Method for adjusting the height and flatness of a monopolar and / or bipolar plate

Abstract

The invention relates to a method for adjusting the height and flatness (14, 16, 50) of a monopolar and / or bipolar plate (72), which is manufactured from a base plate (10) or from a base plate (10) and a top plate (12) and is joined by resistance welding. Indentations (32, 34) or protrusions (28) are embossed into the base plate (10) or the top plate (12), the depressions or protrusions (28) serving as tolerance compensation elements (60). The base plate (10) and the top plate (12) are then placed one on top of the other between two flat electrodes (36, 38), which are brought together to a defined distance (44) determined by at least one spacer (46).Subsequently, the depressions or protrusions (28) in the lower sheet (10) or the upper sheet (12), which serve as tolerance compensation elements (60), are pressed into the opposing lower or upper sheet (10, 12), forming an indentation geometry (54) in the latter. A current pulse is then applied to the electrodes (36, 38) to increase the temperature at the contact points formed by the depressions or protrusions (28) and the indentation geometry (54), thereby creating a metallurgical bond.

Description

Technical field

[0001] The invention relates to a method for adjusting the height and flatness of a monopolar and / or bipolar plate, which are manufactured from a base plate or from a base plate and a top plate and are joined together by resistance welding. Furthermore, the invention relates to the use of the method for joining monopolar / bipolar plates with defined flatness in a fuel cell stack arrangement or an electrolyzer stack arrangement. State of the art

[0002] DE 20 2021 104 930 U1 relates to a resistance welding system, which is used in particular for the production of bipolar plates for fuel cells. During welding, an additional wire material is provided as an auxiliary joining partner, independent of any foil material. The described device or method is based on the concept of forming a weld projection or the like using the described auxiliary joining partner. However, it is also possible to use the auxiliary joining partner in the form of the additional wire together with existing weld projections, for example, if spot welds are also required.The device and method described aim to minimize rejects and defective production, achieve high process quality, and at least partial automation, particularly with regard to high production volumes and short cycle times.

[0003] DE 10 2019 210 633 A1 relates to a method for manufacturing a distributor structure, in particular a bipolar plate for a fuel cell, from several components arranged in a stack. The method allows the components of a distributor structure, in particular a bipolar plate—namely a cathode structure, a separator, and an anode structure—to be joined together in a single operation by means of resistance welding. Furthermore, multiple welds or weld points can be produced in parallel to achieve a short cycle time, particularly in series production.

[0004] A key component of fuel cells is the fuel cell stack, where the chemical reaction between oxygen and hydrogen, and thus the generation of electricity, takes place. The stack can be composed of several hundred individual cells, which in turn consist of an anode plate, a membrane electrode assembly, and a cathode plate. The connection between the anode and cathode plates forms the bipolar plate. The main function of the bipolar plate is to guide and separate hydrogen, air, and the cooling medium, for example, a water / glycol mixture. Minimal electrical resistance within the bipolar plate is desirable for the fuel cell's performance.Electrical contact is achieved by joining the anode and cathode plates of a fuel cell in the active area using short laser welds to minimize contact resistance between the anode and cathode plates. The channel structure of the active area is typically created through a forming process, such as embossing. Due to the nature of laser welding, the upper plate is welded through to create the electrical contact, either by penetrating or welding through the underlying plate. This poses a risk of leakage due to defects at the top or bottom. Sealing between the different media in the ports of the anode and cathode plates, both externally and internally, is typically achieved using laser beam welding.This requires complex clamping tools to ensure gap-free contact between the anode and cathode plates, as otherwise leaks are likely to occur. Resistance welding can be used instead of laser beam welding, which does not have the aforementioned disadvantages, namely welding through the top plate and the need for a complex clamping system, which are inherent to laser beam welding.

[0005] Resistance welding creates a joint between the metal sheets without molten metal reaching the top or bottom surface. This is because the ohmic resistance at the contact surface between the anode and cathode sheets is higher than in the component through which the welding current flows. Consequently, the majority of the energy is converted into heat at this point, generating the molten metal. This inherently prevents leakage. Furthermore, the electrodes apply the necessary welding force to the components, closing any gaps that may be present. Should a gap remain, which is highly unlikely due to the low stiffness of the thin sheets, no current flows, and therefore no joint is formed.

[0006] DE 102022204913.6 relates to a method for manufacturing a bipolar plate. According to this solution, an anode plate and a cathode plate of a fuel cell are processed according to the following process steps: A first embossing step is carried out in the anode plate and / or the cathode plate to form channels with the largest possible radii to create an initial channel depth. In a subsequent post-embossing step, reduced radii and the required channel depth, as well as flat areas, are created in the anode plate and / or the cathode plate. Due to a suitable design of the embossing tool, protrusions remain in the initial channel depth in the anode plate and / or the cathode plate after the first embossing step. Tack welds are created on these protrusions between the anode plate and the cathode plate by resistance welding.Subsequently, a joint is created to ensure a tight seal between the anode plate and the cathode plate. The proposed method is used to manufacture a bipolar plate comprising at least one anode plate and at least one cathode plate.

[0007] WO 2019 / 144174 A1 relates to a resistance welding device comprising two welding heads with welding electrodes. The first welding head has a contact electrode, and the second welding head has a current bridge, which is electrically coupled to the second welding electrode. The contact electrode can be brought into direct contact with the current bridge, and the workpieces to be welded can be clamped between the first and second welding electrodes. In one embodiment, the first welding electrode and the contact electrode of the first welding head are arranged offset from each other in the transverse direction of the resistance welding device. This allows the contact electrode to be passed between the workpieces and thus brought into direct contact with the current bridge.

[0008] DE 10 2019 103 649 A relates to a method for joining a sandwich sheet by means of resistance welding. In one embodiment, the first welding electrode is preheated and then positioned in such a way that it heats the welding area by means of heat transfer and melts a plastic layer. Description of the invention

[0009] According to the invention, a method for adjusting the height and flatness of a monopolar and / or bipolar plate is proposed, which are made from a bottom sheet or from a bottom sheet and a top sheet and are joined together by means of resistance welding, wherein the following process steps are carried out: a) Embossing of depressions or protrusions into the lower sheet or the upper sheet; b) The lower sheet and the upper sheet are placed one on top of the other between two flat electrodes, which are moved together to a defined distance specified by at least one spacer. c) Pressing the recesses serving as tolerance compensation elements in the lower or upper sheet into the opposing lower or upper sheet and forming an indentation geometry in this and d) Applying a current pulse to the electrodes to increase the temperature at contact points formed from depressions / protrusions and indentation geometries, and creating a metallurgical bond there.

[0010] The solution proposed according to the invention makes it possible to achieve a defined flatness, particularly in bipolar plates, so that they can be stacked on top of each other in large numbers, forming a stacking arrangement, thereby largely eliminating sealing problems and tolerance problems.

[0011] In an advantageous further development of the method proposed according to the invention, the depressions or protrusions are embossed as weld bumps into a channel structure of a flow field according to process step a). The embossing enables a largely rounded contour of the protrusions or depressions, so that sharp-edged structures are avoided.

[0012] In an advantageous further development of the method proposed according to the invention, a holding force is applied to one of the two electrodes in process step b), which reduces an initially prevailing first distance between the lower sheet and the upper sheet to a defined second distance. The defined second distance can be determined in a process-engineering optimal manner.

[0013] In an advantageous further development of the method proposed according to the invention, the defined second distance between the first electrode and the second electrode is defined by the height of at least one spacer, which is preferably made of a poorly conductive material, for example ceramic. Depending on the selected height of the at least one spacer used, defined second distances can be specified as required.

[0014] In the method proposed according to the invention, the stiffness of the depressions or protrusions in the lower or upper sheet is higher than the stiffness of the channel structure in the lower or upper sheet. This allows the depressions and protrusions to be advantageously used to compensate for tolerances.

[0015] In the method proposed according to the invention, the depressions or protrusions are pressed into flattened areas of the channel structure in process step c), creating an indentation geometry. Through the interaction of the depressions and protrusions with the indentation geometries they each generate, contact points can be created between the components to be joined by material bonding, at which a planar, material-bonded connection can be executed, for example, by resistance welding.

[0016] In the method proposed according to the invention, in process step d), the modulus of elasticity and / or the yield strength of the material of the lower or upper sheet are significantly reduced at the contact points of the depressions or protrusions in the lower or upper sheet. Due to these phenomena, a reliable, metallurgical bond can be created at said contact points, for example, by means of resistance welding.

[0017] Advantageously, the method proposed according to the invention is designed such that residual stresses and elastic strain components in the lower sheet and / or the upper sheet are reduced and a reshaping of the lower sheet and / or the upper sheet after removal of the holding force and execution of process step b) is minimized, resulting in a defined flatness.

[0018] In the method proposed according to the invention, the depressions or elevations according to process step a) are advantageously formed on one or both sides of the lower / upper sheets.

[0019] In the method proposed according to the invention, the material-joining process is carried out by resistance welding, ultrasonic welding, laser welding or furnace processes in accordance with process step b).

[0020] In the method proposed according to the invention, in process step b) a reshaping of the lower sheet and / or the upper sheet is carried out by a first electrode and / or second electrode having a bend.

[0021] Furthermore, the invention relates to the use of the method for the material-bonded joining of monopolar / bipolar plates with defined flatness of a fuel cell stack arrangement or a stack arrangement for an electrolyzer. Advantages of the invention

[0022] The solution proposed according to the invention allows manufacturing tolerances and thus the resulting overall tolerances to be significantly reduced during joining, enabling the production of bipolar plates with greater flatness, which offers numerous further advantages. For example, bipolar plates with a defined, predetermined greater flatness result in better stacking compared to uneven plates. This facilitates both manual and, in particular, automated stacking of fuel cell stacks. Furthermore, a bipolar plate with greater flatness leads to a more uniform pressure distribution on the prestressed bipolar plate. Uneven pressure distribution can damage individual components of the stack and should be avoided whenever possible.

[0023] The bipolar plates proposed according to the invention, which have a greater flatness, enable a more uniform pressure distribution, particularly in the active area of ​​the prestressed bipolar plate, during its operation. Since the active area is extremely pressure-sensitive, a more uniform pressure distribution allows for better utilization of the membrane-electrode assembly. Furthermore, a more uniform pressure distribution improves the sealing of the gaskets between the membrane-electrode assembly and the bipolar plate assembly. Brief description of the drawings

[0024] The invention is described in more detail below with reference to the drawings. The drawings show: Fig. 1. Sustained total tolerances when joining upper or lower sheets without tolerance compensation, Fig. 2 an enlarged representation of a depression in a flattened area of ​​a lower or upper sheet metal, Fig. 3 an initial distance of a combination of lower and upper sheet, recorded between two planar electrodes opposite each other, Fig. 4. A flatness achieved by spacers is defined by applying a holding force. Fig. 5. The comparison of total tolerances with tolerance compensation in the case of tolerance compensation elements formed on the lower or upper sheet, Fig. 6. A variant design of indentation geometries or height reduction on a raised or recessed area created by embossing. Fig. 7 the top view of a number of embossed weld bumps and Fig. 8 a welding result that develops during material-joining by means of resistance welding.

[0025] According to the representation Fig. Figure 1 shows that the lower sheets 10 and upper sheets 12 are depicted with their sum tolerances, without any tolerance compensation. In the example shown above, according to... Fig. 1. A first flatness 14 is formed in the composite of the lower sheet 10 and the upper sheet 12. In the embodiment shown below, according to the illustration in Fig. 1. A second flatness 16 forms between the lower sheet 10 and the upper sheet 12. The first flatness 14 and the second flatness 16 differ from each other. In the example above, deformations 18 in the lower sheet 10 and deformations 20 in the upper sheet 12 lie on top of each other in a complementary pattern 22, so that the first flatness 14 is formed. In the second embodiment shown below, according to the illustration in Fig. 1. The lower sheets 10 and upper sheets 12 with their deformations 18, 20 lie less favorably against each other, so that an opposite course 24 of the deformations 18, 20 results, in contrast to a complementary course 22 according to the upper sketch in Fig. 1, which leads to a less favorable second flatness 16. This is less favorable than the first flatness 14.

[0026] Fig. Figure 2 shows that the lower sheets 10 and upper sheets 12, which are stamped sheet metal parts and the starting materials for monopolar plates and bipolar plates 72 respectively, have laterally extending flattened areas 26. These laterally extending flattened areas 26 can have depressions or elevations representing weld projections 28. According to Figure 2, these have... Fig. 2. A deformation height 30 is achieved and can be formed, for example, by means of an embossing 32 in the corresponding components, i.e., in the lower sheet 10 or the upper sheet 12. An embossing 32 of a weld depression or a weld protrusion, also referred to as a weld bump 28, represents a deliberately applied deformation in the material of the lower sheet 10 or in the material of the upper sheet 12. The aforementioned components, i.e., the lower sheet 10 and the upper sheet 12, are sheet metal components that have been previously rolled and may optionally be provided with coatings. Embodiments of the invention

[0027] In the following description of embodiments of the invention, identical or similar elements are designated by the same reference numerals, and repeated descriptions of these elements are omitted in individual cases. The figures represent the subject matter of the invention only schematically.

[0028] Fig. Figure 3 shows that a composite of the lower sheet 10 and the upper sheet 12 is inserted between two essentially planar electrodes, namely a first planar electrode 36 and a second planar electrode 38. In the Fig. In the illustrated embodiment 3, the flat electrodes 36, 38 are shown separated. A first distance 42, representing an initial position, is established between the top surface of the composite of lower sheet 10 and upper sheet 12 on the one hand and the flat surface of the second electrode 38 on the other.

[0029] As soon as a holding force 40 is applied to one of the two planar electrodes 36, 38, in this case to the upper surface of the first planar electrode 36, the first distance 42 changes to a second defined distance 44. According to the embodiment in Fig. 4. The holding force 40 is applied to the first flat electrode 36. At least one spacer 46 is inserted between the facing sides of the first flat electrode 36 and the second flat electrode 38. This spacer is made of a poorly conductive material, such as ceramic, and is dimensionally accurate. The at least one inserted spacer 46 has a height 48, which defines the second defined distance 44 that is established between the first flat electrode 36 and the second flat electrode 38 before the metallurgical bond is created, preferably by resistance welding, between the lower sheet 10 and the upper sheet 12. Otherwise, the current flow between the electrodes 36 and 38 would pass through the spacers 46. Ceramic material is mentioned here as an example.It is possible to adjust the height by measuring the distance at the tool or in the drive unit.

[0030] The holding force 40 therefore holds the lower sheet 10 and the upper sheet 12 in position during the execution of the material-joining process, i.e. the resistance welding process.

[0031] Fig. Figure 5 shows a schematically enlarged representation indicating that in this embodiment, for example, individual weld bumps serving as tolerance compensation elements 60 (i.e., protrusions or depressions as in Figure 5) are located on the lower sheet 10. Fig. 2 shown, compare position 28 there), are formed. In the illustration according to Fig. 5 A gap width 74 is established between the upper sheet 12 and the lower sheet 10, which is essentially determined by the tolerance compensation elements 60. The same applies to the arrangement shown below in Fig. 5, in which the deformations 18, 20 in the lower sheet 10 and in the upper sheet 12 have a different position and the aforementioned components, i.e. the lower sheet 10 and the upper sheet 12, are arranged unfavorably one above the other. In this embodiment, a second profile 76 of the gap width between the lower sheet 10 and the upper sheet 12 is established.

[0032] The tolerance compensation elements 60 shown are provided by the elements associated with Fig. The deformations shown in Figure 3, in the form of depressions 28 and protrusions in the material of the lower sheet 10 and the upper sheet 12 respectively, which are represented by embossing 32, 34, are compensated for. From the design variants according to Fig. Figure 5 shows that a defined, predetermined flatness 50 is produced between the lower sheet 10 and the upper sheet 12. The distance between the electrodes 36, 38, the geometry of the monopole plates 72, i.e., the lower sheet 10 and the upper sheet 12, as well as the weld bosses 28, which are designed as depressions 28 and protrusions respectively, are adapted to each other in such a way that contact over the entire surface of the depressions 28 and protrusions produced by the embossing 32, 34 is ensured. This can be achieved because the stiffness of the depressions 28 and protrusions is higher than that of the channel structure 58, 70 into which these depressions 28 and protrusions are embossed by the embossing 32, 34. From the illustration according to Fig. 6 shows that when the holding force 40 is applied according to the illustration in Fig. 4 the depression 28 or elevation forms, for example, presses into the opposite sheet metal at the base of a channel structure 58 and deforms it. A deformation is caused, for example, by the in Fig. The indentation geometry 54 is indicated in Figure 6. Alternatively, instead of forming an indentation geometry 54, a reduction in height 56 ​​can also occur at the depression 28 or elevation in the channel structure 58, 70 formed by embossing 32, 34, in which a deformation height 30 decreases, as shown in the illustration according to Figure 6. Fig. Figure 2 shows that the depressions 28 or protrusions in the flats 26 of superimposed lower sheets 10 or upper sheets 12 cause these depressions 28 or protrusions to press into the opposite sheet, i.e., the opposite lower sheet 10 or the opposite upper sheet 12, and deform it, resulting in the aforementioned indentation geometries 54. Depending on the design of the geometry and the subsequent resistance welding process, it is also possible, as shown in the illustration according to Fig. 2 indicated, a deformation of the depression 28 or elevation is realized, so that corresponding contact points are created in both possible ways, at which, for example, a material-jointed connection can be formed by means of resistance welding, even in a semi-automated or highly automated manner.

[0033] According to the solution proposed according to the invention, the height between the lower sheets 10 and upper sheets 12 to be joined is no longer defined by the sheet geometry, but by the at least one spacer 46, preferably made of electrically poorly conductive material, for example ceramic, wherein tolerance compensation elements 60 in the form of the recesses 28 or protrusions produced by means of embossing 32, 34 ensure the electrical contact, so that a material-bonded connection, for example by means of resistance welding between the superimposed components is possible.

[0034] Applying an electric current pulse significantly increases the temperature in the contact areas between the depressions 28 and the raised areas created by the embossing 32, 34, on the one hand, and the indentation geometry 54, on the other. This results in a temporary and substantial reduction in the modulus of elasticity and / or the yield strength. Consequently, residual stresses and elastic strain components are reduced or at least significantly diminished. This minimizes springback of the metallurgically bonded components, the lower sheet 10 and the upper sheet 12, after the release of the clamping force 40. Preferably, the electric current pulse applied to the electrodes 36, 38 is designed to achieve both the height calibration described above using the tolerance compensation elements 60 and electrical contact.As a result, the specified defined flatness 50 of the materially bonded components bottom sheet 10 and top sheet 12 is obtained.

[0035] Fig. Figure 7 shows that the depressions 28 or elevations, which serve on the one hand as weld bumps and on the other hand as tolerance compensation elements 60, are embedded in the channel structure 58, 70. Fig. Figure 7 shows a section of a flowfield 68, as it is formed, for example, in monopolar plates which are welded together as bottom sheet 10 and top sheet 12 to form bipolar plates 72.

[0036] According to the representation Fig.Figure 8 shows a resulting weld 66, which depicts the individual weld points formed in the channel structure 58, 70. The bottom sheets 10 and top sheets 12 are the aforementioned monopolar plates, two of which are joined one above the other, i.e., one bottom sheet 10 and one top sheet 12, to form a bipolar plate 72. The depicted depressions 28 and protrusions, which are embossed into the channel structure 58, 70 of a flow field 68 by means of an embossing 32, 34, are to be considered exemplary. In general, a protrusion or depression 28 on the contact surfaces of the monopolar plate 72 is possible on one or both sides in any type and dimension.The protrusions or depressions 28, which serve as welding bumps and as tolerance compensation elements 60, can in principle also be used as tolerance compensation elements 60 without joining, purely by applying a holding force 40.

[0037] In addition to resistance welding as a method for introducing energy to reduce the Young's modulus, other material-bonding joining processes can also be used. In principle, alternative methods for introducing energy, such as ultrasonic welding, laser beam welding, or furnace processes for material-bonding, are also possible. Heating the material of the lower sheet 10 or the upper sheet 12 can also be carried out without joining. In principle, it is also possible to use an unevenly shaped electrode 36, 38 as the first and second electrodes, which can have any desired height profile. During joining, reshaping of the bipolar plate 72 can be achieved, for example, by a slightly curved electrode 36, 38. The electrode for calibrating the height can be flat and / or mechanically reinforced.It can also be designed in such a way that it is matched to the spring forces of all process components, so that after relief, i.e. removal of the holding force 40, the resulting bipolar plate 72 has a substantially homogeneous thickness.

[0038] The method proposed according to the invention is preferably used to produce a stacked arrangement of a number of monopolar plates or bipolar plates 72 as a stacked arrangement for a fuel cell or as a stacked arrangement for an electrolyzer. Due to the improved defined flatness 50 exhibited by the joined bipolar plates 72, more precise stacking with lower overall tolerances and greater tightness are ensured, which significantly increases the performance of the resulting fuel cell stack or stacked arrangement for use in an electrolyzer.

[0039] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 20 2021 104 930 U1

[0002] DE 10 2019 210 633 A1

[0003] DE 102022204913.6

[0006] WO 2019 / 144174 A1

[0007] DE 10 2019 103 649 A

[0008]

Claims

[1] Method for adjusting a height and a flatness (14, 16, 50) of a monopolar and / or a bipolar plate (72) which are manufactured from a bottom sheet (10) or from a bottom sheet (10) and a top sheet (12) and are joined by means of resistance welding, with the following method steps: a) embossing (32, 34) of depressions or elevations (28) into the lower sheet (10) or into the upper sheet (12); b) placing the lower sheet (10) and the upper sheet (12) on top of each other between two flat electrodes (36, 38) which are moved together to a defined distance (44) which is predetermined by spacers (46), c) pressing the depressions or elevations (28) serving as tolerance compensation elements (60) in the lower sheet (10) or in the upper sheet (12) into the opposite lower or upper sheet (10, 12) and forming an indentation geometry (54) in this and d) applying a current pulse to the electrodes (36, 38) to increase the temperature at contact points, each formed by a depression or elevation (28) and an indentation geometry (54) and producing a material connection there. [2] Method according to claim 1, characterized by that according to method step a) the depressions or elevations (28) are embossed as welding projections into a channel structure (58, 70) of a flow field (68). [3] Method according to claims 1 to 2, characterized by that according to method step b) a hold-down force (40) is applied to one of the electrodes (36, 38), which reduces a first distance (42) between the lower sheet (10) and the upper sheet (12) to a defined second distance (44). [4] Method according to claims 1 to 3, characterized bythat the defined second distance (44) between the first electrode (36) and the second electrode (38) is defined by a height (48) of at least one spacer (46), preferably at least one spacer (46) made of electrically poorly conductive material, preferably ceramic material. [5] Method according to claims 1 to 4, characterized by that the rigidity of the depressions or elevations (28) in the lower plate (10) or in the upper plate (12) is higher than the rigidity of the channel structure (58, 70) in the lower plate (10) or in the upper plate (12). [6] Method according to claims 1 to 5, characterized by that according to method step c) the depressions or elevations (28) are pressed into flattened portions (26) of the channel structure (58, 70) and there represent the indentation geometry (54). [7] Method according to claims 1 to 5, characterized bythat according to method step c) the depressions or elevations (28) in the lower sheet (10) or in the upper sheet (12) cause a height reduction (56) of the depressions (28). [8] Method according to claims 1 to 7, characterized by that according to method step a) at the contact points or depressions or elevations (28) in the lower sheet (10) or in the upper sheet (12) in the material of the modulus of elasticity and / or the yield strength of the material of the lower sheet (10) or the upper sheet (12) are greatly reduced. [9] Method according to claims 1 to 8, characterized by that residual stresses and elastic expansion components are reduced in the lower sheet (10) and in the upper sheet (12) and a reshaping of the lower sheet (10) and / or the upper sheet (12) after removal of the hold-down force (40) and implementation of method step b) is minimized and a defined flatness (50) is produced. [10] Method according to claims 1 to 9, characterized bythat the depressions (28) or elevations according to process step a) are made on one or both sides of the lower / upper sheet (10, 12). [11] Method according to claims 1 to 10, characterized by that, according to process step b), the material-to-material joining is carried out by resistance welding, ultrasonic welding, laser welding or by furnace processes. [12] Method according to claims 1 to 11, characterized by that during process step b) a reshaping of the lower sheet (10) and / or the upper sheet (12) is carried out by a first electrode (36) having a bend or a second electrode (38). [13] Use of the method according to one of claims 1 to 12 for the material-to-material joining of monopolar / bipolar plates (72) with defined flatness (50) of a fuel cell stack arrangement or of an electrolyzer.

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