Arc welding control method

Abstract

In a consumable electrode type arc welding control method, arc welding of a base material 18 is performed by alternately repeating a pulse welding period Tp and a short-circuit welding period Ts. In the pulse welding period Tp, a peak current Ip and a base current Ib are caused to flow alternately to a welding wire 15 to generate an arc 17 between the base material 18 and the welding wire 15. A transition from the short-circuit welding period Ts to the pulse welding period Tp is made through a droplet formation period Tdf. In the droplet formation period Tdf, a first current Idf having a current value Idf different from the current value Ib of the base current Ib is caused to flow through the welding wire 15.

Description

Arc welding control method

[0001] The present disclosure relates to a method for controlling arc welding.

[0002] Conventionally, in consumable electrode arc welding, a so-called PulseMIX welding method is known in which a base material, which is an object to be welded, is arc-welded by alternately repeating a pulse welding period in which pulse welding is performed and a short-circuit welding period in which short-circuit welding is performed (see, for example, Patent Documents 1 and 2).

[0003] According to the conventional methods shown in Patent Documents 1 and 2, by alternately repeating low-heat-input short-circuit welding and high-heat-input pulse welding, it is possible to suppress burn-through of the base material and also to improve the appearance of the weld bead.

[0004] Patent No. 6695030 Patent No. 6596669

[0005] However, in the conventional methods disclosed in Patent Documents 1 and 2, droplets are transferred from the welding wire at the end of the short-circuit welding period. Even when the welding wire transitions from this state to the pulse welding period, there are no droplets at the tip of the welding wire. Therefore, droplets are not transferred from the welding wire to the base metal immediately after the first peak current flows through the welding wire during the pulse welding period. Furthermore, until droplets are formed at the tip of the welding wire and the state stabilizes, the transfer of droplets from the welding wire to the base metal becomes irregular, which may disrupt the so-called one-pulse, one-drop transfer.

[0006] The present disclosure has been made in view of the above points, and its purpose is to provide an arc welding control method that can stabilize droplet detachment in PulseMIX welding.

[0007] In order to achieve the above object, the arc welding control method according to the present disclosure is a consumable electrode arc welding control method in which a base material is arc-welded by alternately repeating a pulse welding period in which pulse welding is performed and a short-circuit welding period in which short-circuit welding is performed, wherein the pulse welding period involves alternately flowing a peak current and a base current as a welding current through a welding wire to generate an arc between the base material and the welding wire, transitioning from the short-circuit welding period to the pulse welding period via a preset droplet formation period, and during the droplet formation period, flowing a first current to the welding wire, the first current having a current value different from the current value of the base current.

[0008] According to the present disclosure, droplet detachment can be stabilized when transitioning from a short circuit welding period to a pulse welding period, and the stability of arc welding can be improved while spatter can be reduced.

[0009] FIG. 1 is a schematic diagram of an arc welding apparatus according to an embodiment. FIG. 2 is a schematic enlarged cross-sectional view showing a welded portion during arc welding. FIG. 3 is a time chart of a welding voltage waveform and a welding current waveform. FIG. 4 is a time chart of a wire feed speed waveform, a welding voltage waveform, and a welding current waveform before and after a droplet formation period. FIG. 5 is a time chart of a welding current waveform during a droplet formation period and at the beginning of a pulse welding period according to Modification 1. FIG. 6 is a time chart of another welding current waveform during a droplet formation period and at the beginning of a pulse welding period according to Modification 1. FIG. 7 is a time chart of a welding current waveform during a droplet formation period and at the beginning of a pulse welding period according to Modification 2.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0011] (Embodiment) [Configuration of Arc Welding Apparatus] Fig. 1 is a schematic diagram of an arc welding apparatus according to an embodiment. The arc welding apparatus 50 is mainly composed of a welding power source 19 that supplies power between a welding wire 15, which is a consumable electrode, and a base material 18, which is an object to be welded, a welding torch 16, and a wire feeder 14 that feeds the welding wire 15. Note that the welding torch 16 is attached to, for example, a welding robot, and welding is performed using the welding torch 16 by the welding robot. Alternatively, the welding torch 16 is held by, for example, an operator, and welding is performed using the welding torch 16 by the operator. The wire feeder 14 can feed the welding wire 15 in a forward feed direction D101 toward the base material 18 and a reverse feed direction D102 away from the base material 18 in the opposite direction of the forward feed direction D101.

[0012] In welding power supply unit 19, AC power input from input power supply 1 is rectified by primary rectifier unit 2, converted to AC by switching unit 3, stepped down by transformer 4, rectified by secondary rectifier unit 5 and DCL (inductance) 6, and applied between welding wire 15 and base material 18. The applied power generates an arc 17 between welding wire 15 and base material 18, thereby performing welding. Welding power supply unit 19 also includes a welding voltage detector 7 that detects welding voltage V, which is the voltage of welding wire 15, a welding current detector 8 that detects welding current I flowing through welding wire 15, and a counter 9 that counts the elapsed time of pulse welding period Tp and short-circuit welding period Ts or the number of pulse outputs.

[0013] Welding power supply unit 19 also includes a control switching unit 10 that switches control of the welding output based on the number counted by counter unit 9, a short-circuit welding control unit 11 that controls the welding current I during short-circuit welding period Ts, a pulse welding control unit 12 that controls the welding current I during pulse welding period Tp, a drive unit 13, and a setting unit 20 for setting welding conditions, etc. Counter unit 9 detects the first contact between welding wire 15 and base material 18 after a welding start command is issued by operating a torch switch (not shown) provided on welding torch 16 or by executing an operation program for the welding robot, and counts the time and the number of pulse outputs. Setting unit 20 also sets the set welding current to be set for welding, the set welding voltage to be set for welding, the feed speed of welding wire 15, the type of shielding gas, the material of welding wire 15, the wire diameter of welding wire 15, the pulse welding period and the number of waveform outputs, the short-circuit welding period and the number of waveform outputs, etc. Each component of welding power supply unit 19 may be configured independently as needed, or multiple components may be combined to form a single unit.

[0014] Next, a description will be given of the operation of the arc welding device 50. Fig. 2 is an enlarged schematic cross-sectional view showing a welded portion for arc welding.

[0015] In the arc welding device 50, a shielding gas is supplied from a gas supply port to shield the arc and the welded area from the outside air, while a current is supplied from a welding power source 19 to the welding wire 15. This generates an arc 17 between the welding wire 15 and the base metal 18, and the heat of the arc 17 melts the tip of the welding wire 15 and a portion of the base metal 18. The molten welding wire 15 drips onto the base metal 18 and forms a molten pool 15P together with the portion of the base metal 18 melted by the heat of the arc 17. As the welding torch 16 moves in a welding direction D15 relative to the base metal 18, the molten pool 15P formed in the base metal 18 moves relative to the welding direction D15, forming a weld bead 18A and welding the base metal 18.

[0016] In this case, the welding conditions are preset by setting unit 20, and the feed speed of welding wire 15 is also preset by setting unit 20. The output of welding power source unit 19 and the rotation of the motor of wire feeder 14 are controlled to achieve these set conditions. The welding conditions are controlled by monitoring welding power source unit 19 and controlling welding power source unit 19 so that the welding conditions match the set conditions. The welding current I and the waveform of welding current I used for this control are acquired from the output of welding current detection unit 8.

[0017] [Arc welding control method] Fig. 3 is a time chart of the welding voltage waveform and the welding current waveform. In Fig. 3, the vertical axis represents the welding current I and the welding voltage V, and the horizontal axis represents time. Fig. 3 also shows the transfer state of the droplet 15B.

[0018] As shown in Figure 3, arc welding is performed by alternating between a short-circuit welding period Ts during which short-circuit welding is performed and a pulse welding period Tp during which pulse welding is performed. That is, short-circuit welding is performed during the short-circuit welding period Ts, and pulse welding is performed during the pulse welding period Tp. The welding voltage waveform is the time-varying waveform of the welding voltage V, and the welding current waveform is the time-varying waveform of the welding current I.

[0019] The short circuit welding period Ts includes short circuit periods Tss1, Tss2, and Tss3 in which welding wire 15 and base metal 18 are short-circuited, and arc generation periods Tsa1 and Tsa2 in which arc 17 is generated between welding wire 15 and base metal 18, and the short circuit periods and arc generation periods occur alternately. Note that the number of short circuit periods and the number of arc generation periods are not particularly limited to those shown in this embodiment.

[0020] A short circuit between the welding wire 15 and the base material 18 during the short-circuit welding period Ts can be detected, for example, by monitoring the welding voltage V with the welding voltage detection unit 7. When the welding voltage V is an instantaneous voltage, it can be detected by detecting a change from a value greater than a predetermined threshold value Vs to a value less than the threshold value Vs. To avoid determining a minute short circuit during the short-circuit periods Tss1, Tss2, and Tss3 as a short circuit, a single short circuit can be determined when the welding voltage V remains less than the threshold value Vs for a predetermined period of time after the change from a value greater than the threshold value Vs to a value less than the threshold value Vs. The short-circuit detection method is not limited to this example, and any other method may be used as long as it can detect each short circuit. Furthermore, the release of the short circuit between the welding wire 15 and the base material 18 during the short-circuit welding period Ts is detected by detecting the formation of a neck 15A in the welding wire 15. Here, the neck 15A is a constriction that occurs in the welding wire 15 immediately before the short circuit is released, as shown in FIG. 1B . When neck 15A is formed in welding wire 15, the cross-sectional area of ​​welding wire 15 decreases and the resistance value increases, which in turn increases welding voltage V. By monitoring voltage change per unit time dv / dt, it is possible to detect that welding wire 15 is constricted and neck 15A occurs just before the short circuit is released. In other words, the release of the short circuit between welding wire 15 and base material 18 during short-circuit welding period Ts is detected by monitoring welding voltage V with welding voltage detection unit 7.

[0021] In addition, during the short-circuit welding period Ts, the value of the welding voltage V (Vs shown in Figure 3) that allows short-circuit welding to be performed stably at the wire feed speed set by the setting unit 20 is preset by the setting unit 20.

[0022] During short-circuit periods Tss1, Tss2, and Tss3, welding wire 15 is fed in forward feed direction D101, welding wire 15 and base material 18 are short-circuited, and droplet 15B formed at the tip of welding wire 15 is transferred to base material 18. Thereafter, welding wire 15 is fed backward in reverse feed direction D102 (state a).

[0023] During the arc generation periods Tsa1 and Tsa2, the welding wire 15 is fed in the forward feed direction D101, and an arc 17 is generated between the welding wire 15 and the base material 18. During this period, a droplet 15B is formed at the tip of the welding wire 15 and grows (state b). During the arc generation periods Tsa1 and Tsa2, the welding wire 15 is fed forward in the forward feed direction D101. The change in the feed direction of the welding wire 15 is performed by the wire feeder 14.

[0024] During the pulse welding period Tp, the pulse welding control unit 12 controls the welding current I so that six peak currents Ip1 to Ip6 flow through the welding wire 15 at intervals. In this embodiment, the peak currents Ip1 to Ip6 are collectively referred to as peak currents Ip. As shown in FIG. 3 , the peak current values ​​of the peak currents Ip1 to Ip6 are Ip1 to Ip6. In this embodiment, the current values ​​Ip1 to Ip6 are the same value Ip. However, the current values ​​Ip1 to Ip6 may be different from one another. Furthermore, after each of the peak currents Ip1 to Ip6 flows through the welding wire 15, a constant value of the welding current I flows. The welding current I during this period is referred to as the base current Ib. During the pulse welding period Tp, there are five periods during which the base current Ib flows, and the respective current values ​​are Ib1 to Ib5. In this embodiment, the current values ​​Ib1 to Ib5 are the same value Ib. However, the current values ​​Ib1 to Ib5 may be different from one another.

[0025] That is, during the pulse welding period Tp, the pulse welding control unit 12 controls the welding current I so that the peak current Ip and the base current Ib alternately flow through the welding wire 15. The number of times the peak currents Ip1 to Ip6 occur is not particularly limited to the example shown in FIG.

[0026] During each period during which peak currents Ip1 to Ip6 flow, an arc 17 is generated between welding wire 15 and base material 18, and droplet 15B is formed and grows at the tip of welding wire 15. Furthermore, at the end of each period during which peak currents Ip1 to Ip6 flow or the period following this, that is, at the beginning of each period during which base current Ib flows, droplet 15B moves toward base material 18 (state c).

[0027] The number of times that the base current Ib flows through the welding wire 15 also changes depending on the number of peak currents Ip. As will be described later, the wire feeder 14 controls the feeding of the welding wire 15 so that a command value for the feeding speed WF of the welding wire 15 (hereinafter referred to as the wire feeding speed command value WF) becomes a positive value Wff (see FIG. 5).

[0028] The occurrence of peak currents Ip1 to Ip6 during the pulse welding period Tp is detected by monitoring the time-varying waveform of the welding current detected by welding current detection unit 8. For example, when the welding current I is an instantaneous current, the peak currents Ip1 to Ip6 can be detected by the change from a value greater than a preset threshold value Is to a value smaller than the threshold value Is. Therefore, the occurrence of peak currents Ip1 to Ip6 during the pulse welding period Tp can be detected by comparing the welding current I with the threshold value Is. Note that the method for detecting the peak currents Ip1 to Ip6 is not limited to this example, and other methods may be used as long as they can detect each of the peak currents Ip1 to Ip6.

[0029] As shown in Fig. 3, a droplet formation period Tdf is provided during the transition from the short-circuit welding period Ts to the pulse welding period Tp. During the droplet formation period Tdf, the pulse welding control unit 12 controls the welding current I so that the current value of the welding current I is a constant value Idf (hereinafter referred to as the first current Idf). The droplet formation period Tdf is set in advance and is determined based on one or more of the material of the welding wire 15, the wire diameter, the set current, and the set feed speed. The set current is the average current value of the welding current I in the welding section of the base metal 18. The set feed speed is the average feed speed of the welding wire 15 in the welding section of the base metal 18. The control of the welding current I before and after the droplet formation period Tdf and the wire feed speed command value WF will be further described.

[0030] [Droplet Formation Period] FIG. 4 is a time chart showing the wire feed speed waveform, welding voltage waveform, and welding current waveform before and after the droplet formation period.

[0031] As shown in Fig. 4, during the arc generation period Tsa2, the welding wire 15 is fed forward in the forward feed direction D101, and the wire feed speed command value WF changes from a negative constant value Wfb (hereinafter referred to as the first speed command value Wfb) to a positive constant value Wff (hereinafter referred to as the second speed command value Wff) and is maintained at that value. Furthermore, when the arc generation period Tsa2 transitions to the short circuit period Tss3, the welding wire 15 is fed backward in the reverse feed direction D102, and the wire feed speed command value WF changes from the second speed command value Wff to the first speed command value Wfb and is then maintained at the first speed command value Wfb. Furthermore, when the release of the short circuit between the welding wire 15 and the base metal 18 is detected during the short circuit period Tss3, the period transitions to the droplet formation period Tdf, as shown in Fig. 4.

[0032] When the period transitions to the droplet formation period Tdf, the wire feed speed command value WF changes from the first speed command value Wfb to a negative constant value Wfd (hereinafter referred to as the third speed command value Wfd) and is maintained at the third speed command value Wfd. That is, during the droplet formation period Tdf, the welding wire 15 is fed backward in the reverse feed direction D102. The third speed command value Wfd is a negative value, and its absolute value is set to a value smaller than the first speed command value Wfb. That is, 0 < |Wfd| < |Wfb| holds. Furthermore, when the period transitions to the droplet formation period Tdf, the welding current I increases to the first current Idf and is maintained at the current value Idf. During the droplet formation period Tdf, the welding current I is controlled by the pulse welding control unit 12 so that the current value Idf is greater than the current value Ib of the base current Ib and less than the current value Ip of the peak current Ip.

[0033] After the predetermined droplet formation period Tdf has elapsed, the pulse welding period Tp transitions to a first pulse period Tp1, and the wire feed speed command value WF changes from the third speed command value Wfd to a positive constant value Wfp (hereinafter referred to as a fourth speed command value Wfp). Just before the transition to the first pulse period Tp1, the welding current I changes from the first current Idf to an intermediate inflection point current Ibp and then increases to a peak current Ip. In the example shown in FIG. 4 , the intermediate inflection point current Ibp has a current value Ibp greater than the base current Ib during the pulse welding period Tp and less than the first current Idf. However, the intermediate inflection point current Ibp is not limited to this value and may have any value as long as it is greater than the base current Ib during the pulse welding period Tp and less than the peak current Ip. Specifically, the current value Ibp of the intermediate inflection point current Ibp may be equal to or greater than the first current Idf.

[0034] In the first pulse period Tp1, a peak current Ip1 is generated, and after a predetermined period has elapsed, the welding current I decreases to a base current Ib having a current value Ib. After the base current Ib flows through the welding wire 15 and a predetermined period has elapsed, the welding current I shifts to a second pulse period Tp2, and a peak current Ip2 flows through the welding wire 15.

[0035] When the current value Ib of the base current Ib is used as a reference, the time integral value of the first current Idf (area S1 shown in FIG. 4) differs from the time integral value of the peak current Ip1 (area S2 shown in FIG. 4).

[0036] [Effects, etc.] As described above, the arc welding control method according to this embodiment is a consumable electrode type arc welding control method, in which arc welding of the base material 18 is performed by alternately repeating a pulse welding period Tp in which pulse welding is performed and a short-circuit welding period Ts in which short-circuit welding is performed.

[0037] During the pulse welding period Tp, a peak current Ip and a base current Ib are alternately applied to the welding wire 15 as the welding current I, thereby generating an arc 17 between the base material 18 and the welding wire 15 .

[0038] The welding process transitions from the short-circuit welding period Ts through a droplet formation period Tdf to a pulse welding period Tp. During the droplet formation period Tdf, a first current Idf having a current value Idf different from the current value Ib of the base current Ib is passed through the welding wire 15. The current value Idf of the first current Idf is controlled to be greater than the current value Ib of the base current Ib and smaller than the current value Ip of the peak current Ip.

[0039] The droplet formation period Tdf is set in advance and is determined based on one or more of the material of the welding wire 15, the wire diameter, the set current, and the set feed speed.

[0040] In the conventional methods disclosed in Patent Documents 1 and 2, droplets 15B are transferred from welding wire 15 to base material 18 before the transition to pulse welding period Tp, and the welding current I is also low, so welding wire 15 is not sufficiently heated. In this state, even if peak current Ip is passed through welding wire 15, droplets 15B do not grow to a sufficient size, and detachment of droplets 15B is unlikely to occur at the end of the period during which peak current Ip flows or during the period during which base current Ib flows.

[0041] On the other hand, according to the present embodiment, by providing a droplet formation period Tdf, which is a period during which the first current Idf flows through the welding wire 15, immediately before the transition to the pulse welding period Tp, a droplet 15B of an appropriate size can be formed at the tip of the welding wire 15 at the time of the transition to the pulse welding period Tp. This allows the droplet 15B to be stably detached from the welding wire 15 at the beginning of the pulse welding period Tp, and the one-pulse, one-drop transition can be reliably performed. As a result, the shape of the weld bead 18A can be stabilized.

[0042] Furthermore, by setting the current value Idf of the first current Idf to be greater than the current value Ib of the base current Ib and smaller than the current value Ip of the peak current Ip, it is possible to form a droplet 15B at the tip of the welding wire 15 at the time of transition to the pulse welding period Tp. It is also possible to suppress detachment of the droplet 15B during the droplet formation period Tdf.

[0043] The peak current Ip and the base current Ib are parameters that change depending on the feed rate of the welding wire 15. Furthermore, the preferable ranges of the respective current values ​​also vary depending on the material and diameter of the welding wire 15.

[0044] For example, when the welding wire 15 is made of hard aluminum and has a wire diameter of 1.2 mm, the preferred range of the peak current Ip is 350 A or more and 450 A or less, and the preferred range of the base current Ib is 15 A or more and 160 A or less. When the welding wire 15 is made of hard aluminum and has a wire diameter of 1.6 mm, the preferred range of the peak current Ip is 380 A or more and 420 A or less, and the preferred range of the base current Ib is 30 A or more and 240 A or less.

[0045] When the welding wire 15 is made of soft aluminum and has a wire diameter of 1.2 mm, the preferred range of the peak current Ip is 300 A or more and 450 A or less, and the preferred range of the base current Ib is 30 A or more and 300 A or less. When the welding wire 15 is made of soft steel and has a wire diameter of 1.2 mm, the preferred range of the peak current Ip is approximately 540 A, and the preferred range of the base current Ib is 40 A or more and 200 A or less. When the welding wire 15 is made of stainless steel and has a wire diameter of 1.2 mm, the preferred range of the peak current Ip is 350 A or more and 450 A or less, and the preferred range of the base current Ib is 45 A or more and 350 A or less.

[0046] The current value Idf of the first current Idf is preferably equal to or greater than 100 A and equal to or less than 300 A. In this way, at the time of transition to the pulse welding period Tp, it is possible to reliably form a droplet 15B at the tip of the welding wire 15. Furthermore, it is possible to reliably suppress detachment of the droplet 15B during the droplet formation period Tdf.

[0047] If the current value Idf is smaller than 100 A, it becomes difficult to form droplet 15B at the tip of welding wire 15. Alternatively, it takes a long time to form droplet 15B. On the other hand, if the current value Idf is larger than 300 A, droplet 15B will detach from welding wire 15 during droplet formation period Tdf, and one pulse one drop transfer will not be possible.

[0048] It is preferable that droplet formation period Tdf be 1 msec or more and 5 msec or less. By doing so, droplet 15B can be reliably formed at the tip of welding wire 15 at the time of transition to pulse welding period Tp, and the shape of weld bead 18A can be stabilized.

[0049] If droplet formation period Tdf is shorter than 1 msec, droplet 15B may not be sufficiently formed during droplet formation period Tdf. If droplet formation period Tdf is longer than 5 msec, the time required for droplet 15B to separate may become too long, which may result in a distortion in the shape of weld bead 18A.

[0050] Furthermore, the wire feed speed command value during the droplet formation period Tdf, i.e., the third speed command value Wfd, is a negative value. This makes it possible to maintain an appropriate distance between the welding wire 15 and the base material 18 when the welding wire 15 has a droplet 15B formed at its tip. If the third speed command value Wfd were a positive value, the distance between the welding wire 15 and the base material 18 would become too close, which could result in a micro-short circuit or spatter due to the arc reaction force.

[0051] Furthermore, the absolute value of the third speed command value Wfd is preferably smaller than the wire feed speed command value during the immediately preceding short-circuit welding period Ts, i.e., the absolute value of the first speed command value Wfb. By doing so, the distance between the welding wire 15 with a molten metal 15B formed at the tip and the base metal 18 can be maintained at an appropriate value, and the arc 17 generated between the welding wire 15 and the base metal 18 can be stabilized. If the absolute value of the third speed command value Wfd is larger than the absolute value of the first speed command value Wfb, the distance between the welding wire 15 and the base metal 18 becomes too large, and the arc 17 becomes unstable.

[0052] The third speed command value Wfd is preferably equal to or greater than -40 m / min and equal to or less than -5 m / min. By doing so, the distance between the welding wire 15 with the molten metal 15B formed at the tip and the base metal 18 can be maintained at an appropriate value, and the arc 17 generated between the welding wire 15 and the base metal 18 can be stabilized. Furthermore, the generation of spatter can be suppressed.

[0053] If the third speed command value Wfd is smaller than −40 m / min, the distance between the welding wire 15 and the base material 18 becomes too large, resulting in an unstable state of the arc 17. If the third speed command value Wfd is larger than −5 m / min, the distance between the welding wire 15 and the base material 18 becomes too small, which may cause a micro-short circuit or spatter due to the arc reaction force.

[0054] It is preferable to change the welding current I so that the welding current I has an intermediate bending point immediately after the droplet formation period Tdf and before the peak current Ip is passed through the welding wire 15. In this way, the melting of the welding wire 15 can be precisely controlled.

[0055] The welding current I at the intermediate bending point, i.e., the current value Ibp of the intermediate bending point current Ibp, is preferably greater than the current value Ib of the base current Ib and less than the current value Ip of the peak current Ip. By doing so, droplets 15B can be formed at the tip of the welding wire 15 at the time of transition to the pulse welding period Tp. Furthermore, detachment of droplets 15B during the droplet formation period Tdf can be suppressed.

[0056] Furthermore, the time integral value of the first current Idf, i.e., the area S1 shown in FIG. 4, based on the current value Ib of the base current Ib, is different from the time integral value of one peak current Ip during the pulse welding period Tp, i.e., the area S2 shown in FIG. 4.

[0057] Furthermore, when the material of the base metal 18 and the welding wire 15 is mild steel, aluminum, or an aluminum alloy, it is preferable that the time integral value of the first current Idf is smaller than the time integral value of the peak current Ip following the droplet formation period Tdf.

[0058] When the base metal 18 and the welding wire 15 are made of stainless steel, the time integral value of the first current Idf is preferably greater than the time integral value of the peak current Ip following the droplet formation period Tdf.

[0059] Aluminum and aluminum alloys have a lower melting point than iron-based materials such as mild steel and stainless steel, but have a higher thermal conductivity.

[0060] Considering these factors, aluminum and aluminum alloys and mild steel have similar heat inputs for forming droplets 15B during the droplet formation period Tdf, in other words, the area S1 shown in FIG. 4 . Furthermore, when heat equivalent to the time integral of the peak current Ip following the droplet formation period Tdf, in other words, the area S2 shown in FIG. 4 , is applied to the welding wire 15, the droplet 15B formed at the tip of the welding wire 15 is reliably detached from the welding wire 15. Therefore, when the base material 18 and the welding wire 15 are made of mild steel, aluminum, or an aluminum alloy, the droplet 15B can be reliably formed during the droplet formation period Tdf by making the time integral of the first current Idf smaller than the time integral of the peak current Ip following the droplet formation period Tdf. Furthermore, the detachment of the droplet 15B during the droplet formation period Tdf can be suppressed.

[0061] On the other hand, stainless steel has a melting point equivalent to that of mild steel and a lower thermal conductivity. The base material 18 receives a relatively low heat input during the short-circuit period (Tss1 to Tss3) of the short-circuit welding period Ts before the pulse welding period Tp. Furthermore, stainless steel has a relatively low thermal conductivity, making it difficult for heat to be transferred to the base material 18. Therefore, in order to reliably form a droplet 15B at the tip of the welding wire 15 during the droplet formation period Tdf immediately before the pulse welding period Tp, the heat input must be relatively larger than when the base material 18 and the welding wire 15 are made of mild steel. However, at the time when the peak current Ip is first applied to the welding wire 15 following the droplet formation period Tdf, the welding wire 15 is sufficiently heated, so only a small amount of heat input is required to detach the droplet 15B. Therefore, when the base material 18 and the welding wire 15 are made of stainless steel, the droplets 15B can be reliably formed during the droplet formation period Tdf by making the time integral value of the first current Idf larger than the time integral value of the peak current Ip following the droplet formation period Tdf. Furthermore, the droplets 15B can be reliably detached during or immediately after the period in which the peak current Ip first flows through the welding wire 15 following the droplet formation period Tdf.

[0062] Although the droplet formation period Tdf is set immediately before the pulse welding period Tp, it may be set in the initial region of the pulse welding period Tp.

[0063] Furthermore, in view of the above, with respect to the current value Ib of the base current Ib as a reference, the time integral value of the first current Idf when the materials of the base metal 18 and the welding wire 15 are stainless steel is larger than the time integral value of the first current Idf when the materials of the base metal 18 and the welding wire 15 are mild steel, aluminum, or an aluminum alloy.

[0064] <Modification 1> Fig. 5 is a time chart of a welding current waveform during a droplet formation period and at the beginning of a pulse welding period according to Modification 1. Fig. 6 is a time chart of another welding current waveform during a droplet formation period and at the beginning of a pulse welding period according to Modification 1. For ease of explanation, in Fig. 5 and Fig. 7 shown later, parts that are the same as those in the embodiment are designated by the same reference numerals, and detailed explanations thereof will be omitted.

[0065] As shown in Figures 5 and 6, multiple intermediate bending points may be provided in the welding current I during the period after the start of the droplet formation period Tdf and before the peak current Ip is made to flow through the welding wire 15. In this case, during the period after the start of the droplet formation period Tdf and before the peak current Ip is made to flow through the welding wire 15, the welding current waveform is configured with one or more straight lines or curves, or a combination of straight lines or curves. In the example shown in Figure 5, the welding current waveform is configured with a downwardly convex curve, and intermediate bending points Ibp1 to Ibp3 are provided. In the example shown in Figure 6, the welding current waveform is configured with a straight line, and intermediate bending points Ibp4 and Ibp5 are provided.

[0066] According to this modification, it is possible to more precisely control the melting of the welding wire 15. As a result, it is possible to form a droplet 15B at the tip of the welding wire 15 at the time of transition to the pulse welding period Tp, and it is also possible to suppress the detachment of the droplet 15B during the droplet formation period Tdf.

[0067] <Modification 2> FIG. 7 is a time chart of the welding current waveform before and after the droplet formation period according to Modification 2. In FIG.

[0068] The welding current waveform shown in Fig. 7 differs from the welding current waveform of the embodiment shown in Fig. 4 in that the cleaning pulse current Ipc is superimposed on the period during which the base current Ib flows during the pulse welding period Tp. In this modification, the cleaning pulse current Ipc has the same current value Ipc1 to Ipc8. The current value Ipc is set to be greater than the current value Ib of the base current Ib and smaller than the current value Ip of the peak current Ip.

[0069] When the base metal 18 and the welding wire 15 are made of aluminum or an aluminum alloy, oxides of molten aluminum may adhere to the surface of the base metal 18 as black, soot-like smut. When smut occurs in this manner, the aesthetic appearance of the surface of the base metal 18, including the weld bead 18A, is impaired. By superimposing the cleaning pulse current Ipc having the above-mentioned current value Ipc during the period when the base current Ib flows, the aluminum oxides that make up the smut are destroyed, and the adhesion of smut to the surface of the base metal 18 can be suppressed.

[0070] Furthermore, this modification can achieve the same effects as the configuration described in the embodiment. That is, droplets 15B of an appropriate size can be formed at the tip of welding wire 15 at the time of transition to pulse welding period Tp, while droplet detachment during droplet formation period Tdf can be suppressed. This allows droplets 15B to be stably detached from welding wire 15 at the beginning of pulse welding period Tp, ensuring a one-pulse, one-drop transition. As a result, the shape of weld bead 18A can be stabilized.

[0071] The arc welding control method disclosed herein is useful because it can stabilize droplet detachment when transitioning from a short-circuit welding period to a pulse welding period, improve the stability of arc welding, and reduce spatter.

[0072] REFERENCE SIGNS LIST 1 Input power supply 2 Primary rectifier 3 Switching unit 4 Transformer 5 Secondary rectifier 6 DCL (inductance) 7 Welding voltage detection unit 8 Welding current detection unit 9 Counter unit 10 Control switching unit 11 Short circuit welding control unit 12 Pulse welding control unit 13 Drive unit 14 Wire feed unit 15 Welding wire 15A Neck 15B Droplet 16 Welding torch 17 Arc 18 Base metal 18A Weld bead 19 Welding power source unit 20 Setting unit D101 Forward feed direction D102 Reverse feed direction Ib Base current Ibp Intermediate bending point current Ip Peak current Ipc Cleaning pulse current Idf First current Tdf Droplet formation period Tp Pulse welding period Ts Short circuit welding period Tss1 to Tss3 Short circuit period Tsa1 to Tsa3 Arc generation period WF Wire feed speed command value Wfb First speed command value Wff Second speed command value Wfd Third speed command value Wfp Fourth speed command value

Claims

1. A consumable electrode arc welding control method for arc welding a base material by alternately repeating pulse welding periods for performing pulse welding and short circuit welding periods for performing short circuit welding, wherein during the pulse welding period, a peak current and a base current are alternately passed through a welding wire as a welding current to generate an arc between the base material and the welding wire, the method transitions from the short circuit welding period to the pulse welding period via a preset droplet formation period, and during the droplet formation period, a first current having a current value different from the current value of the base current is passed through the welding wire.

2. The arc welding control method according to claim 1, wherein the droplet formation period is determined based on one or more of the material of the welding wire, the wire diameter, the set current, and the set feed speed.

3. The arc welding control method according to claim 1, wherein the current value of the first current is greater than the current value of the base current and less than the current value of the peak current.

4. The arc welding control method according to claim 1, wherein the current value of the first current is 100 A or more and 300 A or less.

5. The arc welding control method according to claim 1, wherein the droplet formation period is 1 msec or more and 5 msec or less.

6. The arc welding control method according to claim 1, wherein the wire feed speed command value during the droplet formation period is a negative value.

7. An arc welding control method according to claim 6, characterized in that the absolute value of the wire feed speed command value during the droplet formation period is smaller than the absolute value of the wire feed speed command value during the immediately preceding short-circuit welding period.

8. The arc welding control method according to claim 6, wherein the wire feed speed command value during the droplet formation period is not less than -40 m / min and not more than -5 m / min.

9. The arc welding control method according to claim 1, wherein the welding current is changed so that the welding current has an intermediate bending point immediately after the droplet formation period and before the peak current is passed through the welding wire.

10. An arc welding control method according to claim 9, wherein the welding current has one or more intermediate bending points, and during the period immediately after the droplet formation period and before the peak current is passed through the welding wire, the welding current waveform is composed of one or more straight lines or curves, or a combination of the straight lines and the curves.

11. The arc welding control method according to claim 9, wherein the current value of the welding current at the intermediate bending point is greater than the current value of the base current and less than the current value of the peak current.

12. The arc welding control method according to claim 1, wherein the time integral value of the first current is different from the time integral value of one peak current during the pulse welding period, with the current value of the base current as a reference.

13. The arc welding control method according to claim 12, wherein, when the base metal and the welding wire are made of mild steel, aluminum, or an aluminum alloy, the time integral value of the first current is smaller than the time integral value of the peak current following the droplet formation period.

14. The arc welding control method according to claim 12, wherein, when the base metal and the welding wire are made of stainless steel, the time integral value of the first current is greater than the time integral value of the peak current following the droplet formation period.

15. An arc welding control method according to claim 1, wherein, based on the current value of the base current, the time integral value of the first current when the base metal and the welding wire are made of stainless steel is greater than the time integral value of the first current when the base metal and the welding wire are made of mild steel, aluminum, or an aluminum alloy.

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