Laser welding method

Abstract

To provide a laser welding method in which poor welding caused by blow-off of steam of plated metal such as zinc can be reduced, without requiring cumbersome work.SOLUTION: A laser welding method, in which a plurality of plated metal plates plated with metal which is lower in melting point than a metal plate of a base material are overlapped and welded, includes: an overlapping step of overlapping the plurality of plated metal plates; a plated layer evaporating step of emitting laser light for removing plating to weld regions on surfaces of the plated metal plates on a top layer overlapped in the overlapping step and evaporating a plated layer between the overlapped plated metal plates, by making the laser light for removing plating reach the plated metal plate on a bottom layer; and a welding step of emitting laser light for main welding which is larger in condensing diameter than the laser light for removing plating to the weld region after the plated layer evaporating step, and welding the plurality of plated metal plates by melting the metal plate of the base material.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to laser welding methods. [Background technology]

[0002] A galvanized steel sheet is a steel sheet material in which the surface of a steel sheet, which is a base metal sheet, is plated with zinc for rust prevention, and is widely used, for example, as a structural material for automobile bodies, etc. As described in Patent Document 1, a laser welding method is known in which two galvanized steel sheets are overlapped and a laser beam is irradiated to the overlapping portion to melt and bond the steel sheet materials.

[0003] It is known that when performing the above-mentioned laser welding, welding defects occur due to the fact that the boiling point of zinc (approximately 900°C) is lower than the melting point of steel sheets (iron) (approximately 1500°C). In other words, when the overlapping parts are irradiated with laser light, the steel sheets melt, and at this time, the zinc on the overlapping surface is gasified. The zinc gas then passes through the molten steel sheets and tries to escape to the outside. As a result, part of the molten steel sheet is blown away, or part of the zinc gas remains inside the steel sheet, forming pores called blowholes, which deteriorate the welding strength and deteriorate the appearance.

[0004] In order to prevent such welding defects, the laser welding method described in Patent Document 1 intentionally shifts the focal position of the laser beam from the surface of the zinc-plated steel sheet when irradiating the sheet. By shifting the focal position of the laser beam, the area of ​​the molten pool formed by melting the base metal increases, and the plating metal gas can be stably released to the outside through the molten pool at low pressure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-115836 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above method requires a complicated adjustment process of shifting the focal position of the laser above or below the surface of the metal plate. A technology that can reduce welding defects caused by the blowing out of vapor of the plating metal such as zinc without requiring complicated adjustment process is desired. [Means for solving the problem]

[0007] The present disclosure can be realized in the following forms. [Mode 1] A laser welding method for overlapping and welding multiple metal-plated sheets, each plated with a metal having a lower melting point than a base metal sheet, comprising: a superposing step of overlapping the multiple metal-plated sheets; a plating layer evaporation step of irradiating a welding area on the surface of the topmost metal-plated sheet overlapped in the superposing step with a laser light for plating removal and allowing the laser light for plating removal to reach the bottommost metal-plated sheet to evaporate the plating layer between the overlapped metal-plated sheets; and a joining step of irradiating the welding area with a laser light for main welding, which has a larger focused diameter than the laser light for plating removal, after the plating layer evaporation step, to melt the base metal sheet and join the multiple metal-plated sheets, wherein in the plating layer evaporation step, the laser light for plating removal is irradiated to the welding area multiple times so as to sequentially form molten pools of an area smaller than the welding area in the welding area.

[0008] (1) According to one embodiment of the present disclosure, there is provided a laser welding method for overlapping and welding a plurality of metal-plated sheets, each plated with a metal having a melting point lower than that of a base metal sheet, the method including a superposing step of overlapping the plurality of metal-plated sheets, a plating layer evaporating step of irradiating a welding region on a surface of the topmost metal-plated sheet overlapped in the superposing step with a plating removal laser beam and allowing the plating removal laser beam to reach the bottommost metal-plated sheet to evaporate a plating layer between the overlapped metal-plated sheets, and a joining step of irradiating the welding region with a main welding laser beam having a larger focused diameter than the plating removal laser beam and melting the base metal sheet to join the plurality of metal-plated sheets after the plating layer evaporating step. According to this form of the laser welding method, in the plating layer evaporation step, a plating removal laser beam is irradiated onto the welding area on the surface of the uppermost metal-plated sheet, and the plating layer between each metal-plated sheet is evaporated and removed. Then, in the joining step, a main welding laser beam having a larger focused beam diameter than the plating removal laser beam is irradiated onto the welding area, and each metal-plated sheet is joined. In this manner, when the joining step as the main welding is performed, the plating layer between each metal-plated sheet at the portion corresponding to the melting area has been removed. Therefore, for example, without the need for a complicated adjustment operation such as intentionally shifting the focal position of the laser beam from the surface of the steel sheet, in the joining step, welding defects due to the blowing out of plating metal vapor can be reduced, and welding quality can be improved. (2) In the laser welding method of the above aspect, the plating removal laser light may be irradiated to the welding area multiple times in the plating layer evaporation step so that molten pools smaller than the welding area are successively formed in the welding area. According to the laser welding method of this aspect, the plating removal laser light is irradiated to the welding area multiple times in the plating layer evaporation step so that molten pools smaller than the welding area are successively formed in the welding area. This makes it possible to preferably prevent large pores from being generated due to the blowing out of plating metal vapor. (3) In the laser welding method of the above aspect, the molten pools successively formed in the welded region by irradiation with the plating removal laser light in the plating layer evaporation step may be spaced apart from each other during successive irradiations. According to the laser welding method of this aspect, in the plating layer evaporation step, the molten pools are spaced apart from each other during successive irradiations. Therefore, the molten pools in a molten state do not merge to form a large weld pool, and the generation of large pores due to the blowing out of plating metal vapor can be suitably avoided. (4) In the laser welding method of the above embodiment, the welding area may be circular, the molten pool formed by a single irradiation of the plating removal laser light may be circular and smaller than the welding area, and the diameter of the molten pool may be less than one-third and more than one-quarter of the diameter of the welding area. Generally, if the diameter of the molten pool is smaller than the diameter of the welded area, the occurrence of welding defects can be suppressed, but the welding cycle time will be longer. According to the laser welding method of the above embodiment, the diameter of the molten pool is less than or equal to one-third and more than one-quarter of the diameter of the welded area. By appropriately setting the diameter of the molten pool in this manner, it is possible to suppress welding defects and prevent the welding cycle time from becoming significantly longer. (5) In the laser welding method of the above aspect, the base metal sheet may be a steel sheet, and the metal of the plating layer may be zinc. According to the laser welding method of this aspect, in joining of zinc-plated steel sheets by laser welding, the zinc forming the plating layer can be suitably removed, and the welding quality can be improved. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a schematic configuration of a laser welding device used in a laser welding method according to a first embodiment of the present disclosure. [Diagram 2] 3 is a flowchart showing each step of a laser welding method according to a first embodiment of the present disclosure. [Diagram 3] 1A to 1C are schematic cross-sectional views for explaining steps of a laser welding method. [Figure 4] FIG. 11 is a schematic plan view for explaining a plating layer evaporation step. [Diagram 5] 1A to 1C are schematic cross-sectional views for explaining steps of a laser welding method. [Figure 6] FIG. 11 is a schematic plan view for explaining a bonding step. [Figure 7] FIG. 2 is a diagram illustrating the state of zinc removal from a galvanized steel sheet. [Figure 8] FIG. 2 is a diagram illustrating the state of zinc removal from a galvanized steel sheet. [Figure 9] FIG. 13 is a graph showing the incidence rate of welding defects and cycle time when the ratio of the diameter of the molten pool to the diameter of the welded area is changed. [Figure 10] FIG. 4 is a schematic plan view for explaining a plating layer evaporation step in the laser welding method according to the first embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A. First embodiment: A1. Configuration of the laser welding device 100: A laser welding method according to a first embodiment of the present disclosure will be described with reference to Fig. 1 to Fig. 9. First, the configuration of a laser welding device 100 used in the laser welding method according to the first embodiment will be described. Fig. 1 is a diagram showing a schematic configuration of a laser welding device 100 used in the laser welding method according to the first embodiment of the present disclosure.

[0011] As shown in Fig. 1, the laser welding apparatus 100 includes a laser oscillator 10 and a galvanometer scanner 20. The laser oscillator 10 is connected to the galvanometer scanner 20 by an optical fiber connector 11. A collimator lens 30 is disposed inside the galvanometer scanner 20. The galvanometer scanner 20 includes a first reflecting mirror 21, a diffractive optical element (DOE) 22, a Z lens 23, a Z lens driving unit 24, a second reflecting mirror 25, a condenser lens 26, a galvanometer scanner unit 27, a protective glass 28, and a galvanometer scanner driver 29. In addition, a return light detection device 50 is attached to the galvanometer scanner 20 together with a dichroic mirror 40.

[0012] When a laser beam is emitted from the laser oscillator 10, the laser beam enters the inside of the galvano scanner 20 via the optical fiber connector 11. The laser beam is then adjusted to a parallel state by the collimator lens 30. Thereafter, the laser beam is reflected by the dichroic mirror 40 and the first reflecting mirror 21, and reaches the DOE 22.

[0013] The DOE 22 can adjust the irradiation pattern of the laser light. Specifically, the DOE 22 can emit the incident laser light as a laser light having a power density distribution shape different from that at the time of the incident. The DOE 22 is attached to a sliding part and configured to be slidable.

[0014] The laser light adjusted by the DOE 22 reaches the Z lens 23. The Z lens 23 is used to correct the focus shift of the laser light. The Z lens 23 is configured to be movable by being driven by the Z lens drive unit 24.

[0015] Thereafter, the laser light is reflected by the second reflecting mirror 25, passes through the condenser lens 26, enters the galvano scanner unit 27, and is emitted onto the surface of the workpiece 200 through the protective glass .

[0016] The galvano scanner driver 29 is connected to the laser oscillator 10, the Z lens drive unit 24, and the galvano scanner unit 27, and is configured to be able to control these by a built-in program. Therefore, the galvano scanner driver 29 can control the output of the laser light, the irradiation position, the focused diameter, etc. Since this control is possible, the laser welding apparatus 100 is configured to be able to perform automatic program operation.

[0017] The return light detector 50 detects light (hereinafter referred to as "return light") that is generated and returned from the processing point I when the processing point I becomes so hot that it exceeds 1000°C when the metal is melted during laser irradiation. As shown by the dashed line RL in FIG. 1, the return light passes through the second reflecting mirror 25, the first reflecting mirror 21, the dichroic mirror 40, etc. as appropriate, and enters the return light detector 50. The return light detector 50 detects light in a predetermined frequency band (e.g., 800 nm to 1000 nm, etc.) that is selected in advance based on the type of laser light, etc., and converts the light intensity into a voltage value. The return light detector 50 can obtain the change in the voltage value over time as a waveform of the light intensity.

[0018] The configuration of the laser welding apparatus 100 described above is merely one example, and the laser welding apparatus 100 may have other configurations as long as it is capable of carrying out the laser welding method according to this embodiment described below.

[0019] A2. Laser welding method: Next, a laser welding method according to a first embodiment of the present disclosure using the laser welding apparatus 100 will be described. In the first embodiment, three galvanized steel sheets are laser welded as the multiple metal sheets. FIG. 2 is a flowchart showing each step of the laser welding method according to the first embodiment of the present disclosure. As shown in FIG. 2, the laser welding method includes a laminating step (S101), a plating layer evaporation step (S102), and a joining step (S103), and these steps (S101, S102, S103) are performed in order.

[0020] Fig. 3 is a cross-sectional schematic diagram for explaining the steps of the laser welding method, and is a diagram for explaining the overlapping step (S101) and the plating layer evaporation step (S102). As shown in Fig. 3, in the laser welding method of the first embodiment, three zinc-plated steel sheets 61, 62, and 63 are used as the multiple metal sheets, and these zinc-plated steel sheets 61, 62, and 63 are joined by laser welding.

[0021] In the overlapping step (S101), three galvanized steel sheets 61, 62, 63 are overlapped. At this time, each galvanized steel sheet 61, 62, 63 is pressed from above and below with a fixing jig (not shown) so that there is no gap between the galvanized steel sheets 61, 62, 63 and they are placed on a processing table (not shown) provided in the laser welding device 100. In the state where they are placed on the processing table, they are arranged in order from the top, as the top layer galvanized steel sheet 61, the middle galvanized steel sheet 62, and the bottom layer galvanized steel sheet 63. Each of the galvanized steel sheets 61, 62, 63 has a plating layer 65 plated with zinc having a lower melting point than the steel sheet 64 on the front and back surfaces of the steel sheet 64 as the base metal sheet.

[0022] As shown in Fig. 3, in the plating layer evaporating step (S102), a plating removing laser beam R1 (hereinafter also simply referred to as "plating removing laser beam R1") is spot irradiated onto a welding region W1 on the surface of the topmost zinc-plated steel sheet 61, and the plating removing laser beam R1 reaches the bottommost zinc-plated steel sheet 63 to evaporate the plating layer 65. In Fig. 3, the portion through which the plating removing laser beam R1 passes is indicated by cross-hatching.

[0023] Fig. 4 is a schematic plan view for explaining the coating layer evaporation step (S102), showing a view of the welding area W1 on the surface of the uppermost zinc-plated steel sheet 61 as viewed from above. As shown in Fig. 4, the welding area W1 is circular. In the coating layer evaporation step (S102), the plating removal laser light R1 is irradiated to the welding area W1 multiple times (nine times in this embodiment) so that circular molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 smaller than the welding area W1 are formed sequentially in the welding area W1. The diameter D1 of each molten pool 71, 72, 73, 74, 75, 76, 77, 78, 79 is approximately 1 / 3 or less and greater than 1 / 4 of the diameter D2 of the welding area W1.

[0024] Next, the order of irradiation of the plating removal laser light R1 in the welding area W1 will be described. In Fig. 4, the numbers written in the areas of each molten pool 71, 72, 73, 74, 75, 76, 77, 78, 79 indicate the order of irradiation. Here, the molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 formed by each irradiation are referred to as the first molten pool 71, the second molten pool 72, the third molten pool 73, the fourth molten pool 74, the fifth molten pool 75, the sixth molten pool 76, the seventh molten pool 77, the eighth molten pool 78, and the ninth molten pool 79, in accordance with the order of irradiation.

[0025] In this embodiment, the plating removal laser light R1 is first irradiated once onto the center position of the welding area W1 to form a first molten pool 71. Next, when the outer periphery of the first molten pool 71 in the welding area W1 is divided into eight parts approximately equally in the circumferential direction in a plan view, the plating removal laser light R1 is irradiated onto the part located at the upper left of the first molten pool 71 to form a second molten pool 72. Next, the plating removal laser light R1 is irradiated onto the part located at the lower right of the first molten pool 71 to form a third molten pool 73. At this time, the first molten pool 71, the second molten pool 72, and the third molten pool 73 are spaced apart from each other.

[0026] Similarly, the first molten pool 71 is irradiated successively from the upper right, lower left, directly above, right, left, and directly below, thereby forming the fourth molten pool 74 to the ninth molten pool 79. The reason for using this irradiation order is to prevent the formation of continuous molten pools in successive irradiations.

[0027] By irradiating the plating removal laser light R1 in the above irradiation order, molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 are successively formed in the welding area W1, and are spaced apart from one another during successive irradiations. More specifically, the first molten pool 71 is spaced apart from the second molten pool 72, and the second molten pool 72 is spaced apart from the third molten pool 73. Similarly, the third molten pool 73 is spaced apart from the fourth molten pool 74, the fourth molten pool 74 is spaced apart from the fifth molten pool 75, the fifth molten pool 75 is spaced apart from the sixth molten pool 76, the sixth molten pool 76 is spaced apart from the seventh molten pool 77, the seventh molten pool 77 is spaced apart from the eighth molten pool 78, and the eighth molten pool 78 is spaced apart from the ninth molten pool 79.

[0028] If successively irradiated regions are close to each other and a molten pool is formed by the next irradiation before the molten pool by the first irradiation has completely solidified, the adjacent molten pools will be continuous in a molten state, forming a large molten pool. If a large molten pool is formed, a large hole will be created and there will be less iron, so that there will be insufficient iron during the joining process (S103) as the main welding described below, and a recess will be formed on the joining surface, causing a defect. Therefore, in this embodiment, the molten pools formed by successive irradiations are irradiated in an order that separates them from each other, thereby avoiding the above-mentioned defects on the joining surface.

[0029] When nine irradiations are performed in the above irradiation order, about 90% of the welding area W1 is covered by the molten pools 71, 72, 73, 74, 75, 76, 77, 78, and 79. In this case, the "area filling rate", which is the ratio of the total area of ​​the molten pools 71, 72, 73, 74, 75, 76, 77, 78, and 79 to the welding area W1, is preferably 70% or more. This is because a high area filling rate ensures that the plating layer 65 corresponding to the welding area W1 can be evaporated reliably. In this embodiment, the area filling rate is about 90%, and the plating layer 65 in the welding area W1 can be suitably removed.

[0030] The coating layer evaporation process (S102) evaporates and removes the coating layer 65 on the upper surface of the topmost zinc-plated steel sheet 61, the coating layer 65 between the topmost zinc-plated steel sheet 61 and the intermediate zinc-plated steel sheet 62, and the coating layer 65 between the intermediate zinc-plated steel sheet 62 and the bottommost zinc-plated steel sheet 63.

[0031] 3, the plating removal laser light R1 penetrates the lowermost zinc-plated steel sheet 63, but it is sufficient that the plating removal laser light R1 reaches the lowermost zinc-plated steel sheet 63, and does not necessarily have to reach the plating layer 65 on the lower surface of the lowermost zinc-plated steel sheet 63. The laser output of the plating removal laser light R1 is set appropriately.

[0032] FIG. 5 is a schematic cross-sectional view for explaining the steps of the laser welding method, and is a diagram for explaining the joining step (S103). In the joining step (S103), a laser beam for main welding (hereinafter also simply referred to as "main welding laser beam R2") is irradiated to the welding area W1 to melt the base metal plate and join the zinc-plated steel sheets 61, 62, and 63. The focused beam diameter C2 of the main welding laser beam R2 is adjusted to be larger than the focused beam diameter C1 of the plating removal laser beam R1. The laser output of the main welding laser beam R2 is appropriately set to be approximately the same as the laser output of the plating removal laser beam R1. In FIG. 5, the portion through which the main welding laser beam R2 passes is illustrated by cross-hatching.

[0033] Fig. 6 is a schematic plan view for explaining the joining step (S103), showing a welded region W1 on the surface of the uppermost zinc-plated steel sheet 61 as viewed from above. As shown in Figs. 5 and 6, the focused diameter C2 of the main welding laser beam R2 is larger than the focused diameter C1 of the plating removal laser beam R1, and as a result, the diameter D3 of one molten pool 81 formed in the joining step (S103) as main welding is larger than the diameter D1 of each of the molten pools 71, 72, 73, 74, 75, 76, 77, 78, and 79 formed in the plating layer evaporation step (S102). In the joining step (S103), as shown by the arrow A in Fig. 6, the main welding laser beam R2 is irradiated multiple times, for example, counterclockwise, so as to cover the entire welding region W1.

[0034] In this joining process (S103), since the plating layer 65 between each of the zinc-plated steel sheets 61, 62, 63 corresponding to the welding area W1 has been removed in the plating layer evaporation process (S102), even if welding is performed with a focused beam diameter C2 larger than the focused beam diameter C1 of the plating removal laser light R1, no zinc gas is generated and no air holes called blowholes are formed.

[0035] [effect] (1) In the laser welding method of the first embodiment described above, in the plating layer evaporation process (S102), the plating layer 65 between each of the zinc-plated steel sheets 61, 62, 63 is removed, and then in the joining process (S103), a main welding laser beam R2 having a larger focused diameter than the plating removal laser beam R1 is irradiated onto the welding area W1 to join each of the zinc-plated steel sheets 61, 62, 63.

[0036] Fig. 7 is a diagram for explaining the state of zinc removal from the zinc-plated steel sheets 61, 62, 63, and shows a photograph of the intermediate zinc-plated steel sheet 62 viewed from below after the plating layer evaporating step (S102) in the above-mentioned laser welding method. Fig. 8 is a diagram for explaining the state of zinc removal from the zinc-plated steel sheets, and shows a photograph of the bottom-most zinc-plated steel sheet 63 viewed from above after the plating layer evaporating step (S102) in the above-mentioned laser welding method. As shown in Figs. 7 and 8, the zinc-plated layer 65 has been removed in a region obtained by extending the welding region W1 in the irradiation direction (hereinafter referred to as "region W2 corresponding to the melting region W1").

[0037] In this way, when the joining step (S103) as the main welding is performed, the zinc plating layer 65 is removed from the portion W2 corresponding to the molten region W1. Therefore, for example, it is possible to reduce welding defects caused by the blowing out of plating metal vapor in the joining step (S103) without requiring a complicated adjustment operation such as intentionally shifting the focal position of the laser light upward or downward from the surface of the steel sheet as has been conventionally performed.

[0038] In addition, the plating layer evaporation step (S102) and the joining step (S103) as main welding can be performed in the same facility using the same laser welding apparatus 100. Therefore, compared to a method in which a process using a facility other than the main welding, such as plasma jet heating or welding with a laser torch, is performed in advance to remove the zinc plating layer 65, the facility cost and process space can be reduced, and production efficiency can be improved.

[0039] (2) In the laser welding method of the first embodiment, in the plating layer evaporating step (S102), the plating removal laser beam R1 is irradiated to the welding area W1 multiple times in such a way that successively formed molten pools are spaced apart from each other, and molten pools having areas smaller than the welding area W1 are successively formed within the welding area W1. This makes it possible to remove the zinc plating layer 65 while avoiding the generation of large pores due to the blowing out of zinc vapor, and improves the welding quality in the joining step (S103).

[0040] (3) The diameter D1 of each molten pool 71, 72, 73, 74, 75, 76, 77, 78, 79 is approximately equal to or smaller than 1 / 3 and larger than 1 / 4 of the diameter D2 of the welding area W1. Fig. 9 is a graph showing the incidence of welding defects and the time (cycle time) required for the coating layer evaporation step (S102) when the ratio L [(diameter D1 of molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79) / (diameter D2 of welding area W1)] of the diameter of the molten pool by the plating removal laser beam R1 to the diameter of the welding area W1 is changed. The horizontal axis shows the ratio L, and the vertical axis shows the incidence of welding defects and the welding cycle time. As shown in Fig. 9, the smaller the ratio L, the lower the defect rate, while the longer the cycle time. The applicant's investigation has revealed that a ratio L of 1 / 3 or less and greater than 1 / 4 is appropriate in terms of the balance between the defect rate and the cycle time.

[0041] In the laser welding method of the first embodiment, the ratio L is 1 / 3 or less and greater than 1 / 4, so that the defective rate of the joined product can be appropriately improved and the cycle time is not unnecessarily extended, allowing laser welding to be performed suitably.

[0042] (4) In the second embodiment, the area filling rate of the molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 relative to the welding area W1 is high at about 90%, so that the zinc plating layer 65 can be removed more reliably, thereby improving welding defects.

[0043] B. Second embodiment: Next, a laser welding method according to a second embodiment of the present disclosure will be described with reference to Fig. 10. Fig. 10 is a schematic plan view for explaining the plating layer evaporation step (S102) in the laser welding method according to the first embodiment of the present disclosure. Note that the same reference numerals are used for configurations that are substantially similar to those in the first embodiment, and descriptions thereof will be omitted. In the laser welding method according to the second embodiment, the sizes of molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 formed by irradiation of plating removal laser light R1 in the plating layer evaporation step (S102) are different from those in the laser welding method according to the first embodiment.

[0044] The diameters of the first molten pool 71 to the fifth molten pool 75 are the same as in the first embodiment. The diameter D4 of the sixth molten pool 76 to the ninth molten pool 79 is larger than the diameter D1 of the first molten pool 71 to the fifth molten pool 75, and is larger than 1 / 3 and smaller than 1 / 2 of the diameter D2 of the welding area W1. The order of irradiation is the same as in the first embodiment.

[0045] The laser welding method of the second embodiment can achieve the same effects as those of the first embodiment. Furthermore, by making the diameter D4 of the molten pools 75-79 in the latter irradiation order (6-9) larger than the diameter D1 of the molten pools 71-75 in the first irradiation order (1-5), the area filling rate of the welded region W1 can be reliably increased.

[0046] As in the second embodiment, the size of each molten pool 71, 72, 73, 74, 75, 76, 77, 78, 79 can be changed as appropriate. In the molten pools in which irradiation is performed in succession, the diameter size and irradiation order can be changed as appropriate so long as the molten pools do not overlap each other and have a sufficient area filling rate for the welding region W1.

[0047] C. Other embodiments: (C1) In the laser welding method of each of the above embodiments, laser welding is performed on three zinc-plated steel sheets 61, 62, 63 in a stacked state, but the method can also be applied to the case where laser welding is performed on two or more zinc-plated steel sheets in a stacked state.

[0048] (C2) The metal-plated sheet to be laser-welded is not limited to the zinc-plated steel sheets 61, 62, 63, but may be a metal-plated sheet obtained by plating the surface of a steel sheet with a metal having a boiling point lower than the melting point of the steel sheet, such as aluminum or tin. The material of the base metal sheet is not limited to iron, and may be, for example, an alloy of iron and other elements.

[0049] (C3) In the laser welding methods of the above embodiments, the welded area W1 is circular, but may be other shapes. For example, it may be rectangular. In addition, although point laser irradiation is performed to form spot-shaped weld marks, line laser irradiation may be performed to form linear weld marks. In addition, a circular molten pool may be formed by line laser irradiation.

[0050] (C4) In the laser welding method of each of the above embodiments, in the coating layer evaporation step (S102), the plating removal laser light R1 is irradiated multiple times to sequentially form circular molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 smaller than the welding area W1, but they may be formed by a single irradiation. Also, the molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 do not have to be circular.

[0051] (C5) In the laser welding method of each of the above embodiments, the molten pools 71, 72, 73, 74, 75, 76, 77, 78, 79 successively formed in the welding area W1 in the coating layer evaporation step (S102) are spaced apart from one another during successive irradiations, but they do not have to be spaced apart. It is sufficient that each molten pool 71, 72, 73, 74, 75, 76, 77, 78, 79 is sufficiently small so that no welding defects due to zinc vapor occur even if the molten pools are continuous during successive irradiations.

[0052] The present disclosure is not limited to the above-mentioned embodiments, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in each embodiment corresponding to the technical features in each form described in the Summary of the Invention column can be appropriately replaced or combined in order to solve some or all of the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0053] 10...laser oscillator, 11...optical fiber connector, 20...galvanometer scanner, 21...first reflecting mirror, 23...Z lens, 24...Z lens driving unit, 25...second reflecting mirror, 26...condensing lens, 27...galvanometer scanner unit, 28...protective glass, 29...galvanometer scanner driver, 30...collimating lens, 40...dichroic mirror, 50...photodetector, 61...top layer zinc-plated steel sheet, 62...intermediate zinc-plated steel sheet, 63...top Lower layer zinc-plated steel sheet, 64...steel sheet, 65...zinc-plated layer, 71...first molten pool, 72...second molten pool, 73...third molten pool, 74...fourth molten pool, 75...fifth molten pool, 76...sixth molten pool, 77...seventh molten pool, 78...eighth molten pool, 79...ninth molten pool, 100...laser welding device, 200...workpiece, C1...focused beam diameter, C2...focused beam diameter, I...processing point, R1...plating removal laser beam, R2...main welding laser beam, W1...welding area, W2...area corresponding to welding area

Claims

1. A laser welding method for overlapping and welding a plurality of metal-plated plates each plated with a metal having a lower melting point than a base metal plate, comprising: a stacking step of stacking the plurality of metal-plated plates; a plating layer evaporation process in which a plating removal laser light is irradiated onto a welding region on the surface of the uppermost metal-plated sheet overlapped in the overlapping process, and the plating removal laser light is caused to reach the lowermost metal-plated sheet, thereby evaporating the plating layer between the overlapped metal-plated sheets; a joining step of irradiating the welding area with a laser beam for main welding having a larger focused diameter than the laser beam for plating removal after the plating layer evaporation step, thereby melting the base metal plate and joining the plurality of metal-plated plates; having a laser welding method in which, in the plating layer evaporation step, the plating removal laser light is irradiated onto the welding area a plurality of times so as to sequentially form molten pools in the welding area each having an area smaller than the welding area.

2. 2. The laser welding method according to claim 1, wherein in the plating layer evaporation process, the molten pools successively formed in the welding area by irradiating the plating removal laser light are spaced apart from each other during successive irradiation.

3. The weld area is circular; The molten pool formed by one irradiation of the plating removal laser light has a circular shape smaller than the welding area, 3. The laser welding method according to claim 1, wherein the diameter of the molten pool is less than or equal to one-third and more than one-quarter of the diameter of the welded area.

4. 3. The laser welding method according to claim 1, wherein the base metal plate is a steel plate, and the metal of the plating layer is zinc.

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