DC arc welding control method

Abstract

During the DC arc welding alternating repetitive short circuit period Ts and the arc period Ta, the arc period Ta includes first to fourth periods T1 to T4. During the first period T1, the welding current Aw is increased to the first current value Ip, during the second period T2, the welding current Aw is decreased to the second current value Ib at a time gradient Islp, during the third period T3, the welding current Aw is maintained at the second current value Ib, and after the welding current Aw is increased to the third current value Ib2 during the fourth period T4, this value is maintained. During the short circuit period Ts and the arc period Ta, the wire feeding speed WF is constant. During the second period T2, constant voltage control is performed on the welding output, and constant current control is performed on the welding output during the third period T3 and the fourth period T4 respectively.

Description

Technical Field

[0001] The present invention relates to a direct current arc welding control method. Background Art

[0002] So far, arc welding is known in which a welding wire is fed at a prescribed wire feed speed, and the base material is welded by alternately repeating a short-circuit period and an arc period. In this case, arc welding is performed while spraying a shielding gas onto the welding portion.

[0003] In such arc welding, a method is known in which a peak current having a high current value is passed through the welding wire at the beginning of the arc period to suppress the occurrence of a short circuit between the welding wire and the base material and reduce spatter (for example, see Patent Documents 1 and 2).

[0004] Patent Document 1: Japanese Patent Laid-Open Publication No. 10-109163

[0005] Patent Document 2: Japanese Patent Laid-Open Publication No. 2006-021227 Summary of the Invention

[0006] -Technical Problem to be Solved by the Invention-

[0007] When a mixed gas mainly composed of an inert gas such as Ar (argon) gas and mixed with carbon dioxide gas is used as the shielding gas, the detachability of the molten droplet formed at the tip of the welding wire is improved.

[0008] However, when arc welding is performed using the aforementioned mixed gas under the existing methods disclosed in Patent Documents 1 and 2, when the peak current is applied, the molten droplet detaches from the welding wire at irregular times, and the periodicity of the detachment time is disrupted. Therefore, the arc is unstable, and a slight short circuit between the welding wire and the base material is likely to occur. As a result, spatter may occur, damaging the appearance of the weld formed on the base material, or welding defects may occur.

[0009] The present invention has been completed to solve the above technical problems, and an object thereof is to provide a direct current arc welding control method capable of stabilizing the detachment time of the molten droplet and suppressing the occurrence of spatter.

[0010] -Technical Solution for Solving the Technical Problem-

[0011] In order to achieve the above object, the DC arc welding control method according to the present invention performs welding by alternately repeating a short - circuit period and an arc period, and is characterized in that: the arc period at least includes the following periods: a first period, a second period, a third period, and a fourth period, and at least includes the following steps: in the first period, a step of increasing the welding current flowing through the welding wire to a first current value; in the second period, a step of reducing the welding current from the first current value to a second current value at a prescribed time gradient; in the third period, a step of maintaining the welding current at the second current value; and in the fourth period, a step of increasing the welding current from the second current value to a third current value that is lower than the first current value and higher than the second current value, and then maintaining the welding current at the third current value until the end of the fourth period. The wire feeding speed of the welding wire is constant during the short - circuit period and the arc period. Constant voltage control is performed on the welding output during the second period, and constant current control is performed on the welding output at least during the third period and the fourth period respectively.

[0012] - Effects of the Invention -

[0013] According to the present invention, it is possible to stabilize the droplet detachment moment and suppress the occurrence of spatter. Description of the Drawings

[0014] Figure 1 FIG. is a diagram showing a general configuration of an arc welding apparatus according to an embodiment of the present invention;

[0015] Figure 2 FIG. is a timing chart showing output waveforms of welding current and welding voltage during welding, wire feeding speed, and droplet transfer state. Detailed Embodiment

[0016] Hereinafter, this embodiment will be described in detail with reference to the drawings. The following description of the preferred embodiment is merely an example in nature, and has no intention of limiting the present invention, the application object of the present invention, or the use of the present invention at all.

[0017] [Configuration of Arc Welding Apparatus]

[0018] Figure 1 FIG. is a schematic configuration diagram of the arc welding apparatus in this embodiment. The arc welding apparatus 100 includes: a primary rectifying unit 2 that rectifies the alternating current input from the input power source 1; a switching unit 3 that controls the welding output; and a transformer 4 that inputs the output of the switching unit 3 and converts the output into electric power suitable for welding. The arc welding apparatus 100 in this embodiment is a semi - automatic welding apparatus in which an operator holds a welding torch 14 for welding.

[0019] The arc welding apparatus 100 further includes: a secondary rectifying unit 5 that rectifies the output of the secondary side of the transformer 4; a reactor 6 that smoothes the output of the secondary rectifying unit 5; a driving unit 7 that drives the switching unit 3; a welding current detecting unit 8 that detects the welding current; a welding voltage detecting unit 9 that detects the welding voltage; and a necking detecting unit 10 that detects a situation where necking has occurred in the molten droplet 21 (see Figure 2 ) formed at the tip portion of the welding wire 18.

[0020] 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: set current, set voltage, wire feed rate, shielding gas type, welding wire type, and welding wire diameter.

[0021] The storage unit 12 stores information set by the welding condition setting unit 13, the wire feed speed WF of the welding wire 18 (see Figure 2 ), wire feed amount, inductance values of reactors under electronic reactor control at each different wire feed speed WF, and various other parameters. It should be noted that the wire feed amount of the welding wire 18 is determined in proportion to the set current set by the operator.

[0022] The arc welding apparatus 100 further includes an arc control unit 11. The arc control unit 11 outputs a signal for controlling the current or voltage when the arc is generated, based on the outputs from the welding current detecting unit 8, the welding voltage detecting unit 9, the necking detecting unit 10, and the storage unit 12. The driving unit 7 controls the switching unit 3 according to the output of the arc control unit 11. It should be noted that although not shown, the arc control unit 11 has a short-circuit detecting unit that detects and determines a short circuit between the molten droplet 21 formed at the tip portion of the welding wire 18 and the base material 17, based on the output of the welding voltage detecting unit 9. The short-circuit detecting unit may also be provided outside the arc control unit 11.

[0023] The welding wire 18 is fed by a wire feed motor controlled by a wire feed unit 19. Welding power is supplied to the welding wire 18 via a welding tip 15 mounted on a torch 14, and an arc 20 is generated between the welding wire 18 and the base material 17 to perform welding.

[0024] It should be noted that each component constituting Figure 1 the arc welding apparatus 100 shown may be separately configured individually, or may be configured by combining a plurality of components together.

[0025] [Welding Output Control during Arc Welding]

[0026] Figure 2 Shows the output waveforms of the welding current and welding voltage during welding, the wire feed speed, and the droplet transfer state according to this embodiment.

[0027] It should be noted that, in the arc welding process shown in this embodiment, based on the preset voltage and current before welding operation, the welding output, namely the welding voltage Vw and the welding current Aw, is controlled.

[0028] In this embodiment, the wire diameter of the welding wire 18 is, for example, 1.2 mm. The base material 17 is a plate made of iron, and its plate thickness is, for example, 4.5 mm, which is a so-called medium plate thickness. The shielding gas sprayed onto the base material 17 is a gas containing carbon dioxide gas. Here, the "gas containing carbon dioxide gas" means a gas containing 10% or more and 30% or less of carbon dioxide, and preferably contains 20% of carbon dioxide. It should be noted that an inert gas is contained as a component other than the carbon dioxide gas, and the representative gas is argon.

[0029] The arc welding shown in this embodiment is performed with a cycle of the sum of the short-circuit period Ts and the subsequent arc period Ta, that is, the welding period T. By continuously repeating the welding period T, in other words, by alternately repeating the short-circuit period Ts and the arc period Ta, DC arc welding of the base material 17 is performed. The welding wire 18 is fed forward to the base material 17 at a constant wire feeding speed Wf based on the set current within the welding period T, in other words, within the short-circuit period Ts and the arc period Ta. It should be noted that, in this embodiment, the speed Wf is about 7 m / min to 8 m / min. It should be noted that in DC arc welding, there are reverse polarity welding in which the negative side is connected to the base material 17 and the positive side is connected to the electrode, that is, the welding wire 18, via the welding nozzle 15, and straight polarity welding in which the negative side is connected to the electrode, that is, the welding wire 18, via the welding nozzle 15 and the positive side is connected to the base material 17. The description in this application specification is for reverse polarity welding.

[0030] When the welding voltage Vw detected by the welding voltage detection unit 9 is lower than the threshold voltage Vth, it is determined that the welding wire 18 and the base material 17 have been short-circuited. That is to say, a short circuit is detected. From this time point t0, the short-circuit period Ts ( Figure 2 as shown in (a) of the figure), the molten droplet 21 formed at the tip of the welding wire 18 contacts the base material 17, and the short-circuit state continues. It should be noted that during the short-circuit period Ts, the welding output is current-controlled. During the short-circuit period Ts, the output is based on the waveform diagram of the welding current Aw determined in advance through experiments. Specifically, the waveform diagram of the welding current Aw during the short-circuit period Ts is composed of the value of the welding current Aw that remains constant after short-circuit detection, its specified holding time, the rising slope of the first inclination after the specified holding time (specified period), the value of the welding current at the inflection point, and the rising slope of the second slope. The welding current Aw of this waveform diagram is output according to the wire feeding speed WF of the welding wire 18.

[0031] It should be noted that the threshold voltage Vth is preferably set to a low voltage of several volts to about a dozen volts. In this embodiment, it is set to 10V. However, it is not particularly limited thereto, and other values can be appropriately taken, for example, in the range of 7V or more and 12V or less.

[0032] After a predetermined period has elapsed from the time point t0, the welding current Aw is increased with the first and second rising slopes of the inclination to burn the welding wire 18, thereby promoting the disconnection (short - circuit opening) of the short - circuit between the base material 17 and the welding wire 18. Furthermore, when the welding current Aw is increased, due to the electromagnetic constriction force, a necking starts to occur in the molten droplet 21 formed at the tip of the welding wire 18, and along with this, the time - change amount of the welding voltage detected by the welding voltage detection unit 9 starts to change. When the necking detection unit 10 detects this change (necking) based on the output of the welding voltage detection unit 9 ( Figure 2 in the (b) figure), the arc control unit 11 reduces the welding current Aw.

[0033] The time point t1 is the time point when the molten droplet 21 necked and completely transferred from the tip of the welding wire 18 to the base material 17, thus detecting that the short - circuit has been disconnected. At this time point, the short - circuit state ends, and an arc state starts from the time point t1, and it transfers to the arc period Ta. It should be noted that, similar to the start of the short - circuit, when the welding voltage Vw exceeds the threshold voltage Vth, it is determined that the short - circuit has been disconnected.

[0034] It should be noted that, for the sake of simplicity of explanation, the threshold voltage for determining that the welding wire 18 and the base material 17 have been short - circuited and the threshold voltage for the disconnection of the short - circuit at the time point t1 are set to the same threshold voltage Vth.

[0035] However, in order to perform the detection more stably, the threshold voltage for the disconnection of the short - circuit at the time point t1 can also be a threshold voltage Vth' whose value is larger than the threshold voltage for determining that the welding wire 18 and the base material 17 have been short - circuited.

[0036] From the time point t1 to the time point t2, an arc 20 is generated between the welding wire 18 and the base material 17 by increasing the welding current Aw ( Figure 2 in the (c) figure), and the arc length becomes longer. It should be noted that the period from the time point t1 to the time point t2 is referred to as the first period T1. In the first period T1, the welding output is controlled by constant current.

[0037] At the time point t2, when the welding current Aw becomes the first current value Ip, the arc control unit 11 switches the control mode so that the welding output becomes constant - voltage control. Specifically, the welding output is controlled so that the moving average value of the welding voltage Vw becomes the set voltage.

[0038] The welding current Aw reaches the first current value Ip, ensuring a predetermined arc length ( Figure 2(d) of the figure). Next, when the welding voltage detection unit 9 detects that the welding voltage Vw starts to decrease, the arc control unit 11 decreases the welding current Aw from the first current value Ip to the second current value Ib at a time gradient Islp. Here, the time gradient Islp is the degree of change of the welding current Aw with respect to time, and it is obvious from Figure 2 that the time gradient Islp is a negative value. However, in the specification of the present application, the time gradient Islp is described by its absolute value.

[0039] It should be noted that the period from the time point t2 to the time point t3 when the welding current Aw decreases to the second current value Ib is referred to as the second period T2. As described above, in the second period T2, the welding output is under constant voltage control. By changing the inductance value of the reactor 6 and the added value of the inductance value of the electronic reactor based on the electronic reactor control, specifically, by selecting an appropriate value from the inductance values of the electronic reactor stored in the storage unit 12, the arc control unit 11 performs constant voltage control on the welding output.

[0040] In the present embodiment, the first current value Ip is 470 A, but it is not particularly limited thereto, and other values can be appropriately taken, for example, in the range of 400 A or more and 500 A or less. The second current value Ib is 150 A, but it is not particularly limited thereto, and other values can be appropriately taken, for example, in the range of 100 A or more and 200 A or less. The time gradient Islp is 600 A / msec, but it is not particularly limited thereto, and other values can be appropriately taken, for example, in the range of 300 A / msec or more and 700 A / msec or less.

[0041] When the welding current detection unit 8 detects that the welding current Aw has reached the second current value Ib, from this time point t3, the arc control unit 11 switches the control mode again so that the welding output becomes constant current control. The welding output is controlled by constant current so that the welding current Aw maintains the second current value Ib until the time point t4. It should be noted that the period from the time point t3 to the time point t4 is referred to as the third period T3. At a certain time point in the third period T3, a part of the molten droplet 21 formed at the tip of the welding wire 18 is brought into contact with the molten pool 22 formed on the base material 17 so as to be able to prevent the molten droplet 21 from becoming too large and detaching at an unexpected and irregular moment. In this way, a part of the molten droplet 21 is absorbed into the molten pool 22 ( Figure 2 (e)), ensuring that the molten droplet 21 does not become too large. That is to say, the third period T3 is also a short - circuit period in which the welding wire 18 is short - circuited with the base material 17.

[0042] It should be noted that, in this embodiment, the third period T3 is set to 1 msec, but it is not particularly limited thereto, and other values can be appropriately taken, for example, in the range of 0.3 msec or more and 3 msec or less.

[0043] The third period T3 is set to be 1 / 3 or less of the short-circuit period Ts. In this case, it is preferable that the third period T3 is 1 msec or more and 2 msec or less, and the short-circuit period Ts is 2 msec or more and 6 msec or less.

[0044] From the time point t4, the arc control unit 11 controls the welding output so that the welding current Aw rises from the second current value Ib to the third current value Ib2, and the welding current Aw is maintained at the third current value Ib2 until the time point t0 of the next welding period T. It should be noted that the period from the time point t4 to the time point t0 of the next welding period T is referred to as the fourth period T4. In the fourth period T4, the welding output is controlled by constant current. In the fourth period T4, before the short-circuit moment of the welding wire 18 and the base material 17 during the short-circuit period Ts, in a manner that suppresses the molten droplet 21 from becoming too large and detaching at an unexpected irregular moment, in other words, to the extent that suppresses the molten droplet 21 from detaching at an unexpected irregular moment, the molten droplet 21 regrows at the tip of the welding wire 18. This molten droplet 21 short-circuit transfers to the base material 17 during the short-circuit period Ts of the next welding period T.

[0045] In this embodiment, the third current value Ib2 is 180 A, but it is not particularly limited thereto, and other values can be appropriately taken, for example, in the range of 100 A or more and 200 A or less. However, the third current value Ib2 is set to be higher than the second current value Ib.

[0046] [Effects, etc.]

[0047] In summary, the DC arc welding control method according to this embodiment is a DC arc welding control method that performs welding by alternately repeating the short-circuit period Ts and the arc period Ta, and the arc period Ta includes at least the first period T1, the second period T2, the third period T3, and the fourth period T4.

[0048] The arc welding control method includes: a step of increasing the welding current Aw flowing through the welding wire 18 to a first current value Ip during a first period T1; and a step of decreasing the welding current Aw from the first current value Ip to a second current value Ib at a time gradient I slp during a second period T2. Further, it at least includes: a step of maintaining the welding current Aw at the second current value Ib during a third period T3; and a step of maintaining the welding current Aw at a third current value Ib2 lower than the first current value Ip and higher than the second current value Tb after increasing the welding current Aw from the second current value Ib to the third current value Ib2 until the end of the fourth period T4.

[0049] During a short-circuit period Ts and an arc period Ta, the wire feed speed WF of the welding wire 18 is constant (Wf).

[0050] During the second period T2, constant voltage control is performed on the welding output, and during other periods of the welding period T, at least during the third period T3 and the fourth period T4, constant current control is performed on the welding output, respectively.

[0051] During the short-circuit period Ts, the welding wire 18 is short-circuited with the base material 17, and the molten droplet 21 formed at the tip of the welding wire 18 is short-circuit transferred to the base material 17. During the first period T1, an arc 20 is generated between the welding wire 18 and the base material 17. During the second period T2, the arc length becomes a specified value, and a molten droplet 21 is formed at the tip of the welding wire 18. During the third period T3, a part of the welding wire 18 is brought into contact with the molten pool 22 formed on the base material 17, and a part of the molten droplet 21 is absorbed by the molten pool 22. During the fourth period T4, the arc 20 generated between the welding wire 18 and the base material 17 is maintained, and the molten droplet 21 grows at the tip of the welding wire 18.

[0052] According to the present embodiment, the welding current Aw is decreased from the first current value Ip to the second current value Ib at a steep time gradient Islp. Further, during the third period T3, the welding current Aw is maintained at the second current value Ib, a part of the molten droplet 21 is brought into contact with the molten pool 22, and this part is absorbed by the molten pool 22. During the fourth period T4, the welding current Aw is maintained at a third current value Ib2 lower than the first current value Ip and higher than the second current value Ib. Thereby, it is possible to suppress the molten droplet 21 from becoming too large before the short-circuit moment between the welding wire 18 and the base material 17 during the short-circuit period Ts and separating at an unexpected irregular moment. It is possible to suppress the separation of the excessive molten droplet 21 and suppress the splashing of large-sized spatter.

[0053] After increasing the welding current Aw to the first current value Ip, in the second period T2, the welding current Aw is rapidly decreased from the first current value Ip to the second current value Ib, whereby the heat input difference to the welding wire 18 and the base material 17 can be increased. Thereby, detachment of the molten droplet 21 in the second period T2 can be suppressed, and the start of the third period T3 can be reliably initiated, enabling stabilization of the short-circuit cycle, and further, the periodicity of the arc period Ta and the welding period T. Since the periodicity of the welding period T is stabilized, the base material 17 can be welded stably and at high speed.

[0054] In the fourth period T4, by maintaining the welding current Aw at the third current value Ib2, detachment of the molten droplet 21 at an unexpected and irregular moment can be suppressed, the molten droplet 21 can grow again, and reliable transfer to the base material 17 during the short-circuit period Ts at the next moment can be achieved, enabling maintenance of the periodicity of detachment of the molten droplet 21. Further, vibration of the molten pool 22 is suppressed, and during the fourth period T4, the occurrence of spatter due to the occurrence of minute short circuits can be suppressed.

[0055] By performing constant voltage control of the welding output during the second period T2 of the arc period Ta, stability of the arc 20 against disturbances such as hand tremors can be ensured, and the occurrence of arc interruption etc. can be suppressed.

[0056] On the other hand, during other periods in the arc period Ta, particularly during the third period T3 and the fourth period T4, by performing constant current control of the welding output, the welding current Aw can be stably maintained at the second current value Ib and the third current value Ib2 during each period.

[0057] For example, during the third period T3, if constant voltage control is performed on the welding output, the second current value Ib becomes unstable and sometimes a large deviation occurs. If the second current value Ib becomes excessively higher than the set value, all of the molten droplet 21 will be transferred to the base material 17, the periodicity of detachment of the molten droplet 21 cannot be maintained, sometimes the appearance of the welded part is impaired, or welding defects occur. If the second current value Ib becomes excessively lower than the set value, the welding wire 18 will sink into the base material 17, and sometimes welding defects occur.

[0058] Similarly, during the fourth period T4, if constant voltage control is performed on the welding output, the third current value Ib2 becomes unstable and sometimes a large deviation occurs. If the third current value Ib2 becomes excessively higher than the set value, the molten droplet 21 will grow excessively, the periodicity of detachment of the molten droplet 21 cannot be maintained, sometimes the appearance of the welded part is impaired, or welding defects occur. If the third current value Ib2 becomes excessively lower than the set value, the arc 20 cannot be maintained, causing arc interruption, and sometimes welding defects occur.

[0059] According to this embodiment, by appropriately switching the control of the welding output in Ta during the arc, the occurrence of the above-mentioned adverse conditions can be prevented, and stable arc welding can be performed.

[0060] According to this embodiment, during the short-circuit period Ts and the arc period Ta, the wire feeding speed WF of the welding wire 18 is constant.

[0061] In this way, it is no longer necessary to endow the wire feeding unit 19 with the function of variably controlling the wire feeding speed WF. Since the wire feeding direction of the welding wire 18 is only in one direction, and only forward wire feeding in this case, the structure of the wire feeding motor controlled by the wire feeding unit 19 can be simplified. Thereby, the arc welding device 100 can be simplified, and the device cost can be reduced.

[0062] The first current value Ip is preferably 400 A or more and 500 A or less. The first current value Ip is more preferably 470 A.

[0063] If the first current value Ip is less than 400 A, the arc length is unstable, and there may be a slight short circuit and spatter flying. On the other hand, if the first current value Ip is higher than 500 A, the growth of the molten droplet 21 can be promoted during the second period T2, so the molten droplet 21 may break away at an unexpected early moment and fly as a large spatter, and the short-circuit period becomes unstable.

[0064] The time gradient Is]p is preferably 300 A / msec or more and 700 A / msec or less. The time gradient Is]p is more preferably 600 A / msec.

[0065] If the time gradient Is]p is less than 300 A / msec, the heat input is excessive, and the molten droplet 21 may break away before the short circuit during the third period T3. On the other hand, if the time gradient Islp is greater than 700 A / msec, there may be a short circuit with the base material 17 at a high current value when the welding current Aw decreases, and it may fly as a spatter.

[0066] The second current value Ib is preferably 100 A or more and 200 A or less. The second current value Ib is more preferably 150 A.

[0067] If the second current value Ib is less than 100 A, the arc 20 may become unstable due to insufficient heat input. On the other hand, if the second current value Ib is higher than 200 A, the molten droplet 21 is excessively absorbed by the base material 17 during the third period T3, and it may fly as a spatter.

[0068] The third current value Ib2 is preferably 100 A or more and 200 A or less. The third current value Ib2 is more preferably 150 A.

[0069] If the third current value Ib2 is less than 100 A, the melting at the tip of the welding wire 18 becomes insufficient, and the arc 20 may become unstable. On the other hand, if the third current value Ib2 is higher than 200 A, the molten pool 22 will vibrate greatly during the fourth period T4, so there may be a micro short circuit and splashing as spatter.

[0070] The third period T3 is preferably 0.1 msec or more and 3 msec or less. The third period T3 is more preferably 0.3 msec.

[0071] If the third period T3 is shorter than 0.1 msec, there will be a deviation in the current value when the welding wire 18 contacts the molten pool 22, so the periodicity of the third period T3 becomes unstable. On the other hand, if the third period T3 is longer than 3 msec, in this case too, the periodicity of the third period T3 becomes unstable due to insufficient heat input.

[0072] The third period T3 is preferably 1 / 3 or less of the short circuit period Ts.

[0073] By doing so, the periodicity of the arc period Ta can be stabilized. Therefore, the regularity of the weld edge of the weld (not shown) formed on the base material 17 is stabilized, and the generation of spatter during welding can be reduced.

[0074] Preferably, the third period T3 is 1 msec or more and 2 msec or less, and the short circuit period Ts is 2 msec or more and 6 msec or less.

[0075] Preferably, the short circuit between the welding wire 18 and the base material 17 is judged based on whether the welding voltage Vw becomes below the threshold voltage Vth.

[0076] In this way, the short circuit between the welding wire 18 and the base material 17 can be reliably judged.

[0077] The threshold voltage Vth is preferably 7 V or more and 12 V or less. The threshold voltage Vth is more preferably 10 V.

[0078] The shielding gas sprayed onto the base material 17 during welding is preferably a mixed gas of an inert gas and carbon dioxide gas.

[0079] As described above, if such a mixed gas is used as the shielding gas, the detachability of the molten droplet 21 formed at the tip of the welding wire 18 is better. In other words, since the detachability becomes excessively good, for example, when welding a base material such as medium plate thickness, the size of the molten droplet 21 formed at the tip of the welding wire 18 becomes larger. As the molten droplet 21 becomes larger, the molten droplet 21 detaches from the welding wire 18 at irregular times, and the periodicity of the detachment time is disordered. Therefore, the arc becomes unstable, and it is likely to easily cause a micro short circuit between the welding wire and the base material.

[0080] On the other hand, according to the present embodiment, by controlling the welding output, namely the welding current Aw and the welding voltage Vw, as described above, it is possible to stabilize the detachment time of the molten droplet 21, ensure the periodicity of the arc period Ta, and suppress the generation of spatter.

[0081] (Other embodiments)

[0082] In the present embodiment, the semi-automatic welding device, namely the arc welding device 100, has been described as an example. However, the DC arc welding control method of the present invention is of course also a method useful for high-speed welding using a robot.

[0083] -Industrial applicability-

[0084] [[ID= 12]]The DC arc welding control method of the present invention can stabilize the detachment time of the molten droplet and suppress the generation of spatter, so it is extremely useful.

[0085] -Symbol description-

[0086] 1 Input power supply

[0087] 2 Primary rectifying section

[0088] 3 Switching section

[0089] 4 Transformer

[0090] 5 Secondary rectifying section

[0091] 6 Reactor

[0092] 7 Driving section

[0093] 8 Welding current detection section

[0094] 9 Welding voltage detection section

[0095] 10 Necking detection section

[0096] 11 Arc control section

[0097] 12 Storage section

[0098] 13 Welding condition setting section

[0099] 14 Torch

[0100] 15 Nozzle

[0101] 17 Base material

[0102] 18 Welding wire

[0103] 19 Wire feeding section

[0104] 20 Arc

[0105] 21 Molten droplet

[0106] 22 Molten pool

[0107] 100 Arc welding device

Claims

1. A DC arc welding control method that performs welding by alternately repeating a short - circuit period and an arc period, characterized in that: The arc period at least includes the following periods: a first period, a second period, a third period, and a fourth period. This DC arc welding control method at least includes the following steps: in the first period, a step of increasing the welding current flowing through the welding wire to a first current value; In the second period, a step of reducing the welding current from the first current value to a second current value at a prescribed time gradient; In the third period, a step of maintaining the welding current at the second current value; and In the fourth period, after increasing the welding current from the second current value to a third current value that is lower than the first current value and higher than the second current value, until the end of the fourth period, a step of maintaining the welding current at the third current value. During the short - circuit period and the arc period, the wire feeding speed of the welding wire is constant. During the second period, constant - voltage control is performed on the welding output. At least during the third period and the fourth period, constant - current control is respectively performed on the welding output. During the short - circuit period, the welding wire is short - circuited with the base material, and the molten droplet formed at the tip of the welding wire is short - circuit transferred to the base material. During the first period, an arc is generated between the welding wire and the base material. During the second period, the arc length is made a prescribed value, and a molten droplet is formed at the tip of the welding wire. During the third period, the welding wire is brought into contact with the molten pool formed on the base material, and a part of the molten droplet is absorbed by the molten pool. During the fourth period, the arc generated between the welding wire and the base material is maintained, and the molten droplet grows at the tip of the welding wire.

2. The DC arc welding control method according to claim 1, characterized in that: The first current value is 400 A or more and 500 A or less.

3. The DC arc welding control method according to claim 1, characterized in that: The time gradient is 300 A / msec or more and 700 A / msec or less.

4. The DC arc welding control method according to claim 1, characterized in that: The second current value is 100 A or more and 200 A or less.

5. The DC arc welding control method according to claim 1, characterized in that: The third current value is 100 A or more and 200 A or less.

6. The DC arc welding control method according to claim 1, characterized in that: The third period is 0.1 msec or more and 3 msec or less. [[ID= ​ ​ ​ ​ ​ The shielding gas sprayed onto the base metal during welding is a mixed gas of inert gas and carbon dioxide gas.

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