Patent Application
20210394305
The present disclosure relates to a laser welding method and an apparatus.
In a case where laser welding is performed by abutting or superimposing a plurality of workpieces on each other, when a foreign matter or a gap is present at a joining interface, there is a possibility that a welding defect of a hole or an unwelded portion may occur.
As a countermeasure against this, in the related art, occurrence of a welding defect is prevented by performing a second laser irradiation at a same location with just focus, after defocusing and melting a workpiece widely during a first laser irradiation using one laser oscillator (Japanese Patent No. 5224349). In addition, in another technique in the related art, the occurrence of welding defect is prevented by simultaneously irradiating the same welded portion of a workpiece with two laser beams from different directions using two laser oscillators (Japanese Patent Unexamined Publication No. 2019-5760).
According to an aspect of the present disclosure, there is provided a laser welding method of welding a joint surface between a plurality of workpiece members by emitting a laser beam, a locus of the laser beam being controlled so as to perform wobbling scanning by a combination of (i) a scanning motion moving along a first direction parallel to the joint surface and (ii) a swing motion including a first swing component along the first direction and a second swing component along a second direction perpendicular to the first direction. the method includes a defect determination step of determining occurrence of a welding defect; and an output control step of increasing or decreasing an output of the laser beam to be emitted again toward the welding defect when occurrence of the welding defect is determined in the defect determination step.
In addition, according to another aspect of the present disclosure, there is provided a laser welding apparatus that includes a laser oscillator that supplies a laser beam; a condensing optical system that condenses the laser beam on a joint surface between a plurality of workpiece members; a wobbling scanning optical system that controls a position of the laser beam so that a locus of the laser beam performs wobbling scanning by a combination of a scanning motion moving along a first direction parallel to the joint surface and a swing motion including a first swing component along the first direction and a second swing component along a second direction perpendicular to the first direction; a defect determination unit that determines occurrence of a welding defect; and an output controller that increases or decreases an output of the laser beam when the laser beam is radiated again toward the welding defect in a case where the welding defect occurs.
In the related art, in order to prevent a welding defect of a hole or an unwelded portion, since one laser oscillator is used to irradiate the laser twice, or two laser oscillators are used to irradiate with two laser beams, approximately twice as much energy as normal is input to a workpiece. Therefore, a thermal load on the workpiece is approximately doubled, and for example, there is a problem that thermal damage is likely to occur in a product in which a weakly heat-resistant component is in the vicinity of a welded portion. In addition, when laser irradiation is performed twice using one laser oscillator and welding is performed, the productivity is twice as low as that of one irradiation, and when two laser oscillators are used to irradiate at the same time, there is also a problem that the equipment cost increases as compared with the one irradiation.
Furthermore, even when the above-described method is adopted, there is a problem that such a welding defect cannot be completely prevented, and even when such a welding defect occurs, the welding defect cannot be detected.
The present disclosure solves the above-described problems in the related art, and an object thereof is to provide a laser welding method and an apparatus capable of efficiently achieving good welding quality.
Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the following exemplary embodiments. In addition, the present disclosure can be appropriately changed as long as the present disclosure does not deviate from the range in which the effect of the present disclosure is exhibited. Furthermore, the present disclosure can be combined with other exemplary embodiments.
Laser oscillator 1 includes, for example, a gas laser such as a carbon dioxide gas laser, a solid-state laser such as a YAG laser, a semiconductor laser, or a fiber laser, and supplies laser beam LB having a predetermined wavelength and a predetermined output. As an example, laser beam LB is a continuous wave (CW) having a wavelength of 1070 nm. Laser oscillator 1 is communicatively connected to overall controller 10, and the output of laser beam LB can be controlled in response to a command from overall controller 10.
Collimated optical system 2 converts laser beam LB supplied from laser oscillator 1 into a parallel beam.
Dichroic mirror 3 has a property of reflecting light in a specific wavelength range and transmitting light in a different wavelength range, and here, dichroic mirror 3 has a function of reflecting laser beam LB and transmitting welding light LW described later.
Each of galvanometer mirror 4a and 4b is provided with a reflection mirror and an angular displacement mechanism that positions the reflection mirror at a desired angle of rotation and/or rotates the reflection mirror at a desired angular velocity. Galvanometer mirror controller 5 is communicatively connected to overall controller 10, and the angle of rotation or angular velocity of each of galvanometer mirrors 4a and 4b is individually controlled in response to a command from overall controller 10. For example, galvanometer mirror 4a has a function of scanning laser beam LB along the X direction illustrated in
X=AX·cos(ωX·t) (1A)
Y=AY·sin(ωY·t+Δ) (1B)
here, AX is the amplitude of X component, ωX is the angular velocity of 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 component and the Y component. As an example, in a case where AX=AY, ωX=ωY, and Δ=0, it represents a circular motion. As another example, in a case where AX≠AY, ωX=ωY, and Δ=0, it represents an elliptical motion.
Condensing optical system 6 condenses laser beam LB scanned by galvanometer mirrors 4a and 4b to form a light spot having a predetermined shape on the surface of workpiece W. A large amount of heat energy is applied to an irradiation region of the light spot, a portion exceeding the melting point is a molten region, and workpiece W is welded. In the present exemplary embodiment, end face welding of a cylindrical battery is exemplified as workpiece W, and the present disclosure is not limited thereto.
Machining table 7 includes a XYZθ stage, is communicatively connected to overall controller 10, and the three-dimensional position of workpiece W and the angle around the optical axis of laser beam LB can be controlled in response to a command from overall controller 10.
When welding workpiece W, welding light LW (broken line in the figure) is emitted from the molten region of workpiece W. Welding light LW includes thermal radiant light, plasma light, laser reflected light, and the like. A portion of welding light LW passes through condensing optical system 6, galvanometer mirrors 4a and 4b, dichroic mirror 3, and condensing optical system 8 and is incident on optical detector 9. In order to promote understanding, welding light LW is drawn shifted from laser beam LB in
Optical detector 9 includes a photodiode, an A/D converter, and the like, is communicatively connected to overall controller 10, and the detection signal thereof is input to overall controller 10. Optical detector 9 has a function of detecting such welding light LW and converting welding light LW into an electric signal proportional to the intensity of welding light LW.
Overall controller 10 includes a computer having an arithmetic processor, a memory, a mass storage, and the like, performs various operations according to a program set in advance, and for example, oscillation control of laser oscillator 1, laser output control, synchronous control with galvanometer mirror controller 5, signal processing from optical detector 9, and the like are performed.
In the present exemplary embodiment, as an example, a case where an abutting surface between the outer peripheral surface of sealing plate 19 and the upper end of the inner surface of exterior can 11 is welded by laser beam irradiation is described, and the present disclosure is not limited thereto.
When a circular boundary portion between exterior can 11 and sealing plate 19 is irradiated with laser beam LB, the abutting surface between exterior can 11 and sealing plate 19 is melted, and molten region M is formed. By performing circular scanning motion Sa along the abutting surface of laser beam LB in this state, cylindrical exterior can 11 and circular sealing plate 19 are joined over the entire circumference. In
x=Bx·cos(ωx·t) (2A)
y=By·sin(ωy·t+δ) (2B)
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. As an example, in a case where Bx=By, ωx=ωy, and δ=0, it represents a circular motion. As another example, in a case where Bx≠By, ωx=ωy, and δ=0, it represents an elliptical motion.
In this manner, the loci of laser beam LB is controlled to perform wobbling scanning Sw by a combination of scanning motion Sa moving along first direction x parallel to the abutting surface of workpiece W and swing motion Sb including first swing component Bx along first direction x and second swing component By along second direction y perpendicular to first direction x.
In the present exemplary embodiment, an optical system including two galvanometer mirrors 4a and 4b and galvanometer mirror controller 5 and capable of wobbling scanning Sw of laser beam LB is referred to as a wobbling scanning optical system.
Next, the scanning locus when viewed above exterior can 11 of the cylindrical battery, that is, from the laser beam irradiation direction will be described.
Hereinafter, a linear scanning model as illustrated in
By wobbling scanning Sw on laser beam LB, the width of molten region M increases as compared with the linear scanning, and as a result, higher joining strength can be obtained.
Next, with reference to
Next, a method of detecting the occurrence of hole Fh as a welding defect during the laser welding will be described with reference to
Here, as welding light LW, thermal radiant light LH having a wavelength in the infrared region, for example, a wavelength of 1300 nm is a monitoring target. The intensity of thermal radiant light LH depends on the temperature of molten region M and the surface area, and a rapid temperature change in molten region M can be detected. As can be found from
As another example, the plasma light in the visible light region emitted during the laser welding may be a monitoring target as welding light LW. When such hole Fh occurs, an abnormal plasma light occurs from molten region M, so that such plasma light can be used as a detection signal.
Furthermore, as another example, the reflected light reflected by laser beam LB in molten region M may be a monitoring target as welding light LW. When hole Fh occurs in molten region M, the molten shape is changed. Therefore, it is possible to determine the occurrence of hole Fh by analyzing the change in signal intensity of the reflected light of the laser beam.
Next, a method of eliminating generated hole Fh defect and joining a good product, specifically, a method of backfilling generated hole Fh with a molten metal to repair the hole and joining a good product, will be described with reference to
As parameters defining wobbling scanning Sw, as illustrated in
P[mm]=V[mm/s]/N[rps] (3)
In a case where hole Fh is repaired by laser re-irradiation, the repair can be verified by performing a preliminary experiment in advance whether hole Fh is filled how much the laser output is increased to irradiate. In a case where the laser welding is performed on the actual product, when hole Fh actually occurs during the wobbling welding, it is possible to perform laser irradiation so that hole Fh is filled by controlling the laser output verified in the preliminary experiment.
Next, the timing for increasing or decreasing the laser output will be described with reference to
As illustrated in
A time interval T1 [s] (=Tb−T0) between time T0 at which hole Fh occurs and time Tb at which laser beam LB returns for half a cycle by wobbling scanning Sw is represented by the following equation (4).
T1[s]=(½)/N[rps] (4)
Furthermore, the time interval between time Tb when laser beam LB returns for half a cycle by wobbling scanning Sw and central time Te when laser beam 2 returns to the position of hole Fh and the laser output is increased is defined as T2. The number of times K that laser beam LB rotates around the reference point during wobbling scanning Sw during this time interval T2 is represented by the following equation (5).
K[Rotation]=ROUND(D[mm]/P[mm]) (5)
here, ROUND ( ) is a function that rounds the numbers in a parenthesis to an integer after the decimal point. For example, ROUND (2.4) is an integer 2 and ROUND (4.6) is an integer 5.
It is noted here that laser beam LB always returns to the vicinity of hole Fh by wobbling scanning Sw, so that the number of rotations K of laser beam LB is an integer. Therefore, it is necessary to round off the calculation result by the calculation formula D [mm]/P [mm] to convert the calculation result into an integer.
In addition, time T2 [s] during which laser beam LB is K [rotated] is represented by the following equation (6).
T2[s]=K[rotation]/N[rps] (6)
Furthermore, according to the equations (3), (5) and (6), time T2 [s] during which laser beam LB is K [rotated] is represented by the following equation (7) using rotation diameter D [mm] of laser beam LB, rotation speed N [rps], and scanning speed V [mm/s] as a whole.
T2[s]=ROUND(D[mm]×N[rps]/V[mm/s])/N[rps] (7)
A time interval T from time T0 when hole Fh occurs to central time Te when laser beam LB returns to the position of hole Fh and the laser output is increased is the sum of T1 and T2, and is represented by the following equation (8) using rotation diameter D [mm] of laser beam LB, rotation speed N [rps], and scanning speed V [mm/s] as a whole from the equations (4) and (7).
T[s]=T1+T2=(½)/N[rps]+ROUND(D[mm]×N[rps]/V[mm/s])/N[rps] (8)
Next, specifically, from which stage the laser output may be gradually increased and by which stage the laser output may be decreased to the standard condition will be described with reference to
Specifically, it is necessary that the laser output starts to increase at the timing before laser beam LB returns (
Furthermore, it is preferable that the laser output is gradually reduced after laser beam LB is passed through hole Fh, and the laser output is returned to the standard laser output at the timing (
The change in the laser output at this time is illustrated in
In the present exemplary embodiment, as an example, time intervals D1 and D2 are both set to a quarter cycle and are represented by the following equation (9).
D1[s]=D2[s]=(¼)/N[rps] (9)
In addition, increase start time Tstart of the laser output and time Tend for returning the laser output to the original standard output with reference to time T0 are represented by the following equations (10) and (11) using rotation diameter D [mm] of laser beam LB, rotation speed N [rps], and scanning speed V [mm/s] as a whole from the equations (8) and (9).
Tstart[s]=(¼)/N[rps]+ROUND(D[mm]×N[rps]/V[mm/s])/N[rps] (10)
Tend[s]=(¾)/N[rps]+ROUND(D[mm]×N[rps]/V[mm/s])/N[rps] (11)
Next, how much the laser output is increased to irradiate the position portion of hole Fh to fill hole Fh will be described with reference to
Furthermore, relative peak intensity Rp when hole Fh occurs is “2” or more. Therefore, for example, it is preferable to set a numerical value smaller than the relative peak intensity “2”, for example, “1.5” as the determination reference value of hole Fh, and when the determination reference value is exceeded, it can be determined that there is a possibility that hole Fh occurs. On the other hand, the signal intensity when hole Fh does not occur is not equal to or greater than 1.5 times average intensity Iav.
In
Next, in a case where hole Fh occurs in the molten region,
Referring to
That is, it is preferable to increase the rate of increase in the laser output in proportion to a magnitude of relative peak intensity Rp when hole Fh occurs. Specifically, as illustrated in the graph of
Next, as a specific welding example, the effectiveness of the present disclosure was verified in the full-circled welding with exterior can 11 of the cylindrical battery and sealing plate 19 described above.
As a laser welding method in the related art, laser scanning was performed simply in a circumferential shape at a laser output of 1000 W and a scanning speed of 500 mm/s to perform the full-circled welding. At this time, hole Fh was generated with a probability of 20% (that is, holes were generated in 2 workpieces out of 10 workpieces). The cause of this hole Fh is due to a joining interfacial foreign matter, an electrolytic solution residual, a gap, and the like.
On the other hand, in the laser welding method according to the present disclosure, the laser output 1000 W and scanning speed V: 500 mm/s were the same, and the wobbling scanning conditions were rotation diameter D: 0.5 mm and rotation number N: 2000 rps.
In addition, at the same time, in a case where the emission signal intensity of the welding light generated during laser welding was measured, and peak intensity Ip in which hole Fh seems to be generated, relative peak intensity Rp with respect to average intensity Iav during the normal welding was calculated, and when it was equal to or higher than a predetermined determination reference value (1.5 in this case), it was determined that a welding defect was generated.
In addition, since the time from the time when hole Fh occurs until laser beam LB returns to the position of hole Fh is a rotation number of 2000 rpm, a rotation diameter of 0.5 mm, and a welding speed of 500 mm/s, the time is 1.25 ms from the equation (8). That is, it can be found that laser beam LB returns 1.25 ms after it is found that hole Fh occurs.
Furthermore, for measured relative peak intensity Rp, the relative laser output required for filling the holes was calculated using the graph of
As described above, according to an aspect of the present disclosure, good welding quality can be efficiently achieved. For example, according to the present exemplary embodiment, in a case where laser welding is performed by wobbling scanning in which the rotation motion is performed on the welding surface while moving laser beam LB along the joining interface, it is determined that a welding defect such as a hole occurs by detecting the welding light generated during the laser welding, the timing at which the locus of laser beam LB returns to the position where the welding defect occurs is calculated by the wobbling scanning, and at that timing, the laser output is increased and laser re-irradiation is performed. Therefore, the welding defect such as a hole can be efficiently repaired. Furthermore, since good welding quality can be obtained by only one wobbling scanning, no thermal load is applied and no thermal damage occurs as in the related art. In addition, since only one wobbling scanning is required using one laser oscillator, high productivity can be obtained and equipment cost can be reduced.
In the present exemplary embodiment, butt welding of two workpieces is described as an example, and the present disclosure can also be applied to lap welding or fillet welding of two workpieces. In addition, the present disclosure is not limited to two workpieces, and the present disclosure can be applied to various laser welding of three or more workpieces.
In addition, in the present exemplary embodiment, a hole is exemplified as a welding defect, and the present disclosure can also be applied to a welding defect such as an unwelded portion or spatter generation.
In addition, in the present exemplary embodiment, although the case where scanning motion Sa is a circular motion or a linear motion and swing motion Sb is a circular motion is illustrated, as an alternative, scanning motion Sa may be an elliptical motion, a rectangular motion, or any other motion indicating a Lissajous figure, and swing motion Sb may be an elliptical motion, a rectangular motion, or any other motion indicating a Lissajous figure.
As described above, according to the present disclosure, it is possible to prevent welding defects of the hole or an unwelded portion that occur when laser welding is performed by abutting or superimposing a plurality of workpieces. The present disclosure can be applied to, for example, the full-circled welding of an exterior can of a cylindrical battery or a square battery and a sealing plate, and a high-quality battery without a hole or an unwelded portion can be realized.
The present disclosure is significantly useful in industry in that good welding quality can be efficiently achieved.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-106450 | Jun 2020 | JP | national |
