Method for manufacturing welded products and laser welding method

Abstract

This invention provides a method for manufacturing welded products and a laser welding method that can suppress the occurrence of porosity and other defects by removing vaporized plating components present between stacked metal-plated steel sheets. [Solution] A method for manufacturing a welded product, which includes a welding process in which multiple laser beams 15 obtained by a diffractive optical element are irradiated onto the surface 2a of the upper plate 2 in the overlapping portion 6 of multiple metal-plated steel sheets to join the upper plate 2 to the lower plate 3. The multiple laser beams 15 include a main laser beam group 30 and a rear laser beam 40. The main laser beam group 30 includes a surface plating layer removal beam 31 that removes the plating layer 5 on the surface 2a of the upper plate 2, and a main melting beam 32 that is irradiated onto the molten pool 7a melted by the surface plating layer removal beam 31 to generate a first through hole 38 that penetrates to the back surface 3b of the lower plate 3. The rear laser beam 40 is irradiated onto the molten pool 7b after the first through hole 38 has been backfilled to generate a second through hole 43 that penetrates to the back surface 3b of the lower plate 3.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing welded products and a laser welding method. [Background technology]

[0002] Conventionally, galvanized steel sheets, which are steel sheets with a zinc coating applied to their surface, are known. Galvanized steel sheets possess durability and corrosion resistance, and are used in components that require resistance to rust, such as structural materials for automobile bodies. Laser welding is also used as one method of joining galvanized steel sheets. When a laser is irradiated onto the surface of a galvanized steel sheet, the steel sheet melts and a molten pool is formed. However, since the melting point of zinc is lower than that of the steel sheet, it is known that zinc evaporates and remains in the molten pool, which can cause welding defects.

[0003] Patent Document 1 discloses a laser welding method that suppresses the occurrence of welding defects such as porosity in butt welding of metals. In this laser welding method, the laser beam is split using a diffractive optical element, and the laser beam is irradiated to a leading spot and a main spot. By irradiating the leading spot with laser beam of lower energy intensity than the main spot, substances such as dirt on the surface of the weld area are gasified and diffused. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-205327 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when welding a plate assembly made by overlapping multiple galvanized steel plates, zinc plating is applied not only to the surface of the upper plate but also to the spaces between the overlapping plates and to the back surface of the lower plate. Therefore, in the laser welding method described in Patent Document 1, although it is possible to remove the zinc from the surface of the upper plate, the zinc present in the spaces between the overlapping plates remains in the molten area in a vaporized state, making it difficult to suppress the occurrence of porosity and other defects.

[0006] This invention was conceived in view of the above points, and the problem that this invention aims to solve is to provide a method for manufacturing welded products and a laser welding method that can suppress the occurrence of porosity and other issues by removing vaporized plating components present between stacked metal-plated steel sheets during laser welding of stacked sheets. [Means for solving the problem]

[0007] To solve the above problems, the method for manufacturing welded products and the laser welding method according to the present invention employ the following means.

[0008] The first invention of the present invention is a method for manufacturing a welded product, which includes a welding step of irradiating the surface of the upper plate of an overlapping portion formed by stacking multiple metal-plated steel plates with multiple laser beams obtained by a diffractive optical element, thereby joining the overlapping portion from the upper plate to the lower plate, wherein the multiple laser beams comprise a main laser beam group in which multiple irradiation spots are arranged on the front side in the direction of travel of the multiple laser beams, and a rear laser beam in which one irradiation spot is arranged at a distance behind the main laser beam group in the direction of travel, and the main laser beam group comprises the upper The system includes a surface plating layer removal beam that is irradiated with an output that melts the plated layer on the surface of the plate to a depth that does not reach the back surface of the upper plate, and a main melting beam that, after irradiation with the surface plating layer removal beam, is irradiated with an output that melts the molten pool melted by the surface plating layer removal beam from the surface of the upper plate to the back surface of the lower plate, thereby generating a first through-hole that penetrates to the back surface of the lower plate. The rear laser beam is irradiated with an output weaker than the main laser beam group into the molten pool after the first through-hole has been filled in, thereby generating a second through-hole that penetrates to the back surface of the lower plate.

[0009] The second invention of the present invention is a method for manufacturing a welded product according to the first invention, wherein the plurality of laser beams comprises a group of preceding laser beams in which a plurality of irradiation spots are arranged at intervals in front of the main group of laser beams in the direction of travel, and the group of preceding laser beams comprises a preceding plating layer removal beam that is irradiated with a lower output than the surface plating layer removal beam to melt the plating layer on the surface of the upper plate, and a preceding melting beam that is irradiated with a lower output than the main melting beam after irradiation by the preceding plating layer removal beam to generate a preceding hole that is melted to a depth that does not reach the back surface of the upper plate.

[0010] A third aspect of the present invention is a method for manufacturing a welded product according to the first or second invention, wherein the main laser beam group has a plurality of main melting beams, and each of the main melting beams is irradiated onto a central spot where the first through hole is formed and a plurality of auxiliary spots arranged around the central spot to assist in the melting of the central spot by heat conduction.

[0011] The fourth invention of the present invention is a method for manufacturing a welded product according to the third invention, wherein the rear laser beam is irradiated with an output weaker than the total output of the main laser beam group and with an irradiation area smaller than the irradiation area of the main laser beam group.

[0012] The fifth invention of the present invention is a laser welding method for irradiating the surface of the upper plate of the overlapping part of a plurality of electroplated steel plates stacked together with a plurality of laser beams obtained by a diffractive optical element, and joining the overlapping part from the upper plate to the lower plate, wherein the plurality of laser beams include a main laser beam group in which a plurality of irradiation spots are arranged on the front side in the traveling direction of the plurality of laser beams, and a rear laser beam in which one irradiation spot is arranged at an interval behind the main laser beam group in the traveling direction, the main laser beam group is irradiated with a surface plating layer removing beam that melts to a depth that does not reach the back surface of the upper plate in order to remove the plating layer on the surface of the upper plate, and after irradiation with the surface plating layer removing beam, it is irradiated with an output that melts from the surface of the upper plate to the back surface of the lower plate in the molten pool melted by the surface plating layer removing beam to generate a first through hole that penetrates to the back surface of the lower plate. The main melting beam, the rear laser beam is irradiated with an output weaker than the main laser beam group to the molten pool in which the first through hole is filled, and a second through hole that penetrates to the back surface of the lower plate is generated.

Advantages of the Invention

[0013] According to the means of the present invention described above, in the laser welding of stacked electroplated steel plates, it is possible to provide a method for manufacturing a welded product and a laser welding method that can remove vaporized plating components existing between the stacked plates and suppress the occurrence of porosity and the like.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic diagram of a laser welding apparatus according to the present embodiment. [Figure 2]It is a diagram showing the arrangement of irradiation spots of a plurality of laser beams according to this embodiment. [Figure 3] It is a cross-sectional view schematically showing the state of the overlapping portion during irradiation of a plurality of laser beams. [Figure 4] It is a diagram schematically showing the planar shape of the molten pool formed by irradiation of a plurality of laser beams. [Figure 5] It is a schematic diagram showing an example of a welded product. [Figure 6] It is a schematic diagram showing an example of a welded product to which spot welding has been performed. [Figure 7] It is a schematic diagram showing an example of an overlapping portion in a welded product. [Figure 8] It shows a cross-section of a joint welded by the laser welding method according to this embodiment. [Figure 9] It shows a cross-section of a joint welded by a conventional laser welding method.

Mode for Carrying Out the Invention

[0015] <Method for Manufacturing a Welded Product> Hereinafter, embodiments of the present invention will be described with reference to the drawings. The method for manufacturing a welded product according to this embodiment includes a forming step of forming members constituting the welded product, and a laser welding step of combining the formed plurality of members and joining them by laser welding. <Welded Product> The welded product is composed of, for example, a combination of members made of a plurality of galvanized steel sheets (metal-plated steel sheets), and is used for automobile parts, vehicle body structural materials, etc. In the forming step, for example, by press forming, the galvanized steel sheet is formed into a predetermined shape.

[0016] <Laser Device> The laser device 10 used for laser welding comprises a laser oscillator 11 and a scanner 12, as shown in Figure 1. The laser oscillator 11 is connected to the scanner 12 by an optical fiber. The scanner 12 is equipped with a diffractive optical element 13, which spectrally separates the light into multiple laser beams 15. The scanner 12 is configured to be movable, for example, by being mounted on a robot arm, and can move the multiple laser beams 15 to irradiate the workpiece 16. The multiple laser beams 15 are configured with multiple irradiation spot patterns, as shown in Figure 2.

[0017] <Laser welding process> In the laser welding process, components made of multiple formed galvanized steel sheets are combined and joined by laser welding. In this embodiment, as shown in Figure 3, two galvanized steel sheets are overlapped in the thickness direction of the sheet surfaces. In this overlapping portion 6, the galvanized steel sheet located on the side that is irradiated with the laser is called the upper plate 2, and the side that is irradiated with the laser is called the surface 2a. The galvanized steel sheet overlapped on the back surface 2b side of the upper plate 2 is called the lower plate 3. Both the upper plate 2 and the lower plate 3 have a galvanized layer 5 on both sides. A galvanized layer 5 exists between the upper plate 2 and the lower plate 3 in the overlapping portion 6. In the laser welding process, multiple laser beams 15 obtained by a diffractive optical element are irradiated onto the surface 2a of the upper plate 2 in the overlapping portion 6, melting down to the back surface 3b of the lower plate 3.

[0018] The direction of travel of the multiple laser beams 15 will be described as the front-to-back direction, and the direction intersecting the direction of travel will be described as the left-to-right direction. As shown in Figures 2 and 3, the multiple laser beams 15 form a spot pattern consisting of multiple irradiation spots, with the leading laser beam group 20, the main laser beam group 30, and the rear laser beam 40 irradiating in order from the front in the direction of travel. The irradiation area of ​​the leading laser beam group 20 in the spot pattern will be called the leading spot area 24, the irradiation area of ​​the main laser beam group 30 will be called the main spot area 34, and the irradiation area of ​​the rear laser beam 40 will be called the rear spot area 42.

[0019] As shown in Figure 3, the leading laser beam group 20 has multiple leading zinc removal beams 21 (leading plating layer removal beams) and multiple leading melting beams 22. In other words, the leading zinc removal beams 21 and leading melting beams 22 are multi-point beams spectrally separated into multiple beams. As shown in Figures 2 and 4, the leading spot region 24 is positioned ahead of the main spot region 34 in the direction of propagation of the multiple laser beams 15 and is composed of multiple irradiation spots. Specifically, as irradiation spots for the leading melting beam 22, one leading melting spot 26 is positioned on the welding centerline P along the front-to-back direction, and multiple auxiliary spots 27 are positioned around the leading melting spot 26. For example, eight auxiliary spots 27 are positioned at equal intervals in the circumferential direction on the circumference of a circle F1 centered on the leading melting spot 26. The distance between the leading melting spot 26 and the center of each auxiliary spot 27 is the radius R1 of circle F1. Also, two auxiliary spots 27 are located on the welding centerline P.

[0020] Multiple pre-zinc removal spots 25, which are irradiated with the pre-zinc removal beam 21, are positioned further forward from the auxiliary spots 27 located in front of the pre-molten spot 26. For example, three pre-zinc removal spots 25 are arranged on the circumference of a circle F2 centered on the pre-molten spot 26. The distance between the center of the pre-molten spot 26 and the center of each pre-zinc removal spot 25 is the radius R2 of circle F2. The three pre-zinc removal spots 25 are adjacent to the three auxiliary spots 27 located in front of the pre-molten spot 26. The central pre-zinc removal spot 25 in the left-right direction is located on the weld centerline P.

[0021] Each irradiation spot in the preceding spot region 24 is, for example, roughly circular in shape, and its size is set as appropriate. The size of each irradiation spot may be the same, or they may be different sizes.

[0022] The pre-zinc removal beam 21, as shown in Figure 3, is irradiated at a lower output than the zinc removal beam 31 of the main laser beam group 30, which will be described later, in order to melt the zinc plating layer 5 on the surface 2a of the upper plate 2. The output of the pre-zinc removal beam 21 for each irradiation spot is set as appropriate. The pre-melting beam 22 is irradiated at a lower output than the main melting beam 32, which will be described later, after irradiation with the pre-zinc removal beam 21. The output of the main melting beam 32 for each irradiation spot is set as appropriate. In this embodiment, the pre-melting beam 22 is irradiated at the same output to the pre-melting spot 26 and the auxiliary spot 27, respectively. The pre-melting beam 22 creates a pre-hole 28 in the pre-melting spot 26 that is melted to a depth that does not reach the back surface 2b of the upper plate 2. In addition, the pre-melting beam 22 irradiating the auxiliary spot 27 assists the melting of the pre-melting spot 26 by heat conduction.

[0023] The distance between the leading spot region 24 and the main spot region 34 is set so that the temperature of the leading molten portion 29, which has been melted by irradiation with the leading laser beam group 20, decreases and solidifies before the main laser beam group 30 reaches it. For example, the distance L3 between the centers of the leading molten spot 26 and the main molten spot 36 is set to a predetermined interval.

[0024] As shown in Figure 3, the main laser beam group 30 has multiple zinc removal beams 31 (surface plating layer removal beams) and multiple main melting beams 32. In other words, the zinc removal beams 31 and the main melting beams 32 are multi-point beams spectrally separated into multiple beams. As shown in Figures 2 and 4, the main spot area 34 is composed of multiple irradiation spots. Specifically, one main melting spot 36 (central spot) is positioned on the welding centerline P as the irradiation spot of the main melting beam 32, and multiple auxiliary spots 37 are positioned around the main melting spot 36. For example, eight auxiliary spots 37 are positioned at equal intervals in the circumferential direction on the circumference of a circle F3 centered on the main melting spot 36. The distance between the center of the main melting spot 36 and each auxiliary spot 37 is the radius R3 of circle F3. Also, two auxiliary spots 37 are located on the welding centerline P.

[0025] Multiple zinc removal spots 35, which are irradiated with the zinc removal beam 31, are positioned in front of the auxiliary spots 37 located in front of the main molten spot 36. For example, three zinc removal spots 35 are arranged on the circumference of a circle F4 centered on the main molten spot 36. The distance between the center of the main molten spot 36 and the center of each zinc removal spot 35 is the radius R4 of circle F4. The three zinc removal spots 35 are adjacent to the three auxiliary spots 37 located in front of the main molten spot 36. The central zinc removal spot 35 in the left-right direction is located on the welding centerline P.

[0026] In this embodiment, the number and arrangement of irradiation spots in the main spot area 34 are set to be the same as the number of irradiation spots in the preceding spot area 24. Each irradiation spot in the main spot area 34 is, for example, roughly circular in shape, and its size is set as appropriate. The size of all irradiation spots may be the same, or they may be of different sizes.

[0027] As shown in Figure 3, the zinc removal beam 31 is irradiated with an output that melts the zinc plating layer 5 on the surface 2a of the upper plate 2 to a depth that does not reach the back surface 2b of the upper plate 2, in order to remove the zinc plating layer 5. The output of the zinc removal beam 31 for each irradiation spot is set as appropriate. Irradiation with the zinc removal beam 31 forms a shallow molten pool 7a that is melted to a depth deeper than the pre-drilled hole 28, for example, to a depth of about half the thickness of the upper plate 2.

[0028] The main melting beam 32 is irradiated onto the shallow molten pool 7a after irradiation with the zinc removal beam 31, at an output that melts from the surface 2a of the upper plate 2 to the back surface 3b of the lower plate 3. The output of the main melting beam 32 for each irradiation spot is set as appropriate. In this embodiment, the main melting spot 36 and the auxiliary spot 37 are irradiated with the main melting beam 32 at the same output. The main melting beam 32 creates a first through-hole 38 in the main melting spot 36 that penetrates to the back surface 3b of the lower plate 3. In addition, the irradiation of the auxiliary spot 37 with the main melting beam 32 assists the melting of the main melting spot 36 through heat conduction. Irradiation with the main melting beam 32 creates a molten pool 7b that melts from the surface 2a of the upper plate 2 to the back surface 3b of the lower plate 3. As shown in Figure 4, the molten pool 7b has a shape that narrows toward the rear in the direction of travel when viewed from above. In other words, the molten pool 7b becomes narrower as it moves away from the main spot area 34 toward the rear.

[0029] The rear spot region 42, to which the rear laser beam 40 is irradiated, is positioned on the welding centerline P at a distance behind the main spot region 34 in the direction of travel, as shown in Figure 4. The distance between the rear spot region 42 and the main spot region 34 is set so that the rear laser beam 40 irradiates the molten pool 7b, which has narrowed in width after irradiation by the main molten beam 32. For example, the distance L4 between the irradiation spot of the rear spot region 42 and the center of the main molten spot 36 is set to a predetermined interval. The rear spot region 42 is set to be smaller than the main spot region 34. The irradiation spot of the rear spot region 42 is, for example, approximately circular in shape, and its size is set as appropriate.

[0030] As shown in Figure 3, the rear laser beam 40 is irradiated into the molten pool 7b, where the first through-hole 38 has been backfilled, with an output that reaches the back surface 3b of the lower plate 3, creating a second through-hole 43 that penetrates to the back surface 3b of the lower plate 3. The output of the rear laser beam 40 is set appropriately to an output weaker than the total output of the main laser beam group 30.

[0031] (Placement of illumination spots) In this embodiment, as shown in Figure 4, the irradiation spots for the pre-melting spot 26, the main melting spot 36, and the rear spot area 42 are arranged on the welding centerline P. These irradiation spots may also be arranged at the same interval, i.e., L3 = L4.

[0032] The auxiliary spots 27 in the leading spot region 24 each have their centers located on the circumference of circle F1. That is, the distance between the centers of each auxiliary spot 27 and the leading molten spot 26 is the same, and is the radius R1 of circle F1. The centers of the auxiliary spots 27 positioned before and after the leading molten spot 26 are located on the welding centerline P. Furthermore, if we define auxiliary line Q1 as a line passing through the center of the leading molten spot 26 and perpendicular to the welding centerline P, then the centers of the auxiliary spots 27 positioned to the left and right of the leading molten spot 26 are located on auxiliary line Q1. Auxiliary spots 27 are also positioned between the welding centerline P and auxiliary line Q1. The eight auxiliary spots 27 are arranged at equal intervals in the circumferential direction.

[0033] The centers of the three pre-zinc removal spots 25 are each located on the circumference of circle F2. The distance between the centers of each pre-zinc removal spot 25 and the pre-melting spot 26 is the same, and is the radius R2 of circle F2. The center of the central pre-zinc removal spot 25 is located on the welding centerline P. That is, the pre-melting spot 26, two auxiliary spots 27, and one pre-zinc removal spot 25 are arranged in a line on the welding centerline P. The distance (R2-R1) between the centers of the front auxiliary spot 27 and the pre-zinc removal spot 25 on the welding centerline P is set to be smaller than the distance R1 between the centers of the pre-melting spot 26 and the auxiliary spot 27. Also, if L1 is the distance from the welding centerline P to the centers of the pre-zinc removal spots 25 on both the left and right sides, then L1 = R1 is set. That is, the width of the irradiation area of ​​the pre-zinc removal beam 21 and the pre-melting beam 22 is the same in the left-right direction.

[0034] The auxiliary spots 37 in the main spot area 34 each have their centers located on the circumference of circle F3. That is, the distance between the centers of each auxiliary spot 37 and the main molten spot 36 is the same, and is the radius R3 of circle F3. The centers of the auxiliary spots 37 positioned before and after the main molten spot 36 are located on the welding centerline P. Furthermore, if we define auxiliary line Q2 as a line passing through the center of the main molten spot 36 and perpendicular to the welding centerline P, then the centers of the auxiliary spots 37 positioned to the left and right of the main molten spot 36 are located on auxiliary line Q2. Auxiliary spots 37 are also positioned between the welding centerline P and auxiliary line Q2. The eight auxiliary spots 37 are arranged at equal intervals in the circumferential direction.

[0035] The centers of the three zinc removal spots 35 are each located on the circumference of circle F4. The distance between the centers of each zinc removal spot 35 and the main molten spot 36 is the same, and is the radius R4 of circle F4. The center of the central zinc removal spot 35 is located on the welding centerline P. That is, the main molten spot 36, two auxiliary spots 37, and one zinc removal spot 35 are arranged in a line on the welding centerline P. The distance between the centers of the front auxiliary spot 37 and the zinc removal spot 35 on the welding centerline P (R4-R3) is set to be smaller than the distance R3 between the centers of the main molten spot 36 and the auxiliary spot 37. Also, if the distance from the welding centerline P to the centers of the zinc removal spots 35 on both the left and right sides is L2, then L2 = R3 is set. That is, the width of the irradiation area of ​​the zinc removal beam 31 and the main molten beam 32 is the same in the left-right direction.

[0036] The arrangement of irradiation spots in the preceding spot area 24 and the main spot area 34 is set to be the same. That is, R1=R3, R2=R4, and L1=L2, respectively.

[0037] The arrangement of the irradiation spots in the above-described preceding spot region 24 and main spot region 34 is an example, and other arrangements can be applied. For example, in the main spot region 34, more than eight auxiliary spots 37 may be arranged, or fewer may be arranged. Also, the distances between the centers of the main melting spot 36 and the auxiliary spots 37 may not all be the same, and some may be different. For example, some of the plurality of auxiliary spots 37 may be arranged at positions shifted outside or inside the circle instead of on the circumference of the same circle. Also, more than three zinc removal spots 35 may be arranged, or fewer may be arranged. Also, the plurality of zinc removal spots 35 may be arranged not on the circumference of the same circle, but, for example, in a curved curve shape or arranged linearly in the left-right direction. Similarly, in the preceding spot region 24, the arrangement and number of the irradiation spots may be changed.

[0038] (Output of laser beam) As shown in FIGS. 3 and 4, the total output E of the preceding laser beam group 20 20 is set to be weaker than the total output E of the main laser beam group 30. The output E of the rear laser beam 40 30 is weaker than the total output E of the main laser beam group 30 40 and stronger than the total output E of the preceding laser beam group 20. That is, the value of the total output is set such that 30 < E 20 < E 20 < E 40 < E 30 is satisfied.

[0039] For example, the output of the preceding zinc removal beam 21 is set to be the same for each preceding zinc removal spot 25. The output of the preceding melting beam 22 is set to be the same for the preceding melting spot 26 and each auxiliary spot 27. The output of the zinc removal beam 31 is set to be the same for each zinc removal spot 35. The output of the main melting beam 32 is set to be the same for the main melting spot 36 and each auxiliary spot 37. Here, the value of the output for one irradiation spot of the preceding zinc removal beam 21 is X 21 , X is the value of the output for one irradiation spot of the pre-melted beam 22. 22 , Y is the value of the output for one irradiation spot of the zinc removal beam 31. 31 , Y is the value of the output for one irradiation spot of the main melting beam 32. 32 , Therefore, the relationship between the output settings for each irradiation spot is: X 21 <Y 31 X 21 × (Number of 25 pre-zinc removal spots) <Y 31 × (number of zinc removal spots 35). Also, X 22 <Y 32 X 22 × (Number of pre-melted spots 26 and auxiliary spots 27) <Y 32 × (Number of main molten spots 36 and auxiliary spots 37) Also, X 21 <X 22 X 21 × (Number of 25 pre-zinc removal spots) <X 22 × (number of pre-molten spots 26 and auxiliary spots 27). Also, Y 31 <Y 32 Y 31 × (Number of zinc removal spots 35) <Y 32 × (Number of main molten spots 36 and auxiliary spots 37) Also, X 22 <Y 31 X 22 × (Number of pre-melted spots 26 and auxiliary spots 27) > Y 31 This is multiplied by (the number of zinc removal spots 35).

[0040] The laser beam output settings described above are just examples; the output value can be changed for each irradiation spot.

[0041] Next, the process of forming a joint by laser welding at the overlapping portion of galvanized steel sheets will be explained. The components of the welded product are placed in a predetermined position in an assembled state. Multiple laser beams 15 obtained from a diffractive optical element are moved and irradiated onto the surface 2a of the upper plate 2 at the overlapping portion 6 of the two galvanized steel sheets. The group of leading laser beams 20 is irradiated onto the portion of the upper plate 2a surface 2a to be welded. Irradiation with the leading zinc removal beam 21 melts the surface 2a of the upper plate 2, and the galvanized layer 5 vaporizes. Then, irradiation with the leading melting beam 22 creates a leading melted portion 29 where the upper plate 2 is melted to a depth that does not reach the back surface 2b of the upper plate 2 from the surface, and shallow leading holes 28 are created in the leading melted spots 26 where the area near the surface 2a of the upper plate 2 is recessed in the thickness direction.

[0042] After the preceding laser beam group 20 is irradiated, the main laser beam group 30 is irradiated. By the time the main laser beam group 30 reaches the pre-molten portion 29, the pre-hole 28 is filled in, and the temperature of the pre-molten portion 29 decreases and it solidifies. Irradiation with the zinc removal beam 31 of the main laser beam group 30 melts to a depth deeper than the depth of the pre-molten portion 29, but not to the back surface 2b of the upper plate 2. The zinc removal beam 31 has a wider range of zinc removal than the preceding zinc removal beam 21 and can remove vaporized zinc that could not be completely removed by the preceding zinc removal beam 21.

[0043] Irradiation with the main molten beam 32 creates a molten pool 7b extending from the surface 2a of the upper plate 2 to the back surface 3b of the lower plate 3, causing the zinc plating layer 5 between the upper plate 2 and the lower plate 3, and on the back surface 3b of the lower plate 3, to vaporize. A first through-hole 38 is created in the main molten spot 36, penetrating from the surface 2a of the upper plate 2 to the back surface 3b of the lower plate 3. The vaporized zinc plating components can be removed through the first through-hole 38.

[0044] After the main laser beam group 30 has irradiated the molten pool 7b, the rear laser beam 40 is irradiated. The rear laser beam 40 irradiates the portion of the molten pool 7b that has narrowed after the first through-hole 38 has been backfilled. Irradiation with the rear laser beam 40 creates a second through-hole 43 in the rear spot region 42 that penetrates from the surface 2a of the upper plate 2 to the back surface 3b of the lower plate 3. Through the second through-hole 43, any zinc plating components remaining inside after irradiation with the main laser beam group 30 can be removed.

[0045] After irradiation with the rear laser beam 40, the second through-hole 43 is backfilled, the temperature of the molten pool 7b decreases and it solidifies, and the upper plate 2 and lower plate 3 of the overlapping portion 6 are welded together. This forms a joint in the overlapping portion 6 of the two galvanized steel plates, joined from the upper plate 2 to the lower plate 3.

[0046] As an example, as shown in Figure 5, a welded product 50 is manufactured by joining the two members 51 and 52 through the laser welding process according to the above embodiment. The welded product 50 has a joint 54 that is continuously welded to the overlapping portion 53 of the two members 51 and 52.

[0047] The laser welding method according to this embodiment is the same as the embodiment of the laser welding process according to the above embodiment. The embodiment of the laser welding method according to the present invention can be applied to welded products made by welding various metal-plated steel sheets. For example, as shown in Figure 5, an overlapping portion 53 made by combining U-shaped members 51 and 52 can be joined by laser welding. A continuously welded joint portion 54 is formed in the overlapping portion 53. This improves the performance of the part (welded product) compared to the case where a joint portion 59 is formed by spot welding on an overlapping portion made by combining two members 57 and 58, as shown in Figure 6, for example. Furthermore, by using the laser welding method according to the above embodiment, it is not necessary to provide a flange as shown in Figure 6, and the weight of the part (welded product) can be reduced. Also, as shown in Figure 7, by using the laser welding according to the above embodiment, a watertight function can be provided to the joint portion 63 of the two members 61 and 62 of the welded product 60 to prevent the intrusion of water 64 and the like.

[0048] <Effects of this embodiment> In the manufacturing method of the welded product according to the above embodiment, a plurality of zinc removal beams 31 and a plurality of main melting beams 32 arranged behind them are irradiated as a main laser beam group 30 during the laser welding process. By irradiating with the zinc removal beams 31, the zinc plating layer 5 on the surface 2a of the upper plate 2 can be vaporized and removed. Then, by irradiating with the main melting beams 32, the overlapping portion 6 of the galvanized steel sheet melts from the surface 2a of the upper plate 2 to the back surface 3b of the lower plate 3, and a first through hole 38 is formed that penetrates to the back surface 3b of the lower plate 3. This makes it possible to remove the vaporized zinc between the upper plate 2 and the lower plate 3, and on the back surface 3b of the lower plate 3.

[0049] According to the above embodiment, in the laser welding process, the width of the molten pool 7b formed by the main laser beam group 30 narrows in the left-right direction as it moves towards the rear in the direction of travel of the multiple laser beams 15, and the first through hole 38 is filled in. By irradiating the rear portion of this narrowed molten pool 7b with a single spot rear laser beam 40, a second through hole 43 is formed that penetrates to the back surface 3b of the lower plate 3, and residual zinc can be removed. In other words, the occurrence of porosity due to vaporized plating components between the overlapping galvanized steel plates can be further suppressed. Therefore, it becomes easier to join the overlapping portion 6 by continuous laser welding, and the strength of the welded product can be improved. In addition, since the rear laser beam 40 is irradiated onto the molten pool 7b where heat remains, the output can be reduced compared to the main laser beam group 30.

[0050] According to the above embodiment, in the laser welding process, a group of preceding laser beams 20 is irradiated at a position spaced in front of the main group of laser beams 30 in the direction of propagation of the multiple laser beams 15, with a lower output than the main group of laser beams 30. As a result, the upper plate 2 is melted to a depth that does not reach the back surface 2b from the surface 2a, and the zinc plating layer 5 on the surface 2a of the upper plate 2 can be vaporized and removed. In addition, the pre-molten portion 29 of the surface 2a of the upper plate 2 solidifies before the main group of laser beams 30 reaches it. Because the heat from the initial melting of the surface 2a of the upper plate 2 remains, the heating efficiency of the irradiation by the main group of laser beams 30 is improved, and the overlapping portion 6 of the upper plate 2 and the lower plate 3 can be melted efficiently.

[0051] According to the above embodiment, in the main spot region 34, a plurality of auxiliary spots 37 are arranged around the main melting spot 36 (central spot), and the main melting beam 32, which is spectrally split into multiple parts, is irradiated onto them. As a result, the melting of the main melting spot 36 is assisted by heat conduction, and the overlapping portion 6 can be melted more efficiently down to the back surface 3b of the lower plate 3. Furthermore, since each auxiliary spot 37 is located at the same distance from the main melting spot 36 and is arranged at equal intervals in the circumferential direction, a balanced arrangement is achieved, making it easier to set the output of the main melting beam 32.

[0052] According to the above embodiment, the zinc removal spot 35 is positioned adjacent to the auxiliary spot 37 located in front of the main melting spot 36. By reducing the distance between the irradiation of the zinc removal beam 31 and the main melting beam 32, the preheating effect of the zinc removal beam 31 can be improved. Furthermore, by making the width of the irradiation areas of the zinc removal beam 31 and the main melting beam 32 the same in the left-right direction, the preheating effect of the zinc removal beam 31 can be improved. Therefore, the heating efficiency of the main melting beam 32 can be improved.

[0053] According to the above embodiment, in the leading spot region 24, a plurality of auxiliary spots 27 are arranged around the leading melt spot 26, and the leading melt beam 22, which is spectrally separated into multiple beams, is irradiated onto them. As a result, the melting of the leading melt spot 26 is assisted by heat conduction, and the surface 2a of the upper plate 2 can be melted more efficiently. Furthermore, since each auxiliary spot 27 is located at the same distance from the leading melt spot 26 and is arranged at equal intervals in the circumferential direction, a balanced arrangement is achieved, making it easier to set the output of the leading melt beam 22.

[0054] According to the above embodiment, the pre-zinc removal spot 25 is positioned adjacent to the auxiliary spot 27, which is in front of the pre-melting spot 26. By reducing the distance between the irradiation of the pre-zinc removal beam 21 and the pre-melting beam 22, the preheating effect of the pre-zinc removal beam 21 can be improved. Furthermore, by making the width of the irradiation areas of the pre-zinc removal beam 21 and the pre-melting beam 22 the same in the left-right direction, the preheating effect of the pre-zinc removal beam 21 can be improved. Therefore, the heating efficiency of the pre-melting beam 22 can be improved.

[0055] According to the above embodiment, by setting the arrangement and number of irradiation spots in the preceding spot area 24 and the main spot area 34 to be the same, the preheating effect of the preceding laser beam group 20 can be improved, and the heating efficiency of the main laser beam group 30 can be improved.

[0056] Figure 8 shows a cross-section of the joint in the overlapping portion of galvanized steel sheets welded by the laser welding method according to the above embodiment, demonstrating that porosity is suppressed. In other words, vaporized zinc from the galvanized layers of the upper plate 2 and lower plate 3 is also removed. Figure 9 shows a cross-section of a joint welded by a conventional laser welding method as a comparative example. Porosity 70 due to residual vaporized zinc is generated inside the overlapping portion of the galvanized steel sheets.

[0057] <Other Embodiments> Although specific embodiments of the present invention have been described above, the present invention can also be implemented in various other forms. For example, the manufacturing method and laser welding method of the above embodiments can be widely applied to various types of welded products, including vehicle parts such as automobiles, welded products used in construction and civil engineering, and welded products used in electrical products.

[0058] In the above embodiment, an example was shown in which a group of preceding laser beams 20 is included in a group of multiple laser beams 15 in the laser welding process. However, it is also possible to have an embodiment in which the group of preceding laser beams 20 is not provided, and the main laser beam group 30 and the rear laser beam 40 are irradiated.

[0059] In the above embodiment, a configuration in which galvanized steel sheets are stacked is shown as an example, but the method for manufacturing welded products and the laser welding method according to the present invention can also be applied to other metal-plated steel sheets. That is, the metal plating layer may be another metal having a boiling point lower than the melting point of the base steel sheet.

[0060] In the above embodiment, a configuration in which two galvanized steel sheets are stacked is shown as an example, but three galvanized steel sheets may also be stacked. That is, an intermediate plate may be positioned between the upper plate 2 and the lower plate 3.

[0061] The arrangement and number of irradiation spots may differ between the main spot area 34 and the preceding spot area 24.

[0062] <Effects and effects of each invention described in "Means for solving the problem"> Finally, the effects and benefits of the above embodiments corresponding to each invention in the "Means for Solving the Problems" described above should be noted.

[0063] According to the first invention, in the laser welding process, multiple laser beams obtained by a diffractive optical element are irradiated onto the surface of the upper plate of the overlapping portion where multiple metal-plated steel sheets are stacked. When the surface plating layer removal beam of the main laser beam group is irradiated, the upper plate melts to a depth that does not reach the back surface. In addition, the plating layer on the surface of the upper plate vaporizes, and the vaporized plating components can be removed. Furthermore, by irradiating with the main melting beam positioned behind the surface plating layer removal beam, a first through-hole is created that penetrates from the surface of the upper plate to the back surface of the lower plate. As a result, the plating layer located between the overlapping plates and the plating layer on the back surface of the lower plate vaporize, and the vaporized plating components can be removed through the first through-hole. Furthermore, by irradiating the molten pool, which has been backfilled with the first through-hole, with the rear laser beam, a second through-hole is created. If any plating components remain when the main laser beam group is irradiated, the remaining plating components can be removed through the second through-hole. Therefore, the occurrence of porosity due to vaporized plating components between the stacked metal-plated steel sheets can be suppressed. Therefore, it becomes easier to perform continuous laser welding on the joints of welded products made by overlapping and joining multiple metal-plated steel sheets, which can improve the strength of the welded product.

[0064] According to the second invention, the preceding laser beam group is irradiated onto the surface of the upper plate in front of the main laser beam group. The output of the preceding laser beam group is set to be weaker than that of the main laser beam group, so that the upper plate is melted to a depth where the irradiation does not reach the back surface from the front surface, and the plating layer on the surface of the upper plate can be vaporized and removed. Because there is a gap between the preceding laser beam group and the main laser beam group, the temperature of the part melted by the irradiation of the preceding laser beam group decreases while a moderate amount of heat remains, so that the overlapping part can be melted more efficiently when irradiated by the main laser beam group.

[0065] According to the third invention, multiple main melting beams are irradiated onto a central spot and auxiliary spots arranged around the central spot. By irradiating the auxiliary spots with the main melting beams, the melting of the central spot is assisted by heat conduction. This makes it possible to melt overlapping areas more efficiently when irradiating with the main laser beam group.

[0066] According to the fourth invention, the irradiation area of ​​the rear laser beam is set to be smaller than the irradiation area of ​​the main laser beam group, and the rear laser beam is irradiated with a lower output than the total output of the main laser beam group. Since the molten pool generated by the main laser beam group narrows toward the rear in the direction of laser beam propagation, the irradiation area of ​​the rear laser beam is set to be smaller. Therefore, plating components can be removed more efficiently in the laser welding process.

[0067] According to the fifth invention, multiple laser beams obtained by a diffractive optical element are irradiated onto the surface of the upper plate of an overlapping section formed by stacking multiple metal-plated steel sheets. When the surface plating layer removal beam of the main laser beam group is irradiated, the upper plate melts to a depth that does not reach the back surface. In addition, the plating layer on the surface of the upper plate vaporizes, and the vaporized plating components can be removed. Furthermore, by irradiating with the main melting beam positioned behind the surface plating layer removal beam, a first through-hole is created that penetrates from the surface of the upper plate to the back surface of the lower plate. As a result, the plating layer located between the overlapping plates and the plating layer on the back surface of the lower plate vaporize, and the vaporized plating components can be removed through the first through-hole. Furthermore, by irradiating the molten pool, which has been backfilled with the first through-hole, with the rear laser beam, a second through-hole is created. If any plating components remain when the main laser beam group is irradiated, the remaining plating components can be removed through the second through-hole. Therefore, the occurrence of porosity due to vaporized plating components between the stacked metal-plated steel sheets can be suppressed. Therefore, it becomes easier to perform continuous laser welding on the welded portion of a component that is joined by overlapping multiple metal-plated steel sheets, which can improve the strength of the component. [Explanation of symbols]

[0068] 2 Top board 3 Lower plate 5. Zinc plating layer (metal plating layer) 6. Overlapping parts 7a Melting pool 7b Melting pool 10 Laser device 11. Laser Oscillator 12 Scanners 13 Diffractive optical elements 15 Multiple laser beams 20 Leading laser beam group 21. Pre-zinc removal beam (pre-plating layer removal beam) 22 Pre-molten beam 24 Prior Spot Area 25 Pre-zinc removal spots 26 Pre-melted spots 27 Auxiliary Spot 28 Pre-drilled holes 29 Pre-molten portion 30 Major Laser Beam Groups 31. Zinc removal beam (surface plating layer removal beam) 32. Main molten beams 34 Major Spot Areas 35 Zinc removal spots 36. Main melting spots (central spots) 37 Auxiliary Spot 38 First through hole 40 Rear laser beam 42 Rear spot area 43 Second through hole

Claims

1. A method for manufacturing a welded product, which includes a welding step of irradiating the surface of the upper plate of an overlapping portion formed by stacking multiple metal-plated steel plates with multiple laser beams obtained from a diffractive optical element, thereby joining the overlapping portion from the upper plate to the lower plate, The plurality of laser beams comprises a main laser beam group in which a plurality of irradiation spots are arranged on the forward side in the direction of propagation of the plurality of laser beams, and a rear laser beam in which one irradiation spot is arranged at a distance behind the main laser beam group in the direction of propagation. The aforementioned main laser beam group is A surface plating layer removal beam is irradiated with an output that melts the plating layer on the surface of the upper plate to a depth that does not reach the back surface of the upper plate, in order to remove the plating layer on the surface of the upper plate. After irradiation with the surface plating layer removal beam, the system has a main melting beam that is irradiated onto the melt pool melted by the surface plating layer removal beam with an output that melts from the surface of the upper plate to the back surface of the lower plate, thereby generating a first through-hole that penetrates to the back surface of the lower plate. The aforementioned rear laser beam, A method for manufacturing a welded product, comprising irradiating the molten pool, in which the first through-hole has been backfilled, with a lower output than the main laser beam group to generate a second through-hole that penetrates to the back surface of the lower plate.

2. A method for manufacturing a welded product according to claim 1, The plurality of laser beams includes a group of preceding laser beams in which multiple irradiation spots are arranged at intervals ahead of the main group of laser beams in the direction of propagation. The preceding group of laser beams is A pre-plating layer removal beam is irradiated with a lower output than the surface plating layer removal beam and melts the plating layer on the surface of the upper plate, A method for manufacturing a welded product, comprising: a pre-melting beam that is irradiated with a lower output than the main melting beam after irradiation with the pre-plating layer removal beam, and which generates pre-holes that are melted to a depth that does not reach the back surface of the upper plate.

3. A method for manufacturing a welded product according to claim 1 or claim 2, The aforementioned main laser beam group has multiple main melting beams, A method for manufacturing a welded product, wherein the main melting beam is irradiated onto a central spot where the first through-hole is formed, and onto a plurality of auxiliary spots arranged around the central spot to assist in the melting of the central spot by heat conduction.

4. A method for manufacturing a welded product according to claim 3, A method for manufacturing welded products, wherein the rear laser beam has an irradiation area smaller than the irradiation area of ​​the main laser beam group and is irradiated with an output weaker than the total output of the main laser beam group.

5. A laser welding method in which multiple laser beams obtained by a diffractive optical element are irradiated onto the surface of the upper plate of an overlapping portion formed by stacking multiple metal-plated steel plates, thereby joining the overlapping portion from the upper plate to the lower plate, The plurality of laser beams comprises a main laser beam group in which a plurality of irradiation spots are arranged on the forward side in the direction of propagation of the plurality of laser beams, and a rear laser beam in which one irradiation spot is arranged at a distance behind the main laser beam group in the direction of propagation. The aforementioned main laser beam group is A surface plating layer removal beam is irradiated with an output that melts the plating layer on the surface of the upper plate to a depth that does not reach the back surface of the upper plate, in order to remove the plating layer on the surface of the upper plate. After irradiation with the surface plating layer removal beam, the system has a main melting beam that is irradiated onto the melt pool melted by the surface plating layer removal beam with an output that melts from the surface of the upper plate to the back surface of the lower plate, thereby generating a first through-hole that penetrates to the back surface of the lower plate. The aforementioned rear laser beam, A laser welding method comprising irradiating the molten pool, in which the first through-hole has been backfilled, with a lower output than the main laser beam group to generate a second through-hole that penetrates to the back surface of the lower plate.

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