EP4182985A1

EP4182985A1 - Method and system for connecting plate-like components of a bipolar plate

Info

Publication number: EP4182985A1
Application number: EP21739609.2A
Authority: EP
Inventors: Franz Wetzl; Volker Henrichs; Philipp Krueger; Friedrich Kneule
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-07-16
Filing date: 2021-06-30
Publication date: 2023-05-24
Also published as: WO2022012931A1; CN116195101A; DE102020208927A1; US20230352697A1

Abstract

The invention proposes a method for connecting plate-like components of a bipolar plate, comprising the steps of placing a first plate-like component on a clamping surface, placing a second plate-like component onto the first plate-like component, fitting a plurality of hold-down devices on an outer surface of the second plate-like component, said outer surface facing away from the first plate-like component and the clamping surface, wherein an envisaged seam line is kept free between the hold-down devices, pressing the plate-like components together using all of the hold-down devices, wherein, for this purpose, a magnetic force acting in the direction of the clamping surface is applied to at least one of the hold-down devices, and welding the plate-like components along the seam line in a continuous operation.

Description

description

Title:

Method and system for connecting plate-shaped components of a bipolar plate

The present invention relates to a method and system for connecting plate-shaped components of a bipolar plate.

State of the art

A fuel cell system often has a stack of several fuel cells, in each of which an electrochemical process between oxygen and hydrogen takes place while providing electrical power. A single fuel cell essentially consists of a membrane-electrode arrangement surrounded by bipolar plates. Such a device has fine flow channels (the so-called "flow field") on opposite surfaces for the supply of educts and the removal of reaction products. A bipolar plate can consist of an anode sheet and a cathode sheet, which are welded to one another and allow a cooling medium to pass through on the inside. The material thickness of the sheets, which are often made of steel, can be a tenth of a millimeter or less.

The welding can be done by laser beam welding. In order to achieve low distortion, the process parameters for the welding process are selected in such a way that the energy input is as low as possible. This results in very narrow weld seams, the seam width of which can usually be only a tenth of a millimeter or less, with a low melt pool volume. Overall, this, in combination with the high process speeds required as a result, leads to poor quality Ability to bridge gaps, so that even gaps of 30 - 50 pm between the sheets can lead to defects and thus leaks in the bipolar plate.

Since the welding process is very sensitive to the presence of component gaps, a clamping device is used to create a technical zero gap in the area of the joint. Due to tolerances in the anode and cathode sheets, it is therefore necessary for the sheets to be held down on both sides of a weld seam to be produced. In the case of bipolar plates, a closed weld path is produced to ensure a closed sealing contour. For this purpose, welding masks are placed one after the other on the sheets to be joined in several steps and hold down part of the contour. Therefore, the weld path includes several individual seams with a beginning and end as well as their overlaps, which ultimately leads to a closed seam. Compared to a constantly running process, this can lead to process instabilities and an increased susceptibility to errors.

Disclosure of Invention

It is the object of the invention to provide a method and/or a system for connecting plate-shaped components of a bipolar plate, which avoids the aforementioned disadvantages and in particular enables a completely closed welding path.

The object with regard to the method is solved by the features of independent claim 1. Advantageous embodiments and developments can be found in the dependent claims and the following description.

A method for connecting plate-shaped components of a bipolar plate is proposed, comprising the steps of placing a first plate-shaped component on a clamping surface, placing a second plate-shaped component on the first plate-shaped component, applying several hold-down devices on the second plate-shaped component a side facing away from the first plate-shaped component and the mounting surface, with a planned seam course being kept free between the holding-down devices, the pressing together of the plate-shaped components by all holding-down devices, with a magnetic force acting in the direction of the mounting surface being applied to at least one of the holding-down devices for this purpose, and of Welding of the plate-shaped components along the course of the seam in one uninterrupted operation.

As mentioned above, the two plate-shaped components can comprise an anode sheet and a cathode sheet. They are preferably designed as sheet steel and have a material thickness of preferably well under one millimeter, about a tenth of a millimeter or less. The first plate-shaped component, which can be the anode sheet or the cathode sheet, is first placed on a clamping surface. The flow field formed on the first plate-shaped component is already embossed and directed towards the clamping surface. The second plate-shaped component is then placed on the first plate-shaped component, with the flow field of the second plate-shaped component facing away from the mounting surface. It is intended to connect the two plate-shaped components to one another in this arrangement.

Several hold-down devices are used to form a zero gap in the planned course of the seam. These are designed to press the second plate-shaped component onto the first plate-shaped component, so that a flush contact is produced between the two plate-shaped components in the intended course of the seam. In this case, all hold-down devices are pressed onto the second plate-shaped component at the same time, instead of placing them one after the other as usual. By using a magnetic force acting on at least one of the hold-down devices, a closed course of the seam can also be enclosed on both sides without restricting the accessibility for a welding device from outside the second plate-shaped component. The application of the magnetic force could be achieved by a magnet unit, such as a permanent magnet or a selectively activatable electromagnet. The at least one hold-down device to which a magnetic force is applied could also be a Permanent magnets, an electromagnet or a body of magnetic material. Since all hold-down devices are used at the same time to press the plate-shaped components together, a closed seam course can be defined that is kept completely free. In particular, the hold-down device or hold-down devices can be subjected to a magnetic force which, because of their location on the course of the seam, would require mechanical linkage, which would represent an obstacle for a welding device.

This leads to a significant improvement in the properties of the weld seam of a bipolar plate that can be realized in this way, since defects, local leaks and thus rejects can be reliably and reproducibly reduced. The cost of manufacturing a bipolar plate can be further reduced because the number of work steps and the overall length of the weld are reduced.

In an advantageous embodiment, the welding includes laser welding. It is conceivable to use an Nd:YAG or CO2 laser, for example. With appropriate process control, these types of lasers can enable very narrow weld seams and a low weld pool volume. Nd:YAG lasers in particular can be focused very precisely and produce particularly fine weld seams.

As previously mentioned, the course of the seam preferably comprises a circumferential track. Since there are no obstacles along the course of the seam, the weld seam can be produced without interruption in a single operation along the course of the seam and thus overcome the disadvantages of the prior art by using the at least one magnet-supported hold-down device.

In the method according to the invention, the application of hold-down devices can also include arranging at least one inner hold-down device within the course of the seam and at least one hold-down device outside of the course of the seam, with the magnetic force being applied to the at least one inner hold-down device. A within the course of the seam, ie a The hold-down device arranged on the inside of the edge along the intended course of the seam then does not require any other mechanical means to carry out its fixation. Consequently, no mechanical means projecting beyond the course of the seam, which would impede the welding device, are necessary. Only one, in particular internal, hold-down device can be sufficient if a zero gap can be ensured.

The object with regard to the system is solved by a system with the features of the independent system claim. A system for connecting plate-shaped components of a bipolar plate is proposed, having a clamping plate with a clamping surface, several hold-down devices for pressing two plate-shaped components together on the clamping surface, at least one magnet unit, and a welding device, with the at least one magnet unit on one facing away from the hold-down devices side of the clamping surface, wherein the at least one magnet unit is designed to exert a magnetic force on at least one of the hold-down devices, so that the at least one hold-down device in question is pressed in the direction of the clamping surface, wherein the hold-down devices are designed to be positioned between the hold-down devices in one keeping the plate-shaped components free in the pressed-on state along an intended course of the seam, and wherein the welding device is designed to weld the plate-shaped components along the course of the seam.

The clamping plate can have a flat surface onto which one of the plate-shaped components can be placed directly. This surface, also called clamping surface, could also have grooves, projections, grooves or other features that can be brought into engagement with a geometry of the first plate-shaped component. When the plate-shaped components are designed as thin metal sheets that each form a flow field on their outer sides, flow channels of a flow field can consequently be used for precisely positioning the first plate-shaped component on the clamping surface. The at least one magnet unit can have at least one permanent magnet and/or at least one electromagnet. The magnet unit can be arranged below or at least partially in the clamping plate, with the magnetic field lines having to be able to extend through the clamping plate and the plate-shaped components located thereon. The at least one magnet unit can pull one or more of the hold-down devices in the direction of the mounting surface, so that the plate-shaped components placed thereon are pressed together at the edges of the planned seam line. A flush contact, as described above, can thus be achieved at the intended course of the seam.

In an advantageous embodiment, the hold-down devices have at least one outer hold-down device and at least one inner hold-down device, the at least one inner hold-down device being shaped to enclose the course of the seam to the at least one outer hold-down device. The at least one inner hold-down device is completely surrounded by a closed course of the seam. It can be placed on the inside edge of the seam. The outer hold-down devices are placed on the outside edge of the seam. Instead of being held by the magnet unit, these can also be held by conventional mechanical mechanisms, for example clamping tools, clamps, levers, actuators or the like, since these do not cover the planned course of the seam.

In an advantageous embodiment, the at least one inner hold-down device comprises at least two segments that are mechanically coupled to one another. The segments form separate hold-down bodies which are coupled to one another by mechanical means. The coupling could be realized by form-elastic connections, for example compression or tension springs. The subdivision into several segments allows a more elastic support to be achieved on the plate-shaped components. In order to ensure a zero gap over the entire course of the seam, high hold-down forces are sometimes required, with which local deformations of the plate-shaped components occur. The subdivided segments are particularly suitable for avoiding local contact only at certain points. However, the coupling between the segments allows them to be laterally aligned with one another. Particularly preferably, the at least one inner hold-down device comprises at least two segments that are mechanically independent of one another. The segments could be aligned via a separate guide device or via shape features of the second plate-shaped component. It cannot be ruled out that an inner hold-down device has both mechanically coupled and independent segments.

For alignment purposes, the at least one hold-down device could include at least one projection for engaging in a depression in the plate-shaped components. The indentation could be realized, for example, by a flow channel of a flow field, into which an appropriately shaped indentation can engage and fix the lateral position of the hold-down device in question.

In a preferred embodiment, at least one of the hold-down devices is beveled in a region adjacent to the intended course of the seam in a direction away from the course of the seam. The welding device can thus be provided with more space to reach the course of the seam.

In a particularly advantageous embodiment, the magnet unit comprises at least one electromagnet. This can be activated after the plate-shaped components have been placed and switched off after the welding process has ended, which makes handling the components much easier. It can also be part of a conveyor unit in a flow process in which several bipolar plates are produced continuously and one after the other.

Further measures improving the invention are presented in more detail below together with the description of the preferred exemplary embodiments of the invention with the aid of figures.

exemplary embodiments

It shows: Figure 1 is a schematic view of a system in side section. Figure 2 is a plan view of the system

FIGS. 3 to 5 the system with a segmented inner hold-down device

Figure 6a and 6b different flow fields on the plate-shaped components

Figure 7 to 10 detailed sectional views of the system

FIG. 11 shows a modification of the system for flow production

FIG. 12 shows a schematic, block-based representation of the method.

1 shows a system 2 for connecting two plate-shaped components 4 and 6 of a bipolar plate. For this purpose, the system 2 has a clamping plate 8 with a clamping surface 10 . Furthermore, several hold-down devices 12, 14 and 16 are provided, which serve to press the two plate-shaped components 4 and 6 together on the clamping surface 10. While the laterally outer hold-down devices 12 and 16 shown in the plane of the drawing can also be pressed in the direction of the platen 8 by a mechanical clamping or holding device, the inner hold-down device 14 is pushed in the direction of the platen 8 by a magnetic force. For this purpose, a magnet unit 18 is arranged below the clamping plate 8 . If the hold-down devices 12, 14 and 16 are formed at least partially from a magnetic material, they are attracted by the magnet unit 18. In doing so, they each press with a contact section 20 on the plate-shaped components 4 and 6 . A welding device 24 embodied as a laser welding device, for example, which emits a laser beam 26 , can weld the two plate-shaped components 4 and 6 along the course of the seam 22 . To follow the arbitrarily shaped course of the seam 22, the welding device 24 can, for example, rotate about two axes and/or be moved translationally along two axes. To keep the course of the seam 22 sufficiently clear, the side edges 28 of the hold-down devices 12, 14 and 16 are, for example, beveled in a direction away from the course of the seam 22. In order to prevent the plate-shaped components 4 and 6 from being welded to the clamping plate 8 , a recess 30 is also provided below the intended course of the seam 22 .

In figure 2 the system 2 is shown in a plan view. Here, the two lateral hold-down devices 12 and 16 are shown as elongate components which are parallel to one another and spaced apart from one another. They can be supplemented by additional hold-down devices 32 and 34 running perpendicular thereto, which are also arranged parallel to one another and at a distance from one another. The inner hold-down 14 is provided in the shape of a rounded rectangle. The hold-down devices 12, 14, 16, 33 and 34 enclose the intended course of the seam 22, which likewise has the shape of a rounded rectangle as an example.

A modification is shown in FIG. 3 in which the inner hold-down device 14 is divided into a plurality of segments 36 and 40 . The two segments 36 on the left in the plane of the drawing are each mechanically coupled to one another by a coupling spring 38 . This can be a compression or tension spring that is designed to push into a predetermined neutral position. The two segments 40 arranged on the right in the plane of the drawing are independent of the other segments 36 and are also not connected to other components. They could thus be guided, for example, via guide geometries that are arranged on the second plate-shaped component 6 or are formed therein by the flow field arranged thereon.

A further modified variant is shown in FIG. 4, in which several segments 36 and 40 are provided, which are mechanically coupled or designed independently. The segments 36 and 40 each have a recess 42 through which the welding device 24 shown above can carry out spot welds, for example in the form of a stitched seam. This can improve the shape fidelity of larger bipolar plates in particular. Sectional planes BB and CC are marked in Figure 5 which identify the sectional views in Figures 7 and 8 where the stitching and alignment can be better seen.

6a and 6b each show a flow field 44 and 46, which have flow channels 48 for supplying starting materials and removing reaction products. The flow field 44 shown in FIG. 6a has flow channels 48 running in directions perpendicular to one another. The flow field 44 is consequently a cross-flow flow field (“cross-flow”). The flow field 46 from FIG. 6b, on the other hand, has flow channels 48 with exclusively parallel extensions, so that it can be referred to as a counter-current flow field (“counter-flow”). When a segment 40 is applied to one of the flow fields 44 or 46, shape features of the flow channels 48 can be used for alignment. While the flow field 44 from FIG. 6a enables easy alignment in two directions in space, this is easily possible in the case of the flow field 46 in only one direction in space. However, if individual flow channels 48 have locally different heights, shape features can thereby be created on which precise alignment in two spatial directions is possible.

Fig. 7 shows the section plane B-B. A lateral hold-down device 36 with the recess 42 can be seen there, through which the laser beam 26 can produce a stitched seam 50 .

In Fig. 8, the hold-down 36 is shown having a plurality of projections 52 and 54 which mate with indentations 56 of the first panel member 6 and align the hold-down 36 therewith. In this case, the projections 52 are dimensioned in such a way that although they protrude into the depressions 56, they do not touch the second plate-shaped component 6. This only happens at the projection 54 in order to produce a defined surface contact only there.

9 shows the inner hold-down device 14 whose support section 20 is centered on flanks 58 of the second plate-shaped component 6 . As a result, the inner hold-down device 14 can be applied precisely to the second plate-shaped component are placed and consequently be arranged on the inside edge of the planned seam course 22 .

10 shows the inner hold-down device 14 with a projection 59 whose cross-section is rounded at its outer end and engages in a rounded depression 60 of the second plate-shaped component 6 . The rounded shape results in simple self-centering and can sometimes prevent tilting when the inner hold-down device 14 is placed.

11 shows a possible development in the form of a continuous system 62 for the flow production of bipolar plates. Here, several clamping plates 8 are guided continuously on a first conveyor unit 64 . The clamping plates 8 can be fitted (see II) with supplied plate-shaped components 4 and 6 (see I) along a useful path 66 . Subsequently, hold-down devices 74 are fed in (III) and placed on the plate-shaped components 4 and 6 (IV). A magnetic force is exerted on the hold-down device 74 (V) and the two plate-shaped components 4 and 6 are then welded together (VI). The hold-down devices 74 are then removed again (VII) so that the resulting bipolar plates 68 (VIII) can be removed (IX). The hold-down devices 74 can be transported via a second conveyor unit 70, which could also transport and place additional magnetic chucks 72, which can also be used to transport the hold-down devices 74.

Finally, FIG. 12 shows the schematic representation of the method according to the invention. This involves the steps of placing 76 a first panel-shaped component 4 on a clamping surface 10, placing 78 a second panel-shaped component 6 on the first panel-shaped component 4, applying 80 a plurality of hold-down devices to the second panel-shaped component 6 on one of the first panel-shaped components Component 4 and the clamping surface 10 side facing away, wherein between the hold-down clamps an intended seam course 22 is kept free. The plate-shaped components 4, 6 are then pressed together 82 by all hold-down devices, with a magnetic force acting in the direction of the clamping surface 10 being applied to at least one of the hold-down devices 84. Finally the welding 86 of the plate-shaped components 4, 6 takes place along the course of the seam 22 in an uninterrupted operation.

Claims

Expectations

1. A method for connecting plate-shaped components (4, 6) of a bipolar plate, comprising the steps:

Placing (76) a first panel-shaped component (4) on a clamping surface (10),

Placing (78) a second panel-shaped component (6) on the first panel-shaped component (4),

Applying (80) a plurality of hold-down devices (12, 14, 16, 32, 34, 74) to the second plate-shaped component (6) on a side remote from the first plate-shaped component (4) and the clamping surface (10), with between the hold-down devices (12, 14, 16, 32, 34, 74) an intended course of the seam (22) is kept free, pressing together (82) the plate-shaped components (4, 6) by all hold-down devices (12, 14, 16, 32, 34, 74) , wherein for this purpose a magnetic force acting in the direction of the clamping surface (10) is applied to at least one of the hold-down devices (12, 14, 16, 32, 34, 74), and

Welding (84) of the plate-shaped components (4, 6) along the course of the seam (22) in an uninterrupted operation.

The method of claim 1, wherein the welding (86) comprises laser welding.

3. The method according to claim 1 or 2, wherein the application (80) of hold-down devices (12, 14, 16, 32, 34, 74) includes arranging at least one inner hold-down device (14) within the seam line (22) and at least one hold-down device ( 12, 16, 32, 34, 74) outside of the course of the seam (22), and wherein the magnetic force is applied to the at least one inner hold-down device (14).

4. System (2, 62) for connecting plate-shaped components (4, 6) of a bipolar plate, having: a clamping plate (8) with a clamping surface (10), several hold-down devices (12, 14, 16, 32, 34, 74) for pressing together two plate-shaped components (4, 6) on the clamping surface (10), at least one magnet unit (18), and a welding device (24), the at least one magnet unit (18) being mounted on one of the hold-down devices (12, 14, 16 , 32, 34, 74) facing away from the clamping surface (10), wherein the at least one magnet unit (18) is designed to exert a magnetic force on at least one of the hold-down devices (12, 14, 16, 32, 34, 74). so that the at least one hold-down device (12, 14, 16, 32, 34, 74) in question is pressed in the direction of the clamping surface (10), the hold-down devices (12, 14, 16, 32, 34, 74) being shaped for this purpose, between the hold-down devices (12, 14, 16, 32, 34, 74) in one on the plate-shaped components (4, 6) aufged to keep an intended course of the seam (22) free in the advanced state, and wherein the welding device (24) is designed to weld the plate-shaped components (4, 6) along the course of the seam (22).

5. System (2, 62) according to claim 4, wherein the hold-down devices (12, 14, 16, 32, 34, 74) have at least one outer hold-down device (12, 16, 32, 34, 74) and at least one inner hold-down device (14 ) have, wherein the at least one inner hold-down device (14) is shaped to enclose the course of the seam (22) to the at least one outer hold-down device (12, 16, 32, 34, 74).

The system (2, 62) of claim 4 or 5, wherein the at least one inner hold-down (14) comprises at least two segments (36) mechanically coupled together.

7. System (2, 62) according to any one of claims 4 to 6, wherein the at least one inner hold-down (14) comprises at least two segments (40) which are mechanically independent of one another.

8. System (2, 62) according to one of claims 4 to 7, wherein the at least one hold-down device (12, 14, 16, 32, 34, 74) has at least one projection (52, 54) for engaging in a recess (56) of the plate-shaped components (4, 6).

9. System (2, 62) according to one of claims 4 to 8, wherein at least one of the hold-down devices (12, 14, 16, 32, 34, 74) in an area adjacent to the intended seam line (22) in one of the seam line (22) is beveled in the opposite direction.

10. System (2, 62) according to any one of claims 4 to 9, wherein the magnet unit (18) comprises at least one electromagnet.