Laser welding method

Abstract

This invention provides a laser welding method in which a state where the irradiation energy density becomes excessively high by a plurality of times of irradiation with laser is not caused and a defect, such as a hole, does not occur in a workpiece. In order to achieve the object, a laser welding method for welding a plurality of workpieces by irradiating the workpieces in a stacked state with a laser beam is characterized in that, when the laser beam is reciprocatingly emitted along a fixed welding line, the irradiation positions of a start end A and a termination end A″ of the irradiation are shifted away from each other so that the irradiation energy can be dispersed. Moreover, when the laser beam is emitted a plurality of times in the same direction along the fixed welding line, the irradiation positions of the start ends or/and the termination ends of the irradiation are shifted away from each other so that the irradiation energy can be dispersed.

Claims

1. A laser welding method, comprising: welding a plurality of workpieces by irradiating the workpieces in a stacked state with a laser beam, wherein the welding comprises performing a first irradiation by emitting the laser beam along a fixed welding line so as to weld a first workpiece and a second workpiece, and performing a second irradiation by reciprocatingly emitting the laser beam along a fixed welding line in performing the second irradiation so as to weld a third workpiece to the first and the second workpiece welded by the first irradiation, in a same process using a same irradiation device, and during the second irradiation, shifting irradiation positions of a start end and a termination end of the irradiation away from each other so as to disperse irradiation energy.

2. A laser welding method, comprising: welding a plurality of workpieces by irradiating the workpieces in a stacked state with a laser beam, wherein the welding comprises performing a first irradiation by emitting the laser beam along a fixed welding line so as to weld a first workpiece and a second workpiece, and performing a second irradiation by emitting the laser beam a plurality of times in a same direction along a fixed welding line in performing the second irradiation so as to weld a third workpiece to the first and the second workpiece welded by the first irradiation, in a same process using a same irradiation device, and during the second irradiation, shifting irradiation positions of start ends or/and termination ends of the irradiation away from each other so as to disperse irradiation energy.

3. The laser welding method according to claim 1, wherein: the first and second workpieces are fuel cell separators, and the third workpiece is an accessory component attached to the fuel cell separator.

4. The laser welding method according to claim 2, wherein: the first and second workpieces are fuel cell separators, and the third workpiece is an accessory component attached to the fuel cell separator.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a plan view illustrating an example of a fuel cell constituent component serving as a workpiece in a laser welding method according to an example of the present invention.

(2) FIGS. 2(A), 2(B), and 2(C) are process explanatory views of the laser welding method.

(3) FIGS. 3(A) and 3(B) are explanatory views of laser irradiation positions in the laser welding method.

(4) FIG. 4 is an explanatory view of laser irradiation positions in a laser welding method according to another example of the present invention.

(5) FIG. 5 is a plan view illustrating an example of a fuel-cell cell serving as a workpiece in a laser welding method according to a conventional example.

(6) FIG. 6 is a cross-sectional view of a principal portion of the fuel-cell cell and is an enlarged cross-sectional view along the D-D line in FIG. 5.

(7) FIG. 7 is a plan view illustrating an example of a fuel cell constituent component serving as a workpiece in a laser welding method according to a conventional example.

(8) FIG. 8 is a cross-sectional view of a principal portion of the fuel cell constituent component and is an enlarged cross-sectional view along the E-E line in FIG. 7.

(9) FIG. 9 is a plan view illustrating another example of the fuel cell constituent component serving as a workpiece in the laser welding method according to the conventional example.

(10) FIGS. 10(A) and 10(B) are process explanatory views of the laser welding method according to the conventional example.

(11) FIG. 11 is an explanatory view of laser irradiation positions in a laser welding method according to another conventional example.

DESCRIPTION OF EMBODIMENTS

(12) The present invention contains the following embodiments.

(13) (1) A separate component (accessory component) is joined by welding to welded separators in which an anode separator and a cathode separator are welded to thereby form a seal line. The welding of the seal line and the welding of the separate component are carried out in the same process (same facility) and, when the separate component is welded to the separators, laser irradiation is performed a plurality of times in the same welding line. It is configured so that the welding lines of a start portion and a termination end of the welding are shifted away from each other when the laser irradiation is performed a plurality of times in the same welding line.

(14) (2) In the case where the welding of the seal line and the welding of the separate component are carried out in the same process (same facility), when the laser irradiation is performed a plurality of times in the same welding line in welding the separate component to the separators, the welding lines of the start portion and the termination end of the laser irradiation are shifted away from each other so as not to be overlapped. This makes it possible to avoid that the density of the energy (heat input amount) to be emitted to the start portion and the termination end become excessive and to take measures against a defect, such as a hole.

(15) (3) According to the present invention, by carrying out the welding of the seal line and the welding of the separate component in the same process, the number of processes decreases and the facility decreases, so that a cost reduction can be expected. By avoiding the concentration of the energy density (heat input amount) in the start portion and the termination end of the welding, a defect of a hole does not occur, so that the quality is stabilized.

EXAMPLES

(16) Next, examples of the present invention are described according to the drawings.

(17) As illustrated in FIGS. 1 and 2, a laser welding method according to this example includes joining a pair of fuel cell separators 11 and 12 as workpieces (welding target) thereof by laser welding, i.e., includes laser welding the outer periphery of the anode separator (first workpiece) 11 and the cathode separator (second workpiece) 12 stacked on each other and the periphery of a manifold 13 (a welded portion by the laser welding is denoted by the reference numeral L.sub.1) to thereby form a welded seal (welded seal line) 14 and joining an accessory component (third workpiece) 20 to the pair of laser-welded separators 11 and 12 similarly by performing laser welding (a welded portion by the laser welding is denoted by the reference numeral L.sub.2). As the accessory component 20, a voltage monitoring component is illustrated. However, the type of the component is not particularly limited and a component for positioning between separators illustrated in FIG. 9 above or the like may be acceptable, for example. In the plan view of FIG. 1, the welded seal 14 is indicated by the dotted line and the rubber seal (rubber seal line) 16 by the gasket 15 is indicated by the solid line.

(18) Moreover, as a method for not performing the welding of the accessory component 20 and the welding of the separators 11 and 12 in separate processes, the welding of the pair of separators 11 and 12 and the welding of the pair of separators 11 and 12 and the accessory component 20 are performed in the same process using the same laser irradiation device (not illustrated) in the laser welding method according to this example.

(19) The procedure is as follows.

(20) <Welding of Separators 11 and 12>

(21) More specifically, first, the pair of separators 11 and 12 are stacked on each other, and then the separators 11 and 12 are irradiated with a laser beam (first irradiation) to form the welded portion L.sub.1, i.e., the welded seal 14, of the separators 11 and 12 as illustrated in FIG. 2(A).

(22) <Welding of Separators 11 and 12 and Accessory Component 20>

(23) Subsequently, as illustrated in FIGS. 2(B) and 2(C), the accessory component 20 is stacked on the pair of welded separators 11 and 12, and then the separators 11 and 12 and the accessory component 20 are irradiated with a laser beam (second irradiation) to form the welded portion L.sub.2 of the accessory component 20. When the separators 11 and 12 and the accessory component 20 are welded, the welded portion L.sub.2 of the accessory component 20 is reciprocatingly irradiated with laser along a fixed welding line. Herein, the description “the welded portion L.sub.2 of the accessory component 20 is reciprocatingly irradiated with laser along a fixed welding line” means that the irradiation is performed twice (one reciprocation) along the fixed welding line. However, when the start end and the termination end of the irradiation are set at the same position while overlapping each other on the plane, a state where the density of the energy to be emitted becomes excessively high is caused, so that a defect, such as a hole, occurs in some cases as described above.

(24) Thus, in this example of the present invention, when the laser beam is emitted a plurality of times along the fixed welding line, the irradiation positions of the ends of the irradiation are shifted away from each other so that the irradiation energy can be dispersed. Specifically, when the laser beam is reciprocatingly emitted along the fixed welding line, the irradiation positions of the start end and the termination end of the irradiation are shifted away from each other so that the irradiation energy can be dispersed. A specific procedure is as follows.

(25) First Scanning of Second Irradiation (Forward Scanning, FIG. 2(B))

(26) As illustrated in FIG. 3(A), when laser is emitted along the fixed welding line from an A point to a B point in the welded portion L.sub.2 of the accessory component 20, the laser is emitted from the A point to the B point (arrow a) with the A point as the start end of the irradiation.

(27) Second Scanning of Second Irradiation (Return Scanning, FIG. 2(C))

(28) As illustrated in the figure, the laser is continuously emitted from the B point to the A point by returning at the B point (arrow b). However, the direction of the irradiation is changed at an A′ point (branched portion) before (immediately before) reaching the A point, whereby a branched line of the welding line is set (arrow c) and an A″ point close to the A point but different from the A point is set as the termination end of the irradiation.

(29) Hence, according to this procedure, the welded portion L.sub.2 of the accessory component 20 can be reciprocatingly irradiated with laser along the fixed welding line and the irradiation energy is dispersed by shifting the irradiation positions of the start end (A point) and the termination end (A″ point) of the irradiation when the laser beam is reciprocatingly emitted along the fixed welding line, and therefore a state where the irradiation energy density becomes excessively high in the start end and the termination end of the irradiation is not caused. Hence, the occurrence of a defect, such as a hole, in a workpiece due to the fact that a state where the irradiation energy density becomes excessively high by a plurality of times of laser irradiation is caused can be prevented as expected by the present invention.

(30) When there is a concern that the irradiation energy density increases not only in the start end and the termination end of the irradiation but at a returning portion (B point) of the irradiation, the welding line may be reversed in a U shape or a substantially U shape at the returning portion (B point) of the irradiation as illustrated in FIG. 3(B).

(31) Moreover, it is also assumed that a laser beam is emitted a plurality of times in the same direction along the fixed welding line instead of reciprocatingly emitting a laser beam along the fixed welding line as with the example described above. Therefore, in this case, the irradiation positions of the start ends or/and the termination ends of the irradiation are shifted away from each other so that the irradiation energy can be dispersed. A specific procedure is as follows.

(32) First Scanning of Second Irradiation

(33) As illustrated in FIG. 4, when laser is emitted along the fixed welding line in the welded portion L.sub.2 of the accessory component 20, the A point is set as the start end of the irradiation and the B point is set as the termination end of the irradiation (arrow a).

(34) Second Scanning of Second Irradiation

(35) The second scanning is continuously performed as illustrated in the figure. At this time, an A′ point close to the A point but different from the A point is set as the start end of the irradiation and a B′ point close to the B point but different from the B point is set as the termination end of the irradiation (arrow a′). The irradiation line of the first scanning and the irradiation line of the second scanning overlap each other on and after an A″ point close to the A point and the A′ point but different from the A point and the A′ point and are branched on and after a B″ point close to the B point and the B′ point but different from the B point and the B′ point.

(36) Therefore, according to this procedure, the welded portion L.sub.2 of the accessory component 20 can be irradiated with laser a plurality of times along the fixed welding line and, when the laser beam is emitted a plurality of times along the fixed welding line, the irradiation energy is dispersed by shifting the irradiation positions of the start ends (A point and A′ point) and the termination ends (B point and B′ point) of the irradiation from each other, and therefore a state where the irradiation energy density becomes excessively high in the start ends and the termination ends of the irradiation is not caused. Therefore, the occurrence of a defect, such as a hole, in a workpiece due to the fact that a state where the irradiation energy density becomes excessively high by a plurality of times of laser irradiation is caused can be prevented as expected the present invention.

DESCRIPTION OF REFERENCE NUMERALS

(37) 11,12 separator (first and second workpieces) 13 manifold 14 welded seal 15 gasket 16 rubber seal 17 hydrogen flow passage 18 oxygen flow passage 19 cooling water flow passage 20 accessory component (third workpiece) L.sub.1 separator welded portion L.sub.2 accessory component welded portion