JP4028075B2 - Short-circuit transfer type arc welding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a short-circuit transfer type arc welding method in which a consumable electrode is used for welding while repeating short-circuiting and arcing.
[0002]
[Prior art]
In order to perform stable welding by consumable electrode type arc welding, it is necessary to control so that the consumable electrode fed at a constant speed is melted at a constant speed comparable to the feeding speed of the consumable electrode. In particular, in the short-circuit transfer type arc welding method, it is difficult to control the amount of melting because the consumable electrode and the work piece are short-circuited or the phenomenon in which arcs are generated alternately is repeated. Conventionally, the control of the consumable electrode melting amount in such welding is performed by keeping the average voltage during welding constant.
[0003]
FIG. 6 shows an example of an apparatus for performing a conventional short-circuit transfer type arc welding method. In the figure, reference numeral 1 denotes an AC power source, and a commercial AC power source is used. Reference numeral 2 denotes a power conversion circuit that converts power from the AC power source 1 into a DC output having a substantially constant voltage characteristic corresponding to the output command signal Sw1. Reference numeral 3 denotes a DC reactor, which gives the output current of the power conversion circuit 2 a current change time constant suitable for short-circuit transfer arc welding. 4 is a welding torch, and a consumable electrode 8 fed toward the workpiece 7 is inserted by a feed roll 6 driven by an electric motor 5, and power from the power conversion circuit 2 is fed to this electrode. Reference numeral 9 denotes an electric motor control circuit that controls the rotation speed of the electric motor 5 to be constant. 10 is a voltage detector that detects the instantaneous value Vd of the welding voltage, 11 is a welding voltage smoothing circuit that smoothes the output of the voltage detector 10 to obtain the average value Vda of the welding voltage, and 12 is a welding voltage setting circuit. Set the voltage setting value Vs. A comparator 13 compares the set value Vs of the welding voltage setting circuit 12 with the output signal Vda of the welding voltage smoothing circuit 11 and outputs a difference signal ΔV = Vs−Vda. An amplifier 14 amplifies the output signal ΔV of the comparator 13 as necessary. Reference numeral 15 denotes an arc period detector. When the output signal Vd of the voltage detector 10 is higher than a predetermined value, it is determined as an arc period and a high level arc period signal Sad is output. Reference numeral 16 denotes an output voltage setting device for a short-circuit period, which outputs an output voltage setting signal Vss having a value lower than the output voltage during the arc period so that the output current of the power conversion circuit 2 during the short-circuit period does not become excessive. A signal switching circuit 17 switches the signal to the (a) side when the arc period signal Sad of the arc period detector 15 is high level, and switches the signal to the (b) side when the arc period signal Sad is low level. An analog switch for transmitting to the conversion circuit 2 is used.
[0004]
In FIG. 6, the voltage during welding is detected by the voltage detector 10, smoothed by the welding voltage smoothing circuit 11, and the detected voltage smoothing signal Vda is obtained. The comparator 13 compares the welding voltage setting signal Vs which is an output from the welding voltage setting circuit 12 and the detected voltage smoothing signal Vda, and outputs a difference signal ΔV = Vs−Vda. The output ΔV of the comparator 13 is then input to the amplifier 14 and amplified to a level corresponding to the output voltage of the short-circuit period output voltage setter 16 to become the output voltage command signal Vud during the arc period. Since a short circuit and an arc occur alternately during welding, the output of the voltage detector 10 is also supplied to the arc period detector 15, and when the instantaneous value Vd of the welding voltage is higher than a predetermined value, the arc period signal Sad is output. Output as a high level signal. The signal switching circuit 17 selects the output signal Vud of the amplifier 14 while the arc period signal Sad is at a high level, that is, during the arc period, the signal switching circuit 17 is set to the (a) side. When the arc period signal Sad is at a low level, that is, during the short circuit period, the signal switching circuit 17 is set to the (b) side and the output signal Vss of the short circuit period output voltage setting device 16 is selected. The output command signal Sw1 selected in this way is sent to the power conversion circuit 2.
[0005]
FIG. 7 shows a timing chart of the operation of the apparatus shown in FIG. 7, (a) shows an instantaneous value Vd of the welding voltage, which is an output signal of the voltage detector 10, and (b) shows a detected voltage smoothing signal Vda obtained by smoothing the instantaneous value Vd of the welding voltage by the welding voltage smoothing circuit 11. (C) is the output ΔV of the comparator 13, (d) is the output signal Vud of the amplifier 14, (e) is the output signal Sad of the arc period detector 15, and (f) is the signal switching circuit 17. The output command signal Sw1 selected by is shown with the passage of time.
6 and 7, during the welding, the consumable electrode 8 repeats the arc generation and the short circuit with respect to the work piece 7 several tens of times per second. When a short circuit occurs, the welding current increases rapidly, and when the increased current flows, the short circuit part is cut by an electromagnetic pinch force acting on the short circuit part to promote the regeneration of the arc. At this time, if the current becomes excessive, spatter is generated during arc regeneration. Therefore, during the short circuit period, the signal switching circuit 17 is switched to the (b) side, and the output voltage of the power conversion circuit 2 is set to the output voltage for the short circuit period. It is reduced to a low value determined by the setting signal Vss of the device 16. Usually, the lower limit and the upper limit of the welding current at the time of this short circuit are determined by obtaining the electromagnetic pinch force necessary for eliminating the short circuit and the allowable spatter amount at the time of arc regeneration.
[0006]
[Problems to be solved by the invention]
In the above conventional method, since the control is to make the average voltage constant, the welding voltage must be sufficiently smoothed and used as output control information of the welding power source. For this reason, the response speed of the control is slow and sufficient control cannot be performed.
[0007]
This point will be described in detail with reference to FIG. FIG. 8 shows a state in which the level difference between the welding torch 4 and the protruding length of the consumable electrode 8 is suddenly shortened by overcoming the step during welding. FIG. 4A shows the welding voltage instantaneous value Vd and a detected voltage smoothing signal Vda obtained by smoothing the welding voltage, FIG. 5B shows the welding current instantaneous value Ia and the average arc current Ida, and FIG. The average distance between the tip of the electrode 8 and the workpiece 7, that is, the average arc length La and the state of the workpiece 7 are shown for each time.
[0008]
Between the start of welding and time t1, the average arc length is L1. When the step of the work piece 7 is passed at the time t1, the average arc length is suddenly reduced to L2, and the distance between the tip of the consumable electrode 8 and the work piece 7 is close, so that a short circuit is likely to occur. Then, although the output signal Vd of the voltage detector 10 immediately decreases, the output signal Vda of the welding voltage smoothing circuit 11 that is actually used for control as shown in FIG. However, the output signal Vud of the amplifier 14 does not change much. Further, as shown in (b), the welding current Ia increases as the number of short-circuits increases. However, since the arc time itself is short, the consumable electrode 8 cannot be sufficiently melted. As a result, it takes time t2 to return to the original arc length after overcoming the step as shown in FIG.
[0009]
FIG. 9 shows the appearance of the bead and the amount of spatter when passing through the step as shown in FIG. As shown in the figure, since the number of short-circuits suddenly increases at the time t1, the generated spatter also increases rapidly, and the heat input of the welded portion decreases, so that the bead appearance is greatly disturbed.
[0010]
[Means for Solving the Problems]
In order to solve the problems of the conventional method, a first invention of the present invention is a short-circuit transfer type arc welding method in which a consumable electrode is used and welding is performed while repeating short-circuiting and arc generation. Detects the length of the generation period, reduces the output voltage of the welding power source in the next arc generation period in proportion to the detected arc generation period, and inversely proportional to the length of one arc generation period A short-circuit transfer type arc welding method for increasing the welding current during the next arc generation period is proposed.
[0011]
Furthermore, the second invention of the present invention is a short-circuit transfer type arc welding method that uses a consumable electrode and performs welding while repeating short-circuiting and arc generation. Set to a constant voltage lower than the output voltage of the welding power source, detect the length of one arc generation period, and output the welding power source in the next arc generation period in proportion to the length of the detected arc generation period The present invention proposes a short-circuit transfer type arc welding method that reduces the voltage and increases the welding current in the next arc generation period in inverse proportion to the length of one arc generation period.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a connection diagram showing an example of an apparatus for carrying out the short-circuit transfer type arc welding method of the present invention. In the figure, 18 is an output voltage corrector, which receives an arc period signal Sad output from the arc period detector 15 and outputs an output voltage correction signal Vms for the next arc period corresponding to the length of the arc period. . Reference numeral 19 denotes a subtracter that subtracts the output Vms of the output voltage corrector 18 from the output ΔV of the comparator 13 and amplifies the result to a level corresponding to the level of the signal of the output voltage setter 16 for the short-circuit period. In the figure, the other parts having the same functions as those of the conventional apparatus shown in FIG.
[0013]
In the figure, a voltage during welding is detected by a voltage detector 10, and a detected voltage smoothing signal Vda which is smoothed by a welding voltage smoothing circuit 11 and becomes an average voltage is obtained. The comparator 13 compares the welding voltage setting signal Vs, which is an output from the welding voltage setting circuit 12, and the detected voltage smoothing signal Vda, and outputs a difference signal ΔV. Since a short circuit and an arc occur alternately during welding, the determination is made by the arc period detector 15 and a high level arc period signal Sad is output during the arc period. The arc period signal Sad is counted by the output voltage corrector 18 and outputs an output voltage correction signal Vms having a magnitude corresponding to the duration of the arc period signal Sad. The output of the amplifier 14 obtained by amplifying the output ΔV of the comparator 13 and the output Vms of the output voltage corrector 18 are input to the subtracter 19 and Vuh = A · ΔV−Vms.
It becomes. (However, A is a constant determined by the amplification factor of the amplifier 14)
[0014]
During the arc period, the arc period signal Sad of the arc period detector 15 becomes high level, the signal switching circuit 17 is set to the (a) side, and the output signal Vuh of the subtractor 19 is selected. On the contrary, during the short circuit period, the arc period signal Sad of the arc period detector 15 becomes low level, the signal switching circuit 17 is switched to the (b) side, and the output voltage setting signal Vss of the short circuit period output voltage setting device 16 is changed. select. The output command signal Sw1 selected in this way is supplied to the power conversion circuit 2.
[0015]
FIG. 2 shows a specific example of the output voltage corrector 18. In FIG. 2, MM1 and MM2 are mono-multivibrators, which are triggered when the input signal falls and output a pulse having a short duration. IG1 is an integration circuit that integrates the output signal Sad of the arc period detector 15 and outputs it as a signal Sig, and is reset by the output signal of the mono multivibrator MM2. Reference numeral SH1 denotes a sample and hold circuit, which receives the output signal Sig of the integration circuit IG1 that integrates the input signal Sad as an input, stores the input signal at the time of rising of the output signal of the monomultivibrator MM1, and then stores the monomultivibrator MM1. Is held until the rising edge of the output signal is output as the output voltage correction signal Vms.
[0016]
FIG. 3 is a timing chart showing the operation when the output voltage corrector of FIG. 2 is used in the apparatus of FIG. In the figure, (a) shows the output signal of the voltage detector 10, that is, the instantaneous value Vd of the welding voltage, and (b) shows the output signal Vda of the welding voltage smoothing circuit 11 obtained by smoothing the instantaneous value Vd of the welding voltage. Show. (C) shows the output of the amplifier 14 that amplifies the output signal ΔV of the comparator 13 that compares the detected voltage smoothing signal Vda with the welding voltage setting value Vs that is the output signal of the welding voltage setting circuit 12. (D) shows the output signal Sad of the arc period detector 15, (e) shows the output signal of the mono multivibrator MM1 of the output voltage corrector 18, and (f) shows the output of the mono multivibrator MM2 of the output voltage corrector 18. (G) is an output signal of the integration circuit IG1 of the output voltage corrector 18, and (h) is an output signal of the sample hold circuit SH1 of the output voltage corrector 18, that is, the output voltage correction signal Vms. (I) is the output signal Vuh of the subtractor 19 that subtracts the output voltage correction signal Vms from the output signal A · ΔV of the amplifier 14, and (j) is the short circuit period and the arc period depending on the output signal Sad of the arc period detector 15. An output command signal Sw1 of the signal switching circuit 17 for switching the output voltage setting signal to Vuh or the output voltage setting signal Vss during the short circuit period is shown.
[0017]
1 to 3, a welding voltage Vd is detected by a voltage detector 10, an average value Vda is derived by a welding voltage smoothing circuit 11, and compared with a set value Vs of a welding voltage setting circuit 12 by a comparator 13. Thus, the difference signal ΔV is calculated. On the other hand, the output of the voltage detector 10 is also supplied to the arc period detector 15, and when the signal Vd is higher than a certain value, it is determined as an arc period and a high level arc period signal Sad is output. The high level arc period signal Sad is integrated by the integration circuit IG1 of the output voltage corrector 18 to become an integration signal Sig, which is output to the sample hold circuit SH1. The output Sad of the arc period detector 15 is also supplied to the mono multivibrator MM1 of the output voltage corrector 18, and the mono multivibrator MM1 has a short pulse immediately after the falling edge of the input signal Sad, that is, immediately after the end of the arc period. Output a signal. The pulse output of the mono multivibrator MM1 is supplied to the mono multivibrator MM2 and the sample hold circuit SH1, and the sample hold circuit SH1 stores the input signal Sig at the rising edge of the output signal of the mono multivibrator MM1 and corrects the output voltage. Output as signal Vms. The mono multivibrator MM2 is triggered by the rise of the output signal of the mono multivibrator MM1, and outputs a short-time pulse signal. The integration circuit IG1 is reset by the fall of the output pulse of the mono multivibrator MM2, and the output signal is Return to zero.
[0018]
On the other hand, the output of the arc period detector 15 is also supplied to the signal switching circuit 17 so that when the arc period signal Sad is at a high level, the signal switching circuit 17 is set to the (a) side, and the arc period signal Sad is at a low level. At this time, the signal switching circuit 17 is switched to the (b) side. As a result, the arc period signal Sad is integrated by the integrating circuit IG1 of the output voltage corrector 18 from the beginning of the arc generation period when the arc period signal Sad becomes high level, and the arc period signal Sad becomes low level at the end of the arc period. When inverted, the output signal of the integration circuit IG1 at that moment is stored in the sample-and-hold circuit SH1, and then the integration circuit IG1 is reset by the output of the mono multivibrator MM2 at the fall of the output pulse of the mono multivibrator MM1, and the output signal Sig returns to zero and waits until the next arc period begins and the arc period signal Sad goes high. As a result, the length of one arc period is calculated by the integration circuit IG1 of the output voltage corrector 18, and this is stored in the sample hold circuit SH1 with the end of the arc period, and the end of the next arc period is completed. The output voltage correction signal Vms is output to the subtracter 19 after being held until the time. The subtracter 19 subtracts the output signal Vms of the sample hold circuit SH1 from the output signal of the amplifier 14 to obtain Vuh = A · ΔV−Vms, and outputs it to the signal switching circuit 17 as an output command signal in the arc period.
[0019]
Thus, when the arc period is long, the output voltage correction signal Vms becomes large, the output signal Vuh of the subtractor 19 in the next arc period becomes low, and the output voltage of the power conversion circuit 2 becomes low. On the contrary, when the arc period is short, the output voltage correction signal Vms is small, the output signal Vuh of the subtracter 19 in the next arc period is high, and the output voltage of the power conversion circuit 2 is high.
[0020]
FIG. 4 is a view schematically showing a state when the arc length is suddenly shortened by overcoming a step during welding when the welding method of the present invention is carried out using the apparatus of FIG. FIG. 5A shows the instantaneous value Vd of the welding voltage and the detected voltage smoothing signal Vda. (B) shows the instantaneous value Ia and average arc current Ida of the welding current. (C) shows the distance between the consumable electrode 8 and the workpiece 7, that is, the change in the average arc length La and the state of the workpiece 7. Between the start of welding and time t1, the average arc length is L1. When the level difference of the work piece 7 is passed at time t1, the average arc length is suddenly reduced to L2, and the distance between the tip of the consumable electrode 8 and the work piece 7 is close, so that a short circuit is likely to occur. Then, the instantaneous value Vd of the welding voltage decreases as shown in FIG. On the other hand, since the actual detection voltage smoothing signal Vda is a sufficiently smooth value, the change is slow and does not change much. However, since the number of short circuits increases and the arc time is shortened, the output voltage correction signal Vms is small in the negative direction, the output signal Vuh of the subtractor 19 in the next arc period becomes a large value, and the output voltage during the arc period increases. . As a result, the arc current increases rapidly, and a sufficient melting amount of the consumable electrode is obtained. As a result, the consumable electrode 8 is rapidly melted as shown in (c), and the time required to return to the original arc length after overcoming the step is significantly reduced as compared with the prior art.
[0021]
FIG. 5 shows the appearance of the weld bead and the amount of spatter generated when it passes through the step of the workpiece. As shown in the figure, the number of short-circuits suddenly increases at time t1, resulting in an increase in spatter. However, the welding current rapidly increases in inverse proportion to the decrease in the arc period, resulting in a rapid increase in the melting rate of the consumable electrode. Since the arc length immediately recovers, the spatter generation period and the period during which the bead appearance is disturbed are shorter than in the conventional method.
[0022]
【The invention's effect】
Since the short-circuit transfer type arc welding method of the present invention is as described above, even when the distance between the consumable electrode and the workpiece is suddenly changed, the melting amount of the consumable electrode is changed immediately, and an appropriate arc is obtained. It is possible to return quickly to the state.
[Brief description of the drawings]
FIG. 1 is a connection diagram showing an example of an apparatus for performing a short-circuit transfer type arc welding method of the present invention.
FIG. 2 is a connection diagram showing an embodiment of an output voltage corrector 18 used in the apparatus of FIG.
3 is a timing chart for explaining the operation when the output voltage corrector of FIG. 2 is used in the apparatus of FIG.
4 is a schematic diagram showing the welding voltage, welding current, and the positional relationship between the consumable electrode and the work piece when the short-circuit transfer type arc welding method of the present invention is carried out with the apparatus of FIG. 1 over time. is there.
FIG. 5 is a diagram showing the appearance of a weld bead and the amount of spatter when passing through a step of a workpiece when the short-circuit transfer type arc welding method of the present invention is performed.
FIG. 6 is a connection diagram showing an example of an apparatus for performing a conventional short-circuit transfer type arc welding method.
FIG. 7 is a diagram for explaining the operation of the conventional apparatus of FIG. 6;
FIG. 8 is a schematic view showing the welding voltage, welding current, and the positional relationship between the consumable electrode and the work piece when the conventional short-circuit transfer type arc welding method is performed by the apparatus of FIG. 6 with the passage of time. .
9 is a diagram showing the appearance of the weld bead and the amount of spatter when passing through the step of the workpiece when the conventional short-circuit transfer type arc welding method is performed by the apparatus of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 AC power supply 2 Power conversion circuit 3 DC reactor 4 Welding torch 5 Electric motor 6 Feeding roll 7 Work piece 8 Consumable electrode 9 Motor control circuit 10 Voltage detector 11 which detects instantaneous value Vd of welding voltage 11 Welding voltage smoothing circuit 12 Welding voltage setting circuit 13 Comparator 14 Amplifier 15 Arc period detector 16 Short-circuit period output voltage setting unit 17 Signal switching circuit 18 Output voltage corrector 19 Subtractor MM1 Mono multivibrator MM2 Mono multivibrator IG1 Integration circuit SH1 Sample hold circuit Vd Instantaneous value of welding voltage Vs Welding voltage setting value ΔV Difference signal between welding voltage setting value Vs and detection voltage smoothing signal Vda Sad Arc period signal Vss Output voltage setting signal Vda during short circuit period Detection voltage smoothing signal Vms Output voltage correction signal Vud Output signal Vuh of amplifier 14 Output signal Sw1 of subtractor 19 Output command signal Si g Output signal of integration circuit IG1

Claims (2)

In a short-circuit transfer type arc welding method that uses a consumable electrode and performs welding while repeating short-circuiting and arcing, the length of a single arcing period is detected and proportional to the length of the detected arcing period. A short-circuit transfer arc welding method that reduces the output voltage of the welding power source during the next arc generation period and increases the welding current during the next arc generation period in inverse proportion to the length of one arc generation period. In a short-circuit transfer type arc welding method that uses a consumable electrode and performs welding while repeating short-circuiting and arc generation, the output voltage of the welding power source during the short-circuit occurrence period is a constant value lower than the output voltage of the welding power source during the arc-generation period In addition, the length of one arc generation period is detected, and the output voltage of the welding power source in the next arc generation period is reduced in proportion to the length of the detected arc generation period. A short-circuit transfer arc welding method in which the welding current is increased in the next arc generation period in inverse proportion to the length of the period.

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