Additively manufactured magnetic sheet, lamination stack and method for manufacturing magnetic sheet

Abstract

The invention relates to an additively manufactured rotationally symmetrical magnetic sheet (2) for a lamination stack (8) of an electric motor (10), the magnetic sheet comprising at least two material layers (4, 6), wherein in each material layer (4, 6) there are at least two material components (12, 14) separated from each other in the extension of a plane: a first material component (12) and a second material component (14), wherein the material components (12, 14) form a material layer layout (16), characterized in that at least two material layers (4, 6) have an identical material layer layout (16) of two material components (12, 14), and the layout (16) of at least two material layers (4, 6) is rotationally offset by an angle α.

Description

[0001] The invention relates to an additively manufactured magnetic sheet according to claim 1 , a laminated core according to claim 12 , and a method for producing a magnetic sheet according to claim 15 .

[0002] Screen printing or template printing is a new method for producing magnetic sheets for electric motors. In this process, a printing paste is printed onto a substrate with the aid of a template, in which the free areas can also be provided with a screen. This involves template printing or screen printing, wherein template printing is a general term for screen printing. In addition to solvents and / or adhesives, the printing paste also contains metal powders, which have a functional influence on subsequent components. The green body is manufactured by screen printing technology, and after further heat treatment, the green body is usually first debonded and then sintered at a higher temperature, wherein the metal powder particles sinter to each other to form a structured sheet, i.e. a magnetic sheet.

[0003] In order to achieve a higher mechanical strength of such sheets, especially when the motor rotor rotates at high speeds, the manufacturability of two-component magnetic sheets is becoming increasingly important. An example of this is described in EP 3723249 A1. EP3 629 453 A1, EP 3 932 591 A1 and EP 3 725 435 A1 should also be mentioned here. The fundamental problem with such two-component magnetic sheets manufactured using a stencil printing process is that different materials usually have different thermal expansion coefficients while having good magnetic properties on the one hand and high strength on the other hand. For example, the expansion coefficient of high-strength steel, which is a component used to form the mechanical strength of the magnetic sheet, is 16×10 -6 K -1 Another soft magnetic material has a magnetic field strength of 10-12×10 -6 K -1 When these different material components or material pairs in the green body are sintered together to form a magnetic sheet, due to the different thermal expansion coefficients, higher mechanical stress is generated in the connection area or seam area between these material components, especially when cooling from the sintering temperature to room temperature. This may cause warping, cracks in the magnetic sheet, or mechanical stress on the whole, which significantly deteriorates the mechanical properties or magnetic properties.

[0004] The technical problem to be solved by the present invention is to provide a magnetic sheet and thereby a laminated core and an electric machine, which have higher strength and lower internal stress compared to the prior art when at least two material components are used in the magnetic sheet.

[0005] This object is achieved by a laminated core according to claim 12 and a method for producing a magnetic disk according to claim 15 .

[0006] The rotationally symmetrical magnetic sheet manufactured by additive manufacturing according to patent claim 1 comprises at least two material layers, and the magnetic sheet is used as a component of a lamination stack of an electric machine, wherein at least two material components are present in each material layer of the magnetic sheet, and the two material components are separated from each other in the extension of the plane. This involves a first material component and a second material component, which together constitute a material layer layout. The invention is characterized in that at least two material layers have the same material layer layout of two material components. The layout of at least two material layers is rotationally offset relative to each other at an angle α. Rotation here refers to rotation around an axis perpendicular to the plane of the magnetic sheet, which axis extends through the center point of the rotationally symmetrical magnetic sheet.

[0007] According to the prior art, the printed two-component magnetic sheet is composed of a separate material layer, and the difference between the present invention and the prior art is first that the magnetic sheet of the present invention is composed of multiple material layers. These material layers are arranged in a stacked structure in a stacked manner. On the other hand, the difference between the present magnetic sheet and the prior art is that at least two material layers have the same layout of two material components, and are respectively offset relative to each other at an angle α. Two or more material layers with the same layout are usually arranged in a stacked manner. This is preferably achieved by template printing or screen printing, wherein these layers are offset relative to the layer below them in the magnetic sheet at an angle α. The offset at an angle α is superimposed in multiple material layers, thereby forming an overlapping area, in which there is actually an average thermal expansion coefficient, which extends in a gradient manner in the direction of its plane, and is respectively between the individual thermal expansion coefficients of the first and second material components. As a result (especially when cooled from the sintering temperature), the thermomechanical stress between the regions of the various material components is significantly reduced, which causes the magnetic sheet or the lamination stack composed of it to have a higher mechanical strength when rotating at high speed.

[0008] On the other hand, it has also been found to have a positive effect that the described construction can largely eliminate torque fluctuations in an electric motor using the described magnetic laminations or a laminated core formed from the described magnetic laminations.

[0009] It should therefore be noted that the described material layers, which are rotated relative to each other, are an integral component of a corresponding screen-printed or template-printed magnetic sheet. The material layers themselves are therefore not independent magnetic sheets, but rather the individual material layers are connected to each other by sintered connections preferably produced by a sintering process of the entire magnetic sheet, and thus constitute a magnetic sheet.

[0010] The following definitions are used here below: As described in patent claim 15, the magnetic sheet and the individual material layers are formed by green sheets. Green sheets are understood here as molded bodies for subsequent heat treatment, which usually contain binders and / or solvents for improving the molding. The green sheets themselves are usually mechanically self-supporting and can be mechanically loaded to a limited extent. The green sheets from which these binders and / or solvents have been removed are referred to as preforms. The preforms contain only functional components of the final body, which also effectively participate in the sintering process, which are usually metal particles. The preform is transformed into a sintered body by a heat treatment in the form of a sintering process, in which, unlike the melting process, the individual grains (particles) in the preform form a continuous, material-bonded structure through a diffusion process. After the sintering process has been carried out, the resulting body is referred to as a magnetic sheet. However, different reprocessing of such magnetic sheets is still possible.

[0011] The material layers described are fed together into the sintering process and even form a sintered connection at their planar interfaces.

[0012] A stencil printing process is understood to be a process in which a printing paste is applied to a substrate, for example by means of a doctor blade, wherein a layer with solvent, binder and functional particles is produced as described. The paste is here only printed on the substrate in certain uncovered areas left free by means of the stencil. The paste is usually embossed here by means of a screen, but this is not mandatory. Stencil printing using a screen is referred to as a screen printing process, and therefore screen printing processes are termed stencil printing processes. However, when using the term screen printing process, the general term stencil printing process can also be understood.

[0013] The magnetic sheets in the sintered state usually have a thickness of 70μm to 300μm, especially 100μm to 250μm. The existing magnetic sheets have a thickness preferably between 300μm and 2000μm. This is due to the various material layers, which are thinner than traditional magnetic sheets in the prior art and preferably have a thickness of 10μm to 100μm. This makes the number of 10 to 20 material layers suitable for the magnetic sheets. It is also advantageous that a larger layer thickness can produce greater strength and rigidity for the green body and the subsequent sintering process to prevent warping and delamination. This makes it possible to achieve higher mechanical strength, especially tensile strength and bending strength or fatigue strength, when the magnetic sheets are in operation, which enables higher rotation speeds to be achieved in the rotor whose main component is a lamination stack composed of the magnetic sheets.

[0014] As described above, the magnetic sheet comprises at least two different material components, which differ in particular in terms of mechanical and magnetic properties. In this way, the technical properties required there can be taken into account in a targeted manner in certain areas of the magnetic sheet. Therefore, the first material component has an iron alloy with an austenitic structure of at least 25% by volume. This austenitic structure, which can be achieved in particular using high-alloy steel, has very high strength, in particular tensile strength and bending strength.

[0015] The second material component, on the other hand, comprises an iron alloy having at least 95% by weight, in particular at least 97% by weight, of iron. The second material component is preferably pure iron, which has very good magnetic properties, in particular soft magnetic properties, and can be remagnetized very well in the form of hysteresis. It should be noted here that the data relating to the austenitic structure are given in volume %, while the alloy data are given in weight %. This is because in micrographs, the structure can be more clearly represented microscopically in volume %, while the alloy composition is represented in weight %, which is common in technology and represents a clear manufacturing specification for the composition of the alloy.

[0016] The second material component having very good soft magnetic properties also has a preferred ferrite and / or martensite structure.

[0017] The first material component, which has a high mechanical strength and ensures the strength of the entire magnetic disk during rotational movement, is also preferably an iron-chromium-nickel alloy. The iron-chromium-nickel alloy also preferably has a chromium content of preferably between 22% by weight and 28% by weight, in particular between 24% by weight and 26% by weight. In addition, the iron-chromium-nickel alloy has a nickel content of between 4% by weight and 10% by weight, in particular between 6% by weight and 8% by weight.

[0018] Another aspect of the invention is a lamination stack for a rotor of an electric machine, comprising a plurality of magnetic sheets according to one of the preceding claims. The advantages of such a lamination stack, in particular as a component of a rotor of an electric machine, have already been described in detail with respect to the advantages of the individual magnetic sheets. Such a lamination stack has a higher resistance, in particular to the high temperatures generated at high rotational speeds, which resists delamination of two-component magnetic sheets, in particular produced by screen printing or stencil printing.

[0019] Since the described lamination stack has a plurality of magnet sheets with the described properties, it is expedient to continue the construction of a single magnet sheet when stacking a plurality of magnet sheets together, so that the uppermost material layer of the first magnet sheet and the lowermost material layer of the second magnet sheet are preferably also offset relative to each other at an angle α. The sum of the angles α in the entire lamination stack is 7° to 36°. On the one hand, this overall offset is suitable for providing a sufficiently large overlap area for each magnet sheet to reduce the thermal expansion coefficient there, and on the other hand, this total angle is also used to eliminate torque fluctuations in the rotor in the widest possible range.

[0020] Another aspect of the present invention is a method for manufacturing a magnetic sheet, the method comprising the steps of:

[0021] a) applying a first printing paste to a substrate through a template by means of template printing,

[0022] b) applying a second printing paste on the substrate so that the two printing pastes are adjacent to each other, forming a discrete boundary line, and forming a first material layer,

[0023] c) drying the first material layer,

[0024] d) rotating the orientation of the substrate and / or template by an angle α relative to an axis perpendicular to the substrate,

[0025] e) applying a second material layer according to steps a) to c),

[0026] f) Sintering the green body produced through steps a) to e) to form a magnetic sheet.

[0027] The method for producing a magnetic sheet produces a magnetic sheet having the same advantages as those already explained with respect to claims 1 and 12. The rotation of the individual material layers that finally form the magnetic sheet relative to one another results in a corresponding offset at the described angle α in the overlapping region between the individual material components, so that the thermal expansion coefficients are adapted in a gradient between the expansion coefficients of the individual material components. This has a positive effect on the strength of the laminated core.

[0028] In order to achieve the angle α, on the one hand, the substrate can be slightly rotated, and on the other hand or in addition, the template or the frame of the template can also be slightly rotated by the angle α. In principle, of course, the two components can also be twisted. The two printing pastes are adjacent and form a discrete boundary line, which means that the overlap of the two printing pastes and, if necessary, the two printing pastes flow into each other along the discrete boundary line according to the tolerances of the process technology are completely possible and actually occur. However, in practice, the discrete boundary line should be as narrow as possible. Although the transition area between the two material components is also suitable for different thermal expansion coefficients, the transition area leads to different thicknesses in the area of ​​the boundary line, which is not conducive to the construction of the entire magnetic sheet.

[0029] Advantageous designs and other features of the present invention are described in detail with reference to the following figures. Features with the same name but in different designs are respectively provided with the same reference numerals. This is a purely schematic view which does not itself constitute a limitation of the scope of protection. In the drawings:

[0030] Figure 1 An exploded view of a typical electric machine, which may be a motor or a generator, is shown with a housing, a rotor and a stator.

[0031] FIG. 2 shows a lamination stack with stacked magnetic sheets according to the prior art,

[0032] Figure 3 A top view of a dual-component magnetic sheet is shown,

[0033] Figure 4 shows the layout with Figure 3 Three-dimensional top view of different dual-component magnetic sheets.

[0034] Figure 5 Shows Figure 4 A magnified view of a local area V in

[0035] Figure 6 Shows Figure 5 An enlarged view of a local area VI in which the overlapping areas of the various material layers can be seen.

[0036] Figure 7 A schematic diagram of a manufacturing method for manufacturing the magnetic sheet is shown.

[0037] In order to better classify the magnetic sheet 2, first Figure 1 1 shows an exploded view of the electric machine 10. The electric machine comprises a rotor 38 and a stator 40 surrounded by a housing 42. The electric machine 10 can be an electric motor or a generator. The rotor 38 in turn comprises Figure 1 In the lamination stack 8 not explicitly shown in the drawing, the conductive wire is arranged in a certain manner as a coil around the lamination stack 4. FIG. 2 shows such a lamination stack 8 according to the prior art, for example. The lamination stack 8 according to FIG. 2 has a stacked structure of a plurality of magnetic sheets 2 according to the prior art, wherein the layout of the magnetic sheets 2 is designed so that the magnetic sheets form corresponding recesses and grooves for the conductor winding.

[0038] Figure 3 An example of a magnetic disk 2 is shown, which has two components, namely a first material component 12 and a second material component 14. The two material components 12 and 14 have different technical properties. The first material component 12 comprises in particular a high-alloy chromium-nickel steel, which preferably comprises more than 25% by volume of an austenite structure. The chromium content is, for example, 25% by weight and the nickel content is, for example, 7% by weight. This alloy is a very high-strength stainless steel alloy. Figure 3 It can be seen that the first material component 12 is arranged centrally inside the magnet disk 2 , so that when the rotor 38 performs a rotational movement, the first material component is subjected to the highest tensile load acting on the magnet disk 2 or on the lamination stack 8 formed by the magnet disks.

[0039] The second material component 14 is particularly focused on magnetic properties in terms of material properties. Ideally, the material of the second material component 14 is made of pure iron and has a ferrite structure or a martensite structure. Pure iron has the best soft magnetic properties and is easy to repolarize in this regard. This is of great significance for AC motors or generators.

[0040] like Figure 3 The manufacture of the magnetic sheet 2 consisting of at least two components will be based on Figure 7 The schematic diagram in FIG. 1 is used to further explain the above.

[0041] Although the two different material components are usually composed of iron alloys, their electrical expansion coefficients still have certain differences. Depending on the alloy composition, the expansion coefficients of the individual iron alloys can vary, for example, from 10×10 -6 K -1 and 20×10 -6 K -1 In addition, a temperature increase from room temperature to 200°C (which may be the operating temperature of a high-performance motor running at high speed) may also cause the expansion coefficient to change by 10×10 -6 K -1 However, this difference between the individual expansion coefficients, which depends on the material composition and also on the operating temperature range of the machine, leads to significant thermomechanical stresses at the interface 15 between the individual material components 12 and 14. Further high thermomechanical stresses already occur during cooling from the desired sintering temperature.

[0042] according to Figures 4 to 6 Advantageous solutions for reducing these thermomechanical stresses caused by different expansion coefficients and thermal fluctuations of the machine are described. Figure 4 and Figure 3 Similarly, the magnetic sheet 2 is shown, although it has the same Figure 3 Different layouts 16, but the construction is essentially the same. The magnetic sheet has an area with a first material component 12 and an area with a second material component 14. Here, there is also an interface 15 between the material components 12, 14. In the circular partial area marked with V, the two material components 12, 14 meet at their interface 15, which is Figure 5 It is also shown in the circle marked VI that the magnetic sheet 2 is composed of a plurality of material layers 4, 6, namely, a first material layer 4 and a second material layer 6 and an additional material layer 6'. Figure 6 A further enlarged view of circle VI is shown.

[0043] The sequence of the material layers 4, 6 is here again enlarged and clearly shown. It can be seen that between the first material layer 4 and the second material layer 6, the layout 16 of the two material layers is twisted by an angle α, but otherwise the layout is largely identical. This twisting by an angle α continues in the other material layers 6' and subsequent material layers 6', which are not marked but are identical in terms of process accuracy. Figure 6 As shown, an overlapping area 54 is produced. If a cross section is set through the overlapping area 54, the same material proportion of the first material component 12 and the second material component 14 is produced. However, this exists in the gradual extension of the corresponding material components 12 and 14. Therefore, the overlapping area 54 has a thermal expansion coefficient that changes gradiently from the first material layer 12 to the second material layer 14. This in turn has the effect of reducing the thermomechanical stress generated by the different basic coefficients of the various material components 12 and 14. This allows the expansion coefficient to gradually transition from one material component to another. This greatly reduces the local thermomechanical stress and distributes it to a larger range, which in turn significantly improves the strength of the magnetic sheet itself.

[0044] Figure 6 The magnetic sheet 2 shown has six material layers 4, 6, 6'. Figure 6 The magnetic sheet 2 has a thickness of 600 μm, and depending on the manufacturing tolerances, each individual material layer 4, 6, 6' has a thickness of about 100 μm. Figures 4 to 6 The magnetic sheet 2 correspondingly constructed in the manner shown has a thickness between 300 μm and 2000 μm. The thickness of the magnetic sheet manufactured according to the conventional screen printing or template printing process is usually 100 μm. Compared with these magnetic sheets, the advantage of the magnetic sheet 2 in the form shown here is that, although the magnetic sheet also has individual material components connected to each other by the sintering process, it has a higher relative inherent stability of the entire magnetic sheet 2 through the stacking sequence, and reduces the warping caused by the arch during the sintering process.

[0045] Furthermore, it may be appropriate to stack the correspondingly designed magnetic sheets 2 into a laminated sheet group 8 as follows, so that when the magnetic sheets 2 are stacked on top of each other, as shown in FIG. Figure 6 The offset shown at the angle α is continued, so that the angular offsets at the individual angles α are added up. This in turn has an effect on the magnetic properties of the laminated core 8 and the rotor 38. It has been found that, depending on the number of pole pairs of the electric machine, an offset of the cumulative angle α of between 7.2° and 36° is suitable. For a higher number of pole pairs 50, a smaller offset of the cumulative angle α of 7.2° is suitable in order to compensate for torque fluctuations in the rotor. For a lower number of pole pairs 10, an angle of 36° is suitable, and for a number of pole pairs 36, an angle sum (also called inclination) of 10° is suitable.

[0046] Figure 7 A possible method sequence is described, in which the magnetic disk 2 described above can be formed. Figure 7 The method sequence is described very schematically and variants common in the art are possible for the individual method steps. First, a printing paste (not shown here) is printed onto a substrate 28 by means of a stencil printing process 30 and by means of a stencil 26 using a doctor blade 44. Figure 7 The template is replaced or substituted as shown separately in a, and a second printing paste is printed on the same substrate 28, so that the two material components 12 and 14 are present adjacent to each other on the substrate 28. In the subsequent progress of the method, the terms first material component 12 and second material component 14 have been used for the respective material components, wherein strictly speaking, this is still a preparatory stage for the material components 12 and 14 that are later present in the magnetic sheet. Therefore, in accordance with Figure 7 In the view of FIG. 1 a, the material components 12 and 14 are dried slurries separated from the solvent by means of a drying device.

[0047] according to Figure 7 b. A second step is performed by means of the same template printing process 30, wherein a second material layer 6 having the same layout 16 is printed on the same substrate 28, specifically on the already existing and dried material components 12 and 14 constituting the first material layer 4. A further drying process is then performed.

[0048] The second material layer 6 differs from the first material layer 4 , which is not visible here, in that the template 26 and / or the substrate 28 is rotated by an angle α about an axis 34 perpendicular to the substrate 28 .

[0049] To form the magnet disk 2 or its green body 36 , a plurality of further material layers (not shown here) are preferably present, which are also rotated in their arrangement by an angle α relative to the corresponding underlying material layers.

[0050] Auxiliary materials can be inserted between the individual material layers. For example, boron, lithium and phosphorus can be used for this purpose, which contribute to temporary liquid phase sintering in the boundary area and are then embedded in the tissue by suction. This improves the connection between the material layers after the sintering process and prevents possible delamination of the material layers. These auxiliary materials can be applied, for example, by a spraying process after the corresponding material layer has dried.

[0051] The green compact 36 thus produced is then fed into a sintering process. For this purpose, a sintering furnace is suitable, which is usually designed in the form of a batch furnace, in which a plurality of components to be sintered are placed, heated to the sintering temperature and then cooled again.

[0052] However Figure 7c shows an advantageous design, in which the green body 36 is fed into a continuous heating furnace via a conveyor belt 52, wherein the continuous heating furnace is divided into two sub-areas, one of which is a debinding furnace 48, in which the organic components in the green body 36 are first thermally decomposed and removed, and the other is a sintering furnace 50, in which the green body is heated to a sintering temperature, at which diffusion processes between the individual particles of the material components applied by template printing occur. When leaving the sintering furnace 50, the components are referred to as magnetic sheets 2. These magnetic sheets have, for example, Figures 4 to 6 The structure shown.

Claims

1. A rotationally symmetrical magnetic sheet (2) for additive manufacturing of a lamination stack (8) for an electric machine (10), the magnetic sheet comprising at least two material layers 4, 6, wherein: In each material layer 4, 6 there are at least two material components (12, 14) separated from one another in the extension of the plane. - a first material component (12) and a second material component (14), wherein the material components 12 , 14 here form a material layer arrangement 16 , It is characterized in that At least two material layers 4 , 6 have an identical material layer arrangement 16 of the two material components 12 , 14 , and the arrangement 16 of at least two material layers 4 , 6 is rotationally offset by an angle α.

2. The magnetic sheet according to claim 1, characterized in that: At least three material layers 4 , 6 , 6 ′ are provided, wherein the third material layer 6 ′ is also rotated by an angle α in the same direction relative to the second material layer 6 .

3. The magnetic sheet according to any one of claims 1 or 2, characterized in that: At least two material layers 4 , 6 are connected to one another by a sintered connection.

4. The magnetic sheet according to any one of the preceding claims, characterized in that The thickness 18 of the magnetic sheet 2 is between 300 μm and 2000 μm.

5. The magnetic sheet according to any one of the preceding claims, characterized in that The material layers 4 , 6 have a thickness between 10 μm and 150 μm.

6. The magnetic sheet according to any one of claims 1 to 5, wherein: The first material composition (12) comprises a ferrous alloy having an austenitic structure of at least 25% by volume.

7. The magnetic sheet according to any one of claims 1 to 6, characterized in that: The second material component (14) comprises an iron alloy having at least 95% by weight, in particular at least 97% by weight, of iron.

8. The magnetic sheet according to claim 7, characterized in that: The second material component (14) has a ferrite or martensite structure.

9. The magnetic sheet according to any one of claims 1 to 8, characterized in that: The first material component (12) is an iron-chromium-nickel alloy.

10. The magnetic sheet according to claim 9, characterized in that: The first material component (12) is an iron-chromium alloy having a chromium content of 22% to 28% by weight, in particular 24% to 26% by weight.

11. The magnetic sheet according to claim 9 or 10, characterized in that: The first material component (12) has a nickel content of 4% to 10% by weight, in particular 6% to 8% by weight.

12. A lamination stack for a rotor (38) of an electric machine (10), the lamination stack comprising a plurality of magnetic laminations (2) according to any one of claims 1 to 11.

13. The lamination stack according to claim 12, characterized in that: The uppermost material layer of the first magnet sheet and the lowermost material layer of the second magnet sheet are offset by an angle α.

14. The laminated core according to claim 1, characterized in that The sum of the angles α in the laminated core 8 is 7° to 36°.

15. A method for manufacturing a magnetic sheet, the method comprising the following steps: a) applying a first printing paste 22 to a substrate 28 through a template 26 by means of template printing 30, b) applying the second printing paste 24 to the substrate 28 so that the two printing pastes 22, 24 are adjacent and form a discrete border line 32, and forming the first material layer 4, c) drying the first material layer 4, d) rotating the orientation of the substrate 28 and / or the template 26 by an angle α relative to an axis 34 perpendicular to the substrate 28, e) applying a second material layer 6 according to steps a) to c), f) Sintering The green body 36 produced through steps a) to e) is formed into a magnetic sheet.

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