Metal plate joined body

Abstract

This metal plate joined body comprises welded portions (21) and overlapping portions (22). The welded portions (21) have a determined length and are obtained by using laser irradiation to laser-weld together metal plates that are stacked in the thickness direction. The overlapping portions (22) are locations where an end portion E1 of a welded portion (21) and another end portion E2 of the welded portion (21) overlap. At least one of the end portion E1 and the other end portion E2 of each welded portion (21) is formed with a weakly irradiated portion (24) in which the laser irradiation intensity during the laser welding is weaker than in other portions. At least one of the locations, among the end portion E1 of the welded portion (21) and the other end portion E2 of the welded portion (21), where the overlapping portion (22) is formed is a weakly irradiated portion (24).

Description

Metal plate joined body

[0001] The present disclosure relates to a metal plate joined body.

[0002] As a joined body in which metal plates stacked in the thickness direction are joined to each other, in order to ensure the sealing property between the metal plates, for example, as shown in Patent Document 1, a joined body having a welded portion and an overlapping portion is known. The welded portion is obtained by laser-welding metal plates stacked in the thickness direction by laser irradiation. The welded portion in Patent Document 1 is a plurality of welded portions having a defined length. The overlapping portion is a portion where an end portion of the welded portion and another end portion of the welded portion overlap. And, by making the welded portion into a closed circuit shape as a whole by the welded portion and the overlapping portion, the sealing property between the metal plates in the metal plate joined body is ensured.

[0003] Japanese Patent No. 6112932

[0004] By the way, in laser welding of metal plates, after the portion irradiated with laser on the metal plate is melted, the joining of the metal plates is performed through the solidification of the melted portions between the metal plates. For this reason, in order to make the welded portion into a closed circuit shape as a whole, when forming an overlapping portion where an end portion of the welded portion and another end portion of the welded portion overlap, melting of the metal plate is performed a plurality of times at a location corresponding to the overlapping portion. As a result, at the location corresponding to the overlapping portion in the metal plate, there is a possibility of perforation accompanying the melting of the metal plate by laser irradiation.

[0005] A metal plate joined body according to one aspect of the present disclosure includes a welded portion and an overlapping portion. The welded portion has a defined length obtained by laser-welding metal plates stacked in the thickness direction by laser irradiation. The overlapping portion is a portion where an end portion E1 of the welded portion and another end portion E2 of the welded portion overlap in the metal plate joined body. At least one of the end portion E1 and the other end portion E2 of the welded portion has a weak irradiation portion where the laser irradiation intensity during laser welding is made weaker than the others, and at least one of the portions forming the overlapping portion at the end portion E1 and the other end portion E2 of the welded portion is the weak irradiation portion.

[0006] Figure 1 is an exploded perspective view showing a single cell of a fuel cell. Figure 2 is a front view showing the cathode-side separator of the single cell in Figure 1 as seen from the direction of arrow A in Figure 1. Figure 3 is a schematic diagram showing an enlarged view of the end of the weld where the separators of the single cell in Figure 1 are laser-welded together. Figure 4 is a schematic diagram showing an enlarged view of the end of the weld where the separators of the single cell in Figure 1 are laser-welded together. Figure 5 is a schematic diagram showing another example of the end of the weld in Figure 3. Figure 6 is a schematic diagram showing another example of the end of the weld in Figure 4. Figure 7 is a schematic diagram showing another example of the weld in Figure 3. Figure 8 is a schematic diagram showing another example of the weld in Figure 3.

[0007] Hereinafter, an embodiment of the metal plate assembly will be described with reference to Figures 1 to 4. Figure 1 shows a single cell 11 for forming a cell stack of a fuel cell. The single cell 11 comprises a resin plate 12, a membrane electrode gas diffusion layer assembly 13, and a separator 14. The resin plate 12 is formed in the shape of a rectangular frame. The outer edge of the membrane electrode gas diffusion layer assembly 13 is joined to the resin plate 12. The resin plate 12 and the membrane electrode gas diffusion layer assembly 13 are sandwiched between the separator 14 from both sides in the thickness direction. The separator 14 sandwiching the resin plate 12 and the membrane electrode gas diffusion layer assembly 13 is located on the anode side and the cathode side of the membrane electrode gas diffusion layer assembly 13. The separator 14 is formed in the shape of a rectangular plate from a metal such as stainless steel, titanium, or aluminum.

[0008] The cell stack of the fuel cell is formed by stacking the single cells 11 described above in the thickness direction. Multiple holes 16 are formed in the resin plate 12 and separator 14 of the single cell 11. Of the multiple holes 16, three are located at one end in the long side direction of the single cell 11, and the other three are located at the other end in the long side direction of the single cell 11. The multiple holes 16 are arranged in pairs, one on one side and one on the other side in the long side direction of the single cell 11. Each pair of holes 16 is used to allow fluids such as fuel gas such as hydrogen, oxidizing gas such as air, and refrigerant such as cooling water to flow. A sealing member 17 is placed between the separator 14 and the resin plate 12. The sealing member 17 is heat-welded to the separator 14.

[0009] The sealing member 17 heat-welded to the anode-side separator 14, i.e., the right-side separator 14 in Figure 1, surrounds a pair of holes 16 located on one of the two diagonals of the resin plate 12 and separator 14, and the anode side of the membrane electrode gas diffusion layer assembly 13. This allows fuel gas to flow through the pair of holes 16 to the anode side of the membrane electrode gas diffusion layer assembly 13. Similarly, the sealing member 17 heat-welded to the cathode-side separator 14, i.e., the left-side separator 14 in Figure 1, surrounds a pair of holes 16 located on the other diagonal of the two diagonals of the resin plate 12 and separator 14, and the cathode side of the membrane electrode gas diffusion layer assembly 13. This allows oxidizing gas to flow through the pair of holes 16 to the cathode side of the membrane electrode gas diffusion layer assembly 13.

[0010] In a cell stack of single cells 11, fuel gas is flowed to the anode side of the membrane electrode gas diffusion layer assembly 13, and oxidizing gas is flowed to the cathode side of the membrane electrode gas diffusion layer assembly 13. When fuel gas and oxidizing gas are flowed to the anode and cathode sides of the membrane electrode gas diffusion layer assembly 13 in this way, power is generated based on the reaction between the fuel gas and oxidizing gas in the membrane electrode gas diffusion layer assembly 13.

[0011] Figure 2 shows a separator 14 of a single cell 11, located on the cathode side of the membrane electrode gas diffusion layer assembly 13, as viewed from the direction of arrow A in Figure 1. This separator 14 is adjacent to the anode-side separator 14 of another single cell 11 that is in contact with the aforementioned single cell 11. These adjacent separators 14 are welded together as shown by the dashed line.

[0012] More specifically, adjacent separators 14 are welded together so as to encircle two sets of holes 16 located diagonally opposite each other, and the entire outer edge of each separator 14 is also welded. This allows refrigerant to flow between adjacent separators 14 through the holes 16 located in the center of the short side of each separator 14. By allowing refrigerant to flow between the separators 14 of adjacent single cells 11 in this way, the cell stack can be cooled when its temperature rises during power generation.

[0013] <Formation of the Cell Stack of the Fuel Cell> The cell stack of the fuel cell is formed using bipolar plates made of welded separators 14 as described above. These bipolar plates serve as a metal plate joint. The cell stack of the fuel cell is formed by alternately stacking the above bipolar plates and resin plates 12 to which the membrane electrode gas diffusion layer joint 13 shown in Figure 1 is joined, in the thickness direction. Laser welding is used for welding the separators 14 together to form the above bipolar plates.

[0014] In this type of laser welding, a laser from a laser head is irradiated from one separator 14 to the other between two adjacent separators 14 that are overlapping in the thickness direction. As a result, one separator 14 and the portion of the other separator 14 closer to the first separator 14 melt. The molten portion then solidifies, joining the separators 14 together.

[0015] <Details of the Bipolar Plate> The bipolar plate includes a welded section 21 and an overlapping section 22 as shown in Figure 2. The welded section 21 is formed by laser welding together separators 14 that are stacked in the thickness direction by laser irradiation. In this example, the welded section 21 consists of multiple welded sections 21 having a predetermined length. The overlapping section 22 is the point where one end 23 of the welded section 21 overlaps with another end 23 of the welded section 21. The welded section 21 and the overlapping section 22 form a closed circuit shape that extends along the outer edge of the separator 14 and a closed circuit shape that extends to surround the hole 16. This ensures a seal between the separators 14 in the bipolar plate.

[0016] The closed-circuit shaped welded portion 21 extending along the outer edge of the separator 14 is formed by two welded portions 21. That is, the ends 23 of the two welded portions 21 overlap, so that the welded portion 21 as a whole has a closed-circuit shape. One end 23 of one of the two welded portions 21 acts as end E1, and the other end 23 of the other welded portion 21 acts as another end E2. In addition, an overlapping portion 22 is formed where the ends 23 of the two welded portions 21 overlap. Figure 3 shows a magnified view of the overlapping ends 23 of the two welded portions 21.

[0017] As shown in Figure 2, the closed-circuit shaped welded portion 21 extending around the hole 16 is also formed by two welded portions 21. That is, the ends 23 of the two welded portions 21 overlap, so that the welded portion 21 as a whole has a closed-circuit shape. One end 23 of one of the two welded portions 21 acts as end E1, and the other end 23 of the other welded portion 21 acts as another end E2. In addition, an overlapping portion 22 is formed where the ends 23 of the two welded portions 21 overlap. Figure 4 shows a magnified view of the overlapping ends 23 of the two welded portions 21.

[0018] As shown in Figures 3 and 4, at least one of the ends 23 of the welded portion 21 and the other end 23 of the welded portion 21 that overlaps with the end 23 to form the overlapping portion 22 is formed on at least one of them, where the laser irradiation intensity during laser welding is weaker than on the other. In this example, weak irradiation portions 24 are formed on both the end 23 and the other end 23.

[0019] Each of the above-mentioned end 23 and the above-mentioned other end 23 is provided with a base end 25 and a tip end 26. The tip end 26 is connected to the base end 25 and is oriented to extend in a direction different from the direction in which the base end 25 extends. The overlapping portion 22 is formed by the tip end 26 of the above-mentioned end 23 of the welded portion 21 and the base end 25 of the above-mentioned other end 23 of the welded portion 21. Furthermore, of the base end 25 and tip end 26 of the above-mentioned end 23 and the above-mentioned other end 23, only the tip end 26 is the weakly irradiated portion 24. As a result, only one of the locations that form the overlapping portion 22 in the above-mentioned end 23 and the above-mentioned other end 23 is the weakly irradiated portion 24.

[0020] In the welded joint 21 shown in Figure 3, the base end 25 at the end 23 of one welded joint 21 and the base end 25 at the other end 23 of the other welded joint 21 are formed in a straight line that extends parallel to each other. The tip 26 at the end 23 of one welded joint 21 and the tip 26 at the other end 23 of the other welded joint 21 are oriented toward the same side in the direction that intersects with the base end 25. More specifically, the tip 26 is oriented as described above by bending relative to the straight base end 25.

[0021] In the welded joint 21 shown in Figure 4, the base end 25 at the end 23 of one welded joint 21 and the base end 25 at the other end 23 of the other welded joint 21 are formed in a straight line extending in an intersecting direction. The tip 26 at the end 23 of one welded joint 21 is directed toward the side approaching the base end 25 at the other end 23 of the other welded joint 21. More specifically, the tip 26 at the end 23 of one welded joint 21 is directed as described above by bending relative to the straight base end 25 at that end 23. Also, the tip 26 at the other end 23 of the other welded joint 21 is directed toward the side approaching the base end 25 at the end 23 of one welded joint 21. More specifically, the tip 26 at the other end 23 of the other welded joint 21 is directed as described above by bending relative to the straight base end 25.

[0022] According to this embodiment, the following effects can be obtained. (1) At the ends 23 of the two welded parts 21 which form a closed circuit shape as a whole, a weak irradiation area 24 is formed where the laser irradiation intensity during laser welding is weaker than elsewhere. Specifically, a weak irradiation area 24 is formed at least one of the ends 23 of one welded part 21 and the other end 23 of the other welded part 21, which is a different end 23 from the above end 23. Therefore, at least one of the locations that form the overlapping portion 22 between the above end 23 of one welded part 21 and the above different end 23 of the other welded part 21 is a weak irradiation area 24. As a result, when laser irradiation for laser welding is performed at the above location, the laser irradiation intensity is weakened. This makes it possible to suppress the occurrence of holes when the separator 14 melts due to laser irradiation.

[0023] (2) In the weakly irradiated area 24, the laser irradiation intensity during laser welding is weak, resulting in lower joint strength due to laser welding. Taking this into consideration, it is possible to designate only one of the locations forming the overlapping portion 22 between the end 23 of one welded portion 21 and the other end 23 of the other welded portion 21 as the weakly irradiated area 24. In this way, it is possible to suppress the decrease in joint strength due to laser welding in the overlapping portion 22, which occurs when both locations are designated as weakly irradiated areas 24.

[0024] (3) When the end portion 23 of the welded portion 21 is formed by laser welding, misalignment of the end portion 23 is likely to occur. Taking such misalignment into consideration, the end portion 23 of the welded portion 21 is formed by a base portion 25 and a tip portion 26 that extends in a direction different from the direction in which the base portion 25 extends. In this case, when forming two welded portions 21 that form a closed circuit shape as a whole, the tip portion 26 at the end portion 23 of one welded portion 21 and the base portion 25 at the other end portion 23 of the other welded portion 21 are more likely to overlap. As a result, even if the above misalignment occurs, it is easier to form an overlapping portion 22 by the tip portion 26 at the end portion 23 of one welded portion 21 and the base portion 25 at the other end portion 23 of the other welded portion 21.

[0025] (4) When forming two welds 21 that form a closed circuit shape overall, only the tip portion 26 of the end 23 of one weld 21 and the other end 23 of the other weld 21 is designated as the weakly irradiated portion 24. As a result, when forming an overlapping portion 22 where the tip portion 26 of the end 23 of one weld 21 and the base end portion 25 of the other end 23 of the other weld 21 overlap, only one of the locations forming the overlapping portion 22 can be designated as the weakly irradiated portion 24.

[0026] (5) In the welded portion 21 extending along the outer edge of the separator 14, that is, the two welded portions 21 that form a closed circuit shape as a whole, the end portion 23 of the welded portion 21 is formed by laser welding as shown in Figure 3. At that time, the linear base portion 25 of the end portion 23 is prone to displacement in the direction of parallel movement. Taking this displacement into consideration, the tip portion 26 of the end portion 23 of one of the two welded portions 21 and the tip portion 26 of the other end portion 23 of the other welded portion 21 are oriented toward the same side in the direction in which they intersect with the base portion 25. As a result, even if the displacement occurs, it becomes easier to overlap the tip portion 26 of the end portion 23 of one welded portion 21 and the base portion 25 of the other end portion 23 of the other welded portion 21.

[0027] (6) In the two welded sections 21 that extend to surround the hole 16, that is, the two welded sections 21 that form a closed circuit shape as a whole, the ends 23 of the welded sections 21 are formed by laser welding as shown in Figure 4. At that time, the linear base end 25 of the end 23 is prone to displacement in the direction of parallel movement. Taking this displacement into consideration, of the two welded sections 21, the tip 26 of the end 23 of one welded section 21 is directed toward the side approaching the base end 25 of the other end 23 of the other welded section 21. Also, of the two welded sections 21, the tip 26 of the other end 23 of the other welded section 21 is directed toward the side approaching the base end 25 of the end 23 of the one welded section 21. As a result, even if the above displacement occurs, it becomes easier to overlap the tip 26 of the end 23 of one welded section 21 and the base end 25 of the other end 23 of the other welded section 21. As a result, even if the above-mentioned misalignment occurs, the tip portion 26 at the end 23 of one welded portion 21 and the base portion 25 at the other end 23 of the other welded portion 21 make it easier to form an overlapping portion 22.

[0028] The above embodiment can also be modified as follows, for example. The above embodiment and the following modifications can be combined and implemented to the extent that they are not technically contradictory. The end 23 of one welded portion 21 that forms the overlapping portion 22 and the other end 23 of the other welded portion 21 do not necessarily have to overlap as shown in Figure 3, but may overlap as shown in Figure 5, for example.

[0029] - The end 23 of one welded portion 21 that forms the overlapping portion 22 and the other end 23 of the other welded portion 21 do not necessarily have to overlap as shown in Figure 4, but may overlap as shown in Figure 6, for example.

[0030] - The portion of the welded joint 21 other than the end portion 23 does not necessarily have to be straight, and may have a shape as shown in Figures 7 and 8, for example. - The tip portion 26 of the end portion 23 may be curved instead of bent relative to the base portion 25 of the end portion 23 so that it extends in a different direction from the base portion 25.

[0031] - The weak irradiation portion 24 does not necessarily have to be formed only on the tip portion 26, but may be formed to extend from the tip portion 26 to the base portion 25. - The base portion 25 of the end portion 23 may have a shape other than a straight line.

[0032] - The weakly irradiated portion 24 may be formed on only one of the end portions 23 that form the overlapping portion 22. - The end portions 23 do not necessarily need to be distinguishable between the base end portion 25 and the tip end portion 26. That is, they may be indistinguishable because the base end portion 25 and the tip end portion 26 extend in the same direction.

[0033] - The welded joint 21, which forms a closed circuit shape overall, does not necessarily have to consist of two welded joints 21; it may consist of one welded joint 21 or three or more welded joints 21. In the case of two or more welded joints 21, it becomes possible to form a bipolar plate in a shorter time by forming multiple welded joints 21 simultaneously.

[0034] The metal plate assembly may be made of a material other than a bipolar plate.

Claims

1. A metal plate joint comprising a welded portion and an overlapping portion, wherein the welded portion has a predetermined length formed by laser welding metal plates stacked in the thickness direction by laser irradiation, and the overlapping portion is the location where the end E1 of the welded portion and another end E2 of the welded portion overlap, wherein at least one of the end E1 and the other end E2 of the welded portion has a weakly irradiated portion formed where the laser irradiation intensity during laser welding is weaker than the other, and at least one of the locations forming the overlapping portion between the end E1 and the other end E2 of the welded portion is the weakly irradiated portion.

2. The metal plate joint according to claim 1, wherein only one of the locations forming the overlapping portion at the end E1 of the welded portion and the other end E2 of the welded portion is the weakly irradiated portion.

3. The metal plate joint according to claim 1, wherein each of the end E1 of the welded portion and the other end E2 of the welded portion comprises a base end and a tip that is connected to the base end and directed to extend in a direction different from the direction in which the base end extends, and the overlapping portion is formed by the tip at the end E1 of the welded portion and the base end at the other end E2 of the welded portion.

4. The metal plate joint according to claim 3, wherein only the tip portion of the base portion and the tip portion is the weakly irradiated portion.

5. The metal plate joint according to claim 3 or 4, wherein the base end of the end E1 of the weld and the base end of the other end E2 of the weld are formed in a straight line extending parallel to each other, and the tip of the end E1 of the weld and the tip of the other end E2 of the weld are directed toward the same side in a direction intersecting the base end.

6. The metal plate joint according to claim 3 or 4, wherein the base end of the end E1 of the weld and the base end of the other end E2 of the weld are formed in a straight line extending in an intersecting direction, the tip of the end E1 of the weld is directed toward the side approaching the base end of the other end E2 of the weld, and the tip of the other end E2 of the weld is directed toward the side approaching the base end of the end E1 of the weld.

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