Bipolar plate and method for embossing channel structures

Abstract

The present invention relates to a method for embossing a channel structure (3) with a plurality of parallel channel portions (5) in a planar metal sheet (11), in particular to form half plates (2, 2') for a bipolar plate (1) of an electrochemical cell, the method comprising the following steps: Providing a planar metal sheet (11) having a uniform initial thickness (d5); inserting the metal sheet (11) into a forming tool (12), wherein a base surface (BE) of the sheet (11) defined by the undeformed planar metal sheet (11) is provided to rest on a tool plane defined by a tool portion (13) of the forming tool (12); and forming a plurality of channel portions (5), wherein each channel portion (5) is designed to have two non-parallel sides (7, 8) so as to allow material from embossed portions (9, 10) of the metal sheet (11), located outside the sides and remaining in a plane parallel to the base surface (BE) and / or the base surface (BE) throughout the forming process, to be displaced to the sides (7, 8), each side (7, 8) extending from the base surface (BE) to an adjacent parallel plane.

Description

[Technical field]

[0001] The present invention relates to a method for embossing a channel structure with a plurality of parallel channel portions in a planar metal sheet to form a half-plate or metal sheet, and further relates to a bipolar plate for an electrochemical cell, in particular a fuel cell, manufactured using such a method. [Background technology]

[0002] A method for forming plate-shaped blanks is known, for example from DE 10 200 43 336 A1. Products which can be produced using this known forming method have walls with reduced thickness. Before forming, the blank from which the product is produced is provided with weld paths in the areas where the blank material flows during the forming process, which results in a reduced wall thickness compared to the wall thickness of the blank, the weld paths running in the direction of the material flow occurring during the forming process.

[0003] The forming method disclosed in Patent Document 2 is designed to produce pot-shaped metal parts from flat material. The forming method is a combination of deep drawing and pressing processes and is said to be particularly suitable for producing parts with highly complex shapes that have eccentric parts or areas of small material thickness. In particular, the forming method according to Patent Document 2 should make it possible to eliminate welded seams.

[0004] Patent Document 3 describes a molding method for forming a predetermined overpressure break point in a battery cover, where material from the battery cover needs to flow into a molded recess by moving a stamp part of a molding tool closer to the molded recess so that the remaining distance corresponds to the minimum wall thickness at the predetermined overpressure break point.

[0005] Patent document 4 discloses a compression tool intended for the production of half shells with high dimensional stability. When forming the half shells, the side walls of the tool are moved perpendicular to the direction of movement of the stamp. Thus, during forming, several tool parts perform adjustment movements in mutually perpendicular directions.

[0006] For example, US Pat. No. 5,399,633, US Pat. No. 5,499,623, US Pat. No. 5,499,633 and US Pat. No. 5,499,623 describe various forming methods for forming metal sheets under the influence of temperature.

[0007] US Pat. No. 5,399,633 and US Pat. No. 5,499,623 disclose various devices for electrohydraulic or electromagnetic forming of metal sheets.

[0008] Patent document 10 describes a press forming method in which a flat metal sheet is formed by press forming, where a shear deformation process occurs in which the material flows towards the curved section.

[0009] Patent document 11 discloses a forming tool and a method for producing deep-drawn sheet metal parts. In addition to the deep-drawing, a second production step is carried out, in particular in the form of extrusion.

[0010] DE 10 200 033 337 A1 describes a method for the continuous production of vehicle parts from metal sheets. For this purpose, the metal sheets are heated before they are separated and / or shaped. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] German Patent No. 19755964 [Patent Document 2] DE 102008031421 A1 [Patent Document 3] DE 102019103606 [Patent Document 4] DE 102013103612 [Patent Document 5] European Patent No. 3485992 [Patent Document 6] European Patent No. 0946311 [Patent Document 7] German Patent No. 19529429 [Patent Document 8] European Patent Application Publication No. 2292343 [Patent Document 9] German Patent No. 102007013017 [Patent Document 10] US Patent Application Publication No. 2016 / 158821 [Patent Document 11] DE 102010044788 A1 [Patent Document 12] DE 102017124724 A1 Summary of the Invention [Problem to be solved by the invention]

[0012] The object of the present invention is to specify a metal sheet forming option, further developed with respect to the aforementioned prior art, which is particularly suitable for the manufacture of channel structures of bipolar plates of electrochemical cells, in particular fuel cells, and which allows wall thickness variations within the final product. [Means for solving the problem]

[0013] This object is achieved according to the invention by a method for embossing a channel structure, comprising a step according to claim 1. The embossing method according to claim 1 is particularly suitable for producing at least one metal sheet or half plate for a bipolar plate according to claim 7. The embodiments and advantages of the invention described below in relation to a device, i.e. a bipolar plate, or a bipolar plate part which is part of a bipolar plate, in particular in the form of a half plate, also apply mutatis mutandis to the embossing method, i.e. the moulding method, and vice versa.

[0014] The method for embossing a channel structure with a plurality of parallel channel portions in a planar metal sheet, in particular for forming a half plate or a metal sheet for a bipolar plate, comprises: providing a planar metal sheet having a uniform initial wall thickness; Inserting the metal sheet into a forming tool, the base surface of the metal sheet defined by the undeformed planar metal sheet being provided to rest on a tool plane defined by a tool portion of the forming tool; forming a plurality of channel portions, each of which is formed to have two non-parallel sides, each of which extends from the base surface to an adjacent parallel surface, such that material of the embossed portion of the metal sheet that is located outside the sides and that remains in the base surface and / or in a plane parallel to the base surface throughout the molding process is displaced to the sides.

[0015] The invention is based on the idea that during deep drawing of a metal sheet the flat structure of the starting product, i.e. the initially planar metal sheet, is essentially preserved, while the wall thickness of the metal sheet in different metal sheet sections does not change or is reduced by forming.

[0016] The reduction in wall thickness occurs during deep drawing, especially in areas where material is displaced from the base surface of the metal sheet used as starting product, in order to produce walls that are inclined relative to the base surface, and in extreme cases perpendicular to the base surface. In the condition that the parts of the starting product located outside the inclined part remain in an unchanged position throughout the forming process, only the material that was originally in the surface part is available to form the inclined part, which corresponds to the perpendicular projection of the inclined part on the base surface.

[0017] This means that the more pronounced the inclination of the corresponding part of the final product that protrudes from the base surface, the less material is available to shape it using deep drawing. It must also be borne in mind that, depending on the material used, a high degree of forming can lead to work hardening, making the product more susceptible to cracking. Such a risk can be countered in traditional methods by avoiding steep sides in the embossed structure, but if the embossed structure restricts the channels for liquid and / or gas fluids, this can mean compromising fluidic optimality.

[0018] The embossing method according to the present application effectively deals with the conflict of objectives between the forming surface and the flow surface in that the material flows to a large extent in the planes where the metal sheet is located between the areas of different inclination in relation to the base surface as the reference surface in each case. Compared to the conventional deep drawing method, the embossing method has more features of extrusion. The part where the material flows to the side, i.e. the embossed part, remains in its original position during the embossing process. That is, the whole part is not drawn to the side during forming.

[0019] In particular, the embossed portions can be located on the base surface. Similarly, there can be embossed portions, each constituting the bottom of a channel portion. The material from at least one embossed portion located outside the channel portion and in the base surface is preferably pressed into at least one of the side surfaces adjacent thereto. Furthermore, the material from at least one embossed portion located in a plane parallel to the base surface, located between two side surfaces and constituting the bottom of the channel portion parallel to the base surface, is preferably displaced into one of the side surfaces adjacent thereto. The channel portion, the side surfaces of which are reinforced with material from the base surface and / or from a plane parallel to the base surface, can in particular have a cross section with a trapezoidal basic shape. The side surfaces of the channel portion are inclined, for example, at an angle of at least 45° and at most 78° to the base surface, although it is not necessary that both sides have the same angle of inclination. Also realizable are embodiments in which the shape of the side surfaces is completely or partially arcuate, for example arcuate or elliptical. Similarly, a completely planar shape of the channel bottom formed between the side surfaces is not required. It is also possible to eliminate the extensive channel bottom, in which case the channel can in particular have a U- or V-shape.

[0020] According to various possible variants of the method, the thickness of the metal sheet can be reduced, for example to a minimum of 70% of the initial thickness, by forming an originally planar metal sheet. Other values ​​that affect the material distribution arise when the projection is considered relative to the base surface. In this respect, material can accumulate in the side regions, which can be expressed as a projected thickness of 105% to 150% of the initial thickness.

[0021] When embossing of the planar areas displaces particularly large amounts of material, the flow of material from the planar metal sheet used as the starting product to the sides of the channel structure can even be so significant that the maximum wall thickness of the final product is found in the side areas rather than in the planar areas.

[0022] The embossing of the flat area, which is carried out to accumulate material in the side areas, results in a wall thickness of the embossed area of, for example, 50%-95%, in particular 60%-90%, of the initial wall thickness of the metal sheet. Embossing also has the advantage that it is possible to produce a final product with a relatively narrow wall thickness tolerance at different surface areas, even when using metal sheets whose wall thickness varies greatly due to quality variations within one and the same metal sheet.

[0023] The embossing depth of the channel structure produced by forming the metal sheet is, for example, from 2 to up to 10 times the initial wall thickness of the metal sheet. If all planar areas of the metal sheet are processed in the same way as the embossed parts, the wall thickness of the final product can theoretically be uniform. On the other hand, if the forming process results in a wall thickness that varies from surface part to surface part, and the mentioned parts can have a linear shape in plan view, in particular of the structured plate, i.e. of the formed metal sheet, the minimum wall thickness of the half plate is, for example, more than 2 / 3 of the maximum wall thickness of the half plate of the final product. The minimum wall thickness of the half plate can in particular be present in the outer planar area of ​​the lateral side of the channel structure, i.e. in the embossed area. The maximum wall thickness can also be present in the planar area of ​​the structured half plate, but instead, as already mentioned, in the lateral area of ​​the half plate.

[0024] The forming method can be carried out on already coated or uncoated metal sheets. The metal sheets are in particular steel sheets. The formed metal sheets with channel structures can in particular be used for bipolar plates of fuel cell systems or electrolysis systems for producing hydrogen. The bipolar plate can comprise at least one metal sheet embossed according to the invention. In particular, however, the bipolar plate comprises two metal sheets embossed according to the invention, one for the anode side of the bipolar plate and one for the cathode side of the bipolar plate. The two embossed half plates are usually joined to each other by welding to form the bipolar plate.

[0025] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings, here in simplified and partly exaggerated form, in which: [Brief description of the drawings]

[0026] [Figure 1] 1 shows an embossed structure of a metal sheet or half plate. [Diagram 2] 1 shows the features of a tool for embossing a metal sheet or half plate. [Diagram 3] 1 shows a bipolar plate. [Figure 4] 1 shows a fuel cell system with multiple fuel cells. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Figure 1 shows a half-plate 2, designated by reference number 2. Two such half-plates 2, 2' can be joined together, for example by welding, to form a bipolar plate 1 (see Figure 3). In a fuel cell system 100 (see Figure 4), the bipolar plate 1 separates a half-cell of a first fuel cell from a half-cell of a further fuel cell. Regarding the basic function of the bipolar plate 1, reference is made to the prior art cited at the beginning.

[0028] The half-plates 2 have an embossed structure 3, which in this case is a channel structure with a number of parallel channel portions 5, which are located in the active field of the subsequent fuel cell system 100. The channels for the fluids flowing through the fuel cell system 100 can be formed on the outer surface of the bipolar plate 1, between the two overlapping half-plates 2, 2'. The fluids are the coolant and working material of the fuel cell system 100.

[0029] The channel portion 5 formed by the embossed structure 3 has a wall generally indicated at 4. The wall 4 is constituted by two side surfaces 7, 8 and a bottom 9. A planar main area of ​​the half-plate 2, located at the base surface BE, indicated at 6, is located outside the channel portion 5. The wall thickness of the planar main area 6 is indicated at d1, unless otherwise reduced, as will be explained in more detail below.

[0030] The channel portion 5 has a trapezoidal cross-sectional shape, the inclination angle of the side surfaces 7, 8 relative to the main area 6 and thus relative to the base surface BE is indicated with α. Deviating from the outlined exemplary embodiment, it is also possible for the various side surfaces 7, 8 to be inclined at different angles relative to the base surface BE. In any case, the bottom 9 is located here in an embossing surface PE that is parallel to the base surface BE. The distance between the base surface BE and the embossing surface PE constitutes the embossing depth, indicated with PT, of the embossed structure 3.

[0031] When forming the embossed structure 3, firstly the undeformed planar metal sheet 11 is inserted into the forming tool 12, the tool underside of which is designated 13 and the tool upper side by 14. The tool underside 13 provides a tool plane WE on which rests the base surface BE of the half-plate 2 to be formed from the metal sheet 11. The basic shape of the embossed structure 3 of the half-plate 2 is predetermined by the cross-sectional shape of the tool parts 13, 14 which for this purpose have tool contours 16, 17.

[0032] Furthermore, in the example shown in FIG. 2, an embossing contour 15 of the tool top 14 can be seen, which is located directly next to the area where the channel structure 3 is to be formed. This embossing contour 15 ensures a reduced wall thickness d2 in the corresponding area of ​​the half-plate 2, called the embossed area 10, and a material displacement. The reduced wall thickness d2 is the minimum wall thickness that occurs due to forming. The material displacement means that the material flows laterally of the half-plate 2, in particular to the side surfaces 7, 8. This results in a wall thickness d3 in the area of ​​the side surfaces 7, 8, which is greater than the imaginary wall thickness that would occur without the embossing process. PW denotes the projected wall thickness of the side surfaces 7, 8, which means the projection relative to the base surface BE.

[0033] Furthermore, in this case, embossing also takes place in the region of the bottom 9, so that here the material from the bottom 9, which constitutes the embossed part, flows into the side surfaces 7, 8. The wall thickness of the bottom 9 is indicated with d4. The material flow that occurs during forming takes place both from the main region 6 to the side surfaces 7, 8 and from the bottom 9 to the side surfaces 7, 8, ensuring that the cavities formed between the tool contours 16, 17 in the closed forming tool 12 are completely filled. The material flows not only into the curved regions adjacent to the flat regions, but also over the entire length of the formed side surfaces 7, 8. The initial wall thickness, indicated with d5, of the undeformed metal sheet 11 is in the range of 50 μm to 100 μm in the exemplary embodiment.

[0034] Figure 3 shows a bipolar plate 1 with two half plates 2, 2' made of stainless steel, formed by the method according to the invention and joined together by welding. The bipolar plate 1 has an inlet area 30a for the fluid with an opening 40 and an outlet area 30b for the fluid with an opening 40'. A gas distribution structure 50 with a channel structure 3 is arranged between them and comprises a channel portion 5 (see Figure 1).

[0035] Figure 4 shows, as an example of an electrochemical cell, a fuel cell system 100 with a number of fuel cells 20. The same reference numerals as in Figure 3 indicate the same elements. The fuel cell 20 comprises two bipolar plates 1, 1', between which is disposed a polymer electrolyte membrane 70 or membrane electrode unit (MEA), which is usually covered on both sides by gas diffusion layers. [Explanation of symbols]

[0036] 1,1´ Bipolar Plate 2, 2´ Half Plate 3 Embossed structure, channel structure 4. Wall 5 Channel Part 6 Planar main area 7. Aspect 8. Side 9 Bottom 10 Embossed area 11 Undeformed metal sheet 12 Molding Tools 13 Tool bottom 14 Tool Top 15 Embossed Contours 16 Tool contour at top of tool 17 Tool contour at bottom of tool 20 Fuel Cell 30a Inflow area 30b Exit area 40, 40´ opening 50 Gas distribution structure 70 Polymer electrolyte membrane 100 Fuel Cell System α angle BE Base surface d1, d2, d3, d4, d5 wall thickness PE embossed surface PT Embossing Depth PW Projected wall thickness WE Tool Plane

Claims

1. A method for embossing a channel structure (3) with a plurality of parallel channel portions (5) in a planar metal sheet (11) to form half plates (2, 2'), comprising the steps of: Providing said flat metal sheet (11) having a uniform initial wall thickness (d5); - inserting said metal sheet (11) into a forming tool (12), the base surface (BE) of said sheet (11) defined by said undeformed planar metal sheet (11) being provided to rest on a tool plane (WE) defined by a tool portion (13) of said forming tool (12); forming said plurality of channel portions (5), each of said channel portions (5) being formed with two non-parallel sides (7, 8) such that material of the embossed portions (9, 10) of said metal sheet (11), which are located outside of said sides (7, 8) and which remain in said base surface (BE) and / or in a plane parallel to said base surface (BE) throughout the forming process, is displaced to said sides (7, 8), each side (7, 8) extending from said base surface (BE) to an adjacent parallel surface; A method comprising:

2. 2. The method according to claim 1, characterized in that the material of at least one embossed portion (10) located outside the channel portion (5) and within the base surface (BE) is pressed into at least one of the adjacent side surfaces (7, 8).

3. 3. The method according to claim 1 or 2, characterized in that the material of at least one embossed portion (9) in a plane parallel to the base surface (BE) and constituting the bottom of a channel portion (5) located between two side surfaces (7, 8) and parallel to the base surface (BE) is displaced to one of the side surfaces (7, 8) adjacent to the at least one embossed portion (9).

4. 4. The method according to claim 1, wherein the forming step results in a wall thickness (d3) of the side surfaces (7, 8) being reduced to 70% or more of the initial wall thickness (d5).

5. 5. The method according to claim 1, wherein the forced inflow of material into the side surfaces (7, 8) results in a projected wall thickness (PW) of the side surfaces (7, 8), measured in a normal direction to the base surface (BE), of at least 105% and up to 150% of the initial wall thickness (d5).

6. 6. The method according to any one of claims 1 to 5, characterized in that the embossing depth (PT) of the channel structure (5) is selected to be at least twice and at most ten times the initial wall thickness (d5) of the metal sheet (11).

7. A bipolar plate (1, 1') of an electrochemical cell, comprising at least one half plate (2, 2') having a channel structure (3) for a medium flowing through said electrochemical cell, the half plate (2, 2') being manufactured according to the method according to any one of claims 1 to 6.

8. 8. Bipolar plate (1, 1') according to claim 7, characterized in that the half-plates (2, 2') have a minimum wall thickness (d2) which is greater than or equal to 2 / 3 of the maximum wall thickness of the half-plates (2, 2').

9. 9. Bipolar plate (1, 1') according to claim 8, characterized in that the minimum wall thickness (d2) is defined outside the side surfaces (7, 8) of the channel structure (5).

10. 10. Bipolar plate (1, 1') according to claim 9, characterized in that the maximum wall thickness (d3) is defined in the area of ​​the side surfaces (7, 8) of the channel structure (5).

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