JP2014024068A - Bead inspection method in laser welding and laser welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bead inspection method and a laser welding method, capable of stably performing quality determination of the whole of a weld bead or a wide range thereof while avoiding influence of a plume.SOLUTION: In a bead inspection method, after laser welding for a prescribed section is finished, in a state where heat remains in a weld bead within a range of the prescribed section, the weld bead is re-irradiated with a laser beam at a low energy density, and then an image of the weld bead is obtained while the weld bead is allowed to emit light by heat,. From the obtained image, quality determination of the weld bead is performed.

Description

  The present invention relates to a bead inspection method in laser welding and a laser welding method including an inspection step according to the method.

Laser welding is capable of high-speed processing, but in lap welding for plated steel sheets, hole defects due to vaporized metal gas or the like, and weld defects such as sink marks may occur at the end of welding due to the flow of molten metal. Therefore, conventionally, while strictly managing the welding conditions, it has been performed to monitor the welding location with an imaging means and determine in real time whether or not there is a welding defect and the quality of the weld bead through image analysis or the like (Patent Document 1). reference).

  In this case, it is difficult to determine the quality of the weld bead directly in the vicinity of the laser irradiation point due to the high-luminance plume or spatter, so the effect of the plume or the like can be reduced by optical conditions or image processing. Has been studied. However, when the amount of plume ejection is large, such as three-ply welding, the influence of the plume cannot be completely eliminated, and there is a problem that the image processing process becomes complicated.

  Therefore, in order to avoid the influence of the plume, a method has been proposed in which an image of the weld bead is acquired in a state in which heat emission from the metal remains immediately after the end of laser welding, not during laser welding, and the quality is determined. (See Patent Document 2). However, this method is limited to the quality determination of the weld bead end portion where thermoluminescence remains, and for other portions, the light emission ends with a decrease in temperature, or there is a large luminance difference between the end portion and the start end side. Therefore, it is impossible to make a judgment including the entire weld bead.

JP 2006-43741 A JP 2012-45610 A

  The present invention has been made in view of such a situation of the prior art, and the object thereof is a bead inspection capable of stably performing pass / fail judgment of the entire weld bead or a wide range while avoiding the influence of the plume. It is to provide a method and a laser welding method.

  In order to solve the above-described problem, a welding bead inspection method according to the present invention is a laser having a low energy density on a weld bead in a state where residual heat is present in the weld bead over the predetermined section after the laser welding of the predetermined section is completed. , The weld bead is imaged while thermally emitting light, and the quality of the weld bead is determined from the obtained image.

  According to the above method, after laser welding is completed, reirradiation with a laser having a low energy density in a state of having residual heat, the heat input of reirradiation is added to the residual heat of the weld bead, and appropriate thermoluminescence is obtained. In addition, it is possible to carry out a pass / fail judgment inspection of the weld bead without depending on complicated image processing or the like. Moreover, since imaging is performed while re-irradiating (simultaneously or immediately after re-irradiation), the laser to be re-irradiated may have the minimum energy density, and spatter and plume do not occur, and a good image can be stably obtained. In addition, laser scanning can be performed at as high a speed as possible in a short time, and there is almost no influence on the overall processing time due to the addition of the reirradiation step.

  In the present invention, it is preferable that the laser re-irradiation is performed at a higher speed than the optical axis scanning during the laser welding. The heat input to the workpiece by laser irradiation is a function of energy density and speed (time) and is generally proportional to the laser output and inversely proportional to the spot diameter and speed. Therefore, in terms of shortening the processing time, it is advantageous to obtain a desired energy density by speed control rather than output control.

  In the present invention, the laser re-irradiation may be performed within the width of the welding bead and shifted from the optical axis scanning during the laser welding. Since the temperature drop of the weld bead after the laser welding has progressed from the peripheral part and the central part in the width direction is kept at a relatively high temperature, shifting the re-irradiation on the same scanning line will cause a temperature drop. This is advantageous in performing heat input for compensation.

  For the same reason as described above, the laser re-irradiation can be performed with a larger defocus amount than during the laser welding.

The present invention is also directed to a laser welding method including the bead inspection method as described above.
That is, the present invention performs a laser scan over a predetermined section to form a weld bead, and the welding bead over the predetermined section after the welding bead forming step has residual heat. A laser welding method, comprising: re-irradiating a laser beam at a low energy density and imaging while causing the weld bead to thermally emit light; and determining whether the weld bead is good or bad from the image obtained by the imaging There is also.

  The present invention also provides a step of performing laser scanning over a predetermined section to form a weld bead and the welding bead over the predetermined section after the welding bead formation step, with the residual heat in the weld bead over the predetermined section. Re-irradiating the bead with a laser at a low energy density, causing the welding bead to thermally emit light, and simultaneously storing the irradiation position, and imaging the welding bead at the irradiation position after a predetermined time has elapsed since the irradiation position was stored There is also a laser welding method including a step of performing and a quality determination of the weld bead from the image obtained by the imaging.

  According to the present invention, after the laser welding of the predetermined section is completed, the welding bead over the predetermined section has residual heat, and the welding bead is irradiated again with a laser at a low energy density to cause the welding bead to thermally emit light. At the same time, the step of storing the irradiation position, the step of imaging the weld bead at the irradiation position after a lapse of a predetermined time from the time of storing the irradiation position, and the quality determination of the weld bead from the image obtained by the imaging. Performing a welding bead inspection method.

  As described above, according to the bead inspection method and the laser welding method according to the present invention, it is possible to stably perform pass / fail judgment of the entire weld bead or a wide range while avoiding the influence of the plume.

1 is a schematic view of a laser welding apparatus according to a first embodiment of the present invention. It is a typical perspective view which shows (a) weld bead formation and (b) laser reirradiation and imaging in the bead inspection method concerning a 1st embodiment of the present invention. It is the schematic of the laser welding apparatus which concerns on 2nd Embodiment of this invention. It is a typical perspective view which shows (a) weld bead formation in the bead inspection method concerning 2nd Embodiment of this invention, and (b) laser reirradiation and imaging. It is a distribution map which shows the correlation of the laser output at the time of re-irradiation, and speed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic view of a laser welding apparatus 1 according to the first embodiment of the present invention. In FIG. 1, a laser welding apparatus 1 includes a laser irradiation head 11, a laser irradiation control unit 12, a laser irradiation unit 10 including a laser oscillator 13, an imaging means 21 for a weld bead B, and an image processing unit 22. Part 20.

  The laser irradiation head 11 irradiates a laser beam transmitted from the laser oscillator 13 via a fiber optical system or the like at a predetermined energy density at a predetermined position on the surface of the workpiece w1 with 2 laser optical axes on the surface. Means (for example, galvano scanner or XY table, or multi-axis head) for scanning in the axial direction or more in multiple axes, and focus control means (for example, focus lens) for controlling the focal length / defocus amount of the laser Etc.

  The laser irradiation control unit 12 controls the laser irradiation head 11 based on a preset program, and performs laser irradiation ON / OFF and laser output control. In particular, the present invention has a function as a switching means between laser irradiation for welding and laser reirradiation for inspection with low energy density (low output and / or high speed).

  As the image pickup means 21, a well-known image pickup means (for example, a CCD camera or the like) capable of picking up an area including preferably the whole of at least one unit weld bead B can be suitably used. The images acquired by the imaging means 21 are sequentially accumulated in the storage unit 23 and sent to the image processing unit 22 where defect inspection and quality determination of the weld bead B are performed.

  Next, the weld bead defect inspection and pass / fail judgment process based on the above embodiment will be described in detail with reference to the drawings.

  As shown in FIG. 1, in a state where two workpieces (steel plates) w1 and w2 are overlapped, laser irradiation is performed from one (w1) surface side and lap welding is performed. For example, as shown in FIG. 2A, as an alternative to conventional spot welding, laser scanning Sa is performed in an arc shape (loop shape) with a predetermined radius from a start point Ss to an end point St, and an arc-shaped weld bead B Form.

  At this time, plume and spatter are generated from the irradiated part during the laser irradiation, but at the stage where the laser optical axis reaches the end point St and the laser irradiation is stopped, the plume and spatter disappear and the end B1 emits residual heat. Yes. However, although the temperature of the other start end portion B0 decreases and infrared radiation remains, the luminance in the image acquired by the imaging means 21 decreases below the threshold value. In FIG. The weld bead shape of B0 cannot be confirmed.

  Next, as shown in FIG. 2B, the laser optical axis is moved again to the starting point Ss, and the energy density determined by the laser output, the focal diameter, and the scanning speed is set to about 20 to 45% during welding. The image is picked up by the imaging means 21 while the laser beam is re-irradiated (Sb) to the end point St and the weld bead B is thermally emitted (B2).

  In such laser re-irradiation Sb, since the energy density is small, plume or spatter does not occur on the weld bead B, and the heat-emitted weld bead B2 can be imaged during the laser re-irradiation, and is imaged by the imaging means 21 together with the laser scanning. The image X to be detected can detect a welding defect such as a hole defect without performing complicated image processing, and the inspection is completed at the end of the laser re-irradiation Sb.

  As a specific inspection method, the imaging means 21 includes the entire weld bead B2 in the field of view, and sequentially captures images X in the same range in synchronization with the laser re-irradiation Sb. For example, in FIG. 2B, the position of the laser re-irradiation Sb ′ in the image X is stored, and a defect recognized as a low-luminance pixel group in a region including the position after a predetermined time has been detected. Such an operation, that is, a time difference scan may be performed continuously, or the entire length (entire circumference) of the weld bead B2 may be divided into several segments and the time difference scan may be performed for each segment. By performing such a time difference scan, a high-luminance irradiation region can be excluded from the inspection range even though no plume or spatter is generated, and a more reliable inspection can be performed.

(Second Embodiment)
FIG. 3 is a schematic view of a laser welding apparatus 2 according to the second embodiment of the present invention. In FIG. 3, the laser welding apparatus 2 includes a laser irradiation head 11, a laser irradiation control unit 12, a laser irradiation unit 10 including a laser oscillator 13, and an inspection unit including an imaging unit 31 and an image processing unit 32 of the weld bead B. Part 30. The laser irradiation unit 10 is basically the same as that of the first embodiment. The same elements are denoted by the same reference numerals, and the description thereof is omitted. Hereinafter, the inspection unit 30 will be described.

  The inspection unit 30 according to the second embodiment includes a spectroscopic unit 34 such as a half mirror installed on the laser optical axis and a filter 35, and cuts other than a specific wavelength by using the filter 35 from an image acquired through the laser output optical system. The imaging means 31 is configured to take an image. As the imaging means 31, a high-speed camera with a high frame rate that can be imaged while moving with the laser optical axis can be suitably used. The images acquired by the imaging means 31 are sequentially accumulated in the storage unit 33 and sent to the image processing unit 32, where a defect inspection of the weld bead B and a pass / fail determination are performed.

  In the case of the second embodiment, since the laser output optical system is used for imaging, the imaging range is limited to the vicinity of the irradiation position as shown in FIG. In addition, since the reflected light is incident from the irradiation position even though the low energy density is re-irradiated, the inspection may be performed without the irradiation position. In this case, the inspection range becomes narrow, but the imaging range moves coaxially with the irradiation position, so that an accurate inspection range can be acquired with respect to the irradiation position.

(First embodiment)
Next, examples of energy density in laser re-irradiation will be described.
In the experiment, three workpieces (upper: 0.65 mm thick non-plated steel plate, center: 1.4 mm thick non-plated steel plate, lower: 0.8 mm thick galvanized steel plate with a 0.1 mm gap) As shown in FIG. 2A, laser scanning Sa was performed in an arc shape with a focal diameter of 0.6 mm, a laser output of 4000 W, and a scanning speed of 3.7 m / min, and a weld bead B was formed.

  Next, as shown in FIG. 2B, when the laser speed was increased to 13.7 m / min with the same laser output of 4000 W and the laser was re-irradiated (Sb), the bead B was produced without any plume or spattering. Thermoluminescence was possible. In this case, even if the same laser output is 4000 W, the energy input to the weld bead B per unit time, that is, the energy density becomes 1 / 3.7 by increasing the scanning speed to 3.7 times speed. This was the same as the laser output was reduced to about 1081 W (about 27%).

(Second embodiment)
In the above embodiment, the case where the scanning speed is increased by 3.7 times while the output at the laser re-irradiation Sb is kept equal to that at the time of the laser welding Sa is shown, but the degree of the acceleration is reduced and the laser output is reduced. The same thermoluminescence can be obtained even when the laser re-irradiation Sb is performed by actually decreasing the energy density and performing the laser re-irradiation Sb.

Therefore, in order to verify the correlation between the speed and output in laser re-irradiation and the range of effective combinations, an experiment was conducted in which re-irradiation was performed at various combinations of scanning speed and laser output. The results are shown in the distribution diagram of FIG.
In FIG. 5, (1) the symbol “◯” indicates a combination in which good thermoluminescence B2 was obtained and no plume or spatter occurred, and (2) the symbol “Δ” indicates a plume or (3) The symbol “×” indicates that the high-speed side has insufficient luminance and the low-speed side has plumes and spatters, resulting in a weld bead quality test. Indicates combinations that could not be implemented.

  The heat input to the workpiece by laser irradiation is generally proportional to the laser output and inversely proportional to the focal spot diameter and the scanning speed. That is, when the laser output P, the scanning speed V, and the focal diameter d are set, the energy density of laser irradiation is expressed by P / dV. In FIG. 5, the critical value (upper limit value) on the left side of the effective combination range of the speed V and the output P is a straight line P = 500 V from (V, P) = (7,3500) to (9,4500). Yes, the critical value (lower limit) on the right side is on the straight line P = 250 V from (V, P) = (14,3500) to (18,4500).

  Here, if the focal diameters of the welding laser (4 m / min, 4000 W) and the re-irradiation laser are the same, the energy density can be defined by the output speed ratio (P / V) based on the laser output P and the scanning speed V. For the welding laser output speed ratio (P / V) = 1000 (W · min / m), the upper limit value of the re-irradiation laser output speed ratio is (P / V) = 500 (W · min / m). ), The lower limit value is (P / V) = 250 (W · min / m). That is, it can be seen that thermoluminescence suitable for the pass / fail inspection can be obtained when the output speed ratio (P / V) of the re-irradiation laser is in the range of 25 to 50% during laser welding.

Furthermore, when a sufficiently high scanning speed V (m / min) with respect to the focal diameter d = 0.6 mm is converted into (mm / sec) and the output P is converted into energy (W · sec = J), unit time The energy P / dV input to the hit irradiation area is 25 to 50 (J / mm ² ) at the time of laser re-irradiation with respect to 100 (J / mm ² ) at the time of laser welding. Thus, it can be seen that there is a certain correlation between the combination of the scanning speed V, the laser output P, and the focal spot diameter d, and it is possible to qualitatively select the re-irradiation output value and scanning speed value.

  The laser welding method (welding bead inspection method) according to the present invention is characterized in that the inspection laser re-irradiation Sb is performed at a low energy density immediately after the end of the welding laser irradiation Sa. The explanation was centered on two operations, low output and high speed. Operations that bring about results similar to these include operations for shifting the position of the re-irradiation Sb in the width direction of the weld bead B and operations for increasing the defocus amount. Each example will be described below.

(Third embodiment)
Immediately after the end of the welding laser irradiation Sa, the inspection laser re-irradiation Sb is shifted in the width direction of the weld bead B, so that heat input to the weld bead B is suppressed, and laser re-irradiation is performed under the same conditions as during welding. Even if Sb is performed, the same result as that obtained when the laser having a substantially low energy density is re-irradiated can be obtained. In order to verify this effect, the following experiment was conducted.

  First, similarly to the first embodiment, a laser scan Sa is performed in an arc shape at a focal diameter of 0.6 mm, a laser output of 4000 W, and a scanning speed of 3.7 m / min, and a weld bead B is formed. Next, as in the first embodiment, the laser optical axis is moved again to the starting point Ss, and when the laser re-irradiation Sb is performed with the scanning speed increased to 13.7 m / min, the irradiation position is determined by laser scanning during welding. The Sa was re-irradiated by shifting to the radially outer peripheral side and the inner peripheral side (Sb), and the bead B was thermally emitted and imaged.

  As a result, good images were obtained up to 0.7 mm on both the outer peripheral side and the inner peripheral side. Rather, as compared with the case of laser scanning Sa at the time of welding, there was a tendency that the peripheral portion where the temperature decrease first was reheated and the thermoluminescence of the weld bead B was made uniform. However, when the deviation is 0.8 mm or more, a dark portion is generated on the opposite side, and the defect detection accuracy in that region is lowered.

  Considering this point, the width of the weld bead B formed with respect to the laser irradiation focal diameter of 0.6 mm is about 1 mm. Therefore, until the deviation is 0.7 mm, the reirradiation Sb has a focal diameter of 0.6 mm and welding. There is an overlap with bead B. However, when the deviation is 0.8 mm or more, there is no overlap with the weld bead B, and the heat input is solely due to solid heat conduction, and it is considered that the energy of the re-irradiated laser is hardly transmitted to the weld bead B. In any case, the ability to allow deviation in re-irradiation is advantageous in securing practical stability.

(Fourth embodiment)
Immediately after the end of the welding laser irradiation Sa, by performing the inspection laser re-irradiation Sb with a large defocus amount, the energy of the laser at the time of re-irradiation is dispersed over a wide area of the welding bead B. The same result as re-irradiation with a low energy density laser is obtained. In order to verify this effect, re-irradiation was performed while changing the defocus amount, and a good image was obtained up to a focal diameter of 1.0 mm where the defocus amount is equal to the width of the weld bead B under the same conditions. However, it has been determined that if it is more than that, a low-luminance part is observed in the intermediate part or the like because of insufficient heating, and the defect detection accuracy is lowered.

  This is a result when the scanning speed is increased to 13.7 m / min. If the degree of the acceleration is reduced, it is predicted that heating that generates the necessary thermoluminescence is possible even with the above defocus amount. However, since the processing time is increased accordingly, there is no point in selecting such a defocus amount. The fourth embodiment can be an advantageous parameter in terms of suppressing plume and spatter during re-irradiation and ensuring practical stability.

  Although several embodiments of the bead inspection method according to the present invention have been described above, in addition to the laser output and the scanning speed, the setting of shifting the irradiation position of the third embodiment and the setting of the defocus amount of the fourth embodiment are described. By performing the above, it is added that the quality of the weld bead can be determined while achieving both processing time and stability.

DESCRIPTION OF SYMBOLS 1 Laser welding apparatus 10 Laser irradiation part 11 Laser irradiation head 12 Laser irradiation control part 13 Laser oscillator 20,30 Inspection part 21,31 Imaging means 22,32 Image processing part 23,33 Storage part 34 Spectroscopic means 35 Filter B Welding bead B0 Start end side B1 Terminal end B2 Weld bead whole Sa Laser irradiation (laser welding)
Sb Laser re-irradiation Ss Start point St End point w1, w2 Workpiece

Claims (7)

  After completion of laser welding in a predetermined section, the welding bead over the predetermined section has residual heat, and the welding bead is re-irradiated with a laser at a low energy density, and imaging is performed while causing the welding bead to thermally emit light. A weld bead inspection method, wherein the quality of the weld bead is determined from the obtained image.   The welding bead inspection method according to claim 1, wherein the laser re-irradiation is performed at a higher speed than optical axis scanning during the laser welding.   The welding bead inspection method according to claim 1, wherein the laser re-irradiation is performed within a width of the welding bead and shifted from the optical axis scanning during the laser welding.   The welding bead inspection method according to claim 1, wherein the laser re-irradiation is performed with a larger defocus amount than that during the laser welding. Performing laser scanning over a predetermined section to form a weld bead;
After completion of the welding bead forming step, in a state where the welding bead over the predetermined section has residual heat, re-irradiating the welding bead with a laser at a low energy density, and imaging while causing the welding bead to thermally emit light; and ,
Performing pass / fail judgment of the weld bead from an image obtained by the imaging;
A laser welding method comprising: Performing laser scanning over a predetermined section to form a weld bead;
After completion of the welding bead formation step, the welding bead over the predetermined section has residual heat, and the welding bead is re-irradiated with a laser at a low energy density to simultaneously emit light from the welding bead and its irradiation position. The step of memorizing
Imaging a weld bead at the irradiation position after a predetermined time from the time of storing the irradiation position;
Performing pass / fail judgment of the weld bead from an image obtained by the imaging;
A laser welding method comprising: After completion of laser welding in a predetermined section, with the residual heat in the weld bead over the predetermined section, the welding bead is re-irradiated with a laser at a low energy density, and the irradiation position of the welding bead is simultaneously emitted. Memorizing step;
Imaging a weld bead at the irradiation position after a predetermined time from the time of storing the irradiation position;
Performing pass / fail judgment of the weld bead from an image obtained by the imaging;
Including a weld bead inspection method.

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