METHOD FOR JOINING AT LEAST TWO COMPONENTS OF A FUEL CELL AND DEVICE FOR CARRYING OUT THE METHOD

Abstract

A method for joining at least two components of a fuel cell, especially for joining two single plates of a fuel cell to make a bipolar plate, comprises: providing a first component of the fuel cell and providing at least one second component of the fuel cell; and directing a pulsed laser beam of a laser apparatus onto a rotating mirrored polygon wheel, by which the laser beam forms a joint line consisting of a plurality of overlapping pointlike and/or line-shaped joining locations on the components. A device for carrying out the method is also provided.

Claims

1. A method for joining at least two components of a fuel cell, comprising: providing a first component of the fuel cell and providing at least one second component of the fuel cell; and directing a pulsed laser beam of a laser apparatus onto a rotating mirrored polygon wheel, by which the laser beam forms a joint line consisting of a plurality of overlapping pointlike and/or line-shaped joining locations on the components.

2. The method according to claim 1, wherein the components and the laser beam are moved relative to each other, and a two-dimensional joint contour is formed by the relative movement.

3. The method according to claim 2, wherein the relative movement is created by a feed of a transport device for transporting the components.

4. The method according to claim 3, wherein in order to form the joint line, which includes a portion oriented perpendicular to the feed direction of the transport device, the laser beam partially broadened by the polygon wheel is deflected by an adjustable optical deflection device in dependence on the feed.

5. The method according to claim 4, wherein the optical deflection device is moved with a speed compensating for the feed rate in order to form a joint line on the components oriented perpendicular to the feed direction.

6. The method according to claim 1, wherein the relative movement is generated by moving a movable laser head of the laser apparatus with entrainment of the polygon wheel.

7. A device for carrying out a method for joining at least two components of a fuel cell, including providing a first component of the fuel cell and providing at least one second component of the fuel cell, and directing a pulsed laser beam of a laser apparatus onto a rotating mirrored polygon wheel, by which the laser beam forms a joint line consisting of a plurality of overlapping pointlike and/or line-shaped joining locations on the components, the device comprising: a laser apparatus; and a rotatably driven mirrored polygon wheel, wherein the laser apparatus is adapted to direct a pulsed laser beam onto the rotatably driven mirrored polygon wheel, and which is wherein the rotatably driven mirrored polygon wheel is adapted to deflect the laser beam and thus form a joint line of a plurality of overlapping pointlike and/or line-shaped joining locations on the components.

8. The device according to claim 7, wherein a transport device is present and adapted to move the components relative to the laser beam impinging on the components in order to form a two-dimensional joint contour.

9. The device according to claim 8, wherein a movable optical deflection device is placed downstream from the polygon wheel in the path of the laser beam, which is adapted to deflect the laser beam in dependence on a feed rate of the transport device.

10. The device according to claim 7, wherein a movable laser head of the laser apparatus is present, which is movably mounted with entrainment of the polygon wheel.

11. The method according to claim 1, wherein the method for joining at least two components of a fuel cell is a method for joining two single plates of a fuel cell to make a bipolar plate.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0030] Further benefits, features and details will emerge from the claims, the following description of embodiments, and the drawings.

[0031] FIG. 1 shows a cross sectional detail view of one portion of a fuel cell stack with a bipolar plate formed from two single plates.

[0032] FIG. 2 shows a schematic side view of a device for joining of at least two components of a fuel cell, especially for joining of single plates to form a bipolar plate.

[0033] FIG. 3 shows a schematic detail view of the surface of an already partly joined bipolar plate.

[0034] FIG. 4 shows a schematic view of the device of FIG. 3, in which the making of the line is illustrated, showing for sake of clarity the bipolar plate in a top view and the device in a side view.

DETAILED DESCRIPTION

[0035] FIG. 1 shows a cutout view of a fuel cell stack, formed from multiple fuel cells 220. Each fuel cell 220 is formed with a membrane electrode assembly 222, which comprises a proton-conducting membrane associated with an electrode on either side. The membrane electrode assembly 222 is designed to carry out the electrochemical reaction of the fuel cell. In this process, a fuel (such as hydrogen) is taken to the electrode forming the anode, where it is oxidized catalytically to protons, giving off electrons. These protons are transported through the proton-conducting membrane (or ion exchange membrane) to the cathode. The electrons taken away from the fuel cell flow across an electrical consumer, such as across an electric motor for driving a vehicle, or to a battery. The electrons are then taken to the cathode or electrons are provided at it. At the cathode, the oxidation medium (such as oxygen or air containing oxygen) is reduced to anions by uptake of electrons, which react immediately with the protons to form water.

[0036] With the aid of bipolar plates 216, the fuel or the cathode gas is taken to gas diffusion layers 224, which distribute the respective gases diffusely and take them to the electrodes of the membrane electrode assembly 222. The fuel, the oxidation medium and optionally a cooling medium are taken through ducts 208 of the bipolar plate 216, which are bounded on both sides by webs 206 of the bipolar plate 216 having web backs. As can be seen from FIG. 1, a set of the web backs lie against a gas diffusion layer 224, so that a reactant flowing in the ducts 208 can be dispensed to the gas diffusion layer 224 and thus to the electrode of the membrane electrode assembly 222.

[0037] The bipolar plate 216 in the present instance comprises two single plates 200, 202 placed on one another and joined together selectively at their facing webs 206, especially at their respective web backs, in particular by welding. The facing webs 206 of the single plates 200, 202 typically form conduits for a cooling medium with the ducts 208 lying between the webs 206.

[0038] It is furthermore evident from FIG. 1 that the webs 206 or their web backs of the single plates 200, 202 need not have the same width, so that different widths and or depths may be present for the ducts 208. However, for a permanent connection of two single plates 200, 202, it should be assured that at least two of the oppositely positioned webs 206 which lie against each other can be permanently connected to each other, namely joined, and especially welded together.

[0039] FIG. 2 presents a device 100 for joining at least two components of a fuel cell 218, being designed in the present instance especially for joining two single plates 200, 202 to make a bipolar plate 216. This device 100 comprises a laser apparatus 108, having a laser source 106 for the emission of a pulsed laser beam 110. The laser source 108 can be a gas laser, a semiconductor laser or a solid state laser, while in particular a CO.sub.2 laser or a Nd:YAG laser or a semiconductor laser/diode laser or a Yb:YAG laser can be used. The individual components of the laser apparatus 108 are activated by laser controls 104.

[0040] The laser source 106 directs the laser beam 110 onto a mirrored polygon wheel 114, driven in rotation by an electric motor. This mirrored polygon wheel 114 is adapted to deflect the laser beam 110 very rapidly and in dependence on the angular position of the polygon wheel 114 among a plurality of angles. The laser controls 104 can be adapted to switch the laser apparatus 108, especially the laser source 106, on and off with a high-frequency clock rate, in order to further guarantee that no excessively long line-shaped laser beams 110 are formed, resulting in a large heat input in the raw material and therefore in the single plates 200, 202 of the bipolar plate 216.

[0041] Moreover, the laser apparatus 108 comprises an adjustable optical deflection device 112 situated downstream from the polygon wheel 114 in the path of the laser beam 110, being adapted to deflect the laser beam 110 in dependence on a feed rate of a transport device 116. The transport device 116 transports the single plates 200, 202 in a feed direction 118. Thanks to the feeding of the transport device 116, two-dimensional joint contours can be realized. In order to provide any other desired two-dimensional joint contours for the joining process, the laser apparatus 108 can furthermore be outfitted with a laser head 102, which can be moved or “travel” by electric motor perpendicular to the feed direction 118 of the transport device 116, as indicated by the diagonally positioned double arrow shown next to the laser apparatus 108.

[0042] The functioning of the device 100 is illustrated with the aid of FIG. 3, which shows a top view of a surface 218 of the single plates 200, 202. Once the transport device 116 has arranged or positioned the components of the fuel cell 218 opposite the laser apparatus 108, the laser beam 110 is directed onto the rotating, mirrored polygon wheel 114. In this way, the laser beam 110 is deflected at a number of angles due to the rotation of the wheel and forms on the single plates 200, 202 a joint line 122 consisting of a plurality of overlapping pointlike and/or line-shaped joining locations 120, by which the two plates are joined together in permanent intimate manner. The laser beam 110 can or should impinge on the components in focused manner in order to effectively bring about a specific melting of the material and a joining of the components. In order to produce any given joint contours, the plates are moved relative to the laser beam 110, either by the feeding of the transport device 116 and/or by the movable laser head 102.

[0043] Thanks to this successive pointlike or dashlike arrangement, not a slight amount of heat is put into the material when producing a continuous joint line 122, so that there is less heat-induced warpage of the component. Optionally, a given line can also be traveled repeatedly with the pointlike joining locations 120, in order to form a closed or thicker joint line 122 from the overlapping joining locations 120.

[0044] Moreover, it can be seen from FIG. 3 that the pointlike and/or line-shaped joining locations 120 need not necessarily be circular round in shape. Therefore, the use of other melting spot geometries may also be considered, which can be created for example by means of suitable beam-shaping elements. Thus, the joint line 122 shown at the bottom of FIG. 3 is an overlapping series of rectangular, especially square, pointlike joining locations 120, requiring less overlap than round circular joining locations 120 in order to result in a desired tightness of the assemblage.

[0045] In order to further speed up the process of making the joined assemblage, the optical deflection device 112 is used, which shall be discussed below with reference to FIG. 4. For sake of clarity, FIG. 4 combines the side view of the device 100, shown only simplified, and the top view of the surface 218 of the single plates 200, 202 which are to be welded to make a bipolar plate 216.

[0046] The bipolar plate 216 is transported by the transport device 116 along the feed direction 118. If the optical deflection device 112 were not used, this would result in the dashed representation of the joint line 122 formed from multiple pointlike and/or line-shaped joining locations 120. The optical deflection device 112, which is formed in particular as a mirror or a prism, can be moved or swiveled in the manner of a scanner. The optical deflection device 112 can be moved in this process in dependence on the feed rate of the transport device 116. In this way, thanks to the use of the optical deflection device 112, it is possible to create a joint line 122 oriented perpendicular to the feed direction 118, as can be seen in the figure. The movement or deflection of the laser beam 110 may occur at a speed which just compensates for the feed rate of the transport device 116. In this way, a joint line 122 can also be created when the bipolar plate 216 is being transported by the transport device 116 in the feed direction 118.

[0047] Hence, a device 100 and a method are indicated for the joining of at least two components of a fuel cell 218, being distinguished from the prior art of known methods by a shortened clock cycle. The device 100 and the method described herein are therefore suited to a mass production and they reduce the reject rate of the production as compared to known methods and devices, especially in the production of bipolar plates 216, on account of less heat input in the (raw) material of the components. The joint lines 122 formed as described herein assure the necessary tightness and the required electrical contacting, and because of less heat input in the raw materials there is little or no heat-induced warpage, which might be detrimental in the following production stages.

[0048] Aspects of the various embodiments described above can be combined to provide further embodiments. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.