Laser welding device and laser welding method

Abstract

A laser welding method in which a first base material (8) and a second base material (9), which are overlapped, are welded by scanning a laser beam in a scanning direction, the second base material (9) being different from the first base material (8) in material or type, and an insert material (10) having a base material and a through microspace provided in the base material being interposed between the first base material (8) and the second base material (9).

Description

Technical Field

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

[0002] When welding two base materials, a laser welding technique in which the base materials are heated and melted by irradiating a laser for welding is well known. For example, the content of irradiating a laser to an aluminum material is disclosed in the following patent document in the welding of two different types of metal base materials, i.e., an aluminum material and a copper material.

[0003] Prior Art Documents

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-211981 Summary of the Invention

[0005] Problems to be Solved by the Invention

[0006] Generally, in laser welding between metals of different types of materials, brittle intermetallic compounds are likely to be formed in the molten portion. Therefore, compared with welding between metals of the same type of materials, the joint strength is significantly reduced, showing a brittle failure behavior. As an example, in the welding of an aluminum material and a copper material, CuAl2 with a high aluminum content and low strength is likely to be formed. In particular, when a copper material with a higher melting point is overlapped on an aluminum material with a lower melting point and a laser is irradiated from the copper material side for welding, this problem becomes obvious.

[0007] An object of the present invention is to reliably perform laser welding on two base materials of different materials or types and improve the joint strength thereof.

[0008] Means for Solving the Problems

[0009] A laser welding method according to one aspect of the present disclosure is as follows:

[0010] A laser welding method for welding an overlapping first base material and a second base material by scanning a laser in a scanning direction,

[0011] wherein the second base material is different from the first base material in material or type,

[0012] an insert material having a base material and a through-micro space provided on the base material is interposed between the first base material and the second base material.

[0013] It is conceivable to irradiate the laser toward the surface of the first base material (the exposed outer surface, i.e., the surface opposite to the insert material and the second base material). However, the laser welding method of the present invention is not limited thereto. For example, the laser can also be irradiated to the surface of the second base material (the exposed outer surface, i.e., the surface opposite to the insert material and the first base material).

[0014] Specifically, it is preferable that the melting point of the insert material is higher than the melting points of the first base material and the second base material respectively. In addition, it is preferable that the ductility of the insert material is higher than that of the intermetallic compound that may be formed between the first base material and the second base material.

[0015] The first base material and the second base material are generally plate-shaped materials respectively. Moreover, the thickness of the insert material is thinner than the thickness of the first base material and thinner than the thickness of the second base material.

[0016] The insert material is typically in a mesh shape, and the through-micro spaces are its mesh holes.

[0017] The first base material is, for example, copper or a copper-containing alloy. The second base material is, for example, aluminum or an aluminum alloy. And the insert material is, for example, nickel or a nickel-containing alloy.

[0018] The keyhole formed by irradiating the laser does not penetrate the first base material. It is preferable to adjust the output of the laser to this extent. That is, when irradiating the laser to the first base material, direct irradiation of the laser to the second base material should be avoided.

[0019] The laser welding method of the present invention is: after overlapping a first base material, a second base material different in material or type from the first base material, and an insert material having through-micro spaces between the first base material and the second base material, irradiate the surface of the first base material with laser from one side of the first base material to weld the two base materials.

[0020] Effects of the Invention

[0021] According to the present invention, two base materials different in material or type can be reliably laser-welded and the joint strength thereof can be improved.

[0022] Brief Description of the Drawings

[0023] Figure 1 A diagram showing the structure of a laser processing apparatus for implementing the laser welding method of one embodiment of the present invention.

[0024] Figure 2 A cross-sectional view showing the object of laser welding for implementing the laser welding method of the present invention.

[0025] Figure 3 A plan view showing the structure of the insert material used in the laser welding method of the present invention.

[0026] Figure 4 A cross-sectional view showing the pattern of laser welding in the laser welding method of the present invention.

[0027] Figure 5 A cross-sectional view showing the pattern of laser welding observed in the scanning direction of the laser in the laser welding method of the present invention.​​​​​

[0028] Figure 6 shows a pattern in which, by laser welding using the laser welding method of the present invention, the first base material melts and flows into the through-micro spaces of the insert material.

[0029] Figure 7 shows a perspective view of a fracture testing machine for measuring the joint strength between base materials welded by the laser welding method of the present invention. Detailed Description of the Preferred Embodiment

[0030] A first embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 The shown laser welding apparatus can perform the laser welding method of the present invention. It is an apparatus for overlapping a first base material 8, which is a metal plate, and a second base material 9, which is also a metal plate, and performing laser welding on the first base material 8 and the second base material 9. The first base material 8 and the second base material 9 are different types of metals from each other, and the melting point of the first base material 8 is higher than that of the second base material 9. The first base material 8 is, for example, copper or a copper-containing alloy. Additionally, the second base material 9 is, for example, aluminum or an aluminum-containing alloy.

[0031] As Figure 1 shown, the laser welding apparatus used in the present embodiment includes: a laser light source (oscillator) 1; a processing nozzle 2, which faces the first base material 8 and the second base material 9 as welding objects and irradiates the laser L supplied by the light source 1 toward the first base material 8; a unit 3, which internally includes an optical system for transmitting the laser L output by the light source 1 to the processing nozzle 2 and supports the processing nozzle 2; an angle adjustment mechanism 4, which can variably adjust the posture, i.e., the angle θ, of the unit 3 and the processing nozzle 2 with respect to the base materials 8, 9; a gas cylinder 5, which stores a shielding gas; a gas flow path 6, which guides the shielding gas discharged from the gas cylinder 5 to the processing nozzle 2; and a support 7, which supports the base materials 8, 9 (and the part where the insert material 10 is overlapped).

[0032] The processing nozzle 2 is internally provided with a condenser lens (or objective lens) for condensing the laser L irradiated on the base materials 8, 9. The optical system of the unit 3 is constructed by combining known optical elements such as optical fibers, mirrors, and lenses. The lens only needs to be used to form the projection shape (spot shape) of the laser L into a desired shape, and includes, for example, a cylindrical lens, a collimating lens, etc.

[0033] The angle adjustment mechanism 4 can adjust the angle θ between the optical axis of the laser L emitted from the processing nozzle 2 and the normal line of the surface of the first base material 8 to a desired magnitude. Details will be described later. In the present embodiment, θ is not 0°. That is, the optical axis of the laser L is not orthogonal to the surface of the first base material 8 and is inclined backward with respect to the surface of the first base material 8.

[0034] ​​The shielding gas supplied from the gas cylinder 5 to the processing nozzle 2 through the gas flow path 6 is a gas for shielding the molten metal so that the molten metal does not react with oxygen or hydrogen in the air, such as chemically stable nitrogen, argon, etc. The shielding gas is ejected from the processing nozzle 2 towards the surface of the first base material 8 during laser welding. The gas flow path 6 may include a deformable flexible tube (or hose).

[0035] In addition, the present laser welding apparatus is provided with a drive mechanism (not shown), which can displace the unit 3 and the processing nozzle 2 relative to the first base material 8 and the second base material 9 to be welded in a specified direction. The specific configuration of the drive mechanism is arbitrary, and multiple methods can be considered. For example, the support 7 supporting the first base material 8 and the second base material 9 can be mounted on a stage having a linear motor carriage or the like, and the support 7 can be moved in a direction parallel to the surface of the first base material 8 through this stage. Conversely, the unit 3 supporting the processing nozzle 2 can be mounted on a stage having a linear motor carriage or the like, and the unit 3 can be moved in a direction parallel to the surface of the first base material 8 through this stage. In the present invention, the angle adjustment mechanism 4 and the drive mechanism constitute a scanning mechanism.

[0036] Next, the laser welding method according to the present invention implemented by the above laser welding apparatus will be described in detail.

[0037] In the laser welding method of the present invention, when laser welding the first base material 8 and the second base material 9, as Figure 2 shown, an insert material 10 made of different kinds of metals is inserted between the first base material 8 and the second base material 9 in advance. On this basis, the first base material 8 and the second base material 9 are welded by irradiating the first base material 8 with a laser L on the surface of the first base material 8 (the exposed outer surface, that is, the surface on the opposite side of the insert material 10 and the second base material 9). In the present invention, the thickness of the insert material 10 between the first base material 8 and the second base material 9 (along the direction in which the first base material 8, the insert material 10, and the second base material 9 overlap) is thinner than that of the first base material 8 and thinner than that of the second base material 9.

[0038] The insert material 10 used in this embodiment is as Figure 3 shown. The insert material 10 has several or multiple minute through spaces 101. The through minute spaces 101 are spaces that penetrate the insert material 10 along the direction in which the first base material 8 and the second base material 9 to be welded face each other, and are spaces that communicate between the back surface of the first base material 8 (the surface on the opposite side of the surface irradiated with the laser L) and the surface of the second base material 9 opposite thereto. The insert material 10 is, for example, a material obtained by arranging in a specified direction ( Figure 3A mesh material formed by integrating a plurality of metal wires 10a extending longitudinally and parallel to each other and a plurality of metal wires 10b extending in a direction intersecting therewith and parallel to each other. In this embodiment, the mesh 101 of the mesh material corresponds to the above-mentioned through micro-space.

[0039] In the above embodiment, the shape and structure of the insert material 10 are the mesh 101 of the mesh material, but the insert material 10 in the present invention is not limited thereto. For example, it may also be a non-mesh shape or structure based on a plurality of metal wires extending in a specified direction and parallel to each other. In this case, the gap between the parallel extending wires corresponds to the through micro-space. In addition, the insert material 10 may also be a perforated metal sheet with a plurality of through holes drilled therein. In this case, the through holes drilled in the metal sheet correspond to the through micro-space. Alternatively, small metal materials such as cut metal films may be arranged in a dispersed manner at the interface between the first base material 8 and the second base material 9, and these metal materials are used as the insert material 10. At this time, the gap between the metal materials corresponds to the through micro-space.

[0040] In the present invention, the insert material 10 is a different kind of metal from both the first base material 8 and the second base material 9. The insert material 10 is, for example, nickel or a nickel-containing alloy. The melting point of the insert material 10 is higher than the melting point of the first base material 8 and higher than the melting point of the second base material 9. In addition, the ductility of the insert material 10 is higher than the ductility of the intermetallic compound that may be formed during welding between the first base material 8 and the second base material 9 (in the welding of copper 8 and aluminum 9, for example, CuAl2). In addition, the insert material 10 is not limited to nickel or a nickel-containing alloy, and for example, titanium or a titanium-containing alloy may also be used.

[0041] Next, Figure 4 The laser irradiation in the laser welding method of the present invention will be described in detail.

[0042] As Figure 4 shown, in this embodiment, while maintaining the posture in which the optical axis of the laser L is inclined backward with respect to the surface of the first base material 8, the laser L is scanned relative to the first base material 8 along a specified direction, that is, a direction D parallel to the surface of the first base material 8. A keyhole H is formed on the first base material 8 irradiated with the laser L. In this embodiment, by adjusting the irradiation conditions of the laser, the keyhole H does not penetrate the first base material 8 and does not penetrate the second base material 9. The adjusted irradiation conditions are, for example, the wavelength of the laser L, the output of the laser L, the projected shape and size (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, etc. The above conditions are all conditions that affect the absorption energy (energy density) per unit area of the first base material 8 and the second base material 9.

[0043] The wavelength of the laser L also depends on the types of the first base material 8 and the second base material 9, and is, for example, a near-infrared laser. The type of the laser is not limited to a near-infrared laser, and a laser L formed by overlapping a near-infrared laser and a blue laser may be irradiated onto the base material 8 or the like, and multiple lasers may be used. In addition, the laser L may be a continuous-wave laser or a pulsed laser.

[0044] Whether the keyhole H formed when irradiating the laser L penetrates the first base material 8 can be confirmed through experiments. For example, a high-speed camera capable of shooting the molten metal and the keyhole H generated during laser welding with high precision and high frame rate is used for shooting, and confirmation is made with reference to the captured image (still image or moving image). Alternatively, after irradiating the first base material 8 with the laser L alone, the cross section of the first base material 8 may be observed to confirm that the keyhole does not penetrate the first base material 8.

[0045] In the present invention, the optical axis of the laser L is inclined backward along the scanning direction D. At this time, the angle θ at which the optical axis intersects the normal of the surface of the base material 8 is set to a forward angle within the range of 15° to 50°. More preferably, the angle θ at which the axis intersects the normal of the surface of the base material 8 is 30°. Thereby, a keyhole H that penetrates but does not penetrate the first base material 8 can be formed in laser welding.

[0046] The keyhole H formed on the first base material 8 is inclined from the rear toward the front along the scanning direction D as it approaches the second base material 9 (becomes deeper). It is speculated that a part of the laser L irradiated onto the first base material 8 hits the front-side wall of the keyhole H and is reflected toward the lower or rear-side wall of the second base material 9.

[0047] Figure 6 A photograph of the pattern in which the molten metal 11 flows into the through-micro spaces of the nickel-made insert material 10 (mesh material) after the surface of the first base material 8 is irradiated with the laser L and the first base material 8 is actually melted is taken. In Figure 6 the insert material 10 and the first base material 8 are photographed from the back surface of the first base material 8. The melted first base material 8 invades the through-micro spaces and at the same time winds around the wire 10 constituting the mesh material.

[0048] Moreover, the molten metal of the first base material 8 that reaches the surface of the second base material 9 through the through-micro spaces of the insert material 10 is joined to the second base material 9 to form a welded joint.

[0049] In the past, when laser welding two base materials with different materials or types, since hard but brittle intermetallic compounds are generated in the molten part, the joint strength may be reduced.

[0050] According to the laser welding method of the present invention, by tilting the optical axis of the laser L backward with respect to the surface of the first base material 8, it is possible to suppress the keyhole H from penetrating through the first base material 8. Thereby, the irradiation amount of the laser L directly irradiated onto the second base material 9 can be reduced. According to the above structure, the second base material 9 is melted by the conduction of the heat generated by the first base material 8 absorbing the energy of the laser L. Thereby, the region where brittle intermetallic compounds are formed at the boundary between the first base material 8 and the second base material 9 can be reduced.

[0051] In addition, as Figure 4 shown by the short arrow in, the molten metal M of the first base material 8 flows in the direction opposite to the scanning direction. Therefore, not only is the state of the weld B appearing on the surface of the first base material 8 good, but also the spatter is extremely small. It is also difficult to generate pores (a general term for welding defects such as blowholes (voids) generated in the welding metal and pits opening to the surface).

[0052] In this way, by setting an appropriate advance angle θ for the optical axis of the laser L, even for the same keyhole H size, the length of the molten region becomes larger. Even for a material 8 with a high thermal conductivity and a fast cooling rate, a good molten pool flow can be formed, and it is difficult to generate a phenomenon where the molten metal M behind the keyhole H covers the keyhole H and blocks it.

[0053] In addition, if the optical axis of the laser L is made substantially perpendicular to the surface of the base material 8, that is, the angle θ is set to be approximately 0°, the possibility that the keyhole H penetrates through the first base material 8 and even penetrates to the second base material 9 becomes high. Thereby, it is easy to generate fragile intermetallic compounds at the boundary between the first base material 8 and the second base material 9. In addition, the molten metal M flows more upward, that is, to the surface of the first base material 8, the state of the weld B appearing on the surface of the first base material 8 deteriorates, and it is easy to generate spatter and pores.

[0054] In addition, an insert material 10 having a through - minute space 10 is interposed between the first base material 8 and the second base material 9 to be welded in the laser welding method of the present invention. The melting point of the insert material 10 used in the laser welding method of the present invention is higher than that of the first base material 8 and the second base material 9. During the process of the first base material 8 and the second base material 9 melting and then solidifying, part or all of the mesh of the insert material 10 remains solid and does not melt. In addition, the ductility of the insert material 10 is higher than that of the intermetallic compound that may be formed at the boundary between the first base material 8 and the second base material 9. Thereby, even if an intermetallic compound is generated during the laser welding process, since the insert material 10 suppresses the damage caused by the cracking phenomenon caused by the intermetallic compound, the fracture strength of the welded joint is further improved.

[0055] When the destruction of the brittle intermetallic compound formed between the first base material 8 and the second base material 9 by welding begins, the fracture will continue to progress, possibly leading to an immediate breakage at the welded part. However, if the laser welding method of the present embodiment is adopted, the destruction caused by the cracking phenomenon of the intermetallic compound can be suppressed by the highly ductile insertion material 10 remaining between the first base material 8 and the second base material 9.

[0056] In addition, as the effect of the mesh-like insertion material 10, an increase in the glossiness exhibited on the surface of the base material 8 can also be cited. The insertion material 10 is provided with through-micro spaces 101, and the molten base material 8 flows into the through-micro spaces 101, so that the surface of the weld bead B is at the same height position as the surface of the surrounding part adjacent to the weld bead B, or even the surface of the weld bead B is slightly lower. Thus, the surface of the weld bead B also receives a large amount of reflected light and becomes a shiny weld bead B. Moreover, the surface roughness of the weld bead B will also be reduced.

[0057] In addition, the present invention is not limited to the embodiments described in detail above. For example, the angle θ of the optical axis of the laser L can be as close to 0° as possible, or the output of the laser L can be further increased to make the keyhole H reach the side of the base material 9 that is not directly irradiated by the laser L.

[0058] Hereinafter, examples of welding using the laser welding method of the present embodiment are shown. The first base material 8 to be welded is a thin plate of oxygen-free copper (C1020), and the second base material 9 is a thin plate of pure aluminum (A1050). The laser L used is a continuous-wave laser with a wavelength of 1080 nm. The angle θ of the optical axis of the laser L is set as an advancing angle of 30°. Then, in order to weld the first base material 8 and the second base material 9, the laser L is scanned so that five weld beads B parallel to each other are formed at the welded part.

[0059] The difference between the following examples and comparative examples lies only in the conditions of the insertion material 10 used during laser welding. Other conditions are the same in all examples and comparative examples.

[0060] Example 1: A nickel mesh material with a wire diameter of 100 μm for the wire. The aperture ratio is 58.3% (60 wires are arranged per inch of width)

[0061] Example 2: A nickel mesh material with a wire diameter of 100 μm for the wire. The aperture ratio is 36.8% (100 wires are arranged per inch of width)

[0062] Example 3: A nickel mesh material with a wire diameter of 50 μm for the wire. The aperture ratio is 36.8% (200 wires are arranged per inch of width)

[0063] Comparative Example 1: A nickel foil with a thickness of 50 μm. There are no through-micro spaces (not open)

[0064] Comparative Example 2: No insertion material was used (no insertion material was sandwiched between the two base materials)

[0065] The first base material 8 and the second base material 9 that had been laser welded under the above respective conditions were placed on Figure 7 the fracture testing machine shown, and a load was applied in a direction perpendicular to the joint surface (interface) of the two base materials to peel the first base material 8 from the second base material 9 for a fracture test. In the fracture test, the magnitude of the load at the time of fracture occurring on the joint surface due to welding was measured.

[0066] For each of the examples and comparative examples, three measurements were made, and the average value of the three measurements was obtained. The magnitudes of the average load (load) at the time of fracture are as follows.

[0067] Example 1: 730 N

[0068] Example 2: 856 N

[0069] Example 3: 685 N

[0070] Comparative Example 1: 499 N

[0071] Comparative Example 2: 339 N

[0072] Comparing Examples 1 to 3 using a nickel mesh material as the insertion material 10 and Comparative Example 2 without using the insertion material 10, it is obvious that the fracture strength of Examples 1 to 3 is higher. In addition, compared with Examples 1 to 3 and Comparative Example 1 using a nickel foil as the insertion material 10, the fracture strength of Examples 1 to 3 is higher. Thus, it was confirmed that copper materials and aluminum materials can be firmly welded by laser welding using a nickel mesh material.

[0073] In order to prevent damage caused by cracking, it is preferable to appropriately set the wire diameters of the metal wires 10a, 10b constituting the insertion material 10 and the aperture ratio of the insertion material 10. In view of the results of Example 2, it is preferable that the wire diameter is thicker than a certain level and the aperture ratio is smaller than a certain level. Of course, the aperture ratio of the insertion material 10 can be appropriately selected from the viewpoints of the aperture size required to guide the molten first base material 8 to the second base material 9 through the minute space and the ductility of the insertion material 10.

[0074] In the above embodiment, the laser L may be irradiated to the copper or copper alloy as the first base material 8, or the laser L may be irradiated to the aluminum or aluminum alloy as the second base material 9.

[0075] In addition, the specific configurations and processing sequences of each part can be variously modified within the scope not departing from the gist of the present invention.

[0076] This application is based on Japanese Patent Application No. 2022-197265 filed on December 9, 2022, the content of which is incorporated herein by reference.

Claims

1. A laser welding method, which is a laser welding method for welding an overlapping first base material and second base material by scanning a laser along a scanning direction, wherein the second base material is different from the first base material in terms of material or type, and an insert material having a base material and a through-micro space provided on the base material is interposed between the first base material and the second base material.

2. The laser welding method according to claim 1, wherein, The melting point of the insert material is higher than the respective melting points of the first base material and the second base material.

3. The laser welding method according to claim 1 or 2, wherein, the thickness of the insert material is thinner than the respective thicknesses of the first base material and the second base material.

4. The laser welding method according to claim 1 or 2, wherein, the insert material has higher ductility than the intermetallic compound that may be formed between the first base material and the second base material.

5. The laser welding method according to claim 1 or 2, wherein, the through-micro space of the insert material is constituted by the net-shaped base material.

6. The laser welding method according to claim 1 or 2, wherein, the first base material is copper or a copper-containing alloy, the second base material is aluminum or an aluminum-containing alloy, and the insert material is nickel or a nickel-containing alloy.

7. The laser welding method according to claim 1 or 2, wherein, the keyhole formed by irradiating the laser does not penetrate the first base material.

8. A laser welding apparatus, which welds the first base material and the second base material by the method according to claim 1 or 2.

9. The laser welding apparatus according to claim 8, comprising: a support for supporting a material formed by overlapping the insert material having a through-micro space interposed between the first base material and the second base material; a processing nozzle for irradiating the laser to a material formed by overlapping the first base material, the insert material, and the second base material; an operating mechanism for scanning the processing nozzle in a state of being tilted backward with respect to the support along a welding direction.

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