Method of manufacturing laser-welded joint and laser-welded joint

Abstract

To provide a method of manufacturing a laser-welded joint, the method enabling suppression of deformation of a steel plate occurring when removing a plated layer on the surface of the steel plate and, thereby enabling prevention of the generation of blow hole.SOLUTION: A manufacturing method of a laser-welded joint includes a removal process of removing plated layers by applying laser beams 12 to plated layers of a first region 1a on a first steel plate 1 and plated layers of a second region on a second steel plate 2. In the removal process, when WA (mm) denotes a length in crosswise direction in a removal region in which the plated layer are removed by applying laser beams 12, and t (mm) denotes a plate thickness in the removal region, the laser beams 12 are applied in such a manner that the width WA becomes a value WC or less calculated by the formula (1). Thereafter, the first region 1a and the second region are oppositely arranged and, in a joining process, the laser welding is performed in such a manner that the welded metal is formed in a range inside the removal region. The equation (1):WC=0.70 t6-0.37 t3+6.00.SELECTED DRAWING: Figure 1A

Description

[Technical field]

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

[0002] Zinc-based plated steel sheets are widely used for automobile parts and the like. Examples of methods for joining zinc-based plated steel sheets include lap welding by laser welding. When joining zinc-based plated steel sheets by laser welding, if laser welding is performed in an area where a zinc-based plating layer exists, zinc vaporizes and blowholes occur in the weld metal.

[0003] One effective method for reducing the occurrence of blowholes is to provide a gap between steel sheets (hereafter referred to as the "gap"). However, because the molten part in laser welding is small, a large gap can make the welding unstable. Furthermore, controlling this gap at the production site requires advanced technology and highly accurate tools. For this reason, a technology has been put into practical use in which the plating layer of the steel sheet is removed in advance using laser light, before welding.

[0004] For example, Patent Document 1 describes a method of removing residues after component processing using a laser beam, while Patent Document 2 proposes a laser welding device that irradiates a laser beam onto the surface of a region to be welded of a conductor and controls the removal of the coating on the surface of the region to be welded. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-275889 A [Patent Document 2] JP 2010-253492 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when attempting to remove the plating layer of a zinc-based plated steel sheet by irradiating it with a laser beam, the steel sheet may be deformed by the irradiation of the laser beam. Furthermore, in order to remove the plating layer by the laser beam while suppressing deformation of the steel sheet, a dedicated laser processing machine (a single-mode laser capable of femtosecond to nanosecond pulse oscillation) is required, and therefore the introduction of expensive equipment is required.

[0007] The present invention has been made in consideration of such problems, and has an object to provide a method for manufacturing a laser welded joint that can suppress deformation of a steel sheet when removing a plating layer from the surface of the steel sheet without using a specific laser processing machine, thereby preventing the occurrence of blowholes during welding without leaving a sheet gap, and a laser welded joint manufactured by this manufacturing method. [Means for solving the problem]

[0008] The above object of the present invention is achieved by the following configuration [1] relating to a method for manufacturing a laser welded joint.

[0009] [1] A method for manufacturing a laser welded joint, comprising: an arrangement step of arranging a first region of a first steel plate and a second region of a second steel plate so as to face each other and overlap; and a joining step of joining the first steel plate and the second steel plate by laser welding, At least one of the first steel sheet and the second steel sheet has a zinc-based plating layer, a removing step, prior to the arranging step, of irradiating the zinc-based plating layer in the first region and the second region with a laser beam to remove the zinc-based plating layer in the first region and the second region; In the removing step, the length in the short direction of the removal area from which the zinc-based plating layer is removed is defined as a width W A (mm), and the plate thickness in the removal area is t (mm), A is the value W calculated by the following formula (1) C The laser light is irradiated so as to satisfy the following: A method for manufacturing a laser welded joint, characterized in that, in the joining step, laser welding is performed so that a weld metal is formed in an area inside the removal area. Formula (1): W C =0.70t 6 -0.37t 3 +6.00

[0010] Further, preferred embodiments of the present invention relating to a method for producing a laser welded joint relate to the following [2] to [5].

[0011] [2] The method for manufacturing a laser welded joint described in [1], characterized in that in the removal step, the laser light is irradiated using a multimode laser.

[0012] [3] A method for manufacturing a laser welded joint as described in [1] or [2], characterized in that in the removal process, the laser light is oscillated continuously.

[0013] [4] A method for manufacturing a laser welded joint described in any one of [1] to [3], characterized in that in the removal process, a plurality of the removal areas are formed, and the distance between adjacent removal areas is 5 mm or more.

[0014] [5] The method for producing a laser welded joint according to any one of [1] to [4], wherein in the removing step, the laser light is irradiated while performing a wobbling or weaving scan.

[0015] The above object of the present invention is achieved by the following configuration [6] relating to a laser welded joint.

[0016] [6] A laser welded joint manufactured by the manufacturing method according to any one of [1] to [5], the first steel plate and the second steel plate are arranged in a stacked manner such that the first region of the first steel plate not having the zinc-based plating layer faces the second region of the second steel plate not having the zinc-based plating layer; The weld metal is formed in a region where the first region and the second region are overlapped, The length in the short direction of the removed area from which the zinc-based plating layer has been removed is defined as width W A (mm), and the plate thickness in the removal area is t (mm), A is the value W calculated by the following formula (1) C 1. A laser welded joint, characterized in that: Formula (1): W C =0.70t 6 -0.37t 3 +6.00 Effect of the Invention

[0017] According to the present invention, it is possible to provide a method for manufacturing a laser welded joint that can suppress deformation of a steel sheet when removing a plating layer from the surface of the steel sheet without using a specific laser processing machine, thereby preventing the occurrence of blowholes during welding without creating a sheet gap, and a laser welded joint manufactured by this manufacturing method. [Brief description of the drawings]

[0018] [Figure 1A] FIG. 1A is a diagram showing a method for manufacturing a laser welded joint according to an embodiment of the present invention, and is a perspective view showing a removal step. [Figure 1B] FIG. 1B is a diagram illustrating a method for producing a laser welded joint according to an embodiment of the present invention, and is a perspective view illustrating a steel sheet from which a zinc-based plating layer has been removed by a removing step. [Figure 1C] FIG. 1C is a diagram showing a method for manufacturing a laser welded joint according to an embodiment of the present invention, and is a perspective view showing an arrangement step. [Figure 1D] FIG. 1D is a diagram showing a method for manufacturing a laser welded joint according to an embodiment of the present invention, and is a perspective view showing a joining step. [Diagram 2] FIG. 2 is a photograph, substituted for a drawing, showing a cross section of a laser welded joint produced by a production method according to an embodiment of the present invention. [Diagram 3]FIG. 3 is a graph showing the relationship between the cube of the plate thickness t in the removal region and the value WC obtained by formula (1). [Figure 4] FIG. 4 is a perspective view showing a steel plate on which a plurality of removed regions are formed. [Diagram 5] FIG. 5 is a schematic diagram showing a method for evaluating the deformation amount of a steel plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present inventors have conducted extensive research into a method for suppressing deformation of a steel sheet when removing a plating layer from a zinc-based plated steel sheet by irradiating the steel sheet with a laser beam. As a result, the present inventors have found that the above-mentioned problems can be solved by controlling the relationship between the width of the region irradiated with the laser beam and the thickness of the steel sheet irradiated with the laser beam. The present invention has been made based on these findings.

[0020] Hereinafter, a method for manufacturing a laser welded joint according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be modified as desired without departing from the gist of the present invention. In addition, in this specification, a zinc-based plated steel sheet may simply be referred to as a plated steel sheet or a steel sheet, and a zinc-based plated layer may simply be referred to as a plated layer.

[0021] [Method of manufacturing laser welded joints] 1A to 1D are perspective views showing a process sequence of a method for manufacturing a laser welded joint according to an embodiment of the present invention. Also, Fig. 2 is a photograph, used as a substitute for a drawing, showing a cross section of a laser welded joint manufactured by the manufacturing method according to an embodiment of the present invention. In this embodiment, a laser welded joint obtained by joining a first steel sheet 1 and a second steel sheet 2 is described, and both the first steel sheet 1 and the second steel sheet 2 are zinc-based plated steel sheets having a zinc-based plated layer.

[0022] <Removal process> The removal step is performed before the arrangement step described later. First, as shown in FIG. 1A, the zinc-based plating layer in the first region 1a, which is a region to be welded on the surface of the first steel sheet 1, and the zinc-based plating layer in the second region, which is a region to be welded on the surface of the second steel sheet 2 (see FIG. 1C), are irradiated with a laser beam 12. As a result, the zinc-based plating layer in the first region 1a and the second region is removed. As an apparatus for irradiating the laser beam 12, for example, a galvano scanner 11 for a multimode laser can be used, and the irradiation range can be advanced in the direction of the arrow A2 while performing wobbling or weaving scanning in the direction of the arrow A1. The first region 1a of the first steel sheet 1 and the second region of the second steel sheet 2 are regions that are brought into contact with each other when the first steel sheet 1 and the second steel sheet 2 are joined together, and are regions that include a position where a weld metal is to be prepared. As a result, as shown in FIG. 1B and FIG. 1C, removal regions 1b and 2b are formed in which the zinc-based plating layer is removed by irradiation with the laser beam 12. In this embodiment, the length in the short side direction (width W A The relationship between the width W of the removal area and the plate thickness (plate thickness t) in the removal area is appropriately controlled. A The relationship between the thickness (thickness t) will be described in detail later.

[0023] <Placement process> Next, as shown by arrow A3 in Figure 1C, the first steel plate 1 is arranged so that the removal area 1b (first area 1a) and the second steel plate 2 are arranged so that the removal area 2b (second area) face each other and are overlapped so that the removal area 1b and the removal area 2b are in contact.

[0024] <Joining process> Thereafter, as shown in Fig. 1D, a laser beam 12 is irradiated from above the second steel plate 2 so that a weld metal 3 is formed in a range inside a region where the removal region 1b of the first steel plate 1 and the removal region 2b of the second steel plate 2 overlap on the surface where the first steel plate 1 and the second steel plate 2 face each other. In this embodiment, the same galvanometer scanner 11 for a multimode laser as that used in the above-mentioned removal step can be used as a device for irradiating the laser beam 12, and the irradiation position is moved in the direction in which the removal region 1b and the removal region 2b extend. As a result, a laser welded joint 4 can be manufactured in which the first steel plate 1 and the second steel plate 2 are joined by the weld metal 3, as shown in Fig. 2.

[0025] According to the above-mentioned manufacturing method of the laser welded joint, the zinc-based plating layer is removed at the position where the weld metal 3 is to be formed, so that it is possible to prevent the zinc from vaporizing due to the heat of the laser welding and causing blowholes in the weld metal. A and the plate thickness t are appropriately controlled, it is possible to suppress deformation of the first steel plate 1 and the second steel plate 2 due to the laser heat in the removing step.

[0026] (Width of removal area W A ≦ Value Wc obtained by formula (1) Width W in each of the removed regions 1b and 2b A The relationship between the width W of the removed area and the sheet thickness t will be described in detail below. A Specifically, the bending stiffness of the steel plate is proportional to the cube of the plate thickness t, so the width W of the removal area that can suppress deformation of the steel plate is A The range of the thickness was derived using a formula using the cube of the plate thickness t. Figure 3 shows the relationship between the cube of the plate thickness t in the removal area and the value W obtained by formula (1). C 1 is a graph showing the relationship between Equation (1) and Formula (1): W C =0.70t 6 -0.37t 3+6.00

[0027] Width of removal area W A changes depending on plate thickness t C If the value is larger than the value of t (mm), the deformation of the steel plate irradiated with the laser beam becomes large, making it difficult to manufacture a laser welded joint having the desired shape. In addition, the strength of the joint may decrease. Therefore, when removing a zinc-based coating layer by irradiating a laser beam on a steel plate having a thickness of t (mm), the width W of the removal area is A (mm) is the value W obtained by formula (1) C In other words, the broken line in Figure 3 shows formula (1), and when the plate thickness is t, the width of the removal area is W A The width W of the removal area must be on the broken line or below the broken line. A The narrower the width W (mm), the shorter the processing time required to remove the plating layer. A (mm) is 0.9 x W C It is preferable that the value is less than 0.8×W C It is more preferable to set it as follows:

[0028] On the other hand, the width of the removal area W A There is no particular lower limit to the width, but it is sufficient that the width is equal to or greater than the width at which welding can be performed with laser light 12 in the joining process, i.e., the beam diameter of laser light 12, and that the width allows removal area 1b and removal area 2b to be easily arranged opposite each other and overlapping.

[0029] (Use of multimode lasers) Conventionally, a single mode laser has been used to remove the plating layer of a zinc-based plated steel sheet, and a multimode laser has been used in the subsequent joining process. This is because it was thought that the use of a multimode laser would cause a large thermal effect on the steel sheet, making it impossible to remove the plating layer. According to the manufacturing method for a laser welded joint according to this embodiment, as described above, the width W ABecause the relationship between the laser power and the thickness t of the steel sheet is appropriately controlled, even when a multimode laser is used, it is possible to remove the plating layer while suppressing deformation of the steel sheet.

[0030] In this embodiment, the galvanometer scanner 11 for the multimode laser can be used in the removal process. That is, by using the galvanometer scanner 11, the multimode laser light 12 can be irradiated at high speed to a desired range while performing wobbling or weaving scanning, and the plating layer can be completely removed. The laser scanning speed can be, for example, 0.6 (m / sec) or more and 4.8 (m / sec) or less. However, since the optimal values ​​of the laser output and the laser scanning speed in the removal process differ depending on the spot diameter of the laser light, etc., it is preferable to appropriately adjust them depending on the conditions in the removal process.

[0031] In this embodiment, the width W of the removal area A If the relationship between the laser power and the thickness t of the steel sheet is controlled as described above, the deformation of the steel sheet can be suppressed even when a single mode laser is used, similar to the case where a multimode laser is used. Therefore, the type of laser used may be either a single mode laser or a multimode laser. However, since a multimode laser is used in the joining process, the work efficiency can be improved by using a multimode laser in the removal process.

[0032] Furthermore, when a multimode laser is used to remove the plating layer of a zinc-based plated steel sheet, fine irregularities are formed on the surfaces of the removal area 1b of the first steel sheet 1 and the removal area 2b of the second steel sheet 2. When the removal area 1b and the removal area 2b are placed opposite each other and overlapped, a gap is formed between the first steel sheet 1 and the second steel sheet 2. When the laser beam 12 is then irradiated in the joining process, even a small amount of gas that is generated can be discharged to the outside through the gap. Therefore, it is preferable to use a multimode laser from the viewpoint of suppressing the occurrence of blowholes in the weld metal 3.

[0033] (Continuous oscillation of laser light) Conventionally, when removing a plating layer from a zinc-based plated steel sheet, laser light is irradiated by pulse oscillation in order to reduce the thermal effect on the steel sheet. A Since the relationship between the laser power and the thickness t of the steel sheet is controlled as described above, even if the laser light is irradiated by continuous oscillation in the removal process, the plating layer can be removed with almost no thermal effect on the steel sheet.

[0034] In the above embodiment, the laser light 12 is irradiated to only one region of each of the first steel sheet 1 and the second steel sheet 2 to remove the plating layer, but the region to be removed from the plating layer is not limited to one region, and the laser light 12 may be irradiated to multiple regions. FIG. 4 is a perspective view showing a steel sheet on which multiple removal regions have been formed. As shown in FIG. 4, the laser light may be irradiated to two regions on the surface of the first steel sheet 1 to form removal regions 1b and 1c. In such a case, if the adjacent removal regions 1b and 1c are too close to each other, the first steel sheet 1 may be deformed due to the effect of heat. Therefore, when multiple removal regions are formed in the steel sheet, the distance d between the adjacent removal regions 1b and 1c is preferably 5 mm or more.

[0035] In the above embodiment, both the first steel sheet 1 and the second steel sheet 2 are zinc-based plated steel sheets, but the present invention is not limited to this. For example, the present invention can be applied even when at least one of the first steel sheet 1 and the second steel sheet 2, for example only the first steel sheet 1, has a zinc-based plated layer. In this case, in the removal step, the zinc-based plated layer in the first region 1a of the first steel sheet 1 is irradiated with laser light under the above-mentioned conditions to remove the zinc-based plated layer in the first region 1a. Furthermore, in the above embodiment, an example of lap welding is shown, but the manufacturing method of a laser welded joint according to the present invention is not affected by the joint shape and can also be applied to, for example, lap fillet welding.

[0036] [Laser welded joints] The laser welded joint according to this embodiment is manufactured by the manufacturing method of the laser welded joint according to the embodiment. As shown in Fig. 1C and Fig. 2, the laser welded joint 4 is a joint in which a first steel sheet 1 having a zinc-based plating layer and a second steel sheet 2 having a zinc-based plating layer are joined by a weld metal 3 by laser welding. Specifically, the first steel sheet 1 and the second steel sheet 2 are arranged overlapping each other so that a first region of the first steel sheet 1 not having a zinc-based plating layer and a second region of the second steel sheet 2 not having a zinc-based plating layer face each other. The weld metal 3 is formed in the region where the first region and the second region are overlapped. In addition, the removal region 1b where the zinc-based plating layer of the first steel sheet 1 is removed and the removal region 1c where the zinc-based plated steel sheet of the second steel sheet 2 is removed respectively satisfy the following conditions.

[0037] The length in the short direction of the removed area from which the zinc-based plating layer has been removed is defined as width W A (mm), and the plate thickness in the removal area is t (mm), the width W A is the value W calculated by the following formula (1) C The following is the result. Formula (1): W C =0.70t 6 -0.37t 3 +6.00

[0038] In the laser welded joint 4 according to this embodiment configured in this manner, the first steel plate 1 and the second steel plate 2 are joined by a weld metal in which deformation of the steel plates is suppressed and the occurrence of blowholes is suppressed. Therefore, the laser welded joint has excellent shape and strength, and is excellent in joint performance. EXAMPLES

[0039] Hereinafter, examples of the method for manufacturing a laser welded joint according to this embodiment will be specifically described.

[0040] [Manufacturing of laser welded joints] <Removal process> First, zinc-based plated steel sheets having various thicknesses were prepared, and a part of the steel sheet was irradiated with a laser beam to remove the plating layer. The types of zinc-based plated steel sheets, the amount and thickness of the plating layer, and the irradiation conditions of the laser beam in the removal process are shown below.

[0041] (galvannealed (GA) steel sheet) Plate thickness: 0.6 mm, plating layer amount: 45 g / m 2 Plate thickness: 1.8 mm, plating layer amount: 45 g / m 2 Plate thickness: 1.4 mm, plating layer amount: 80 g / m 2

[0042] (Laser light irradiation conditions) Heat source: Fiber laser (IPG photonics YLS-6000) Galvanometer scanner: Manufactured by YE Data Corporation Spot diameter: 0.3mm Laser power: 750~1500W Laser scanning speed: 0.6~4.8m / s Width of removal area W A :3.4~30.0mm Length of removal area: 40mm or 60mm Cleaning points: 1 or 2 points (spacing d: 5~10mm) Laser irradiation position: 5 to 10 mm from the edge

[0043] <Evaluation of deformation amount> Next, the deformation amount was evaluated for the steel plate from which a part of the plating layer on the surface had been removed. FIG. 5 is a schematic diagram showing a method for evaluating the deformation amount of the steel plate. As shown in FIG. 5, the first steel plate 1 on which the removal area 1b was formed was placed on a flat surface, and an iron shim plate 31 having a thickness of 0.5 mm was moved in the direction indicated by the arrow A4 toward the side perpendicular to the direction in which the removal area 1b extends. When the iron shim plate 31 entered under the first steel plate 1, the deformation amount was judged to be more than 0.5 mm, and was marked as poor (×). On the other hand, when the iron shim plate 31 did not enter under the first steel plate 1, the deformation amount was judged to be 0.5 mm or less, and was marked as good (◯). In addition, when deformation occurs in the steel plate, the limit (upper limit) value of the plate gap that can be welded is about 0.5 mm, so in this embodiment, the deformation amount of 0.5 mm or less was judged to be good. The conditions in the removal process and the evaluation results of the deformation are shown in Table 1 below.

[0044] [Table 1]

[0045] As shown in Table 1 above, in Examples 1 to 8, the width W A is the value W obtained by equation (1). C Since the width W of the removal area was 5 mm or less, the deformation of the steel plate was suppressed. Even when two or more removal areas were formed, the distance between adjacent removal areas was 5 mm or more, so the deformation of the steel plate was 5 mm or less. On the other hand, in Comparative Examples 1 to 3, the width W of the removal area was 5 mm or less. A is the value W C Since the value was larger than the above, deformation of 5 mm or more was confirmed.

[0046] <Placement process / joining process> Next, for Example 6 of the invention, in which the deformation amount was evaluated as good, steel plates (first steel plate 1 and second steel plate 2) having the same plate thickness were arranged overlapping each other with removal area 1b and removal area 2b facing each other, as shown in Fig. 1C. Thereafter, as shown in Fig. 1D, laser light 12 was irradiated so that weld metal 3 was formed in the overlapping area of ​​removal area 1b and removal area 2b, thereby joining the first steel plate 1 and the second steel plate 2 to produce a laser welded joint. The welding conditions in the joining process are shown below.

[0047] (Welding conditions) Steel plate: thickness t 1.4mm (zinc-based plating layer removed) Heat source: Fiber laser (IPG photonics YLS-6000) Galvanometer scanner: Manufactured by YE Data Corporation Spot diameter: 0.3mm Laser power: 3250W Laser scanning speed: 4m / min Weld length: 40 mm (welded at the center of the short side of the removal area) Joint shape: Lap welded joint

[0048] <Blowhole evaluation> As shown in Figure 2, the laser welded joint 4 was welded using a steel plate from which the plating layer had been removed, so no large blowholes were observed. In addition, the removal process and the joining process were performed using the same multimode laser, which resulted in excellent manufacturing efficiency. Furthermore, in the removal process, the width W A Because the relationship between the weld length and the plate thickness t is appropriately controlled, deformation is suppressed and a laser welded joint with excellent joint performance is obtained. [Explanation of symbols]

[0049] 1 1st steel plate 1a 1st area 1b, 1c, 2b removed area 2 Second steel plate 3. Weld metal 4 Laser welded joints 11 Galvanometer Scanner 12 Laser light

Claims

1. A method for manufacturing a laser welded joint, comprising: an arrangement step of arranging a first region of a first steel plate and a second region of a second steel plate so that they face each other and overlap; and a joining step of joining the first steel plate and the second steel plate by laser welding, At least one of the first steel sheet and the second steel sheet has a zinc-based plating layer, a removing step, prior to the arranging step, of irradiating the zinc-based plating layer in the first region and the second region with laser light to remove the zinc-based plating layer in the first region and the second region; In the removing step, the length in the short direction of the removal area from which the zinc-based plating layer is removed is defined as a width W Ａ (mm) and the plate thickness in the removal area is t (mm), Ａ is the value W calculated by the following formula (1) Ｃ The laser light is irradiated so as to satisfy the following conditions: A method for manufacturing a laser welded joint, characterized in that in the joining step, laser welding is performed so that weld metal is formed in an area inside the removal area. Formula (1): W Ｃ =0.70t ６ -0.37t ３ +6.00

2. 2. The method for manufacturing a laser welded joint according to claim 1, wherein the laser beam is irradiated using a multimode laser in the removing step.

3. The method for manufacturing a laser welded joint according to claim 1 , wherein the laser beam is continuously oscillated in the removing step.

4. The method for manufacturing a laser welded joint according to claim 1, wherein in the removing step, a plurality of the removal regions are formed, and the distance between adjacent removal regions is 5 mm or more.

5. The method for manufacturing a laser welded joint according to claim 1, wherein the removing step includes irradiating the laser beam while performing a wobbling or weaving scan.

6. A laser welded joint manufactured by the manufacturing method according to any one of claims 1 to 5, the first steel plate and the second steel plate are arranged in a stacked manner such that the first region of the first steel plate not having the zinc-based plating layer faces the second region of the second steel plate not having the zinc-based plating layer, the weld metal is formed in a region where the first region and the second region overlap, The length in the short direction of the removed area from which the zinc-based plating layer has been removed is defined as width W Ａ (mm) and the plate thickness in the removal area is t (mm), Ａ is the value W calculated by the following formula (1) Ｃ A laser welded joint, characterized in that: Formula (1): W Ｃ =0.70t ６ -0.37t ３ +6.00

Images