JP2019195816A - Laser welding method - Google Patents

Abstract

To provide a laser welding method which can suppress crack generation at a specific site of a base material.SOLUTION: When scanning a laser beam irradiation position from one side toward the other side with respect to a joint region of two overlapped metal plates W1, W2 and performing lap fillet welding, output of laser beam, which scans an irradiation position in a prescribed range C in a direction along an extension direction of the joint area, is gradually decreased from one side (upstream side in a scanning direction) toward the other side (downstream side in the scanning direction) in the prescribed range. Thus, rise of temperature of the metal plates W1, W2 is suppressed at a downstream side part of laser beam scanning in the prescribed range C, a temperature difference between a specific site and other sites, and a stress at the specific site can be suppressed. Further, since rise of temperature at the specific site is suppressed, decrease in strength thereof can be also suppressed. Consequently, it can be suppressed that crack occurs in the metal plate (lower plate) W2.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a laser welding method for performing lap fillet welding with laser light.

  Conventionally, lap fillet welding is known as a technique for joining a plurality of metal plates. In Patent Document 1, in the overlap fillet welding of the upper plate and the lower plate, a step of melting and joining a predetermined portion in the edge portion of the upper plate and a predetermined portion of the lower plate corresponding to the predetermined portion, Before starting this process, a welding method is disclosed that includes a step of forming a notch at the beginning and end of the predetermined location in the welding direction. By forming this notch, it is possible to suppress the occurrence of welding defects at the welding start end.

JP 2017-225999 A

  However, the thing of patent document 1 requires the process of forming a notch part in a metal plate, and welding work is complicated. In addition, in the case of lap fillet welding, there is a possibility that a welding defect may occur even in a region other than the welding start end portion. For example, overlapped fillet welding is performed by scanning the laser beam irradiation position from one side to the other side in the extending direction with respect to a joining region (region where a bead is formed) that is a boundary portion between the upper plate and the lower plate. When performing the above, a crack occurs in the unmelted base material (lower plate) upstream by a predetermined dimension from the end of the other side (downstream in the laser beam scanning direction) in this joining region. there is a possibility. FIG. 9 shows a state where a crack c extending in a direction orthogonal to the extending direction of the joining region d is generated in the lower plate b. Further, the arrows in FIG. 9 indicate the scanning direction of the laser light. If such a crack c occurs, the strength at the joint portion between the upper plate a and the lower plate b is reduced, or the appearance of the joint portion is deteriorated. Hereinafter, the part where the crack c occurs is referred to as a specific part of the lower plate b.

  The cause of the occurrence of the crack c is that a large stress is generated at a specific part of the lower plate b and the strength of the specific part of the lower plate b is reduced. That is, when the temperature of the specific part of the lower plate b rises due to laser light irradiation and the temperature difference between the specific part and the other part becomes large, the amount of thermal expansion due to the high temperature of the specific part and Since the amount of solidification shrinkage due to cooling becomes larger than that of other parts, a large stress is generated in this specific part. In addition, the strength decreases due to the high temperature of the specific part. Thus, in the specific part of the lower board b, it is thought that the crack c generate | occur | produces because the balance of stress and intensity collapse | crumbles.

  The above phenomenon is particularly remarkable when the metal plate is an aluminum-based metal plate. The same phenomenon may occur when the metal plate is a steel plate.

  In view of the above points, the inventors of the present invention are able to cool the entire body substantially uniformly if the temperature distribution gradient of the specific portion of the base material (lower plate) and its peripheral portion is small, and the stress becomes small. The present inventors have reached the present invention based on a new finding that if the amount of heat input to a specific part of the material is reduced, the strength of the specific part can be kept high, and cracks are less likely to occur.

  This invention is made | formed in view of this point, The place made into the objective is to provide the laser welding method which can suppress generation | occurrence | production of the crack in the specific site | part of a base material.

  In order to achieve the above-mentioned object, the solution means of the present invention is directed to a laser beam directed from one side to the other side in the extending direction of the bonding region with respect to the bonding region set in advance in a plurality of stacked metal plates. A laser welding method in which the irradiation position is scanned and overlapped fillet welding is performed is assumed. In this laser welding method, the output of the laser beam whose irradiation position is scanned in a predetermined range in the direction along the extending direction of the joining region is gradually increased from the one side to the other side in the predetermined range. It is characterized by being made smaller.

  The predetermined range here is a range including the specific part of the base material (metal plate) described above, and is a range defined based on experiments and simulations (a place where a crack has occurred in the base material in the prior art) Range).

  Due to the above-mentioned specific matters, when performing overlapped fillet welding by irradiating a laser beam onto a joining region between a plurality of superposed metal plates, it is within a predetermined range in a direction along the extending direction of the joining region. Thus, the output of the laser beam whose irradiation position is scanned is changed from one side (upstream side of scanning in the direction along the extending direction of the bonding region) to the other side (in the extending direction of the bonding region) in the predetermined range. Gradually down toward the downstream side of scanning in the direction). As a result, the temperature rise of the metal plate is suppressed at the downstream portion of the laser beam scanning in the predetermined range (the specific portion of the base material described above), and the temperature difference between the specific portion and other portions is reduced. (The temperature distribution gradient can be reduced), and the stress at this specific portion can be reduced. Moreover, the fall of the intensity | strength can also be suppressed because the temperature rise of this specific site | part can be suppressed. Thereby, it can suppress that a crack generate | occur | produces in a metal plate.

  In the present invention, the output of the laser beam whose irradiation position is scanned in a predetermined range in the direction along the extending direction of the joining region of the metal plate where the lap fillet welding is performed is changed from one side to the other side in the predetermined range. I gradually try to make it smaller. Thereby, in the downstream part (specific part) of the scanning of the laser beam in a predetermined range, the temperature rise of the metal plate can be suppressed, and the temperature difference between this specific part and other parts can be reduced, The stress at this specific part is reduced. Moreover, the fall of the intensity | strength can also be suppressed because the temperature rise of this specific site | part can be suppressed. Thereby, it can suppress that a crack generate | occur | produces in a metal plate.

It is a schematic block diagram which shows the laser welding apparatus used for the laser welding which concerns on embodiment. It is a perspective view of the workpiece | work for demonstrating the scanning of the laser beam which concerns on embodiment. It is a figure for demonstrating the locus | trajectory of a laser beam irradiation position. It is a figure which expands and shows the welding location of the workpiece | work for demonstrating the movement state of the laser beam irradiation position in the laser welding which concerns on embodiment. It is a figure which shows an example of the relationship between a laser beam irradiation position and a laser beam output. It is a figure which shows an example of the relationship between a laser beam irradiation position and the temperature in the position. It is a figure which shows an example of the temperature change of a specific part. It is a figure which shows the result of having measured transition of the temperature difference of a specific part and a bead center part in an experiment example. It is a perspective view of the workpiece | work which shows the state which the crack generate | occur | produced in the lower board in the prior art.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied as a laser welding method performed by a laser welding apparatus used in a manufacturing process of an automobile body will be described.

-Schematic configuration of laser welding equipment-
FIG. 1 is a schematic configuration diagram showing a laser welding apparatus 1 used for laser welding according to the present embodiment. As shown in FIG. 1, the laser welding apparatus 1 includes a laser oscillator 2, a laser scanner 3, a welding robot 4, and a robot controller 5.

  The laser oscillator 2 generates laser light. The generated laser light is guided to the laser scanner 3 through the optical fiber cable 21. As the laser light, for example, a carbon dioxide laser, a YAG laser, a fiber laser, or the like can be used.

  The laser scanner 3 is a workpiece W formed by superposing two aluminum alloy plate materials (aluminum-based metal plate; hereinafter, also simply referred to as a metal plate) W1 and W2 on a laser beam guided through an optical fiber cable 21. (See the dashed line in FIG. 1). The laser scanner 3 accommodates a lens group (not shown) and a plurality of mirrors 31 (only one mirror 31 is shown in FIG. 1). The lens group includes a collimating lens for making the laser light parallel light, and a condensing lens for condensing the laser light so as to focus at a processing point of the workpiece W (a predetermined laser beam irradiation position on the workpiece W). Etc. are provided. Each mirror 31 is configured to be rotatable about a rotation shaft 32. Specifically, the rotation shaft 32 is connected to a scanning motor 33, and each mirror 31 is rotated by the rotation of the rotation shaft 32 accompanying the operation of the scanning motor 33. Then, the laser beam is scanned by the rotation of the mirror 31, and the laser beam irradiation position can be moved within a predetermined range of the workpiece W. Thereby, it is possible to move the laser light irradiation position without moving the laser scanner 3 itself. Each mirror 31 can be configured using a galvanometer mirror, for example.

  The welding robot 4 is configured to allow the laser scanner 3 to move. The welding robot 4 is constituted by an articulated robot. Specifically, the present embodiment includes a base base 41, a rotation mechanism (not shown) accommodated in the base base 41, joints 42, 43, 44, and arms 45, 46, 47. Yes. The laser scanner 3 can be moved in an arbitrary direction by the rotation operation of the rotation mechanism and the swinging operation of the arms 45, 46, 47 in the joints 42, 43, 44.

  The robot controller 5 stores in advance information (information such as the rotation angle amount of each joint 42, 43, 44) for moving the laser scanner 3 toward the welding target portion by offline teaching. Then, when the vehicle body is conveyed to the welding process location on the vehicle body production line, the welding robot 4 is operated based on the information according to the control signal from the robot controller 5, so that the laser scanner 3 is welded to the location to be welded. Laser welding is sequentially performed by irradiating a laser beam from the laser scanner 3 toward a welding target portion.

  The robot controller 5 is provided with a laser beam scanning control unit 51 that outputs a control signal for moving the laser beam irradiation position on the workpiece W. The laser beam scanning control unit 51 outputs a control signal to the scanning motor 33. When the scanning motor 33 operates according to this control signal, each mirror 31 rotates about the rotation shaft 32 to scan the laser beam, and the laser beam irradiation position on the workpiece W is moved. The movement of the laser beam irradiation position on the workpiece W will be described later.

-Welding method-
Next, the welding method (laser welding method) in this embodiment is demonstrated. The feature of the present embodiment is in the output of the laser beam irradiated toward the workpiece W. Before describing the output of the laser beam, scanning of the laser beam will be described.

  In this embodiment, it is a case where the overlap fillet welding of the two metal plates W1, W2 overlapped in the vertical direction is performed, and the overlap portion (the overlap fillet portion) of the metal plates W1, W2 is performed. The case where the laser beam emitted from the laser scanner 3 is irradiated from above will be described. For this reason, hereinafter, the upper metal plate is referred to as an upper plate W1, and the lower metal plate is referred to as a lower plate W2.

  FIG. 2 is a perspective view of the workpiece W for explaining the scanning of the laser beam according to the present embodiment. FIG. 3 is a diagram for explaining the locus (movement locus) of the laser light irradiation position.

  As shown in these drawings, the lap fillet welding in the present embodiment is performed by melting the metal material along the weld line L that is the overlapping portion of the upper plate W1 and the lower plate W2 that are overlapped. W1 and the lower plate W2 are welded. Specifically, the position of the front end surface (front end surface in FIG. 2) W2a of the lower plate W2 is slightly on the front side with respect to the position of the front end surface (front end surface in FIG. 2) W1a. The laser beam is scanned in a bonding region (region where a bead is formed) within a predetermined range from the upper surface W1b and the front end surface W1a of the upper plate W1 to the upper surface W2b of the lower plate W2. The metal material is melted (by scanning the laser beam condensing point (focal point)), and the upper plate W1 and the lower plate W2 are thereby welded. This type of welding technique is generally called laser wobbling welding.

  As the scanning of the laser beam (movement of the laser beam irradiation position on the upper plate W1 and the lower plate W2), as shown by the solid line arrow (the locus of the laser beam irradiation position) in FIG. While moving along the elliptical trajectory so as to straddle the weld line L, which is the overlapping portion of the plate W1 and the lower plate W2, the center of the ellipse in the trajectory is a direction along the weld line L (left in FIG. 2). Direction). In FIG. 2, a line connecting the centers of the trajectories is indicated by a one-dot chain line M, and the one-dot chain line M is parallel to the welding line L.

  Further, specifically, the moving direction along the elliptical locus of the laser beam irradiation position is more than the range in which the laser beam has already passed in the direction along the weld line L (range X in FIG. 2). 2 on the downstream side (left side in FIG. 2) and unmelted portions of the upper plate W1 and lower plate W2 (the portions not yet irradiated with laser light, and in FIG. 2, on the left side of the point X1) When the laser beam passes through a region located at (1), the laser beam is applied to the lower plate W2 after the upper plate W1 is irradiated with the laser beam. That is, while moving the elliptical locus in FIG. 2 counterclockwise, the laser beam is scanned so that the elliptical center in the locus moves to the left along the welding line L. . As described above, the movement of the laser beam irradiation position is such that a control signal from the laser beam scanning control unit 51 is output to the scanning motor 33 that rotates the mirrors 31, and the scanning motor 33 is operated to This is done by rotating the mirror 31.

  Further, in detail about the elliptical trajectory of the laser light irradiation position, for example, when the thickness of the upper plate W1 and the lower plate W2 is 1.5 mm to 3.0 mm, as shown in FIG. The length dimension (amplitude) A of the elliptical long axis direction (the vertical direction in FIG. 3 and the direction perpendicular to the weld line L) is set to a predetermined value in the range of 2.5 mm to 3.5 mm. The Further, the length dimension (width) D of the elliptical short axis direction (the horizontal direction in FIG. 3 and parallel to the weld line L) is set to a predetermined value in the range of 1.0 mm to 2.4 mm. The Further, the pitch in the direction along the weld line L (the amount of scanning movement in the direction along the weld line L per rotation when the center of the ellipse in the locus is moved in the direction along the weld line L) is P: It is set to a predetermined value in the range of 0.8 mm to 1.6 mm. These values are not limited to this, and are appropriately set by experiments or simulations according to the plate thickness dimensions of the upper plate W1 and the lower plate W2.

  Further, as a laser beam condition in the present embodiment, the scanning speed along the elliptical locus is set to a predetermined value in the range of 2500 to 5000 cm / min. This value is not limited to this, and is appropriately set by experiment or simulation according to the plate thickness dimensions of the upper plate W1 and the lower plate W2.

  Next, the molten state of the metal material by laser welding will be described. FIG. 4 is an enlarged view showing a welding portion of the workpiece W for explaining the movement state of the laser beam irradiation position in the laser welding. Points S1 to S4 in FIG. 4 indicate laser beam irradiation positions. That is, in FIG. 4, as moving from FIG. 4A to FIG. 4D, the laser light irradiation position moves in the order of S1, S2, S3, and S4 on an elliptical locus indicated by a one-dot chain line. It means to go.

  As shown in FIG. 4, in the lap fillet welding in the present embodiment, when the lap fillet welding is performed by irradiating the overlap portion of the upper plate W1 and the lower plate W2 with the laser beam, As described above, while moving along the elliptical trajectory so as to straddle the welding line L that is the overlapping portion of the upper plate W1 and the lower plate W2, the center of the elliptical shape in the trajectory is the welding line L. It moves in the direction (left direction in FIG. 4) along. As the movement of the laser beam irradiation position in FIG. 4, the elliptical center in the locus moves to the left along the welding line L while moving the elliptical locus in the counterclockwise direction. Yes. That is, the moving direction along the elliptical locus of the laser beam irradiation position is downstream of the range X (see FIG. 2) in which the laser beam has already passed in the direction along the weld line L, and the upper plate W1 and When the laser beam passes through the unmelted portion of the lower plate W2, the laser beam is applied to the upper plate W1, and then the laser beam is applied to the lower plate W2.

  Accordingly, in the laser light irradiation state (irradiation position S1) shown in FIG. 4A, the upper plate W1 is irradiated with the laser light, so that the metal material of the upper plate W1 is melted at the irradiation position S1. The upper plate W1 and the lower plate W2 are cross-linked. In this case, the heat of the laser light is transmitted not only to the upper plate W1 but also to the lower plate W2, and the upper plate W1 and the lower plate W2 are well welded at this laser light irradiation position. Further, since the heat of the laser light is transmitted to both the upper plate W1 and the lower plate W2, the upper plate W1 at this time is surrounded by a broken line in the region around the laser light irradiation position S1 (for example, FIG. 4A). In this case, the heat input is relatively small and the metal material is not sufficiently melted (for example, in a semi-molten state). Thereafter, as shown in FIG. 4B, the laser light irradiation position S2 moving on the locus passes on the lower plate W2 as shown in the laser light irradiation state (irradiation position S2) shown in FIG. As in the laser light irradiation state (irradiation position S3), when the laser light irradiation position S3 reaches the upper plate W1 again, the region of the upper plate W1 that has not been sufficiently melted (the upper plate W1). In the region around the position where the lower plate W2 and the lower plate W2 are already welded; the region surrounded by the broken line in FIG. 4C), the metal material is completely melted by the irradiation of the laser beam. Even if it exists in a light irradiation position, the upper board W1 and the lower board W2 are favorably welded. That is, when the laser light irradiation state (irradiation position S4) shown in FIG. 4D is reached, the region surrounded by the broken line in FIG. 4D is solidified, so that the upper plate W1 and the lower plate in this region are solidified. W2 is well welded. Such an operation is continuously performed every time the laser beam irradiation position rotates once along the elliptical locus, so that the metal material is melted along the weld line L and the upper plate W1 and the lower plate W2 are melted. And will be welded.

  In the case of this embodiment, when the upper plate W1 is irradiated with laser light, the molten metal of the upper plate W1 easily flows into the molten portion of the lower plate W2 due to the action of gravity, and the molten metal Will be mixed. In other words, when the overlapping direction of the upper plate W1 and the lower plate W2 is set to the vertical direction, the upper plate W1 and the lower plate W2 are more effectively bridged by effectively using gravity, and the welding location Thus, the upper plate W1 and the lower plate W2 are welded with an even higher joint strength.

  In such a laser welding method, when the laser beam irradiation position moving along the elliptical trajectory reaches the upper plate W1 again, the irradiation position on the upper plate W1 has been sufficiently melted until then. The area that did not exist will be melted. That is, it is not intended to irradiate the laser beam toward the completely melted region. For this reason, it is suppressed that the molten metal (molten metal) is blown off by the pressure of the keyhole by irradiating the laser beam toward the completely melted region, and the welded portion (solidified after the metal material is melted). ) (The throat thickness in the bead) can be sufficiently ensured, and the bonding strength (joint strength) at the welded portion can be sufficiently ensured.

-Laser light output-
The feature of this embodiment is in the output of laser light. This will be specifically described below.

  As described above, in the lap fillet welding in the prior art, as shown in FIG. 9, with respect to the joining region (region where the bead is formed) d which is a boundary portion between the upper plate a and the lower plate b. When performing overlapped fillet welding by scanning the laser light irradiation position from one side (right side in FIG. 9) to the other side (left side in FIG. 9) in the extending direction, the other side ( There is a possibility that a crack c may occur in the unmelted base material (lower plate b) on the upstream side by a predetermined dimension from the end portion on the downstream side in the scanning direction of the laser beam. As the cause of the occurrence of the crack c, a large stress is generated at a specific portion of the lower plate b (the portion where the crack c is generated), and the strength of the specific portion of the lower plate b is reduced. . That is, when the temperature of the specific part of the lower plate b rises due to laser light irradiation and the temperature difference between the specific part and the other part becomes large, the amount of thermal expansion due to the high temperature of the specific part and Since the amount of solidification shrinkage due to cooling becomes larger than that of other parts, a large stress is generated in this specific part. In addition, the strength decreases due to the high temperature of the specific part. Thus, in the specific part of the lower board b, it is thought that the crack c generate | occur | produces because the balance of stress and intensity collapse | crumbles.

  In view of this point, in the present embodiment, the entire portion is made substantially uniform by reducing the temperature distribution gradient of the specific portion of the base material (lower plate W2) (the portion where the crack has occurred in the prior art) and its peripheral portion. By cooling, thereby reducing the stress and reducing the amount of heat input to the specific part of the base material, the strength of the specific part is maintained high, and the crack is hardly generated.

  As a means for this, in this embodiment, the output of the laser beam whose irradiation position is scanned in a predetermined range in the direction along the extending direction of the bonding region is changed from the one side to the other in the predetermined range. The size is gradually reduced toward the side.

  Specifically, a range from a substantially intermediate position between the upstream end and the downstream end in the laser beam scanning direction in the direction along the extending direction of the joining region to the downstream end is defined as the predetermined range, and the predetermined range. The laser light output is gradually reduced from the upstream side to the downstream side in the scanning direction.

  FIG. 5 is a diagram illustrating an example of a relationship between a laser beam irradiation position and a laser beam output. In FIG. 5, the left end at the laser beam irradiation position on the horizontal axis is the upstream end (the right end in FIG. 2) in the laser beam scanning direction, and the right end at the laser beam irradiation position is the laser beam scanning. It is the downstream end in the direction (the left end in FIG. 2). As shown in FIG. 5, a range from a substantially intermediate position (position B in FIG. 5) between the upstream end and the downstream end in the scanning direction of the laser beam to the downstream end (range C in FIG. 5; referred to in the present invention, In a predetermined range in the direction along the extending direction of the bonding region), the output of the laser beam is gradually reduced from I (W) to II (W). As an example, it is gradually reduced from 5000 W to 4000 W. These values are not limited to this, and are set by experiment or simulation. In the range from the upstream end in the scanning direction of the laser beam to the substantially intermediate position (position B) (range E in FIG. 5), the output of the laser beam is fixed at I (W). 2, portions corresponding to the position B and the range C in FIG. 5 are denoted by the same reference numerals in FIG.

  More specifically, as described above, in this embodiment, the laser beam irradiation position is moved along the elliptical locus, and the center of the elliptical shape in the locus is moved in the direction along the weld line L. That is, in the direction along the extending direction of the joining region, the laser light irradiation position partially reciprocates (operation that temporarily returns to the upstream side). For this reason, as an example of the change in the output of the laser beam in the range C, the output of the laser beam is gradually reduced every time the elliptical scanning locus is rotated once. Further, the output of the laser beam may be decreased continuously (even during one rotation of the scanning locus) regardless of the position of the scanning locus. For this reason, in the present embodiment, “the laser light output is gradually reduced from one side to the other side in the predetermined range” in the present invention means that the laser light irradiation position is the upper plate W1. This means that the output of the laser beam when reaching the welding line L when moving from the lower plate W2 to the lower plate W2 is smaller than the output of the laser beam when reaching the welding line L on the upstream side. .

  By adjusting the output of the laser beam in this way, in the range C, the prior art (the laser beam output is constant from the upstream end to the downstream end in the laser beam scanning direction). In comparison, the temperature in this range C becomes lower. FIG. 6 is a diagram illustrating an example of the relationship between the laser light irradiation position and the temperature at the position. In FIG. 6, the temperature of each part in the prior art is indicated by a one-dot chain line, and the temperature of each part in the present embodiment (the present invention) is indicated by a solid line. As is clear from FIG. 6, in this embodiment, the temperature change of the specific part is lower than that of the prior art, and the temperature difference between the specific part and other parts is also small. ing. For this reason, the amount of thermal expansion due to high temperature and the amount of solidification shrinkage due to cooling are not significantly increased compared to other regions, and a large stress is applied to this specific region. Will not occur. Further, the strength does not decrease due to the high temperature of the specific part. For this reason, in this specific site | part, the balance of stress and intensity | strength can be kept favorable and generation | occurrence | production of a crack can be suppressed.

  Further, as another feature of the present embodiment, when the scanning position of the laser beam reaches the downstream end, the laser beam irradiation to the downstream end is temporarily continued. As an example, when the scanning position of the laser beam reaches the downstream end, the irradiation of the laser beam to the downstream end is continued for 0.1 sec. This value is not limited to this, and is set by experiment or simulation so that the temperature at the downstream end rises to a preset temperature. Thereby, the temperature of this downstream end can be made high and the amount of thermal expansion in this part is made large. That is, the cooling rate at the downstream end is brought close to the cooling rate at the specific part. Also by this, the specific portion and the downstream end have substantially the same amount of thermal expansion due to high temperature and the amount of solidification shrinkage due to cooling, and no large stress is generated in the specific portion. For this reason, it is avoided that stress concentrates on this specific part, and also by this, generation | occurrence | production of a crack can be suppressed.

  FIG. 7 is a diagram illustrating an example of a temperature change at a specific portion. In FIG. 7, the temperature change of the specific part in the prior art is indicated by a one-dot chain line, and the temperature change of the specific part in the present embodiment (the present invention) is indicated by a solid line. In addition, at the timing T1 in FIG. 7, the temperature of the specific part is increased because the laser light irradiation position has reached the specific part. In the prior art, the laser beam irradiation position reaches the downstream end at timing T2, and the laser beam irradiation is canceled. In the present embodiment, after the timing T2 is reached. Also, the laser beam is continuously irradiated to the downstream end for a predetermined time, and then the laser beam irradiation is canceled.

  As is apparent from FIG. 7, in this embodiment, the cooling rate (temperature decrease amount per unit time) at a specific portion is lower than that of the prior art, and solidification shrinkage per unit time. By reducing the amount, the amount of strain can be reduced, thereby suppressing the occurrence of cracks.

-Experimental example-
Next, an experimental example performed to confirm the above effect will be described. In this experimental example, the temperature difference between the specific part and the central part of the bead generated in the joining region (the central part in the extending direction of the bead) was measured for each of the prior art and the present embodiment. .

  FIG. 8 shows the measurement result. As is apparent from FIG. 8, in the present embodiment (the present invention), the temperature difference between the specific portion and the central portion of the bead is significantly smaller than that of the prior art. As a result, it was confirmed that a large stress was not generated at the specific part as described above, and the occurrence of cracks at the specific part could be suppressed.

-Other embodiments-
In addition, this invention is not limited to the said embodiment, All the deformation | transformation and applications included in a claim and the range equivalent to this range are possible.

  For example, in the above-described embodiment, the case where the present invention is applied as the laser welding method performed by the laser welding apparatus 1 used in the manufacturing process of a car body of an automobile has been described, but also for laser welding of other members. The present invention can be applied.

  Further, in the above-described embodiment, a case has been described in which overlap fillet welding is performed between the upper plate W1 and the lower plate W2 made of two aluminum-based metal plates while moving the laser beam irradiation position along an elliptical locus. . The present invention is not limited to this, and lap fillet welding may be performed while moving the laser beam irradiation position along a circular (perfect circle) locus. Further, the moving direction along the locus is not limited to the counterclockwise direction, and may be the clockwise direction. The present invention can also be applied to the case of performing the fillet welding on the three metal plates. That is, the laser beam irradiation position is moved along a circular or elliptical trajectory across three metal plates. The present invention can also be applied when performing lap fillet welding on a steel plate. In addition, the present invention can be applied to the case where overlapped fillet welding is performed in which the overlapping direction of each metal plate is the horizontal direction or other directions.

  In the above-described embodiment, the plurality of mirrors 31 are rotated by scanning with laser light that moves along the elliptical locus in the direction along the welding line L while moving along the elliptical locus. It was done by. The present invention is not limited to this, and scanning that moves the laser light irradiation position along an elliptical locus is performed by turning the mirror 31, and the movement along the welding line L at the center of the elliptical shape in the locus is performed by the welding robot. It may be realized by the swinging motion of the four arms 45, 46, 47.

  In the present invention, the laser beam irradiation position may be scanned linearly along the weld line L. In this case, the output of the laser beam that is gradually reduced in the range C may be reduced stepwise or continuously.

  The present invention is applicable to a laser welding method for performing overlapped fillet welding of an aluminum-based metal plate with a laser beam.

DESCRIPTION OF SYMBOLS 1 Laser welding apparatus 2 Laser oscillator 31 Mirror 33 Scanning motor 51 Laser beam scanning control part W Work W1 Upper plate (metal plate)
W2 Lower plate (metal plate)
L welding line C predetermined range in the direction along the extending direction of the joining region

Claims (1)

Laser welding method for performing overlapped fillet welding by scanning a laser beam irradiation position from one side to the other side in the extending direction of the joining region with respect to a preset joining region in a plurality of superimposed metal plates Because
The output of the laser beam whose irradiation position is scanned in a predetermined range in a direction along the extending direction of the bonding region is gradually reduced from the one side to the other side in the predetermined range. Laser welding method.

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