JP2017113789A - Laser welding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser welding apparatus capable of specifying cause of a poor weld by determining quickly soundness of a weld zone, even in the case of a welder having a complicated beam paths such as wobbling.SOLUTION: A laser welding apparatus includes a laser irradiation part 1 for irradiating a workpiece W which is a weld object with a laser beam RB, an infrared light detector 2 for measuring intensity of infrared light IR generated from the workpiece W, and a judgement part 4 for judging existence of incomplete penetration in a welding region by comparing intensity of infrared light IR measured in each fixed welding region by the infrared light detector 2 with a threshold set beforehand related to the intensity of the infrared light IR.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser welding apparatus that measures the intensity of infrared light from a welded part and determines whether or not the welded part is healthy when welding workpieces using a laser beam.

As such a laser welding apparatus, there is a conventional one shown in Patent Document 1, for example.
This technique is intended to detect welding defects caused by laser beam welding in a short time. When welding workpieces with a pulsed laser, the wavelength of the infrared light that can be detected from the keyhole formed in the molten pool is selected from the infrared light emitted from the welded portion. The quality of the welded part is determined based on the strength of the weld.

  The prior art utilizes the following mechanism during welding. During one pulse output of the pulse laser, the waveform of the infrared light intensity when there is no lack of penetration in the welded part of the workpiece is more than the waveform of the infrared light intensity when the lack of penetration occurs in the welded part of the workpiece. The peak value is large and the value is large as a whole. This is based on the fact that a keyhole is formed during welding of a workpiece when a desired penetration depth can be achieved without a lack of penetration in the welded portion of the workpiece.

  That is, when a keyhole is formed in the molten pool, a large penetration depth can be achieved. When the keyhole is formed, the ambient temperature reaches approximately the boiling point of the workpiece, and the surface area of the molten pool is increased by the keyhole, so that the infrared light intensity increases. Therefore, based on the integrated value calculated by integrating the infrared light intensity during one pulse output of the pulse laser with respect to time, it is determined whether or not there is insufficient penetration in the welded portion of the workpiece. (Paragraph 1 [0049] paragraph).

International Publication 2013 / 171848A1

  In the above prior art, infrared light generated from a molten pool at a specific welding location is a detection target. The laser to be irradiated is a pulse laser, but the pulse interval is very short. Therefore, when examining the melting phenomenon of the workpiece in the molten pool, energy is continuously injected into the welded workpiece, but it can be regarded as the same as normal continuous welding. In addition, it is thought that the irradiation process of the beam in the said well-known technique is a straight line.

  That is, in this technique, inadequate detection of the strength of the weld bead is detected in the entire welded portion formed continuously in the region where the pulse laser irradiation continues. Here, it determines based on the detected value of the infrared light intensity from the start to the end of welding. Therefore, even if a lack of penetration occurs in a part of the weld bead, and the infrared light intensity decreases at that location, the data related to this decrease is incorporated into a large amount of other healthy data and defective. Judgment may not be possible.

  In addition, when the laser beam is wobbled, the intensity of infrared light from the weld bead varies greatly, but the conventional technology does not describe a configuration that can cope with this variation. When one infrared light threshold is set as in the prior art, setting a low threshold may be considered in order to accurately detect the low infrared light intensity during wobbling. There are many factors that cause a decrease in the intensity of infrared light during wobbling, such as a problem in laser output and a problem in the groove on the workpiece side.

  However, the infrared light intensity decreased due to the irradiation of the unheated area of the workpiece during wobbling despite the decrease in infrared light intensity caused by these problems and the sound welding. When compared with the decrease, the difference between the two is not large. That is, as the threshold value is set lower, it becomes more difficult to determine that the decrease in infrared light intensity is based on poor welding.

  Further, in the related art, when the intensity of infrared light is reduced, the cause cannot be specified, and it is impossible to improve the welding conditions promptly and there is a problem that efficient welding work cannot be performed. .

  Therefore, in order to solve such problems, in the laser beam welding machine having a complicated beam stroke such as wobbling, it is possible to quickly determine the soundness of the welded portion, and when the defect is determined, the cause is What can be identified is required.

  A characteristic configuration of the laser welding apparatus according to the present invention includes a laser irradiation unit that irradiates a workpiece to be welded with a laser, an infrared light detection unit that measures the intensity of infrared light generated from the workpiece, and the infrared light. A determination unit for comparing the intensity of the infrared light measured for each welding region by the detection unit with a threshold value relating to a preset infrared light intensity to determine whether there is insufficient penetration in the welding region; It is in the point prepared.

  As in this configuration, if the lack of penetration is determined for each fixed welding region, the detection accuracy of the lack of penetration can be increased. That is, in the case of measuring the intensity of infrared light for each long welded area, if there is insufficient penetration in the extremely small area and the intensity of infrared light is reduced, the reduction in the intensity is caused by another large intensity. There is a possibility of being buried in the measurement result of infrared light from the welding region and not being evaluated. However, in the case of measuring infrared light intensity for each fixed welding area as in this configuration, the amount of measurement data of infrared light is reduced, and as a result, changes in the intensity of infrared light are captured sensitively. Can do. Therefore, it is possible to accurately evaluate the lack of penetration.

  In the laser welding apparatus according to the present invention, the laser irradiation pattern by the laser irradiation unit can be set as wobbling, and the intensity of the measured infrared light can be set as the average intensity of the infrared light for each period of the wobbling. .

  When the laser irradiation pattern is wobbling, the laser beam moves alternately between the high temperature region and the low temperature region of the workpiece, and the detection intensity of the infrared light changes periodically. In that case, strictly, the threshold value is individually set in consideration of the state of the welded portion at the position where the intensity of infrared light is maximized or the state of the welded portion at the position where the intensity of infrared light is minimized. It is also possible. However, since the measurement time of the infrared light is originally set to be short, the soundness of the welding state in the region can be evaluated by paying attention to the total heat input during the measurement time.

  Therefore, by evaluating the intensity of infrared light for one period of wobbling as in this configuration, it is possible to determine the presence of insufficient penetration based only on the maximum value of the measurement. However, although it can be determined whether or not there is insufficient penetration at the position where the infrared light is maximized, that is, where the keyhole is soundly formed, other areas where the penetration is not yet sufficient particularly in the low temperature region Is not always accurate. When the intensity of infrared light in the high temperature region is excessive, the intensity of infrared light in the low temperature region may be excessive. However, providing a number of thresholds related to the intensity of infrared light complicates the measurement. Therefore, as in this configuration, in the case of wobbling, the intensity of infrared light for each period is measured and averaged to improve the evaluation accuracy while simplifying the measurement of infrared light.

  The laser welding apparatus according to the present invention includes a monitor output measurement unit that measures the output of the laser emitted from the laser irradiation unit, and the determination unit distinguishes the monitor output measured by the monitor output measurement unit. An upper limit value and a lower limit value for holding in advance, based on the monitor output and the upper limit value, the lower limit value, and further the intensity of the measured infrared light, the soundness of the penetration state in the welding region, When the penetration state is determined to be defective, the cause of occurrence of the defect can be specified.

As described above, by measuring the intensity of infrared light emitted from the welding region, the melted state of the welded portion can be specified, and whether or not there is insufficient penetration can be determined.
In addition, the monitor output is measured, and the measured value is compared with the upper limit value and the lower limit value of the monitor output. If the monitor output is between the upper limit value and the lower limit value, laser irradiation is appropriate.
Thus, for example, when the monitor output exceeds the upper limit even if the intensity of infrared light is sufficient, the determination unit determines that the laser output is excessive for some reason and there is a possibility of poor welding.

On the other hand, when the intensity of infrared light is insufficient, the laser output may be insufficient. In this case, attention is paid to the lower limit value of the monitor output. If the monitor output is equal to or greater than the lower limit value, it is determined that there is no abnormality in the laser irradiation unit and that the abnormality is related to the workpiece. On the other hand, when the monitor output is below the lower limit, it is determined that the abnormality is related to the laser irradiation unit or the workpiece.
Thus, by providing the monitor output detection function, the cause of the lack of penetration can be more specifically specified, and the state of the laser device can be appropriately maintained.

It is a block diagram which shows the laser welding apparatus which concerns on this embodiment. It is explanatory drawing which shows the wobbling aspect of a laser beam. It is explanatory drawing which shows the measurement point of the intensity | strength of infrared light. It is a flowchart which specifies a welding state and the cause of welding failure.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.
[Configuration of laser welding equipment]
The configuration of a laser welding apparatus S (hereinafter referred to as “welding apparatus S”) used in the present embodiment is shown in FIG. The welding apparatus S mainly includes a laser irradiation unit 1 that irradiates a laser beam RB, an infrared light detection unit 2 that measures the intensity of infrared light IR generated from a welding portion of the workpiece W, and irradiation with a laser beam RB. A drive control unit 3 that controls the position and a determination unit 4 that determines the soundness of the weld from the intensity data of the infrared light IR obtained by the infrared light detection unit 2 are provided. Hereinafter, each configuration will be described.

[Laser irradiation part]
The irradiation intensity of the laser beam RB irradiated to the workpiece W is appropriately determined according to the material of the workpiece W to be welded and the groove shape. Specifically, the irradiation intensity of the laser beam RB is determined by the laser output controller 11, excited to a predetermined intensity by the laser oscillator 12, and then sent to an optical system provided inside the welding head H. The optical system includes a repeater 14 that receives the laser beam RB excited by the laser oscillator 12 and transmitted through the optical fiber 13 and the like, a collimator lens 15 that adjusts the laser beam RB via the repeater 14 to parallel light, A condensing lens 16 and the like for condensing the parallel light on the workpiece W are provided.

  With respect to the laser beam RB irradiated from the laser oscillator 12, the irradiation intensity is measured by the monitor output measuring unit 17 provided in the laser oscillator 12. The intensity of the laser beam RB obtained by the monitor output measurement unit 17 is sent to the determination unit 4 described later, and is used for determination of the soundness of the welded portion.

(Drive control unit)
The welding head H is constructed, for example, on an articulated robot arm R, and the posture of the operation of the robot arm R is controlled by the drive control unit 3. Thereby, the irradiation position of the laser beam RB is determined. As for the irradiation position of the laser beam RB, coordinates for specifying a weld line on the workpiece W are input to the drive control unit 3 in advance. Further, beam scanning such as wobbling described later is also possible. Of course, other robots can be used. For example, a dedicated device for swinging the welding head H on a cart traveling on a linear rail may be used.

[Infrared light detector]
In order to determine whether or not there is insufficient penetration in the welded portion of the workpiece W, the infrared light detection unit 2 is provided. This utilizes the fact that the intensity of the infrared light IR generated from the welded portion exhibits a predetermined value when welding is performed in a sound manner.

  The infrared light detection unit 2 is provided inside the welding head H. The infrared light IR generated from the welded portion is converted into parallel light by the condenser lens 16 and is bent by the first half mirror 21 provided between the condenser lens 16 and the collimator lens 15. Thereafter, the light is guided to the second condenser lens 23 via the second half mirror 22. The infrared light IR collected here is selected by the filter 24 and is received by the photodetector 25. The photodetector 25 transmits an electrical signal converted according to the intensity of the infrared light IR to the data processing unit 26. The data processing unit 26 calculates the average intensity of the infrared light IR.

  The data processing unit 26 integrates and averages the infrared light intensity generated from a predetermined welding region, that is, the infrared light intensity generated over a period of one wobbling period as will be described later. Thereby, a value for evaluating the lack of penetration is calculated.

  This value is output to the determination unit 4. In the determination unit 4, in addition to the detection value of the infrared light IR, a signal related to the output of the laser beam RB transmitted from the monitor output measurement unit 17 is received, and the soundness of the weld is determined as described later, Notify the notification unit 5.

  The laser output control unit 11, the drive control unit 3, the infrared light detection unit 2, the determination unit 4, and the notification unit 5 are installed, for example, in one control panel 6.

(Welding procedure)
In FIG. 2, an example of the irradiation mode of the laser beam RB on the workpiece W is shown. The welding groove F is, for example, a so-called I-shaped groove in which the end faces of the resin material are butted together. The stroke of the laser beam RB is a so-called wobbling that is swung along the I-shaped groove and reciprocated back and forth, and proceeds on the weld line while drawing a continuous ellipse.

As the welding device S, various devices such as a pulse laser or a continuous wave laser can be used as long as the workpiece W that is an object can be melted. Further, a YAG laser, a CO ₂ laser, or the like can be used as appropriate for the type of laser.

[Infrared light detection]
In FIG. 2, the line types are displayed differently for each cycle in order to make the wobbling route easy to see. When wobbling is performed, the laser beam RB alternately passes through unmelted portions and already melted portions of the workpiece W to be welded. For example, when the irradiation position of the laser beam RB is at point A on the path indicated by the solid line, the laser beam RB is retreating with respect to the traveling direction and reenters the once melted region. The point B that penetrates deeply into the already melted region is the position where the maximum temperature is reached, and the intensity of the infrared light IR emitted from the welded portion increases as the laser beam RB approaches the point B. After passing through point B, the laser beam RB again reaches the unmelted region and reaches point C. In the region from point A to point C, the workpiece W is sufficiently melted, and the surface of the molten pool sinks due to the vapor pressure of the workpiece W to form a keyhole. At these positions, a larger amount of heat is input by the beam irradiated for the second time, and the intensity increases as the amount of infrared light IR generated from the molten pool with an increased surface area increases.

  In the future, the heat quantity of the laser beam RB is consumed to melt the workpiece W. During the melting, the workpiece W is heated from room temperature to the melting temperature, but the intensity of the infrared light IR generated therefrom is low. At the moment when the laser beam RB passes through the point D located on the most distal side in the welding progress direction, the temperature of the welded portion becomes the lowest. Since the point D is closest to the tip side compared to the area where welding has already been completed, heat transfer from the already melted area is small. Therefore, the temperature of the welded portion is the lowest at point D. Thereafter, the traveling direction of the laser beam RB moves backward, and reaches the point E while approaching the welded portion once melted. From point D to point E, the intensity of infrared light IR increases, and the intensity of infrared light at point E is substantially the same as the intensity of infrared light at point A above. In welding with wobbling, such a process from point A to point E is repeatedly performed.

[Detection of infrared light]
FIG. 3 shows an example of detecting the intensity of infrared light IR. The upper diagram shows the time change of the infrared light intensity detected by the photodetector 25 provided in the welding head H. FIG. One peak of the broken line constituting the graph shows one cycle of wobbling. In addition, in the middle I region of the graph, the infrared light intensity is generally lower than that of the right region where the infrared light intensity is strong. This is probably because, for example, the intensity of the laser beam RB irradiated from the welding head H has decreased for some reason.

  In the upper graph, the lower graph is an enlarged portion related to the region II. In this area, waveforms for several wobbling cycles are shown. In this figure, a thin line indicates a state where appropriate welding is performed, and a thick line indicates a state where there is a possibility that welding is insufficient due to inconvenience in the welding state. That is, the thick broken line has a smaller infrared light intensity maximum value than that of the thin line. This is considered to be caused, for example, by a decrease in the irradiation intensity of the laser beam RB due to contamination of the protective glass constituting the laser beam RB transmission system.

  The insufficiency of infrared light IR often occurs particularly when the peak value of the infrared light waveform decreases. In the lower diagram, a plot from point A to point E shows the position of the laser beam RB during wobbling in FIG. That is, normally, in the region from point A to point B and to point C, the laser beam RB returns to the region where it has once melted and becomes high temperature, so the intensity of infrared light IR generated from the weld increases. . However, the thick broken line does not reach point B particularly at the position of the maximum peak, and the infrared light intensity is reduced. In such a case, it can be inferred that, for example, the output of the laser beam RB was insufficient for some reason, and as a result, the temperature of the molten pool did not rise properly and no keyhole was formed.

[Monitor output of laser beam output and calculation of infrared light intensity]
As described above, infrared light IR is emitted from the weld bead, and the infrared light detector 2 detects the intensity of the infrared light IR. At that time, it is necessary to verify whether the measured infrared light intensity value is appropriate. In the present embodiment, verification is performed by setting a threshold value y1 as follows.

  Specifically, the monitor output of the laser beam RB irradiated from the laser oscillator 12 is used. The actual infrared light intensity emitted from the workpiece W is proportional to the actual laser output irradiated from the welding apparatus S. The actual laser output is obtained by, for example, irradiating the workpiece W with the laser beam RB in a normal state, measuring the value of the infrared light emitted from the workpiece W, or measuring the actual temperature rise of the workpiece W. Can be calculated. However, during actual welding, it is not known whether the laser beam RB is correctly irradiated. Therefore, the monitor output value detected by the monitor output measurement unit 17 for the irradiated laser beam RB is used as an index for indirectly knowing the laser output.

The monitor output and the actual laser output are in a proportional relationship. Therefore, by knowing the monitor output, the laser output can be indirectly known, and the infrared light intensity from the weld can be calculated. These relationships can be expressed by the linear function equation (1) as follows.

y1 = ax + b (1)

y1: Infrared light intensity threshold x: Monitor output of laser oscillator a, b: Constant

  In this way, the infrared light intensity calculated from the monitor output assuming that the laser beam RB is normally irradiated is set as the threshold value y1 for determining the quality of the welding state. In this embodiment, since the laser beam RB is wobbled, the intensity of infrared light actually emitted from the molten pool varies. Therefore, the infrared light intensity value to be compared with the threshold value y1 is an average value of the infrared light intensity obtained during one wobbling cycle. When this average value is smaller than the threshold value y1, it is determined that the heat input to the welded portion is small and there is a possibility of insufficient penetration.

[Sampling period]
The sampling of the infrared light intensity is performed by dividing it into a predetermined welding length or a predetermined welding time. By doing so, a change in infrared light intensity can be sensitively measured for a welding portion having a relatively short length. In the case of performing wobbling welding, it is preferable to evaluate the obtained waveform of the infrared light intensity by dividing it every wobbling period. On the other hand, when performing linear welding, for example, a waveform of infrared light intensity may be divided for each preset bead length or time.

[Judgment flow]
FIG. 3 shows an example in which the infrared light intensity is sampled at the wobbling period T. FIG. 4 shows a determination flow for evaluating the lack of penetration. Along with the start of welding, the monitor output of the laser oscillator 12 and the infrared light intensity from the weld are measured (# 10). Next, an average value in the wobbling period T is calculated for each of the monitor output and the infrared light intensity (# 20). Based on the average value of the obtained monitor outputs, the threshold value y1 calculated using the above equation (1) is compared with the measured average value of infrared light intensity (# 30). This threshold value y1 is obtained from a welding experiment or the like conducted in advance, and specifies the intensity of infrared light that does not cause insufficient penetration. Of course, the threshold value y1 varies depending on the shape of the workpiece W to be welded, the value of the laser output to be irradiated, the preheating / postheating conditions of the workpiece W during welding, and the like. If the infrared light intensity is greater than or equal to the threshold y1 at # 30, it may be determined that insufficient penetration has occurred. On the other hand, if it is below the threshold value y1, it can be judged that the possibility of insufficient penetration is very high.

  However, even when the infrared light intensity is greater than or equal to the threshold value y1 in the determination of # 30, the welded portion is not always healthy. For example, if the intensity of infrared light is excessively high, heat input may be excessive, causing inconveniences such as melting at the welding groove F or lowering of the strength of the welded portion.

  Therefore, in this embodiment, a threshold value y2 that is an upper limit value is provided for the monitor output (# 40). This threshold value y2 is specified in advance by experiments, and when the monitor output is equal to or greater than the threshold value y2, a sound welded part is often not obtained. That is, it is determined whether or not the infrared intensity is appropriate in # 30, and it is determined whether or not the monitor output is appropriate in # 40 for those determined to be appropriate here. Only when both conditions are satisfied, the weld is determined to be healthy (# 50). The data processing unit 26 outputs a determination result that the welded part is healthy to the determination unit 4. The determination unit 4 notifies the notifying unit 5 such as a monitor screen provided in any part of the welding apparatus S that the welding unit is normal.

  On the other hand, even if the infrared intensity is appropriate at # 30, if the monitor output is excessive at # 40, there may be a cause such as an abnormality in the laser optical path. The increase in the monitor output suggests that there is a high possibility that an abnormality already exists at the time when the laser beam RB is irradiated from the laser irradiation unit 1. In this case, the determination unit 4 determines that the apparatus is abnormal (# 60), and outputs an abnormality determination signal to the notification unit 5.

  If the infrared light intensity falls below the threshold value y1 at # 30, there is a high possibility that some inconvenience has occurred in the welded portion. In order to determine this, a threshold value y3 which is a lower limit value for the monitor output is set (# 70). This threshold value y3 is also specified in advance by experiments. When the monitor output is equal to or higher than the threshold value y3, a normal welded portion is highly likely to be obtained. However, even if the monitor output is greater than or equal to the threshold value y3, if the infrared light intensity is low at # 30, there is a possibility that the work W is not heated well, for example, there is a problem with the irradiation condition of the laser beam RB on the work W. It is determined that there is (# 80).

  On the other hand, when the monitor output is lower than the threshold value y3 in # 70, it can be clearly determined that the laser beam RB is abnormally irradiated (# 90). For example, contamination of the optical system at any location up to the workpiece W, such as the optical fiber 13 from the laser oscillator 12 to the repeater 14, is conceivable. In this case, first, it is determined that there is an abnormality in any of the laser light paths. Furthermore, since there is little heat input with respect to the workpiece | work W, it determines with the amount of heat input with respect to the workpiece | work W having abnormality. The determinations of # 80 and # 90 are also notified to the notification unit 5 such as the monitor screen of the welding apparatus S in the same manner as described above.

  In this way, by calculating the average value of the infrared light intensity for each fixed welding region and comparing it with the threshold value y1, it is possible to detect the slight fluctuation of the infrared light intensity and determine whether or not the weld has insufficient penetration. be able to. Further, by observing the monitor output of the laser beam RB and comparing it with the threshold values y2 and y3 related to the monitor output, it is possible to identify the possibility of the welding failure and its cause.

[Other Embodiments]
When the infrared light intensity of the molten pool is measured, for example, the maximum value may be measured instead of the average value for each fixed period as described above. When laser beam welding with wobbling is performed, if the inconvenience of the beam irradiation position or the intensity of the laser beam RB is insufficient, the influence of the influence easily appears at the position where the temperature of the molten pool becomes maximum. That is, if the intensity of the laser beam RB is inappropriate, the workpiece W is not sufficiently melted and the amount of generated steam is insufficient, so that a healthy molten pool cannot be formed. As a result, the infrared light IR that should be obtained is not observed. Whether or not a healthy molten pool is formed in this way occurs particularly in a portion with a large heat input.

  Therefore, it is possible to monitor the waveform of the infrared light intensity and evaluate the soundness of the welded portion based on whether or not the maximum peak intensity exceeds a predetermined threshold. As described above, the method of obtaining the peak value of the infrared light intensity greatly simplifies the arithmetic processing as compared with the method of obtaining the average value of the infrared light intensity over a predetermined time.

  The present invention can be widely used particularly for laser welding apparatuses that perform welding while oscillating a laser beam.

DESCRIPTION OF SYMBOLS 1 Laser irradiation part 2 Infrared light detection part 3 Determination part 17 Monitor output measurement part IR Infrared light RB Laser beam S Laser welding apparatus W Work y1 Threshold value y2 Upper limit (threshold value)
y3 lower limit (threshold)

Claims (3)

A laser irradiation unit for irradiating a workpiece to be welded with a laser beam;
An infrared light detector for measuring the intensity of infrared light generated from the workpiece;
The infrared light detection unit compares the intensity of infrared light measured for each welding region with a preset threshold value relating to the intensity of infrared light to determine whether or not there is insufficient penetration in the welding region. The laser welding apparatus provided with the determination part. The laser irradiation pattern by the laser irradiation unit is wobbling,
The laser welding apparatus according to claim 1, wherein the measured intensity of infrared light is an average intensity of infrared light for each period of the wobbling. A monitor output measuring unit for measuring the output of the laser beam irradiated from the laser irradiation unit,
The determination unit holds in advance an upper limit value and a lower limit value for distinguishing the monitor output measured by the monitor output measurement unit, and the monitor output and the upper limit value, the lower limit value, and further, the measured infrared 3. The laser welding according to claim 1, wherein the soundness of the penetration state in the welding region and the cause of the occurrence of the failure when it is determined that the penetration state is defective are determined based on the intensity of light. apparatus.

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