Laser welding device and laser welding method

Abstract

This laser welding device comprises 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 emits the first laser beam and the second laser beam onto a workpiece, wherein: the first laser beam and the second laser beam are emitted substantially parallel to one other in a direction along the welding direction with a predetermined gap therebetween; and the second laser beam is emitted toward a keyhole formed by the first laser beam.

Description

Laser welding device and laser welding method

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

[0002] Patent Document 1 discloses a method for generating a laser beam by coupling a laser beam at a fiber end of a multi-clad fiber, particularly a double-clad fiber, and outputting the laser beam from the other fiber end of the multi-clad fiber to generate an output laser beam having different beam profile characteristics. In the laser beam generating method, an input laser beam is optically coupled to at least a fiber core of the multi-clad fiber or at least one ring core of the multi-clad fiber, or a laser beam is coupled at least to a fiber core of the multi-clad fiber and at least to at least one ring core.

[0003] US Patent Application Publication No. 2013 / 0223792

[0004] Nakamura, Improving welding quality with beam profile control BrightLine Weld, Proceedings of the 91st Laser Processing Society Conference, (2019), pp. 87-91.

[0005] The present disclosure has been devised in view of the conventional circumstances, and provides a laser welding apparatus and a laser welding method that more effectively prevent welding defects such as porosity or spatter.

[0006] 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 substantially parallel to each other in a direction along the welding direction at a predetermined interval, and the second laser beam is irradiated toward a keyhole formed by the first laser beam.

[0007] 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, wherein the first laser beam and the second laser beam are irradiated substantially parallel to each other in a direction along the welding direction at a predetermined interval, and the second laser beam is irradiated toward a keyhole formed by the first laser beam.

[0008] According to the present disclosure, welding defects such as porosity or spatter can be more effectively prevented.

[0009] FIG. 1 is a diagram showing an example of the outline configuration of a laser welding apparatus according to the first and second embodiments; FIG. 2 is a diagram showing an example of the configuration of a processing head in the first embodiment; FIG. 3 is a diagram explaining an example of the positional relationship of a first laser beam and a second laser beam with respect to a welding line; FIG. 4 is a top view explaining an example of the arrangement of a first laser beam and a second laser beam; FIG. 5 is a cross-sectional view taken along line AA-AA showing an example of a molten pool and a keyhole in the first and second embodiments; FIG. 6 is a diagram explaining an example of a first scanning trajectory of a second laser beam; FIG. 7 is a diagram explaining an example of a second scanning trajectory of a second laser beam; FIG. 8 is a diagram explaining an example of a third scanning trajectory of a second laser beam;

[0010] (Background to the present disclosure) Laser light has a high power density, is capable of performing high-speed, high-quality welding, and is applied to welding a variety of workpieces. Various types of processing heads are used for laser welding. For example, they range from simple ones consisting of a collimator lens and a condenser lens with a fixed optical axis to highly functional ones such as galvanometer heads that can scan laser light (in other words, a laser beam) toward a welding point on a workpiece at high speed.

[0011] Here, a keyhole KH formed by a conventional laser processing method will be described. Fig. 13 is a diagram showing an example of a conventional molten pool WP and keyhole KH. Note that the keyhole KH shown in Fig. 13 is an instantaneous shape shown for ease of understanding, and is not limited to this.

[0012] When the laser power density is sufficiently high, the laser beam LB forms a keyhole KH with a depth L in the molten pool WP. Although not shown, the depth L of the keyhole KH is approximately equal to the penetration depth of the weld bead WB. The laser beam LB is absorbed while being multiple-reflected by the inner wall of the keyhole KH. When laser welding is performed while moving the processing head HD, the front wall KHF of the keyhole KH, located on the welding direction WD side of the inner wall of the keyhole KH, is inclined at a predetermined angle relative to the laser beam LB and absorbs the laser beam LB. Meanwhile, the rear wall KHR of the keyhole KH, located on the opposite side of the welding direction WD, absorbs the laser beam reflected by the front wall KHF and vibrates due to the evaporation of molten metal generated at the front wall KHF of the keyhole KH, resulting in a more unstable shape.

[0013] As shown by laser beam LB0, after entering the inside of keyhole KH, laser beam LB is multiply reflected at points A1, C, and E on the front wall KHF of keyhole KH and points B1 and D on the rear wall KHR of keyhole KH, and is absorbed at the bottom (point F) of keyhole KH.

[0014] Although not shown in FIG. 13, the laser beam LB (energy) that is not completely absorbed by the keyhole KH is again multiple-reflected by the front wall KHF and the rear wall KHR of the keyhole KH, and exits the keyhole KH, resulting in loss.

[0015] The laser beam LB is absorbed at points A1, C, and E on the front wall KHF of the keyhole KH, causing intense evaporation A', C', and E'. The front wall KHF of the keyhole KH is a very thin layer of molten metal, and solid portions of the workpiece WK exist near this layer. On the other hand, the rear wall KHR of the keyhole KH is a thick layer of molten metal (molten pool WP).

[0016] Therefore, compared to the front wall KHF, the rear wall KHR is more susceptible to deformation due to the force of the intense evaporations A', C', and E' of the softer and thicker molten metal (molten pool WP), resulting in an unstable shape. As a result, a bulge Bg1 is formed at the opening of the keyhole KH formed on the surface of the workpiece WK, and similarly, bulges Bg2 and Bg3 are formed inside the keyhole KH. Furthermore, because the rear wall KHR moves violently and irregularly, constrictions N1 and N2 are formed in contrast to the bulges Bg1 to Bg3.

[0017] Near the necks N1 and N2, the front wall KHF and the rear wall KHR come into contact and close due to the violent movement of the rear wall KHR of the keyhole KH, forming a closed space (cavity) in the lower depth direction. The formed cavity becomes a gas bubble in the molten pool WP. If the gas bubble cannot escape from the molten pool WP before the molten metal solidifies, it will form porosity (welding defects) in the workpiece WK. Furthermore, when a keyhole KH with such a closed space (cavity) is irradiated with a laser beam LB to form a new keyhole KH, the entire keyhole KH moves violently, which may cause the molten metal to splash and form spatter.

[0018] As described above, actual laser processing tends to form keyholes due to the high power density of the laser, and in the past, if the shape of the keyhole formed became unstable, it could cause porosity or spatter.

[0019] Therefore, various methods have been proposed to solve the welding process problems caused by the formation of keyholes (Patent Document 1, Non-Patent Document 1). For example, Patent Document 1 discloses a method for creating various beam profiles by controlling the incident position of a beam entering a double-clad fiber and applying the created beam to laser welding. Non-Patent Document 1 also reports the spatter reduction effect of the method proposed in Patent Document 1. However, these methods have had limited applicability because once the fiber is produced, the beam profile that can be created for each fiber is limited.

[0020] Therefore, in the following embodiments, examples of a laser welding apparatus and a laser welding method that more effectively prevent welding defects such as porosity or spatter will be described.

[0021] Hereinafter, with reference to the drawings as appropriate, detailed descriptions of embodiments specifically disclosing a laser welding apparatus and a laser welding method according to the present disclosure will be provided. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matter recited in the claims.

[0022] (Embodiment 1) The laser welding apparatus 100 according to embodiment 1 irradiates multiple laser beams (first laser beam LB1 and second laser beam LB2) from the processing head HD toward the workpiece WK, thereby suppressing the occurrence of porosity or spatter within the molten pool WP formed in the workpiece WK.

[0023] 1 is a diagram showing an example of a schematic configuration of laser welding apparatuses 100 and 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 and 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.

[0024] In the following description, the direction in which the first laser beam LB1 and the second laser beam LB2 are irradiated from the machining head HD to the workpiece WK will be referred to as the Z direction, and the two directions constituting the surface direction perpendicular to the Z direction will be referred to as the X direction and the Y direction.

[0025] 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 configured as a single laser light source or may be configured as a plurality of laser modules.

[0026] The second laser oscillator LOC2 is a laser light source that receives power from a laser drive power supply (not shown) and generates the second laser beam LB2. The second laser oscillator LOC2 may be configured as a single laser light source or may be configured as a plurality of laser modules.

[0027] The laser light source or laser module used in each of the first laser oscillator LOC1 and the second laser oscillator LOC2 is selected appropriately depending on the material of the workpiece WK to be welded, the shape of the welding portion, etc.

[0028] For example, a fiber laser, a disk laser, or a YttrialuminumGarnet (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 to the range of 1000 nm to 1100 nm.

[0029] Alternatively, for example, a semiconductor laser may be used as the laser light source or laser module. In this case, the wavelength of the laser beam LB is set in the range of 800 nm to 1000 nm. Alternatively, a visible light laser may be used as the laser light source or 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 the blue wavelength band of 420 nm to 500 nm and the green wavelength band of 480 nm to 560 nm. Note that it is desirable that the wavelength λ1 of the first laser beam LB1 be equal to or greater than the wavelength λ2 of the second laser beam LB2 (λ1≧λ2).

[0030] The optical fiber F1 has one end (incoming end) optically coupled to the first laser oscillator LOC1 and the other end (outgoing end) optically coupled to the processing head HD. The optical fiber F1 has a core (not shown) at its axial center, and a cladding (not shown) coaxially disposed in contact with the outer circumferential surface of the core. The core and cladding are primarily composed of quartz, with the refractive index of the core being higher than that of the cladding. Therefore, the first laser beam LB1 generated by the first laser oscillator LOC1 is incident on the incoming end of the optical fiber F1 and propagates through the core toward the outgoing end, repeatedly reflecting and otherwise propagating. The outer circumferential surface of the cladding is provided with a coating (not shown) or a resin-based protective layer (not shown) that mechanically protects the optical fiber F1.

[0031] The optical fiber F2 has one end (input end) optically coupled to the second laser oscillator LOC2 and the other end (output end) optically coupled to the machining head HD. It has a core (not shown) at its axis, and a cladding (not shown) coaxially disposed in contact with the outer circumferential surface of the core. The core and cladding are primarily composed of quartz, with the refractive index of the core being higher than that of the cladding. Therefore, the second laser beam LB2 generated by the second laser oscillator LOC2 is incident on the input end of the optical fiber F2 and propagates through the core toward the output end, repeatedly reflecting. Furthermore, the outer circumferential surface of the cladding is provided with a coating (not shown) or a resin-based protective layer (not shown) that mechanically protects the optical fiber F2.

[0032] The machining head HD is attached to the output ends of the optical fibers F1 and F2 and houses at least one optical element and a protective glass PW. An example of the internal configuration of the machining head HD according to the first embodiment will be described in detail with reference to FIG. 2 . The machining head HD first collimates the first laser beam LB1 and the second laser beam LB2, which are transmitted through the optical fibers F1 and F2 and then expanded, into parallel light. The machining head HD then combines and focuses the collimated parallel light, transmits it through the protective glass PW, and irradiates it toward the workpiece WK as the first laser beam LB1 and the second laser beam LB2, respectively. This enables the machining head HD to machine the workpiece WK by laser welding.

[0033] 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 the robot arm equipped with the manipulator MN. The manipulator MN can grasp the machining head HD via a gripping part (not shown) attached to the sixth joint axis, and movably controls the position of the machining head HD based on command signals transmitted from the controller CON.

[0034] 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 laser oscillation of each of the first laser oscillator LOC1 and the second laser oscillator LOC2.

[0035] Specifically, the controller CON controls laser oscillation and laser output in the control unit PRO by supplying control signals such as output current and on / off time to laser drive power supplies (not shown) connected to the first laser oscillator LOC1 and the second laser oscillator LOC2. 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 laser welding (processing) the workpiece WK, which is 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.

[0036] 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 related to the scanning trajectory of the second laser beam LB2 that has been taught in advance using a teaching pendant (not shown) or the like.

[0037] 2. Configuration Example of Processing Head 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 schematically showing a configuration example of the processing head HD according to the first embodiment.

[0038] The processing head HD houses, in a housing along the Z direction, a first fiber coupling section FC1 and a second fiber coupling section 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.

[0039] The first fiber coupling section FC1 is connected to the other end of the optical fiber F1 (see above), and guides the first laser beam LB1 guided through the optical fiber F1 into the housing of the processing head HD.

[0040] The first collimator lens CL1 is an example of an optical element, and collimates the first laser beam LB1 that spreads from the first fiber coupling portion FC1.

[0041] 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) disposed in the machining head HD, for example. The mirror DM transmits the first laser beam LB1 and causes it to travel toward the condenser lens FL, and reflects the second laser beam LB2 and causes it to travel toward the condenser lens FL. The mirror DM may be configured as a dichroic mirror.

[0042] 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 from multiple lenses.

[0043] The protective glass PW prevents contamination inside the processing head HD due to the intrusion of scattered deposits (e.g., spatter, fumes) that are generated when the first laser beam LB1 and the second laser beam LB2 are irradiated onto the workpiece WK to perform welding. The protective glass PW transmits the first laser beam LB1 and the second laser beam LB2 that have passed through the condenser lens FL.

[0044] The second fiber coupling unit FC2 is connected to the other end of the optical fiber F2 (see above), and guides the second laser beam LB2, which is guided through the optical fiber F2, into the housing of the machining head HD. The second collimator lens CL2 is an example of an optical element, and collimates the second laser beam LB2 which spreads from the second fiber coupling unit FC2. The collimated second laser beam LB2 travels toward the galvano unit GU.

[0045] 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 drive control by the controller CON of a motor (not shown) arranged in the machining 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 along the trajectories shown in a first scan trajectory RAa (see FIG. 6), a second scan trajectory RAb (see FIG. 7), a third scan trajectory RAc (see FIG. 8), and a fourth scan trajectory RAd (see FIG. 9), which will be described later.

[0046] 2 is the optical axis c-c' of the first laser beam LB1 directed from the first fiber coupling portion FC1 toward a predetermined welding point on the workpiece WK. The first laser beam LB1 widens when it enters the machining head HD from the first fiber coupling portion FC1 and is collimated by the first collimator 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.

[0047] The optical axis d''''-d' shown in FIG. 2 is the optical axis of the second laser beam LB2 traveling from the second fiber coupling portion FC2 toward a predetermined welding point on the workpiece WK. The second laser beam LB2 expands upon entering the machining head HD from the second fiber coupling portion FC2, is collimated by the second collimator lens CL2, and then travels toward the galvanometer unit GU (optical axis d''''-d''''). The second laser beam LB2 is reflected by the X-axis mirror MX or the Y-axis mirror MY within the galvanometer unit GU (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-d').

[0048] When the X-axis mirror MX and the Y-axis mirror MY are both at their origin positions due to the galvano unit GU, the optical axis (optical axis c-c') of the first laser beam LB1 and the optical axis (optical axis d-d') of the second laser beam LB2 become substantially parallel, and they are irradiated toward a predetermined welding point on the workpiece WK at an inter-beam distance LB12. This inter-beam distance LB12 can be adjusted by the position of the mirror DM in the MD direction.

[0049] 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.

[0050] When welding a weld line WL in the welding direction WD, the processing head HD irradiates the weld line WL with a first laser beam LB1 and a second laser beam LB2 along a predetermined trajectory (see FIGS. 6 to 9 ) 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 line connecting the optical axis O1 of the first laser beam LB1 and the scan center O of the second laser beam LB2 (see FIGS. 6 to 9 ) coincides with the tangential direction of the weld line WL, and the distance between the optical axis O1 of the first laser beam LB1 (see FIGS. 6 to 9 ) and the scan center O of the second laser beam LB2 (see FIGS. 6 to 9 ) is an inter-beam distance LB12.

[0051] 4 and 5, an example of the arrangement of the first laser beam LB1 and the second laser beam LB2 and a keyhole KH formed by the first laser beam LB1 and the second laser beam LB2 in the first and second embodiments 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. Fig. 5 is a cross-sectional view taken along the line AA-AA showing an example of the molten pool WP and the keyhole KH in the first and second embodiments.

[0052] The processing head HD rotates or scans the second laser beam LB2 at high speed in the direction RD and irradiates the irradiation area RA on the rear wall KHR of the keyhole KH, thereby pressing down the weld metal on the rear wall KHR rearward in the welding direction WD and widening the gap between the front wall KHF and rear wall KHR of the keyhole KH. This allows the laser welding apparatus 100 to more effectively prevent the keyhole KH from closing (i.e., forming a closed space or bubbles) and prevent welding defects such as porosity or spatter that can occur due to the closure of the keyhole KH.

[0053] The first laser beam LB1 and the second laser beam LB2 are aligned in the welding direction WD, spaced a predetermined beam distance LB12 apart. The first laser beam LB1 is irradiated onto the workpiece WK (optical axis c-c') to form a keyhole KH with a depth M. Although not shown, the depth L of the keyhole KH formed by the first laser beam LB1 is approximately equal to the penetration depth of the weld bead WB. The second laser beam LB2 is positioned to be irradiated onto the rear wall KHR of the keyhole KH formed by the first laser beam LB1 (optical axis d-d'). Here, the central axis ee' of the keyhole KH formed by the first laser beam LB1 does not coincide with the optical axis cc' of the first laser beam LB1. Typically, the inclination angle of the central axis ee' of the keyhole KH relative to the Z direction is greater than the inclination angle of the optical axis cc' of the first laser beam LB1 relative to the Z axis.

[0054] The workpiece WK is irradiated with the first laser beam LB1 and the second laser beam LB2 to form a molten pool WP and a weld bead WB formed by solidifying the molten pool WP.

[0055] The inter-beam distance LB12 between the first laser beam LB1 and the second laser beam LB2 can be any distance, but it is desirable that the relationship of the following (Equation 1) be established: LB12≦w1+w2 (Equation 1)

[0056] Here, the first beam radius w1 indicates the beam radius of the first laser beam LB1 on the surface of the workpiece WK. The second beam radius w2 indicates the beam radius of the second laser beam LB2 on the surface of the workpiece WK. When the second laser beam LB2 is rotated or scanned at high speed, the inter-beam distance LB12 indicates the distance between the optical axis of the first laser beam LB1 and the center of rotation or scanning of the second laser beam LB2.

[0057] Furthermore, it is desirable that the first beam radius w1 of the first laser beam LB1 and the second beam radius w2 of the second laser beam LB2 satisfy the relationship expressed by the following formula 2: w2≦w1 (formula 2).

[0058] 4. Examples of Scanning Locus of Second Laser Beam Next, examples of the scanning locus of the second laser beam LB2 will be described with reference to FIGS. 6 to 9. FIG.

[0059] 6 is a diagram illustrating an example of the first scanning locus RAa 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.

[0060] The first scanning trajectory RAa is an arc-shaped trajectory having two points P1 and P2, one end A and the other end B, where a circle RA1 having a center point on the optical axis O1 of the first laser beam LB1 and a radius equal to the interbeam distance LB12 intersects with a line parallel to the weld line WL at a perpendicular distance LL1 from the weld line WL. Note that the perpendicular distance LL1 between the one end A and the other end B and the weld line WL is preferably equal to or less than the first beam radius w1 of the first laser beam LB1 (LL1≦w1).

[0061] Based on a processing program for laser welding, the processing head HD controls the optical axis (not shown) of the second laser beam LB2 to move back and forth between two points (one end A and the other end B) on the first scan trajectory RAa.

[0062] 7 is a diagram illustrating an example of the second scanning locus RAb of the second laser beam LB2. In this example, the optical axis O1 of the second laser beam LB2 and the scanning center O of the second laser beam LB2 are both located on the weld line WL.

[0063] The second scan trajectory RAb is a vertical line perpendicular to the weld line WL, with one end A and the other end B being points P3 and P4, which are respectively located at a vertical distance LL2 from the weld line WL. Note that the vertical distance LL2 between the one end A and the other end B and the weld line WL is preferably equal to or less than the first beam radius w1 of the first laser beam LB1 (LL2≦w1).

[0064] The processing head HD controls the optical axis (not shown) of the second laser beam LB2 to move back and forth between two points (one end A and the other end B) on the second scan trajectory RAb based on a processing program for laser welding.

[0065] 8 is a diagram illustrating an example of the third scan trajectory RAc of the second laser beam LB2. In FIG. 8, the optical axis O1 of the first laser beam LB1 and the scan center O of the second laser beam LB2 are both positioned on the weld line WL.

[0066] The third scan trajectory RAc is a straight line having one end A and the other end B of points P5 and P6, which are located at a distance Δa from the scan center O of the second laser beam LB2 in the direction along the welding direction WD. Note that the distance Δa between the one end A and the other end B and the scan center O of the second laser beam LB2 is preferably equal to or less than the first beam radius w1 of the first laser beam LB1 (Δa≦w1).

[0067] Based on a processing program for laser welding, the processing head HD controls the optical axis (not shown) of the second laser beam LB2 to move back and forth between two points (one end A and the other end B) on the third scan trajectory RAc.

[0068] 9 is a diagram illustrating an example of the 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.

[0069] The fourth scan locus RAd is a circumference of a circle with a radius Δb, with the scan center O located 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. Note that it is desirable that the radius Δb of the fourth scan locus RAd be equal to or smaller than the first beam radius w1 of the first laser beam LB1 (Δb≦w1).

[0070] The processing head HD is controlled to rotate based on a processing program for laser welding so that the optical axis O2 of the second laser beam LB2 moves along the fourth scan trajectory RAd.

[0071] 5. Example of Scanning Speed ​​Control of Second Laser Beam Next, the scanning speed of the second laser beam LB2 will be described. In the simplest case, the scanning speed of the second laser beam LB2 along each trajectory (first scanning trajectory RAa to fourth scanning trajectory RAd shown in FIGS. 6 to 9 ) can be constant regardless of the beam position. Furthermore, it is desirable to adjust the interaction time with the keyhole KH according to the irradiation position and change the scanning speed according to the beam position to further stabilize the keyhole KH ( FIGS. 6 to 8 ). The latter will be described with reference to FIGS. 10 and 11 . FIG. 10 is a diagram illustrating a first example of scanning speed control of the second laser beam LB2. FIG. 11 is a diagram illustrating a second example of scanning speed control of the second laser beam LB2.

[0072] The machining head HD scans with the second laser beam LB2 at a scan frequency of 1 Hz to 10 kHz. In the scan speed graphs shown in Figures 10 and 11, the vertical axis represents the speed, and the horizontal axis represents the position of the optical axis of the second laser beam LB2 (the actual laser irradiation position). The horizontal axis represents positions included in each scan trajectory, including one end A, the other end B, and the scan center O of the second laser beam LB2, which is a position shifted backward from the optical axis O1 of the first laser beam LB1 along the welding direction WD by the inter-beam distance LB12.

[0073] The first scan speed control graph shown in Figure 10 illustrates an example of first scan speed control in which the scan speed of the second laser beam LB2 varies depending on the irradiation position within the scan range (first scan trajectory RAa to third scan trajectory RAc). The processing head HD accelerates the beam scan in the forward direction toward one end A, and then accelerates the beam scan in the reverse direction toward the other end B after reaching the one end A. After reaching the other end B, the processing head HD causes the second laser beam LB2 to scan in the forward direction again. The first scan speed control graph changes the scan speed at a constant rate (acceleration, notation omitted) depending on the irradiation position of the second laser beam LB2 in both the forward and reverse directions, but changes the acceleration sign to the opposite sign when the one end A or the other end B is reached. By performing the above speed control, the speed of the second laser beam LB2 becomes the slowest at the scan center O (i.e., 0 (zero)), so the interaction time of the second laser beam LB2 at the point where the rear of the welding direction WD of the keyhole KH intersects with the welding line WL becomes the longest, and the rear wall KHR of the keyhole KH can be further stabilized.

[0074] The second scan speed control graph shown in Figure 11 shows an example of second scan speed control when the movement speed of the second laser beam LB2 is changed depending on the irradiation position within the scan range (first scan trajectory RAa to third scan trajectory RAc).

[0075] Here, the second scan speed control graph shown in FIG. 11 differs from FIG. 10 in that the acceleration of the beam scan at the irradiation position on the horizontal axis is changed. In the case of the first scan speed control graph shown in FIG. 10 , in addition to the above-mentioned features, the sign of the acceleration is changed between one end A and the other end B. This may cause a sudden change in acceleration under certain conditions, resulting in a sudden impact of the beam on the keyhole KH at one end A or the other end B, potentially causing keyhole instability. Therefore, in the second scan speed control graph shown in FIG. 11 , the processing head HD accelerates the beam in the forward direction toward one end A, then decelerates near one end A, and after reaching one end A, begins accelerating the beam scan in the reverse direction toward the other end B. As a result, the second laser beam LB2 has the maximum scan speed at either end A or the other end B, but its acceleration is 0 (zero). Therefore, the beam has the smallest impact on the keyhole KH at one end A and the other end B.

[0076] The above scan speed control slows down the scan speed of the second laser beam LB2 at the scan center O, thereby lengthening the interaction time of the second laser beam LB2 at the point where the rear of the keyhole KH in the welding direction WD intersects with the weld line WL. Furthermore, the beam scan acceleration of the second laser beam LB2 becomes 0 (zero) when the second laser beam LB2 reaches one end A or the other end B of the scan, thereby minimizing the impact of the second laser beam LB2 on the keyhole KH and further stabilizing the rear wall KHR of the keyhole KH.

[0077] In the second scan speed control graph shown in FIG. 11, the relationship between the scan speed and each scan position of the second laser beam LB2 (i.e., one end A, the other end B, and the scan center O) may be a sine wave.

[0078] Furthermore, even when the processing head HD rotates around the circumference indicated by the fourth scan trajectory RAd, the irradiation position of the second laser beam LB2 is moved along the fourth scan trajectory 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.

[0079] (Embodiment 2) The laser welding apparatus 100 according to embodiment 1 has a processing head HD having a galvano unit GU, and an example has been shown in which the irradiation position (scanning position) of the second laser beam LB2 is controlled by the galvano unit GU. An example will be described in which the laser welding apparatus 100A according to embodiment 2 has a processing head HDA having a mirror unit MU, and an example will be described in which the irradiation position (scanning position) of the second laser beam LB2 is controlled by the mirror unit MU.

[0080] Laser welding apparatus 100A according to embodiment 2 has the same configuration as laser welding apparatus 100 shown in embodiment 1. Therefore, in the following description of laser welding apparatus 100A, only the configuration that differs from laser welding apparatus 100 will be described.

[0081] 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.

[0082] 6. Configuration Example of Machining Head> A configuration example of the machining head HDA according to the second embodiment will be described with reference to Fig. 12. Fig. 12 is a diagram schematically showing a configuration example of the machining head HDA according to the second embodiment.

[0083] The processing head HDA accommodates 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.

[0084] The mirror unit MU can perform scanning in the rotation direction RDM around either the X-axis or the Y-axis, or both, as the central axis. The mirror unit MU performs high-speed scanning with the second laser beam LB2, thereby achieving the scanning trajectories shown as the first scanning trajectory RAa to the fourth scanning trajectory RAd.

[0085] The optical axis d''''-d' shown in Figure 12 is the optical axis of the second laser beam LB2 that travels from the second fiber coupling portion FC2 toward a predetermined welding point on the workpiece WK. The second laser beam LB2 expands when it enters the machining head HD from the second fiber coupling portion FC2, is collimated by the second collimator lens CL2, and then travels toward the mirror unit MU (optical axis d''''-d'''). The second laser beam LB2 is scanned within the mirror unit MU around the X-axis, the Y-axis, or both as its central axis (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, 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-d').

[0086] (Additional Notes) The above description of each embodiment discloses the following techniques.

[0087] (Technology 1) A laser welding device 100, 100A includes: a first laser oscillator LOC1 that generates a first laser beam LB1; a second laser oscillator LOC2 that generates a second laser beam LB2; and a processing head HD, HDA that irradiates a workpiece WK with the first laser beam LB1 and the second laser beam LB2, wherein the first laser beam LB1 and the second laser beam LB2 are irradiated substantially parallel to a direction along a welding direction WD at a predetermined interval (beam distance LB12), and the second laser beam LB2 is irradiated toward a keyhole KH formed by the first laser beam LB1. With this configuration, the laser welding device 100, 100A irradiates the second laser beam LB2 from behind by the beam distance LB12 in the welding direction, thereby preventing the keyhole KH formed by the first laser beam LB1 from closing and more effectively preventing welding defects such as porosity or spatter.

[0088] (Technology 2) The laser welding device 100, 100A according to (Technology 1), wherein the second laser beam LB2 is irradiated in a direction opposite to the welding direction WD and toward the rear of the keyhole KH. With this configuration, the laser welding device 100, 100A can stabilize the rear wall KHR, which is more unstable inside the keyhole KH formed by the first laser beam LB1, prevent the keyhole KH from closing, and more effectively prevent welding defects such as porosity or spatter.

[0089] (Technology 3) The laser welding device 100, 100A according to (Technology 1) or (Technology 2), wherein the processing head HD, HDA controls the irradiation position of the second laser beam LB2 so that the second laser beam LB2 traces a predetermined trajectory (first scan trajectory RAa, second scan trajectory RAb, third scan trajectory RAc, fourth scan trajectory RAd). With this configuration, the laser welding device 100, 100A irradiates the second laser beam LB2 along the predetermined trajectory (first scan trajectory RAa, second scan trajectory RAb, third scan trajectory RAc, fourth scan trajectory RAd) to further stabilize the shape of the rear wall KHR of the keyhole KH formed by the first laser beam LB1 over a wide range, thereby more effectively preventing the keyhole KH from closing and more effectively preventing welding defects such as porosity or spatter.

[0090] (Technology 4) The laser welding apparatus 100, 100A according to (Technology 3), wherein the predetermined trajectory (first scan trajectory RAa) is an arc connecting two intersections of two parallel straight lines parallel to the weld line WL of the workpiece WK and a circumference of a circle RA1 whose center is the irradiation position of the first laser beam LB1, and the distance between the parallel straight lines and the weld line is a first distance. With this configuration, the laser welding apparatus 100, 100A irradiates the second laser beam LB2 along the predetermined trajectory (first scan trajectory RAa) to further stabilize the shape of a wide range of the rear wall KHR of the keyhole KH formed by the first laser beam LB1, thereby more effectively preventing the keyhole KH from closing and more effectively preventing welding defects such as porosity and spatter.

[0091] (Technology 5) The laser welding apparatus 100, 100A according to (Technology 3), wherein the predetermined trajectory (second scan trajectory RAb) is a trajectory along an orthogonal direction perpendicular to the weld line WL of the workpiece, and is a line segment connecting two points that are a second distance from the weld line. With this configuration, the laser welding apparatus 100, 100A irradiates the second laser beam LB2 along the predetermined trajectory (second scan trajectory RAb) to further stabilize the shape of a wide range of the rear wall KHR of the keyhole KH formed by the first laser beam LB1, thereby more effectively preventing the keyhole KH from closing and more effectively preventing welding defects such as porosity or spatter.

[0092] (Technology 6) The laser welding device 100, 100A according to (Technology 3), wherein the predetermined trajectory (third scan trajectory RAc) is a trajectory along a direction connecting the irradiation position of the first laser beam LB1 and the scan center position of the second laser beam LB2, and is a line segment connecting two points located at a third distance from a position that is a predetermined distance (beam distance LB12) away from the first laser beam LB1 as a center. With this configuration, the laser welding device 100, 100A irradiates the second laser beam LB2 along the predetermined trajectory (third scan trajectory RAc), thereby more stabilizing the shape of the rear wall KHR of the keyhole KH formed by the first laser beam LB1 over a wide range, and thereby more effectively preventing the keyhole KH from closing and more effectively preventing welding defects such as porosity and spatter.

[0093] (Technology 7) The laser welding device 100, 100A according to (Technology 3), wherein the predetermined trajectory (fourth scan trajectory RAd) is a circumference having a center at a position spaced a predetermined distance (beam-to-beam distance LB12) from the irradiation position of the first laser beam LB1. With this configuration, the laser welding device 100, 100A irradiates the second laser beam LB2 along the predetermined trajectory (fourth scan trajectory RAd) to further stabilize the shape of the rear wall KHR of the keyhole KH formed by the first laser beam LB1 over a wide range, thereby more effectively preventing the keyhole KH from closing and more effectively preventing welding defects such as porosity or spatter.

[0094] (Technology 8) The laser welding device 100, 100A according to (Technology 7), wherein the radius of the circumference is equal to or less than the beam radius (first beam radius w1) of the first laser beam LB1. With this configuration, the laser welding device 100, 100A can irradiate the second laser beam LB2 within a scanning range approximately equal to the width of the keyhole KH formed by the first laser beam LB1.

[0095] (Technology 9) The laser welding device 100, 100A according to any one of (Technology 4) to (Technology 6), wherein the first distance, the second distance, or the third distance is equal to or less than the beam radius (first beam radius w1) of the first laser beam LB1. With this configuration, the laser welding device 100, 100A can irradiate the second laser beam LB2 within a scanning range approximately equal to the width of the keyhole formed by the first laser beam LB1.

[0096] (Technology 10) The laser welding device 100, 100A according to (Technology 1), wherein the first laser beam LB1 and the second laser beam LB2 are irradiated in the welding direction in the order of the first laser beam LB1 and the second laser beam LB2. With this configuration, the laser welding device 100, 100A can irradiate the second laser beam LB2 behind the keyhole KH formed by the first laser beam LB1.

[0097] (Technology 11) The laser welding device 100, 100A according to (Technology 1), wherein the beam radius of the first laser beam LB1 (first beam radius w1) is equal to or larger than the beam radius of the second laser beam LB2 (second beam radius w2). With this configuration, the laser welding device 100, 100A can irradiate the second laser beam LB2 around the rear wall of the keyhole formed by the first laser beam LB1.

[0098] (Technology 12) The laser welding device 100, 100A according to (Technology 1), wherein the processing head HD, HDA has a galvanometer unit GU capable of controlling the irradiation position of the second laser beam LB2. With this configuration, the laser welding device 100, 100A can scan the irradiation of the second laser beam LB2 at high speed.

[0099] (Technology 13) The laser welding device 100, 100A according to (Technology 1), wherein the processing head HD, HDA has a mirror (mirror unit MU) that can control the irradiation position of the second laser beam LB2 on a two-dimensional coordinate system. With this configuration, the laser welding device 100, 100A can scan the irradiation of the second laser beam LB2 at high speed.

[0100] (Technology 14) A laser welding method performed by a laser welding apparatus 100, 100A including: a first laser oscillator LOC1 that generates a first laser beam LB1; a second laser oscillator LOC2 that generates a second laser beam LB2; and a processing head HD, HDA that irradiates a workpiece WK with the first laser beam LB1 and the second laser beam LB2, the laser welding method comprising: irradiating the first laser beam LB1 and the second laser beam LB2 substantially parallel to each other in a direction along a welding direction WD at a predetermined interval (beam-to-beam distance LB12); and irradiating the second laser beam LB2 toward a keyhole KH formed by the first laser beam LB1. With this configuration, the laser welding apparatus 100, 100A can prevent the keyhole KH formed by the first laser beam LB1 from closing by irradiating the second laser beam LB2 from behind at a beam-to-beam distance LB12 in the welding direction, thereby more effectively preventing welding defects such as porosity or spatter.

[0101] 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, alterations, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the various embodiments described above may be combined in any manner without departing from the spirit of the invention.

[0102] This application is based on a Japanese patent application (Patent Application No. 2023-116130) filed on July 14, 2023, the contents of which are incorporated herein by reference.

[0103] The present disclosure is useful for a laser welding apparatus and a laser welding method that more effectively prevent welding defects such as porosity or spatter.

[0104] 100, 100A Laser welding device 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 KH Keyhole KHF Front wall KHR Rear wall LB Laser beam LB0 Laser beam LB1 First laser beam LB2 Second laser beam LB12 Beam-to-beam distance LL1 Vertical distance LL2 Vertical distance LOC1 First laser oscillator LOC2 Second laser oscillator MN Manipulator MU Mirror unit RAa First scanning trajectory RAb Second scanning trajectory RAc Third scanning trajectory RAd Fourth scanning trajectory w1 First beam radius w2 Second beam radius WD Welding direction WK Work WL Welding line

Claims

1. 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 approximately in parallel with each other in a direction along a welding direction at a predetermined interval, and the second laser beam is irradiated toward a keyhole formed by the first laser beam.

2. The laser welding device according to claim 1, wherein the second laser beam is irradiated in a direction opposite to the welding direction and toward the rear of the keyhole.

3. The laser welding device according to claim 1, wherein the processing head controls the irradiation position of the second laser beam so that the second laser beam traces a predetermined trajectory.

4. The laser welding device according to claim 3, wherein the predetermined trajectory is a circular arc connecting two intersection points between two parallel straight lines parallel to the weld line of the workpiece and a circumference of a circle centered on the irradiation position of the first laser beam, and the distance between the intersection points and the weld line is a predetermined distance.

5. The laser welding device according to claim 3, wherein the predetermined trajectory is a trajectory along a direction perpendicular to the weld line of the workpiece, and is a line segment connecting two points that are a predetermined distance away from the weld line.

6. A laser welding device as described in claim 3, wherein the predetermined trajectory is a trajectory along a direction connecting the irradiation position of the first laser beam and the irradiation position of the second laser beam, and is a line segment connecting two points located at a predetermined distance from a position separated by the predetermined distance from the first laser beam.

7. The laser welding device according to claim 3, wherein the predetermined trajectory is a circumference having a center at a position spaced the predetermined distance from the irradiation position of the first laser beam.

8. The laser welding apparatus according to claim 7, wherein the radius of the circumference is equal to or smaller than the beam radius of the first laser beam.

9. The laser welding device according to any one of claims 4 to 6, wherein the predetermined distance is equal to or less than a first beam radius of the first laser beam.

10. The laser welding device according to claim 1, wherein the first laser beam and the second laser beam are irradiated in the welding direction in the order of the first laser beam and the second laser beam.

11. The laser welding apparatus according to claim 1, wherein the beam radius of the first laser beam is equal to or larger than the beam radius of the second laser beam.

12. The laser welding device according to claim 1, wherein the processing head has a galvano unit capable of controlling the irradiation position of the second laser beam.

13. The laser welding device according to claim 1, wherein the processing head has a mirror capable of controlling the irradiation position of the second laser beam on a two-dimensional coordinate system.

14. A laser welding method performed by a laser welding device 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, the laser welding method comprising: irradiating the first laser beam and the second laser beam approximately in parallel with each other in a direction along the welding direction at a predetermined interval; and irradiating the second laser beam toward a keyhole formed by the first laser beam.

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