Apparatus and method for welding half sheets to form bipolar plates

Abstract

The invention relates to a device (5) and a method for welding half-sheets (2, 3) to form a bipolar plate (1). The device comprises at least three tool parts, namely a lower tool part (6a) and a multi-part upper tool part (6b), in which 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). The multi-part upper tool part (6b) comprises a plurality of individual parts (7; the individual parts (7, 8) of the multi-part upper tool part (6a) can be arranged one after the other and only alternately above the lower tool part (6a), and wherein both at least one first opening (9) for introducing a pressurized gas and at least one second opening (10) for introducing a pressurized gas are formed in each of the individual parts (7, 8) of the multi-part upper tool part (6a). The half-sheets (2, 3) can be pressed against each other by means of a pressurized gas, and a second opening (10, 10 ') for introducing joining energy during the welding process for welding the half-sheets (2, 3), the second opening (10, 10') in the individual part (7, 8) of the multi-part upper tool part (6b) as viewed perpendicular to the plane of the half-sheets (2, 3), and the second opening (10, 10 ') being formed in the individual part (7, 8) of the multi-part upper tool part (6b), as viewed perpendicular to the plane of the half-sheets (2, 3). 10 ') are largely complementary to each other and overlap only in some areas, such that only a part of the integral weld to be formed can be produced using individual parts (7, 8) of the multi-part upper tool part (6b).

Description

Technical Field

[0001] This invention relates to a method for welding half-sheets to form bipolar plates for electrochemical battery stacks. Furthermore, this invention relates to apparatus suitable for performing this method. Background Technology

[0002] CN 112388166 A discloses various devices that can be used to fix bipolar plates during laser welding. It is assumed here that a tool system combining a lower tool portion and an upper tool portion is known. In this context, a welding process is performed from both sides of the bipolar plate using two laser units through openings in the lower and upper tool portions.

[0003] The apparatus described in CN 113967805 B is designed to enable ultrathin sheets to be held in place during laser welding. The apparatus includes a base plate and multiple other plates, wherein the various components of the apparatus are movably connected to each other.

[0004] A laser welding apparatus for fuel cell separators made of half-sheet material is known from KR 102241379 B1. This apparatus includes a main block with recesses as a fastening profile. Here, two or more so-called island blocks are mounted on the main block. Openings exist in the main block, i.e., the lower tooling portion, leading to media flow opening areas in the half-sheet material to be welded. Inert gas can be supplied through these openings during welding. The inert gas is used to reduce or prevent oxidation of the weld seam.

[0005] KR 20130025527 A describes an apparatus and method for holding a separator plate used in a fuel cell in place during welding, wherein a vacuum is used to hold the components in place.

[0006] CN 108838240 A discloses an automated forming and welding method for a metal bipolar plate constructed according to a "two-plate, three-field" scheme. In this case, resistance welding is suggested as the welding method. A shielding gas is also used.

[0007] In the production of bipolar plates, the clamping technique used when welding metal sheets is crucial to pressing the sheets together without any gaps. A defect-free welding process is only possible when the metal sheets are positioned directly on top of each other, i.e., without any gaps in between. If this is not the case, and there are gaps between the metal sheets that are approximately 10% larger than the sheet thickness, the resulting molten metal sags during welding and forms holes. Due to weight considerations, technological trends are moving towards increasingly thinner sheets, and this effect is even more pronounced in this case.

[0008] The present invention is based on the possibility of providing a bipolar plate for welding for electrochemical systems, which is a further development compared to the prior art and is characterized by a particularly high degree of process reliability and precision. Summary of the Invention

[0009] According to the present invention, this objective is achieved by an apparatus for welding half-sheets of a bipolar plate as designed according to claim 1. This objective is also achieved by a method for welding half-sheets of a bipolar plate according to claim 7.

[0010] The apparatus according to the invention for welding half-sheets to form a bipolar plate comprises at least three tooling portions, namely a lower tooling portion and a multi-part upper tooling portion, wherein the half-sheets to be welded together can be inserted between the lower tooling portion and the multi-part upper tooling portion. The multi-part upper tooling portion comprises a plurality of individual portions, which may be arranged one after another and alternately above the lower tooling portion. Each individual portion of the multi-part upper tooling portion has both at least one first opening and at least one second opening formed therein. The first opening is for introducing pressurized gas through which the half-sheets can be pressed against each other, and the second opening is for introducing bonding energy during the welding process for welding the half-sheets. As observed in a plane perpendicular to the half-sheets, the shapes of the second openings in the individual portions of the multi-part upper tooling portion are designed to be largely complementary and only regionally overlapping, such that, in each case, only a portion of the integral weld to be formed can be produced using the individual portions of the multi-part upper tooling portion.

[0011] "Half-sheet" is understood here as a thin metal foil, particularly one with a thickness ≤100 μm. In its undeformed state or in areas without three-dimensional deformation, this metal foil is flexible and difficult to handle. Multiple such half-sheets can be welded together to form a bipolar plate, specifically two half-sheets can be welded together. However, multiple half-sheets, such as three half-sheets, can also be present.

[0012] The delayed application of weld seams on the half-sheet, achieved by replacing different individual parts of the multi-part tool section, results in a localized reduction of thermal stress on the thin half-sheet and improves the overall quality of the weld seams and bipolar plates. Fewer welding defects, such as formed holes, occur. The device according to the invention enables mass production of a large number of bipolar plates.

[0013] The lower tool section without an opening has a relatively simple shape, while the multi-part upper tool section has a much more complex design.

[0014] Various first and second openings for different purposes are located in separate sections of the tool section on the multi-part form.

[0015] Preferably, there are multiple first openings distributed on corresponding individual portions to ensure that the half-sheets are pressed together over a large area.

[0016] The second opening in each individual section allows only a portion of all the welds required to form the bipolar plate to be formed. This allows the individual sections to be replaced while the half-sheet arrangement structure cools again before the next welding process begins.

[0017] Multiple interchangeable multi-part upper tool sections can be assigned to a single lower tool section. In this context, the multi-part upper tool section is designed such that: a single part of the multi-part upper tool section cannot individually specify the location of all welds connecting the half-sheets to each other, but rather specifies the location of all welds connecting the half-sheets to each other only in relation to the overall combination of each single part of the multi-part upper tool section with the lower tool section.

[0018] In particular, the second opening in a separate section of the multi-part upper tool portion has a V-shaped cross-section that widens in the direction away from the lower tool portion. This makes the welding process easier.

[0019] Specifically, the first and second individual parts together form a multi-part upper tool part. However, three or more individual parts can also form a corresponding multi-part upper tool part.

[0020] Preferably, each individual portion of the multi-part upper tool section has a plurality of raised pressure stamps on its downward-facing tool section side adjacent to the second opening. This produces particularly good contact pressure between the half-sheets, enabling the formation of a continuous and strong weld seam during the welding process.

[0021] Depending on the geometry of the bipolar plate, one or each half-sheet can have a three-dimensional structure. The three-dimensional structure of the half-sheet is preferably introduced by embossing prior to the welding process. In this respect, the half-sheets are not necessarily formed to be perfectly mirror-symmetrical to each other. This structure results in greater stiffness in the formed areas of the half-sheets, and thus better handling. However, the undeformed areas remain flexible and the deformed areas are still easily deformable, allowing them to be pressed together by a gas flow.

[0022] The method according to the invention for welding half-sheets to form a bipolar plate by means of the device according to the invention assumes that the arrangement of the half-sheets located on top of each other is achieved by welding the half-sheets together by inserting them between a lower tool portion and a first separate portion of a multi-part upper tool portion. Pressurized gas passes through at least one first opening in the first separate portion, using this pressurized gas to press the half-sheets together, while simultaneously, bonding energy for welding the half-sheets is introduced through at least one second opening in the first separate portion, forming the first portion of the weld. The first separate portion is then replaced with at least one second separate portion of the multi-part upper tool portion, such that pressurized gas passes through at least one first opening in the at least one second separate portion, using this pressurized gas to press the half-sheets together. Simultaneously, bonding energy for welding the half-sheets is introduced through at least one second opening in the second separate portion, forming the remaining portions of the weld.

[0023] This method allows for rapid and high-quality mass production of bipolar plates.

[0024] Compressed air or inert gas can be used as pressurizing gas.

[0025] During the execution of this method, each individual portion of the multi-part upper tooling section presses against the half-sheet and the lower tooling section. In particular, optional pressure stampings on the first individual portion and at least one second individual portion press the half-sheet against the lower tooling section.

[0026] This allows gas flow from at least one first opening to flow between the individual section and the adjacent half sheet, and in particular allows the existing flexible areas of the half sheet to be pressed against each other without gaps.

[0027] In particular, laser welding can be chosen as the welding method. Depending on the material used to manufacture the half-sheet, different welding methods, such as electron beam welding, can also be considered.

[0028] Regardless of the materials and welding methods chosen, the lower tool section can be mounted on a rigid substructure or a rotary table. In the latter case, the individual sections of the corresponding multi-part upper tool section can move relatively little, making these individual sections almost static components. It is precisely this quasi-static arrangement of the individual sections of the multi-part upper tool section that facilitates the supply of compressed air or gas to these individual sections. The first opening for supplying pressurized gas can be located in any region of the bipolar plate, such as in the active field and / or port region.

[0029] The apparatus according to the invention for welding half-sheets to form bipolar plates is adapted to create an airtight connection between thin half-sheets. Such metal sheets are preferably made of steel, more preferably stainless steel or titanium. Here, the sheet thickness, i.e., the thickness of the half-sheet, can be ≤100 μm, for example 75 μm or even less. Therefore, such half-sheets are more like metal foils. Optional coatings can be applied to the half-sheets either before or after welding.

[0030] In any case, subjecting one half of the sheet to compressed air or another pressurized gas, especially an inert gas, compensates for geometric inaccuracies, so that the areas of the thin half-sheets to be welded together are positioned on top of each other with almost no gaps during the welding process.

[0031] According to one possible variation of the method, a leak test is performed after welding, in which the same pressurized gas source previously used to press the half sheets together can be used for the test. Attached Figure Description

[0032] In the following explanation, exemplary embodiments of the invention are illustrated with reference to the accompanying drawings. In the partially schematic drawings:

[0033] Figure 1 An apparatus for welding half-sheets into bipolar plates is shown.

[0034] Figure 2 It shows the use of according to Figure 1 , Figure 3 and Figure 4 A top view of the shape of the weld seam of the bipolar plate produced by the device, and

[0035] Figure 3 and Figure 4 Each showed that it would be based on Figure 1 The lower tool part of the device is combined with the upper tool part, which is a separate part of the multi-part upper tool part. Detailed Implementation

[0036] The production system, generally indicated by reference numeral 12, includes an apparatus 5 for welding the half-sheets 2 and 3 of the bipolar plate 1. The production system 12 includes the apparatus 5 and a welding apparatus 13 suitable for welding metal sheets, which is in the form of a laser of a known type herein.

[0037] The device 5 includes a lower tool section 6a and a multi-part upper tool section 6b, which here includes a first separate section 7 and a second separate section 8. During operation of the production system 12, the lower tool section 6a is located on the lower structure 14, which in this case is a rotary table.

[0038] Even before inserting the half-sheets 2 and 3 made of steel sheet, particularly stainless steel sheet, into the tool or device 5, a three-dimensional structure 4 is created in the half-sheets 2 and 3 in an upstream production step. The structure 4 of the half-sheets 2 and 3, in this case a protrusion, can be achieved using any continuous and / or discontinuous method known per se. Alternatively, the tool or device 5 can be used to perform at least partial forming of the half-sheets 2 and 3.

[0039] A cavity is formed between the half-sheets 2 and 3 by means of structure 4, through which a coolant—more generally, a heat transfer medium—can flow in the subsequent battery stack, which includes a plurality of bipolar plates 1 of the aforementioned type. Depending on the operating stage of the electrochemical battery stack and environmental conditions, the battery stack can also be heated by the heat transfer medium. In the present case, the electrochemical battery stack is particularly a fuel cell stack. Alternatively, the electrochemical battery stack can be designed, for example, as an electrolyzer for hydrogen production. The working medium of the electrochemical battery flows later in the final product, on the outer surface of the bipolar plates 1, i.e., on the outer portion of the half-sheets 2 and 3.

[0040] like Figure 1 As can be seen, the lower tool portion 6a has a simple shape in which there are no openings intended for supplying pressurized gas or for inputting energy during welding. The absence of openings is unsuitable for, for example, holes that might be present for positioning pin or screw connections. In contrast to the lower tool portion 6a, the upper tool portion 6b, or either in the first separate portion 7 and the second separate portion 8, contains multiple first openings 9 for introducing pressurized gas and multiple second openings 10, 10' of different shapes that can be used for welding (see also...). Figure 3 and Figure 4 ).

[0041] A first opening 9, intended for supplying pressurized gas, is present at different points on individual portions 7 and 8. The opening, located in the central region of individual portions 7 and 8, and therefore also in the central region of halves 2 and 3, allows pressurized gas, such as compressed air, used to form the airflow LS, to be introduced into the region of the subsequent active field of the bipolar plate 1. On the other hand, an opening located further out on individual portions 7 and 8 (see...) Figure 3 and 4 It is used to supply pressurized gas to the port area of ​​bipolar plate 1.

[0042] In general, pressurized gas is used to press the top half-sheet 2 against the bottom half-sheet 3. This pressurized gas is supplied through the first opening 9 into the volume between the respective individual portions 7, 8 and the half-sheet 2, such that any gaps between the half-sheets 2, 3 completely or almost completely disappear in the area where the half-sheets 2, 3 are to be welded together. The pressure experienced by the airflow LS must be selected such that undesirable plastic deformation of the half-sheets 2, 3 does not occur.

[0043] Each of the individual portions 7 and 8 of the multi-part upper tool portion 6b has a second opening 10 and 10' that allows welding of the half-sheets 2 and 3, spatially separated from the first opening 9 described for supplying gas. Figure 1 In this process, the laser 13 used for welding is pointed at one of the openings 10 of the second opening in the first individual portion 7 to form a weld seam 11. (As shown from...) Figure 1 It can also be seen that the second opening 10, which allows welding, has a V-shaped cross-section that widens upwards, i.e., in the direction of the laser 13. The V-shape is adjusted so that the laser beam can be incident on the workpiece, i.e., the bipolar plate 1, at a certain angle and converge in a conical manner toward a defined point in a focused manner.

[0044] In the simplified example shown in the depicted top view, all second openings 10, 10' have a straight groove shape (see...). Figure 3 and Figure 4 This is followed by a straight weld seam 11. In fact, there are weld seams 11 with more complex shapes. In particular, the segments of the weld seam 11 may be bent or inclined relative to the outer contour of the half-sheets 2 and 3.

[0045] Figure 2 The overall shape of the weld 11 connecting the half-sheets 2 and 3 is shown. A portion of this overall shape is composed of… Figure 3 The shape of the groove-shaped second opening 10 in the first individual section 7 shown is predetermined. After a portion of the weld seam 11 is produced using the first individual section 7, the first individual section is replaced with the second individual section 8. This is achieved by rotating the rotary table and positioning the lower tool section 6a and the partially welded half-sheets 2 and 3 below the second individual section 8.

[0046] like Figure 3 and Figure 4 As the comparison shows, the shape of the opening 10' in the second individual portion 8 is largely complementary to the shape of the opening 10 in the first individual portion 7. The openings 10 and 10' partially overlap. Overall, the successive application of the two individual portions 7 and 8 results in... Figure 2The overall shape of the identifiable weld seam 11. An optional fixing device, not shown, is provided to prevent any change in the position of the half-sheets 2, 3 or the partially completed bipolar plate 1 during production when replacing individual parts 7, 8.

[0047] Furthermore, a variation of the method can be implemented using device 5, in which initial partial welding is performed on multiple half-sheets 2, 3 having a consistent design using a first individual portion 6b. After processing such a batch of half-sheets 2, 3, the first individual portion 7 is replaced with a different second individual portion 8, and the welding process is completed. In this case, positioning contours must be provided on the lower tool portion 6a and on at least one of the half-sheets 2, 3, ensuring that the half-sheets 2, 3 are positioned in precisely defined locations during each welding process.

[0048] A method variation can also be implemented in which initial partial welding of multiple half-sheets 2, 3 with a consistent design is performed using a first multi-part upper tool portion 6b. After processing such batches, the first multi-part upper tool portion 6b is replaced with a different second multi-part upper tool portion 6b, and the second multi-part upper tool portion 6b is used to weld multiple half-sheets 2, 3 with a consistent design but different designs. In this case, positioning profiles must also be provided on the lower tool portion 6a and at least one of the half-sheets 2, 3, which ensures that the half-sheets 2, 3 are positioned in precisely defined locations during each welding process to form different bipolar plates 1.

[0049] List of reference numerals

[0050] 1 bipolar plate

[0051] 2 half-sheet

[0052] 3 half-sheet

[0053] 4 Structure

[0054] 5 devices

[0055] Tools section under 6a

[0056] 6b Multi-part Upper Tool Section

[0057] 7. Individual parts of the tool section in a multi-part structure

[0058] 8. Individual parts of the tool section in a multi-part structure

[0059] 9. Openings for air supply

[0060] 10 Welding Openings

[0061] 10' Welding Opening

[0062] 11 Welded seams

[0063] 12 Production System

[0064] 13 Welding equipment, laser

[0065] 14. Substructure

[0066] 15. Side view

[0067] 16. Pressure stamping parts

[0068] LS gas flow

Claims

1. An apparatus (5) for welding half-sheets (2, 3) to form a bipolar plate (1), said apparatus comprising at least three tooling parts (6, 7, 8), namely a lower tooling part (6a) and a multi-part upper tooling part (6b), wherein, The half-sheets (2, 3) to be welded together can be inserted between the lower tool portion (6a) and the multi-part upper tool portion (6b), wherein the multi-part upper tool portion (6b) includes a plurality of individual portions (7, 8), which can be arranged one after another and alternately above the lower tool portion (6a), wherein each of the individual portions (7, 8) of the multi-part upper tool portion (6a) has both at least one first opening (9) and at least one second opening (10, 10'), the first opening being used to introduce pressurized gas. The half-sheets (2, 3) can be pressed together by the pressurized gas, and the second opening is used to introduce bonding energy during the welding process for welding the half-sheets (2, 3). As observed in a plane perpendicular to the half-sheets (2, 3), the shapes of the second openings (10, 10') in the individual portions (7, 8) of the multi-part upper tooling portion (6a) are designed to be largely complementary to each other and overlap only regionally, such that, in each case, only a portion of the integral weld to be formed can be produced using the individual portions (7, 8) of the multi-part upper tooling portion (6a).

2. The device (5) according to claim 1, characterized in that, The second opening (10, 10') has a V-shaped cross-section that widens in the direction away from the lower tool portion (6a).

3. The apparatus (5) according to claim 1 or 2, characterized in that, Multiple interchangeable multi-part upper tool sections (6b) can be combined with the lower tool section (6a).

4. The apparatus (5) according to claim 3, characterized in that, The second opening (10, 10') in the individual portions (7, 8) of the multi-part upper tool portion (6b) is used to specify the location of all weld seams (11) for connecting the half-sheets (2, 3).

5. The apparatus (5) according to any one of claims 1 to 4, characterized in that, The first separate part (7) and at least one second separate part (8) together form the multipart tool part (6a).

6. The apparatus (5) according to any one of claims 1 to 5, characterized in that, The individual portions (7, 8) of the multi-part upper tool portion (6b) have a plurality of raised pressure stampings (16) adjacent to the second opening (10, 10') on the side of the individual portion facing the lower tool portion (6a).

7. A method for welding half-sheets (2, 3) to form a bipolar plate (1) by means of an apparatus (5) according to any one of claims 1 to 6, wherein, The arrangement of the half-sheets (2, 3) located on top of each other is welded together, wherein the half-sheets (2, 3) are inserted between the lower tool portion (6a) and the first separate portion (7) of the multi-part upper tool portion (6b), and pressurized gas is passed through at least one of the first openings (9) in the first separate portion (7) to press the half-sheets (2, 3) together, wherein simultaneously, bonding energy for welding the half-sheets (2, 3) is introduced through at least one second opening (10) in the first separate portion (7), and And forming a first portion of the weld seam (11), wherein the first separate portion (7) is then replaced with at least one second separate portion (8) of the multi-part upper tool portion (6b), wherein pressurized gas passes through at least one of the first openings (9') in at least one second separate portion (8), and the half-sheets (2, 3) are pressed together with each other by the pressurized gas, wherein simultaneously, bonding energy for welding the half-sheets (2, 3) is introduced through at least one second opening (10') in the second separate portion (8), and forming the other portions of the weld seam (11).

8. The method according to claim 7, characterized in that, The pressure stamping (16) on the first individual portion (7) and the at least one second individual portion (8) presses the half sheet (2, 3) against the lower tool portion (6a).

9. The method according to claim 8, characterized in that, The welding is performed using laser welding.

10. The method according to claim 8, characterized in that, The welding is performed using electron beam welding.

Images