Laser welding method and laser welding apparatus

Abstract

For example, the present invention provides an improved and novel laser welding method and laser welding apparatus that can suppress deformation of keyholes over time, thereby suppressing the generation of spatter and voids. [Solution] The laser welding method comprises, for example, a first step of melting a workpiece by irradiating it with laser light to form a molten pool, and a second step of cooling and solidifying the molten pool, wherein the laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a sub-irradiation beam having a power density not capable of forming a keyhole in the workpiece on its own and at least partially located outside the main beam, and in the first step, the sub-irradiation beam is irradiated onto the inner circumferential surface of the keyhole to suppress the movement of the inner circumferential surface toward the center of the keyhole relative to the center of the keyhole.

Description

Technical Field

[0001] The present invention relates to a laser welding method and a laser welding apparatus.

Background Art

[0002] Conventionally, a laser welding method of irradiating a processing object with a laser beam for welding has been known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventor has intensively studied the change over time of the keyhole in the laser welding method, and has found that by a new method, it is possible to suppress the deformation of the keyhole over time, and thus suppress the generation of spatter and voids.

[0005] Therefore, one of the problems of the present invention is to provide an improved and novel laser welding method and a laser welding apparatus that can suppress, for example, the deformation of the keyhole over time, and thus suppress the generation of spatter and voids.

Means for Solving the Problems

[0006] The laser welding method of the present invention is a laser welding method comprising, for example, a first step of melting a workpiece by irradiating it with laser light to form a molten pool, and a second step of cooling and solidifying the molten pool, wherein the laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a sub-irradiation beam having a power density not capable of forming a keyhole in the workpiece on its own and at least partially located outside the main beam, and in the first step, the sub-irradiation beam is irradiated onto the inner circumferential surface of the keyhole to suppress the movement of the inner circumferential surface toward the center of the keyhole relative to the center of the keyhole.

[0007] In the laser welding method described above, in the first step, when viewed in the direction of irradiation of the laser beam, more than half of the irradiation area of ​​the secondary irradiation light on a virtual plane perpendicular to the irradiation direction, passing through a position that is the end of the irradiation area of ​​the laser beam on the surface of the workpiece before irradiation of the laser beam in the opposite direction to the irradiation direction, may be located inside the opening edge of the keyhole.

[0008] The laser welding method of the present invention is a laser welding method comprising, for example, a first step of melting a workpiece by irradiating it with laser light to form a molten pool, and a second step of cooling and solidifying the molten pool, wherein the laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a sub-irradiation beam having a power density not capable of forming a keyhole in the workpiece on its own and at least partially located outside the main beam, wherein in the first step, the sub-irradiation beam is irradiated to the side of the keyhole that is closer to the center of the keyhole than the inner surface of the keyhole, thereby suppressing the relative movement of the inner surface toward the center of the keyhole.

[0009] In the laser welding method described above, the laser beam may be scanned relatively along the surface of the workpiece in the first step.

[0010] In the laser welding method described above, the secondary irradiation light may include a plurality of first secondary beams arranged circumferentially around the optical axis of the laser light, as the secondary beam.

[0011] In the laser welding method described above, the secondary irradiation light may include a second secondary beam formed circumferentially around the optical axis of the laser beam, as the secondary beam.

[0012] In the laser welding method described above, the secondary irradiation light may include a third secondary beam formed as the secondary beam, having an outer peripheral edge that surrounds the optical axis of the laser light.

[0013] In the laser welding method described above, in the first step, a keyhole may be formed in the workpiece by the main irradiation light, and the maximum diameter of the keyhole may be enlarged by the secondary irradiation light compared to when the main irradiation light is irradiated alone.

[0014] In the laser welding method described above, in the first step, the ratio of the width of the spot of the secondary irradiation light in a virtual plane perpendicular to the irradiation direction, passing through a position that is the end of the irradiation area of ​​the laser light on the surface of the workpiece before irradiation with the laser light, to the width of the spot of the main irradiation light may be set to 2.23 or more and 5.05 or less.

[0015] In the laser welding method described above, the ratio may be set to 3.03 or less in the first step.

[0016] The laser welding apparatus of the present invention comprises, for example, a laser light source and an optical head that irradiates a workpiece with laser light output from the laser light source, and is used to weld the workpiece, wherein the laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a secondary irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and the movement of the inner surface toward the center of the keyhole is suppressed by irradiating the inner surface of the keyhole with the secondary irradiation beam.

[0017] Furthermore, the laser welding apparatus of the present invention comprises, for example, a laser light source and an optical head that irradiates the laser light output from the laser light source toward a workpiece, and is a laser welding apparatus for welding the workpiece, wherein the laser light includes a main irradiation light that has a power density capable of forming a keyhole in the workpiece on its own, and a sub-irradiation light that has a power density that cannot form a keyhole in the workpiece on its own, and the sub-irradiation light is irradiated from the inner circumferential surface of the keyhole toward the center of the keyhole to suppress the relative movement of the inner circumferential surface toward the center of the keyhole. [Effects of the Invention]

[0018] According to the present invention, for example, it is possible to provide an improved and novel laser welding method and laser welding apparatus that can suppress deformation of keyholes over time, and thereby suppress the generation of spatter and voids. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is an illustrative schematic diagram of a laser welding apparatus according to the first embodiment. [Figure 2] Figure 2 is an explanatory diagram illustrating the concept of the principle of the diffractive optical element included in the laser welding apparatus of the first embodiment. [Figure 3]FIG. 3 is a schematic plan view showing an example of a spot on a virtual plane of a processing object of laser light output from the laser welding apparatus of the embodiment. [Figure 4] FIG. 4 is an exemplary flowchart showing the procedure of the laser welding method of the embodiment. [Figure 5] FIG. 5 is a diagram showing a schematic shape of a spot of laser light irradiated on the surface of a processing object in the laser welding method of the embodiment and a state at time t11 of a photographic image of a molten pool formed on the surface by the laser light. [Figure 6] FIG. 6 is a diagram showing a schematic shape of a spot of laser light irradiated on the surface of a processing object in the laser welding method of the embodiment and a state at time t12 after time t11 of a photographic image of a molten pool formed on the surface by the laser light. [Figure 7] FIG. 7 is a diagram showing a schematic shape of a spot of laser light irradiated on the surface of a processing object in the laser welding method of the embodiment and a state at time t13 after time t12 of a photographic image of a molten pool formed on the surface by the laser light. [Figure 8] FIG. 8 is a diagram showing a schematic shape of a spot of laser light irradiated on the surface of a processing object in the laser welding method of the first reference example and a state at time t21 of a photographic image of a molten pool formed on the surface by the laser light. [Figure 9] FIG. 9 is a diagram showing a schematic shape of a spot of laser light irradiated on the surface of a processing object in the laser welding method of the first reference example and a state at time t22 after time t21 of a photographic image of a molten pool formed on the surface by the laser light. [Figure 10] FIG. 10 is a diagram showing a schematic shape of a spot of laser light irradiated on the surface of a processing object in the laser welding method of the first reference example and a state at time t23 after time t22 of a photographic image of a molten pool formed on the surface by the laser light. [Figure 11]Figure 11 shows the schematic shape of the laser beam spot irradiated onto the surface of the workpiece in the laser welding method of the second reference example, and the state of the molten pool formed on the surface by the laser beam at time t31 in a photographic image. [Figure 12] Figure 12 shows the schematic shape of the laser beam spot irradiated onto the surface of the workpiece in the laser welding method of the second reference example, and the state of the molten pool formed on the surface by the laser beam at time t32, after time t31. [Figure 13] Figure 13 shows the schematic shape of the laser beam spot irradiated onto the surface of the workpiece in the laser welding method of the second reference example, and the state of the molten pool formed on the surface by the laser beam at time t33, after time t32. [Figure 14A] Figure 14A is an exemplary and schematic cross-sectional view of a workpiece when scanned while being irradiated with laser light in the laser welding method of the embodiment, showing the case where the keyhole penetrates the workpiece. [Figure 14B] Figure 14B is an exemplary and schematic cross-sectional view of a workpiece when scanned while being irradiated with laser light in the laser welding method of the embodiment, showing a case where the keyhole does not penetrate the workpiece. [Figure 15A] Figure 15A is an exemplary and schematic cross-sectional view of a workpiece when scanned while being irradiated with laser light in the laser welding method of the first reference example, showing the case where the keyhole penetrates the workpiece. [Figure 15B] Figure 15B is an exemplary and schematic cross-sectional view of a workpiece when scanned while being irradiated with laser light in the laser welding method of the first reference example, and shows a case where the keyhole does not penetrate the workpiece. [Figure 16] Figure 16 is a graph showing the relationship between scanning speed and sputter count for various cases in the laser welding method of the embodiment, where the width of the secondary irradiation spot is changed in various ways. [Figure 17]Figure 17 is a graph showing the relationship between the scanning speed and the keyhole diameter (maximum diameter) for various cases in the laser welding method of the embodiment, where the width of the secondary irradiation spot is changed in various ways. [Figure 18] Figure 18 is a schematic plan view showing another example of a spot of laser light output from the laser welding apparatus of the embodiment on a virtual plane of the workpiece. [Figure 19] Figure 19 is a schematic plan view showing another example of a spot of laser light output from the laser welding apparatus of the embodiment on a virtual plane of the workpiece. [Figure 20] Figure 20 is a schematic plan view showing another example of a spot of laser light output from the laser welding apparatus of the embodiment on a virtual plane of the workpiece. [Figure 21] Figure 21 is a schematic plan view showing another example of a spot of laser light output from the laser welding apparatus of the embodiment on a virtual plane of the workpiece. [Figure 22] Figure 22 is a schematic plan view showing another example of a spot of laser light output from the laser welding apparatus of the embodiment on a virtual plane of the workpiece. [Figure 23] Figure 23 is a schematic plan view showing another example of a spot of laser light output from the laser welding apparatus of the embodiment on a virtual plane of the workpiece. [Figure 24] Figure 24 shows an example of the power density distribution along a line segment passing through the center of the spot on the virtual plane of the workpiece when laser light is irradiated using the pattern shown in Figure 23. [Figure 25] Figure 25 shows an example of the power density distribution along a line segment passing through the center of the spot on the virtual plane of the workpiece when laser light is irradiated using the pattern shown in Figure 3. [Figure 26] Figure 26 is an illustrative schematic diagram of a laser welding apparatus according to a second embodiment. [Modes for carrying out the invention]

[0020] Illustrative embodiments and modifications of the present invention are disclosed below. The configurations of the embodiments and modifications shown below, as well as the functions and effects brought about by such configurations, are examples only. The present invention can also be realized by configurations other than those disclosed in the following embodiments and modifications. Furthermore, according to the present invention, it is possible to obtain at least one of the various effects (including derived effects) that can be obtained by such configurations.

[0021] Multiple embodiments and modifications include similar components. Hereinafter, these similar components are given common reference numerals, and redundant descriptions may be omitted.

[0022] In each figure, the X direction is represented by arrow X, the Y direction by arrow Y, and the Z direction by arrow Z. The X, Y, and Z directions intersect and are orthogonal to each other. The Z direction is opposite to the average irradiation direction of the laser beam L from the laser welding apparatus 100. For example, the X and Y directions are roughly aligned horizontally, and the Z direction is roughly aligned vertically upward, but this is not limited to this.

[0023] Furthermore, in this specification, ordinal numbers are assigned for convenience to distinguish directions, processes, components, parts, laser beams, etc., and do not limit priority, order, number, etc.

[0024] [First Embodiment] [Configuration of a laser welding system] Figure 1 is a diagram showing the schematic configuration of the laser welding apparatus 100A(100) of the first embodiment. As shown in Figure 1, the laser welding apparatus 100 comprises a laser device 110, an optical head 120, an optical fiber 130, and a drive mechanism 140.

[0025] The laser welding apparatus 100 irradiates the surface of the object W (workpiece) to be laser-welded with laser light L. The energy of the laser light L partially melts the object W, and as it cools and solidifies, the object W is welded. The object W has multiple components, and these multiple components are joined together by laser welding.

[0026] The multiple components that make up the object W can each be made of, for example, copper-based metal materials such as copper or copper alloys, aluminum-based metal materials such as aluminum or aluminum alloys, nickel-based metal materials such as nickel or nickel alloys, iron-based metal materials such as iron or iron alloys, or titanium-based metal materials such as titanium or titanium alloys. The multiple components may be made of the same metal material or of different metal materials. The multiple components that make up the object W may be conductors or not. Furthermore, the object W may be a metal foil.

[0027] The laser device 110 has a laser oscillator and is configured to output, for example, a single-mode laser beam with a power of several kW. Alternatively, the laser device 110 may have, for example, multiple semiconductor laser elements internally, and be configured to output a multi-mode laser beam with a power of several kW as the combined output of these multiple semiconductor laser elements. Furthermore, the laser device 110 may have various laser light sources, such as fiber lasers, YAG lasers, and disk lasers. The laser device 110 also outputs laser beams with wavelengths between 400 nm and 1200 nm. These laser beams may include blue laser beams, green laser beams, infrared laser beams, and the like.

[0028] The optical fiber 130 optically connects the laser device 110 and the optical head 120. In other words, the optical fiber 130 guides the laser light output from the laser device 110 to the optical head 120. When the laser device 110 outputs single-mode laser light, the optical fiber 130 is configured to propagate the single-mode laser light. In this case, the M of the single-mode laser light 2 The beam quality is set to, for example, 1.3 or less. Also, when the laser device 110 outputs multimode laser light, the optical fiber 130 is configured to propagate the multimode laser light. In this case, the M of the multimode laser light 2 The beam quality is set to, for example, between 4 and 30. 2Beam quality is M 2 It can also be called a factor.

[0029] The optical head 120 is an optical device for irradiating the laser light input from the laser device 110 toward the object W. The optical head 120 includes a collimating lens 121, a focusing lens 122, a mirror 123, a DOE 125 (diffractive optical element), and a galvanoscanner 126. The collimating lens 121, focusing lens 122, mirror 123, DOE 125, and galvanoscanner 126 may also be referred to as optical components.

[0030] Each collimating lens 121 collimates the laser light input via the optical fiber 130. The collimated laser light becomes parallel light.

[0031] The mirror 123 reflects the laser light, which has become parallel light by the collimating lens 121, and directs it towards the galvanoscanner 126. Depending on the configuration of the optical path in the optical head 120, the mirror 123 may not be necessary. A DOE 125 is provided between the mirror 123 and the galvanoscanner 126. The DOE 125 will be described later.

[0032] The galvanoscanner 126 has multiple mirrors 126a and 126b, and by controlling the angles of these mirrors 126a and 126b, the direction of emission of the laser beam L from the optical head 120 can be switched, thereby changing the irradiation position of the laser beam L on the surface of the object W. The angles of the mirrors 126a and 126b are changed by motors (not shown) controlled, for example, by a controller. By changing the emission direction of the laser beam L while irradiating it, the laser beam L can be scanned on the surface of the object W. The galvanoscanner 126 is an example of a laser scanner. The laser welding apparatus 100 may have a laser scanner different from the galvanoscanner.

[0033] The focusing lens 122 focuses the laser light, which arrives from the galvanoscanner 126 as parallel light, and irradiates the target object W with the laser light L (output light).

[0034] However, the optical components of the optical head 120 are not limited to these, and the optical head 120 may have other optical components.

[0035] The drive mechanism 140 changes the relative position of the optical head 120 with respect to the object W. The drive mechanism 140 includes, for example, a rotation mechanism such as a motor, a reduction mechanism that reduces the rotational output of the rotation mechanism, and a motion conversion mechanism that converts the rotation reduced by the reduction mechanism into linear motion. The controller can control the drive mechanism 140 so that the relative position of the optical head 120 with respect to the object W in the X, Y, and Z directions changes. The drive mechanism 140 can change (switch) the object W to be laser-welded from among a plurality of objects W supported by a support mechanism (not shown). The drive mechanism 140 can also change the irradiation position of the laser beam L on the object W. Furthermore, the drive mechanism 140 can be used to change the irradiation point in conjunction with changing the irradiation direction of the laser beam on the object W. In addition, the drive mechanism 140 can change the irradiation position while the laser beam L is irradiated onto the surface of the object W. In other words, the drive mechanism 140 can scan the laser beam L on the surface of the object W.

[0036] [DOE] Figure 2 is an explanatory diagram illustrating the concept of the DOE125 principle. As conceptually illustrated in Figure 2, the DOE125 has a configuration in which multiple diffraction gratings 125a with different periods are superimposed. The DOE125 can shape the beam by bending or superimposing parallel light in the direction influenced by each diffraction grating 125a. The DOE125 may also be called a beam shaper. The DOE125 splits collimated laser light into multiple beams. Alternatively, the beam may be split using optical components such as splitters, prisms, or mirrors instead of the DOE125.

[0037] [Beam (spot) shape] Figure 3 is a schematic diagram (plan view) showing the spot of the laser beam L on the virtual plane VP of the object W. The virtual plane VP is defined as a plane perpendicular to the Z direction, passing through the position that is the edge in the Z direction of the irradiation area of ​​the laser beam L on the surface Wa of the object W. If the surface Wa of the object W is a plane and the laser beam L is irradiated perpendicularly to the surface Wa, then the surface Wa becomes the virtual plane VP.

[0038] As shown in Figure 3, the laser beam L includes a main beam B1 and a secondary beam B2. Main beam B1 is an example of a main beam, and secondary beam B2 is an example of a secondary beam.

[0039] The main beam B1 is irradiated onto a region containing the optical axis Ax of the laser beam L. The main beam B1 is irradiated with a power density capable of forming a keyhole on the surface Wa of the target object W on its own. The main beam B1 is included in the main irradiation light L1. Note that the main irradiation light L1 may contain two or more main beams B1.

[0040] The secondary beam B2 illuminates a region that includes an area further away from the optical axis Ax than the main beam B1. In other words, the secondary beam B2 illuminates at least partially outside the main beam B1. In the example in Figure 3, multiple secondary beams B2 are arranged circumferentially, surrounding the optical axis Ax and the main beam B1. The secondary beam B2 is included in the secondary illumination light L2 and illuminates the target object W with a power density that, on its own, cannot form a keyhole. That is, the power density of the secondary beam B2 is lower than the power density of the main beam B1. The secondary beam B2 is an example of a first secondary beam. In the example in Figure 3, the secondary beam B2 does not overlap with the main beam B1, but this is not limited to this, and the secondary beam B2 and the main beam B1 may partially overlap. Also, although the multiple secondary beams B2 are arranged discretely along approximately the sides of a regular octagon, this is not limited to this, and they may be arranged along approximately the sides of other polygons, or discretely along approximately the outer circumference of a circle or ellipse.

[0041] Furthermore, the diameters of the main beam B1 and the sub-beam B2 can be, for example, 14 [μm] or more and 50 [μm] or less if the laser device 110 is a single-mode fiber laser, and 50 [μm] or more and 500 [μm] or less if it is a multi-mode fiber laser.

[0042] [Laser welding method] Figure 4 is a flowchart of the laser welding method. As shown in Figure 4, first, the object W is positioned so that laser light L is irradiated onto the surface Wa of the object W from the laser welding apparatus 100 at an appropriate power density (S1). Next, the laser light L is irradiated onto the surface Wa, and the object W is partially melted, forming a molten pool (S2). Next, the molten pool is cooled by natural cooling or forced cooling, and the molten pool solidifies to form the weld (weld metal) (S3). S2 is an example of the first step, and S3 is an example of the second step.

[0043] [Formation of molten pools and changes in molten pools over time] Figures 5 to 7 show the changes over time when the laser beam L of this embodiment shown in Figure 3 is scanned while irradiating the surface Wa of the object W. Figure 5 shows the state at time t=t11, Figure 6 shows the state at time t=t12 (later than Figure 5), and Figure 7 shows the state at time t=t13 (later than Figure 6). In all the states shown in Figures 5 to 7, a keyhole KH is formed on the surface Wa, substantially along the outer edge of the laser beam L (sub-irradiation light L2, multiple sub-beams B2), and a molten pool WP is formed surrounding the keyhole KH.

[0044] Figures 8-10 show the changes over time when scanning the surface Wa of an object W while irradiating it with the laser beam L of the first reference example, which has only a main beam B1 (main irradiation light L1) and no sub-beam B2 (sub-irradiation light L2). Figure 8 shows the state at time t=t21, Figure 9 shows the state at time t=t22 (later than Figure 8), and Figure 10 shows the state at time t=t23 (later than Figure 9). From Figures 8-10, it can be seen that in the first reference example, the keyhole KH is smaller and the change in the shape of the keyhole KH over time is larger compared to the examples in Figures 5-7 of this embodiment.

[0045] Figures 11-13 show the changes over time when scanning the surface Wa of an object W while irradiating it with laser light L from a second reference example, in which the distance between the main beam B1 (main irradiation light L1) and the sub-beam B2 (sub-irradiation light L2) is longer than in the example in Figure 3 (second reference example). Figure 11 shows the state at time t=t31, Figure 12 shows the state at time t=t32 (later than in Figure 11), and Figure 13 shows the state at time t=t33 (later than in Figure 12). From Figures 11-13, it can be seen that, in the second reference example as well, the keyhole KH is smaller and the change in the shape of the keyhole KH over time is greater compared to the examples in Figures 5-7 of this embodiment, similar to the first reference example. Furthermore, it can be seen that more sputtering S occurs in the second reference example.

[0046] Figures 14A and 14B are estimated cross-sectional views of the object W and molten pool WP corresponding to the cases shown in Figures 5 to 7 of this embodiment. Figures 15A and 15B are estimated cross-sectional views of the object W and molten pool WP corresponding to the cases shown in Figures 8 to 10 of Reference Examples A and B, which are the first reference examples. Figures 14A and 15A show the case where the keyhole KH penetrates the object W, while Figures 14B and 15B show the case where the keyhole KH does not penetrate the object W. Referring to Figures 14A and 14B, it is estimated that the phenomenon shown in the examples of Figures 5 to 7 is due to the secondary irradiation light L2 irradiating the inner circumferential surface KHb of the keyhole KH, thereby suppressing the relative approach of the inner circumferential surface KHb toward the center C of the keyhole KH. In this case, the secondary irradiation light L2 forms a relatively large keyhole KH, and maintains the keyhole KH in a relatively open state, suppressing deformation of the keyhole KH over time (expansion and contraction, opening and closing). This stabilizes the molten pool WP and makes it less likely for sputter S and voids V (see Figures 15A and 15B) to occur. On the other hand, in the examples of Figures 8-10, as shown in Figures 15A and 15B, the absence of secondary irradiation light L2 results in a relatively small keyhole KH being formed, and it becomes difficult to maintain the open state. This causes deformation of the keyhole KH over time (expansion and contraction, opening and closing), which makes the molten pool WP unstable and makes it more likely for sputter S and voids V to occur. In this embodiment, it is presumed that the secondary irradiation light L2 does not need to constantly irradiate the inner circumferential surface KHb. This is because, even when the sub-beam B2 is irradiating the inner surface KHb at a distance from the center C side of the keyhole KH, it is presumed that when the inner surface KHb approaches the sub-beam B2 as the molten pool WP moves and comes into contact with the sub-beam B2, the sub-beam B2 will suppress the inner surface KHb from moving further toward the center C side. Note that v in the figure represents vapor.

[0047] [Irradiation conditions] Figure 16 is a graph showing the relationship between scanning speed and sputter count for various cases where the width w (see Figure 3) of the spot of the secondary irradiation light L2 on the virtual plane VP is changed, and Figure 17 is a graph showing the relationship between scanning speed and the diameter (maximum diameter) of the keyhole KH for the same width w as in Figure 16. The width w is the width in the direction perpendicular to the scanning direction SD, as shown in Figure 3, and is the distance between the centers of the secondary beam B2 located at both ends in the direction perpendicular to the scanning direction. The graphs in Figures 16 and 17 are all experimental results, the output of the laser device 110 is 3kW (infrared light), the target object W is a SUS304 plate material, and the intensity ratio of the main irradiation light L1 to the secondary irradiation light L2 is 7:3. In the graph, the legend is as follows: ×: Main irradiation light L1 (main beam B1) only (no secondary irradiation light L2), △: w=1800 [μm], ◇: w=1400 [μm], □: w=1000 [μm], ▽: w=800 [μm], ◎: w=600 [μm], ○: w=440 [μm]. Also, the diameter d of the main irradiation light L1 is 198 [μm]. Here, the diameter d is 1 / e of the peak intensity. 2 This is defined as the diameter of the outer edge of the main beam B1. Note that this diameter d is an example of the width of the main beam B1 in the direction perpendicular to the scanning direction SD.

[0048] Figure 16 shows that when the scanning speed is less than 5 [m / min], irradiating with laser light including the main irradiation light L1 and the sub-irradiation light L2 reduces the number of sputters compared to irradiating with only the main irradiation light L1. This is presumed to be because a molten pool WP is formed around the keyhole KH, and the molten pool WP mitigates the metal vapor pressure generated inside the keyhole KH, and the molten pool WP also mitigates the molten metal flow around the keyhole KH.

[0049] Furthermore, Figure 16 shows that when the scanning speed is 1 [m / min] or less, the number of sputters decreases when w [μm] is 440 or more and 1000 or less (440 ≤ w ≤ 1000) compared to other cases (no sub-beam B2, w = 1400, w = 1800). Given that the diameter of the main beam B1 is d [μm], and d = 198, it was found that the number of sputters decreases when the ratio of the width w of the sub-beam B2 to the diameter d of the main beam B1 (w / d) is 2.23 or more and 5.05 or less. This is presumed to be because the sub-beam expands the diameter of the keyhole KH and sufficiently expels the metal vapor generated inside the keyhole KH, thus stably maintaining the internal shape of the keyhole KH without change.

[0050] Figure 17 shows that when w [μm] is between 440 and 600 (440 ≤ w ≤ 600), the diameter (maximum diameter) of the keyhole KH is larger compared to other cases (no sub-beam B2, w is between 800 and 1800). The diameter of the keyhole KH is defined as the maximum diameter (maximum width) of the opening edge KHa at the Z-direction end of the keyhole KH (see Figure 14A). In other words, it was found that the diameter of the keyhole KH is larger when the ratio of the width w of the sub-beam B2 to the diameter d of the main beam B1 (w / d) is between 2.23 and 3.03. As is clear from Figure 16, it was found that the number of sputters is lowest when w is between 440 and 600.

[0051] [Differentiation] Figures 18-23 are plan views showing modified laser beam spot configurations that achieve effects equivalent to or better than those in Figure 3 (Figures 5-7).

[0052] In the example shown in Figure 18, the spot of the secondary illumination light L2 (secondary beam B2) overlaps with the aperture edge KHa of the keyhole KH. In other words, the secondary illumination light L2 also partially illuminates the outside of the keyhole KH. In this case, the secondary illumination light L2 constantly illuminates the inner surface KHb of the keyhole KH, and it is possible to suppress the movement of this inner surface KHb toward the center C. The secondary beam B2 in Figure 18 is an example of the first secondary beam.

[0053] Through the inventor's diligent experimental research, it has been found that when the spot of the secondary irradiation light L2 (secondary beam B2) overlaps with the aperture edge KHa of the keyhole KH, it is preferable for more than half of the irradiation area of ​​the secondary irradiation light L2 on the virtual plane VP to be located inside the aperture edge KHa of the keyhole KH, as this reduces sputter S and void V. This is because the closer the irradiation area is to the aperture edge KHa side, i.e., the outside, the less the secondary irradiation light L2 contributes to suppressing the inward movement of the inner circumferential surface KHb, i.e., its efficiency. Furthermore, if the molten pool WP outside the aperture edge KHa is excessively heated by the secondary irradiation light L2, the molten pool WP may become unstable, potentially causing sputter S and void V.

[0054] In the example shown in Figure 19, the spot of the secondary illumination light L2 (secondary beam B2) is formed in a circumferential (ring-shaped in this example) manner, surrounding the optical axis Ax of the laser beam L and the main beam B1. Although the shape of the spot of the secondary illumination light L2 differs from that in Figure 3, the same effect as in Figure 3 is obtained in this case as well. The secondary beam B2 in Figure 19 is an example of a second secondary beam.

[0055] In the example in Figure 20, similar to the example in Figure 19, the spot of the secondary illumination light L2 (secondary beam B2) is formed circumferentially (ring-shaped in this example) surrounding the optical axis Ax of the laser beam L and the main beam B1. However, in the example in Figure 20, similar to the example in Figure 18, the secondary illumination light L2 overlaps with the aperture edge KHa of the keyhole KH. In other words, the secondary illumination light L2 also illuminates the outside of the keyhole KH in part. Although the shape of the spot of the secondary illumination light L2 differs from that in Figure 18, the same effect as in Figure 18 is obtained in this case as well. The secondary beam B2 in Figure 20 is an example of a second secondary beam.

[0056] In the example shown in Figure 21, the spot of the secondary illumination light L2 (secondary beam B2) is circular in shape. In other words, the outer edge of the spot is formed in a circumferential (ring-shaped in this example) manner surrounding the optical axis Ax and the main beam B1, and the entire area inside this outer edge is the illumination region of the secondary illumination light L2. Although the shape of the spot of the secondary illumination light L2 differs from that in Figure 3, the same effect as in Figure 3 can be obtained in this case as well. Note that in the example shown in Figure 21, the outer edge of the secondary illumination light L2 is circular, but it is not limited to this and may be elliptical, polygonal, or otherwise. The secondary beam B2 in Figure 21 is an example of a third secondary beam.

[0057] In the example in Figure 22, similar to the example in Figure 21, the spot of the secondary illumination light L2 (secondary beam B2) has a circular shape. However, in the example in Figure 22, similar to the example in Figure 18, the secondary illumination light L2 overlaps with the aperture edge KHa of the keyhole KH. In other words, the secondary illumination light L2 also illuminates the outside of the keyhole KH in part. Although the shape of the spot of the secondary illumination light L2 differs from that in Figure 18, the same effect as in Figure 18 is obtained in this case as well. The secondary beam B2 in Figure 22 is an example of a third secondary beam.

[0058] In the example shown in Figure 23, the spot is shown when the main irradiation light L1 (main beam B1) and the secondary irradiation light L2 (secondary beam B2) are both laser light with a wavelength of 600 [nm] or less, more preferably laser light with a wavelength of 400 [nm] or more and 550 [nm] or less. In this example, the diameters of the main beam B1 and secondary beam B2 are set to approximately 600 [μm], and the width w (see Figure 3) of the spot of the secondary irradiation light L2 on the virtual plane VP is set to 1200 [μm].

[0059] Figure 24 shows the power density at each position on the line segment passing through center C on the virtual plane VP when irradiated using the pattern in Figure 23. Figure 25 shows the power density at each position on the line segment passing through center C on the virtual plane VP when irradiated using the pattern in Figure 3. In both Figures 24 and 25, the intensity ratio of the main irradiation light L1 to the secondary irradiation light L2 is 7:3. According to the pattern in Figure 23, the unirradiated region between the main irradiation light L1 and the secondary irradiation light L2, as seen in the pattern in Figure 3, is eliminated. In this case, as shown in Figure 24, the power density on the virtual plane VP gradually increases as it approaches center C. According to the pattern in Figure 23, the change in power density depending on the location on the virtual plane VP becomes more gradual compared to the pattern in Figure 3, and the increase and decrease in power density can be eliminated. In other words, according to the pattern in Figure 23, the deformation of the keyhole KH over time (expansion and contraction, opening and closing) is suppressed compared to the pattern in Figure 3, which in turn stabilizes the molten pool WP and suppresses the generation of sputter S and void V.

[0060] The spots in Figures 21 and 22 can also be formed by laser light L output from an optical head 120 equipped with a double-clad optical fiber as the output optical fiber. The double-clad optical fiber has a core, a first cladding surrounding the core, and a second cladding surrounding the first cladding. In this configuration, for example, laser light is input to the core and the first cladding, respectively. As a result, the laser light transmitted mainly in the core is emitted to form the main irradiation light L1 (main beam B1), and the laser light transmitted mainly in the core and the first cladding forms the secondary irradiation light L2 (secondary beam B2). In this case as well, a power density that gradually increases as it approaches the center C, as shown in Figure 24, can be obtained. In this case as well, the main irradiation light L1 (main beam B1) and the secondary irradiation light L2 (secondary beam B2) may both be laser light with a wavelength of 600 [nm] or less, more preferably laser light with a wavelength of 400 [nm] or more and 550 [nm] or less.

[0061] [Second Embodiment] Figure 26 is a schematic diagram of the laser welding apparatus 100B (100) of the second embodiment. The laser welding apparatus 100B of this embodiment differs from the first embodiment in that it has two laser devices 111 and 112 as the laser device 110.

[0062] Laser devices 111 and 112 each output laser light of different wavelengths. Laser device 111 outputs laser light with a wavelength longer than the second laser light, for example, a wavelength of 800 nm to 1200 nm. Laser device 111 has, for example, a fiber laser or a semiconductor laser (device) as its laser light source.

[0063] Furthermore, the laser device 112 outputs a second laser beam with a shorter wavelength than the first laser beam, for example, a laser beam with a wavelength of 600 nm or less. The laser device 112 has, for example, a semiconductor laser (element) as a laser light source. It is also preferable that the laser device 112 outputs a second laser beam with a wavelength of 400 nm to 550 nm, which has a higher absorption rate for the object W.

[0064] Collimating lens 121-1 collimates the first laser beam, and collimating lens 121-2 collimates the second laser beam.

[0065] Mirror 123 reflects the first laser beam, which has become parallel light by the collimating lens 121-1, and directs it towards the galvanoscanner 126.

[0066] Filter 124 is a high-pass filter that transmits the first laser beam but reflects the second laser beam without transmitting it. The first laser beam passes through filter 124 and heads towards the galvanoscanner 126. On the other hand, the second laser beam from the collimating lens 121-2 is reflected by filter 124 and heads towards the galvanoscanner 126.

[0067] DOE125 splits the second laser beam into multiple beams. Note that DOE125 is optional.

[0068] The optical head 120 outputs a laser beam L including a first laser beam and a second laser beam, which is irradiated onto the object W. In this embodiment, the first laser beam can be used as the main irradiation beam L1, and the second laser beam as the secondary irradiation beam L2. The spot of the laser beam L can be a spot as shown in Figures 3, 18 to 22.

[0069] According to this embodiment, because the absorption rate of the second laser light is high, rapid temperature changes depending on the location in the molten pool WP can be suppressed, and consequently, the generation of sputter S and void V can be further suppressed.

[0070] As described above, in the above embodiment or modified version, in S1 (first step), the secondary irradiation light L2 is irradiated onto the inner circumferential surface KHb of the keyhole KH. According to this feature, the secondary irradiation light L2 maintains the keyhole KH in a relatively wide open state, suppressing deformation of the keyhole KH over time (expansion and contraction, opening and closing), thereby stabilizing the molten pool WP and the keyhole KH, and suppressing the generation of sputter S and void V.

[0071] Furthermore, the secondary irradiation light L2 may be continuously irradiated onto the inner surface KHb. In this case, the movement of the inner surface KHb toward the center C of the keyhole KH is constantly suppressed, stabilizing the molten pool WP and keyhole KH, and suppressing the generation of sputter S and void V.

[0072] Furthermore, the secondary irradiation light L2 may be irradiated to the center C side of the keyhole KH rather than the inner surface KHb. In this case, when the inner surface KHb moves closer to the center C of the keyhole KH, the secondary irradiation light L2 is applied to the inner surface KHb, and it is possible to suppress the movement of the inner surface KHb toward the center C from the irradiation position of the secondary irradiation light L2 at that point. In this case as well, the molten pool WP and keyhole KH can be stabilized, and the generation of sputter S and void V can be suppressed.

[0073] Furthermore, if the laser device 112 is a semiconductor laser device, the M of the second laser beam 2The beam quality is set to, for example, 60 or higher and 230 or lower. In that case, the diameter of each sub-beam B2 can be, for example, 200 [μm] or higher and 1500 [μm] or lower.

[0074] Although embodiments and modifications of the present invention have been illustrated above, these embodiments and modifications are merely examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. Furthermore, each configuration, shape, and other specifications (structure, type, orientation, model, size, length, width, thickness, height, number, arrangement, position, material, etc.) can be modified as appropriate. [Explanation of Symbols]

[0075] 100, 100A, 100B… Laser welding equipment 110, 111, 112… Laser devices 120…Optical head 121, 121-1, 121-2… Collimating lenses 122... Focusing lens 123...Mirror 124... Filter 125...Diffractive optical element (DOE) 125a...Diffraction grating 126... Galvanometer scanner (laser scanner) 126a, 126b…Mirror 130… Fiber optic 140…Drive mechanism Ax…Optical axis B1... Main beam B2... Sub-beam C…center d…Diameter (width) KH...Keyhole KHa... Opening edge KHb…Inner peripheral surface L... Laser light L1…Main irradiation light L2…Sub-irradiation light S...Spatter S1…Process S2…Process (first process) S3…Process (second process) SD... scanning direction t11~t33…Time V...Void VP…Virtual Plane W...Object (object to be processed) Wa... Surface WP…Melting pool w…width X…direction Y... Direction Z…direction

Claims

1. A laser welding method comprising: a first step of irradiating a workpiece with laser light to melt the workpiece and form a molten pool; and a second step of cooling and solidifying the molten pool, The laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a secondary irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, A laser welding method in which, in the first step, the secondary irradiation light is irradiated onto the inner circumferential surface of the keyhole to suppress the movement of the inner circumferential surface toward the center of the keyhole.

2. The laser welding method according to claim 1, wherein, in the first step, when viewed in the direction of irradiation of the laser beam, at least half of the irradiation area of ​​the secondary irradiation light on a virtual plane perpendicular to the irradiation direction, passing through a position that is the end of the irradiation area of ​​the laser beam on the surface of the workpiece before irradiation of the laser beam in the direction opposite to the irradiation direction, is located inside the opening edge of the keyhole.

3. A laser welding method comprising: a first step of irradiating a workpiece with laser light to melt the workpiece and form a molten pool; and a second step of cooling and solidifying the molten pool, The laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a secondary irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, In the first step, the secondary irradiation light is irradiated to the side of the keyhole that is closer to the center of the keyhole than the inner surface of the keyhole, thereby suppressing the relative movement of the inner surface toward the center of the keyhole.

4. The laser welding method according to any one of claims 1 to 3, wherein in the first step, the laser beam is scanned relative to the surface of the workpiece.

5. The laser welding method according to any one of claims 1 to 3, wherein the secondary irradiation light includes a plurality of first secondary beams arranged circumferentially around the optical axis of the laser light as the secondary beam.

6. The laser welding method according to any one of claims 1 to 3, wherein the secondary irradiation light includes a second secondary beam formed circumferentially around the optical axis of the laser light as the secondary beam.

7. The laser welding method according to any one of claims 1 to 3, wherein the secondary irradiation light includes a third secondary beam formed as the secondary beam, having an outer peripheral edge surrounding the optical axis of the laser light.

8. The laser welding method according to any one of claims 1 to 3, wherein in the first step, a keyhole is formed in the workpiece by the main irradiation light, and the maximum diameter of the keyhole is enlarged by the sub-irradiation light compared to when the main irradiation light is irradiated alone.

9. The laser welding method according to claim 8, wherein in the first step, the ratio of the width of the spot of the sub-irradiation light in a virtual plane perpendicular to the irradiation direction, passing through a position that is the end of the irradiation area of ​​the laser light on the surface of the workpiece before irradiation with the laser light, to the width of the spot of the main irradiation light is set to 2.23 or more and 5.05 or less.

10. The laser welding method according to claim 9, wherein in the first step, the ratio is set to 3.03 or less.

11. A laser light source, An optical head that directs the laser light output from the laser light source toward the workpiece, A laser welding apparatus equipped with, for welding the workpiece, The laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a secondary irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, A laser welding apparatus that suppresses the movement of the inner surface of the keyhole toward the center of the keyhole by irradiating the inner surface of the keyhole with the aforementioned secondary irradiation light.

12. A laser light source, An optical head that directs the laser light output from the laser light source toward the workpiece, A laser welding apparatus equipped with, for welding the workpiece, The laser light includes a main irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, and a secondary irradiation beam having a power density capable of forming a keyhole in the workpiece on its own, A laser welding apparatus that suppresses the relative movement of the inner surface of the keyhole toward the center of the keyhole by irradiating the aforementioned secondary irradiation light from the inner surface of the keyhole toward the center of the keyhole.

Images