JPH0557071B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an arc welding method in which welding is performed by feeding a consumable electrode at a constant rate, and in particular to an arc welding method suitable for greatly reducing spatter generated during welding. Regarding welding methods.

[Background of the invention]

In the arc welding method in which welding is performed by feeding a consumable electrode at a constant speed, a circuit consisting of a power source 1 with constant DC voltage characteristics and a DC reactor 2 as shown in Figure 1 has been put into practical use. ing. When welding is performed using a circuit configured in this manner, welding phenomena vary greatly depending on the magnitude of the welding current. That is, in a region where the welding current value is relatively low, a so-called short-circuit transfer phenomenon is observed in which the molten metal at the tip of the consumable electrode contacts and transfers to the base metal. Second
The figure shows the changes in welding current and arc voltage when short circuits and arcs are repeated.
KPR indicates the external characteristic curve of the power supply, L ₀ , L ₁ , L ₂
are the arc characteristics when the arc lengths are L ₀ , L ₁ , and L ₂ respectively, and L ₀ is the arc characteristic when the arc length is zero. When a short circuit starts, the current increases rapidly from 1 to 2, and when the short circuit breaks at 2, an arc voltage of 3 is generated, and the arc length immediately increases, and the arc length becomes L ₂ and the arc voltage
Move to 3′. However, since the electrode is constantly fed, the arc length gradually becomes shorter and changes from 3' to 4 to 5, and at 5, the arc length is shorted again. When the welding phenomenon at this time is observed using a high-speed camera, spatter is most noticeable at the moment when an arc becomes a short circuit and at the moment when a short circuit becomes an arc. Among these, the spatter that occurs when a short circuit occurs from an arc can be reduced by setting the inductance of the DC reactor in Figure 1 to an appropriate value and controlling the rising speed of the current from 1 to 2 in Figure 2. be able to. For this purpose, various methods have been considered and implemented. For example, 2 in the reactor
A method has been considered in which a secondary control winding is provided and an appropriate inductance is selected according to the welding conditions. Also, methods are being considered to control the rise of the current during a short circuit and the fall of the current when the short circuit turns into an arc. These methods are effective in reducing spatter that occurs when the aforementioned arc becomes a short circuit. However, at the moment when a short circuit becomes an arc, as shown in Figure 2, in the conventional method, the current value is always high in principle, so the arc force generated by this high current is strong, and the arc column undergoes rapid thermal expansion. Since there are many degrees of this, spatter occurs. For this reason, it has not yet been possible to significantly reduce spatter generated during welding.

On the other hand, in a region where the welding current is relatively high, as shown in Figure 3, the arc is strong and pushes up the molten metal at the tip of the electrode, making it difficult to short-circuit, resulting in larger droplets and severe partial melting. Many large spatters occur. Therefore, in this current range, conventional methods have been used to actively lower the arc voltage and use the bleed arc method to trap the generated spatter in the molten pool and prevent it from coming out, or to reduce the inductance of the power supply circuit. Methods have been considered to reduce current fluctuations in the event of a short circuit by making it extremely large (more than 600 μH), but none of these methods have led to a significant reduction in spatter.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a novel method that generates almost no spatter and provides a stable arc in a wide welding current range from low current to high current. The object of the present invention is to provide an arc welding method.

[Summary of the invention]

The present invention detects a short circuit state and an arc state in an arc welding method in which welding is performed by feeding a consumable electrode at a constant speed, and uses this detection signal to determine an optimal pulse current based on a value sufficiently smaller than the pulse current. By superimposing the welding current on the current and controlling the welding current so that it becomes the base current when it transitions to an arc, it is possible to prevent spatter that occurs when a short circuit turns into an arc, and also to prevent the electrode wire and base metal from being separated during the arcing period. The optimal first arc pulse current for melting and the arc pulse current that is smaller than the first arc pulse current and gradually attenuates in order to stabilize the arc are set to be sufficiently smaller than the first pulse current. By superimposing it on the base current, a short circuit is forced, the arc voltage is detected, this detection signal is compared with the set value, and the current value during the arc period is controlled according to the difference. Therefore, the arc voltage is kept almost constant, and a stable arc can be obtained with almost no spatter in a wide range of welding conditions from low current to high current.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 4 to 7.

In Fig. 4, 3 is a transformer, 4 is a rectifier, 5 is a current limiting element that controls the output current, 6 is a drive circuit for 5, 7 is a welding part, 7a is a base material, 7b is an arc, 7
7d is a consumable electrode, 7d is a power supply chip, 7e is a feeding roller that feeds the consumable electrode, 8 is a consumable electrode feeding motor, 9 is an arc voltage detection circuit, 10 is a reference signal generation circuit 11 that detects short circuits and arcs. 12 is a short-circuit pulse current delay circuit; 13 is a short-circuit pulse current signal generation circuit; 14
15 is the first arc pulse current delay circuit, 15 is the first arc pulse current signal generation circuit, 16 is the arc voltage averaging circuit, and 17 is the signal of the reference signal generation circuit 18 and the signal obtained in 16. 19 is a base current signal generation circuit, 20 is a current wire feed control device, and 21 is a delay circuit for second arc pulse current.

Next, to explain the operation of the above embodiment, the transformer 3 transforms the normal 200V to 60 to 80V, the rectifier 4 rectifies it to DC, and when the voltage is output, current is applied to the electrode 7c through the current limiting element 5 and the power supply chip 7d. An arc 7d is generated between the electrode 7c and the base material 7a. At this time, the electrode 7c is fed at a constant speed by a feed roller 7e driven by a feed motor 8. In this case, when transitioning from an arc to a short circuit, there is a sudden change from several tens of volts to around zero volts as shown in FIG. By comparing the value detected in step 9 with the determination circuit 10, it can be determined that a short circuit has occurred. When determining a short circuit, the determination circuit 10 activates the short circuit pulse current signal generation circuit 13 through the delay circuit 12. At this time, the delay circuit 12 applies a signal to the short circuit pulse current signal generation circuit 13 after a preset delay time after the signal from the discrimination circuit 10 is applied. When the signal from the delay circuit 12 is applied, the short-circuit pulse current signal generation circuit 13 outputs a preset waveform signal to the drive circuit 6, and the current-limiting element 5
A short circuit pulse current is output from. Further, the signal from the short-circuit pulse signal circuit 13 to the drive circuit 6 stops instantaneously when the arc state signal from the discrimination circuit 10 is applied. As a result, it is possible to prevent spatter from occurring due to short-circuit pulse current flowing during an instantaneous short-circuit of approximately 0.5 ms or less, which does not occur just by momentarily touching the molten pool at the tip of the electrode. Since a pulsed current flows, it is possible to prevent spatter that occurs when an arc transitions to a short circuit.

Moreover, when the arc state is determined by the determination circuit 10,
After a signal from the arc pulse current signal generation circuit 10 is applied through the first arc pulse delay circuit 14, a signal is applied to the arc pulse current signal generation circuit 15 after a preset delay time. Similarly, the second arc pulse current is also applied to the delay circuit 2.
After the time set in 1, a signal is applied to the arc pulse current signal generation circuit 15. When the signals from the delay circuits 14 and 21 are applied, the arc pulse current signal generating circuit 15 outputs a preset waveform signal to the drive circuit 6, and the current limiting element 5 outputs an arc pulse current. The above-mentioned short circuit pulse current and arc pulse current are superimposed on the base current which is sufficiently smaller than the pulse current outputted by the signal from the base current signal generation circuit 19.

Further, the average voltage during the arcing period is detected by the detection circuit 16, and compared with the signal from the reference signal generation circuit 18 by the comparison circuit 17. Change the arc pulse current width in step 1. In this case, if the voltage V _a detected by the detection circuit 16 becomes higher than the set voltage V _s of the reference signal generation circuit 18 (V _s < V _a ), the pulse current width is made shorter than the set value. control. As a result, the amount of electrode melting during the arc period decreases and the arc voltage becomes lower and equal to the set value. As a result of the above, stable short-circuit transition welding can always be performed even if the distance between the power supply chip 7d and the base metal 7a changes.

FIG. 5 shows an example of current and voltage waveforms according to this embodiment. Point A is the moment of transition from arc to short circuit, and point B is the moment of transition from short circuit to arc. If there is a short circuit at point A, the discrimination circuit 10 detects it, and the delay circuit 12 outputs a signal from the short circuit pulse current signal generation circuit 13 with a delay of T _DS to output the signal to the current limiting element 5.
As a result, a short-circuit pulse current called _IPS flows. Since this short circuit pulse current is output until the signal from the discrimination circuit 10 is applied, the width t _PS of I _PS varies depending on the state of the short circuit. Figure 6a shows a case where the short-circuit time is relatively short and the signal from the discrimination circuit 10 is applied while the set value I _PS is being reached, and Figure b shows a case where the signal is applied after reaching the set value I _PS . . Further, when a short-circuit to arc state is detected at point B, the delay circuit 14 outputs a signal from the arc pulse current signal generation circuit 15 with a time delay of T _DA , and the current limiting element 5 outputs a signal from the first signal, which is I _PA . Arc pulse current flows.
As a result of the above, a low base current is passed to maintain the arc for a while from the moment the short circuit changes to an arc, so it is possible to prevent spatter from occurring when the short circuit changes to an arc.
On the other hand, during the arc period, the first arc pulse current I _PA is applied for a set time in order to generate a certain amount of molten metal at the electrode tip and at the same time melt the base metal, and then the first arc pulse current I A decaying arc pulse current is applied. At this time, while the first arc pulse I _PA is flowing, a certain amount of molten metal is generated at the electrode tip and a molten pool is generated in the base metal, but the molten metal is pushed up to the electrode tip by the arc force. Not easily short-circuited. Next, by superimposing an arc pulse current that is smaller than the first arc pulse current and attenuates sequentially on the base current, the arc force gradually weakens, so that the molten metal moves toward the base metal, and the arc pulse gradually attenuates. The current gives the arc rigidity, so the arc is stable without moving around irregularly. If the sequentially attenuating arc pulse current is not superimposed, that is, if only the base current is passed after the first arc pulse is superimposed, the arc voltage during the base current period becomes very unstable as shown in Figure 7a,
In the worst case, arc breakage will occur. However, if we superimpose a sequentially attenuating arc pulse current, Fig. 7b
As shown, the arc voltage is very stable, the voltage gradually decreases, and a short circuit occurs at point C. Since the short circuit is forcibly performed in this way, it is possible to perform short circuit transition welding in a high current range without generating spatter, which was impossible with conventional methods.

〔Effect of the invention〕

As described below, according to the method of the present invention, short circuits and arcs are detected, and this signal is used to superimpose optimal pulse currents on a base current that is sufficiently smaller than the pulse current, respectively, during short circuits and arcs. Since it is possible to short-circuit the welding current, it is possible to obtain a stable arc with almost no spatter in a wide range of welding conditions from low current to high current. Therefore, the transfer of the droplets occurs regularly, resulting in a good bead, and since spatter does not occur, there is no need for post-treatment after welding, and high-speed welding becomes possible, which significantly improves work efficiency. .

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional arc welding power source, Figure 2 is a circuit diagram of a conventional arc welding power source.
3 is an explanatory diagram of the operation and phenomena of a conventional arc welding power source, FIG. 4 is an example of the method according to the present invention, FIG. 5 is a waveform diagram according to the example, and FIGS. FIG. 7 is another waveform diagram according to an example. 5... Current limiting element, 6... Drive circuit, 9... Arc voltage detection circuit, 10... Discrimination circuit, 12, 1
4, 21...delay circuit, 13...short circuit pulse current signal generation circuit, 15...arc pulse current signal generation circuit, 16...arc voltage averaging circuit, 17...
... Comparison circuit, 19 ... Base current signal generation circuit,
20... Electrode wire feeding control circuit.

Claims (1)

[Claims] 1. In an arc welding method in which welding is performed by feeding a consumable electrode at a constant rate, a short circuit state and an arc state are detected, and during the arc period, a first arc pulse current and a first arc pulse An arc pulse current that is smaller than the current and gradually attenuates is superimposed on a base current that is sufficiently smaller than the first arc pulse current, and when a short circuit is detected, a predetermined period of time is elapsed until the short circuit is resolved after a preset time. An arc welding method characterized by superimposing a short circuit pulse current on the base current. 2 Detects the average value of the arc voltage during the arc period, compares this detection signal with a set value, and controls the current value during the arc period according to the difference to keep the arc voltage almost constant. The arc welding method according to claim 1, characterized in that: 3. Detect the average value of the arc voltage during the first arc pulse period, compare this detection signal with the set value, and control the current value during the arc period according to the difference to keep the arc voltage almost constant. The arc welding method according to claim 1, wherein the arc welding method is characterized in that: 4 Detecting the average value of the arc voltage during the period of the arc pulse current that gradually attenuates, comparing this detection signal with the set value, and controlling the current value during the arc period according to the difference, the arc voltage can be approximately reduced. The arc welding method according to claim 1, characterized in that the welding temperature is constant. 5. Claims 2 and 3, characterized in that the current value during the arc period is controlled by changing the peak value of the first arc pulse current.
The arc welding method described in Items 1 and 4. 6. Claims 2 and 3, characterized in that the current value during the arc period is controlled by changing the pulse width of the first arc pulse current.
The arc welding method described in Items 1 and 4. 7. Claim 2, characterized in that the current value during the arcing period is controlled by changing the peak value of the arc pulse current that gradually attenuates.
The arc welding method described in Items 1, 3 and 4. 8. Claim 2, characterized in that the current value during the arc period is controlled by changing the pulse width of the arc pulse current that gradually attenuates.
The arc welding method described in Items 1, 3 and 4. 9. Claims 2 and 3, characterized in that the current value during the arc period is controlled by changing the ratio (duty) between the pulse time and the rest time of the arc pulse current that gradually attenuates. The arc welding method described in Items 1 and 4.