JP2019188434A - Control method of ac arc-welding - Google Patents

Abstract

To transfer a droplet to a base material in thick plate welding time by using shield gas including carbon dioxide.SOLUTION: AC arc-welding is executed by alternately repeating a reverse polarity period T1 and a positive polarity period T2. A first step of monotonously increasing a welding current I up to a positive second current value I2 from a negative first current value I1, a second step of controlling so as to continuously reduce the welding current I up to a third current value I3 from the second current value I2 and then continuously increase the welding current I up to a positive fourth current value I4, a third step of detecting a separation start of a droplet 21, a fourth step of monotonously reducing the welding current up to the first current value I1 from the fourth current value I4 after detecting the separation start of the droplet 21 and a fifth step of holding the first current value I1 for a prescribed period, are executed in a welding period Tc being the sum total of the reverse polarity period T1 and the positive polarity period T2. When executing the fourth step or the fifth step, separation of the droplet 21 is completed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control method for AC arc welding.

  In arc welding in which welding is performed by generating an arc between a welding wire and a base material, the transfer form of droplets becomes spray transfer when the critical current value is exceeded. A welding method in which a peak current higher than the critical current value and a base current lower than the critical current value for maintaining the arc are alternately repeated is called pulse arc welding, which is more than direct current spray transfer welding. The spray transfer can be performed with a low average current.

  In the pulse arc welding method, in order to maintain the arc, the droplet transfer is performed during a base current period in which the influence of the arc force is least. Therefore, it is possible to greatly reduce spatter. On the other hand, there are significant restrictions on the shielding gas used during arc welding, and in particular, the use of carbon dioxide gas greatly reduces the spatter reduction effect. Moreover, when it is going to improve a welding speed, there exists a subject that the cycle of a droplet will become unstable, the balance of heat input will be biased, and bead nonuniformity will generate | occur | produce.

  In order to solve such a problem, in AC pulse arc welding, both the electrode positive polarity (reverse polarity) period and the electrode negative polarity (positive polarity) period are provided with a base period and a peak period, respectively. The electrode negative polarity current ratio is a large value by constricting the droplet with the electrode, transferring the droplet to the base material during the electrode negative polarity peak period, and forming the droplet at the tip of the welding wire during the electrode negative polarity base period. Has been proposed (see, for example, Patent Document 1).

JP 2010-075983 A

  However, the prior art disclosed in Patent Document 1 is intended for the welding of aluminum materials, and is intended to form a weld bead with a shallow penetration portion and a large surplus portion. That is, it is intended for thin plate welding, and in order to prevent the base metal from being melted down, it is necessary to increase the heat input to the welding wire while growing the heat input to the base material and grow the droplets. Accordingly, it is necessary to lengthen the positive polarity period or increase the positive current.

  However, when such a method is applied to thick plate welding as it is, the base metal has a poor penetration, and there is a possibility that a weld bead with sufficient strength cannot be obtained. In addition, it has been difficult to form a flat weld bead with a small extra portion.

  The present invention has been made in view of this point, and an object of the present invention is to provide a method for controlling AC arc welding suitable for thick plate welding while reliably removing droplets at a desired timing.

  In order to achieve the above object, a control method for AC arc welding according to the present invention includes a reverse polarity period in which a welding wire is set to a positive potential with respect to a base material, and a negative potential for the welding wire to the base material. A control method for AC arc welding in which welding is performed by alternately repeating positive polarity periods, and the welding current flowing through the welding wire is monotonously increased from a positive first current value to a second current value of opposite polarity. A first step of controlling the welding current to decrease continuously from the second current value to a third current value having a reverse polarity and then continuously increase to a fourth current value having a reverse polarity; A third step of detecting the start of detachment of the droplet formed on the tip of the welding wire; and detecting the start of detachment of the droplet, and then detecting the welding current from the fourth current value to the first 4th monotonically decreasing to current value And a fifth step of controlling the welding current so as to maintain the first current value for a predetermined period, during a welding period that is a sum of the reverse polarity period and the positive polarity period, During the execution of the fourth step or the fifth step, the detachment of the droplet is completed.

  According to this method, a droplet is formed at the tip of the welding wire during the reverse polarity period to detect the start of detachment of the droplet, and during the positive polarity period, a positive current having a predetermined magnitude is applied for a predetermined period. By flowing it through the welding wire, the arc reaction force can be reduced when the droplets are detached, and the droplets can be reliably transferred to the base material during the positive polarity period. In addition, by applying heat to the base material during the reverse polarity period, the arc is stabilized, deep penetration is formed in the base material, and a flat weld bead with few surplus portions can be formed.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to transfer a droplet to a base material reliably at a desired timing, a flat weld bead with few surplus parts can be formed.

It is a schematic diagram which shows the structure of the arc welding apparatus which concerns on one Embodiment of this invention. It is a figure which shows the various output waveforms at the time of the arc welding which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the output waveform of the welding current at the time of arc welding, an arc reaction force, and a heat input state.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

(Embodiment)
[Configuration of arc welding equipment]
FIG. 1 is a schematic configuration diagram of an arc welding apparatus 100 in the present embodiment. The arc welding apparatus 100 includes a primary rectifying unit 2 that rectifies AC power input from an input power supply 1, a switching unit 3 that controls welding output, and an output of the switching unit 3 that is input to convert the power into a power suitable for welding. The transformer 4 is provided.

  The arc welding apparatus 100 includes a secondary rectification unit 5 that rectifies the secondary output of the transformer 4, a reactor 6 that smoothes the output of the secondary rectification unit 5, a drive unit 7 that drives the switching unit 3, and a welding current. A welding current detector 8 for detecting the welding voltage, a welding voltage detector 9 for detecting the welding voltage, and a droplet 21 (see FIG. 5) at the tip of the welding wire 18 based on the outputs of the welding current detector 8 and the welding voltage detector 9. 2), and a droplet detachment detecting unit 10 for detecting detachment.

  The arc welding apparatus 100 further includes a welding condition setting unit 13 and a storage unit 12. The welding condition setting unit 13 sets welding conditions such as a set current, a set voltage, a wire feed amount, a shield gas type, a wire type, and a wire diameter.

  The set current corresponds to the moving average value of the welding current, and the set voltage corresponds to the moving average of the welding voltage.

  The storage unit 12 stores various parameters such as the information set by the welding condition setting unit 13 and the inductance value of the reactor of the electronic reactor control for each wire feed speed. Further, the storage unit 12 stores a feeding amount that is a speed at which the welding wire 18 is fed. The feed amount of the welding wire 18 is determined in proportion to the set current Is set by the operator. The set current Is and the feed amount of the welding wire 18 that is proportional to the set current Is are experimentally derived in advance before the welding operation. The storage unit 12 also stores a plurality of values of welding control parameters corresponding to a plurality of values of the feeding amount of the wire 18.

  The arc welding apparatus 100 further includes an arc control unit 11. The arc control unit 11 controls current and voltage at the time of arc generation based on outputs from the welding voltage detection unit 9, the droplet detachment detection unit 10, and the storage unit 12. Output a signal. Further, the arc control unit 11 has a polarity switching unit 11 a inside, and the polarity switching unit 11 a outputs an output for switching the polarity of the welding current flowing through the welding wire 18 based on the output from the droplet detachment detection unit 10. Generate a signal. From another viewpoint, the polarity switching unit 11 a switches the polarity of the potential of the welding wire 18 with respect to the base material 17 based on the output from the droplet detachment detection unit 10. The drive unit 7 controls the switching unit 3 based on the output of the arc control unit 11 including the polarity switching unit 11a.

  The welding wire 18 is fed by a feeding motor controlled by a wire feeding unit 19. A welding power is supplied to the welding wire 18 via a tip 15 provided on the torch 14, and an arc 20 is generated between the welding wire 18 and the base material 17 to perform welding.

  In addition, each component which comprises the arc welding apparatus 100 shown in FIG. 1 may each be comprised independently, and you may comprise combining a some component.

[Output control during arc welding]
FIG. 2 shows various output waveforms during arc welding according to the present embodiment. The welding current I and the welding voltage V, which are welding outputs, the welding resistance R which is the ratio of the welding voltage V to the welding current I, and the welding wire 18. The transition state of the droplet 21 formed at the tip of the liquid is shown. FIG. 3 shows the relationship between the output waveform of the welding current during arc welding, the arc reaction force, and the heat input state.

  In the arc welding shown in the present embodiment, the welding voltage V and the welding current I, which are welding outputs, are set based on the set voltage Vs that sets the output of the welding voltage V and the set current Is that sets the output of the welding current I. Is controlled. Here, the set voltage Vs is set in advance before the welding operation. During arc welding, disturbances such as fluctuations in the protruding length of the welding wire 18 protruding from the torch 15 and displacement of the base material 17 occur. For this reason, the arc welding shown in this embodiment mainly performs constant voltage control resistant to disturbance based on the set current Is and the set voltage Vs. However, constant current control is performed in some periods.

  In the present embodiment, the base material 17 is a thick plate made of mild steel or high-tensile steel. Here, the “thick plate” refers to a plate material having a plate thickness of 3.2 mm or more. The shield gas sprayed onto the base material 17 is a gas mainly composed of carbon dioxide. Here, the “gas mainly composed of carbon dioxide” refers to a gas containing 30% or more of carbon dioxide. In addition, as a component other than carbon dioxide gas, for example, argon gas is included.

  In the following description, “reverse polarity” means a case where the welding wire 18 is at a positive potential with respect to the base material 17, and the moving direction of electrons in the arc 20 is from the base material 17 to the welding wire 18. The direction of movement. Further, as shown in FIG. 3, when the arc 20 is generated in this state, heat is input to the base material 17. The welding current I flowing through the welding wire 18 in the reverse polarity state may be referred to as a reverse polarity current. “Positive polarity” refers to the case where the welding wire 18 has a negative potential with respect to the base material 17, and the direction in which electrons move in the arc 20 moves from the welding wire 18 to the base material 17. . Further, as shown in FIG. 3, when the arc 20 is generated in this state, heat is input to the base material 17. The welding current I flowing through the welding wire 18 in a positive state may be referred to as a positive current.

  In the present embodiment, the reverse polarity current is a current having a positive current value, and the positive current is a current having a negative current value. Therefore, for example, when changing a reverse polarity welding current having a predetermined finite value to a positive polarity welding current having another finite value, it is said that the welding current I is decreased, and the positive polarity having a predetermined finite value. When the welding current is changed to a welding current of reverse polarity having another finite value, the welding current I is said to be increased.

  Further, a period in which the reverse polarity current flows in the welding wire 18 is a period T1, and a period in which the positive current flows is a period T2 (see FIGS. 2 and 3).

  Hereinafter, AC arc welding using the arc welding apparatus 100 of the present embodiment will be described.

  The welding output is controlled by constant current control from the time point when the welding current I shown in FIG. 2 reaches the fourth current value I4 to the time point t2. Further, as shown in FIG. 2, the welding current I is zero at the time point t1, the welding current I is monotonously increased with time, and reaches the second current value I2 at the time point t2 (first step). . Further, during this period, as shown in the droplet transfer state (a) at the time point ta, the tip of the welding wire 18 starts to melt, but does not reach the formation of the droplet 21. In this period, the welding voltage V and the welding resistance R also monotonously increase. Note that the welding current I increases monotonously with a predetermined slope α from time t1 to time t2.

  At time t2, the arc control unit 11 switches the control of the welding output to the constant voltage control. At this time, as shown in FIG. 2, the welding voltage V is controlled by the arc control unit 11 so that the moving average becomes equal to the set voltage Vs.

  Further, the welding current I is controlled to continuously decrease from the second current value I2, and reaches the third current value I3 at time t3. Further, as time elapses from time t3, the welding current I is controlled to increase continuously and reaches the fourth current value I4 (second step).

  In the period from the time point t2 to the time point t3, although continuously decreasing, a welding current I sufficient to melt the welding wire 18 flows. Therefore, as shown in the droplet transfer state (b) at the time point tb, during the period from the time point t2 to the time point t3, the droplet 21 is formed at the tip of the welding wire 18 and grows.

  In a period in which the welding current I continuously increases from the time point t3, the droplet 21 formed at the tip of the welding wire 18 further grows, and as shown in the droplet transfer state (c) at the time point tc, Constriction begins to form at the top of the drop 21. In such a state, the arc length of the arc 20 becomes longer and the welding voltage V starts to rise. As the welding voltage V increases, the welding resistance R also increases. The droplet detachment detecting unit 10 monitors the time change of the welding resistance R and outputs it to the arc control unit 11. When the amount of time change of the welding resistance R exceeds a predetermined value, the arc control unit 11 21 is determined to have started to be released, and the polarity of the welding wire 18 is switched from the reverse polarity to the positive polarity by the output signal from the polarity switching portion 11a (time t4). Further, the control of the welding output is switched to the constant current control from the time t4, and the welding current I decreases monotonously from the fourth current value I4, changes from the reverse polarity to zero, and further becomes positive, and then becomes negative at the time t5. The first current value I1 that is the value of is reached (fourth step). Note that the welding current I decreases monotonously from the time t4 to the time t5 with a predetermined slope β, and the absolute value of the slope α of the increase in the welding current I from the time t1 to the time t2 is the absolute value of the slope β. It is set to be smaller than the value.

  In the period from time t2 to time t4, the welding current I is controlled so that the output waveform becomes a downwardly convex curve, and is the difference between the third current value I3 and the fourth current value I4. The current fluctuation value It is adjusted so as to be within a predetermined range. Here, the predetermined range is a width of ± 25% or more and ± 45% or less of the center value centered on the moving average value of the welding current I from the time point t2 to the time point t4 or the center value that is the set current Is, More preferably, the width is within a range of ± 25% to ± 30% of the center value. Further, the current fluctuation value It is changed by adding the inductance value of the reactor 6 and the inductance value of the electronic reactor by the electronic reactor control, and specifically, the inductance value of the electronic reactor stored in the storage unit 12. By selecting an appropriate value from among the values, adjustment is made so as to be within the predetermined range.

  Further, the welding resistance R that has monotonously decreased from the time t2 starts to increase with the increase of the welding voltage V immediately before the time t4, decreases rapidly at the time t4, becomes zero, and then reaches a predetermined value at the time t5. The value of is reached.

  From time t5 to time t6, the welding current I is controlled to maintain the first current value I1, and during this period, the welding voltage V and the welding resistance R are substantially constant (fifth step). Here, the first current value I1 is set corresponding to a value obtained experimentally in advance for each set current Is or each feed amount of the welding wire 18. The absolute value of the first current value I1 is set to be smaller than the welding current I in the period from the time point t2 to the time point t4. Also, during this period, as shown in the droplet transfer state (d) at time td, the droplet 21 falls from the tip of the welding wire 18 to the molten pool 22 formed in the base material 17, and the droplet 21 Exit is complete. From time t6, the welding current I is monotonously increased with a slope α, and reaches zero at time t7 (first step).

  As apparent from FIG. 2, the period from the time point t1 to the time point when the welding current I between the time point t4 and the time point t5 becomes zero corresponds to the reverse polarity period T1, and the welding between the time point t4 and the time point t5. The period from the time when the current I becomes zero to the time t7 when the welding current I reaches zero after the elapse of time t6 corresponds to the reverse polarity period T2.

  Further, assuming that the sum of the reverse polarity period T1 and the subsequent positive polarity period T2 is a welding period Tc (see FIG. 2), in the AC arc welding shown in the present embodiment, the welding period Tc is one cycle, and the welding wire is used in this period. The droplet 21 is dropped from 18 to the base material 17 and transferred. Further, by repeating the welding period Tc continuously, in other words, alternating arc welding is performed on the base material 17 by alternately repeating the reverse polarity period T1 and the positive polarity period T2.

  Note that the period from time t5 to time t6 is shorter than the reverse polarity period T1, for example, shorter than the period from time t6 in one welding cycle Tc to time t2 in the next welding cycle Tc. Is set. The absolute value of the first current value I1 is set to be smaller than the third current value I3.

[Effects]
As described above, the AC arc welding control method according to the present embodiment has the reverse polarity period T1 in which the welding wire 18 is positive with respect to the base material 17 and the negative potential with respect to the base material 17. This is a control method in which AC arc welding is performed on the base material 17 by alternately repeating the positive polarity period T2 to be performed.

  In this method, the first step of monotonously increasing the welding current I flowing through the welding wire 18 from the positive (negative) first current value I1 to the reverse polarity (positive) second current value I2, and the welding current Control is performed so that I is continuously decreased from the second current value I2 to the reverse polarity (positive) third current value I3 and then continuously increased to the reverse polarity (positive) fourth current value I4. A second step of detecting the start of detachment of the droplet 21 formed at the tip of the welding wire 18, and a welding current I from the fourth current value I4 after detecting the start of detachment of the droplet 21. A fourth step of monotonously decreasing to the first current value I1, and a fifth step of controlling the welding current I so as to hold the first current value I1 for a predetermined period, and a reverse polarity period T1 and a positive polarity period T2 It is executed during the welding period Tc which is the sum of Further, during the execution of the fifth step, the detachment of the droplet 21 is completed.

  According to this embodiment, the arc 20 is stabilized by heat input to the base material 17 during the second step executed in the reverse polarity period T2, and a deep penetration is formed in the base material 17 so that stable melting is achieved. A pond 22 is formed.

  Moreover, by performing the first step and the second step, the welding wire 10 can be melted to form the droplet 21 at the tip, and the droplet 21 can be further grown. Moreover, a constriction can be produced in the upper part of the droplet 21 grown to a predetermined size. In addition, by doing so, the detachment of the droplets 21 can be promoted.

  In addition, in the third step executed in the reverse polarity period T2, the start of detachment of the droplet 21 is detected, and in the fourth step, the welding current I is reduced to the positive first current value I1, thereby causing the droplet 21 to The acting arc reaction force can be reduced. This will be further described.

  As is well known, in arc welding using carbon dioxide gas, the arc reaction force increases in a reverse polarity state where heat is input to the base material 17 (see FIG. 3). Due to this arc reaction force, the drop of the droplet 21 onto the base material 17 is obstructed, and there is a possibility that the timing and the number of times the droplet 21 is released vary.

  On the other hand, according to the present embodiment, after detecting the start of detachment of the droplet 21, the welding current 18 is monotonously decreased to be positive, so that the welding wire 18 is mainly heat input and the arc reaction force is increased. Reduced. For this reason, detachment of the droplet 21 is promoted. Further, by maintaining the welding current I at the positive first current value I1 for a predetermined period, that is, by executing the fifth step during the positive period T2, the constriction formed on the top of the droplet 21 is formed. The melting of the portion is promoted, and the detachment of the droplet 21 toward the base material 17 can be completed.

  In addition, since a stable molten pool 22 is formed in the base material 17 until the start of detachment of the droplet 21 is detected, the dropped droplet 21 is absorbed by the molten pool 22 and the occurrence of spatter is suppressed. Is done.

  Further, when the welding speed is high, for example, when it is 1 m / min or more, if the droplet 21 is transferred to the base material 17 in a state where the arc reaction force is large, the droplet 21 moves at a desired timing. Otherwise, there was a risk that the droplet 21 would fall on the base material 17 before the molten pool 22 was formed. In such a case, a large amount of spatter was generated and the appearance of the weld bead was impaired. Further, as described above, the timing of detachment of the droplets 21 becomes unstable, the bead pitch and width become non-uniform, and the appearance of the weld bead is impaired.

  On the other hand, according to the present embodiment, even when the welding speed is increased, the timing of detachment of the droplets 21 can be kept constant, and a weld bead having a good pitch and width and a good appearance can be formed on the base material 17. Can do.

  When the droplet 21 is grown in the positive polarity state, heat is mainly input to the welding wire 18, so that the molten pool 22 is hardly formed on the base material 17 and only the melting of the welding wire 18 proceeds. The arc 20 formed between the material 17 and the welding wire 18 becomes unstable, and it becomes difficult to obtain a stable penetration into the base material 17.

  Further, during the period in which the tip of the welding wire 18 begins to melt during the execution of the first step and the welding current I in the second step continuously decreases (period from time t2 to time t3 shown in FIGS. 2 and 3). The droplet 21 formed at the tip of the welding wire 18 grows. Further, in a period during which the welding current I in the second step continuously increases (a period from time t3 to time t4 shown in FIGS. 2 and 3), a constriction is formed on the top of the droplet 21.

  Further, it is preferable that the output waveform of the welding current I in the second step is a downwardly convex curve.

  By controlling the welding current I in this way, in particular, by controlling the current fluctuation width It, when the droplet 21 grows at the tip of the welding wire 18, the welding current I is reduced and is formed above the droplet 21. When the constriction is caused, the welding current I can be increased.

  If the current fluctuation width It is too large, the amount of heat input to the welding wire 18 when the droplet 21 grows is insufficient. Therefore, the growth of the droplet 21 becomes insufficient, and the tip of the welding wire 18 and the base material 17 may be short-circuited before the droplet 21 is detached. In such a state, the arc 20 becomes unstable and spatter is generated and the appearance of the weld bead is impaired.

  On the other hand, if the current fluctuation width It is too small, the droplet 21 becomes larger than a desired size, or the arc reaction force when the droplet 21 grows increases. If the droplet 21 becomes too large, the droplet 21 may drop in the reverse polarity period T1, and the pitch of the weld beads is not stable. On the other hand, if the arc reaction force is too large, the droplet 21 is pushed back toward the welding wire 18, so that the arc 20 becomes unstable, and the droplet 21 scatters immediately before or during the fall, resulting in spattering. End up.

  According to the present embodiment, as described above, the occurrence of the above-described problem can be suppressed by controlling the output waveform of the welding current I to be a downwardly convex curve in the second step.

  The prior art disclosed in Patent Document 1 mainly targets welding of an aluminum material, and aims at forming a bead having a shallow penetration portion and a large surplus portion. That is, it is intended for thin plate welding. Therefore, in order to prevent the base metal from being melted down, it is necessary to increase the heat input to the welding wire while growing the heat input to the base material to grow the droplets. Accordingly, it is necessary to lengthen the positive polarity period or increase the positive current.

  On the other hand, the AC arc welding of the present embodiment is intended for thick plate welding made of mild steel or high-tensile steel, and is intended to form a flat bead with a deep penetration portion and a small surplus portion. Therefore, while the reverse polarity period T1 is lengthened so that the heat input to the base material 17 is increased, the positive polarity period T2 is used only for the detachment of the droplets 21, so that the current value of the welding current I (= first) Control is performed so that the current value I1) becomes smaller.

  The reverse polarity period T1 is preferably 2 msec or more and 12 msec or less.

  When the reverse polarity period T1 is less than 2 msec, the heat input to the base material 17 is insufficient, and the droplets 21 formed at the tip of the welding wire 10 do not grow sufficiently, so that the arc 20 is stably maintained. Therefore, it becomes difficult to secure a desired penetration depth and to form a weld bead having a good appearance. On the other hand, when the reverse polarity period T1 is longer than 12 msec, the period during which the arc reaction force is large becomes longer, and thus the droplet 21 is not stably detached during the predetermined welding period Tc. For this reason, the arc 20 during high-speed welding is not stable. As the spatter increases, the bead width becomes non-uniform, and it becomes difficult to form a weld bead with good appearance.

  Further, in the positive polarity period T2, the period during which the first current value I1 is held, that is, the period from the time point t5 to the time point t6 shown in FIGS. Preferably, it is 0.5 msec or more and 0.8 msec or less.

  When the said period is less than 0.3 msec, the period when the arc reaction force concerning the welding wire 18 and the droplet 21 is small becomes short, and the separation promotion effect of the droplet 21 is blunted. For this reason, the detachment of the droplet 21 becomes unstable, and the formation of the weld bead becomes unstable. On the other hand, if it is longer than 1.5 msec, the droplet 21 grows larger than the desired size due to excessive heat input to the welding wire 18, so that the separation of the droplet 21 is not stable. The detachment of the droplet 21 may not be completed, the arc 20 becomes unstable, and the spatter at the time of detachment of the droplet 21 increases.

  The first current value I1 is preferably 30 A or more and 200 A or less, and more preferably 100 A or less.

  When the first current value I1 is less than 30 A, the effect of reducing the arc reaction force is small, so that the effect of promoting the detachment of the droplet 21 is not obtained so much, and the detachment of the droplet 21 occurs during the period from time t5 to time t6. May not complete.

  On the other hand, when the first current value I1 is larger than 200A, not only the constricted portion formed on the top of the droplet 21, but also the entire tip of the welding wire 18 is melted greatly, and the droplet 21 becomes large at once. There is a possibility that the detachment of the droplet 21 may not be completed normally. In such a state, the arc 20 becomes unstable.

  Further, in the third step, the start of detachment of the droplet 21 is detected based on the time change amount of the welding resistance R, which is the ratio of the welding voltage V and the welding current I. The start of detachment of the droplet 21 may be detected based on the amount of change in the welding voltage V over time.

  In a state where the droplet 21 falls and moves to the base material 17, the welding voltage V reacts and changes sensitively to the fluctuation of the arc length. For this reason, if the detachment of the droplet 23 is detected based on the amount of change in the welding voltage V over time or the absolute value of the welding voltage V, there is a risk of erroneous detection due to pulsation, which is a minute fluctuation of the welding voltage V. On the other hand, since the welding resistance R is not sensitive with respect to the pulsation of the welding voltage V and changes gradually, the detection of the start of the detachment of the droplet 21 based on the amount of change in the welding resistance R over time causes the occurrence of erroneous detection. Can be suppressed. Further, since the influence of the pulsation is small, it is possible to set the threshold value of the temporal change amount of the welding resistance R relating to the detection of the start of the detachment of the droplet 21 to be small. Therefore, it is possible to detect the start of the detachment of the droplet 21 early and accurately compared to the welding voltage V and the amount of change over time.

  In the second step, the welding voltage V is controlled to be a predetermined value based on the set voltage Vs for setting the output of the welding voltage V. In the fifth step, the setting for setting the output of the welding current I is set. The first current value I1 is set based on the current Is or a value obtained in advance for each feed amount of the welding wire 18.

  By controlling in this way, during a period in which heat is mainly input to the base material 17, the influence of disturbance, for example, fluctuation of the protruding length of the welding wire 18, position shift of the base material 17, and the like is suppressed by constant voltage control. In a period in which the welding wire 18 is mainly heated to complete the detachment of the droplets 21, a predetermined first current value I1 based on a set current Is or a value obtained for each feeding amount of the welding wire 18 is obtained. The constricted portion of the droplet 21 can be stably melted by flowing a positive current having the current to the welding wire 18, and the detachment of the droplet 21 can be completed at a desired timing.

  In the second step, by changing the added value of the inductance value of the reactor 6 electrically connected to the welding wire 18 and the inductance value of the electronic reactor by the electronic reactor control stored in the storage unit 12, The welding current I may be controlled so that the current fluctuation width It, which is the difference between the three current value I3 and the fourth current value I4, falls within the predetermined range with the set current Is as the center.

  Moreover, in the alternating current arc welding in this embodiment, it is preferable that the shielding gas sprayed on the base material 17 is gas which has a carbon dioxide gas as a main component.

  The arc reaction force acting on the droplet 21 increases when a shield gas containing carbon dioxide as a main component is used. However, the control method of the present embodiment reduces the influence of the arc reaction force to achieve a desired timing. Thus, the droplet 21 can be reliably transferred to the base material 17.

  The base material 17 preferably has a thick plate made of mild steel or high-tensile steel, for example, a plate thickness of 3.2 mm or more.

  By performing AC arc welding by applying the control method of the present embodiment to such a base material 17, the base material 17 can be sufficiently deeply melted, and a flat weld bead with a small surplus portion can be formed. Can be formed. Further, it is possible to form a weld bead having a low spatter and a good appearance with a stable pitch and bead width.

  In addition, the absolute value of the slope α of the change in the welding current I from the time point t1 to the time point t2 is preferably smaller than the absolute value of the slope β from the time point t4 to the time point t5.

  When the inclination α of the increase in the welding current I increases, the current flows through the welding wire 18 at a stroke and becomes red hot, and the force pushing the molten pool 21 becomes too large, which may increase the generation of spatter. Also, if the absolute value of the slope of decrease of the welding current β is made larger than the slope α, the period during which the positive current flows through the welding wire 18 becomes too long and the arc 20 becomes unstable.

(Other embodiments)
In the above embodiment, the detachment of the droplet 21 is completed during the execution of the fifth step. However, even when the detachment of the droplet 21 is completed during the execution of the fourth step in the positive polarity period T2. Good. In the fourth step, the arc reaction force acting on the droplet is reduced in the process of monotonously decreasing the welding current I from the fourth current value I4 having the reverse polarity to the first current value I1 having the positive polarity. Therefore, for example, even if the droplet 21 sufficiently grown in the second step falls by its own weight during the execution of the fourth step in the positive polarity period T2, it may be pushed back by the arc reaction force and fall outside a predetermined position. In addition, since the molten pool 22 itself has already been formed, the occurrence of spatter is also suppressed.

  The control method for AC arc welding according to the present invention is applicable to arc welding using a shielding gas containing carbon dioxide as a main component because the droplet can be detached at a desired timing while reducing the influence of the arc reaction force. It is useful to do.

DESCRIPTION OF SYMBOLS 1 Input power supply 2 Primary rectification part 3 Switching part 4 Transformer 5 Secondary rectification part 6 Reactor 7 Drive part 8 Welding current detection part 9 Welding voltage detection part 10 Droplet separation detection part 11 Arc control part 11a Polarity switching part 12 Storage part 13 Welding condition setting unit 14 Torch 15 Tip 17 Base material 18 Welding wire 19 Wire feeding unit 20 Arc 21 Droplet 22 Molten pool

Claims (12)

This is a control method for AC arc welding in which welding is performed by alternately repeating a reverse polarity period in which a welding wire is positive with respect to a base material and a positive polarity period in which the welding wire is negative with respect to the base material. And
A first step of monotonically increasing a welding current flowing through the welding wire from a first current value of positive polarity to a second current value of opposite polarity;
A second step of controlling the welding current to continuously decrease from the second current value to a third current value of reverse polarity and then to continuously increase to a fourth current value of reverse polarity;
A third step of detecting the start of detachment of the droplet formed on the tip of the welding wire;
A fourth step of monotonously decreasing the welding current from the fourth current value of reverse polarity to the first current value of positive polarity after detecting the start of desorption of the droplet;
A fifth step of controlling the welding current so as to maintain the first current value in the positive polarity period for a predetermined period is executed during a welding period that is a sum of the reverse polarity period and the positive polarity period. And
The control method for AC arc welding, wherein the detachment of the droplet is completed during the execution of the fourth step or the fifth step in the positive polarity period. In the control method of AC arc welding according to claim 1,
The control method of AC arc welding, wherein an output waveform of the welding current in the second step is a downwardly convex curve. In the control method of AC arc welding according to claim 1 or 2,
The second and third steps are performed during the reverse polarity period;
The AC arc welding control method, wherein the fifth step is executed during the positive polarity period. In the control method of AC arc welding according to any one of claims 1 to 3,
During the first step, the tip of the welding wire starts to melt, and the droplet formed at the tip of the welding wire grows during a period in which the welding current in the second step continuously decreases. A control method of AC arc welding characterized by the above. In the control method of AC arc welding according to claim 4,
A control method for AC arc welding, wherein a constriction is formed on an upper portion of the droplet during a period in which the welding current in the second step continuously increases. In the control method of the alternating current arc welding of any one of Claim 1 thru | or 5,
In the third step, the AC arc welding is characterized in that the start of the drop of the droplet is detected based on the time change amount of the welding voltage or the time change amount of the welding resistance obtained from the welding voltage and the welding current. Control method. In the control method of the alternating current arc welding of any one of Claim 1 thru | or 6,
In the second step, based on a set voltage for setting the output of the welding voltage, the welding voltage is controlled to be a predetermined value,
In the fifth step, the first electric current value is set based on a preset current for setting the output of the welding current or a value obtained in advance for each feed amount of the welding wire. Control method. In the control method of AC arc welding according to claim 7,
In the second step, the third current value and the fourth current are changed by changing an addition value of the inductance value of the reactor electrically connected to the welding wire and the inductance value of the electronic reactor by the electronic reactor control. A control method for AC arc welding, wherein the welding current is controlled so that a difference from a value falls within a predetermined range. In the control method of the alternating current arc welding of any one of Claim 1 thru | or 8,
The period for holding the first current value in the positive polarity period is 0.3 msec or more and 1.5 msec or less. In the control method of the alternating current arc welding of any one of Claim 1 thru | or 9,
The control method of AC arc welding, wherein the first current value is 30A or more and 200A or less. In the control method of the alternating current arc welding of any one of Claim 1 thru | or 10,
The control method of AC arc welding, wherein the shielding gas blown onto the base material is a gas mainly composed of carbon dioxide. In the control method of the alternating current arc welding of any one of Claims 1 thru | or 11,
The control method of AC arc welding, wherein the base material is a thick plate made of mild steel or high-tensile steel.

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