JPS6133766A - Method and device for monitoring welding in gas shielded arc welding - Google Patents

Abstract

PURPOSE:To make detection at a high speed with a simple device and with high sensitivity and accuracy by subjecting the dynamical spiky voltage generated by the intrusion of air to a frequency sepn. and detecting the intrusion of the air. CONSTITUTION:An arithmetic circuit 7, to which the output S from a frequency band filter 6-1 and the output N from a low-frequency filter 6-2 are derived, operates an S/N ratio (detected intensity value) and outputs a detection signal M. A decision circuit 8 compares the detected intensity value S/N with the 1st criterion value K1 for the purpose of deciding the presence or absence of the generation of the spiky voltage S and outputs the signal C of the fixed waveform corresponding to the generation frequency of the pulse signal in a multivibrator circuit 9 when S/N>K1. An integration circuit 10 generates the voltage P corresponding to the generation frequency of the pulse signal. An air intrusion detector 11 delivers an air intrusion detection signal L as a command signal for driving alarm to an alarm device 12 when the output P from the circuit 10 attains the 2nd criterion value K2 for the purpose of discriminating the generation frequency of the voltage S.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding monitoring method and apparatus for gas shielded arc welding.

Generally, in gas-shielded arc welding, settings are made to completely shield the welding area with a shielding gas such as argon to prevent nitridation and oxidation caused by air in the welding area and to obtain good welding results. During work, air may get mixed into the arc due to the shielding effect being reduced due to some reason such as a change in the arc length, or due to atmospheric wind hitting the arc directly, which may cause the welding to fail. This results in not only deterioration of mechanical properties such as the IH shock value of the part, but also the occurrence of welding defects such as bubbles.

For example, in co-metal TIG welding of 9% Ni steel, in order to ensure high low-temperature toughness of the as-welded ferritic weld metal, gas components such as oxygen and nitrogen, and impurity elements such as phosphorus and sulfur are reduced as much as possible. Air to the welding area (
Intrusion of oxygen, nitrogen) is a major problem.

Conventionally, methods for monitoring the state of air intrusion into the welding zone include (a) monitoring the welding arc voltage and current with ordinary instruments, and (bl) using a nozzle to collect nitrogen oxides generated due to air intrusion. (C) A method of detecting the mixed air component by measuring the emission spectrum (Japanese Patent Application Laid-open No. 56-43536). ) etc. have been proposed.

However, the above method (a) is difficult to measure and is not practical because the fluctuations in voltage and current caused by air inclusion are minute. In addition, the method (bl) has problems with shielding gas disturbance and speed, and the method (fc) requires a device for collecting the arc light, resulting in a complicated apparatus.

The inventors of the present invention have conducted various studies and experiments in order to eliminate the above-mentioned conventional drawbacks and problems, and have found that when air enters the arc atmosphere, the welding arc voltage waveform becomes spike-like in the steady state voltage waveform. The present invention was completed by discovering that the voltage waveform is a waveform in which many voltage waveforms are superimposed, and by extracting this spike-like voltage and subjecting it to signal processing. .

The present invention monitors the welding arc voltage, detects when a spike-like voltage in a specific cycle range is superimposed, and compares the detected value with a preset criterion, By configuring the system to generate an air intrusion detection signal when the determination standard is exceeded, air intrusion can be detected practically and reliably, albeit purely electrically.Therefore, the detection speed is excellent. An object of the present invention is to provide a welding monitoring method and device for gas-shielded arc welding that can perform highly accurate monitoring with a simple device.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a diagram of a device embodying the present invention, and FIG. 2 shows a welding arc voltage waveform diagram. In Figure 1, 1
is a welding power source, 2 is an arc electrode, 3 is a shielding gas atmosphere, 4 is an isolation amplifier to which the arc voltage is guided, and 5 is a level converter (amplifier) that converts the input into a signal at a level suitable for signal processing. . 6-1 is a frequency band filter, and the spike-like voltage (dynamically fluctuating part) S shown in FIG.
The specific frequency range S of is set as a pass band, and this spike-like voltage S is separated from the welding arc voltage shown in FIG. 2 whose level has been converted by a level converter 5 and is output. 6-2 is a low frequency filter which receives the output of the level converter 5 and passes the steady state voltage N of the welding arc voltage shown in FIG. 7 is an arithmetic circuit which receives the output S of the frequency band filter 6-1 and the output N of the low frequency filter 6-2, calculates the S/N ratio (detection intensity value), and calculates the S/N ratio. A detection signal M having a certain magnitude is output. Reference numeral 8 denotes a determination circuit (comparison circuit) which compares the detected strength value S/N with 1 to a first determination reference value for determining the presence or absence of the spike-like voltage S, and determines that S/N>Kl In this case, the next multi-by-break circuit 9 outputs a signal C of a regular wave according to the frequency of occurrence of the pulse signal. Reference numeral 10 denotes a frequency/voltage conversion circuit (integration circuit), which generates a voltage P depending on the frequency of pulse signal generation. Reference numeral 11 denotes an air intrusion detector, which generates an air intrusion detection signal when the output P of the frequency/voltage conversion circuit 10 reaches a second determination reference value 2 for determining the frequency of occurrence of the spike voltage S. For example, in addition to being sent to the alarm device 12 as an alarm drive command signal Y, it is also used as a control signal such as a welding interruption command or a command to increase the shielding gas flow rate as necessary.

The spike-like voltage S of the welding arc voltage shown in FIG. 2 is considered to be caused by fluctuations in the spectral lines of the emission spectrum in the arc. That is, according to the experimental results of the present inventors, it was confirmed that a spike-like voltage S is generated during TIG welding when air enters, but at this time, when there is no wind in the arc and no air enters, a spike voltage S is generated. A large number of missing iron spectral lines were detected. This is thought to be because molten iron in the molten pool comes in contact with oxygen from the invading air, producing iron oxide with a relatively high vapor pressure, which mixes into the arc column and causes a change in electrical resistance. The magnitude of the above-mentioned spike-like voltage corresponds to the intensity of the above-mentioned iron spectrum, and the period of occurrence is quite wide, but since 10 to 20 m-5ee occurs frequently, this is difficult from the viewpoint of monitoring or detection accuracy. Experiments have confirmed that a periodic range is suitable.

The frequency band filter 6-1 of the embodiment has these 10 to 20
A specific frequency band S (
The pass band is approximately 50 to 100 Hz).

Therefore, the frequency band filter 6-1 does not output when the spike-like voltage S is not superimposed on the steady-state voltage N, but when the spike-like voltage S is generated due to the intrusion of air, it separates it and outputs it. The spike-like voltage component S separated by the frequency band filter 6-1 is divided by the steady state voltage component N in the calculation circuit 7 to calculate the detected strength value S/N. This is to eliminate the effects associated with this.

The first judgment reference value 1 of the judgment circuit 8 measures the correlation between the nitrogen content and the toughness (absorbed energy) of the weld metal by changing the amount of air entering the shield atmosphere, and determines the tolerance of the above toughness. Value of detection signal M (detection intensity value S/N) at the time of intruding air amount when a preset limit nitrogen concentration is given based on the value
(However, when the noise of the normal welding arc voltage is Vs, K1 is set so that M>Vs.) is used. Of course, other welding defect conditions such as the number of pores generated in the weld metal can be used in addition to the nitrogen content as the characteristic value for setting the first criterion value to 1. The judgment circuit 8 detects a pulse whose magnitude of the detection signal M, that is, the pulse height value exceeds the first judgment reference value by 1 when the arithmetic circuit 8 outputs it, and outputs a judgment signal C at a constant level each time. do. This output C is a signal having a frequency corresponding to the period of the spike voltage S, and is converted by the multi-by-break circuit 9 into a rectangular wave voltage signal (2) having a predetermined width and a thickness proportional to the frequency.

In this way, the occurrence of a spike-like voltage S whose period is within the range of 10 to 20 m-5 ec and whose wave height exceeds a predetermined magnitude is detected, but in this embodiment, the frequency of occurrence of the spike-like voltage S is also used as a determination condition. In order to increase the detection accuracy by taking into consideration
The air intrusion detector 11 operates to output an air intrusion detection signal when the air intrusion detection signal reaches this point. This criterion value of 2 is determined by experimentally determining the relationship between wind speed and Charpy value or between wind speed and the number of pores per unit length, and is determined to emit a signal at that wind speed.

Therefore, only when the spike-like voltage S is superimposed on the welding arc voltage, the spike-like voltage S is within the periodic range, has a magnitude greater than a predetermined value, and occurs frequently, the air intrusion detection signal I2 is activated. When this occurs, the alarm 12 is activated and the presence of air intrusion is notified. This prevents erroneous detection such as the alarm 12 going off unnecessarily, and the detection accuracy is extremely high.

Note that the above embodiment has been described with reference to the case where the shielding gas is Ar gas, but when He gas is added to Ar gas, the iron spectral line intensity increases due to the increase in arc temperature, and a corresponding spike occurs. Since the wave height of the voltage becomes higher, detection sensitivity can be further increased.

Below, the results of an experiment conducted using the apparatus shown in FIG. 1 will be explained.

[First experimental results] <Welding conditions> Electrode: 2% Th-containing W (inφ) Wire: 9% Ni steel (1.2mφ) C: 0.02%, Mn: 0.45%, Sl: 0. 05
%, P: 0.002%, Ni: 11.15%: O:
0.005%N: O, OO2%.

Base material: JTS G3127 5L9N60, polarity: D
C- Posture: Vertical (weaving) Welding current 72 B OA, Welding voltage: 11V, Welding speed: 5cm/min, Shielding gas flow rate: Ar, 254! /min.

(double shield) Wire feeding speed: 20g/min, Electrode protrusion length: 15mm, Power source: Commercially available 500A TIG welding power source.

Under the above conditions, the amount of air intrusion was adjusted by controlling the wind speed, and the detected intensity value S/N and the total amount of nitrogen in the weld metal at each wind speed were measured. On the other hand, the allowable limit amount of nitrogen is determined from the toughness aspect (
Considering this, the limit S/N ratio is
That is, a criterion value K was determined. FIG. 3 shows the monitoring situation, and it can be seen that the air intrusion situation with respect to the allowable nitrogen amount is detected with high accuracy.

Next, an example will be shown in which the discrimination reference value is set to 2 based on the number of generated pores.

[Second experimental results] <Welding conditions> Wire: MOS 0 (1.6 mmφ) C: 0.09
%, Mn: 1.09%, Si 1.46%, P: 0.01
3%, S: 0.012%, Base material: JISG3106.5M50A.

Polarity: DC (+) Posture 2 downward (straight), Welding current: 375A, Welding voltage: 30V, Welding speed:
89 cm/min.

Shield gas flow rate: C0125j! /min.

Wire feeding speed: 940cm/min, electrode protrusion length: 19mm, power supply 2 Commercially available CO welding power source with 500A capacity.

Under the above conditions, the percentage of nitrogen in the shielding gas was varied, the detection signal M at each concentration was measured, and the change in the concentration table was determined, while the number of pores generated at each concentration was determined. The allowable number of pores in CO welding has been set to approximately 200/
Assuming 6 inches (15.24 cm) (equivalent to JTS class), an air intrusion detection signal was generated when the corresponding value of the detection signal M was reached. FIG. 4 shows the monitoring situation at this time, and it can be seen that an alarm is generated when the amount of nitrogen corresponds to the above-mentioned allowable value, and that the situation of air intrusion is reliably detected.

Although the above description has been made regarding the case of alloy TIG welding of 9% Ni steel, it is clear that similar effects can be obtained by applying the present invention to general consumable electrode type gas shield arc welding.

Furthermore, it is understood that the present invention is an effective method for evaluating arc stability in arc welding if the period of the spike voltage is appropriately selected.

As described above, according to the present invention, the dynamic spike-like voltage generated due to air intrusion is frequency-separated and detected based on the presence or absence of the spike-like voltage. Unlike detection based on changes, air intrusion can be reliably detected, and since it is purely electrically detected, it is quick, the equipment is simple, and the detection is highly sensitive and accurate. It can be carried out.

[Brief explanation of the drawing]

Fig. 1 is a block diagram implementing the welding monitoring method in gas-shielded arc welding according to the present invention, Fig. 2 is a waveform diagram of welding arc voltage, and Figs. 3 and 4 are graph diagrams showing alarm generation states in experiments. It is. 5- Level converter, 6-1 =- Frequency band filter, 6-2- Low frequency filter, 7- Arithmetic circuit, 8 =- Judgment circuit, 9- Multi-by-break circuit, 1°- Frequency/voltage conversion circuit, 11 - Air intrusion detector.

Claims (7)

[Claims] (1) Monitor the welding arc voltage, detect when a spike-like voltage in a specific periodic range is superimposed, and compare the detected value with a preset judgment standard, and if the detected value exceeds the above judgment standard. A welding monitoring method for gas shield welding, characterized in that an air intrusion detection signal is generated when an air intrusion is detected. (2) The specific periodic range of spike voltage is 10 to 20 m.
2. The welding monitoring method in gas shield welding according to claim 1, wherein the welding monitoring method is sec. (3) The gas shield according to claim 1 or 2, wherein one of the criteria is the magnitude of the spike voltage, and another one is the frequency of occurrence of the spike voltage. Welding monitoring method in welding. (4) Welding in gas shield welding according to claim 1, 2, or 3, characterized in that the ratio of the spike voltage to the steady state voltage of the welding arc voltage is compared with a criterion. Monitoring method. (5) The welding monitoring method in gas shield welding according to claim 1 or 2 or 3 or 4, wherein the gas shield welding is cometal TIG welding of 9% Ni steel. (6) An amplifier that converts the level of the welding arc voltage, a filter circuit that separates the spike voltage component in a specific frequency range from the steady state voltage component from the output of the amplifier, and a comparison between the spike voltage component and the steady state voltage component. an arithmetic circuit that outputs an output when the output of the arithmetic circuit exceeds a first judgment reference value, and an air intrusion detection circuit that outputs an output when the output of the arithmetic circuit exceeds a second judgment reference value. A welding monitoring device for gas shield welding, characterized by comprising a circuit that generates a signal. (7) A welding monitoring device for gas shield welding according to claim 6, wherein the arithmetic circuit calculates a ratio between a spike voltage component and a steady state voltage component.