Method for producing a flux-oriented multipole magnet

Abstract

The invention relates to a method for producing a magnet for a rotor of an electric machine, the method comprising a first phase (P1) of producing a magnet blank which comprises a step (ET4) of pressing powders into a magnet mould in the presence of a magnetic field while subjecting the powders to a magnetic field generated by a first magnetisation tool, a step (ET6) of densifying the obtained magnet blank and a second phase (P2) of finishing the magnet blank comprising at least one final magnetisation step in order to obtain a magnet, characterised in that the mould is arranged in a densifying chamber and in that the densifying step (ET6) is carried out by flash SPS sintering in the densifying chamber.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR MANUFACTURING A MULTIPOLE MAGNET WITH ORIENTED FLUX

[0003] Technical field of the invention

[0004] The invention relates to a method for manufacturing a magnet, and in particular a multipolar magnet with oriented flux for a rotor of an electric machine of the electric motor, generator or sensor type, and a tool for implementing this method.

[0005] Technical background

[0006] The state of the art includes documents DE-10 / 2015-006916-A1 and US-2017 / 170695-A1.

[0007] 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.

[0008] 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 compared to the North / South orientation.

[0009] This property is particularly useful in the manufacture of multipole ring magnets. These magnets help limit magnetic leakage when used in electrical machines. Thus, a multipole ring magnet with oriented flux constitutes a so-called Halbach magnet network, which has the advantage of increasing the magnetic field on one side of the magnet while almost completely eliminating the magnetic field on the other side.

[0010] When such a magnet is implemented in a rotor of an electrical machine, this configuration makes it possible to have field lines oriented mainly towards the outside of the rotor, i.e. towards its stator, with a magnetic field of overall higher intensity, and almost non-existent field lines towards the inside of the rotor. This therefore makes it possible to obtain electrical machines with better efficiency than an electrical machine equipped with traditional magnets.

[0011] The magnetization of such magnets is widely known in the state of the art and is notably documented by document WO-97 / 37362-A1

[0012] When manufacturing an electrical machine rotor, such a magnet also has the advantage of being a single-piece design. In a conventional design using unidirectional magnets, it is necessary to glue a large number of these magnets onto an annular support. This operation is not very advantageous in terms of manufacturing time and cost, whereas a design using a single-piece magnet allows for reduced manufacturing times.

[0013] Document EP-3637060-A2 describes a method for manufacturing such a magnet. Conventionally, such a method comprises a first step during which materials are selected to provide metal powders for magnets. These materials are melted in an induction furnace, then the ingots obtained undergo a first grinding phase to obtain grains with a size close to 500 pm and which are then pulverized by ball milling or pressurized gas jet milling to reach a size close to 10 pm.

[0014] Then, a second step follows during which these powders are mixed, a third step during which the powders are placed in a mold, and a fourth step during which the powders are pressed at room temperature while being subjected to a magnetic field generated by a first magnetization tool.

[0015] Then, during a fifth step, the magnetic field generated by the first magnetization tool is stopped, and during a sixth step, the resulting magnet blank is densified by a conventional sintering process. This blank can then be machined during a seventh step, then permanently magnetized during an eighth final magnetization step.

[0016] This process has several drawbacks.

[0017] Firstly, this method is limited to obtaining simple shapes that are easy to unmold.

[0018] Secondly, the steps of pressing at room temperature, densification, and final magnetization are separated and generally carried out in independent tools, which increases the complexity of the production range and results in long manufacturing times. It also induces a problem of repositioning the magnet blank to be magnetized between the different steps, in order to reinforce 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 after densification must be minimized.

[0019] Thirdly, the densification step is often carried out without the blank being maintained under pressure, in so-called "free" sintering, which requires, to achieve high densification levels above 90%, significant densification times and temperatures.

[0020] 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 creating a rotating field because the total energy consumed is distributed over a wide range of angular domains of the field, with the consequence of a reduction in the amplitude of the field for each orientation.

[0021] There is therefore a real need for a manufacturing process that allows the manufacture of a multipole magnet with oriented flux in a reduced number of steps.

[0022] Summary of the invention

[0023] The invention overcomes these drawbacks by proposing a new manufacturing process in which the room temperature pressing and densification steps are carried out in the same tool and in which the densification step is carried out by SPS flash sintering (Spark Plasma Sintering), or arc plasma sintering.

[0024] For this purpose, the invention proposes a method for manufacturing a rotor magnet of an electrical machine, said method comprising a first phase of producing a magnet blank comprising:

[0025] - a first stage during which metallic and / or ceramic powders for magnets are supplied,

[0026] - a second step during which the said powders are mixed,

[0027] - a third step during which said powders are placed in a mold and a first magnetization tool is placed around said mold,

[0028] - a fourth step of pressing under a magnetic field during which said powders are pressed at room temperature to obtain the magnet blank, and they are simultaneously subjected to a magnetic field generated by the first magnetization tool,

[0029] - a fifth step during which the magnetic field generated by the first magnetization tool is stopped, and

[0030] - a sixth step during which the magnet blank is densified, said method further comprising a second phase of finishing the magnet blank comprising at least one step of machining the magnet blank and a step of final magnetization of the magnet blank, to obtain the magnet, 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.

[0031] Thus, the method which is the subject of the invention makes it possible to carry out the steps of pressing at room temperature and densification in the same tool, which eliminates transfer times from one tool to another and angular positioning errors. In addition, carrying out the densification step by SPS flash sintering makes it possible to substantially reduce the duration of this step because it is then no longer necessary to carry out a long temperature increase of the enclosure in which the densification is carried out.

[0032] According to another characteristic of the process, the second phase of finishing the magnet blank comprises, according to a first variant:

[0033] - a seventh step during which the magnet blank is allowed to cool to a Curie temperature of the magnet,

[0034] - an eighth step forming the final magnetization step during which the magnet blank is again subjected to a magnetic field generated by the first magnetization tool, and

[0035] - a ninth step of machining the blank of the magnet outside the mold, at the end of which the magnet is obtained.

[0036] In this first variant, the steps of pressing at room temperature, densification and magnetization are advantageously all carried out in the same tool, which allows a substantial saving of time and a reduction in the number of tools used.

[0037] 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 tool, 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. According to another characteristic of the process, the second phase of finishing the magnet blank comprises, according to a second variant:

[0038] - a seventh step of machining the magnet blank outside the mold,

[0039] - an eighth step during which the magnet blank is placed in a second magnetization tool independent of the mold in an orientation similar to a position occupied by the magnet blank in the first magnetization tool at the end of the fourth step, and

[0040] - a ninth step forming the final magnetization step during which the magnet blank is again subjected to a magnetic field generated by the second magnetization tool independent of the mold.

[0041] In this second variant, the room temperature pressing and densification steps are advantageously carried out in the same tool, which allows for substantial time savings and a reduction in the number of tools used. The magnetization step is carried out in a second magnetization tool independent of the mold. This allows the mold to be freed to prepare another magnet.

[0042] According to another characteristic of the process, in the second phase of finishing the blank magnet, according to a third variant, the ninth magnetization step can also be carried out in a second magnetization tool independent of the mold consisting of a stator of an electrical machine intended to receive the magnet. This ninth magnetization step (ET'9) is therefore an in situ magnetization.

[0043] According to another feature of the process, during the fourth stage of pressing under magnetic field, the powders are pressed under an increasing pressure of less than 10OMpa.

[0044] According to another feature of the process, during the sixth stage, the powder is densified by rapidly raising its temperature to between 900 and 1200°C.

[0045] The invention also relates to a device for implementing the manufacturing method of the type described above, which comprises at least:

[0046] - a metal mold comprising a fixed die delimiting a cavity and at least one 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 closes the cavity and penetrates into said cavity according to a determined stroke,

[0047] - an SPS flash sintering tool comprising at least one pulsed current generator, 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

[0048] - a first magnetization tool, comprising an annular magnetic circuit housed in the enclosure and surrounding the mold.

[0049] According to other characteristics of the device:

[0050] - the device also includes an annular heat shield interposed between the mold and the magnetic circuit,

[0051] - the device also includes an annular cooling exchanger arranged around the magnetic circuit inside the enclosure,

[0052] - the device is configured for the manufacture of a multipolar annular magnet with X-axis oriented flux, and: • the mold cavity is annular with X axis,

[0053] • 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 axis X and distributed angularly in a regular manner around said axis X.

[0054] - the magnetic core is crossed by a number of magnetic coils between 4 and 16, and preferably between 8 and 16,

[0055] - the mold is made of graphite or based on tungsten carbides or ternary carbides,

[0056] - the current-conducting means are graphite conductors.

[0057] The invention also relates to an installation for manufacturing a multipolar annular magnet with X-axis oriented flux in accordance with the second and third variants of the manufacturing method described above, characterized in that it comprises a manufacturing device and a second magnetization tool external to said manufacturing device and of similar configuration to the first magnetization tool, capable of surrounding the magnet blank.

[0058] According to another characteristic of this manufacturing installation, the second magnetization tool is a stator of an electric machine whose rotor is intended to receive the oriented flux magnet.

[0059] Brief description of the figures

[0060] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

[0061] [Fig. 1] Figure 1 is a schematic sectional view of the principle of a unidirectional magnet;

[0062] [Fig. 2] Figure 2 is a schematic sectional view of a variable orientation or oriented flux magnet;

[0063] [Fig. 3] Figure 3 is a perspective view of a conventional electric machine rotor ring having unidirectional magnets;

[0064] [Fig. 4] Figure 4 is a perspective view of an electric machine rotor ring according to the invention comprising multipole magnets with oriented flux;

[0065] [Fig. 5] Figure 5 is a schematic view of the steps of a conventional method of manufacturing a magnet;

[0066] [Figure. 6] Figure 6 is a principle view of a manufacturing device according to the invention;

[0067] [Figure. 7] Figure 7 is an axial half-sectional view of a first manufacturing device according to the invention;

[0068] [Figure. 8] Figure 8 is a perspective view of a portion of the first device of Figure 7;

[0069] [Figure. 9] Figure 9 is a perspective view with cutaway of the part of the first device of Figure 7;

[0070] [Figure. 10] Figure 10 is a cross-sectional view of a second manufacturing device according to the invention;

[0071] [Figure. 1 1 ] Figure 1 1 is a developed view of the magnetic circuit of a first variant of the device of Figure 10;

[0072] [Figure. 12] Figure 12 is a developed view of the magnetic circuit of a second variant of the device of Figure 10;

[0073] [Figure. 13] Figure 13 is a block diagram illustrating the steps of a first variant of the manufacturing method of the invention; [Figure. 14] Figure 14 is a block diagram illustrating the steps of second or third variants of the manufacturing method of the invention,

[0074] Detailed description of the invention

[0075] Figure 1 schematically illustrates a rectilinear unidirectional magnet 10 known per se from the state of the art.

[0076] As illustrated by the arrow in Figure 1, such a magnet has a unidirectional orientation of its magnetic field B between its two North poles N and South poles 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.

[0077] Variable orientation magnets, such as for example magnet 16 which has been shown in figure 2, have a variable orientation of their magnetic field which is thus capable of following several directions similar to magnetic fields B1, B2, B3, B4, B5, etc., between their two North poles N and South poles S, and this in a continuous manner between their two North poles N and South poles S.

[0078] 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, whereas on the other side of the North-South axis 14, the field lines 18 are further apart, a sign of a weaker magnetic field.

[0079] This property is of particular interest in the context of the manufacture of an annular magnet intended to equip an electric motor. It is possible with such a magnet, during its manufacture and in particular its magnetization, to maximize the magnetic field inside or outside this magnet, so as to reciprocally minimize the magnetic field, and therefore the magnetic losses on the opposite side of the annular magnet, that is to say reciprocally outside or inside the annular magnet.

[0080] The invention relates more particularly to the manufacture of an annular magnet for an electric machine rotor for which it is sought 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 which surrounds the rotor. This makes it possible to improve the efficiency of the electric machine comprising such an annular magnet.

[0081] Figure 3 shows an annular rotor 22 comprising a plurality of unidirectional magnets 12. Such a rotor 22 comprises an annular support 24 on which unidirectional magnets 12 are bonded. For example, a little less than 400 magnets 12 must be bonded to the support 24. This is an extremely time-consuming operation and does not allow a rotor 22 to be obtained providing the best efficiency. In addition, there is always a risk of the magnets detaching, which could cause irreversible damage to the electric motor.

[0082] Indeed, another advantage of multipolar annular magnets with oriented flux, in addition to the efficiency they allow the electric machine to achieve, is their single-piece configuration. 4 thus shows a rotor 26 comprising eight multipolar annular magnets 20 with oriented flux. This configuration makes it possible to avoid the use of a support such as the support 24 previously described and considerably reduces the number of magnets to be assembled.

[0083] Figure 5 illustrates the steps of a conventional method for obtaining a magnet 20. The method mainly comprises a first phase P1 of producing a magnet blank, and a second phase P2 of finishing the magnet blank.

[0084] The first phase P1 of producing the magnet blank comprises a first step ET1 during which metal powders for the magnet are provided. This first step ET1 comprises a sub-step 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 comprises a sub-step SET2 during which the raw materials 28 are melted in an induction furnace 30, then a sub-step SET3 during which they are ground in a grinder 32 until particles with a size of less than 500 μm are obtained and a sub-step SET4 during which they are pulverized in a ball milling or pressurized gas jet milling installation 34 until particles with a size of less than 10 μm are obtained.

[0085] Then during a second step ET2, said powders are mixed, and during a third step ET3 the powders 36 are placed in a mold 38 and a first magnetization tool 40 is placed around this mold.

[0086] Then, during 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 they are simultaneously subjected to a magnetic field B generated by the first magnetization tool 36. The purpose of this operation, while compacting them, is to orient the grains of the powder in a preferential direction in which a subsequent definitive magnetization will be established more easily than in other directions. A blank magnet 42 is obtained. Then, during a fifth step ET5, the magnetic field generated by the first magnetization tool is stopped, and during a sixth step ET6 the blank magnet 42 is densified by a conventional sintering process such as a furnace 44.

[0087] At the end of this first phase P1 of producing the magnet blank, the second phase P2 of finishing the magnet blank 42 takes place. This second phase P2 comprises at least one machining step ET7 of the magnet blank in a machining machine 46 and a final magnetization step ET8 of the magnet blank in a magnetization tool 48, to obtain the final magnet 20.

[0088] As seen previously, in this process, the steps of pressing at room temperature ET4, densification ET6 and final magnetization ET8 are separated and carried out in independent tools, which increases the complexity of the production range and generates long manufacturing times in order to obtain a magnet 20.

[0089] The densification step is conventionally carried out in an enclosure heated to a high temperature such as the furnace 44. The introduction of the magnet blanks 42 into the furnace 44 requires that the latter be initially at a temperature close to ambient temperature before causing it to rise in temperature, which, taking into account the fact that the densification itself is a long-term operation requiring several hours, results in a total immobilization time of the magnet blank 42 in the furnace which is particularly high.

[0090] The invention overcomes this drawback by proposing a method in which, during the third step ET3, the mold 38 is placed in a densification enclosure, this enclosure being a particular enclosure allowing, during the sixth step ET6, to carry out SPS flash sintering in this densification enclosure.

[0091] SPS flash sintering, an acronym for 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 graphite, steel, or tungsten carbide matrix 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 a very rapid temperature rise and complete sintering in a few minutes.

[0092] 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 occur according to the method of the invention in a single device 50, the principle of which has been shown in FIG. 6 in a schematic form. This device 50 allows the formation of a cylindrical magnet blank 42.

[0093] According to the invention, the device 50 comprises at least one metal mold 38 comprising a fixed die 52 delimiting 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 jack 57 of a hydraulic press between a position outside the cavity 54 and a position in which it closes the cavity and penetrates into said cavity 54 according to a determined stroke. Here, the device 50 has been shown as comprising two opposing punches 56, but this configuration is not limiting of the invention.

[0094] The device 50 further comprises an SPS flash sintering tool comprising at least one pulsed current generator 58, current conducting means 60 arranged in the matrix 52 and the punches 56. Typically, these current conducting means are graphite-based conductors. The tool also comprises a densification enclosure 64 containing the mold 38, which is capable of being selectively evacuated or filled with a neutral gas.

[0095] The device 50 comprises a first magnetization tool 66, comprising an annular magnetic circuit 68 housed in the enclosure 64 and surrounding the mold 38.

[0096] With the device 50, it is therefore possible to arrange powders with a particle size <10 pm (Samarium-Cobalt SmCo, Neodymium NdFeB, Ferrites or others) used during step ET3 to design a magnet. These powders are placed in the mold 38 made of graphite or WC (Tungsten carbides) or MAX phase ceramic (ternary carbides), having the shape of the part to be produced with the punches 56 closing the cavity 54 of the mold. The magnetization tool 66 is positioned around the mold 38 and the assembly is placed in the densification enclosure 64.

[0097] Then during step ET4, the densification chamber 64 is placed under vacuum 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 jacks 57 stops.

[0098] Once this state is reached, the magnetic field is cut off following step ET5 and the atmosphere in the densification chamber 64 is adapted by injecting a suitable atmosphere such as a neutral gas instead of vacuum.

[0099] During step ET6, a pulsed current is supplied by the generator 58 to the mold 38 in order to quickly raise the temperature between 900 and 1200°C and thus densify the powder. The stress exerted by the jacks 57 can be controlled during this step, by bringing it back to 0 MPa then increasing it again according to different stages, independently. In any case, the applied pressure remains less than 100 MPa. Then a temperature stage is applied for a period of 5 to 40 minutes until complete densification of the powders. The magnet blank 42 is then obtained.

[0100] As illustrated in Figures 11 and 12, after this first phase P1 of producing the blank magnet 42, a second phase P2 of finishing the blank magnet 42 takes place, comprising at least one step of machining the blank magnet 42 and a step of final magnetization of the blank magnet 42, to obtain the magnet.

[0101] This second phase P2 can occur partly in the device 50 or outside the device 50.

[0102] According to a first variant of the invention, as shown in Figure 13, the second phase P2 of finishing the magnet blank 42 firstly 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 down to a Curie temperature of the magnet. The cooling temperature is for example controlled using a thermocouple inserted in the mold.

[0103] The Curie temperature depends on the nature of the powders 36 used. For example, it is 400 to 500°C for Fe ferrite powders, 700 to 900°C for Samarium-Cobalt SmCo powders and 300 to 400°C for NdFeB neodymium powders.

[0104] In this first variant, the second phase P2 of finishing 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 generated by the first magnetization tool 66.

[0105] This configuration is particularly advantageous because it allows the final magnetization of the magnet blank 42 to be carried out in the device 50 with the same first magnetization tool 66 previously used. The magnet blank 42 therefore leaves the device 50 practically ready to be used, and it is therefore no longer necessary to complete its finishing except during a ninth step ET9 of machining the magnet blank 42 outside the mold 38, at the end of which the magnet 20 is obtained.

[0106] According to second and third variants of the invention, as shown in Figure 14, the magnet blank 42 is extracted from the device 50 at the end of the first phase P1 and the second phase P2 of finishing the magnet blank 42 takes place outside the device 50, which advantageously makes it possible to release the latter for the manufacture of the following magnet blank 42.

[0107] In these second and third variants of the invention, the phase P2 of finishing the magnet blank 42 comprises a seventh step ET'7 of machining the magnet blank 42 outside the mold.

[0108] Then, during an eighth step ET'8, the magnet blank 42 is placed in a second magnetization tool (not shown) independent of the mold 38, in an orientation similar to a position occupied by the magnet blank 42 in the first magnetization tool 66 at the end of the fourth step ET4. The purpose of this arrangement is to orient the magnet blank 42 in accordance with the preferred direction in which, during step ET4, the grains of the powder 42 were previously oriented. As a reminder, this preferred direction allows for a subsequent definitive magnetization to be established more easily. Then, during a ninth step ET'9, the magnetization of the magnet blank 42 is carried out by again subjecting the magnet blank 42 to a magnetic field generated by the second magnetization tool independent of the mold 38.

[0109] The second magnetization tool is, in the second variant of the process, a specific magnetization tool dedicated to this single task.

[0110] However, in the third variant of the method, the ninth step ET'9 can advantageously be carried out by using as a second magnetization tool independent of the mold a stator of an electrical machine intended to receive a rotor comprising the magnet. This configuration makes it possible to dispense with a second specific magnetization tool, and to carry out the magnetization of the blank magnet 42 of the rotor in situ, directly in the electrical machine.

[0111] A device 50 is now described, more particularly intended for the manufacture of a multipolar annular magnet 20 with X-axis oriented flux for a rotor of an electric machine of the electric motor, generator or sensor type.

[0112] As previously, the device 50 comprises at least one metal mold 38 comprising a fixed die 52 delimiting a cavity 54 of annular shape with axis X intended to receive the powders 36 and at least one punch 56, also annular with axis X, which is consequently complementary to an annular section of the cavity 54. The punch is moved by a jack of a hydraulic press (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 determined stroke C along the axis X, corresponding to the desired compaction of the powder 36. The device 50 which has been shown in FIG. 6 comprises only one punch 56.

[0113] As previously, the device 50 further comprises an SPS flash sintering tool comprising at least one current generator and current conducting means (not shown) arranged in the matrix 52 and the punches 56. This tooling allows the passage of a high intensity electric current through the powders 36 and their agglomeration by sintering.

[0114] The tooling also includes an enclosure 64 containing the mold 38, which has only been shown in Figures 7 and 10, and which, as previously, is capable of being selectively evacuated or filled with a neutral gas.

[0115] The device 50 comprises a first magnetization tool 66, comprising an annular magnetic circuit 68 housed in the enclosure and surrounding the mold 38. This annular magnetic circuit comprises a substantially annular magnetic core 70 with axis X crossed by a plurality of magnetic coils 72 with axes parallel to the axis X and distributed angularly in a regular manner around the axis X.

[0116] In Figures 8 and 9, a device 50 is shown comprising a magnetic circuit 68 comprising eight magnetic coils 72 connected in series by transverse links 74, which makes it possible to produce 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 with which it is desired to provide the magnet, the magnetic circuit can comprise a greater number of coils 72.

[0117] For example, as illustrated in Figure 10, a device 50 according to the invention comprises a magnetic circuit 68 comprising 16 magnetic coils 72 making it possible to produce a magnet with 16 poles (eight North poles N and eight South poles S). The coils may comprise a magnetic circuit 68 of coils 72 comprising a single conductor 73, as illustrated by the developed diagram of the magnetic circuit 68 in Figure 11, or a magnetic circuit 68 of coils 72 comprising two conductors 73, 75 as illustrated by the developed diagram of the magnetic circuit 68 in Figure 12.

[0118] 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 makes it possible to protect the coils 72 from the heat of the mold 38 when it is heated by the SPS flash sintering tool.

[0119] As illustrated in Figure 7, the device 50 may also additionally comprise 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 method forming the subject of the invention for which this annular cooling exchanger 78 makes it possible to control and pilot the cooling temperature according to the first variant of the method forming the subject of the invention, between the seventh step ET7 and the eighth step ET8.

[0120] When it is intended to implement the second or third variants of the method which is the subject 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 previously described and a second magnetization tool (not shown) external to the device 50. This second manufacturing tool is of a similar configuration to the first magnetization tool, capable of surrounding the magnet blank 42. By similar tool, it will be understood in particular that this second magnetization tool comprises 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.

[0121] More particularly, when it is intended to implement the second variant of the method which is the subject of the invention, the second external magnetization tool is substantially identical to the first external magnetization tool. When it is intended to implement the third variant of the method, it is not a specific tool but simply a stator of an electrical machine to accommodate a rotor receiving the flux-oriented magnet 20. This configuration is very advantageous because it makes it possible to reduce the occupation time of the mold 38 by the magnet blank 42 in order to free it up for other blanks, and to carry out the final magnetization of the magnet according to step ET'9 directly in the electrical machine.

[0122] The invention therefore makes it possible to considerably reduce the production times of a multipolar magnet with oriented flux 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 phase (P1) 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 process 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 process according to claim 1, characterized in that the second finishing phase (P2) of 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 magnetization step during which the magnet blank (42) is again subjected to a magnetic field generated by the second independent magnetization tooling 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 manufacturing process according to any one of the preceding claims, characterized in that during the fourth step (ET4) of pressing under a magnetic field, the powders are pressed under an increasing pressure of less than 100Mpa.

6. A manufacturing process according to any one of the preceding claims, characterized in that during the sixth step (ET6), the powder is densified by rapidly raising its temperature between 900 and 1200°C.

7. 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) delimiting 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) according to a determined stroke (C), - SPS flash sintering tooling 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 an inert gas, and - a first magnetization tool (66), comprising an annular magnetic circuit (68) housed in the enclosure and surrounding the mold (38).

8. 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).

9. Device (50) according to any one of claims 7 and 8, characterized in that it further comprises an annular cooling exchanger arranged (78) around the magnetic circuit (68) inside the enclosure (64).

10. Device (50) according to any one of claims 7 to 9, characterized in that it is configured for manufacturing a multipolar ring magnet with oriented flux along the X-axis, and in that: - the cavity (54) of the mold (38) is annular with axis X, - the annular magnetic circuit (68) of the first magnetization tool (66) comprises a substantially annular magnetic core (70) crossed along 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. 1 1. Device according to the preceding claim, characterized in that the magnetic core (70) is traversed by a number of magnetic coils (72) between 4 and 16, and preferably between 8 and 16.

12. Device according to any one of claims 7 to 10, characterized in that the mold (38) is made of graphite or based on tungsten carbides or ternary carbides.

13. Device according to any one of claims 7 to 12, characterized in that the current-conducting means (60) are graphite conductors.

14. Installation for manufacturing a multipolar ring magnet (20) with X-axis oriented flux according to the manufacturing process according to any one of claims 3 to 6, 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).

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

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