Laser welding method and laser welding device

Abstract

This laser welding method includes a welding step in which a workpiece is welded by irradiating the surface of the workpiece with a laser beam that is scanned two-dimensionally so as to trace a prescribed pattern, while causing the laser beam to advance in a welding direction (WD). The prescribed pattern has a center (O), a first closed curve (CL1), and a second closed curve (CL2). The first closed curve (CL1) and the second closed curve (CL2) are tangential to each other at one point or share one line. In the welding step, while the center (O) is being advanced in a direction parallel to the welding direction (WD), the laser beam is scanned along the first closed curve (CL1) in a first rotation direction (CD1), and the laser beam is then scanned along the second closed curve (CL2) in a second rotation direction (CD2), which is the opposite rotation direction to the first rotation direction (CD1).

Description

Laser welding method and laser welding apparatus

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

[0002] In laser welding, the beam diameter of laser light can be focused down to a range from several millimeters to 100 μm or less, so high-speed, high-quality welding can be performed on workpieces of various types and materials. On the other hand, when the beam diameter is reduced, for example, in lap welding of two plate members arranged at an interval, constraints on welding conditions increase, that is, there is a risk that the gap tolerance in lap welding may decrease. Further, if the beam diameter is made too small, there is a risk that the bead width required to obtain a predetermined welding strength cannot be obtained. Furthermore, in lap welding, butt welding, and the like, there is a risk that a favorable bead shape cannot be obtained for a workpiece including plate members with greatly different heat balance.

[0003] Accordingly, various scanning welding methods have been proposed, in which welding is performed while scanning the surface of a workpiece with laser light at high speed (see, for example, Patent Documents 1 to 3).

[0004] Patent Document 2 discloses that it is effective to use a Lissajous pattern or the like as a laser beam scanning pattern, particularly when performing laser welding on a thick workpiece.

[0005] Further, Patent Document 3 discloses a method of scanning a laser beam so as to continuously draw two asymmetric annular patterns. In a pattern leading along the welding direction, the width intersecting the welding direction is made wider than that of the trailing pattern and the output is reduced, thereby suppressing the occurrence of welding defects and obtaining a weld bead of favorable shape in lap welding of a plate member on which a coating layer such as a galvanized layer is formed.

[0006] Japanese Patent No. 7481327, Japanese Unexamined Patent Publication No. 11-104877, Japanese Patent No. 7213440

[0007] With the conventional methods disclosed in Patent Documents 1 to 3, gap tolerance or the bead width of a weld bead can be increased within a certain range, and a favorable bead shape can be obtained in laser welding of workpieces with different heat balance.

[0008] On the other hand, there is a demand for even faster welding speeds in laser welding. However, in the conventional methods disclosed in Patent Documents 1 to 3, it becomes difficult to maintain a uniform amount of heat input to the molten pool as the welding speed increases. Furthermore, since the tip shape of the molten pool is determined by the shape of the laser beam scanning pattern, it becomes difficult to form a smooth and gentle tip shape.

[0009] This disclosure provides a laser welding method and a laser welding apparatus that enable a balanced distribution of heat input to the molten pool on either the welding line or the scanning center of the laser beam during laser scanning welding, and that also improve the shape of the molten pool's tip.

[0010] The laser welding method according to this disclosure comprises a welding step of welding a workpiece by irradiating the surface of the workpiece with a laser beam that is advanced in the welding direction, which is along the welding line, and scanning the laser beam in two dimensions to draw a predetermined pattern, wherein when the welding speed, which is the speed at which the laser beam advances in the welding direction, is zero, the predetermined pattern has a center, and the predetermined pattern has at least a first closed curve and a second closed curve, and the first closed curve and the second closed curve are tangent at one point or share one line, and in the welding step, the laser beam is scanned in a first rotational direction along the first closed curve while the center of the predetermined pattern advances in a direction parallel to the welding direction, and then the laser beam is scanned in a second rotational direction along the second closed curve, the second rotational direction being the opposite rotational direction to the first rotational direction.

[0011] The laser welding apparatus according to this disclosure comprises a laser oscillator for generating laser light, a laser head for receiving the laser light and irradiating it toward a workpiece, and a controller for controlling the operation of at least the laser head, wherein the laser head has a laser light scanner for scanning the laser light in a first direction and a second direction intersecting the first direction, and when laser welding is performed by advancing the laser light in the welding direction which is the direction along the welding line, the controller drives and controls the laser light scanner so that the laser light draws a predetermined pattern on the surface of the workpiece, wherein the predetermined pattern has at least a center, a first closed curve and a second closed curve, the first closed curve and the second closed curve are tangent at one point or share one line, the controller advances the center of the predetermined pattern in a direction parallel to the welding direction, the laser light scanner scans the laser light along the first closed curve in a first rotation direction, and then scans the laser light along the second closed curve in a second rotation direction, the second rotation direction being the opposite rotation direction to the first rotation direction.

[0012] According to this disclosure, in laser scanning welding, the amount of heat input to the molten pool can be balanced well with respect to the weld line or the scanning center of the laser beam, and the shape of the tip of the molten pool can be improved, thereby enabling the production of a weld bead with a good shape.

[0013] Figure 1 is a schematic diagram of a laser welding apparatus according to an embodiment of the present disclosure. Figure 2 is a schematic diagram of a laser light scanner according to an embodiment of the present disclosure. Figure 3 is a diagram showing the scanning pattern of laser light in Embodiment 1 of the present disclosure. Figure 4 is a diagram showing the scanning trajectory of laser light along the welding direction when the X direction is the welding direction in Embodiment 1 of the present disclosure. Figure 5 is a diagram showing the scanning trajectory of laser light along the welding direction when the Y direction is the welding direction in Embodiment 1 of the present disclosure. Figure 6 is a diagram showing the scanning trajectory of laser light along the welding direction when conventional spin scanning is used when the X direction is the welding direction. Figure 7A is a diagram showing a conventional Lissajous scanning pattern of laser light. Figure 7B is a diagram showing the scanning trajectory of laser light along the welding direction when conventional Lissajous scanning is used when the X direction is the welding direction. Figure 8 is a diagram showing the scanning trajectory of laser light along the welding direction when the X direction is the welding direction, and is a diagram showing a comparison of the molten pool tip shape when conventional Lissajous scanning is used and when laser light scanning is used in Embodiment 1 of the present disclosure. Figure 9 is a diagram showing the scanning trajectory of a laser beam along the welding direction when the Y direction is the welding direction, and is a diagram showing a comparison of the molten pool tip shape when conventional Lissajous scanning is used and when laser beam scanning is used in Embodiment 1 of this disclosure. Figure 10 is a diagram showing the scanning pattern of a laser beam according to Embodiment 2 of this disclosure. Figure 11 is a diagram showing the scanning trajectory of a laser beam along the welding direction according to Embodiment 2 when the X direction is the welding direction. Figure 12 is a diagram showing the scanning trajectory of a laser beam along the welding direction according to Embodiment 2 when the Y direction is the welding direction. Figure 13 is a diagram showing the scanning pattern of a laser beam according to Embodiment 3 of this disclosure. Figure 14A is a diagram showing an example of a scanning pattern of a laser beam according to Embodiment 4 of this disclosure. Figure 14B is a diagram showing another example of a scanning pattern of a laser beam according to Embodiment 4 of this disclosure. Figure 14C is a diagram showing yet another example of a scanning pattern of a laser beam according to Embodiment 4 of this disclosure. Figure 15 is a diagram showing the scanning pattern of a laser beam according to Embodiment 5 of this disclosure. Figure 16A is a diagram showing an example of a scanning pattern of a laser beam according to Embodiment 6 of this disclosure. Figure 16B is a diagram showing another example of a scanning pattern of a laser beam according to Embodiment 6 of this disclosure.

[0014] The embodiments of this disclosure will be described below with reference to the drawings. The following description of preferred embodiments is illustrative in nature and is not intended to limit this disclosure, its applications, or its uses.

[0015] (Embodiment 1) [Configuration of Laser Welding Apparatus and Laser Optical Scanner] Figure 1 is a schematic diagram of the configuration of a laser welding apparatus 100 according to an embodiment of the present disclosure, and Figure 2 is a schematic configuration diagram of a laser optical scanner 40 according to an embodiment of the present disclosure.

[0016] In the following explanation, the direction parallel to the direction of propagation of the laser beam LB from the reflective mirror 33 toward the laser beam scanner 40 may be referred to as the X direction, and the direction parallel to the optical axis of the laser beam LB emitted from the laser head 30 may be referred to as the Z direction. Furthermore, the direction perpendicular to the X direction and the Z direction may be referred to as the Y direction. The XY plane, which includes the X and Y directions, may be approximately parallel (including parallel) to the surface of the workpiece 200 if the surface of the workpiece 200 is a flat surface, or it may be at a certain angle to the surface.

[0017] As shown in Figure 1, the laser welding apparatus 100 comprises a laser oscillator 10, an optical fiber 20, a laser head 30, a controller 50, a manipulator 60, and a stage 70.

[0018] The laser oscillator 10 is a laser light source that generates laser light LB when power is supplied from a power source (not shown). The laser oscillator 10 may consist of a single laser light source or multiple laser modules. In the latter case, the laser oscillator 10 combines the laser light emitted from each of the multiple laser modules and emits it as laser light LB. The laser light source or laser module used in the laser oscillator 10 is appropriately selected according to the material of the workpiece 200 and the shape of the welding area, etc.

[0019] For example, a fiber laser, disk laser, or YAG (Yttrium Aluminum Garnet) laser can be used as the laser light source. In this case, the wavelength of the laser light LB is set in the range of 1000 nm to 1100 nm. Alternatively, a semiconductor laser may be used as the laser light source or laser module. In this case, the wavelength of the laser light 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 wavelength of the laser light LB is set in the range of 400 nm to 600 nm.

[0020] The optical fiber 20 is optically coupled to the laser oscillator 10. The laser light LB generated by the laser oscillator 10 enters the optical fiber 20 and is transmitted within it towards the laser head 30.

[0021] The laser head 30 is attached to the end of the optical fiber 20 and irradiates the workpiece 200 with the laser light LB transmitted from the optical fiber 20.

[0022] Furthermore, the laser head 30 includes a collimation lens 32, a reflective mirror 33, a focusing lens 34, and a laser light scanner 40 as optical components, and these optical components are housed inside the housing 31 while maintaining a predetermined arrangement.

[0023] The collimation lens 32 receives the laser beam LB emitted from the optical fiber 20, converts it into parallel light, and directs it onto the reflection mirror 33. The collimation lens 32 is also connected to a drive unit (not shown) and is configured to be displaceable in the Z direction according to a control signal from the controller 50. By displacing the collimation lens 32 in the Z direction, the focal position of the laser beam LB can be changed, allowing the laser beam LB to be appropriately irradiated onto the workpiece 200 according to its shape. In other words, the collimation lens 32, in combination with the drive unit (not shown), also functions as a focal position adjustment mechanism for the laser beam LB. Alternatively, the focal position of the laser beam LB may be changed by displacing the focusing lens 34 using the drive unit.

[0024] The reflective mirror 33 reflects the laser beam LB that has passed through the collimation lens 32 and directs it into the laser beam scanner 40. The surface of the reflective mirror 33 is positioned at an angle of approximately 45 degrees with respect to the optical axis of the laser beam LB that has passed through the collimation lens 32.

[0025] The focusing lens 34 focuses the laser beam LB, which has been reflected by the reflective mirror 33 and scanned by the laser beam scanner 40, onto the surface of the workpiece 200. In the example in Figure 1, the focusing lens 34 is placed in front of the laser beam scanner 40, but the focusing lens 34 may also be placed behind the laser beam scanner 40. A detailed explanation of this is omitted.

[0026] As shown in Figure 2, the laser light scanner 40 is a galvanometer scanner having a first galvanometer mirror 41 and a second galvanometer mirror 42. The first galvanometer mirror 41 has a first mirror 41a, a first rotation shaft 41b, and a first drive unit 41c, and the second galvanometer mirror 42 has a second mirror 42a, a second rotation shaft 42b, and a second drive unit 42c. The laser light LB that has passed through the focusing lens 34 is reflected by the first mirror 41a, and further reflected by the second mirror 42a, and irradiated onto the surface of the workpiece 200 (see the dashed line in Figure 2).

[0027] For example, the first drive unit 41c and the second drive unit 42c are galvanometer motors, and the first rotating shaft 41b and the second rotating shaft 42b are the output shafts of the motors. Although not shown in the figures, the first drive unit 41c is rotationally driven by a driver that operates in response to a control signal from the controller 50, causing the first mirror 41a attached to the first rotating shaft 41b to rotate around the axis of the first rotating shaft 41b. Similarly, the second drive unit 42c is rotationally driven by a driver that operates in response to a control signal from the controller 50, causing the second mirror 42a attached to the second rotating shaft 42b to rotate around the axis of the second rotating shaft 42b.

[0028] The first mirror 41a rotates to a predetermined angle around the axis of the first rotation axis 41b, causing the laser beam LB to be scanned in the X direction. Similarly, the second mirror 42a rotates to a predetermined angle around the axis of the second rotation axis 42b, causing the laser beam LB to be scanned in the Y direction. In other words, the laser beam scanner 40 is configured to scan the laser beam LB two-dimensionally in the XY plane and illuminate the workpiece 200 with it.

[0029] Returning to Figure 1, the controller 50 controls the laser oscillation of the laser oscillator 10. Specifically, it controls the laser oscillation by supplying control signals such as output current and on / off time to a power supply (not shown) connected to the laser oscillator 10. The controller 50 also controls the output of the laser beam LB.

[0030] Furthermore, the controller 50 controls the operation of the laser head 30 according to the content of the selected laser welding program. Specifically, the controller 50 controls the drive of the laser light scanner 40 and the collimation lens 32 or focusing lens 34, which are provided on the laser head 30 (not shown).

[0031] Furthermore, the controller 50 controls the operation of the manipulator 60. The laser welding program is stored in a memory unit (not shown) located inside or elsewhere within the controller 50, and is retrieved by the controller 50 upon command.

[0032] The controller 50 has an integrated circuit such as an LSI or microcomputer (not shown), and the functions of the controller 50 are realized by executing a laser welding program, which is software, on this integrated circuit. Alternatively, separate controllers 50 may be provided for controlling the operation of the laser head 30 and for controlling the output of the laser beam LB.

[0033] The manipulator 60 is a multi-joint robot to which the housing 31 of the laser head 30 is attached. The manipulator 60 is connected to the controller 50 so as to be able to exchange signals and moves the laser head 30 to follow a predetermined trajectory according to the laser welding program described above. Alternatively, another controller (not shown) may be provided to control the operation of the manipulator 60.

[0034] The stage 70 is a base on which the workpiece 200 is placed. In this embodiment of the disclosure, the manipulator 60 to which the laser head 30 is attached moves along a predetermined welding direction WD (see Figure 3, etc.). The workpiece 200 is laser-welded by irradiating the workpiece 200 with laser light LB while moving the manipulator 60 along the welding direction WD. During laser welding, the laser light LB is irradiated onto the welding surface of the workpiece 200 in such a way as to draw the scanning pattern shown in Figure 3 and subsequent figures.

[0035] If the manipulator 60 is a fixed fixture, a moving mechanism (not shown) is provided on the stage 70. The moving mechanism moves the stage 70 in the X direction and / or Y direction. As the stage 70 moves, the laser beam LB moves along the welding direction WD and irradiates the surface of the workpiece 200 placed on the stage 70.

[0036] [Regarding the scanning pattern of the laser beam] Figure 3 shows an example of the scanning pattern of the laser beam LB in Embodiment 1 of this disclosure.

[0037] The laser beam LB is scanned in the XY plane, in this case on the surface of the workpiece 200, to draw the pattern shown in Figure 3. Note that Figure 3 shows the scanning pattern of the laser beam LB when the movement speed V of the manipulator 60 along the welding direction WD (hereinafter referred to as welding speed V) is zero, i.e., when the laser head 30 is stationary.

[0038] By appropriately selecting the rotational motion of the first mirror 41a and the second mirror 42a, that is, the amount of rotation and rotational frequency of each, the scanning pattern of the laser beam LB becomes the scanning pattern shown in Figure 3.

[0039] As shown in Figure 3, the scanning pattern has a center O, which is the center point of the pattern. The outer shape of the scanning pattern is a circumferential curve (CLR) with center O. Furthermore, the scanning pattern has a semicircle C1, which is a curve between point A (first point A) and point C (second point C) on the circumferential CLR, and a semicircle C2, which is a curve between point E (third point E) and point D (fourth point D) on the circumferential CLR. The scanning pattern also has a first line C3, which is a straight line connecting point C and point E, and a second line C4, which is a straight line connecting point D and point A. In the following explanation, semicircle C1 may be referred to as the first curve C1, and semicircle C2 may be referred to as the second curve C2.

[0040] Furthermore, a closed curve CL1 passing through the center O, point A, and point C is sometimes called the first closed curve CL1. A closed curve CL2 passing through the center O, point E, and point D is sometimes called the second closed curve CL2. In the example shown in Figure 3, the first closed curve CL1 includes the first curve C1 and the first line C3, and the second closed curve CL2 includes the second curve C2 and the second line C4.

[0041] In this embodiment, points A and E are at the same position on the circumference CLR, and points C and D are at the same position on the circumference CLR. The first line C3 and the second line C4 are straight lines passing through the center O. That is, the first line C3 and the second line C4 are located on the diameter of the circumference CLR. Also, the first line C3 and the second line C4 extend in the X direction and share one line. Furthermore, as is clear from this, the semicircles C1 and C2 do not overlap except at their ends.

[0042] Furthermore, in this embodiment, the laser beam LB moves in the following order along the scanning pattern shown in Figure 3.

[0043] First, the laser beam LB moves from point A through point B to point C along the semicircle C1. The scanning direction at this time is defined as A1. Next, the laser beam LB moves from point C (=point D) through the center O to point E (=point A) along the first line C3. The scanning direction at this time is defined as A2. Next, the laser beam LB moves from point E through point F to point D along the semicircle C2. The scanning direction at this time is defined as A3. Next, the laser beam LB moves from point D through the center O to point A along the second line C4. The scanning direction at this time is defined as A4. In this way, the laser beam LB is scanned to return to point A after passing through point A, point B, point C, the center O, point E, point F, point D, and the center O in sequence. The scanning start point of the laser beam LB is not limited to point A, and may be any one point on the circumference CLR, the first line C3, or the second line C4. Further, the scanning direction of the laser beam LB may be a direction reverse to the aforementioned scanning directions A1 to A4. That is, in the example shown in FIG. 3, the scanning direction CD1 (direction of the closed curve CL1) of the laser beam LB from the first point A through point B and the second point C to the first point A is set as the clockwise direction, but the scanning direction may be counterclockwise. Further, in the example of FIG. 3, the scanning direction CD2 (direction of the closed curve CL2) of the laser beam LB from the third point E located at the same position as the first point A through point F and the fourth point D to the third point E is set as the counterclockwise direction, but the scanning direction CD2 may be clockwise.

[0044] Further, points A to F may be located at positions rotated by a predetermined angle around the center O from the example shown in FIG. 3.

[0045] [Laser welding method] FIG. 4 is a diagram illustrating an example of a scanning trajectory of the laser beam LB on a workpiece 200 along the welding direction when the X direction is the welding direction WD (FIG. 3), that is, when the laser head 30 moves in the X direction, in the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of a scanning trajectory of the laser beam LB along the welding direction when the Y direction is the welding direction WD (not shown in FIG. 3), in the first embodiment of the present disclosure.

[0046] The symbol WL indicates a welding line connecting positions at which a workpiece 200 is to be welded. In FIGS. 4 and 5, the welding line WL coincides with the X axis and the Y axis, respectively. It should be noted that the specific position of the welding line WL may vary depending on the shape of the joint to be welded. For example, in the case of butt welding, the welding line WL generally refers to the abutting surfaces of two workpieces 200. In the case of lap fillet welding, it is difficult to clearly define the welding line WL, but defining either the upper edge of the upper workpiece 200, the lower edge of the upper workpiece 200 at the contact portion between the upper workpiece 200 and the lower workpiece 200, or the central portion of the upper workpiece 200 in the plate thickness direction as the welding line WL does not affect the description of the present embodiment. There are also many examples of joints other than butt welding and lap fillet welding, and detailed description thereof is omitted herein.

[0047] In the present embodiment, while the laser head 30 is moved in the welding direction WD at a welding speed V by a manipulator 60, a laser beam LB is irradiated onto the surface of the workpiece 200. Furthermore, using a laser beam scanner 40, the laser beam LB is two-dimensionally scanned so as to draw the scanning pattern shown in FIG. 3 on the surface of the workpiece 200.

[0048] The outer shapes of the plurality of scanning patterns shown in FIGS. 4 and 5 substantially correspond to the outer shape of a weld bead. In addition, the plurality of scanning patterns shown in FIGS. 4 and 5 respectively show position changes of the scanning pattern shown in FIG. 3 over time when the laser beam LB travels along the welding direction WD.

[0049] In the examples shown in FIGS. 4 and 5, the center O of the scanning pattern may move not on the welding line WL but on an imaginary line (dotted line) separated from the welding line WL by an offset distance WLOS (hereinafter referred to as a first distance WLOS) along the Y direction (FIG. 4) or the X direction (FIG. 5). The offset distance WLOS is appropriately set according to the plate thickness of the workpiece 200, the joint shape, and the like. A description in which butt welding is taken as an example of the joint is as follows.

[0050] When two workpieces 200 are butt-welded and have the same thickness, the heat capacities on both sides of the butt-joint surfaces of the two workpieces 200, which form the weld line WL, are the same. Therefore, the center O of the scanning pattern should be aligned with the butt-joint surfaces of the two workpieces 200. In this case, the offset distance WLOS is zero, and the scanning trajectory will be as shown by the solid lines in Figures 4 and 5. On the other hand, when two workpieces 200 are butt-welded and have different thicknesses, the heat capacities on both sides of the butt-joint surfaces of the two workpieces 200, which form the weld line WL, are different. For this reason, if the center O of the scanning pattern is aligned with the butt-joint surfaces of the two workpieces 200, an imbalance in the melting of the workpieces 200 will occur on both sides of the butt-joint surface, which may result in the formation of a poor weld bead. In this case, the thinner side of the workpiece 200 will melt too much, and the thicker side will not melt enough, which may result in defects in the shape of the weld bead. Therefore, when welding joints with different heat capacities, the center O of the scanning pattern should be shifted by a predetermined distance, an offset distance WLOS, towards the workpiece 200 with a larger heat capacity, i.e., a thicker plate.

[0051] In the example shown in Figure 4, the welding direction WD is in the X direction. Therefore, the laser beam LB is scanned across the surface of the workpiece 200 so that a portion of the first line C3 and the second line C4 overlap during welding. If the first distance WLOS is not zero, the first line C3 and the second line C4 are located on virtual lines (shown as dotted lines) at a distance of WLOS from the welding line.

[0052] On the other hand, in the example shown in Figure 5, the welding direction WD is the Y direction. In this case, the laser beam LB is scanned across the surface of the workpiece 200 so that the first line C3 and the second line C4 are separated in the Y direction during welding.

[0053] [Effects, etc.] As described above, the laser welding method according to this embodiment comprises at least the following welding steps. In other words, in the welding step, the laser beam LB is advanced in the welding direction WD, which is the direction along the welding line WL, and the laser beam LB is scanned two-dimensionally and irradiated onto the surface of the workpiece 200 to draw a predetermined scanning pattern, thereby welding the workpiece 200.

[0054] As mentioned above, when the welding speed V is zero, the outline of the scanning pattern is a circumferential CLR with a center O. In the welding step, the laser beam LB is scanned two-dimensionally while the center O is advanced in a direction parallel to the welding direction WD, and the surface of the workpiece 200 is irradiated in such a way that it draws the scanning pattern shown in Figure 3.

[0055] According to this embodiment, the scanning trajectory of the laser beam LB is symmetrical on either side of the welding line WL or virtual line (dotted line in Figure 4 or Figure 5) through which the center O is progressing. Therefore, the amount of heat input by the laser beam LB can be balanced on both sides of the welding line WL or center O on the surface of the molten pool. Furthermore, if viewed over a sufficiently large area compared to the spot diameter of the laser beam LB on the surface of the workpiece 200, the amount of heat input in the area irradiated by the laser beam LB can be made uniform. In addition, the tip shape of the molten pool can be improved, resulting in a well-shaped weld bead. These effects will be explained further.

[0056] Figure 6 shows the scanning trajectory of the laser beam along the welding direction when using conventional spin (circular) scanning. Figure 7A shows the conventional Lissajous scanning pattern (solid line) of the laser beam. Figure 7B shows the scanning trajectory of the laser beam along the welding direction when using conventional Lissajous scanning.

[0057] Figure 8 shows the scanning trajectory of the laser beam along the welding direction when the X direction is the welding direction, and is a diagram comparing the shape of the molten pool tip when using conventional Lissajous scanning and when using laser beam scanning in this embodiment. Figure 9 shows the scanning trajectory of the laser beam along the welding direction when the Y direction is the welding direction, and is a diagram comparing the shape of the molten pool tip when using conventional Lissajous scanning and when using laser beam scanning in this embodiment.

[0058] In the examples shown in Figures 6, 7B, 8, and 9, the center of the scanning pattern of the laser beam LB passes along the X-axis (Figures 6, 7B, and 8) and the Y-axis (Figure 9), respectively.

[0059] First, in the example shown in Figure 6, when the laser beam LB is advanced in the X direction while spin scanning, the time the laser beam LB irradiates the workpiece 200 differs between the first scan end SA, which is one end of the scanning pattern on the X axis, and the second scan end SB, which is the other end. Specifically, the irradiation time of the laser beam LB is longer at the second scan end SB than at the first scan end SA. As a result, the amount of heat input differs on both sides of the X axis, and the amount of heat input by the laser beam LB becomes non-uniform on the surface of the molten pool. Consequently, the shape of the weld bead also differs on both sides of the X axis, making it impossible to obtain a weld bead with a good shape.

[0060] On the other hand, when the scanning pattern of the laser beam LB is a Lissajous pattern as shown in Figure 7A, the scanning trajectory of the laser beam LB approaches symmetry on both sides of the X-axis, as shown in Figure 7B. Specifically, the irradiation time of the laser beam LB is the same at the first scan end SA and the second scan end SB over a predetermined welding length. As a result, the amount of heat input is the same on both sides of the X-axis. In other words, the amount of heat input by the laser beam LB becomes uniform at the surface of the molten pool.

[0061] However, in conventional Lissajous scanning, as shown in Figure 7A, the scanning trajectory of the laser beam LB includes portions OA1 to OA4 at the four corners that extend outward from the circumferential CLR0 (corresponding to the spin scanning shown in Figure 6). In addition, the scanning trajectory of the laser beam LB includes portions OB1 to OB2 that are recessed inside the circumferential CLR0. For this reason, when performing laser welding by moving the laser beam LB in one direction, especially in the X direction, while drawing a Lissajous pattern, the flow of molten metal tends to become complex at the leading edge of the molten pool corresponding to portions OA1 to OA4 or portions OB1 to OB2.

[0062] For example, in the example shown in Figure 8, the scanning trajectory LSJX of the laser beam LB forms a molten pool WPLX (hereinafter also referred to as the forward portion WPLX) in front of the welding direction WD, and when the molten pool WPLX solidifies, a weld bead WBX is formed. Note that, for the sake of simplicity, the boundary between the molten pool WPLX and the weld bead WBX is not explicitly shown in Figure 8. As shown in Figure 8, in conventional Lissajous scanning, in the forward portion WPLX along the welding direction WD in the scanning trajectory LSJX, the molten pool shape at both ends in the Y direction is convex with respect to the welding direction, and the molten pool shape near the X axis is concave with respect to the welding direction. Therefore, the flow of molten metal in the forward portion of the welding direction WD becomes complex, and the flow of molten metal at both ends in the Y direction is faster than in the central part near the X axis. The shape of the front portion WPLX corresponds to the portions OA2 and OA4 that protrude from the circumferential CLR0 mentioned above at both ends in the Y direction, but to the recessed portion OB2 of the circular CLR0 mentioned above in the central part near the X axis. Furthermore, the tip shape of the weld bead WBX after welding is also a recessed shape with the central part receding relative to the welding direction WD, reflecting the shape of the front portion WPLX.

[0063] If the front WPLX takes the shape shown in Figure 8, it may cause welding defects such as undercuts. Furthermore, as the welding speed V increases, the flow of molten metal becomes faster at both ends of the front WPLX in the Y direction, which may increase the frequency of welding defects.

[0064] In order to suppress or eliminate welding defects that may occur in the conventional Lissajous scanning described above, especially when the welding speed is high, it is desirable to make the shape of the molten pool in the forward portion of the welding direction WD a convex shape that is close to a circle, as shown by the symbol WPRX in Figure 8. This makes the flow of molten metal in the forward portion of the welding direction WD smoother, and welding defects are suppressed or eliminated. This is achieved by this embodiment.

[0065] According to this embodiment, the scanning pattern of the laser beam LB has the shape shown in Figure 3, and its movement trajectory has the shape shown in Figure 4. Therefore, as shown by the dashed line in Figure 8, the front portion WPRX of the molten pool reflects the circumferential CLR shown in Figure 3, and is close to a circular shape with the center located further forward than both ends in the Y direction. More precisely, as shown in Figure 4, it is a shape formed by the joining of semicircles C1 and C2 with the weld line WL in between, but the scanning trajectories of both deviate from a circle by the amount of the displacement between the first line C3 and the second line C4. In actual welding, it is possible to select the scanning conditions so that this displacement does not become a problem. Furthermore, even if there is a minute displacement between the scanning trajectories, the solid metal around the laser beam LB melts, so the shape of the front portion WPRX of the molten pool approaches a circular shape. For this reason, in Figure 8, the front portion WPRX is depicted as a circle. As described above, according to this embodiment, the tip shape of the weld bead WBX can be made closer to a circular shape, thereby reducing welding defects such as undercuts.

[0066] Furthermore, as shown in Figure 9, in conventional Lissajous scanning, when laser welding is performed by advancing the laser beam LB in the Y direction (see Figure 7A), the shape of the front portion WPLY of the molten pool at both ends in the X direction is not a convex shape as shown in Figure 8, and the shape near the center of the Y axis is not a concave shape as shown in Figure 8. In the example in Figure 9, the flow of molten metal at both ends in the X direction is slower than that of the front portion WPLX shown in Figure 8. However, due to the presence of portions OA1 to OA2 shown in Figure 7A, even if the front portion WPLY of the molten pool is not concave, if the welding speed is high, the flow of molten metal still tends to be faster at both ends in the X direction than at the center of the Y axis. Therefore, there is a risk of welding defects such as undercuts occurring in the weld bead WBY.

[0067] On the other hand, according to this embodiment, even when the laser beam LB is advanced in the Y direction, the scanning pattern of the laser beam LB is the shape shown in Figure 3, and its movement trajectory is the shape shown in Figure 5. As a result, as shown by the dashed line in Figure 9, the tip shape of the front part of the molten pool WPRY, and consequently the tip shape of the weld bead WBY, approaches a circular shape, and welding defects such as undercuts can be reduced.

[0068] Furthermore, when scanning the laser beam LB along the trajectory shown in Figure 4, the conditions under which the laser beam LB irradiates the surface of the workpiece 200 during actual welding can be selected such that the first line C3 and the second line C4 largely overlap. Therefore, the amount of heat input from the laser beam LB along the welding line WL along the X axis can be made greater than in other parts. For example, by scanning the laser beam LB in the shape shown in Figure 4 and performing laser welding, the workpiece 200 can be reliably welded in a fillet weld of two overlapping plates, and the welding quality can be improved.

[0069] On the other hand, when performing laser welding by scanning the laser beam LB along the trajectory shown in Figure 5, the amount of heat input in and around the welding line WL can be distributed more widely than when scanning the laser beam LB along the trajectory shown in Figure 4. This makes it possible to reliably weld the workpiece 200 while suppressing the occurrence of burn-through, for example, in butt welding with a gap.

[0070] Furthermore, if the heat balance of the workpiece 200 is equal on both sides of the welding line WL, it is preferable to move the laser beam LB so that the center O travels along the welding line WL.

[0071] On the other hand, if the thermal balance (heat capacity) of the workpiece 200 differs on either side of the weld line WL, it is preferable to position the imaginary line through which the center O passes on the side with the larger heat capacity on either side of the weld line WL. In other words, it is preferable to move the laser beam LB so that the center O travels along an imaginary line that is a first distance WLOS away in the direction intersecting the weld line WL. In this case, the first distance WLOS is greater than zero. By doing so, the laser beam LB can be irradiated onto the surface of the workpiece 200 according to the difference in thermal balance, or in other words, heat capacity, of the workpiece 200 on either side of the weld line WL. This makes it possible to balance the amount of heat input by the laser beam LB on the surface of the molten pool on either side of the weld line WL. As a result, a weld bead with a good shape can be formed.

[0072] Furthermore, the laser welding apparatus 100 according to this embodiment includes at least a laser oscillator 10, a laser head 30, and a controller 50.

[0073] The laser oscillator 10 generates laser light LB, and the laser head 30 receives the laser light LB and irradiates it toward the workpiece 200. The controller 50 controls the operation of at least the laser head 30.

[0074] The laser head 30 has a laser light scanner 40 that scans the laser light LB in the X direction (first direction) and in the Y direction (second direction) which intersects the X direction.

[0075] When performing laser welding by advancing the laser beam LB in the welding direction WD, which is along the welding line WL, the controller 50 drives and controls the laser beam scanner 40 so that the laser beam LB draws the scanning pattern shown in Figure 3 on the surface of the workpiece 200.

[0076] According to this embodiment, since the scanning trajectory of the laser beam LB is symmetrical with respect to the welding line progressing through the center O, the amount of heat input by the laser beam LB on the surface of the molten pool can be made uniform across that surface. Furthermore, since the tip shape of the molten pool in the welding direction WD can be improved, a weld bead with a good shape can be obtained.

[0077] The laser welding apparatus 100 further comprises a manipulator 60 to which a laser head 30 is attached, and a controller 50 controls the operation of the manipulator 60. The manipulator 60 moves the laser head 30 in a predetermined direction relative to the surface of the workpiece 200. This predetermined direction corresponds to the welding direction WD, and the speed at which the laser head 30 moves along the welding direction WD corresponds to the welding speed V.

[0078] By providing the manipulator 60 in this way, the welding direction WD can be changed. Furthermore, laser welding can be easily performed on workpieces 200 with complex shapes, such as three-dimensional shapes.

[0079] If the position of the laser head 30 is fixed, the controller 50 controls the movement of the stage 70 on which the workpiece 200 is placed. The stage 70 moves the workpiece 200 in a predetermined direction relative to the laser head 30. This predetermined direction corresponds to the welding direction WD, and the movement speed of the stage 70 along the welding direction WD corresponds to the welding speed V.

[0080] The laser oscillator 10 and the laser head 30 are connected by an optical fiber 20, and the laser beam LB is transmitted from the laser oscillator 10 to the laser head 30 through the optical fiber 20.

[0081] By providing the optical fiber 20 in this way, it becomes possible to perform laser welding on a workpiece 200 that is located at a distance from the laser oscillator 10. This increases the degree of freedom in arranging the various parts of the laser welding apparatus 100.

[0082] The laser light scanner 40 consists of a first galvanometer mirror 41 that scans the laser light LB in the X direction and a second galvanometer mirror 42 that scans the laser light LB in the Y direction.

[0083] By configuring the laser light scanner 40 in this way, the laser beam LB can be easily scanned in two dimensions. Furthermore, since a known galvanometer scanner can be used as the laser light scanner 40, the cost of the laser welding apparatus 100 can be kept from increasing.

[0084] (Embodiment 2) Figure 10 is a diagram showing the scanning pattern of the laser beam LB according to Embodiment 2 of the present disclosure. Figure 11 is a diagram showing the scanning trajectory of the laser beam LB according to Embodiment 2 along the welding direction WD when the X direction is the welding direction WD. Figure 12 is a diagram showing the scanning trajectory of the laser beam LB according to Embodiment 2 along the welding direction WD when the Y direction is the welding direction WD.

[0085] In Figure 10 and the subsequent drawings, components similar to those in Embodiment 1 are denoted by the same reference numerals, and detailed explanations are omitted. Furthermore, the scanning trajectory of the laser beam LB shown in Figure 11 corresponds to the scanning trajectory of the laser beam LB in the X direction shown in Figure 10, and the scanning trajectory of the laser beam LB shown in Figure 12 corresponds to the scanning trajectory of the laser beam LB in the Y direction shown in Figure 10.

[0086] In this embodiment, as shown in Embodiment 1, the first closed curve CL1 passes through the center O, point A, and point C, and the second closed curve CL2 passes through the center O, point E, and point D. In the example shown in Figure 10, the first closed curve CL1 includes the first curve C5, a portion of the straight line C7, and a portion of the straight line C8, while the second closed curve CL2 includes the second curve C6, a portion (other part) of the first line C7, and a portion (other part) of the second line C8.

[0087] The scanning pattern of the laser beam LB shown in Figure 10 differs from the scanning pattern of the laser beam LB of Embodiment 1 shown in Figure 3 in the following respects.

[0088] First, points A, C, E, and D are located at different positions on the circumference CLR. Also, the first line C7 and the second line C8 intersect at the center O (they are tangent at one point). The first line C7 and the second line C8 intersect at an angle α (>0). In other words, the curve C5 (first curve C5) connecting the first point A and the second point C is not the semicircle C1 shown in Figure 3, but a part of the arc of the circumference CLR. Similarly, the curve C6 (second curve C6) connecting the third point E and the fourth point D is not the semicircle C2 shown in Figure 3, but a part of the arc of the circumference CLR. Furthermore, the first line C7 is the straight line connecting the first point A and the fourth point D, and the second line C8 is the straight line connecting the third point E and the second point C.

[0089] According to this embodiment, it is possible to prevent the amount of heat input from concentrating on the welding line WL through which the center O passes, and to reliably distribute the amount of heat input to both sides of the welding line WL.

[0090] For example, in a butt weld without a gap, if laser welding is performed using the scanning trajectory shown in Figure 9, the amount of heat applied to the butt joint may become too large. In this case, welding defects such as burn-through may occur.

[0091] On the other hand, according to this embodiment, by positioning the weld line WL through which the center O passes in the butt joint, it is possible to suppress the amount of heat input near the weld line WL from becoming too large. This suppresses the occurrence of welding defects such as burn-through and allows for the formation of a well-shaped weld bead. Furthermore, according to this embodiment, even if there is a difference in heat capacity between the overlapping portion and the other portions in lap welding, it is possible to suppress the amount of heat input to either portion from becoming too large. This suppresses the occurrence of welding defects such as burn-through and allows for the formation of a well-shaped weld bead.

[0092] (Embodiment 3) Figure 13 is a diagram showing the scanning pattern of the laser beam LB according to Embodiment 3 of the present disclosure.

[0093] The scanning pattern of the laser beam LB shown in Figure 13 differs from the scanning pattern of the laser beam LB in Embodiment 2 shown in Figure 10 in the following respects.

[0094] First, the connection point between the first line C7 and the first curve C5 is the curve C9 (the fifth curve C9) which changes continuously between the first inflection point A' and the second inflection point A''. Also, the connection point between the first line C7 and the second curve C6 is the curve C11 (the eighth curve C11) which changes continuously between the seventh inflection point D' and the eighth inflection point D''.

[0095] Furthermore, the connection point between the second line C8 and the first curve C5 is a curve C10 (the sixth curve C10) that changes continuously between the third inflection point C' and the fourth inflection point C''. Also, the connection point between the second line C8 and the second curve C6 is a curve C12 (the seventh curve C12) that changes continuously between the fifth inflection point E' and the sixth inflection point E''.

[0096] The first inflection point A' is the connection point between the first curve C5 and the fifth curve C9, and the second inflection point A'' is the connection point between the first line C7 and the fifth curve C9. The third inflection point C' is the connection point between the first curve C5 and the sixth curve C10, and the fourth inflection point C'' is the connection point between the second line C8 and the sixth curve C10. The fifth inflection point E' is the connection point between the second curve C6 and the seventh curve C12, and the sixth inflection point E'' is the connection point between the second line C8 and the seventh curve C12. The seventh inflection point D' is the connection point between the second curve C6 and the eighth curve C11, and the eighth inflection point D'' is the connection point between the first line C7 and the eighth curve C11.

[0097] In this embodiment, the first closed curve CL1 passes through the center O, the first inflection point A', the second inflection point A'', the third inflection point C', and the fourth inflection point C''. The second closed curve CL2 passes through the center O, the fifth inflection point E', the sixth inflection point E'', the seventh inflection point D', and the eighth inflection point D''. In the example shown in Figure 13, the first closed curve CL1 includes the first curve C5, the fifth curve C9, the sixth curve C10, a part of the first line C7, and a part of the second line C8. The second closed curve CL2 includes the second curve C6, the seventh curve C12, the eighth curve C11, a part (other part) of the first line C7, and a part (other part) of the second line C8.

[0098] In the scanning pattern of the laser beam LB of Embodiment 2 shown in Figure 10, the angle at which the scanning trajectory of the laser beam LB switches from the first curve C5 to the first line C7 at the second point C, and when it switches from the second line C8 to the second curve C6 at the third point E, is approximately 90 degrees. Similarly, the angle at which the scanning trajectory of the laser beam LB switches from the second curve C6 to the first line C7 at the fourth point D, and when it switches from the first line C7 to the first curve C5 at the first point A, is also approximately 90 degrees.

[0099] In the embodiment shown in Embodiment 2, as the scanning speed of the laser beam LB by the laser beam scanner 40 increases, the vibration of the molten pool at the first to fourth points A, C, E, D, and their vicinity, which are the switching points of the laser beam LB as described above, becomes rapid accordingly. Furthermore, even if rapid vibration does not occur in the molten pool, the scanning speed or scanning direction of the laser beam LB changes rapidly in the vicinity of the first to fourth points A, C, E, D, in accordance with the change in scanning direction. Normally, rapid changes in scanning speed or scanning direction may lead to welding defects, so restrictions are placed on the time change of scanning speed or the angle change of scanning direction. However, if the scanning direction is changed rapidly while maintaining the accuracy of the scanning trajectory at the first to fourth points A, C, E, D, it becomes necessary to reduce the scanning speed. As a result, the amount of heat input at the first to fourth points A, C, E, D, and their vicinity becomes larger than in other parts, and there is a risk of partial heat input.

[0100] On the other hand, according to this embodiment, by making the scanning trajectories near the first to fourth points A, C, E, and D in Figure 10 the fifth to eighth curves C9, C10, C12, and C11, respectively, as shown in Figure 13, rapid vibration of the molten pool can be suppressed. This prevents the molten pool from becoming disordered and the shape of the weld bead from deteriorating. Furthermore, according to this embodiment, the change in scanning direction before and after the switching point of the scanning trajectory can be made gradual. This eliminates the need to reduce the scanning speed near the switching point, avoids excessive heat input, and prevents the shape of the molten pool, and consequently the shape of the weld bead, from becoming uneven.

[0101] Furthermore, by scanning the laser beam LB so that the fifth to eighth curves C9, C10, C12, and C11 each form part of a circular arc, sudden vibrations of the molten pool can be reliably suppressed, and the scanning speed can be maintained before and after the switching point of the scanning trajectory. Even if it needs to be changed, the speed change can be made reliably gradual.

[0102] (Embodiment 4) Figure 14A is a diagram showing an example of a scanning pattern of a laser beam LB according to Embodiment 4 of the present disclosure. Figure 14B is a diagram showing another example of a scanning pattern of a laser beam LB according to Embodiment 4. Figure 14C is a diagram showing yet another example of a scanning pattern of a laser beam LB according to Embodiment 4. For the sake of explanation, the first closed curve CL1 and the second closed curve CL2 are not explicitly shown in Figures 14A to 14C.

[0103] The scanning pattern of the laser beam LB shown in Figure 14A corresponds to the scanning pattern of the laser beam LB in Embodiment 1 shown in Figure 3. The scanning pattern of the laser beam LB shown in Figure 14B corresponds to the scanning pattern of the laser beam LB in Embodiment 2 shown in Figure 10. Furthermore, the scanning pattern of the laser beam LB shown in Figure 14C corresponds to the scanning pattern of the laser beam LB in Embodiment 3 shown in Figure 13.

[0104] The scanning pattern of the laser beam LB shown in Figure 14A differs from the scanning pattern of the laser beam LB of Embodiment 1 shown in Figure 3, in that the first line C3 and the second line C4 do not pass through the center O. Similarly, the scanning patterns of the laser beam LB shown in Figures 14B and 14C differ from the scanning pattern of the laser beam LB of Embodiment 2 shown in Figure 10 and the scanning pattern of the laser beam LB of Embodiment 3 shown in Figure 13, respectively, in that the first line C7 and the second line C8 do not pass through the center O.

[0105] As mentioned above, when laser welding a workpiece 200 with significantly different heat capacities on either side of a weld line WL, it is necessary to increase the amount of heat input on the side with the larger heat capacity. In this embodiment, the first lines C3, C7 and the second lines C4, C8 are arranged so that they do not pass through the center O. This makes it possible to make the length of the scanning trajectory of the laser beam LB, or in other words, the irradiation time of the laser beam LB, different on both sides of the weld line WL that passes through the center O. In other words, by making the scanning trajectory of the laser beam LB, and consequently the irradiation time of the laser beam LB, longer on the side with the larger heat capacity, the amount of heat input on both sides of the weld line WL is balanced (adjusted), and the workpiece 200 can be reliably laser welded. Furthermore, the occurrence of welding defects such as burn-through or insufficient penetration can be suppressed, thereby improving the welding quality.

[0106] (Embodiment 5) Figure 15 is a diagram showing the scanning pattern of the laser beam LB according to Embodiment 5 of the present disclosure.

[0107] In the examples shown in Embodiments 1 to 4, the first curves C1 and C5 and the second curves C2 and C6 in the scanning pattern of the laser beam LB are each located on the circumferential CLR.

[0108] However, the disclosure is not limited thereto, and the laser beam LB may be scanned so that the first curves C1, C5 and the second curves C2, C6 are located on the outer circumference of the elliptical ELP, as shown in Figure 15. In this case as well, the same effects as those achieved by the methods and configurations shown in Embodiments 1 to 4 can be achieved. Furthermore, by changing the arrangement angle of the major axis of the elliptical ELP with respect to the weld line WL, the irradiation width of the laser beam LB perpendicular to the weld line WL can be easily changed within the range from the minor axis to the major axis of the elliptical ELP. This makes it easy to change the width of the molten pool and, consequently, the width of the weld bead.

[0109] (Embodiment 6) Figure 16A is a diagram showing an example of a scanning pattern of a laser beam LB according to Embodiment 6 of the present disclosure. Figure 16B is a diagram showing another example of a scanning pattern of a laser beam LB according to Embodiment 6 of the present disclosure.

[0110] In this disclosure, the figure in which the first and second curves are located in the scanning pattern of the laser beam LB is not particularly limited to the outer circumference of the aforementioned circular CLR or elliptical ELP, but may be any closed curve. For example, the laser beam LB may be irradiated onto the surface of the workpiece 200 to draw the scanning pattern shown in Figure 16A or Figure 16B.

[0111] In the scanning pattern shown in Figure 16A, the closed curve CCV consists of the first curve CCV1 to the fourth curve CCV4. The first curve CCV1 and the second curve CCV2 are not tangent to each other, and the third curve CCV3 and the fourth curve CCV4 are not tangent to each other. The first line CV1 is the curve connecting the first point CA, which is the connection point between the first curve CCV1 and the fourth curve CCV4, and the fourth point CD, which is the connection point between the second curve CCV2 and the third curve CCV3. The second line CV2 is the curve connecting the second point CC, which is the connection point between the first curve CCV1 and the third curve CCV3, and the third point CE, which is the connection point between the second curve CCV2 and the fourth curve CCV4.

[0112] Furthermore, the closed curve passing through the intersection point of the first line CV1 and the second line CV2 (hereinafter simply referred to as the intersection point), the first point CA, and the second point CC, and including the first curve CCV1, corresponds to the aforementioned first closed curve CL1, and the closed curve passing through the intersection point, the third point CE, and the fourth point CD, and including the second curve CCV2, corresponds to the aforementioned second closed curve CL2.

[0113] Furthermore, the third closed curve is one that passes through the intersection point, the second point CC, and the fourth point CD, and includes the third curve CCV3. The fourth closed curve is one that passes through the intersection point, the third point CE, and the first point CA, and includes the fourth curve CCV4.

[0114] When scanning the laser beam LB along the scanning pattern shown in Figure 16A, the laser beam LB moves in the following order, for example.

[0115] First, the laser beam LB travels from the intersection to the first point CA via the first line CV1, then through the first curve CCV1 to the second point CC, and then along the second line CV2 back to the intersection. At this time, the scanning direction SD1 of the laser beam LB is clockwise.

[0116] Next, the laser beam travels from the intersection to the third point CE via the second line CV2, then through the second curve CCV2 to reach the fourth point CD, and then along the first line CV1 back to the intersection. At this time, the scanning direction SD2 of the laser beam LB is counterclockwise.

[0117] Next, the laser beam travels from the intersection to the fourth point CD via the first line CV1, then through the third curve CCV3 to reach the second point CC, and then along the second line CV2 back to the intersection. At this time, the scanning direction SD3 of the laser beam LB is counterclockwise.

[0118] Next, the laser beam travels from the intersection to the third point CE via the second line CV2, then through the fourth curve CCV4 to reach the first point CA, and then along the first line CV1 back to the intersection. At this time, the scanning direction SD4 of the laser beam LB is clockwise.

[0119] In the scanning pattern shown in Figure 16A, the scanning start point is not limited to the aforementioned intersection point, but the operation of the laser beam LB may be started from any point on the closed curve CCV, the first line CV1, or the second line CV2. Also, although scanning directions SD1 and SD4 are set to clockwise and scanning directions SD2 and SD3 are set to counterclockwise, scanning directions SD1 and SD4 may be set to counterclockwise and scanning directions SD2 and SD3 may be set to clockwise.

[0120] Furthermore, the scanning pattern shown in Figure 16B differs from the scanning pattern shown in Figure 3 in that the closed curve CCV consists of a first curve CCV5 and a second curve CCV6, the closed curve CCV is not circular, and the first line CV1 and the second line CV2 are not straight lines. However, the scanning direction and scanning order of the laser beam LB are the same. Therefore, a detailed explanation is omitted.

[0121] Even when laser welding the workpiece 200 while scanning the laser beam LB with the scanning patterns shown in Figures 16A and 16B, the same effects as those achieved by the method and configuration shown in Embodiment 1 can be obtained. In other words, the amount of heat input by the laser beam LB at the surface of the molten pool can be balanced evenly at that surface. Furthermore, since the tip shape of the molten pool can be improved, a weld bead with a good shape can be obtained.

[0122] (Summary) Looking at the methods and configurations shown in Embodiments 1 to 6 together, it can be said that this specification discloses the following methods and configurations.

[0123] (Method 1) A laser welding method comprising a welding step of welding a workpiece 200 by advancing a laser beam LB in the welding direction WD, which is in the direction along the welding line WL, and irradiating the surface of the workpiece 200 by scanning the laser beam LB in two dimensions to draw a predetermined pattern.

[0124] When the welding speed V, which is the rate at which the laser beam LB travels in the welding direction WD, is zero, the predetermined pattern has a center O, and the predetermined pattern has at least a first closed curve CL1 and a second closed curve CL2. The first closed curve CL1 and the second closed curve CL2 are tangent at one point. This point is the intersection of the first line C3 and the second line C4. Alternatively, the first closed curve CL1 and the second closed curve CL2 share a line. This line is, for example, the first line C3 and the second line C4 shown in Figure 3, or the first line CV1 and the second line CV2 shown in Figure 16B.

[0125] In the welding step, the laser beam LB is scanned along the first closed curve CL1 in a first rotational direction while the center O of a predetermined pattern is advanced in a direction parallel to the welding direction WD, and then scanned along the second closed curve CL2 in a second rotational direction. The second rotational direction is the opposite direction to the first rotational direction. For example, if the first rotational direction is clockwise, then the second rotational direction is counterclockwise.

[0126] According to Method 1, the amount of heat input to the molten pool can be made uniform or well-balanced on either side of the welding line WL or the scanning center O of the laser beam LB. Furthermore, the tip shape of the molten pool in the welding direction WD can be improved, resulting in a well-shaped weld bead. In addition, if the first closed curve CL1 and the second closed curve CL2 are in contact at a single point, it is possible to prevent the amount of heat input from concentrating on the welding line WL through which the contact point between the first closed curve CL1 and the second closed curve CL2 passes, and to reliably distribute the amount of heat input to both sides of the welding line WL.

[0127] (Method 2) In Method 1, the first closed curve CL1 includes the first curve, and the second closed curve CL2 includes the second curve. One end of the first curve and one end of the second curve are connected by the first line, and the other end of the first curve and the other end of the second curve are connected by the second line.

[0128] According to Method 2, the scanning pattern of the laser beam LB can be simplified, and the laser beam LB can be scanned at high speed.

[0129] (Method 3) In Method 2, the first line and the second line are straight lines. Also, the first line and the second line share the first line mentioned above. The first line and the second line are parallel to the weld line WL.

[0130] According to Method 3, the laser beam LB is irradiated onto the surface of the workpiece 200 such that the first line, corresponding to the first line, and the second line largely overlap. Therefore, the amount of heat input from the laser beam LB in the area where the first line and the second line overlap can be made greater than in other areas. For example, by scanning the laser beam LB in the shape shown in Figure 4 and performing laser welding, the workpiece 200 can be reliably welded in a fillet weld of two overlapping plates, and the welding quality can be improved.

[0131] (Method 4) In Method 2, the first line and the second line are both straight lines. Also, the first line and the second line share the aforementioned line 1. The first line and the second line intersect the weld line WL.

[0132] According to Method 4, the amount of heat input at or near the weld line WL can be widely distributed in a direction intersecting the weld line WL. This makes it possible to reliably weld the workpiece 200 while suppressing the occurrence of burn-through, for example, in butt welding with a gap.

[0133] (Method 5) In any one of Methods 1 to 4, the point of tangency between the first closed curve CL1 and the second closed curve CL2 is the center O. This point of tangency corresponds to the intersection of the first line and the second line.

[0134] According to Method 5, the scanning trajectory of the laser beam LB can be made symmetrical or nearly symmetrical with respect to the welding line WL through which the center O is progressing, thus enabling a well-balanced distribution of heat input by the laser beam LB at the surface of the molten pool.

[0135] (Method 6) In any one of Methods 1 to 4, the point of tangency between the first closed curve CL1 and the second closed curve CL2 is at a different position from the center O.

[0136] According to Method 6, if the thermal balance (heat capacity) of the workpiece 200 differs on either side of the weld line WL, the laser beam LB can be irradiated onto the surface of the workpiece 200 according to the difference in thermal balance, or in other words, the difference in heat capacity, and the amount of heat input by the laser beam LB at the surface of the molten pool can be balanced evenly at that surface. As a result, a weld bead with a good shape can be formed.

[0137] (Method 7) In any one of Methods 1 to 6, the given pattern further comprises a third closed curve and a fourth closed curve. The first closed curve CL1 is tangent to the second closed curve CL2 at one point, and the third closed curve is tangent to the fourth closed curve at one point.

[0138] In the welding step, the laser beam LB is scanned along the first closed curve CL1 in a first rotational direction while the center O is advanced in a direction parallel to the welding direction WD, and then scanned along the second closed curve CL2 in a second rotational direction. Furthermore, the laser beam LB is scanned along the third closed curve in a third rotational direction, and then scanned along the fourth closed curve in a fourth rotational direction. The fourth rotational direction is the opposite direction to the third rotational direction. For example, if the third rotational direction is clockwise, then the fourth rotational direction is counterclockwise.

[0139] Method 7 can achieve the same effect as Method 1. In other words, the amount of heat input to the molten pool can be balanced effectively. Furthermore, since the tip shape of the molten pool in the welding direction WD can be improved, a weld bead with a good shape can be obtained.

[0140] (Method 8) In any one of Methods 1 to 7, a portion of the first closed curve CL1, i.e., the first curve, and a portion of the second closed curve CL2, i.e., the second curve, lie on the circumference CLR of the same circle.

[0141] According to Method 8, the tip shape of the molten pool in the welding direction WD can be made closer to an arc, thus enabling the creation of a well-shaped weld bead.

[0142] (Method 9) In any one of Methods 1 to 7, a portion of the first closed curve CL1, i.e., the first curve, and a portion of the second closed curve CL2, i.e., the second curve, lie on the outer circumference of the same ellipse ELP.

[0143] According to Method 9, by changing the arrangement angle of the major axis of the elliptical ELP relative to the weld line WL, the irradiation width of the laser beam LB perpendicular to the weld line WL can be easily changed within the range from the minor axis to the major axis of the elliptical ELP. This makes it easy to change the width of the molten pool and, consequently, the width of the weld bead.

[0144] (Method 10) In Method 3 or 4, each of the connection points between the first curve and the first line, the connection point between the first curve and the second line, the connection point between the second curve and the first line, and the connection point between the second curve and the second line is a continuously changing curve.

[0145] According to method 10, when the scanning speed of the laser beam LB increases, the rapid vibration of the molten pool can be suppressed. This prevents the molten pool from becoming disordered and the shape of the weld bead from deteriorating. In addition, the scanning speed can be maintained before and after the switching point of the scanning trajectory, and even if it is changed, the speed change can be made gradual. This prevents excessive heat input near the switching point, and prevents the shape of the molten pool, and consequently the shape of the weld bead, from becoming uneven.

[0146] (Method 11) In any one of Methods 1 to 10, the center O moves along the weld line WL.

[0147] According to method 11, when the heat balance of the workpiece 200 is equal on both sides of the weld line WL, the amount of heat input by the laser beam LB on the surface of the molten pool can be balanced evenly on that surface, and a weld bead with a good shape can be formed.

[0148] (Method 12) In any one of Methods 1 to 10, the center O travels along a virtual line that is a first distance WLOS away from the weld line WL in a direction intersecting the welding direction WD.

[0149] According to Method 12, if the heat balance of the workpiece 200 is uneven and the heat capacity is large on one side of the weld line WL, the laser beam LB can be irradiated onto the surface of the workpiece 200 in proportion to that heat capacity. This allows the amount of heat input by the laser beam LB on the surface of the molten pool to be evenly balanced on that surface. As a result, a weld bead with a good shape can be formed.

[0150] (Configuration 1) The laser welding apparatus 100 comprises a laser oscillator 10, a laser head 30, and a controller 50.

[0151] The laser oscillator 10 generates laser light LB, and the laser head 30 receives the laser light LB and irradiates it toward the workpiece 200. The controller 50 controls the operation of at least the laser head 30.

[0152] The laser head 30 has a laser light scanner 40 that scans the laser light LB in a first direction and in a second direction that intersects the first direction.

[0153] When performing laser welding by advancing the laser beam LB in the welding direction WD, which is along the welding line WL, the controller 50 drives and controls the laser beam scanner 40 so that the laser beam LB draws the predetermined pattern described in Method 1 on the surface of the workpiece 200.

[0154] According to configuration 1, the amount of heat supplied to the molten pool can be uniform or well-balanced across the scanning center O of the welding line WL or laser beam. Furthermore, since the shape of the tip of the molten pool can be improved, a weld bead with a good shape can be obtained.

[0155] (Configuration 2) Configuration 1 further includes a manipulator 60 to which a laser head 30 is attached, and the controller 50 controls the operation of the manipulator 60. The manipulator 60 moves the laser head 30 in the welding direction WD relative to the surface of the workpiece 200.

[0156] According to configuration 2, the welding direction WD can be changed. Furthermore, laser welding can be easily performed on workpieces 200 with complex shapes, such as three-dimensional shapes.

[0157] If the position of the laser head 30 is fixed, the controller 50 controls the movement of the stage 70 on which the workpiece 200 is placed. The stage 70 moves the workpiece 200 in the welding direction WD relative to the laser head 30.

[0158] (Configuration 3) Configuration 1 or 2 further comprises a stage 70 on which the workpiece 200 is placed and which is configured to be movable. The controller 50 controls the operation of the stage 70, which moves the workpiece 200 in the welding direction WD.

[0159] According to configuration 3, the welding direction WD can be changed, and laser welding can be easily performed on a workpiece 200 in which the shape of the joint changes within the plane of the welding surface.

[0160] (Configuration 4) In any one of Configurations 1 to 3, the laser oscillator 10 and the laser head 30 are connected by an optical fiber 20, and the laser light LB is transmitted from the laser oscillator 10 to the laser head 30 through the optical fiber 20.

[0161] According to configuration 4, laser welding can be performed on a workpiece 200 that is located at a distance from the laser oscillator 10. This increases the degree of freedom in arranging the various parts of the laser welding apparatus 100.

[0162] (Configuration 5) In any one of Configurations 1 to 4, the laser light scanner 40 is composed of a first galvanometer mirror 41 that scans the laser light LB in the X direction and a second galvanometer mirror 42 that scans the laser light LB in the Y direction.

[0163] According to configuration 5, the laser beam LB can be easily scanned in two dimensions. Furthermore, since a known galvanometer scanner can be used as the laser beam scanner 40, the cost of the laser welding apparatus 100 can be kept from increasing.

[0164] (Program) A laser welding program (hereinafter simply referred to as "program") for executing one of the methods 1 to 12 may be incorporated into the controller 50 of the laser welding apparatus 100 of any one of the configurations 1 to 5, specifically one or more integrated circuits (CPUs). In this case, by executing the program, the manipulator 60 or stage 70 can be operated to advance the laser beam LB in the welding direction WD, and the center O can be advanced in a direction parallel to the welding direction WD. Simultaneously, by executing the program, the laser beam scanner 40 can be operated to irradiate the surface of the workpiece 200 with the laser beam LB to scan two-dimensionally and draw a predetermined pattern.

[0165] By executing this program, the same effects as those achieved by methods 1 to 12 can be obtained. Furthermore, by describing the operation procedure of the manipulator 60, stage 70, or laser light scanner 40 as a program, methods 1 to 12 can be executed simply and reliably. In addition, the scanning procedure of the laser light LB shown in methods 1 to 12 can be reliably executed in each of the multiple laser welding apparatuses 100.

[0166] The laser welding method described herein is useful because it allows for a well-balanced distribution of heat input to the molten pool on either side of the welding line or the scanning center of the laser beam, and also improves the shape of the leading edge of the molten pool, thereby enabling the acquisition of a well-shaped weld bead.

[0167] 10 Laser oscillator 20 Optical fiber 30 Laser head 31 Housing 32 Collimation lens 33 Reflection mirror 34 Focusing lens 40 Laser light scanner 41 First galvanometer mirror 41a First mirror 41b First rotation axis 41c First drive unit 42 Second galvanometer mirror 42a Second mirror 42b Second rotation axis 42c Second drive unit 50 Controller 60 Manipulator 70 Stage 100 Laser welding device 200 Workpiece A First point, point A' First inflection point A'' Second inflection point A1-A4 Scanning direction B Point C Second point, point C' Third inflection point C'' Fourth inflection point C1 Semicircle, first curve C2 Semicircle, second curve C3, C7 First line C4, C8 Second line C5 First curve C6 Second curve C9 Fifth curve C10 Sixth curve C11 Eighth curve C12 Seventh curve CA First point CC Second point CD Fourth point CE Third point CCV Closed curve CCV1, CCV5 First curve CCV2, CCV6 Second curve CCV3 Third curve CCV4 Fourth curve CD1, CD2 Scanning direction CL1 First closed curve, closed curve CL2 Second closed curve, closed curve CLR Circumference CV1 First line CV2 Second line D Fourth point, point D' Seventh inflection point D'' Eighth inflection point E Third point, point E' Fifth inflection point E'' Sixth inflection point ELP Ellipse F Point LB Laser beam LSJX Scanning trajectory O Center SD1-SD4 Scanning direction V Welding speed, movement speed WBX, WBY Weld bead WD Welding direction WL Weld line WLOS First distance, offset distance WPRX, WPRY Forward portion α Angle

Claims

1. A laser welding method comprising a welding step of welding a workpiece by irradiating the surface of the workpiece with a laser beam that is advanced in the welding direction, which is along the welding line, and scanning the laser beam in two dimensions to draw a predetermined pattern, wherein when the welding speed, which is the speed at which the laser beam advances in the welding direction, is zero, the predetermined pattern has a center, the predetermined pattern has at least a first closed curve and a second closed curve, the first closed curve and the second closed curve are tangent at one point or share one line, and in the welding step, while advancing the center of the predetermined pattern in a direction parallel to the welding direction, the laser beam is scanned in a first rotational direction along the first closed curve, and then the laser beam is scanned in a second rotational direction along the second closed curve, the second rotational direction being the opposite rotational direction to the first rotational direction.

2. A laser welding method according to claim 1, wherein the first closed curve includes a first curve, the second closed curve includes a second curve, one end of the first curve and one end of the second curve are connected by a first line, and the other end of the first curve and the other end of the second curve are connected by a second line.

3. A laser welding method according to claim 2, wherein the first line and the second line are each straight lines, the first line and the second line share the first line, and the first line and the second line are parallel to the welding line.

4. A laser welding method according to claim 2, wherein the first line and the second line are each straight lines, the first line and the second line share the first line, and the first line and the second line intersect the welding line.

5. A laser welding method according to claim 1, wherein the point of tangency between the first closed curve and the second closed curve is the center.

6. A laser welding method according to claim 1, wherein the point of tangency between the first closed curve and the second closed curve is located at a position different from the center.

7. A laser welding method according to claim 1, wherein the predetermined pattern further comprises a third closed curve and a fourth closed curve, the first closed curve is tangent to the second closed curve at the same point, the third closed curve is tangent to the fourth closed curve at the same point, and in the welding step, the laser beam is scanned along the second closed curve in a second rotational direction, then along the third closed curve in a third rotational direction, and further along the fourth closed curve in a fourth rotational direction, the fourth rotational direction being opposite to the third rotational direction.

8. A laser welding method according to claim 1, wherein a portion of the first closed curve and a portion of the second closed curve lie on the circumference of the same circle.

9. A laser welding method according to claim 1, wherein a portion of the first closed curve and a portion of the second closed curve lie on the outer circumference of the same ellipse.

10. A laser welding method according to claim 3 or 4, wherein each of the connection portion between the first curve and the first line, the connection portion between the first curve and the second line, the connection portion between the second curve and the first line, and the connection portion between the second curve and the second line is a continuously changing curve.

11. A laser welding method according to claim 1, characterized in that the center moves along the welding line.

12. A laser welding method according to claim 1, wherein the center travels along a virtual line that is a first distance away from the welding line in a direction intersecting the welding direction.

13. A laser oscillator that generates laser light, a laser head that receives the laser light and irradiates it toward a workpiece, and a controller that controls the operation of at least the laser head, wherein the laser head has a laser light scanner that scans the laser light in a first direction and a second direction intersecting the first direction, and when laser welding is performed by advancing the laser light in the welding direction which is the direction along the welding line, the controller drives and controls the laser light scanner so that the laser light draws a predetermined pattern on the surface of the workpiece, the predetermined pattern has at least a center, a first closed curve and a second closed curve, the first closed curve and the second closed curve are tangent at one point or share one line, the controller advances the center of the predetermined pattern in a direction parallel to the welding direction, and the laser light scanner scans the laser light in a first rotational direction along the first closed curve, and then scans the laser light in a second rotational direction along the second closed curve. A laser welding apparatus in which the second rotation direction is opposite to the first rotation direction.

14. A laser welding apparatus according to claim 13, further comprising a manipulator to which the laser head is attached, wherein the controller controls the operation of the manipulator, and the manipulator moves the laser head in the welding direction relative to the surface of the workpiece.

15. A laser welding apparatus according to claim 13, further comprising a stage on which the workpiece is placed and which is configured to be movable, wherein the controller controls the operation of the stage, and the stage moves the workpiece in the welding direction.

16. A laser welding apparatus according to claim 13, wherein the laser oscillator and the laser head are connected by an optical fiber, and the laser light is transmitted from the laser oscillator to the laser head through the optical fiber.

17. A laser welding apparatus according to claim 13, wherein the laser light scanner comprises a first galvanometer mirror that scans the laser light in a first direction and a second galvanometer mirror that scans the laser light in a second direction.

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