Method for producing a permanent magnet and permanent magnet in GBD design

Abstract

The invention relates to a method for producing a permanent magnet, in which a magnetic material (18) is filled layer by layer into a sintering mold (12), wherein the respective layers of the magnetic material (18) are separated from one another by respective separating layers (20), and the permanent magnet is produced by sintering the multiple layers of the magnetic material (18) in the sintering mold (12).

Description

The invention relates to a method for producing a permanent magnet and to a permanent magnet.U.S. Pat. No. 9,154,004 B2 discloses a magnet sintered from rare earths.Furthermore, U.S. Pat. No. 10,242,778 B2 discloses a production method for a rare earth magnet which is based on the heat treatment of a fine powder. In the manufacturing method, an alloy for the rare earth magnet is first roughly crushed and then finely crushed by a jet mill to obtain a fine powder. The fine powder is heated in vacuum or in an inert gas atmosphere at a temperature of 100 degrees Celsius to 1,000 degrees Celsius for six minutes to 24 hours. Then, the fine powder is compacted in a magnetic field and sintered in vacuum or under an inert gas atmosphere at a temperature of 950 degrees Celsius to 1,140 degrees Celsius, thereby obtaining a sintered magnet. Optionally, this magnet is subjected to grain boundary diffusion, which is also referred to as grain boundary diffusion.The object of the present invention is to provide a solution by means of which permanent magnets can be produced particularly easily and quickly.This object is achieved according to the invention by the subject matter of the independent claims. Further possible embodiments of the invention are disclosed in the dependent claims, the description and the figures. Features, advantages and possible configurations which are set forth in the context of the description for one of the subject matters of the independent claims are to be regarded at least analogously as features, advantages and possible configurations of the respective subject matter of the other independent claims and of each possible combination of the subject matters of the independent claims, optionally in conjunction with one or more of the dependent claims.The invention relates to a method for producing a permanent magnet. This permanent magnet is configured in particular to be used in a traction machine which is configured to drive a motor vehicle by means of electrical energy. For example, this permanent magnet can be used as part of a rotor of the traction machine. A permanent magnet is a permanent magnet which has a constant magnetic field without the need to use electrical power, as in an electromagnet. In the method, it is provided that a magnetic material, in particular a metallic alloy, is filled layer by layer into a sintering mold. In this case, the respective layers of the magnetic material are separated from one another by respective separating layers. By sintering the multilayer layers of the magnetic material in the sintering mold, at least one permanent magnet is produced. In this case, one or more permanent magnets can be produced simultaneously with a layer structure. Alternatively, a plurality of permanent magnets, each of which comprises only one layer of the magnetic material, can be produced simultaneously. The layer-by-layer configuration of the permanent magnet enables particularly low eddy current losses of an active part of an electric machine, in particular of the rotor, which active part has the permanent magnet, during operation.Permanent magnets are usually produced in large blocks (limited to the installation) by sintering. Subsequently, these large blocks of sintered magnetic material are separated mechanically and with high wear, in particular into respective layers or layers and subsequently several layers are assembled to form a permanent magnet.The method described for producing the permanent magnet enables a reduction in waste and wear compared to the production of permanent magnets from a block. In the method according to the invention for producing the permanent magnet, it is already defined, during the production of the green compact, by adjusting the heights of the respective layers of the magnetic material and arranging the separating layers between the layers of the magnetic material, how thick the respective layers of the layer structure of the permanent magnet are to be after the sintering process. As a result, it can be achieved that even after the sintering without further cutting, the permanent magnet having the layer structure has its predetermined shape. It is possible that the permanent magnet is divided after sintering in the stacking direction in which the respective layers of magnetic material are stacked on top of each other in the sintering mold to reach a predetermined base area of the permanent magnet. After sintering, the entire permanent magnet having the layered structure may be used or the respective layers of the magnetic material may be separated from each other at the respective separation layers and the individual layers of the magnetic material may be used as respective permanent magnets.In a possible development of the invention, it is provided that, for the arrangement of the respective separating layer, a layer of a separating material between the layers of the magnetic material is filled into the sintering mold. It is thus then possible to produce a plurality of permanent magnets simultaneously in a particularly simple manner during the sintering. It is possible that the resulting block is divided not at each separating layer but only at individual separating layers, whereby a plurality of permanent magnets, at least one of which has a layer structure, can be produced simultaneously during the sintering. The method enables one or more permanent magnets having a layer structure to be produced particularly quickly or a plurality of permanent magnets to be produced simultaneously by sintering and thus particularly quickly.In a possible development of the invention, it is provided that, for the arrangement of the respective separating layer, a layer of a separating material between the layers of the magnetic material is filled into the sintering mold. This means that a layer of the separating material is arranged one above the other in the stacking direction of the respective layers of the magnetic material between two layers of magnetic material directly adjacent to one another. In this case, the layer of the separating material completely covers at least the directly adjoining layer of the magnetic material having the smaller base area in the stacking direction towards the other adjoining layer of the magnetic material. This makes it possible to ensure that the respective layers of the magnetic material directly adjacent to one another are reliably separated from one another by means of the separating material, even after sintering. The separating material thus enables a particularly simple, reliable keeping of the respective layers of the magnetic material separated.In a further possible embodiment of the invention, it is provided that, for the arrangement of the respective separating layers between the respective layers of the magnetic material, a surface of the respective layers of the magnetic material is subjected to a processing step before the respective next layer of the magnetic material is introduced into the sintering mold, as a result of which a structural change of the respective layer of the magnetic material takes place at the surface thereof. This means that a first layer of the magnetic material is filled into the sintering mold. Subsequently, a free surface of this layer of the magnetic material is subjected to the processing step, whereby the magnetic material on this free surface is changed in its structure. This structural change serves to ensure that a further layer of the magnetic material filled onto this surface does not bond to the first layer of the magnetic material during sintering and that the two layers of the magnetic material directly adjoining one another are thus reliably separated from one another even during sintering and after sintering. By changing the structure of the respective surfaces of the layers of the magnetic material before the filling of a respective further layer of magnetic material, it is possible that the filling of a separating material for forming the respective separating layer is not absolutely necessary. As a result, with a given height of the sintering mold extending in the stacking direction, particularly many layers of magnetic material can be filled into the sintering mold and sintered, since filling of respective layers of separating material between the layers of magnetic material can be dispensed with. This enables that, within the scope of the method, the at least one permanent magnet can be produced with particularly many layers in its layer structure, or particularly many permanent magnets can be produced simultaneously.In this context, it can be provided in particular that at least the surface of the respective layers of the magnetic material is subjected to a temperature treatment in the respective processing step. This means that the structure of the magnetic material on the surface subjected to the processing step is changed by the temperature treatment, in particular by heating and / or cooling. This temperature treatment makes it possible to achieve the structural change of the surface of the magnetic material in a particularly simple manner.In a further possible embodiment of the invention, it is provided that the layers of the magnetic material are pressed together during sintering in the stacking direction in which the layers of the magnetic material are stacked on top of one another. In this case, the layers of the magnetic material can be pressed together, in particular by means of a punch which is pressed onto the layers of the magnetic material in the stacking direction. By means of the punch, the force with which the layers of the magnetic material are pressed against one another in the stacking direction can be adjusted particularly precisely and can be held reliably and constant for a predefined time interval. By pressing the respective layers of the magnetic material together, the magnetic material can be subjected to a pressure in a particularly reliable manner during the sintering, as a result of which the respective layers of the magnetic material solidify in a particularly reliable manner.In a further possible embodiment of the invention, it is provided that at least one heavy rare earth metal is introduced at least between the respective layers of the magnetic material, as a result of which this heavy rare earth metal diffuses at least partially into the respective layer of the magnetic material during a heat treatment phase of the sintering, in particular in a so-called grain boundary diffusion process. This process is also referred to as grain boundary diffusion. This is a collective term for the mass transport in a solid body via respective grain boundary paths of a crystal lattice. In the case of polycrystalline metals, the grain boundaries represent typical lattice order defect regions with a significantly reduced packing density or increased void concentration and are therefore predestined for the penetration and migration of impurity atoms in comparison with the undisturbed lattice. Grain boundary diffusion thus describes the diffusion path via which atoms in a material diffuse. In grain boundary diffusion, the atoms migrate via the grain boundaries into an adjacent grain. The method described thus makes it possible to produce a permanent magnet with at least one rare earth metal particularly quickly by the grain boundary diffusion process being carried out simultaneously with the sintering of the permanent magnet from the layers of the magnetic material. A heat treatment process of sintering thus leads on the one hand to bonding respective grains of the magnetic material to form a solid block and on the other hand to grain boundary diffusion of the at least one heavy rare earth material on the respective surfaces of the layers of the magnetic material to which at least one heavy rare earth metal has been introduced. The process of grain boundary diffusion of a heavy rare earth metal from the surfaces of the respective layers of the magnetic material toward the cores of the layers of the respective magnetic material enables a particularly high temperature resistance of the permanent magnet to be achieved when using particularly little of this heavy rare earth metal.In this connection, it can be provided in particular that each layer of the magnetic material is completely sheathed with a substrate comprising a heavy rare earth metal. This substrate may be, for example, a paste comprising a heavy rare earth metal. This paste can thus be introduced into the sintering mold, for example, and only then can the first layer of the magnetic material be filled. If the paste is applied both to a base of the sintering mold and applied to respective side walls of the sintering mold and the paste or the substrate is then arranged between the respective layers of the magnetic material, it can be ensured that each layer of the magnetic material is completely surrounded by the substrate. This allows a heavy rare earth metal to uniformly diffuse from an outer surface of each layer of the magnetic material toward the center of each layer of the magnetic material in the grain boundary diffusion process. Thus, uniform properties of the permanent magnet formed of one layer of the magnetic material or having the layered structure including the plurality of layers of the magnetic material can be obtained with respect to all outer sides.In a further possible embodiment of the invention, it is provided that the at least one heavy rare earth metal is part of the separating material. This means that for arranging the respective separating layer, the layer of the separating material between the layers of the magnetic material is filled into the sintering mold, wherein the separating material serves on the one hand for reliably separating the respective layers of the magnetic material and on the other hand comprises the at least one heavy rare earth metal, whereby it is ensured that the at least one rare earth metal is reliably introduced between the respective layers of the magnetic material and thus the magnetic material can diffuse via the respective surfaces of the layers into the respective layers of the magnetic material within the framework of the grain boundary diffusion process. At the same time, it is made possible for the sintering mold to be able to be filled with the magnetic material and the separating material alternately in layers particularly quickly and at the same time it is ensured that the heavy rare earth metal is reliably arranged between the layers of the magnetic material.In a further possible embodiment of the invention, it is provided that the magnetic material filled layer by layer into the sintering mold has the same composition in the respective layers. This ensures that the plurality of permanent magnets produced simultaneously or the plurality of layers of the at least one permanent magnet produced with the layer structure have the same properties, in particular the same magnetic properties. As a result, a constant high quality of permanent magnets can be achieved in the context of the method during production.The invention furthermore relates to a permanent magnet which has been produced in a method as has already been described in connection with the method according to the invention for producing a permanent magnet. In this case, the permanent magnet has a layer structure composed of a plurality of layers of a magnetic material, the respective layers of the magnetic material being separated from one another by respective separating layers. The permanent magnet has been produced particularly quickly and simply within the scope of the method. At the same time, the production method ensures that respective layer thicknesses of the layers of the magnetic material are set particularly precisely, in particular all layers of the magnetic material have the same layer thickness in the stacking direction in which the respective layers of the magnetic material are stacked on one another.Further features of the invention can be derived from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description and the features and combinations of features shown below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or alone without departing from the scope of the invention.The drawing shows in: FIG. 1 shows a schematic sectional view of a sintering tool, by means of which a permanent magnet is produced.FIG. 1 shows a schematic sectional view of a sintering tool 10 having a sintering mold 12. The sintering mold 12 delimits a receptacle 14, in which a material to be sintered can be received. For the sintering of the material to be sintered, which is accommodated in the receptacle 14, the material to be sintered is pressurized, in particular pressed, by means of a punch 16 of the sintering tool 10. For the sintering, the material to be sintered, which is pressurized in the receptacle 14, is heated.It is provided that a permanent magnet is produced by means of the sintering tool 10 within the scope of a method. This permanent magnet can be used in particular in a traction machine of a motor vehicle, in particular in a rotor. For producing the permanent magnet, a magnetic material 18 is filled layer by layer and thus in respective layers into the receptacle 14 of the sintering mold 12. Here, the respective layers of the magnetic material 18 are separated from each other by respective separating layers 20. This means that, in a stacking direction S in which the respective layers of the magnetic material 18 are stacked one on top of the other in the receptacle 14, a respective layer of the magnetic material 18 and a separating layer 20 are arranged alternately one on top of the other in the receptacle 14. In the present case, respective layers of the magnetic material 18 arranged directly one above the other in the stacking direction S are completely separated from one another by a separating layer 20 lying therebetween. For the arrangement of the respective separating layers 20, a surface of a respectively most recently filled layer of the magnetic material 18 can be changed in its structure by machining in a machining step before the filling of a further layer of the magnetic material 18 into the receptacle 14. For example, the surface of the respective layer of magnetic material 18 to be processed in the processing step can be subjected to a temperature treatment. In the present case, however, it is alternatively provided that for the arrangement of the respective separating layers 20, the magnetic material 18 and a separating material 22 are filled alternately layer by layer into the receptacle 14. This means that, for the arrangement of the respective separating layer 20, a layer of the separating material 22 between the respective layers of the magnetic material 18 is filled into the sintering mold 10. In other words, in the stacking direction S, first a layer of the magnetic material 18 is filled into the receptacle 14, and then a layer of the separating material 22 is applied to the layer of the magnetic material 18. Subsequently, a layer of the magnetic material 18 is again applied to the layer of the separating material 22. In this way, in the stacking direction S, a respective layer of the magnetic material 18 and a respective layer of the separating material 22 are introduced alternately. After all layers of the magnetic material 18 have been filled into the receptacle 14 of the sintering tool 10, the punch 16 is moved into the receptacle 14, as a result of which a force is applied to the layers of the magnetic material 18 separated from one another by respective separating layers 20 in the stacking direction S and are thereby compressed. For the sintering, the magnetic material 18 is additionally heated.After sintering, a plurality of layers of the magnetic material 18 separated from one another by respective separating layers 20 can be used as a permanent magnet having a layer structure. Alternatively, the block formed during sintering can be separated on at least one separating layer 20 in a plane running perpendicular to the stacking direction S, so that the block is divided into at least two, in particular a plurality of, permanent magnets. In this case, the permanent magnets produced can comprise one or more of the layers of the magnetic material 18. The method described thus enables a plurality of permanent magnets to be produced simultaneously in a single sintering process, which can subsequently be separated from one another by separating the block formed during sintering at respective separating layers 20, or at least one permanent magnet having a layer structure to be produced particularly easily, wherein the permanent magnet having the layer structure comprises a plurality of layers of magnetic material 18, wherein the respective layers of magnetic material 18 are separated from one another by respective separating layers 20. This layered structure of the permanent magnet makes it possible for eddy current losses in the permanent magnet to be kept particularly low.In order to ensure a particularly high temperature resistance of the permanent magnet produced in the context of the method, it is provided that at least one heavy rare earth material is introduced into the permanent magnet. In this case, this at least one heavy rare earth metal is to be diffused into the permanent magnet, in particular into all layers of the magnetic material, within the scope of a grain boundary diffusion process. For this purpose, it is provided that the at least one heavy rare earth metal is arranged at least between the layers of the material material 18 stacked on top of one another in the stacking direction S. In the present case, it is provided that each layer of the magnetic material 18 is completely sheathed with a substrate comprising the at least one heavy rare earth metal. This can ensure that, during the grain boundary diffusion process, the at least one heavy rare earth metal diffuses uniformly from an entire outer surface of the respective layer of magnetic material 18 toward a center of the respective layer of magnetic material 18. The grain boundary diffusion process takes place in particular during sintering. Heating the multiple layers of the magnetic material 18 arranged in the receptacle 14 thus serves on the one hand for sintering the magnetic material 18 and on the other hand for grain boundary diffusion of the at least one heavy rare earth metal. In order to enable a particularly simple and rapid arrangement of the at least one heavy rare earth metal in the stacking direction between the respective layers of the magnetic material 18, it can be provided that the at least one heavy rare earth metal is part of the separating material 22. This means that the at least one heavy rare earth metal is a component of the separating material 22, wherein the separating material 22 can comprise a plurality of components. In the present case, it is provided that the magnetic material 18 filled layer by layer into the receptacle 14 of the sintering mold 12 has the same composition. In this way, it can be achieved that all layers of the magnetic material 18 have at least substantially the same properties after sintering.In the method, a plurality of layers are thus introduced into the receptacle 14 of the sintering mold 12 before the pressing of the at least one permanent magnet. First, a layer of the magnetic material 18 is introduced into the receptacle 14, in particular in the thickness in which a layer of the magnetic material 18 is to be segmented. After this layer of magnetic material 18, a separating layer 20 is introduced. This separating layer 20 can be introduced by filling the separating material 22 into the receptacle 14 or by machining the surface of the recently introduced layer of the magnetic material 18 as part of a preliminary process in which a structural change of the magnetic material 18 takes place. Within the scope of this preliminary process, the magnetic material 18 in the sintering mold 12 is thus subjected to the processing step. This alternating filling of a layer of the magnetic material 18 into the receptacle 14 and the introduction of the respective separating layers 20 are repeated until a predetermined block size in the stacking direction S is reached. The block size can be predefined in a plant-specific and / or material-specific and / or production process-specific manner. The sintering process can then take place, in which the respective separating layers 20 lead to the individual layers of the magnetic material 18 not being joined to one another but being easily separated from one another, even after sintering. In the course of the processing step, the surface of the respective layer of the magnetic material 18 can be changed in its structure, for example by means of laser processing or plasma processing.The grain boundary diffusion process, in which the at least one heavy rare earth metal diffuses into the respective layers of the magnetic material 18, enables a proportion of heavy rare earth elements in the permanent magnet produced to be kept particularly low, since the at least one heavy rare earth element is enriched only in edge regions of the respective layers of the magnetic material 18.In order to produce permanent magnets having at least one heavy rare earth metal, the release material 22 may additionally serve as a support for depositing the at least one heavy rare earth metal on respective surfaces of the layers of magnetic material 18. Here, the at least one heavy rare earth metal may be contained in a paste that is mixed with the separation material 22. If each layer of the magnetic material 18 is to be enriched circumferentially with the at least one heavy rare earth metal, then the block formed from the plurality of layers in the receptacle 14 is to be covered on the respective outer sides with the substrate comprising the at least one heavy rare earth metal, for example the separating material 22.This method allows joining the sintering process to a downstream aging process for interfacial diffusion. This makes it possible to dispense with the process steps of cooling after sintering and heating for grain boundary diffusion. Furthermore, a facility investment can be reduced by integrating two temperature treatment steps, one for sintering and the other for grain boundary diffusion, into a single temperature treatment step which can be performed by a single furnace.Overall, the invention shows a production method for permanent magnets, in particular using grain boundary diffusion.List of reference characters10 Sintering tool 12 Sintering mold 14 Holder 16 Punch 18 Magnetic material 20 Separating layer 22 Separating material S Stacking directionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 9,154,004 B2

[0002] U.S. Pat. No. 10,242,778 B2

[0003]

Claims

A method for manufacturing a permanent magnet, comprising filling a magnetic material (18) layer by layer into a sintering mold (12), the respective layers of the magnetic material (18) being separated from each other by respective separating layers (20), and manufacturing the permanent magnet by sintering the plurality of layers of the magnetic material (18) in the sintering mold (12).Method according to Claim 1, characterized in that, for the arrangement of the respective separating layer (20), in each case one layer of a separating material (22) between the layers of the magnetic material (18) is filled into the sintering mould (12).Method according to claim 1 or 2, characterised in that, for the arrangement of the respective separating layers (20) between the respective layers of the magnetic material (18), a surface of the respective layers of the magnetic material (18) is subjected to a processing step before the respective next layer of the magnetic material (18) is filled into the sintering mould (12), whereby a structural change of the respective layer of the magnetic material (18) takes place at the surface thereof.Method according to claim 3, characterized in that at least the surface of the respective layers of the magnetic material (18) is subjected to a temperature treatment in the respective processing step.Method according to one of the preceding claims, characterized in that the layers of the magnetic material (18) are pressed together during the sintering in a stacking direction (S) in which the layers of the magnetic material (18) are stacked one on top of the other.Method according to one of the preceding claims, characterized in that at least one heavy rare earth metal is introduced at least between the respective layers of the magnetic material (18), as a result of which this heavy rare earth metal at least partially diffuses into the respective layer of the magnetic material (18) during a heat treatment phase of the sintering.Method according to claim 6, characterised in that each layer of magnetic material (18) is completely coated with a substrate comprising the at least one heavy rare earth metal.Method according to claim 6 or 7 when appended to claim 2, characterized in that the at least one heavy rare earth metal is part of the separating material (22).Method according to one of the preceding claims, characterized in that the magnetic material (18) filled layer by layer into the sintering mould has the same composition in the respective layers.Permanent magnet produced in a method according to any of the preceding claims, wherein the permanent magnet comprises a layer structure of several layers of a magnetic material (18) separated from each other by respective separating layers (20).

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