JP2021115585A - Pulse arc welding defect detection device and defect detection method - Google Patents

Abstract

To provide a pulse arc welding defect detection device and defect detection method which can detect a welding defect with high accuracy.SOLUTION: A pulse arc welding defect detection device 9 comprises: a welding current detection unit 10; a Fourier transformation unit 20; an index value calculation unit 30; and a warning unit 40. The welding current detection unit 10 detects a welding current of the pulse arc welding. The Fourier transformation unit 20 performs the Fourier transformation of the welding current in the prescribed time detected by the welding current detection unit to obtain a power spectrum. The index value calculation unit 30 calculates a welding defect index value in which a frequency having the maximum amplitude in the power spectrum obtained by the Fourier transformation unit is the fundamental frequency and the sum of the amplitudes of the frequencies in a prescribed range including the fundamental frequency is normalized with the amplitude of the fundamental frequency. The warning unit 40 issues a warning when the welding defect index value calculated by the index value calculation unit is equal to or greater than a threshold.SELECTED DRAWING: Figure 1

Description

The present invention relates to a defect detection device and a defect detection method for pulse arc welding.

Pulse arc welding has rapidly become widespread since its development because it is possible to positively control the behavior of welding by changing the waveform of the pulsed welding current. In pulse arc welding as well as other welding, it is desired to detect welding defects during or immediately after welding.

At present, as a method of evaluating whether or not there is an abnormal state such as a welding defect, each power spectrum is obtained in advance by frequency analysis of each welding current in the normal state and the abnormal state, and the power spectrum is learned by a neural network. Above, a method of using a trained model has been proposed (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 10-235490

However, although the power spectrum by the method described in Patent Document 1 is suitable for training a neural network, it is not suitable for directly detecting a welding defect. As described in paragraph [0026] of Patent Document 1, in order to train the neural network, a power spectrum in which even small fluctuations are not reproduced is preferable, but such a power spectrum directly causes welding defects. This is because it is too coarse to detect. Therefore, even if the power spectrum by the method described in Patent Document 1 is used, welding defects cannot be directly detected with high accuracy.

Therefore, an object of the present invention is to provide a defect detection device and a defect detection method for pulse arc welding capable of detecting welding defects with high accuracy.

In order to solve the above problems, the defect detection device for pulse arc welding according to the first invention includes a welding current detection unit that detects the welding current for pulse arc welding.
A Fourier transform unit that obtains a power spectrum by Fourier transforming the welding current for a predetermined time detected by the welding current detection unit.
The frequency at which the amplitude is maximum in the power spectrum obtained by the Fourier transform unit is set as the fundamental frequency, and the sum of the amplitudes of frequencies in a predetermined range including this fundamental frequency is standardized by the amplitude of the fundamental frequency. The index value calculation unit that calculates the index value and the index value calculation unit
It is provided with a warning unit that warns if the welding defect index value calculated by the index value calculation unit is equal to or greater than the threshold value.

Further, in the pulse arc welding defect detection device according to the second invention, in the pulse arc welding defect detection device according to the first invention, the predetermined range of the peripheral frequency is a frequency centered on the fundamental frequency.

Further, in the pulse arc welding defect detection device according to the third invention, in the pulse arc welding defect detection device according to the first or second invention, the predetermined range of the peripheral frequency is 0.5 times the basic frequency. The frequency is 1.5 times or less.

In addition, the pulse arc welding defect detection device according to the fourth invention is warned by the warning unit a plurality of times in succession in the pulse arc welding defect detection device according to any one of the first to third inventions. It is provided with a defect determination unit for determining that a welding defect has occurred in pulse arc welding.

Further, in the pulse arc welding defect detection device according to the fifth invention, in the pulse arc welding defect detection device according to any one of the first to fourth inventions, the threshold value of the warning unit is the index value calculation unit. The predetermined value is added to the time average of the welding defect index value for each predetermined time calculated in.

Further, the method for detecting defects in pulse arc welding according to the sixth invention includes a welding current detection step for detecting a welding current in pulse arc welding and a welding current detection step.
A Fourier transform step of obtaining a power spectrum by Fourier transforming the welding current for a predetermined time detected in the welding current detection step,
The frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step is set as the fundamental frequency, and the sum of the amplitudes of the frequencies in a predetermined range including this fundamental frequency is standardized by the amplitude of the fundamental frequency. The index value calculation process for calculating the index value and the index value calculation process
This method includes a warning step of warning if the welding defect index value calculated in the index value calculation step is equal to or greater than a threshold value.

According to the pulse arc welding defect detection device and the defect detection method according to the present invention, welding defects can be detected with high accuracy.

It is a schematic block diagram of the pulse arc welding equipment provided with the defect detection device of the pulse arc welding which concerns on embodiment of this invention. It is a graph which shows the fluctuation with time of the welding current detected by the welding current detection part of the defect detection apparatus. It is a graph which shows the power spectrum obtained by the Fourier transform part when the pulse arc welding is stable. It is a graph which shows the power spectrum obtained by the Fourier transform part when the pulse arc welding is unstable. It is a flowchart which shows the defect detection method of the pulse arc welding which concerns on embodiment of this invention. It is a schematic block diagram of the defect detection apparatus of pulse arc welding which concerns on embodiment of this invention. It is a graph which shows the measured value (welding defect index value, time average and the occurrence of a short circuit) by this defect detection apparatus. It is a graph which shows the measured value (welding defect index value, time average, occurrence of short circuit) extracted more than FIG. 7, and set the threshold value as a fixed value. It is a graph showing the same measured values (welding defect index value, time average, occurrence of short circuit) as in FIG. 8, and the threshold value is a value obtained by adding an offset value to the time average. It is a flowchart which shows the method of using the defect detection apparatus.

Hereinafter, the defect detection device for pulse arc welding according to the embodiment of the present invention will be described with reference to the drawings.

First, a pulse arc welding facility equipped with the pulse arc welding defect detection device (hereinafter, simply referred to as a defect detection device), that is, pulse arc welding is performed and the defect of the pulse arc welding is detected by the defect detection device. The equipment will be explained.

As shown in FIG. 1, the pulse arc welding equipment 1 has a welding torch 2 for performing pulse arc welding by generating an arc A from the tip of a welding wire W on a base material B, and welding to the welding torch 2. A feeding device 3 for feeding the wire W and a wire reel 4 around which the welded wire W is wound so as to be drawn out are provided. Further, the pulse arc welding equipment 1 includes a shield gas supply device 5 that supplies the shield gas G from the welding torch 2 around the arc A, and a gas hose that sends the shield gas G from the shield gas supply device 5 to the welding torch 2. 6 and. Further, the pulse arc welding facility 1 electrically connects a welding power source 7 that supplies pulsed electric power to the welding torch 2 and the base material B, and the welding power source 7 and the welding torch 2 and the base material B, respectively. It is provided with a welding cable 8 to be used. In addition, the pulse arc welding equipment 1 includes a defect detection device 9 provided on a welding cable 8 that electrically connects the welding power source 7 and the base material B.

Hereinafter, the configuration of the defect detection device 9 will be described in detail.

As shown in FIG. 1, the defect detection device 9 includes a welding current detection unit 10, a Fourier transform unit 20, an index value calculation unit 30, and a warning unit 40.

The welding current detection unit 10 is provided on a welding cable 8 that electrically connects the welding power source 7 and the base material B, and detects the welding current of pulse arc welding. The time variation of the detected welding current is shown in FIG. In the graph shown in FIG. 2, the horizontal axis is time and the vertical axis is current. As is clear from this graph, in the welding current of pulse arc welding, a high current peak current Ip and a low current base current Ib appear periodically.

The Fourier transform unit 20 obtains a power spectrum as shown in FIG. 3 or 4 by Fourier transforming the welding current for a predetermined time detected by the welding current detection unit 10. The predetermined time may be any time as long as the period of the welding current is included a plurality of times, for example, 1 second. If the pulse arc welding is stable, most of the frequencies of the welding current detected by the welding current detection unit 10 are fundamental frequencies. Therefore, as shown in FIG. 3, the fundamental frequency is obtained in the obtained power spectrum. fo (maximum amplitude) becomes dominant. On the other hand, if the pulse arc welding is unstable, the frequency of the welding current detected by the welding current detection unit 10 is mixed with other frequencies in addition to the fundamental frequency fo. Therefore, as shown in FIG. In the obtained power spectrum, components other than the fundamental frequency fo (maximum amplitude) also appear prominently. That is, if the pulse arc welding is unstable, the frequency around the fundamental frequency fo becomes noise in a predetermined range, so that the obtained power spectrum is disturbed.

The index value calculation unit 30 sets the frequency at which the amplitude is maximum in the power spectrum obtained by the Fourier transform unit 20 as the fundamental frequency fo. In the examples shown in FIGS. 3 and 4, the frequency fo in which the largest amplitudes h1 and h2 are observed is defined as the fundamental frequency fo. Then, the index value calculation unit 30 calculates the partial sum of each amplitude at a frequency in a predetermined range including the fundamental frequency fo. The formula for this calculation is represented by the following formula (1) when the partial sum is displayed as Pfo, the amplitude of the frequency f is displayed as p (f), and the predetermined range is displayed as a to b. Will be done.

Further, the index value calculation unit 30 calculates the welding defect index value by dividing (that is, standardizing) the partial sum calculated by the equation (1) by the amplitudes h1 and h2 of the fundamental frequency fo. .. According to this standardization, the welding defect index value becomes an appropriate value as an index of welding defects because it is the addition of each amplitude of another frequency group (however, a frequency in a predetermined range) to the amplitude of the fundamental frequency. In the standardization, even when the partial sum as described above is calculated and then divided by the amplitudes h1 and h2 of the fundamental frequency fo, the amplitude of each frequency in a predetermined range is defined as the fundamental frequency before the partial sum is calculated. The case of dividing by the amplitudes h1 and h2 of fo is also included.

Here, in the formula (1), the predetermined ranges a to b are not particularly limited as long as they include the fundamental frequency fo (a ≦ fo ≦ b), but it is preferable that the fundamental frequency fo is centered. In other words, it is preferable that the fundamental frequency fo is located between the upper limit (b) and the lower limit (a) [fo = (a + b) / 2]. Further, the predetermined ranges a to b are preferably 0.5 times or more and 1.5 times or less (a = 0.5fo, b = 1.5fo) of the fundamental frequency fo. This is because the calculated welding defect index value appropriately reflects the disturbance of the power spectrum in such a predetermined range.

The index value calculation unit 30 does not necessarily have to calculate the partial sum by the above formula (1) in order to calculate the welding defect index value. For example, the index value calculation unit 30 removes frequencies in the predetermined range that do not have a large effect as an index of welding defects, instead of the partial sum, and sums only the amplitudes of the frequencies that are not removed. It may be adopted. Here, the frequency to be removed is, for example, a frequency in which an amplitude reference value is set separately and is equal to or less than the amplitude reference value.

The warning unit 40 warns if the welding defect index value calculated by the index value calculation unit 30 is equal to or greater than the threshold value. The threshold value may be a preset fixed value, a value appropriately set during the construction of the pulse arc welding, or a value calculated based on the state of the pulse arc welding.

Hereinafter, the pulse arc welding and its defect detection method will be described. The defect detection method for pulse arc welding is not limited to the method using the defect detection device 9 as long as it is the method described below.

First, as shown in FIG. 1, while the welding wire W is fed from the wire reel 4 to the welding torch 2 via the feeding device 3, pulsed power is supplied from the welding power source 7 to the welding torch 2 and the base metal. Along with being supplied to B, the shield gas G is supplied from the shield gas supply device 5 to the welding torch 2 via the gas hose 6. As a result, an arc A is generated from the tip of the welding wire W toward the base material B, and the arc A is protected by the shield gas G. That is, pulse arc welding is performed on the base material B. This welding current defect is detected by the pulse arc welding defect detecting method described below.

The defect detection method of pulse arc welding obtains a power spectrum by Fourier transforming a welding current detection step of detecting a welding current of pulse arc welding and a welding current of a predetermined time detected in the welding current detection step. It includes a Fourier transform step. Further, in the defect detection method of the pulse arc welding, the frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step is set as the fundamental frequency, and the sum of the amplitudes of the frequencies in a predetermined range including this fundamental frequency is the basic frequency. It is provided with an index value calculation process for calculating a welding defect index value, which is standardized by the amplitude of the frequency. Further, the pulse arc welding defect detection method includes a warning step of warning if the welding defect index value calculated in the index value calculation step is equal to or greater than a threshold value. In the index value calculation step, the frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step is set as the fundamental frequency, and the partial sum of each amplitude is calculated at a frequency in a predetermined range including this fundamental frequency. It may be a step of calculating the welding defect index value by dividing the partial sum by the amplitude of the fundamental frequency.

Each step of the defect detection method of the pulse arc welding will be described with reference to the flowchart shown in FIG.

First, the welding current detection unit 10 or the like detects the welding current of pulse arc welding as the welding current detection step (S10). Next, the Fourier transform unit 20 or the like obtains a power spectrum by Fourier transforming the welding current for a predetermined time detected in the welding current detection step as the Fourier transform step (S20). After that, the index value calculation unit 30 or the like sets the frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step as the fundamental frequency (S31) as the index value calculation step, and a predetermined frequency including this fundamental frequency is set. The sum of the amplitudes is calculated at the frequencies in the range (S32), and the welding defect index value is calculated by dividing the sum by the amplitude of the fundamental frequency (S33). Then, if the welding defect index value calculated in the index value calculation step is equal to or greater than the threshold value (S41), the warning unit 40 or the like warns the warning step (S42).

As described above, according to the pulse arc welding defect detection device 9 and the defect detection method, the welding defect is detected based on the disturbance of the power spectrum obtained by Fourier transforming the welding current of the pulse arc welding, so that the welding defect can be detected with high accuracy. Can be detected.

Hereinafter, the defect detection device 9 according to the embodiment in which the embodiment is shown more concretely will be described with reference to FIG. In this embodiment, the description will be focused on a configuration different from that of the embodiment, and the same configuration as that of the embodiment will be designated by the same reference numerals and the description thereof will be omitted.

In FIG. 6, for the sake of simplicity, the pulse arc welding equipment 1 according to the present embodiment includes a defect detection device 9, a welding power source 7, a welding torch 2, and the welding torch 2 according to the present embodiment. Only the welding cable 8 for electrically connecting the base material B and the welding power source 7 is shown, and other configurations are omitted. As shown in FIG. 6, the defect detection device 9 according to the present embodiment has a welding current detection unit 10, a Fourier transform unit 20, an index value calculation unit 30, and a warning unit 40 described in the above embodiment. It includes one memory 71, a second memory 72, a time average calculation unit 73, a threshold value setting unit 74, a defect determination unit 50, and a display unit 60. Hereinafter, these configurations will be described in order.

The welding current detection unit 10 includes a current sensor 11 such as a shunt resistor or a clamp meter that converts a welding current into a voltage value, and a preamplifier 12 that amplifies the voltage value converted by the current sensor 11. Further, the welding current detection unit 10 has a low-pass filter 13 that cuts off the high frequency range of the voltage value amplified by the preamplifier 12, and an AD conversion that AD-converts the value that has passed through the low-pass filter 13. It has a vessel 14. Further, the welding current detection unit 10 stores the AD conversion value, which is the value AD-converted by the AD converter 14, in the first memory 71, and determines that the AD conversion value is the actual welding current. For example, it has a controller 15 that operates the Fourier conversion unit 20.

When the Fourier transform unit 20 is operated by the controller 15, the Fourier transform unit 20 obtains a power spectrum by Fourier transforming the welding current for a predetermined time. The Fourier transform for obtaining this power spectrum is preferably a fast Fourier transform in order to shorten the processing time.

The index value calculation unit 30 includes a fundamental frequency selection unit 31, a partial sum calculation unit 32, and a normalization unit 33. The fundamental frequency selection unit 31 selects a frequency having the maximum amplitude, and uses this frequency as the fundamental frequency. The partial sum calculation unit 32 calculates the partial sum of each amplitude at a frequency in the predetermined range according to the equation (1). The normalization unit 33 calculates the welding defect index value by dividing the partial sum calculated by the partial sum calculation unit 32 by the amplitude of the fundamental frequency. The welding defect index value calculated by the standardization unit 33 is stored in the second memory 72 at predetermined time intervals and transmitted to the warning unit 40. Since the first memory 71 and the second memory 72 store different types of values, they have been described as having different configurations, but the same memory may be used.

The time average calculation unit 73 calculates the time averages of the welding defect index values for each predetermined time stored in the second memory 72. The welding defect index value used to calculate this time average is 4 points before and after the continuous predetermined time including the target predetermined time (5 points in total), or 4 points before the continuous including the target predetermined time. It is preferably ~ 6 points (5 to 7 points in total). This is because the processing time can be shortened and the welding defect can be detected with high accuracy.

The threshold value setting unit 74 sets a threshold value to be compared with the welding defect index value. The threshold value to be set may be a value (fixed value) as it is input from the outside, but in order to detect welding defects with high accuracy, it is outside the time average calculated by the time average calculation unit 73. It is preferable that the value is obtained by adding the predetermined value (offset value) input from. Even if the predetermined value (offset value) is set based on the past welding defect index value stored in the second memory 72 for each predetermined time and the position where it is determined that the welding defect has occurred. good. Specifically, at the position where it is determined that a welding defect has occurred in the past, the past welding defect index value becomes equal to or greater than the time average of the past welding defect index values plus a predetermined value (offset value). As described above, the predetermined value (offset value) is set by the operator from the outside.

In the warning unit 40, a welding defect index value is input from the standardization unit 33, and a threshold value set by the threshold value setting unit 74 is input, so that the welding defect index value is equal to or higher than the threshold value. If so, warn. Of course, the warning unit 40 may warn if the welding defect index value exceeds the threshold value.

The defect determination unit 50 determines that a welding defect has occurred when the warning unit 40 warns the user a plurality of times in succession. The plurality of times is not particularly limited as long as it is two or more times, but it is preferably two or three times in order to reduce the detection omission of welding defects.

The display unit 60 provides information on the welding defect determined by the defect determination unit 50 when the welding current is no longer detected by the welding current detection unit 10 (pulse arc welding is interrupted), as a welding result. Display as. The welding result may simply be the presence or absence of a welding defect, but it is preferable to display the position of the welding defect in the welding bead. As a form of this display, for example, the position of the welding defect in the welding bead is displayed as a percentage (the starting point of the welding bead is 0% and the ending point is 100%). The position of the welding defect in this display format is calculated based on the start and end times of pulse arc welding, the speed of the pulse arc welding, and the time determined by the defect determination unit 50 to be a welding defect. ..

Here, graphs of measured values by the defect detection device 9 are shown in FIGS. 7 to 9. In each of FIGS. 7 to 9, the welding defect index value for each predetermined time is shown by a solid line, and the time average of four consecutive points before and after the predetermined time including the target time is shown by a broken line, which is the cause of the welding defect. The amount of short circuit generated is shown in a bar graph.

As shown in FIG. 7, the welding defect index value and the time average tended to increase when a short circuit occurred. The occurrence of a short circuit induces blowholes and thus causes welding defects. That is, it can be said that the welding defect index value and the time average are values suitable for being used as an index of welding defects. Further, FIGS. 8 and 9 are graphs in which more actually measured values are extracted than in FIG. 7, and only the threshold values shown by virtual lines are different. The threshold value was set to a fixed value in FIG. 8, whereas in FIG. 9, a predetermined value (offset value) was added to the time average. As shown in FIGS. 8 and 9, the time when the welding defect index value becomes equal to or higher than the threshold value and the time when a short circuit occurs correspond well. Therefore, if the welding defect index value is equal to or higher than the threshold value, it can be said that the welding defect can be detected with high accuracy by giving a warning. In particular, by using the threshold value shown in FIG. 9, the time when the welding defect index value exceeds the threshold value and the time when a short circuit occurs correspond extremely well, so that the accuracy is even higher. It can be said that welding defects can be detected.

Hereinafter, a method of using the defect detection device 9 according to the present embodiment will be described with reference to the flowchart shown in FIG.

First, when the welding current is detected by the welding current detection unit 10 (S10), a power spectrum is obtained by Fourier transforming the welding current stored in the first memory 71 for a predetermined time (S20). .. After that, the fundamental frequency selection unit 31 sets the frequency having the maximum amplitude in the power spectrum as the fundamental frequency (S31). Next, the partial sum calculation unit 32 calculates the partial sum of each amplitude at a frequency in a predetermined range including the fundamental frequency (S32). Further, the standardization unit 33 calculates the welding defect index value by dividing the partial sum by the amplitude of the fundamental frequency (S33). Then, if the welding defect index value is equal to or greater than the threshold value (S41), the warning unit 40 warns (S42). If this warning is issued a plurality of times in succession (S51), the defect determination unit 50 determines that a welding defect has occurred (S52).

If the welding defect index value is less than the threshold value (S41), if the warning is not repeated a plurality of times (S51), or if it is determined that a welding defect has occurred (S52), the welding current is again obtained. The process returns to the flow (S10) of whether or not the welding current is detected by the detection unit 10. Then, when the welding current is no longer detected by the welding current detection unit 10, that is, when the pulse arc welding is interrupted, the display unit 60 displays the welding result (S60).

As described above, according to the pulse arc welding defect detection device 9 according to the present embodiment, the effect of the defect detection device 9 according to the embodiment is exhibited, and the welding defect is determined by the defect determination unit 50. , Welding defects can be detected with higher accuracy.

By the way, in the above-described embodiments and examples, a value obtained by standardizing the partial sum is used as a welding defect index value for knowing the disturbance of the power spectrum, but a statistical method such as dispersion or kurtosis of the power spectrum is used. You may use it.

Further, in the above-described embodiments and examples, they are examples in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. Of the configurations described in the above-described embodiment, the configurations other than those described as the first or sixth invention in "Means for Solving Problems" are arbitrary configurations, and can be appropriately deleted and changed. Is.

1 Pulse arc welding equipment 2 Welding torch 3 Feeding device 4 Wire reel 5 Shield gas supply device 6 Gas hose 7 Welding power supply 8 Welding cable 9 Defect detection device 10 Welding current detection unit 20 Fourier conversion unit 30 Index value calculation unit 40 Warning unit

Claims (6)

Welding current detector that detects the welding current of pulse arc welding,
A Fourier transform unit that obtains a power spectrum by Fourier transforming the welding current for a predetermined time detected by the welding current detection unit.
The frequency at which the amplitude is maximum in the power spectrum obtained by the Fourier transform unit is set as the fundamental frequency, and the sum of the amplitudes of frequencies in a predetermined range including this fundamental frequency is standardized by the amplitude of the fundamental frequency. The index value calculation unit that calculates the index value and the index value calculation unit
A defect detection device for pulse arc welding, comprising a warning unit that warns if the welding defect index value calculated by the index value calculation unit is equal to or greater than a threshold value. The defect detection device for pulse arc welding according to claim 1, wherein a predetermined range of the frequencies is a frequency centered on a fundamental frequency. The defect detection device for pulse arc welding according to claim 1 or 2, wherein the predetermined range of the frequency is a frequency of 0.5 times or more and 1.5 times or less of the fundamental frequency. The pulse arc welding according to any one of claims 1 to 3, further comprising a defect determining unit that determines that a welding defect has occurred in the pulse arc welding when the warning unit warns the user a plurality of times in succession. Defect detector. Any of claims 1 to 4, wherein the threshold value of the warning unit is the time average of the welding defect index values for each predetermined time calculated by the index value calculation unit plus a predetermined value. The defect detection device for pulse arc welding according to item 1. Welding current detection process that detects the welding current of pulse arc welding,
A Fourier transform step of obtaining a power spectrum by Fourier transforming the welding current for a predetermined time detected in the welding current detection step,
The frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step is set as the fundamental frequency, and the sum of the amplitudes of the frequencies in a predetermined range including this fundamental frequency is standardized by the amplitude of the fundamental frequency. The index value calculation process for calculating the index value and the index value calculation process
A defect detection method for pulse arc welding, comprising a warning step of warning if the welding defect index value calculated in the index value calculation step is equal to or greater than a threshold value.

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