Method for manufacturing a bipolar plate string, method for manufacturing a bipolar plate and device for performing the method

Abstract

The invention relates to a method for manufacturing a bipolar plate string (214), the method comprising the steps of: - providing a monopolar plate string (200, 202), - guiding the monopolar plate string (200, 202) in the direction of a roll gap (104) of a roll pair (106) of a roll arrangement (102) provided with a roll structure (112), - emitting a laser beam (110) of a laser arrangement (108) onto a rotating, mirrorized polygonal wheel (146), whereby the laser beam (110) is aligned towards a plurality of individual positions of a surface (210, 212) of one or both of the monopolar plate strings (200, 202) and thus the individual positions are heated to a joining temperature directly before or at the time the monopolar plate string (200, 202) enters the roll gap (104), and - joining the monopolar plate string (200, 202) into the bipolar plate string (214) at at least one of the individual positions of the surface (210, 212) under pressure while the monopolar plate string (200, 202) is transported through the roll gap (104). The invention also relates to a method for manufacturing a bipolar plate and to an apparatus (100) for performing the method.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for producing a bipolar plate string having a plurality of connected bipolar plates of a fuel cell. The invention also relates to a method for producing a bipolar plate for a fuel cell and to an apparatus for carrying out both methods. BACKGROUND

[0002] Bipolar plates are used in fuel cells and fuel cell stacks. By means of the bipolar plates, fuel is conducted and distributed to adjacent anodes of a first fuel cell and cathode gas is conducted and distributed to adjacent cathodes of a second fuel cell, wherein the bipolar plates are furthermore provided with conduits for guiding a cooling medium. Bipolar plates are mostly produced from two monopolar plates which are formed as half-shells and which are bonded to one another in bipolar plates formed from graphite. Metal bipolar plates usually comprise two monopolar plates which are at least sectionwise welded to one another.

[0003] EP 2 090 395 A2 describes an apparatus for producing metal material composites and composite semi-finished products by warm plating. Short-time heating of at least one metal strip by means of electromagnetic induction and laser radiation is carried out before the at least two strips enter into the gap of the rolls. Due to the extreme metallurgical incompatibility of the base material and the coating material, each one intermediate layer material is introduced between the base material and the coating material. DE 10 2018 219056 A1 shows an apparatus for the continuous production of bipolar plates using a laser welding device.

[0004] JP 2009 193 868 A and JP 2013 152 941 A describe a seam welding method in which two monopolar plate strings are joined at the edge-side seams. DE 10 2016 125 502 A1 describes an apparatus for producing bipolar plates for fuel cells using a seam welding machine.

[0005] DE 10 2016 125 502 A1 describes an apparatus for producing bipolar plates for fuel cells, wherein a base plate is first automatically transported to a forming device and then to a joining device. The forming device punches a channel into the base plate by means of a punching tool.

[0006] A method for manufacturing bipolar plates is described in DE 10 2010 054 617 A1, in which method the shaping of the pole plates is first carried out and the pole plates are then joined to bipolar plates. A cleaning process for cleaning the pole plates by means of a liquid medium is carried out within the production line. It is also pointed out in this document that the joining of the metal pole plates can be carried out by means of a fusion welding process or a soldering process, wherein other joining methods, such as adhesion, or mechanical joining methods, such as flanging, should also be possible.

[0007] A welding method for welding two monopolar plates to one bipolar plate is described in US 2005 / 0 252 892 A1. US 2004 / 0 072 053 A1 also describes a method and apparatus for welding two monopolar plates to one bipolar plate or for welding these two monopolar plates with a spacer plate. Finally, WO 2007 / 135 509 A1 also shows the possibility of welding two monopolar plates to one bipolar plate by means of a laser beam.

[0008] Some of the methods and apparatuses described in the previously mentioned documents use the laser beam for welding aligned essentially perpendicularly to the plane in which the monopolar plates extend. Here a weld seam is produced, in which a continuous seam can be produced which fulfils the sealing function. But so-called stepwise seams can also be formed, which provide mechanical stability of the bipolar plate and improved electrical contact of the monopolar plates.

[0009] It has proved to be that in such laser-welded bipolar plates there is a risk of pore formation which can lead to local impermeability in terms of the medium flow. Such impermeabilities occur statistically especially at the weld seams which have particularly far- extending extensions. Furthermore, it is known that impermeabilities occur with increased frequency at the beginning or end of the weld seam. That is to say the risk of impermeabilities increases with the number of weld seams used and their length. Furthermore, it has proved to be time-consuming and difficult for laser welding that the two monopolar plates can be tensioned in a tensioning device in such a way that the laser beam is thereby focused at the desired, to be welded, site. Some bipolar plate manufacturers therefore transition to providing additional stampings at the channels and / or tabs of the monopolar plates in order to provide a place for the tensioning means of the tensioning device, which stampings exhibit sufficient width for the weld seams to be provided. The additional stampings furthermore provide a margin in terms of sufficient production tolerances when positioning the components. SUMMARY

[0010] It is therefore the object of the present application to specify a method for manufacturing a bipolar plate string, a method for manufacturing a bipolar plate and a device for carrying out the method, which reduce or completely eliminate at least some of the above-mentioned disadvantages.

[0011] The object is achieved by a method for manufacturing a bipolar plate string having the features according to the application, by a method for manufacturing a bipolar plate having the features according to the application and by a device having the features according to the application. The application has a plurality of advantageous design variants, which have suitable improvements of the application.

[0012] The method for manufacturing a bipolar plate string, which has a plurality of connected bipolar plates of a fuel cell, comprises in particular the following steps:

[0013] providing a first monopolar plate string and a second monopolar plate string, wherein the monopolar plate strings comprise a plurality of at least preformed tabs and a plurality of at least preformed channels running between each two adjacent tabs,

[0014] guiding the monopolar plate strings in the direction of the roll gap of a roll pair of a roll arrangement provided with a roll structure,

[0015] emitting a laser beam of a laser arrangement onto a rotating, mirrorized polygon wheel, whereby the laser beam is aligned towards a plurality of individual locations of a surface of one or both monopolar plate strings and thus the individual locations are heated to a joining temperature directly before or at the time of the monopolar plate strings entering the roll gap, and

[0016] joining the monopolar plate strings into a bipolar plate string at at least one of the individual locations of the surface under pressure while the monopolar plate strings are transported through the roll gap.

[0017] The joining process is here carried out in particular point-like but line- oriented by using a new laser technology, which uses a polygon wheel. Here, the joining geometry to be achieved is produced by arranging point-like melting portions together, which are produced by the transport of the monopolar plate strings (or individual monopolar plates) and by the laser beam deflected by the polygon wheel.

[0018] The method is in particular suitable for line-oriented, surface-type applications, since by this the process time can be greatly reduced. Furthermore, by using a rotating polygon wheel, a generally lower heat input into the raw material can be achieved. Since, in addition, the omission of a tensioning technology can be achieved, the channel and tab geometry of the bipolar plates can also be further optimized in terms of flow technology.

[0019] It is possible to use beam distribution directions, whereby it is also possible to irradiate several polygonal wheels with separate laser beams. Thereby, it is possible to heat not only a single location on one monopolar strip string, but also several monopolar strip strings in different production lines.

[0020] It can be the case that the heating by means of the laser device is either not sufficient to heat the material of the two monopolar strip strings to their joining temperature, either due to the laser beams being separated, or due to the short-time radiation with the laser alone. It therefore proves to be meaningful for at least one, preferably both, of the monopolar strip strings to be preheated before being guided to the roll gap. There can be an induction heating device or an infrared radiator for this purpose.

[0021] If the two regions of the monopolar strip string to be joined have not yet been preformed and, if necessary, are still flat, i.e. exist as flat material, it proves to be advantageous for the tabs and the channels to be punched by means of at least one punching device before the monopolar strip string is provided to the roll device. Here, it is also possible, in addition, for the tabs and channels of the monopolar strip string to already be pressed into their final shape; i.e. not in a preformed state, but in a finished shape, to be supplied to the roll pair.

[0022] If, however, the preformed tabs and channels are only constructed at the bipolar strip string by means of the punching device, it is advantageous for the preformed tabs and the preformed channels to be pressed into their final shape under pressure when being conveyed through the roll gap by means of the roll arrangement.

[0023] Depending on the material selection or material combination of the monopolar strip or monopolar strip string, it proves to be meaningful for the bipolar strip string to be stress relieved, in particular reheated or annealed, by means of a thermal device. This increases the connection strength of the two monopolar strips to bipolar strips.

[0024] In order to provide a seal against the reaction medium and / or a reliable seal against coolant escape, which is required for use in a fuel cell stack, it is advantageous for at least one seal to be applied to at least one, preferably both, of the outer surfaces of the bipolar strip string by means of an application device. For this purpose, the application device can be a printing device, for example, which prints a sealing material onto the outer surfaces of the bipolar strip string in screen printing. After the application of the sealing material, this can be hardened at a predetermined temperature, for which the application device can additionally have a suitable heating device.

[0025] Depending on the chosen material concept of the entire fuel cell, additional coatings of the bipolar plates are generally desired. Thus, it proves to be meaningful in this regard to apply at least one coating to at least one of the outer surfaces, preferably to both outer surfaces, of the bipolar plate string by means of a coating device. For this purpose, a printing device can also be used, which applies the desired coating material to the outer surfaces, for example by means of roller printing. The printing device can also comprise suitable heating devices here in order to dry the applied coating material. The coating can take place, for example, after the application of the seal. However, the possibility also exists that the coating is applied first and the outer surfaces are provided with at least one seal only subsequently.

[0026] In order to manufacture bipolar plates for use in a fuel cell stack, which are cut to final size, the possibility is opened up that the bipolar plate string is cut open into individual bipolar plates by means of a cutting device. The cutting of the bipolar plates, which are still connected to one another at the end of the manufacturing process, into stackable units has the advantage that the positional tolerances of the individual process steps can be significantly reduced in this way.

[0027] The uniform intensity of the laser beam can be achieved in that there is a drive unit for rotating the polygon wheel, which is configured to drive the polygon wheel at at least 1000 revolutions per minute. A drive of up to 12000 revolutions per minute is preferred. In this regard and in order to avoid intensity fluctuations, the drive unit is preferably additionally configured to keep the number of revolutions of the polygon wheel constant.

[0028] The radiation of the at least one polygon wheel, preferably a high-speed galvanometer, is achieved here with a laser device, which is in particular configured as a cw laser. Currently, "cw" stands for "continuous wave" and means a "wave that is emitted constantly over time". The possibility exists that the laser device is a pulsed laser. There can also be a plurality of laser devices.

[0029] The advantages and preferred implementation variants described for the method for manufacturing a bipolar plate string also apply to the method for manufacturing a bipolar plate for a fuel cell according to the application, since the device used for this is also suitable and designed to join, thus weld, single plates that have already been cut to final size into bipolar plates instead of rod material.

[0030] The method for manufacturing a bipolar plate according to the application thus comprises in particular the following steps:

[0031] - providing a first single plate and a second single plate, wherein the single plates comprise a plurality of at least preformed tabs and a plurality of at least preformed channels running between each two adjacent tabs,

[0032] - guiding the monopolar plates in the direction of the roll gap of a roll pair of the roll arrangement provided with a roll structure,

[0033] - locally heating at least one surface region of the surface of one or both of the monopolar plates, wherein the surface region is heated to the joining temperature directly before or at the time of entry of the monopolar plates into the roll gap, and

[0034] - joining the monopolar plates into bipolar plates at the at least one surface region under pressure action when transporting the monopolar plates through the roll gap,

[0035] - emitting a laser beam of a laser arrangement onto a rotating, mirrorized polygon wheel, thereby aligning the laser beam towards a plurality of individual locations of the surface of one or both of the monopolar plates, and thus the individual locations are heated to the joining temperature directly before or at the time of entry of the monopolar plates into the roll gap, and

[0036] - joining the monopolar plates into bipolar plates at at least one of the individual locations of the surface when transporting the monopolar plates through the roll gap under pressure action.

[0037] The method for joining two monopolar plates into bipolar plates also eliminates the disadvantages known from the prior art.

[0038] The device for carrying out the above-mentioned method according to the invention comprises a laser arrangement, which is configured to heat at least one surface region of the surface of one or both of the monopolar plate strings or of the monopolar plates to the joining temperature by means of at least one laser beam. Furthermore, there is a roll arrangement, which has a roll pair between which a roll gap is configured, wherein the rolls of the roll pair are provided with a roll structure, which is configured to press the plurality of heated to the joining temperature surface regions of the two monopolar plates or of the two monopolar plate strings when transporting through the roll gap, so that the two monopolar plate strings are joined into a bipolar plate string, or so that the two monopolar plates are joined into a bipolar plate at the surface regions. The laser arrangement is assigned at least one rotationally driven, mirrorized polygon wheel, so that the laser beam is aligned towards a plurality of individual locations of the surface of one or both of the monopolar plate strings or of the monopolar plates, and thus the individual locations are heated to the joining temperature directly before or at the time of entry of the monopolar plate strings or of the monopolar plates into the roll gap.

[0039] The feeding of the raw material and the point-like and / or line-like melting of this material caused by the polygon wheel lead to particularly tight joining seams (welding seams), which are required, in particular, in the case of bipolar plates, which require a reliable separation of the operating media of the fuel cell stack. The apparatus is therefore particularly suitable for linearly oriented, planar applications, since the process time can be greatly reduced by means of the apparatus. Furthermore, by using a rotating polygon wheel, a generally lower heat input into the raw material can be achieved. Since, in addition, the omission of tensioning technology can be achieved, the channel and web geometry of the bipolar plates can also be further optimized in terms of flow technology.

[0040] For example, when the monopolar plates or the strings of monopolar plates are pressed under pressure while being conveyed through the roller gap, the surface area configures, in the roller gap, a plurality of contact lines of the webs of two monopolar plates or two strings of monopolar plates lying on top of one another.

[0041] In other words, the laser device is thus formed in such a way that the material of the monopolar plates is heated to the joining temperature at the regions at which they are to be joined, thus locally at the surface of the monopolar plates, in particular locally at the webs of the strings of monopolar plates or the monopolar plates. The subsequent roller device is thus formed in such a way that the required joining force is applied when the two monopolar plates or the two strings of monopolar plates are conveyed through the roller gap in order to permanently connect the two monopolar plates or the two strings of monopolar plates to one another as bipolar plates or as strings of bipolar plates.

[0042] The laser device is preferably equipped with a control device which is configured to operate the optical system of the laser device and also the drive of the polygon wheel. Here, the polygon wheel can be moved so quickly that a plurality of surface regions can be heated by means of the laser beam in order to configure a plurality of joined contact lines or contact points between the two monopolar plates or between the two strings of monopolar plates when being conveyed through the roller gap.

[0043] By using this apparatus, the risk of impermeability in the subsequent bipolar plates is substantially reduced by principle, whereby the production rejects to be expected are also significantly reduced. The laser device, in particular the optical system of the laser device, allows a good positionally and temporally controllable (or, if required, adjustable) heat source and thus a robust process guidance and a high welding quality.

[0044] An advantageous refinement of the apparatus is provided in that at least one of the monopolar plates or at least one of the strings of monopolar plates is straightened (thus leveled) by means of a straightening device before the webs or channels are introduced therein. To this end, the apparatus has one, preferably even two, straightening devices.

[0045] Furthermore, the possibility is opened that there is a punching device in order to at least pre-form the plurality of tabs and the plurality of channels, in particular to punch them into the material. Here, it is possible that each monopolar string is provided with its own punching device. Alternatively, it is also possible that there is a combined punching device which punches two monopolar strings.

[0046] In order to pre-heat the monopolar string or the monopolar plate before it is guided into the roll gap, it proves to be advantageous that there is at least one induction heating device which inductively heats one of the monopolar plates or the monopolar string. Alternatively or in addition, there can also be an infrared radiator for pre-heating the material. Thereby, the subsequent introduced laser beam has to have a smaller energy in order to heat the material to its joining temperature, whereby the laser device can be designed smaller.

[0047] Furthermore, the device can comprise a thermal device which is post-positioned to the roll device and which is configured to stress-free the material of the bipolar string or the bipolar plate, in particular to anneal it.

[0048] Furthermore, the device can comprise an application device which is post-positioned to the roll device and which is configured to apply a seal to at least one of the outer surfaces of the bipolar string or the bipolar plate. Here, a printing device as already explained above can be used.

[0049] Furthermore, the possibility is opened that the device comprises a coating device which is post-positioned to the roll device and which is configured to provide at least one of the outer surfaces of the bipolar string or the bipolar plate with a coating. For this purpose, the device can also comprise a printing device as already mentioned above which applies the coating, for example in a roller printing method.

[0050] The device can furthermore comprise a cutting device which is configured to separate the bipolar string into individual bipolar plates or to cut the bipolar plate to the final size.

[0051] The features and combinations of features mentioned in the description above and the features and combinations of features mentioned in the description of the figures below and / or shown in the figures alone can be used not only in the respective combination mentioned, but also in other combinations or on their own, without leaving the scope of the present application. Thus, embodiments which are not explicitly shown or explained in the figures, but which are known and can be derived from the explained embodiments by separate combinations of features, are also included in and considered disclosed by the present application. BRIEF DESCRIPTION OF DRAWINGS

[0052] Further advantages, features and details of the present application result from the following description of preferred embodiments and in accordance with the drawings. Therein:

[0053] Figure 1a detailed view of a cross-section of a segment of a fuel cell stack with bipolar plates formed by two monopolar plates,

[0054] Figure 2 a schematic diagram of a system for manufacturing a bipolar plate string consisting of two monopolar plate strings and / or a bipolar plate consisting of two monopolar plates,

[0055] Figure 3 a detailed view of a roll gap of a roller pair and a monopolar plate in it or a monopolar plate string in it, and

[0056] Figure 4 a schematic diagram of a system for manufacturing a bipolar plate string consisting of two monopolar plate strings and / or a bipolar plate consisting of two monopolar plates. DETAILED DESCRIPTION

[0057] In Figure 1 a segment of a fuel cell stack consisting of a plurality of fuel cells 220 can be seen. Each fuel cell 220 is formed with a membrane electrode assembly 222, which comprises a membrane that can conduct protons, which on both sides is respectively assigned an electrode. The membrane electrode assembly 222 is designed to carry out the electrochemical reaction of the fuel cell. Here, a fuel, for example hydrogen, is introduced at the electrode that forms the anode, where the fuel is catalytically oxidized to protons with the emission of electrons. These protons are transported through the membrane that can conduct protons (or ion exchange membrane) to the cathode. The electrons that are drawn out of the fuel cell flow through an electrical consumer, preferably through an electric motor for driving a vehicle, or to a battery. Subsequently, the electrons are introduced at or provided at the cathode. At the cathode, an oxidation medium, for example oxygen or air containing oxygen, is reduced to anions by receiving electrons, which anions directly react with the protons to water.

[0058] By means of the bipolar plate 216, the fuel or the cathode gas is introduced at the gas diffusion layer 224, which introduces the respective gas in a diffusely distributed manner to the electrode of the membrane electrode assembly 222. The fuel, the oxidation medium and, if necessary, a cooling medium are introduced through the channels 208 of the bipolar plate 216, which are limited on both sides by the tabs 206 of the bipolar plate 216 with the tab back. As can be taken from Figure 1 for this, a set of tab backs respectively lies against the gas diffusion layer 224, so that the reactants flowing in the channels 208 can be output to the gas diffusion layer 224 and thus to the electrode of the membrane electrode assembly 222.

[0059] In the present case, the bipolar plate 216 comprises two stacked unipolar plates that are selectively joined to one another, in particular welded, at their facing webs 206, in particular at their respective web backs. The facing webs 206 of the unipolar plates, together with the channels 208 located between the webs 206, typically form a conduit for the cooling medium.

[0060] from Figure 1 As can also be seen in the figure, the webs 206 of the monopolar plates or their web backs do not necessarily have to have the same width, so that different widths and / or depths of the channels 208 can also exist. However, for a permanent connection of the two monopolar plates, it should be ensured that at least two of the opposite webs 206 are arranged one above the other and can be permanently connected to one another, in particular welded.

[0061] in accordance with Figure 2 An apparatus is illustrated for manufacturing a bipolar plate string 214 having a plurality of connected bipolar plates 216 for a fuel cell 220. The apparatus is also configured to directly manufacture the bipolar plates 216; even without previously manufacturing such a bipolar plate string 214.

[0062] A plurality of raw materials or a single raw material for the bipolar plates 216 are currently provided to an unwinding device 140 or to a plurality of unwinding devices 140, which include a first roller 128 and a second roller 130. The rollers 128, 130 provide the raw material for the first unipolar plate string 200 and the second unipolar plate string 202. To straighten the material of the first roller 128, a first straightening device 132 is located downstream of the first unwinding device 140 of the first roller 128. To straighten the material of the second roller 130, a second straightening device 134 is located downstream of the second unwinding device 140 of the second roller 130. The raw material unwound from the first roller 128 and straightened by the first straightening device 132 is processed by means of the first punching device 114 in such a way that the first unipolar plate string 200 is provided with a plurality of at least preformed webs 206 and a plurality of at least preformed channels 208 extending between each two adjacent webs 206. The raw material unwound from the second roller 130 and straightened by the second straightening device 134 is processed by means of the second punching device 116 in such a way that the second monopolar plate string 202 is provided with a plurality of at least preformed webs 206 and a plurality of at least preformed channels 208 extending between each two adjacent webs 206 .

[0063] The thus shaped monopolar plate string 200, 202 is then moved in the direction of the roll arrangement 102, if necessary by means of suitable diverting devices, towards the roll gap 104 of the roll pair 106 provided with the roll arrangement 112. The two monopolar plate strings 200, 202 are here led into one another at an entry angle with respect to the roll gap 104. Before the two monopolar plate strings 200, 202 meet at the roll gap 104, the two monopolar plate strings are first preheated, if necessary. The preheating of the first monopolar plate string 200 takes place by means of a first induction heating device 136 for inductively heating the material of the first monopolar plate string 200. The preheating of the second monopolar plate string 202 takes place by means of a second induction heating device 138 for inductively heating the material of the second monopolar plate string 202.

[0064] The device further comprises a laser device 108 which is configured to emit a laser beam 110. The laser device 108 here comprises a rotating, mirror-finished polygon wheel 146 through which the laser beam 110 is aligned towards a plurality of individual positions of the surface 210, 212 of one or both of the monopolar plate strings 200, 202 and thus the individual positions are heated to the joining temperature directly before or at the time of the entry of the monopolar plate strings 200, 202 into the roll gap 104. In the case of a suitable number of revolutions, the polygon wheel 146 can also be formed in such a way that the laser beam is enlarged, so that a ("quasi-static") laser line can be produced for heating the material to the joining temperature. In any case, the laser beam 110 can also be focused or focusable or suitably shaped in or at the roll gap 104 or in the vicinity of the roll gap 104 with the polygon wheel 146. The laser beam 110 is configured to locally heat at least one surface region, but preferably a plurality of surface regions, of the surfaces 210, 212 of the two monopolar plate strings 200, 202. Here, the heating takes place at the surface regions of the facing surfaces 210, 212, in particular when the monopolar plate strings 200, 202 enter the roll gap 104. Preferably, the faces to be heated here have or are formed by some of the tab backs of the tabs 206. Due to the preheating by means of the induction heating devices 136, 138 and the heating action generated by the laser beam 110, the material of the monopolar plate strings 200, 202 is heated to the joining temperature. Here, it is not necessarily required that the joining temperature is present over the entire material cross section of the monopolar plate strings 200, 202, so that a gradient temperature distribution can be present in the cross section. In the case of a continuous conveying of the two then one on top of the other arranged monopolar plate strings 200, 202, the roll pair 106 of the roll arrangement 102 exerts a joining pressure at the at least one surface region heated to the joining temperature, so that the two monopolar plate strings 200, 202 are joined (and thus welded) into a common bipolar plate string 214 at these regions.

[0065] At least one laser beam 110 or a plurality of distributed laser beams 110 from the laser device 108 are aligned using a suitable optical system toward a rotating, mirror-coated polygon wheel 146 before striking one or both of the monopolar plate strings 200 , 202 or individual monopolar plates. The mirror-coated polygon wheel 146 preferably has a base formed as a regular polygon (e.g., a polygon), a top surface corresponding to the base, and a circumference formed by a mirror-coated rectangle connecting the base and top surfaces. The polygon wheel 146 is rotatably mounted about an axis of rotation, wherein an electric drive unit is provided and is configured to rotationally drive the polygon wheel 146 about an axis of rotation oriented perpendicularly to the direction of incidence of the laser beam 110. When the laser beam 146 strikes the mirror-coated rectangle on the circumference of the polygon wheel 146, it is reflected, with the rotation of the polygon wheel 146 optionally causing the laser beam to be expanded. By means of the polygonal wheel 146 , surface areas of the monopolar plate strings 200 , 202 can thus be locally (regionally) heated to the joining temperature, ie in particular before the two rollers press the individual strings together and thus join them.

[0066] By using the polygon wheel 146, the material is brought to the joining temperature or even melted in spots, wherein a joining line formed by these spots is produced by feeding in the production line. These spots preferably partially overlap, thereby producing a fluid-tight joining line composed of spots.

[0067] exist Figure 3 As can be seen in FIG, the roller structure 112 of the rollers of the roller pair 106 can have different roller projections 142, 144, which in the contact region 204 either cause the two monopolar plate strings 200, 202 to join due to the acting joining pressure, or in which case this is not the case. Thus, according to the present invention, on the one hand, there are active roller projections 142, between which the roller gap 104 causes the two monopolar plate strings 200, 202 located therein to join, and on the other hand, there are passive roller projections 144, between which the roller gap 104 does not cause a permanent connection between the two monopolar plate strings 200, 202. The roller projections 142, 144 can also be present only in sections at the circumference of the respective roller. For example, active roller projections 142 are arranged radially at predefined intervals around the periphery, thereby enabling step seams or seams to be produced between the sheet metal strands, thereby reducing the weld seam length and process time. This opens up the possibility of each roller being able to produce a defined number of short seams / step seams during unwinding, depending on the roller configuration 112. Furthermore, there is the possibility of designing passive roller projections 144 or all passive rollers solely as guides for the sheet metal strands.

[0068] As derived from the above description of the device Figure 2 The roll device 102 is followed by a thermal device 120 for stress relieving the produced bipolar plate string 214, in particular for annealing the bipolar plate string 214. The thermal device 120 is followed by an application device 122 which is configured to apply a seal on at least one, preferably both outer surfaces 218 of the bipolar plate string 214. Furthermore, the application device 122 of the device is followed by a coating device 124 which is configured to apply a suitable coating on at least one of the outer surfaces 218, preferably both outer surfaces, of the bipolar plate string 214. Furthermore, the coating device 124 is followed by a cutting device 126 in order to separate the bipolar plates 216 which are connected to each other in the bipolar plate string 214 and, if necessary, to cut to the desired final size; thus, single bipolar plates 216 are also provided.

[0069] In Figure 4 a further variant of the device for manufacturing bipolar plates 216 is shown which differs from the variant according to Figure 2 the variant only in the design of the punching device. Here, the punching device is formed as a combined punching device 118 which can punch the raw material of the first monopolar plate string 200 and the raw material of the second monopolar plate string 202 jointly. Thus, the necessity of a more complex design with a first punching device 114 and a second punching device 116 is dispensed with. Furthermore, the entry angle of the two monopolar plate strings 200, 202 into the roll gap 104 of the roll device 102 is reduced, thereby resulting in an improved non-deformability of the bipolar plate string 214 and the bipolar plates 216 which are separated from this bipolar plate string.

[0070] Thus, with the present application a device and a method for manufacturing bipolar plates 216 or bipolar plate strings 214 are explained which provide for the production of bipolar plates 216 in very large piece numbers and with a short cycle time. The device and the explained method are thus suitable for series production and reduce the share of rejects in the production of bipolar plates 216 relative to known methods and devices. The welding connection formed according to the present application ensures the required sealing and the required electrical contact of the two monopolar plates or strings thereof.

[0071] List of reference signs

[0072] 102 roll device

[0073] 104 roll gap

[0074] 106 roller pair

[0075] 108 laser device

[0076] 110 laser beam

[0077] 112 roll structure

[0078] 114 first punching device

[0079] 116 second punching device

[0080] 118 combined punching device

[0081] 120 heating device

[0082] 122 application device (seal)

[0083] 124 coating device (coating)

[0084] 126 cutting device

[0085] 128 first roller (first coil)

[0086] 130 second roller (second coil)

[0087] 132 first straightening device

[0088] 134 second straightening device

[0089] 136 first induction heating device

[0090] 138 second induction heating device

[0091] 140 unwinding device

[0092] 142 roller protrusion, active (roller configuration)

[0093] 144 roller protrusion, passive (roller configuration)

[0094] 146 polygonal wheel (mirrorized)

[0095] 200 first monopolar string

[0096] 202 second monopolar string

[0097] 204 contact area

[0098] 206 web

[0099] 208 channel

[0100] 210 surface (first monopolar string / first monopolar plate)

[0101] 212 surface (second monopolar string / second monopolar plate)

[0102] 214 bipolar string

[0103] 216 bipolar plate

[0104] 218 outer surface

[0105] 220 fuel cell

[0106] 222 membrane electrode assembly

[0107] 224 gas diffusion layer

Claims

1. A method for manufacturing a bipolar plate string (214) having a plurality of connected bipolar plates (216) for a fuel cell (220), the method comprising the steps of: - providing a first monopolar plate string (200) and a second monopolar plate string (202), wherein, The monopolar plate string (200, 202) includes a plurality of at least preformed tabs (206) and a plurality of at least preformed channels (208) extending between each two adjacent tabs (206). - guiding the monopolar plate string (200, 202) in the direction of the roller gap (104) of a roller pair (106) provided with a roller structure (112) of a roller device (102), - directing a laser beam (110) of a laser device (108) onto a rotating, mirrored polygonal wheel (146), thereby directing the laser beam (110) toward a plurality of individual locations of the surface (210, 212) of one or both of the monopolar plate strings (200, 202), and thereby heating the individual locations to a joining temperature immediately before or when the monopolar plate strings (200, 202) enter the roller gap (104), and - joining the monopolar plate strings (200, 202) into a bipolar plate string (214) under pressure at at least one of the single locations on the surface (210, 212) while the monopolar plate strings (200, 202) are conveyed through the roller gap (104).

2. The method according to claim 1, characterized in that Before providing the monopolar plate string (200, 202), the tabs (206) and the channels (208) are punched by means of at least one punching device (114, 116, 118).

3. The method according to claim 1 or 2, characterized in that The preformed web (206) and the preformed channel (208) are pressed into their final shape by means of the roller arrangement (112) under pressure while being conveyed through the roller gap (104).

4. The method according to any one of claims 1 to 2, characterized in that The bipolar plate string (214) is stress relieved by means of a thermal device (120).

5. The method according to any one of claims 1 to 2, characterized in that At least one seal is applied to at least one of the outer surfaces (218) of the bipolar plate string (214) by means of an application device (122).

6. The method according to any one of claims 1 to 2, characterized in that At least one coating is applied to at least one of the outer surfaces (218) of the bipolar plate string (214) by means of a coating device (124).

7. The method according to any one of claims 1 to 2, characterized in that The bipolar plate string (214) is cut into individual bipolar plates (216) by means of a cutting device (126).

8. The method according to any one of claims 1 to 2, characterized in that The polygonal wheel is driven around at a rotational speed of at least 1000 revolutions per minute.

9. A method for manufacturing a bipolar plate (216) for a fuel cell (220), the method comprising the steps of: - providing a first unipolar plate and a second unipolar plate, wherein the unipolar plates include a plurality of at least preformed webs (206) and a plurality of at least preformed channels (208) extending between each two adjacent webs (206), - guiding the monopolar plate in the direction of the roller gap (104) of a roller pair (106) provided with a roller structure (112) of a roller device (102), - directing a laser beam (110) of a laser device (108) onto a rotating, mirrored polygonal wheel (146), thereby directing the laser beam (110) toward a plurality of individual locations on the surface (210, 212) of one or both of the monopolar plates and thereby heating the individual locations to a joining temperature immediately before or while the monopolar plates enter the roller gap (104), and - joining the monopolar plates to form bipolar plates (216) under pressure at at least one of the individual locations on the surfaces (210, 212) while the monopolar plates are conveyed through the roller gap (104).

10. A device for carrying out the method for producing a bipolar plate string (214) according to any of the preceding claims 1 to 8 or the method for producing a bipolar plate (216) for a fuel cell (220) according to claim 9, the device comprising a laser device (108) configured to heat at least one surface area of ​​a surface (210, 212) of one or both of the two monopolar plate strings (200, 202) or one or both of the monopolar plates to a joining temperature by means of at least one laser beam (110), wherein: A rolling device (102) is provided, the rolling device having a pair of rollers (106) with a roller gap (104) formed therebetween, wherein the rollers of the pair of rollers (106) are provided with a rolling structure (112) which is configured to press a plurality of surface areas of the two monopolar plates or the two monopolar plate strings (200, 202) heated to a joining temperature when conveyed through the roller gap (104) in such a way that the two monopolar plate strings (200, 202) are joined to form a bipolar plate string (214), or the two monopolar plates are joined at the surface areas. A composite bipolar plate (216) is characterized in that the laser device (108) is equipped with at least one rotationally driven, mirrored polygonal wheel (146) so that the laser beam (110) is directed toward a plurality of individual locations of the surface (210, 212) of one or two of the monopolar plate strings (200, 202) or one or two of the monopolar plates, and thus the individual locations are heated to the joining temperature immediately before or at the time when the monopolar plate strings (200, 202) or the monopolar plates enter the roller gap (104).

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