Laser welding device and laser welding method

Abstract

To improve the crack resistance of a weld bead.SOLUTION: A laser welding device comprises: a first laser oscillator for generating a first laser beam; a second laser oscillator for generating a second laser beam; and a processing head for irradiating a workpiece with the first laser beam and the second laser beam. The first laser beam and the second laser beam are irradiated with at a prescribed interval in a direction along a welding direction. The second laser beam is irradiated rearward of a first molten pool formed by the first laser beam, that is in a reverse direction of the direction along the welding direction.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a laser welding apparatus and a laser welding method. [Background technology]

[0002] Patent Document 1 discloses a heat treatment method for laser welds of high-tensile steel plate, which is characterized in that, in laser welding of high-tensile steel plate, a heating means is used to locally heat a portion including the weld metal to a temperature of Ac1 point or lower and 400°C or higher for a time of 0.1 seconds to 10 minutes after one second or more has passed since the passage of the welding laser beam, and cooling is performed using cooling means to cool the heat-affected zone on both sides of the weld metal of the steel plate both when the welding laser beam passes and when the steel plate passes through the heating means. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-209497 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure has been devised in view of the conventional circumstances, and provides a laser welding apparatus and a laser welding method that improve the crack resistance of a weld bead. [Means for solving the problem]

[0005] The present disclosure provides a laser welding device comprising a first laser oscillator that generates a first laser beam, a second laser oscillator that generates a second laser beam, and a processing head that irradiates the first laser beam and the second laser beam onto a workpiece, wherein the first laser beam and the second laser beam are irradiated at a predetermined interval in a direction along the welding direction, and the second laser beam is irradiated in a direction opposite to the welding direction, toward the rear of a first molten pool formed by the first laser beam.

[0006] The present disclosure also provides a laser welding method performed by a laser welding apparatus including a first laser oscillator that generates a first laser beam, a second laser oscillator that generates a second laser beam, and a processing head that irradiates the first laser beam and the second laser beam onto a workpiece, in which the first laser beam and the second laser beam are irradiated at a predetermined interval in a direction along the welding direction, and the second laser beam is irradiated in a direction opposite to the welding direction toward the rear of a first molten pool formed by the first laser beam. Effect of the Invention

[0007] According to the present disclosure, the crack resistance of the weld bead is improved. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a schematic configuration example of a laser welding device according to first and second embodiments. [Diagram 2] FIG. 2 is a diagram showing a schematic configuration example of a processing head according to the first embodiment; [Diagram 3] FIG. 1 is a diagram for explaining an example of the positional relationship of a first laser beam and a second laser beam with respect to a weld line; [Figure 4] FIG. 1 is a diagram illustrating a molten pool and a keyhole formed by a first laser beam and a second laser beam; [Diagram 5] FIG. 2 is a cross-sectional view taken along the line AA-AA showing an example of a molten pool and a keyhole formed by a first laser beam and a second laser beam. [Figure 6] A diagram showing an example of the molten pool shape and temperature distribution [Figure 7] FIG. 1 shows an example of control of a first laser beam and a second laser beam. [Figure 8] FIG. 13 is a diagram for explaining an example of a first scanning locus of a second laser beam; [Figure 9] FIG. 13 is a diagram for explaining an example of a second scanning locus of a second laser beam; [Figure 10] FIG. 13 is a diagram for explaining an example of a third scanning trajectory of a second laser beam; [Figure 11] FIG. 13 is a diagram for explaining an example of a fourth scanning trajectory of a second laser beam; [Figure 12] FIG. 13 is a diagram showing an example of a first scanning speed of a second laser beam; [Figure 13] FIG. 13 is a diagram showing an example of a second scanning speed of a second laser beam. [Figure 14] FIG. 13 is a diagram showing a schematic configuration example of a processing head according to a second embodiment; [Figure 15] FIG. 1 shows an example of the shape of the molten pool, the temperature distribution, and the solidification form during conventional high-speed welding. [Figure 16] FIG. 1 shows an example of the shape of the molten pool, the temperature distribution, and the solidification form during conventional low-speed welding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (Background to this disclosure) Laser light has a high power density and can perform high-speed, high-quality welding, so it is used to weld a variety of workpieces, such as mild steel and high-tensile steel. However, in actual laser welding of high-tensile steel, if the welding speed is too fast, the amount of heat input per unit length decreases and the cooling rate of the molten part increases, causing the formed weld metal to solidify rapidly, increasing the hardness of the weld metal part and decreasing its toughness, which is a problem.

[0010] Here, an example of the shape, temperature distribution, and solidification form of the molten pool WP formed by a conventional laser processing method will be described. Fig. 15 is a diagram showing an example of the shape, temperature distribution, and solidification form of the molten pool WP during conventional high-speed welding. Fig. 16 is a diagram showing an example of the shape, temperature distribution, and solidification form of the molten pool WP during conventional low-speed welding.

[0011] In the case of high-speed welding, a temperature gradient occurs in the direction indicated by the dashed arrow TGD in the molten pool WP (see Figure 15), and the molten pool WP solidifies along this temperature gradient (dashed arrow TGD). In high-speed welding, in which the welding speed of the laser beam LB moving in the welding direction WD is fast, the heat input per unit length to the workpiece WK is small and the cooling rate is high, so the direction of the temperature gradient indicated by the dashed arrow TGD is an approximately linear shape that is approximately perpendicular to the isothermal line ETL of the molten pool WP. The molten pool WP solidifies at high speed from the boundary between the molten pool WP and the workpiece WK toward the welding point of the laser beam LB (the center of the molten pool WP).

[0012] As a result, in the solidified weld bead WB, in the columnar crystal region CCA shown in Fig. 15, columnar crystals are formed that extend in a direction substantially perpendicular to the isothermal line ETL of the molten pool WP in the direction of the dashed arrow TGD (i.e., the direction of the temperature gradient) from the boundary between the molten pool WP and the workpiece WK along the welding direction WD toward the welding point of the laser beam LB (the center of the molten pool WP). The growth direction of these columnar crystals is substantially the same as the dashed arrow TGD. As the welding speed increases, the length of these columnar crystals increases, and they grow from the boundary between the molten pool WP and the workpiece WK toward the center of the molten pool WP so as to collide with each other at the center of the molten pool WP.

[0013] The weld bead WB after solidification usually contains a large amount of impurities near the final solidification position B of the molten pool WP, so hot cracks are likely to occur near the final solidification position B. If hot cracks occur, the entire center of the weld line (welding point of the laser beam LB) may crack. Even if hot cracks do not occur in the weld bead WB after solidification, the workpiece WK may become dirty, or hydrogen may dissolve in the molten metal after welding if the shielding gas contains moisture. If hydrogen dissolves, for example, the weld bead WB after solidification may become brittle in materials such as high tensile steel. Therefore, the weld bead WB after solidification may suffer from low-temperature cracks due to hydrogen.

[0014] On the other hand, in the case of low-speed welding, a temperature gradient occurs in the direction indicated by the dashed arrow TGD in the molten pool WP (see FIG. 16) in the same manner as in the case of high-speed welding, and the molten pool WP solidifies along this temperature gradient (dashed arrow TGD). The temperature gradient in low-speed welding bends more gently near the final solidification position B of the molten pool WP compared to the temperature gradient in high-speed welding. This means that the temperature gradient toward the weld center line near the final solidification position B of the molten pool WP is small. As a result, in the case of low-speed welding, columnar crystals with a substantially linear shape are formed near the boundary between the molten pool WP and the workpiece WK along the welding direction WD (columnar crystal area CCA), but substantially equiaxed crystals are formed in the central region (equiaxed crystal area ECA) of the weld line (welding point of the laser beam LB). Even if some columnar crystals are formed in the equiaxed crystal area ECA depending on the welding conditions, the formed columnar crystals generally have a small difference between the length in the welding direction and the length in the direction perpendicular to the welding direction.

[0015] When the equiaxed crystal region ECA is formed, impurities at the time of final solidification are dispersed not only near the final solidification position B of the molten pool WP but also in the equiaxed crystal region ECA. The weld bead WB after solidification is not only less susceptible to high temperature cracking, but also to low temperature cracking caused by dissolved hydrogen. Therefore, even when performing high speed welding, it is desirable for equiaxed crystals to be formed near the final solidification position B of the molten pool, but this was difficult to achieve with conventional technology.

[0016] As shown in the temperature distribution of the molten pool WP in Figures 15 and 16, respectively, the temperature gradient becomes higher during high-speed welding. In the temperature distribution of the molten pool WP shown in Figures 15 and 16, the vertical axis indicates the temperature of the molten pool WP, and the horizontal axis indicates the position of the molten pool WP starting from the molten tip A. The melting point Tm indicates the melting point of the workpiece WK. The temperature gradient near the final solidification position B during high-speed welding is equal to the tangent to the temperature distribution curve, but the larger the inclination angle αH between this tangent and the horizontal axis, the larger the temperature gradient TGC. On the other hand, the temperature gradient near the final solidification position B during low-speed welding has an inclination angle αL between the tangent to the temperature distribution curve and the horizontal axis that is smaller than the inclination angle αH during high-speed welding (αH>αL), and it can be seen that the temperature gradient TGC is smaller.

[0017] As a method for solving such a problem, it has been proposed to add another laser beam for heating after performing laser welding (see Patent Document 1). However, although this method can reduce the hardness of the weld metal, if the welding speed is too fast, not only does the weld metal become hard, but columnar crystals are formed from the solidified weld metal, which may cause hot cracks to form in the center of the weld bead, and hydrogen embrittlement may occur after welding due to the influence of the atmosphere during welding. Therefore, the conventional proposed methods can reduce the hardness of the metal structure after welding, but cannot change the shape of the metal structure itself that has become columnar crystals.

[0018] In the following embodiments, an example of a laser welding apparatus and a laser welding method for improving the crack resistance of a weld bead will be described.

[0019] Hereinafter, with reference to the drawings as appropriate, each embodiment specifically disclosing the laser welding apparatus and the laser welding method according to the present disclosure will be described in detail. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted. This is to avoid the following explanation becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the attached drawings and the following explanation are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0020] (Embodiment 1) The laser welding apparatus 100 of embodiment 1 irradiates multiple laser beams (first laser beam LB1 and second laser beam LB2) from the processing head HD toward the workpiece WK, and prevents high-temperature cracking that occurs during solidification or low-temperature cracking that occurs after solidification by changing the shape of the metal structure at the final solidification position B when the molten pool solidifies.

[0021] <1. Configuration of laser welding equipment> 1 is a diagram showing a schematic configuration example of laser welding apparatuses 100, 100A according to embodiments 1 and 2. The laser welding apparatus 100 includes a first laser oscillator LOC1, a second laser oscillator LOC2, two optical fibers F1, F2, a processing head HD, a manipulator MN, and a controller CON. Note that the laser welding apparatus 100A according to embodiment 2 will be described later, and will not be described here.

[0022] In the following description, the direction in which the first laser beam LB1 and the second laser beam LB2 are respectively irradiated from the machining head HD to the workpiece WK is referred to as the Z direction, and the two directions constituting the planar direction perpendicular to the Z direction are referred to as the X direction and the Y direction.

[0023] The first laser oscillator LOC1 is a laser light source that receives power from a laser driving power supply (not shown) and generates the first laser beam LB1. The first laser oscillator LOC1 may be composed of a single laser light source or may be composed of multiple laser modules.

[0024] The second laser oscillator LOC2 is a laser light source that receives power from a laser driving power supply (not shown) and generates the second laser beam LB2. The second laser oscillator LOC2 may be composed of a single laser light source or may be composed of multiple laser modules.

[0025] The laser light source or laser module used in each of the first laser oscillator LOC1 and the second laser oscillator LOC2 is appropriately selected depending on the material of the workpiece WK to be welded, the shape of the welded portion, and the like.

[0026] For example, a fiber laser, a disk laser, or a Yttrium Aluminum Garnet (YAG) laser can be used as the laser light source. In this case, the wavelengths of the first laser beam LB1 and the second laser beam LB2 are set in the range of 1000 [nm] to 1100 [nm].

[0027] Also, for example, a semiconductor laser may be used as the laser light source or the laser module. In this case, the wavelengths of the first laser beam LB1 and the second laser beam LB2 are set in the range of 800 [nm] to 1000 [nm]. Also, a visible light laser may be used as the laser light source or the laser module. In this case, the wavelengths of the first laser beam LB1 and the second laser beam LB2 are set in the range of a blue wavelength band of 420 [nm] to 500 [nm] and a green wavelength band of 480 [nm] to 560 [nm]. Note that it is desirable that the wavelength λ1 of the first laser beam LB1 is equal to or greater than the wavelength λ2 of the second laser beam LB2 (λ1 ≧ λ2).

[0028] The optical fiber F1 has one end (incident end) optically coupled to the first laser oscillator LOC1 and the other end (exit end) optically coupled to the processing head HD, has a core (not shown) at its axis, and is provided with a clad (not shown) coaxially with the core in contact with the outer circumferential surface of the core. The core and the clad are each mainly composed of quartz, and the refractive index of the core is higher than that of the clad. Therefore, the first laser beam LB1 generated by the first laser oscillator LOC1 is incident on the incident end of the optical fiber F1 and is transmitted through the inside of the core toward the exit end while repeatedly being reflected. In addition, a coating (not shown) or a resin-based protective layer (not shown) that mechanically protects the optical fiber F1 is provided on the outer circumferential surface of the clad.

[0029] The optical fiber F2 has one end (incident end) optically coupled to the second laser oscillator LOC2 and the other end (exit end) optically coupled to the processing head HD, has a core (not shown) at its axis, and is provided with a clad (not shown) coaxially with the core in contact with the outer circumferential surface of the core. The core and the clad are each mainly composed of quartz, and the refractive index of the core is higher than that of the clad. Therefore, the second laser beam LB2 generated by the second laser oscillator LOC2 is incident on the incident end of the optical fiber F2 and is transmitted through the inside of the core toward the exit end while repeatedly being reflected. In addition, a coating (not shown) or a resin-based protective layer (not shown) that mechanically protects the optical fiber F2 is provided on the outer circumferential surface of the clad.

[0030] The processing head HD is attached to the output ends of the optical fibers F1 and F2, and contains at least one optical element (see FIG. 2) and a protective glass PW (see FIG. 2). An example of the internal configuration of the processing head HD according to the first embodiment will be described in detail with reference to FIG. 2. The processing head HD collimates the first laser beam LB1 and the second laser beam LB2, which are transmitted and spread through the optical fibers F1 and F2, into parallel light. The processing head HD combines and focuses the collimated parallel light, transmits the light through the protective glass PW, and irradiates the light toward the workpiece WK as the first laser beam LB1 and the second laser beam LB2, respectively. This enables the processing head HD to process the workpiece WK by laser welding.

[0031] The manipulator MN is, for example, a known vertical six-axis robot having six joint axes. The sixth joint axis is provided at the tip of a robot arm equipped to the manipulator MN. The manipulator MN can grasp the processing head HD via a gripping part (not shown) from the sixth joint axis, and controls the position of the processing head HD so that it can be moved based on a command signal transmitted from the controller CON.

[0032] The controller CON has a control unit PRO configured with a processor etc., and a storage unit MEM configured with a memory etc. The controller CON controls the timing, output, start, end, etc. of the laser oscillation of each of the first laser oscillator LOC1 and the second laser oscillator LOC2.

[0033] Specifically, the controller CON controls the laser oscillation and laser output in the control unit PRO by supplying control signals such as output current and on / off time to welding power sources (not shown) connected to the first laser oscillator LOC1 and the second laser oscillator LOC2, respectively. The controller CON also controls the position of the processing head HD via a driver (not shown) in accordance with the contents of a processing program for performing laser welding (processing) on ​​the workpiece WK stored in the memory unit MEM. The controller CON also generates command signals for controlling the operation of the manipulator MN and sends them to the manipulator MN.

[0034] The memory unit MEM stores a processing program for laser welding. The memory unit MEM may be provided inside the controller CON as shown in Fig. 1, or may be provided outside the controller CON and configured to be able to exchange data with the controller CON. The memory unit MEM stores information about the scanning trajectory of the second laser beam LB2 that is taught in advance by a teaching pendant (not shown) or the like.

[0035] <2. Processing head configuration example> Next, a configuration example of the processing head HD according to the first embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram showing a schematic configuration example of the processing head HD according to the first embodiment.

[0036] The processing head HD houses within a housing along the Z direction a first fiber coupling portion FC1 and a second fiber coupling portion FC2, a first collimating lens CL1 and a second collimating lens CL2, a mirror DM, a galvano unit GU, a focusing lens FL, and a protective glass PW.

[0037] The first fiber coupling portion FC1 is connected to the other end side (see above) of the optical fiber F1, and causes the first laser beam LB1 guided via the optical fiber F1 to be incident (guided) into the housing of the processing head HD.

[0038] The first collimating lens CL1 is an example of an optical element, and collimates the first laser beam LB1 diverging from the first fiber coupling portion FC1.

[0039] The mirror DM is configured to be drivable in a direction MD (Z direction or -Z direction) based on drive control by a controller CON of a motor (not shown) arranged in the processing head HD, for example. The mirror DM transmits the first laser beam LB1 and causes it to proceed toward the condenser lens FL, and reflects the second laser beam LB2 and causes it to proceed toward the condenser lens FL. The mirror DM may be configured of a dichroic mirror.

[0040] The condenser lens FL is an example of an optical element, and condenses the first laser beam LB1 collimated by the first collimator lens CL1 and the second laser beam LB2 collimated by the second collimator lens CL2 toward a predetermined welding point on the workpiece WK. The condenser lens FL may be configured as a single lens or may be configured with multiple lenses.

[0041] The protective glass PW prevents contamination inside the processing head HD caused by flying debris (e.g., spatter, fumes) that is generated when the first laser beam LB1 and the second laser beam LB2 are irradiated onto the workpiece WK to perform welding, from entering the processing head HD.

[0042] The second fiber coupling portion FC2 is connected to the other end side (see above) of the optical fiber F2, and causes the second laser beam LB2 guided via the optical fiber F2 to be incident (guided) into the housing of the processing head HD.

[0043] The second collimator lens CL2 is an example of an optical element, and collimates the second laser beam LB2 diverging from the second fiber coupling portion FC2. The collimated second laser beam LB2 travels toward the galvano unit GU.

[0044] The galvano unit GU controls the X-axis mirror MX and the Y-axis mirror MY in two axes in the X direction or the Y direction, based on the drive control by the controller CON of a motor (not shown) arranged in the processing head HD, for example. The galvano unit GU controls the irradiation position of the second laser beam LB2 on the workpiece WK by controlling the X-axis mirror MX and the Y-axis mirror MY in two axes. For example, the galvano unit GU controls the irradiation position of the second laser beam LB2 irradiated toward the workpiece WK on the trajectories shown in the first scan trajectory RAa (see FIG. 8), the second scan trajectory RAb (see FIG. 9), the third scan trajectory RAc (see FIG. 10), and the fourth scan trajectory RAd (see FIG. 11) described later.

[0045] The optical axis cc' shown in Fig. 2 is the optical axis of the first laser beam LB1 that travels from the first fiber coupling part FC1 toward a predetermined welding point on the workpiece WK. The first laser beam LB1 spreads when it enters the processing head HD from the first fiber coupling part FC1 and is collimated by the first collimating lens CL1. After being collimated, the first laser beam LB1 passes through the mirror DM and is focused by the focusing lens FL, passes through the protective glass PW, and is then irradiated toward the predetermined welding point on the workpiece WK.

[0046] The optical axis d''''-d'' shown in FIG. 2 is the optical axis of the second laser beam LB2 that travels from the second fiber coupling part FC2 to a predetermined welding point on the workpiece WK. When the second laser beam LB2 enters the processing head HD from the second fiber coupling part FC2, it spreads out and is collimated by the second collimator lens CL2. After being collimated, it travels toward the galvano unit GU (optical axis d''''-d''''). In the galvano unit GU, the second laser beam LB2 is reflected by the X-axis mirror MX or the Y-axis mirror MY (optical axis d''-d''), and travels toward the mirror DM (optical axis d''-d). The second laser beam LB2 is reflected by the mirror DM and collected by the collecting lens FL, passes through the protective glass PW, and is then irradiated toward the predetermined welding point on the workpiece WK (optical axis dd'').

[0047] Here, when the X-axis mirror MX and the Y-axis mirror MY are both in the origin position by the galvano unit GU, the optical axis (optical axis cc') of the first laser beam LB1 and the optical axis (optical axis dd') of the second laser beam LB2 become approximately parallel, and are irradiated toward a specified welding point on the workpiece WK with a beam distance LB12.

[0048] Next, an example of the positional relationship between the first laser beam LB1 and the second laser beam LB2 during welding will be described with reference to Fig. 3. Fig. 3 is a diagram illustrating an example of the positional relationship between the first laser beam LB1 and the second laser beam LB2 with respect to the weld line WL.

[0049] When welding a weld line WL in the welding direction WD, the processing head HD irradiates the first laser beam LB1 along the weld line WL and the second laser beam LB2 along a predetermined trajectory (see Figs. 8 to 11) so as to follow the first laser beam LB1. The first laser beam LB1 and the second laser beam LB2 are arranged such that a straight line connecting the optical axis of the first laser beam LB1 and the scan center O of the second laser beam LB2 (see Figs. 8 to 11) coincides with the tangential direction of the weld line WL, and the distance between the optical axes of the first laser beam LB1 and the scan center of the second laser beam LB2 is an inter-beam distance LB12.

[0050] <3. Example of irradiation with the first laser beam and the second laser beam> Next, with reference to Fig. 4 and Fig. 5, an example of irradiation of the first laser beam LB1 and the second laser beam LB2 in the first and second embodiments and keyholes KH1, KH2 formed by the first laser beam LB1 and the second laser beam LB2 will be described. Fig. 4 is a top view illustrating an example of the arrangement of the first laser beam LB1 and the second laser beam LB2. The molten pool WPC1 when only the first laser beam LB1 is irradiated is shown by a dotted line, and the molten pool WPC2 (or the molten pool WP) when both the first laser beam LB1 and the second laser beam LB2 are irradiated is shown by a solid line. Fig. 5 is an AA-AA cross-sectional view showing an example of the molten pool WP and keyholes KH1, KH2 in the first and second embodiments.

[0051] The processing head HD performs high-speed welding while moving in the welding direction WD. The processing head HD is disposed so that the first laser beam LB1 and the second laser beam LB2 are spaced apart by an inter-beam distance LB12, and irradiates the first laser beam LB1 and the second laser beam LB2 in that order along the welding direction WD toward the weld line WL of the workpiece WK.

[0052] The first laser beam LB1 is irradiated to the workpiece WK to form a molten pool WP and a keyhole KH1 in the molten pool WP. If the second laser beam LB2 is not irradiated, the temperature gradient (inclination angle αH) is large (see FIG. 15) near the final solidification position B (see FIG. 4) of the molten pool WP indicated by the dotted line, and columnar grains are formed after welding is completed.

[0053] As shown in Figure 4, in the present invention, a keyhole KH2 is formed by irradiating a second laser beam LB2 at a distance LB2D in the opposite direction to the welding direction WD from the final solidification position B of the molten pool WP formed by irradiating only the first laser beam LB1 (see Figure 5).

[0054] That is, the first laser beam LB1 is irradiated to the workpiece WK (optical axis cc') to form a keyhole KH1 with a penetration depth M1. The second laser beam LB2 is irradiated to the workpiece WK (optical axis dd') to form a keyhole KH2 with a penetration depth M2. Here, the central axis ee' of the keyhole KH1 formed by the first laser beam LB1 does not coincide with the optical axis cc' of the first laser beam LB1. Usually, the inclination of the keyhole KH1 with respect to the Z direction is larger than the optical axis of the first laser beam LB1. Similarly, the central axis ff' of the keyhole KH2 formed by the second laser beam LB2 does not coincide with the optical axis dd' of the second laser beam LB2. In this case, too, the inclination of the keyhole KH2 with respect to the Z direction is larger than the optical axis of the second laser beam LB2.

[0055] Although not shown, it is desirable to set the keyhole depth M2 of the molten pool WP formed by the second laser beam LB2 to a depth of approximately 1 / 2 or less of the keyhole depth M1 of the molten pool WP formed by the first laser beam LB1. By doing so, the heat input to the molten pool near the keyhole KH2 is suppressed, and the size of the molten pool is reduced.

[0056] As described above, the second laser beam LB2 changes the molten pool shape at the final solidification position B of the molten pool WP formed when the first laser beam LB1 is irradiated alone, which is similar to that of high-speed welding (see Figure 15), to a molten pool shape at the final solidification position C similar to that of low-speed welding (see Figure 16), thereby changing the metal structure in the vicinity of the final solidification position C from columnar crystals to equiaxed crystals, thereby improving the crack resistance of the weld bead formed on the workpiece WK.

[0057] In other words, the second laser beam LB2 changes the teardrop-shaped molten pool WPC1 formed by irradiating only the first laser beam LB1 into a gourd-shaped molten pool WPC2, thereby changing the metal structure near the final solidification position C from columnar crystals to equiaxed crystals, thereby improving the crack resistance of the weld bead formed on the workpiece WK.

[0058] Moreover, it is desirable that the first beam radius w1 of the first laser beam LB1 on the surface of the workpiece WK and the second beam radius w2 of the second laser beam LB2 on the surface of the workpiece WK satisfy the relationship given by the following formula 1. w2≦(1 / 4×w1)~(w1) (Formula 1)

[0059] Here, the first beam radius w1 indicates the beam radius of the first laser beam LB1, and the second beam radius w2 indicates the beam radius of the second laser beam LB2.

[0060] When rotating the second laser beam LB2 at high speed, the processing head HD rotates with a rotation radius of 1 / 2 or less of the width LL of the maximum molten pool formed by the single irradiation of the first laser beam LB1. The width LL of the maximum molten pool is the size of the molten pool WP in a direction perpendicular to the weld line WL. The processing head HD scans in a direction perpendicular to the second laser beam LB2 with an amplitude of 1 / 2 or less of the width LL of the maximum molten pool formed by the single irradiation of the first laser beam LB1. The size of the width LL of the maximum molten pool may be measured in advance by performing laser welding.

[0061] When rotating or scanning while irradiating the second laser beam LB2, it is desirable to suppress the heat input to the workpiece WK without widening the width LL of the largest molten pool formed by irradiation with the first laser beam LB1 alone as much as possible. Therefore, the width LL of the largest molten pool formed by irradiation with the first laser beam LB1 alone is usually hardly affected by the second laser beam. This is why the widths of the molten pool WPC1, molten pool WPC2, and molten pool WP in Figure 4 are all written as LL.

[0062] When the workpiece WK has a thin plate thickness, the second laser beam LB2 only needs to be capable of thermal conduction welding, and there is no need to form the keyhole KH2.

[0063] <4. Example of temperature distribution and temperature gradient in molten pool> In the above explanation, it has been explained that the metal structure in the vicinity of the final solidification position C is changed from columnar crystals to equiaxed crystals when the second laser beam LB2 is irradiated from the viewpoint of the molten pool shape or the keyhole shape. Next, the temperature distribution and temperature gradient of the molten pool WP formed by the irradiation of the first laser beam LB1 and the second laser beam LB2 in the first and second embodiments will be explained with reference to Fig. 6, and the formation of equiaxed crystals will be explained. Fig. 6 is a diagram showing an example of the molten pool shape and the temperature gradient.

[0064] The molten pool WPC1 indicated by the dashed line in Figure 6 is a molten pool formed only by irradiation with the first laser beam LB1. The molten pool WPC1 has a teardrop shape. The molten pool WPC2 is a molten pool formed by irradiating the second laser beam LB2 after irradiation with the first laser beam LB1. The molten pool WPC2 has a gourd shape. In other words, the molten pool WPC1 has a pointed shape at the final solidification position B (see Figure 15), whereas the molten pool WPC2 has a rounded shape at the final solidification position C (see Figure 16).

[0065] When high speed welding is performed by irradiating only the first laser beam LB1 as in the conventional case, the temperature gradient at the final solidification position B has an inclination angle αH.

[0066] In contrast, when high speed welding is performed by irradiating the first laser beam LB1 and the second laser beam LB2 as shown in the present disclosure, the temperature gradient at the final solidification position C is the inclination angle αM. Here, the relationship between the inclination angles is inclination angle αH>αM. Although not shown, the magnitude of the inclination angle αM is usually smaller than the inclination angle αH and larger than the inclination angle αL.

[0067] As a result, in the conventional method of irradiating only the first laser beam LB1, columnar crystals are formed in the center of the weld bead (see Figure 15), whereas in the method disclosed herein, equiaxed crystals can be formed, thereby improving the crack resistance of the weld bead.

[0068] Next, the output timing of the first laser beam LB1 and the second laser beam LB2 in the first and second embodiments will be described with reference to Fig. 7. Fig. 7 is a diagram showing an example of control of the first laser beam and the second laser beam.

[0069] The first laser oscillator LOC1 turns on the output of the first laser beam at the timing when welding of the weld line WL starts. The second laser oscillator LOC2 starts (On) the output of the second laser beam LB2 at a timing delayed by a time Δt from the timing when the output of the first laser beam LB1 starts (On).

[0070] The first laser oscillator LOC1 turns off the output of the first laser beam at the timing when welding of the weld line WL ends. The second laser oscillator LOC2 turns off the output of the second laser beam LB2 at a timing delayed by a time Δt from the timing when the output of the first laser beam LB1 ends (Off).

[0071] The above-mentioned time Δt is calculated based on the inter-beam distance LB12 and the welding speed v by the following (Equation 2). Δt=LB12 / v (Equation 2)

[0072] As a result, the laser welding apparatus 100 in the present embodiments 1 and 2 can irradiate the second laser beam LB2 over the entire length of the molten pool WP formed by irradiation with the first laser beam LB1, and can change the central portion of the weld bead from columnar crystals to equiaxed crystals over the entire length of the weld bead, including the start position and end position of welding.

[0073] <5. Example of scanning trajectory of second laser beam> Next, examples of the scanning locus of the second laser beam LB2 will be described with reference to each of FIGS.

[0074] <5-1. Example of first scan trajectory> 8 is a diagram illustrating an example of a first scanning locus RAa of the second laser beam LB2. In FIG. 8, an example is shown in which the optical axis O1 of the first laser beam LB1 and the scanning center O of the second laser beam LB2 are both located on the weld line WL.

[0075] The first scan trajectory RAa is located on an arc RA1 of a circle whose center point is the optical axis O1 of the first laser beam LB1 and whose radius is the inter-beam distance LB12, and whose scan center (i.e., the scan center O of the second laser beam LB2) is a position away from the optical axis O1 of the first laser beam LB1 by the inter-beam distance LB12 in the direction opposite to the welding direction WD, and is an arc-shaped trajectory having one end D and the other end E, each of which has a distance LL1 perpendicular to the weld line WL of the workpiece WK. Note that the distance LL1 between the one end D and the other end E is preferably equal to or less than 1 / 2 of the width LL (not shown) of the weld bead formed by the first laser beam LB1 alone (LL1≦(LL / 2)).

[0076] The processing head HD controls the optical axis (not shown) of the second laser beam LB2 to reciprocate between two points (one end D and the other end E) on the first scan trajectory RAa based on a processing program for laser welding.

[0077] <5-2. Example of second scan trajectory> 9 is a diagram illustrating an example of the second scanning locus RAb of the second laser beam LB2. In FIG. 9, an example is shown in which the optical axis O1 of the first laser beam LB1 and the scanning center O of the second laser beam LB2 are both located on the weld line WL.

[0078] The second scan trajectory RAb is a straight line perpendicular to the weld line WL, separated from the optical axis O1 of the first laser beam LB1 by an inter-beam distance LB12, and has a length LL2 as its midpoint, which is the scan center O of the second laser beam LB2. Note that the length LL2 is desirably equal to or less than 1 / 2 the width LL (not shown) of the weld bead formed by the first laser beam LB1 alone (LL2≦(LL / 2)).

[0079] The processing head HD controls the optical axis (not shown) of the second laser beam LB2 to reciprocate between two points (one end D and the other end E) on the second scan trajectory RAb based on a processing program for laser welding.

[0080] <5-3. Example of the third scan trajectory> Fig. 10 is a diagram illustrating an example of the third scanning locus RAc of the second laser beam LB2. Fig. 10 shows an example in which the optical axis O1 of the first laser beam LB1 and the scanning center O of the second laser beam LB2 are both located on the weld line WL.

[0081] The third scan trajectory RAc is a straight line having one end D and the other end E positioned at a distance Δa from the scan center O of the second laser beam LB2 in the direction along the welding direction WD, the one end D and the other end E being separated from the optical axis O1 of the first laser beam LB1 by an inter-beam distance LB12. Note that the length between the one end D and the other end E (=distance Δa×2) is desirably equal to or less than 1 / 2 of the width LL (not shown) of the weld bead formed by the first laser beam LB1 alone ((Δa×2)≦(LL / 2)).

[0082] The processing head HD controls the optical axis (not shown) of the second laser beam LB2 to reciprocate between two points (one end D and the other end E) on the third scan trajectory RAc based on a processing program for laser welding.

[0083] <5-4. Example of 4th scan trajectory> 11 is a diagram illustrating an example of a fourth scanning locus RAd of the second laser beam LB2. In this example, the optical axis O1 of the first laser beam LB1 and the scanning center O of the second laser beam LB2 are both located on the weld line WL.

[0084] The fourth scan locus RAd is a circumference with a diameter LL3 centered at a position rearward of the optical axis O1 of the first laser beam LB1 by the inter-beam distance LB12 in the welding direction WD (i.e., the scan center O of the second laser beam LB2). Note that the diameter LL3 of the fourth scan locus RAd is desirably equal to or less than 1 / 2 of the width LL (not shown) of the weld bead formed by the first laser beam LB1 alone (LL3≦(LL / 2)).

[0085] The processing head HD is rotationally controlled based on a processing program for laser welding so that the optical axis O2 of the second laser beam LB2 moves on the fourth scan trajectory RAd.

[0086] <6. Example of scanning speed control of the second laser beam> Next, the scanning speed of the second laser beam LB2 will be described. In the simplest case, the scanning speed in the various trajectories of the second laser beam LB2 (the first scanning trajectory RAa to the fourth scanning trajectory RAd shown in Figs. 8 to 11) can be constant regardless of the beam position. Also, it is desirable to change the scanning speed according to the beam position in order to adjust the interaction time with the keyhole according to the irradiation position and make the keyhole more stable (Figs. 8 to 11). The latter will be described with reference to Figs. 12 and 13. Fig. 12 is a diagram for explaining a first scanning speed control example of the second laser beam LB2. Fig. 13 is a diagram for explaining a second scanning speed control example of the second laser beam LB2.

[0087] The processing head HD scans the second laser beam LB2 at a scan frequency of 1 Hz to 10 kHz. In the scan speed graphs shown in Fig. 12 and Fig. 13, the vertical axis indicates the speed, and the horizontal axis indicates the position of the optical axis of the second laser beam LB2 (actual laser irradiation position). The horizontal axis indicates positions included in each scan trajectory, including one end D, the other end E, and the scan center O of the second laser beam LB2, which is a position moved by the inter-beam distance LB12 from the optical axis O1 of the first laser beam LB1 in the direction opposite to the welding direction WD.

[0088] The first scan speed control graph shown in FIG. 12 shows an example of first scan speed control in the case where the scan speed of the second laser beam LB2 changes depending on the irradiation position within the scan range (first scan locus RAa to third scan locus RAc).

[0089] The processing head HD accelerates the second laser beam LB2 in the forward direction toward one end D, and then accelerates the second laser beam LB2 in the reverse direction toward the other end E after it reaches the one end D, and scans the second laser beam LB2 in the forward direction again after it reaches the other end E. The first scan speed control changes the scan speed at a constant ratio (acceleration, notation omitted) according to the irradiation position of the second laser beam LB2 in both the forward and reverse directions, but changes the acceleration to an opposite sign when it reaches the one end D or the other end E. By performing the above first scan speed control, the processing head HD has the slowest speed at the scan center O (i.e., the speed becomes 0 (zero)), so that the interaction time of the second laser beam LB2 with the point on the rear welding line WL with respect to the welding direction WD of the keyhole KH2 is the longest, and the rear wall of the keyhole KH2 becomes more stable, and a good weld bead can be formed.

[0090] The second scan speed control graph shown in Fig. 13 shows an example of the second scan speed control in which the moving speed of the second laser beam LB2 is changed according to the irradiation position within the scan range (first scan trajectory RAa to third scan trajectory RAc). The second scan speed control differs from the first scan speed control shown in Fig. 12 in that the acceleration of the beam scan at each irradiation position shown on the horizontal axis is further changed.

[0091] In the case of the first scan speed control described in FIG. 12, in addition to the above-mentioned features, since the sign of acceleration is changed between one end D and the other end E, a sudden change in acceleration may occur depending on the conditions, and the second laser beam LB2 may give a sudden impact to the keyhole KH2 at one end D or the other end E, which may cause keyhole instability. In the case of the second scan speed control shown in FIG. 13, the processing head HD accelerates the second laser beam LB2 in the forward direction toward one end D, then decelerates it near one end D, and starts accelerating the beam scan in the reverse direction toward the other end E after reaching the one end D. At either one end D or the other end E, the second laser beam LB2 has a maximum scan speed, but its acceleration is 0 (zero).

[0092] Therefore, the impact of the second laser beam LB2 on the keyhole KH2 is minimized. By performing the above-mentioned second scan speed control, the processing head HD has a slow speed at the scan center O, so that the interaction time of the second laser beam LB2 with the point on the welding line WL behind the keyhole KH2 in the welding direction WD becomes long. In addition, the acceleration of the scan of the second laser beam LB2 becomes 0 (zero) when the processing head HD reaches one end D or the other end E of the scan, so that the impact of the second laser beam LB2 on the keyhole KH2 is minimized, the rear wall KHR of the keyhole KH2 becomes more stable, and a good weld bead can be formed.

[0093] In addition, in the second scan speed control graph shown in FIG. 13, the relationship of the scan speed with respect to each scan position of the second laser beam LB2 (that is, one end D, the other end E, and the scan center O) may be a sine wave.

[0094] In addition, even when the processing head HD rotates around the circumference indicated by the fourth scan locus RAd, the processing head HD moves the irradiation position of the second laser beam LB2 along the fourth scan locus RAd at the same speed or while changing the speed, using control similar to the first scan speed control or the second scan speed control.

[0095] (Embodiment 2) The laser welding apparatus 100 according to the first embodiment has a processing head HD having a galvano unit GU, and an example in which the irradiation position (scanning position) of the second laser beam LB2 is controlled by the galvano unit GU has been described. The laser welding apparatus 100A according to the second embodiment has a processing head HDA having a mirror unit MU, and an example in which the irradiation position (scanning position) of the second laser beam LB2 is controlled by the mirror unit MU will be described.

[0096] Laser welding apparatus 100A according to embodiment 2 has a similar configuration to laser welding apparatus 100A shown in embodiment 1. Therefore, in the following description of laser welding apparatus 100A, only the configuration different from laser welding apparatus 100A will be described.

[0097] The laser welding apparatus 100A includes a first laser oscillator LOC1, a second laser oscillator LOC2, two optical fibers F1 and F2, a processing head HDA, a manipulator MN, and a controller CON.

[0098] <7. Example of processing head configuration> A configuration example of the machining head HDA according to the second embodiment will be described with reference to Fig. 14. Fig. 14 is a diagram illustrating a schematic configuration example of the machining head HDA according to the second embodiment.

[0099] The processing head HDA houses within a housing along the Z direction a first fiber coupling portion FC1 and a second fiber coupling portion FC2, a first collimating lens CL1 and a second collimating lens CL2, a mirror DM, a mirror unit MU, a focusing lens FL, and a protective glass PW.

[0100] The mirror unit MU can perform scanning in a rotation direction RDM around either the X-axis or the Y-axis, or both, as a central axis. The mirror unit MU performs high-speed scanning with the second laser beam LB2, thereby realizing scanning trajectories shown as the first scanning trajectory RAa to the fourth scanning trajectory RAd.

[0101] The optical axis d''''-d'' shown in FIG. 2 is the optical axis of the second laser beam LB2 that travels from the second fiber coupling portion FC2 to a predetermined welding point on the workpiece WK. When the second laser beam LB2 enters the processing head HD from the second fiber coupling portion FC2, it spreads out and is collimated by the second collimating lens CL2. After being collimated, it travels toward the mirror unit MU (optical axis d''''-d''''). The second laser beam LB2 is scanned around the X-axis, Y-axis, or both within the mirror unit MU (optical axis d''''-d''), and travels toward the mirror DM (optical axis d''-d). The second laser beam LB2 is reflected by the mirror DM and collected by the collecting lens FL, passes through the protective glass PW, and is then irradiated toward the predetermined welding point on the workpiece WK (optical axis dd'').

[0102] (Additional Note) The above description of each embodiment discloses the following techniques.

[0103] (Technology 1) a first laser oscillator LOC1 that generates a first laser beam LB1; a second laser oscillator LOC2 that generates a second laser beam LB2; A processing head HD, HDA for irradiating the first laser beam LB1 and the second laser beam LB2 onto a workpiece WK, The first laser beam LB1 and the second laser beam LB2 are irradiated at a predetermined interval (beam distance LB12) in a direction along the welding direction WD, The second laser beam LB2 is irradiated in a direction opposite to the welding direction toward the rear of the first molten pool (molten pool WPC1) formed by the first laser beam LB1. Laser welding device 100, 100A. With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B when the first laser beam LB1 is irradiated alone by irradiating the molten pool WPC1 formed by the first laser beam LB1 with the second laser beam LB2, and change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals. This allows the laser welding apparatus 100, 100A to improve the crack resistance of the weld bead.

[0104] (Technology 2) The predetermined interval (beam distance LB12) is greater than the distance between the irradiation position of the first laser beam LB1 and the final solidification position B of the first molten pool (molten pool WPC1). The laser welding apparatus 100, 100A described in (Technology 1). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B when the first laser beam LB1 is irradiated alone, and change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0105] (Technology 3) The second laser beam LB2 starts to be irradiated after a predetermined time (time Δt) from the timing of starting irradiation of the first laser beam LB1. The laser welding apparatus 100, 100A according to (Technology 1) or (Technology 2). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B when the first laser beam LB1 is irradiated alone, and change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0106] (Technology 4) The depth (penetration depth M2) of the second molten pool (molten pool WPC2) formed by the second laser beam LB2 is smaller than the depth (penetration depth M1) of the first molten pool (molten pool WPC1) formed by the first laser beam LB1. The laser welding device 100, 100A according to any one of (Technical Technique 1) to (Technical Technique 3). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B where columnar crystals are likely to form, and can change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0107] (Technology 5) The processing heads HD and HDA control the irradiation position of the second laser beam LB2 so that the second laser beam LB2 traces a predetermined trajectory (for example, a first scanning trajectory RAa, a second scanning trajectory RAb, a third scanning trajectory RAc, and a fourth scanning trajectory RAd). The laser welding device 100, 100A according to any one of (Technical Technique 1) to (Technical Technique 4). With this configuration, laser welding apparatus 100, 100A can adjust the width of the weld bead formed by irradiation with first laser beam LB1, where the metal structure is changed from columnar crystals to equiaxed crystals.

[0108] (Technology 6) The predetermined trajectory (first scanning trajectory RAa) is an arc, The arc is a circumference of a circle whose center is the irradiation position of the first laser beam LB1 and whose radius is the predetermined interval (beam distance LB12), and whose size in a direction perpendicular to the weld line WL of the workpiece WK is equal to or less than 1 / 2 of the size of the first molten pool (molten pool WPC1) in the vertical direction. The laser welding apparatus 100, 100A described in (Technology 5). With this configuration, laser welding apparatus 100, 100A can increase the width of the weld bead formed by irradiation with first laser beam LB1, where the metal structure is changed from columnar crystals to equiaxed crystals, by using the scanning locus of second laser beam LB2.

[0109] (Technology 7) The predetermined trajectory (second scan trajectory RAb) is a straight line perpendicular to the weld line WL of the workpiece WK, The length of the straight line in the vertical direction is equal to or less than 1 / 2 of the size (width LL) of the first molten pool in the vertical direction. The laser welding apparatus 100, 100A described in (Technology 5). With this configuration, laser welding apparatus 100, 100A can increase the width of the weld bead formed by irradiation with first laser beam LB1, where the metal structure is changed from columnar crystals to equiaxed crystals, by using the scanning locus of second laser beam LB2.

[0110] (Technology 8) The predetermined trajectory (third scan trajectory RAc) is a straight line in a direction along the weld line WL of the workpiece WK, the length of the straight line is equal to or less than half the size of the first molten pool in the vertical direction; The laser welding apparatus 100, 100A described in (Technology 5). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B when the first laser beam LB1 is irradiated alone, and change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0111] (Technology 9) The predetermined trajectory (fourth scanning trajectory RAd) is a circle, The diameter of the circle is equal to or less than 1 / 2 of the size (width LL) of the first molten pool in a direction perpendicular to the weld line WL of the work WK. The laser welding apparatus 100, 100A described in (Technology 5). With this configuration, laser welding apparatus 100, 100A can increase the width of the weld bead formed by irradiation with first laser beam LB1, where the metal structure is changed from columnar crystals to equiaxed crystals, by using the scanning locus of second laser beam LB2.

[0112] (Technology 10) The beam radius (first beam radius w1) of the first laser beam LB1 is equal to or larger than the beam radius (second beam radius w2) of the second laser beam LB2. The laser welding device 100, 100A according to any one of (Technical Technique 1) to (Technical Technique 9). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B where columnar crystals are likely to form, and can change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0113] (Technology 11) The processing head HD, HDA has a galvano unit GU capable of controlling the irradiation position of the second laser beam LB2. The laser welding device 100, 100A according to any one of (Technical Technique 1) to (Technical Technique 10). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B where columnar crystals are likely to form, and can change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0114] (Technology 12) The processing heads HD and HDA each have a mirror (mirror unit MU) capable of controlling the irradiation position of the second laser beam LB2 on a two-dimensional coordinate system. The laser welding device 100, 100A according to any one of (Technical Technique 1) to (Technical Technique 10). With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B where columnar crystals are likely to form, and can change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals.

[0115] (Technology 13) a first laser oscillator LOC1 that generates a first laser beam LB1; a second laser oscillator LOC2 that generates a second laser beam LB2; A laser welding method performed by a laser welding apparatus 100, 100A including a processing head HD, HDA that irradiates a workpiece WK with the first laser beam LB1 and the second laser beam LB2, The first laser beam LB1 and the second laser beam LB2 are irradiated in a direction along the welding direction WD at a predetermined interval (beam distance LB12), The second laser beam LB2 is irradiated in a direction opposite to the welding direction toward the rear of a first molten pool (molten pool WPC1) formed by the first laser beam LB1. Laser welding method. With this configuration, the laser welding apparatus 100, 100A can change the temperature near the final solidification position B when the first laser beam LB1 is irradiated alone by irradiating the second laser beam LB2 behind the molten pool WPC1 formed by the first laser beam LB1, and change the metal structure at the final solidification position B from columnar crystals to equiaxed crystals. This allows the laser welding apparatus 100, 100A to improve the crack resistance of the weld bead.

[0116] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, corrections, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present disclosure. In addition, the components in the various embodiments described above may be arbitrarily combined within the scope of the invention. [Industrial Applicability]

[0117] The present disclosure is useful for a laser welding apparatus and a laser welding method for improving the crack resistance of a weld bead. [Explanation of symbols]

[0118] 100,100A laser welding equipment CL1 First collimating lens CL2 Second collimating lens CON Controller F1 Optical Fiber F2 Optical Fiber FL Condenser Lens GU Galvano Unit HD, HDA Processing Head LB Laser Beam LB1 First laser beam LB2 Second laser beam LB12 Beam Distance LL width LOC1 First laser oscillator LOC2 Second laser oscillator MN Manipulator MU Mirror Unit RAa 1st scan trajectory RA1 Arc RAb 2nd scan trajectory RAc 3rd scan trajectory RAd 4th scan trajectory w1 First beam radius w2 Second beam radius WD Welding direction WK Work WL welding line

Claims

1. a first laser oscillator that generates a first laser beam; a second laser oscillator that generates a second laser beam; a processing head that irradiates the first laser beam and the second laser beam onto a workpiece, The first laser beam and the second laser beam are irradiated at a predetermined interval in a direction along the welding direction, the second laser beam is irradiated in a direction opposite to the welding direction toward a rear of the first molten pool formed by the first laser beam; Laser welding equipment.

2. the predetermined interval is greater than a distance between an irradiation position of the first laser beam and a final solidification position of the first molten pool; 2. The laser welding apparatus of claim 1.

3. The second laser beam is started to be irradiated a predetermined time after the timing of starting irradiation of the first laser beam.

2. The laser welding apparatus of claim 1.

4. a depth of the second molten pool formed by the second laser beam is smaller than a depth of the first molten pool formed by the first laser beam; 2. The laser welding apparatus of claim 1.

5. The processing head controls the irradiation position of the second laser beam so that the second laser beam traces a predetermined trajectory.

2. The laser welding apparatus of claim 1.

6. The predetermined trajectory is a circular arc, the arc is a circumference of a circle having a center at the irradiation position of the first laser beam and a radius of the predetermined interval, and a size of the arc in a direction perpendicular to the weld line of the workpiece is equal to or smaller than 1 / 2 of a size of the first molten pool in the vertical direction.

6. The laser welding apparatus according to claim 5.

7. The predetermined trajectory is a straight line perpendicular to the weld line of the workpiece, the length of the straight line in the vertical direction is equal to or less than half the size of the first molten pool in the vertical direction; 6. The laser welding apparatus according to claim 5.

8. The predetermined trajectory is a straight line in a direction along the weld line of the workpiece, the length of the straight line is equal to or less than half the vertical size of the first molten pool; 6. The laser welding apparatus according to claim 5.

9. The predetermined trajectory is a circle, The diameter of the circle is equal to or smaller than ½ of the size of the first molten pool in a direction perpendicular to the weld line of the workpiece.

6. The laser welding apparatus according to claim 5.

10. The beam radius of the first laser beam is equal to or larger than the beam radius of the second laser beam.

2. The laser welding apparatus of claim 1.

11. The processing head has a galvano unit capable of controlling the irradiation position of the second laser beam.

2. The laser welding apparatus of claim 1.

12. The processing head has a mirror capable of controlling the irradiation position of the second laser beam on a two-dimensional coordinate system.

2. The laser welding apparatus of claim 1.

13. a first laser oscillator that generates a first laser beam; a second laser oscillator that generates a second laser beam; A laser welding method performed by a laser welding apparatus including a processing head that irradiates a workpiece with the first laser beam and the second laser beam, The first laser beam and the second laser beam are irradiated at a predetermined interval in a direction along a welding direction, irradiating the second laser beam in a direction opposite to the welding direction toward a rear of the first molten pool formed by the first laser beam; Laser welding method.

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