JP4642790B2 - Laser weld formation method - Google Patents

Description

  The present invention relates to a laser weld formation method for forming a spot weld on a workpiece by laser beam irradiation.

As a technique related to this type of field, for example, there is a laser welding control apparatus described in Patent Document 1. In this conventional laser welding control apparatus, the welding output is feedback-controlled based on the plasma emission intensity and the welding part temperature at the time of laser welding detected by a plasma light sensor and a temperature sensor arranged in the vicinity of the processing point, and a blow in the welding part is performed. The generation of holes is suppressed.
JP 2003-19589 A

  By the way, in laser welding, a spot-like welded part may be formed on a workpiece. In such a case, in addition to the welding quality of the welded portion, it is necessary to determine whether there is an abnormality in the formation position of the welded portion. However, if a sensor is prepared for each determination item, there is a problem that the types of output signals to be analyzed increase and the processing becomes complicated.

  In the case of forming a spot-like weld, for example, a high energy density laser typified by a YAG laser is instantaneously applied to the surface of the workpiece. For this reason, the output signals detected by various types of sensors are greatly undulated, and may further include an instantaneous peak (overshoot). Therefore, if the determination method such as the conventional laser welding control device described above is applied as it is, it may be difficult to detect the presence or absence of abnormality in the welding quality of the welded portion and the formation position.

  The present invention has been made in order to solve the above-described problems, and is capable of accurately determining whether or not there is an abnormality in the welding quality and formation position of a weld formed in a spot shape by simple processing. An object is to provide a forming method.

  In order to solve the above problems, a laser welded part forming method according to the present invention is a laser welded part forming method in which a spot-like welded part is formed on a workpiece by irradiation with a laser beam. A change in the output intensity of the laser beam is detected by the output intensity detection means, a signal acquisition step for acquiring an output signal output from the output intensity detection means, and an output value of the output signal acquired in the signal acquisition step Based on whether or not the set reference output signal is within the allowable range set between the upper control limit value and the lower control limit value, the weld quality of the weld and the possibility of the formation position are determined. And a judging step.

  In this laser welded portion forming method, an allowable region set between an upper control limit value and a lower control limit value for a reference output signal set in advance is used for monitoring a spot-like welded portion. The upper control limit value and the lower control limit value are obtained by calculating the standard deviation of the output value of the reference output signal, and then outputting the normalized value obtained by multiplying the standard deviation by an integer to the output of the reference output signal. It is a value obtained by adding and subtracting to a value. For this reason, the allowable region is set with a certain numerical value width in a state including the undulation and overshoot portion of the output value of the reference output signal. Moreover, since the spot-like welded portion is a detection target, the allowable region is set in a comb-teeth shape corresponding to the formation position of the welded portion. Therefore, in this laser welded portion forming method, it is possible to determine whether or not the output value of the output signal for measurement is within the allowable range without preparing a sensor for each determination item, so that the weld quality of the welded portion is determined. And the formation position can be accurately determined at a time.

  Further, the standard deviation of the moving average value of the output value in the reference output signal is calculated, and the normalized value obtained by multiplying the standard deviation by an integer is added to the moving average value as the upper management limit value. It is preferable to use a value obtained by subtracting the normalized value from the moving average value as the lower management limit value. In this way, by calculating the moving average value of the output values of the acquired output signal, the fluctuation of the allowable area between the upper management limit value and the lower management limit value is flattened, and the processing is further simplified. Figured.

  According to the laser welded part forming method according to the present invention, it is possible to accurately determine the weld quality of the welded part formed in a spot shape by a simple process and the presence or absence of abnormality in the forming position.

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

  FIG. 1 is a configuration diagram showing a laser welding system that realizes a laser weld formation method according to an embodiment of the present invention. A laser welding system 1 shown in FIG. 1 is a system for lap welding, for example, an outer panel and a bone member (hereinafter referred to as “workpieces 10A and 10B”) used in a railway vehicle structure. The laser welding system 1 irradiates a laser beam to a planned welding region R of the workpieces 10A and 10B, and forms a plurality of spot welds W1 to W5 (see FIG. 4) in the planned welding region R, and welding. And an evaluation device 3 that evaluates the weld quality of the portions W1 to W5 and the possibility of the formation position.

  As shown in FIG. 1, the laser welding apparatus 2 includes a feeding device 21, a workpiece fixing device 22, a workpiece fixing device 22, and a gas supply device 24. Each of these devices 21 to 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.

  This is a device for scanning 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 can be 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. Upon receiving the operation instruction information for instructing the start of irradiation from the control device, the laser irradiation device 23 emits 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 example.

  Further, the laser irradiation device 23 includes an output switching mechanism (not shown) inside. With this output switching mechanism, the laser irradiation device 23 can continuously irradiate the workpieces 10A and 10B with a laser beam, and can also irradiate the laser beam in a pulsed manner.

  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 to a laser output intensity detection sensor 4 for detecting a change in the output intensity of the laser beam emitted from the laser irradiation device 23 when the welds W1 to W5 are formed on the workpieces 10A and 10B. ing. The laser output intensity detection sensor 4 is arranged in the vicinity of the irradiation position of the laser beam in the laser head 27 and outputs an output signal corresponding to the intensity of light having the same wavelength as the laser beam 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 determination unit 31 is a part that receives an output signal from the laser output intensity detection sensor 4. In addition, the abnormality determining unit 31 forms a waveform pattern on the received output signal, and determines whether or not the welding quality and the formation position of the welded portions W1 to W5 formed on the workpieces 10A and 10B are based on the waveform pattern. It is.

  The abnormality determination unit 31 generates determination result information indicating the determination results of the welding quality and formation position of the welded portions W1 to W5, and outputs the determination result information 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 is a part that receives and stores the determination result information output from the abnormality determination unit 31. The details of the determination of whether or not the welding quality and the formation position are acceptable in the abnormality determination unit 31 will be described later.

  Next, the operation of the laser welding system 1 having the above-described configuration will be described with reference to FIGS. 2 and 3 are flowcharts showing the operation of the laser welding system 1.

  In the laser welding system 1, first, as shown in FIG. 2, workpieces 10 </ b> A and 10 </ b> B (hereinafter referred to as “reference workpieces 10 </ b> A and 10 </ b> B”) when it is determined that the weld quality and formation position of the welded portion are normal. Laser welding) is performed.

  When a predetermined operation is performed by the user while the reference workpieces 10A and 10B are placed on the movable stage 25, operation instruction information is output from the host control device 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 workpiece fixing device 22, 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. The The YAG laser is pulse-irradiated from the laser head 27 at a predetermined interval, and the movable stage 25 scans the workpieces 10A and 10B in the direction of arrow A (see FIG. 1) at a workpiece feed speed of about 10 m / s.

  Accordingly, spot welds W1 to W5 having a substantially circular planar shape are sequentially formed at predetermined intervals in the planned welding region R of the reference workpieces 10A and 10B (step S01). In the present embodiment, as shown in FIG. 4, the spot welds W1 to W5 are non-penetrating spot welds that are not exposed on one surface side of the workpiece 10B so that welding marks on the workpiece 10B are not noticeable. It has become.

  During the welding, the laser output intensity is detected by the laser output intensity detection sensor 4. The abnormality determination unit 31 of the evaluation device 3 acquires a reference output signal output from the laser output intensity detection sensor 4, and acquires a waveform pattern of this output signal (step S02).

  FIG. 5 shows an example of the waveform pattern of the output signal. The waveform pattern A shown in FIG. 5 plots each output signal from the laser output intensity detection sensor 4 when forming the spot welds W1 to W5, the vertical axis is the voltage of the output signal, and the horizontal axis is the time. It has become. In forming the spot welds W1 to W5, the YAG laser is instantaneously applied to the planned welding region R, and thus the waveform pattern A has five peaks. At each peak, the output intensity increases abruptly with the start of laser beam irradiation, and becomes almost flat for a certain time after an overshoot portion. Thereafter, the output intensity rapidly decreases as the laser beam irradiation ends, and the detection ends.

  After acquiring the waveform pattern, the abnormality determination unit 31 calculates the upper management limit value and the lower management limit value based on the acquired waveform pattern (step S03). In calculating the upper control limit value and the lower control limit value, first, a moving average value for each predetermined data point (for example, 50 data points) of the output value in the reference output signal is obtained, and the waveform pattern is flattened. .

  Next, each output value included in the waveform pattern after moving average is normalized based on the standard deviation σ. Then, the normalized value obtained by multiplying the standard deviation σ by 3 is added to the moving average value (+ 3σ) as the upper control limit value, and the normalized value subtracted from the moving average value (−3σ) is Control limit value.

  FIG. 6 shows an example of the waveform pattern of the upper management limit value and the lower management limit value calculated. The waveform pattern B and the waveform pattern C shown in FIG. 6 are obtained by plotting the upper control limit value and the lower control limit value of the output intensity of the laser beam when forming the reference welds W1 to W5, respectively. The axis is the voltage of the output signal, and the horizontal axis is time.

  As described above, since the waveform pattern B and the waveform pattern C are obtained by adding or subtracting the normalized value to the moving average value of the reference output signal, the waveform pattern A shown in FIG. In addition, the shape is enlarged or reduced in the vertical axis direction. A comb-like region having a predetermined numerical width between the waveform pattern B and the waveform pattern C is set as an allowable region.

  That is, if the waveform pattern of the output signal when forming the spot welds W1 to W5 on the workpieces 10A and 10B for measurement to be described later is within this allowable region, the weld quality of the spot welds W1 to W5 and The formation position can be determined to be equivalent to the reference welds W1 to W5. The upper management limit value and the lower management limit value calculated in this way are stored in the abnormality determination unit 31.

  After the calculation of the upper control limit value and the lower control limit value is completed, laser welding is performed on the workpieces 10A and 10B to be evaluated (hereinafter, “measurement workpieces 10A and 10B”). As shown in FIG. 3, this procedure is the same as steps S01 and S02 described above, and the spot welds W1 to W5 are sequentially formed along the planned welding regions R of the workpieces 10A and 10B for measurement (steps). S11) A waveform pattern with respect to the time axis of the measurement output signal output from the laser output intensity detection sensor 4 during welding is acquired (step S12).

  After acquiring the waveform pattern, the abnormality determination unit 31 performs measurement based on whether or not the acquired waveform pattern is within an allowable area between the upper management limit value and the lower management limit value calculated in step S03. The welding quality of the spot welded portions W1 to W5 formed on the workpieces 10A and 10B for use and the possibility of the formation position are determined (step S13).

  More specifically, the abnormality determination unit 31 determines that when a vertical shift occurs in the peak included in the acquired waveform pattern, that is, the peak included in the acquired waveform pattern has a portion that exceeds the upper management limit value. When it is recognized, and when a portion less than the lower control limit value is recognized, it is determined that the welding quality of the spot welds W1 to W5 corresponding to the peak is not possible. In addition, the abnormality determination unit 31 may be a part of the peak included in the acquired waveform pattern, that is, the portion earlier in time with respect to the set allowable range in the peak included in the acquired waveform pattern or When a slow part is recognized, it is judged that the formation positions of the spot welds W1 to W5 are impossible.

  Specific examples are shown in FIGS. In the example shown in FIG. 7, all the five peaks of the waveform pattern D acquired in step S12 are within the allowable region between the upper management limit value and the lower management limit value. In this case, the abnormality determination unit 31 determines that both the welding quality and the formation position of the spot welds W1 to W5 formed on the workpieces 10A and 10B for measurement are acceptable.

  On the other hand, in the example shown in FIG. 8, the second to fourth peaks of the five peaks of the waveform pattern D acquired in step S12 are less than the upper management limit value and the lower management limit value. Part is allowed. In this case, the abnormality determination unit 31 determines that the welding quality of the spot welds W2 to W4 corresponding to the second to fourth peaks is not possible, assuming that the output intensity of the laser beam at the time of laser welding is abnormal. To do.

  In the example shown in FIG. 9, the fifth peak does not exist in the waveform pattern D acquired in step S12. Such a waveform pattern D is such that, for example, the feed speed of the workpieces 10A and 10B by the feeder 21 is faster than the set value, and the laser head before the laser beam for forming the spot weld W5 is emitted from the laser head 27. This may occur when 27 reaches the end of the planned welding region R and the laser irradiation device 23 is automatically stopped. In this case, the abnormality determination unit 31 determines that the formation positions of the spot welds W1 to W5 are not possible including the spot welds W5 that are not actually formed, assuming that the feed rates of the workpieces 10A and 10B are abnormal. To do.

  In the example shown in FIG. 10, the appearance position of each peak of the waveform pattern D acquired in step S12 is gradually earlier with respect to the set allowable range. Such a waveform pattern D may occur, for example, when the output switching mechanism in the laser irradiation device 23 is abnormal and the pulse irradiation interval of the laser beam emitted from the laser head 27 deviates from a specified value. In this case, the abnormality determination unit 31 determines that the formation positions of the spot welds W1 to W5 are not possible, assuming that the pulse irradiation interval of the laser beam is abnormal.

  Thereafter, the abnormality determination unit 31 generates determination result information in which the determination results of the weld quality and formation position of the spot welds W1 to W5 are associated with the product numbers of the workpieces 10A and 10B, and the determination result storage unit (Step S14). When the processing from step S11 to step S14 is completed for all the workpieces 10A and 10B for measurement, the operation of the laser welding system 1 ends.

  In this laser welded portion forming method, when monitoring the spot welded portions W1 to W5 formed on the workpieces 10A and 10B for measurement, between the upper control limit value and the lower control limit value set in advance for the reference output signal. The set allowable area (see FIG. 6) is used. Such an allowable region is set with a certain numerical width in a state including the undulation and overshoot portion of the output value of the reference output signal. Moreover, since the spot welded portions W1 to W5 are set as detection targets, the allowable region is set in a comb shape corresponding to the formation positions of the welded portions W1 to W5. Therefore, in this laser welded portion forming method, it is possible to determine whether or not the output value of the output signal for measurement is within the allowable region without preparing a sensor for each determination item, so that the spot welded portions W1 to W1. The welding quality and formation position of W5 can be accurately determined at a time.

  In this laser weld formation method, the standard deviation of the moving average value of the output value in the reference output signal is calculated. Then, the normalized value obtained by multiplying the standard deviation by an integer is added to the moving average value as the upper management limit value, and the normalized value subtracted from the moving average value is used as the lower management limit value. Yes. In this way, by calculating the moving average value of the output values of the acquired output signal, even if an overshoot portion is included in the reference output signal when forming the spot welds W1 to W5, the upper management is performed. It is possible to flatten the variation of the tolerance region between the limit value and the lower control limit value. This realizes further simplification of processing.

It is a block diagram which shows the laser welding system which implement | achieves the laser welding part formation method which concerns on one Embodiment of this invention. It is a flowchart which shows operation | movement of the laser welding system shown in FIG. 3 is a flowchart showing a subsequent operation of FIG. 2. It is sectional drawing which shows the state of the spot welding part formed in a workpiece | work. It is a figure which shows an example of the waveform pattern of the output signal for a reference | standard. It is a figure which shows an example of the waveform pattern of an upper management limit value and a lower management limit value. It is a figure which shows an example of the waveform pattern of the output signal for a measurement when it is judged that the welding quality and formation position of a spot weld part are possible. It is a figure which shows an example of the waveform pattern of the output signal for a measurement when it is judged that the welding quality of a spot weld part is impossible. It is a figure which shows an example of the waveform pattern of the output signal for a measurement when it is judged that the formation position of a spot weld part is impossible. It is a figure which shows the other example of the waveform pattern of the output signal for a measurement in case it is judged that the formation position of a spot weld part is improper.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser welding system, 4 ... Laser output intensity detection sensor (output intensity detection means), 10A, 10B ... Workpiece (workpiece), A ... Waveform pattern of reference output signal, B ... Waveform of upper control limit value Pattern, C ... Waveform pattern of lower control limit value, D ... Waveform pattern of output signal for measurement, W1-W5 ... Spot weld.

Claims (1)

A laser weld formation method for forming a spot weld on a workpiece by laser beam irradiation,
A change in output intensity of the laser beam immediately before entering the weld when forming the weld is detected by an output intensity detector, and a waveform pattern of an output signal output from the output intensity detector is obtained. A signal acquisition step;
The output value included in the waveform pattern of the output signal acquired in the signal acquisition step is set between the waveform pattern of the upper control limit value and the waveform pattern of the lower control limit value set in advance for the reference output signal. A determination step of determining whether or not the welding quality of the welded portion and the formation position based on whether or not it is within the allowable region,
In the determining step, the standard deviation of the waveform pattern of the moving average value obtained from the output value included in the waveform pattern of the reference output signal is calculated, and the normalized value obtained by multiplying the standard deviation by an integer is calculated as the normalized value. What is added to the moving average value is used as the waveform pattern of the upper management limit value , and what is obtained by subtracting the normalized value from the moving average value is used as the waveform pattern of the lower management limit value Part forming method.

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