Device and method for welding half sheets to form a bipolar plate
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-17
- Publication Date
- 2026-03-18
Smart Images
Figure DE2024100327_14112024_PF_FP_ABST
Abstract
Description
[0001] Device and method for welding half sheets to a bipolar plate
[0002] The invention relates to a method for welding half-sheets to form a bipolar plate for a stack of electrochemical cells. Furthermore, the invention relates to a device suitable for carrying out such a method.
[0003] CN 112388166 A discloses various devices for securing bipolar plates during laser welding. Tool systems that combine a lower tool part with an upper tool part are assumed to be known. The welding process is carried out from both sides of the bipolar plate using two laser units through openings in the lower and upper tool parts.
[0004] A device described in CN 113967805 B is intended to enable the mounting of ultra-thin plates during laser welding. This device comprises a bottom plate and a plurality of additional plates, with individual components of the device being movably coupled to one another.
[0005] KR 102241379 B1 discloses a laser welding device for fuel cell separators constructed from half-sheet metal sheets. The device has a main block with recesses as fastening contours. Two or more so-called island-shaped blocks are to be fastened to the main block. The main block, i.e., the lower part of the tool, contains openings that open into the area of media flow openings in the half-sheet metal sheets to be welded. Inert gas can be passed through these openings during welding. The inert gas is used to reduce or prevent oxidation of the weld seam. KR 20130025527 A describes a device and a method for holding separator plates for fuel cells during welding, using a vacuum to fix components.
[0006] CN 108838240 A deals with the automated forming and welding of metallic bipolar plates constructed according to the "two plates, three fields" principle. Resistance welding is proposed as the welding process in this case. Shielding gas is also proposed.
[0007] When welding sheets in the production of bipolar plates, the clamping technology used is essential to press the sheets together without gaps. A flawless weld is only possible if the sheets lie directly on top of each other, i.e., without a gap between them. If this is not the case and there is a gap between the sheets that is larger than approximately 10% of the sheet thickness, the molten metal formed during welding will sag, creating holes. For weight reasons, technical developments are moving toward ever thinner sheet thicknesses, where this problem is even more prevalent.
[0008] The invention is based on the object of providing possibilities for welding bipolar plates for electrochemical systems which are further developed compared to the cited prior art and are characterized by particularly high process reliability and precision.
[0009] This object is achieved according to the invention by a device for welding half-sheets of a bipolar plate, designed according to claim 1. The object is also achieved by a method for welding the half-sheets of a bipolar plate, according to claim 7.
[0010] The device according to the invention for welding half-sheets to form a bipolar plate comprises at least three tool parts, namely a lower tool part and a multi-part upper tool part, wherein the half-sheets to be welded together can be inserted between the lower tool part and the multi-part upper tool part. The multi-part upper tool part comprises several individual parts that can be arranged one after the other and only alternatively above the lower tool part, wherein each of the individual parts of the multi-part upper tool part is formed with at least one first opening for introducing compressed gas, by means of which the half-sheets can be pressed against one another, and at least one second opening for introducing joining energy during a welding process for welding the half-sheets.A shape of the second openings in the individual parts of the multi-part tool upper part is, viewed perpendicular to the plane of the half-sheets, largely complementary to one another and only overlapping in some areas, such that using an individual part of the multi-part tool upper part only one part of a weld to be formed as a whole can be produced.
[0011] A "half sheet" is understood here to be a thin metal foil, especially with a thickness in the range of < 100 μm. In the undeformed state or in areas not three-dimensionally deformed, such metal foils are pliable and difficult to handle. Several such half sheets can be welded together to form a bipolar plate, in particular, two half sheets are welded together. However, several half sheets can also be present, for example, three half sheets.
[0012] The staggered application of the weld seams on the half-sheets, which is achieved by changing the various individual parts of the multi-part tool upper part, leads to a local reduction in the thermal stress on the thin half-sheets and an overall improvement in the quality of the weld seams and the bipolar plate. Fewer welding defects, such as the formation of holes, occur, and the device according to the invention enables series production of high quantities of bipolar plates.
[0013] The lower tool part, which is not provided with openings, has a comparatively simple design, while the multi-part upper tool part is significantly more complex. The various first and second openings, which serve different purposes, are located in the individual parts of the multi-part upper tool part.
[0014] Preferably, several first openings are provided, which are distributed over the respective individual part in order to ensure that the half sheets are pressed against one another over a large area.
[0015] The second openings in each individual part allow only a portion of the weld seams required to create the bipolar plate to be formed. This allows the half-sheet assembly to cool down again while the individual parts are being changed before the next welding process begins.
[0016] In this case, several interchangeable, multi-part upper tool parts can be assigned to a single lower tool part. The multi-part upper tool parts are designed in such a way that the position of all weld seams connecting the half-sheets is determined not by any individual part of a multi-part upper tool part alone, but rather by the entirety of the individual parts of the respective multi-part upper tool part to be combined with the lower tool part. In particular, the second openings in the individual parts of the multi-part upper tool part have a V-shaped cross-section that widens in the direction away from the lower tool part. This facilitates the welding process.
[0017] In particular, a first individual part and a second individual part together form the multi-part tool upper part. However, three or more individual parts can also form a corresponding multi-part tool upper part.
[0018] Preferably, the individual parts of the multi-part upper tool part have several raised pressure stamps on their side facing the lower tool part, which are adjacent to the second openings. This creates a particularly good contact pressure between the half-sheets, so that a continuous and strong weld seam can be formed during the welding process.
[0019] Depending on the geometric design of the bipolar plate, either a single half sheet or each half sheet can have a three-dimensional structure. The three-dimensional structure of the half sheets is applied, preferably by embossing, before the welding process. The half sheets are not necessarily completely mirror-symmetrical to each other. The structure leads to greater rigidity in the formed areas of a half sheet and thus better handling. Nevertheless, the undeformed areas remain flexible, and the deformed areas are also still slightly deformable, allowing them to be pressed against each other by the gas flow.
[0020] The inventive method for welding half-sheets to form a bipolar plate using an inventive device is based on the assumption that an arrangement of superimposed half-sheets is welded together by inserting the half-sheets between the lower tool part and a first individual part of the multi-part upper tool part. Compressed gas is passed through the at least one first opening in the first individual part, with which the half-sheets are pressed against each other. At the same time, joining energy for welding the half-sheets is introduced through at least one second opening located in the first individual part, and a first set of weld seams is formed.Subsequently, the first individual part is exchanged for at least one second individual part of the multi-part tool upper part, such that compressed gas is passed through the at least one first opening in at least one second individual part, pressing the half-sheets together. At the same time, joining energy for welding the half-sheets is introduced through at least one second opening located in the second individual part, and a further set of weld seams is formed.
[0021] The process enables fast and high-quality series production of bipolar plates.
[0022] Compressed air or an inert gas can be used as the compressed gas.
[0023] During the process, each individual part of the multi-part upper mold part is pressed against the half-sheets and the lower mold part. In particular, the optional pressure dies on the first individual part and on at least one second individual part press the half-sheets against the lower mold part.
[0024] This allows the gas flow from the at least one first opening to flow between the individual part and the adjacent half-sheet and, in particular, to press the existing flexible areas of the half-sheets against each other without a gap.
[0025] Laser welding is a particularly suitable welding process. Depending on the materials from which the half-sheets are made, another welding process, such as electron beam welding, may also be considered.
[0026] Regardless of the choice of materials and the welding process, the lower tool section can be mounted either on a rigid substructure or on a rotating plate. In the latter case, the individual parts of the respective multi-part upper tool section are relatively rigid, so they are designed as virtually static components. It is precisely this quasi-static arrangement of the individual parts of the multi-part upper tool section that facilitates the supply of compressed air or gas to these individual parts. The first openings through which compressed gas is to be supplied can be located in any area of the bipolar plate, for example, in the active field and / or in port areas.
[0027] The device according to the invention for welding half-sheets to form a bipolar plate is suitable for producing gas-tight connections between thin half-sheets. Such a sheet is preferably made of steel, preferably stainless steel, or titanium. The sheet thickness, i.e., the thickness of a half-sheet, can be < 100 μm, for example, 75 μm or even less. Accordingly, such a half-sheet is more like a metal foil. An optional coating can generally be applied to a half-sheet either before or after welding.
[0028] In any case, by applying compressed air or another pressurized gas, especially inert gas, to one of the half-sheets, geometric inaccuracies are compensated for, so that the areas of the thin half-sheets to be welded together lie on top of each other with virtually no gaps during the welding process. According to one possible process variant, a leak test follows the welding process, using the same compressed gas source that was previously used to press the half-sheets together.
[0029] An exemplary embodiment of the invention is explained below with reference to a drawing. The drawings show, partially schematically:
[0030] Fig. 1 shows a device for welding half sheets to a bipolar plate,
[0031] Fig. 2 shows in plan view the shape of weld seams of a bipolar plate produced with the device according to Figs. 1, 3 and 4, and
[0032] Fig. 3 and 4 each show an individual part of the multi-part tool upper part to be combined with a tool lower part of the device according to Fig. 1.
[0033] A manufacturing system, designated overall by reference numeral 12, comprises a device 5 used for welding half-sheets 2, 3 of a bipolar plate 1. The manufacturing system 12 comprises the device 5 and a welding device 13 suitable for welding sheet metal, here in the form of a laser of a known design.
[0034] The device 5 comprises a lower tool part 6a and a multi-part upper tool part 6b, which here comprises a first individual part 7 and a second individual part 8. During operation of the production system 12, the lower tool part 6a is located on a substructure 14, which in this case is a turntable.
[0035] Even before the half-sheets 2, 3 made of sheet steel, in particular stainless steel, were inserted into the tool or device 5, three-dimensional structures 4 were created in the half-sheets 2, 3 in a preliminary production step. The structuring 4, in this case an embossing, of the half-sheets 2, 3 can be carried out using any known continuous and / or discontinuous processes. Alternatively, it is possible to perform at least part of the forming of the half-sheets 2, 3 only using the tool or device 5.
[0036] Between the half-sheets 2, 3, a flow-through cavity is formed by means of the structures 4, through which a coolant—more generally, a heat transfer medium—can flow within the subsequent cell stack, which comprises a plurality of bipolar plates 1 of the type outlined. Depending on the operating phase of an electrochemical cell stack and the ambient conditions, heating of the cell stack by the heat transfer medium is also possible. In the present case, the electrochemical cell stack is in particular a fuel cell stack. Alternatively, the electrochemical cell stack can be designed, for example, as an electrolyzer for hydrogen production. Operating media of the electrochemical cells flow along the outer surfaces of the bipolar plate 1, i.e., along the outer sides of the half-sheets 2, 3, within the subsequent end product.
[0037] As shown in Fig. 1, the lower tool part 6a has a simple shape, in which there are no openings intended for the supply of compressed gas or for the input of energy during welding. The absence of openings does not apply to bores, which may be present, for example, for positioning pins or screw connections. In contrast to the lower tool part 6a, the upper tool part 6b, or rather the first individual part 7 and the second individual part 8, contains several first openings 9 that can be used to introduce compressed gas, and several second openings 10, 10' (see also Figs. 3 and 4) of various shapes that can be used for welding.
[0038] At various locations on the individual parts 7, 8, there are first openings 9, i.e., holes intended for the supply of compressed gas. Holes arranged in the central region of the individual part 7, 8 and thus also of the half-sheets 2, 3 allow the introduction of a compressed gas, such as compressed air to form an air flow LS, into the area of the future active field of the bipolar plate 1. Holes located further out on the individual part 7, 8 (see Figures 3 and 4), in contrast, serve to supply compressed gas to port areas of the bipolar plate 1.
[0039] Overall, the upper half-sheet 2 is pressed against the lower half-sheet 3 by the compressed gas, which is directed through the first openings 9 into the space between the respective individual parts 7, 8 and the half-sheet 2, so that any gaps between the half-sheets 2, 3 in areas where the half-sheets 2, 3 are to be welded together disappear completely or almost completely. The pressure under which the air flow LS is applied must be dimensioned such that undesirable plastic deformation of the half-sheets 2, 3 does not occur.
[0040] Spatially separated from the described first openings 9, which serve for the gas supply, each of the individual parts 7, 8 of the multi-part tool upper part 6b has second openings 10, 10', which enable the welding of the half-sheets 2, 3. In Fig. 1, the laser 13 used for welding is directed at one of the second openings 10 of the first individual part 7 in order to create a weld seam 11. As can also be seen from Fig. 1, the second openings 10 which enable welding have a V-shaped cross-sectional shape which widens upwards, i.e. in the direction of the laser 13. The V-shape is designed so that the laser beam can strike the workpiece, i.e. the bipolar plate 1, at an angle and tapers conically in a focused manner towards a defined point.
[0041] In the sketched, simplified example, all second openings 10, 10' have a straight slot shape in plan view (compare Figures 3 and 4), which corresponds to a straight shape of the subsequent weld seams 11. In fact, more complex shapes of the weld seams 11 exist. For example, sections of the weld seams 11 can be curved or inclined relative to the outer contours of the half-sheets 2, 3.
[0042] Fig. 2 shows the overall shape of the weld seams 11 that connect the half-sheets 2, 3 to one another. Part of this overall shape is predetermined by the shape of the slot-like second openings 10 in the first individual part 7, sketched in Fig. 3. After part of the weld seam 11 has been created using the first individual part 7, this part is exchanged for the second individual part 8. This is done by rotating the turntable with the tool base 6a and the already partially welded half-sheets 2, 3 under the second individual part 8.
[0043] As a comparison of Figures 3 and 4 shows, the shape of the openings 10' in the second individual part 8 is largely complementary to the openings 10 in the first individual part 7. The openings 10, 10' partially overlap. Overall, the sequential application of the two individual parts 7, 8 results in the overall shape of the weld seams 11 shown in Figure 2. Optional fixing means (not shown) are available to prevent any change in position of the half-sheets 2, 3 in production or the partially finished bipolar plate 1 when changing the individual parts 7, 8.
[0044] Likewise, process variants can be realized with the device 5 in which a plurality of half-sheets 2, 3 of uniform design are initially partially welded using a first individual part 6b. After processing such a batch of half-sheets 2, 3, the first individual part 7 is exchanged for a second, different individual part 8, and the welding process is completed. In this case, positioning contours must be provided on the tool base 6a and on at least one of the half-sheets 2, 3, which ensure that the half-sheets 2, 3 are positioned in a precisely defined position during each welding process.
[0045] Process variants are also feasible in which a plurality of half-sheets 2, 3 of uniform design are initially partially welded using a first multi-part tool upper part 6b. After processing such a batch, the first multi-part tool upper part 6b is exchanged for a second, different multi-part tool upper part 6b, and a plurality of half-sheets 2, 3 of a different uniform design are welded using the second multi-part tool upper part 6b. In this case, positioning contours must also be provided on the tool lower part 6a and on at least one of the half-sheets 2, 3, which ensure that the half-sheets 2, 3 are positioned in a precisely defined position for forming different bipolar plates 1 during each welding process.
[0046] List of reference symbols
[0047] Bipolar plate
[0048] Half sheet
[0049] Half sheet
[0050] structuring
[0051] device
[0052] Tool base multi-part tool top
[0053] Single part of the multi-part tool upper part
[0054] Single part of the multi-part tool upper part
[0055] Opening for air supply
[0056] Opening for welding
[0057] Opening for welding
[0058] Weld seam
[0059] manufacturing facility
[0060] Welding device, laser
[0061] Substructure
[0062] flank
[0063] Proof stamp
[0064] Gas flow
Claims
Patent claims 1. Device (5) for welding half-sheets (2, 3) to form a bipolar plate (1), comprising at least three tool parts (6, 7, 8), namely a lower tool part (6a) and a multi-part upper tool part (6b), wherein the half-sheets (2, 3) to be welded together can be inserted between the lower tool part (6a) and the multi-part upper tool part (6b), wherein the multi-part upper tool part (6b) comprises several individual parts (7, 8) which can be arranged one after the other and only alternatively above the lower tool part (6a), wherein in each of the individual parts (7, 8) of the multi-part upper tool part (6a) there is at least one first opening (9) for introducing compressed gas, through which the half-sheets (2, 3) can be pressed against one another, as well as at least one second opening (10, 10') for introducing joining energy during a welding process for welding the half-sheets (2, 3), wherein a shape of the second openings (10, 10') in the individual parts (7,8) of the multi-part tool upper part (6a) are designed to be largely complementary to one another when viewed perpendicular to the plane of the half-sheets (2, 3) and to overlap only in certain areas, such that only one part of a weld to be formed as a whole can be produced using an individual part (7, 8) of the multi-part tool upper part (6a).
2. Device (5) according to claim 1, characterized in that the second openings (10, 10') have a V-shaped cross-sectional shape widening in the direction away from the lower tool part (6a).
3. Device (5) according to claim 1 or 2, characterized in that several interchangeable multi-part tool upper parts (6b) can be combined with the tool lower part (6a).
4. Device (5) according to claim 3, characterized in that the totality of the second openings (10, 10') in the individual parts (7, 8) of the multi-part tool upper part (6b) determines the position of all weld seams (11) for connecting the three Specify half sheets (2, 3).
5. Device (5) according to one of claims 1 to 4, characterized in that a first individual part (7) and at least one second individual part (8) together form the multi-part tool upper part (6a).
6. Device (5) according to one of claims 1 to 5, characterized in that the individual parts (7, 8) of the multi-part tool upper part (6b) have, on their side facing the tool lower part (6a), a plurality of raised pressure stamps (16) which adjoin the second openings (10, 10').
7. A method for welding half-sheets (2, 3) to form a bipolar plate (1) using a device (5) according to one of claims 1 to 6, wherein an arrangement of superimposed half-sheets (2, 3) is welded together by inserting the half-sheets (2, 3) between the lower tool part (6a) and a first individual part (7) of the multi-part upper tool part (6b), and compressed gas is passed through the at least one first opening (9) in the first individual part (7), with which compressed gas the half-sheets (2, 3) are pressed against each other, wherein at the same time, joining energy for welding the half-sheets (2, 3) is introduced through at least one second opening (10) located in the first individual part (7) and a first part of weld seams (11) is formed, wherein the first individual part (7) is subsequently exchanged for at least one second individual part (8) of the multi-part upper tool part (6b),that compressed gas is passed through the at least one first opening (9') in at least one second individual part (8), with which gas the half-sheets (2, 3) are pressed against each other, wherein at the same time joining energy for welding the half-sheets (2, 3) is introduced through at least one second opening (10') located in the second individual part (8) and a further part of the weld seams (11) is formed.
8. Method according to claim 7, characterized in that the pressure stamps (16) on the first individual part (7) and on the at least one second individual part (8) press the half sheets (2, 3) against the lower tool part (6a).
9. Method according to claim 8, characterized in that the welding is carried out by laser welding.
10. Method according to claim 8, characterized in that the welding is carried out by electron beam welding.