Method for manufacturing a multilayer magnet

Abstract

The invention relates to a method for manufacturing a multilayer magnet, the method comprising the following sequence of steps: a) a layer (42a-42g) of a magnetic material powder is introduced into a press (22) and pressed or pre-compacted (24); b) a layer of electrically insulating material powder is introduced into the press onto the layer of magnetic material powder (28) and pressed or pre-compacted (30); c) steps a) and b) are successively repeated to produce a multilayer composite (40, 50) in accordance with the number of desired layers (42a-42g) of the magnetic material; and d) the multilayer composite is sintered (34). This method allows multilayer magnets to be manufactured cost-effectively.

Description

[0001] Mercedes-Benz Group AG

[0002] Method for manufacturing a multilayer magnet

[0003] The present invention relates to a method for manufacturing a multilayer magnet for electrical machines, in particular for permanent magnet motors. It is known to date to segment the permanent magnets of permanent magnet motors in order to reduce eddy current losses during operation of the electrical machine. For this purpose, prefabricated parts of a permanent magnet are bonded together, with an insulating layer forming at the bonding points. In this way, the permanent magnet is formed by a plurality of partial magnets, which effectively reduces eddy current losses. A disadvantage of this known method is that the mechanical bonding and alignment of the partial magnets is time-consuming and requires considerable effort, particularly when reducing tolerances.

[0004] It is therefore an object of the invention to provide a method for producing a multilayer magnet for an electric machine that causes low eddy current losses and is cost-effective to manufacture.

[0005] This problem is solved by a method according to claim 1 and a multilayer magnet according to claim 12. Advantageous embodiments of the invention are the subject of the associated dependent claims.

[0006] According to the invention, a layer of a magnetic material powder is placed in a press and compacted. Subsequently, a layer of an electrical insulating material powder is placed in the press on top of the magnetic material powder layer and compacted. The compaction process behind each layer of the magnetic or insulating material not only smooths but also pre-compacts the layer. The steps of placing the magnetic and insulating materials in the press are repeated as many times as required to achieve the desired number of layers in the multilayer magnet being produced.Finally, the entire assembly within the press is optionally compacted and then sintered, whereby a continuous permanent magnet is formed from the powder layer of the magnetic material and a continuous, particularly ceramic, insulating layer is formed from the powder layer of the insulating material. In this way, a finished multilayer magnet is obtained after sintering, requiring no further mechanical processing to adjust the layer arrangement.

[0007] Depending on which layer is introduced first or last in the press, the resulting top layers are either an insulating layer or a layer of permanent magnet material.

[0008] After sintering, the manufactured multilayer magnet can be finished, for example surface-treated, in order to be used in the rotor of an electric machine, in particular a permanent magnet motor.

[0009] The reduction in layer thickness during any intermediate compaction of the layers and final compaction of the entire composite is known. The shrinkage of the entire composite during sintering is also known, so that the layer thickness to be poured into the press, both of the permanent magnet material and the insulating layer, can be determined from the achievable layer thickness in the finished composite.

[0010] The magnetic material is preferably a conventional alloy of iron-boron-neodymium or ferrite, or other known permanent magnet materials. Aluminum oxide, aluminum nitride, or manganese-zinc ferrite are preferably used as insulating materials, as they exhibit similar shrinkage during sintering to the permanent magnet materials described above, thus preventing internal stresses in the composite during sintering.

[0011] Preferably, after the application of a layer of the magnetic material and / or the insulating material, pre-compaction is carried out to reduce the porosity of the sintered end product. This pre-compaction also creates a smooth surface for the application of the next layer. In an advantageous embodiment of the invention, the multilayer composite is final-compacted before sintering, in particular isostatically in a magnetic field. This significantly reduces the porosity of the sintered multilayer magnet, with the isostatic pressing achieving a uniform reduction in porosity in all spatial directions. Furthermore, isostatic pressing in a magnetic field ensures optimal alignment of the powder particles of the permanent magnetic material before sintering and thus also in the sintered end product.

[0012] In one embodiment of the invention, the magnetic material is melted and hardened to produce the powder, after which the hardened material is pulverized. In this way, a homogeneous structure is achieved, particularly with alloys, so that the properties of the resulting powder of the magnetic material are essentially constant during subsequent pulverization.

[0013] Preferably, the molten magnetic material is cured using a strip casting process, which ensures that the homogeneity achieved in the melt is maintained through the rapid cooling process. The cured magnetic material is preferably embrittled with hydrogen, making it easier to pulverize. The cured or embrittled magnetic material can then preferably be pulverized using a jet milling process, yielding a powder with a grain size optimized for sintering, for example, between 3 and 8 pm.

[0014] In an advantageous embodiment of the invention, the particle size of the powder of the magnetic material and / or the insulating material is selected between 1 and 15 pm, particularly between 3 and 8 pm, in the manufacturing process. This particle size or particle size distribution leads to a good sintering result, whereby care must be taken to ensure that the particle size of the powder of the magnetic material does not deviate too much from the particle size of the powder of the insulating material in order to achieve homogeneous sintering behavior in the multilayer composite.

[0015] The invention also relates to a multilayer magnet produced by the method described above. It should be noted that the manufacturing process is suitable for producing both radially segmented and axially segmented permanent magnets, so that both radial flux motors and axial flux motors can be manufactured with these magnets.

[0016] The following describes an exemplary embodiment for the production of an eight-layer permanent magnet.

[0017] Nd₂Fei₄b is used as the magnetic material. Aluminum oxide is used as the insulating material. The powder of both the magnetic and insulating materials is selected such that the maximum particle size distribution is 4 µm. A press with a base area of ​​12 x 6 cm is used. First, a 20 mm thick layer of the magnetic powder is introduced into the press. This layer is homogenized, for example, by vibration, and then pre-compacted using the press ram at a pressure of 50 MPa. After pre-compaction, the insulating layer of aluminum oxide powder is introduced, also homogenized, and likewise pre-compacted at a pressure of 50 MPa. The thickness of the insulating layer after insertion is 3 mm. These steps are then repeated eight times, with the final layer being the magnetic material.After pre-compaction, the pre-compacted multi-layer composite is removed from the press and, surrounded by a film, placed in an isostatic press, where the entire composite is finally compacted at a pressure of 250 MPa.

[0018] The fully compacted composite is then sintered in an oven under a protective gas atmosphere at a pressure of 1 MPa and a sintering temperature of 1050 degrees.

[0019] The sintering time is four hours.

[0020] This is only one specific embodiment. The grain size distribution can be selected to deviate from this embodiment, for example, by varying the grain size of the magnetic material and the insulating material between 2 and 10 pm. Intermediate compaction can also be performed at lower pressures, for example, only 10 MPa, particularly between 10 and 70 MPa. This isostatic final compaction is optional but desirable. Unidirectional final compaction is also possible. The pressing pressure should be between 200 MPa and 400 MPa, regardless of whether it is isostatic or uniaxial. The sintering temperature will be between 940 and 1500 degrees Celsius, depending on the grain size and type of material.

[0021] If the pre-compacted multilayer composites are placed in a press and then layered with a powder layer of insulating material in the same manner as described above, permanent magnets with insulating layers running in two directions can be produced. In this case, sintering only takes place when the corresponding number of multilayer composites and the intervening insulating layers are placed in the press and pre-compacted, then finally compacted and sintered.

[0022] The invention thus makes it possible not only to produce uniaxially segmented multilayer magnets, but also bidirectionally segmented permanent magnets, in which eddy current losses can be very effectively reduced by segmentation in two spatial directions.

[0023] The above embodiments can be combined with one another as desired. The following terms are used synonymously: multilayer composite - multilayer composite;

[0024] The invention is described below with reference to the exemplary drawing. These show:

[0025] Fig. 1 shows a flowchart for the production of the powder of a magnetic

[0026] material

[0027] Fig. 2 shows a flowchart for the production of a multilayer magnet,

[0028] Fig. 3a shows a side view of a horizontally layered pressed pellet with seven magnetic layers divided by six insulating layers.

[0029] Fig. 3b Side view of the pressed piece shown in Fig. 3a after sintering to illustrate sintering shrinkage. Figs. 4a and 4b identical views to Fig. 3a and Fig. 3b in a vertically layered multilayer composite and

[0030] Fig. 5 shows a pellet segmented in two spatial directions, produced by three vertically segmented pellets according to Fig. 4a.

[0031] Figure 1 briefly describes a method for producing a powder of a permanent magnetic material.

[0032] In step 10, a permanent magnetic alloy, such as Nd₂Fei₄b, is melted and homogenized. In the subsequent step 12, the melt is cooled and solidified using a strip casting process. In the following hydrogen embrittlement process 14, the solidified permanent magnetic material is embrittled to facilitate pulverization, which takes place in the jet milling pulverization step 16. The pulverization is carried out in such a way that the maximum particle size of the ground powder is approximately 3 to 8 pm.

[0033] Figure 2 shows a process for manufacturing a multilayer magnet. The process starts with step 20, in which a press of a suitable size for producing a green body of a multilayer composite is provided. In step 22, a first layer of powdered magnetic material, produced, for example, by the pulverization process described in Fig. 1, is introduced into the press. In the subsequent pre-compaction step 24, the inserted layer is smoothed by a press ram and, if necessary, pre-compacted, for example, at pressures between 10 and 30 MPa. In decision step 26, it is checked whether the intended number of permanent magnet layers has been reached.If this is not the case, decision step 26 branches to step 28, in which a comparatively much thinner layer of insulating powder, for example, with a thickness between 1 and 3 mm, is poured into the press onto the underlying smoothed or pre-compacted layer of the magnetic material. In the subsequent step 30, this insulating layer is pressed down again and, if necessary, pre-compacted. The process branches back to step 22, where another layer of permanent magnet material is introduced into the press. These steps are repeated until the required number of permanent magnet layers is reached, at which point the process branches from decision step 26 to step 32, where isostatic final compaction of the multilayer green body (green body refers to a material before sintering) takes place. The pressing pressure is preferably between 200 and 400 MPa.The final compaction, particularly isostatic compaction, can preferably be carried out in a magnetic field to promote an alignment of the elementary magnet particles contained in the permanent material that is favorable for the electric machine. After final compaction in step 32, the composite is sintered in step 34 at temperatures between 900 and 1400 degrees Celsius, depending on the materials used, for a period of several hours. After sintering, during which the green compact typically shrinks by between 10 and 25 percent, the finished permanent magnet composite is obtained, which can then be further processed, for example, surface-treated, for use in the electric machine.

[0034] By using appropriate molds, it is possible to produce not only flat, i.e., rectangular, permanent magnets, but also permanent magnets in the shape of the shell of a cylindrical segment. This method is ideal for manufacturing permanent magnets for axial flux machines, for example.

[0035] Figure 3a shows a green compact 40 after final compaction step 32 in the manufacturing process of Fig. 2. The green compact has seven layers 42a to 42g of a permanent magnet powder layer with a thickness of, for example, 12 to 36 mm. Between the permanent magnet powder layers are insulating layers 44a to 44f, the thickness of which is approximately one-fifth to one-tenth that of the permanent magnet layers. The green compact is isostatically compacted under a higher pressure, for example, 250 MPa, and is ready for sintering. After sintering, a sintered, stable multilayer composite 46 (Fig. 3b) is obtained, in which the powder particles of the permanent magnet layers are bonded together as a result of sintering to form a homogeneous, coherent permanent magnet block.The same applies to the sintered intermediate insulating layers 44a to 44f, which now form thin, continuous ceramic insulating layers that effectively electrically insulate the permanent magnet layers from one another. Such a sintered multilayer composite 46 can potentially undergo further processing, for example, surface treatment, in order to be subsequently used in a permanent magnet motor.

[0036] Figures 4a and 4b show a green compact 40 of a multilayer magnet with vertical segmentation, and Figure 4b shows the sintered multilayer composite 46 ready for installation in an electric machine. The descriptions of Figures 3a and 3b also apply in full to the embodiment shown in Figures 4a and 4b.

[0037] Figure 5 shows an unsintered multilayer composite 50, i.e., a green compact, produced by stacking three multilayer composites 40a, 40b, 40c from Fig. 4a in a press with an insulating layer 48a, 48b arranged between each of the multilayer composites 40a, 40b, 40c. The same process as in Fig. 2 can be applied here, with the difference that instead of a permanent magnet layer, a finished multilayer composite is inserted into the press. In this way, permanent magnets with both horizontal and vertical segmentation can be used. As already described in relation to Fig. 3, permanent magnets in the form of the lateral surface of a cylindrical segment can also be produced to manufacture axial flux machines. After final compaction of the bidirectionally segmented multilayer composite, it can be isostatically compacted to reduce its porosity in the final product.The multilayer composite is then sintered.

[0038] The invention is not limited to the illustrated embodiments, but can instead be varied within the scope of protection of the following claims.

[0039] Reference symbol list

[0040] 10 Melting the magnetic material

[0041] 12. Curing of the magnetic material, especially strip casting

[0042] 14 Embrittlement of the magnetic material, especially in the

[0043] hydrogen

[0044] 16. Pulverizing the magnetic material, especially in jet-

[0045] Milling process

[0046] 20 Preparing the press

[0047] 22. Pouring the layer of magnetic material powder into the press.

[0048] 24 Pressing down or pre-compacting the powder layer of the magnetic

[0049] material

[0050] 26. Decision step: whether the desired number of magnetic

[0051] layers in multi-layer composite are achieved

[0052] 28. Pouring the layer of insulating material powder into the

[0053] press

[0054] 30 Pressing down or pre-compacting the powder layer of the

[0055] Insulation material

[0056] 32 (anisotropic) final compaction of the multilayer composite

[0057] 34 Sintering of the multilayer composite

[0058] 40 Multilayer composite (green body) before sintering

[0059] 42a-g layers of the magnetic material

[0060] 44a-f arranged between the layers of the magnetic material

[0061] Layers of the insulating material

[0062] 46 sintered multilayer composite - multilayer composite - finished

[0063] multilayer permanent magnet

[0064] 48a, b Insulation layers between the multilayer composites (green bodies)

[0065] 50 Multilayer composite with bidirectional segmentation (green body)

Claims

Mercedes-Benz Group AG Patent claims 1. A method for producing a multilayer magnet, characterized by a sequence of the following steps: a) a layer (42a - 42g) of a powder of a magnetic material is placed in a press (22) and pressed or pre-compacted (24), b) a layer of a powder of an electrical insulating material is placed in the press on top of the layer of powder of the magnetic material (28) and pressed or pre-compacted (30), c) steps a) and b) are successively repeated to produce a multilayer composite (40, 50) according to the number of desired layers (42a - 42g) of the magnetic material, d) the multilayer composite is sintered (34).

2. Method according to claim 1, characterized in that an alloy of iron, boron and neodymium is used as the magnetic material.

3. Method according to claim 1, characterized in that ferrite is used as the magnetic material.

4. Method according to one of the preceding claims, characterized in that aluminium oxide or manganese-zinc ferrite is used as the insulating material.

5. Method according to one of the preceding claims, characterized in that the multilayer composite (40, 50) is prepared before sintering (34) in step d) end compaction (32) is achieved, particularly in the magnetic field.

6. Method according to claim 5, characterized in that the final compaction (32) is carried out isostatically.

7. Method according to one of the preceding claims, characterized in that the magnetic material is melted (10) to produce the powder and the melted material is hardened (12), after which the hardened material is pulverized (16).

8. Method according to claim 7, characterized in that the molten magnetic material is cured (12) in the stripcasting process.

9. Method according to claim 7 or 8, characterized in that the hardened magnetic material is embrittled (14) by hydrogen.

10. Method according to claim 8 or 9, characterized in that the hardened or embrittled magnetic material is pulverized in the jet milling process (16).

11. Method according to one of the preceding claims, characterized in that powder of the magnetic material with a maximum of the grain size distribution between 1 and 15 pm, in particular between 3 and 8 pm, is used.

12. Multilayer magnet (46), produced by a method according to one of the preceding claims.

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