JP2007326134A - Method and apparatus for judging welding performance and root gap accuracy in laser butt welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent poor weld from occurring by exactly estimating a root gap by conducting in-process monitoring for laser butt welding, and by determining root gap accuracy and welding performance. <P>SOLUTION: A laser head 2 is provided with sensors 7, 5 which detects the intensity of reflected light and thermal radiation light from a fusion part 6 of an irradiation laser, and monitores changes with time of the intensity of the reflected light or the thermal radiation light from the fusion part during butt welding, to determine the root gap accuracy. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for determining whether welding is possible and whether a root gap is appropriate in laser butt welding, and an apparatus therefor.

The root gap in butt laser welding, especially laser micro welding, is on the order of μm, which is smaller than the laser beam spot diameter, so it is difficult to set an appropriate value, and the laser head that irradiates the laser beam to this root gap is aligned. It is also an important factor that affects the welding result because it is difficult to do. Conventionally, the root gap is measured by photographing a groove to be welded before laser irradiation and processing the photographed image. For example, the illumination is applied to the root gap, the light passing through the root gap is imaged, the root gap is measured by image processing, or the entire sample is illuminated and the sample surface including the root gap is imaged, and then There is a method of measuring the route gap by processing.
When the butt groove is an I type, the root gap measured by image processing by applying illumination light perpendicularly to the root gap by the above method matches the actual root gap, but the I groove with R on the upper surface. When the groove shape is different, or when the illumination is not vertical, the measured route gap does not coincide with the actual route gap, resulting in a measurement error. In addition, machining lasers and welding dust may damage precision equipment for route gap measurement, resulting in measurement errors. In the latter case, a route gap inspection point is provided at a location different from the processing point, and inspection is performed. However, this causes an increase in inspection cost and a reduction in production tact, resulting in a decrease in productivity.

When a measurement error occurs, the center, which is the maximum power density portion of the irradiated laser beam, is shifted from the center of the root gap, resulting in incomplete joining, resulting in weld cracks and weld defects. Such weld cracks and weld defects are fatal in electrical and electronic parts that require precision joining of thin plates, which is the main object of butt laser welding of the present invention.
This is because, in general, the initial equipment investment cost of laser welding is higher by one digit or more than other joining machines, so that high-speed production tact is required. Therefore, in a production line for electrical / electronic parts, for example, a laser head that emits a laser beam is stopped, and a member to be welded having a butt I groove is intermittently sent at high speed and butt welding is repeatedly performed by a laser. Since the seam welded joint has been obtained and the workpiece to be welded is fed at a high speed to improve the processing efficiency, once the laser head and the root gap are aligned at the start, butt seam welding is continued without adjusting the position thereafter. The And since the number of weldings by the laser head is enormous, for example, several hundred million shots per year, even if the position is adjusted every week, if the alignment at the time of start is shifted due to the measurement error of the route gap, enormous defective products will appear. become. In particular, if there are several other processing steps after welding, these processing steps are completely wasted, causing great losses, and if defective products are put on the market, it will be even more expensive to recover. It will be.

  In addition, when the weld defect, so-called underfill, occurs where the weld pool descends and the surface of the welding material sinks due to the wide root gap, it is necessary to insert filler again and weld, and in that case, the production tact is greatly reduced.

By the way, the present inventors have recently proposed a new technique related to a method for preventing or repairing a hole defect in laser spot welding (Patent Document 1, Non-Patent Document 1). In this method, in the lap welding of aluminum alloy thin plate by pulse laser, the reflected light and thermal radiation from the melted part during laser irradiation are measured, the process state is judged based on the information, and the laser power and irradiation The time is controlled and the perforation is repaired in-process to obtain a good joint at all times.
However, there is no research literature or patent literature that discloses the welding process when welding a butt groove with a root gap with a pulse laser, the relationship between the root gap and welding failure, and the product yield and productivity due to welding failure. The current situation is that it is inevitable.
JP2005-246434 Y. Kawahito and S. Katayama: "In-process monitoring and adaptive control for stable production of sound welds in laser micro-spot lap welding of aluminum alloy", J. Laser Applications, Vol. 17, No. 1, (2005) , pp. 30-37

  The present invention was devised in view of the problems of the prior art. The object of the present invention is to replace the root gap with a laser at the time of laser butt welding, instead of the conventional method of photographing and image processing that is susceptible to measurement errors. Establish a method that can be accurately estimated based on the intensity of the reflected laser light or thermal radiation from the melted part, and determine whether the root gap is suitable and whether or not welding is possible, thereby eliminating welding defects. It is to be.

As a result of earnestly conducting various experiments and researches for in-process monitoring of the welding phenomenon of laser butt welding, the inventors have elucidated the mechanism by which the root gap is filled in the melted part and led to the present invention.
That is, the determination method in laser butt welding according to the present invention irradiates a material having a predetermined root gap with a laser having a beam diameter larger than the root gap with the maximum power density portion of the laser beam positioned in the root gap. Then, in the process of butt welding, the intensity of the reflected light of the irradiation laser from the melting part or the thermal radiation light from the melting part was measured, and the change over time of the measured light intensity was obtained in advance for a sample made of the same material. Compared with the reference data, whether or not welding is possible and whether or not a route gap is appropriate are determined.

According to the experiments and research by the inventors, in laser butt welding with a root gap, it is possible to accurately estimate the root gap based on the change over time in the intensity of the reflected laser light from the fusion zone or the thermal radiation from the fusion zone. It was revealed.
That is, until the melted portion fills the root gap, the irradiation laser passes through the root gap, and the scattered light from the periphery of the root gap is mainly measured, so the intensity of the reflected light is small. However, when the melted portion fills the root gap, the irradiation laser is totally reflected on the surface of the melted portion, and the intensity of the reflected light rapidly increases beyond a substantially constant value (threshold value). There is a proportional relationship between the root gap and the time from the start of welding until the root gap is filled and the intensity of reflected light suddenly increases. On the other hand, until the root gap is filled, the heat radiation from the melted part comes out of the part that is heated in the peripheral part of the laser beam and melted in a separated state, so the intensity is weak, and when the root gap is filled, the melted part reaches the maximum. Since heating / heating is performed at the center of the power density laser beam, the intensity of the heat radiation light rapidly increases beyond a certain value (derivative threshold). There is also a proportional relationship between the root gap and the time from the start of welding until the root gap is filled and the intensity of the heat radiation light suddenly increases. In the determination method of the present invention, in order to compare the temporal change of the measured light intensity, the above-described proportional relationship obtained in advance for the same sample as the material to be welded is provided as reference data. Therefore, if the time from the time-dependent change in the intensity of the reflected laser light or heat radiation from the melted part to the above time is read, it can be determined that the root gap is properly joined, and the root gap can be accurately estimated. On the other hand, if there is no sudden increase in reflected light and thermal radiation that exceed the threshold even if welding is continued, the root gap cannot be joined due to inappropriateness (excessive), and it can be determined that welding is impossible.

In one embodiment of the present invention, when the reference data is welded with a laser having a predetermined waveform while changing the root gap with respect to a predetermined sample, and the melting part fills the root gap, the reflected light of the irradiation laser is reflected. Threshold beyond which the intensity increases, or differential threshold at which the time derivative of the intensity of the reflected laser light or heat radiation increases beyond that, the elapsed time from the start of welding to the above point, and the root gap It is a data table comprising a set of values and the predetermined waveform.
In this embodiment, until the intensity of the reflected light or thermal radiation light being measured or the time derivative thereof exceeds the threshold value or derivative threshold value of the data table obtained in advance by welding the same sample with the same laser waveform. From the elapsed time, the corresponding route gap can be obtained by collating the data table.

One embodiment of the present invention is characterized in that the waveform of the laser applied to the sample has a low peak output sufficient for the melted portion to fill the root gap and a predetermined laser irradiation duration.
In the experiments and research that form the basis of the present invention, it has been clarified that the proportional relationship is clear and remarkable when the peak output (power) of the laser is low under the condition that the root gap is filled in the melted portion. . Therefore, according to this embodiment, the route gap can be estimated accurately and reliably.

In one embodiment of the present invention, a material having a root gap listed in the data table is welded with a pulse laser having a waveform listed in the data table, and the light intensity to be measured reaches the threshold value before the elapsed time has passed. When the time derivative of the light intensity that exceeds or exceeds the above-described derivative threshold value, the welding is judged to be possible or the route gap is appropriate and welding is continued. When the threshold value is not exceeded or the time derivative of the light intensity to be measured does not exceed the derivative threshold value, it is determined that welding is impossible or the root gap is inappropriate, and welding is stopped.
In this embodiment, when it is determined that welding is possible or the route gap is appropriate, welding is continued. When it is determined that welding is not possible or the route gap is inappropriate, welding is stopped. The product yield can be improved by adjusting the gap and the laser head position again.

One embodiment of the present invention is characterized in that the peak output of the waveform of the laser irradiating the material is low when it is determined that the peak output is low at the beginning of irradiation and that welding is possible or the route gap is appropriate.
In this embodiment, since the peak output of the laser is low at the initial stage of irradiation, the route gap can be estimated accurately and reliably by effectively using the data table obtained by irradiating the sample with a laser having a low peak output. After filling in the molten part, the peak output is increased and welding is performed, so that the penetration depth can be increased, and welding defects such as underfill that are likely to occur when the molten pool descends when the root gap is wide can be eliminated. it can.

The butt seam welding method of the present invention can be welded by the determination method in the laser butt welding of the present invention when irradiating a pulse laser to a material having a predetermined root gap and repeatedly performing butt seam welding by changing the irradiation point. Or after determining with root | route gap appropriateness, the process of returning an irradiation point to a reverse direction with respect to a seam welding direction and irradiating a laser is characterized.
In experiments and research that form the basis of the present invention, it has been clarified that in butt seam welding without changing the traveling direction, the root gap decreases on the traveling direction side and increases on the opposite side. Therefore, after determining that the joining can be surely performed by the determination method of the present invention, that is, welding is possible or the route gap is appropriate, the irradiation point is returned to the reverse direction with respect to the seam welding direction and the laser is irradiated. It was found that the root gap on the opposite side to the welding direction can be reduced by adding a process. According to this seam welding method, a better butt seam welded joint can be obtained with a high yield.

The apparatus for determining whether welding is possible and whether the root gap is suitable according to the present invention includes a monitor unit that measures the intensity of at least one of the reflected light of the irradiation laser from the melting part and the thermal radiation light from the melting part during laser irradiation, and the monitor. The time-dependent change of the measurement signal from the part was determined in advance for the same material to be welded, and compared with the stored reference data to determine whether welding was possible and whether the root gap was appropriate. When the control unit outputs a signal to maintain or change the set pulse waveform and outputs a signal to stop welding when it is determined that welding is not possible or the route gap is inappropriate, the operation is controlled by the output signal from this control unit. It is characterized by having a laser oscillator.
In the determination apparatus of the present invention, the monitor unit measures the intensity of at least one of the reflected light of the irradiation laser from the melting unit and the heat radiation light from the melting unit during laser irradiation, and the control unit receives from the monitoring unit. The time-dependent change of the measurement signal of the same material to be welded is obtained in advance and compared with the stored reference data to determine whether or not welding is possible and whether or not the root gap is appropriate. A signal for maintaining or changing the set laser waveform is output, and when it is determined that welding is impossible or the root gap is inappropriate, a signal for stopping welding is output. The operation of the laser oscillator is controlled by the output signal from the control unit. When the welding is possible or the route gap is appropriate, the laser is continuously irradiated with a waveform that is maintained or changed. Otherwise, the laser irradiation is stopped. Stop welding. Therefore, according to this determination apparatus, welding failure can be prevented in advance by stopping welding, and the operator can adjust the route gap and the laser head to an appropriate route gap. Product yield can be improved by preventing an increase in cost and a decrease in production tact.

Hereinafter, the present invention will be described in detail with reference to illustrated embodiments.
FIG. 1 is a schematic diagram of a laser butt welding apparatus that is used for basic research of a method for determining the suitability of a root gap in laser butt welding according to the present invention and is also an apparatus for the determination method according to the present invention. In FIG. 1, reference numeral 1 denotes an adaptive control YAG pulse laser generator (hereinafter abbreviated as a laser generator) as a laser oscillator that generates a pulse laser having a wavelength of 1.064 μm, and 2 denotes an optical fiber 3 from the laser generator 1. A laser head 5 for irradiating a butt joint 4 made of a metal to the butt joint 4 made of metal is provided at the top of the laser head 2 and captures heat radiation light having a wavelength of 1.3 μm from the melting portion 6 during laser irradiation. An optical sensor 7 is provided on the side of the laser head 2, and a reflected light sensor 10 captures reflected light having a wavelength of 1.064 μm of the irradiation laser from the melting part 6 during laser irradiation, and 10 is input via signal lines 8 and 9, respectively. The time-dependent changes in the measurement signals of the thermal radiation light sensor 5 and the reflected light sensor 7 are compared with the reference data obtained in advance for the same material to be welded and stored, and whether or not welding is possible and When it is determined whether or not welding is possible or the root gap is appropriate, a signal to maintain or change the set pulse waveform is output, and when it is determined that welding is not possible or the root gap is inappropriate, a signal to stop welding is output. It is a computer as a control part. The thermal radiation sensor 5 and the reflected light sensor 7 constitute a monitor unit that measures the light intensity over one pulse period.

The laser generator 1 has an average output of 50 W, and can control the peak output of the pulse laser at intervals of 0.1 ms within a range of 5 kW or less by a command signal from the computer 10.
The laser head 2 emits a laser beam from the optical fiber 3 through the dichroic mirror 11, and guides the reflected light of the irradiated laser to the reflected light sensor 7 through the dichroic mirror 12 to selectively attenuate the reflected light. Via the notch filter 13 and the interference filter 14, weak thermal radiation light on the order of nW is guided to the thermal radiation light sensor 5. The detection signal of the reflected light sensor 7 is measured by a measuring instrument, and the detection signal of thermal radiation light captured by the thermal radiation sensor 5 with a spot diameter of 500 μm is amplified by a preamplifier having a cutoff frequency of 100 kHz and an amplification factor of 6.8 × 10 ^5. And measured.
In addition, the surface state of the butt joint 4 was photographed at high speed in order to analyze the welding phenomenon during laser irradiation. The He-Ne laser oscillator 15 on the upper left side was irradiated with a back light for high-speed shooting on the melted part 6, and the surface state was shot at 9,000 frames per second by the high-speed camera 16 on the upper right side. Note that argon is supplied at a predetermined flow rate as a shielding gas from a cylinder (not shown) to the melting portion 6 irradiated with the laser.

  First, in order to elucidate the relationship between the root gap of the I-type groove and the butt pulse laser welding result, welding is performed by irradiating the butt joint 4 made of a pair of titanium plates with a pulse laser under the welding conditions shown in Table 1. It was. In addition, a pair of titanium plates are artificially created with a root gap by sandwiching one or more copper foils with a thickness of 0.03mm at both ends, and the adhesive tape is wound around the root gap to prevent the root gap from being compressed. It is fixed on a table, the above-mentioned route gap is measured, and while the image of the high-speed camera 16 is observed, the x, y table is moved to align the center of the route gap with the center of the laser head 2 at a fixed position. .

FIG. 2A shows a photographed image of the melt surface at each time point (ms) during welding under the welding conditions where the peak output P _k is 0.4 kW, the pulse duration W _k is 15 ms, and the root gap is 98 μm. Similar captured images are shown under welding conditions with an output P _k of 1.6 kW, a pulse duration W _k of 2 ms, and a root gap of 98 μm. Moreover, the photograph of the welded part surface after welding and the cross section of a welded part is shown in the upper right and the lower side of the photographed image of the melted part.
At the peak output of 0.4 kW, after starting laser irradiation, the titanium plates on both sides of the root gap were heated and melted, and when laser irradiation was continued, the volume of the melted portion gradually increased. When the volume of the molten part reached an amount sufficient to fill the root gap, butt welding was completed by joining the melts on both sides. At a peak output of 1.6 kW, immediately after the start of the laser, the titanium plates on both sides of the root gap are heated and melted, and immediately after that, the molten melt flows down into the root gap and melts at a position lower than the focal position of the laser. Butt welding was completed by joining together.

FIG. 3 shows a groove plane before welding, a joint plane after welding, and a cross-sectional shape after welding under the welding conditions shown in Table 1 for two route gaps. FIG. 4 shows the relationship between the diameter in the butt direction of the joint surface and the root gap at each peak output, FIG. 5 shows the relationship between the root gap before and after welding, and FIG. 6 shows the relationship between the penetration depth and the root gap. FIG. 7 shows the relationship between the depth of the underfill and the route gap.
Looking at the middle part of FIG. 3 and FIG. 4, the shape of the joint was circular, but the diameter decreased as the root gap widened. This is because the stronger the laser output, the more the melt flows into the root gap, and the area of the melted portion on the surface becomes smaller. Moreover, as shown in FIG. 5, it turned out that a root gap reduces after welding. This is because the root gap is reduced by pulling the titanium plates on both sides when the melts on both sides of the root gap are joined and cooled and solidified after the end of laser irradiation.
Referring to the lower part of FIG. 3 and FIG. 6, the penetration depth becomes deeper as the root gap widens. Moreover, the tendency is so remarkable that laser output is strong. This is because the melt flows down into the root gap, and the amount of melt that flows down increases as the output increases. However, since the melt flowed down to the root gap, it was found that underfill also occurred as shown in FIG. The underfill increases as the root gap widens, and the tendency becomes more pronounced as the laser output becomes stronger. On the other hand, as seen in the lower part of FIG. 3, it can be seen that the porosity decreases as the route gap widens. This is considered to be because the porosity escapes from the bottom of the joint because there is a space below the keyhole due to the root gap in the process of the keyhole collapsing after the laser irradiation.
From the above, under the welding conditions shown in Table 1 in butt welding with a root gap, the root gap decreases after joining. However, it was clarified that the melted portion on the surface is reduced and the penetration depth is deepened due to the root gap, but the underfill is generated while the porosity is reduced.

Next, in-process monitoring was performed to elucidate the welding phenomenon during butt welding with the above-mentioned route gap. FIG. 8 shows an example of the laser pulse output in this in-process monitoring, the measurement result of the reflected light of the irradiation laser from the melting part, the measurement result of the intensity of the thermal radiation from the melting part, and the photographed image of the melting part by the high-speed camera 16. And shown in FIG.
The welding conditions in FIG. 8 are the peak output P _k = 0.4 kW in Table 1, pulse duration W _k = 15 ms, laser focusing, laser spot diameter 150 μm, Ar gas flow rate 40 liter / min, route gap 98 μm. In the upper graph of FIG. 8, the horizontal axis represents the time from the start of laser irradiation, and the vertical axis represents the actually measured laser output and the units of reflected light and thermal radiation light in different units ([kW], [mW], [ × 5μW]), and each plot with a common scale. The middle figure shows a photographed image of the melted part, and the lower figure shows a macro photograph of the cross section. The macro photograph is a photograph in which butt welding was performed on another sample under the same conditions, laser irradiation was stopped at each irradiation time shown in the photograph, and the molten portion was cut perpendicularly to the bead and macro-corroded. The welding conditions in FIG. 9 differ from the welding conditions in FIG. 8 only in that the peak output P _k = 1.6 kW, the pulse duration W _k = 2 ms, and the root gap is 106 μm.

The following can be seen from FIG. From the start of laser irradiation until 5 ms when the molten titanium members on both sides of the root gap are joined, the intensity of thermal radiation increases in proportion to time, and the intensity of reflected light is constant at a low value. After the titanium member melted in 5 ms from the start of laser irradiation, the heat radiation intensity and the reflected light intensity increase rapidly. Thereafter, the heat radiation light gradually increased while increasing and decreasing as time passed. This is considered to be a result of the increase in the molten pool due to a part of the reflected light passing through the root gap and the heat radiation light being heated by the laser light hitting the periphery of the root gap before the joining. . At 5 ms, a molten pool was formed across the root gap, the reflected light returned strongly, the heat radiation increased rapidly, and then the same trend as when there was no root gap was observed. This is considered to be due to the fact that the absorption of the reflected laser beam is greatly increased as a result of the laser beam not passing through. As described above, the intensity of the heat radiation light and the reflected light greatly varies depending on the presence or absence of the molten pool. Therefore, in the case of butt welding having a root gap, it is considered to be effective as a means for determining whether or not the joining has been achieved. Also, from the observation of the cross-section, if laser irradiation is stopped before joining, the molten melt is cooled and returns to its original shape, and after joining, the penetration depth is confirmed not to become significantly deeper. It was done.
The following can be seen from FIG. The changes in the intensity of the heat radiation light and the intensity of the reflected light before and after the joining are not as remarkable as in the case of FIG. This is because the peak output is as high as 1.6 kW, so a large amount of melt vibrates or flows down into the root gap and joins, so the effect appears in the intensity of thermal radiation and reflected light. .
From the above, it has been clarified that in butt welding with a root gap, if the peak output of the pulse laser is low, it is possible to detect whether or not the joining has been performed by monitoring the thermal radiation light and the reflected light.

Furthermore, it was investigated whether or not sudden changes in the heat radiation light intensity and the reflected light intensity occurred at the time of joining in butt welding with a root gap. Based on the captured image of the high-speed camera as shown in the middle of Fig. 9 obtained by in-process monitoring of the welding with the peak output of the pulse laser changed to 3 and the root gap changed to 5, The relationship between the time until the molten pool is formed and the root gap is plotted in FIG. 10, with time plotted on the vertical axis and route gap plotted on the horizontal axis. From FIG. 10, it can be seen that the longer the root gap and the lower the laser peak output P _k , the longer the bonding takes. When the peak output is 0.4 kW, the thermal radiation intensity rapidly increases, that is, the relationship between the time when the time derivative of the thermal radiation intensity exceeds the threshold value of 6 mW / s and the route gap is shown in FIG. FIG. 12 shows the relationship between the time increased over 0.08 mW and the route gap. 10, 11, and 12, it can be seen that the time at which bonding occurs and the time at which abrupt changes occur in the thermal radiation light intensity and the reflected light intensity are substantially the same.
From the above, it has been clarified that the intensity of the heat radiation light and the intensity of the reflected light change rapidly when a weld pool is formed by butt welding with a root gap and a weld pool is formed.

Therefore, from the proportional relationship shown in FIG. 12, as a criterion for determining whether or not joining has occurred in butt welding monitoring with a root gap and a criterion for estimating the root gap, when the peak output of the pulse laser is low (0.4 kW) The time when the reflected light intensity exceeds the predetermined threshold (0.08 mW) or the time when the time derivative of the thermal radiation intensity exceeds the predetermined derivative threshold (6 mW / s) is selected from the proportional relationship shown in FIG. .
As can be seen from the fact that there is no plot point at the position corresponding to the route gap of 54 μm in FIG. 11, the thermal radiation intensity does not show a significant threshold of the time derivative when the route gap becomes small. Not an estimation criterion. This is apparent from FIG. FIG. 13 shows the increment of thermal radiation light intensity every 0.04 ms near the time when joining occurs in the butt welding monitoring with a root gap of 54 μm and 98 μm with a pulse laser with a peak output of 0.4 kW on the left and right sides, respectively. . From the photographed image, bonding occurs at 1.44 ms when the root gap is 54 μm and at 4.81 ms when 98 μm. In the figure on the right side where the root gap is large, the time gradient of the thermal synchrotron radiation intensity increases sharply at the time of joining, while in the figure on the left side where the root gap is small, there is a noticeable change in the temporal gradient of the thermal synchrotron radiation intensity. Absent.

Based on the result of the above in-process monitoring, the intensity of the reflected light from the melting part of the irradiation laser is shown in the computer 10 which is the control part of the laser butt welding apparatus shown in FIG. FIG. 12 or FIG. 11 shows a predetermined threshold value that increases beyond or a predetermined derivative threshold value that increases the intensity of the heat radiation light from the melted portion at an increase rate exceeding the predetermined threshold value, and the elapsed time from the start of welding to the point in time. A data table composed of a set of such a relationship, a welding condition, a root gap value, and a pulse laser waveform (peak output, pulse duration) is stored in advance as reference data.
When welding is performed by a pulse laser generated by the laser generator 1 and emitted from the laser head 2, the computer 10 generates a route gap-elapsed time data table corresponding to the welding conditions input by the operator from the reference data. The time-dependent changes in the detection signals from the thermal radiation light sensor 5 and the reflected light sensor 7 that are selected and monitored are compared with the selected data table, and before the reflected light intensity that changes with time passes the elapsed time of the data table. When the specified threshold value is exceeded or the time derivative of the thermal radiation intensity exceeds the specified derivative threshold value before the elapsed time of the data table, it is determined that welding is possible or the root gap is appropriate, and welding is continued under the welding conditions. On the other hand, the light intensity changing with time does not exceed the predetermined threshold even after the elapsed time of the data table, or the time derivative of the light intensity is given. When the definite coefficient threshold is not exceeded, it is determined that welding is impossible or the root gap is inappropriate, and welding is stopped.
According to the computer 10 of the laser butt welding apparatus, welding is stopped, so that it is possible to prevent welding failure due to inadequate root gap or beam alignment, and an operator can adjust the proper root gap and laser head position. By reworking, it is possible to prevent a great loss due to poor welding, an increase in inspection cost, and a decrease in production tact, and to improve the product yield.

As an embodiment of the route gap suitability determination method of the present invention, an adaptive control method for underfill reduction will be described below.
As described in FIG. 6 in the previous embodiment, when the peak output of the pulse laser is high, the melt flows down to the root gap and underfill occurs. On the other hand, when the peak output is low, the underfill is reduced. A sufficient penetration depth cannot be obtained. Therefore, in this embodiment, irradiation is performed with a laser having a low peak output immediately after the start of laser irradiation, and the peak output is increased after the melted portion is joined to obtain deep penetration. This is because if the molten pool is formed by joining, the melt does not flow down to the root gap even at a high peak output. Whether or not bonding has occurred is determined by monitoring the reflected light from the melted portion of the irradiation laser, as in the previous embodiment.
FIG. 14A and FIG. 14B show the flow chart of the adaptive control method and the temporal change in reflected light intensity and laser output at that time, respectively. When the adaptive control starts, the computer 10 starts monitoring the detection signals from the thermal radiation sensor 5 and the reflected light sensor 7 every 0.15 ms, and the peak output of the laser is as low as 0.4 kW in step S1 of FIG. 12A. In step S2, it is determined whether or not bonding has occurred depending on whether or not the reflected light intensity exceeds 0.08 mW. If NO is determined in step S2, the process returns to step S1 to maintain the peak output at 0.4 kW. If YES is determined, the process proceeds to step S4, where the junction is generated and the peak output is increased to 1.6 kW. Then, in step S4, it is determined whether or not the underfill is suppressed depending on whether or not the heat radiation light intensity exceeds 1.7 μW, and whether or not the molten pool is stabilized to obtain a sufficient penetration depth. If it is determined that the peak output is maintained at 1.6 kW, if it is determined affirmative, the laser irradiation is stopped and the adaptive control is terminated.

Using the above-mentioned adaptive control method for preventing underfill, five titanium butt joints with different root gaps of 60 μm, 78 μm, 84 μm, 95 μm and 106 μm were laser welded. The upper graph of FIG. 15 and the lower graph of FIG. 15 show the laser output in the butt welding of the joint having a root gap of 95 μm, the temporal change of reflected light intensity and thermal radiation light intensity, and the image taken by the high-speed camera of the melted part. Shown in each photo. However, the vertical axis of the graph plots the measured laser output and the intensity of reflected light and thermal radiation light on a common scale using different units ([kW], [× 0.1mW], [× 2μW]). ing. The welding conditions were a titanium joint material, a pulse laser with a spot diameter of 150 μm focused on a heat source, and an Ar gas flow rate of 40 liters / min.
Referring to FIG. 15, during the laser irradiation with the initial peak output of 0.4 kW, the titanium members on both sides of the root gap were heated and melted. Meanwhile, the intensity of heat radiation increased in proportion to the time, and the intensity of reflected light was constant at about 0.04 mW. When 5.4 ms passed from the start of laser irradiation, the melts joined together, and the intensity of heat radiation and reflected light increased rapidly. Then, it was determined that the reflected light intensity exceeded 0.08 mW, and the peak output was increased to 1.6 kW. Even if the peak power was increased, the melt did not flow down and welding could be continued. Finally, after 7.0 ms from the start of laser irradiation, the intensity of heat radiation exceeded 1.7 μW, so laser irradiation was terminated.

FIG. 16 shows the state of the surface and cross section of the welded portion after the butt welding. The number below each photo is the root gap of the joint before welding. From FIG. 16, it was found that if the root gap is 106 μm, underfill can be reduced and deep penetration can be obtained by using adaptive control. 17, 18, and 19 show the relationship between the melted part surface diameter, the penetration depth, and the underfill and route gap measured after welding, respectively. For comparison, the values obtained by butt welding with a laser peak output of 1.6 kW and an irradiation time of 2 ms are also plotted as points without adaptive control for comparison. From FIG. 17, it can be seen that the surface diameter of the melted part when adaptive control is used does not decrease even when the root gap becomes larger and is stable at a substantially constant value than when adaptive control is not used. I understand. It can be seen from FIG. 18 that the penetration depth is not different depending on the presence or absence of adaptive control, and tends to become deeper as the route gap becomes larger. It can be seen from FIG. 19 that the underfill when adaptive control is used is considerably reduced as compared with the case where adaptive control is not used, and depression of the surface of the weld is suppressed. However, a tendency to increase as the route gap increases is recognized.
From the above, it has been clarified that the adaptive control of this embodiment has an effect of reducing the underfill in the butt welding having the root gap and stabilizing the melted part surface diameter.
The computer 10 which is the control unit of the laser butt welding apparatus of FIG. 1 which also serves as the determination apparatus of the present invention includes the initial and increase of lasers determined in advance corresponding to the welding conditions including the plate thickness of the material to be welded and the root gap. The later peak output is stored as reference data in the data table described above. When adaptive control for underfill reduction is selected by the operator, the peak output corresponding to the welding conditions is read from the data table and the adaptive control is performed. Therefore, if the laser butt welding apparatus of FIG. 1 is used, underfill can be reduced and the surface diameter of the melted part can be stabilized.

As another embodiment of the route gap suitability determination method of the present invention, butt seam welding using this determination method will be described below.
In the previous embodiment, the pulse laser is irradiated to one point of the material to be welded without relatively moving the material to be welded and the laser head. Welding is performed so that the welded portion is connected by changing this irradiation point. Repeated butt seam welding is also frequently used in the field of manufacturing electrical and electronic components. Therefore, as a basic study, butt seam welding with a root gap was performed, and changes in the root gap after welding were investigated. Butt seam welding was performed by irradiating a pure titanium material with a root gap of 0.101 mm with a pulsed laser with a peak output of 1.6 kW and a duration of 2 ms, and repeating the irradiation 10 times while shifting the irradiation position by 0.34 mm. In addition, seam welding was performed using the adaptive control described in the previous embodiment under the same conditions.
The surface and cross-sectional state of the seam after welding when application control is not used and when it is used are shown in the upper and lower photographs of FIGS. 20A and 20B, respectively. The left and right sides of the surface state photograph show the root gaps at the left and right ends of the joint. The order of laser irradiation is from left to right as viewed in the photo.

The relationship between the order of laser irradiation and the melted part surface diameter, penetration depth, and underfill is plotted on the horizontal axis in both cases where adaptive control is used and not used, with the horizontal axis plotted in FIGS. 22 and FIG. 23, respectively. In addition, the underfill was plotted as a positive value when it was lowered with respect to the surface of the base material, and a negative value when it was raised.
When the adaptive control is not used, the melted part surface diameter in FIG. 21 decreases and becomes stable as the melted part diameter by the first laser irradiation decreases. On the other hand, when adaptive control is used, there is less fluctuation from the melted portion due to the first laser irradiation and stabilization compared to when adaptive control is not used. This tendency is conspicuous in the first three laser irradiations without using adaptive control, but from the fourth time onward, the diameter was almost the same as when using adaptive control.
The penetration depth in FIG. 22 decreases as laser irradiation is repeated, whether or not adaptive control is used.
When the adaptive control is not used, the underfill in FIG. 23 became deeper by the first irradiation, but became shallower and stabilized as the laser irradiation was repeated. When adaptive control was used, it was shallow at the first irradiation, but the second and subsequent times were not much different from the case where adaptive control was not used. From this, it is considered that the molten state changes as the laser irradiation is repeated. 20A and 20B, when the photographs of both ends of the sample after butt welding are seen, the root gap at the right end, which is the irradiation position movement direction, is decreased, and the root gap at the opposite left end is increased. . As described in the first embodiment, when the root gap is reduced after welding, as shown in FIG. 24, when the laser irradiation is repeated, the root gap in the irradiation position movement direction is reduced by the laser irradiation. This is probably because the route gap in the reverse direction increases. Therefore, as the laser irradiation is repeated, the root gap decreases, and the melt does not flow down into the root gap. Therefore, the melted part diameter becomes stable, the underfill becomes shallow, and the penetration depth becomes shallow.
From the above, it was clarified that when butt seam welding with a root gap is performed, the root gap in the irradiation position movement direction decreases and the underfill becomes shallow.

In the basic research described above, it has been found that the root gap decreases in the traveling direction when butt welding is repeated, but increases in the opposite direction. Therefore, in this embodiment, a butt seam welding method that does not increase the root gap will be described. In this embodiment, the laser irradiation position is moved so as to spread from the inside to the outside. That is, as shown in FIG. 25, after the laser is irradiated twice in order in the right direction, the third time is irradiated to the left side of the first irradiation point. This is expected to reduce the left route gap. Next, irradiation is performed sequentially in such a manner that the fourth irradiation is performed on the right side of the second irradiation point and the fifth irradiation is performed on the left side of the third irradiation point. Seam welding of butt joints with a root gap of 0.095 mm was performed in this order using the adaptive control method described above for underfill reduction. The surface and cross-sectional state of the seam after welding are shown in the upper and lower photographs in FIG. The left and right sides of the surface state photograph show the root gaps at the left and right ends of the joint. As is clear from FIG. 26, both the root gaps at the left and right ends of the joint could be reduced.
From the above, it became clear that the root gap can be reduced by changing the order of laser irradiation in butt seam welding with a root gap.

In the previous embodiment, it has been described that when butt seam welding is performed in a certain direction, the root gap opposite to the traveling direction increases, and when butt welding with a large root gap is performed, the porosity decreases. Therefore, we examined whether the laser irradiation order can be changed to increase the root gap and simultaneously reduce the porosity. For example, as shown in FIG. 27, after laser irradiation is performed twice in the left direction, the third irradiation is performed on the right side of the first time with a distance of one laser irradiation, and the fourth time is performed on the left side of the third time. Irradiate. This is expected to increase the right route gap. Next, irradiation is performed sequentially in such a manner that the fifth irradiation is performed on the right side that is one time away from the third irradiation point, and the sixth irradiation is performed on the left side of the fifth. Seam welding of butt joints with a root gap of 0.092 mm was performed in this order using the adaptive control method described above for underfill reduction. The state of the surface and cross section of the seam after welding is shown in the upper and lower photographs in FIG. 28, respectively. The left and right sides of the surface state photograph show the root gaps at the left and right ends of the joint. From the cross-sectional photograph of FIG. 28, no significant decrease in porosity was observed.
FIG. 29 is a graph obtained by monitoring the reflected light from the melted part of the irradiation laser and plotting the time from the start of laser irradiation until the reflected light intensity rapidly increases in the order in which the laser irradiation was performed. In the previous embodiment, when the peak output of the laser is low, the time until the reflected light intensity increases rapidly is proportional to the root gap. Also, in adaptive control for underfill reduction, irradiation with a low peak output laser is initially performed when determining whether or not bonding has occurred. Therefore, in the graph of FIG. 29, a considerable root gap is generated in the first, third, and fifth laser irradiations that take a long time until the reflected light intensity rapidly increases, and the root gap is generated in other laser irradiations. It can be seen that is very narrow. In other words, even if seam welding was performed with the laser irradiation order changed as described above, it was difficult to increase the root gap, and as a result, the reduction in porosity could not be realized as seen in the cross-sectional photograph of FIG. It can be concluded that

  A method for determining the suitability of a root gap in laser butt welding according to the present invention and an apparatus therefor are used for seam welding of metal electronic parts and battery packages in the electronic / electric field, and blades for cutting large plates of glass such as plasma televisions and liquid crystals. Can be used for welding.

FIG. 1 is a schematic view of a laser butt welding apparatus which is an apparatus for the determination method of the present invention. FIG. 2A is a photographed image of the surface of the melted part during butt welding and a photograph of the surface and cross section of the welded part after welding. FIG. 2B is a similar image and photograph during and after butt welding with different pulse waveforms. FIG. 3 is a photograph showing the state of the groove plane before welding and the joint plane and cross-section after welding when welding a butt joint having three root gaps with three kinds of pulse waveforms. FIG. 4 is a graph showing the relationship between the joint surface diameter welded at each peak output and the root gap. FIG. 5 is a graph showing the relationship between the root gap before and after welding at each peak output. FIG. 6 is a graph showing the relationship between the penetration depth and the root gap of the joint welded at each peak output. FIG. 7 is a graph showing the relationship between the underfill and the root gap of the joint welded at each peak output. FIG. 8 shows the laser pulse output in in-process monitoring during butt welding with a root gap, the intensity of reflected light of the irradiation laser from the melting part, the measurement result of the intensity of thermal radiation from the melting part, and the melting part by a high-speed camera. It is a figure which shows the picked-up image. FIG. 9 is a view similar to FIG. 7 in in-process monitoring during butt welding with different pulse waveforms. FIG. 10 is a graph showing the relationship between the time from the start of laser irradiation to the time when the melted portion joins and the root gap. FIG. 11 is a graph showing the relationship between the time from the start of laser irradiation until the time derivative of the intensity of thermal radiation exceeds the threshold (6 mW / s) and the root gap. FIG. 12 is a graph showing the relationship between the time from the start of laser irradiation until the reflected light intensity exceeds the threshold (0.08 mW) and the root gap. FIG. 13 is a graph showing the increment of thermal radiation light intensity every 0.04 ms in the vicinity of the time when the fusion zone is joined by butt welding with two types of root gaps by a pulse laser having a peak output of 0.4 kW. FIG. 14A is a flowchart showing a flow of an adaptive control method for preventing underfill. FIG. 14B is a graph showing changes in reflected light intensity and laser output over time during this adaptive control. FIG. 15 is a graph showing changes over time in laser output, reflected light intensity, and thermal radiation light intensity when pulsed laser welding is performed on a butt joint having a predetermined root gap using an adaptive control method for preventing underfill, and a high speed of a melted portion. It is a photograph which shows the picked-up image by a camera. FIG. 16 is a photograph showing the surface and cross-sectional states of the welded portion after pulse laser welding of a butt joint having five types of route gaps under predetermined welding conditions using underfill prevention adaptive control. FIG. 17 is a graph showing the relationship between the melt surface diameter and the root gap measured with the sample of FIG. 16 together with a comparative example by butt welding without underfill prevention adaptive control. FIG. 18 is a graph showing the relationship between the penetration depth and the root gap measured with the sample of FIG. 16 together with a comparative example by butt welding without underfill prevention adaptive control. FIG. 19 is a graph showing the relationship between the underfill and the root gap measured with the sample of FIG. 16 together with a comparative example by butt welding without underfill prevention adaptive control. FIG. 20A is a photograph showing the surface and cross-sectional shape of a seam after butt seam welding without adaptive control of underfill prevention. FIG. 20B is a similar photograph after butt seam welding using adaptive control to prevent underfill. FIG. 21 is a graph showing the relationship between the melted part surface diameter measured with the samples of FIGS. 20A and 20B and the order of laser irradiation. FIG. 22 is a graph showing the relationship between the penetration depth actually measured for the samples of FIGS. 20A and 20B and the order of laser irradiation. FIG. 23 is a graph showing the relationship between the underfill measured in the samples of FIGS. 20A and 20B and the order of laser irradiation. FIG. 24 is a schematic diagram showing changes in the root gap when the laser irradiation position is moved in one direction and butt seam welding is performed. FIG. 25 is a schematic diagram showing a change in the root gap when the laser irradiation position is moved in both directions and butt seam welding is performed. FIG. 26 is a photograph showing the surface and cross-sectional shape of the seam after butt seam welding by the method of FIG. FIG. 27 is a schematic diagram showing a change in the root gap when the irradiation position is moved in both directions with a distance of one laser irradiation and butt seam welding is performed. FIG. 28 is a photograph showing the surface and cross-sectional shape of the seam after butt seam welding by the method of FIG. FIG. 29 is a graph showing the relationship between the time from the start of laser irradiation until the reflected light intensity suddenly increases and the order of laser irradiation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Adaptive control type YAG pulse laser generator 2 Laser head 3 Optical fiber 4 Butt joint 5 Thermal radiation sensor 6 Melting part 7 Reflected light sensor 10 Computer 11,12 Dichroic mirror 13 Notch filter 14 Interference filter 15 He-Ne laser oscillator ( (For back light)
16 High-speed camera

Claims (7)

In the process of butt welding by irradiating a material having a predetermined root gap with a laser having a beam diameter larger than the root gap with the maximum power density portion of the laser beam positioned in the root gap,
We measure the intensity of the reflected light from the laser irradiated from the fusion zone or the intensity of the thermal radiation from the fusion zone, and compare the time-dependent change in the measured light intensity with the reference data obtained in advance for a sample made of the same material. A determination method in laser butt welding, characterized in that determination is made as to whether or not a route gap is appropriate and whether or not a route gap is appropriate.   2. The determination method according to claim 1, wherein the reference data is a reflection of an irradiation laser when a predetermined sample is welded with a laser having a predetermined waveform while changing a root gap, and the melted portion fills the root gap. A threshold value over which the intensity of light increases, or a differential coefficient threshold value over which the time derivative of the intensity of reflected light or heat radiation of the irradiation laser increases, and the elapsed time from the start of welding to the above point, A determination method comprising a data table including a set of a root gap value and the predetermined waveform.   3. The determination method according to claim 2, wherein the waveform of the laser applied to the sample has a low peak output sufficient for the melted portion to fill the root gap and a predetermined laser irradiation duration.   3. The determination method according to claim 2, wherein a material having a root gap on the data table is welded with a laser having a waveform on the data table, and the light intensity to be measured before the elapsed time exceeds the threshold value. Or when the time derivative of the measured light intensity exceeds the derivative threshold, welding is determined to be possible or the route gap is appropriate and welding is continued. A determination method comprising: determining that welding is impossible or route gap inadequate and stopping welding when the threshold value does not exceed or the time derivative of the light intensity to be measured does not exceed the derivative threshold value.   5. The determination method according to claim 4, wherein the laser waveform irradiated to the material has a low peak output at the beginning of irradiation, and the peak output increases when it is determined that welding is possible or the route gap is appropriate. Method.   In the method of repeatedly butt seam welding by changing the irradiation point to irradiate a material having a predetermined route gap with laser, after determining that welding is possible or the route gap is appropriate by the determination method according to claim 4, A butt seam welding method comprising a step of irradiating a laser by returning an irradiation point in a direction opposite to a seam welding direction. An apparatus for determining whether or not welding is possible and whether or not a root gap is appropriate in laser butt welding,
A monitor unit that measures the intensity of at least one of the reflected light of the irradiation laser from the melting part and the heat radiation light from the melting part during laser irradiation;
The change over time of the measurement signal from the monitor unit is obtained in advance for the same material to be welded and compared with the stored reference data to determine whether or not welding is possible and whether or not the route gap is appropriate. A control unit that outputs a signal for maintaining or changing the set laser waveform when it is determined, and that outputs a signal for stopping welding when it is determined that welding is impossible or the route gap is inappropriate;
A determination apparatus comprising a laser oscillator whose operation is controlled by an output signal from the control unit.