ADDITIVE MANUFACTURING PROCESS FOR A LAMINATED FERROMAGNETIC PART

Abstract

The invention relates to an additive manufacturing process for a layered ferromagnetic part (33) comprising: i - a step of spreading a first bed of powder (34) of ferromagnetic material and a step of melting the first bed of powder (34) swept by a flow of inert gas (35) to obtain a conductive layer, said process further selectively comprising: ii - a heat treatment step by heating a surface of the previously obtained conductive layer and simultaneously sweeping it with a flow of reactive gas (38), or iii - a step of spreading a second bed of powder (40) of ferromagnetic material and a step of melting the second bed of powder (40) swept by a flow of reactive gas (38) to obtain an insulating layer, - steps i and (ii or iii) being repeated so as to obtain a layered ferromagnetic part (33). Figure 1

Description

Title of the invention: METHOD FOR THE ADDITIVE MANUFACTURING OF A LAMINATED FERROMAGNETIC PART

[0001] The present invention relates to an additive manufacturing process for a laminated ferromagnetic part. The invention finds particularly advantageous, but not exclusive, application in the field of power electronics for the manufacture of ferromagnetic parts, as well as in the field of rotating electrical machines, particularly motors, generators, or electric actuators. The invention can also be implemented with any other ferromagnetic part used to manufacture transformer or inductor components, for example.

[0002] In a manner known per se, a rotating electrical machine comprises a stator associated with a rotor that rotates relative to the stator. The stator generally comprises a body made of a ferromagnetic material and a polyphase winding inserted into slots in the stator body. The rotor comprises a body made of a ferromagnetic material and permanent magnets made of ferrite or rare-earth materials. The variations in the magnetic field generated by the different phases of the stator winding cause the rotor to rotate.

[0003] These variations in magnetic field over time induce eddy currents (called "eddy currents" according to Anglo-Saxon terminology) responsible for part of the losses (called eddy current losses) in the magnetic circuits of electrical machines.

[0004] This is why the stator body and the rotor body are conventionally made of laminated sheets in order to limit these currents and the resulting Joule effect losses by limiting the propagation path of the induced currents within the thin laminated layers. This improves the overall efficiency of the electric machine.

[0005] The stator body and the rotor body are thus formed by alternating layers of ferromagnetic material and insulating layers covering the layers. However, assembling these laminated parts into a stack of sheets is complex. This generates variations in magnetic performance. This principle is limited to unidirectional assembly.

[0006] It is also known to produce magnetic parts for electronic machines by sintering a powder made of SMC material, for "Soft Magnetic Composite" according to Anglo-Saxon terminology, comprising magnetic particles coated by an insulator. However, such magnetic cores exhibit poor mechanical strength as well as poor temperature resistance.

[0007] The invention aims to effectively overcome the aforementioned drawbacks by proposing an additive manufacturing process for a layered ferromagnetic part comprising: i - a step of spreading a first powder bed containing a powder made of a ferromagnetic material and a step of melting the first powder bed swept by a flow of inert gas to obtain a layer of ferromagnetic material, called the conductive layer, said process further comprising selectively: ii - a heat treatment step by heating a surface of the previously obtained conductive layer and simultaneously sweeping the surface of the conductive layer with a reactive gas flow, or iii - a step of spreading a second powder bed containing the powder made in said ferromagnetic material and a step of melting the second powder bed swept by a reactive gas flow to obtain a layer of ferromagnetic material containing components having electrical insulating properties, called the insulating layer, - steps i and (ii or iii) being repeated so as to obtain a laminated ferromagnetic part having an alternation of conductive layers and insulating layers.

[0008] The invention thus makes it possible, by changing the melting atmosphere of the ferromagnetic material, to produce a laminated ferromagnetic part with good mechanical strength, good temperature resistance, and excellent magnetic performance, limiting the occurrence of eddy currents. Furthermore, the ferromagnetic parts obtained via the process according to the invention do not require assembly time, unlike bundles of sheet metal. The invention allows the use of a wide range of high-performance materials. Moreover, while sheet metal is limited to two dimensions, the invention makes it possible to create three-dimensional electrical barriers, allowing access to more varied topologies of rotating electrical machines, such as rotating flux machines, for example.The resulting ferromagnetic parts also have the advantage of possessing homogeneous properties throughout their volume, thus avoiding disturbances associated with conventional sheet metal forming processes (cutting, stamping, welding).

[0009] According to one embodiment of the invention, the ferromagnetic material is chosen from: an Iron-Silicon, Iron-Nickel, or Iron-Cobalt alloy.

[0010] According to one embodiment of the invention, the inert gas stream contains argon.

[0011] According to one embodiment of the invention, the reactive gas flow is selected from air or oxygen to generate oxidation of the ferromagnetic material or nitrogen to generate nitriding of the ferromagnetic material.

[0012] According to one embodiment of the invention, laser parameters used to perform the melting and heat treatment steps are adapted to the conductive layer and the insulating layer to avoid a remelting phenomenon of previously deposited layers.

[0013] According to one embodiment of the invention, the thickness of the insulating layer is between 20pm and 100pm, and is preferably of the order of 60pm.

[0014] The invention also relates to an additive manufacturing device comprising: - a manufacturing chamber, - a manufacturing platform located inside the manufacturing chamber, - means of generating a laser beam capable of ensuring the fusion of a powder bed, - said additive manufacturing device further comprising: - a blowing device capable of generating a gas flow inside the manufacturing chamber, - an inert gas source connected to a first solenoid valve, - a source of reactive gas associated with a second solenoid valve, and - a control module capable of controlling the blowing device, the first solenoid valve and the second valve, so as to selectively generate a flow of inert gas or a flow of reactive gas intended to sweep a bed of powder deposited on the manufacturing platform.

[0015] According to one embodiment of the invention, a vacuum pump associated with a filter is capable of drawing the inert gas flow or the reactive gas flow out of the manufacturing chamber.

[0016] According to one embodiment of the invention, said device comprises reactive or inert gas probes used to monitor a level of reactive or inert gas respectively in the reactive or inert gas flow sweeping the powder bed and in the manufacturing chamber.

[0017] The invention further relates to a laminated ferromagnetic part characterized in that it comprises, alternately: - a layer of ferromagnetic material constituting a layer of electrically conductive material, called the conductive layer, and - a layer of ferromagnetic material containing components with good electrical insulation properties chosen from ceramics and iron nitrides so as to form a weakly electrically conductive layer, called insulating layer, so that, following a direction of stacking of material layers, the ferromagnetic part comprises a conductive layer, then an insulating layer, then a conductive layer, then an insulating layer, and so on.

[0018] The present invention will be better understood and other features and advantages will become apparent upon reading the following detailed description, which includes embodiments given by way of illustration with reference to the accompanying figures, presented by way of non-limiting examples, which may serve to complete the understanding of the present invention and the explanation of its implementation and, where appropriate, contribute to its definition, on which:

[0019] [Fig-1] Fig. 1 is a schematic representation of a manufacturing device additive according to the present invention;

[0020] [Fig.2a] [Fig.2b] Figures 2a and 2b are schematic representations of steps of the additive manufacturing process according to the invention;

[0021] [Fig.3] Fig.3 is a schematic cross-sectional representation of a part layered ferromagnetic according to the invention;

[0022] [Fig.4] Fig.4 is a schematic representation illustrating a confinement of currents induced within the conductive layers of the laminated ferromagnetic part according to the invention.

[0023] It should be noted that the structural and / or functional elements common to the different embodiments may have the same reference numerals. Thus, unless otherwise specified, such elements have identical structural, dimensional and material properties.

[0024] Figure 1 shows a powder bed additive manufacturing device 10 for producing a layered ferromagnetic part 33 according to the invention. This device 10 comprises a build chamber 11 inside which is arranged a build platform 12 that moves vertically. The build platform 12 is located below a powder reservoir 13. The powder is made of a ferromagnetic material preferably selected from: an iron-silicon, iron-nickel, or iron-cobalt alloy.

[0025] A system 15, in particular of the scraper type, makes it possible to equalize the thickness of a powder bed deposited on the manufacturing platform 12. A powder bed thus has a controlled thickness.

[0026] The device 10 also includes means 16 for generating a laser beam coupled to a scanner 20 controlled by a control module 27 to orient and move the laser beam 17 along the three dimensions X, Y and Z. The scanner 20 may include a set of oscillating mirrors controlled by the control module 27.

[0027] A blowing device 21 is capable of generating a gas flow 35, 38 inside the manufacturing chamber 11. The gas flow 35, 38 is intended to sweep a powder bed 34, 40 deposited on the manufacturing platform 12. The blowing device 21 is disposed at a distance from the powder bed.

[0028] An inert gas source 23 is associated with a first solenoid valve 24.1. The first solenoid valve 24.1 is capable of selectively taking a closed state so as to isolate the inert gas source 23 from the blowing device 21 and an open state so as to connect the inert gas source 23 with the blowing device 21. The inert gas 23 can be argon or any other gas that protects the structure of the ferromagnetic material during the melting of a powder bed.

[0029] A reactive gas source 26 is associated with a second solenoid valve 24.2. The second solenoid valve 24.1 is capable of selectively taking a closed state so as to isolate the reactive gas source 26 from the blowing device 21 and an open state so as to connect the reactive gas source 26 with the blowing device 21. The reactive gas is chosen from air or oxygen to generate oxidation of the ferromagnetic material or nitrogen to generate nitriding of the ferromagnetic material during melting or heat treatment of the surface of the fused powder bed.

[0030] The control module 27 is capable of controlling the first solenoid valve 24.1 and the second valve 24.2, so that the blowing device 21 is capable of selectively generating a flow of inert gas 35 or a flow of reactive gas 38 intended to sweep a bed of powder 34, 40 deposited on the manufacturing platform 12. A purging time of both gases is then necessary to ensure the correct working atmosphere of the laser.

[0031] The control module 27 may include a programmable card, a microcontroller or a computer. The control of the first solenoid valve 24.1 and the second solenoid valve 24.2 is carried out via an electromagnetic control relay 28 connected on one side to the control module 27 and on the other side to the solenoid valves 24.1, 24.2.

[0032] A vacuum pump 30 associated with a filter 32 allows the inert gas flow 25 or the reactive gas flow 38 to be drawn out of the manufacturing chamber 11.

[0033] Reactive or inert gas probes 31, in particular oxygen probes, can be used to monitor a reactive or inert gas level respectively in the reactive or inert gas flow sweeping the powder bed 34, 40 and in the manufacturing chamber 11.

[0034] A memory 29 can record changes in the levels of reactive or inert gas during the implementation of the process. Alternatively or in addition, it is also possible to record changes in temperature inside the manufacturing chamber 11.

[0035] The additive manufacturing process of a laminated ferromagnetic part 33 is described below with reference to Figures 2a and 2b.

[0036] As shown in [Fig. 2a], the process includes a step of spreading a first powder bed 34 containing the powder made of a ferromagnetic material. The control module 27 controls the first valve 24.1 and the blowing device 21 so as to generate a flow of inert gas 35 sweeping over the first powder bed 34.

[0037] The control module 27 also controls the means 16 for generating a laser beam 17, so as to achieve melting of the first powder bed 34 simultaneously swept by the inert gas flow 35 to obtain a layer of ferromagnetic material, called the conductive layer 37. The melting of the powder bed 34 by the laser beam 17 occurs at a temperature above 1000°C, in particular between 1500°C and 1600°C. This temperature depends on the melting temperature of the material.

[0038] A thickness of layer 37 can be between 20pm and 100pm and is preferably of the order of 60pm.

[0039] The process can then include a heat treatment step by heating a surface of the previously obtained conductive layer 37 and simultaneously sweeping the surface of the conductive layer 37 with a flow of reactive gas 38.

[0040] To this end, the control module 27 operates the second valve 24.2 and the blowing device 21 so as to generate a flow of reactive gas 38 sweeping across a first bed of powder 34. The control module 27 simultaneously operates the means for generating a laser beam 17 to heat the surface of the conductive layer 37. The heat treatment temperature is lower than the melting temperature and is, for example, on the order of 500°C. By "on the order of," we mean a variation of plus or minus 10% around the stated value. The energy density of the laser beam 17, defined in particular by the power, speed, and laser beam width 17, is lower than that used during a melting phase.

[0041] As illustrated in [Fig. 2b], instead of the heat treatment step, the process includes a step of spreading a second powder bed 40 containing the powder made from a ferromagnetic material. This powder is the same as that used to produce the conductive layer 37. The second powder bed 40, distinct from the first powder bed 34, is deposited onto the build platform 12 after the latter is moved downwards by a distance corresponding to the thickness of the conductive layer 37.

[0042] The control module 27 controls the second valve 24.2 and the blowing device 21 so as to generate a flow of reactive gas 38 sweeping the second powder bed 40.

[0043] The control module 27 also controls the means for generating a laser beam 17 16, so as to achieve fusion of the second powder bed 40 simultaneously swept by the reactive gas flow 38. The melting of the powder bed 40 occurs at a temperature above 1000°C, specifically between 1500°C and 1600°C. This temperature depends on the melting temperature of the material.

[0044] The heat treatment step or the melting step of the powder bed 40 swept by the reactive gas flow allows obtaining a layer of ferromagnetic material containing components having electrical insulating properties, called insulating layer 4L. In other words, the step of sweeping the powder bed 40 by the reactive gas flow 38 during the melting of the powder bed 40 or the heat treatment step allows altering the electrical conductive properties of the ferromagnetic material contained in the powder bed 40.

[0045] The reactive gas flow 38 can be an air flow or an oxygen flow to generate oxidation of the ferromagnetic material, or a nitrogen flow to generate nitriding of the ferromagnetic material. In-situ oxidation of the ferromagnetic material creates ceramic-type components (Fe3O4) within the insulating layer 4L. In-situ nitriding of the ferromagnetic material creates iron nitrides within the insulating layer 4L. The iron nitrides can be of the type Fe2N, Fe3Ni+x (0.10 < x < 0.39), Fe4N, or Fe6N2. The ceramics and iron nitrides exhibit good electrical insulating properties.

[0046] The thickness of the insulating layer 41 obtained by heat treatment is small, in particular between 1 µm and 20 µm. The thickness of the insulating layer 41 obtained by melting the powder bed 40 can be between 20 µm and 100 µm, and is preferably on the order of 60 µm. The thickness of the insulating layer 41 is adjusted according to the applied laser treatment time, the number of times the laser passes over the same area, the atmosphere used during melting, in particular the oxygen or nitrogen content, and the orientation angle of the blowing device 21.

[0047] The spreading and melting steps of the powder bed 34 swept by the inert gas flow 35 and heat treatment, or the spreading and melting steps of the powder bed 40 swept by the reactive gas flow 38, are repeated with new powder beds 34, 40 so as to obtain a layered ferromagnetic part 33 having alternating conductive layers 37 and insulating layers 4L

[0048] Advantageously, laser parameters used to perform the melting and heat treatment steps are adapted to the conductive layer 37 and the insulating layer 41 to avoid a remelting phenomenon of the previously deposited layers.

[0049] As can be seen in [Fig. 3], the laminated ferromagnetic part 33 obtained at the end of the manufacturing process comprises, alternately: - a layer of ferromagnetic material constituting a layer of electrically conductive material, called the conductive layer 37 and - a layer of ferromagnetic material containing components with good electrical insulation properties chosen from ceramics and iron nitrides so as to form a weakly electrically conductive layer, called insulating layer 41.

[0050] Thus, following a stacking direction D of the material layers, the ferromagnetic part 33 comprises a conductive layer 37, then an insulating layer 41, then a conductive layer 37, then an insulating layer 41, and so on.

[0051] In this way, as illustrated in [Fig.4], the induced currents represented by the arrows 42 are confined in the conductive layers 37 defined during the design of the part 33 and electrically insulated from each other by the insulating layers 41.

[0052] The material layers 37, 41 can extend parallel to each other in a planar shape or in a curved shape to produce ferromagnetic parts 33 having complex shapes.

[0053] Of course, the different features, variants and / or embodiments of the present invention can be combined with each other in various ways insofar as they are not incompatible or mutually exclusive.

[0054] Furthermore, the invention is not limited to the embodiments described above and provided solely by way of example. It encompasses various modifications, alternative forms, and other variants that a person skilled in the art may consider within the scope of the present invention, and in particular all combinations of the different modes of operation described above, which may be taken separately or in combination.

Claims

Demands

1. An additive manufacturing process for a layered ferromagnetic part (33) characterized in that it comprises: i - a step of spreading a first powder bed (34) containing a powder made of a ferromagnetic material and a step of melting the first powder bed (34) swept by a flow of inert gas (35) to obtain a layer of ferromagnetic material, said conductive layer (37), said process further comprising selectively: ii - a heat treatment step by heating a surface of the previously obtained conductive layer (37) and simultaneously sweeping the surface of the conductive layer (37) with a flow of reactive gas (38),or iii - a step of spreading a second powder bed (40) containing the powder made in said ferromagnetic material and a step of melting the second powder bed (40) swept by a reactive gas flow (38) to obtain a layer of ferromagnetic material containing components having electrical insulating properties, called the insulating layer (41), - the reactive gas flow (38) being air or oxygen to generate oxidation of the ferromagnetic material, - steps i and (ii or iii) being repeated so as to obtain a layered ferromagnetic part (33) having alternating conductive layers (37) and insulating layers (41).

2. A method according to claim 1, characterized in that the ferromagnetic material is chosen from: an Iron-Silicon, Iron-Nickel, or Iron-Cobalt alloy.

3. A method according to claim 1 or 2, characterized in that the inert gas stream (35) contains argon.

4. A method according to any one of claims 1 to 3, characterized in that the laser parameters used to perform the melting and heat treatment steps are adapted to the conductive layer (37) and the insulating layer (41) to avoid a remelting phenomenon of previously deposited layers.

5. A method according to any one of claims 1 to 4, characterized in that a thickness of the insulating layer (41) is between 20pm and 100pm, and is preferably of the order of 60pm.

6. Additive manufacturing device (10) comprising: - a build chamber (11), - a build platform (12) disposed inside the build chamber (11), - means for generating (16) a laser beam (17) capable of melting a bed of ferromagnetic powder material, characterized in that said additive manufacturing device (10) further comprises: - a blowing device (21) capable of generating a gas flow (35, 38) inside the build chamber (11), - an inert gas source (23) associated with a first solenoid valve (24.1), - a reactive gas source (26) associated with a second solenoid valve (24.2), the reactive gas being air or oxygen for generating oxidation of the ferromagnetic material during melting or heat treatment of a surface of the fused powder bed, and - a control module (27) capable of control the blowing device (21), the first solenoid valve (24.1) and the second valve (24.2); so as to selectively generate an inert gas flow (35) or a reactive gas flow (38) intended to sweep a powder bed (34, 40) deposited on the manufacturing tray (12).

7. Device according to claim 6, characterized in that a vacuum pump (30) associated with a filter (32) is capable of drawing the inert gas flow (35) or the reactive gas flow (38) out of the manufacturing chamber (11).

8. Device according to claim 6 or 7, characterized in that it comprises reactive or inert gas probes (31) used to monitor a reactive or inert gas level respectively in the reactive or inert gas flow sweeping the powder bed (34, 40) and in the manufacturing chamber (11).

9. A layered ferromagnetic part (33) characterized in that it comprises, alternately: - a layer of ferromagnetic material constituting a layer of electrically conductive material, referred to as the conductive layer (37), and - a layer of ferromagnetic material containing components having good electrical insulation properties of the ceramic type (Fe3O4) resulting from the oxidation of the ferromagnetic material in a to form a weakly electrically conductive layer, called an insulating layer (41), so that, following a stacking direction (D) of the material layers (37, 41), the ferromagnetic part (33) comprises a conductive layer (37), then an insulating layer (41), then a conductive layer (37), then an insulating layer (41), and so on.

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