KR890002517B1 - Out put control of short circuit welding power source - Google Patents

Abstract

A method for controlling the output current levels of a power source for gas shield is for welding where between a consumable electrode and a work-piece short circuits and arcings are produced in succession, wherein the short circuit between the consumable electrode and the workpiece is detected by a short dircuit detecting means, and in response thereto a timer for measuring a set time is switched on, after the expiration of which set time of the short circuit current is adjusted by a control means to a relatively high level, during the flow of which the welding voltage is kept in level between the terminal of the consumable electrode and the workpiece.

Description

Short Circuit Welding Power Output Control

1 is a schematic diagram showing the steps in which a molten drop is formed and carried out.

2 is a waveform diagram of a welding current and a voltage in a conventional method of welding a consumed electrode arc.

3 is a waveform diagram of a welding current and voltage in arc welding of a consumed electrode according to the method of the present invention.

4 and 5 are waveform diagrams of welding current and voltage shown on an oscilloscope in Example 2 of the present invention.

6 and 7 are waveform diagrams of welding current and voltage shown on an oscilloscope in Comparative Example 2 showing a conventional method.

8 is a block diagram of an output control system embodying the present invention.

9 is a diagram showing rise characteristics of a short circuit current according to the control of the FIG. 8 system and a short circuit current by a conventional power supply.

Figure 10 is a weld current and voltage waveform diagram used to illustrate the detection of necking in a short circuit phase from changes in the weld voltage.

11 is a block diagram of an output control system configured to operate in accordance with the principles of FIG.

12 is a diagram showing the wire feed rate of the secondary function.

Fig. 13 is a diagram showing the wire feed speed of the linear function.

값 사이의 관계를 나타낸 도.14 shows the wire feed rate

Figure showing the relationship between values.

FIG. 15 shows the relationship between peak-peak arc current I _AP and peak-current retention time T _AP .

16 shows the relationship between welding voltage and current at different welding current change rates.

The present invention relates to a method for controlling a welding power source, particularly a method for controlling the output of a power source in short circuit welding in which a short phase and an arc phase alternately freeze between the consumed electrode and the base material.

FIG. 1 shows a continuous step in which a volume is formed and carried out within one period of the electrode welding process in which a short circuit and arc phase alternately occur. In this figure, 1 is a consumable electrode (hereinafter simply referred to simply as “welding wire”), 2 is a volume formed at the tip end of the welding wire 1, 3 is an arc, 4 is a welding pool or a workpiece. Furthermore, (a) denotes the initial stage of a short circuit in which volume 2 begins to contact the welding pool 4, and (b) denotes a short circuit in which the volume 2 is brought into contact with the welding pool 4; (C) indicates the final stage of the short circuit occurring between the welding wire (1) and the welding pool (4) as a result of the necking (2) being transferred to the welding pool (4), (d) indicates the moment of retrying the arc (3), (e) indicates the initial arc stage at which the tip end of the welding wire (1) melts and the volume (2) is increasing at the tip end, (f ) And (g) denote arc steps immediately before forming a short circuit by the volume 2 intended to contact the welding pool 4. Steps (a) to (g) are repeated during the welding operation.

Referring to FIG. 2, a waveform diagram of a welding current and voltage of a conventional welding power source having a constant potential characteristic by using a combination of reactors is shown. In Fig. 2, reference characters (a) to (g) indicate the details of the waveform and correspond to the volume forming and transitioning steps (a) to (g) of Fig. 1, respectively.

값에 비례하여 용접전류는 전류(I=E/R)를 향하여 감소한다. 그러나 용접전압이 높은 평균값을 가질 경우, 즉 용접전류가 높은 평균값을 가질 경우 큰 전류가 (g)단계에서 흐르게 되어 단락화를 억압시킨다. 그밖에 용접전원이 일정한 전위특성을 가질때 전류증가에 의해 아아크 길이의 감소가 초래된다. 결과적으로 단락화가 매우 어렵게 되어 용적이 큰 크기로 성장하며 불규칙한 단락주기뿐 아니라 매우 큰 용적이 튀는 결과가 발생된다.In the case of such a conventional welding power source, various problems often occur as follows. That is, in step (a), if the welding current starts to increase with a constant time constant immediately after the short circuit between the volume 2 and the welding pool 4, the contact portion A of the volume 2 and the welding pool 4 is increased. When the cross-sectional area is small, that is, when the welding current increases before the volume 2 is transferred to the welding pool 4, the short circuit collapses and arcs are generated, causing spattering. In steps (c) and (d), necking is generated in the volume (2), and the short circuit collapses to cause arcing again. The welding current reaches its peak at this rearking time and a large amount of spatter is generated by the repulsive energy of the arc that vibrates with the welding pool 4. In step (d) and (e), which occurs following the onset of arc, the welding current increases if the short-circuit period immediately preceding is long, and the welding current decreases if it precedes the short-circuit period. Therefore, the volume (2) size is formed in step (d), becomes irregular in steps (e) and (f), and the non-melting portion of the welding wire (1) is too small in the step (g) when the bending size is too small. And the welding operation is performed in a very unstable state. Furthermore, the welding current should be small in step (g) to advance the volume (2) towards the welding pool to facilitate short circuiting. However, at this stage, as shown in FIG. 2, according to the inductance L, the output voltage E and the equivalent resistance R in the circuit.

In proportion to the value, the welding current decreases toward the current I = E / R. However, when the welding voltage has a high average value, that is, when the welding current has a high average value, a large current flows in step (g) to suppress the short circuit. In addition, when the welding power source has a constant potential characteristic, the arc length is reduced by increasing the current. As a result, short circuiting becomes very difficult, resulting in large volumes, resulting in splashing of very large volumes as well as irregular short-circuit periods.

Related art U.S. 4 column 43-63 of patent 3,792,225.

In view of the state of the art as described above, an object of the present application is a method of controlling the output level of a consumable electrode arc welding power supply in a manner to reduce sputtering by stabilizing alternately repeating short circuits and arc phases. To provide.

A more detailed object of the present invention is to provide a method for controlling the output of the power supply on the short circuit and arc of the immersion electrode immersion transition welding in a manner that ensures a stable and high performance in a state that sputtering is reduced to a detectably reduced level. will be.

Another object of the present invention is to consider the reaction between molten metal and arc, in addition to the optimum level of power output in immersion welding, as well as changes in other conditions that adversely affect the arc extension length, welding wire feed rate or quality of welding operation. To provide a way to control it.

According to the basic feature of the present invention, in the method of controlling the power output of the arc electrode arc welding, in which the short and arc phases alternately occur between the electrode and the workpiece in the shield gas atmosphere, the method is a short circuit between the electrode and the workpiece. A first step of maintaining the welding current at a relatively low level first value in accordance with the setting of? A second step of maintaining the welding current at a second value of a relatively high level following the first step; A third step of lowering the welding current to a low level third value upon detection of the necking as a notice of collapse of the short-circuit molten metal between the electrode and the workpiece; A fourth step in which arcing occurs across the gap between the electrode and the workpiece at the end of the third step, while maintaining the welding current at a relatively high level of fourth value exceeding the average welding current value; And a fifth step of maintaining the welding current at a relatively low level fifth value until the gap between the electrode and the workpiece is shorted under the control of a substantially constant current characteristic to supply a constant level current regardless of the change in arc length. There is provided a method comprising repeating an operation cycle consisting of.

The above described method of the present invention can be reduced by various means acting on other principles or other variables which will be discussed in detail later.

The foregoing and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the appended claims shown by some preferred embodiments of the invention.

In the present invention, the welding wire is supplied toward the workpiece through the contact tube while the shield gas is blown from the nozzle by the arc enclosing across the gap between the welding wire and the workpiece, and the arc and short phases alternately. The present invention relates to output control of a power source in repeated arc arc welding.

Referring to FIG. 3, the output waveforms of known currents and voltages are shown to be optimal as a result of a detailed study on the welding current during the arcing electrode arc welding process including alternating short and arc phases. In Fig. 3, reference characters (a) to (g) pointing out specific points above the current voltage waveforms correspond to steps (a) to (g), respectively, which form and implement the volume of Fig. 1.

Immediately after the short-circuit of the welding wire 1 and the welding pool 4 in steps (a) and (b), the welding current is measured by the volume (2) and the contact portion (A) of the welding pool (4) with the volume (2) and welding pool. It should be low level (I _D ) so as not to weaken the force of welding current which prevents strong contact between them. The current is maintained at low level I _D for optimally 1.5 to 2.5 msec for 1 to 4 msec time period T _D. In order that the pinching force of the current does not reach the contact portion A between the volume 2 and the welding pool 4, it is desired that the current is as small as possible and is generally less than 100A. It has also been found that when the welding wire 1 is at a low feed rate, the current I _D must be lower than that.

In step (b) where the coupling between the volume 2 and the welding pool 4 becomes strong, a high current (I _SP ) having suitable joule energy and pinching force is applied to transfer the volume 2 to the welding pool 4. Accelerate This peak current is applied for the purpose of prompting the transition of the volume 2 before the non-melted portion of the welding wire is inserted into the welding pool 4 and rebuilding the molten metal necking after the transition. If the peak current (I _SP ) is not applied, the welding state becomes extremely unstable. The peak current (I _SP ) is applied during the intervening time until the necking step (c) occurs in the molten metal (2), which varies in the range of 1 to 5 mese and is difficult to propose as a specific value. However, in order to stop the application of peak-to-peak current (I _SP ) according to the range of necking and to automatically control the current, detecting the necking of molten metal by the change of resistance, voltage or current through the welding wire and the workpiece is required. need. For example, the necking of molten metal can be detected by a change in voltage per constant time (differential value dv / dt) through the weld wire and the workpiece or by various methods to be described later.

In step (c) where the necking occurs in the molten metal (2), the welding current is rapidly reduced to low level (I _RA ) and arc is generated through the gap in the next step (d). In step (c), the abrupt decrease in the welding current is partially caused by the weakening of the arc pressure applied to the welding pool during the arcing and arcing caused by the collapse of the neck portion of the molten metal 2. If the arc pressure is increased, the welding pool 4 is damaged even if a bead is pushed toward the outer circumference of the bead or a portion of the welding pool is spattered.

In step (c), a question may arise that the decrease in current makes it difficult to collapse the molten metal and resume the arc. However, once the volume is necked to some extent, it collapses by surface tension. Therefore, the high current I _SP is applied until the necking proceeds to the extent that the molten metal 2 collapses due to surface tension and gravity. On the other hand the low level current I _RA varies depending on the wire feed rate but preferably in the range of 20 to 200 A. If the current I _RA is less than 20 A, the likelihood of arc stop during rearking will be increased and if greater than 200 A the amount of spatter will be increased. Ideally, the current I _RA should be at the lowest level at which no arc stop occurs and its lower limit is not limited to 20A.

At the time of arc generation, the welding current is increased to the peak level (I _AP ) in step (d) and maintained at that level for a predetermined time extended to step (e). The period T _AP from step (d) to step (e) is a period in which a volume is formed at the tip of the welding wire for the transition to the welding pool at the next short. The period T _AP and the current value I _AP are determined such that the volume grows to the desired size during the period T _AP . If a short circuit is formed between the welding wire and the molten pool during this period (T _AP ), the non-melting portion of the welding wire will be immersed in the welding pool due to premature growth of the volume, delaying rearking and damaging the stability of the welding operation. This will go The current I _{AP in} this period T _AP must therefore be at a high level sufficient to prevent the occurrence of a short circuit.

The peak current I _AP sufficient to prevent a short circuit during the period T _AP varies with the welding wire feed rate. For example, when the wire feed speed is 5.2m / min, it is about 260A (average welding current: 180A), and when the wire feed speed is 8.4m / min, it is about 340A (average welding current: 240A). The current level I _AP must be higher than the average welding current value. Furthermore, increasing the current to a sufficiently high level is useful for preventing short circuits during the period T _AP as described above, but is also effective for returning to a constant potential characteristic that suppresses short circuits by increasing the current with decreasing arc length. to be. In this case, the increase in current is related to the arcing force, as well as the exhaustion speed of the welded wire to widen the gap between the volume and the molten pond.

During the time T _AP , following the formation of the volume, in the following steps (e) and (f), the welding current is kept at a low level (I _AB ) in order to short the volume to the molten pool as much as possible. This means that in the case of constant dislocation characteristics, the current increases with decreasing arc length, so the arc force increases with the approach of the short circuit and the welding pool is increased by increasing the arc force in a way that maintains the gap between the volume and the welding pool. The state which suppresses and therefore suppresses a short circuit arises. Therefore, it is desirable to have a substantially constant current characteristic in steps (e) and (f) to supply a constant current regardless of the decrease in the arc length. In addition, if the level of the current I _AB is too high, the short circuit is delayed and the volume is unnecessarily increased to a large size, causing an irregular short period, and a large volume spatter is generated. The low arcing current I _AB is maintained until step (g) where a short occurs.

The states in the five stages described above occur continuously in one period of work and are subsequently repeated. Since the steps are related to each other, omission of any of these steps does not satisfy three fundamental conditions: spatter reduction, good bead shape and arc stability.

Given below is an example of the above-described method of the present invention compared with the corresponding example of the conventional method.

[Yes]

The following are the welding conditions commonly used in Examples 1 to 3 below.

Welding Wire: YCW-2, Diameter 1.2mm

Sealed gas: Co ₂ , 20ℓ / min

Workpiece: SS41, thickness 12mm

Welding method: Bead-on-plate welding for 10 minutes using a welding torch supported on the carriage.

Other welding conditions such as wire feed rate, time T _D and T _AP , current level I _D , I _SP , I _RA , and I _{AP of the} example of the invention are listed along with the wire feed rate and average current level of the conventional example. It is shown in 1.

TABLE 1

The quality of the work was evaluated according to the amount of spatter measured using the weight of spatter accumulated in the nozzle for 10 minutes, the arc stability and the bead geometry observed from the welding current waveform shown on the oscilloscope. The results of the evaluation are shown in Table 2 together with the results of the evaluation of the conventional examples 1 to 3.

TABLE 2

4 and 5, the waveforms of the welding current and voltage in Example 2 observed by the oscilloscope are shown. In FIG. 5, the waveform is shown on the time axis of the scale smaller than FIG. On the other hand, Figs. 6 and 7 show waveforms of the welding current and voltage in the conventional example 2 observed in the oscilloscope, and the time axis of Fig. 7 is smaller than that of Fig. 6.

As is apparent from Table 2, in any of Examples 1 to 3 of the present invention, the amount of spatter is reduced from 1/5 to 1/6 of the amount indicated by the conventional method.

As shown in FIG. 4, the welding current in the method of the present invention is regular in the period and peak value of the welding current. This means that shorting and arcing are repeated regularly with stability in arcing force, arc length, volume diameter, shorting characteristics and weld pool conditions. In other words, according to the method of the present invention, it is possible to reduce the amount of spatters and obtain a uniform and clean bead contour while improving the work quality of the welding operation that does not require any supporting method. On the other hand, in the conventional method, the waveform of the welding current is irregular in period and peak, as shown in FIG. It is shown that shorting and arcing occur in an irregular fashion with variations in arc force, arc length and volume diameter. In other words, the operation according to the conventional method is difficult due to the instability of the arc, the disturbance of the welding pool and the large amount of spatter. It is sometimes damaged by varying arcing forces, which sometimes reach extremely high levels.

According to the method of the present invention in actual operation, the stability of the arc was confirmed from the neck side and the arc sound corresponding to the waveform of FIG.

In the first step described above, it is desirable to adjust the duration of time to the first step depending on whether or not the arc is present immediately before the generation of the short. 8 and 9 show an output control system that can be used for this purpose.

A system for detecting the welding voltage and controlling the output of the welding power source including a welding voltage detector 5 connected to the input terminal of the shorting detector 6 and the arc extinction detector 7 is shown in more detail in FIG. The output terminal of the short circuit detector 6 is connected to the first input terminal of the OR circuit 8, the first reverse phase input terminal of the AND circuit 9, and the first input terminal of the AND circuit 10. The output terminal of the arc extinction detector 7 is connected to the second input terminal of the OR circuit 8 and the second reverse phase input terminal of the AND circuit 9. The output terminal of the OR circuit 8 is connected to the input terminal of the switch driving circuit 14 which opens and closes the switch 11. On the other hand, the output terminal of the AND circuit 9 is connected to the input terminal of the switch driving circuit 14 which opens and closes the switch 13. The switches 11 and 13 are connected in series between a power supply for supplying a positive voltage + V and a negative voltage -V, respectively. The node P1 between the switches 11 and 13 is connected to the first input terminal of the operational amplifier 16 via a resistor 15, and the capacitor 17 is connected to the output terminal of the operational amplifier 16. It is connected between the input terminals of 1. The second input terminal of the operational amplifier 16 is grounded. Furthermore, the output terminal P2 of the operational amplifier 16 is connected to the first input terminal of the comparator 18. The second input terminal of the comparator 18 is grounded and its output terminal P3 is connected to the second input terminal of the AND circuit 10. The output terminal of the AND circuit 10 is connected to the input terminal of the circuit 19 for setting the second stage current I _SP, and the output terminal of the circuit 19 is connected to the input terminal of the welding power supply 20. The timer is formed by a portion surrounded by a chain, including the switches 11 and 13, resistor 15, capacitor 17, operational amplifier 16, and comparator 18 described above.

When the welding operation is performed by alternately shorting and arcing, a short circuit is detected by the short circuit detector 6 receiving a signal from the welding voltage detector 5 indicating the welding voltage level. In the detection of a short circuit, the detector 6 generates an output signal of "high" level, and the OR and AND circuits 8 and 9 generate output signals of "high" and "low" level, respectively. The switch 11 is then closed by the operation of the switch driving circuit 12 and the switch 13 is opened by the operation of the switch driving circuit 14. Therefore, the voltage at the output terminal P2 of the operational amplifier 16 is reduced in accordance with the time constant determined by the resistor 15 and the capacitor 17. If the voltage at output P2 drops to OV or lower, comparator 18 generates a signal of "high" level at its output P3. The signal at the terminal P3 is supplied to the second stage current I _SP setting circuit 19 through the AND circuit 10, and the circuit 19 outputs the welding power supply 20 to the second stage high level current I _SP . Generates a signal to send. Thus, the second stage current I _SP is supplied to the welding wire 1.

When there is no short circuit or arc extinction In other words, when there is an arc, the thrust signals of the short circuit detector 6 and the arc extinction detector 7 are both "low" levels so that the output signals of the OR and AND circuits 8 and 9 are respectively "low". ”And“ high ”levels. Therefore, the switch 11 is opened by the operation of the switch driving circuit 12 and the switch 13 is closed by the operation of the switch driving circuit 14. Therefore, the output terminal P2 of the operational amplifier 16 has a positive voltage and the output terminal P2 of the comparator 18 is at the "low" level. The output signal of the AND circuit 10 is at the "low" level, so that the signal command output of the short circuit current is not supplied from the second stage current I _SP setting circuit 19 to the welding power supply 20. If arc dissipation occurs during the arcing period, it is detected by the arc dissipation detector (7) and its output, making the output signals of the OR and AND circuits (8 and 9) the "high" and "low" levels, respectively. The signal goes up to the "high" level. As a result, the switch 11 is closed by the operation of the switch driving circuit 12, and the switch 13 is opened by the operation of the switch driving circuit 14, and is determined by the resistor 15 and the capacitor 17. . The voltage at the output terminal P2 of the operational amplifier 16 is lowered in accordance with the time constant. As soon as the voltage at terminal P2 drops lower to OV, the output terminal P3 of comparator 18 goes to the "high" level. From there, if the short circuit occurs due to the contact of the volume at the end of the welding wire with the welding pool, the output signal of the OR circuit 8 is continuously made high while the output signal of the OR circuit 8 is continuously made. The output stage of the short circuit detector 6 is at the "high" level while maintaining the "high" level. The short circuit current setting circuit 19 thus functions to supply the welding power supply 20 with the signal command output of the second stage current I _SP . In response to this signal, the welding power supply 20 supplies a second stage current to the welding wire.

Prior to the start of welding, there is no arc between the gaps so that the arc extinction detector 7 acts to maintain the output signals of the OR and AND circuits 8 and 9 at the "high" and "low" levels, respectively. Furthermore, the switches 11 and 13 are closed and kept open by the switch drive circuits 12 and 14, respectively.

Thus, a negative voltage appears at the output terminal P2 of the operational amplifier 16 while generating an output signal of "high" level at the output terminal P3. If the welding wire 1 is shorted to the workpiece 4 to cause arcing in this state, the short circuit detector 6 acts to produce a “high” level signal at its output and a signal of the second stage current I _SP . The output of the AND circuit 10 is brought to a "high" level while acting to operate the second stage current I _SP setting circuit 19 to supply the welding power supply 20 to the command output. In response, the welding power supply 20 supplies a second stage current I _SP of the "high" level. In other words, when the arc starts, a high level second stage current I _SP is supplied as soon as the welding wire is shorted to the workpiece, forming arc at the rupture of the molten metal bridge and forming a short volume at the end of the welding wire. do.

In such a system, an arc dissipation detector 7 consists of a comparator for outputting a "high" level signal which receives a no-load voltage from the welding voltage detector 5 with a preset comparison level signal. While no-load voltage is about 65V when arc disappears, welding voltage is 20-45V when arc is generated. Thus, the detector can detect arc disappearance by setting a comparison level between the welding voltage and the no-load voltage in advance. Another extinction detector 7 consists of a comparator which emits a signal of "high" level when there is no current signal from the welding current detector 4 (as indicated by the dotted line in FIG. 8).

As is apparent from the current increase diagram in FIG. 9, the short circuit current is short circuited without a first stage when arc starts and under normal welding operation, as opposed to the low rate of increase of the short circuit current supplied from a conventional power supply. After a preset time of the first stage, there is a rapid increase to the second stage current level immediately.

V가 미리 설정된 값에 도달할 때, 즉

V=V_M-V_L의 값이 미리 설정된 값과 같을때 용접전류를 낮추도록 조정되어 있다. 비록 스패터가 이러한 조절에 의해 상당한 정도까지 감소될 수 있지만, 다음 식으로 표현할 수 있듯이 제 2 단계로부터 경과된 시간 t-5 에 와이어 신장의 저항에 있어서의 증가에 따른 전압증가 V_N을 조절하는 것이 바람직하다.In order to prevent the spatter from spawning at the start of the arc, the control circuit is forced to terminate the second phase period in the short circuit when the necking occurs in the shorting molten metal between the welding wire and the workpiece. Difference between the minimum welding voltage V _L at time and the voltage V _M at the next instant

When V reaches a preset value, i.e.

It is adjusted to lower the welding current when the value of V = V _M -V _L is equal to the preset value. Although the spatter can be reduced to a significant extent by this adjustment, it can be expressed by the following equation that adjusts the voltage increase V _N with an increase in the resistance of the wire extension at the time t-5 elapsed from the second step. It is preferable.

Where V (t) is the welding voltage in the second step, k is a constant depending on the welding wire diameter and material. The integration starts to calculate V _N at the beginning of the second phase.

동안의 전압증가

는 특별한 함수 V(t)에 따라서 계산된다. 이후에 용접전압 V_M은 계속적으로 측정되고 용접전류는 네킹이 생기는 순간에 해당하는,

V=V_M-(V_L+V_N)가 미리 설정된 시간에 도달할때의 시간 t₁에서 낮아진다. 실험결과에 따르면 용접와이어 직경은 1.2mm, 첨두치 전류 I_SP는 400A,

V는 0.3-0.6V 그리고 1msec후의 전압 V_N은 0.2-0.25V이다. 제11도에 보인 것은 이러한 효과를 내기 위해 만들어진 제어시스템의 한 예이다. 여기서 적분회로(111)은 한단자(111a)에서 용접토치(104)와 공작물(106)사이의 전압을 검지하는 전압검지기(112)의 출력을 받고 다른 단자(111b)에서는 용접와이어(103)을 통해 흐르는 전류를 표시하는 용접전류 검지기(113)로부터 제공되는 신호를 받아서 와이어(103)를 통한 용접전류가 제 2 단계 전류레벨 I_SP에 도달하는 시점으로부터, 예를들면 제10도의 점b로부터, 용접전압을 적분한다. 최소전압 메모리(114)는 단락상태에서 용접전류가 제 2 단계 전류레벨 I_SP에 도달한 후의 가장 낮은 전압값을 저장한다.In the short circuit state of the welding operation, the minimum welding voltage V _L is stored in the memory after the welding current reaches the second stage level I _{SP as shown} in FIG. Then period

Voltage increase during

Is calculated according to the special function V (t). After that, the welding voltage V _M is continuously measured and the welding current corresponds to the moment when the necking occurs.

It decreases at time t ₁ when V = V _M- (V _L + V _N ) reaches a preset time. Experimental results show that the weld wire diameter is 1.2mm, peak current I _SP is 400A,

V is 0.3-0.6V and the voltage V _N after 1 msec is 0.2-0.25V. Shown in FIG. 11 is an example of a control system designed to achieve this effect. Here, the integrating circuit 111 receives the output of the voltage detector 112 which detects the voltage between the welding torch 104 and the workpiece 106 at one terminal 111a and the welding wire 103 at the other terminal 111b. From the time point at which the welding current through the wire 103 reaches the second stage current level I _SP in response to the signal provided from the welding current detector 113 indicating the current flowing through, for example from point b of FIG. Integrate the welding voltage. The minimum voltage memory 114 stores the lowest voltage value after the welding current reaches the second stage current level I _SP in a short circuit state.

V=V_M-(V_L+V_N)을 계산하는 감산기이다. 계산결과

V는 다른 입력단에서 네킹전압 제어로부터 미리 설정된 값 E_V의 신호를 받는 비교기(116)의 한 입력단자에 공급된다. 비교기(116)는

V=E_V의 조건이 도달할때 아아크화 할때 시패터를 발생시키는 많은 레벨까지 용접전류를 낮추도록 전원에 신호를 보낸다.Shown at 115 is the signal of the welding voltage V _M from the voltage detector 112, the signal of the voltage V _N integrated from the integrating circuit 111, and the signal of the lowest voltage V _L from the minimum voltage memory 114.

A subtractor that calculates V = V _M- (V _L + V _N ). Calculation result

V is supplied to one input terminal of the comparator 116 which receives a signal of a predetermined value E _V from the necking voltage control at the other input terminal. Comparator 116

When the condition of V = E _V is reached, it sends a signal to the power supply to lower the welding current to a large level, which generates a shifter when arcing.

R=R_M-(R_L+R_N)의 값이 각 단락상에서 미리 설정된 값에 도달할때 용접전류를 낮춘다. 전번식에서 R_M은 네킹이 생기는 시점에서의 저항, R_L은 단락상에서 최소 저항이고 R_N은 단락화 후에 주어진 길이의 시간의 저항의 증가이다.Similar effects can be obtained by adjusting the output control system to lower the welding current by detecting the necking of the shorting volume from the calculation of the resistance of the welding wire on each short. These systems

When the value of R = R _M- (R _L + R _N ) reaches the preset value in each short circuit, lower the welding current. In the previous formula, R _M is the resistance at the time of necking, R _L is the minimum resistance in the short and R _N is the increase in the resistance of the given length of time after the short.

Alternatively, the necking of the molten metal bridge reduces the welding current when the differential value dv / dt of the welding current V reaches a predetermined value determined by the duration and wire extension length of the second stage. It is detected by continuously detecting the welding current to increase to the necking point by the decrease in the partial region of the short-circuit metal bridge on each short-circuit shown in Figs. This method makes it possible to detect the timing of necking free of errors due to changes in wire elongation lengths and durations in short circuits that sometimes occur in actual welding operations.

까지의 전압증가를 미분하는 용접전압 검지기의 출력신호를 받는 미분기를 포함한다. 미분기에 의해서 생성되는 dv/dt의 신호는 dv/dt의 값과 미리 설정된 값을 비교하는 비교기에 공급되면 만일 미분값 dv/dt가 미리 설정된 값보다 더 커지게 되면, 용접전류를 낮추기 위해 전원의 전류제어에 신호를 보낸다.In this case, the control system is time

It includes a differentiator that receives the output signal of the welding voltage detector to differentiate the voltage increase up to. The signal of dv / dt generated by the differentiator is supplied to the comparator comparing the value of dv / dt with the preset value. If the derivative value dv / dt becomes larger than the preset value, the power supply is lowered to lower the welding current. Send a signal to the current control.

The point of necking on a short can also be detected in a similar way by measuring the resistance between the welding wire and the workpiece on the short and using the differential resistance dR / dt as the working element instead of the differential voltage dv / dt.

Furthermore, to minimize spatter generation and to systematically repeat shorting and arcing, a waveform generator connected to the wire feed motor speed detector and designed to generate a function f (WFR) that changes as indicated by the dotted line in FIG. By using, it is desirable to change the short-circuit peak current I _SP as a function of the wire feed rate WFR in order to control the peak current I _SP at the best level for a given wire feed rate.

The relationship between the wire feed rate WFR and the function f (WFR) is determined experimentally so that the peak I _SP is at the best level to ensure smooth and spatter-free welding operation in the following manner.

Experiments show that the peak-to-peak current I _SP in the short circuit has a varying threshold level for the wire feed rate WFR shown in solid lines in FIG. In other words, the short-circuit peak current in the range below the threshold level is too low to make the necking within a suitable period, which extends the time interval T _SP and destabilizes the welding operation due to the wire sticking to the workpiece. On the other hand, welding the threshold level conforms to the capacity of the power supply apparatus is possible, but, even though the peak-to-peak maximum acceptable level of the current I _SP supplies power to the welding wire in the above range, the higher the peak current I _SP higher, The amount of spatter is higher. Therefore, the function I _SP = f (WFR), which controls the short-circuit peak current I _SP according to the wire feed speed, must be determined to fall within a range sufficiently higher than the threshold level indicated by the solid line in FIG. 12 to ensure stable welding operation. At the same time it is desirable to place it as close to the solid line as possible to keep the spatter to a minimum.

Too high a peak current I _SP will shorten the peak current period T _SP to increase sputtering. It is known from many experiments that the high current period T _SP , which also depends on the diameter of the weld wire, is optimal in the range of about 1 to 3 msec to regularly repeat short circuits and arcs. Therefore, it is desirable to determine the function by considering these factors.

Taking into account the peak current I _SP in relation to the type and diameter of the weld wire and its critical level with respect to the wire feed rate WFR, the function f (WFR) is expressed as a quadratic function as indicated by the dotted line in FIG. Can be. Instead of the second function, it may be close to the first function as indicated by the dashed line in FIG. 13 within a range that does not cause a problem in the actual operation. As for the control of the arc current, it is experimentally known that the peak current value I _AP in the arc phase should be determined in relation to the peak current bow time value T _AP in terms of suppressing the spatter and performing stable supply of the volume. For example, the peak retention time T _AP is preferably shortened with a high level of peak arc current I _AP . In dip transmission welding, the formation of the volume is considered to proceed in relation to the wire supply speed WFR and the effective value of the welding current, that is, the value of (current) ² x (time).

의 값들은 약 590이었다. 이러한 점에 있어서, 제14도와 같이

의 값들이 서로 다른 와이어 공급속도에서 나타나 있다. 이로부터 알 수 있는바와 같이, 적은 스패터링으로 안정한 아아크상태를 보증할 수 있는 첨두 아아크전류 I_AP와 첨두전류 보유시간 T_AP의 값들은 와이어 공급속도 WFR의 함수로서 표시될 수 있다. 예를들면,

의 값은 제14도에 나타낸 바와같이 와이어 공급속도 WFR의 1차함수로서 표시될 수 있다.

=a·WFR+b(단, a와 b는 상수)로 근사시키면, 적합한 I² _AP과 T_AP의 값

는 와이어 공급속도 WFR로부터 결정될 수 있다.A study of the relationship between peak arc current I _AP and / or peak current retention time T _AP with respect to wire feed rate WFR has shown that I ² _AP × T _AP takes similar values at a given wire feed rate WFR. For example, if the welding wire feed rate is 3.6 m / min

The values of were about 590. In this respect, as shown in FIG.

Are shown at different wire feed rates. As can be seen from this, the values of the peak arc current I _AP and the peak current holding time T _AP , which can guarantee a stable arcing condition with less sputtering, can be expressed as a function of the wire feed rate WFR. For example,

Can be expressed as the first-order function of the wire feed rate WFR as shown in FIG.

= a · WFR + b (where a and b are constants), the appropriate values of I ² _AP and T _AP

Can be determined from the wire feed rate WFR.

Referring to the relationship between the peak current level I _AP and the peak current period T _AP , FIG. 15 shows various ranges defined by the other peak current value I _AP and the peak current period T _AP showing the following trend.

)용적을 형성하기 위한 에너지가 낮기 때문에 용적의 크기가 작고, 또한 높은 용접 와이어 공급속도(WFR)일때에 와이어의 비용단부가 단락 순간에 용접푸울에 달라붙어서 용접작업은 시작된다.(1) Range of low I _AP and short T _AP

Due to the low energy to form the volume, the volume is small, and at the high welding wire feed rate (WFR), the cost end of the wire sticks to the welding pool at the moment of short-circuit and the welding operation starts.

) 비록 용적은 충분히 커지지만 첨두전류 보우시간치 T_AP가 너무 길고 그렇기때문에 용적이 용접푸울에 도착하기 전에 단락시의 아아크의 배척력에 의해서 파괴되어 버려서, 큰 부피의 스패터가 분산하게 한다.(2) Range of low I _AP and long T _AP

Although the volume is large enough, the peak current bow time value T _AP is so long that it is destroyed by the arc's retraction force in the short-circuit before it reaches the welding pool, causing large volumes of spatter to disperse.

) 짧은 첨두전류 보유시간 T_AP뒤에는 긴 낮은 전류(I_AB) 주기가 뒤따르므로서 용적이 커짐에도 불구하고 낮은 전류 주기동안에 아아크 소멸이 일어난다.(3) Range of high I _AP and short T _AP

The short peak current holding time T _AP is followed by a long low current (I _AB ) cycle, leading to arc dissipation during the low current cycle, although the volume increases.

) 용적으 큰 부피로 자라게 되고 따라서 낮은 용접와이어 공급속도(WFR)에서의 작업시에 아아크가 작열해서, 접촉 첨단에 화상을 주고 단락되어질 용적을 파열시키게 된다.(4) Range of high I _{AP and} long T _AP

The volume grows to a large volume and, therefore, the arc burns during operation at a low weld wire feed rate (WFR), which burns the contact tip and ruptures the volume to be shorted.

The optimal range of peak current value I _AP and peak current retention time T _AP , in which the arc is stabilized and the spatter is reduced, changes with the welding wire feed rate.

In controlling the welding current with a constant peak current holding time on the arc, the above-described spatter reduction effect is often canceled by changes in wire supply speed, wire elongation length, and shape and condition of the welding pool. When controlling under a constant peak arc current holding time T _AP , the arc length increases when the welding wire in the peak current period increases due to an increase in wire extension or an external disturbance such as a decrease in the wire supply speed. _This extends the low current period T _AB following the _AP . The result is a reduction in the number of short circuits per unit time, raising the average welding voltage, especially during welding in grooves. On the contrary, when there is a decrease in the wire extension length or an increase in the wire supply speed, the low current vapor is shortened, which causes an increase in the short circuit frequency and a decrease in the average welding voltage. Now, considering only the change in the wire extension length, the wire melt MR is expressed by the following equation.

MR = T _AP (øI _AP + RexI ² _AP ) /11.1 [mm ³ ]

Ø is the anode voltage contributing to the metal melting, the energy to change the welding wire of 25 ℃ to molten steel of 1600 ℃ is 11.1J / mm ³ , Rext is the resistance of the welding wire. Table 3 below shows that when the wire extension length is 10 mm and 20 mm under the condition that the resistance per unit length of the welding wire of T _AP = 11 msec, ø = 4.0V, I _AP = 300A and 1.2 mm diameter is 10 ^-3 l / mm. The volume of the blown wire during the T _AP and the length of the blown wire corresponding thereto are shown.

TABLE 3

As evident from the table above, the volume of the blown wire during T _AP under constant welding current is greater for longer arc elongation and longer wire elongation with less short circuit times. This condition occurs due to the oversupply of energy in the peak current cycle, which is undesirable in terms of quality of work performance.

Therefore, despite changes in external conditions within a certain range, for example, in spite of changes in wire feed speed, etc., in order to reduce the amount of spatter and stabilize the arc, the peak current period T _AP on the arc is extended or shortened. It is desirable to regulate the energy supply to the welding wire. The oversupply or undersupply of energy in the peak current period T _AP is, for example, a change in the length of the low current period T _AP , a change in the sum of the peak current period T _AP and the low current period T _AB , and a change in the short circuit frequency or an average arc. Can be detected from a change in voltage.

Optionally, the control of the peak current I _{AP on} the arc is controlled using a current-voltage characteristic that prevents occurrence of a short circuit in the peak current period T _AP or occurrence of excessive arc length, that is, higher than 10 A / V. The rate is achieved by controlling the increase and decrease of the current that occurs as the welding voltage changes.

To prevent short circuits in the peak current period T _AP on the arc, the welding voltage in the peak current period must be controlled as close to the constant voltage characteristic as possible to keep the arc length constant at the appropriate dimensions. For this purpose, the output of the welding power source is such that the decrease in the welding current due to the increase in the welding voltage or the increase in the welding current due to the decrease in the welding voltage stays at a rate larger than the predetermined value in the peak current period, K. Controlled.

In this example, peak current period T appropriate arc voltage V _REF and the arc current Io preset hameuroseo, peak current period by the equation for T welding current in the _AP for an _AP I _AP is based on the deviation of the actual arc voltage V _FB Is corrected.

I _AP = K (V _REF -V _FB ) + Io

As shown in FIG. 16, as a result of experiments employing a different welding current change rate K in peak current period T _AP , if the current reduction rate due to voltage increase in peak current period is greater than 10 A / V, in particular, the reduction rate is It was heard that greater than 63A / V, the amount of spatter is reduced and the quality of work is improved. Thus, by controlling the peak current period T _AP using the current-voltage characteristic, the possibility of a short circuit in the peak current period T _AP on the arc can be significantly reduced as compared to the constant current control. As a result, it is possible to reduce the melt rate of the welding wire, reduce the arc length, and reduce the size of the volume, thereby preventing large volume spattering. In addition, the increase in the frequency of short circuits accelerates the elimination of arc fluctuations, and maintains a certain distance between the welding wire and the welding pool, preventing the welding pool from shaking and restricting the bead shape. do.

Although the method of the present invention has been described as a preferred embodiment, the present invention is not limited to this particular form, but may be made within the scope of the invention as defined by the appended claims of various changes or modifications.

Claims (15)

A method of controlling the output of a power source in arc welding, in which a short-phase and arc phases occur alternately between a consumed electrode and a workpiece in a sealed gas atmosphere: a short circuit between the gap between the consumed electrode and the workpiece. Forming a first welding current at a relatively low level of a first value; A second step of maintaining the welding current at a relatively high level of a second value following the first step; A third step of lowering a welding current to a third value at a low level when detecting a necking foretelling breakage of the short-circuit steel between the electrode and the workpiece; A fourth step of maintaining a welding current at a relatively high level of a fourth value above the average welding current if arc occurs between the gap between the electrode and the workpiece after the third step; And controlling the substantially constant current characteristic to supply a constant level of current regardless of the change in arc length, thereby maintaining the welding current at a relatively low fifth value until the gap between the electrode and the workpiece is shorted. And a repetition of an operation cycle consisting of a fifth step. The method of claim 1, wherein the time for maintaining the supply of the current of the first value in the first step varies depending on whether or not arc is present between the gap between the electrode and the workpiece just before a short circuit is formed. How to. 3. The method of claim 2, wherein the presence of an arc immediately before short-circuit is detected from a change in welding current. 3. The method of claim 2, wherein the presence of an arc immediately before short-circuit is detected from a change in welding current. 3. A method according to claim 2, wherein the time for maintaining the supply of said current of said first value is lengthened when there is an arc immediately before a short circuit and shortened when it is not present. The method of claim 1, wherein as soon as the value of V = V _M -V _L reaches a predetermined value, the welding voltage is detected and the welding current is lowered to the third value of the third step, wherein v _L is The lowest voltage in the second stage and V _M is the voltage occurring at one subsequent point in the second stage. The method of claim 1 further comprising:

As soon as the value of V = V _M- (V _L + V _N ) reaches a predetermined value, the welding voltage is detected and the welding current is lowered to the third value of the third step, where L _L is the second step. And V _M is the voltage occurring at one subsequent point in the second step, and V _N is the voltage change caused by the change in resistance of the weld wire extension. The method of claim 1, wherein the welding current in the second step is controlled as a function of the supply speed of the consumed electrode. The method of claim 1, wherein the level or duration of the welding current in the fourth step is controlled as a function of the supply speed of the consuming electrode. The method of claim 1, wherein the duration of the high level current in the fourth stage is controlled in accordance with the state of the previous operating cycle. 12. The method of claim 10, wherein the duration of the high level current of the fourth step is controlled in accordance with the length of the low level current period of the fifth step in the immediately preceding operation period. 11. The method of claim 10, wherein the duration of the high level current of the fourth step is controlled in accordance with the sum of the high or low level current periods of the fourth and fifth steps of the immediately preceding operation period. 11. A method according to claim 10, wherein the duration of the high level current of the fourth stage of the next operation period is controlled in accordance with the number of short circuits per unit time. 11. The method of claim 10, wherein the duration of the high level current of the fourth stage of the next operating period is controlled in accordance with the average value of the arc voltage. 2. The method according to claim 1, wherein in the fourth step, the rate of increase or increase of current due to the increase or decrease of the voltage between the gap between the electrode and the workpiece is controlled at a value greater than 10 A / V.

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