JPH04200977A - Gas shielded state detecting method and device for gas shielded arc welding - Google Patents

Abstract

PURPOSE:To detect a gas shielded state in real time and to prevent defective gas shielding by detecting welding current, waveforms at the plus side and the minus side, obtaining an effective value of a waveform signal of the difference between the mutual welding current waveforms and detecting a welding arc state by the change of the effective value. CONSTITUTION:A resistor 21 and a resistor 22 with the same characteristic as the resistor 21 are connected on the way of a feeder at the plus side of a welding power source 1 and on the way of a feeder at the minus side thereof, respectively to detect welding current waveform signals at the plus side and the minus side. These signals are then amplified by amplifiers 31 and 32 and only a waveform component of the difference between the welding current waveforms at the plus side and the minus side is taken out through a waveform subtracter 9. The influence of a low frequency component is then reduced and the effective value is obtained by an RMS circuit 11 by passing the waveform of the difference through a high-pass filter 10. Since this effective value becomes higher when the gas shielded state is defective, size of this effective value is detected by a determination circuit 12 and when it exceeds a specified value, a signal is produced and an alarm is produced by an alarm circuit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting a gas shield state during gas shield arc welding and an apparatus for detecting a gas shield state.

[Prior art and problems to be solved by the invention] In arc welding, if air gets mixed into the arc atmosphere, welding defects will occur. Gas-shielded arc welding is performed to exclude gas from the weld area.

On the other hand, arc welding work generates a large amount of fume, so it is necessary to ventilate the hot water area at the welding work site for the hygiene of the workers. In some cases, wind may also hit the welded parts that provide gas shielding. As a result, the gas shield may become defective and weld defects may occur. In addition, if the nozzle is clogged, the carbon dioxide gas supply pressure is reduced, which may cause a gas seal failure.

A conventional method for ensuring a good gas shielding effect is to use a large flow rate of shielding scum and a dedicated nozzle. However, this method has a problem in that since the gas shielding state cannot be directly known during the welding operation, only indirect defect prevention measures such as using a large amount of shielding gas can be taken.

Furthermore, a method of detecting the gas shield state by detecting fluctuations in welding current and voltage has been conventionally used.

However, this method has a problem in that detection accuracy cannot be improved because changes due to gas shield failure are minute.

In addition, Japanese Patent Laid-Open No. 61-33766 proposes a method of detecting gas shield failure by detecting spike voltages generated during TIG welding.

However, in TIG welding, droplets are transferred in a spray transfer mode, which is a very stable transfer mode, whereas in normal carbon dioxide gas shielded arc welding, the transfer mode of droplets is a Gu-Buhl transfer or a short-circuit transfer mode. It is. Furthermore, while TG welding uses a non-consumable electrode, carbon dioxide shielded arc welding uses a consumable electrode, and the shape of the electrode changes greatly. Therefore, the level fluctuations in welding current and voltage are extremely large, and the detected waveform is buried in these fluctuations, making it impossible to apply this method to carbon dioxide shielded arc welding, which uses consumable electrodes.

As described above, it has been difficult to obtain a good gas shielding state using any of the conventional methods.

It is an object of the inventions of the present application to solve these problems, and to solve this problem, it is possible to detect welding defects due to gas shield failure by detecting the gas shield "state" during gas shield arc welding. It is an object of the present invention to provide a gas shield state detection method and device that can prevent this.

[Means for Solving the Problems] In order to achieve this objective, the present inventor has conducted various experiments and conducted studies, and has found that the spike-like waveform included in the welding current waveform is different on the plus side and the minus side. We have found that these waveform fluctuations are closely linked to changes in the Casseal I condition, especially in the high frequency range, which has not been considered important as a welding signal source in the past.

The inventions of this application make use of this newly discovered phenomenon, that is, "in gas shielded arc welding,
The welding current waveforms on the plus side and the minus side are detected, a waveform signal of the difference between the welding current waveforms is obtained, an effective value of the waveform signal of the difference is obtained, and a welding arc state is detected based on the change in the effective value. A first invention comprising: a gas shield state detection method characterized in that a welding current waveform detector and an amplifier of the same performance are provided on the plus side and minus side of a welding power source output section; a subtraction circuit that calculates the difference between the signals; an effective value calculation circuit that calculates the effective value of the difference;
A second gas shield state detection device characterized by having a determination circuit that determines the quality of the gas shield based on the magnitude of the effective value, and an alarm circuit that issues an alarm based on the determination result of the determination circuit. invention, ``In gas-shielded arc welding, detect the welding current waveforms on the plus side and minus side, obtain the waveform signal of the difference between the welding current waveforms, perform fast Fourier transform on the waveform signal of the difference, and its frequency distribution. A third invention comprising: a method for detecting a welding arc state by detecting a welding arc state based on a change in the welding arc state; Create a current waveform detector and amplifier, and a subtraction circuit to find the difference between these signals.
It is characterized by having a fast Fourier transform circuit that fast Fourier transforms the difference, a determination circuit that determines whether the gas shield is good or bad based on the waveform signal converted by the fast Fourier transform circuit, and an alarm device that issues an alarm based on the determination result of the determination circuit. A fourth aspect of the present invention is provided, which is a gas shield state detection device.

[Operation] Each of the inventions of the present application has the above-mentioned configuration, and in the first invention and the second invention, a cassealt failure is detected by the increase in the effective value, and in the third invention and the fourth invention,
In the invention, a cassealt failure is detected in real time based on a change in the frequency component.

[Example] Hereinafter, an example in which the present invention is applied to consumable electrode type carbon dioxide gas arc welding will be described with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment for explaining the gas shield state detection method of a welding apparatus according to the first invention and the gas shield state detection apparatus according to the second invention using analog signal processing.

In this block diagram, l is a welding power source, 2I and 2
2 is a welding current detection means which is a resistor having exactly the same characteristics connected to the positive side and negative side welding power source output parts, respectively; 31 and 32 are for amplifying the current waveform taken out from the resistors 21 and 22; amplifier, and these two
The zero level and amplification degree of the two amplifiers are exactly the same. 4
5 is a welding object, 5 is carbon dioxide for shielding, 6 is a welding nozzle, 7 is a contact tip, and 8 is a welding wire.

Further, 9 is an analog waveform subtracter that subtracts one signal from the other amplified by the amplifiers 31 and 32, and 10 is the influence of waveform fluctuations caused by droplet transfer period, power supply rectification ripple waveform, power supply frequency noise, etc. 11 is a root mean square (RMS) circuit that performs effective value averaging processing to reduce signal fluctuation;
12 is a determination circuit having a threshold value; 13 is an alarm circuit that issues an alarm signal based on the determination result of the determination circuit.

Note that this bypass filter 10 is caused by the presence of the droplet transfer period, power rectification ripple, power frequency noise, etc., so it can be omitted if these problems do not exist.

Next, the operation of the welding apparatus shown in FIG. 1 will be explained using FIGS. 2 and 3.

In FIG. 1, the welding current flows along the path of the positive terminal of the welding power source 1 → the contact tip 7 → the welding wire 8 → the welding arc air column → the workpiece 4 → the negative terminal of the welding power source 1. A resistor 21 and a resistor 22 having exactly the same characteristics as the resistor 2I are connected in the middle of the positive side power supply line of this current path, and the resistor 22 is connected in the middle of the negative side power supply line, and these resistors 21 and 22 detect the welding current waveform signals on the plus side and the minus side, respectively.

The positive and negative welding current waveform signals detected in this manner are amplified by amplifiers 31 and 32 having exactly the same zero level and the same amplification degree.

FIG. 2(a) shows a waveform diagram of the positive side welding current after amplification in the welding apparatus shown in FIG. 1, and FIG. 2(b) shows a waveform diagram of the negative side welding current after amplification.

As is clear from these figures, there is a difference between the positive welding current waveform and the negative welding current waveform.

This is because while the welding current flows through the arc air column, the arc air column acts as a kind of gas condenser, and the degree of absorption of the peak value of the welding current waveform, which is a high frequency component, changes depending on the type of gas. At the same time, the discharge characteristics of the arc also change slightly, resulting in a subtle difference between the positive and negative welding current waveforms.

By passing these welding current waveforms through an analog type waveform subtracter 9, only the waveform component of the difference between the welding current waveforms on the plus side and the minus side is extracted.

FIG. 2(C) shows the waveform surface of the difference between the plus side welding current waveform and the minus side welding current waveform obtained by passing the waveform subtracter 9 through the analog type waveform subtracter 9. As is clear from this figure, in this way, the waveform of the absolute difference between the positive welding current waveform and the negative welding current waveform can be extracted in a clear form without being affected by waveform level fluctuations. .

By passing the difference waveform obtained in this way through the bypass filter 10, the influence of low frequency components such as the droplet transfer period, power supply rectification ripple waveform, power supply frequency noise, etc. is reduced, and this is processed by the RMS circuit. Get the effective value.

This effective value depends on the wind speed in the welding area, that is, the gas shielding condition, and if the gas shielding condition is poor, the effective value becomes large. This situation is shown in the 31st ffl (
This is a graph of (b), and the wind speed at that time is shown in (a) of the same figure.

In these figures, the horizontal axis is the time axis with 1 division of 4 seconds, and the vertical axis represents the wind speed of ±9 m/s of full scale in logarithmic scale in (a), and the wind speed of ±2 full scale in (b). ■Represents the effective value of. As is clear from these figures, the gas shield failure shown in (a) with a wind speed of 2 m/s or more corresponds to the effective value range of about 1■, that is, the gas shield failure signal area shown in (b).

The magnitude of this effective value is detected by a determination circuit 12, and if it exceeds a certain threshold, a signal is generated and an alarm is generated by an alarm circuit.

Although the case of carbon dioxide arc welding has been described above, similar effects can be obtained when the present invention is applied to gas shielded arc welding other than carbon dioxide arc welding.

Next, FIG. 4 shows a block diagram of a second embodiment for explaining the gas shield state detection method of the third invention and the gas shield state detection apparatus of the fourth invention using digital signal processing.

The welding method of the third invention and the welding device of the fourth invention, the embodiment of which is shown in FIG. 4, differ from the welding method and device of the embodiment shown in FIG. In contrast, in welding equipment, the quality of the gas shield condition is determined based on the magnitude of the effective value of the high frequency component in the current waveform obtained through the waveform subtractor path 9, bypass filter 10, and RMS circuit 11. In the welding apparatus of the second embodiment, the current waveform obtained by passing through the waveform subtraction circuit 9 is subjected to frequency analysis by passing it through the fast Fourier transform (FFT) circuit 14, and the result is used to determine whether the gas shield condition is good or bad. This is the point where the judgment is made.

FIG. 5 shows the welding apparatus of the second embodiment shown in FIG.
This is a comparison of frequency analysis data regarding the quality of gas shields. FIG. 5(a) shows the frequency distribution when the gas shield is defective, and FIG. 2(b) shows the frequency distribution when the gas shield is good. As is clear from these figures, when the gas shield is good, there is no frequency component at all above 2-4 KHz, whereas when the gas shield is bad, there is no frequency component at all above 2-4 KHz. Frequency components continuously exist in the portion above 4 kHz.

In addition, the sum of all frequency signal strengths when the gas shield was good was about -30 dBV, whereas when the gas shield was bad, there was a signal strength difference of about -27 dBV and 3 dBV.
The total frequency signal strength from 2.4KHz to 8KT (z), which blocks the effects of line noise and power supply ripple frequency, is about -37dBV when the gas shield is good, and a difference of about -31dBV and 6dBV when the gas shield is bad.
This is sufficiently large as a signal difference.

Since these processing results are digitally processed, the change values can be continuously obtained with high precision and almost in real time, and it is easy to output a gas shield failure time signal through the discrimination circuit.

The method using analog processing shown in the first embodiment has a relatively simple configuration and is capable of high-speed analog processing, but because it detects changes in the overall signal power, it is possible to clearly detect subtle changes in the gas shield state. Difficult to grasp. On the other hand, the digital processing method shown in the second embodiment has a complicated equipment configuration and requires a slightly longer processing time, but because the frequency distribution state is constantly analyzed, subtle changes in the gas shield state can be detected. It is possible to detect at all times.

In each of the above embodiments, a resistor is used as the welding current waveform detector, but other detectors, such as a current transformer or other alternating current detecting means, can be used, for example, by taking advantage of the fact that the waveform component to be extracted is alternating current. It is possible to use it.

In addition, although this embodiment has described the gas shield state detection method and device, if appropriate FFT processing items are selected, it is possible to detect the droplet transfer state in gas shield arc welding.
It is also useful as a multidimensional evaluation method for arc conditions such as detecting short circuit conditions.

[Effects of the Invention] As explained above, according to the methods of the inventions of the present application, it is not only possible to detect the gas shield state in real time with a relatively simple equipment configuration, but also it is possible to detect the gas shield state in real time with a relatively simple equipment configuration. Even if the welding power source current waveform changes significantly, as in the case where the waveform of the welding power source current changes significantly, the signal source is the absolute difference between the instantaneous waveforms of the positive side waveform and the negative side waveform, so it is not easily affected by the change.

In addition, since the signal can be taken from the welding power source output section,
The torch part etc. are easy to handle.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a device that realizes the present invention, Fig. 2 is a welding current original waveform and welding current subtraction waveform, Fig. 3 is a gas shield failure state signal waveform, and Fig. 4 is a device with another combination. The block diagram of FIG. 5 is a gas shield signal frequency analysis waveform diagram. In the figure, 1... Welding power source, 21. 22... Resistor, 3+, 32... Amplifier, 8... Welding wire, 9... Waveform subtractor, 10... Bypass filter, 11. ... Effective value averaging circuit, 12... Gas shield judgment circuit, 13... Alarm circuit, 14... Fast Fourier transform circuit,

Claims (4)

[Claims] (1) In gas shielded arc welding, detect the welding current waveforms on the plus side and minus side, find the waveform signal of the difference between the welding current waveforms, find the effective value of the waveform signal of the difference, and calculate the effective value of the waveform signal of the difference. A gas shield state detection method characterized by detecting a welding arc state based on a change. (2) A welding current waveform detector and an amplifier with the same performance are provided on the positive and negative sides of the welding power source output section, a subtraction circuit that calculates the difference between these signals, and an effective value calculation circuit that calculates the effective value of the difference; A gas shield state detection device comprising: a determination circuit that determines the quality of the gas shield based on the magnitude of the effective value; and an alarm circuit that issues an alarm based on the determination result of the determination circuit. (3) In gas-shielded arc welding, detect the welding current waveforms on the plus side and minus side, obtain the waveform signal of the difference between the welding current waveforms, perform fast Fourier transform on the waveform signal of the difference, and calculate the frequency distribution. A gas shield state detection method characterized by detecting a welding arc state based on a change. (4) A subtraction circuit that is equipped with welding current waveform detectors and amplifiers of the same performance on the positive and negative sides of the welding power source output section, and that calculates the difference between these signals, and a fast Fourier transform circuit that performs fast Fourier transform on the difference; A gas shield state detection device comprising: a determination circuit that determines the quality of the gas shield based on the waveform signal converted by the fast Fourier transform circuit; and an alarm device that issues an alarm based on the determination result of the determination circuit.