JP7474597B2 - Pulse arc welding defect detection device and defect detection method - Google Patents

Description

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

Pulsed arc welding has rapidly spread since its development because it is possible to actively control the behavior of the weld by changing the waveform of the pulsed welding current. As with other types of welding, with pulsed arc welding, it is desirable to detect weld defects during or immediately after welding.

Currently, a method has been proposed for evaluating whether there are any abnormal conditions, such as welding defects, in which the power spectrum of each welding current in normal and abnormal states is obtained in advance by frequency analysis, the power spectrum is trained into a neural network, and then the trained model is used (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 10-235490

However, although the power spectrum in the method described in Patent Document 1 is suitable for training a neural network, it is not suitable for directly detecting welding defects. As described in paragraph [0026] of Patent Document 1, in order to train a neural network, a power spectrum that does not reproduce even the smallest fluctuations is preferable, but such a power spectrum is too coarse to directly detect welding defects. For this reason, even if the power spectrum in the method described in Patent Document 1 is used, welding defects cannot be directly detected with high accuracy.

Therefore, the present invention aims to provide a defect detection device and defect detection method for pulse arc welding that can detect welding defects with high accuracy.

In order to solve the above problems, a defect detection device for pulse arc welding according to a first aspect of the present invention includes a welding current detection unit that detects a welding current of pulse arc welding;
a Fourier transform unit that obtains a power spectrum by performing a Fourier transform on the welding current for a predetermined time period detected by the welding current detection unit;
an index value calculation unit that calculates a welding defect index value from a fundamental frequency, the fundamental frequency being a frequency at which the amplitude is maximum in the power spectrum obtained by the Fourier transform unit;
A warning unit that issues a warning when the welding defect index value calculated by the index value calculation unit is equal to or greater than a threshold value,
The welding defect index value calculated by the index value calculation unit is a value obtained by dividing the sum of the amplitudes of frequencies in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency, or a sum of the values obtained by dividing the amplitudes of each frequency in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency .

The second invention relates to a defect detection device for pulsed arc welding, which is the same as the first invention, except that the predetermined range of cyclic frequencies is a frequency centered on the fundamental frequency.

Furthermore, the pulse arc welding defect detection device according to the third invention is the pulse arc welding defect detection device according to the first or second invention, in which the predetermined range of the cyclic frequency is a frequency that is 0.5 to 1.5 times the fundamental frequency.

In addition, the pulse arc welding defect detection device according to the fourth invention is a pulse arc welding defect detection device according to any one of the first to third inventions, which is provided with a defect determination unit that determines that a welding defect has occurred in the pulse arc welding when the warning unit issues a warning multiple times in succession.

The fifth aspect of the present invention is a pulse arc welding defect detection device according to any one of the first to fourth aspects of the present invention, in which the threshold value of the warning unit is calculated by adding a predetermined value to the time average of the welding defect index value for each predetermined time calculated by the index value calculation unit.

A sixth aspect of the present invention provides a method for detecting defects in pulse arc welding, comprising: a welding current detection step of detecting a welding current in pulse arc welding;
a Fourier transform step of obtaining a power spectrum by Fourier transforming the welding current for a predetermined time period detected in the welding current detection step;
a frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step is set as a fundamental frequency, and an index value calculation step of calculating a welding defect index value from the fundamental frequency;
and a warning step of issuing a warning if the welding defect index value calculated in the index value calculation step is equal to or greater than a threshold value,
The method is such that the welding defect index value calculated by the index value calculation process is a value obtained by dividing the sum of the amplitudes of frequencies in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency, or a value obtained by dividing the amplitudes of each frequency in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency .

The pulse arc welding defect detection device and defect detection method of the present invention can detect welding defects with high accuracy.

1 is a schematic configuration diagram of a pulse arc welding facility equipped with a defect detection device for pulse arc welding according to an embodiment of the present invention. 4 is a graph showing the change over time of the welding current detected by the welding current detection unit of the defect detection device. 11 is a graph showing a power spectrum obtained by a Fourier transform unit when pulse arc welding is stable. 11 is a graph showing a power spectrum obtained by a Fourier transform unit when pulse arc welding is unstable. 2 is a flowchart showing a method for detecting a defect in pulse arc welding according to an embodiment of the present invention. 1 is a schematic configuration diagram of a defect detection device for pulse arc welding according to an embodiment of the present invention. 1 is a graph showing actual measured values (welding defect index value, time average, and occurrence of short circuit) obtained by the defect detection device. 8 is a graph showing more extracted actual measurement values (welding defect index value, time average, occurrence of short circuit) than those in FIG. 7, with the threshold value set to a fixed value. 9 is a graph showing the same measured values (welding defect index value, time average, occurrence of short circuit) as in FIG. 8, with the threshold value being the time average plus an offset value. 4 is a flowchart showing a method of using the defect detection device.

The following describes a pulse arc welding defect detection device according to an embodiment of the present invention with reference to the drawings.

First, we will explain pulse arc welding equipment equipped with the pulse arc welding defect detection device (hereinafter simply referred to as the defect detection device), that is, equipment that performs pulse arc welding and detects defects in the pulse arc welding using the defect detection device.

As shown in FIG. 1, the pulse arc welding equipment 1 includes a welding torch 2 that performs pulse arc welding by generating an arc A from the tip of a welding wire W on a base material B, a feeding device 3 that feeds the welding wire W to the welding torch 2, and a wire reel 4 around which the welding wire W is wound so that it can be withdrawn. The pulse arc welding equipment 1 also includes a shielding gas supply device 5 that supplies shielding gas G from the welding torch 2 to the periphery of the arc A, and a gas hose 6 that sends shielding gas G from the shielding gas supply device 5 to the welding torch 2. The pulse arc welding equipment 1 also includes a welding power source 7 that supplies pulsed power to the welding torch 2 and the base material B, and a welding cable 8 that electrically connects the welding power source 7 to the welding torch 2 and the base material B, respectively. In addition, the pulse arc welding equipment 1 includes a defect detection device 9 provided on the welding cable 8 that electrically connects the welding power source 7 to the base material B.

The configuration of the defect detection device 9 is described in detail below.

As shown in FIG. 1, the defect detection device 9 has 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 the welding cable 8 that electrically connects the welding power source 7 and the base material B, and detects the welding current of the pulse arc welding. The fluctuation of the detected welding current over time is shown in FIG. 2. In the graph shown in FIG. 2, the horizontal axis represents time and the vertical axis represents current. As is clear from this graph, the welding current of the pulse arc welding periodically has a high peak current Ip and a low base current Ib.

The Fourier transform unit 20 obtains a power spectrum as shown in FIG. 3 or FIG. 4 by performing a Fourier transform on the welding current for a predetermined time detected by the welding current detection unit 10. The predetermined time may be a time that includes at least a plurality of periods of the welding current, for example, 1 second. If the pulse arc welding is stable, the frequency of the welding current detected by the welding current detection unit 10 is mostly the fundamental frequency, so that the fundamental frequency fo (maximum amplitude) dominates the obtained power spectrum as shown in FIG. 3. 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 includes other frequencies in addition to the fundamental frequency fo, so that components other than the fundamental frequency fo (maximum amplitude) also appear prominently in the obtained power spectrum as shown in FIG. 4. In other words, if the pulse arc welding is unstable, the frequencies around the fundamental frequency fo in the predetermined range become noise, so that the obtained power spectrum is disturbed.

The index value calculation unit 30 determines 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 Fig. 3 and Fig. 4, the frequency fo at which the largest amplitudes h1 and h2 are observed is determined as the fundamental frequency fo. The index value calculation unit 30 then calculates a partial sum of each amplitude at frequencies in a predetermined range including the fundamental frequency fo. The formula for this calculation is expressed by the following formula (1) when the partial sum is represented as Pfo, the amplitude of frequency f is represented as p(f), and the predetermined range is represented as a to b.

Furthermore, the index value calculation unit 30 calculates the welding defect index value by dividing (i.e., normalizing) the partial sum calculated by the formula (1) by the amplitudes h1 and h2 of the fundamental frequency fo. This normalization causes the welding defect index value to be an addition of the amplitudes of other frequencies (but within a specified range) to the amplitude of the fundamental frequency, making it an appropriate value as an index of welding defects. Note that the normalization includes the case where the partial sum is calculated as described above and then divided by the amplitudes h1 and h2 of the fundamental frequency fo, and the case where the amplitudes of each frequency in a specified range are divided by the amplitudes h1 and h2 of the fundamental frequency fo before calculating the partial sum.

Here, in the formula (1), the predetermined range a to b is not particularly limited as long as it includes the fundamental frequency fo (a≦fo≦b), but it is preferable that it is centered on the fundamental frequency fo, in other words, it is preferable that the fundamental frequency fo is located halfway between the upper limit (b) and the lower limit (a) [fo=(a+b)/2]. Furthermore, it is preferable that the predetermined range a to b is 0.5 to 1.5 times the fundamental frequency fo (a=0.5fo, b=1.5fo). This is because such a predetermined range allows the calculated welding defect index value to appropriately reflect the disturbance of the power spectrum.

The index value calculation unit 30 does not necessarily need to calculate the partial sum using the formula (1) to calculate the welding defect index value. For example, instead of the partial sum, the index value calculation unit 30 may remove frequencies from the predetermined range that do not have a significant effect as an index of welding defects, and use the sum of the amplitudes of only the frequencies that have not been removed. Here, the frequencies to be removed are, for example, frequencies that are equal to or less than a separately set amplitude reference value.

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

The pulse arc welding and the defect detection method thereof will be described below. The defect detection method for this pulse arc welding is not limited to the method using the defect detection device 9, so long as it is a 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 feeder 3, pulsed power is supplied from the welding power source 7 to the welding torch 2 and the base material B, and shielding gas G is supplied from the shielding gas supply device 5 to the welding torch 2 via a 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 this arc A is protected by the shielding gas G. In other words, pulse arc welding is performed on the base material B. Defects in this welding current are detected by the defect detection method for pulse arc welding described below.

The defect detection method for pulse arc welding includes a welding current detection step of detecting the welding current of pulse arc welding, and a Fourier transform step of performing a Fourier transform on the welding current for a predetermined time detected in the welding current detection step to obtain a power spectrum. The defect detection method for pulse arc welding also includes an index value calculation step of calculating a welding defect index value, which is a sum of the amplitudes of frequencies in a predetermined range including the fundamental frequency, normalized by the amplitude of the fundamental frequency, with the frequency being the maximum in the power spectrum obtained in the Fourier transform step. The defect detection method for pulse arc welding also includes a warning step of issuing a warning if the welding defect index value calculated in the index value calculation step is equal to or greater than a threshold value. The index value calculation step may also be a step of calculating a welding defect index value by setting the frequency in the power spectrum obtained in the Fourier transform step as the fundamental frequency, calculating a partial sum of each amplitude at a predetermined range of frequencies including the fundamental frequency, and dividing the partial sum by the amplitude of the fundamental frequency.

Each step of the pulse arc welding defect detection method will be explained based on the flowchart shown in Figure 5.

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

In this way, the pulse arc welding defect detection device 9 and defect detection method detect welding defects based on the disturbance in the power spectrum obtained by Fourier transforming the welding current of pulse arc welding, so that welding defects can be detected with high accuracy.

The following describes a defect detection device 9 according to an example that more specifically illustrates the above embodiment, with reference to FIG. 6. In this example, the description focuses on configurations that are different from the above embodiment, and configurations that are the same as those in the above embodiment are given the same reference numerals and descriptions thereof are omitted.

In FIG. 6, for the sake of simplicity, only the defect detection device 9 according to the present embodiment, the welding power source 7, the welding torch 2, and the welding cable 8 electrically connecting the welding torch 2 and the base material B to the welding power source 7 are shown as components of the pulse arc welding equipment 1 according to the present embodiment, and other components are omitted. As shown in FIG. 6, the defect detection device 9 according to the present embodiment includes the welding current detection unit 10, the Fourier transform unit 20, the index value calculation unit 30, and the warning unit 40 described in the above embodiment, as well as a first 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. Below, these components will be described in order.

The welding current detection unit 10 has a current sensor 11, such as a shunt resistor or clamp meter, that converts the welding current into a voltage value, and a preamplifier 12 that amplifies the voltage value converted by the current sensor 11. The welding current detection unit 10 also has a low-pass filter 13 that blocks the high frequencies of the voltage value amplified by the preamplifier 12, and an AD converter 14 that AD converts the value that passes through the low-pass filter 13. The welding current detection unit 10 also has a controller 15 that stores the AD conversion value, which is the value AD converted by the AD converter 14, in a first memory 71, and operates the Fourier transform unit 20 if it determines that the AD conversion value is the actual welding current.

When the Fourier transform unit 20 is operated by the controller 15, it performs a Fourier transform on the welding current for a predetermined time to obtain a power spectrum. The Fourier transform used to obtain this power spectrum is preferably a fast Fourier transform in order to shorten the processing time.

The index value calculation unit 30 has a fundamental frequency selection unit 31, a partial sum calculation unit 32, and a normalization unit 33. The fundamental frequency selection unit 31 selects the frequency at which the amplitude is maximum, and sets this frequency as the fundamental frequency. The partial sum calculation unit 32 calculates the partial sum of each amplitude at the predetermined range of frequencies using the formula (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 normalization unit 33 is stored in the second memory 72 at predetermined time intervals and transmitted to the warning unit 40. Note that the first memory 71 and the second memory 72 are described as having different configurations because they store different types of values, but they may be the same memory.

The time average calculation unit 73 calculates the time average from the welding defect index values for each predetermined time stored in the second memory 72. It is preferable that the welding defect index values used to calculate this time average are four consecutive points before and after the target predetermined time (five points in total), or four to six consecutive points before the target predetermined time (five to seven points in total). This is because it is possible to shorten the processing time while simultaneously detecting welding defects with high accuracy.

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

The warning unit 40 receives the welding defect index value from the standardization unit 33 and the threshold value set by the threshold setting unit 74, and issues a warning if the welding defect index value is equal to or greater than the threshold value. Of course, the warning unit 40 may also issue a warning 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 issues a warning multiple times in succession. The number of times is not particularly limited as long as it is two or more times, but it is preferable that the number be two or three times in order to reduce the risk of missing a welding defect.

When the welding current is no longer detected by the welding current detection unit 10 (pulse arc welding is interrupted), the display unit 60 displays information about the welding defect determined by the defect determination unit 50 as the welding result. This 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 weld bead. As an example of the display format, the position of the welding defect in the weld bead is displayed as a percentage (the start point of the weld bead is 0 percent, and the end point is 100 percent). In this display format, the position of the welding defect is calculated based on the start and end times of the pulse arc welding, the speed of the pulse arc welding, and the time at which the defect determination unit 50 determines that there is a welding defect.

Graphs of the actual measurements taken by the defect detection device 9 are shown in Figures 7 to 9. In each of Figures 7 to 9, the welding defect index value for each specified time is shown by a solid line, the time average of four consecutive points before and after the specified time in question is shown by a dashed line, and the occurrence of short circuits that cause welding defects is shown by a bar graph.

As shown in FIG. 7, the welding defect index value and the time average tended to be high when a short circuit occurred. The occurrence of a short circuit induces blowholes, which causes welding defects. In other words, it can be said that the welding defect index value and the time average are suitable values for use as indicators of welding defects. Also, FIG. 8 and FIG. 9 are graphs in which more actual measured values than FIG. 7 are extracted, and only the threshold value shown by the virtual line is different. The threshold value is a fixed value in FIG. 8, whereas in FIG. 9, it is a value obtained by adding a predetermined value (offset value) to the time average. As shown in FIG. 8 and FIG. 9, the time when the welding defect index value becomes equal to or greater than the threshold value corresponds well to the time when a short circuit occurs. Therefore, it can be said that welding defects can be detected with high accuracy by issuing a warning if the welding defect index value is equal to or greater than the threshold value. In particular, by using the threshold value shown in FIG. 9, the time when the welding defect index value becomes equal to or greater than the threshold value corresponds very well to the time when a short circuit occurs, so it can be said that welding defects can be detected with even higher accuracy.

The method of using the defect detection device 9 according to this embodiment will be described below with reference to the flowchart shown in FIG. 10.

First, when the welding current is detected by the welding current detection unit 10 (S10), the welding current stored in the first memory 71 is Fourier transformed for a predetermined time to obtain a power spectrum (S20). Then, the fundamental frequency selection unit 31 selects the frequency at which the amplitude is maximum 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 predetermined range of frequencies including the fundamental frequency (S32). Furthermore, the normalization unit 33 calculates a 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 a threshold value (S41), the warning unit 40 issues a warning (S42). If this warning is issued multiple times in succession (S51), the defect judgment unit 50 judges that a welding defect has occurred (S52).

If the welding defect index value is less than the threshold value (S41), if the warning has not been issued multiple times in succession (S51), or if it is determined that a welding defect has occurred (S52), the flow returns to the flow of determining whether or not the welding current is detected by the welding current detection unit 10 (S10). 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).

In this way, the pulse arc welding defect detection device 9 according to this embodiment has the same effects as the defect detection device 9 according to the above embodiment, and the defect determination unit 50 determines welding defects, making it possible to detect welding defects with even greater accuracy.

In the above embodiment and examples, the normalized partial sum is used as the welding defect index value for determining the disturbance of the power spectrum, but statistical methods such as the variance or kurtosis of the power spectrum may also be used.

The above-described embodiments and examples are illustrative in all respects and are not restrictive. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications that are equivalent in meaning and scope to the claims. Among the configurations described in the above-described embodiments, those other than those described as the first or sixth invention in the "Means for solving the problem" are optional configurations and may be deleted or modified as appropriate.

REFERENCE SIGNS LIST 1 Pulse arc welding equipment 2 Welding torch 3 Wire feeder 4 Wire reel 5 Shielding gas supply device 6 Gas hose 7 Welding power source 8 Welding cable 9 Defect detection device 10 Welding current detection unit 20 Fourier transform unit 30 Index value calculation unit 40 Warning unit

Claims (6)

A welding current detection unit that detects a welding current of pulse arc welding;
a Fourier transform unit that obtains a power spectrum by performing a Fourier transform on the welding current for a predetermined time period detected by the welding current detection unit;
an index value calculation unit that calculates a welding defect index value from a fundamental frequency, the fundamental frequency being a frequency at which the amplitude is maximum in the power spectrum obtained by the Fourier transform unit;
A warning unit that issues a warning when the welding defect index value calculated by the index value calculation unit is equal to or greater than a threshold value,
A pulse arc welding defect detection device characterized in that the welding defect index value calculated by the index value calculation unit is a value obtained by dividing the sum of the amplitudes of frequencies in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency, or a value obtained by dividing the amplitudes of each frequency in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency . The pulse arc welding defect detection device according to claim 1, characterized in that the predetermined frequency range is a frequency centered on the fundamental frequency. The pulse arc welding defect detection device according to claim 1 or 2, characterized in that the predetermined frequency range is a frequency between 0.5 and 1.5 times the fundamental frequency. The pulse arc welding defect detection device according to any one of claims 1 to 3, characterized in that it is provided with a defect determination unit that determines that a welding defect has occurred in the pulse arc welding when the warning unit issues multiple consecutive warnings. A pulse arc welding defect detection device according to any one of claims 1 to 4, characterized in that the threshold value of the warning unit is a predetermined value added to the time average of the welding defect index value calculated by the index value calculation unit for each predetermined time. A welding current detection step of detecting a welding current of the pulse arc welding;
a Fourier transform step of obtaining a power spectrum by Fourier transforming the welding current for a predetermined time period detected in the welding current detection step;
a frequency at which the amplitude is maximum in the power spectrum obtained in the Fourier transform step is set as a fundamental frequency, and an index value calculation step of calculating a welding defect index value from the fundamental frequency;
and a warning step of issuing a warning if the welding defect index value calculated in the index value calculation step is equal to or greater than a threshold value,
A method for detecting defects in pulse arc welding, characterized in that the welding defect index value calculated by the index value calculation process is a value obtained by dividing the sum of the amplitudes of frequencies in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency, or a value obtained by dividing the amplitudes of each frequency in a predetermined range including the fundamental frequency by the amplitude of the fundamental frequency .

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