JPS62259674A - Pulse arc welding method - Google Patents

Abstract

PURPOSE:To stabilize the welding by changing pulse frequency according to a change of the arc voltage and adjusting the pulse width or a peak current based on comparison between a detected welding current and a reference current set value. CONSTITUTION:An arc voltage detector 13 and a current detector 18 are provided in an output circuit of a welding machine and a comparator 15 and a pulse width setting circuit 19 are connected with the detector 13 and the detector 18 respectively. If the distance between a tip 7 and a work 9 is varied, the arc voltage Vf of the detector 13 is varied and a differential signal ev of the comparator 15 is changed and the pulse frequency is changed. On this occasion, the pulse width is reduced or increased by a current change of the detector 18 and after all, an excessive variation of incresase and decrease of the current frequency with respect to a change of the distance between the tip and the work is prevented. Consequently, the arc length is maintained constant with respect to a change of the projecting length of a wire and the welding can be stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pulsed arc welding method using a welding wire fed at a constant speed as a consumable electrode.

[Conventional technology] Pulsed current (pulsating current) is fed to a welding wire at a constant speed.
In pulsed arc welding, in which welding is performed by flowing a wire, a technology to adjust the wire protrusion length (hereinafter referred to as extension) is known as a means of suppressing arc length fluctuations that occur mainly due to fluctuations in the distance between the tip and the base metal. It is being As for the specific method to adjust the extension, ■
The first method of increasing or decreasing the pulse frequency f in accordance with the extension, ①Similarly, the pulse width T or the peak current r
A second method of increasing or decreasing p is known. Each of these elements in the pulse waveform is shown in FIG. In addition, in Figure 2,
TB is the low current base period, and ■8 is the base period T.
The current value at B is shown.

The first method is to adjust the extension by changing the melting speed of the wire by increasing the frequency f when the arc length becomes short and by decreasing the frequency f when the arc length becomes long. This keeps the arc length constant.

On the other hand, the second method is to increase the pulse width TP or peak current IP when the arc length becomes short, and by increasing the pulse width TP or peak current IP when the arc length becomes long. By reducing the arc length, the extension is adjusted using the same principle as in the first method to keep the arc length constant.

[Problems to be Solved by the Invention] In the conventional method described above, when the distance between the tip and the base metal changes, the melting speed of the wire is increased or decreased by performing the control method described above, and the extension is made to the desired length. It brings us back to normality. In other words, when the distance between the tip and the base metal is long, the extension is controlled to be lengthened, and when the distance is short, the extension is controlled to be shortened, so the arc length is maintained as constant as possible, resulting in stable welding. is being carried out.

However, none of the above-mentioned conventional techniques can be said to be reliable control methods, and each has the following problems.

That is, in the first method, when the arc length is long and the extension is short, the arc length is controlled by lowering the frequency, but as a result, the extension returns to an appropriate length, and when it further exceeds a predetermined value. If it becomes long,
If the frequency remains small, the base period T[l of the low τ flow becomes longer, which causes the arc to lose its rigidity and become unstable, causing arc breakage. Also, as a result of controlling the arc length in the opposite direction to the above,
If the extension becomes shorter than the appropriate length, and the frequency f remains large, there will be insufficient energy per period given to the wire, so m? 'F4 transition becomes difficult, and large-diameter droplets remain at the tip of the wire, causing spatter.

On the other hand, in the second method, when the extension is short, the pulse width or peak current is reduced to suppress the electrode and control the arc length. If the pulse width T or the peak current rp remains small when the pulse width becomes longer than this, the energy of the pulse becomes insufficient, resulting in several pulses per droplet eruption. Also, if the arc length control is performed in the opposite direction to the above, and the extension becomes shorter than the appropriate length, the pulse width TP or the peak current r
If p remains large, the energy of the pulse becomes excessive and several droplets are transferred in one pulse. In either case, there are eight lines of droplets that are not synchronized with the pulse frequency, resulting in unstable welding.

In this way, in both the first and second methods, stable welding can only be achieved within a very limited, minute range, and is unstable in other areas. It was a perfect weld. Therefore, in order to perform stable welding by applying method 1.2, a technology is required to control the extension at high speed so that it is always within an appropriate range.
To date, such technology has not been realized.

The present invention has been made to solve the technical problems of the prior art as described above, and its purpose is to maintain a constant arc length in response to wide-ranging variations in extension. Its purpose is to provide a technology for stable welding.

[Means for Solving the Problems] The present invention that achieves the above object is based on a change in arc voltage detected when performing pulse arc welding using a welding wire fed at a constant speed as a consumable electrode. The main point is that the pulse frequency is changed in accordance with the current, and the pulse width or peak current is adjusted in accordance with the wire protrusion length determined by comparing the detected welding current with a predetermined reference current. This is a pulsed arc welding method.

[Operation] The inventors of the present invention have diligently researched a technique for performing stable welding while compensating for the mutual drawbacks of the above-mentioned conventional techniques. the result,'? 5. We were confident that by adopting the above-mentioned configuration, all the problems of the prior art could be solved and stable pulsed arc welding could be performed, and we have now completed the present invention.

The present invention is configured as described above, but the key point is to change the pulse frequency in response to changes in the detected arc voltage, and to
The current extension is determined by comparing the detected welding current with a predetermined reference current, and when the extension is long, the pulse width or peak current is decreased, and when the extension is short, the pulse width or peak current is increased. . The amount of adjustment of the pulse width or peak current is within the range shown by hatching in FIG. 3, that is, within the range of pulse energy that allows transfer of one droplet per pulse. In this way, the contribution of pulse width or peak current adjustment to the wire melting rate is taken into account, so that fluctuations in pulse frequency can be kept to a minimum.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

[Example] FIG. 1 is a schematic explanatory diagram showing the electrical configuration of an apparatus configured to implement the method of the present invention.

The electricity taken in from the commercial AC power supply 1 is passed through the rectifier circuit 2.
After being rectified into direct current by, the output is adjusted by an output adjustment switching circuit 3 realized by a power transistor or the like, further converted to a voltage suitable for welding by a transformer 4, and then rectified by a rectifier circuit 5. It is applied to the chip 7 through the smoothing reactor 6. When a voltage is applied to the tip 7, an arc is generated between the welding wire 8 that is in contact with the tip 7 and the workpiece (base metal) 9, and the wire 8 and workpiece 9 are melted. Welding is performed. At this time, a predetermined command value is input from the feed speed setting device 10 to the feed motor drive circuit 11, and the feed motor drive circuit 11 is activated, thereby causing the wire feed motor 12 to rotate. Welding wire 8 is fed at a constant speed.

At this time, the output value Vf of the arc voltage detected by the arc voltage detector 13 and the output V ref set in advance by the arc voltage setting device 14 according to the wire feeding speed
are compared by the comparator 15.

Then, the pulse frequency f is uniformly adjusted in the pulse frequency setter 16 using the difference signal ev between the outputs Vf and Vref compared by the comparator 15 and the signal e from the feed rate setter 10. Furthermore, the signal from the pulse frequency setter 16 is manually input to the switching control circuit 17, which controls the output adjustment switching circuit 3, and changes the pulse frequency f in response to the detected change in the arc voltage. Ru.

On the other hand, in the pulse width setting circuit 19, the current detector 18
The extension of the wire 8 is determined by the welding current detected by the welding current and the command value from the feed speed setting device 10, and the pulse width T is adjusted accordingly, and the signal is manually input to the switching control circuit 17. Ru.

A specific example of the pulse width setting circuit 19 is shown in FIG.
The operation of the pulse width setting circuit 19 will be described in detail with reference to the drawings.

Based on the command value from the feed speed setting value 10, a reference current I ref corresponding to the optimum extension at that feed speed is set by the reference current setter 20.

This set reference current I ref and the actual welding current If detected by the current detector 18 are compared by a comparator 21 to determine the amount of displacement from the reference value of the extension. Then, based on the difference signal eI corresponding to the amount of displacement, the pulse width T is determined according to a predetermined function by the pulse width setter 22, and the signal T, r
cf is manually input to the switching control circuit 17. Here, the reference 'rL flow 1 re set by the reference current setting device 20
Let f be a function approximately proportional to the wire feeding speed. Further, the signal T pref from the pulse width setter 22 is inversely proportional to the difference signal -3-el, and has a pulse width T to obtain a pulse energy that achieves droplet transfer as shown in FIG. , the minimum time T Pm1n and the maximum time T
The range shall not exceed P+nax.

In the configurations shown in FIGS. 1 and 4, a case is now assumed in which the distance between the chips (the distance between the chips 7 and the object to be welded 9) increases. In this case, the arc voltage V
f increases, the difference signal ev becomes a negative value, and the pulse frequency is reduced, thereby reducing the melting rate of the wire 8 and lengthening the extension, making the arc length constant. It is made to be preserved. At this time, by reducing the pulse frequency, the Ti flow that flows due to the arc load per unit time is reduced. Also, the longer the extension, the greater the Joule heat generation when current flows through the extension, and at the same wire speed, the wire will melt with less current.
The current decreases.

Therefore, since the welding current detected by the current detector 18 becomes smaller, the difference signal e takes on a positive value, and the pulse width TP eventually increases in response to the longer extension.
is adjusted so that it becomes smaller. Since the melting speed is reduced by reducing the pulse width TP in this manner, the frequency f does not decrease significantly.

Next, let us assume that the distance between the chip and the base metal becomes smaller. In this case, the situation is the opposite of the above case, and the pulse width T increases and the melting rate increases, so the frequency f does not increase significantly.

In either case, the pulse width TP is adjusted within the range of one droplet elongation per pulse.

The inventors carried out implementation to confirm the usefulness of the present invention. The results are shown in FIGS. 6 and 7. Figure 6 is a graph showing the relationship between extension and pulse frequency f when the wire feeding speed is constant, and Figure 7 is a graph showing the relationship between extension and pulse width Tp when the wire feeding speed is constant. This is a graph showing. Also, F in Figure 6
1 and T in FIG. 7 are the results when the arc length is controlled by the frequency f while keeping the pulse width TP constant, and F2 in FIG. 6 and F2 in FIG. These are the results when the arc length is controlled by the pulse width TP, which is kept constant. F3 in FIG. 6 and F3 in FIG. 7 show the results of arc control according to the method of the present invention.

In FIG. 6, f max and fmin respectively indicate the maximum frequency and minimum frequency adjusted according to the method of the present invention, and in FIG. 7, T max and T min indicate the maximum pulse width and minimum frequency set by the method of the present invention. The pulse width is shown respectively.

As is clear from the results shown in FIGS. 6 and 7, the pulse width T increases as the power output of the extension increases.

By setting the frequency f to a function that decreases between Tmax and Tm1n at which droplet transfer is possible, the frequency f is set to fmax.
, fmin can be adjusted within a small range. This has made it possible to control the arc length to ensure stable droplet transfer in response to wide variations in extension due to variations in the distance between the tip and the base metal.

In the above-described embodiment, a configuration was adopted in which the pulse width T was adjusted in accordance with the extension, but in another embodiment of the present invention, a configuration in which the peak current IP was adjusted instead of adjusting the pulse width TP was adopted. It's okay. In this case, a peak current setting circuit may be used in place of the pulse width setting circuit 19 shown in FIG. Therefore, in this case, a peak current setter is used in place of the pulse width setter 22 shown in FIG. Even when such a configuration is adopted, the maximum peak current I pmaX and the minimum peak current I Pm1n at which one pulse transfer can be performed
By setting the arc current command value 1 pref from the arc current setting device to a function inversely proportional to the difference signal e within the range of , the same effect as in the above embodiment can be achieved.

[Effects of the Invention] As described above, according to the present invention, by employing the above-described configuration, stable welding can be performed while keeping the arc length constant in response to wide variations in the extension. became.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing the electrical configuration of a device configured to carry out the method of the present invention, FIG. 2 is a graph showing each element in a pulse waveform, and FIG. 3 is a pulse adjusted according to the present invention. A graph showing the range of the width T or peak current 2, Fig. 4 is a block diagram showing the details of the pulse width setting circuit 19, and Fig. 5 shows the minimum time 7 p in the pulse width TP.
A graph showing the range of min and maximum time T pmaX,
Figure 6 is a graph showing the relationship between extension and pulse frequency f when the wire feeding speed is constant, and Figure 7 is a graph showing the relationship between extension and pulse width TP when the wire feeding speed is constant. This is a graph showing. 7... Chip 8... Wire 9... Work to be welded (base metal) 13... Arc voltage detector 16... Pulse frequency setting device

Claims (1)

[Claims] When performing pulsed arc welding using a welding wire fed at a constant speed as a consumable electrode, the pulse frequency is changed in response to changes in the detected arc voltage, and the detected welding current is set to a predetermined standard. A pulsed arc welding method characterized by adjusting the pulse width or peak current in accordance with the wire protrusion length determined by comparing the current with the wire protrusion length.