JP7633615B2 - Laser welding method and laser welding apparatus - Google Patents

Description

The present invention relates to a laser welding method and a laser welding device.

Laser welding technology may be used to join metal components together. Metal components are joined using laser welding technology by irradiating the area where the metal components are in contact or close to each other with laser light, melting and solidifying part of the metal components.

Patent Document 1 discloses a method for joining overlapping steel plates using laser welding technology. In the laser welding method disclosed in Patent Document 1, a laser beam is irradiated from one of the steel plates onto the lap area where the steel plates overlap, and the laser beam is scanned so that the spot of the laser beam orbits a predetermined location, forming a weld that is dot-shaped in plan view.

In addition, in the welding method disclosed in Patent Document 1, after forming the dot-shaped welds in plan view as described above, the outermost periphery of the welds is again irradiated with laser light to anneal the peripheral portion of the welds. Patent Document 1 states that by performing this annealing process, it is possible to improve the joint strength.

JP 2018-153851 A

When joining metal members using laser welding methods, there is a demand for further improvements in the joining strength. In response to this, it is thought that, for example, in the technology disclosed in Patent Document 1, the joining strength can be improved by increasing the diameter of the dot-shaped welds (by increasing the area of the dot-shaped welds).

However, when the diameter of the dot weld is increased using the technology disclosed in Patent Document 1, burn-through is more likely to occur. In particular, burn-through is more likely to occur when there is a gap between the metal members in the welded area. Therefore, it is considered difficult in practice to increase the diameter of the dot weld in order to improve the joint strength.

The present invention has been made to solve the above problems, and aims to provide a laser welding method and laser welding device that can further improve the joining strength between metal members.

A laser welding method according to one aspect of the present invention is a laser welding method for joining a plurality of metal members arranged in contact with or adjacent to each other by laser welding, and includes a laser light irradiation step of oscillating a laser beam and focusing the oscillated laser beam at a welding location on a first main surface of a first metal member located outside the arrangement, and a scanning step of scanning a spot of the laser beam within the first main surface.

The scanning step includes a dot portion forming sub-step of scanning the laser light spot in a circular motion around a predetermined location to melt the metal member to form a dot-shaped weld that has a dot shape in a planar view, and a straight portion forming sub-step of scanning the laser light spot away from the outer peripheral edge of the dot weld while the metal member in the dot weld is in a molten state to melt the metal member to form a straight weld that has a straight shape in a planar view and is continuous with the dot weld.

Here, an external force is applied to the metal member such that stress acts in a first direction along the first main surface. In the laser welding method according to this aspect, taking into account the above-mentioned stress acting direction, in the straight portion forming sub-step, the spot of the laser light is scanned so that the straight weld portion extends in the first direction.

In the laser welding method according to the present embodiment, a laser beam irradiation step and a scanning step are performed to join multiple metal members by laser welding, so the welding speed is faster and there is less thermal impact compared to joining by resistance welding. In addition, in the laser welding method according to the present embodiment, the metal members can be joined without contacting the metal members, so processing efficiency is high and rigidity can be increased by continuous welding.

In addition, in the laser welding method according to this embodiment, in the dot portion forming sub-step, the laser light spot is rotated to melt and stir the metal in that portion, and in the straight portion forming sub-step, the straight weld portion is formed with the metal of the dot weld portion molten, so that even if there is a gap between the metal members, some of the molten metal of the dot weld portion can flow into the gap between the metal members where the straight weld portion is to be formed. Therefore, in the laser welding method according to this embodiment, even if there is a gap between the metal members, problems such as gouging and burn-through can be suppressed.

In addition, in the laser welding method according to this aspect, in the straight line portion forming sub-step, a straight line weld is formed so as to extend in the direction of the stress acting on the multiple metal members after welding (first direction), so that the strength of the multiple metal members after welding against an external load can be increased. In particular, the laser welding method according to this aspect can achieve high tensile shear strength in the multiple metal members after welding.

Furthermore, in the laser welding method according to the present embodiment, a linear weld is formed that is continuous with the dot weld, so that the joint strength can be further improved without increasing the diameter of the dot weld (the area of the dot weld in a plan view) compared to the technique disclosed in the above-mentioned Patent Document 1, where the weld is composed of only dot welds. Therefore, the laser welding method according to the present embodiment can further improve the joint strength while preventing the welding time from becoming longer and suppressing the occurrence of burn-through.

In the laser welding method according to the above aspect, in the dot portion forming sub-step, the amount of heat input by the irradiation of the laser light at the outer periphery of the dot-shaped weld may be greater than the amount of heat input at the inner periphery, which is located inside the outer periphery.

In the laser welding method according to the present embodiment, in the dot portion forming sub-step, the heat input for forming the outer peripheral portion of the dot weld is set to be greater than the heat input for forming the inner peripheral portion. Therefore, in the laser welding method according to the present embodiment, in the execution of the straight portion forming sub-step following the formation of the dot weld, it is easy to maintain the molten metal state of at least the outer peripheral portion of the dot weld. In other words, in the laser welding method according to the present embodiment, it is possible to lengthen the time until the metal of at least the outer peripheral portion of the dot weld solidifies. Therefore, in the laser welding method according to the present embodiment, in the straight portion forming sub-step, the molten metal in the outer peripheral portion of the dot weld can be effectively poured into the straight weld, which is effective in realizing a joint with high strength. In addition, in the laser welding method according to the present embodiment, since it is easy to ensure the amount of metal flowing into the straight weld, even if there is a gap between the metal members, the gap can be sufficiently filled with molten metal, which is also effective in avoiding the occurrence of burn-through.

In the laser welding method according to the above aspect, the scanning may be performed so that the irradiation density of the laser light in the outer peripheral portion is higher than the irradiation density of the laser light in the inner peripheral portion, and the difference in irradiation density may cause the heat input in the outer peripheral portion to be greater than the heat input in the inner peripheral portion.

In the laser welding method according to this embodiment, in the dot portion forming sub-step, the irradiation density of the laser light is made higher in the outer peripheral portion than in the inner peripheral portion, so that the heat input in the outer peripheral portion is greater than in the inner peripheral portion. In this case, as in the laser welding method according to the above embodiment, the time until the metal in the outer peripheral portion of the dot weld solidifies can be extended, making it easier to ensure the amount of metal that flows into the linear weld. Therefore, the laser welding method according to this embodiment can also achieve a high-strength joint and prevent burn-through.

In the laser welding method according to the above aspect, in the straight-line portion forming sub-step, the heat input to a starting portion of the straight-line weld, which includes an intersection with the outer peripheral edge of the dot-shaped weld, may be greater than the heat input to a separation portion, which is a portion separated from the starting portion.

In the laser welding method according to this aspect, in the straight section forming step, the heat input at the starting point portion including the intersection with the outer periphery of the dot weld is greater than the heat input at the separation portion. Therefore, in the laser welding method according to this aspect, in the straight section forming sub-step following the formation of the dot weld, it is easy to maintain the molten metal state of the outer periphery of the dot weld. In other words, in the laser welding method according to this aspect, it is possible to extend the time until the metal of at least the outer periphery of the dot weld solidifies. Therefore, in the laser welding method according to this aspect, in the straight section forming sub-step, the molten metal in the outer periphery of the dot weld can be effectively flowed into the straight weld, which is effective in achieving a high strength joint.

In the laser welding method according to this embodiment, it is not necessarily necessary to make the heat input amount around the entire outer circumference greater than the heat input amount around the inner circumference when forming the dot-shaped weld, as in the laser welding method according to the above embodiment. In other words, in the laser welding method according to this embodiment, by increasing the heat input amount at the starting point in the straight section formation sub-step, the molten metal can be effectively flowed into the straight section molten part without necessarily increasing the heat input amount around the entire outer circumference in the dot section formation sub-step, which is effective in avoiding the occurrence of burn-through.

In the laser welding method according to the above aspect, the scanning may be performed so that the irradiation density of the laser light at the starting point portion is higher than the irradiation density of the laser light at the spaced portion, and the difference in irradiation density may cause the heat input at the starting point portion to be greater than the heat input at the spaced portion.

In the laser welding method according to this embodiment, in the straight section forming sub-step, the irradiation density of the laser light at the starting point is made higher than at the spaced portion, so that the heat input at the starting point is greater than at the spaced portion. In this case, as with the laser welding method according to the above embodiment, the time until the metal of the dot-shaped weld at the starting point of the straight weld solidifies can be extended, making it easier to ensure the amount of metal that flows into the straight weld. Therefore, the laser welding method according to this embodiment can also achieve a high-strength joint and avoid the occurrence of burn-through.

In the laser welding method according to the above aspect, the laser output at the starting point may be made higher than the laser output at the spaced apart portion, so that the difference in laser output causes the heat input at the starting point to be greater than the heat input at the spaced apart portion.

In the laser welding method according to this embodiment, in the straight section forming sub-step, the laser output at the starting point is made higher than that at the spaced portion, so that the heat input at the starting point is greater than that at the spaced portion. In this case, as in the laser welding method according to the above embodiment, the time until the metal at the starting point of the straight weld (the outer periphery of the dot weld) solidifies can be extended, making it easier to ensure the amount of metal that flows into the straight weld. Therefore, the laser welding method according to this embodiment can also achieve a high-strength joint and avoid burn-through.

In the laser welding method according to the above aspect, in the straight line portion forming sub-step, the straight line weld may be formed so that the length of the straight line weld is longer than the diameter of the dot weld.

In the laser welding method according to this aspect, in the straight section forming sub-step, the length of the straight weld is made longer than the diameter of the dot weld, so that the strength against the stress acting on the multiple metal components after welding can be further increased.

When attempting to make the length of the linear weld longer than the diameter of the dot weld, as in the laser welding method according to this embodiment, it is particularly effective to ensure a large amount of molten metal flows into the linear weld by making the heat input to the outer periphery of the dot weld greater than that to the inner periphery, or by making the heat input to the starting point of the linear weld greater than that to the spaced apart portion.

In the laser welding method according to the above aspect, in the straight line portion forming sub-step, the straight line weld may be formed so that the length of the straight line weld is shorter than the diameter of the dot weld.

In the laser welding method according to this embodiment, in the straight section forming sub-step, the length of the straight weld is made shorter than the diameter of the dot weld, so that burn-through can be prevented without increasing the heat input to the outer periphery of the dot weld compared to the inner periphery, or increasing the heat input to the starting point of the straight weld compared to the spaced apart portion.

In the laser welding method according to the above aspect, when the linear weld is a first linear weld, in the linear portion forming sub-step, while the metal member in the dot weld is in a molten state, the spot of the laser light is scanned away from the outer periphery of the dot weld to melt the metal member, and a second linear weld that is continuous with the dot weld and linear in plan view and extends in a second direction different from the first direction is also formed, and when a first virtual center line extending along the longitudinal direction is drawn at the center of the width direction of the first linear weld and a second virtual center line extending along the longitudinal direction is drawn at the center of the width direction of the second linear weld, the first virtual center line and the second virtual center line may intersect with each other in the region where the dot weld is formed.

In the laser welding method according to this embodiment, the first virtual center line and the second virtual center line intersect with each other in the area where the dot welds are formed, so that the strength difference against stress in directions other than the linear weld direction can be eliminated. Therefore, the laser welding method according to this embodiment is even more effective for high-strength joining.

In the laser welding method according to the above aspect, an external force is applied to the plurality of metal members after welding so that stress acts along the first main surface and in a second direction different from the first direction, and when the linear weld is the first linear weld, in the linear portion forming sub-step, while the metal members in the dot weld are in a molten state, the spot of the laser light is scanned away from the outer periphery of the dot weld to melt the metal members, and a second linear weld that is continuous with the dot weld and linear in plan view extending in the second direction is also formed, and in the linear portion forming sub-step, the first linear weld and the second linear weld may be formed so that the length of the first linear weld is longer than the length of the second linear weld.

In the laser welding method according to this aspect, a first linear weld extending in the first direction and a second linear weld extending in the second direction are formed for each direction in which stress acts (first direction, second direction). In the laser welding method according to this aspect, the length of the first linear weld is made longer than the length of the second linear weld. By changing the lengths of the first linear weld and the second linear weld in this way, it is possible to achieve a high-strength joint without unnecessarily lengthening the welding time, for example, even when the magnitude of the stress acting in the first direction is greater than the magnitude of the stress acting in the second direction.

Here, when forming multiple linear welds, it is possible to uniformly determine the length of all linear welds based on the largest stress acting on them. However, in this case, the welding time becomes longer and productivity decreases. In contrast, in the laser welding method according to this embodiment, the length of the first linear weld extending in the first direction in which a large stress acts is increased, and the length of the second linear weld extending in the second direction in which a small stress acts is decreased, so that it is possible to ensure both high joint strength and high productivity.

A laser welding device according to one aspect of the present invention is a laser welding device that joins multiple metal members arranged in contact with or close to each other by laser welding, and includes a laser oscillator that oscillates laser light, a focusing unit that focuses the laser light on a welding location on a first main surface of a first metal member located outside the arrangement, a scanning unit that scans a spot of the laser light within the first main surface, and a control unit that controls the laser oscillator and the scanning unit.

The control unit executes a process of forming a dot-shaped weld that is dot-shaped in plan view by scanning the spot of the laser light around a predetermined location while the laser oscillator is oscillating the laser light, and a process of forming a linear weld that is linear in plan view and continuous with the dot-shaped weld by scanning the spot of the laser light away from the outer periphery of the dot-shaped weld while the metal member in the dot-shaped weld is in a molten state, and melting the metal member.

Here, an external force is applied to the multiple metal members after welding so that stress acts in a first direction along the first main surface. In the laser welding device according to this aspect, taking into account the above-mentioned stress acting direction, in executing the process of forming the linear weld, the control unit causes the scanning unit to scan the spot of the laser light so that the linear weld extends in the first direction.

The laser welding device according to this embodiment joins multiple metal members by laser welding, which allows for faster welding speeds and less thermal impact than resistance welding. In addition, the laser welding device according to this embodiment can join metal members without contacting the metal members, which allows for high processing efficiency and increased rigidity through continuous welding.

In addition, in the laser welding device according to this embodiment, the control unit controls the scanning unit to rotate the spot of the laser light to melt and stir the metal in that area, and form a linear weld with the metal of the dot weld molten. Therefore, even if there is a gap between the metal members, some of the molten metal of the dot weld can flow into the gap between the metal members where the linear weld is to be formed. Therefore, with the laser welding device according to this embodiment, even if there is a gap between the metal members, problems such as gouging and burn-through can be suppressed.

In addition, the laser welding device according to this embodiment forms a linear weld so that it extends in the direction of the stress acting on the multiple metal members after welding (first direction), so that the strength of the multiple metal members after welding against an external load can be increased. In particular, the laser welding device according to this embodiment can achieve high tensile shear strength in the multiple metal members after welding.

Furthermore, the laser welding device according to this embodiment forms a linear weld that is continuous with the dot weld, so that the joint strength can be further improved without increasing the diameter of the dot weld (the area of the dot weld in a plan view) compared to the technique disclosed in Patent Document 1, where the weld is made up of only dot welds. Therefore, the laser welding device according to this embodiment can prevent the welding time from becoming longer and further improve the joint strength while suppressing the occurrence of burn-through.

In the laser welding device according to the above aspect, the control unit may control the laser oscillator and the scanning unit in executing the process of forming the dot-shaped weld so that the amount of heat input by the irradiation of the laser light at the outer periphery of the dot-shaped weld is greater than the amount of heat input at the inner periphery that is more inward than the outer periphery.

In the laser welding device according to the present embodiment, when forming the dot welds, the heat input for forming the outer periphery of the dot welds is set to be greater than the heat input for forming the inner periphery. Therefore, in the laser welding device according to the present embodiment, when forming the linear welds following the formation of the dot welds, it is easy to maintain the molten state of the metal at least in the outer periphery of the dot welds. In other words, in the laser welding method according to the present embodiment, it is possible to lengthen the time until the metal at least in the outer periphery of the dot welds solidifies. Therefore, in the laser welding device according to the present embodiment, when forming the linear welds, the molten metal in the outer periphery of the dot welds can be effectively flowed into the linear welds, which is effective in realizing a joint with high strength. In addition, since the laser welding device according to the present embodiment makes it easy to ensure the amount of metal flowing into the linear welds, it is also effective in avoiding the occurrence of burn-through.

In the laser welding device according to the above aspect, the control unit may control the laser oscillator and the scanning unit in executing the process of forming the linear weld so that the amount of heat input at a starting portion of the linear weld, which includes an intersection with the outer periphery of the dot weld, is greater than the amount of heat input at a separation portion that is a portion separated from the starting portion.

In the laser welding device according to this embodiment, when forming a linear weld, the heat input at the starting point, including the intersection with the outer periphery of the dot weld, is greater than the heat input at the separation portion. Therefore, in the laser welding device according to this embodiment, when forming a linear weld following the formation of the dot weld, it is easy to maintain the molten state of the metal at the outer periphery of the dot weld. In other words, the laser welding device according to this embodiment can lengthen the time until the metal at least at the outer periphery of the dot weld solidifies. Therefore, in forming a linear weld, the laser welding device according to this embodiment can effectively flow the molten metal at the outer periphery of the dot weld into the linear weld, which is effective in achieving a high strength joint.

In addition, in the laser welding device according to this embodiment, when forming the dot weld, unlike the laser welding device according to the above embodiment, it is not necessary to make the heat input amount around the entire outer circumference greater than the heat input amount around the inner circumference. In other words, in the laser welding device according to this embodiment, by increasing the heat input amount at the starting point when forming the linear weld, the molten metal can be effectively flowed into the linear weld without necessarily increasing the heat input amount at the outer circumference when forming the dot weld, which is effective in avoiding the occurrence of burn-through.

In each of the above aspects, it is possible to further improve the bonding strength between metal members while suppressing a decrease in productivity.

1 is a schematic diagram showing a schematic configuration of a laser welding device according to a first embodiment. FIG. 1A and 1B are diagrams showing the arrangement of metal members before welding, in which FIG. 1A is a plan view from above, and FIG. 1B is a side view from the side. 1A and 1B are diagrams showing a laser welding method, in which FIG. 1A is a schematic diagram showing a method for forming a dot-shaped weld, and FIGS. 1B and 1C are schematic diagrams showing a method for forming a linear weld. FIG. 4 is a plan view showing the shape of a welded portion and the direction in which a load is applied. 5 is a cross-sectional view showing the cross section along line VV in FIG. 4. 5A to 5C are schematic diagrams showing a laser welding method according to a second embodiment. 13A is a schematic diagram showing a laser welding method according to a third embodiment, and FIG. 13B is a schematic diagram showing a laser welding method according to a fourth embodiment. 13A is a plan view showing a weld formed by a laser welding method according to a fifth embodiment, and FIG. 13B is a schematic diagram showing the relationship between imaginary center lines of linear welds. FIG. 13 is a plan view showing a welded portion formed by a laser welding method according to a sixth embodiment. 13A is a plan view showing a welded portion formed by the laser welding method according to the seventh embodiment, FIG. 13B is a plan view showing a welded portion formed by the laser welding method according to the eighth embodiment, and FIG. 13C is a plan view showing a welded portion formed by the laser welding method according to the ninth embodiment. 10A and 10B are diagrams showing a laser welding method according to a tenth embodiment, in which (a) is a schematic diagram showing a method of forming a dot-shaped weld, (b) is a schematic diagram showing a process of irradiating laser light again to the outer circumferential edge of the dot-shaped weld, and (c) is a schematic diagram showing a method of forming a linear weld. 1A is a plan view showing a weld used in confirmation experiment 1, and FIG. 1B is a graph showing the relationship between the length of a linear weld and the tensile shear strength. 1A is a plan view showing samples used in confirmation experiment 2, where (a) is sample 1, (b) is sample 2, (c) is sample 3, (d) is sample 4, and (e) is sample 5. 1A is a graph showing the results of a tensile test performed using Samples 1 to 5, and FIG. 1B is a graph showing the results of a tensile test performed using Samples 3 to 7.

The following describes an embodiment of the present invention with reference to the drawings. Note that the embodiment described below is an example of the present invention, and the present invention is not limited to the embodiment described below except for its essential configuration.

[First embodiment]
1. General Configuration of Laser Welding Apparatus 1 A general configuration of a laser welding apparatus 1 according to a first embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, the laser welding device 1 according to this embodiment includes a laser oscillator 10, an optical path 11, a focusing unit 12, and a welding robot 13. The laser oscillator 10 emits a laser beam in accordance with commands from a controller (control unit) 15 connected to the laser oscillator 10. The focusing unit 12 functions as a scanning unit and is attached to the tip of the arm of the welding robot 13.

The controller 15 is configured with a microprocessor including an MPU/CPU, ASIC, ROM, RAM, etc. The controller 15 controls the laser oscillator 10 and the focusing unit 12 by executing firmware stored in advance.

The laser light generated by the laser oscillator 10 is propagated through the optical path 11 to the focusing unit 12. In the focusing unit 12, the propagated laser light is focused (a spot is formed) on the surface of the metal member 501. In addition, the focusing unit 12 scans the spot of the laser light within the wrap region 500, which is the overlapping portion of the metal members 501 and 502, according to instructions from the controller 15.

In this embodiment, an optical fiber cable is used as an example of the optical path 11, but various other optical paths can also be used.

The laser welding device 1 also includes a drive circuit unit 14 for driving the welding robot 13. The welding robot 13 can move the arm tip, to which the light collecting unit 12 is attached, in three dimensions according to commands from a controller 15 connected to the drive circuit unit 14.

2. Arrangement of Metal Members 501 and 502 The arrangement of metal members 501 and 502 to be joined will be described with reference to FIG.

As shown in Figs. 2(a) and (b), in this embodiment, metal plates are used for the metal members 501 and 502. Each of the metal members 501 and 502 has a rectangular planar shape. As shown in Fig. 2(a), the metal members 501 and 502 are arranged with both sides in the short direction aligned and offset from each other in the long direction.

As shown in FIG. 2(b), metal member 501 and metal member 502 are arranged with a gap G between them in the thickness direction when viewed from the side. Gap G is, for example, 0.5 mm to 1.0 mm.

In this embodiment, welding is performed in the lap region 500 between metal member 501 and metal member 502.

2(a) and (b), an external force F is applied in the longitudinal direction to the metal members 501 and 502 after welding. The application of this external force F causes stress (tensile shear stress) to act on the joint between the metal members 501 and 502. The laser welding according to this embodiment takes into account the direction of the stress acting on the joint after welding. The direction indicated by the arrow F in this embodiment corresponds to the "first direction."

3. Laser Welding Method First, in performing laser welding, the controller 15 causes the laser oscillator 10 to emit laser light and causes the light focusing unit 12 to focus the laser light at a predetermined location on the wrap region 500 (laser light irradiation step).

Next, the controller 15 instructs the laser oscillator 10 to oscillate the laser beam and causes the focusing unit 12 to scan the laser beam spot within the wrap region 500 (scanning step). The method of scanning the laser beam spot during laser welding will be described with reference to FIG. 3.

3A, in the laser welding according to this embodiment, a spot of laser light is scanned so as to circle around a predetermined location P1 in the wrap region 500 (scanning trajectory L1). This melts the metal members 501, 502 in the region around which the spot of laser light has circled. This forms a dot-shaped weld 101 in a plan view (in this embodiment, as an example, a substantially circular shape in a plan view).

3B, while the metal members 501, 502 in the dot welds 101 are in a molten state, a spot of laser light is scanned from the outer periphery 101a of the dot welds 101 to the radially outer side of the dot welds 101 (scanning trajectory L2), as shown by arrow A1. This forms linear welds 102 that are continuous with the outer periphery 101a of the dot welds 101 and have a straight shape in plan view.

In addition, in the laser welding method according to this embodiment, the direction in which the laser light spot is scanned (the direction in which the scanning trajectory L2 extends) is aligned with the direction in which the above-mentioned stress acts (the direction in which the external force F is applied).

3(c), while the metal members 501, 502 in the dot welds 101 are in a molten state, the spot of the laser light is scanned from the outer peripheral edge 101b of the dot welds 101 in the opposite direction to the extension of the linear welds 102, as shown by the arrow A2, to the radially outward side of the dot welds 101 (scanning trajectory L3). This forms a linear weld 103 that is continuous with the outer peripheral edge 101b of the dot welds 101 and has a linear shape in a plan view.

In addition, in the laser welding method according to this embodiment, the direction in which the laser light spot is scanned (the direction in which the scanning trajectory L3 extends) is also aligned with the direction in which the above-mentioned stress acts (the direction in which the external force F is applied).

In this embodiment, a weld 100 is formed, which consists of a dot weld 101 and linear welds 102 and 103.

4. Structure of the Welded Part 100 The structure of the welded part 100 formed as described above will be described with reference to FIGS.

As shown in FIG. 4, the weld 100 formed by executing the laser light irradiation step and the scanning step (dot portion forming sub-step, straight portion forming sub-step) is a weld in which the dot weld 101 and the straight portion welds 102, 103 are continuous with each other. That is, in the laser welding method according to this embodiment, the straight portion forming sub-step is executed while the metal members 501, 502 of the dot weld 101 are in a molten state, thereby forming the weld 100 consisting of the dot weld 101 and the straight portion welds 102, 103.

In this embodiment, the lengths L102, L103 of the linear welds 102, 103 in plan view are set shorter than the diameter D101 of the dot weld 101 in plan view.

As shown in FIG. 5, in joining using the laser welding method according to this embodiment, the gap G between the metal members 501 and 502 is filled not only in the dot weld 101 but also in the linear welds 102 and 103. This is because the linear section formation sub-step is started while the metal members 501 and 502 of the dot weld 101 are in a molten state, and some of the molten metal in the dot weld 101 flows into the gap G in the linear welds 102 and 103.

Returning to FIG. 4, in the laser welding method according to this embodiment, the spot of the laser light in the straight line portion forming sub-step is scanned so as to match the direction of the stress acting on the metal members 501, 502 after welding (scanning trajectories L2, L3). As a result, the straight line weld 102 is formed to extend from the outer peripheral edge 101a of the dot weld 101 along the direction in which the stress acts (the direction in which the external force F is applied), and the straight line weld 103 is formed to extend from the outer peripheral edge 101b of the dot weld 101 along the direction in which the stress acts (the direction in which the external force F is applied) toward the opposite side to the straight line weld 102.

5. Effects In the laser welding method according to the present embodiment, the two metal members 501, 502 are joined by irradiation and scanning of a laser beam, so the welding speed is faster and the thermal effect is smaller than in the case of joining by resistance welding. In addition, in the laser welding method according to the present embodiment, the metal members 501, 502 can be joined without contacting the metal members 501, 502, so the processing efficiency is high and the rigidity can be increased by continuous welding.

In addition, in the laser welding method according to this embodiment, in the dot portion forming sub-step, the laser light spot is rotated to melt and stir the metal in the corresponding portion, and in the straight portion forming sub-step, the straight welds 102, 103 are formed in a state in which the metal members 501, 502 of the dot weld 101 are melted. Therefore, even if there is a gap G between the metal members 501, 502 as shown in FIG. 2(b), it is possible to make a part of the molten metal of the dot weld 101 flow into the gap G in the portion where the straight welds 102, 103 are to be formed. Therefore, in the laser welding method according to this embodiment, even if there is a gap G between the metal members 501, 502, it is possible to suppress the occurrence of problems such as gouging and burn-through.

The process of forming the dot welds 101 can be said to be a process for generating molten metal that flows from the dot welds 101 to the linear welds 102, 103 in order to form the linear welds 102, 103 while suppressing the occurrence of burn-through.

In addition, in the laser welding method according to this embodiment, in the straight line portion forming sub-step, the laser light spot is scanned in the direction of the stress acting on the multiple metal members 501, 502 after welding (the direction in which the external force F is applied). As a result, the linear welds 102, 103 formed by the laser welding method according to this embodiment extend along the direction in which the stress acts. Therefore, the metal members 501, 502 joined by the laser welding method according to this embodiment can have increased strength against an externally applied load (external force F). In particular, the metal members 501, 502 after welding have high tensile shear strength.

In addition, in the laser welding method according to this embodiment, as shown in FIG. 4, the lengths L102, L103 of the linear welds 102, 103 in plan view are shorter than the diameter D101 of the dot weld 101 in plan view, so that burn-through and other problems can be prevented when performing the linear section formation sub-step.

Furthermore, in the laser welding method according to this embodiment, linear welds 102, 103 are formed that are continuous with the dot welds 101, so that the joint strength can be further improved without increasing the diameter of the dot welds (the area of the dot welds in a plan view) compared to the case where the welds are made up of only dot welds, as in the technology disclosed in the above-mentioned Patent Document 1. Therefore, the laser welding method according to this embodiment can further improve the joint strength while preventing the welding time from becoming longer and suppressing the occurrence of burn-through.

As described above, the laser welding method according to this embodiment can join the metal members 501 and 502 with a high joint strength that can sufficiently withstand the external load F applied after joining.

[Second embodiment]
A laser welding method according to a second embodiment of the present invention will be described with reference to Fig. 6. Note that the laser welding method according to this embodiment differs from the laser welding method according to the first embodiment in the method of scanning the spot of the laser light in the dot portion forming sub-step. Therefore, the following mainly describes the method of scanning the spot of the laser light in the dot portion forming sub-step.

As shown in FIG. 6, in the laser welding method according to this embodiment, in the dot portion forming sub-step, the spot of laser light is scanned so as to circle around a predetermined location P1 in the wrap region 500 (scanning trajectory L1). In the laser welding method according to this embodiment, the spot of laser light is scanned so that the irradiation density of the laser light at the outer peripheral portion 1011 of the dot weld 101 is higher than the irradiation density of the laser light at the inner peripheral portion 1010.

More specifically, in the laser welding method according to this embodiment, in the dot portion forming sub-step, the spacing between the lines showing the scanning trajectory of the laser light spot in the inner peripheral portion 1010 is made relatively sparse, and the spacing between the lines showing the scanning trajectory of the laser light spot in the outer peripheral portion 1011 is made relatively dense. By changing the irradiation density of the laser light in the dot portion forming sub-step in this way between the outer peripheral portion 1011 and the inner peripheral portion 1010, the amount of heat input in the outer peripheral portion 1011 can be made greater than the amount of heat input in the inner peripheral portion 1010.

In the laser welding method according to the present embodiment, in the dot portion forming sub-step, the irradiation density of the laser light in the outer peripheral portion 1011 is made higher than the irradiation density of the laser light in the inner peripheral portion 1010, so that the heat input in the outer peripheral portion 1011 is made greater than the heat input in the inner peripheral portion 1010. As a result, in the laser welding method according to the present embodiment, the time until the molten metal solidifies in the outer peripheral portion 1011 of the dot weld 101 can be extended, and the amount of metal flowing into the linear welds 102, 103 can be easily secured. Therefore, in the laser welding method according to the present embodiment, the lengths L102, L103 of the linear welds 102, 103 can be made longer than the diameter D101 of the dot weld 101, so that a joint with high strength can be realized and the occurrence of burn-through can be avoided.

In this embodiment, the irradiation density of the laser light is changed between the outer peripheral portion 1011 and the inner peripheral portion 1010 in order to make the heat input amount at the outer peripheral portion 1011 of the dot-shaped welded portion 101 greater than the heat input amount at the inner peripheral portion 1010, but the present invention is not limited to this. For example, it is also possible to adopt a method in which the laser output of the laser light at the outer peripheral portion 1011 is made higher than the laser output of the laser light at the inner peripheral portion 1010 in the dot portion formation sub-step.

[Third embodiment]
A laser welding method according to a third embodiment of the present invention will be described with reference to Fig. 7(a). Note that the laser welding method according to this embodiment differs from the laser welding method according to the first embodiment in the method of scanning the spot of the laser light in the straight line portion forming sub-step. Therefore, the following mainly describes the method of scanning the spot of the laser light in the straight line portion forming sub-step.

As shown in FIG. 7A, in the laser welding method according to this embodiment, in the straight-line portion forming sub-step, the starting portion 103a including the intersection with the outer periphery 101b of the dot-shaped weld 101 and its neighboring portion is scanned so that the laser light spot revolves around a predetermined location (scanning trajectory L31). Then, following the scanning of the starting portion 103a, the laser light spot is linearly scanned in the separated portion 103b that is farther away from the dot-shaped weld 101 than the starting portion 103a (scanning trajectory L32). That is, in the laser welding method according to this embodiment, in the straight-line portion forming sub-step, the laser light spot is revolved around the starting portion 103a (scanning trajectory L31), and linearly scanned in the separated portion 103b so as to continue from the scanning of the laser light spot at the starting portion 103a (scanning trajectory L32).

Although only the formation of the linear weld 103 has been described, the linear weld 102 can also be formed by a similar method. Specifically, the spot of the laser light can be scanned so as to circle around a predetermined location at the starting point 102a, which includes the intersection with the outer periphery 101a of the dot weld 101 and the area nearby, and the spot of the laser light can be scanned linearly at the separated area that is farther away from the dot weld 101 than the starting point 102a.

In the laser welding method according to the present embodiment, in the straight portion forming sub-step, the spot of the laser light is scanned along the scanning trajectory L3 consisting of the scanning trajectory L31 and the scanning trajectory L32, so that the irradiation density of the laser light at the starting point portion 103a can be made higher than that at the spaced portion. Therefore, in the laser welding method according to the present embodiment, the heat input at the starting point portion 103a can be made greater than the heat input at the spaced portion 103b, and the time until the metal at the starting point portion 103a of the linear welded portion 103, i.e., the outer peripheral edge 101b of the dot welded portion 101, solidifies can be lengthened, and the amount of metal flowing into the linear welded portion 103 can be easily secured. Therefore, in the laser welding method according to the present embodiment, the length L103 of the linear welded portion 103 can be made longer than the diameter D101 of the dot welded portion 101, so that a joint with high strength can be realized and the occurrence of burn-through can be avoided.

As with the linear weld 103, the laser light spot is rotated and scanned at the starting point 102a of the linear weld 102, which lengthens the time it takes for the metal at the starting point 102a (the outer peripheral edge 101a of the dot weld 101) to solidify, making it easier to ensure the amount of metal that flows into the linear weld 102. As a result, the length L102 of the linear weld 102 can be made longer than the diameter D101 of the dot weld 101, achieving a high-strength joint and preventing burn-through.

[Fourth embodiment]
A laser welding method according to a fourth embodiment of the present invention will be described with reference to Fig. 7(b). Note that the laser welding method according to this embodiment differs from the laser welding method according to the third embodiment in the scanning method of the spot of the laser light in the straight portion forming sub-step, particularly the scanning method of the starting point portion 103a. Therefore, hereinafter, the scanning method of the spot of the laser light on the starting point portion 103a in the straight portion forming sub-step will be mainly described.

As shown in FIG. 7(b), in the straight line portion forming sub-step, in the laser welding method according to this embodiment, the spot of the laser light scans a zigzag scanning trajectory L33 at the starting point portion 103a, which includes the intersection with the outer peripheral edge 101b of the dot weld 101 and the vicinity thereof. The scanning of the spot of the laser light at the spaced portion 103b is the same as in the laser welding method according to the third embodiment.

In the laser welding method according to this embodiment, in the straight portion forming sub-step, the spot of the laser light scans the zigzag scanning trajectory L33 at the starting point 103a, so that the irradiation density of the laser light at the starting point 103a can be made higher than that at the spaced portion. Thus, in the laser welding method according to this embodiment, like the laser welding method according to the third embodiment, the heat input at the starting point 103a can be made greater than the heat input at the spaced portion 103b, and the time until the metal at the starting point 103a of the linear weld 103, i.e., the outer periphery 101b of the dot weld 101 solidifies can be lengthened, making it easier to ensure the amount of metal flowing into the linear welds 102 and 103. Thus, in the laser welding method according to this embodiment, the length L103 of the linear weld 103 can be made longer than the diameter D101 of the dot weld 101, so that a high-strength joint can be realized and the occurrence of burn-through can be avoided.

In this embodiment, as in the third embodiment, when forming the linear weld 102, the starting point 102a is scanned with a zigzag laser light spot, which lengthens the time it takes for the metal at the starting point 102a (the outer peripheral edge 101a of the dot weld 101) to solidify, making it easier to ensure the amount of metal that flows into the linear weld 102. As a result, the length L102 of the linear weld 102 can be made longer than the diameter D101 of the dot weld 101, achieving a high-strength joint and avoiding burn-through.

[Fifth embodiment]
A laser welding method according to a fifth embodiment of the present invention will be described with reference to Fig. 8. Note that the laser welding method according to this embodiment differs from the first embodiment in the number of linear welds formed in the linear portion forming sub-step. The following mainly describes the shape of the linear welds formed in the linear portion forming sub-step.

As shown in FIG. 8(a), the weld 100 formed by the laser welding method according to this embodiment includes four linear welds 102-105 that are continuous with the dot weld 101. In this embodiment as well, the four linear welds 102-105 are formed before the metal of the dot weld 101 solidifies (while in a molten state).

The four linear welds 102-105 have starting points at locations distributed around the circumference of the dot weld 101. In this embodiment, specifically, as shown in FIG. 8(a), the four linear welds 102-105 are formed at angles of 90° to each other.

As shown in FIG. 8(b), imaginary center lines LN1 and LN2 are drawn at the center of each of the linear welds 102-105 in the width direction. In this embodiment, the linear welds 102 and 103 share the imaginary center line LN1, and the linear welds 104 and 105 share the imaginary center line LN2. However, the present invention is not limited to this. The linear welds 102-105 may be formed so that the linear welds 102-105 have imaginary center lines that intersect with each other.

As shown in FIG. 8(b), the imaginary center line LN1 and the imaginary center line LN2 intersect with each other within the formation area of the dot weld 101.

In the laser welding method according to this embodiment, the virtual center lines LN1 and LN2 intersect each other in the region where the dot welds 101 are formed, so that the stress acting in the direction (first direction) in which the linear welds 102 and 103 extend and the stress acting in the direction (second direction) in which the linear welds 104 and 105 extend are combined at the intersection P2 in the region where the dot welds 101 are formed. The combined stress at the intersection P2 in the region where the dot welds 101 are formed is dispersed from the intersection P2 toward the radial outside of the dot welds 101. Therefore, the laser welding method according to this embodiment is even more effective for high-strength joining.

Sixth Embodiment
A laser welding method according to a sixth embodiment of the present invention will be described with reference to Fig. 9. Note that the laser welding method according to this embodiment differs from the fifth embodiment in terms of the length of the linear weld portion formed in the linear portion forming sub-step. The following mainly describes the differences from the fifth embodiment.

As shown in FIG. 9, the laser welding method according to this embodiment also forms a weld 100 consisting of a dot weld 101 and four linear welds 102-105 that are continuous with the dot weld 101. The laser welding method according to this embodiment also forms the four linear welds 102-105 while the metal of the dot weld 101 is in a molten state.

In the laser welding method according to this embodiment, the length L103 of the linear weld 103 is set to be longer than the lengths L102, L104, and L105 of the other linear welds 102, 104, and 105. This is because, of the loads F1 and F2 applied to the metal members 501 and 502 after welding, the load F1 is greater than the external force F2.

That is, the length L103 of the linear weld 103 formed in the direction in which a relatively large stress acts is longer than the lengths L104, L105 of the linear welds 104, 105 formed in the direction in which a relatively small stress acts. Also, the length L103 of the linear weld 103 is longer than the diameter D101 of the dot weld 101. It is also possible to make the length L102 of the linear weld 102 as long as the linear weld 103.

In the laser welding method according to this embodiment, in the straight section forming sub-step, the length L103 of the linear weld 103, which is subjected to a relatively large load F1 and extends in a direction in which a large stress acts, is made longer than the lengths L104, L105 of the linear welds 104, 105, which are subjected to a relatively small load F2 and extend in a direction in which a small stress acts. Therefore, when joining metal members using the laser welding method according to this embodiment, high joint strength can be achieved even when stress acts on the metal members 501, 502 in two directions after welding.

[Seventh embodiment]
A laser welding method according to a seventh embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 10(a), in the laser welding method according to this embodiment, a weld 100 consisting of a dot weld 101 and a linear weld 103 continuous with the dot weld 101 is formed, and metal members 501 and 502 are joined. In this embodiment as well, the linear weld 103 is formed while the metal of the dot weld 101 is in a molten state. This allows a portion of the molten metal of the dot weld 101 to flow toward the linear weld 103, and the metal members 501 and 502 can be joined with high joint strength.

In the laser welding method according to this embodiment, the external load acting on the metal members 501, 502 after welding is taken into consideration, and the linear weld 103 is formed so as to extend in the direction in which the stress acts. Therefore, the laser welding method according to this embodiment can achieve the same effects as the first embodiment.

In addition, the laser welding method according to this embodiment has fewer linear welds than the first embodiment, which shortens the time required for welding and achieves higher productivity.

[Eighth embodiment]
A laser welding method according to an eighth embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 10(b), in the laser welding method according to this embodiment, a weld 100 consisting of a dot weld 101 and three linear welds 103, 106, and 107 that are continuous with the dot weld 101 is formed, and metal members 501 and 502 are joined. In this embodiment, too, the linear welds 103, 106, and 107 are formed while the metal of the dot weld 101 is in a molten state. This allows some of the molten metal of the dot weld 101 to flow toward the linear welds 103, 106, and 107, and the metal members 501 and 502 can be joined with high joint strength.

In the laser welding method according to this embodiment, the linear welds 103, 106, and 107 are formed so as to extend in the respective directions in which the stress acts, taking into consideration the external load applied to the metal members 501 and 502 after welding. Therefore, the laser welding method according to this embodiment can achieve the same effects as the first embodiment.

[Ninth embodiment]
A laser welding method according to a ninth embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 10(c), in the laser welding method according to this embodiment, a weld 100 consisting of a dot weld 101 and five linear welds 103, 108-111 that are continuous with the dot weld 101 is formed, and the metal members 501, 502 are joined. In this embodiment as well, the linear welds 103, 108-111 are formed while the metal of the dot weld 101 is in a molten state. This allows some of the molten metal of the dot weld 101 to flow toward the linear welds 103, 108-111, and the metal members 501, 502 can be joined with high joint strength.

In the laser welding method according to this embodiment, the linear welds 103, 108-111 are formed so as to extend in the respective directions in which the stress acts, taking into consideration the external load applied to the metal members 501, 502 after welding. Therefore, the laser welding method according to this embodiment can achieve the same effects as the first embodiment.

[Tenth embodiment]
A laser welding method according to a tenth embodiment of the present invention will be described with reference to FIG.

11A, in the laser welding according to this embodiment, a spot of laser light is scanned so as to circle around a predetermined location P1 in the overlap region (scanning trajectory L1), as in the first embodiment, to form dot-shaped welds 101 having a dot shape in plan view.

(2) Re-irradiation of laser light to the outer peripheral edge of the dot-shaped weld 101 Next, as shown in FIG. 11(b), after forming the dot-shaped weld 101 and before forming the linear welds 102, 103, the outer peripheral edge of the dot-shaped weld 101 is scanned in a circular motion with a laser light spot (scanning trajectory L4).

11(c), after the laser light is irradiated again to the outer periphery of the dot welds 101, while the metal member of the dot welds 101 is in a molten state, the spot of the laser light is scanned so as to move away from the outer periphery 101a of the dot welds 101 radially outward from the dot welds 101 (scanning trajectory L2). This forms linear welds 102 that are continuous with the outer periphery 101a of the dot welds 101 and have a straight shape in plan view.

In the laser welding method according to this embodiment, the direction in which the laser light spot is scanned (the direction in which the scanning trajectory L2 extends) is also aligned with the direction in which stress acts after welding (the direction in which the external force F is applied).

Next, while the metal member in the dot weld 101 is in a molten state, the spot of the laser light is scanned from the outer peripheral edge 101b of the dot weld 101 in the opposite direction to the extension direction of the linear weld 102, so as to move away radially outward from the dot weld 101 (scanning trajectory L3). This forms a linear weld 103 that is continuous at the outer peripheral edge 101b of the dot weld 101 and has a linear shape in a plan view.

In the laser welding method according to this embodiment, the direction in which the laser light spot is scanned (the direction in which the scanning trajectory L3 extends) is also aligned with the direction in which the above-mentioned stress acts (the direction in which the external force F is applied).

In this embodiment, after forming the dot welds 101, and before forming the linear welds 102 and 103, the outer periphery of the dot welds 101 is re-irradiated with laser light while the metal component of the welds 101 is in a molten state, thereby lengthening the time until the metal at the outer periphery 101a and 101b of the dot welds 101 solidifies.

If more linear welds are to be formed in addition to the linear welds 102 and 103 as described above, it is sufficient to alternate between re-irradiating the outer periphery of the dot welds with laser light and forming linear welds. By alternating between re-irradiating the outer periphery of the dot welds with laser light and forming linear welds in this way, the time it takes for the metal at the outer periphery of the dot welds to solidify can be extended.

Therefore, by using the laser welding method according to this embodiment, it becomes easier to ensure the amount of metal flowing into the linear welds 102, 103, and the length of the linear welds 102, 103 can be further increased, realizing a joint with high strength and preventing the occurrence of burn-through.

[Confirmation Experiment 1]
Confirmatory experiment 1 will be described with reference to FIG.

1. Experimental Conditions In confirmation experiment 1, the following materials were used as the metal members 501 and 502.

・Material: SPFC590
Dimensions: L = 100 mm, W = 40 mm, T = 1.0 mm
In addition, in confirmation experiment 1, the metal member 501 and another metal member were laser-welded as follows.

・Lap width: 40mm
・Gap: G=0.5mm
Diameter of dot-shaped weld 101: D101 = φ4 mm to φ6 mm
Length of linear welds 102, 103: L102 = L103 = 0 mm to 6 mm
However, the lengths L102 and L103 are set to be equal to or less than the diameter D101.

Laser welding was performed under the above conditions, and the tensile shear strength was measured.

12(b), when the linear welds 102, 103 were not formed (when L102, L103 were 0 mm), the tensile shear strength changed according to the diameter D101 of the dot weld 101. Specifically, when the diameter D101 of the dot weld 101 was φ5 mm, the tensile shear strength was higher than when the diameter D101 was φ4 mm, and when the diameter D101 was φ6 mm, the tensile shear strength was even higher than when the diameter D101 was φ5 mm.

In addition, when the diameter D101 was φ4 mm, the tensile shear strength increased slightly as the lengths L102, L103 of the linear welds 102, 103 increased. Similarly, when the diameter D101 was φ5 mm, the tensile shear strength increased as the lengths L102, L103 of the linear welds 102, 103 increased. Note that when the diameter D101 was φ5 mm, the degree of increase in the tensile shear strength with the increase in the lengths L102, L103 of the linear welds 102, 103 was greater than when the diameter D101 was φ4 mm.

Even when the diameter D101 was φ6 mm, the tensile shear strength increased as the lengths L102, L103 of the linear welds 102, 103 increased. When the diameter D101 was φ6 mm, the degree of increase in the tensile shear strength with the increase in the lengths L102, L103 of the linear welds 102, 103 was the same as when the diameter D101 was φ5 mm.

From the above, it can be seen that by forming a weld 100 having a dot-shaped weld 101 and linear welds 102, 103, it is possible to increase the tensile shear strength of the metal members 501, 502 after welding. In addition, it can be said that it is desirable to make the lengths L102, L103 of the linear welds 102, 103 long within a range that does not cause burn-through in order to obtain high weld strength.

[Confirmation Experiment 2]
Confirmatory experiment 2 will be described with reference to FIGS.

1. Experimental Conditions In confirmation experiment 2, the following materials were used as the metal members 501 and 502.

・Material: Steel (SPCC-SD, SPFC590, SPFC980Y)
Dimensions: L501 = L502 = 100 mm, W = 40 mm, T = 1.0 mm
In addition, in confirmation experiment 2, the metal member 501 and another metal member were laser-welded as follows.

・Wrap length: L500 = 40mm
Laser output: 3000W (SPCC-SD is 3100W)
Scanning speed: dot welds: 250 mm/s; linear welds: 100 mm/s

(1) Sample 1
13A, in sample 1, metal members 501 and 502 were joined by forming a weld 100 consisting of a dot-shaped weld 101 and linear welds 102 and 103. In sample 1, similar to the first embodiment, the linear welds 102 and 103 were formed to extend in the direction in which stress acts.

The gap G between the metal members 501 and 502 was set to 0 mm (in contact). The lengths L102 and L103 of the linear welds 102 and 103 were set to 4.5 mm.

(2) Sample 2
13(b), in sample 2, metal members 501 and 502 were joined by forming a weld 100 consisting of a dot-shaped weld 101 and linear welds 112 and 113. However, in sample 2, the linear welds 112 and 113 were formed to extend in a direction perpendicular to the direction in which stress acts.

The gap G between the metal members 501 and 502 was set to 0 mm (in contact). The length of the linear welds 112 and 113 was set to 4.5 mm.

(3) Sample 3
As shown in FIG. 13C, in sample 3, a welded portion 900 was formed by spot welding.

The conditions for spot welding with SPCC-SD are a current of 11,000 A, pressure of 0.2 MPa, and current flow time of 10 Hz. The conditions for spot welding with SPFC590 are a current of 9,500 A, pressure of 0.3 MPa, and current flow time of 9 Hz. The conditions for spot welding with SPFC980Y are a current of 9,500 A, pressure of 0.4 MPa, and current flow time of 9 Hz.

The diameter of the welded portion 900 was φ5.5 mm to φ6.0 mm. The gap G between the metal members 501 and 502 was 0 mm (in contact).

(4) Sample 4
13D, in sample 4, a linear weld 901 was formed to join the metal members 501 and 502. In sample 4, the linear weld 901 was formed so as to extend in the direction in which stress acts.

The laser welding conditions were a laser output of 2000 W and a scanning speed of 80 mm/s. The gap G between the metal members 501 and 502 was 0 mm (in contact). The length of the linear weld 901 was 15 mm.

(5) Sample 5
13( e), in sample 5, a linear weld 902 was also formed to join the metal members 501 and 502. However, in sample 5, the linear weld 902 was formed so as to extend in a direction perpendicular to the direction in which the stress acts.

The laser welding conditions were a laser output of 2000 W and a scanning speed of 80 mm/s. The gap G between the metal members 501 and 502 was 0 mm (in contact). The length of the linear weld 901 was 15 mm.

(6) Sample 6
Although not shown in the figure, Sample 6 was produced under basically the same conditions as Sample 1 shown in Fig. 13A. However, in producing Sample 6, the gap G between the metal members 501 and 502 was set to 0.7 mm.

(7) Sample 7
Although not shown in the figure, Sample 7 was produced under basically the same conditions as Sample 2 shown in Fig. 13B. However, in producing Sample 7, the gap G between the metal members 501 and 502 was set to 0.7 mm.

2. Experimental Results First, Fig. 14(a) shows the results of a tensile test performed on each of Sample 1 (Sam1) to Sample 5 (Sam5). The tensile direction (direction in which a load is applied from the outside) in the tensile test is the direction indicated by the arrow F in Figs. 13(a) to 13(e).

As shown in FIG. 14(a), Sample 4 (Sam4) and Sample 5 (Sam5) had tensile shear strengths that were only about half that of Sample 3 (Sam3: a sample that underwent spot welding), regardless of the material of the metal members 501 and 502. Also, Sample 4 (Sam4) and Sample 5 (Sam5) had interface fractures. Therefore, if the metal members 501 and 502 are joined only by the linear welds 901 and 902, high joint strength cannot be obtained.

Sample 2 (Sam2) also had a tensile shear strength equal to or less than that of Sample 3 (Sam3), regardless of the material of the metal members 501, 502. In other words, if the linear welds 112, 113 were formed to extend in a direction perpendicular to the direction in which the stress acts, the stress would act on the outer periphery of the dot welds 101, and it is believed that the stress relaxation effect of the linear welds 112, 113 could not be obtained.

In addition, in sample 2 (Sam2), fracture during testing occurred not at the tips of the linear welds 112 and 113, but at the outer periphery of the dot weld 101.

On the other hand, in sample 1 (Sam1), regardless of whether the material of the metal members 501, 502 was SPCC-SD, SPFC590, or SPFC980Y (whether the base material strength was 300 MPa, 614 MPa, or 1065 MPa), a higher tensile shear strength was obtained than in sample 3 (Sam3: a sample that was spot welded).

In addition, in sample 1 (Sam1), fracture started at the tip of the linear welds 102, 103, and it was found that the linear welds 102, 103 had a stress relaxation effect. In sample 1 (Sam1), the fracture mode in the linear welds 102, 103 was plug fracture, not interface fracture as in sample 2 (Sam2).

Next, Figure 14(b) shows the results of tensile tests performed on each of Sample 3 (Sam3) to Sample 7 (Sam7). Note that in Figure 14(b), the experimental results for Sample 3 (Sam3) to Sample 5 (Sam5) are the same as those shown in Figure 14(a).

As shown in FIG. 14(b), sample 7 (Sam7) had almost the same tensile shear strength as sample 3 (Sam3). In other words, sample 7 (Sam7), which was laser welded with a gap G of 0.7 mm between metal members 501 and 502, also had linear welds 112, 113 formed to extend in a direction perpendicular to the direction in which stress acts, and is therefore considered to have almost no stress relaxation effect.

On the other hand, sample 6 (Sam6) was able to obtain a higher tensile shear strength than sample 3 (Sam3) even when the gap G between the metal members 501, 502 was 0.7 mm. In particular, when the material of the metal members 501, 502 was SPFC980Y (base material strength: 1065 MPa), a significantly higher tensile shear strength was obtained.

In addition, in sample 6 (Sam6), the fracture started at the tip of the linear welds 102, 103, and it was found that the linear welds 102, 103 had a stress relaxation effect. In sample 6 (Sam6), the fracture mode in the linear welds 102, 103 was also plug fracture.

From the above results, it can be said that by forming the weld 100 from the dot-shaped weld 101 and multiple linear welds 102, 103 that are continuous with the dot-shaped weld 101, and by forming the linear welds 102, 103 to extend in the direction in which stress acts, the metal members 501, 502 can be joined with high strength.

[Modification]
In the first to tenth embodiments, two plate-shaped metal members 501 and 502 are joined together, but the present invention is not limited to this. The present invention can also be used to join three or more metal members.

The metal members to be joined are not limited to the plate-shaped metal members 501, 502 used in the first to ninth embodiments, but can be various metal members such as pipe-shaped or rod-shaped.

In addition, in the first to tenth embodiments, the dot welds 101 are generally circular in plan view, but the present invention is not limited to this. For example, they may be elliptical, oval, or even polygonal.

In addition, in the second embodiment, the irradiation density of the laser light at the outer peripheral portion 1011 of the dot-shaped weld 101 is made higher than the irradiation density of the laser light at the inner peripheral portion 1010, so that the heat input at the outer peripheral portion 1011 is made higher than the heat input at the inner peripheral portion 1010, but the present invention is not limited to this. For example, the heat input at the outer peripheral portion 1011 can also be increased by making the laser output at the outer peripheral portion 1011 higher than the laser output at the inner peripheral portion 1010, increasing the number of revolutions, or making the laser rotate in an overlapping manner in discontinuous circles.

In addition, the increase in heat input to the outer peripheral portion 1011 of the dot weld 101 does not necessarily need to be carried out up to the outer peripheral edge of the dot weld 101, and the heat input may be increased slightly radially inward from the outer peripheral edge. Even in this case, the solidification of the metal can be delayed by heat transfer at the outer peripheral edge of the dot weld 101, and molten metal can flow into the linear welds 102 and 103.

In the third and fourth embodiments, the irradiation density of the laser light at the starting point 103a of the linear weld 103 is made higher than the irradiation density of the laser light at the spaced apart portion 103b, so that the heat input at the starting point 103a is made higher than the heat input at the spaced apart portion 103b, but the present invention is not limited to this. For example, the heat input at the starting point 103a can also be increased by making the laser output at the starting point 103a higher than the laser output at the spaced apart portion 103b. In this case, too, a portion of the molten metal at the dot weld 101 can be made to flow toward the linear weld 103.

When shortening the length of the linear welds 102-111 relative to the diameter D101 of the dot weld 101, it is not necessarily necessary to increase the heat input at the outer periphery 1011 of the dot weld 101 or the heat input at the starting point 103a of the linear weld 103. In other words, when shortening the length of the linear welds 102-111 relative to the diameter D101 of the dot weld 101, burn-through and the like are unlikely to occur even without increasing the heat input as described above.

REFERENCE SIGNS LIST 1 Laser welding device 10 Laser oscillator 12 Focusing unit 15 Controller (control unit)
Reference Signs List 100 Welded portion 101 Dot-shaped welded portion 102 to 113 Linear welded portion 103a Starting point portion 103b Spaced portion 500 Lap region 501, 502 Metal member 1010 Inner peripheral portion 1011 Outer peripheral portion G Gap

Claims (13)

A laser welding method for joining a plurality of metal members arranged in contact with or adjacent to each other by laser welding, comprising the steps of:
a laser light irradiation step of emitting a laser light and focusing the oscillated laser light on a welding spot on a first main surface of a first metal member located outside the arrangement;
a scanning step of scanning the spot of the laser light within the first principal surface;
Equipped with
The scanning step includes:
a dot portion forming sub-step of forming a dot-shaped weld portion having a dot shape in a plan view by scanning the spot of the laser light so as to circle around a predetermined location and melting the metal member;
a linear portion forming sub-step of forming a linear weld portion that is linear in a plan view and continuous with the dot weld portion, in which the spot of the laser light is scanned away from the outer periphery of the dot weld portion while the metal member in the dot weld portion is in a molten state to melt the metal member;
having
An external force is applied to the plurality of metal members after welding so that stress acts in a first direction along the first main surface,
In the straight line portion forming sub-step, the spot of the laser light is scanned so that the straight line weld portion extends in the first direction.
Laser welding method. 2. The laser welding method according to claim 1,
In the dot portion forming sub-step, a heat input amount by the irradiation of the laser light at an outer circumferential portion of the dot-shaped weld is set to be greater than a heat input amount at an inner circumferential portion that is located inside the outer circumferential portion.
Laser welding method. The laser welding method according to claim 2,
performing the scanning so that the irradiation density of the laser light in the outer circumferential portion is higher than the irradiation density of the laser light in the inner circumferential portion, and the difference in irradiation density causes the amount of heat input in the outer circumferential portion to be greater than the amount of heat input in the inner circumferential portion;
Laser welding method. The laser welding method according to any one of claims 1 to 3,
In the straight portion forming sub-step, a heat input amount at a start portion of the straight weld portion including an intersection with the outer peripheral edge of the dot-shaped weld portion is set to be greater than a heat input amount at a separation portion that is a portion separated from the start portion.
Laser welding method. The laser welding method according to claim 4,
The scanning is performed so that the irradiation density of the laser light at the starting point portion is higher than the irradiation density of the laser light at the separated portion, and the amount of heat input at the starting point portion is made larger than the amount of heat input at the separated portion due to the difference in irradiation density.
Laser welding method. The laser welding method according to claim 4 or 5,
A laser output at the starting point portion is set to be higher than a laser output at the separated portion, so that a heat input amount at the starting point portion is made larger than a heat input amount at the separated portion due to the difference in laser output.
Laser welding method. In the laser welding method according to any one of claims 2 to 6,
In the straight line portion forming sub-step, the straight line weld portion is formed so that the length of the straight line weld portion is longer than the diameter of the dot-shaped weld portion.
Laser welding method. The laser welding method according to claim 1,
In the straight line portion forming sub-step, the straight line weld portion is formed so that the length of the straight line weld portion is shorter than the diameter of the dot-shaped weld portion.
Laser welding method. The laser welding method according to any one of claims 1 to 8,
When the linear weld portion is a first linear weld portion,
In the straight line portion forming sub-step, while the metal member in the dot weld is in a molten state, the spot of the laser light is scanned away from the outer periphery of the dot weld to melt the metal member, and a second straight line weld is formed that is continuous with the dot weld and extends in a second direction different from the first direction.
when a first imaginary center line is drawn extending along the longitudinal direction at a center in the width direction of the first linear weld and a second imaginary center line is drawn extending along the longitudinal direction at a center in the width direction of the second linear weld, the first imaginary center line and the second imaginary center line intersect with each other in a region where the dot-shaped weld is formed.
Laser welding method. The laser welding method according to any one of claims 1 to 8,
An external force is applied to the plurality of metal members after welding so that stress acts along the first main surface and in a second direction that is different from the first direction,
When the linear weld portion is a first linear weld portion,
In the straight line portion forming sub-step, while the metal member in the dot weld is in a molten state, the spot of the laser light is scanned away from the outer periphery of the dot weld to melt the metal member, and a second straight line weld is formed that is continuous with the dot weld and extends in the second direction.
In the straight line portion forming sub-step, the first straight line weld portion and the second straight line weld portion are formed such that a length of the first straight line weld portion is longer than a length of the second straight line weld portion.
Laser welding method. A laser welding apparatus for joining a plurality of metal members arranged in contact with or adjacent to each other by laser welding, comprising:
a laser oscillator that emits laser light;
a focusing unit that focuses the laser light on a welding spot on a first main surface of a first metal member located outside the arrangement;
a scanning unit that scans the spot of the laser light within the first principal surface;
A control unit that controls the laser oscillator and the scanning unit;
Equipped with
The control unit, in a state where the laser oscillator is caused to oscillate the laser light,
a process of forming a dot-shaped welded portion having a dot shape in a plan view by scanning the spot of the laser light so as to circle around a predetermined location and melting the metal member;
a process of forming a linear weld that is continuous with the dot weld and linear in a plan view, by scanning the spot of the laser light away from an outer periphery of the dot weld while the metal member in the dot weld is in a molten state, and melting the metal member;
Run
An external force is applied to the plurality of metal members after welding so that stress acts in a first direction along the first main surface,
The control unit, in executing the process of forming the linear welded portion, causes the scanning unit to scan the spot of the laser light so that the linear welded portion extends in the first direction.
Laser welding equipment. 12. The laser welding apparatus according to claim 11,
The control unit controls the laser oscillator and the scanning unit in a process of forming the dot-shaped welds such that a heat input amount by irradiation of the laser light at an outer periphery of the dot-shaped welds is greater than a heat input amount at an inner periphery of the dot-shaped welds that is located inside the outer periphery.
Laser welding equipment. 13. The laser welding apparatus according to claim 11 or 12,
the control unit controls the laser oscillator and the scanning unit in executing the process of forming the linear weld so that a heat input amount at a start portion of the linear weld including an intersection with the outer circumferential edge of the dot weld is greater than a heat input amount at a separation portion that is a portion separated from the start portion.
Laser welding equipment.