FR3142598A1 - Method of manufacturing a magnetic core comprising an element enclosed in an arm - Google Patents

Abstract

Method for manufacturing a magnetic core (1) comprising: - an impression of a first part (73) of the magnetic core comprising an arm (75, 76, 77) having an open chamber (79, 110, 111), - an impression of a second part (74) of the magnetic core comprising a junction piece (112, 113, 114), - an insertion of an element (115, 116, 117) in the chamber, and - a fixing of the first part and the second part so that the junction piece encloses the element in the chamber, the arm is included in a plurality of arms of the core, the plurality of arms being arranged along edges of a convex polyhedron, and the junction piece is included in a plurality of junction pieces of the core, each junction piece being located at a vertex of the polyhedron. Figure to be published for the abstract: Figure 1

Description

Method of manufacturing a magnetic core comprising an element enclosed in an arm FIELD OF THE INVENTION

The invention relates to magnetic cores, that is, magnetic parts configured to channel magnetic field lines and magnetically couple with another magnetic core.

STATE OF THE ART

In aeronautics, magnetic cores are used in particular in power electronics in multi-phase couplers of a motor driving a turbomachine shaft.

The magnetic cores currently used can be designed by uniaxial compression or by powder injection molding (also known as powder injection molding or PIM). These processes require a mold and consequently limit the geometries of the manufactured cores to demoldable parts. These two processes require a mold for each geometry and are suitable for large series production.

There is also a core machining process from a solid block, but this process is poorly suited to magnetic materials which are fragile and whose magnetic properties are sensitive to the surface condition obtained. This process does not offer great precision or great complexity in the shape of the part produced, which can again have an impact on the magnetic performance of the part produced. Finally, machining leads to losses of material which are not always recyclable and, when they are, they require prior treatment.

These processes limit the achievable shapes of the magnetic cores, which limits the optimization of the size of the cores, the optimization of the integration of the cores and the implementation of functions ancillary to the magnetic function, such as for example a function of core cooling.

There is therefore a need for a process for manufacturing magnetic cores allowing greater freedom of shape of the manufactured cores.

An aim of the invention is to propose a process for manufacturing magnetic cores allowing greater freedom of shape of the manufactured cores.

The aim is achieved in the context of the present invention thanks to a process for manufacturing a magnetic core, the process comprising:

- an impression of a first part of the magnetic core comprising an arm, the arm having an open chamber,

- an impression of a second part of the magnetic core including a junction piece,

- an insertion of an element in the room, and

- fixing the first part and the second part so that:

-- the junction piece locks the element in the chamber,

-- the arm is included in a plurality of arms of the magnetic core, the plurality of arms being arranged along edges of a convex polyhedron, each arm forming a right cylinder, and

-- the junction part is included in a plurality of junction parts of the magnetic core, each junction part being located at a vertex of the polyhedron.

Such a process is advantageously and optionally supplemented by the following different characteristics taken alone or in combination:

- the element is chosen from an element made of phase change material, an element of amorphous material, an element of nanocrystalline material, and a hollow ferrite tube comprising an internal wall and at least one fin which extends radially to the inside the tube from the internal wall;

- the printing of the first part and the second part is carried out from a spinel ferrite powder by jet of binder or by deposition of molten material;

- the printing of the first part and the second part is carried out by binder jet, the process comprising before the insertion step a step of removing grains of powder separated from the core;

- the element is chosen from an element made of phase change material, an element of amorphous material, and an element of nanocrystalline material, the method comprising before the insertion step a step of sintering the first part and the second part, the fixing being carried out by gluing or screwing;

- the element is a hollow tube, the process comprising manufacturing the hollow tube by stereolithography, and preferably the fixing is carried out by co-sintering;

- the element is a hollow tube, the fixing being carried out by co-sintering and preferably the method comprises manufacturing the hollow tube by stereolithography;

- the printing of the first part is configured so that the arm of the first part is a first arm, the first part comprising a first portion of a second arm of the plurality of arms of the magnetic core, the first portion being full, the printing of the second part is configured so that the second part comprises a second portion of the second arm, the second portion being full, and the fixing of the first part and the second part is configured to place the first portion facing each other and the second portion along two faces extending perpendicularly to an axis of the cylinder corresponding to the second arm, the material located between the two faces being non-magnetic; And

- the material located between the two faces includes glue.

The invention also relates to a magnetic core obtained by a process as just presented.

DESCRIPTION OF FIGURES

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and must be read with reference to the appended drawings in which:

there is a schematic representation of a magnetic core obtained according to one mode of implementation of the invention,

Figures 2 and 3 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in ,

Figures 4 and 5 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in ,

Figures 6 and 7 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in ,

Figures 8 and 9 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in ,

Figures 10 and 11 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in ,

Figures 12 and 13 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in ,

Figures 14 and 15 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in .

Figures 16 and 17 are schematic representations of a type of arm of a magnetic core in a radial section in and an axial section in .

there is a schematic representation of a magnetic core obtained according to one mode of implementation of the invention,

DETAILED DESCRIPTION OF THE INVENTION Magnetic core

In connection with the , a magnetic core 1 comprises a plurality of arms referenced 31 to 42.

Each arm forms a straight cylinder. This means that the smallest convex volume which contains the arm defines a surface which is the surface of a right cylinder. A volume is convex when, for any pair of two points contained in the volume, the segment which joins these two points is entirely contained in the volume.

Each cylinder has a main axis A on which the cylinder is centered, this main axis giving the direction of the generators of the cylinder. The cylinder may in particular have a circular section, that is to say that a section perpendicular to the main axis has a circular external perimeter.

The cylinder may have a radial dimension or an external diameter greater than or equal to 5 millimeters and less than or equal to 30 millimeters. A radial dimension of the cylinder or arm is a length of the cylinder or arm measured in a radial direction orthogonal to the principal axis A.

Each cylinder extends an axial length along the principal axis between two faces forming the axial ends of the cylinder. A straight cylinder means that these two faces are orthogonal to the main axis. The arms of the core can all be of the same axial length or have different axial lengths.

Each arm can be made of ferrite and in particular of spinel ferrite. Materials called “spinel ferrites” are magnetic ceramics. These are magnetic oxides of the MeFe ₂ O ₄ type, the term “Me” designating an alloy metal such as MnZn, NiZn, etc. It is possible to add copper or other metals to this alloy. This addition allows for additional specifics. These ceramics have high melting temperatures.

Each arm is configured to receive a winding of a conductive wire. The arm can receive two windings of conductive wire which can be magnetically coupled thanks to the material making up the magnetic core.

The arms of the core are arranged along edges, referenced 51 to 62 in , of a convex polyhedron, referenced 7 in .

This means that each arm is associated with one and only one edge of the polyhedron and conversely that each edge of the polyhedron is associated with one and only one arm of the core. An edge is aligned with the main axis of the cylinder formed by the arm associated with the edge. The arm extends along this main axis over an axial length entirely contained in the edge associated with the arm.

A polyhedron is convex when for any pair of two points contained in the polyhedron, the segment which joins these two points is entirely contained in the polyhedron.

The polyhedron has different faces which are each polygons. Each of these polygons can include the same number of edges and therefore the same number of vertices. In the example of the , polyhedron 7 is a cube comprising a total of 12 edges and 8 vertices. The cube has 6 faces which are all squares, each square having 4 edges and 4 vertices.

The polyhedron can therefore have one and only one type of polygon on each of these sides: triangle with 3 sides, quadrilateral with 4 sides, pentagon with 5 sides, etc.

The number of faces of the polyhedron is greater than or equal to 4. This number does not depend on the type of polygon that forms the faces of the polyhedron. For example, the polyhedron can have triangular faces and include 4 faces as in the case of a tetrahedron or 8 faces as in the case of an octahedron.

The polyhedron is not necessarily regular. In other words, the polygons forming the faces of the polyhedron are not necessarily all identical. The arms of the core do not necessarily all have the same axial length.

The magnetic core further comprises junction parts, referenced 81 to 89 in , located at the vertices of the polyhedron. More precisely, at each vertex of the polyhedron there is one and only one connecting piece. These junction parts are preferably made of ferrite, and in particular of spinel ferrite.

Each junction piece is contiguous to the ends of at least three of the arms of the magnetic core. Each of these ends is an axial end, that is to say an end of the arm in the direction of the main axis of the cylinder of the arm. The junction part is contiguous to an arm via an axial end of an arm means that the junction part is monolithic with the arm or in direct contact with the arm according to this end or even glued to the arm along this end.

A polyhedron has at least four faces. A vertex of a polyhedron connects at least three different edges. For a polyhedron comprising more than four faces, a vertex of the polyhedron can connect more than three different edges. Each connecting piece located at a vertex of the polyhedron is contiguous to the ends of each of the arms associated with the edges which are connected by the vertex, that is to say it is contiguous to the ends of at least three arms.

A core as we have just explained therefore has a three-dimensional shape corresponding to a polyhedron, each arm of the core corresponding to an edge of the polyhedron.

The polyhedron structure makes it possible to define as many closed magnetic circuits as there are closed polygons in the polyhedron. Each of these polygons corresponds in the core to a succession of ferrite arms and ferrite junction pieces contiguous to each other, this succession forming a closed mesh of magnetic material.

Each arm can be the seat of a magnetic coupling between two conductive wires wound around the arm. More generally, it may be possible to couple two windings of conductive wire which are located around different arms, such as arms connected by the same junction piece or even arms more spatially distant from each other in the core.

The convex polyhedron structure of the magnetic cores presented here allows a wide variety of shapes of these cores. Such a core can couple many different electrical windings and with different coupling strengths. It is thus possible to produce within a single magnetic core different magnetic couplings which in the prior art would require a plurality of magnetic cores.

Each arm can fulfill a particular function, such as for example magnetic coupling between two windings wound around the arm or even cooling of the arm and therefore more generally of the magnetic core. The core can thus perform a plurality of functions, these functions being carried out in locations spatially separated from each other so that it is possible to implement these functions independently of each other. In particular, this implementation is carried out more independently than in the case of a two-dimensional kernel. The core presented here ultimately makes it possible to perform more functions than in the prior art and this in a smaller spatial volume and more independently of each other.

Furthermore, a magnetic core in the form of a three-dimensional assembly of arms makes it possible to implement topological optimization. Such a core defines a structure comprising empty zones while exhibiting significant absorption of mechanical vibrations, in particular mechanical vibrations linked to magnetic resonance. The structure fulfills its magnetic function or its magnetic functions, while having both a lower weight thanks to the empty zones and at the same time good mechanical strength.

Magnetic core arm types

The arms of the magnetic core can be of different types.

According to a first type and in relation to Figures 2 and 3, an arm 301 can be a solid ferrite cylinder which extends along a main axis A. In other words, the arm 301 does not have any hollow or cavity so that the arm defines a cylinder volume entirely filled with magnetic material. There is a radial section of the arm, that is to say a section in a plane orthogonal to the main axis A. The is an axial section of the arm, that is to say a section along a plane which contains the main axis A.

A solid arm of this first type is particularly suitable for producing a strong magnetic coupling between two electric wires wound around this arm. A magnetic core as presented above can include one or more arms of this first type. All the arms of the core can be of this type.

According to a second type and in relation to Figures 4 and 5, an arm 303 can have a closed housing 9, the housing 9 being centered on the axis A of the cylinder 303, the axis A passing through the housing 9. The arm comprises an internal wall which defines the closed housing 9, that is to say that the closed housing 9 is not in fluid communication with the exterior of the arm. In other words, the housing 9 is included - that is to say enclosed - in a full ferrite volume which defines the arm 303. The internal wall can have the shape of an internal cylinder centered on an axis which coincides with the main axis A of cylinder 303. The internal cylinder can be of circular section. Housing 9 is centered on axis A and axis A passes through housing 9. In other words, there is a central zone in the arm surrounding axis A which is not occupied by the material of the arm. Housing 9 is surrounded by arm material. In the radial directions which start from axis A outwards, the thickness of the material of the arm which surrounds the housing is substantially the same in all these different radial directions. The thickness of the arm defined between the internal wall and the external wall of the cylinder is greater than or equal to 500 µm. When the arm and the internal wall each have the shape of a cylinder centered on the main axis A of the cylinder, they define radii whose difference is greater than or equal to 500 µm.

Housing 9 contains a material 10 chosen from a phase change material and an amorphous or nanocrystalline material.

When the housing 9 comprises a phase change material, the arm of this second type is particularly adapted to filter temperature peaks. The phase change material is chosen to be solid at the nominal operating temperature of the core, but liquid beyond that. The latent heat of the material requires that significant thermal energy be supplied or removed from the material to leave this temperature level, which imposes a constant temperature on the system during this phase change, lower than that of the peak. Therefore, rapid variations in core temperature can be absorbed locally and smoothed out by repeated phase changes of the material.

When the housing comprises an amorphous or nanocrystalline material, the arm of this second type is particularly adapted to increase the magnetic permeability of the arm. This is particularly relevant if the core is used with alternating signals in certain frequency ranges. Typically in the range of a few tens of kiloHertz to a few hundred kiloHertz, ferrite cores can have a magnetic induction of less than 0.5 Tesla. The presence of the amorphous or nanocrystalline material reinforces the magnetic induction of the “arm + material in the housing” assembly. It is also possible by adding the material in the housing, to reduce the size of the core necessary to achieve a certain magnetic induction. This additional degree of freedom makes it possible to achieve an identical magnetic function with a smaller radial dimension of the arm. Certain space requirements and/or integration constraints can thus be more easily respected.

A magnetic core as presented above can include one or more arms of this second type. All the arms of the core can be of this second type.

According to a third type and in relation to Figures 6 and 7, an arm 302 can be crossed by a passage 11 opening out of the arm at each end of the arm. In other words, passage 11 extends inside the arm along axis A from one axial end to the other. Passage 11 is centered on axis A of the cylinder, the axis passing through passage 11.

The arm 302 has a hollow cylinder structure, defining an internal wall 13 and an external wall 14. These walls 13 and 14 are preferably concentric and of the same shape defining a uniform ferrite thickness.

The passage 11 is defined by an internal wall 13. The internal wall 13 can have a cylindrical shape centered on the axis A, and in particular a cylindrical shape with a circular section. The thickness of the arm defined between the internal wall 13 and the external wall 14 is greater than or equal to 500 µm. When the arm and the internal wall each have the shape of a cylinder centered on the main axis A of the cylinder, they define radii whose difference is greater than or equal to 500 µm.

A hollow arm of this third type is particularly suitable for passing a cooling fluid through the opening passage so as to cool the arm and more generally the core. A magnetic core as presented above can include one or more arms of this third type. All the arms of the core can be of this type.

According to a fourth type and in relation to Figures 8 and 9, an arm 304 can comprise two internal walls 17 and 19 facing one another, the two walls 17 and 19 defining between them a passage opening 15 out of the arm at each end of the arm. In other words, passage 15 extends inside the arm along axis A from one axial end to the other.

In this fourth type, the arm includes a single through passage which is defined by two different walls facing each other.

A first internal wall 17 is located radially outside the second internal wall 19, so that the first internal wall 17 surrounds the second internal wall 19.

Passage 15 is centered on axis A of the cylinder, but axis A does not pass through passage 15. In other words, arm 304 has a central part 16 which is located radially inside the second internal wall 19 The second internal wall 19 is included in the central part 16 and delimits the central part 16. The central part 16 is solid and is crossed by the axis A. The opening passage 15 extends radially around this central part 16. The opening passage 15 separates the central part 16 from a peripheral part 18 of the arm 304. The peripheral part 18 extends radially outwards from the first internal wall 17. The first internal wall 17 is included in the. peripheral part 18 and delimits the peripheral part 18. To fix the central part 16 and the peripheral part 18, the arm 304 can comprise at least one spacer E which extends in a radial direction from the central part 16 to the part peripheral 18 or in other words from the second internal wall 19 to the first internal wall 17. Preferably, the arm comprises at least two spacers E, distributed at different heights and at different angles in the radial plane. The spacers E have for example the shape of a rod or beam, the spacers not extending over the entire axial length of the arm 304. The spacers can be distributed over the axial length of the arm 304 and/or radially around the axis of the cylinder.

The opening passage 15 allows fluid circulation, between the peripheral part 18 and the central part 16. In this passage 15 the spacers do not hinder the fluid circulation.

There represents a radial section of the arm 304 along a plane of a magnetic core in which there are two spacers.

There represents an axial section of the arm 304 along a plane not intersecting the spacer(s), the passage 15 thus appears as a continuous ring around the central part 16 of the arm.

The first internal wall 17 and the second internal wall 19 may have a cylindrical shape centered on the axis A, and in particular a cylindrical shape with a circular section. The opening passage 15 then has an annular section. The radial dimension of each of the central part 16, the peripheral part 18 and the through passage 15 is greater than or equal to 500 µm. When the arm and the internal walls 17 and 19 each have the shape of a cylinder centered on the main axis A of the cylinder, the arm and the internal wall 17 define radii whose difference is greater than or equal to 500 µm and the internal walls 17 and 19 define radii whose difference is greater than or equal to 500 µm. In this preferred mode the peripheral part 18 is an outer hollow cylinder and the central part 16 is an inner cylinder. The opening passage 15 allows fluid circulation between the outer hollow cylinder 18 and the inner cylinder 16. These cylinders are secured by at least one spacer E. The spacer E or the spacers E extend radially between the outer wall 19 of the inner cylinder 16 and the inner wall 17 of the outer cylinder 18. Structurally, the outer hollow cylinder 18, the inner cylinder 16 and the spacers E can be formed in one piece by additive manufacturing. The two walls 17 and 19 face each other and define the opening passage 15. In this passage the spacers do not hinder the fluid circulation.

A hollow arm of this fourth type is particularly adapted to pass a cooling fluid through the opening passage 15 so as to cool the arm and more generally the core. A magnetic core as presented above can include one or more arms of this fourth type. All the arms of the core can be of this type.

It should be noted that we can combine the characteristics of an arm of the second type and the characteristics of an arm of the fourth type in an arm of a fifth type. According to this fifth type and in relation to Figures 10 and 11, an arm 306 can comprise on the one hand the two internal walls 17 and 19 facing each other, the two walls 17 and 19 defining between them the opening passage 15 and on the other hand the closed housing 9, the housing 9 being centered on the axis A of the arm 306, the axis A passing through the housing 9. In other words the closed housing 9 is located inside the central part 16. The housing 9 is surrounded by the second internal wall 19. The thickness - measured in a radial direction - of material of the arm between the housing 9 and the second internal wall 19 is greater than or equal to 500 µm. When the arm and the housing 9 each have the shape of a cylinder centered on the main axis A of the cylinder, the arm and the housing 9 define radii whose difference is greater than or equal to 500 µm.

A hollow arm of this fifth type makes it possible to produce simultaneously or separately the technical effects associated with the arms of the second type and the fourth type. A magnetic core as presented above can include one or more arms of this fifth type. All the arms of the core can be of this type.

According to a sixth type and in relation to Figures 12 and 13, an arm 305 can comprise two internal walls 25 and 27, each internal wall defining a passage opening out of the arm at each end of the arm, the axis of the cylinder not passing through neither passage. In other words :

the first internal wall 25 defines a first passage 21 which extends inside the arm along the axis A from one axial end to the other,

the second internal wall 27 defines a second passage 23 which extends inside the arm along the axis A from one axial end to the other, and

the axis of cylinder A passes neither through the first passage 21 nor through the second passage 23.

In this sixth type, the arm includes two different opening passages, each passage being through a single wall. The arm therefore comprises two different walls which each define an opening passage.

The arm 305 has a central part 26 which is located radially between the first internal wall 25 and the second internal wall 27. The central part 26 is solid, that is to say made of ferrite, and it is crossed by the axis HAS.

The first internal wall 25 and the second internal wall 27 extend radially around the central part 26 over angular sectors of an extent less than or equal to 180°. The first internal wall 25 and the second internal wall 27 can be symmetrical with respect to each other with respect to the main axis A of the arm 305. For example, each of the internal walls 25 and 27 has in radial section a circular part centered on the axis of the cylinder and a rectilinear part which connects the two ends of the circular part, each of the internal walls being generated by translation of this radial section by a translation along the main axis A of the arm 305. In a another example, each of the internal walls 25 and 27 has an elliptical shape in radial section, each of the internal walls being generated by translation of this radial section by a translation along the main axis A of the arm 305.

In a preferred mode of the sixth type of arm, the first internal wall 25 and the second internal wall 27 each have two parts of cylindrical shape centered on the axis A, the two parts facing each other. The first passage 21 and the second passage 23 then have a radial section which has the shape of a ring portion.

The arm 305 has in the preferred mode a peripheral part 28 which is located radially around the first internal wall 25 and the second internal wall 27.

In the preferred mode, the opening passages 21 and 23 are located between the central part 26 and the peripheral part 28 of the arm 305. The central part 26 and the peripheral part 28 are connected to each other by two partitions C which extend in a radial direction from the central part 26 to the peripheral part 28. The partitions C extend over the entire axial length of the arm 304. The partitions C separate the opening passages 21 and 23, so that on the entire axial length of the arm 304, a fluid cannot pass from one opening passage to the other. The partitions C then define part of the internal walls 25 and 27. Each internal wall in the preferred mode is formed of a part of the surface of each of the two partitions C and the two parts of cylindrical shape centered on the axis A in facing each other, the two parts being for each internal wall connected by the two partitions.

The radial dimension of each of the central part 16, the peripheral part 18 and the opening passages 21 and 23 is greater than or equal to 500 µm. When the central part 16 and the peripheral part 18 each have the shape of a cylinder centered on the main axis A of the cylinder, the central part 16 and the peripheral part 18 define radii whose difference is greater than or equal to 1 millimeter .

A hollow arm of this sixth type is particularly adapted to pass two flows of cooling fluid through the two opening passages 21 and 23 so that each opening passage is crossed by a flow of fluid. This makes it possible to implement cooling of the arm using two separate fluids or one fluid which passes twice through the arm. A magnetic core as presented above can include one or more arms of this sixth type. All the arms of the core can be of this type.

It should be noted that we can combine the characteristics of an arm of the second type and the characteristics of an arm of the sixth type in an arm of a seventh type. According to this seventh type and in relation to Figures 14 and 15, an arm 307 can comprise on the one hand the two internal walls 25 and 27, each internal wall defining a passage opening out of the arm at each end of the arm, the axis of the cylinder not passing through either of the two passages and on the other hand the closed housing 9, the housing 9 being centered on the axis A of the arm 307, the axis A passing through the housing 9. In other words the closed housing 9 is located inside the central part 26. The thickness - measured in a radial direction - of material of the arm between the housing 9 and the opening passages 21 and 23 is greater than or equal to 500 µm.

A hollow arm of this seventh type makes it possible to produce simultaneously or separately the technical effects associated with the arms of the second type and the sixth type. A magnetic core as presented above can include one or more arms of this seventh type. All the arms of the core can be of this type.

Cooling fin

Optionally for arms of the third type, the arm may further comprise a fin which extends from the internal wall inside the passage, the fin being configured to increase a heat exchange surface area between the arm and a fluid passing through the passage.

In the case where a fin is included in one of these arms, it extends into the passage emerging from the arm or at least into at least one of the two passages emerging from the arm, the fin extending from of the wall or one of the two walls which defines the passage. The fin therefore projects from an internal wall of the arm towards the inside of the passage.

In a first embodiment of the cooling fin, and with reference to Figures 4 and 5, the arm 302 of the third type comprises a fin 12 which extends from the internal wall 13 inside the passage 11 Here the fin 12 takes the shape of a rectangular parallelepiped which extends in the direction of the axis of the cylinder over the entire axial length of the arm 302 and is located radially in the same angular sector of the cylinder over this entire length. .

In a second embodiment of the cooling fin, and in relation to Figures 16 and 17, the opening passage is a primary passage and the arm 302 of the third type houses a hollow sleeve 70 inside this first passage. The hollow sleeve 70 has an interior wall 71 defining a secondary passage 72 narrower than the first passage. The secondary passage 72 opens out of the arm at each end of the arm 302. The secondary passage 72 extends inside the arm along the axis A from one axial end to the other. The secondary passage 72 is centered on the axis A of the cylinder, the axis passing through the secondary passage. The hollow sleeve 70 has an outer wall which is adjusted to the shape of the inner wall 13 of the arm 302. The inner wall 71 of the hollow sleeve is preferably concentric with the inner wall 13 and of the same shape defining a uniform thickness. The interior wall of the hollow sleeve may have a cylindrical shape centered on axis A, and in particular a cylindrical shape with a circular section. The thickness of the hollow sleeve defined between the internal wall 13 and the internal wall of the hollow sleeve is greater than or equal to 500 µm. Preferably, the hollow sleeve 70 is made of ferrite.

In this second embodiment of the cooling fin, the hollow sleeve comprises a fin 12 which extends from the interior wall inside the secondary passage. Here the fin 12 takes the shape of a rectangular parallelepiped which extends in the direction of the axis of the cylinder over the entire axial length of the arm 302 and is located radially in the same angular sector of the cylinder over this entire length.

Common to both embodiments, the fin can take different shapes, it can extend in different directions in the primary or secondary passage, for example helically around the axis of the cylinder. The fin can also extend over only a portion of the axial length of the arm, for example the fin can extend over half or a quarter of the axial length of the primary or secondary passage.

The fin is configured to increase a heat exchange surface area between the arm and a fluid flowing in the primary or secondary passage. In this way, the cooling of the core by the fluid is greater.

When the magnetic core comprises an arm of the third type, the core can be connected to an external cooling system so that a fluid allowing cooling circulates in the opening passage(s), primary or secondary. The junction parts are then chosen to allow the passage(s) leading to the external cooling system to be connected. The fluid can be water or any other heat transfer fluid. Cooling water can optionally be loaded with nanoparticles (graphene, carbon nanotubes) in order to increase its thermal conductivity.

The cooling fluid can be set in motion using an external pump and connected to the core. The fluid can be cooled using at least one external heat exchanger. The external cooling system then includes the pump and the heat exchanger.

Junction parts

The connecting pieces located at the vertices of the polyhedron make it possible to connect the different arms of the core and ensure that the core is held in all three dimensions.

For this purpose, a junction part has a shape adapted to the number of arms with which it is in contact. A junction part may have one or more flanges whose dimension is adjusted to the dimensions of the arms in contact with the junction part. Each collar defines a housing which allows one of the arms to be received. Each arm can thus be retained at the junction piece.

A connecting room can be solid, that is to say, contain no housing or be crossed by any passage.

In addition to this junction role, a junction part can also fulfill fluid connection functions when the core contains one or more arms crossed by an opening passage. In this case the junction piece is not full.

To fulfill a fluidic connection function in a junction part, the magnetic core comprises an arm crossed by an opening passage, or first opening passage, the arm being contiguous to a junction part, the junction part comprising an internal conduit in communication fluidic with the opening passage.

This internal conduit can open outside the magnetic core. In this first case, the junction part allows a fluid to circulate between the outside and the inside of the core.

If the internal conduit does not open outside the magnetic core, then the internal conduit is in fluid communication with a second emerging passage different from the first emerging passage, the second emerging passage passing through the arm or another arm contiguous to the junction piece. In this second case, the junction part makes it possible to circulate a fluid inside the core between two different through passages.

Air gap

A core as presented above can include an air gap, that is to say that one of the arms of the core and a connecting piece of the core contiguous to the arm comprise two faces, the two faces are extending perpendicularly to the axis of the cylinder, the material located between the two faces being non-magnetic. The cylinder corresponds to the arm of the core mentioned above. The air gap is the space located between the two faces and which does not include magnetic material.

The air gap can in particular correspond to a bonding strip or an empty or air-filled space.

The air gap allows the core to deform by thermal expansion or contraction due, for example, to a temperature variation during assured magnetic coupling within the core. The air gap corresponding to a space more elastic than the rest of the core allows the deformation of the core without breaking the core.

The air gap corresponding to an empty space can make it easier to place a coil of electrical wire around the arm.

The two faces which define the air gap between them can both be included in the arm.

Process for manufacturing a magnetic core

Generally speaking, the core can be produced as just described using additive manufacturing techniques without melting and in particular using binder jet printing and molten material deposition printing.

Binder Jetting is also known by the English name “Binder Jetting”. This method consists of spraying a liquid adhesive binder onto thin layers of powder material, in this case spinel ferrite powder.

Fused deposition printing is also known by the English name “Fused Filament Fabrication” abbreviated to FFF. This method includes mixing the powder with a polymer binder, then the printing itself. The polymer must then be removed in a step called thermal debinding.

The core as explained previously can be produced by additive manufacturing in a single block or in several elements. When several elements are manufactured, they are then assembled in an appropriate manner using all known techniques, including bonding, screwing, sintering, co-sintering.

Sintering a part increases its density. Sintering makes it possible to reduce porosity within the sintered parts. For example, we can carry out sintering which increases the density of the parts up to 90% of the density of the material which composes it, or for example here 90% of the density of the spinel ferrite ceramic which composes the parts. The sintering operation is accompanied by a contraction or shrinkage of the sintered part, that is to say that in all three dimensions the size of the part is reduced. This shrinkage can be taken into account in a preliminary stage of computer-aided design of the part.

Additive manufacturing techniques can be applied to manufacture in a single piece a core comprising an arm with an through passage, that is to say an arm of the third type, the fourth type or the sixth type, if this through passage is in communication with the outside of the core via conduits located in junction parts.

For the arms of the fourth type, the E spacers can be produced by additive manufacturing. Structurally, the outer hollow cylinder 18, the inner cylinder 16 and the spacers E can be formed in one piece by this type of manufacturing. The two walls 17 and 19 face each other and define the opening passage 15. In this passage the spacers do not hinder the fluid circulation.

For the arms of the sixth type, the C partitions can be produced by additive manufacturing.

Process for manufacturing a magnetic core having a chamber

In connection with the , we now present a method of manufacturing a magnetic core 1.

In a first step of manufacturing the core 1, a first part 73 of the core is printed, this first part 73 comprising an arm 75, 76 or 77, the arm having an open chamber 79, 110 or 111.

Arm 75, 76 or 77 corresponds to the arms as we have been able to describe them until now. In particular, the arm forms a straight cylinder and it is intended to be included in a plurality of arms of the magnetic core, the plurality of arms being arranged along edges of a convex polyhedron.

The term “chamber” is understood here as a niche or recess in the core arm. The chamber is open, meaning that the interior of the chamber is in communication with the exterior of the core.

• un passage débouchant d’un bras 75 ou 76 du troisième type, ou
• un logement fermé d’un bras 77 du deuxième type, du cinquième type ou du septième type.

Compared to the types of arms described previously, the chamber can correspond at least in part to:

• a passage emerging from an arm 75 or 76 of the third type, or
• a closed housing of an arm 77 of the second type, fifth type or seventh type.

During a second step, a second part 74 of the magnetic core is printed, this second part 74 comprising a junction part 112, 113 or 114.

The junction part 112, 113 or 114 corresponds to the junction parts as they have been described so far. In particular, the junction part is intended to be included in a plurality of junction parts of the magnetic core, each junction part being located at a vertex of the polyhedron.

The printing of the first part and the second part can be carried out using different additive manufacturing techniques. Preferably, they are made from a spinel ferrite powder by jet of binder or by deposition of molten material.

Materials called ferrite or “spinel ferrites” are magnetic ceramics. These are magnetic oxides of the MeFe ₂ O ₄ type, the term “Me” designating an alloy metal such as MnZn, NiZn, etc. It is possible to add copper or other metals to this alloy. This addition allows additional specificities. These ceramics have high melting temperatures.

The advantage of using spinel manufacturing by binder jet or by deposition of molten material is due to the fact that it is not possible to use manufacturing processes with fusion in the case of ferrite, in particular because of the states necessary surface area and the nature of the materials (volatilization of zinc in ferrites).

Each of these processes is an additive manufacturing process. The use of this type of process has the following advantages in particular:

- a deposition of the magnetic material, and in particular of spinel ferrite, layer by layer making it possible to adjust the quantity of material used,

- the application of the process to the field of signal electronics and power electronics,

- the absence of machining: we speak of a “net-shape” process (also known as “ net-shape ”) in which all of the – or almost all of – the material used is part of the final part,

- the absence of melting of material, which makes it possible to avoid changes in the chemical composition of the ferrites and cracking of the part during printing, and

- the possibility of producing “non-mouldable” shaped cores, such as for example shapes with internal cavities; a “demouldable” shape is a part shape that can be obtained by a part molding process; a “non-mouldable” shape is a part shape that cannot be obtained by a part molding process.

During a third step, an element 115, 116 or 117 is inserted into the chamber.

During a fourth step, the first part 73 and the second part 74 are fixed so that the junction piece 112, 113 or 114 encloses the element 115, 116 or 117 in the chamber 79, 110 or 111.

The junction piece 112, 113 or 114 is fixed to the arm 75, 76 or 77 containing the chamber 79, 110 or 111. The junction piece 112, 113 or 114 and the arm 75, 76 or 77 are fixed contiguous to one another. to the other. With this attachment, the magnetic core is formed more completely so that

- the arm 75, 76 or 77 is included in a plurality of arms of the magnetic core, the plurality of arms being arranged along the edges of a convex polyhedron, and

- the junction part 112, 113 or 114 is included in a plurality of junction parts of the magnetic core, each junction part being located at a vertex of the polyhedron.

Inserting an element into the chamber and then enclosing the element in the chamber by attaching the second part to the first part makes it possible to functionalize the core in the chamber area. Depending on the nature of the inserted element, this allows greater freedom of shape of the core obtained allowing in particular the optimization of the size of the cores, the optimization of the integration of the cores and the implementation of additional functions to the magnetic function, such as for example a cooling function of the core through the through passage.

When the printing of the first part and the second part is carried out from a spinel ferrite powder by jet of binder or by deposition of molten material, the manufacturing allows greater freedom in the shape of the core obtained because according to in the prior art the magnetic materials forming the core, such as spinel ferrites, are difficult to machine, particularly on small dimensions.

According to a first mode of implementation of the method, the element can be chosen from an element made of phase change material, an element of amorphous material, and an element of nanocrystalline material.

This first mode corresponds in to the arm 77 presenting the housing 111 in which is inserted a cartridge 117 of a phase change material or of an amorphous material, or of a nanocrystalline material.

The arm 77 in the core once manufactured then corresponds to an arm of the second type, the fifth type or the seventh type. This arm 77 has a closed housing which corresponds to the chamber 111 once it has been closed by the junction piece 114 of the second part 74. The closed housing of the arm 77 enclosing a cartridge of a phase change material or an amorphous material, or a nanocrystalline material can fulfill different functions which have been presented previously in relation to the arms of the second type.

According to a second mode of implementation of the method, the element is a hollow ferrite tube 115, 116 comprising an internal wall and at least one fin 118, 119 which extends radially inside the tube 115, 116 from the internal wall.

This second mode corresponds in to the arms 75 and 76 having respectively the housings 79 and 110 in which the hollow tubes 115 and 116 are inserted. The hollow tube 115 is traversed on its internal wall by a fin 118 in a helical trajectory around the axis of the arm 75. The hollow tube 116 is traversed on its internal wall by a fin 119 along a rectilinear trajectory parallel to the axis of the arm 76.

The arm 75 of the first part 73 is fixed to the junction piece 112 of the second part 74. The arm 76 of the first part 73 is fixed to the junction piece 113 of the second part 74.

The arms 75 and 76 in the core once manufactured then correspond to arms of the third type. These arms 75 and 76 are crossed by an through passage extending along the axis of the cylinder of the arm from one end to the other of the arm. The initial chambers of the arms 75 and 76 are therefore open on both sides of the cylinders formed by the arm. The element inserted in each chamber of arms 75 and 76 is a hollow ferrite tube which corresponds to a hollow sleeve. In this way, the arms 75 and 76 correspond to the second embodiment of the fin as presented previously.

Core 1 represented in allows the circulation of a fluid through a channel 123 which passes through the junction parts 112, 120, 122 and 113 as well as the arms 75, 121 and 76. The junction parts 112 and 113 are each crossed by a conduit which makes channel 123 communicate with the outside of the core. The secondary passages of the arms 75 and 76 in which the fins 118 and 119 extend form part of the channel 123. The junction pieces 120 and 122 are each crossed by an internal conduit which communicates the secondary passage of one of the arm 75, 76 with the passage opening out to arm 121.

As an option, when the printing of the first part and the second part is carried out by binder jet, the process comprises, before the insertion step, a step of removing powder grains separated from the core. In particular, the chamber being open, the powder grains separated from the core located in the chamber can be taken out of the chamber towards the outside of the core. This operation is called “depowdering” and makes it possible to obtain a single piece for the first part and the second part without any residue that could come off.

In the case where the printing of the first part and the second part is carried out from a spinel ferrite powder by jet of binder or by deposition of molten material and that the element 117 is chosen from an element made of material phase change, an element made of amorphous material, and an element made of nanocrystalline material, the method advantageously comprises before the insertion step a step of sintering the first part and the second part, the fixing then being carried out by gluing or screwing.

Sintering the first part and the second part makes it possible to increase the density. Sintering makes it possible to reduce porosity within the sintered parts. For example, we can carry out sintering which increases the density of the parts up to 90% of the density of the material which composes it, or for example here 90% of the density of the spinel ferrite ceramic which composes the parts.

The sintering operation is accompanied by a contraction or shrinkage of the parts, that is, in all three dimensions the size of the first part and the second part is reduced. This removal is taken into account in a preliminary computer-aided design step.

The first part and the second part are sintered separately. Once this densification has been achieved, the element is introduced into the chamber then the two parts are fixed so as to enclose the element. For this attachment, the two parts can be glued, screwed, or both.

In the case where the printing of the first part and the second part is carried out from a spinel ferrite powder by binder jet and the element 116, 117 is a hollow tube, the method preferably comprises manufacturing by stereolithography of the hollow tube, and preferably the fixation is carried out by co-sintering.

Manufacturing the hollow tube by stereolithography (SLA) makes it possible to achieve better resolution in the hollow tube obtained, and in particular for the fin 118, 119.

The co-sintering operation consists of placing the hollow tube in the chamber, the first part and the second part against each other and then carrying out a sintering operation on all of these parts arranged together.

As a variant in this same case, the hollow tube can be produced by a technique other than stereolithography, for example by binder jet, and the fixing can be carried out by co-sintering.

As an option for the various implementations of the process presented so far, the process may further comprise a densification step by flash sintering (also known by the English expression " Spark Plasma Sintering " abbreviated as SPS) following the one of the sintering steps or instead of one of these. This densification step makes it possible to densify the ferrite material to a greater density than with a sintering step. The density of the core can reach up to 98% of the density of the material which composes it, for example 98% of the density of the spinel ferrite ceramic which composes the material. Flash sintering also makes it possible to maintain a fine grain size for the ferrite. A suitable flash sintering or SPS cycle can be as follows: temperature between 1000°C and 1300°C maintained for 5 to 20 minutes under a uniaxial pressure of 30-70 MPa.

Fabrication of a core including an air gap

During the process that we were able to present above, the step of fixing the first part and the second part can be carried out by gluing. In this case, the arm of the first part and the junction part of the second part are not necessarily in direct contact. The arm and the connecting piece can be separated and held together with a layer of glue. This thickness of glue then corresponds to an air gap in the form of a bonding strip as presented previously.

As an option for the different implementations of the process presented so far, the following steps can also be planned:

- the printing of the first part 73 is configured so that the arm 75, 76, 77 of the first part is a first arm 75, 76, 77, the first part comprising a first portion 78A of a second arm 78 of the plurality of arms of the magnetic core, the first portion 78A being full,

- the printing of the second part 74 is configured so that the second part 78A comprises a second portion 78B of the second arm 78, the second portion 78B being full, and

- the fixing of the first part and the second part is configured to place the first portion and the second portion facing each other along two faces 78C, 78D extending perpendicularly to an axis of the cylinder corresponding to the second arm, the material located between the two faces 78C, 78D being non-magnetic.

These steps are illustrated in relation to the arm 78 of the . The arm 78 is formed of a first portion 78A initially included in the first part 73 and of a second portion 78B initially included in the second part 74. The axial length, that is to say along the axis of the cylinder corresponding to the arm 78, of each of the first portion 78A and the second portion 78B is less than the axial length of the arm 78, measured between the junction pieces located at the ends of the arm 78, the junction pieces 122 and 126 in . More precisely, the sum of the axial length of the first portion 78A and the axial length of the second portion 78B is also less than the axial length of the arm 78. In this way, a space separates the first portion 78A and the second portion 78B.

The first portion 78A has a face 78C perpendicular to the axis of the cylinder of the arm 78.

The second portion 78B has a face 78D perpendicular to the axis of the cylinder of the arm 78.

The two faces 78C, 78D are located opposite each other, with a gap corresponding to the difference between on the one hand the axial length of the arm 78 and on the other hand the sum of the axial length of the first portion 78A and the axial length of the second portion 78B.

The space between the faces can be left empty or glue can be placed there.

In this method implementation option, it is possible to position an air gap within one or more arms depending on the desired magnetic circuit.

Claims (10)

Process for manufacturing a magnetic core (1), the process comprising:
- an impression of a first part (73) of the magnetic core (1) comprising an arm (75, 76, 77), the arm (73) having an open chamber (79, 110, 111),
- an impression of a second part (74) of the magnetic core comprising a junction piece (112, 113, 114),
- an insertion of an element (115, 116, 117) in the chamber, and
- fixing the first part and the second part so that:
-- the junction piece locks the element in the chamber,
-- the arm is included in a plurality of arms of the magnetic core, the plurality of arms being arranged along edges of a convex polyhedron, each arm forming a right cylinder, and
-- the junction part is included in a plurality of junction parts of the magnetic core, each junction part being located at a vertex of the polyhedron. Method according to claim 1 in which the element is chosen from:
- an element made of phase change material,
- an element made of amorphous material,
- an element made of nanocrystalline material, and
- a hollow ferrite tube (115, 116) comprising an internal wall and at least one fin which extends radially inside the tube from the internal wall. Method according to any one of claims 1 to 2 in which the printing of the first part and the second part is carried out from a spinel ferrite powder by jet of binder or by deposition of molten material. Method according to claim 3 in which the printing of the first part and the second part is carried out by binder jet, the method comprising before the insertion step a step of removing grains of powder separated from the core. Method according to claim 3 in which the element (117) is chosen from an element made of phase change material, an element of amorphous material, and an element of nanocrystalline material, the method comprising, before the insertion step, a step sintering of the first part and the second part, the fixing being carried out by gluing or screwing. Method according to claim 4 in which the element (115, 116) is a hollow tube, the method comprising manufacturing the hollow tube by stereolithography, and preferably the fixing is carried out by co-sintering. Method according to claim 4 in which the element (115, 116) is a hollow tube, the fixing being carried out by co-sintering and preferably the method comprises manufacturing by stereolithography of the hollow tube. Method according to any one of claims 1 to 7 in which
- the printing of the first part (73) is configured so that the arm (75, 76, 77) of the first part is a first arm (75, 76, 77), the first part comprising a first portion (78A) a second arm (78) of the plurality of arms of the magnetic core, the first portion (78A) being full,
- the printing of the second part (74) is configured so that the second part (78A) comprises a second portion (78B) of the second arm (78), the second portion (78B) being full, and
- the fixing of the first part and the second part is configured to place the first portion and the second portion facing each other along two faces (78C, 78D) extending perpendicularly to an axis of the cylinder corresponding to the second arm, the material located between the two faces (78C, 78D) being non-magnetic. Method according to claim 8 in which the material located between the two faces comprises glue. Magnetic core obtained by a process according to any one of claims 1 to 9.