JPH0342149B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention provides a method for delivering a consumable electrode at a substantially constant rate;
This invention relates to an arc welding method in which short circuits and arcs are alternately and repeatedly generated between a consumable electrode and a base metal, and in particular to a method for controlling the output of a welding power source suitable for reducing spatter and improving arc stability. .

[Conventional technology]

Generally, CO ₂ arc welding or MAG welding that involves short circuits is performed using a DC constant voltage power supply and by feeding a consumable electrode (wire) at a nearly constant speed. The outline of the arc phenomenon is shown in Figure 3. In the figure, 1 is a wire, 2 is a droplet, 3 is a molten pool, and 4 is an arc. is the initial state of a short circuit when the droplet and molten pool are in contact, and is the middle stage of a short circuit when the droplet and molten pool are completely short-circuited. The late short-circuit state, when the droplet is constricted by the electric current's Joule heat, the electromagnetic pinch force, and the surface tension of the molten metal, and the droplet is about to complete its transfer to the molten pool, is the short-circuit state. The initial state of the arc, where a broken arc occurs, is the middle stage of the arc, when the wire tip melts and a droplet grows.As the welding current decreases, the wire feeding speed becomes greater than the wire melting speed, and the arc The lengths become shorter and the molten pool is on the verge of shorting between the droplet and the molten pool, indicating the late stage of the arc.

FIG. 4 shows the current/voltage waveforms, and .about. in the figure corresponds to .about. in FIG. 3 indicating the arc phenomenon. However, this welding method relies on the self-control action of the welding power source, and the short circuit current, arc current, short circuit time, and arc time are uncontrolled factors determined by the reactor built into the power source, the external characteristics of the power source, etc. be. Therefore, it is difficult to obtain a periodic and uniform current waveform, and a large amount of spatter occurs due to variations in short-circuit current and short-circuit time, uneven bead toes, fins, and arcing time. It has problems such as abnormal growth of droplets due to variations in arc current.

In order to solve these problems,
No. 108179 proposes using a current waveform as shown in FIG.

That is, it detects a short circuit and maintains the first current value I _D (10 to 50 A) at a relatively low level for 1.5 to 2.5 mS to prevent the generation of pinch force that would inhibit the short circuit.
Next, a relatively high level second current value I _SP (350~
450A), the constriction of the droplet that occurs on the verge of arc generation is detected from the detected values such as resistance change, current change, voltage change, etc., and the third low-level current value I _RA (20 to 200A) is set. reduce the current to. This is to suppress the increase in arc pressure that occurs at the moment of arc generation, to prevent the scattering of droplets, to prevent spatter, and to make the bead appearance uniform. When an arc occurs, a fourth current value at a relatively high level
I _AP (approximately 200 to 400 A, depending on the wire feed rate) is maintained for about 10 to 20 mS to promote droplet formation and prevent short circuits. next,
In order to accelerate the short circuit, the fifth current value I _AB (50 to 85 A), which is a relatively low level with almost constant current characteristics, is held until a short circuit occurs. By sequentially carrying out the above steps ~, the phenomenon shown in Figure 3 can be
Short circuits and arcs occur at the positions indicated by ~ in the diagram, and as short circuits and arcs are regularly repeated, and unstable disturbances of the arc and molten pool do not occur, the amount of spatter generated is reduced to 1/5 to 1/6 compared to conventional methods. However, it is stated in the examples that a beautiful and uniform bead appearance can be obtained without the occurrence of fins that cause irregularities in the bead toe.

However, in this known method, (1) a short circuit is detected and the current is reduced to _ID , but no matter which method is used, there is always a slight detection delay and the current value is Since it takes some time for the level to switch from I _AB to _ID , initial control, which greatly affects the short-circuit condition, is not sufficient.

(2) Detect the constriction of the droplet and change the current from I _SP to I _RA
However, in order to detect a constriction, it is necessary to detect minute changes in voltage, etc., the time from the occurrence of a constriction to the occurrence of an arc is short, and it is _necessary to Because it takes some time to switch the current at current level _IRA , considerable ingenuity is required in the detection circuit and control circuit in order to obtain the desired effect, and in order to ensure stable operation. There are considerable difficulties.

(3) In the latter stages of the arc, the current is switched from I _AP to I _AB in order to accelerate the short circuit, but since I _AB is almost constant current control, arc length control is hardly performed in this section. Also, the section of I _AB is
This is the section necessary for heating the base metal (molten pool), and if the current value is set solely for the purpose of promoting short circuits, there will be insufficient heat input to the base metal, resulting in a phenomenon known as poor melt flow. . Furthermore, it is also undesirable from the viewpoint of arc stability to suddenly change the current value during the arc period.

The following points can be cited as disadvantages.

The present invention was made to solve the problems of the prior art described above, and its purpose is to further improve workability by improving arc stability, reducing the amount of spatter, and making the bead appearance more beautiful. An object of the present invention is to provide a good consumable electrode type arc welding method.

[Means for solving problems]

The present invention delivers a consumable electrode at a substantially constant rate;
In arc welding, which is performed by repeatedly generating short circuits and arcs between a consumable electrode and the base metal,
An arc welding method characterized by detecting the occurrence of a short circuit and the occurrence of an arc, and performing each of the following processes (A) to (F) sequentially or in combination of two or more of them for each short circuit cycle. It is.

(A) After a short circuit occurs, for a predetermined time T _D , the welding power source output is controlled at a constant current to maintain the welding current at a predetermined value determined by the constant current setting level immediately before the short circuit, and the short circuit condition is made uniform. The process of doing.

(B) Next, adjust the welding current to the specified constant current setting level I _u
The process of opening the short circuit by rapidly increasing the current to a constant current setting level I _S with a predetermined time constant S _S to a higher constant current setting level I S sufficient to open the short circuit.

(C) After the arc occurs, the welding power source output is controlled at a constant voltage to maintain the welding voltage near the relatively high constant voltage setting level V _h for a predetermined time T _h , and during that time, the constant voltage setting level V h is maintained at the above constant voltage setting level V _h. The process of forming and growing droplets on the consumable electrode by using both constant current control that regulates the maximum current value to a constant current setting level that is slightly higher than the current value determined by the arc condition.

(D) After a predetermined time T _h has elapsed, the constant voltage setting level is gradually decreased from the above high level V _h to a predetermined low level V _L with a predetermined time constant S _V , and accordingly, the constant voltage setting level is decreased. The constant current setting level, which is slightly higher than the current value determined by the level and arc condition, is gradually decreased with a predetermined time constant S _i toward a predetermined low level I _L to heat the base material while reducing the arc force. The process of doing.

(E) A process in which the increase in current caused by the self-control action of the welding power source as the arc length decreases is prevented by constant current control at the above-mentioned low level I _L , and excessive growth of droplets is suppressed.

(F) A process in which the current value is shifted to a lower constant current setting level I _n after a predetermined time (T _h + T _L ) has elapsed after arc generation to suppress melting of the consumable electrode and promote short circuiting. .

[Effect]

FIG. 1 is a current/voltage waveform diagram for explaining the operation of the present invention. Compare the magnitude of the welding voltage, which changes from moment to moment, and the short circuit/arc judgment voltage V _j ,
Determine whether there is a short circuit or an arc. The optimum value of V _j varies depending on the average welding current value, but it is 10~
It is about 20V, and if set to 16 to 17V, it can be applied to almost the entire current range.

The section is a section for equalizing the short circuit state between the droplet and the molten pool. For example, as shown in Figure 3, if the current increases from the moment a part of the droplet comes into contact with the molten pool, the droplet will be pushed up to the surface of the molten pool due to the increase in arc force and arc pressure that accompanies the increase in current. is depressed and the short circuit may rupture before the droplet has sufficiently migrated into the weld pool. When this phenomenon occurs, a considerable amount of droplets remain at the tip of the electrode, and more droplets grow until the next short circuit.
It becomes an excessively large droplet and causes a short circuit. Furthermore, since the short circuit period becomes shorter, the short circuit occurs at a relatively large current value with a small amount of decrease from the short circuit peak current.
As a result, a large amount of spatter is generated when the short circuit is broken.

Therefore, when the welding voltage becomes smaller than V _j and a short circuit is determined, the welding current is kept at a value determined by the previous constant current setting level for a predetermined period of time.
Hold for T _D to suppress the increase in current. For example, if a short circuit occurs at a constant value I _n as shown in Figure 1, the current will be maintained at I _n during T _D after the short circuit, and if the constant current setting level changes in a slope as shown in Figure 1. If a short circuit occurs during the short circuit, the current after the short circuit is controlled on an extension of the slope. By doing this, the droplet and the molten pool are reliably short-circuited as shown in Figure 3, so even if the current increases and the short circuit is released, the droplet does not fully transfer to the molten pool. does not occur.

Note that the lower the level at which the current is held immediately after a short circuit, the greater the effect, but the effect is still present even at a relatively high current value in the middle of a slope-like change in the constant current setting level. T _D is closely related to the size of the droplet, and its appropriate value differs depending on the wire feed rate and wire diameter.

The section is a section for opening a short circuit, and when a predetermined time T _D has elapsed after short circuit detection, the current is rapidly increased to I _u , and then a higher constant current setting level I _S that regulates the maximum current value is established. Toward this end, the current is gradually increased with a predetermined time constant S _S to open the short circuit. In a normal short circuit, the short circuit is broken before it reaches I _S as shown in Figure 1, and an arc occurs, but if the short circuit is relatively long, as shown in Figure 1, the short circuit is broken before reaching I _S
The short circuit is opened after reaching .

Assuming that the current value I _P is held at a constant value until the short circuit is released, if I _P is selected under appropriate conditions, the occurrence of spatter can be suppressed, but the occurrence of spatter can be suppressed due to fluctuations in wire feeding, etc. If a large short circuit occurs, _IP cannot deal with it and arc instability will occur.
Conversely, if I _P is set to a sufficiently large value in consideration of arc instability, an excessive current will flow during a normal short circuit.
It causes spatter and fins.

However, as shown in Figure 1, if the current is increased according to the short circuit time to open the short circuit, the short circuit will be opened with the minimum necessary current value depending on the short circuit condition, resulting in spatter and fins. There are few.

I _u needs to be changed depending on the wire feeding speed and wire diameter, but S _S may be set to a substantially constant value.

The section is the section for forming droplets at the electrode tip, where the welding voltage is greater than V _j ,
A predetermined period of time after it is determined that the arc state is present.
During T _h , the welding power source output is controlled at a constant voltage so as to maintain the welding voltage near a relatively high voltage level V _h , and droplets are formed and grown while controlling the arc length using constant voltage characteristics. In the figure, the constant current setting level (indicated by the broken line) that regulates the maximum current value in this section is shown as I _S , but if necessary, it can be set to a lower level or set to a predetermined level.
Techniques such as gradual reduction towards _IR may also be used.

The section is a section for heating the molten pool and the base material. If the current value in this section is small, the amount of heat input to the molten pool and base metal will be insufficient, leading to a decrease in penetration depth or a worsening of the molten pool's followability during high-speed welding, so-called molten metal flow. It is undesirable from the viewpoint of workability to lower the current value. In addition, in this section, the droplet that had been pushed upward hangs downward due to the decrease in arc force accompanying the decrease in welding current, and the shape of the droplet is reshaped in preparation for the next short circuit. As a result, the arc length is constantly changing, and if arc length management in this section is inadequate, arc instability will occur.

Therefore, the constant voltage setting level is gradually decreased from the high level V _h to the low level V _L at a predetermined time constant S _V. In this way, the arc length is controlled by the self-control effect due to constant voltage characteristics, and the heat input to the molten pool and base metal can be set to suitable values for S _V and V _L depending on the type of work. According to
Can be controlled arbitrarily.

However, in CO ₂ arc welding, MAG welding, etc., a short circuit (instantaneous short circuit) is likely to occur due to fluctuations in the droplets and molten pool in this area. When such a short circuit occurs in constant voltage control, droplets that have hung down due to the next short circuit are pushed upward again by the increase in current, which has a negative effect on the next short circuit. Therefore, as the voltage decreases, the constant current setting level, which is slightly higher than the current value determined by V _h , V _L , S _V and the arc state, is gradually decreased from I _R to I _L with a predetermined time constant S _i (the broken line in the figure ).
By setting the constant current setting level that regulates the maximum current value in this way, even if a momentary short circuit occurs, the current increases only slightly, and the adverse effect on the next short circuit can be reduced.

The section is a section for suppressing abnormal growth of droplets. In the later stages of the arc, the current decreases to a low level, so the amount of wire fed is greater than the amount of melted wire, and the arc length gradually becomes shorter. However, with constant voltage characteristics, the current increases due to the self-control effect and attempts to prevent the arc length from clogging, which may cause the droplets to become even larger and cause phenomena such as short circuits.

In the present invention, since the constant current setting level I _L is provided in the section following the section, even if the current increases due to the decrease in the arc length as described above, the I _L
is regulated, and abnormal growth of droplets does not occur.

The section is a section for promoting short circuiting, and after a predetermined time T _L has elapsed since the constant voltage setting level started decreasing from V _h to V _L with a time constant S _V ,
That is, after (T _h +T _L ) has elapsed since arc generation, the current value is shifted to a lower constant current setting level I _n to suppress melting of the wire and cause a short circuit to occur quickly.

Welding is performed sequentially through each of the above sections, and each factor is set so that a short circuit normally occurs in the section, but it is also expected that a short circuit may occur in the section due to disturbances, etc.

If a short circuit is detected in any period of ~, the current value determined by the previous constant current setting level is held for a time T _D as shown in Figure 4, and the short circuit is detected even after T _D has elapsed. If it does not break, change the current to I _u
and execute the subsequent sections. if,
If an arc is detected (the short circuit is opened) before T _D elapses, the circuit will continue in the same order and will not return to the section.

FIG. 2 is a diagram for explaining the above steps ~ again in relation to the external characteristics of the power supply.

(1); During T _D after a short circuit occurs, the constant voltage setting level is
It is held at a point on the external characteristic that is V _L and constant current setting level I _n .

(2); When T _D elapses, the external characteristics switch to constant voltage setting level V _h and constant current setting level I _u , so the operating point moves to .

(3);Next, leave the constant voltage setting level V _h as it is,
Increase the constant current setting level from I _u to I _S with a time constant S _S. Now, if the short circuit is opened at a point above the constant current setting level I ₁ on the way from I _u to I _S , the operating point will move →→ due to the voltage increase due to arc generation.

(4); After the arc occurs, it remains in that state for a predetermined time T _h , and the operating point moves in the vicinity according to the arc length.

(5); When a predetermined time T _h has passed after the arc occurs, the constant voltage setting level decreases from V _h to V _L with a time constant S _V , and at the same time, the constant current setting level rapidly decreases from I _S to I _R. Thereafter, it decreases from I _R to I _L with a time constant S _i . For example, the external characteristic along the way is V ₂
−B−I ₂ , the operating point is as follows.

(6); When the arc length becomes shorter in the latter stage of the arc, the current increases from to C due to the self-control effect due to constant voltage characteristics, but it increases depending on the constant current setting level I _L. is suppressed and the operating point is set on _IL as .

(7); When a predetermined time (T _h +T _L ) has passed after the arc occurs, the constant current setting level shifts to an even lower level I _n , so the operating point also shifts.

(8); After that, the operating point falls above _In , a short circuit occurs and returns to , and the above operation is repeated thereafter.

Note that if the short circuit time is less than T _D , the short circuit is ignored and the above operation continues as it is, and if it is longer than T _D , the operation point is reached.

In Figure 2, the constant voltage setting level in the section is
Although V _L is used, in order to prevent arc breakage due to small current, the constant voltage setting level in this section may be set to V _h or an even higher level.

The operating points .about. in FIG. 2 correspond to those of FIG. 1. Furthermore, ~ also corresponds to the states in Figure 3~.

In addition, in the above explanation, the case was described in which the control methods for each process (A) to (F) from a short circuit to an arc state to the next short circuit are executed continuously, but among the control methods for each of these processes, A certain effect can be obtained even if two or more of these are executed in combination. In this case, in other steps, the current and voltage may be controlled by methods other than those described above, or may depend on the self-control action of the welding power source.

〔Example〕

Examples of the present invention will be described below.

Example 1 (a) Using a thyristor-controlled constant-voltage characteristic power source, setting the output voltage to the optimum voltage of 19V for the amount of wire feeding, feeding a 1.2mmφ wire at a speed of 3.2m/min, and CO ₂ by the conventional method. When performing arc welding and (b) using the inverter-controlled welding power source shown in Fig. 16, each waveform factor that determines the welding power source output is set as shown below, and the same 1.2 mmφ wire is
The generation of spatter and the current/voltage waveforms were compared and observed when CO ₂ arc welding according to the present invention was performed by feeding at a speed of 10 min. In both cases, the gas used was CO ₂ and the gas flow rate was 15/min.

I _u = 185A, I _S = 550A, I _R = 270A I _L = 70A, I _n = 40A V _h = 30V, V _L = 18.5V DCL = 36μH (DC reactance inductance) S _S = 20mS, S _i = 7 mS, S _v = 39 mS T _D = 2 mS, T _h = 4 mS, T _L = 11 mS As a result, it was found that the amount of spatter generated was significantly smaller in the method (b) of the present invention than in the conventional method (a). .

Figures 6a and 6b are current and voltage oscilloscope waveforms corresponding to (a) and (b) above, respectively.Compared to (a) of the conventional method, (b) of the present invention has more uniformity and periodicity. A certain waveform was obtained, indicating that the arc condition was extremely stable.

Example 2 (a') Using a thyristor controlled constant voltage characteristic power supply,
Set the output voltage to 24.5V and connect the 1.2mmφ wire to 8
When performing CO ₂ arc welding by the conventional method by feeding at a speed of m/min, and (b') using the inverter-controlled welding power source shown in Fig. 16, each waveform factor was set as shown below. , same 1.2mmφ wire as 8
The generation of spatter and current/voltage waveforms were compared and observed when CO ₂ arc welding according to the present invention was performed by feeding at a speed of m/min. The gas used and the gas flow rate are the same as in Example 1.

I _u = 300A, I _S = 550A, I _R = 370A I _L = 150A, I _n = 80A V _h = 37.5V, V _L = 25.5V DCL = 36μH S _S = 20mS, S _i = 18mS, S _V = 56 mS T _D = 3.5 mS, T _h = 10.5 mS, T _L = 15 mS As a result, it was found that the amount of spatter generated was drastically reduced in the method (b') of the present invention compared to the conventional method (a'). Figures 7a and 7b are current and voltage oscilloscope waveforms corresponding to (a') and (b') above, respectively.Similar to Figure 6, compared to the conventional method (a'), the present invention In (b'), a more uniform and periodic waveform is obtained.

Example 3 In the explanation of FIG. 1 above, it was mentioned that the current value in the latter stage of the arc is related to the heating of the molten pool and base material. From this point of view, reducing the current to _In to promote short circuiting is not preferable in cases such as high-speed welding where sufficient heat input to the base metal is required.

In order to solve the above problem, the wire feeding speed was set at 3.2 m/min so that the section where I _n did not occur.
We observed the spatter generation and current/voltage waveforms during CO ₂ arc welding. FIG. 8 shows oscilloscope waveforms of current and voltage. In this example, among the set values of the waveform factors described in Example 1, V _h was changed to 26 V, T _h was changed to 2.5 mS, and T _L was changed to ∞, and the other values were kept the same.

The reason for reducing V _h and T _h is to reduce the amount of droplets formed and shorten the arc length to shorten the short-circuit period, and to reduce the abnormal growth of droplets caused by longer arc times. This is to prevent this.

In this example, the occurrence of spatter is slightly more than in (b) of Example 1, but less than in (a) of the conventional method. Furthermore, uniform waveforms with no significant periodicity were obtained for the current and voltage waveforms.

Fig. 14 shows the actual measurement results of the weight of spatter adhering to the nozzle and base material in Examples 1 to 3 above.
In the figure, condition (1) of the present invention is when the interval I _n is included, and condition (2) is when the interval I _n is not included. In addition, under condition (2) at a wire feeding speed of 8 m/min, T _L
= ∞, and welding was performed by changing only V _h to 33.5V. The spatter adhering to the base material when the wire feeding speed was 3.2 m/min was omitted because it was a very small amount in either method.

The actual measurement results of the amount of spatter adhesion showed that the amount of adhesion was drastically reduced under condition (1) of the present invention compared to the conventional method, and it was found that some amount of spatter was sacrificed in order to secure heat input to the base material. Even under condition (2), the amount of spatter deposited is smaller than that of the conventional method.

Figures 9 to 12 show CO ₂ using 1.2 mmφ wire.
It is a figure showing an example of the appropriate value of each waveform factor of the present invention with respect to wire feeding speed in arc welding.

In the figure, (1) and (2) are added after the waveform factor to differentiate it, meaning the value (1) when the I _n interval is included and (2) when it is not included. In addition, the reason why the wire bends when the wire feed speed is 4.5 m/min due to some factors corresponds to the fact that when the feed speed increases beyond this point, the droplet transfer form changes from short-circuit transfer to globular transfer. are doing. Wire feeding speed 10m/
The fact that T _D is a constant value above min means that this is the upper limit value of T _D that does not cause arc instability. If T _D is set too long, the wire continues to be fed during the short circuit period, so an excessive current will be required to open the short circuit, resulting in an increase in spatter as the current increases, and an increase in the short circuit period. This causes phenomena such as arc instability due to uniformity or, in extreme cases, arc breakage. _IS and
There is no mention of S _S , respectively.
This is because it was kept constant at 20mS.

In Figures 9 to 12, the values of each waveform factor are shown with respect to the wire feed speed, but when welding is performed using these setting conditions, the wire feed speed and average welding current
Since there is a relationship between I _ave and the average welding voltage V _ave as shown in FIG. 13, it goes without saying that the values of each waveform factor can be arranged in terms of I _ave or V _ave .

Figure 15 is an example of setting each waveform factor when performing CO ₂ arc welding using a 1.0 mmφ wire.
Condition (1) is when there is an I _n interval, and condition (2) is when there is no I _n interval.

In addition, when finely adjusting the arc length (arc voltage), it is sufficient to increase or decrease the factors that determine the output during the arc period, that is, V _h , V _L , S _V , T _h and the wire feeding speed. Among these factors, V _h・T h in the small current region of short circuit transition, and V h・T _h in the small current region of short circuit transition, and
In the large current range, the effect of V _L and S _V is large. The wire feeding speed is a factor that determines the arc length in any current range, but the larger the current range, the greater the amount of change must be.

FIG. 16 is a block diagram showing an example of the configuration of a welding power source for carrying out the present invention.

1 is a primary rectifier circuit for converting alternating current into direct current, 2 is an inverter circuit for controlling output,
3 is a welding transformer, and 4 is a secondary rectifier circuit for converting the high frequency alternating current (for example, 20 KHz) generated by the inverter circuit 2 into direct current after being transformed by the welding transformer 3. 5 is a welding wire fed by a wire feeding roller 6 to weld the base material 7; 11 is a welding current detector that detects current by the output of the shunt 8; and 12 is a welding voltage detector. be.

28 is a short circuit/arc judgment circuit, which combines the output of the judgment voltage V _j setter 25 and the welding voltage detector 12.
The magnitude of the output is compared, and a determination signal indicating whether it is a short circuit or an arc is sent to the _TD timer 22 and the input/output device (I/O) 23.

The T _D timer 22 starts operating from the moment a short circuit occurs, and sends an interrupt signal iRQ2 to the microprocessor (MPU) 24 if the short circuit continues even after a predetermined time T _D has elapsed. i/o23 is
Interrupt signal when transitioning from short circuit to arc
Send iRQ3 to MPU24.

26 is a condition selector for specifying the output pattern (setting condition of welding waveform factor) used for welding, and specifically, any one of wire feeding speed, average welding current, and average welding voltage. Obtain and display two values. Reference numeral 27 is a setting device for finely adjusting the arc length, and it is a setting device that adjusts one or more of V _h , T _h , S _V and V _L , which are factors related to voltage setting during the arc period. Factors are combined to increase or decrease the predetermined set condition level. Which factor or combination of factors should be chosen?
Specify in the program that controls the MPU 24.

The condition selection signal and fine adjustment signal set in 26 and 27 are sent to A/D converters 29, 30 and I/O.
31, it is input to the MPU 24.

Reference numeral 20 denotes a memory that stores the values of each waveform factor shown in FIGS. 9 to 12 for each setting condition of each waveform factor such as wire feeding speed, average welding current, or average welding voltage. In response to a signal from the device 26, data for setting a predetermined waveform factor is sent to the MPU 24. The MPU 24 uses data from the memory 20 as a setting device 27 for fine adjustment.
The setting level of each waveform factor is determined by adding an increase/decrease command for a predetermined factor from .

21 is a timer for controlling T _h and T _L , and when the interrupt signal iRQ3 notifying that an arc has occurred is input to the MPU 24, the MPU 2
4, and when a predetermined time T _h has elapsed, an interrupt signal iRQ1 is sent to the MPU 24.
When the interrupt signal iRQ1 is input, an operation start command is sent from the MPU 24 to the timer 21 again, and when the predetermined time T _L has elapsed, the interrupt signal iRQ1 is output again.
It is input to the MPU24.

Note that no matter what state the timer 21 is in,
When the interrupt signal iRQ2 is generated, a command to stop the operation is sent from the MPU 24.

A control command for the wire feeding speed is input from the MPU 24 to the wire feeding roller drive circuit 13 via the I/O 19 and the D/A converter 14, and a control command for the waveform factor is input from the MPU 24 to the I/O 19 and the D/A converter 14. CR for current control via A converters 16 and 18
Integrating circuit 15 and voltage control CR integrating circuit 17
is input. It is assumed that these control commands are held in the I/O 19 until the next control command is issued. The CR integration circuits 15 and 17 are for performing slope control to change the set level of current and voltage with a predetermined time constant, and a command as to which time constant to select is separately sent from the I/O 19. FIG. 17 is a diagram showing an example of the configuration of the CR integrating circuits 15 and 17, each of which is composed of a circuit in which resistors R ₁ to _Ro and analog switches S ₁ to _{S o} are connected in a ladder shape, and an integrating capacitor C ₁ . , the time constant is made variable by opening and closing an analog switch connected in parallel to each resistor using an n-bit time constant selection signal.

The current setting signal output from the current control CR integration circuit 15 is inputted to the pulse width control circuit 10 after calculating the difference with the current feedback signal from the welding current detector 11 using an adder 32. The voltage setting signal output from 17 is input to the pulse width control circuit 10 as is. FIG. 18 is a diagram showing a configuration example of the pulse width control circuit 10, in which the control bias obtained by amplifying the input current setting signal by the amplifier 34 and the sawtooth wave from the sawtooth wave generator 33 are compared by the comparator 36. A pulse train P _A having a pulse width corresponding to the current setting signal obtained by The comparator 37 compares the pulse train P _B with the pulse width corresponding to the voltage setting signal.
As the other input of the NAND circuit 38, the narrower pulse train is selected by the NAND circuit 38 and the NOT circuit 39 and sent to the inverter drive circuit 9 as a pulse width control signal. The conduction width of the MOSFET, which is the switching element of the inverter circuit 2, is determined by the pulse width of the applied pulse width control signal.
The output of the welding power source is thereby controlled.

With such a configuration, the current/voltage waveforms shown in FIG. 1 can be controlled.
That is, the occurrence of a short circuit is detected by a signal from the short circuit/arc determination circuit 28, and the _TD timer 22 starts operating, and when a predetermined time _TD has elapsed, an interrupt signal iRQ2 is generated. Meanwhile, the current and voltage set levels remain unchanged.
When the interrupt signal iRQ2 is generated, the constant current setting level becomes I _u and the constant voltage setting level becomes V _h . After that, the constant voltage setting level remains V _h and only the constant current setting level moves from I _u to I _S. Then, it gradually increases with the time constant S _S of the CR integration circuit 15 set by the MPU 24.

When an interrupt signal iRQ3 notifying that an arc has occurred is generated based on a signal from the short circuit/arc determination circuit 28, the timer 21 is activated by a command from the MPU 24, and when a predetermined time T _h has elapsed, an interrupt signal iRQ1 is generated. Occur.

When the interrupt signal iRQ1 is generated, the constant current setting level rapidly decreases to I _R , and then gradually decreases from I _R to I _L with the time constant S _i of the CR integration circuit 15 set by the MPU 24. At the same time, the constant voltage setting level is set by the MPU 24 from V _h to V _L.
It gradually decreases with the time constant S _V of the CR integration circuit 17.
Furthermore, when the predetermined time T _h has elapsed, the timer 21 starts operating again according to a command from the MPU 24, and when the predetermined time T _L has elapsed, the interrupt signal is sent again.
Generate iRQ1.

Due to this interrupt signal iRQ1, the constant current setting level shifts to I _n , but the constant voltage setting level shifts to V _L
It remains as it is.

Note that if a short circuit occurs while the timer 21 is operating,
The T _D timer 22 starts operating, but only after a predetermined time.
If an arc occurs before T _D elapses, T _D timer 2
2 stops operation and does not generate interrupt signal iRQ2. Furthermore, in that case, the interrupt signal iRQ3 notifying the occurrence of an arc is not generated. iRQ3 will only occur if iRQ2 occurs.

When the interrupt signal iRQ2 is generated while the timer 21 is operating, the timer 21 stops operating, and no matter what level the current/voltage was immediately before, the constant current setting level is set to I u, and the constant voltage setting level is set to I _u. is set to V _h .

In addition, in order to ensure heat input to the base metal and molten pool, if the current setting in the latter stage of the arc is not lowered to _In , the timer 21 sends a second interrupt signal.
The MPU 24 is operated by a separately created control program so as not to generate iRQ1, that is, so as not to issue a command to start the operation of the timer 21 after T _h ends.

When controlling the output of a welding power source using a microprocessor as described above, all output control is
This can be done by interrupt processing of the MPU 24, and each processing time is relatively short, so the surplus time can be used for processing welding sequences, etc.

〔Effect of the invention〕

The effects of the present invention are as follows.

(1) Output control in any of the processes (A) to (F) is effective in reducing the amount of spatter generated, and since the amount of spatter generated is small, the work to remove spatter attached to the base material and nozzle is reduced. This effect is particularly large in the intermediate current range of globular transition.

(2) Similarly, output control in any process contributes to uniformity of current and voltage waveforms. The current and voltage waveforms are made uniform and short circuit periodicity is improved, resulting in improved arc stability and a beautiful bead shape.

(3) By controlling the output in each process (D), (E), and (F), the amount of heat input to the base metal and molten pool can be easily controlled depending on the type of work, making high-speed welding possible. can be,
Improves work efficiency.

(4) Through each process of (C) and (D), constant voltage control is mainly performed during the arc period, so it is possible to accurately control the arc length according to the arc condition, and a separate arc length control circuit etc. There's no need to add it.

(5) Since there is a unique relationship between the wire feeding speed, average welding current or average welding voltage and the waveform factor of each process, it is possible to uniformly set the waveform factor and it is easy to set conditions. .

(6) In the process (B) in the latter half of the short circuit, the current value is increased at a predetermined time constant according to the short circuit time to open the short circuit, so control is easy and stable operation can be expected. .

(7) Even during the arcing period, the current value is controlled to change continuously as shown in Figure 1, so the arc will not become unstable due to sudden changes in the current value.

[Brief explanation of drawings]

Figure 1 shows the current flow for explaining the action of the present invention.
Voltage waveform diagram, Fig. 2 is an explanatory diagram of output control of the welding power source in the present invention, Fig. 3 is an explanatory diagram of an arc phenomenon accompanied by a short circuit, Fig. 4 is a current/voltage waveform diagram in a general prior art, Figure 5 is a current/voltage waveform diagram of a known example closest to the present invention, and Figures 6a and b are CO ₂ under the conditions (a) and (b) described in Example 1, respectively.
The oscilloscope waveform diagrams of current and voltage when performing arc welding, Figures 7a and b, are CO ₂ arc welding performed under the conditions (a') and (b') described in Example 2, respectively. Fig. 8 is an oscilloscope waveform diagram of current and voltage when CO ₂ arc welding is performed under the conditions described in Example 3, Figs. 9, 10, and 11. 12 is a graph showing an example of the appropriate value of each waveform factor in the present invention, FIG. 13 is a graph showing an example of the relationship between wire feeding speed and average welding current/average welding voltage, and FIG. A chart showing the actual measurement results of the weight of spatter attached to the nozzle and base material in each example, Fig. 15 is a chart showing an example of setting each waveform factor in other embodiments with different wire diameters, and Fig. 16 is a chart showing the present invention. FIG. 17 is a detailed diagram of the CR integration circuit in FIG. 16, and FIG. 18 is a detailed diagram of the pulse width control circuit. 2... Inverter circuit for output control, 5... Consumable electrode (wire), 6... Wire feeding roller, 7
... Base material, 9 ... Inverter drive circuit, 10 ...
Pulse width control circuit, 11... Welding current detector, 1
2... Welding voltage detector, 13... Wire feed roller drive circuit, 15... CR integral circuit for current control,
17...CR integration circuit for voltage control, 20...Memory for waveform factor setting, 21...Timer for T _h /T _L control, 22... Timer for T _D control, 24... Microprocessor for output control, 25... Short circuit/arc judgment voltage V _j setting device, 26... Condition setting device, 27
...Fine adjustment setting device, 28...Short circuit/arc judgment circuit.

Claims (1)

[Claims] 1. In arc welding in which a consumable electrode is fed at a substantially constant speed and short circuits and arcs are alternately and repeatedly generated between the consumable electrode and the base material, short circuit occurrence and arc generation are prevented. Detected and the following (A) ~ for each short circuit cycle
An arc welding method characterized by carrying out each step (F) sequentially or in combination of two or more of them. (A) After a short circuit occurs, for a predetermined time T _D , the welding power source output is controlled at a constant current to maintain the welding current at a predetermined value determined by the constant current setting level immediately before the short circuit, and the short circuit condition is made uniform. The process of doing. (B) Next, adjust the welding current to the specified constant current setting level I _u
The process of opening the short circuit by rapidly increasing the current to a constant current setting level I _S with a predetermined time constant S _S to a higher constant current setting level I S sufficient to open the short circuit. (C) After the arc occurs, the welding power source output is controlled at a constant voltage to maintain the welding voltage near the relatively high constant voltage setting level V _h for a predetermined time T _h , and during that time, the constant voltage setting level V h is maintained at the above constant voltage setting level V _h. The process of forming and growing droplets on the consumable electrode by using both constant current control that regulates the maximum current value to a constant current setting level that is slightly higher than the current value determined by the arc condition. (D) After a predetermined time T _h has elapsed, the constant voltage setting level is gradually decreased from the above high level V _h to a predetermined low level V _L with a predetermined time constant S _V , and accordingly, the constant voltage setting level is decreased. The constant current setting level, which is slightly higher than the current value determined by the level and arc condition, is gradually decreased with a predetermined time constant S _i toward a predetermined low level I _L to heat the base material while reducing the arc force. The process of doing. (E) A process in which the increase in current caused by the self-control action of the welding power source as the arc length decreases is prevented by constant current control at the above-mentioned low level I _L , and excessive growth of droplets is suppressed. (F) A process in which the current value is shifted to a lower constant current setting level I _n after a predetermined time (T _h + T _L ) has elapsed after arc generation to suppress melting of the consumable electrode and promote short circuiting. . 2 The time T _D for holding the welding current at a predetermined value is:
The arc welding method according to claim 1, characterized in that the variables are determined by the diameter of the consumable electrode and the feed rate. 3 The constant current setting level I _u is a variable determined by the diameter of the consumable electrode and the feeding speed, and the constant current setting level I _S and the time constant S _S for changing the constant current setting level from I _u to I _S The arc welding method according to claim 1, wherein is constant regardless of the feeding speed of the consumable electrode. 4 After the short circuit occurs, only if the short circuit continues even after the predetermined time T _D has elapsed, the process moves to the process of opening the short circuit, and if arcing is detected before the predetermined time T _D has elapsed. 2. The arc welding method according to claim 1, wherein: continues the process being executed. 5 Constant voltage setting levels V _h , V _L , constant current setting levels I _S , I _u , I _L , I _n and time constants S _S , S _V , S _i are the feeding speed of the consumable electrode, the average welding current The arc welding method according to claim 1, wherein the variable is determined based on one of: and an average welding voltage.