JP4818029B2 - Laser welding evaluation method - Google Patents

Description

  The present invention relates to a laser welding evaluation method.

As a technique for evaluating welding quality such as distortion amount and strength of a welded portion formed on a workpiece by laser welding, there is a laser welding quality inspection method described in Patent Document 1, for example. In this conventional laser welding quality inspection method, light emission of a plasma plume generated on the surface of a workpiece during laser welding is detected, and whether or not the welding quality is determined based on the amplitude value of a predetermined frequency band in the detection signal. Judging. For example, in the laser processing inspection method described in Patent Document 2, sound generated from a laser welding portion is detected, and whether or not the welding quality of the workpiece is acceptable is determined based on the amplitude value of the detection signal.
JP 2003-103387 A Japanese Patent Laid-Open No. 58-9783

  In the conventional inspection method as described above, the output pattern of the detection signal at the time of laser welding when the weld quality of the welded part is determined to be good (or determined to be defective) is used as a model pattern. Further, based on a simple comparison between the output pattern of the detection signal at the time of laser welding of the workpiece to be evaluated and the model pattern, whether or not the weld quality of the welded portion is acceptable is determined. For this reason, when the difference between both patterns itself is small, for example, when the output pattern of the detection signal at the time of evaluation and the model pattern overlap, it is difficult to determine whether or not the welding quality is acceptable. However, even if the difference between the two patterns at first glance is small, an abnormality may be recognized in the weld quality of the welded portion, and thus a technique capable of accurately determining whether the weld quality is acceptable is desired. Yes.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a laser welding evaluation method capable of accurately determining whether welding quality is acceptable.

  In order to solve the above problems, a laser welding evaluation method according to the present invention is a laser welding evaluation method for evaluating the welding quality of a weld formed on a workpiece by irradiation with a laser beam. A change in the physical quantity of the environmental state at the time of irradiating the workpiece with the laser beam is detected by the welding environment detection means, and each output value of the reference output signal output from the welding environment detection means is normalized to obtain the first value. A step of calculating a normalization value, and a measurement output from the welding environment detection unit by detecting a change in a physical quantity of an environmental state when the workpiece to be evaluated is irradiated with a laser beam. Normalizing each output value of the output signal for use and calculating a second normalized value; first comparison data comparing the first normalized value and each output value of the reference output signal; Based on the difference between the second normalized value and the second comparison data obtained by comparing each output value of the output signal for measurement, the welding quality of the weld formed on the workpiece to be evaluated And a step of determining whether or not it is possible.

  In this laser welding evaluation method, the first normalized value is calculated in advance from each output value of the reference output signal, and each output value of the measurement output signal is normalized to separately obtain the second normalized value. To calculate. The first comparison data comparing the first normalized value and each output value of the reference output signal, and the second comparison value comparing the second normalized value and each output value of the measurement output signal. Based on the difference with the comparison data of 2, whether or not the welding quality of the welded portion is acceptable is determined. Here, the difference between the first normalized value and the second normalized value is the amount of deviation between the distribution of each output value of the reference output signal and the distribution of each output value of the measurement output signal. Proportional. Therefore, even if the difference between the output signal for reference and the output signal for measurement is small at first glance, if there is an abnormality in the weld quality of the welded part, the amount of deviation in the distribution of the output value of each output signal Due to the difference, a clear difference is generated between the first comparison data and the second comparison data, so that it is possible to accurately determine whether or not the welding quality is acceptable.

  The first comparison data is the number of each output value of the reference output signal exceeding the first normalized value, and the second comparison data is the measurement output exceeding the second normalized value. Preferably the number of each output value of the signal. In this case, for example, even when the amplitude of the reference output signal and the amplitude of the measurement output signal are substantially the same, the difference between the first comparison data and the second comparison data can be clarified. Whether or not the welding quality is acceptable can be accurately determined by simple processing.

  The reference output signal and the measurement output signal are waveform patterns, and the first comparison data is the number of times the reference output signal crosses the first normalized value, and the second comparison data Is preferably the number of times the measurement output signal crosses the second normalized value. By making the reference output signal and the measurement output signal into waveform patterns, it is possible to visually grasp the environmental state during welding. Further, for example, even when the amplitude of the reference output signal and the amplitude of the measurement output signal are substantially the same, the difference between the first comparison data and the second comparison data can be clarified. With this process, it is possible to accurately determine whether or not the welding quality is acceptable.

  The output signal is preferably a waveform pattern. By making the output signal into a waveform pattern, it is possible to visually grasp the environmental state during welding.

  According to the laser welding evaluation method according to the present invention, it is possible to accurately determine whether or not the welding quality is acceptable.

  Hereinafter, preferred embodiments of a laser welding evaluation method according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram showing an embodiment of a laser welding system for realizing a laser welding evaluation method according to the present invention. A laser welding system 1 shown in FIG. 1 is a system for lap welding a skin panel and a bone member (hereinafter referred to as “work”) used in, for example, a railway vehicle structure. A laser welding device 2 that forms a welded portion by irradiating a laser beam and an evaluation device 3 that evaluates whether or not the weld quality of the formed welded portion is acceptable are configured. In addition, in the following description, the case where the linear welding part W is formed in the approximate center part of workpiece | work (workpiece) 10A, 10B is illustrated.

  As shown in FIG. 1, the laser welding apparatus 2 includes a feeding device 21, a workpiece fixing device 22, a laser irradiation device 23, and a gas supply device 24. Each of these devices 21, 22, 23, and 24 is connected to a host control device (not shown), and automatically executes each operation in accordance with operation instruction information output from this control device.

  The feeding device 21 is a device that scans the irradiation position of the laser beam onto the workpieces 10A and 10B. The feeding device 21 has a movable stage 25 on which the workpieces 10A and 10B are placed. When the feeding device 21 receives the operation instruction information to instruct the start of scanning from the control device, the feeding device 21 scans the movable stage 25 in the direction of arrow A at a constant speed. Thereby, the workpieces 10A and 10B placed on the movable stage 25 move relative to the irradiation position of the laser beam by the laser irradiation device 23 along the planned welding region R.

  The workpiece fixing device 22 is a device that fixes the workpieces 10 </ b> A and 10 </ b> B to the movable stage 25. The work fixing device 22 includes a plurality (two in this embodiment) of pressure jigs 26 each having a long pressing plate 26a. When the work fixing device 22 receives the operation instruction information for instructing the operation start from the control device, the work fixing device 22 lowers the long pressure jig 26 from above the workpieces 10A and 10B mounted on the movable stage 25. And the adhesiveness of the workpiece | work 10A, 10B of the welding scheduled area | region R vicinity is improved by pressing the both ends of the workpiece | work 10A, 10B which pinched | interposed the welding planned area | region R against the movable stage 25 with the elongate pressing plate 26a.

  The laser irradiation device 23 is a device that irradiates a laser beam toward the planned welding region R of the workpieces 10A and 10B. The laser irradiation device 23 has a laser head 27 disposed above the workpieces 10A and 10B. When receiving the operation instruction information for instructing the start of irradiation from the control device, the laser irradiation device 23 emits, for example, a YAG laser having a wavelength of 1.06 μm and an output of about 4.0 kW from the tip of the laser head 27 for a predetermined time.

  The gas supply device 24 is a device that supplies assist gas to the planned welding region R of the workpieces 10A and 10B. The gas supply device 24 has a supply nozzle 28 arranged so as to be inclined at about 45 degrees with respect to the workpieces 10A and 10B. When the gas supply device 24 receives operation instruction information for instructing the start of supply from the control device during the operation of the laser irradiation device 23, the gas supply device 24 supplies assist gas to the irradiation position of the laser beam with a predetermined supply amount. As the assist gas, helium gas, argon gas, or the like is used for the purpose of preventing oxidation and sputtering of the workpieces 10A and 10B.

  On the other hand, the evaluation device 3 is physically a computer system including a CPU, a memory, a communication interface, a storage unit such as a hard disk, a display unit such as a display, and the like. The evaluation device 3 is connected with a light intensity detection sensor (welding environment detection sensor) 4 for detecting light generated in the vicinity of the planned welding region R in the workpieces 10A and 10B during laser welding. More specifically, the light intensity detection sensor 4 selectively detects, for example, light intensity having a wavelength of 1100 nm or less, and emits plasma and plume light generated in the planned welding region R of the workpieces 10A and 10B during laser beam irradiation. Detect intensity. Then, the light intensity detection sensor 4 outputs an output signal corresponding to the detected light intensity to the evaluation device 3.

  The evaluation device 3 includes an abnormality determination unit 31 and a determination result storage unit 32 as functional components. The abnormality determining unit 31 is a part that forms an output signal from the light intensity detection sensor 4 into a waveform pattern and determines whether or not the welding quality of the welded portion W formed on the workpieces 10A and 10B is acceptable based on the waveform pattern. . The abnormality determination unit 31 outputs determination result information indicating the determination result of the weld quality acceptability to the determination result storage unit 32 in association with the product numbers of the workpieces 10A and 10B, for example. The determination result storage unit 32 receives and stores the determination result information output from the abnormality determination unit 31. In addition, the method of abnormality determination of the welding part W in the abnormality determination part 31 is mentioned later.

  Next, the operation of the laser welding system 1 having the above-described configuration will be described with reference to FIG. FIG. 2 is a flowchart showing the operation of the laser welding system 1.

  First, laser welding is performed on the workpieces 10A and 10B (hereinafter referred to as “reference workpieces 10A and 10B”) when it is determined that the welding quality is normal. When the user performs a predetermined operation with the reference workpieces 10 </ b> A and 10 </ b> B placed on the movable stage 25, operation instruction information is output from the host controller to the workpiece fixing device 22. The workpiece fixing device 22 that has received the operation instruction information lowers the pressing jig 26 from above the reference workpieces 10A and 10B placed on the movable stage 25, and moves the reference workpieces 10A and 10B to the movable stage 25. Secure to. Next, operation instruction information is output from the control device to each of the laser irradiation device 23, the feeding device 21, and the gas supply device 24, and laser irradiation, workpiece feeding, and supply of assist gas are started. Thereby, the welding part W is sequentially formed in the welding plan area | region R of the workpiece | work 10A for reference | standard, and 10B (step S01).

  During welding, the light intensity detection sensor 4 detects the light intensity of plasma and plume. The abnormality determination unit 31 of the evaluation device 3 acquires a reference output signal output from the light intensity detection sensor 4, and acquires a waveform pattern (see FIG. 5) with respect to the time axis of this signal (step S02). After acquiring the waveform pattern of the reference output signal, the abnormality determination unit 31 normalizes each output value included in the waveform pattern based on the standard deviation σ, and firstly triples the standard deviation σ (+ 3σ). Is calculated as a normalized value (see FIG. 3) (step S03).

  After calculating the first normalized value, laser welding is performed on the workpieces 10A and 10B (hereinafter referred to as “measurement workpieces 10A and 10B”) to be evaluated. This procedure is the same as in steps S01 to S03 described above. The welded portions W are sequentially formed in the planned welding region R of the workpieces 10A and 10B for measurement (step S04), and the light intensity detection sensor 4 is used during welding. A waveform pattern (see FIG. 5) with respect to the time axis of the measurement output signal output from is acquired (step S05). Then, the abnormality determination unit 31 normalizes each output value included in the waveform pattern of the reference output signal based on the standard deviation σ, and triples the standard deviation σ (+ 3σ) to a second normalized value (FIG. 3) (step S06).

Next, the abnormality determination unit 31 extracts a waveform pattern at a predetermined sampling time from the waveform pattern of the reference output signal and the waveform pattern of the measurement output signal. FIG. 3 shows an example of the waveform pattern of the reference output signal and the waveform pattern of the measurement output signal at the sampling time. In the example shown in FIG. 3, the vertical axis represents the voltage V of the output signal, and the horizontal axis represents the sampling time t _1. The waveform pattern of the reference output signal, the waveform pattern of the measurement output signal, and the first regularity The normalized value and the second normalized value are respectively plotted.

After the waveform pattern is extracted, the abnormality determination unit 31 compares the first normalized data obtained by comparing the first normalized value with each output value of the reference output signal, the second normalized value, and the measurement value. Second comparison data obtained by comparing each output value of the output signal is generated, and a determination table used for determining whether or not the welding quality is acceptable is generated. FIG. 4 shows an example of the determination table. In the example shown in FIG. 4, based on each waveform pattern shown in FIG. 3, the sampling time “t ₁ ”, the number of output values of the reference output signal exceeding the first normalized value “7”, and The number “3” of each output value of the output signal for measurement exceeding the second normalized value is associated. Then, the abnormality determination unit 31 calculates the first comparison data and the second comparison data for the other sampling times t ₂ , t ₃ ,... T _{n by} the same method, and sequentially adds each data to the determination table. To do.

  The abnormality determination unit 31 refers to the determination table and calculates a difference between the first comparison data and the second comparison data at each sampling time (step S07). For example, when the difference between the first comparison data and the second comparison data is less than a predetermined threshold (for example, 1) at all sampling times, the abnormality determination unit 31 determines the measurement workpiece 10A, When it is determined that the welding quality of the weld W formed in 10B is normal and the difference between the first comparison data and the second comparison data exceeds the threshold value at any sampling time Then, it is determined that the welding quality of the welded portion W formed on the workpieces 10A and 10B for measurement is abnormal (step S08).

  After determining whether or not the welding quality of the welded portion W is acceptable, the abnormality determining unit 31 determines the determination result information associating the determination table with the determination result of the weld quality of the welded portion W in the workpieces 10A and 10B for measurement. The data is output to the storage unit 32 (step S09). Thereafter, it is determined whether or not the welding of all the workpieces 10A and 10B for measurement is completed (step S10). If the welding is not completed, steps S04 to S04 are performed for the next workpieces 10A and 10B for measurement. Each process up to step S09 is repeated. When the welding and the evaluation of the welding quality for all the workpieces 10A and 10B for measurement are completed, the operation of the laser welding system 1 is completed.

  By the way, when the waveform pattern of the reference output signal and the waveform pattern of the measurement output signal are acquired in Step S02 and Step S05, for example, as shown in FIG. There is. In such a case, when the waveform pattern of the reference output signal and the waveform pattern of the output signal for measurement are simply compared from the pattern shape, etc., as in the prior art, the difference between the two patterns itself is small. It is difficult to determine whether quality is acceptable. However, for example, it is considered that there is a certain correlation between the waveform pattern of the output signal and the shape of the weld bead formed in the weld, and even if the difference between the two patterns is small at first glance. In some cases, there may be an abnormality in the weld quality of the weld.

  For example, when the welded portion W is observed when a waveform pattern equivalent to the waveform pattern of the reference output signal is obtained, the shape of the weld bead 50 forming the welded portion W is as shown in FIG. As shown in FIG. 6B, the cross-sectional shape of the weld bead 50 is also substantially perpendicular to the thickness direction of the workpieces 10A and 10B. On the other hand, when the welded portion W is observed when only the phase of the waveform pattern of the output signal for measurement is slightly shifted from the waveform pattern of the output signal for reference, as shown in FIG. Further, the length in the welding direction of each weld bead 50 forming the welded portion W is non-uniform corresponding to the phase shift amount, and the cross-sectional shape of the weld bead 50 as shown in FIG. Also, distortion occurs in the thickness direction of the workpieces 10A and 10B. Further, the protruding amount of the weld bead 50 on the surface of the workpiece 10A is also about twice that in the case of FIG.

  In contrast, in the laser welding evaluation method according to the present embodiment, the first normalized value is calculated in advance from the waveform pattern of the reference output signal, and the second normalized value is calculated from the waveform pattern of the measurement output signal. Is calculated separately. Then, within a predetermined sampling time, the number of output values of the reference output signal exceeding the first normalized value (first comparison data) and the output signal for measurement exceeding the second normalized value Whether the welding quality of the welded portion W formed on the workpieces 10A and 10B for measurement is acceptable or not is determined based on whether or not the difference from the number of each output value (second comparison data) exceeds a predetermined threshold value.

  In this laser welding evaluation method, the difference between the first normalized value and the second normalized value is the distribution of each output value of the reference output signal and the distribution of each output value of the measurement output signal. It is proportional to the amount of deviation. Therefore, even if the difference between the output signal for reference and the output signal for measurement is small at first glance, if there is an abnormality in the welding quality of the welded portion W, the deviation of the output value distribution of each output signal Since a clear difference is generated between the first comparison data and the second comparison data due to the difference in amount, it is possible to accurately determine whether or not the welding quality is acceptable.

  Taking the waveform pattern of FIG. 3 as an example, if only the first normalized value is used as a reference, the number of output values of the reference output signal exceeding the first normalized value and the output signal for measurement are measured. The number of each output value is “7”, and there is no difference between them. However, by using both the first normalized value and the second normalized value as a reference, the number of output values of the reference output signal exceeding the first normalized value is “7”. On the other hand, the number of output values of the output signal for measurement exceeding the second normalized value is “3”, so that there is a clear difference between them. Thereby, it can be reliably determined that there is an abnormality in the welding quality of the welded portion W of the workpieces 10A and 10B.

  Further, in this laser welding evaluation method, after determining whether or not the welding quality of the welded portion W is acceptable, determination result information that associates the determination table with the determination result of the welded portion W in the workpieces 10A and 10B for measurement. Is stored in the determination result storage unit 32. Thereby, it becomes possible to establish the traceability (traceability) of the product using the workpieces 41 and 42 which are laser-welded.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the light intensity of the plasma and plume is detected by the light intensity detection sensor 4 and the waveform pattern of the output signal is analyzed. For example, the processing point temperature is detected and the waveform of the output signal is detected. The pattern may be analyzed. Further, the first normalization value and the second normalization value may be appropriately set to ± 3σ, ± 1.5σ, and the like.

  Further, in the embodiment described above, the number of output values of the reference output signal exceeding the first normalized value is set as the first comparison data, and each of the output signals for measurement exceeding the second normalized value is set. The number of output values is the second comparison data. Instead, the number of times that the reference output signal crosses the first normalized value is the first comparison data, and the measurement output signal is the first comparison data. The number of crossings with the normalized value of 2 may be used as the second comparison data.

FIG. 8 shows another example of the waveform pattern of the reference output signal and the waveform pattern of the measurement output signal. When the waveform pattern shown in FIG. 8 is obtained, as shown in FIG. 9, the abnormality determination unit 31 determines the sampling time “t ₁ ” and the number of times that the reference output signal crosses the first normalized value “0”. “Times” and the number of times that the measurement output signal crosses the second normalized value “4 times” are stored in the determination table. Even in such a method, as in the above-described embodiment, there is a clear difference between the first comparison data and the second comparison data due to the difference in the deviation of the distribution of the output value of each output signal. As a result, it is possible to accurately determine whether or not the welding quality is acceptable.

It is a figure showing composition of a laser welding system which realizes a laser welding evaluation method concerning one embodiment of the present invention. It is a flowchart which shows operation | movement of the laser welding system shown in FIG. It is a figure which shows an example of the waveform pattern of the output signal for a reference | standard in the predetermined sampling time, and the waveform pattern of the output signal for a measurement. It is a figure which shows an example of a judgment table. It is a figure which shows an example of the waveform pattern of the output signal for a reference | standard, and the waveform pattern of the output signal for a measurement. It is a figure which shows the shape of the welding part when it is judged that welding quality is normal. It is a figure which shows the shape of the welding part when it is judged that welding quality is abnormal. It is a figure which shows the other example of the waveform pattern of the output signal for a reference | standard in the predetermined sampling time, and the waveform pattern of the output signal for a measurement. It is a figure which shows the other example of a judgment table.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser welding system, 4 ... Light intensity detection sensor (welding environment detection means), 10A, 10B ... Workpiece (workpiece), W ... Welding part.

Claims (3)

A laser welding evaluation method for evaluating the welding quality of a weld formed on a workpiece by irradiation with a laser beam,
Changes in the physical quantity of the environmental state at the time of irradiation of the laser beam to the workpiece to be evaluated are detected by the welding environment detection means, and each output value of the reference output signal output from the welding environment detection means Normalizing to calculate a first normalized value;
Changes in the physical quantity of the environmental state when the workpiece to be evaluated is irradiated with the laser beam is detected by the welding environment detection means, and each output value of the output signal for measurement output from the welding environment detection means Normalizing and calculating a second normalized value;
First comparison data comparing the first normalized value and each output value of the reference output signal, and comparing the second normalized value and each output value of the measurement output signal A difference value with respect to the second comparison data is calculated every predetermined sampling time, and is formed on the workpiece to be evaluated when the difference value is less than a predetermined threshold at all sampling times. The welding quality of the welded portion formed on the workpiece to be evaluated when the welding quality of the welded portion is determined to be normal and the difference value is equal to or greater than the predetermined threshold value at any sampling time A method for evaluating laser welding, comprising the step of:   The first comparison data is the number of each output value of the reference output signal that exceeds the first normalized value, and the second comparison data exceeds the second normalized value. 2. The laser welding evaluation method according to claim 1, wherein the number of output values of the output signal for measurement is the number. The reference output signal and the measurement output signal are waveform patterns,
The first comparison data is the number of times the reference output signal crosses the first normalized value, and the second comparison data is the measurement output signal of the second normalized value. The laser welding evaluation method according to claim 1, wherein the number is the number of times of crossing the value.

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