JP2022135403A - Laser welding method and welding device - Google Patents

Abstract

To provide a laser welding method and welding device capable of suppressing occurrence of a defect not only on a surface of a weld part but also inside thereof.CONSTITUTION: A laser welding method includes the steps of: irradiating a processing point Pp of a welded object W with a first laser beam Lp, and forming a key hole 11 and a molten pool Y in the periphery thereof; irradiating a preheating point Ps set in front of the processing point in a sweeping direction 17 of the welded object with a second laser beam L2; setting a post-processing point Pa at a position in rear of the molten pool separated from a boundary surface between the molten pool and a solidification part by a predetermined distance; and controlling surface temperatures of the preheating point, the processing point and the post-processing point to predetermined temperatures by an arithmetic processing device 10, wherein the surface temperature of the preheating point is set to lower than a boiling point Tb of the welded object, and a surface temperature Ta of the post-processing point is set to equal to or lower than the surface temperature Ts of the preheating point.SELECTED DRAWING: Figure 4

Description

TECHNICAL FIELD Embodiments of the present invention relate to a laser welding method and welding apparatus using laser light.

Due to local heating and high-speed laser welding, the temperature of the molten pool and its surroundings changes drastically, which causes defects such as pores, spatter (particles), and weld cracks. In particular, such defects are likely to occur with high thermal conductivity and low viscosity welding materials such as aluminum, magnesium, and copper. Furthermore, while keyhole laser welding performed at high energy density enables deep penetration, the temperature distribution is wide and the risk of defect generation increases.

As mentioned above, it is believed that the occurrence of defects in laser welding is caused by severe temperature changes. Therefore, in order to suppress the occurrence of these defects, we have developed a new laser welding technology that applies a second laser beam or heat source and the welding conditions. A selection method has been proposed. For example, in order to suppress the occurrence of weld cracks, there has been proposed a means of irradiating a second laser beam, which has a lower energy density than the first laser beam, backward in the welding direction.

JP 2018-171623 A

However, in the conventional laser welding means that irradiates the second laser beam backward in the welding direction, the melting and resolidification of the metal melted by the first laser beam is accelerated to provide a slow cooling effect, which results in weld cracking. However, the effect of suppressing defects such as pores and spatter cannot be expected. Furthermore, since the effect of the second laser beam is limited to the vicinity of the surface of the welded portion, there is a problem that the effect of suppressing defects generated inside the welded portion cannot be expected.

The present embodiment has been made to solve the above problems, and aims to provide a laser welding method and a welding apparatus capable of suppressing the occurrence of defects not only on the surface of the welded portion but also on the inside of the welded portion. do.

In order to solve the above-described problems, the laser welding method according to the present embodiment includes steps of irradiating a processing point of an object to be welded with a first laser beam to form a keyhole and a molten pool around the keyhole; A step of irradiating a second laser beam to a preheating point set in front of the processing point with respect to the sweep direction of the object; and a step of controlling the surface temperatures of the preheating point, the working point, and the post-working point to predetermined temperatures by means of an arithmetic processing unit, wherein the The surface temperature of the preheating point is lower than the boiling point of the object to be welded, and the surface temperature of the post-processing point is equal to or lower than the surface temperature of the preheating point.

Further, the laser welding apparatus according to the present embodiment includes a laser oscillator that generates a first laser beam and a second laser beam, and a laser oscillator that is provided above an object to be welded and emits the first laser beam and the second laser beam to the object to be welded. an optical head that irradiates a laser beam; a temperature sensor that measures the surface temperature of the object to be welded; a shield gas nozzle that supplies a rare gas or inert gas to the object to be welded; 2) an arithmetic processing unit for controlling parameters such as energy density, pattern, intensity, irradiation position, sweep speed, etc. of laser light;

According to the laser welding method and welding apparatus according to the present embodiment, it is possible to suppress the occurrence of defects not only on the surface of the welded portion but also on the inside thereof.

1 is an overall configuration diagram of a welding device according to a first embodiment; FIG. A bar graph showing the magnitude of the energy density of the first laser beam and the second laser beam. (a) to (f) are schematic diagrams showing beam profile patterns of a first laser beam and a second laser beam. Explanatory drawing of the welding process using the welding apparatus which concerns on 1st Embodiment. Explanatory drawing of the conventional welding process using only a 1st laser beam. Explanatory drawing when a pore defect occurs in the conventional welding process. Explanatory drawing of the welding process which concerns on 1st Embodiment. FIG. 4 is a relational diagram between the surface temperature of the preheating point and the pore generation rate. FIG. 4 is a relationship diagram between the surface temperature of the preheating point and various parameters. Explanatory drawing of a conventional welding process using only the first laser beam The figure which shows the temperature gradient of a process point and a room temperature point in the conventional welding process. FIG. 4 is a schematic diagram showing an example of surface oscillation of a molten pool in a conventional welding process. Explanatory drawing of the welding process which concerns on 2nd Embodiment. The schematic diagram which shows the temperature gradient of the process point and room temperature point which concern on 2nd Embodiment. Schematic diagram showing an example of surface oscillation of a molten pool according to the second embodiment Explanatory drawing of the welding process based on the modification of 2nd Embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a laser welding method and a welding apparatus according to the present invention will be described with reference to the drawings.

[First Embodiment]
A laser welding method and welding apparatus according to a first embodiment will be described with reference to FIGS. 1 to 9. FIG.

(overall structure)
As shown in FIG. 1, a laser welding apparatus 1 according to this embodiment includes a laser oscillator 2 that oscillates laser light L (Lp, Ls), and an optical head 4 that irradiates an object W to be welded with laser light L. an optical fiber 3 (3p, 3s) for guiding a laser beam L oscillated by a laser oscillator 2 to an optical head 4; A temperature sensor 6 for monitoring, a laser oscillator controller 7 for controlling the laser oscillator 2 from the outside, an optical head controller 8 for controlling the optical head 4 from the outside, and a temperature sensor controller 9 for controlling the temperature sensor 6 from the outside. and an arithmetic processing unit 10 having means for estimating the surface temperature from the parameters and data obtained from the laser oscillator 2 and the temperature sensor 6, and having a medium for storing the database obtained in advance, and the arithmetic processing unit 10 and a feedback means for approximating the desired surface temperature.
In this embodiment, welding materials with high thermal conductivity and low viscosity, such as aluminum, magnesium, and copper, are assumed as the object W to be welded.

(laser oscillator)
The laser oscillator 2 is composed of a first laser oscillator 2p that generates a first laser beam Lp and a second laser oscillator 2s that generates a second laser beam Ls. Here, the first laser beam Lp has an energy density sufficient to form the keyhole 11 (see FIG. 4) when the object W to be welded is irradiated. It has such an energy density that it heats to temperatures below its boiling point when irradiated with W.

In this embodiment, unless otherwise specified, an example using two laser oscillators, the first laser oscillator 2p and the second laser oscillator 2s, will be described. They do not need to be obtained from different laser oscillators, and may be generated from one laser oscillator. For example, the laser light emitted from the first laser oscillator 2p can be split in the middle to generate the first laser light Lp and the second laser light Ls.

In this embodiment, the laser oscillator 2 has a plurality of laser oscillators 2p and 2s inside, and fiber lasers, YAG lasers, disk lasers, for example, are used as the respective laser oscillators 2p and 2s. Note that other laser oscillators can also be used.

In the laser oscillator 2, the first laser oscillator 2p and the second laser oscillator 2s are connected to a controller 2e of the laser oscillator 2, and the controller 2e is connected to an external laser oscillator controller 7. Various parameters such as energy density, wavelength, oscillation frequency, etc. are adjusted, but other parameters can be adjusted as needed. Various parameters are set manually and/or automatically by the laser oscillator controller 7, but other parameters can also be set.

The first laser beam Lp and the second laser beam Ls respectively emitted from the first laser oscillator 2p and the second laser oscillator 2s enter the optical fiber 3 . At this time, the first laser beam Lp and the second laser beam Ls may propagate along the same optical path or may propagate along different optical paths. In this embodiment, as shown in FIG. 1, an example of propagation through different optical paths (first optical fiber 3p and second optical fiber 3s) will be described.

Further, when one laser oscillator 2 is used, for example, the laser light L emitted from the laser oscillator 2 is branched to different optical systems, and the beam profile is shaped by each optical system to shape the optical fiber 3 (3p and 3s) (not shown).

(optical fiber)
In this embodiment, the optical fiber 3 includes a first optical fiber 3p for transmitting the laser light Lp emitted from the first laser oscillator 2p and a second optical fiber for transmitting the laser light Ls emitted from the second laser oscillator 2s. 3s. At that time, the optical characteristics of the optical fibers 3 (3p, 3s) are not particularly specified, and the same fiber core shape as the beam profile pattern of the laser light L (Lp, Ls) irradiated on the object W to be welded may be used.

Thus, the optical fibers 3 ( 3 p, 3 s) are configured for the purpose of transmitting the first laser beam Lp and the second laser beam Ls emitted from the laser oscillator 2 to the optical head 4 .
Although a plurality of optical fibers 3 are used in this embodiment, only one optical fiber may be used.

(optical head)
The optical head 4 converges the laser light L (first laser light Lp, second laser light Ls) emitted from the laser oscillator 2 to a predetermined energy density and irradiates the workpiece W to be welded. It is a device.

For this purpose, the optical head 4 is internally provided with optical elements such as a collimating lens and a condensing lens for condensing the laser light. In addition, the optical element for condensing the laser beam can be changed in position and inclination to set the laser beam L to a desired beam profile. At this time, by using the optical head controller 8 connected to the optical head 4, it is possible to set the laser beam L to a desired beam profile (not shown).

Further, the optical head 4 is provided so as to be able to change its relative position with respect to the object W to be welded in order to sweep the irradiation position of the laser beam L on the object W to be welded. Methods for changing the relative position with the object W to be welded include moving the optical head 4, moving the object W to be welded, and the like. For example, in the example of FIG. 1, the object W to be welded can be swept relative to the optical head 4 by using the variable stage 16 that changes the welding direction. The sweeping of the irradiation position of the laser beam L can be controlled by the optical head controller 8 .

Further, the optical head 4 has adjusting means having a function of changing one or more of the irradiation range enlargement/reduction and the irradiation angle, but may have other functions. For example, regarding enlargement/reduction of the irradiation range, the optical element inside the optical head 4 may be made variable to an arbitrary imaging magnification, and adjustment means may be provided so that the beam profile can be enlarged/reduced to a desired dimension. Furthermore, regarding the irradiation angle, for example, the optical head 4 itself may be tilted (not shown).

(Irradiation point)
Regarding the irradiation points on the workpiece W to be welded, the irradiation point of the first laser beam Lp among the laser beams L emitted from the optical head 4 is the processing point Pp, and the irradiation point of the second laser beam is the preheating point Ps. (See Figure 4).

Further, the post-processing point Pa, which is the object to be welded W after the first laser beam Lp has passed through, is located on the straight line between the preheating point Ps and the processing point Pp, is behind the molten pool Y, and It shall be 1 mm or more behind the interface between the pond Y and the solidified portion toward the solidified portion.

The reason why the post-processing point Pa is defined 1 mm or more behind the boundary surface between the molten pool Y and the solidified portion toward the solidified portion is that the preheating point Ps may be before melting, and any material can be reliably solidified. This is because the position is 1 mm or more behind the interface between the molten pool Y and the solidified portion toward the solidified portion.
Let Ts be the surface temperature of the preheating point Ps, and Ta be the surface temperature of the post-processing point Pa.

(arithmetic processing unit)
The arithmetic processing unit 10 receives laser oscillator welding condition information such as laser output, wavelength, pulse width, and repetition frequency from the laser oscillator controller 7, sweep speed from the optical head controller 8, and irradiation position of the second laser beam. , spot diameter, optical head welding conditions, etc., and information on the surface temperature of the preheating point Ps from the temperature sensor control device 9. The laser oscillator control device 7 and the optical head control device 8 each store information. Connected for input/output.

The arithmetic processing unit 10 compares the welding conditions such as the energy density of the laser light L obtained from the laser oscillator control device 7, the optical head control device 8, and the temperature sensor control device 9 and the surface temperature information with a previously obtained database. It is also possible to have a function of estimating the temperature by calculation from an existing prediction formula, and estimating the welding conditions that suppress the occurrence of defects and the occurrence of defects.

In addition, feedback means may be provided for feeding back the optimum welding conditions based on the estimation results to the laser oscillator 2 and the optical head 4 via the laser oscillator controller 7 and the optical head controller 8, respectively. .

Target parameters to be controlled as the optimum welding conditions include, for example, sweep speed, irradiation position of the second laser beam Ls, laser output, spot diameter, energy density, wavelength, pulse width, repetition frequency, etc. One of them is feedback means. It has the function of controlling one or more parameters to approach the desired surface temperature. Note that other parameters may be controllable.

(Other configurations)
The shield gas nozzle 5 makes it possible to inject into the molten pool Y a shield gas that prevents oxidation during welding, for example, an inert gas such as a rare gas or nitrogen gas.

The temperature sensor 6 measures the surface temperature of the object W to be welded, and temperature information measured by the temperature sensor 6 is output to the temperature sensor control device 9 .
The temperature sensor 6 may be, for example, a thermocouple, which directly measures the temperature, or may be configured by means for back-calculating the temperature from luminance information, such as a CCD camera or a mid-infrared camera.

(Energy density of laser light)
FIG. 2 is a bar graph showing an example of energy density profiles of the first laser beam Lp and the second laser beam Ls, where the horizontal axis represents the first laser beam Lp and the second laser beam Ls, and the vertical axis represents the energy density.

The first laser beam Lp irradiates the object W to be welded, becomes a processing point Pp, and forms the keyhole 11 . Therefore, as shown in FIG. 2, the energy density of the first laser beam Lp is set to a value equal to or higher than the keyhole change value at which the melting of the heat conduction type changes to the keyhole type.

The object W to be welded is irradiated with the second laser beam Ls and becomes a preheating point Ps. The preheating point Ps has an energy density less than the keyhole change value. That is, the energy density is such that the object to be welded W is at a temperature below the boiling point.

Moreover, the pattern of the beam profiles of the first laser beam Lp and the second laser beam Ls is not necessarily the same. For example, as illustrated in FIGS. 3(a) to 3(f), a circular profile pattern (a), a donut-shaped (annular) profile pattern (b), an elliptical profile pattern (c), and an eight-shaped profile. Various patterns such as pattern (d), complex shape profile pattern (e), semi-circular profile pattern (not shown) may be used, and multiple light source shape profile patterns using multiple laser beams ( f) may be used.

Further, when welding the object W to be welded, when the first laser beam Lp and the second laser beam Ls are swept relative to the object W to be welded at the same time, the surface temperature Ts of the preheating point Ps increases during processing. The energy density must be such that the temperature Ta at the rear point Pa is maintained higher than the temperature Ta.

FIG. 4 is an explanatory diagram of the welding process of the present embodiment, and is a schematic diagram showing the positional relationship between the object to be welded W and the first laser beam Lp and the second laser beam Ls.
In FIG. 4, when the sweep direction 17 is the direction of the right arrow, the preheating point Ps is located on the far right side (forward in the sweeping direction), and the processing point Pp is located to the left (rearward in the welding direction). Further, a post-processing point Pa is a point that is located behind the processing point Pp in the sweep direction 17 and is set at a distance of 1 mm or more toward the solidified portion from the boundary between the molten pool Y and the solidified portion.

At this time, the surface temperature Ta of the post-processing point Pa needs to be substantially equal to or lower than the surface temperature Ts of the preheating point Ps. At this time, if Tb is defined as the boiling point of the object to be welded W, the relationship between the surface temperature Ta at the post-processing point Pa and the surface temperature Ts at the preheating point Ps is expressed by the inequality Ta≦Ts<Tb.

(action)
The operation of the laser welding apparatus and welding method configured as described above will be described with reference to FIGS. 5 to 9. FIG.

<Conventional welding method>
First, a conventional welding method that does not use the second laser beam Ls will be described with reference to FIGS. 5 and 6. FIG.
Here, FIG. 5 is an explanatory diagram of a conventional welding process using only the first laser beam Lp, and FIG. 6 is an explanatory diagram of occurrence of pore defects in the conventional welding process.

When the object W to be welded is irradiated with the first laser beam Lp, the metal is evaporated to form a keyhole 11 and deep penetration is generated as shown in FIG. At this time, the keyhole 11 does not collapse unless an external force 13 higher than the surface tension 12 of the molten metal is applied. Here, the external force 13 corresponds to the reaction force due to evaporation of the metal, the vapor pressure due to the ambient atmosphere gas, the melt flow due to the heat transport inside the molten metal due to the spatial temperature change (temperature gradient) and the temporal temperature change, and the like.

However, in laser welding of materials such as aluminum, magnesium, copper, etc., the surface tension 12 holding the keyhole 11 is very weak due to the low viscosity. Therefore, as shown in FIG. 6, the steam inside the keyhole 11 bends the tip of the keyhole 11 due to the flow of molten metal originating from the front molten part, which is a region with a high temperature gradient, and the molten metal entrains the steam inside to create a bubble 14 . generate If solidified as it is, pore defects 15 such as porosity and blowholes will occur.

As described above, it is very difficult to obtain high-quality welding only with the first laser beam for materials with low viscosity such as aluminum, magnesium, and copper, compared to materials with relatively high viscosity such as stainless steel. is.

<Welding method of the first embodiment>
Next, a welding method according to the first embodiment using the second laser beam Ls will be described with reference to FIGS. 7 to 9. FIG. Here, FIG. 7 is an explanatory diagram of the welding process according to the first embodiment, FIG. 8 is a relational diagram between the surface temperature of the preheating point and the pore generation rate, and FIG. 9 is a relational diagram of the surface temperature of the preheating point and various parameters. is.

In the first embodiment, as shown in FIG. 7, the second laser beam Ls is applied to a preheating point Ps in front of the processing point Pp by the first laser beam Lp to preheat it. It is possible to expand the area of As a result, it is possible to increase the volume of the molten metal in the preceding stage, and the distance between the bottom of the keyhole 11 and the solid phase of the entire molten metal is lengthened, so the temperature gradient is relaxed and the molten metal flow can be suppressed. becomes.

At this time, by controlling the surface temperature Ts of the preheating point Ps to a predetermined value, the generation of air bubbles 14 can be suppressed, and the generation of pore defects 15 can be suppressed. For example, from the database stored in the arithmetic processing unit 10, the data of the porosity generation rate with respect to the surface temperature Ts of the preheating point is obtained (see FIG. 8), and the surface temperature Ts of the preheating point Ps is set to a predetermined temperature (for example, FIG. The effect of minimizing the pore generation rate is expected by controlling to T1).

However, if the surface temperature Ts deviates from the predetermined temperature and the occurrence of defects is predicted, the sweep speed, the second laser One or more of light irradiation position, irradiation angle, output, spot diameter, energy density, wavelength, pulse width, and repetition frequency can be controlled to bring the surface temperature closer to a predetermined surface temperature Ts.

For example, as shown in FIG. 9, as a result of referring to the database, the region Z is a process window in which no defect occurs when various parameters such as energy density are plotted on the horizontal axis and the surface temperature Ts of the preheating point Ps is plotted on the vertical axis. In this case, the surface temperature Ts of the region Z can be controlled by using feedback means. ○ and ● shown in FIG. 9 are schematic diagrams showing an example in which the surface temperature ●, which is outside the range of the region Z, shifts to the surface temperature ○ within the range of the region Z as a result of adjusting various parameters.

It should be noted that although parameters other than those described above may be added to the types of parameters controlled to a predetermined temperature by referring to the database, at least one or more of the above must be included in the control target.

(effect)
As described above, according to the laser welding method and welding apparatus according to the first embodiment, even if the object W to be welded has a low viscosity, the second laser beam is used, and the processing point, By optimally controlling the temperatures of the preheating point, the post-processing point, and the like, it is possible to suppress the occurrence of defects such as weld cracks, pores, and spatter.

[Second embodiment]
A laser welding method and welding apparatus according to a second embodiment will be described with reference to FIGS. 10 to 16. FIG. This embodiment suppresses surface oscillation of the molten pool Y and prevents defects such as spatter from occurring.

<Conventional welding method>
First, a conventional welding method that does not use the second laser beam will be described with reference to FIGS. 10 to 12. FIG.

For example, as shown in FIG. 10, when welding is performed by irradiating only the first laser beam Lp with a circular beam profile without using the second laser beam Ls, the processing point Pp is rapidly heated to form a keyhole 11. Therefore, the temperature is equal to or higher than the boiling point Tb or in the vicinity of the boiling point.

On the other hand, a point on the sweep direction line that is the room temperature Tr ahead of the processing point Pp is defined as a room temperature point Pr. At this time, when the distance (first distance) between the processing point Pp using only the first laser beam Lp and the room temperature point Pr, which is the room temperature Tr, is Xp, the first distance corresponding to the slope of the straight line as shown in FIG. A temperature gradient Gxp of is obtained. Tb is the boiling point of the object W to be welded, and Tm is the melting point. A melt flow occurs inside the molten pool Y due to this first temperature gradient Gxp. Due to this molten metal flow, surface fluctuation of the molten pool Y occurs as shown in FIG. 12, which causes defects such as spatter.

<Welding method of the second embodiment>
Next, a welding method according to the second embodiment using the second laser beam will be described with reference to FIGS. 13 to 16. FIG.

In the second embodiment, as shown in FIG. 13, in addition to the first laser beam Lp having a circular beam profile, for example, a second laser beam Ls having a crescent-shaped (semi-annular) beam profile is used.

As a result, the peripheral portion of the processing point Pp is preheated, and the distance (second distance) Xs from the processing point Pp to the point Pr on the weld line at room temperature is the first distance Xp when only the first laser beam is used. , and a second temperature gradient Gxs as shown in FIG. 14 is obtained. Since the second temperature gradient Gxs shown in FIG. 14 is gentler than the first temperature gradient Gxp shown in FIG. can give the effect of being suppressed.

In this case as well, the melt flow causes surface oscillation of the molten pool Y as shown in FIG. 15, but since the temperature gradient Gxs is gentle, the amplitude of the surface oscillation is suppressed more than that shown in FIG. Thus, the use of the second laser beam Ls can suppress the occurrence of defects such as spatter.

As described above, according to the laser welding method and welding apparatus according to the second embodiment, in addition to the effects of the first embodiment, by reducing the surface oscillation of the molten pool Y, It is possible to further suppress the occurrence of defects such as weld cracks, pores, and spatters.

(Modification)
In this modified example, as shown in FIG. 16, the second laser beam Ls has, for example, a doughnut-shaped (annular) beam profile, and the post-processing point Pp is also preheated. As a result, the effect of suppressing the surface oscillation of the latter stage of the molten pool Y can be obtained, and the occurrence of defects such as weld cracks, pores, and spatters can be further suppressed.

Although several embodiments of the invention have been described above, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

W... Object to be welded, L... Laser beam, Lp... First laser beam, Ls... Second laser beam, Gxp... First temperature gradient, Gxs... Second temperature gradient, Pp... Processing point, Ps... Preheating Point, Pa... Point after working, Pr... Room temperature point, Ta... Surface temperature of point Pa after working, Tb... Boiling point of object W to be welded, Ts... Surface temperature of preheating point Ps, Tr... Room temperature, Y... Molten pool , Z... defect-free region, Xp... first distance, Xs... second distance,
Reference Signs List 1 laser welding device 2 laser oscillator 2p first laser oscillator 2s second laser oscillator 2e controller 3 optical fiber 3p first optical fiber 3s second optical fiber 4 Optical head 5 Shield gas nozzle 6 Temperature sensor 7 Laser oscillator controller 8 Optical head controller 9 Temperature sensor controller 10 Arithmetic processor 11 Keyhole 12 Surface tension , 13... external force, 14... bubble, 15... pore defect, 16... variable stage, 17... sweep direction

Claims (5)

a step of irradiating a processing point of an object to be welded with a first laser beam to form a molten pool in and around the keyhole;
a step of irradiating a second laser beam to a preheating point set in front of the processing point with respect to the sweep direction of the object to be welded;
A step of setting a post-processing point at a position separated by a predetermined distance or more behind the molten pool from the interface between the molten pool and the solidified portion;
A laser welding method comprising the step of controlling the surface temperatures of the preheating point, the processing point and the post-processing point to predetermined temperatures by an arithmetic processing unit,
A laser welding method, wherein the surface temperature of the preheating point is less than the boiling point of the object to be welded, and the surface temperature of the post-processing point is equal to or lower than the surface temperature of the preheating point. . 2. The laser welding method according to claim 1, wherein said predetermined distance is 1 mm or more. The arithmetic processing unit calculates at least one or more parameters among a plurality of parameters such as sweep speed, irradiation position of the second laser beam, irradiation angle, output, spot diameter, energy density, wavelength, pulse width, repetition frequency, etc. 3. The laser welding method according to claim 1, wherein the surface temperature of said preheating point is controlled to a predetermined temperature to minimize the porosity. 4. The laser welding according to any one of claims 1 to 3, wherein the beam profile of the second laser light is any one of an annular shape, a semi-annular shape, an elliptical shape, and an eight-shaped shape around the processing point. Method. A laser welding apparatus that performs the laser welding method according to any one of claims 1 to 4,
a laser oscillator that generates a first laser beam and a second laser beam;
an optical head provided above the object to be welded for irradiating the object to be welded with the first laser beam and the second laser beam;
a temperature sensor for measuring the surface temperature of the object to be welded;
a shield gas nozzle that supplies a rare gas or an inert gas to the object to be welded;
and an arithmetic processing unit for controlling parameters such as energy density, pattern, intensity, irradiation position, sweep speed, etc. of the first laser beam and the second laser beam.

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