JP2000042737A - Short circuiting transfer type arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a consumable electrode type arc welding obtaining the high efficiency while repeating the short circuit and the arc development by using an electric source for welding having almost constant characteristic and making the higher output current at the time of developing the short circuit than the output current at the time of developing the arc. SOLUTION: It is desirable that the output current for welding during the interval from the starting time point of the short circuit to a fixed time after completing the short circuit is made higher than the output current in the case of being the other time, or the output current in the electric source for welding during the interval from a fixed time after starting the short circuit to a fixed time after completing the short circuit is made higher than the output current in the case of being the other time. Further, it is desirable that the repeating frequency for developing the arc and developing the short circuit is detached, and according to the difference between the detected repeating frequency and the reference frequency, the output current is decided in the term which is made high output current of the electric source for welding or the repeating frequency for developing the arc and developing the short circuit is detected, and according to the difference between the detected repeating frequency and the reference frequency, the fixed term is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a consumable electrode type arc welding in which a short circuit and an arc are repeatedly performed, that is, a so-called short circuit transfer type arc welding method.

[0002]

2. Description of the Related Art FIG. 14 shows the principle of the prior art. In FIG. 14, reference numeral 1 denotes a welding power source, Vo denotes a DC voltage source, R1 denotes a resistor, and L1 denotes an inductance. 11 is a torch-side cable, 12 is a workpiece-side cable, 14 is an arc, 15 is a workpiece, 16 is a tip, 1
7 is a wire and 18 is a feed roller. The wire 17 is fed through the chip 16 and protrudes from the chip by a length Lex from the chip 16. This Lex portion is called a wire protrusion length. An arc 14 is generated from the tip of the protrusion.

FIG. 15 is a diagram for explaining the operation of the apparatus shown in FIG. In FIG. 15, (a) shows the output voltage of the welding power source 1, (b) shows the welding voltage, and (c) shows the change in the welding current over time. FIG.
Is heated by the arc 14 while being heated by Joule heat generated by the current flowing through the protrusion. By the heating, the tip of the protruding portion is melted. If the wire feeding speed is set to be slightly higher than these melting amounts, the tip of the wire 17 gradually approaches the work 15 and finally short-circuits at time t1. When a short circuit occurs, the arc is extinguished. On the other hand, the current flowing through the wire 17 rapidly increases because the welding power supply 1 has a substantially constant voltage characteristic. After the time t1, the wire 17 is melted only by Joule heat. In addition to gravity and surface tension, an electromagnetic pinch force or the like due to a large short-circuit current acts to move the molten portion to the workpiece 15 side. At time t2, the transition of the fusion zone is completed, and a gap is formed again between the tip of the wire 17 and the workpiece 15. Immediately before the time t2, the inductance L1 stores electromagnetic energy due to a large short-circuit current, and a voltage is generated in such a direction as to prevent a decrease in the current due to the electromagnetic energy, and the voltage is generated between the tip of the wire 17 and the work 15 to be welded. The next arc is generated immediately with the generation of the gap. When an arc is generated, the inductance L1 emits the stored electromagnetic energy as a current. During this discharge, the current decreases over time. At this time, the protruding portion Lex of the wire 17 is heated by both the Joule heat corresponding to the current and the arc 14. Since the wire 17 is melted by this heating, the distance between the tip of the electrode and the workpiece 15 is set at time t2.
Immediately after, the amount of fusion decreases with the decrease in current, the amount of feed exceeds the amount of fusion, the tip of the wire 17 and the workpiece 15 short-circuit again at time t3, and from time t3. The same operation as the operation after time t1 is repeated.

[0004]

As described above, the short-circuit transfer type arc welding method has the following disadvantages.
About 9A or less at 9Φ, about 250A or less at 1.2Φ,
(Approx. 300A at 1.6Φ) Suitable for all position welding. (2) Shallow penetration and suitable for thin plates. (3) Less spatter and beautiful bead appearance. There are advantages such as. However, if this welding method is expanded to a larger current range and applied to high-speed welding, good short-circuit transfer arc welding cannot be achieved. For example, if the output voltage of the DC voltage source Vo is simply increased in order to increase the current, welding without a short-circuit period occurs. In addition, even if the welding speed is increased by increasing the wire feeding speed, the wire 17 is not used. It protrudes from the workpiece and does not arc.

[0005]

The problem of the conventional welding method described above is that a constant voltage characteristic is used for a welding power source, and the same output voltage is used for both a short circuit and an arc. Therefore, in the present invention, a power supply having a substantially constant current characteristic is used as a power supply for welding, the output current at the time of short-circuit is made larger than the output current at the time of arc, and the pulse-like output current at the time of short-circuit is further increased. It is intended to solve the problem and enable higher efficiency.

According to a first aspect of the present invention, there is provided a short-circuit transition type in which a welding power supply having substantially constant current characteristics is used, and the output current of the welding power supply is set to be higher when a short circuit occurs than when an arc is generated. It proposes an arc welding method.

In a second aspect of the present invention, a welding power supply having substantially constant current characteristics is used, and the output current of the welding power supply is changed from another time from the start of short-circuit to a certain time after the end of short-circuit. It proposes a short-circuit transfer type arc welding method that has a higher output current than at time.

In a third aspect of the present invention, a welding power supply having a substantially constant current characteristic is used, and an output current of the welding power supply is changed from a certain time after the start of the short circuit to a certain time after the end of the short circuit. Proposes a short-circuit transfer arc welding method in which the output current is higher than at other times.

In a fourth aspect of the present invention based on the first to third aspects, a repetition frequency of arc generation and short-circuit generation is detected, and the repetition frequency is detected according to a difference between the detected repetition frequency and a reference frequency. The present invention proposes a short-circuit transfer type arc welding method for determining an output current during a period in which an output current of a welding power source is increased.

In a fifth aspect of the present invention based on the second or third aspect, a repetition frequency of arc generation and short-circuit generation is detected, and the repetition frequency is detected according to a difference between the detected repetition frequency and a reference frequency. The present invention proposes a short-circuit transfer type arc welding method in which a fixed time is determined.

[0011]

FIG. 1 is a diagram showing the principle of the present invention. In the figure, reference numeral 10 denotes a welding power source, and DSH denotes a short-circuit detector, which determines that a short-circuit has occurred when a welding voltage has become a predetermined value or less, and outputs a short-circuit detection signal Sh. In the welding power supply 10, S1 is a changeover switch operated by the short-circuit detection signal Sh of the short-circuit detector DSH, IP is a constant current source that outputs a high current, and IB is a constant current source that outputs a low current. In other respects, the same elements as those of the apparatus of the conventional welding method shown in FIG.
Here, when the short-circuit detector DSH detects a short-circuit, the changeover switch S1 switches from (2) to (1),
If the changeover switch S1 switches to the (2) side when the short-circuit detector DSH detects a non-short-circuit, the operation of FIG. 1 is as shown in FIG. In FIG. 2, (a) shows the change in the output of the short-circuit detector DSH, (b) shows the change in the output current set value of the welding power source, and (c) shows the change in the welding current with the passage of time. 1 and 2, when a short circuit occurs, the changeover switch S1 switches from (2) to (1), the DC current source of the welding power source switches from IB to IP, the output current value increases, and the welding current rapidly increases. The rise is larger than the current change in FIG. 15 in the conventional method.

FIG. 3 is a connection diagram showing a specific example of an apparatus for performing the welding method of the present invention. In FIG. 3, reference numeral 20 denotes a welding power source, and DR11 to DR14 and DR
21 to DR28 are rectifiers, C2 is a smoothing capacitor, FET1 to FET4 are field effect transistors,
T11 is an inverter transformer, Ldc is a DC reactor, CT is a current detector, CNT10 is a control unit, and TS1 is a start command torch switch. Otherwise, the same parts or assemblies as in FIG. 1 are assigned the same reference numerals as in FIG. Iof is a feedback signal of the output current,
Vw is a drive signal to the wire feeder, and Ts is a start command signal. Sh is a short-circuit detection signal.

FIG. 4 shows the details of the control unit CNT10. In FIG. 4, CNT21 is a wire feed control unit, ADJ2.
1 is a wire feed speed setting device, and E21 is a DC power supply.
CNT31 is a welding output control unit, which includes a pulse width control circuit PWM31, a changeover switch S31, output current regulators ADJ31, ADJ32, DC power supplies E31, E3.
2 and a comparator CMP31.

3 and 4, an output current is detected by a current detector CT, an output Iof of the current detector CT is compared with an output of a changeover switch S31 by a comparator CMP31, and a difference between the outputs is detected by a pulse width control circuit. The output current is input to the PWM 31 to maintain a desired value. When (output of the changeover switch S31)> (detection output Iof of the current detector CT), the pulse width control circuit PWM31 increases the conduction time ratio of the output pulse signals Pa and Pb, and (output of the changeover switch S31) <( At the time of the detection output Iof of the current detector CT, the pulse width control circuit PWM31 reduces the conduction time ratio of the output pulse signals Pa and Pb. Until receiving the short-circuit detection signal Sh from the short-circuit detector DSH, the changeover switch S31 is on the (2) side, and the output of the changeover switch S31 outputs the set value Ib of the output current regulator ADJ31.
As described with reference to the principle diagram of FIG. 1, the output current Iob becomes low, and the short-circuit detection signal Sh from the short-circuit detector DSH is obtained.
When the switch S31 is received, the changeover switch S31 is set to the (1) side, and its output becomes the high output current set value Ip, and becomes the high output current Iop in the principle diagram of FIG. As a result, the relationship such as the output current from the welding power source becomes similar to the relationship shown in FIG.

Here, since the short-circuit frequency in short-circuit transition type arc welding is usually several tens Hz to several hundreds Hz, if the operating frequency of the inverter is several tens kHz,
It becomes possible to make the output change of the welding power supply follow the change of the welding phenomenon.

FIG. 5 shows the control unit CNT10 of the embodiment of FIG.
This is another embodiment of the present invention. In FIG. 5, ADD is an adder,
S41 is a changeover switch, ADJ41 is an output current regulator, and E41 is a DC power supply. In FIG. 5, the switch S41 is on the (2) side until the short-circuit detection signal Sh is output from the short-circuit detector DSH, and only the output of the output current regulator ADJ31 is supplied to the comparator CMP31. The output state corresponds to the low output current Iob at the time of arc in the principle diagram shown in FIG. Upon receiving the short-circuit detection signal Sh from the short-circuit detector DSH, the changeover switch S41 switches to the (1) side, and the sum of the output of the output current regulator ADJ31 and the output of the output current regulator ADJ41 is supplied to the comparator CMP31. As a result, an output state corresponding to the high output current Iop at the time of short circuit in the principle diagram shown in FIG. 2 is obtained.

On the other hand, in short-circuit transfer arc welding, if the welding conditions are appropriate, a clean bead appearance unique to short-circuit transfer arc welding can be obtained. This bead appearance largely depends on the short circuit frequency. Therefore, the appearance can be adjusted to a desired appearance by changing the short-circuit frequency. Next, with regard to the welding method of the present invention, a welding method capable of adjusting the short-circuit frequency will be described.

When the output current at the time of short-circuit is increased by the output current regulator ADJ32 of FIG. 4 and the output current regulator ADJ41 of FIG. 5, the number of droplets transferred at the time of short-circuit increases, and the short-circuit time and the arc time accordingly increase. However, the short circuit frequency becomes lower.

However, when the short-circuit frequency is adjusted according to the output current at the time of short-circuit, the maximum current at the time of short-circuit and the arc current following the short-circuit change. In general, the average welding current does not change because the wire feed speed is not changed. Therefore, the range of adjustment of the short-circuit frequency by the output current at the time of short-circuit is narrow and not very effective.

FIG. 6 shows an example of the control unit CNT10 capable of adjusting a wider short-circuit frequency. The control unit CNT10 of FIG. 6 is obtained by adding the off-delay timer TM1 started by the short-circuit detection signal Sh to the control unit CNT10 of FIG. 3, and the delay time of the off-delay timer TM1 is set by the time adjuster ADJ42.

FIGS. 7A and 7B are diagrams showing the output voltage and current when the control unit shown in FIG. 6 is used. FIG. 7A shows the welding voltage, FIG. 7B shows the short-circuit detection signal Sh, and FIG. The output state of the off-delay timer TM1, (d) is the output current set value,
(E) shows changes in the welding current with the passage of time.

In FIG. 6 and FIG. 7, the output signal of the off-delay timer TM1 changes to a high level from the rise of the short-circuit detection signal Sh, and the high level state means that the set time of the off-delay timer TM1 elapses after the short-circuit detection signal Sh disappears. Continue until you do. When a short circuit occurs and the short circuit detection signal Sh becomes a high level, the changeover switch S3
1 switches from (2) to (1) and the comparator CMP31
From the low setting value Ib of the output current regulator ADJ31 to the high setting value Ib of the output current regulator ADJ32.
p, and the output current is accordingly reduced to a lower value Iob
To the higher value Iop. When the short circuit time ends,
After the delay time of the off-delay timer TM1, the switch command signal for the switch S31 is inverted from the high level to the low level, the switch S31 switches from (1) to (2), and the output current changes from the high value of Iop to Iob. Return to low value. Since the arc is already formed during this delay time, the distance between the tip of the wire and the workpiece increases immediately after the arc is generated due to the high output current, and it takes a long time until the next short circuit. As a result, the short circuit frequency decreases. However, due to the presence of the DC reactor Ldc, the off-delay timer T
The instantaneous value of the current itself immediately after the occurrence of the arc during the delay time due to M1 does not become extremely large, but the amount of melting during the delay time immediately after the occurrence of the arc is large.

FIG. 8 is a connection diagram showing still another example of the control unit CNT10. In the same figure, the point at which the output current is switched from a low value to a high value is further delayed by an on-delay timer TM2 in addition to the example of FIG.

In FIG. 8, TM2 is an on-delay timer, which starts a time period after a short circuit occurs and the short circuit detection signal Sh goes high, and a time setting unit ADJ43.
The output goes high after the set time. AND1 is an AND gate that outputs a high-level signal when both the output of the off-delay timer TM1 and the output of the on-delay timer TM2 are at a high level, and outputs a low-level signal when any of the input signals is at a low level. I do.
In the other elements of the figure, those having the same functions as those of the control unit CNT10 shown in FIG.

The operation of the control unit of FIG. 8 will be described with reference to the diagram of FIG. 9, (a) shows the welding voltage, (b) shows the short-circuit detection signal Sh, (c) shows the output of the AND gate AND1, (d) shows the output current set value, and (e) shows each change in the welding current. FIG. 3 is a diagram illustrating the state over time. In FIG. 8 and FIG. 9, when a short circuit occurs, the output signal of the off-delay timer TM1 immediately goes to a high level, but the on-delay timer TM2 is set to the time setting unit ADJ43.
After a time set by, its output is inverted to a high level. Therefore, the AND gate AND1 goes high after the short-circuiting occurs and the time limit of the on-delay timer TM2 ends, and the switch S31 is thereby switched from (2) to (1). As a result,
The output current setting signal is switched from the low setting value Ib during the arc to the high output current setting value Ip after the time limit of the on-delay timer TM2. When the short-circuit state progresses, the transfer of the droplet and the melting of the wire progress, and the short-circuit is eliminated and an arc is generated, whereby the short-circuit detection signal Sh is inverted to a low level. Even after the short-circuit detection signal Sh is inverted to the low level, the output of the off-delay timer TM1 outputs a high-level signal during the set time period, so that the output of the on-delay timer TM2 is also at the high level. The output of the AND gate AND1, which is the input, also remains at the high level. Therefore, the output setting signal has a high output current set value Ip from the time when the short circuit is removed to the time when the setting time of the off-delay timer TM1 elapses.

Here, in order to adjust the short-circuit frequency, FIG.
In addition to adjusting the setting time period of the off-delay timer TM1 as described above, it can be changed by adjusting the setting time period of the on-delay timer TM2. in this case,
The effect of changing the time period is off-delay timer T
The time limit of M1 and the time limit of the on-delay timer TM2 have opposite effects. Of course, in order to adjust the short-circuit frequency, either one of the time limit of the off-delay timer TM1 and the time limit of the on-delay timer TM2 may be changed, or both may be changed.

FIG. 10 is a connection diagram showing another example of the control unit CNT10, in which a target short-circuit frequency is set, and the short-circuit frequency is kept at a target value by feedback control. In FIG. 10, FCN1 is a short-circuit frequency control unit. The other elements in FIG. 10 have the same functions as those in the examples shown in FIG. 4, FIG. 6, and FIG.

FIG. 11 shows the short-circuit frequency control unit FCN of FIG.
1 is a connection diagram showing a specific example, E61 is a DC power supply, ADJ61 is a short-circuit frequency setting device, VF is a V / F converter that generates a pulse signal having a frequency proportional to the input voltage, PD is a phase comparator, LF is a low-pass filter. The short-circuit frequency control unit FCN1 of FIG.
1 and the short-circuit frequency setting device ADJ61, a short-circuit frequency setting signal is converted into a signal having a frequency proportional to the set value by the V / F converter VF, and this signal is compared with the frequency of the short-circuit detection signal Sh by the phase comparator PD. Then, the difference signal is converted into a voltage signal by a low-pass filter LF and output as an output current setting signal Ip, thereby controlling the short circuit frequency to coincide with a target value.
The short-circuit frequency control unit FCN1 in FIG. 11 constitutes a PLL circuit by this, the pulse width control circuit in FIG. 10, and the inverter circuit controlled by them, and controls the short-circuit frequency of the welding machine to a target frequency. In the case of FIG. 10, the short-circuit frequency is changed by changing the output current at the time of short-circuit according to the difference between the set short-circuit frequency and the target short-circuit frequency.

FIG. 12 is a connection diagram showing another embodiment of the control unit CNT10 in which a target short-circuit frequency is set and the short-circuit frequency is maintained at a target value by feedback control. FIG. 1
The other components of 2 have the same functions as those in the examples shown in FIGS. 4, 6, 8, and 10, and the description thereof is omitted.

FIG. 13 shows the short-circuit frequency control unit FCN of FIG.
FIG. 4 is a connection diagram showing a specific example of No. 2, in which VR is a voltage / resistance converter that converts an input voltage into a resistance value proportional to the input voltage, and may be a mechanical type or a semiconductor. . TM3 is an off-delay timer, and the delay time is set using the resistance value output of the voltage / resistance converter VR as a time-limit setting resistance value. Other elements in FIG. 13 that have the same functions as those of the short-circuit frequency control unit FCN1 in FIG.

The short-circuit frequency control unit FCN2 in FIG. 13 converts the short-circuit frequency setting signal determined by the DC power supply E61 and the short-circuit frequency setting unit ADJ61 into a signal having a frequency proportional to the set value by the V / F converter VF. This signal and the frequency of the short-circuit detection signal Sh are compared by a phase comparator PD, and the difference signal is converted into a voltage signal by a low-pass filter LF, and the output of this signal is converted into a resistance value by a voltage / resistance converter VR. The time limit of the off-delay timer TM3 is determined according to the resistance value. By setting the output signal of the off-delay timer TM3 as the switch command signal Sh1 to the switch S31, the output current setting signal is switched from Ib to Ip or vice versa so that the short-circuit frequency matches the target value. Control. Therefore, the short-circuit frequency control unit FCN of FIG.
2 is controlled by the pulse width control circuit PWM31 of FIG. 12 and an inverter circuit controlled by the pulse width control circuit PWM31.
The L circuit is configured to control the short-circuit frequency of the welding machine to a target frequency by changing the voltage switching delay time after the start of the short circuit. In the case of FIG. 12, the time from the detection of the short circuit to the switching of the set value of the output current is changed by the difference between the short circuit frequency and the target short circuit frequency to change the short circuit frequency.

[0032]

The present invention is as described above. (1) A short-circuit transfer type arc welding with a large current, which has been impossible in the past, can be stably realized. (2) All-position welding, which is a feature of short-circuit transfer type arc welding, can be performed with a large current. (3) Since short-circuit transfer type arc welding is used, welding with large current and shallow penetration can be performed, and high-speed welding of thin plates can be performed. (4) Since the adjustment of the short-circuit frequency is easy, a desired bead appearance can be easily obtained. (5) Not only steel but also short-circuit transfer type arc welding of other electrode materials is possible. And many other effects.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating the principle of the present invention.

FIG. 2 is a diagram for explaining the operation of the apparatus in FIG. 1;

FIG. 3 is a connection diagram illustrating an embodiment of the present invention.

FIG. 4 is a connection diagram showing a specific example of an output control unit CNT10 of the apparatus shown in FIG.

FIG. 5 is a connection diagram showing another specific example of the output control unit CNT10 of the apparatus shown in FIG.

FIG. 6 is a connection diagram showing another specific example of the output control unit CNT10 of the apparatus shown in FIG.

FIG. 7 FIG. 6 when the output control unit CNT10 is used.
Diagram for explaining the operation of the device of FIG.

FIG. 8 is a connection diagram showing another specific example of the output control unit CNT10 of the apparatus of FIG.

FIG. 9 is a diagram for explaining the operation of the apparatus of FIG. 3 when the output control unit CNT10 of FIG. 8 is used.

FIG. 10 is a connection diagram showing another specific example of the output control unit CNT10 of the apparatus shown in FIG.

FIG. 11 is a connection diagram showing a specific example of the short-circuit frequency control unit FCN1 in FIG. 10;

FIG. 12 is a connection diagram showing another specific example of the output control unit CNT10 of the apparatus in FIG. 3;

FIG. 13 is a connection diagram showing a specific example of the short-circuit frequency control unit FCN2 in FIG. 12;

FIG. 14 is a connection diagram showing the principle of the conventional technique.

FIG. 15 is a diagram for explaining the operation of FIG. 14;

[Explanation of symbols]

REFERENCE SIGNS LIST 1 welding power supply 10 welding power supply 20 welding power supply 11 torch side cable 12 workpiece cable 14 arc 15 workpiece 16 chip 17 wire 18 feed roller Vo DC voltage source R1 resistor L1 inductance DR11 to DR14 rectifier DR21 To DR28 Rectifier T11 Inverter transformer C2 Smoothing capacitor FET1 to FET4 Field effect transistor Ldc DC reactor CT Current detector CNT10 Control unit CNT21 Wire feed control unit CNT31 Welding output control unit CMP31 Comparator TS1 Start command torch switch DSH short circuit detection Switch S1 Changeover switch Iof Output current feedback signal Vw Drive signal to wire feeder Ip Output current set value Ib Output current set value S31 Changeover switch AD 21 Wire feed speed setting device ADJ31, ADJ32, ADJ41 Output current regulator ADJ42 Time setting device for off-delay timer ADJ43 Time setting device for on-delay timer ADJ61 Short circuit frequency setting device E21 DC power source E31, E32 DC power source E41 DC power source E61 DC Power supply ADD Adder S41 Changeover switch AND1 AND gate FCN1, FCN2 Short-circuit frequency control section VF V / F converter PD Phase comparator LF Low-pass filter VR Voltage / resistance converter PWM31 Pulse width control circuit TM1, TM3 Off delay timer TM2 On delay timer

Claims (5)

[Claims] 1. In short-circuit transfer type arc welding in which a short circuit and an arc are repeated while using a welding power supply having substantially constant current characteristics, an output current of the welding power supply is higher when a short circuit occurs than when an arc is generated. Short-circuit transfer type arc welding method. 2. In short-circuit transition type arc welding in which short-circuiting and arcing are repeatedly performed, a welding power supply having substantially constant current characteristics is used, and the output current of the welding power supply is changed from a short-circuit start time to a fixed time after the short-circuit ends. A short-circuit transfer arc welding method in which the output current is higher than at other times. 3. In short-circuit transition type arc welding in which a short circuit and an arc are repeatedly performed, a welding power supply having substantially constant current characteristics is used, and an output current of the welding power supply is supplied after a predetermined time after the start of the short circuit and after the short circuit is completed. A short-circuit transfer arc welding method in which the output current is higher than that at other times until after a certain time. 4. A method for detecting a repetition frequency of the arc generation and the short circuit generation, and determining an output current in a period during which the output current of the welding power supply is increased according to a difference between the detected repetition frequency and a reference frequency. Claims 1 to 3
The short-circuit transfer type arc welding method according to any one of the above. 5. The method according to claim 2, wherein a repetition frequency of the arc generation and the short-circuit generation is detected, and the predetermined time is determined according to a difference between the detected repetition frequency and a reference frequency. Short-circuit transfer type arc welding method.