JP7593355B2 - Laser welding method and laser welding apparatus - Google Patents

Description

This disclosure relates to a laser welding method and a laser welding apparatus.

Conventionally, there is a welding method in which metal plates are welded together by irradiating them with a laser beam (for example, see Patent Document 1). In the method of Patent Document 1, a keyhole is formed in the molten pool by irradiating the laser in the second step. Metal vapor is then discharged from the keyhole, reducing the occurrence of defects such as blowholes.

JP 2012-115876 A

In the method of Patent Document 1, for example, in the second step, two laser irradiations are performed. The first and second laser irradiations have different irradiation conditions, such as the welding radius. If the laser irradiation is interrupted after the first laser irradiation and before the second laser irradiation, the molten metal flow in the molten pool may change suddenly. If the molten metal flow in the molten pool changes suddenly, spatter may occur, which may result in a decrease in welding quality.

This disclosure can be realized in the following forms:

(1) According to one embodiment of the present disclosure, there is provided a laser welding method for welding a plurality of overlapping metal objects together by scanning a laser beam irradiated toward irradiated surfaces of the plurality of overlapping metal objects, the laser welding method including a setting step of setting each set value of irradiation conditions including a laser output, a scanning speed, and a focused beam diameter of the laser beam, a first step of scanning the laser beam with the irradiation conditions set to first irradiation conditions to form a molten pool on the irradiated surface, a second step of scanning the laser beam within a range of the molten pool after the first step, the irradiation conditions set to second irradiation conditions different from the first irradiation conditions, and a connecting step between the first step and the second step, in which the laser beam set to the irradiation conditions with a set value between the set value of the first irradiation condition and the set value of the second irradiation condition is scanned from a scanning end position of the first step to a scanning start position of the second step for the conditions with different set values between the first irradiation condition and the second irradiation condition. According to this embodiment, in the connection process, laser irradiation is continuously performed from the scanning end position of the first process to the scanning start position of the second process, and in the connection process, irradiation conditions that complement the irradiation conditions of the first process and the irradiation conditions of the second process are used, so that sudden changes in the flow of molten metal are suppressed and deterioration of welding quality is suppressed.
(2) In the laser welding method of the above aspect, the set value of the laser power in the second irradiation condition may be smaller than the set value of the laser power in the first irradiation condition, and the set value of the scanning speed in the second irradiation condition may be larger than the set value of the scanning speed in the first irradiation condition. According to this aspect, in the second step, a keyhole can be appropriately formed by setting a laser power smaller than that in the first step, and the molten pool formed in the first step can be stirred by scanning at a scanning speed higher than that in the first step. Furthermore, stirring the molten pool makes it easier to discharge metal vapor from the molten pool, thereby improving welding quality.
(3) In the laser welding method of the above aspect, the connecting step is a first connecting step, and further includes a third step, which is performed after the second step, of scanning the laser beam, in which the irradiation conditions are set to third irradiation conditions different from the second irradiation conditions, around the outer periphery of the molten pool to expand the molten pool, and a second connecting step, which is performed between the second step and the third step, in which, for the conditions in which the setting values differ between the second irradiation conditions and the third irradiation conditions, the laser beam is set to the irradiation conditions in which the setting value is a value between the setting value of the second irradiation condition and the setting value of the third irradiation condition. and a second connecting step of scanning the laser beam from the scanning end position of the second step to the scanning start position of the third step, the set value of the laser output of the third irradiation condition being greater than the set value of the laser output of the second irradiation condition, the laser beam being scanned so as to rotate in the same direction with respect to the center of the scanning pattern drawn by the scanning, and a rotation angle based on the center from the scanning start position of the second connecting step to the scanning end position of the second connecting step being smaller than the rotation angle from the scanning start position of the first connecting step to the scanning end position of the first connecting step. According to this embodiment, the second connecting step in which the laser output is gradually increased can be set to a smaller rotation angle than the first connecting step in which the laser output is gradually decreased. This shortens the section in the second connecting step in which the laser output is scanned with a smaller laser output than the laser output in the third step, stabilizing the melted state and improving the welding quality.
(4) In the laser welding method of the above aspect, the set value of the irradiation condition in the connecting step may be changed so as to decrease or increase from the set value of the first irradiation condition to the set value of the second irradiation condition as moving from the scanning end position of the first step to the scanning start position of the second step, for the condition in which the set value differs between the first irradiation condition and the second irradiation condition. According to this aspect, the condition can be changed gradually, so that a sudden change in the molten metal flow can be further suppressed.
(5) In the laser welding method according to the above aspect, the set value of the irradiation condition in the connecting step may be a value obtained by linearly complementing the set value of the first irradiation condition and the set value of the second irradiation condition. According to this aspect, it is possible to reduce a calculation load of the set value of the irradiation condition in the connecting step.
(6) In the laser welding method of the above aspect, each of the plurality of metal objects may be a metal plate having a plating layer. According to this aspect, by applying the laser welding method of the above aspect to a metal plate on which a plating layer is formed, metal vapor of the metal forming the plating layer can be suitably discharged, thereby improving welding quality.
The present disclosure may be realized in various forms other than the laser welding method, for example, in the form of a laser welding device, a manufacturing method for a laser welding device, a control method for a laser welding device, a computer program for implementing the control method, a non-transitory recording medium on which the computer program is recorded, etc.

4 is a flowchart showing the procedure of a laser welding process. FIG. 1 is a schematic diagram showing a configuration of a laser welding device. The scanning pattern created during the laser welding process. FIG. 2 is a schematic diagram showing a cross-section of a metal object irradiated with a laser. 5A to 5C are diagrams for explaining scanning patterns that are sequentially drawn in a laser welding process. A table listing the settings for irradiation conditions. FIG. 4 is a diagram showing a change in laser output during a laser welding process. FIG. 4 is a diagram showing a change in scanning speed in a laser welding process.

A. Embodiments:
A1. Laser welding equipment:
FIG. 1 is a flow chart showing the procedure of the laser welding process for realizing the laser welding method. FIG. 2 is a schematic diagram showing the configuration of a laser welding device 100 used for irradiating a laser beam LB in the laser welding process. As shown in FIG. 2, the laser welding device 100 irradiates a laser beam LB to a first metal object Wa and a second metal object Wb, which are stacked as a plurality of stacked metal objects. In this embodiment, each of the first metal object Wa and the second metal object Wb is a steel plate having a zinc plating layer as a plating layer. The first metal object Wa and the second metal object Wb are also collectively called the metal object W. The first metal object Wa and the second metal object Wb are welded by irradiating the metal object W with the laser beam LB. Note that this laser welding method can be applied not only to a steel plate having a zinc plating layer, but also to other metal plates such as steel plates and metal products having shapes other than plates.

The laser welding device 100 includes a laser oscillator 10, a laser scanner 20 as a laser irradiation unit, and a control unit 60. The laser scanner 20 is attached to the tip of a robot arm (not shown). The laser scanner 20 is then moved by the robot arm to the target welding position of the metal object W.

The laser oscillator 10 emits a laser beam LB. The laser oscillator 10 and the laser scanner 20 are connected via an optical fiber cable 11. The laser scanner 20 includes a collimator lens 30, a dichroic mirror 40, a first reflecting mirror 21, a diffractive optical element (DOE) 22, a Z lens drive unit 23, a second reflecting mirror 25, a focusing lens 26, a galvano scanner unit 27, and a protective glass 28.

The laser light LB emitted from the laser oscillator 10 enters the inside of the laser scanner 20 via the optical fiber cable 11. The laser light LB is then adjusted to a parallel state by the collimating lens 30. The laser light LB is then reflected by the dichroic mirror 40 and the first reflecting mirror 21, and reaches the DOE 22.

The DOE 22 adjusts the irradiation pattern of the laser light LB. Specifically, the DOE 22 emits the incident laser light LB as laser light LB having a power density distribution shape different from that at the time of incidence.

The laser light LB adjusted by the DOE 22 reaches the Z lens 24 built into the Z lens drive unit 23. The Z lens drive unit 23 has a movement mechanism for moving the position of the Z lens 24 in the optical axis direction, and a driver for driving the movement mechanism. Then, by moving the position of the Z lens 24 in the optical axis direction, the focal position of the laser light LB irradiated from the laser scanner 20 is changed.

The laser light LB is then reflected by the second reflecting mirror 25 and enters the galvano scanner unit 27 via the focusing lens 26. The galvano scanner unit 27 has a mirror that reflects the laser light LB, a change mechanism that changes the angle of the mirror, and a driver that drives the change mechanism. The galvano scanner unit 27 changes the irradiation position of the laser light LB on the irradiated surface WS of the metal object W by changing the angle of the built-in mirror. The laser light LB emitted from the galvano scanner unit 27 is irradiated onto the irradiated surface WS of the metal object W via the protective glass 28.

The control unit 60 is configured as a computer having a CPU and a memory. The memory stores a program for executing the laser welding process. The control unit 60 controls the laser oscillator 10 and the laser scanner 20 by executing the program stored in the memory. Specifically, the control unit 60 commands the output value of the laser light LB to the laser oscillator 10. The control unit 60 also commands the galvano scanner unit 27 to irradiate the irradiated surface WS with the XY coordinates. The control unit 60 also commands the Z lens drive unit 23 to determine the focal position with a distance that is a plus in the direction toward the laser scanner 20 and a minus in the direction away from the laser scanner 20, based on a predetermined reference focal position F0. When the metal object W is positioned so that the position of the irradiated surface WS coincides with the reference focal position F0, the focal position is shifted from the reference focal position F0, and the diameter of the approximately circular irradiation range of the laser light LB on the irradiated surface WS becomes larger. The laser scanner 20 is also called a 3D scanner because it is possible to change the irradiation position on the XY plane, which is the irradiation surface of the irradiated laser light LB, and the focal position in the Z-axis direction when the irradiation direction is in the Z-axis direction.

The control unit 60 has a setting unit 61 that sets the setting values of each of the irradiation conditions described below. The setting unit 61 is realized by executing a program stored in the memory.

In the laser welding process, the irradiation conditions of the irradiated laser light LB are set. The irradiation conditions include the laser output, the scanning speed, and the focal position as the focal diameter. In each process in which the laser is irradiated, the laser light LB is scanned according to a preset scanning pattern.

A2. Overview of laser welding method:
FIG. 3 is a diagram for explaining an outline of the laser welding method, and shows the main scanning patterns drawn by scanning the laser light LB in each process of irradiating the laser light LB. FIG. 4 is a schematic diagram showing the state of a cross section of a metal object W when the metal object W is irradiated with the laser light LB. As shown in FIG. 3, in this embodiment, the laser light LB is scanned in the same rotation direction as the same direction along a circular scanning pattern having the same center CP. In this embodiment, the rotation direction is the counterclockwise direction shown by the arrow. In the case of a circular scanning pattern, the scanning pattern is defined by the coordinates in the XY coordinate system of the center CP, which is the center of the scanning pattern, and the scanning radius R. In the following description, the mutually orthogonal X-axis and Y-axis shown in FIG. 3 are used. The method of welding by scanning the laser light LB along the scanning pattern is also called LSW (Laser Screw Welding).

In the laser welding method according to this embodiment, a first pass for melting the metal to form a molten pool MP (Figure 4) is performed in combination with a second pass for stirring the molten pool MP after the first pass. Specifically, in the second pass, the laser light LB is scanned around the circumferential direction of the molten pool MP, making multiple revolutions.

As shown in FIG. 4, when the laser beam LB is irradiated onto the metal object W in the first pass, the metal melts and a molten pool MP is formed. In addition, near the focal position of the laser beam LB, the metal evaporates due to the high energy supplied from the laser beam LB. Then, a hole called a keyhole KH is formed near the focal position of the laser beam LB due to the pressure of the metal vapor. The metal vapor is also contained inside the molten pool MP. The metal vapor contained inside the molten pool MP easily escapes through the keyhole KH. Therefore, by performing the second pass, the keyhole KH is continuously formed throughout the entire molten pool MP. This allows the metal vapor contained inside the molten pool MP to be efficiently discharged to the outside, improving the welding quality, such as the weld strength.

Here, the inventors have noticed that when the laser irradiation is interrupted between the first and second passes, the melt flow in the molten pool MP changes suddenly due to the disappearance of the keyhole KH due to the interruption of the laser irradiation and the appearance of the keyhole KH due to the resumption of the laser irradiation. If the melt flow in the molten pool MP changes suddenly, spattering occurs, and the welding quality may deteriorate. In detail, as shown on the left side of the paper of the line LN in FIG. 4, as the metal vapor in the keyhole KH moves in the direction toward the irradiated surface WS, convection occurs in the surrounding molten metal as shown by the arrows. When the force pushing out the molten metal by the convection exceeds the surface tension of the molten metal, sputter atoms ST fly out of the molten pool MP. When spattering occurs, the volume of the molten metal decreases, and there is a risk of deteriorating the welding quality. Spattering is likely to occur when the melt flow in the molten pool MP changes suddenly. This is because the molten metal ripples when the melt flow in the molten pool MP changes suddenly.

Therefore, in the laser welding method according to this embodiment, a connection pass is performed between the first and second passes. As will be described in detail later, in the connection pass, the laser light LB is scanned under suitable conditions from the end position of the first pass to the start position of the second pass. This suppresses sudden changes in the molten metal flow in the molten pool MP, improving the welding quality.

In this embodiment, a set of passes consisting of the first pass and the second pass is performed twice. Specifically, as shown in FIG. 3, first, scanning along the first scanning pattern LP1, which is the first pass, and scanning along the second scanning pattern LP2, which is the second pass, which constitute the first set SET1, are performed in sequence. Then, scanning along the third scanning pattern LP3, which is the first pass, and scanning along the fourth scanning pattern LP4, which is the second pass, which constitute the second set SET2, are performed in sequence. In the scanning of the second set SET2, the laser light LB is scanned so as to expand the molten pool MP formed by performing the first set SET1. Specifically, the scanning radii of the third scanning pattern LP3 and the fourth scanning pattern LP4 of the second set SET2 are set to be larger than the scanning radii of the first scanning pattern LP1 and the second scanning pattern LP2 of the first set SET1. In this way, by performing the first set SET1 and the second set SET2 in sequence, the welding quality can be improved for welding with the target welding area.

Since zinc has a low boiling point, it easily turns into vapor. Furthermore, zinc vapor is more difficult to expel from the keyhole KH than other metal vapors. For this reason, when the metal object W is a zinc-plated steel plate, as in this embodiment, it is strongly recommended to perform a second pass to continue forming the keyhole KH.

A3. Laser welding process:
FIG. 5 is a diagram for explaining the scanning patterns drawn sequentially in the laser welding process. FIG. 6 is a table listing the set values of the conditions in each process in which the laser light LB is scanned. FIG. 7 is a diagram showing the change in the laser output in the laser welding process. The horizontal axis of FIG. 7 is time, and the vertical axis is laser output. FIG. 8 is a diagram showing the change in the scanning speed in the laser welding process. The horizontal axis of FIG. 8 is time, and the vertical axis is scanning speed. As shown in FIG. 1, in the setting process P5, the setting unit 61 sets the set values of each condition of the laser output, scanning speed, and focal position in each process. As described above, by setting the focal position, the focused diameter, which is the diameter of the irradiation range of the laser light LB on the irradiated surface WS, is set. In addition, in this embodiment, in the setting process P5, the scanning pattern in each process is also set. The irradiation condition in the first process P10 is also called the first irradiation condition. The irradiation condition in the second process P20 is also called the second irradiation condition. The irradiation condition in the third process P30 is also called the third irradiation condition.

Specifically, as shown in FIG. 6, the setting values for each condition are set: start position SP as the scanning start position, end position EP as the scanning end position, rotation angle, scanning radius R, laser output, scanning speed, and focal position. As shown in FIG. 3, the rotation angle is an angle defined as a counterclockwise angle with a reference line RL from the center CP toward the -Y direction as 0 degrees. For example, as shown in FIG. 5, if the rotation angle in the first process P10 is set to 370 degrees, the laser light LB is scanned 360 degrees around the center CP, that is, one revolution, and then scanned another 10 degrees.

The start position SP and end position EP are expressed as angles around the center CP with respect to the reference line RL, just like the rotation angle. Specifically, they are expressed as angles around the rotation direction between the reference line RL and the straight line connecting the start position and the center CP. For example, the end position EP of the first process P10 is set to 10 degrees because it is scanned 10 degrees after one revolution from the start position SP of 0 degrees. For the sake of understanding, FIG. 6 shows the end position EP and the start position SP after the first connection process P15, but the conditions that actually require input of the setting value are the start position SP of the first process P10 and the rotation angle of each process in which the laser light LB is scanned. This is because when the start position SP in the first process P10 and the rotation angle of each process are determined, the start position SP of each process after the first process P10 and the end position EP of each process are uniquely determined.

The first process P10 and the third process P30 shown in FIG. 1 are the first path. The second process P20 and the fourth process P40 are the second path. The first connection process P15, the second connection process P25, and the third connection process P35 are connection paths. In addition, the first process P10 and the second process P20 are the first set SET1. The third process P30 and the fourth process P40 are the second set SET2.

As described above, the first pass and the second pass have different scanning patterns. In addition to the scanning patterns, the first pass and the second pass also have different laser power, scanning speed, focal position, and rotation angle. As shown in FIG. 7, in the first pass, the laser power is set to be greater than that of the second pass. As shown in FIG. 8, in the first pass, the scanning speed is set to be smaller than that of the second pass. As shown in FIG. 6, in the first pass, the focal position is set to zero, that is, the focal position is set to coincide with the irradiated surface WS. As a result, the energy supplied to the metal object W by the scanning of the laser light LB is increased, so that the metal can be melted efficiently. On the other hand, in the second pass, the laser power and the focal position are set so that the energy supplied to the metal object W is smaller than that of the first pass. As a result, the keyhole KH can be appropriately and continuously formed in the molten pool MP formed by the first pass. In addition, in the second pass, the scanning speed is set to be greater than that of the first pass. And, in the second pass, the rotation angle is set to be greater than that of the first pass. This allows the molten pool MP to be stirred and the keyhole KH to be continuously formed throughout the entire molten pool MP.

In the first step P10 shown in FIG. 1, the laser welding device 100 is used to scan the laser beam LB toward the irradiated surface WS of the metal object W, and a molten pool MP is formed on the irradiated surface WS. Specifically, as shown in FIG. 5, the laser beam LB is scanned along the first scanning pattern LP1 from the start position SP to the end position EP.

In the first connection step P15 shown in FIG. 1, the laser light LB is scanned along the first connection scanning pattern LPC1 (FIG. 5) from the end position EP of the first step P10 to the start position SP of the second step. In addition, the irradiation conditions of the first connection step P15 are irradiation conditions in which the set values of the first step P10 and the second step P20 are set to values between the set values of the first step P10 and the set values of the second step P20 for conditions in which the set values are different between the first step P10 and the second step P20. Specifically, the first step P10 and the second step P20 have different scanning radius, laser output, scanning speed, and focal position. Therefore, the first connection step P15 is set to irradiation conditions in which the set values of the scanning radius, laser output, scanning speed, and focal position are between the set values of the first step P10 and the set values of the second step P20. This allows each condition to be gradually changed from the first step P10 to the second step P20. Therefore, the keyhole KH continues to be formed from the first step P10 to the second step P20, and a sudden change in the molten metal flow is suppressed. This improves the welding quality. Note that scanning from the end position EP of the first step P10 to the start position SP of the second step means scanning from the end position EP of the first step P10 to the start position SP of the second step so that the scanning radius R is a value between the scanning radius R of the first step P10 and the scanning radius R of the second step.

Specifically, referring to FIG. 7, the laser output is explained. The setting value lw2 of the laser output in the second process P20 is smaller than the setting value lw1 of the laser output in the first process P10. Therefore, in the first connection process P15, the laser output value is set so that it gradually decreases from the setting value lw1 to the setting value lw2 over time. In this embodiment, a value calculated by linear interpolation is used. This reduces the load of calculating the setting value. The same applies to the scanning radius, scanning speed, focal position, and scanning radius R.

The scanning time required for scanning from the start position SP to the end position EP in the first connection process P15 is determined by the rotation angle shown in FIG. 6. The larger the rotation angle in the connection path, the smaller the change rate, which indicates the rate of change of the set value of each condition over time, and the better the effect of suppressing sudden changes in the flow of the molten metal. In this embodiment, the rotation angle of the first connection process P15 is 90 degrees. As shown in the first connection process P15 in FIG. 5, scanning is performed by rotating 90 degrees around the center CP from the start position SP to the end position EP. As it moves from the start position SP to the end position EP, the laser output gradually decreases, the scanning speed increases, and the focused diameter increases.

In the second process P20 shown in FIG. 1, the laser light LB, whose irradiation conditions are set to values different from those in the first process P10, is scanned within the range of the molten pool MP. As shown in FIG. 6, the rotation angle is 2735 degrees, so the end position EP of the first connection process P15 is set as the start position SP, and the laser light LB is scanned seven or more times. This stirs the molten pool MP, allowing the metal vapor in the molten pool MP to be discharged from the keyhole KH.

In the second connection process P25 shown in FIG. 1, the laser light LB scans along the second connection scan pattern LPC2 (FIG. 5) from the end position EP of the second process P20 to the start position SP of the third process P30. Similarly to the first connection process P15, the irradiation conditions of the second connection process P25 are irradiation conditions in which the setting value is a value between the setting value of the second process P20 and the setting value of the second process P20 for conditions in which the setting values are different between the second process P20 and the third process P30.

As shown in FIG. 6, the rotation angle of the second connection step P25 is set to 45 degrees, which is an angle smaller than the rotation angle of the first connection step P15. The second connection step P25 is a connection pass performed between the second pass and the next first pass, which is different from the first connection step P15, which is a connection pass performed between the first pass and the second pass. The third step P30, which follows the second connection step P25, is a step for further melting the metal around the already formed molten pool MP. For this reason, the third step P30 is set to have a larger laser output than the second step P20. And, in the second connection step P25, the laser output is set to gradually increase over time. Here, in the second connection step P25, the larger the rotation angle, the longer the section irradiated with a laser output smaller than the laser output in the third step. If the section irradiated with the laser light LB with a small laser output to the unmolten metal becomes longer, the melting state is likely to become unstable. Therefore, in the second connection step P25, the rotation angle is set smaller than in the first connection step P15. By setting the rotation angle smaller, the section in which the laser light LB with a small laser output is irradiated to the unmolten metal is shortened, the molten state is stabilized, and the welding quality is improved.

In the third process P30 shown in FIG. 1, the laser beam LB is scanned around the outer periphery of the molten pool MP, expanding the already formed molten pool MP. As shown in FIG. 7, in this embodiment, the laser output in the third process P30 is set to the same value as the laser output in the first process P10. Also, as shown in FIG. 8, in this embodiment, the scanning speed in the third process P30 is set to a value slightly higher than the scanning speed in the first process P10.

In the third connection process P35 shown in FIG. 1, the laser light LB scans along the third connection scanning pattern LPC3 (FIG. 5) from the end position EP of the third process P30 to the start position SP of the fourth process. Similarly to the first connection process P15, the irradiation conditions of the third connection process P35 are irradiation conditions in which the setting value is a value between the setting value of the third process P30 and the setting value of the fourth process P40 for conditions in which the setting values are different between the third process P30 and the fourth process P40.

In the fourth step P40 shown in FIG. 1, the laser light LB is scanned within the range of the molten pool MP, similar to the second step P20. As shown in FIG. 6, the rotation angle is 1800 degrees, so the end position EP of the third connection step P35 is set as the start position SP, and the laser light LB is scanned five times around the center CP. This stirs the molten pool MP, allowing the metal vapor in the molten pool MP to be discharged from the keyhole KH. When the fourth step P40 is completed, this laser welding process ends.

According to the embodiment described above, in the laser welding process, the first process P10 of forming a molten pool MP on the irradiated surface WS, the first connection process P15, and the second process P20 of scanning the laser light LB within the range of the molten pool MP are performed in sequence. In the first connection process P15, the laser light LB is scanned from the end position EP of the first process P10 to the start position SP of the second process P20. The set value of the irradiation condition in the first connection process P15 is a value between the set value of the irradiation condition in the first process P10 and the set value of the irradiation condition in the second process P20. Therefore, in the first connection process P15, the laser light LB is continuously irradiated from the scanning end position of the first process P10 to the scanning start position of the second process P20, and irradiation conditions that complement the irradiation conditions of the first process P10 and the second process P20 are used, so that a sudden change in the molten metal flow is suppressed and a deterioration in welding quality can be suppressed. Furthermore, according to this embodiment, the process time can be shortened compared to when the laser output is gradually increased or decreased at the start and end of each process in which laser irradiation is performed. For example, it takes less time to gradually decrease the laser output from the set value of the first process P10 to the set value of the second process P20 than to set the laser output to zero once after the first process P10 and then increase it from zero to the set value of the second process P20.

The laser output setting value in the second process P20 is smaller than the laser output setting value in the first process P10. The scanning speed setting value in the second process P20 is larger than the scanning speed setting value in the first process P10. As a result, in the second process P20, a keyhole KH is appropriately formed in the molten pool MP formed in the first process P10, and the position where the keyhole KH is formed is moved quickly, thereby stirring the molten pool MP. Therefore, metal vapor can be discharged from the keyhole KH to improve welding quality.

In addition, in the laser welding process, after the second process P20, the second connection process P25 and the third process are performed in that order. The laser output in the third process P30 is greater than the laser output in the second process P20. The rotation angle in the second connection process P25 is smaller than the rotation angle in the first connection process P15. This shortens the section in the second connection process P25 where the laser output is smaller than the laser output in the third process P30, stabilizing the molten state and improving the welding quality.

In addition, the set value lw2 of the irradiation conditions in the first connection step P15 changes so as to decrease or increase from the set value of the irradiation conditions in the first step P10 to the set value of the irradiation conditions in the second step P20 as it moves from the end position EP of the first step P10 to the start position SP of the second step P20. As a result, the set value can be changed gradually in the first connection step P15, so that a sudden change in the molten metal flow can be further suppressed. In addition, the set value of the irradiation conditions in the first connection step P15 is a value obtained by linearly complementing the set value of the irradiation conditions in the first step P10 and the set value of the irradiation conditions in the second step. This makes it possible to reduce the calculation load of the set value for the first connection step P15. In addition, each of the first metal object Wa and the second metal object Wb is a steel plate having a zinc plating layer. By using the laser welding method according to this embodiment for a metal plate having zinc, which is prone to generate steam and does not easily release steam, the zinc vapor can be efficiently discharged by appropriately forming a keyhole KH, thereby improving the welding quality.

B. Other embodiments:
(B1) In the above embodiment, scanning with the laser light LB is performed using the laser scanner 20, which is a 3D scanner. In addition to this form, scanning with the laser light LB may be performed by moving a laser scanner that does not have a scanning function using a robot arm.

(B2) In the connection path of the above embodiment, the setting value of each condition is calculated by linear interpolation. Alternatively, the setting value of each condition may be calculated by polynomial interpolation. Regardless of the calculation method, the value of the setting condition of the connection path is set to a value between the setting condition of the first path and the setting condition of the second path, thereby suppressing sudden changes in the flow of the molten metal.

(B3) The scanning pattern in the above embodiment is circular. The scanning pattern is not limited to a circle and may be other shapes such as a square.

(B4) In the above embodiment, two sets of a first pass and a second pass are performed. The number of times that a set of a first pass and a second pass is performed is not limited to two, but may be one or three or more times. The number of times may be determined using the target welding area.

(B5) In the above embodiment, the laser output, scanning speed, focusing diameter, and scanning radius are all different between the first and second passes. This is not limited to the above case, but the present laser welding method can be applied to cases where at least one of the laser output, scanning speed, focusing diameter, and scanning radius is different, thereby suppressing abrupt changes in the flow of molten metal.

(B6) In the above embodiment, the setting value of the connection path changes so as to decrease or increase from the setting value of the irradiation conditions of the first pass to the setting value of the irradiation conditions of the second pass as it moves from the end position of the first pass to the start position of the second pass. In addition to this form, the setting value of the connection path may change in a step-like manner. At least by setting the setting value of the connection path to a value between the setting value of the first pass and the setting value of the second pass, it is possible to suppress a sudden change in the flow of the molten metal.

The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features in each form described in the Summary of the Invention column can be replaced or combined as appropriate to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

10...laser oscillator, 11...optical fiber cable, 20...laser scanner, 21...first reflecting mirror, 23...Z lens drive unit, 24...Z lens, 25...second reflecting mirror, 26...condensing lens, 27...galvano scanner unit, 28...protective glass, 30...collimating lens, 40...dichroic mirror, 60...control unit, 61...setting unit, 100...laser welding device, CP...center, EP...end position, F0...reference focal position, KH...keyhole, LB...laser light, LN...line, LP1...first scanning pattern, LP2...second scanning pattern, LP3 ...Third scanning pattern, LP4...Fourth scanning pattern, LPC1...First connection scanning pattern, LPC2...Second connection scanning pattern, LPC3...Third connection scanning pattern, MP...Molten pool, P5...Setting step, P10...First step, P15...First connection step, P20...Second step, P25...Second connection step, P30...Third step, P35...Third connection step, P40...Fourth step, R...Scanning radius, RL...Reference line, SET1...First set, SET2...Second set, SP...Start position, ST...Sputtered atoms, W...Metal object, WS...Irradiated surface, Wa...First metal object, Wb...Second metal object

Claims (7)

1. A laser welding method for welding a plurality of stacked metal objects together by scanning a laser beam irradiated onto irradiated surfaces of the plurality of stacked metal objects, the method comprising the steps of:
A setting step of setting each of the setting values of the irradiation conditions including the laser output, the scanning speed, and the focused diameter of the laser light;
a first step of scanning the laser light, the irradiation conditions of which are set to first irradiation conditions, to form a molten pool on the irradiated surface;
a second step of scanning the laser beam within the range of the molten pool after the first step, the second step being performed while the irradiation conditions are set to second irradiation conditions different from the first irradiation conditions;
a connecting step performed between the first step and the second step, in which the laser light is set to an irradiation condition whose setting value is a value between the setting value of the first irradiation condition and the setting value of the second irradiation condition for the conditions whose setting values are different between the first irradiation condition and the second irradiation condition, and the laser light is scanned from a scanning end position of the first step toward a scanning start position of the second step. 2. The laser welding method according to claim 1,
the set value of the laser output of the second irradiation condition is smaller than the set value of the laser output of the first irradiation condition,
A laser welding method, wherein the set value of the scanning speed of the second irradiation condition is greater than the set value of the scanning speed of the first irradiation condition. 3. The laser welding method according to claim 2,
The connecting step is a first connecting step,
a third step of expanding the molten pool by scanning the laser beam around an outer periphery of the molten pool, the third step being performed after the second step, in which the irradiation conditions are set to third irradiation conditions different from the second irradiation conditions;
a second connection step performed between the second step and the third step, the second connection step being for scanning the laser light from a scanning end position of the second step toward a scanning start position of the third step with the laser light set to an irradiation condition having a setting value between the setting value of the second irradiation condition and the setting value of the third irradiation condition, for the condition having different setting values between the second irradiation condition and the third irradiation condition;
the set value of the laser output of the third irradiation condition is greater than the set value of the laser output of the second irradiation condition,
The laser light is scanned so as to rotate in the same direction with respect to the center of the scanning pattern drawn by the scanning,
A laser welding method, wherein a rotation angle based on the center from the scanning start position of the second connecting process to the scanning end position of the second connecting process is smaller than the rotation angle from the scanning start position of the first connecting process to the scanning end position of the first connecting process. 4. The laser welding method according to claim 1,
a laser welding method in which the set value of the irradiation condition in the connection process changes so as to decrease or increase from the set value of the first irradiation condition to the set value of the second irradiation condition as moving from the scanning end position of the first process to the scanning start position of the second process, for the conditions in which the set values differ between the first irradiation condition and the second irradiation condition. 4. The laser welding method according to claim 1,
A laser welding method, wherein the set value of the irradiation condition in the connecting step is a value obtained by linearly complementing the set value of the first irradiation condition and the set value of the second irradiation condition. 4. The laser welding method according to claim 1,
A laser welding method, wherein each of the plurality of metal objects is a metal plate having a plating layer. A laser welding device that scans a laser beam to be irradiated onto an irradiated surface of a plurality of stacked metal objects, and welds the objects,
a laser irradiation unit that irradiates the laser light;
A setting unit that sets the respective setting values of the irradiation conditions including the laser output, the scanning speed, and the focused diameter of the laser light;
A control unit that controls the laser irradiation unit,
The control unit is
a first step of scanning the laser light, the irradiation conditions of which are set to first irradiation conditions, to form a molten pool on the irradiated surface;
a second step of scanning the laser beam within the range of the molten pool after the first step, the second irradiation condition being set to a second irradiation condition different from the first irradiation condition;
a connecting process performed between the first process and the second process, in which, for the conditions in which the setting values differ between the first irradiation condition and the second irradiation condition, the laser light is set to the irradiation condition whose setting value is a value between the setting value of the first irradiation condition and the setting value of the second irradiation condition, and the connecting process is performed from a scanning end position of the first process to a scanning start position of the second process, the laser light being set to the irradiation condition whose setting value is a value between the setting value of the first irradiation condition and the setting value of the second irradiation condition.

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