Laser welding method and device

Abstract

The present invention provides a laser welding method and apparatus. The laser welding method welds the joint surfaces of multiple workpiece components by irradiating a laser beam (LB). The trajectory of the laser beam (LB) is controlled to perform oscillating scanning (Sw) based on a combination of a scanning motion (Sa) and a oscillating motion (Sb). The scanning motion (Sa) moves along a first direction (x) parallel to the joint surfaces. The oscillating motion (Sb) includes a first oscillating component (Bx) along the first direction (x) and a second oscillating component (By) along a second direction (y) perpendicular to the first direction (x). The laser welding method includes: a defect determination step for determining the occurrence of a welding defect; and an output control step for increasing or decreasing the output of the laser beam (LB) when the laser beam (LB) is re-irradiated toward the welding defect if a welding defect has occurred.

Description

Technical Field

[0001] The invention relates to a laser welding method and a laser welding device. Background Art

[0002] When laser welding is performed by butting or overlapping a plurality of workpieces, if there are foreign matter or gaps at the joint interface, welding defects such as punch-outs or unwelded parts may occur.

[0003] As a countermeasure, a laser oscillator has been used to defocus the first laser irradiation to melt a large area of ​​the workpiece, and then a second laser irradiation is performed at the same location with precise focusing, thereby preventing the occurrence of poor welding (Patent Document 1). In addition, other existing technologies use two laser oscillators to simultaneously irradiate the same welding location of the workpiece with two laser beams from different directions, thereby preventing the occurrence of poor welding (Patent Document 2).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 5224349

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-5760 Summary of the Invention

[0008] One embodiment of the present invention involves a laser welding method that is a laser welding method for welding the joint surfaces between multiple workpiece components by irradiating a laser beam LB, wherein the trajectory of the laser beam LB is controlled to perform a swinging scan Sw based on a combination of a scanning motion Sa and a swinging motion Sb, wherein the scanning motion Sa moves along a first direction x parallel to the joint surface, and the swinging motion Sb includes a first swinging component Bx along the first direction x and a second swinging component By along a second direction y perpendicular to the first direction x. The laser welding method includes: a defect determination step for determining the occurrence of a welding defect; and an output control step for increasing or decreasing the output of the laser beam LB when the laser beam LB is irradiated again facing the welding defect when a welding defect occurs.

[0009] In addition, another embodiment of the present invention relates to a laser welding device comprising: a laser oscillator for supplying a laser beam LB; a focusing optical system for focusing the laser beam LB onto a joining surface between a plurality of workpiece members; an oscillating scanning optical system for controlling the position of the laser beam LB so that the trajectory of the laser beam LB performs an oscillating scan Sw based on a combination of a scanning motion Sa and a swinging motion Sb, wherein the scanning motion Sa moves along a first direction x parallel to the joining surface, and the swinging motion Sb includes a first swinging component Bx along the first direction x and a second swinging component By along a second direction y perpendicular to the first direction x; a defect determination unit for determining the occurrence of a welding defect; and an output control unit for increasing or decreasing the output of the laser beam when the laser beam LB is irradiated again toward the welding defect when a welding defect occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a block diagram showing the configuration of a laser welding device according to an embodiment of the present invention.

[0011] Figure 2 1 is a cross-sectional view showing an example of a welded portion of a workpiece W.

[0012] Figure 3A 1 is an explanatory diagram showing an example of wobbling scanning Sw based on a combination of circular scanning motion Sa and wobbling motion Sb.

[0013] Figure 3B It is an explanatory diagram of the swing motion Sb.

[0014] Figure 4A This diagram illustrates swing welding on a cylindrical battery.

[0015] Figure 4B This diagram illustrates swing welding on a cylindrical battery.

[0016] Figure 4C This diagram illustrates swing welding on a cylindrical battery.

[0017] Figure 4D This diagram illustrates swing welding on a cylindrical battery.

[0018] Figure 5A 1 and 2 are top views and cross-sectional views showing the trajectory of the laser beam.

[0019] Figure 5B 1 and 2 are top views and cross-sectional views showing the trajectory of the laser beam.

[0020] Figure 5C 1 and 2 are top views and cross-sectional views showing the trajectory of the laser beam.

[0021] Figure 6AThese are top views and cross-sectional views showing welding defects that occur when laser welding is performed using a linear scanning beam.

[0022] Figure 6B These are top views and cross-sectional views showing welding defects that occur when laser welding is performed using a linear scanning beam.

[0023] Figure 6C These are top views and cross-sectional views showing welding defects that occur when laser welding is performed using a linear scanning beam.

[0024] Figure 7A These are top views and cross-sectional views showing welding defects that occur when laser welding is performed using an oscillating scanning beam.

[0025] Figure 7B These are top views and cross-sectional views showing welding defects that occur when laser welding is performed using an oscillating scanning beam.

[0026] Figure 7C These are top views and cross-sectional views showing welding defects that occur when laser welding is performed using an oscillating scanning beam.

[0027] Figure 7D These are top views and cross-sectional views showing welding defects that occur when laser welding is performed using an oscillating scanning beam.

[0028] Figure 8A It is a top view showing a state where a perforation occurs.

[0029] Figure 8B Graph showing temporal changes in the signal output of welding light LW generated from the molten region M during laser welding.

[0030] Figure 8C 3 is a cross-sectional view showing thermal radiation light LH emitted from a normal melting region M.

[0031] Figure 8D It is a cross-sectional view showing a state where perforation occurs in the molten region M.

[0032] Figure 9A It is a top view showing the positional relationship between the trajectory of the oscillating scanning beam and the foreign matter.

[0033] Figure 9B It is a top view showing the positional relationship between the trajectory of the oscillating scanning beam and the foreign matter.

[0034] Figure 9C It is a top view showing the positional relationship between the trajectory of the oscillating scanning beam and the foreign matter.

[0035] Figure 9D It is a top view showing the positional relationship between the trajectory of the oscillating scanning beam and the foreign matter.

[0036] Figure 9E It is a top view showing the positional relationship between the trajectory of the oscillating scanning beam and the foreign matter.

[0037] Figure 9F It is a top view showing the positional relationship between the trajectory of the oscillating scanning beam and the foreign matter.

[0038] Figure 10A Graph showing the temporal change of the welding light signal during wobble welding.

[0039] Figure 10B Graph showing changes in intensity of laser output for repairing a perforation.

[0040] Figure 11A is a top view showing the trajectory of the oscillating scanning beam used to fill the through-holes.

[0041] Figure 11B is a top view showing the trajectory of the oscillating scanning beam used to fill the through-holes.

[0042] Figure 11C is a top view showing the trajectory of the oscillating scanning beam used to fill the through-holes.

[0043] Figure 11D is a top view showing the trajectory of the oscillating scanning beam used to fill the through-holes.

[0044] Figure 11E is a top view showing the trajectory of the oscillating scanning beam used to fill the through-holes.

[0045] Figure 12A Graphs showing changes in welding light signal output and laser output.

[0046] Figure 12B Graphs showing changes in welding light signal output and laser output.

[0047] Figure 13A This is a graph showing the output waveform of the welding light signal when perforation occurs during weaving welding.

[0048] Figure 13B It indicates the relative peak intensity Rp when perforation occurs and the actual hole diameter of the perforation. A graph showing an example of the relationship between .

[0049] Figure 13C It is swapped and displayed Figure 13B The vertical axis and horizontal axis of the graph are shown in the figure.

[0050] Figure 14AThis is a graph showing the relationship between the hole diameter of the through hole and the relative laser output required to fill the through hole.

[0051] Figure 14B This is a graph showing the relationship between the measured relative peak intensity Rp of the welding light signal and the relative laser output required for filling the through-hole.

[0052] Explanation of symbols

[0053] 1. Laser oscillator;

[0054] 2. Collimating optical system;

[0055] 3 dichroic mirror;

[0056] 4a, 4b galvanometer mirrors;

[0057] 5. Galvanometer control unit;

[0058] 6. Focusing optical system;

[0059] 7 processing table;

[0060] 8. Focusing optical system;

[0061] 9 photodetector;

[0062] 10 Overall Control Department;

[0063] 11 outer can;

[0064] 12 positive terminal;

[0065] 13 negative terminal;

[0066] 14 coiled body;

[0067] 15 positive electrode;

[0068] 16, 17 connecting parts;

[0069] 18. Insulating resin;

[0070] 19 sealing plate;

[0071] Fh perforation;

[0072] Fs resin foreign matter;

[0073] LB laser beam;

[0074] LH heat radiation light;

[0075] LW welding light;

[0076] M melting region;

[0077] Q-hole repair department;

[0078] Sa scanning motion;

[0079] Sb swing motion;

[0080] Sw Swing sweep;

[0081] W workpiece. DETAILED DESCRIPTION

[0082] In the past, to prevent weld defects such as perforations and unwelded parts, laser irradiation was performed twice using a single laser oscillator, or two laser oscillators were used to irradiate with two laser beams. This resulted in approximately twice the heat input to the workpiece compared to normal. Consequently, the thermal load on the workpiece was approximately doubled, and for products such as those with weak heat resistance near the weld, there was a problem of proneness to thermal damage. Furthermore, there were also issues such as productivity being doubled compared to single irradiation when welding was performed twice using a single laser oscillator, and equipment costs being increased compared to single irradiation when two laser oscillators were used for simultaneous irradiation.

[0083] Furthermore, even if the above-mentioned method is adopted, such welding defects cannot be completely prevented, and there is also a problem that even if such welding defects occur, they cannot be detected.

[0084] An object of the present invention is to solve the above-mentioned conventional problems and to provide a laser welding method and apparatus capable of efficiently achieving good welding quality.

[0085] Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. In addition, the present invention is not limited to the following embodiments. In addition, appropriate changes can be made within the scope of the present invention. Furthermore, combinations with other embodiments are also possible.

[0086] Figure 1 This is a block diagram showing the configuration of a laser welding device according to an embodiment of the present invention. The laser welding device includes a laser oscillator 1, a collimating optical system 2, a dichroic mirror 3, galvanometer mirrors 4a and 4b, a galvanometer mirror control unit 5, a focusing optical system 6, a processing table 7, a focusing optical system 8, a photodetector 9, and an overall control unit 10.

[0087] The laser oscillator 1 is composed of, for example, a gas laser such as a carbon dioxide laser, a YAG laser, a semiconductor laser, or a solid-state laser such as a fiber laser, and supplies a laser beam LB having a predetermined wavelength and a predetermined output. As an example, the laser beam LB is a continuous wave (CW) with a wavelength of 1070 nm. The laser oscillator 1 is connected to be able to communicate with the overall control unit 10, and the output of the laser beam LB can be controlled according to instructions from the overall control unit 10.

[0088] The collimating optical system 2 converts the laser beam LB supplied from the laser oscillator 1 into a parallel beam.

[0089] The dichroic mirror 3 has a characteristic of reflecting light in a specific wavelength range and transmitting light in a different wavelength range, and has a function of reflecting the laser beam LB and transmitting welding light LW described later.

[0090] Each galvano mirror 4a, 4b includes a reflective mirror and an angular displacement mechanism for positioning the reflective mirror at a desired rotation angle and / or rotating it at a desired angular velocity. The galvano mirror control unit 5 is connected to the overall control unit 10 so as to be able to communicate, and controls the rotation angle or angular velocity of each galvano mirror 4a, 4b individually according to the instructions from the overall control unit 10. For example, the galvano mirror 4a has a rotation angle along Figure 1 The function of scanning the laser beam LB in the X direction is shown in FIG. 4 . The galvanometer mirror 4 b has a function of scanning the laser beam LB in the X direction. Figure 1 By combining the two, the trajectory of the laser beam LB can be scanned according to the Lissajous figure, which is a figure that defines the two-dimensional coordinates (X, Y) according to the following equations (1A) and (1B).

[0091] X=AX·cos(ωX·t)...(1A)

[0092] Y=AY·sin(ωY·t+Δ)...(1B)

[0093] Here, AX is the amplitude of the X component, ωX is the angular velocity of the X component, AY is the amplitude of the Y component, ωY is the angular velocity of the Y component, and Δ is the phase difference between the X and Y components. As an example, when AX = AY, ωX = ωY, and Δ = 0, circular motion is represented. As another example, when AX ≠ AY, ωX = ωY, and Δ = 0, elliptical motion is represented.

[0094] The focusing optical system 6 focuses the laser beam LB scanned by the galvanometer mirrors 4a and 4b, forming a light spot of a predetermined shape on the surface of the workpiece W. A large amount of thermal energy is input into the irradiated area of ​​the light spot, and the portion exceeding the melting point becomes a molten area, thereby welding the workpiece W. In this embodiment, the end surface welding of a cylindrical battery is exemplified as the workpiece W, but the present invention is not limited to this.

[0095] The processing table 7 includes an XYZθ table and is connected to the overall control unit 10 for communication. The processing table 7 can control the three-dimensional position of the workpiece W and the angle of the laser beam LB around the optical axis according to instructions from the overall control unit 10 .

[0096] When welding the workpiece W, welding light LW (dashed line in the figure) is radiated from the molten area of ​​the workpiece W. The welding light LW includes thermal radiation light, plasma light, laser reflection light, etc. A portion of the welding light LW passes through the focusing optical system 6, the galvanometer mirrors 4a and 4b, the dichroic mirror 3, and the focusing optical system 8 and enters the light detector 9. In addition, to facilitate understanding, Figure 1 The welding light LW is drawn offset from the laser beam LB, but in reality, both lights are substantially coaxial.

[0097] Photodetector 9 includes a photodiode, an A / D converter, and the like, and is connected to enable communication with overall control unit 10. Its detection signal is input to overall control unit 10. Photodetector 9 has the function of detecting welding light LW and converting it into an electrical signal proportional to the intensity of welding light LW.

[0098] The overall control unit 10 is composed of a computer including a processing unit, a memory, a large-capacity storage device, etc., and performs various actions according to a pre-set program, for example, oscillation control of the laser oscillator 1, laser output control, synchronization control with the galvanometer control unit 5, signal processing from the light detector 9, etc.

[0099] Figure 2 : is a cross-sectional view showing an example of a welding portion of a workpiece W. Here, a cylindrical battery is exemplified as the workpiece W. Inside the outer can 11 of the cylindrical battery, a winding body 14 in which a positive electrode sheet, a negative electrode sheet, and a separator interposed therebetween are wound together, and an electrolyte solution for battery reaction is contained. A positive electrode tab 12 is joined to the inner periphery of the winding body 14, and a negative electrode tab 13 is joined to the outer periphery of the winding body 14. The positive electrode tab 12 is connected to the positive electrode 15 via a connecting portion 16, and the negative electrode tab 13 is connected to the outer can 11 via a connecting portion 17. A sealing plate 19 containing the positive electrode 15 and an insulating resin 18 for electrically insulating the positive electrode 15 is inserted into the opening at the top of the outer can 11.

[0100] In this embodiment, as an example, a case is described where the outer peripheral surface of the sealing plate 19 and the butting surface at the inner upper end of the outer can 11 are welded by laser beam irradiation, but the present invention is not limited thereto.

[0101] When the laser beam LB is irradiated on the circular boundary between the outer can 11 and the sealing plate 19, the butting surface of the outer can 11 and the sealing plate 19 melts, forming a molten area M. In this state, if the laser beam LB is made to perform a circular scanning motion Sa along the butting surface, the cylindrical outer can 11 and the circular sealing plate 19 are joined over the entire circumference. Figure 2 In the figure, for simplification, the laser beam LB is drawn to scan in a simple circular scanning motion Sa, but the actual scanning trajectory is shown in FIG. Figure 3A as well as Figure 3B .

[0102] Figure 3A 1 is an explanatory diagram showing an example of wobbling scanning Sw based on a combination of circular scanning motion Sa and wobbling motion Sb. Figure 3B This is an illustration of the swing motion Sb. The trajectory of the swing motion Sb by the laser beam LB can be scanned according to a Lissajous figure. The Lissajous figure is defined by the following equations (2A) and (2B) as a graph of two-dimensional local coordinates (x, y) with an arbitrary point in the scanning motion Sa as the reference point P.

[0103] x=Bx·cos(ωx·t)...(2A)

[0104] y=By·sin(ωy·t+δ)...(2B)

[0105] Here, Bx is the amplitude of the x-component, ωx is the angular velocity of the x-component, By is the amplitude of the y-component, ωy is the angular velocity of the y-component, and δ is the phase difference between the x-component and the y-component. For example, when Bx = By, ωx = ωy, and δ = 0, circular motion is represented. For another example, when Bx ≠ By, ωx = ωy, and δ = 0, elliptical motion is represented.

[0106] In this way, the trajectory of the laser beam LB is controlled to perform a swinging scan Sw based on a combination of a scanning motion Sa and a swinging motion Sb, wherein the scanning motion Sa moves along the first direction x parallel to the docking surface of the workpiece W, and the swinging motion Sb includes a first swinging component Bx along the first direction x and a second swinging component By along the second direction y perpendicular to the first direction x.

[0107] In the present embodiment, an optical system including the two galvano mirrors 4 a and 4 b and the galvano mirror control unit 5 and capable of performing oscillating scanning Sw of the laser beam LB is referred to as a oscillating scanning optical system.

[0108] Next, a description will be given of the scanning trajectory viewed from above the outer can 11 of the cylindrical battery, that is, from the direction of laser beam irradiation. Figure 4A This is the state before welding, and a sealing plate 19 containing a positive electrode 15 and an insulating resin 18 is inserted into the opening of the outer can 11. Figure 4B As shown, the outer can 11 and the sealing plate 19 are joined together by irradiating the outer can 11 and the sealing plate 19 with a laser beam LB while performing a circular scanning motion Sa. Figure 4C As shown in FIG, the laser beam LB is rotated and moved along the circumference while performing the swing scanning Sw. As a result, as shown in FIG. Figure 4DAs shown, the cylindrical outer can 11 and the circular sealing plate 19 are joined via a fusion region M over a wide range along the entire circumference.

[0109] Below, using Figures 5A to 5C The linear scanning model shown is used for explanation to facilitate understanding of the relationship between the scanning trajectory of the laser beam LB and the bonding state. Figure 5A 1 and 2 are a top view and a cross section along line AA showing the positional relationship between the outer can 11 and the sealing plate 19 before laser welding. Figure 5B These are a top view and a cross-sectional view showing a joining state when the laser beam LB is subjected to a linear scanning motion Sa at the boundary portion between the outer can 11 and the sealing plate 19 . Figure 5C These are a top view and a cross-sectional view showing the bonding state when performing swing scanning Sw in which the laser beam LB is linearly scanned along the boundary between the outer can 11 and the sealing plate 19 while rotating the laser beam LB.

[0110] By performing the swing scanning Sw of the laser beam LB, the width of the molten region M becomes larger than that of the linear scanning, and as a result, higher bonding strength can be obtained.

[0111] Below, refer to Figures 6A to 6C This section describes the welding defects that can occur when laser welding is performed with foreign matter Fs trapped at the joint interface. Examples of foreign matter Fs at the joint interface include resin particles emanating from within the equipment or product components, and deposits of electrolyte contained within cylindrical batteries. Examples of welding defects include perforations, weld failures, and spattering. In particular, perforations and weld failures can cause serious defects in cylindrical batteries, potentially leading to leakage of the electrolyte within the battery.

[0112] Figures 6A to 6C The top view and cross-sectional view show the state where the resin foreign matter Fs is sandwiched between the bonding interfaces of the BB cross section. If the laser beam LB is subjected to a scanning motion Sa in this state to perform laser bonding, the portion without the resin foreign matter Fs is formed as shown in FIG. Figure 6B However, if the laser beam 2 is irradiated on the part where there is resin foreign matter Fs, the resin foreign matter Fs21 suddenly sublimates and expands explosively, and the surrounding molten parts are also blown to the outside, as shown in FIG. Figure 6C As shown, perforation Fh occurs in the molten area M.

[0113] Figures 7A to 7D 1 and 2 are top views and cross-sectional views showing how the laser beam LB is swung and scanned Sw. Figure 6C Similarly, if resin foreign matter Fs exists at the bonding interface, Figure 7CAs shown in FIG, the first irradiation with the laser beam LB may sometimes generate a hole Fh. In contrast, when the swing scan Sw is performed, the laser beam LB returns to the portion melted once, and the second irradiation with the laser beam LB is performed. Therefore, if the hole Fh is small, the hole Fh may be refilled by the second irradiation. However, if the hole Fh is large, the hole Fh may be reduced by the second irradiation, but as shown in FIG. Figure 7D As shown, sometimes it is not completely backfilled and some residue remains.

[0114] Next, as welding failure during laser welding, use Figures 8A to 8D A method of detecting the occurrence of the perforation Fh will be described. Figure 8A It is a top view showing a state in which a punch hole Fh occurs. Figure 8B It is shown in Figure 1 FIG. 1 is a graph showing temporal changes in the signal output of welding light LW generated from the molten region M during laser welding in the laser welding device shown.

[0115] Here, as the welding light LW, the thermal radiation light LH with a wavelength in the infrared region, for example, a wavelength of 1300 nm, is monitored. The intensity of the thermal radiation light LH depends on the temperature and surface area of ​​the molten area M, and can detect sudden temperature changes in the molten area M. Figure 8B It can be seen that the signal intensity in the first half is almost constant, but a sudden change in peak intensity occurs in the second half. Figure 8C As shown in the AA cross-sectional view, the signal intensity of the thermal radiation light LH corresponding to the normal melting state of the molten region M is emitted. On the other hand, the sudden peak intensity portion in the latter half, such as Figure 8D As shown in the BB cross-sectional view, this corresponds to the occurrence of a perforation Fh. When a perforation Fh occurs in the molten region M, the thermal radiation light LH becomes abnormally large due to sublimation of resin foreign matter Fs and splashing of the molten portion. Therefore, by measuring and analyzing the signal intensity of the thermal radiation light LH, it is possible to determine the occurrence of a weld defect, such as a perforation Fh. As an example of a method for determining whether welding is normal or abnormal, preliminary experiments are conducted to establish a relationship between the state of the perforation Fh and the signal intensity of the thermal radiation light LH. A certain judgment reference value is then set. Subsequently, a determination is made as to whether the actually measured signal intensity includes a peak intensity exceeding the judgment reference value, thereby enabling determination of weld defects.

[0116] As another example, plasma light in the visible light region emitted during laser welding can be monitored as welding light LW. If such a perforation Fh occurs, abnormal plasma light is generated from the molten region M, and such plasma light can be used as a detection signal.

[0117] As another example, the reflected light of the laser beam LB reflected from the molten region M can be used as the welding light LW for monitoring. If a perforation Fh occurs in the molten region M, the molten shape changes. Therefore, by analyzing changes in the signal intensity of the reflected light of the laser beam, the occurrence of a perforation Fh can be determined.

[0118] Next, regarding the method of eliminating the defective through-hole Fh and making it a good product, specifically, regarding the method of making it a good product by backfilling the through-hole Fh with molten metal to repair it, the method is as follows: Figures 9A to 9F Provide explanation.

[0119] exist Figure 9A In FIG. 1 , the trajectory of the laser beam LB performing the swing scanning Sw shows a state in which a foreign matter Fs existing at the bonding interface is irradiated and a perforation Fh is generated. Figure 9B The state in which the swing scan Sw has advanced half a cycle is shown. It should be noted that during this period, the laser beam LB returns to the direction in which the welding has been performed on the processed surface of the workpiece (here, the outer can 11 and the sealing plate 19). Figure 9B The opposite direction ( Figure 9B to the left of the ). Figure 9C Shown from Figure 9B The oscillation scanning Sw is further advanced to a state of half a cycle. The trajectory of the laser beam LB advances to a state that is larger than that in Figure 9A The perforation Fh occurs more anteriorly ( Figure 9C The oscillation welding in this embodiment refers to a method of continuously welding by rotating the laser beam LB around the reference point of the scanning motion Sa and moving it in the welding direction. The trajectory of the laser beam LB becomes the oscillation scanning Sw.

[0120] As the parameters defining the swing scan Sw, Figure 9B as well as Figure 9C As shown, the rotation diameter D [mm], the rotation speed N [rps (revolutions / second)] of the laser beam LB, and the scanning speed V [mm / s] of the entire scanning motion Sa can be used. Figure 9C As shown, in the wobbling scan Sw, the wobbling pitch P [mm] by which the reference point of the rocking motion Sb moves in one cycle is expressed by the following equation (3).

[0121] P[mm]=V[mm / s] / N[rps]...(3)

[0122] Figure 9D Shown from Figure 9C Furthermore, the laser beam LB advances by one cycle. Figure 9E Shown from Figure 9D The laser beam LB then advances half a cycle. At this point, the laser beam LB is irradiated for the second time toward the perforation Fh. Before this second irradiation, the output of the laser beam LB is increased compared to the standard output, thereby enabling the laser beam LB to be in a state of being ... Figure 9A The metal around the generated perforation Fh melts more. As a result, there is a possibility that the molten metal will flow into the perforation Fh and fill and repair the perforation Fh. After the second irradiation, the output of the laser beam LB is reduced to the standard output again.

[0123] Figure 9F Shown from Figure 9E Furthermore, when the laser beam LB advances for half a period, the perforation Fh is eliminated and a hole repair portion Q is formed in its place.

[0124] When repairing a perforation Fh by laser re-irradiation, preliminary experiments can be conducted in advance to verify the extent to which the laser output can be increased to fill the perforation Fh. Then, when laser welding is performed on an actual product, if a perforation Fh actually occurs during weaving welding, laser irradiation can be performed to control the laser output verified in the preliminary experiments, thereby filling the perforation Fh.

[0125] Next, the timing for increasing or decreasing the laser output will be described with reference to FIG. 10 . Figure 10A It shows Figures 9A to 9F The graph shown is a graph of the time variation of the welding light signal during wobble welding. Figure 10B This is a graph showing the intensity change of the laser output for repairing the perforation Fh. The graph displays the period from before the perforation Fh occurs in the weaving welding to the point when the perforation Fh actually occurs and is filled, resulting in a good weld.

[0126] like Figure 10A As shown in FIG. 1 , at time T0, the signal intensity of the welding light signal has a peak intensity, and it can be observed that a perforation Fh has occurred. Figure 10A The time T0 at which the peak intensity is generated corresponds to Figure 9A In addition, Figures 9B to 9F The states correspond to Figure 10A For example, the moment when the laser beam LB returns to half a cycle by swing scanning Sw is Tb, and the moment when the laser beam LB returns to the position of the perforation Fh and the laser output increases is Te. In addition, at this moment Te, Figure 10AThe signal output at time t increases slightly with the increase in laser output, but it is clearly different from the peak intensity at time T0 when perforation Fh occurs. The slight increase in signal intensity at time Te cannot be mistaken for the peak intensity at time Th. Furthermore, the increase in signal intensity at time Te falls below the welding abnormality determination standard value obtained in the preliminary verification.

[0127] The time interval T1 [s] (= Tb - T0) between the time T0 at which the perforation Fh occurs and the time Tb at which the laser beam LB returns half a cycle by the oscillating scanning Sw is expressed by the following equation (4).

[0128] T1[s]=(1 / 2) / N[rps]...(4)

[0129] Furthermore, let T2 be the time interval between the time Tb at which the laser beam LB returns half a cycle through the oscillating scan Sw and the central time Te at which the laser beam 2 returns to the position of the perforation Fh and the laser output increases. During this time interval T2, the number of times K that the laser beam LB rotates around the reference point while performing the oscillating scan Sw is expressed by the following equation (5).

[0130] K[rotation]=ROUND(D[mm] / P[mm])...(5)

[0131] Here, ROUND() is a function that rounds off the decimal point of the number in the parentheses to an integer. For example, ROUND(2.4) is the integer 2, and ROUND(4.6) is the integer 5.

[0132] It should be noted that the laser beam LB inevitably returns to the vicinity of the perforation Fh through the swing scanning Sw, so the number of rotations K of the laser beam LB is an integer. Therefore, the calculation result based on the calculation formula D [mm] / P [mm] needs to be rounded to an integer.

[0133] Furthermore, the time T2 [s] during which the laser beam LB performs K [rotations] is expressed by the following equation (6).

[0134] T2[s]=K[rotation] / N[rps]...(6)

[0135] Furthermore, according to equations (3), (5), and (6), the laser beam LB performs K [rotations] for a time T2 [s], and the rotation diameter D [mm], rotation speed N [rps], and overall scanning speed V [mm / s] of the laser beam LB are used to express it as the following equation (7).

[0136] T2[s]=ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps]...(7)

[0137] Moreover, the time interval T from the moment T0 when the perforation Fh occurs to the central moment Te when the laser beam LB returns to the position of the perforation Fh and the laser output increases is the sum of T1 and T2. According to equations (4) and (7), the rotation diameter D [mm], the rotation speed N [rps], and the overall scanning speed V [mm / s] of the laser beam LB are used to express it as the following equation (8).

[0138] T[s]=T1+T2=(1 / 2) / N[rps]+ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps]...(8)

[0139] Next, use Figures 11A to 11E Specifically, it will be described at which stage the laser output is gradually increased and at which stage the laser output is reduced to the standard condition. Figures 11A to 11E Show that Figures 9D to 9F The scanning state is further divided into every 1 / 4 period. In addition, the output change of the welding light signal and the laser output change at this time are shown in FIG. Figure 12A as well as Figure 12B .also, Figures 11A to 11E Corresponding to Figure 12B At the moment Ta~Te. Figure 10B In the example shown in Figure 2, the laser output is suddenly increased or decreased around the center time Te. In this case, although the through-hole Fh is filled, the sudden increase in laser output may cause spattering or unstable melting. To ensure a stable welding state even with changes in laser output, it is preferable to gradually increase and decrease the laser output.

[0140] Specifically, at the timing before the laser beam LB returns ( Figure 11B ), the increase of laser output needs to be started at least at the timing of the position of the aiming hole Fh ( Figure 11C ) is increased to the desired laser output state. On the contrary, even at the timing before the laser beam 2 returns ( Figure 11B ) increases the laser output, but does not contribute much to the repair of the perforation Fh.

[0141] Furthermore, after the laser beam LB passes through the through-hole Fh, the laser output is gradually reduced, preferably at a timing before entering a new joining portion ( Figure 11D ) Completes the restoration of the laser output to the standard. On the contrary, even if the laser output continues to increase after passing through the through-hole Fh, the contribution to the repair of the through-hole Fh is not significant.

[0142] The laser output changes at this time as Figure 12BAs shown, the time when the laser output starts increasing is Tb, and the time when the laser output decreases and returns to the original standard output is Td. The time interval between the time Tb when the laser output starts increasing and the time Tc when the position of the perforation Fh is targeted is D1, and the time interval between the time Tc when the position of the perforation Fh is targeted and the time Td when the laser output has completely returned to the standard output is D2. Furthermore, based on the time T0 when the perforation Fh occurs, the time interval from time T0 to the time Tb when the laser output starts increasing is Tstart, and the time interval from time T0 to the time Td when the laser output has completely returned to the standard output is Tend.

[0143] In this embodiment, as an example, both time intervals D1 and D2 are set to 1 / 4 of a period, which is expressed by the following formula (9).

[0144] D1[s]=D2[s]=(1 / 4) / N[rps]...(9)

[0145] In addition, the start time Tstart of the increase in laser output based on time T0 and the time Tend for the laser output to return to the original standard output are expressed by the following equations (10) (11) using the rotation diameter D [mm], rotation speed N [rps], and overall scanning speed V [mm / s] of the laser beam LB according to equations (8) (9).

[0146] Tstart[s]=(1 / 4) / N[rps]+ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps]...(10)

[0147] Tend[s]=(3 / 4) / N[rps]+ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps]...(11)

[0148] Next, use Figures 13A to 13C and Figures 14A and 14B The following describes how much the laser output can be increased to fill the through-hole Fh at the position where the through-hole Fh is irradiated.

[0149] Figure 13A This graph shows the output waveform of the welding light signal when perforation Fh occurs during weaving welding. In this figure, the signal output when perforation Fh occurs is referred to as peak intensity Ip, and the average value of the welding light signal when perforation Fh does not occur is referred to as average intensity Iav. Regarding peak intensity Ip, the absolute intensity is meaningless; the relative intensity relative to average intensity Iav is the most meaningful information. Specifically, the relative peak intensity Rp (=Ip / Iav), which measures how many times the peak intensity Ip exceeds the average intensity Iav, is important.

[0150] Figure 13B It indicates the relative peak intensity Rp when perforation Fh occurs and the hole diameter of the actual perforation Fh. According to this figure, the hole diameter The larger the relative peak intensity Rp, the larger the relative peak intensity Rp. That is, it can be inferred that the larger the relative peak intensity Rp, the larger the perforation Fh. In addition, in this case, no diameter The following perforation Fh is considered to be not caused by the surface tension of the molten area. The following tiny perforations Fh.

[0151] Furthermore, when perforation Fh occurs, the relative peak intensity Rp becomes greater than "2." Therefore, for example, the perforation Fh determination criterion value is preferably set to a value smaller than the relative peak intensity "2," such as "1.5." When this determination criterion value is exceeded, it can be determined that perforation Fh is likely to occur. On the other hand, when perforation Fh does not occur, the signal intensity does not exceed 1.5 times the average intensity Iav.

[0152] exist Figure 13B The dotted line approximates the lower limit of the relative peak intensity relative to the aperture. The vertical and horizontal axes of the dotted line graph are swapped to show the Figure 13C , represents the maximum pore size relative to the measured relative peak intensity.

[0153] Then, when a hole Fh is formed in the molten area, an example of a graph showing the output level at which the hole Fh can be filled by laser irradiation is as follows: Figure 14A The vertical axis shows the relative laser output, which indicates the relative laser output relative to the standard laser output, in "%." For example, when the relative laser output is 100%, the laser output is the same as the standard laser output. Furthermore, when the relative laser output is 120%, the laser output is 20% greater than the standard laser output. The horizontal axis shows the diameter of the perforation Fh.

[0154] If you refer to Figure 14A For example, when the hole diameter is as small as 50μm, the hole can be filled even with the standard laser output. However, if the hole diameter increases to 200μm, 125% of the standard laser output is required (a 25% increase in output).

[0155] Figure 14B according to Figure 13C and Figure 14AThe graph is obtained by combining the relative peak intensity Ip and the relative peak intensity Rp, which is an example of a graph showing the degree of laser output required to fill the hole Fh. For example, when the relative peak intensity Rp is "2" when the hole Fh occurs, it can be seen that it is sufficient to irradiate with a laser output of 110% of the standard laser output. More specifically, when the relative peak intensity Rp is "2", Figure 13C As shown in FIG, the maximum diameter of the hole Fh is estimated to be only 100 μm. Figure 14A , when the aperture is 100μm, the required laser output becomes 110%, which is the same as Figure 14B The laser output conditions obtained are the same.

[0156] That is, it is preferable that the increase ratio of the laser output also increases in proportion to the magnitude of the relative peak intensity Rp when the perforation Fh occurs. Specifically, as obtained in the prior verification Figure 14B As shown in the graph of FIG. 1 , the laser output can be determined by using the correlation graph between the relative peak intensity Ip and the laser output required for hole filling.

[0157] [Example]

[0158] Next, as a specific welding example, the effectiveness of the present invention was verified in the full-circumference welding of the outer can 11 and the sealing plate 19 of the aforementioned cylindrical battery.

[0159] Using a conventional laser welding method, laser scanning was performed in a circular pattern at a laser output of 1000W and a scanning speed of 500mm / s, welding the entire circumference. This resulted in a 20% probability of perforation Fh (i.e., perforation occurred in 2 of 10 workpieces). Causes of perforation Fh include foreign matter at the joint interface, residual electrolyte, gaps, and other factors.

[0160] In contrast, in the laser welding method according to the present invention, the laser output is 1000 W and the scanning speed V is 500 mm / s. Furthermore, as the oscillating scanning conditions, the rotation diameter D is 0.5 mm and the rotation speed N is 2000 rps.

[0161] In addition, at the same time, the luminous signal intensity of the welding light generated during laser welding is measured. When a peak intensity Ip is generated, as if perforation Fh is considered to have occurred, the relative peak intensity Rp is calculated relative to the average intensity Iav during normal welding. If it is above a predetermined judgment reference value (1.5 in this case), it is judged that a poor weld has occurred.

[0162] Furthermore, the time from the moment perforation Fh occurs to the moment the laser beam LB returns to the position of perforation Fh is 1.25 ms according to equation (8) for a rotation speed of 2000 rpm, a rotation diameter of 0.5 mm, and a welding speed of 500 mm / s. This means that after perforation Fh occurs, the laser beam LB returns 1.25 ms later.

[0163] Furthermore, with respect to the measured relative peak intensity Rp, Figure 14A The relative laser output required to fill the via was calculated using the graph. This was converted to actual laser output and increased during laser irradiation. The results showed that all 10 workpieces achieved good welds without a through hole (Fh), verifying the effectiveness of the present invention.

[0164] As described above, according to one embodiment of the present invention, good welding quality can be achieved efficiently. For example, according to this embodiment, when laser welding is performed by oscillating scanning, which rotates the laser beam LB along the joint interface while rotating on the weld surface, the occurrence of a poor weld such as a perforation is determined by detecting the welding light generated during laser welding. The timing at which the trajectory of the laser beam LB returns to the position where the poor weld occurred due to the oscillating scanning is calculated, and the laser output is increased at this timing to perform laser re-irradiation, thereby efficiently repairing a poor weld such as a perforation. Furthermore, good welding quality can be achieved with only this single oscillating scan, so there is no heat load applied as in the past, and no thermal damage occurs. In addition, since this single oscillating scan can be performed using a single laser oscillator, high productivity can be achieved, and equipment costs can be reduced.

[0165] In addition, in this embodiment, the butt welding of two workpieces is described as an example, but the present invention can also be applied to overlap welding and fillet welding of two workpieces. In addition, it is not limited to two workpieces, and the present invention can also be applied to various laser welding of three or more workpieces.

[0166] Furthermore, in the present embodiment, a perforation is exemplified as a welding defect, but the present invention is also applicable to cases of welding defects such as non-welding and occurrence of spatter.

[0167] In addition, in this embodiment, the case where the scanning motion Sa is a circular motion or a linear motion and the swinging motion Sb is a circular motion is illustrated, but as an alternative, the scanning motion Sa may be an elliptical motion, a rectangular motion, or other motion representing a Lissajous figure, and the swinging motion Sb may be an elliptical motion, a rectangular motion, or other motion representing a Lissajous figure.

[0168] As described above, the present invention can prevent weld defects such as perforations and unwelded parts from occurring when laser welding multiple workpieces together or overlapping them. For example, the present invention can be applied to the full-circumference welding of outer cans and sealing plates for cylindrical and prismatic batteries, achieving high-quality batteries without perforations or unwelded parts.

[0169] Industrial applicability

[0170] The present invention is extremely useful industrially in that it can efficiently achieve good welding quality.

Claims

1. A laser welding method for welding joint surfaces between a plurality of workpiece members by irradiating a laser beam, wherein the trajectory of the laser beam is controlled to perform oscillating scanning based on a combination of a scanning motion and a oscillating motion, wherein the scanning motion moves in a first direction parallel to the joint surfaces, and the oscillating motion includes a first oscillating component along the first direction and a second oscillating component along a second direction perpendicular to the first direction. The laser welding method comprises: a defect determination step of determining the occurrence of a welding defect during the execution of the swing scan and determining a defective portion where the welding defect occurs; and The output control step increases or decreases the output of the laser beam when a welding defect occurs and the trajectory of the laser beam returns to the defective portion by the oscillation scanning.

2. The laser welding method according to claim 1, wherein: In the failure determination step, welding light generated from the molten region of the joining surface is detected, and occurrence of a welding failure is determined based on a detection signal of the welding light.

3. The laser welding method according to claim 2, wherein: In the failure determination step, it is determined that a welding failure has occurred when the detection signal is larger than a predetermined determination reference value.

4. The laser welding method according to any one of claims 1 to 3, wherein: In the output control step, the output of the laser beam is increased before the laser beam passes through the defective portion again, and the output is reduced after the laser beam passes through the defective portion.

5. The laser welding method according to claim 4, wherein: In the output control step, the output of the laser beam is increased in proportion to the magnitude of the relative peak intensity, and the relative peak intensity is obtained by dividing the peak intensity of the detection signal of the welding light generated when poor welding occurs by the average intensity of the detection signal of the welding light when no poor welding occurs.

6. The laser welding method according to claim 4, wherein: The scanning motion has a scanning speed V, The rocking motion is a circular motion with a rotation diameter D and a rotation speed N centered on the reference point of the scanning motion. The timing at which the laser beam passes through the defective portion again is calculated using the rotation diameter D, the rotation speed N, and the scanning speed V.

7. The laser welding method according to claim 6, wherein: The time interval T [s] from the time when the welding failure occurs to the central time when the output of the laser beam increases when the laser beam passes through the position where the welding failure occurs again satisfies the following formula: T[s]=(1 / 2) / N[rps]+ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps] Here, ROUND() is a function that rounds off the decimal places in the brackets to integers, D is the rotation diameter of the laser beam in mm, N is the rotation speed of the laser beam in rps, and V is the scanning speed of the laser beam in mm / s.

8. The laser welding method according to claim 7, wherein: The time Tstart from the time when the welding failure occurs to the start of the increase in laser output and the time Tend until the laser output returns to the original state satisfy the following formula: Tstart[s]=(1 / 4) / N[rps]+ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps] Tend[s]=(3 / 4) / N[rps]+ROUND(D[mm]×N[rps] / V[mm / s]) / N[rps].

9. A laser welding device comprising: a laser oscillator, supplying a laser beam; A focusing optical system for focusing the laser beam onto the joint surfaces between the multiple workpiece components; an oscillating scanning optical system for controlling the position of the laser beam so that the trajectory of the laser beam performs oscillating scanning based on a combination of a scanning motion and a oscillating motion, wherein the scanning motion moves along a first direction parallel to the bonding surface, and the oscillating motion includes a first oscillating component along the first direction and a second oscillating component along a second direction perpendicular to the first direction; a defect determination unit that determines the occurrence of a welding defect during the execution of the oscillating scan and identifies a defective portion where the welding defect has occurred; and The output control unit increases or decreases the output of the laser beam when a welding defect occurs and the trajectory of the laser beam returns to the defective portion by the oscillation scanning.

10. The laser welding device according to claim 9, wherein: The defect determination unit includes: a welding light detection unit that detects welding light generated from a molten region of the joint surface; and The signal processing unit determines the occurrence of welding failure based on the detection signal of the welding light.

11. The laser welding device according to claim 9 or 10, wherein: The laser welding method according to any one of claims 1 to 8 is performed.

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