Laser welding method and laser welding device

Abstract

To provide an improved and novel laser welding method and laser welding device capable of reducing voids in a welded area.SOLUTION: A laser welding method for welding multiple members as a processing object including aluminum die-cast parts comprises for example: a first step of radiating a first laser beam to form a molten pool spanning multiple members; a second step of solidifying the molten pool to form a welded area; a third step of radiating a second laser beam to re-melt the welded area; and a fourth step of solidifying the re-melted portion of the welded area. In the third step, voids remaining inside the welded area may be removed or only the welded area may be melted without melting a base material of a processing object. Additionally, in the second step, the molten pool may be solidified by ensuring that the second laser beam is not radiated for a prescribed time or greater to each position where the first laser beam is radiated in the first step of the processing object.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a laser welding method and a laser welding apparatus. [Background technology]

[0002] Conventionally, a laser welding method has been known in which the cooling rate of the molten pool is slowed down to lengthen the time until solidification, thereby suppressing the remaining of voids (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-683 A Summary of the Invention [Problem to be solved by the invention]

[0004] Through extensive research, the inventors have discovered a method, different from that described in Patent Document 1, that is capable of reducing voids remaining in a welded joint.

[0005] Therefore, one object of the present invention is to provide a new and improved laser welding method and laser welding apparatus that can reduce voids in a weld, for example. [Means for solving the problem]

[0006] The laser welding method of the present invention is a laser welding method for laser welding a plurality of components as processing objects including, for example, an aluminum die-cast product, and includes a first step of irradiating a first laser beam to form a molten pool spanning the plurality of components, a second step of solidifying the molten pool to form a weld, a third step of irradiating a second laser beam to re-melt the weld, and a fourth step of solidifying the re-melted portion of the weld.

[0007] In the laser welding method, in the third step, voids remaining in the welded portion may be removed.

[0008] In the laser welding method, in the third step, only the welded portion may be melted without melting the base material of the processing object.

[0009] In the laser welding method, in the second step, the molten pool may be solidified by not irradiating the second laser light for a predetermined period of time or longer to each position of the object to be processed that was irradiated with the first laser light in the first step.

[0010] In the laser welding method, the predetermined time may be 1 s or more.

[0011] In the laser welding method, in the third step, the second laser light may be irradiated to the same position as the position irradiated with the first laser light in the first step, and a power density of the second laser light may be set to be equal to or lower than a power density of the first laser light.

[0012] In the laser welding method, in the third step, the second laser light may be irradiated to the same position as the position irradiated with the first laser light in the first step, and the power density of the second laser light may be set to the same as the power density of the first laser light.

[0013] In the laser welding method, in the first step, a spot of the first laser light may be scanned over a surface of the object to be processed, and in the third step, a spot of the second laser light may be scanned over the surface of the object to be processed.

[0014] In the laser welding method, in the first step, a spot of the first laser light may be scanned so as to move along a predetermined path on the surface of the object to be processed, and in the third step, a spot of the second laser light may be scanned so as to move along the same path on the surface as in the first step.

[0015] In the laser welding method, in the third step, the spot of the second laser light may be scanned so that the second laser light is irradiated at each position on the path scanned with the spot of the first laser light in the first step after a predetermined time required for forming the welded portion in the second step has elapsed since the first laser light was irradiated in the first step.

[0016] In the laser welding method, a first scanning direction of a spot of the first laser light on the path in the first step and a second scanning direction of a spot of the second laser light on the path in the third step may be the same.

[0017] In the laser welding method, a first scanning direction of a spot of the first laser light on the path in the first step and a second scanning direction of a spot of the second laser light on the path in the third step may be opposite to each other.

[0018] In the laser welding method, the path may be a line segment extending between two ends.

[0019] In the laser welding method, the path may be an endless path.

[0020] In the laser welding method, in the first step, the first laser light may include a plurality of beams.

[0021] In the laser welding method, in the second step, the second laser light may include a plurality of beams.

[0022] In the laser welding method, the multiple beams may be formed by a beam shaper.

[0023] The laser welding apparatus of the present invention is a laser welding method for laser welding a plurality of components as workpieces, including, for example, aluminum die-cast products, the laser welding method comprising a first step of irradiating a first laser light to form a molten pool spanning the plurality of components, a second step of solidifying the molten pool to form a weld, a third step of irradiating a second laser light to re-melt the weld, and a fourth step of solidifying the re-melted portion of the weld, the laser welding apparatus being used in the laser welding method and comprising a laser device capable of outputting the first laser light and the second laser light, and an optical head that irradiates the first laser light or the second laser light output from the laser device onto a surface of the workpieces, and performing the first step and the third step. Effect of the Invention

[0024] SUMMARY OF THE PRESENT DISCLOSURE The present invention provides a new and improved laser welding method and apparatus. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is an exemplary schematic diagram of a laser welding apparatus according to an embodiment. [Diagram 2] FIG. 2 is an explanatory diagram showing the concept of the principle of the diffractive optical element included in the laser welding apparatus of the embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing an example of a laser beam spot formed on the surface of the processing object by the laser welding apparatus of the embodiment. [Figure 4] FIG. 4 is an exemplary flowchart showing a welding procedure according to the laser welding method of the embodiment. [Diagram 5] FIG. 5 is an exemplary schematic cross-sectional view of a welded portion formed on an object to be processed by the laser welding method of the embodiment, the cross-sectional view intersecting with the scanning direction. [Figure 6] FIG. 6 is an exemplary schematic plan view of a linear weld formed on an object to be processed by the laser welding method of the embodiment, showing an example of a scanning direction. [Figure 7]FIG. 7 is a graph showing an example of a change over time in the scanning position of the laser light spot in the laser welding method according to the embodiment. [Figure 8] FIG. 8 is a photographic image showing a cross section along the scanning direction of an example of a weld formed on an object to be processed by the laser welding method of the embodiment. [Figure 9] FIG. 9 is an illustrative schematic plan view of a linear weld formed on an object to be processed by a laser welding method according to a modified example of the embodiment. [Figure 10] FIG. 10 is a schematic plan view illustrating an endless weld formed on an object to be processed by a laser welding method according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Exemplary embodiments of the present invention are disclosed below. The configurations of the embodiments described below and the actions and effects brought about by the configurations are merely examples. The present invention can be realized by configurations other than those disclosed in the following embodiments. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the configurations.

[0027] In each figure, the Z direction is represented by an arrow Z. The laser light is irradiated toward the workpiece W in a direction substantially opposite to the Z direction. The scanning directions SD, SD1, and SD2 are represented by arrows SD, SD1, and SD2. The Z direction and the scanning direction SD intersect each other and are perpendicular to each other.

[0028] In this specification, ordinal numbers are given for the sake of convenience to distinguish between processes, laser beams, etc., and do not limit the priority or order.

[0029] [Embodiment] [Laser welding equipment and processing objects] FIG. 1 is a schematic diagram of a laser welding apparatus 100. The laser welding apparatus 100 irradiates a surface Wa of a processing object W including a metal member 11 and a metal member 12 with a laser beam L to form a weld 14 across the metal member 11 and the metal member 12. Both the metal member 11 and the metal member 12 are made of an aluminum-based material, and at least one of the metal member 11 and the metal member 12 is an aluminum die-cast product. The surface Wa may also be referred to as an irradiated surface. The back surface Wb is the surface of the processing object W opposite to the surface Wa.

[0030] 1 illustrates the case of so-called lap welding, in which a workpiece W in which two metal members 11, 12 are stacked is irradiated with laser light L in the stacking direction of the metal members 11, 12 to weld them. In this case, a weld 14 penetrates the metal member 11 and is partially present in the metal member 12, thereby joining the metal members 11 and 12. Note that the number of metal members included in the workpiece W is not limited to two, and may be three or more. In addition, the welding form is not limited to so-called lap welding, and may be other welding forms such as butt welding and fillet welding.

[0031] The laser welding apparatus 100 includes a laser device 110, an optical head 120, an optical fiber 130, and a movement mechanism 140.

[0032] The laser device 110 has a laser oscillator and is configured to be able to output laser light with a power of, for example, several kW. The laser device 110 outputs laser light with a wavelength of, for example, 400 [nm] or more and 1200 [nm] or less. The laser device 110 has a laser light source therein, for example, a fiber laser, a semiconductor laser (element), a YAG laser, or a disk laser. The laser device 110 may also be configured to be able to output multi-mode laser light with a power of several kW as the sum of the outputs of multiple light sources.

[0033] The optical fiber 130 optically connects the laser device 110 and the optical head 120. The optical fiber 130 guides the laser light output from the laser device 110 to the optical head 120.

[0034] The optical head 120 is an optical device that irradiates the laser light from the laser device 110 onto the workpiece W. The optical head 120 includes a collimator lens 121, a condenser lens 122, a mirror 123, a diffractive optical element 125 (hereinafter, referred to as DOE 125), and a galvanometer scanner 126. The collimator lens 121, the condenser lens 122, the mirror 123, the DOE 125, and the galvanometer scanner 126 are also referred to as optical components.

[0035] The collimating lens 121 collimates the laser light input via the optical fiber 130. The collimated laser light becomes parallel light.

[0036] The mirror 123 reflects the laser light that has been collimated by the collimator lens 121, and directs the laser light toward the galvano scanner 126. Depending on the arrangement of the collimator lens 121 and the galvano scanner 126, the mirror 123 may not be necessary.

[0037] The galvano scanner 126 has a plurality of mirrors 126a, 126b. By changing the angles of the plurality of mirrors 126a, 126b, the output direction of the laser light L from the optical head 120 can be switched. The angles of the mirrors 126a, 126b are each changed by a motor (both not shown) controlled by, for example, a control device. The optical head 120 can relatively scan the laser light L on the surface of the workpiece W by changing the output direction of the laser light L while irradiating the laser light L. The galvano scanner 126 is an example of a laser scanner. Instead of the galvano scanner 126, a laser scanner different from the galvano scanner 126 may be provided.

[0038] The condenser lens 122 condenses the laser light irradiated by the galvano scanner 126 as parallel light, and irradiates the laser light L (output light) onto the workpiece W. On the surface of the workpiece W, a spot of the laser light L passing through the condenser lens 122 is formed.

[0039] The DOE 125 is provided between the collimator lens 121 and the condenser lens 122 and between the collimator lens 121 and the galvano scanner 126 .

[0040] FIG. 2 is an explanatory diagram showing the concept of the principle of the DOE 125. As shown in FIG. 2, the DOE 125 has a configuration in which, for example, a plurality of diffraction gratings 125a with different periods are superimposed. The DOE 125 can shape a beam shape by bending parallel light in a direction influenced by each diffraction grating 125a or by superimposing the light. The DOE 125 can split a laser beam into a plurality of beams and appropriately shape the shape of the spot on the surface. The DOE 125 is an example of a beam shaper.

[0041] Fig. 3 is a plan view showing an example of a beam spot S of laser light L irradiated from the laser welding apparatus 100 on a virtual surface Wa of the workpiece W. In the example of Fig. 3, a plurality of beam spots S2 are arranged circumferentially and substantially annularly around one beam spot S1 on the surface Wa by beam shaping by the DOE 125. As an example, the power density of the spot S2 is set lower than the power density of the spot S1.

[0042] 1 can relatively move the workpiece W and the optical head 120. By operating the moving mechanism 140, the laser light L can be relatively scanned on the surface of the workpiece W. That is, in this embodiment, the relative scanning of the spot of the laser light L on the surface of the workpiece W may be realized by the sole operation of the galvano scanner 126, may be realized by the sole operation of the moving mechanism 140, or may be realized by a combination of the operations of both the moving mechanism 140 and the galvano scanner 126.

[0043] [Laser welding method] FIG. 4 is a flow chart showing an example of a procedure for welding the workpiece W by the laser welding apparatus 100 of the first embodiment.

[0044] As shown in FIG. 4, first, the workpiece W is set at a position where it can be irradiated with laser light L from the laser welding apparatus 100 (S101).

[0045] Next, a molten pool is formed on the workpiece W by irradiating the surface Wa of the workpiece W with a laser beam L (S102). Next, the molten pool formed in S102 is cooled and solidified to form a first welded portion 14f (S103). The molten pool formed in S102, i.e., the first welded portion 14f formed in S103, is formed so as to extend between the multiple metal members 11, 12. Thus, by S102 and S103, a metal joined body 10 in which the multiple metal members 11, 12 are joined via the first welded portion 14f is obtained. S102 is an example of a first step, and S103 is an example of a second step. The laser beam irradiated in S102 is an example of a first laser beam, and the first welded portion 14f is an example of a welded portion.

[0046] It is known that when the multiple metal members 11, 12 include aluminum die-cast products, voids are more likely to remain in the welded joint than when they do not include aluminum die-cast products. This is thought to be partly due to cavities contained in the aluminum die-cast products. Voids in the welded joint are one of the causes of reduced strength and reduced electrical conductivity, so it is preferable to prevent them from remaining as much as possible.

[0047] Therefore, in order to reduce voids in the weld 14, the inventors conducted extensive research and discovered that in some cases it is possible to reduce voids by allowing the molten pool to cool and solidify in the normal manner without maintaining the molten state for any particular length of time, and then at least partially re-melting and re-solidifying the weld.

[0048] Based on this knowledge, in this embodiment, after S103, the first welded portion 14f is at least partially remelted by irradiating the portion of the surface Wa of the workpiece W where the first welded portion 14f is formed with laser light L (S104). Then, the portion of the first welded portion 14f that was remelted in S104 is cooled and solidified to form the second welded portion 14s (S105). S104 is an example of a third step, and S105 is an example of a fourth step. The laser light irradiated in S104 is an example of a second laser light, and the second welded portion 14s is an example of a welded portion.

[0049] As described above, it has been found that by remelting the first welded portion 14f to form a molten pool in S104, it is possible to remove voids from the portion that has become the molten pool. In other words, S104 is a process for removing voids remaining in the first welded portion 14f.

[0050] FIG. 5 is a cross-sectional view showing the welded portion 14 formed in the processing object W (metal bonded body 10) by S102 to S105, and is a cross-sectional view intersecting the scanning direction SD when the laser light L is scanned in the scanning direction SD on the front surface Wa of the processing object W. As shown in FIG. 5, the welded portion 14 has a first welded portion 14f and a second welded portion 14s. The first welded portion 14f and the second welded portion 14s penetrate the metal member 11 from the front surface Wa, and extend beyond the surface 12a of the metal member 12 into the metal member 12. In the example of FIG. 5, the first welded portion 14f and the second welded portion 14s remain inside the metal member 12 and do not reach the back surface Wb of the processing object W, that is, they do not penetrate the metal member 12. However, the present invention is not limited to this, and both the first welded portion 14f and the second welded portion 14s may penetrate the metal member 12, or only the first welded portion 14f may penetrate the metal member 12.

[0051] Through intensive research by the inventors, it has been found that when the base material of the metal members 11 and 12 melts in S104, voids may occur at the site where the base material melts, and may remain in the first welded portion 14f. Therefore, in S104, the laser light L is irradiated at approximately the same position as the irradiation position in S102, and the power density of the laser light L irradiated in S104 is set to be equal to or lower than the power density of the laser light L irradiated in S102. When the spot S of the laser light L is scanned on the surface Wa in S102 and S104, the spot S of the laser light L is scanned on the same path in S102 and S104. This makes it possible to melt only the first welded portion 14f in S104 without melting the base material of the metal members 11 and 12, i.e., the workpiece W. In this case, as shown in FIG. 5, the second welded portion 14s is formed inside the first welded portion 14f.

[0052] Furthermore, through intensive research by the inventors, it has been found that in S104, the laser light L may be irradiated at substantially the same position as the irradiation position in S102, and the power density of the laser light L irradiated in S104 may be set to the same as the power density of the laser light L irradiated in S102. In this case, although not shown, the second welded portion 14s is in a state of substantially overlapping with the first welded portion 14f.

[0053] 6 is a plan view of a linear weld 14 formed on the surface Wa in steps S102 to S105. In this example, the spot S of the laser light L is scanned on the surface Wa along the same linear path Pt in steps S102 and S104, and a bead of the weld 14 extending linearly with a substantially constant width is formed. As described above, the second weld 14s is located inside the first weld 14f. In the figure, the path Pt indicates the path of the irradiation center of the spot S, and substantially coincides with the center line CL of the bead of the weld 14.

[0054] 6, the start point Ps and end point Pe of scanning on the path Pt are the same in S102 and S104, and the scanning direction SD1 on the path Pt in S102 is the same as the scanning direction SD2 on the path Pt in S104. The start point Ps and end point Pe are an example of the end of the line-shaped path Pt. The scanning direction SD1 is an example of a first scanning direction, and the scanning direction SD2 is an example of a second scanning direction.

[0055] Fig. 7 is a graph showing the relationship between time t and the position (scanning position) of the spot S on the path Pt in the case of Fig. 6, except that S102 and S104 are performed under substantially the same conditions, and the first welded portion 14f and the second welded portion 14s are substantially the same size. As shown in Fig. 7, in S102, the spot S is moved from the start point Ps to the end point Pe, i.e., scanned, from time t1s to time t1e. Also, in S104, the spot S is moved from the start point Ps to the end point Pe, i.e., scanned, from time t2s to time t2e. The irradiation of the laser light L is stopped at time t2e.

[0056] In this example, the scanning speed V in S102 and S104 is constant (uniform speed) and is the same, and is expressed by the following formula (1): V = Lp / (T - Tm) (1) Here, Lp is the length of the path Pt from the starting point Ps to the end point Pe (see FIG. 6). Time T is the time from when the spot S of the laser light L is located at S102 to when the spot S of the laser light L is located at S104 at each position P on the path Pt from the starting point Ps to the end point Pe. The time T is the time from time t1s to time t2s at the starting point Ps, and is the time from time t1e to time t2e at the end point Pe. Moreover, time Tm is the time required for the spot S of the laser light L to move from the end point Pe of S102 to the starting point Ps of S104.

[0057] The power density of the laser light L in S102 and S104 is set so that a required size (depth or width) of the first welded portion 14f and the second welded portion 14s is obtained at each position P by scanning at the scanning speed V.

[0058] S103 at each position P is performed by leaving the spot S of the laser light L without irradiating it, i.e., allowing it to cool naturally, during the time from when the spot S of the laser light L is located in S102 to when the spot S of the laser light L again positions at the position P in S104, i.e., time T. The time T at which S102 is performed at each position P is the time that has elapsed from time t1P when the spot S of the laser light L is located in S102 to time t2P when the spot S of the laser light L is located in S104.

[0059] In addition, in S103, if the first welded portion 14f is forcibly cooled by some cooling means instead of natural cooling, the time T may be set shorter. In that case, as can be seen from formula (1), the scanning speed V may be increased as the time T is shortened, and thus the time required for S102 for the entire section of the path Pt, i.e., the time from time t1s to time t1e, may be shortened. However, if the scanning speed V is increased, the power of the laser light L must be increased, and the formation state of the molten pool in the workpiece W changes accordingly, so the upper limit of the scanning speed V is set within a range that satisfies these conditions.

[0060] Furthermore, S105 at each position P is performed by leaving the spot S of the laser light L without irradiating it for a predetermined time after the spot S of the laser light L is located in S104, i.e., by allowing the spot S to cool naturally. When S102 and S104 are performed under the same conditions and the first welded portion 14f and the second welded portion 14s are made to have approximately the same size, the required time for S105 can be set to approximately the same as the required time for S102, i.e., it can be set to time T.

[0061] The two-dot chain line E in the graph of FIG. 7 indicates the time t3P at which S105 ends at each position P on the path Pt. At each position P, the time t3P is the time when a time T has elapsed since the time t2P at which the spot S of the laser light L was located in S104. At the start point Ps, S105 ends at the time t3s, and at the end point Pe, S105 ends at the time t3e. As described above, the irradiation of the laser light L is stopped at the time t2e. Therefore, although the time Tm from the time t2e to the time t3s is the same length as the time Tm from the time t1e to the time t2s when the spot S of the laser light L moves from the end point Pe to the start point Ps, during the time Tm from the time t2e to the time t3s, the spot S of the laser light L is not irradiated and does not move from the end point Pe to the start point Ps.

[0062] Through extensive research by the inventors, when at least one of the metal members 11 and 12 is an aluminum die-cast product, the time T in S103 and S105 is the time required for the molten pool to cease to be in a molten state and to be substantially completely solidified. From this perspective, it has been found that the time T is preferably 1 s or more. The time T is an example of a predetermined time.

[0063] Fig. 8 is a photographic image of a cross section of a metal joined body 10 produced by carrying out the above-mentioned steps S101 to S105. As shown in Fig. 8, it was found that by carrying out the above-mentioned steps S101 to S105, voids can be suitably removed from the welded part 14.

[0064] Furthermore, through intensive research by the inventors, it has been found that it is preferable to split the laser light L irradiated to the workpiece W in S102 and S104 into multiple beams as shown in Fig. 3, and to include multiple spots S1 and S2 in the spot S. This is presumably because splitting the laser light L into multiple beams reduces the temperature difference depending on the location of the molten pool, suppresses the movement of the molten pool, and suppresses the generation of voids due to the movement of the molten pool.

[0065] As described above, according to this embodiment, by performing S102 (first step), S103 (second step), S104 (third step), and S105 (fourth step), it is possible to obtain a metal joined body 10 in which multiple metal members 11, 12 are joined via a suitable weld 14 with few voids.

[0066] [Variation 1] Fig. 9 is a plan view of the metal joined body 10 formed by the first modified example of the embodiment, and is a plan view of the case where a linear weld 14 is formed on the surface Wa in S102 to S105. In this example, similar to Fig. 6 of the above embodiment, the spot S of the laser light L is scanned on the surface Wa along the same linear path Pt in S102 and S104, and a bead of the weld 14 extending linearly with a substantially constant width is formed. As described above, the second weld 14s is located inside the first weld 14f.

[0067] However, in the first modification, as shown in Fig. 9, the scanning direction SD1 on the path Pt in S102 and the scanning direction SD2 on the path Pt in S104 are opposite to each other. That is, the starting point Ps1 of S102 is different from the starting point Ps2 of S104, and the end point Pe1 of S102 is different from the end point Pe2 of S104. Also, the starting point Ps1 of S102 is the same as the end point Pe2 of S104, and the end point Pe1 of S102 is the same as the starting point Ps2 of S104. The starting points Ps1 and Ps2 and the end points Pe1 and Pe2 are examples of the ends of the line-segment path Pt.

[0068] Even in the case where the scanning direction SD1 and the scanning direction SD2 are reversed in this way, a metal joined body 10 in which the metal members 11, 12 are joined via a welded part 14 with few voids can be obtained as long as the time for performing S103 at each position on the path Pt, i.e., the cooling time, can be ensured to be equal to or longer than the above-mentioned time T. In particular, in this example, the time from when the irradiation of the laser light L ends at the end point Pe1 of S102 until the irradiation of the laser light L starts at the start point Ps2 of S104, which is the same position as the end point Pe1, i.e., the time for which the irradiation of the laser light L is temporarily stopped at that position, can be set to be equal to or longer than the above-mentioned time T. The temporary stop time can also be referred to as a standby time.

[0069] [Variation 2] 10 is a plan view of a joined metal body 10 formed by a modified example 2 of the embodiment, in which an endless welded part 14 is formed on a surface Wa in steps S102 to S105. The metal member 11 has a disk-like shape, and the metal member 12 has a cylindrical shape. In the modified example 2, the edge of the metal member 11 and the axial end part of the circular ring-like metal member 11 are joined via the circumferential welded part 14 to obtain the joined metal body 10.

[0070] In this case, in S102 and S104, the path Pt is endless. That is, the start point Ps and the end point Pe of the path Pt are the same. Therefore, the time required to move from the end point Pe to the start point Ps can be eliminated, and the time required for S102 to S105 can be shortened accordingly. In the second modification, the scanning directions SD1 and SD2 are set to the same direction (counterclockwise). Note that the scanning directions SD1 and SD2 may both be clockwise.

[0071] Even when scanning the endless path Pt in this way, a metal joined body 10 in which the metal members 11, 12 are joined via a weld 14 with few voids can be obtained, so long as the time for performing S103 at each position on the path Pt, i.e., the cooling time, can be ensured to be equal to or longer than the above-mentioned time T. As an example, when the scanning directions SD1, SD2 are the same and the scanning speed V is the same and constant in S102, S104, the time required for scanning from the start point Ps to the end point Pe in S102 can be set to be equal to or longer than the above-mentioned time T.

[0072] Although the embodiment of the present invention has been illustrated above, the above embodiment and modified examples are merely examples and are not intended to limit the scope of the invention. The above embodiment and modified examples can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the gist of the invention. In addition, the specifications of each configuration, shape, and the like (structure, type, direction, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be appropriately changed and implemented.

[0073] For example, in the above embodiment and modified example, the scanning speed of the spot of the laser light is constant, but the present invention is not limited to this, and the scanning speed may be changed during scanning. Even if the end point of the path in the first step is different from the start point of the path in the third step, a time (standby time) during which the irradiation of the laser light is temporarily stopped may be provided before the third step in a state in which the start point of the third step can be irradiated with the laser light, in other words, in a state in which the start point is irradiated with the laser light when the laser light is output from the laser device (light source).

[0074] Furthermore, the shape of the path along which the spot is scanned is not limited to a straight line segment or a circle, but may be various other shapes. [Explanation of symbols]

[0075] 10…Metal joint 11...Metal parts 12...Metal parts 12a...side 14…Welded section 14f…First welded section (welded section) 14s…Second welded section (welded section) 100...Laser welding device 110...Laser device 120...Optical head 121...Collimating lens 122...Condenser lens 123…Mirror 125...Diffractive optical element (DOE) 125a...Diffraction grating 126…Galvanometer scanner 126a, 126b…Mirror 130...Optical fiber 140...Movement mechanism E: Two-dot chain line L: Laser light Lp…length P…Position Pe, Pe1, Pe2…End point Ps, Ps1, Ps2...Start point Pt…Path S…Spot S1…Spot S2…Spot SD1…Scanning direction (first scanning direction) SD2: Scanning direction (second scanning direction) t,t1s,t1e,t2s,t2e,t3s,t3e,t1P,t2P,t3P…Time T…time (predetermined time) Tm…time V: Scanning speed W…Processing target Wa…Surface Wb…Back side Z…direction

Claims

1. A laser welding method for laser welding a plurality of members as processing objects including an aluminum die-cast product, comprising: a first step of irradiating a first laser beam to form a molten pool across the plurality of members; a second step of solidifying the molten pool to form a weld; a third step of irradiating the welded portion with a second laser beam to melt the welded portion again; a fourth step of solidifying the remelted portion of the weld; A laser welding method comprising:

2. The laser welding method according to claim 1 , wherein in the third step, voids remaining in the welded portion are removed.

3. The laser welding method according to claim 1 , wherein in the third step, only the welded portion is melted without melting a base material of the object to be processed.

4. 2. The laser welding method according to claim 1, wherein in the second step, the molten pool is solidified by not irradiating the second laser light to each position of the object to be processed that was irradiated with the first laser light in the first step for a predetermined period of time or longer.

5. The laser welding method according to claim 4 , wherein the predetermined time is equal to or longer than 1 second.

6. 6. The laser welding method according to claim 1, wherein in the third step, the second laser light is irradiated to the same position as the position irradiated with the first laser light in the first step, and a power density of the second laser light is set to be equal to or lower than a power density of the first laser light.

7. 6. The laser welding method according to claim 1, wherein in the third step, the second laser light is irradiated to a position identical to a position irradiated with the first laser light in the first step, and a power density of the second laser light is set to be the same as a power density of the first laser light.

8. In the first step, a spot of the first laser light is scanned on a surface of the object to be processed; 6. The laser welding method according to claim 1, wherein in the third step, a spot of the second laser light is scanned on the surface of the object to be processed.

9. In the first step, a spot of the first laser light is scanned so as to move along a predetermined path on a surface of the object to be processed; The laser welding method according to claim 1 , wherein in the third step, the spot of the second laser light is scanned so as to move along the same path on the surface as in the first step.

10. 10. The laser welding method according to claim 9, wherein in the third step, a spot of the second laser light is scanned so that the second laser light is irradiated at each position on the path scanned with the spot of the first laser light in the first step after a predetermined time required for forming the welded portion in the second step has elapsed since the first laser light was irradiated in the first step.

11. 11. The laser welding method according to claim 9 or 10, wherein a first scanning direction of a spot of the first laser light on the path in the first step and a second scanning direction of a spot of the second laser light on the path in the third step are the same.

12. 11. The laser welding method according to claim 9, wherein a first scanning direction of a spot of the first laser light on the path in the first step and a second scanning direction of a spot of the second laser light on the path in the third step are opposite to each other.

13. The laser welding method according to claim 9 , wherein the path is a line segment extending between two ends.

14. The laser welding method of claim 9 , wherein the path is an endless path.

15. The laser welding method according to claim 1 , wherein in the first step, the first laser light includes a plurality of beams.

16. The laser welding method according to claim 1 or 15, wherein in the second step, the second laser light includes a plurality of beams.

17. 17. The laser welding method of claim 16, wherein the multiple beams are formed by a beam shaper.

18. A laser welding method for laser welding a plurality of members as processing objects including an aluminum die-cast product, comprising: a first step of irradiating a first laser beam to form a molten pool across the plurality of members; a second step of solidifying the molten pool to form a weld; a third step of irradiating the welded portion with a second laser beam to melt the welded portion again; a fourth step of solidifying the remelted portion of the weld; A laser welding apparatus for use in a laser welding method, comprising: a laser device capable of outputting the first laser beam and the second laser beam; an optical head that irradiates the first laser light or the second laser light output from the laser device onto a surface of the object to be processed; Equipped with A laser welding device that performs the first step and the third step.

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