Patent Description:
For example, a technique is known which includes laser welding the outer periphery of an anode separator (first workpiece) <NUM> and a cathode separator (second workpiece) <NUM> stacked on each other and the periphery of a manifold <NUM> (welded portion by the laser welding is denoted by the reference numeral L<NUM>) to thereby form a welded seal (welded seal line) <NUM> in a fuel cell as illustrated in <FIG> and <FIG>. In the plan view of <FIG>, the welded seal <NUM> is indicated by the dotted line and a rubber seal (rubber seal line) <NUM> by a gasket <NUM> is indicated by the solid line. In the cross-sectional view of <FIG>, the reference numeral <NUM> denotes a hydrogen flow passage, the reference numeral <NUM> denotes an oxygen flow passage, and the reference numeral <NUM> denotes a cooling water flow passage.

Moreover, a technique is known which includes laser welding the pair of separators (first and second workpieces) <NUM> and <NUM> to thereby form the welded seal <NUM> and joining an accessory component (third workpiece) <NUM> to the pair of laser-welded separators <NUM> and <NUM> similarly by laser welding (welded portion by the laser welding is denoted by the reference numeral L<NUM>) as illustrated in <FIG>. As the accessory component <NUM>, <FIG> illustrate a voltage monitoring component. However, the type of the component is not particularly limited and components for positioning between separators illustrated in <FIG> or the like may be acceptable, for example.

Thus, when the welded seal <NUM> is formed by laser welding the pair of separators <NUM> and <NUM> and the accessory component <NUM> is joined to the pair of laser-welded separators <NUM> and <NUM> similarly by laser welding, the welded portion L<NUM> of the separators <NUM> and <NUM> and the accessory component <NUM> of the latter needs to be welded with an energy density (heat input amount) higher than that of the welded portion L<NUM> between the pair of separators <NUM> and <NUM> because a total thickness t<NUM> due to the three components <NUM>, <NUM>, and <NUM> increases (t<NUM> < t<NUM> when the thickness due to the pair of separators <NUM> and <NUM> is defined as t<NUM>). In the welded portion L<NUM> of the separators <NUM> and <NUM> and the accessory component <NUM>, the three components <NUM>, <NUM>, and <NUM> are preferably penetration welded so as to stabilize the quality. However, it is desirable that a hole or the like is not generated in the three components <NUM>, <NUM>, and <NUM>.

As a technique of laser welding the pair of separators <NUM> and <NUM> to thereby form the welded seal <NUM> and joining the accessory component <NUM> to the pair of laser-welded separators <NUM> and <NUM> similarly by laser welding described above, a technique is mentioned which includes successively performing a process of welding the pair of separators <NUM> and <NUM> and a process of welding the pair of separators <NUM> and <NUM> and the accessory component <NUM> as separate processes by preparing a plurality of laser irradiation devices different in output.

This is a technique, for example, which includes preparing a <NUM> W small output irradiation device and a <NUM> W large output irradiation device (neither is illustrated), and first welding the pair of separators <NUM> and <NUM> in the welded portion L<NUM> using the <NUM> W small output irradiation device as illustrated in <FIG>, and then welding the pair of separators <NUM> and <NUM> and the accessory component <NUM> in the welded portion L<NUM> using the <NUM> W large output irradiation device as illustrated in <FIG>.

However, this technique causes an increase in the number of processes and an increase in the facility cost, and therefore has a problem leading to a cost increase. <CIT> teaches welding along a welding line by forming a plurality of aligned loops on a path. <CIT> teaches welding in a welding line in a zigzag form. <CIT> teaches welding along a welding line in one direction. When at the end, the welding is just moved to the inside, thereby departing from the welding line, and the welding forms the end point. <CIT> teaches welding along a welding line in a particular direction. At the start and at the end, the welding is deviated from the welding line. <CIT> teaches welding along one welding line in a particular direction. At a returning point, the further welding is made on a welding line in a direction that is parallel from the already performed welding. <CIT> teaches an overlap-welding in which a welding line in return direction is offset to the one in forward direction, but overlapping.

As a method in which the process of the welding of the accessory component <NUM> is not separated, the welding of the pair of separators <NUM> and <NUM> and the welding of the pair of separators <NUM> and <NUM> and the accessory component <NUM> are performed in the same process using the same laser irradiation device. In the welding of the pair of separators <NUM> and <NUM> and the accessory component <NUM> of the latter, when the welded portion L<NUM> of the accessory component <NUM> is reciprocatingly irradiated with laser along a fixed welding line to thereby apply an energy density corresponding to an increase in the plate thickness thereto, the three components <NUM>, <NUM>, and <NUM> can be penetration welded.

Herein, the description "the welded portion L<NUM> of the accessory component <NUM> is reciprocatingly irradiated with laser along a fixed welding line" means that, when the laser is emitted along the fixed welding line from an A point to a B point in the welded portion L<NUM> of the accessory component <NUM> as illustrated in <FIG>, for example, the irradiation is performed from the A point to the B point (arrow a) with the A point as a start end of the irradiation and the irradiation is continuously performed from the B point to the A point (arrow b) by returning at the B point so that the A point is set as a termination end of the irradiation, and thus the irradiation is substantially performed twice (one reciprocation) along the fixed welding line.

However, in this case, each of the start end (start portion) and the termination end (terminal) of the laser irradiation is brought into a state where the energy density (heat input amount) is higher than that in the other portions in many cases due to the machine control or the like, and therefore is brought into a state where the melting amount is large. Accordingly, when the start end and the termination end of the irradiation are set at the same position (A point) while overlapping each other on the plane, a state where the density of the energy to be emitted becomes excessively high is caused, and, as a result, there is a possibility that a defect, such as a hole, occurs.

It is an object of the present invention to provide, in view of the above-described respects, a laser welding method in which a state where the irradiation energy density becomes excessively high by a plurality of times of laser irradiation is not caused and a defect, such as a hole, does not occur in a workpiece.

The above-described object is solved by a laser welding method having the features of claim <NUM>. An alternative laser welding method is stated in claim <NUM>. Further developments are stated in the dependent claims.

In the present invention, when a laser beam is emitted a plurality of times along a fixed welding line, the irradiation positions of ends of the irradiation are shifted away from each other so that the irradiation energy can be dispersed, and therefore a state where the irradiation energy density becomes excessively high at the 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 the irradiation energy density becomes excessively high by the plurality of times of laser irradiation can be prevented.

The present invention contains the following embodiments.

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

As illustrated in <FIG> and <FIG>, a laser welding method according to this example includes joining a pair of fuel cell separators <NUM> and <NUM> as workpieces (welding target) thereof by laser welding, i.e., includes laser welding the outer periphery of the anode separator (first workpiece) <NUM> and the cathode separator (second workpiece) <NUM> stacked on each other and the periphery of a manifold <NUM> (a welded portion by the laser welding is denoted by the reference numeral L<NUM>) to thereby form a welded seal (welded seal line) <NUM> and joining an accessory component (third workpiece) <NUM> to the pair of laser-welded separators <NUM> and <NUM> similarly by performing laser welding (a welded portion by the laser welding is denoted by the reference numeral L<NUM>). As the accessory component <NUM>, 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> above or the like may be acceptable, for example. In the plan view of <FIG>, the welded seal <NUM> is indicated by the dotted line and the rubber seal (rubber seal line) <NUM> by the gasket <NUM> is indicated by the solid line.

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

More specifically, first, the pair of separators <NUM> and <NUM> are stacked on each other, and then the separators <NUM> and <NUM> are irradiated with a laser beam (first irradiation) to form the welded portion L<NUM>, i.e., the welded seal <NUM>, of the separators <NUM> and <NUM> as illustrated in <FIG>.

Subsequently, as illustrated in <FIG>, the accessory component <NUM> is stacked on the pair of welded separators <NUM> and <NUM>, and then the separators <NUM> and <NUM> and the accessory component <NUM> are irradiated with a laser beam (second irradiation) to form the welded portion L<NUM> of the accessory component <NUM>. When the separators <NUM> and <NUM> and the accessory component <NUM> are welded, the welded portion L<NUM> of the accessory component <NUM> is reciprocatingly irradiated with laser along a fixed welding line. Herein, the description "the welded portion L<NUM> of the accessory component <NUM> 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.

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.

First scanning of second irradiation (forward scanning, <FIG>).

As illustrated in <FIG>, when laser is emitted along the fixed welding line from an A point to a B point in the welded portion L<NUM> of the accessory component <NUM>, 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.

Second scanning of second irradiation (return scanning, <FIG>).

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.

Hence, according to this procedure, the welded portion L<NUM> of the accessory component <NUM> 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.

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>.

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.

As illustrated in <FIG>, when laser is emitted along the fixed welding line in the welded portion L<NUM> of the accessory component <NUM>, 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).

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.

Claim 1:
A laser welding method comprising:
welding a plurality of workpieces (<NUM>, <NUM>) by irradiating the workpieces (<NUM>, <NUM>) in a stacked state with a laser beam,
wherein the laser beam is reciprocatingly emitted along a fixed welding line, wherein irradiation positions of a start end and a termination end of the irradiation are shifted away from each other so that irradiation energy can be dispersed,
emitting the laser beam from a point A to a point B along the fixed welding line,
characterized by
returning at point B and emitting the laser beam from the point B along the fixed welding line, and
changing the direction of irradiation at a point A' before reaching the point A, whereby a branched line (c) of the welding line is set and a point A" that is different from the point A is set as the termination end of the irradiation,
wherein the point A' is between the point A and the point B, and the point A' is different from the point A and the point B.