JP2009148794A - Laser welding method and laser welding system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welding method, in which welding quality can be improved by preventing generation of porosity. <P>SOLUTION: With a gap given between steel sheets 51, 51 having a rust-preventive layer 53, a laser beam 60 is pre-emitted so as to get such a heating value that the rust-preventive layer 53 evaporates but the steel sheets are unmelted. Then, the steel sheets are brought into contact with each other and welded by irradiating with a laser beam so as to get a weldable heat value. Since the welding is performed after the substance of the rust-preventive layer is fully evaporated from the gap by the preliminary irradiation, generation of porosity can be prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser welding method and a laser welding system.

  In recent years, laser welding has begun to be used for welding steel plates. One of the conventional laser welding techniques is a technique for welding a steel plate that has been rust-proofed by galvanization.

This technique first distorts the steel sheet by strongly pressing the two stacked steel sheets to create a gap in the vicinity thereof. Laser welding is performed in this state. At that time, zinc plating having a melting point lower than that of the steel plate evaporates first, but since it is exhausted as a gas from the gap, generation of porosity in the weld bead can be prevented (Patent Document 1).
JP 2004-283835 A

  However, the conventional laser welding method distorts the steel plate itself in order to open a gap between the two steel plates. Therefore, after welding in this state, the post-weld distortion is fixed, and the product quality is reduced. There is a problem that it may be dropped. Moreover, there is a problem that the formation of the gap due to distortion itself is difficult to adjust, and the zinc gas cannot be discharged well.

  Therefore, an object of the present invention is to provide a laser welding method and a laser welding system capable of reliably preventing the occurrence of porosity without deteriorating the product quality after welding.

  The above object of the present invention is achieved by the following means.

  First, the laser welding method of the present invention is a laser welding method of at least two steel plates, at least one of which has a rust prevention layer. In this method, a gap is formed between the surface of the at least two steel plates having the rust preventive layer and the other steel plates. Thereafter, any one of these at least two steel plates is pre-irradiated with a laser beam having a heat amount for evaporating the rust preventive layer and a heat amount that does not lead to welding. After the pre-irradiation, the gap is closed and the two steel plates are brought into contact with each other, and the pre-irradiated portion is irradiated with a laser beam having a heat amount necessary for welding to be welded.

  The laser welding system of the present invention is a laser welding system for welding at least two steel plates each having a rust prevention layer. This laser welding system includes a laser irradiation means having a laser intensity changing means for changing the intensity of laser light irradiation, a clamping means that can adjust a gap between the steel plates by overlapping at least two steel plates, It has a control means. This control means controls the clamping means so as to leave a gap between at least two steel sheets, and emits laser light that has a heat quantity that evaporates the anticorrosion layer on these at least two steel sheets and that does not lead to welding. The laser irradiation means is controlled to perform pre-irradiation. Further, after the pre-irradiation, the control means controls the clamping means so as to close the gap and bring at least two steel plates into contact. And a laser irradiation means is controlled so that the laser beam used as the amount of heat required for welding may be irradiated to the pre-irradiated part.

  According to the present invention, since a gap is provided between two steel plates and only the rust prevention layer is vaporized first by pre-irradiation with laser light, there is no generation of gas during welding, and generation of porosity can be prevented. it can. In addition, since laser irradiation is performed after the two steel plates are brought into contact with each other during welding, unnecessary distortion does not occur and there is no possibility of reducing the welding quality.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiment shown below, a case where two steel plates having galvanized plating as a rust preventive layer on both surfaces are laser-welded as members to be welded will be described as an example. In addition, the same code | symbol was used for the same member in the figure.

  FIG. 1 is a system configuration diagram for explaining a laser welding system in an embodiment to which the present invention is applied.

  The laser welding system 1 according to this embodiment includes a laser welding apparatus 100 and a clamp apparatus 200 that holds a steel plate as a member to be welded. The laser welding apparatus 100 includes a machining head 10 (laser irradiation means), a robot 20, a laser oscillator 30, and a control device 40 (control means).

  The processing head 10 irradiates laser light 60 on two steel plates (an upper plate 51 (first steel plate) and a lower plate 52 (second steel plate)) to be overlaid. The processing head 10 includes therein an optical system including a plurality of lenses and mirrors, and can move the laser beam 60 while adjusting a position where the laser beam 60 is focused (referred to as an in-focus position) ( Details of the processing head will be described later).

  The robot 20 moves the machining head 10 in the multi-axis direction. The robot 20 of the present embodiment is an articulated arm robot, and the machining head 10 is attached to the arm tip. The robot 20 can also move the laser beam 60 by moving the machining head 10.

  Therefore, the movement of the laser beam 60 is a movement in which the movement of the mirror in the machining head and the movement of the robot 20 are added. For this reason, for example, the processing head 10 is positioned at a position where a plurality of welding points can be welded by the robot 20, and welding is performed by sequentially oscillating the laser beam 60 with a mirror from there to the plurality of welding points. can do. Also, the welding points can be sequentially welded by the mirror while the processing head 10 is always moved toward the next welding point.

  The laser oscillator 30 supplies laser light to the machining head 10. The laser oscillator 30 is, for example, a YAG laser oscillator, and supplies a laser beam 60 to the processing head 10 via the optical fiber cable 35. Further, the laser oscillator 30 can intermittently output laser light in pulses. By changing the pulse frequency, the output intensity of the laser beam can be varied. That is, if the pulse frequency is increased, the irradiation intensity per unit time of the laser beam, that is, the amount of heat applied to the steel sheet increases, and if the frequency is decreased, the irradiation intensity per unit time, that is, the amount of heat applied to the steel sheet decreases.

  The control device 40 controls the machining head 10, the robot 20, and the laser oscillator 30 according to an operation procedure described later. This control device is, for example, a computer used in a production line such as a programmable controller, and each part is controlled according to a program created to execute an operation procedure described later.

  FIG. 2 is a diagram for explaining the machining head.

  As shown in FIG. 2, the processing head 10 of the present embodiment includes a plurality of lenses 11 a to 11 d that transmit laser light incident from an optical fiber cable 35 and mirrors 12 a to 12 c that reflect the laser light.

  Among the plurality of lenses 11a to 11d, the lens 11b is a lens for focusing (focus function). The lens 11b moves in the optical axis direction by being driven by the drive motor 13a. By moving the lens 11b, the focus position of the laser beam 60 is adjusted. That is, the laser beam 60 can be focused on or removed from the surface to be welded. The drive motor 13a is controlled by the control device 40. By adjusting the focal position of the lens 11b, the amount of heat of the portion irradiated with the laser beam 60 (the amount of heat applied to the member to be welded) can be changed.

  Of the plurality of mirrors 12a to 12c, the first and second mirrors 12b and 12c are driven by drive motors 13b and 13c, and rotate about different axes. By rotating the first and second mirrors 12b and 12c, the emission direction of the laser light 60 is freely distributed. The mirrors 12 b and 12 c are controlled by the control device 40.

  In the present embodiment, the laser oscillator 30 and the lens 11b serve as laser intensity changing means each independently or in cooperation.

  Here, the relationship between the focal position by the lens, the change in its spot diameter, and the amount of heat applied to the steel sheet will be described.

  FIG. 3 is an explanatory diagram for explaining the relationship between the focal position, the change in its spot diameter, and the amount of heat applied to the steel plate.

  As shown in the figure, when the focal position is shifted (defocused) with respect to the steel plate (upper plate 51, lower plate 52) on which the zinc plating 53 as a rust preventive layer has been applied, the steel plate surface of the laser beam 60 is The spot diameter 65 becomes larger. For this reason, if the intensity | strength of a laser beam is the same, the calorie | heat amount given to a steel plate will decrease compared with the case where a focus is match | combined with the steel plate. Therefore, by shifting the focal position from the steel plate, it is possible to give a heat amount that does not lead to welding and that can evaporate only zinc (Zn) that is a rust prevention layer. In addition, the laser irradiation at the time of evaporating only such a rust prevention layer is called pre-irradiation.

  FIG. 4 is an explanatory diagram for explaining the relationship between the spot diameter during pre-irradiation and the bead pattern during welding.

  The spot diameter 65 at the time of pre-irradiation is made larger than the spot diameter at the time of welding on the steel plate as described above. Therefore, the galvanized portion 53 wider than the state in which the spot diameter is narrowed to form the weld bead 67 is evaporated. Therefore, at the time of welding, it is preferable to form a weld bead 67 inside the wide spot diameter at the time of this pre-irradiation. FIG. 4 shows an example of a weld bead pattern when a weld bead 67 is formed inside a wide spot diameter 65 during such pre-irradiation. FIG. 4A shows a “C” -shaped weld bead 67 formed inside the spot diameter 65 in the pre-irradiation. FIG. 4B shows a case in which two spot diameters 65 are continuously irradiated during pre-irradiation, and a weld bead 67 is formed in an “S” shape therein. In FIG. 4C, a plurality of spot diameters 65 are made continuous during pre-irradiation, and a linear weld bead 67 is formed inside these continuous spot diameters 65.

  Thus, by forming the weld bead inside the spot diameter in the pre-irradiation, it becomes possible to reliably weld the portion where the zinc plating has evaporated during welding. Therefore, it is possible to prevent the generation of porosity due to evaporation of galvanizing during welding.

  The relationship between the amount of heat applied to the steel sheet during pre-irradiation and the amount of heat applied during welding will be described. For example, when the steel plate is galvanized as the member to be welded, the melting point of the steel plate (iron) is about 1535 ° C., and the boiling point of zinc is about 900 ° C. Therefore, at the time of pre-irradiation, the temperature of the steel sheet may be 900 to 1500 ° C., preferably a heat quantity that is in the range of about 1000 to 1200 ° C. with a margin. As a result, only the zinc evaporates without melting the steel plate. Thus, the amount of heat at the time of pre-irradiation is appropriately changed depending on the material of the member to be welded (material of the steel plate and the rust prevention layer) so that the amount of heat that evaporates the rust prevention layer and not reach welding. .

  As described above, the spot diameter of the laser beam 60 at the time of pre-irradiation is adjusted so that the amount of heat is such. However, depending on the output performance of the laser oscillator, even if the spot diameter is made too large in order to lower the temperature, the rust preventive layer is removed far beyond the welding range. Therefore, not only the adjustment of the spot diameter (adjustment of the focal position) but also the laser oscillator is a pulse laser oscillator, and the laser beam irradiation interval is adjusted according to the spot diameter, so that the optimum spot diameter can be obtained. In addition, an amount of heat suitable for evaporating only zinc can be obtained.

  FIG. 5 is an explanatory diagram for explaining the clamp device.

  The clamp device 200 fixes a work support base 205 on which a member to be welded is placed, an auxiliary clamper 201 (second clamper) for fixing the lower plate 52 placed on the work support base 205, and an upper plate from above the upper plate 51. It has a main clamper 202 (first clamper).

  The auxiliary clamper 201 has different shapes, for example, between the lower plate 52 and the upper plate 52, and can hold and fix only the lower plate 52 at a position where only the lower plate portion can be clamped from above or at a position where it does not interfere with the upper plate 51. It is provided as follows. The auxiliary clamper 201 only needs to be capable of opening and closing (fixing or opening).

  On the other hand, the main clamper 202 is provided at a position where both the lower plate 52 and the upper plate 51 can be clamped from above the upper plate 51. The main clamper 202 is provided with an electromagnet 220 at a portion in contact with the upper plate 51. The electromagnet 220 is connected to the arm of the main clamper 202 by a ball bearing 221 so as to move freely to some extent. For this reason, when the electromagnet 220 abuts on the upper plate 51, the electromagnet 220 is parallel to the upper plate 51 and can reliably attract the upper plate 51.

  Only the upper plate 51 can be lifted by the electromagnet 220. Therefore, the main clamper 202 uses a servo motor type cylinder 210 operated by a servo motor (not shown) in order to freely control the opening / closing amount of the main clamper 202 in addition to the opening / closing operation. Thereby, an arbitrary gap can be provided between the upper plate 51 and the lower plate 52 in a state where the upper plate 51 is attracted by the electromagnet 220.

  The gap created during pre-irradiation is, for example, about 1 to 3 mm. If this gap is too small, the zinc evaporated during pre-irradiation is difficult to escape, so about 1 mm is preferable. On the other hand, if the gap is too large, it is impossible to evaporate both of these galvanized plates when both the plate 52 and the upper plate 51 have a rust preventive layer. For example, when pre-irradiation is performed from the upper plate 51 side, the upper plate 51 is first heated, and the lower plate 52 is heated by the radiant heat. However, if the gap is too large, the lower plate 52 is sufficient. May not be heated. For this reason, the maximum gap is preferably about 3 mm. However, a larger gap may be used as long as a sufficient amount of heat is transmitted to evaporate the zinc plating 53 up to the lower plate 52 in accordance with the amount of heat applied. Further, when the lower plate 52 does not have a rust prevention layer in the first place, it may be opened as long as the gap is 1 mm or more.

  Next, the operation of the laser welding system according to the present embodiment will be described.

  FIG. 6 is a flowchart showing an operation procedure of welding in this laser welding system, and FIGS. 7 to 10 are explanatory diagrams for explaining the operation state of the clamp device 200 for explaining the welding operation. According to this operation procedure, the control device controls each part.

  Here, the steel plates (the upper plate 51 and the lower plate 52) that are the members to be welded are each provided with a zinc plating 53 that is a rust prevention layer on the front and back surfaces.

  First, the lower plate 52 is set on the base of the clamping device 200, and only the lower plate 52 is fixed by the auxiliary clamper 201 (S1, FIG. 7).

  Next, the upper plate 51 is placed on the lower plate 52 and lightly clamped once by the main clamper 202 (for example, the state in which the lower plate 52 and the upper plate 51 are in contact with each other) (S2). .

  From this state, the electromagnet 220 of the main clamper 202 of the clamping device 200 is operated to attract the upper plate 51 and lift only the upper plate 51 by a predetermined amount (S3, FIG. 8). This opens a predetermined gap between the steel plates.

  Subsequently, for pre-irradiation, the processing head 10 is moved to a position where the laser beam can be irradiated to the welding point (S4, FIG. 8). At this time, when there are a plurality of welding points, the machining head 10 is positioned at a position where the plurality of welding points can be irradiated with laser light.

  Subsequently, the lens is moved to adjust the focal position so as to be in a defocused state, and the laser oscillator is instructed to lower the irradiation frequency of the laser light. Then, pre-irradiation with laser light is executed (S5, FIG. 8). At this time, when there are a plurality of welding points, pre-irradiation of laser light is performed on all of the plurality of welding points. Thereby, galvanization in a welding point vaporizes and evaporates.

  After the pre-irradiation is completed, the main clamper 202 is completely closed, and the upper plate 51 and the lower plate 52 are completely contacted (S6, FIG. 9). In this state, the focus position for welding is adjusted by moving the lens so as to match the welding point, and laser irradiation for welding is executed (S7).

(Example)
Next, an experimental example actually welded along the above operation procedure will be described.

  As a member to be welded, two galvanized steel plates (soft iron plates) having a thickness of 10 mm were used. A welding point is a portion where two steel plates are overlapped (joint).

  Laser output during pre-irradiation: 2 kW, pulse frequency: 20 Hz, spot diameter: 10 mm.

  A laser output at the time of welding: 4 kW, no pulse (that is, irradiation without intermittent), a spot diameter: 0.3 mm, and a C-shape was drawn at a welding speed of 4 m / min within the spot diameter at the time of pre-irradiation.

  Under the above conditions, as an example, after pre-irradiating with a gap of about 1 to 3 mm, welding was performed. Further, as a comparative example, welding was performed after pre-irradiation without opening a gap.

  FIG. 10 is a schematic diagram showing a cross section of a welded part after welding in Examples and Comparative Examples.

  In the welding of the examples, as a result of visual inspection, no roughness due to porosity was found on the surface of the weld bead. FIG. 10A is a schematic cross-sectional view showing the results of this example. As shown in the figure, it was considered that since the pre-irradiation was performed with a gap, zinc causing porosity was completely removed at the stage before welding, and thus surface roughness did not occur.

  On the other hand, as a result of visual observation in the comparative example, surface roughness due to porosity was observed. As shown in FIG. 10 (b), although pre-irradiation was performed, since there was no gap, zinc was not completely removed, and porosity 70 was generated during welding and came out to the surface of the weld bead. Is thought to have been damaged.

  Therefore, in the welding to which the present invention is applied, it is found that the weld bead surface is not roughened by the porosity at the portion where the weld bead is formed, a good weld quality can be obtained, and the joining strength is sufficient. It was.

  As described above, according to the embodiments and examples to which the present invention is applied, the following effects can be obtained.

  In the present embodiment, a gap is provided between steel plates having a rust-proof layer, laser light is pre-irradiated so that the amount of heat is such that zinc is evaporated, and then the steel plates are brought into contact with each other for welding. did. Thereby, after zinc is completely evaporated from the gap by pre-irradiation, welding is performed, and therefore generation of porosity due to evaporation of zinc can be prevented. Moreover, since the laser irradiation is performed after the two steel plates are completely brought into contact with each other during welding, unnecessary distortion does not occur, and there is no possibility of reducing the welding quality.

  In addition, the amount of heat during pre-irradiation is adjusted by changing the spot diameter on the steel plate by adjusting the focal position of the laser beam. It can be carried out.

  Further, since the portion to be welded is within the range of the spot diameter at the time of pre-irradiation, the portion from which zinc has been blown off by pre-irradiation can be reliably welded to prevent the occurrence of porosity.

  In addition, for a plurality of welding points, after a gap is formed, pre-irradiation is performed on the plurality of welding points, and then the gap is closed and welding is performed. The laser beam is scanned by moving the mirror from the state where the machining head is stopped, and pre-irradiation and welding can be executed without the operation of the robot. Thereby, pre-irradiation and welding can be performed continuously and efficiently even at a plurality of welding points. In addition, the pre-irradiation also removes the rust prevention layer by laser irradiation, so even if the pre-irradiation is continuously pre-irradiated at multiple welding points to remove the rust prevention layer, the time until the subsequent welding operation is very long. Few. Therefore, it is possible to perform good welding without the rust-preventing layer removed portion being oxidized over time.

  Further, since the electromagnet is provided in the clamp device and the lower plate is separately fixed, the upper plate is attracted and lifted by the electromagnet, so that a gap can be easily formed. Further, since the clamper is operated by a servo motor type cylinder (electric actuator), the adjustment of the gap is easy.

  Although the embodiments and examples to which the present invention is applied have been described above, the present invention is not limited to these embodiments and examples.

  For example, in the above-described embodiment, an electromagnet is used in the clamp device to attract the upper plate. However, instead of the electromagnet, for example, a vacuum suction device may be used. FIG. 11 is a drawing showing an example of a clamping device using a vacuum suction device. In this clamping device 300, a vacuum suction cup 301 is attached to the main clamper 202. The upper plate 51 can be adsorbed by operating a vacuum pump (not shown). The main clamper 202 is opened and closed by a servo motor in the same manner as the clamping device 200 described above. Therefore, the distance between the upper plate 51 and the lower plate 52 can be adjusted. Further, the clamping device 300 is not provided with an auxiliary clamper. This is because when the upper plate 51 is sucked, vacuum suction is used, and there is no fear that the lower plate 52 rises together when the upper plate 51 is sucked. For this reason, it is particularly effective in the case where only the lower plate 52 cannot be clamped. This also eliminates the need to individually fix the lower plate 52, thus simplifying the clamping device. Of course, an auxiliary clamper may be provided if necessary to stabilize the lower plate 52.

  The welding operation using this clamping device 300 is that the clamping operation of the lower plate 52 is omitted, the suction of the upper plate 51 is changed to vacuum suction, and the other operations are the same as in the above-described embodiment. In addition, since the effect in the welding operation is the same, the description is omitted.

  Moreover, in embodiment mentioned above, it demonstrated as an example laser welding the steel plates in which galvanization was formed. However, the joining target may be a bare material in which one of the two steel plates is not rust-proofed. Furthermore, the rust preventive layer covering the steel plate surface is not limited to galvanizing, and may be aluminum plating or chrome plating, and is effective for various rust preventive layers covering the steel plate surface.

  Moreover, in embodiment mentioned above, it demonstrated as an example laser welding the 2 sheet steel plate in which galvanization was formed. However, the object to be welded is not limited to two steel plates, and is applicable even when there are three or more welded portions. That is, with respect to each of the three or more welded portions, a pre-irradiation is performed by opening a gap in a portion where the rust preventive layer is present, and thereafter, the gap is closed and laser irradiation for welding is performed.

It is a system configuration figure for explaining a laser welding system in an embodiment to which the present invention is applied. It is a figure for demonstrating a process head. It is explanatory drawing explaining the relationship between a focal position, the change of the spot diameter, and the calorie | heat amount given to a steel plate. It is explanatory drawing for demonstrating the relationship between the spot diameter at the time of pre irradiation, and the bead pattern at the time of welding. It is explanatory drawing for demonstrating a clamp apparatus. It is a flowchart which shows the operation | movement procedure of welding. It is explanatory drawing explaining the operation state of a clamp device in order to explain welding operation. It is explanatory drawing explaining the operation state of a clamp device in order to explain welding operation. It is explanatory drawing explaining the operation state of a clamp device in order to explain welding operation. It is a cross-sectional schematic diagram of a welding part. It is drawing which shows an example of the clamp apparatus using a vacuum suction apparatus.

Explanation of symbols

1 Laser welding system,
10 processing head,
11a to 11d lenses (laser intensity changing means),
20 robots,
30 Laser oscillator (laser intensity changing means),
40 control device (control means),
200, 300 clamping device,
201 Auxiliary clamper (second clamper),
202 Main clamper (first clamper),
205 workpiece support,
210 cylinders,
220 electromagnet,
301 Vacuum suction cup.

Claims (9)

At least one is a laser welding method of at least two steel plates having a rust prevention layer,
A step of opening a gap between the surface of the at least two steel plates having a rust prevention layer and another steel plate;
Pre-irradiating a laser beam having a heat amount for evaporating the rust preventive layer and a heat amount that does not lead to welding to any one of the at least two steel plates;
After the pre-irradiation step, closing the gap and contacting the at least two steel plates;
Irradiating the pre-irradiated portion with a laser beam having a heat amount necessary for the welding to perform the welding.   In the pre-irradiation step, the focal point of the laser beam to be irradiated is shifted from the laser irradiation surface of the steel sheet to widen the spot diameter of the laser beam, and the amount of heat that evaporates the rust preventive layer is not reached. The laser welding method according to claim 1, wherein the amount of heat is set.   3. The laser welding method according to claim 2, wherein in the welding step, a weld bead is formed by drawing a pattern of a predetermined shape in a portion corresponding to the inside of the spot diameter in the pre-irradiation. After the step of opening the gap, performing the pre-irradiation to a plurality of welding points,
4. The method according to claim 1, wherein after performing the pre-irradiation on the plurality of welding points, the step of closing the gaps and performing the welding to the plurality of welding points is performed. The laser welding method as described. At least one is a laser welding system for welding at least two steel plates having a rust prevention layer,
Laser irradiation means comprising laser intensity changing means for changing the intensity of laser light irradiation;
Clamping means capable of adjusting the gap between the steel plates by overlapping at least two steel plates;
The clamping means is controlled so as to leave a gap between the at least two steel plates, and a laser beam having a heat amount for evaporating the anticorrosive layer and a heat amount that does not lead to welding is applied to the at least two steel plates. The laser irradiation means is controlled to irradiate, and after the pre-irradiation, the gap means is closed and the clamp means is controlled to contact the at least two steel plates, and the weld is applied to the pre-irradiated portion. Control means for controlling the laser irradiation means so as to irradiate a laser beam having a heat amount necessary for
A laser welding system comprising: The clamping means includes
A first clamper sandwiching the first steel plate and the second steel plate which are the at least two steel plates; and
A servo motor type first clamper drive source for controlling the opening / closing amount of the first clamper;
A second clamper for clamping the second steel plate;
A second clamper drive source for opening and closing the second clamper;
An electromagnet attached to the first clamper and capable of adsorbing and detaching the first steel plate;
With
In the pre-irradiation, the control means drives the first clamper so as to create the gap between the first steel plate and the second steel plate while the first steel plate is attracted by the electromagnet. 6. The laser welding system according to claim 5, wherein the source is controlled. The clamping means includes
A first clamper sandwiching the first steel plate and the second steel plate which are the at least two steel plates; and
A servo motor type first clamper drive source for controlling the opening / closing amount of the first clamper;
A vacuum suction means attached to the first clamper and capable of sucking and detaching the first steel plate;
With
In the pre-irradiation, the control means is configured to create the gap between the first steel sheet and the second steel sheet in a state where the first steel sheet is adsorbed by the vacuum suction means. 6. The laser welding system according to claim 5, wherein the clamper driving source is controlled. The laser intensity changing means is a focus adjusting means for changing the focal position of the laser beam,
The control means shifts the focal point of the laser light irradiated by the focus adjusting means during the pre-irradiation from the steel plate surface that is the laser irradiation surface to widen the spot diameter of the laser light, thereby to The laser welding system according to any one of claims 5 to 7, wherein the amount of heat to be evaporated is controlled so as to be a heat amount that does not lead to the welding.   The control means controls the laser irradiation means so as to form a weld bead by drawing a pattern of a predetermined shape in a portion corresponding to the inside of the spot diameter at the time of the pre-irradiation during the welding. The laser welding system according to any one of claims 5 to 8.

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