtained.

[0099] According to second and third variants of the invention, as shown in [Fig.14], the magnet blank 42 is extracted from the device 50 at the end of the first phase PI and the second phase P2 of finishing the magnet blank 42 takes place outside the device 50, which advantageously allows the latter to be freed for the manufacture of the next magnet blank 42.

[0100] In these second and third variants of the invention, the finishing phase P2 of the magnet blank 42 includes a seventh step ET'7 of machining the magnet blank 42 out of the mold.

[0101] Then, in an eighth step ET'8, the magnet blank 42 is placed in a second magnetizing tool (not shown) independent of the mold 38, in an orientation similar to the position occupied by the magnet blank 42 in the first magnetizing tool 66 after the fourth step ET4. This arrangement aims to orient the magnet blank 42 in accordance with the preferred direction in which the powder grains 42 were previously oriented during step ET4. As a reminder, this preferred direction allows for easier subsequent final magnetization. Then, in a ninth step ET'9, the magnetizing of the magnet blank 42 is carried out by again subjecting the magnet blank 42 to a magnetic field generated by the second magnetizing tool independent of the mold 38.

[0102] The second magnetizing tool is, in the second variant of the process, a specific magnetizing tool dedicated to this single task.

[0103] However, in the third variant of the process, the ninth step ET'9 can advantageously be carried out using, as a second magnetization tool independent of the mold, a stator of an electrical machine designed to receive a rotor incorporating the magnet. This configuration eliminates the need for a second specific magnetization tool and allows the magnetization of the rotor magnet blank 42 to be performed in situ, directly within the electrical machine.

[0104] A device 50 is now described, more particularly intended for the manufacture of a multipolar annular magnet 20 with oriented flux of axis X for a rotor of an electric machine of the type electric motor, generator or sensor.

[0105] As before, the device 50 comprises at least one metal mold 38 comprising a fixed die 52 defining an annular cavity 54 with axis X for receiving the powders 36, and at least one punch 56, also annular with axis X, which is therefore complementary to an annular section of the cavity 54. The punch is moved by a hydraulic press cylinder (not shown in [Fig. 7]) between a position outside the cavity 54 and a position shown in which it closes the cavity and enters the cavity 54 along a stroke C determined along the axis X, corresponding to the desired compaction of the powder 36. The device 50 shown in [Fig. 6] comprises only one punch 56.

[0106] As before, the device 50 further comprises an SPS flash sintering tool comprising at least a current generator and current-conducting means (not shown) arranged in the die 52 and the punch 56. This tool allows the passage of a high-intensity electric current through the powders 36 and their agglomeration by sintering.

[0107] The tooling also includes an enclosure 64 containing the mold 38, which has only been shown in figures 7 and 10, and which, as before, is suitable for being selectively evacuated or filled with a neutral gas.

[0108] The device 50 includes a first magnetizing tool 66, comprising an annular magnetic circuit 68 housed in the enclosure and surrounding the mold 38. This annular magnetic circuit includes a substantially annular magnetic core 70 of axis X through which a plurality of magnetic coils 72 of axes parallel to the axis X and distributed angularly in a regular manner around the axis X.

[0109] Figures 8 and 9 show a device 50 comprising a magnetic circuit 68 having eight magnetic coils 72 connected in series by transverse links 74, which makes it possible to make magnets with 8 poles (four North poles N and four South poles S) but it will be understood that depending on the number of poles which one wishes to equip the magnet with, the magnetic circuit can have a greater number of coils 72.

[0110] For example, a device 50 according to the invention comprises a magnetic circuit 68 having 16 magnetic coils 72 for making a 16-pole magnet (eight North poles N and eight South poles S). The coils may comprise a magnetic circuit 68 of coils 72 having a single conductor 73, as illustrated by the development of the magnetic circuit 68 in [Fig. 11], or a magnetic circuit 68 of coils 72 having two conductors 73, 75 as illustrated by the development of the magnetic circuit 68 in [Fig. 12].

[0111] As illustrated in Figures 7, 9 and 10, the device 50 further comprises an annular heat shield 76 interposed between the mold and the magnetic circuit. This heat shield protects the coils 72 from the heat of the mold 38 when it is heated by the SPS flash sintering tooling.

[0112] As illustrated in [Fig.7], the device 50 may also include an annular cooling exchanger 78 arranged around the magnetic circuit 68 inside the enclosure 64. This configuration is more particularly suited to a device 50 intended to implement the first variant of the process of the invention for which this annular cooling exchanger 78 makes it possible to control and control the cooling temperature according to the first variant of the process of the invention, between the seventh step ET7 and the eighth step ET8.

[0113] When intended to implement the second or third variants of the process of the invention, the device 50 is not used for the entire manufacture of the magnet 20, since the final magnetization of the magnet blank 42 is carried out outside the mold 38. In this case, the device is part of a magnet manufacturing installation comprising the manufacturing device described above and a second external magnetization tool (not shown) to the device 50. This second manufacturing tool has a configuration similar to the first magnetization tool, suitable for surrounding the magnet blank 42. By similar tool, it will be understood in particular that this second magnetization tool has coils arranged in a similar manner to the first magnetization tool 66, in order to maintain an orientation of the magnetic fields analogous to those of the fields implemented during step ET4.

[0114] More specifically, when intended to implement the second variant of the process of the invention, the second external magnetization tool is substantially identical to the first external magnetization tool. When intended to implement the third variant of the process, it is not a specific tool but simply a stator of an electrical machine designed to house a rotor receiving the flux-oriented magnet 20. This configuration is very advantageous because it reduces the time the mold 38 is occupied by the magnet blank 42, thus freeing it up for other blanks, and allows the final magnetization of the magnet according to step ET'9 to be carried out directly in the electrical machine.

[0115] The invention therefore makes it possible to considerably reduce the production time of a flux-oriented multipole magnet for an electric machine rotor

Claims

Demands

1. A method for manufacturing a rotor magnet (20) of an electrical machine, said method comprising a first stage (PI) of producing a blank magnet (42) comprising: - a first step (ET1) during which metallic and / or ceramic powders (36) for magnets are supplied, - a second step (ET2) during which the said powders (36) are mixed, - a third step (ET3) during which the said powders (36) are placed in a mold (38) and a first magnetization tool (66) is placed around said mold (38), - a fourth step (ET4) of pressing under a magnetic field during which the said powders (36) are pressed at ambient temperature to obtain the magnet blank (42), and are simultaneously subjected to a magnetic field generated by the first magnetizing tool (66), - a fifth step (ET5) during which the magnetic field generated by the first magnetization tool (66) is stopped, and - a sixth step (ET6) during which the magnet blank (42) is densified, The said process further comprising a second phase (P2) of finishing the magnet blank (42) comprising at least one step of machining the magnet blank (42) and a final magnetization step of the magnet blank (42), to obtain the magnet (20), characterized in that, during the third step (ET3), the mold is placed in a densification chamber (64), in that the sixth step (ET6) is carried out by SPS flash sintering in said densification chamber (64).

2. A manufacturing method according to the preceding claim, characterized in that the second finishing phase (P2) of the magnet blank (42) comprises: - a seventh step (ET7) during which the blank magnet (42) is allowed to cool to a Curie temperature of the magnet, - an eighth step (ET8) forming the final magnetization step during which the blank magnet (42) is again subjected to a magnetic field generated by the first magnetization tool (66), and - a ninth step (ET9) of machining the blank magnet (42) out of the mold (38), at the end of which the magnet (20) is obtained.

3. A manufacturing method according to claim 1, characterized in that the second phase (P2) of finishing the magnet blank comprises: - a seventh step (ET'7) of machining the magnet blank (42) out of the mold (38), - an eighth step (ET'8) during which the magnet blank (42) is placed in a second magnetizing tool independent of the mold (38) in an orientation analogous to a position occupied by the magnet blank (42) in the first magnetizing tool (66) at the end of the fourth step (ET4), and - a ninth step (ET'9) forming the final magnetizing step during which the magnet blank (42) is again subjected to a magnetic field generated by the second magnetizing tool independent of the mold (38).

4. Manufacturing method according to the preceding claim, characterized in that the ninth step (ET'9) is carried out using a stator of an electrical machine as a second magnetizing tool independent of the mold (38).

5. A device (50) for implementing the manufacturing process according to any one of the preceding claims, characterized in that it comprises at least: - a metal mold (38) comprising a fixed die (52) defining a cavity (54) and at least one punch (56) which is complementary to a section of the cavity (54), and which is moved by a hydraulic press between a position outside the cavity (54) and a position in which it closes the cavity (54) and enters said cavity (54) along a predetermined stroke (C), - an SPS flash sintering tool comprising at least one pulsed current generator (58), current-conducting means (60) arranged in said die (52) and said punch (56), and an enclosure (64) containing the mold (38) capable of being selectively evacuated or filled with a neutral gas, and - a first magnetization tool (66), comprising an annular magnetic circuit (68) housed within the enclosure and surrounding the mold (38).

6. Device (50) according to the preceding claim, characterized in that it further comprises an annular thermal screen (76) interposed between the mold (38) and the magnetic circuit (68).

7. Device (50) according to any one of claims 5 and 6, characterized in that it further comprises an annular cooling exchanger arranged (78) around the magnetic circuit (68) inside the enclosure (64).

8. Device (50) according to any one of claims 5 to 7, characterized in that it is configured for the manufacture of a multipolar ring magnet with flux oriented about axis X, and in that: - the cavity (54) of the mold (38) is annular about axis X, - the annular magnetic circuit (68) of the first magnetizing tool (66) comprises a substantially annular magnetic core (70) traversed about axis X by a plurality of magnetic coils (72) with axes parallel to the axis X and distributed angularly in a regular manner around said axis X.

9. Installation for manufacturing a multipolar ring magnet (20) with X-axis oriented flux according to the manufacturing process according to one of claims 3 or 4, characterized in that it comprises a manufacturing device (50) according to claim 8 and a second external magnetizing tooling of said manufacturing device and of similar configuration to the first magnetizing tooling (66), suitable for surrounding the magnet blank (42).

10. Manufacturing installation according to the preceding claim, characterized in that the second magnetizing tool is a stator of an electrical machine, one rotor of which is intended to receive the flux-oriented magnet (20).

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