Method for producing a bipolar plate

Abstract

The invention relates to a method for producing a bipolar plate (14) of a fuel cell (10), comprising an anode plate (22) and a cathode plate (24), comprising at least the following method steps: a) carrying out a first punching step (52) in the anode plate (22) and / or the cathode plate (24) to form channels (32) having as large as possible rounded corners to produce a first channel depth (50), b) in a post-punching step (56), a reduced radius having a desired channel depth (64) and a desired channel depth (64) and a flat region are created in the anode plate (22) and / or the cathode plate (24), c) by suitably forming a stamping die (68, 72), retaining projections (62, 76, 80) in the anode plate (22) and / or the cathode plate (24) at the first channel depth (50) when performing method step b), d) producing a tack weld (82) at the projection (62, 76, 80) between the anode plate (22) and the cathode plate (24) by resistance welding and e) producing a joint seam (84) to ensure a sealing between the anode plate (22) and the cathode plate (24). The invention further relates to the use of the method for producing a bipolar plate (14) comprising at least one anode plate (22) and at least one cathode plate (24).

Description

Technical Field

[0001] The invention relates to a method for producing a bipolar plate having an anode plate and a cathode plate for a fuel cell. The invention also relates to an application of the method for producing a bipolar plate. Background Art

[0002] Publication DE 20 2021 104 930 U1 relates to a resistance welding device, which is particularly used to manufacture bipolar plates for fuel cells. In this case, an additional wire is provided in the form of an auxiliary joining component independently of the film material during welding. The device or method involved is based on the following design: a welding protrusion or the like is formed by the auxiliary joining component described. Nevertheless, the use of an auxiliary joining component in the form of an additional wire together with the welding protrusion that still exists is feasible, for example when an additional, especially point-shaped, welding connection is still desired. The device or method involved will strive to achieve minimization of waste and defective products, high process quality products, and at least partial automation, especially with regard to large quantities or short operating times.

[0003] Publication DE 10 2019 210 633 A1 relates to a method for producing a distribution structure, in particular a method for producing a bipolar plate for a fuel cell, which consists of a plurality of components arranged in a stack. In this case, there is the possibility that the components of the distribution structure, in particular the bipolar plate, namely the cathode structure, the separator and the anode structure, are connected to each other in a material-locked manner by means of resistance welding during operation. In addition, multiple welds or welding points can be produced in parallel to achieve shorter operating times, in particular in production lines.

[0004] Publication DE 10 2010 007 705 A1 relates to a method for producing bipolar plates for fuel cells. In this case, the individual plates are connected to one another in a locking manner by means of a brazing material in order to avoid the disadvantages of other methods, such as laser or resistance welding, such as longer processing times and processing costs or local temperature loads, which may lead to damage to the bipolar plates.

[0005] The core component of a fuel cell is a fuel cell stack, in which a chemical reaction between oxygen and hydrogen occurs and thus generates electricity. The stack can be composed of up to hundreds of individual cells, which in turn come from a stack consisting of an anode plate, a membrane electrode unit and a cathode plate. The connection of the anode plate and the cathode plate forms a bipolar plate. The main task of the bipolar plate is to guide and separate hydrogen, air and a cooling medium, for example, described as a water / ethylene glycol mixture. In terms of the power of the fuel cell, the minimum resistance in the bipolar plate should be pursued. The electrical contact is carried out under the following conditions. The anode plate and the cathode plate of the fuel cell are usually connected in the active area using a shorter laser welding weld to achieve the smallest possible transition resistance between the anode plate and the cathode plate. The channel structure of the active area is usually manufactured by a forming process, such as stamping. Depending on the principle, the upper plate is welded through (durchschweiβen) during laser welding to weld into the lower plate or also weld through the lower plate to produce electrical contact. Therefore, there is a danger that leakage can occur upward or downward through the appearance of a defect point. In order to seal outwardly and inwardly between the individual media at the ends of the anode plate and the cathode plate, the seal is usually achieved by means of laser beam welding. On the one hand, this requires expensive fixing tools to ensure a gap-free contact between the anode plate and the cathode plate, because otherwise leaks are to be expected. Instead of laser beam welding, resistance welding can be used, which does not have the so-called disadvantages inherent in laser beam welding, namely welding through the upper plate and expensive fixing concepts.

[0006] In resistance welding, a joint connection is produced between the plates without a melt being produced above or below. The reason for this is that the ohmic resistance on the contact surface between the anode plate and the cathode plate is greater than the resistance in the component through which it flows, and therefore a larger portion of the energy is converted into heat energy at this location and a melt is produced. Leakage points can therefore be avoided depending on the process. In addition, the electrodes are accompanied by the required joint force on the components, which closes any gaps that may exist. If the gap remains (which is extremely unlikely due to the low component rigidity of the thin plates), no current will flow and therefore no joint connection will be formed. Summary of the invention

[0007] According to the present invention, a method for producing a bipolar plate having an anode plate and a cathode plate for a fuel cell is provided, comprising at least the following method steps:

[0008] a) performing a first punching step in the anode plate and the cathode plate to form channels with as large a radius as possible to produce a first channel depth,

[0009] b) producing reduced radii and the desired channel depths as well as flat areas in the anode and / or cathode plates in a post-punching step,

[0010] c) by suitably designing the stamping tool, a projection remains in the anode plate and / or cathode plate at the first channel depth during the implementation of method step b),

[0011] d) producing a spot weld by resistance welding at the projection between the anode plate and the cathode plate, and

[0012] e) Producing a joint between the anode plate and the cathode plate to ensure a sealing function.

[0013] The solution proposed according to the invention makes it possible to produce welding projections in very thin anode plates or cathode plates with a thickness of less than 300 μm, in particular less than 80 μm, which welding projections can achieve contact with the large electrode by means of resistance welding and thus avoid process-dependent leaks. If additional welding projections are produced in the form of tack welds in the sealing weld area in order to achieve a technically zero gap between the anode plates and cathode plates placed one above the other, the sealing weld can be carried out, for example, by means of a laser beam without the need for expensive fixing technology, which is extremely advantageous for large-scale production.

[0014] In an advantageous development of the method proposed according to the invention, anode plates or cathode plates are used whose plate thickness is less than 300 μm, in particular less than 100 μm.

[0015] In a further advantageous embodiment of the method proposed according to the invention, capacitor discharge welding is used as the preferred resistance welding method. This advantageously generates relatively high, pulsed currents. Another advantage of capacitor discharge welding is the possibility of achieving short operating times.

[0016] In the method proposed according to the invention, the joining seam can be produced according to d) after the spot welds have been produced by a laser welding method which can be automated and allows mass production.

[0017] In the method according to the invention, in an advantageous manner, in the first carrier step According to method step a), a channel with a channel radius is produced, which allows the formation of a first channel depth that exceeds the required channel depth. Thus, in the first punching step, a material reserve is already created, which can be further deformed in an advantageous manner during the subsequent punching step.

[0018] Advantageously, the method according to the invention enables the channel radius formed in the first punching step to be punched again within the framework of the post-punching step according to method step b) to form an angular channel shape and to punch out a flat contact surface.

[0019] In an advantageous extension of the method proposed according to the invention, a stamping die comprising an upper die and a lower die is used when carrying out the post-stamping step in accordance with method steps b) and c), on the one hand using the upper die of the stamping die to produce an angular channel profile, and on the other hand using the lower die of the stamping die having a groove to produce an area constructed at the desired channel depth by reverse extrusion between the protrusions retained in the first channel depth.

[0020] Advantageously, the method proposed according to the invention makes it possible to form a projection which can be embodied on the one hand as a single welding projection or as a double projection or as a reduced welding projection.

[0021] In an advantageous development of the method proposed according to the invention, the spot welds produced in method step d) which are produced by means of resistance welding are used to produce a technically zero gap between anode plates and cathode plates of the bipolar plate to be produced which are arranged one above the other.

[0022] In an advantageous development of the method proposed according to the invention, the joint seam produced according to method step e) can be processed by laser beam welding. Alternatively, there is the possibility of producing the sealing seam by fusion welding methods, such as electron beam welding, laser beam welding and also by plasma welding.

[0023] Advantageously, in the method according to the invention, the tack welds are arranged inside or outside the area to be sealed. The tack welds can be arranged on the left and right side of the continuous weld. Alternatively, the sealing seam can be formed in such a way that the sealing seam extends in the form of a serpentine line, alternatingly to the left and to the right around the tack welds.

[0024] The invention therefore relates to the use of a method for producing a bipolar plate comprising at least one anode plate and at least one cathode plate.

[0025] Advantages of the invention

[0026] The solution proposed according to the invention is characterized in that resistance welding, which is described by capacitor discharge welding, in particular in the mass production of bipolar plates, produces electrical contacts on the one hand and can be used for sealing by pre-positioning welding on the other hand. A series of advantages can therefore be achieved compared to the solutions known from the prior art. Depending on the process, a joint connection is produced in the form of a welding line in the abutment surface during resistance welding. Leakage upward or downward is impossible without molten material, so that a reduced probability of exclusion due to leakage is obtained in the flow field of the bipolar plate to be manufactured. By pre-positioning welding of the anode plate and the cathode plate, a technical zero gap can be ensured near the weld seam of the laser welding to be performed later, so that only the fixing of the entire plate is still required to ensure that the work is in the focal position for the joint seam to be manufactured. This results in a reduced cost for preparing a fixture for the welding sealing profile.

[0027] By means of targeted current conduction, the current is concentrated by means of the punching structures formed in the first punching step and in the subsequent post-punching step, so that the energy available for resistance welding is sufficient to weld all connections with relatively few current pulses. For this purpose, the possibility is created to produce electrical contacts by welding and to carry out pre-positioning welding, both of which can be carried out in one method step.

[0028] It is conceivable to integrate the resistance welding device into a stamping device in which the stamping process is carried out, so that it is possible to benefit from a more robust and rigidly produced bipolar plate which is easier to handle in subsequent processing steps.

[0029] Thermal expansion and contraction during the welding process occur primarily in the stamped structure, so that component deformations can be minimized accordingly.

[0030] The above-mentioned targeted current guidance makes it possible to achieve shorter welding times, which leads to less tempering and material conversion, which in turn has a positive effect on the corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the present invention will be further explained based on the drawings and the following description.

[0032] The accompanying drawings show:

[0033] Figure 1 : Cross section of fuel cell and bipolar plate;

[0034] Figure 2 : Schematic diagram of a channel structure consisting of an anode plate and a cathode plate with a welding seam to reduce contact resistance;

[0035] Figure 3 : Linear support for cathode and anode plates;

[0036] Figure 4: Schematic diagram of resistance welding connection;

[0037] Figure 5 : Schematic diagram of the channel shape according to the first punching step;

[0038] Figure 6 : The channel shape after the post-punching step is performed with the protrusion having a portion cut out to serve as a welding protrusion;

[0039] Figure 7 : By means of the channel structure of a punching die including an upper die and a lower die;

[0040] Figure 8 : A schematic diagram of a protrusion configured as a double protrusion;

[0041] Fig. 9 : A schematic diagram of a reduced protrusion used as a welding protrusion, and

[0042] Fig.10 : Schematic diagram of a positioning weld for illustrating a technically zero gap and a continuously extending weld seam. DETAILED DESCRIPTION

[0043] In the following description of exemplary embodiments of the invention, similar or identical elements are identified with the same reference symbols, wherein a repeated description of these elements in individual cases is omitted. The figures illustrate the subject matter of the invention only schematically.

[0044] Figure 1 The cross section of the fuel cell 10 and the bipolar plate 14 is shown. In addition to the bipolar plate 14, the fuel cell 10 includes a membrane electrode unit 12 (MEA). The gas diffusion layer 20 runs through the membrane electrode unit 12. The cathode is marked with a reference numeral 18 and the anode is marked with a reference numeral 16. Figure 1 As can be seen from the diagram of FIG. 1 , the bipolar plate 14 extends below the membrane electrode unit 12, and the bipolar plate basically includes an anode plate 22 and a cathode plate 24. Channels 32 for a cooling medium flow 30 run in the cathode plate 24 and the anode plate 22, wherein the cooling medium is typically a water-ethylene glycol mixture. In addition, the channels 32 through which the hydrogen flow 28 passes run in the anode plate 22, and the channels 32 through which the air flow 26 passes run in the cathode plate 24.

[0045] according to Figure 2 It can be inferred from the diagram that the channel structure consisting of the anode plate and the cathode plate 22, 24 has a weld seam for reducing the contact resistance. Figure 2As can be seen from the perspective top view of FIG. 3 , the channel 32 is introduced both into the anode plate 22 and into the cathode plate 24. A single short joint section 34 is implemented at the bottom of the channel 32, which can be designed as a laser weld, for example, in order to achieve the smallest possible transition resistance between the anode plate 22 and the cathode plate 24. A flat area 36 runs on both sides of the channel 32 in the anode plate 22 and the cathode plate 24, which is undeformed and is also referred to as a “ground”.

[0046] according to Figure 3 The illustration of shows a channel structure in which the anode plate 22 and the cathode plate 24 are joined to one another in a materially bonded manner at the bottom of the individual channels 32 via a joining section 38 which is designed as an uninterrupted line.

[0047] according to Figure 4 The diagram of FIG. 1 schematically shows a resistance welded connection. Figure 4 As can be seen from the diagram, the first plate 44 and the second plate 46 are connected to each other in a material-locked manner by a nugget 42, in particular a welding nugget. By arranging the nugget 42 between the first plate 44 and the second plate 46, the medium 40 to be sealed can be sealed to prevent flowing through the contact gap between the first plate 44 and the second plate 46.

[0048] According to Figure 5 As can be seen from the diagram of FIG. 5 , the channel 32 is introduced into the anode plate 22 and / or the cathode plate 24 by means of a first punching step 52. By means of a punching die (see Figure 7 ), a first punching step 52 is performed, wherein at least one channel 32 is punched into the material of the anode plate 22 and / or cathode plate 24 with a channel depth 50, taking into account the formation of a relatively large channel radius 54. The anode plate 22 and / or cathode plate 24 has a plate thickness 88 of less than or equal to 300 μm, in particular less than or equal to 100 μm, in particular 80 μm.

[0049] according to Figure 5 The anode plate 22 or cathode plate 24 processed by the first punching step 52 will be Figure 6 The post-punching step 56 is subjected to a deformation of the channel radius 54 in order to achieve an angular channel profile 60 of the channel 32 in the anode plate 22 or cathode plate 24. The post-punching step 56 is carried out using a two-part punching die, wherein the channel radius 54 is deformed according to Figure 7 The upper mold 68 and the lower mold 72 are shown in the figure. Figure 6 In the schematically illustrated post-punching step 56, in addition to forming the angular channel profile 60, the flat contact surface 58 is formed. This results in a reduction in the first channel depth 50, which was formed in the first punching step 52, so that the reduced required channel depth 64 is achieved.

[0050] During the post-punching step 56, as in Figure 6 As schematically shown in FIG. 5 , however, by providing a recess on the lower die 72, the projection 62 configured as a welding projection remains in the recess region of the lower die 72. In the channels 32 of the anode plate 22 and / or the cathode plate 24, respectively, the projections 62 are retained, which are implemented in the first channel depth 50, but the sections of the channels 32 extending between the projections 62 have a reduced desired channel depth 64 of the channels 32. Therefore, in the post-punching step 56, the bottom of the channel 32 is pressed back from the channel depth 50 reached in the first punching step 52 to the reduced desired channel depth 64.

[0051] Therefore, with Figure 5 and 6 Compared to the illustration in , the longer channel 32 in the anode plate 22 and / or cathode plate 24 results in a channel 32 in which a plurality of convex protrusions 62 are generated at intervals from one another along the longitudinal extension direction at the bottom of the channel 32 , which are later used as welding protrusions.

[0052] according to Figure 7 The diagram of FIG. 1 shows that the upper die 68 is adapted to the final contour of the channel 32 and the final contour is formed in the channel 32 by feeding the upper die 68 onto the material of the anode plate 22 and / or cathode plate 24. The lower die 72 of the counter tool, i.e. the punching die, is designed as a flat plate which has the above-mentioned recess for forming the projection 62 in the region of the projection 62.

[0053] According to Figure 8 and 9 The illustration of shows the individual geometries of the projections.

[0054] Figure 8 For example, a channel 32 is shown which is designed as an angular channel profile 60 and in which a projection is punched into the channel wall contour 70 of the channel, in particular on the bottom, in the form of a double projection 76. Two adjacent double projections 76 are separated from each other by a flat section 78. By means of the double projections 76, as in Figure 8 As shown in , an additional centering function can be achieved when engaging with the channel ground structure. Figure 8 It can also be seen from the illustration of that an undeformed flat area 36 , ie the “floor”, extends alongside the channel 32 .

[0055] According to Fig. 9As can be seen from the diagram of the embodiment variant of the channel 32, a reduced protrusion, ie a reduced welding projection 80, is formed on the bottom of the channel 32 formed in the form of an angular channel profile 60, ie in the channel wall contour 70. This structure can achieve a stronger current concentration.

[0056] Depend on Fig.10 This results in a combination of resistance welded spot welds 82 and a continuous laser weld seam, which is designed here, for example, as a continuous weld seam 84. Fig.10 As can be inferred from the illustration, individual tacking spots 82 are arranged at a distance from one another between the first plate 44 and the second plate 46 or between the anode plate 22 and the cathode plate 24. The function of the tacking spots 82 produced within the framework of resistance welding, for example by capacitor discharge welding, is that the plates 44, 46 or the anode plate 22 and the cathode plate 24 are fixed to one another by means of the tacking spots 82, forming the bipolar plate 14 after the production of the continuous joint seam 84. The tacking spots 82 produced by means of resistance welding ensure that a technically zero gap 86 is present between the plates 44, 46 or between the anode plate 22 and the cathode plate 24, in order to produce the continuous joint seam 84 after the resistance welding.

[0057] According to Fig.10 As can be seen from the description of FIG. 8 , the continuously extending joining seam 84 is implemented as a laser welding seam, for example. This embodies the sealing function required in technology.

[0058] The position of the positioning weld 82 between the first plate 44 and the second plate 46 or the anode plate 22 and the cathode plate 24 can be located not only outside the area to be sealed but also inside the area to be sealed. Based on the following assumption, if the medium to be sealed is on the right side of the joint 84 (sealing seam) constructed between the two plates 44 and 46, the inner area extends to the right side of the joint 84 and the outer area extends to the left side of the joint 84. However, the two media can also be separated from each other by the joint 84, so that the two media are sealed by the joint 84. Although according to Fig.10 In the illustration of FIG. 8 , the joint seam 84 has a substantially straight course; alternatively, it is also possible for the joint seam 84 to run around the tack weld 82 in a serpentine or meandering manner.

[0059] According to Fig.10 In addition to laser beam welding, the continuous joint seam 84 can also be processed by alternative joining processes. In accordance with the electrical contact, for current conduction, the punching required for realizing a large number of joint connections using current pulses is implemented in the anode plate 22 and / or the cathode plate 24, for example. Figure 8 and 9 As shown in .

[0060] The invention is not limited to the described embodiments and the aspects highlighted therein. On the contrary, numerous modifications are possible within the scope of the claims, which fall within the scope of skilled working practice.

Claims

1. A method for producing a bipolar plate (14) having an anode plate (22) and a cathode plate (24) for a fuel cell (10), comprising at least the following method steps: a) performing a first punching step (52) in the anode plate (22) and / or the cathode plate (24) to form channels (32) with corners that are as rounded as possible to produce a first channel depth (50), b) in a post-punching step (56), a reduced radius and a desired channel depth (64) as well as flat areas are produced in the anode plate (22) and / or the cathode plate (24), so that c) by suitably configuring the stamping tool (68, 72), during method step b), a projection (62, 76, 80) remains in the anode plate (22) and / or the cathode plate (24) at the first channel depth (50), d) creating a tack weld (82) at the protrusion (64, 76, 80) between the anode plate (22) and the cathode plate (24) by resistance welding and e) Creating a seam (84) to ensure sealing between the anode plate (22) and the cathode plate (24).

2. The method according to claim 1, characterized in that The plate thickness (88) of the anode plate (22) and the cathode plate (24) is less than 300 μm, in particular less than 100 μm.

3. The method according to any one of claims 1 to 2, characterized in that: According to method steps d) and / or e), capacitor discharge welding is used as the resistance welding method.

4. The method according to any one of claims 1 to 2, characterized in that: In method step e), the joining seam (84) is produced by a laser welding method.

5. The method according to any one of claims 1 to 4, characterized in that: In a first punching step (52) according to method step a), a channel (32) is produced having a channel radius (54) which enables the formation of a first channel depth (50) which exceeds a desired channel depth (64).

6. The method according to any one of claims 1 to 5, characterized in that: In a post-punching step (56) according to method step b), the channel radius (54) is punched out again, an angular channel contour (60) is formed and a flat contact surface (58) is punched out.

7. The method according to any one of claims 1 to 6, characterized in that: When implementing the post-punching steps according to b) and c), a punching die comprising an upper die (68) and a lower die (72) is used, on the one hand, an angular channel shape (60) is produced by the upper die (68) of the punching die, and on the other hand, an area constructed at the desired channel depth (64) is produced by reverse extrusion between the protrusions (62, 76, 78) retained at the first channel depth by the lower die (72) of the punching die having a groove.

8. The method according to any one of claims 1 to 7, characterized in that: The projection (62, 76, 80) is implemented as a single welding projection (62) or as a double projection (76) or as a reduced welding projection (80).

9. The method according to any one of claims 1 to 8, characterized in that: According to method step d), the spot welds (82) are used by resistance welding to produce a technically zero gap (86) between the anode plate (22) and the cathode plate (24) of the bipolar plate (14).

10. The method according to any one of claims 1 to 3, characterized in that: According to method step e), the joining seam (84) is produced by laser beam welding or a fusion welding method, such as electron beam welding or plasma welding.

11. The method according to any one of claims 1 to 9, characterized in that: The weld spots (82) are arranged inside or outside the region to be sealed by the joint seam (84), wherein the joint seam (84) runs either straight or in a serpentine or meandering manner between the weld spots (82).

12. Use of the method according to any one of claims 1 to 11 for producing a bipolar plate (14) comprising at least one anode plate (22) and at least one cathode plate (24).

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