METHOD FOR PRODUCING A BIPOLAR PLATE, AND FUEL CELL

Abstract

The invention relates to a method for producing a bipolar plate (5), comprising the following steps: a. providing two planar components (7), which are present in particular in a stacked manner, b. integrally bonding the two planar components (7), in particular by welding, in a joining plane (34), wherein, prior to integrally bonding, internal stresses (9) are introduced into at least one of the two planar components (7). The invention also relates to a fuel cell (1) comprising a bipolar plate (5) produced according to this method.

Claims

1. Method A method for producing a bipolar plate (5), comprising the following steps: a. providing two planar components (7), and b. integrally bonding the two planar components (7), in particular by welding, in a joining plane (34), wherein, prior to integrally bonding, internal stresses (9) are introduced into at least one of the two planar components (7).

2. The method according to claim 1, characterized in that the internal stresses (9) are mechanically introduced.

3. The method according to claim 1, characterized in that, during integrally bonding, at least one of the two planar components (7) is deformed toward the joining plane (34).

4. The method according to claim 1, characterized in that, prior to integrally bonding, tensile stresses (11) are introduced into at least one of the two planar components (7).

5. The method according to claim 1, characterized in that, prior to integrally bonding, at least one temperature field (17) is introduced into at least one of the two planar components (7).

6. The method according to claim 1, characterized in that, when integrally bonding, a part (19) of at least one of the two planar components (7) is moved toward the joining plane (34).

7. The method according to claim 1, characterized in that at least one of the two planar components (7) comprises geometry elements (23) with a direction component perpendicular to a surface (21) of the respective planar component (7).

8. The method according to claim 1, characterized in that the two planar components (7) are sheets.

9. The method according to claim 1, characterized in that the two planar components (7) each have a thickness (25) of not more than 0.1 mm.

10. A method for producing a fuel cell (1), the method comprising producing a bipolar plate (5) according to the method of claim 1.

11. A method for producing a bipolar plate (5), the method comprising the following steps: a. providing two planar components (7) in a stacked manner, b. introducing internal stresses (9) into at least one of the two planar components (7), and c. thereafter integrally bonding the two planar components (7), by welding, in a joining plane (34).

12. The method according to claim 11, characterized in that the internal stresses (9) are mechanically introduced.

13. The method according to claim 12, characterized in that, during integrally bonding, at least one of the two planar components (7) is deformed toward the joining plane (34).

14. The method according to claim 13, characterized in that, prior to integrally bonding, tensile stresses (11) are introduced into at least one of the two planar components (7).

15. The method according to claim 14, characterized in that, prior to integrally bonding, at least one temperature field (17) is introduced into at least one of the two planar components (7).

16. The method according to claim 15, characterized in that, when integrally bonding, a part (19) of at least one of the two planar components (7) is moved toward the joining plane (34).

17. The method according to claim 16, characterized in that at least one of the two planar components (7) comprises geometry elements (23) with a direction component perpendicular to a surface (21) of the respective planar component (7).

18. The method according to claim 17, characterized in that the two planar components (7) are an anode sheet or a cathode sheet in each case.

19. The method according to claim 18, characterized in that the two planar components (7) each have a thickness (25) of not more than 0.1 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0041] Shown are:

[0042] FIG. 1 a fuel cell stack,

[0043] FIG. 2 a cross-section of a fuel cell,

[0044] FIG. 3 a first connecting seam,

[0045] FIG. 4 a second connecting seam,

[0046] FIG. 5 a plan view of a connecting seam,

[0047] FIG. 6 a schematic cross-sectional view of a connecting seam during heating,

[0048] FIG. 7 a schematic cross-sectional view of a connecting seam during cooling,

[0049] FIG. 8 a schematic diagram of integrally bonding two planar components with previously introduced internal stresses,

[0050] FIG. 9 a schematic diagram of integrally bonding with additionally introduced temperature fields, and

[0051] FIG. 10 a schematic diagram of integrally bonding with geometry adjustment.

DETAILED DESCRIPTION

[0052] In the following description of the embodiments of the invention, identical or similar elements are denoted by identical reference signs, wherein a repeated description of these elements is dispensed with in individual cases. The figures show the subject matter of the invention only schematically.

[0053] FIG. 1 shows a schematic diagram of a fuel cell stack 3 comprising a plurality of fuel cells 1. Each fuel cell 1 comprises a membrane 35, two gas diffusion layers 37, an anode 39, and a cathode 41. The individual fuel cells 1 are delimited from one another by bipolar plates 5, which may comprise a cooling plate 43. The fuel cell stack 3, to which hydrogen and oxygen as well as a cooling medium are supplied, is terminated by two end plates 45 and comprises current collectors 47.

[0054] FIG. 2 shows a cross-section of a fuel cell 1. The fuel cell 1 comprises a bipolar plate 5 on which a membrane electrode unit 27 is arranged, which is located between two gas diffusion layers 37. For cooling, hydrogen 29 and water 31 are inter alia guided separately from one another in the bipolar plate 5.

[0055] FIG. 3 shows a cross-sectional view of a first connecting seam 33 in the form of a weld seam. Two planar components 7 are connected in a joining plane 34 to the connecting seam 33. Between the two planar components 7, a medium 51 to be sealed flows. The connecting seam 33 shown here is designed to be flawless so that no medium 51 escapes.

[0056] FIG. 4 shows a second connecting seam 33. In this illustration, the connecting seam 33 has defects 55 through which the medium 51 can escape. Between the planar components 7, there is a gap 53, which is not sufficiently bridged by the connecting seam 33. The defects 55 may occur as a seam collapse, ejection, seam interruption, or cracks in a bipolar plate 5, or as pores or connection interruptions between bipolar plates 5.

[0057] FIG. 5 shows a plan view of a connecting seam 33, which is carried out in a feeding direction 57. To this end, a laser beam 59 is moved in the feeding direction 57, wherein the planar component 7 is heated near the connecting seam 33, thereby causing stresses and a distortion in the planar component 7.

[0058] Heating takes place at the laser beam 59, wherein compressive stresses 13 occur. After passing through the laser beam 59, the planar component 7 cools down again so that tensile stresses 11 directed toward the connecting seam 33 occur.

[0059] FIG. 6 shows a cross-sectional view of a connecting seam 33 during heating. Compressive stresses 13 are present, which results locally in a distortion direction 15.

[0060] FIG. 7 shows a further cross-sectional view of the connecting seam 33 according to FIG. 6. However, in the illustration shown here, the connecting seam 33 is shown during cooling, wherein tensile stresses 11 are present, which result in oppositely directed distortion directions 15 in comparison to FIG. 6.

[0061] FIG. 8 shows a schematic diagram of integrally bonding, wherein two planar components 7 are connected by a connecting seam 33 by means of a laser beam 59. Prior to integrally bonding, internal stresses 9, which comprise tensile stresses 11, were introduced in a shaded region of the planar component 7. These tensile stresses compensate compressive stresses 13 leading the connecting seam 33 and in particular the laser beam 59.

[0062] FIG. 9 shows a further schematic diagram of integrally bonding, wherein temperature fields 17 were additionally introduced into the planar component 7 prior to integrally bonding.

[0063] FIG. 10 shows a further schematic diagram of integrally bonding, wherein the distortion direction 15 indicates a directed weld distortion by geometry optimization in the seam area of the connecting seam 33. A surrounding area of the connecting seam 33 is designed in such a way that compressive stresses 13 leading the connecting seam 33 and thermal expansion result in a movement of a part 19 of the planar component 7 perpendicular to a surface 21 of the planar component 7 and the part 19 of the planar component 7 is deformed toward the joining plane not shown here. This is realized in the illustrated embodiment by geometry elements 23 with a direction component perpendicular to a surface 21 of the planar component 7.

[0064] The invention is not limited to the exemplary embodiments described herein and the aspects highlighted therein. Rather, a variety of modifications, which are within the scope of activities of the person skilled in the art, is possible within the range specified by the claims.