Laser welding device, and laser welding method

Abstract

A laser welding device (1) comprises a support (7) for supporting a base material, a radiating unit (2) for radiating a laser beam onto the base material, and a drive mechanism (50) for causing the radiating unit (2) and the base material to move relative to one another to cause the laser beam to scan, wherein the drive mechanism (50) causes the laser beam to move relative to the base material while an optical axis of the laser beam L remains in backward inclined attitude relative to the scanning direction.

Description

Laser welding device and laser welding method

[0001] The present invention relates to an apparatus and method for laser welding two base materials of different materials or types.

[0002] Laser welding techniques are known in which a laser beam is irradiated onto a welding location to heat and melt the base material, thereby welding the base material to another base material. For example, the following Patent Document discloses that two dissimilar metal base materials, an aluminum material and a copper material, are welded together by irradiating a laser beam from the aluminum material side.

[0003] Japanese Patent Application Publication No. 2015-211981

[0004] In general, laser welding between dissimilar metals often produces hard but brittle intermetallic compounds in the molten area, which is known to significantly reduce joint strength and result in brittle fracture behavior compared to welding between similar metals.

[0005] In laser welding between dissimilar metals, when a keyhole is formed through two base materials of different materials or types by irradiating a laser beam, a large amount of intermetallic compounds that increase brittleness due to evaporation occurs, resulting in a decrease in weld strength. This problem becomes particularly apparent when a copper material with a high melting point is placed on an aluminum material with a relatively low melting point and the laser beam is irradiated from the copper side to perform welding.

[0006] An intended object of the present invention is to reliably laser weld two base materials of different materials or types using a simple method and to improve the welding strength.

[0007] In the present disclosure, a laser welding device that welds base materials by scanning a laser beam along a scanning direction is provided, the laser welding device having a support body that supports the base material, an irradiation unit that irradiates the base material with laser beam, and a drive mechanism that moves the irradiation unit and the base material relative to each other to scan the laser beam, wherein the drive mechanism moves the laser beam relative to the base material while keeping the optical axis of the laser beam tilted backward with respect to the scanning direction.

[0008] The present disclosure is effective when the melting point of the first base material is higher than the melting point of the second base material.

[0009] The magnitude of the acute angle formed between the normal to the surface of the first base material and the optical axis of the laser light is set within the range of 15° to 50°, for example.

[0010] It is desirable that the keyhole formed by irradiating the laser beam does not penetrate the first base material.

[0011] The first base material is, for example, copper or an alloy containing copper, and the second base material is, for example, aluminum or an alloy containing aluminum.

[0012] The laser welding method according to the present invention is a laser welding method for welding overlapping first and second base materials by scanning a laser beam along a scanning direction, characterized in that the laser beam is scanned while the optical axis of the laser beam is tilted backward with respect to the scanning direction so that a keyhole formed in the first base material during welding does not penetrate the first base material and does not reach the second base material.

[0013] According to the present invention, it is possible to reliably laser weld two base materials of different materials or types using a simple technique, thereby improving the welding strength.

[0014] 1 is a diagram schematically illustrating the configuration of a laser processing device according to an embodiment of the present invention; a cross-sectional view schematically illustrating a pattern of laser welding performed by the laser processing device; a cross-sectional view schematically illustrating the action of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; a diagram illustrating the relationship between the angle of the optical axis of a laser beam and the result of laser welding performed by the laser processing device; FIG. 1 is a diagram showing the relationship between the angle of the optical axis of the laser beam and the result of laser welding in laser welding performed by the laser processing device. FIG. 2 is a diagram showing the relationship between the angle of the optical axis of the laser beam and the result of laser welding in laser welding performed by the laser processing device. FIG. 3 is a diagram showing the relationship between the angle of the optical axis of the laser beam and the result of laser welding in laser welding performed by the laser processing device. FIG. 4 is a diagram showing the relationship between the angle of the optical axis of the laser beam and the result of laser welding in laser welding performed by the laser processing device. FIG. 5 is a diagram showing the relationship between the angle of the optical axis of the laser beam and the result of laser welding in laser welding performed by the laser processing device. FIG. 6 is a diagram showing a schematic configuration of a laser processing device according to a modified example of the present invention. FIG. 7 is a cross-sectional view showing a pattern of laser welding performed by the laser processing device of the modified example. FIG. 8 is a diagram showing the result of laser welding performed by the laser processing device of the modified example. FIG. 9 is a diagram showing the result of laser welding performed by the laser processing device of the modified example. FIG. 10 is a diagram showing the result of laser welding performed by the laser processing device of the modified example.FIG. 1 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 2 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 3 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 4 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 5 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 6 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 7 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 8 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 9 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 10 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 11 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 12 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 13 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 14 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 15 shows the result of laser welding performed by the laser processing device of the modified example. FIG. 16 is a perspective view showing a fracture testing machine for measuring joint strength between base materials welded by the laser processing device. A cross-sectional view for explaining a problem to be solved by the present invention.

[0015] A first embodiment of the present disclosure will be described with reference to the drawings. A laser welding apparatus 10 of this embodiment overlaps a first base material 8, which is a thin metal plate, on a second base material 9, which is also a thin metal plate, and irradiates a laser beam onto the surface of the first base material 8 to weld the first base material 8 and the second base material 9. In the following description, the first base material 8 and the second base material 9 may be collectively referred to simply as "base materials."

[0016] In the first embodiment, the first base material 8 is copper, and the second base material 9 is aluminum. The first base material 8 may be, for example, copper or an alloy containing copper, and the second base material 9 may be, for example, aluminum or an alloy containing aluminum. The combination of the first base material 8 and the second base material 9 is not limited to the above-mentioned embodiment. The first base material 8 and the second base material 9 may be made of different metals, and the melting point of the first base material 8 may be higher than the melting point of the second base material 9.

[0017] As shown in FIG. 1 , the laser welding apparatus of this embodiment includes a laser light source (oscillator) 1, a processing nozzle 2 (irradiation unit), an optical transmission unit 3, an angle adjustment mechanism 4, a gas cylinder 5, a gas flow path 6, and a support 7.

[0018] The laser light source 1 is a device that generates laser light. The processing nozzle 2 can irradiate the laser light L supplied from the laser light source 1 onto the base materials to be welded. The processing nozzle 2 incorporates a condenser lens (or objective lens) that condenses the laser light L to be irradiated onto the base materials 8 and 9. The optical system of the light transmission unit 3 is constructed by combining known optical elements such as optical fibers, mirrors, and lenses. The lens is used to shape the projection shape (spot shape) of the laser light L into a desired shape, and includes, for example, a cylindrical lens or a collimating lens. The light transmission unit 3 supports the processing nozzle 2 and incorporates an optical system that propagates the laser light L output from the laser light source 1 to the processing nozzle 2.

[0019] The angle adjustment mechanism 4 can adjust the attitude of the light transmission unit 3 and the processing nozzle 2 with respect to the base material. The angle adjustment mechanism 4 makes it possible to adjust the angle θ of the optical axis of the laser light L emitted from the processing nozzle 2 with respect to the normal to the surface of the first base material 8 to a desired value. In other words, the angle adjustment mechanism 4 can variably adjust the angle θ at which the laser light is incident on the base material. As will be described again later, in this embodiment, θ is not 0°. In other words, the optical axis of the laser light L is not perpendicular to the surface of the first base material 8, but is tilted with respect to the surface of the first base material 8.

[0020] The gas cylinder 5 stores a shielding gas and can guide the shielding gas to the processing nozzle 2 through the gas flow path 6. The shielding gas supplied from the gas cylinder 5 to the processing nozzle 2 through the gas flow path 6 is intended to protect the molten metal from reacting with oxygen or hydrogen in the air, and is, for example, chemically stable nitrogen or argon. The shielding gas is ejected from the processing nozzle 2 toward the surface of the first base material 8 during laser welding. The gas flow path 6 may include a flexible tube (or hose) that is easily deformed. The support body 7 supports the first base material 8 and the second base material 9.

[0021] The laser welding apparatus 10 according to the first embodiment is provided with a drive mechanism 50 that can displace the light transmission unit 3 and the processing nozzle 2 in a predetermined direction relative to the base materials 8, 9 to be welded. The drive mechanism 50 can move the support body 7 that supports the base materials in a direction parallel to the surface of the first base material 8. The specific configuration of the drive mechanism 50 is arbitrary, and multiple embodiments are possible. For example, the light transmission unit 3 that supports the processing nozzle 2 may be mounted on a stage having a linear motor carriage or the like, and the light transmission unit 3 may be moved by this stage in a direction parallel to the surface of the first base material 8.

[0022] 2 and 3 , in this embodiment, scanning is performed by moving the laser light L relative to the first base material 8 along a scanning direction D parallel to the surface of the first base material 8 while maintaining an attitude in which the optical axis of the laser light L is tilted backward with respect to the surface of the first base material 8. In this embodiment, as shown in FIG. 2 , the optical axis of the laser light L is tilted in the direction opposite to the scanning direction D. Here, the scanning direction D is the direction in which the processing nozzle 2 advances. In this embodiment, the front end of the processing nozzle 2 is positioned further forward in the scanning direction D than the rear end, and the processing nozzle 2 is in a backward-tilted attitude in which the laser light L is emitted from the processing nozzle 2 obliquely forward with respect to the scanning direction D, and the processing nozzle 2 scans the base material in this attitude.

[0023] As shown in FIG. 2 , a keyhole H is formed in the first base material 8 irradiated with the laser light L. However, this keyhole H does not penetrate the first base material 8 or the second base material 9. In this embodiment, in order to form the keyhole H in the above-described manner, the wavelength of the laser light L, the output of the laser light L, the projected shape and dimensions (spot diameter) on the surface of the first base material 8, the scanning speed along the direction D, and the angle θ of the optical axis are set in advance. All of these affect the amount of energy absorbed per unit area (energy density) of the base materials 8, 9. The irradiated laser light L depends on the type of base material 8, 9, but may be, for example, a near-infrared laser. It is also possible to use multiple laser beams in combination, such as irradiating the base material 8 with laser light L obtained by superimposing a near-infrared laser and a blue laser. The laser light L may be a continuous wave laser or a pulsed laser.

[0024] It is possible to experimentally confirm whether the keyhole H formed when the laser light L is irradiated does not penetrate the first base material 8. For example, the laser light L is irradiated onto the first base material 8 and the second base material 9 that are superimposed on each other, or onto the first base material 8 alone, and the molten metal and keyhole H that are produced during this process are photographed with a high-speed camera that is capable of capturing images with high resolution and a high frame rate, and the captured images (still images or moving images) are used for confirmation. Alternatively, after the laser light L is irradiated onto the first base material 8 alone, the first base material 8 itself may be observed to confirm that the keyhole does not penetrate the first base material 8.

[0025] The angle θ (hereinafter also referred to as the incident angle) at which the optical axis of the laser beam L intersects with the normal to the surface of the first base material 8 is set in the range of 15° to 50°, assuming that the angle θ when the optical axis of the laser beam L is tilted in the direction opposite to the scanning direction D is positive. This allows a keyhole H that does not penetrate through to be formed in the first base material 8 during laser welding.

[0026] As shown in Fig. 2, the keyhole H formed in the first base material 8 inclines from the rear to the front along the scanning direction D as it approaches (becomes deeper than) the second base material 9. In other words, the keyhole H extends at a different angle from the laser light L. The angle α between the keyhole H and the normal to the surface of the first base material 8 is larger than the angle θ between the laser light L and the normal to the surface of the first base material 8. It is presumed that a portion E of the laser light L irradiated to the first base material 8 (represented by the long arrow in Fig. 2) hits the wall on the front side of the keyhole H and is reflected downward toward the second base material 9 or toward the wall on the rear side.

[0027] Since the keyhole H does not penetrate the first base material 8, the laser light L is hardly or not directly irradiated onto the second base material 9. As shown in Fig. 3, the second base material 9 is melted by the conduction of heat F generated when the first base material 8 absorbs the energy of the laser light L. This makes it possible to reduce the region where a brittle intermetallic compound is generated at the boundary between the first base material 8 and the second base material 9.

[0028] Furthermore, the bottom of the keyhole H is irradiated not with the laser beam L directly but with the reflected beam E of the laser beam. Because the power density of the reflected beam E is lower than the power density of the direct beam (laser beam L), the bottom of the keyhole H can be heated at a low power density. As a result, even if laser beam L with a high power density capable of drilling a keyhole H in a first base material 8 such as copper is used, the bottom of the keyhole H in the first base material 8 and the adjacent second base material 9 can be gently heated. By gently heating the interface between the first base material 8 and the second base material 9 while forming the keyhole H in the first base material 8, it is possible to prevent the rapid evaporation of the second base material 9, thereby reducing porosity and suppressing convection between the first base material 8 and the second base material 9, making it less likely that a brittle intermetallic workpiece will be produced.

[0029] In addition, the molten metal M of the first base metal 8 flows backward in the scanning direction D (indicated by the short arrow in FIG. 2). As a result, not only is the condition of the bead B appearing on the surface of the first base metal 8 improved, but spatter is also extremely reduced. Furthermore, porosity (a general term for welding defects such as blowholes (cavities) that occur in the weld metal and pits that extend to the surface) is less likely to occur.

[0030] In this way, by setting an appropriate incident angle θ for the optical axis of the laser light L, the length of the molten area becomes larger even for the same size keyhole H, and a good molten pool flow can be formed even for the first base material 8, which has a high thermal conductivity and a high cooling rate, and the molten metal M behind the keyhole H is less likely to cover and block the keyhole H.

[0031] In comparison with the method of this embodiment, as shown in FIG. 14 , if the optical axis of the laser light L is made approximately perpendicular to the surface of the first base material 8, that is, if the angle θ is made approximately 0°, the keyhole H will penetrate through the first base material 8 and into the second base material 9, and a brittle intermetallic compound will be more likely to be generated at the boundary between the first base material 8 and the second base material 9.

[0032] Furthermore, since a large amount of molten metal M flows upward (indicated by the short arrow in Figure 14), the condition of the bead B appearing on the surface of the first base material 8 deteriorates, making spatter and porosity more likely to occur.

[0033] Below, we will show an example of welding using the laser welding apparatus 10 of this embodiment. The first base material 8 to be welded is a thin plate of oxygen-free copper (C1020) with a thickness of 1.0 mm, and the second base material 9 is a thin plate of pure aluminum (A1050) with a thickness of 1.2 mm. The laser light L used is a continuous wave laser with a wavelength of 1080 nm and an output of 2.5 kW. The focal length of the condenser lens of the processing nozzle 2 is 200 mm, and the focus of the laser light L is aligned with the surface of the first base material 8. The diameter (spot diameter) of the projected shape of the laser light L on the surface of the first base material 8 is 167 μm, and this is linearly scanned along the predetermined direction D at a speed of 180 mm per second. During laser welding, argon gas as a shielding gas was sprayed from the tip of the processing nozzle 2 with a diameter of 11 mm toward the irradiation position of the laser light L at a flow rate of 40 liters per minute.

[0034] In the example, the angle θ of the optical axis of the laser light L was set to 30°. In the comparative example 1, the angle θ of the optical axis was set to 0°. In the comparative example 2, the angle θ of the optical axis was set to −30° (the optical axis is tilted forward instead of backward).

[0035] In the examples, the keyhole H could be kept relatively stable, and the melting phenomenon was stable. On the other hand, in comparative examples 1 and 2, the surface of the molten metal M undulated and covered part of the keyhole H from above, and a large amount of spatter was scattered. This is thought to be because the molten pool region was present only in a narrow region around and behind the keyhole H, and because the copper, which is the first base material 8, has a high thermal conductivity, it solidifies quickly, making it difficult to ensure a large melting area, and the molten metal M remained around the keyhole H.

[0036] Furthermore, after the laser welding process, a fracture test was attempted in which the first base material 8 and the second base material 9 were peeled off. In the fracture test, the magnitude of the load when fracture occurs at the welded joint surface of the base materials 8, 9 laser welded under each of the conditions of Example 1 and Comparative Examples 1 and 2 described above was measured. The fracture test was performed by setting the base materials 8, 9 in a fracture testing machine such as that shown in Fig. 13 and applying a load (weight) in a direction perpendicular to the joint surface (interface) of the base materials 8, 9 such that the first base material 8 was peeled off from the second base material 9.

[0037] As a result of the fracture test, the load at which fracture occurred in the sample of Comparative Example 1 was approximately 25 MPa, the load at which fracture occurred in the sample of Comparative Example 2 was approximately 12 MPa, and the load at which fracture occurred in the sample of the Example was approximately 30 MPa. Compared to Comparative Example 1, the load at which fracture occurred in the base materials 8 and 9 in the Example increased by approximately 20%. In other words, the welding strength of the Example was clearly improved compared to Comparative Example 1. Compared to Comparative Example 1, the load at which fracture occurred in the base materials 8 and 9 in Comparative Example 2 was significantly reduced.

[0038] In Comparative Examples 1 and 2, there is a large amount of CuAl, an intermetallic compound with a high aluminum content and which is brittle, at the boundary between the base materials 8 and 9, and there is also a large amount of porosity, which is a welding defect, resulting in weak joint strength. In contrast, in the Example, the penetration depth of the base materials 8 and 9 is stable, there is a large amount of CuAl, an intermetallic compound with a high copper content, at the boundary between the base materials 8 and 9, there are few welding defects, and the joint strength is strong.

[0039] 4A to 4H show the results of setting the angle θ of the optical axis of the laser light L to a plurality of angles within a range of positive values, and i 4A to 4D are photographs of the specimens that were laser welded under the angle θ. i is set to 0° in Fig. 4A, 15° in Fig. 4B, 30° in Fig. 4C, and 45° in Fig. 4D. In Figs. 4A to 4D, welding is performed from left to right on the paper. The angle θ of the optical axis of the laser light L i The results will differ depending on the magnitude of θ. i If θ is about 15°, a reasonable effect can be obtained. i There is no significant change in the bead B compared to the perpendicular irradiation at θ = 0°. i If θ is increased to 45° or more, the surface of the bead B becomes unstable. i When the angle is θ = 30°, the surface of the bead B is i 4E and 4F show the results of the surface of the bead B at angles θ = 0° to 15°. i 4G and 4H are cross-sectional photographs perpendicular to the scanning direction and parallel to the scanning direction when the angle θi 4E to 4H are vertical and parallel cross-sectional photographs with respect to the operation direction when θ i It can be said that welding with extremely little porosity is achieved when the angle is 30°.

[0040] FIG. 5 shows the angle θ of the optical axis. i is set to a plurality of angles (specifically, −30°, 0°, 30°), and the angle θ i The size (inner diameter, (a)) of the keyhole H appearing on the surface of the first base material 8 and the area where the first base material 8 melts during welding (the dimension along the scanning direction D of the laser light L, (b)) were measured when laser welding processes were attempted under each of the oblique angle θ. i Even if the angle θ is changed, the size of the keyhole H on the first base material 8 does not increase or decrease significantly. i is set to an appropriate angle (for example, 30°), even if the size of the keyhole H is the same, the range in which the first base material 8 melts is i is enlarged compared to the case where the angle is 0°. As a result, even if the first base material 8 is a base material such as copper, which has a high thermal conductivity and a fast cooling rate, a good molten metal flow can be formed, and the molten metal behind the keyhole H is less likely to swell up and cover the keyhole H, causing the keyhole H to become blocked.

[0041] 6A to 6C show the angle θ of the optical axis. i is set to a plurality of angles, and the angle θ i The images were taken with a high-speed camera of the actual welding points on the first base material 8 while laser welding was being performed under the angle θ i is set to −30° in FIG. 6A, 0° in FIG. 6B, and 30° in FIG. 6C. i When the θ value was −30°, 51 sputters were generated. i When the θ = 0° condition was met, 21 sputters were generated. i When the angle was θ = 30°, there were two spatters. i When θ = 30°, i Compared with angles of -30° and 0°, there was less spatter flying and the welded surface was neater.

[0042] According to this embodiment, the laser beam L irradiated onto the first base material 8 forms an inclined keyhole H in the first base material 8 that does not reach the second base material 9. This prevents the second base material 9 from evaporating, which has a low melting point, without directly irradiating the second base material 9 with the laser beam L, and allows the second base material 9 to melt by gentle and highly efficient heat conduction. This prevents the formation of brittle intermetallic compounds, enabling welding with high joint strength and no brittleness to be achieved. While irradiating the first base material 8 with the laser beam L from the side with a high melting point typically makes heat control difficult and a stable welding process difficult, this embodiment enables reliable laser welding.

[0043] Furthermore, a molten region M extending rearward in the scanning direction D is generated in the first base material 8, which allows for good molten metal flow and makes it difficult for the molten metal behind the keyhole H to cover the keyhole H. This means that the energy of the laser beam L can be continuously and stably injected into the keyhole H.

[0044] Next, a second embodiment of a laser welding apparatus according to the present disclosure will be described. The laser welding apparatus 100 according to the second embodiment is capable of welding a first base material 108 and a second base material 109. As shown in FIG. 7 , the laser welding apparatus 100 includes a first laser light source 101 (oscillator), a second laser light source 110, a processing nozzle 102 (irradiation unit), a light transmission unit 103, an angle adjustment mechanism 104, and a drive mechanism 150. In the second embodiment, the first base material 108 is copper, and the second base material 109 is aluminum. Note that the first base material 108 may be, for example, copper or an alloy containing copper, and the second base material 109 may be, for example, aluminum or an alloy containing aluminum. The combination of the first base material 108 and the second base material 109 is not limited to the above-described embodiment. The first base material 108 and the second base material 109 may be made of different metals, and the melting point of the first base material 108 may be higher than the melting point of the second base material 109.

[0045] The first laser light source 101 is capable of emitting a first laser light L1, and the second laser light source 110 is capable of emitting a second laser light L2. The first laser light source 101 outputs a near-infrared laser as the first laser light L1. The second laser light source 110 outputs a blue laser as the second laser light L2. The second laser light L2 is more easily absorbed by the first base material 108 than the first laser light L1. Note that the laser light emitted by the first laser light source 101 and the second laser light source 110 is not limited to the above-described form. For example, the first laser light L1 and the second laser light L2 may be a continuous wave laser or a pulsed laser. In the following description, the first laser light L1 and the second laser light L2 may be collectively referred to simply as "laser light L1, L2."

[0046] The processing nozzle 102 superimposes the laser light L1 and the second laser light L2 onto the first base material 108 and the second base material 109, and then irradiates the first base material 108 with the superimposed laser light L1 and the second laser light L2. The optical transmission unit 103 contains an optical system that superimposes the first laser light L1 and the second laser light L2 and propagates the superimposed laser light L1 and the second laser light L2 to the processing nozzle 102, and supports the processing nozzle 102. The other configurations of the laser welding apparatus 100 are the same as those of the laser welding apparatus 10 according to the first embodiment.

[0047] 8 , in the second embodiment, the superimposed laser beams L1 and L2 are scanned by moving the laser beams L1 and L2 relative to the first base material 108 in a predetermined direction, i.e., a direction D parallel to the surface of the first base material 108, while maintaining the optical axes of the superimposed laser beams L1 and L2 tilted backward relative to the surface of the first base material 108. The dimensions (spot diameters) of the projected shapes of the laser beams L1 and L2 irradiated onto the surface of the first base material 108 are smaller for the first laser beam L1, which is less easily absorbed by the first base material 108, and larger for the second laser beam L2, which is more easily absorbed by the first base material 108 than the first laser beam L1. In other words, the projected shape of the first laser beam L1 on the surface of the first base material 108 is within the projected shape of the laser beam L2. This allows the first base material 108 to be preheated by the second laser beam L2, and then the first laser beam L1 to drill a keyhole H in the first base material 108, thereby completing the welding of the two base materials 108, 109.

[0048] A keyhole H is formed in the first base material 108 irradiated with the laser beams L1 and L2, but this keyhole H does not penetrate through the first base material 108 and does not penetrate into the second base material 109. To achieve this, the wavelengths of the laser beams L1 and L2, the output power of the laser beams L1 and L2, the shape and dimensions (spot diameter) of the laser beams L1 and L2 projected onto the surface of the first base material 108, the scanning speed along direction D, and the angle θ of the optical axis are set in advance. All of these affect the amount of energy absorbed per unit area of ​​the base material (energy density).

[0049] The angle θ of the optical axis when the second laser beam L2 is superimposed on the first laser beam L1 and irradiated onto the first base material 108 can be set to be larger than the angle θ of the optical axis when the laser beam L alone is irradiated onto the first base material 108 as in the first embodiment. However, it is considered particularly preferable to set the angle θ to about 30°.

[0050] The temperature of the location where the keyhole H is drilled by the first laser beam L1 becomes higher than the boiling point of the first base material 108. When only the first laser beam L1 is irradiated onto the first base material 108, the keyhole H in the first base material 108 becomes very hot, while the temperature of the area around the keyhole H is low, resulting in a large temperature difference between the two. The flow of molten metal occurs according to the temperature gradient within the molten region, but if the temperature difference is large, the molten metal tries to solidify in an extremely short time, causing pulsation on the surface of the molten region, resulting in spattering, disturbance of the bead B, and the molten metal covering the keyhole H.

[0051] In the laser welding apparatus according to the present disclosure, the irradiation unit can irradiate a first laser beam and a second laser beam different from the first laser beam as laser beams, and the second laser beam may be irradiated around the irradiation range of the first laser beam. In the laser welding apparatus 100 according to the second embodiment, the processing nozzle 102 irradiates the first base material 108 with a superimposed first laser beam L1 and a second laser beam L2, which is more easily absorbed by the first base material 108 than the first laser beam L1. This facilitates absorption of the first laser beam L1 and maintains a high temperature around the keyhole H, thereby expanding the area where the metal is molten. At the same time, since the molten metal solidifies over a longer period of time, the surface of the molten area in the first base material 108 is stabilized without pulsation. Therefore, spattering and molten metal covering the keyhole H can be suppressed.

[0052] The welded area created behind the keyhole H expands along the scanning direction D (the direction in which the welding progresses) of the laser beams L1 and L2, and a more stable molten pool flow can be obtained, making it less likely that the molten metal behind the keyhole H will cover and block the keyhole H. This also means that the amount of energy introduced into the keyhole H is stabilized. By stabilizing the amount of energy introduced into the keyhole H, the amount of heat transferred from the first base material 108 to the second base material 109 is also stabilized, enabling stable welding with a constant penetration depth over a wide range.

[0053] Furthermore, since the amount of energy introduced into the keyhole H is stable and a uniform penetration depth can be obtained, for example, when the first base metal 108 is copper and the second base metal 109 is aluminum, as in this embodiment, rapid melting of the aluminum material is unlikely to occur, resulting in welding with fewer welding defects such as brittle intermetallic compounds typified by CuAl and porosity, and a stronger welded joint can be obtained.

[0054] 9A to 9E are photographs showing the results of welding performed by irradiating the first base material 108 with the first laser beam L1 superimposed with the second laser beam L2, and FIGS. 9F to 9J are photographs showing the results of welding performed by irradiating the first base material 108 with only the first laser beam L1. In all of the figures, welding is performed from left to right on the page. The welding speed is 210 mm per second in the example shown in FIGS. 9A and 9F, 220 mm per second in the example shown in FIGS. 9B and 9G, 230 mm per second in the example shown in FIGS. 9C and 9H, 240 mm per second in the example shown in FIGS. 9D and 9I, and 250 mm per second in the example shown in FIGS. 9E and 9J. 9A to 9E, when a laser welding process was attempted using the first laser beam L1 superimposed with the second laser beam L2, the bead of molten metal that appeared on the surface of the first base material 108 flowed neatly backward along the scanning direction D of the laser beams L1 and L2, forming a V-shape. 9F to 9J show the results of a laser welding process attempted using only the first laser beam L1, but the shape of the bead of molten metal was not V-shaped.

[0055] Fig. 10A is a photograph taken with a high-speed camera of a welding point during welding by irradiating a first base material 108 with a first laser beam L1 superimposed with a second laser beam L2. Fig. 10B is a photograph taken with a high-speed camera of a welding point during laser welding by irradiating the first base material 108 with only the first laser beam L1. As shown in Fig. 10A, by irradiating the first base material 108 with the second laser beam L2 superimposed on the first laser beam L1, an expansion of the molten region behind the keyhole H in the first base material 108 is observed, and the surface of the molten region is also smooth. It can also be seen that during laser welding, the molten metal does not rise and cover the keyhole H, and the shape of the keyhole H is clearly maintained.

[0056] 11A to 11F are photographs of a welded joint between a first base material 108 and a second base material 109, obtained by irradiating a first base material 108 with a superimposed second laser beam L2 on the first laser beam L1 and welding the first base material 108. Also, FIGS. 11A to 11F are cross sections of the first base material 108 and the second base material 109 cut along a plane perpendicular to the scanning direction D of the laser beams L1 and L2. The scanning speed of the laser beams L1 and L2 relative to the base materials was set to 210 mm per second in FIG. 11A, 220 mm per second in FIG. 11B, 230 mm per second in FIG. 11C, 240 mm per second in FIG. 11D, and 250 mm per second in FIG. 11E, and the laser welding process was performed. FIG. 11F is an enlarged cross-sectional view of FIG. 11D. 11C, 11D, and 11F, it can be seen that the second base material 109 does not melt over a wide width, and the penetration depth is stable, even though the welding depth of the first base material 108 reaches the interface between the first base material 108 and the second base material 109. According to the configuration of the present disclosure, the second base material 109 is not melted by directly irradiating the first laser light L1 itself onto the second base material 109, but rather the first base material 108 is melted and the heat is conducted to the second base material 109 to melt the second base material 109, which makes it possible to suppress the generation of brittle intermetallic compounds and also reduces melting defects.

[0057] 12A and 12B are also photographs of the welded joint between the two base materials obtained by performing laser welding. FIGS. 12A and 12B are cross-sections of the first base material 108 and the second base material 109 cut along a plane parallel to the scanning direction D of the laser beams L1 and L2. FIG. 12A shows welding performed by irradiating the first base material 108 with only the first laser beam L1 at an angle θ = -30°, while FIG. 12B shows welding performed by irradiating the first base material 108 with the first laser beam L1 and the second laser beam L2 in a superimposed state. In FIG. 12B, the second base material 109 appears to be melted, and a consistent penetration depth can be maintained over a wide area. On the other hand, in FIG. 12A, the first base material 108 is melted so as to penetrate into the second base material 109, and the intermetallic compound CuAl2, which has low fracture strength, is formed inside the first base material 108. Although porosity also occurs, it can be seen that less CuAl2 is generated in the welding using the combined first laser light L1 and second laser light L2 (photographs in the bottom row) compared to the welding using only the first laser light L1 (photographs in the top row).

[0058] In addition, the specific configuration of each part and the processing procedure can be modified in various ways without departing from the spirit of the present invention.

[0059] This application is based on Japanese Patent Application No. 2022-126687 filed on August 8, 2022 and Japanese Patent Application No. 2022-195436 filed on December 7, 2022, the contents of which are incorporated herein by reference.

Claims

1. A laser welding device that scans a laser beam along a scanning direction to weld a base material, A support for supporting the base material; an irradiation unit that irradiates the base material with the laser light; a drive mechanism for relatively moving the irradiation unit and the base material in order to scan the laser light; The driving mechanism moves the laser beam relative to the base material while keeping the optical axis of the laser beam tilted backward with respect to the scanning direction.

2. The laser welding device according to claim 1 , wherein the irradiation unit has an angle adjustment mechanism capable of adjusting an angle of the optical axis of the laser light.

3. The base material includes a first base material to be irradiated with the laser light and a second base material, the second base material is provided on a surface of the first base material opposite to a surface irradiated with the laser light, The laser welding apparatus according to claim 1 or 2, wherein the melting point of the first base material is higher than the melting point of the second base material.

4. 4. The laser welding device according to claim 3, wherein the acute angle formed between the normal to the surface of the first base material and the optical axis of the laser light is within a range of 15 degrees to 50 degrees.

5. 4. The laser welding apparatus according to claim 3, wherein the first base material is copper or an alloy containing copper, and the second base material is aluminum or an alloy containing aluminum.

6. the irradiation unit is capable of irradiating, as the laser light, a first laser light and a second laser light different from the first laser light, The laser welding device according to claim 1 , wherein the second laser beam is irradiated to a periphery of an irradiation range of the first laser beam.

7. A laser welding method for welding an overlapping first base material and a second base material by scanning a laser beam along a scanning direction, comprising the steps of: A laser welding method in which the optical axis of the laser light is tilted backward with respect to the scanning direction while scanning, so that a keyhole formed in the first base material during welding does not penetrate the first base material and does not reach the second base material.

Images