JP2019126832A - Laser welding method - Google Patents

Abstract

To provide a method which is high in inspection accuracy, in the laser welding method including a step of inspecting and correcting positional displacement.SOLUTION: This laser welding method includes: a step of forming a circumferential weld mark by scanning a laser beam in a circumferential shape on a surface of a workpiece by using a laser welding device so that a non-welded part remains in a center; a step of inspecting an image by photographing the circumferential weld mark by an image inspection camera, and grasping a center position of the weld mark on the basis of an external peripheral circle and an internal peripheral circle of the weld mark; a step of calculating a set center position of the laser beam of the laser welding device and a displacement amount of the center position which is grasped by the image inspection; a step of correcting the center position of the laser beam of the laser welding device on the basis of the calculated displacement amount; and a step of welding the workpiece.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser welding method.

  In recent years, secondary batteries such as lithium ion secondary batteries and nickel hydrogen batteries are preferably used as so-called portable power sources such as personal computers and portable terminals and power sources for driving vehicles. Among such secondary batteries, a lithium-ion secondary battery that is lightweight and has a high energy density is a high-output power source used in vehicles such as electric vehicles and hybrid vehicles (for example, a motor connected to a driving wheel of the vehicle). Especially as a power source).

  Such a secondary battery is constructed, for example, as a sealed battery in which an electrode body is accommodated in a sealed battery case. The battery case of the sealed battery is composed of a case main body in which an opening is formed and a plate-like lid which closes the opening of the case main body. When manufacturing the sealed battery having the above-described structure, first, the members constituting the electrode terminal are assembled to the lid, and the electrode body is accommodated inside the case main body. Then, after a plate-like lid is fitted into the opening of the case main body, the peripheral edge of the opening of the case main body and the outer peripheral edge of the lid are welded by laser.

  For laser welding, as described in Patent Document 1, for example, a laser welding apparatus including a laser oscillator and a galvano scanner is used. Patent Document 1 describes a laser processing method for performing positional deviation correction with high accuracy. Specifically, it is described that an actual position is obtained by imaging the processing point where the laser light is irradiated to the galvanic origin with an imaging device and inspecting the image at the irradiation position of the laser light. Further, it is described that a correction value for correcting an offset distance between the imaging device and the laser head and a correction value for correcting distortion of the fθ lens are calculated.

Unexamined-Japanese-Patent No. 2004-276101

  A welding mark is formed at the processing point irradiated with the laser beam. In the case where the laser light irradiation is pulse irradiation, the instability of the oscillator causes the welding mark to become shallower or deeper and the depth and area change. The changes in depth and area affect the inspection accuracy when an image inspection is performed by imaging a weld mark with an imaging device as described above. Therefore, the conventional method has room for improvement in inspection accuracy.

  Therefore, an object of the present invention is to provide a method with high inspection accuracy in a laser welding method including performing inspection and correction of misalignment.

The laser welding method disclosed herein forms a circumferential welding mark by scanning a laser beam circumferentially so that an unwelded portion remains in the center on the surface of a workpiece using a laser welding apparatus. A step of photographing the circumferential welding mark with an image inspection camera to perform an image inspection, and grasping a center position of the welding mark based on an outer circumference circle and an inner circumference circle of the welding trace, the laser A step of calculating a deviation amount between the center position of the laser beam set in the welding apparatus and the center position grasped by the image inspection, and based on the calculated deviation amount, the center position of the laser beam in the laser welding apparatus. A step of correcting, and a step of welding the workpiece.
According to such a configuration, the inspection accuracy can be improved because the center of the circle is obtained from the two circles of the outer circumferential circle and the inner circumferential circle of the welding mark at the time of image inspection. Therefore, according to such a configuration, a method with high inspection accuracy is provided in the laser welding method including the inspection and correction of misalignment.

It is a flowchart which shows each process of the laser welding method which concerns on one Embodiment of this invention. It is the schematic which shows an example of a structure of the laser welding apparatus used for the laser welding method which concerns on one Embodiment of this invention. It is a schematic diagram of an example of the welding mark formed at the laser scanning process of the laser welding method which concerns on one Embodiment of this invention. It is a schematic diagram of an example of the circumference by the setting of a laser welding apparatus.

  Hereinafter, a laser welding method according to an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same reference numerals are given to members and portions that exhibit the same action. Also, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In addition, matters other than the matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field.

  As shown in FIG. 1, the laser welding method according to the present embodiment uses a laser welding apparatus to scan a laser beam in a circumferential shape so that an unwelded portion remains at the center on the surface of a workpiece, Forming a welding mark (laser scanning process) S101, photographing the circumferential welding mark with an image inspection camera to perform image inspection, and based on the outer and inner circles of the welding mark Step of grasping the center position of the welding mark (image inspection step) S102, step of calculating a deviation amount between the center position of the laser beam set by the laser welding apparatus and the center position grasped by the image inspection (deviation amount) Calculation process) S103, a process (correction process) S104 for correcting the center position of the laser beam of the laser welding apparatus based on the calculated displacement amount, and a process for welding the work Welding process) S105 including,.

The laser welding method according to the present embodiment can be preferably performed using a laser welding apparatus including a laser oscillator, a galvano scanner, and an image inspection coaxial camera. Thus, FIG. 2 schematically shows an example of the configuration of a laser welding apparatus used for performing the laser welding method according to the present embodiment.
The laser welding apparatus 100 includes a laser oscillator 10 and a galvano scanner 20, as shown in FIG. The laser oscillator 10 is connected to the galvano scanner 20 by an optical fiber connector 11. A collimating lens 30 is disposed inside the galvano scanner 20. The galvano scanner 20 includes a first reflection mirror 21, a diffractive optical element (DOE) 22, a Z lens 23, a Z lens drive unit 24, a second reflection mirror 25, a condenser lens 26, a galvano scanner unit 27, and a protective glass 28. And a galvano scanner driver 29.
Further, the galvano scanner 20 is mounted with the coaxial mirror 50 for image inspection together with the dichroic mirror 40.

  When the laser beam is emitted from the laser oscillator 10, the laser beam penetrates into the inside of the galvano scanner 20 via the optical fiber connector 11. The laser light is adjusted to a parallel state by the collimating lens 30. Thereafter, the laser light is reflected by the dichroic mirror 40 and the first reflection mirror 21 to reach the DOE 22.

  The DOE 22 can adjust the irradiation pattern of the laser beam. Specifically, the DOE 22 can emit incident laser light as laser light having a power density distribution shape different from that when it is incident. Moreover, DOE22 is attached to the slide part and is comprised so that a slide movement is possible.

  The laser light adjusted by the DOE 22 reaches the Z lens 23. The Z lens 23 is used to correct a laser beam defocus. The Z lens 23 is configured to be movable by being driven by a Z lens driving unit 24.

Thereafter, the laser light is reflected by the second reflecting mirror 25, enters the galvano scanner unit 27 through the condenser lens 26, and is emitted to the surface of the workpiece 200 through the protective glass 28. A welding mark can be formed on the surface of the workpiece 200 by the emitted laser light. The welding mark can be observed and photographed by the coaxial camera 50 for image inspection along the same path as the laser light from the surface of the workpiece 200 to the dichroic mirror 40.
The galvano scanner driver 29 is connected to the laser oscillator 10, the Z lens driving unit 24, and the galvano scanner unit 27, and is configured to be able to control them by a built-in program. Therefore, the galvano scanner driver 29 can control the output of the laser light, the irradiation position, and the like.
Since such control is possible, the laser welding apparatus 100 is configured to be capable of automatic program operation.

  The configuration of the laser welding apparatus 100 described above is merely an example, and the laser welding apparatus 100 may have other configurations as long as the laser welding method according to this embodiment described below can be performed. Good.

  Next, each step of the laser welding method according to this embodiment will be described. In the following example, the case of welding a case body of a sealed battery in which an opening is formed and a plate-like lid closing the opening of the case body will be described.

First, the laser scanning step S101 is performed.
In the laser scanning step S101, a laser beam is scanned on the surface of the workpiece 200 using the laser welding apparatus 100 so that an unwelded portion remains at the center, thereby forming a circumferential welding mark. An example of welding marks formed in the laser scanning step S101 is schematically shown in FIG.
Specifically, for example, a laser beam is scanned circumferentially on the surface of the case lid as the workpiece 200 to form a circumferential welding mark 300 as shown in FIG. At this time, the laser beam continuously irradiates one circumference. The weld mark 300 is formed such that the surface of the workpiece 200 remains at the center (that is, there is a portion where no weld mark is formed). Therefore, the welding mark 300 has an inner circumference circle 310 and an outer circumference circle 320.
In addition, in this specification, a welding trace means the trace formed when the workpiece | work surface solidifies after melting | dissolving by irradiation of a laser beam, and it is not required that two members are joined.

Next, an image inspection step S102 is performed.
In the image inspection step S <b> 102, the circumferential weld mark 300 is photographed by the image inspection camera 50 to perform image inspection, and the center position of the weld mark 300 is based on the inner and outer circumferences 310 and 320 of the weld mark 300. Understand
Specifically, for example, first, the center B (x _B , y _B ) of the inner circumference circle 310 and the center C (x _c , y _c ) of the outer circumference circle 32 are obtained by Hough transformation or the like.
Then, using the two centers (center B and center C), the center D (x _D , y _D ) of the weld mark 300 is determined.

Hereinafter, a method of determining the center D (x _D , y _D ) of the weld mark 300 using the two centers (center B and center C) will be described.
Method (1): The midpoint of the center B and the center C is determined as the midpoint D.
Method (2): The fitting ratio of the inner circumference circle 310 and the fitting ratio of the outer circumference circle 320 of the welding mark 300 are respectively obtained and compared, and the center of the circle with the higher fitting ratio is set to the center D (x Adopted as _D , y _D ). (For example, when the fitting rate of the inner circumferential circle 310 of the weld mark 300 is 80% and the fitting rate of the outer circumferential circle 320 is 20%, the center B of the inner circumferential circle 310 having a high fitting rate is determined as the center D. .)
Method (3): Method (2): The fitting ratio of the inner circumference circle 310 of the weld mark 300 and the fitting ratio of the outer circumference circle 320 are determined respectively. A straight line connecting the centers B and C is drawn, and a point on the straight line, to which the fitting rate is added, is adopted as the center D (x _D , y _D ). (For example, when the fitting rate of the inner circle 310 of the weld mark 300 is 80% and the fitting rate of the outer circle 320 is 20%, when selecting the point on the above-mentioned line, B × 0.8 + C (Consider the fitting rate so that it becomes × 0.2.)

Here, as shown in FIG. 4, the center A (x _A , y _A ) and the radius r of the circumference drawn by the laser beam are determined by the setting of the laser welding apparatus 100 when scanning the laser beam in a circumferential shape. ing. The radius r is a scan radius. Further, the radius r1 of the inner circumference circle 410 and the radius r2 of the outer circumference circle 420 are also determined from the beam shape.
Therefore, in order to calculate the fitting rate, for example, the radius of the circle (inner circle or outer circle) set in the laser welding apparatus 100 when scanning the laser beam circumferentially, and the image inspection by the camera 50 are performed. The difference with the radius of the circle (inner circumference circle or outer circumference circle) obtained by the equation (4) may be obtained for one circumference.

Here, in the manufacturing process of the sealed battery, the workpiece 200 may be damaged during transportation. In addition, foreign matter generated by sliding, sputtering, or the like may adhere to the workpiece 200. If there is a disturbance such as a flaw or adhesion of foreign matter on the surface of the workpiece 200, the shape of the welding mark 300 becomes unstable due to these influences, and an error may occur when determining the position of the center D. . Therefore, in the present embodiment, it is preferable to determine the fitting rate of the inner circumference circle 310 of the weld mark 300 and the fitting rate of the outer circumference circle 320 and place the weight on the circle with the higher fitting rate to determine the center D. . Therefore, among the above, the method (2) and the method (3) are preferable.
When welding mark 300 is affected by a disturbance such as a flaw on the surface of workpiece 200 or the adhesion of a foreign substance, the fitting rate is reduced particularly in the disturbance portion, and therefore the fitting rate is determined when determining the position of center D. By placing weight on the higher circle, the influence of disturbance can be reduced.

Next, a deviation amount calculation step S103 is performed.
In the deviation amount calculation step S103, the deviation amount between the set center position of the laser beam of the laser welding apparatus 100 and the center position grasped by the image inspection is calculated. The set center position of the laser beam of the laser welding apparatus 100 is the position of the center A (x _A , y _A ) in FIG. 4, and the center position grasped by the image inspection is the center D (x _D , y _D ) position. Therefore, the amount of deviation is calculated by comparing these positions. The shift amount calculation step S103 can be implemented, for example, by incorporating a program for calculating the shift amount in the laser welding apparatus 100.

Next, the correction step S104 is performed.
In the correction step S104, the center position of the laser beam of the laser welding apparatus 100 is corrected based on the calculated deviation amount. Specifically, for example, the optical axis system is controlled by the galvano scanner driver 29 to control the center position of the laser beam, and the calculated deviation amount is corrected. The correction step S104 can be implemented, for example, by incorporating a program for correcting the amount of deviation in the laser welding apparatus 100.

Next, welding step S105 is performed.
In the welding step S105, the workpiece 200 is welded. Specifically, here, a lid is disposed in the opening of the case body so as to close the opening, and the peripheral edge of the opening of the case main body and the outer peripheral edge of the lid are welded by laser. Thereby, the battery case is sealed.

  According to the laser welding method according to the present embodiment, since the center of the circle is obtained from the two circles of the outer circumference circle and the inner circumference circle at the time of inspection, the inspection accuracy can be improved. In particular, by continuously irradiating the laser beam for one round, it is possible to obtain a stable welding mark which is not easily affected by the instability of the output of the laser oscillator 10. Therefore, according to such a configuration, a method with high inspection accuracy is provided in the laser welding method including inspection and correction of misalignment.

Hereinafter, the results actually examined by the inventor will be described.
In this study, the laser welding apparatus used was equipped with a 9-point DOE, 3D galvano scanner, and a coaxial camera. In addition, a battery case composed of a case main body and a case lid was prepared as a workpiece.

  Using this laser welding apparatus, welding marks were formed on the case lid. The beam diameter of the laser welding apparatus was φ152 μm. In Study Example 1, a laser beam was pulsed to form an “x” -shaped weld mark. In Study Example 2, the laser beam was continuously irradiated circumferentially to form a circular weld mark. The entire welding mark is formed as a welding mark, and thus the welding mark is also formed at the center of the circle. In Study Example 3, laser light was continuously irradiated circumferentially to form circumferential welding marks. In addition, the welding trace is not formed in the center of the circle. Therefore, Study Example 3 is an example in which the technique of the laser welding method according to the present embodiment is applied.

The formed weld mark was subjected to image inspection using a coaxial camera to determine the center of the weld mark. And position accuracy was computed from the detection position of the center of a welding mark. In Study Example 3, the position of the center is the center of the inner circumference circle and the middle point of the center of the outer circumference circle.
As a result, in Study Example 1, the detection accuracy was ± 25 μm, in Study Example 2 the detection accuracy was ± 22 μm, and in Study Example 3 the detection accuracy was ± 18 μm. Thus, according to the laser welding method according to the present embodiment, it could be confirmed that the detection accuracy is high.

Next, a foreign object was intentionally placed on the case lid, and laser light was continuously irradiated in a circumferential shape to form a circumferential welding mark. In addition, the welding trace is not formed in the center of the circle. Further, in this welding mark, deformation was seen in the outer circumference circle under the influence of foreign matter. Specifically, the outer peripheral circle bulged outward at the portion where the foreign matter was present.
The formed weld mark was subjected to image inspection using a coaxial camera to determine the center of the weld mark. And position accuracy was computed from the detection position of the center of a welding mark.
At this time, in the study example 4, the position of the center was set to the middle point of the center of the inner circumferential circle and the center of the outer circumferential circle. In Study Example 5, the center position was the center of the inner circle so as to exclude the inspection result of the outer circle affected by the foreign matter.
As a result, in Study Example 4, the detection accuracy was ± 38 μm, and in Study Example 5, the detection accuracy was ± 22 μm. Therefore, it can be seen that the accuracy is further improved when the fitting rate of the inner circle and the fitting rate of the outer circle of the welding mark are obtained, and the center is determined by placing importance on the circle with the higher fitting rate.

  Although the specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Reference Signs List 10 laser oscillator 11 optical fiber connector 20 galvano scanner 21 first reflection mirror 22 diffractive optical element (DOE)
23 Z lens 24 Z lens drive unit 25 second reflection mirror 26 focusing lens 27 galvano scanner unit 28 protective glass 29 galvano scanner driver 30 collimate lens 40 dichroic mirror 50 coaxial camera for image inspection 100 laser welding apparatus 200 work 300 welding mark 310 inner circumference circle 320 (of welding trace) outer circumference circle 410 (of welding trace) inner circumference circle 420 outer circumference circle

Claims (1)

Scanning the laser beam circumferentially so that an unwelded portion remains in the center on the surface of the workpiece using a laser welding apparatus, and forming a circumferential welding mark,
Taking a picture of the circumferential weld mark with an image inspection camera to perform image inspection, and grasping the center position of the weld mark based on the outer circumference and inner circumference of the weld trace,
Calculating a shift amount between the set center position of the laser beam of the laser welding apparatus and the center position grasped by the image inspection;
Correcting the center position of the laser beam of the laser welding apparatus based on the calculated displacement amount; and welding the workpiece.
Laser welding method, including:

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