Ac arc welding method and arc welding device

Abstract

Provided is an AC arc welding method for welding a base material 200 by applying a welding current Iw to a welding wire 80 in a welding period Tw including first and second welding periods T1 and T2. In the first welding period T1, the welding wire 80 is sent forward to the base material 200 in a first feed amount Wf1, and a reverse polarity period T11 in which the welding wire 80 serves as a positive electrode and the base material 200 serves as a negative electrode and a positive polarity period T12 in which the welding wire 80 serves as a negative electrode and the base material 200 serves as a positive electrode are alternately performed. The second welding period T2 includes a short-circuit welding period T21 and a positive polarity period T22. In transition from the first welding period T1 to the second welding period T2, the feed amount of the welding wire 80 is changed to a second feed amount Wf2 (Wf2>Wf1).

Description

AC arc welding method and arc welding device

[0001] The present disclosure relates to an AC arc welding method and an arc welding apparatus.

[0002] Conventionally, an AC arc welding method has been known as one technique for consumable electrode arc welding, in which a base material is welded by alternately repeating a positive polarity period in which a welding current is passed through the welding wire, which is a consumable electrode, with the welding wire serving as the negative electrode and the base material, which is the workpiece, serving as the positive electrode, and a reverse polarity period in which a welding current is passed through the welding wire with the welding wire serving as the positive electrode and the base material, serving as the negative electrode (see, for example, Patent Documents 1 and 2).

[0003] During the positive polarity period in which the welding wire is negative, the melting rate of the welding wire increases, and therefore, during the positive polarity period, a droplet is generated at the tip of the welding wire and further grows.

[0004] On the other hand, during the reverse polarity period in which the welding wire is the positive electrode, the stability of the arc generated between the welding wire and the base metal is improved. Also, by setting the reverse polarity period as a pulse welding period in which a base current and a peak current higher than the base current are alternately passed through the welding wire, the transfer of the droplets formed at the tip of the welding wire to the base metal can be promoted.

[0005] International Publication No. 2020 / 235294 Patent No. 5263288

[0006] In recent years, there has been a demand for lighter automobiles, and accordingly, aluminum-based materials have been increasingly used as components for the body and frame. Here, aluminum-based materials refer to aluminum and aluminum alloys. In arc welding using aluminum-based materials, if the heat input to the base metal increases, burn-through of the base metal and other problems may occur.

[0007] On the other hand, when a plurality of components are butt-welded together, a welding method that produces a large amount of deposition is required to ensure a gap tolerance between the components.

[0008] Generally, in AC arc welding, the melting rate of the welding wire is increased during the positive polarity period when the welding wire is the negative polarity, thereby improving the deposition rate. However, increasing the proportion of the positive polarity period in the welding period can lead to an unstable arc. For this reason, it is necessary to ensure a certain proportion of the reverse polarity period, but during the reverse polarity period, the heat input to the base metal increases due to the arc force. It has been difficult to improve the deposition rate while suppressing the heat input to the base metal.

[0009] Furthermore, there is a demand for improved welding speeds when arc welding components in the automobile assembly process. In order to increase the welding speed while maintaining the deposition rate, it is necessary to increase the welding current as well, but this also increases the heat input to the base material.

[0010] Furthermore, depending on the welding application, it is required to improve the deposition rate while suppressing the amount of heat input to the base material, not limited to aluminum-based materials.

[0011] The present disclosure has been made in view of the above points, and its purpose is to provide an AC arc welding method and arc welding apparatus that can ensure a high deposition rate while suppressing the amount of heat input to the base metal.

[0012] In order to achieve the above object, an AC arc welding method according to the present disclosure is an AC arc welding method for welding a base material by flowing a welding current through the welding wire such that a predetermined welding period includes a reverse polarity period in which the welding wire is a positive electrode and the base material is a negative electrode, and a positive polarity period in which the welding wire is a negative electrode and the base material is a positive electrode, wherein the welding period includes a first welding period and a second welding period, wherein in the first welding period, the welding wire is forward fed toward the base material at a first feed rate, and arc welding in the reverse polarity period and arc welding in the positive polarity period are performed alternately, the second welding period includes a short-circuit welding period and the positive polarity period, and in the short-circuit welding period, the welding wire is short-circuited to the base material and then the short circuit between the welding wire and the base material is opened, and when transitioning from the first welding period to the second welding period, the feed rate of the welding wire is changed to a second feed rate that is greater than the first feed rate.

[0013] An arc welding apparatus according to the present disclosure is an arc welding apparatus including at least a welding power source that supplies a welding current to a welding wire, a welding torch that holds the welding wire, a wire feeder that feeds the welding wire forward toward a base material or feeds it backward away from the base material, and a control unit that controls the output of the welding power source and the operation of the wire feeder, wherein the arc welding apparatus welds the base material by flowing the welding current through the welding wire so that a welding period including a first welding period and a second welding period includes a reverse polarity period in which the welding wire is a positive electrode and the base material is a negative electrode, and a positive polarity period in which the welding wire is a negative electrode and the base material is a positive electrode, and the second welding period is a short-circuit welding period. When the welding period includes the positive polarity period, the control unit controls the operation of the wire feeder during the first welding period so that the welding wire is fed forward at a first feed rate toward the base material, and controls the welding current output from the welding power source so that arc welding during the reverse polarity period and arc welding during the positive polarity period are performed alternately; during the short circuit welding period, controls the operation of the wire feeder so that the welding wire is short-circuited to the base material and then the short circuit between the welding wire and the base material is opened; and when transitioning from the first welding period to the second welding period, controls the operation of the wire feeder so that the feed rate of the welding wire is changed to a second feed rate that is greater than the first feed rate.

[0014] According to the present disclosure, a high welding amount can be ensured while suppressing the amount of heat input to the base material.

[0015] FIG. 1 is a schematic diagram of an arc welding apparatus according to a first embodiment. FIG. 2 is an example of a time chart of heat input to a base metal during a welding period. FIG. 3 is a time chart of a welding current and a wire feed rate during a first welding period. FIG. 4 is a time chart of a welding current and a wire feed rate during a second welding period. FIG. 5 is a time chart of a welding current and a wire feed rate during a second welding period according to a second embodiment. FIG. 6 is an example of a time chart of heat input to a base metal during a welding period according to a modified example. FIG. 7 is a time chart of a welding current and a wire feed rate during a transition from a first welding period to a second welding period according to a modified example. FIG. 8 is a schematic diagram showing the appearance of a base metal and the position of a weld line according to a third embodiment. FIG. 9A is a time chart of heat input to a base metal in sections I and VII shown in FIG. 8. FIG. 9B is a time chart of heat input to a base metal in sections II and VI shown in FIG. 8. FIG. 9C is a time chart of heat input to a base metal in sections III and V shown in FIG. 8. Fig. 9D is a time chart of the amount of heat input to the base metal in section IV shown in Fig. 8. Fig. 10 is an example showing the point or timing at which the ratio between the first welding period and the second welding period is switched.

[0016] 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.

[0017] 1 shows a schematic configuration diagram of an arc welding apparatus according to a first embodiment, in which an arc welding apparatus 100 includes a welding power source 40, a welding torch 70, and a wire feeder 60. In this embodiment, the material of a base material 200 is an aluminum-based material. The material of a welding wire 80 is also an aluminum-based material, but it does not have to be the same as the material of the base material 200.

[0018] The welding power source 40 converts AC power supplied from the three-phase AC power source PS into power suitable for arc welding and outputs it to the welding wire 80 held in the welding torch 70. In this embodiment, a welding current Iw is supplied from the welding power source 40 to the welding wire 80. An arc ARC is generated between the tip of the welding wire 80 to which the welding current Iw is supplied and the base material 200, thereby welding the base material 200. The output of the welding power source 40 can be changed depending on the type of arc welding. For example, the output of the welding power source 40 may be a welding voltage Vw applied between the base material 200 and the welding wire 80.

[0019] The welding power source 40 has at least a power conversion unit 10, a welding output detection unit 20, a control unit 30, and an input unit 32, and the power conversion unit 10 has a first rectification unit 11, a first switching unit 12, a transformer 13, a second rectification unit 14, a reactor (DCL) 15, and a second switching unit 16.

[0020] The first rectifier 11 is composed of rectifying elements such as diodes and rectifies AC power received from the three-phase AC power supply PS. The first switching unit 12 is, for example, an inverter circuit composed of multiple transistors and switches the multiple transistors at predetermined timings to control the output of the first rectifier 11 to an output suitable for welding. The transformer 13 is, for example, a transformer with an iron core and converts the output of the first switching unit 12 to an output suitable for welding. The second rectifier 14 has a configuration similar to that of the first rectifier 11 and rectifies the output of the transformer 13. The reactor 15 is connected in series with the second rectifier 14 and smooths the output of the second rectifier 14. The second switching unit 16 has a configuration similar to that of the first switching unit 12 and switches multiple transistors at predetermined timings to adjust the output of the reactor 15.

[0021] In this embodiment, the output of second switching unit 16 is the aforementioned welding current Iw, which is supplied to welding wire 80 held by welding torch 70 via power cable 51. When the output of second switching unit 16 is welding voltage Vw, a predetermined voltage is applied between welding wire 80 and base material 200 via power cables 51 and 52, respectively.

[0022] Welding output detection unit 20 has a welding current detection unit 21 and a welding voltage detection unit 22. Welding current detection unit 21 detects the welding current Iw supplied to welding wire 80, and welding voltage detection unit 22 detects the welding voltage Vw applied between welding wire 80 and base material 200. The results detected by welding current detection unit 21 and welding voltage detection unit 22 are sent to control unit 30 and used to control arc welding. For example, the value of welding voltage Vw detected by welding voltage detection unit 22 can also be used to detect a short circuit between welding wire 80 and base material 200.

[0023] The control unit 30 is configured with one or more central processing units (CPUs), or alternatively, the control unit 30 is configured with one or more micro control units (MCUs).

[0024] In the example shown in FIG. 1 , a storage unit 31 is provided independent of the control unit 30. The storage unit 31 is configured with semiconductor memory such as a random access memory (RAM) or a read-only memory (ROM). The storage unit 31 may also be configured with a hard disk drive (HDD) or a solid state drive (SSD). The storage unit 31 may be a functional block of a CPU or an MCU, that is, a ROM or RAM built into the CPU or MCU. The storage unit 31 stores control programs and welding parameters for various devices used in arc welding.

[0025] Control unit 30 controls the switching operations of first switching unit 12 and second switching unit 16 in accordance with a predetermined welding program. Control unit 30 also receives the detection result of welding output detection unit 20, in this case welding current detection unit 21, and controls the switching operations of first switching unit 12 and second switching unit 16 based on the detection result so that welding current Iw becomes a predetermined set current. The set current refers to the moving average value of welding current Iw during a set welding period Tw.

[0026] Furthermore, the control unit 30 controls the operation of the wire feeder 60 in accordance with a predetermined welding program and in response to the welding current Iw. Specifically, the control unit 30 controls the feed direction and feed amount of the welding wire 80. Note that feeding the welding wire 80 so that the tip of the welding wire 80 approaches the base material 200 is referred to as forward feed, and feeding the welding wire 80 so that the tip of the welding wire 80 moves away from the base material 200 is referred to as reverse feed. The feed amount is the amount that the welding wire 80 moves per unit time, in other words, the feed speed, and the feed amount during forward feed is a positive value, and the feed amount during reverse feed is a negative value. Note that in the following description, the feed amount of the welding wire 80 may be referred to as wire feed amount Wf.

[0027] The input unit 32 is composed of, for example, a display device such as a liquid crystal display and an input device such as a keyboard, input buttons, a rotary encoder with a switch, etc. If the display device is a touch panel, the input device may be omitted.

[0028] The input unit 32 is used to set welding conditions for arc welding, such as a first welding period T1 and a second welding period T2, which will be described later.

[0029] Wire feeder 60 feeds welding wire 80 to welding torch 70. Specifically, wire feeder 60 is provided with a motor (not shown). The feed direction and feed amount of welding wire 80 are controlled by controlling the rotation direction and rotation amount of the motor using control signals from control unit 30. Wire feeder 60 is also provided with a feed amount detection unit (not shown), and the actual feed amount of welding wire 80 detected by the feed amount detection unit is transmitted to control unit 30. Control unit 30 receives the output of the feed amount detection unit and controls the rotation direction and rotation amount of the motor so that the feed direction and feed amount of welding wire 80 are set to preset values.

[0030] Welding torch 70 holds welding wire 80 fed from wire feeder 60 so that welding wire 80 and base material 200 face each other. Welding torch 70 is provided with a welding tip 71 for supplying welding current Iw output from welding power source 40 to welding wire 80.

[0031] Welding torch 70 may be held by a robot (not shown). In this case, the robot moves welding torch 70 at a predetermined speed (welding speed) along a predetermined welding line WL (see FIGS. 8 and 10 ) so that the distance between the tip of welding wire 80 and the surface of base material 200 is within a predetermined range.

[0032] 1, input unit 32 is provided in welding power source 40, but input unit 32 may be provided outside welding power source 40 as long as it is capable of communicating with control unit 30. For example, a teaching pendant (TP) 33 for teaching the robot the movement trajectory of welding torch 70 may be input unit 32. In this case, communication between teaching pendant 33, which is input unit 32, and control unit 30 may be wired or wireless.

[0033] [AC Arc Welding Method] FIG. 2 shows an example of a time chart of the heat input to the base metal during a welding period, FIG. 3 shows a time chart of the welding current and wire feed rate during a first welding period, and FIG. 4 shows a time chart of the welding current and wire feed rate during a second welding period.

[0034] In this embodiment, when arc welding an aluminum-based base metal 200, a welding period Tw including a first welding period T1 and a second welding period T2 is repeated a predetermined number of times, as shown in FIG. 2 . The number of times is changed depending on the length of the required weld and the welding speed. Note that in this embodiment, the welding period Tw includes one first welding period T1 and one second welding period T2, but is not particularly limited to this. As will be described later, for example, the welding period Tw may include the first welding period T1 multiple times.

[0035] The amount of heat input to base material 200 during second welding period T2 is set to be lower than the amount of heat input during first welding period T1. In the example shown in Figure 2, the difference between the amount of heat input during first welding period T1 and the amount of heat input during second welding period T2 is H.

[0036] As shown in Fig. 3, AC pulse welding is performed during the first welding period T1 of the welding period Tw. Specifically, peak currents are applied twice during each of the reverse polarity period T11 and the positive polarity period T12 immediately following the reverse polarity period T11. During the reverse polarity period T11, droplets (not shown) formed at the tip of the welding wire 80 are transferred to the base material 200. During the positive polarity period T12, droplets are transferred to the base material 200 in the same manner as during the reverse polarity period T11. However, during the positive polarity period T12, the melting rate of the welding wire 80 is higher than during the reverse polarity period T11, resulting in a larger amount of metal deposited on the base material 200.

[0037] Note that "reverse polarity" refers to a case where the welding wire 80 is a positive electrode and the base material 200 is a negative electrode, and during this period, i.e., during the reverse polarity period, a reverse polarity current flows through the welding wire 80. In this case, the power cable 51 is a positive side and the power cable 52 is a negative side. "Positive polarity" refers to a case where the welding wire 80 is a negative electrode and the base material 200 is a positive electrode, and during this period, i.e., during the positive polarity period, a positive polarity current flows through the welding wire 80. In this case, the power cable 51 is a negative side and the power cable 52 is a positive side.

[0038] In the example shown in FIG. 3, the value I of the two peak currents generated in the reverse polarity period T11 is ＰＰ１ , I ＰＰ２ are different. Also, the peak current I ＰＰ１ The value of the base current I just before the ＢＰ１ and peak current I ＰＰ２ The value of the base current I just before the ＢＰ２ Also, the values ​​I of the two peak currents generated in the positive polarity period T12 are different. ＰＮ１ , I ＰＮ２ are also different.

[0039] The peak current value I in the reverse polarity period T11 ＰＰ１ , I ＰＰ２ and base current I ＢＰ１ , I ＢＰ２ The values ​​of the peak current I are appropriately set to allow the droplets to be smoothly transferred to the base material 200. For the same reason, the peak current I ＰＰ１ , IＰＰ２ During the period when the base current I ＢＰ１ , I ＢＰ２ The duration for which each message is played is also set appropriately.

[0040] Peak current value I in the positive polarity period T12 ＰＮ１ , I ＰＮ２ and the value of the base current I ＢＮ１ are appropriately set to obtain an appropriate melting rate of the welding wire 80. For the same reason, the peak current I ＰＮ１ , I ＰＮ２ During the period when the base current I ＢＮ１ The duration for which each message is played is also set appropriately.

[0041] 3 , the wire feed rate Wf during the first welding period T1 is basically set to a constant positive value Wf1 (hereinafter, sometimes referred to as the first feed rate Wf1). However, when the first welding period T1 transitions to the second welding period T2, the operation of the wire feeder 60 is controlled so that the wire feed rate Wf changes from the first feed rate Wf1 to a feed rate Wf2 (hereinafter, sometimes referred to as the second feed rate Wf2; Wf2 > Wf1) that is larger than the first feed rate Wf1. Specifically, the controller 30 controls the operation of the wire feeder 60 so that the wire feed rate Wf increases from time ta immediately before the end of the first welding period T1, and becomes the second feed rate Wf2 at time tb immediately after the start of the second welding period T2.

[0042] 4, the second welding period T2 of the welding period Tw includes a short-circuit welding period T21 and a positive polarity period T22. In the short-circuit welding period T21, the tip of the welding wire 80 is brought into contact with the base material 200 and short-circuited, thereby transferring the molten tip of the welding wire 80 to the base material 200.

[0043] Immediately before the start of the second welding period T2, the welding current Iw is set to the base current value I at the start of the reverse polarity period T11 of the first welding period T1. ＢＰ１On the other hand, immediately after the start of second welding period T2, wire feed rate Wf becomes second feed rate Wf2, which is greater than first feed rate Wf1 of first welding period T1. Therefore, the tip of welding wire 80 approaches base material 200. When welding voltage detection unit 22 detects a short circuit between welding wire 80 and base material 200 at time tc, control unit 30 sets welding current Iw to I ＢＰ１ From I ＳＰ１ to prevent welding wire 80 from plunging too far into base material 200. Furthermore, by time td, the molten portion of welding wire 80 is reliably transferred to base material 200. At time td, control unit 30 reduces wire feed rate Wf from second feed rate Wf2 and increases welding current Iw.

[0044] At time te when welding wire 80 changes from forward feeding to reverse feeding and the wire feed rate reaches Wf3 (hereinafter, sometimes referred to as third feed rate Wf3. Wf3 is a negative value), control unit 30 reduces welding current Iw and I ＳＰ１ In this way, the tip of the welding wire 80 starts to move away from the base material 200.

[0045] When the welding voltage detection unit 22 detects a short circuit or open circuit between the welding wire 80 and the base material 200 at time tf, the control unit 30 increases the welding current Iw and further increases I ＳＰ２ In this state, the value of the welding current Iw (= I ＳＰ２ In this way, the welding wire 80 burns up, and the short circuit between the welding wire 80 and the base material 200 is reliably opened.

[0046] After a predetermined period of time has elapsed from time tf, the control unit 30 controls the wire feeder 60 to perform a forward feed operation. More specifically, the control unit 30 increases the wire feed rate Wf from the third feed rate Wf3 to the first feed rate Wf1. Furthermore, the welding current Iw is increased to I ＳＰ２ From I ＢＰ１ The wire feed rate Wf reaches the first feed rate Wf1, and the welding current Iw reaches the value at the end of the first welding period T1 (=I ＢＰ１), this state is maintained. After that, a transition to a positive polarity period T22 occurs. Note that the degree to which the welding current Iw is increased from time tf can be appropriately changed in consideration of both the short-circuit opening between the welding wire 80 and the base material 200 and the state of spatter generation caused by the pinch force.

[0047] The changes over time of the wire feed rate Wf and the welding current Iw during the positive polarity period T22 are similar to those during the positive polarity period T12 of the first welding period T1. Also during the positive polarity period T22, droplets are transferred to the base material 200, as in the positive polarity period T12. Furthermore, during the positive polarity period T22, the melting rate of the welding wire 80 is higher than during the reverse polarity period T11 of the first welding period T1, and as a result, the amount of welding to the base material 200 is also greater.

[0048] The peak current value I in the positive polarity period T22 ＰＮ３ , I ＰＮ４ and base current I ＢＮ３ The values ​​of the peak current I and the peak current I are appropriately set to obtain an appropriate melting rate of the welding wire 80. For the same reason, ＰＮ３ , I ＰＮ４ During the period when the base current I ＢＮ３ However, the values ​​of these signals do not necessarily have to be the same as the corresponding values ​​in the positive polarity period T12 of the first welding period T1.

[0049] The various parameters shown in Figures 2 to 4 may be set as they are in a predetermined welding program stored in memory unit 31, or these values ​​may be changed and set by separately inputting them from input unit 32.

[0050] For example, the welding period Tw, the first welding period T1, and the second welding period T2 may be set by a welding operator through separate input via the input unit 32. The ratio of the first welding period T1 to the second welding period T2 in the welding period Tw may also be set by a welding operator through separate input via the input unit 32. For example, as will be described later, the welding period Tw may be set to include one first welding period T1 and two second welding periods T2. Alternatively, the welding period Tw may be set to include four first welding periods T1 and one second welding period T2.

[0051] Similarly, the welding operator may separately input and set the number of reverse polarity periods T11 and the number of positive polarity periods T12 included in the first welding period T1 and the ratio of the reverse polarity periods T11 and the positive polarity periods T12 via the input unit 32.

[0052] The first feed rate Wf1 in the first welding period T1, and the second and third feed rates Wf2 and Wf3 in the second welding period T2 may also be set by being separately input from the input unit 32.

[0053] The value of the peak current during the reverse polarity period T11 of the first welding period T1, the number of times the peak current is passed, the period for which the peak current is passed, as well as the value of the base current and the period for which the base current is passed may also be set by the welding operator by separately inputting them into the input unit 32.

[0054] The value of the peak current during the positive polarity period T12 of the first welding period T1, the number of times the peak current is passed, the period for which the peak current is passed, and the value of the base current and the period for which the base current is passed may also be set by the welding operator by separately inputting them into the input unit 32.

[0055] The welding operator may separately input and set the number of short circuit welding periods T21 and positive polarity periods T22 included in the second welding period T2 and the ratio between the short circuit welding periods T21 and the positive polarity periods T22 via the input unit 32.

[0056] The value of the welding current Iw during the short-circuit welding period T21 of the second welding period T2 may also be set by the welding operator by separately inputting it through the input unit 32.

[0057] The value of the peak current during the positive polarity period T22 of the second welding period T2, the number of times the peak current is passed, the period for which the peak current is passed, and the value of the base current and the period for which the base current is passed may also be set by the welding operator by separately inputting them into the input unit 32.

[0058] [Effects, etc.] As described above, the AC arc welding method according to this embodiment welds the base material 200 by passing a welding current Iw through the welding wire 80 during a predetermined welding period Tw that includes the first welding period T1 and the second welding period T2. The welding period Tw also includes a reverse polarity period T11 in which the welding wire 80 is the positive electrode and the base material 200 is the negative electrode, and positive polarity periods T12 and T22 in which the welding wire 80 is the negative electrode and the base material 200 is the positive electrode.

[0059] In the first welding period T1, the welding wire 80 is fed forward toward the base material 200 at a first feed rate Wf1, and arc welding in a reverse polarity period T11 and arc welding in a positive polarity period T12 are alternately performed.

[0060] The second welding period T2 includes a short-circuit welding period T21 and a positive polarity period T22. In the short-circuit welding period T21, the welding wire 80 is short-circuited to the base material 200, and then the short circuit between the welding wire 80 and the base material 200 is released.

[0061] At the transition from the first welding period T1 to the second welding period T2, the feed rate of the welding wire 80 (wire feed rate Wf) is changed to a second feed rate Wf2 that is larger than the first feed rate Wf1.

[0062] According to this embodiment, the welding period Tw includes a first welding period T1, which is an AC pulse welding period, and a second welding period T2, which includes a short-circuit welding period T21. By ensuring the penetration depth in the first welding period T1 and performing short-circuit welding in the second welding period T2, the amount of heat input to the base material 200 is reduced. In other words, when viewed over the entire welding period Tw, the amount of heat input to the base material 200 can be reduced while ensuring the penetration depth.

[0063] Furthermore, by including the positive polarity period T12 in the first welding period T1 and the positive polarity period T22 in the second welding period T2, the amount of heat input to the base material 200 can be reduced while increasing the amount of melting of the welding wire 80 during the welding period Tw, and therefore the amount of welding to the base material 200.

[0064] Furthermore, these features ensure a sufficient gap between the members, suppressing burn-through during arc welding, and increasing the welding speed while ensuring a sufficient deposition amount.

[0065] As described above, the first welding period T1 is a pulse welding period in which a base current and a peak current having an absolute value greater than that of the base current are alternately passed through the welding wire 80. Furthermore, the positive polarity period T22 of the second welding period T2 is also a pulse welding period.

[0066] By setting the first welding period T1 as a pulse welding period, the amount of heat input necessary to obtain the desired penetration depth can be ensured. Also, by setting the positive polarity period T22 of the second welding period T2 as a pulse welding period, the droplets formed at the tip of the welding wire 80 can be reliably transferred to the base material 200.

[0067] During short-circuit welding period T21, the wire feed rate Wf is reduced from the second feed rate Wf2, and then the welding wire 80 is fed in the reverse direction so as to move away from the base material 200. After the wire feed rate Wf during the reverse direction is maintained at the third feed rate Wf3 for a predetermined period, the welding wire 80 is fed in the forward direction and maintained at the first feed rate Wf1.

[0068] By controlling the wire feed rate Wf in this manner, it is possible to reliably open the short circuit between the welding wire 80 and the base material 200. In addition, the welding current after the short circuit is opened is set to I ＳＰ１ From I ＳＰ２ By increasing the current I to 1, the burning of the welding wire 80 is promoted, and the short circuit between the welding wire 80 and the base material 200 can be reliably opened. ＳＰ２ can be changed appropriately depending on the set current, the diameter of the welding wire 80, the wire feed rate Wf, etc.

[0069] Arc welding apparatus 100 according to this embodiment includes at least a welding power source 40 that supplies welding current Iw to welding wire 80, a welding torch 70 that holds welding wire 80, a wire feeder 60, and a control unit 30. Wire feeder 60 feeds welding wire 80 forward toward base material 200 or backward away from base material 200. Control unit 30 controls the output of welding power source 40 and the operation of wire feeder 60.

[0070] Consider a case where a welding period Tw including a first welding period T1 and a second welding period T2 includes a reverse polarity period T11 and a positive polarity period T12, T22, and thereby welding the base material 200, and the second welding period T2 includes a short-circuit welding period T21 and a positive polarity period T22. The reverse polarity period T11 is a period during which the welding wire 80 is the positive electrode and the base material 200 is the negative electrode, and the positive polarity periods T12, T22 are periods during which the welding wire 80 is the negative electrode and the base material 200 is the positive electrode.

[0071] In this case, control unit 30 controls the output of welding power source 40 and the operation of wire feeder 60 as described below.

[0072] During first welding period T1, control unit 30 controls the operation of wire feeder 60 so that welding wire 80 is fed in the forward direction at first feed rate Wf1 toward base material 200. Furthermore, control unit 30 controls welding current Iw output from welding power source 40 so that arc welding during reverse polarity period T11 and arc welding during positive polarity period T12 are performed alternately during first welding period T1.

[0073] During the short circuit welding period T21 of the second welding period T2, the control unit 30 controls the operation of the wire feeding device 60 so as to short-circuit the welding wire 80 to the base material 200 and then open the short circuit between the welding wire 80 and the base material 200.

[0074] The control unit 30 controls the operation of the wire feeding device 60 so that, when transitioning from the first welding period T1 to the second welding period T2, the wire feed rate Wf is changed to a second feed rate Wf2 that is larger than the first feed rate Wf1.

[0075] By configuring the arc welding apparatus 100 in this manner, it is possible to reduce the amount of heat input to the base material 200 while ensuring the penetration depth over the entire welding period Tw. In addition, it is possible to increase the amount of melted welding wire 80 during the welding period Tw, and therefore the amount of welding to the base material 200.

[0076] In addition, during each of the first welding period T1 and the positive polarity period T22 of the second welding period T2, the control unit 30 controls the welding current Iw output from the welding power source 40 so that a base current and a peak current having an absolute value greater than that of the base current flow alternately through the welding wire 80.

[0077] By configuring the control unit 30 in this manner, the amount of heat input necessary to obtain the desired penetration depth can be ensured during the first welding period T1. Also, during the positive polarity period T22 of the second welding period T2, the molten metal droplet formed at the tip of the welding wire 80 can be reliably transferred to the base material 200.

[0078] During short-circuit welding period T21, control unit 30 controls the operation of wire feeder 60 to reduce wire feed rate Wf from second feed rate Wf2. Furthermore, control unit 30 controls the operation of wire feeder 60 to feed welding wire 80 in the reverse direction so as to separate welding wire 80 from base material 200, and then feed welding wire 80 in the forward direction to maintain welding wire 80 at first feed rate Wf1.

[0079] By configuring the control unit 30 in this manner, it is possible to reliably open the short circuit between the welding wire 80 and the base material 200. In addition, the control unit 30 controls the welding current Iw after the short circuit is opened to I ＳＰ１ From I ＳＰ２ The welding current Iw output from the welding power source 40 is controlled so as to increase to the value Iw. In this way, the burning of the welding wire 80 is promoted, and the short circuit between the welding wire 80 and the base material 200 can be reliably opened.

[0080] (Embodiment 2) Fig. 5 shows a time chart of the welding current and the wire feed rate during a second welding period according to embodiment 2. In Fig. 5 and the subsequent drawings, for the sake of convenience, the same parts as those in embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0081] The AC arc welding method of this embodiment differs from the short-circuit welding period T21 of the first embodiment in that the short-circuit welding period T21 of the second welding period T2 is a positive polarity period, as shown in Fig. 5. In other words, the control unit 30 controls the welding current Iw output from the welding power source 40 so that the short-circuit welding period T21 is a positive polarity period. In the short-circuit welding period T21 shown in Fig. 5, the value of the welding current Iw at time tc is I ＳＮ１ and the current value is I ＳＮ１ At time te, the current value increases again to I ＳＮ１ After reaching ＳＮ２ The current value I ＳＮ２ is the current value I ＰＮ３ After that, the current value rises again and I ＰＮ４ After the current value I reaches a constant value higher than the value I, the welding period T2 starts. As is clear from FIG. 4, the short circuit welding period T21 shown in the first embodiment is a reverse polarity period. ＳＮ２ can be changed appropriately depending on the set current, the diameter of the welding wire 80, the wire feed rate Wf, etc.

[0082] According to this embodiment, by setting the short-circuit welding period T21 of the second welding period T2 as a positive polarity period, the amount of heat input to the base material 200 during the second welding period T2 can be further reduced compared to the case shown in embodiment 1. In addition, the deposition amount can be further improved compared to the case shown in embodiment 1.

[0083] Furthermore, these features ensure a sufficient gap between the members, suppressing burn-through during arc welding, and increasing the welding speed while ensuring a sufficient deposition amount.

[0084] In addition, if the case in which the short-circuit welding period T21 in the second welding period T2 is changed to a reverse polarity period and a pulse welding period is defined as case A, the example shown in embodiment 1 is defined as case B, and the example shown in embodiment 2 is defined as case C, the relationship between each case and the amount of heat input to the base material 200 and the amount of welding is as shown in the following equations (1) and (2).

[0085] Amount of heat input to base material 200: (Case A) > (Case B) > (Case C) ... (1) Amount of deposition: (Case A) < (Case B) < (Case C) ... (2) As is clear from this, which of Cases A to C is selected is determined appropriately in order to obtain the desired amount of heat input to base material 200 and the desired amount of deposition.

[0086] Fig. 6 is an example of a time chart of the heat input to the base material during a welding period according to a modified example. Fig. 7 is a time chart of the welding current and the wire feed rate during a transition from a first welding period to a second welding period according to a modified example.

[0087] As described above, the ratio of the first welding period T1 to the second welding period T2 in the welding period Tw is not limited to the example shown in embodiment 1 and can be changed as appropriate. For example, as shown in Fig. 6, the second welding period T2 may be provided consecutively after the first welding period T1 has elapsed.

[0088] In this case, as shown in Fig. 7 , after the end of the previous second welding period T2, the wire feed rate Wf is increased from the first feed rate Wf1 to the second feed rate Wf2 for a predetermined period after the start of the next second welding period T2. Furthermore, not limited to the example shown in Fig. 7 , when the second welding period T2 includes consecutive periods in the welding period Tw, the AC arc welding method according to this modification increases the wire feed rate Wf to the second feed rate Wf2 when transitioning from one second welding period T2 to the next second welding period T2. In other words, when the second welding period T2 includes consecutive periods in the welding period Tw, the control unit 30 of the arc welding apparatus 100 according to this modification controls the operation of the wire feeder 60 to increase the wire feed rate Wf to the second feed rate Wf2 when transitioning from one second welding period T2 to the next second welding period T2.

[0089] In this way, the base material 200 and the welding wire 80 can be reliably short-circuited during the short-circuit welding period T21 of the second welding period T2.

[0090] 5, when the second welding period T2 includes consecutive periods and the short-circuit welding period T21 is a positive polarity period, the wire feed rate Wf is increased and changed to the second feed rate Wf2 when transitioning from one second welding period T2 to the next second welding period T2. In this way, the base material 200 and the welding wire 80 can be reliably short-circuited during the short-circuit welding period T21 of the second welding period T2.

[0091] According to this modification, even if the second welding period T2 includes a continuous period in the welding period Tw, the droplets formed at the tip of the welding wire 80 can be reliably transferred to the base material 200 during the short-circuit welding period T21. In addition, the amount of deposition can be improved while reducing the amount of heat input to the base material 200.

[0092] (Embodiment 3) Fig. 8 is a schematic diagram showing the appearance of a base metal and the position of a weld line according to embodiment 3. Fig. 9A is a time chart of the amount of heat input to the base metal in sections I and VII shown in Fig. 8. Fig. 9B is a time chart of the amount of heat input to the base metal in sections II and VI shown in Fig. 8. Fig. 9C is a time chart of the amount of heat input to the base metal in sections III and V shown in Fig. 8. Fig. 9D is a time chart of the amount of heat input to the base metal in section IV shown in Fig. 8.

[0093] FIG. 10 shows an example of the point or timing at which the ratio between the first welding period and the second welding period is switched.

[0094] The base material 200 shown in Fig. 8 is made of two plates, and is arranged so that the side of the standing plate 220 contacts the surface of the bottom plate 210. The standing plate 220 is welded to the bottom plate 210 so as to surround the outer periphery of the contact surface between the bottom plate 210 and the standing plate 220. In other words, as shown in Fig. 8, the weld line WL is an imaginary line that follows the outer periphery of the contact surface between the bottom plate 210 and the standing plate 220. Furthermore, both the bottom plate 210 and the standing plate 220 are made of an aluminum-based material.

[0095] In the base material 200 having the structure shown in Fig. 8, due to its shape, there are portions along the weld line WL where heat is likely to accumulate during welding and portions where heat is unlikely to accumulate. For example, in sections I and VII shown in Fig. 8, heat is most likely to accumulate during welding, and heat is less likely to accumulate as the distance from these sections increases.

[0096] In such a case, by gradually changing the amount of heat input to the base material 200, it is possible to prevent the appearance of the weld bead (not shown) formed along the weld line WL from suddenly changing midway.

[0097] For example, in section IV, where heat buildup is least likely to occur, as shown in Fig. 9A, the first welding period T1 is provided four consecutive times in the welding period Tw, followed by a second welding period T2 with a lower heat input. In sections II and V, which are located on either side of section IV, the first welding period T1 is provided three consecutive times in the welding period Tw, followed by a second welding period T2 with a lower heat input, as shown in Fig. 9B. In sections III and VI, the first welding period T1 is provided two consecutive times in the welding period Tw, followed by a second welding period T2 with a lower heat input, as shown in Fig. 9C. In section IV, where heat buildup is least likely to occur during welding, the first welding period T1 is provided once in the welding period Tw, followed by a second welding period T2 with a lower heat input, as shown in Fig. 9D.

[0098] The method of changing the ratio between the first welding period T1 and the second welding period T2 during the welding period Tw is not limited to the examples shown in Figures 9A to 9D. For example, if the size of the base material 200 is small, arc welding may be performed at the ratio shown in Figure 9C in sections II and V. Alternatively, arc welding may be performed at the ratio shown in Figure 9B in sections III and VI.

[0099] In the following description, the process of gradually changing the ratio of the first welding period T1 to the second welding period T2 included in the welding period Tw may be referred to as slope processing.

[0100] As described above, it is preferable to perform arc welding by performing slope processing before and after a portion where heat is likely to accumulate in the base material 200 during welding. Typical examples of portions where heat is likely to accumulate in the base material 200 include portions where the shape or material of the base material 200 changes along the weld line WL.

[0101] That is, in the AC arc welding method shown in this embodiment, the ratio of the first welding period T1 to the second welding period T2 included in the welding period Tw is changed in accordance with changes in the shape or material of the base metal 200. Furthermore, when the base metal 200 is welded along a predetermined weld line WL and the heat input to the base metal 200 is made smaller in one section of the weld line WL than in other sections, the ratio of the first welding period T1 included in the welding period Tw is made smaller in the one section than in the other sections.

[0102] These controls are executed by the control unit 30 of the welding power source 40 in accordance with the contents preset by the welding operator.

[0103] Furthermore, the point or timing at which the ratio of the first welding period T1 to the second welding period T2 included in the welding period Tw is changed is not limited to a point at which the shape of the base material 200 changes.

[0104] Depending on the shape and material of the base metal 200, the ratio of the first welding period T1 to the second welding period T2 included in the welding period Tw may be changed at intervals of a predetermined distance L along the weld line WL, as shown in Fig. 10. For example, the slope processing described above may be performed at intervals of a predetermined distance L along the weld line WL.

[0105] Furthermore, when the welding torch 70 is held by a robot, as shown in FIG. 10 , predetermined teaching points Pi (i is an integer, 0≦i≦n) are set along the welding line WL. The teaching points Pi are points where the movement trajectory or movement speed of the robot changes. In this case, the ratio of the first welding period T1 to the second welding period T2 included in the welding period Tw may be changed for each teaching point Pi. For example, the slope processing described above may be performed for each teaching point Pi along the welding line WL.

[0106] Furthermore, when the welding speed is constant, the ratio of the first welding period T1 to the second welding period T2 included in the welding period Tw may be changed along the weld line WL for each predetermined period (t(j+1)-tj) (j is an integer, 0≦j≦(n-1)). For example, the slope processing described above may be performed along the weld line WL for each period (t(j+1)-tj).

[0107] In this case, the control is also performed by control unit 30 of welding power source 40 in accordance with the contents preset by the welding operator.

[0108] (Other Embodiments) In the first to third embodiments and the modified examples, the base material 200 and the welding wire 80 are each made of an aluminum-based material, but the materials of the base material 200 and the welding wire 80 are not particularly limited to this. For example, the base material 200 and the welding wire 80 may be made of stainless steel. In this case, too, the material of the welding wire 80 does not have to be the same as the material of the base material 200.

[0109] Furthermore, a pipe for a shielding gas to be sprayed onto the base material 200 during arc welding may be provided integrally with the power cable 51 connected to the welding torch 70 .

[0110] The AC arc welding method of the present disclosure is industrially useful because it can ensure a high deposition rate while reducing the amount of heat input to the base metal.

[0111] REFERENCE SIGNS LIST 10 Power conversion unit 11 First rectification unit 12 First switching unit 13 Transformer 14 Second rectification unit 15 Reactor 16 Second switching unit 20 Welding output detection unit 21 Welding current detection unit 22 Welding voltage detection unit 30 Control unit 31 Memory unit 32 Input unit 33 Teaching pendant (input unit) 40 Welding power source 51 Power cable 52 Power cable 60 Wire feeder 70 Welding torch 71 Welding tip 80 Welding wire 100 Arc welding device 200 Base material 210 Bottom plate 220 Standing plate ARC Arc PS Three-phase AC power supply WL Welding wire

Claims

1. An AC arc welding method for welding a base material by flowing a welding current through the welding wire such that a predetermined welding period includes a reverse polarity period in which the welding wire is the positive electrode and the base material is the negative electrode, and a positive polarity period in which the welding wire is the negative electrode and the base material is the positive electrode, wherein the welding period includes a first welding period and a second welding period, wherein in the first welding period, the welding wire is forward fed toward the base material at a first feed rate, and arc welding in the reverse polarity period and arc welding in the positive polarity period are performed alternately, wherein the second welding period includes a short circuit welding period and the positive polarity period, and in the short circuit welding period, the welding wire is short-circuited to the base material and then the short circuit between the welding wire and the base material is opened, and wherein at the transition from the first welding period to the second welding period, the feed rate of the welding wire is changed to a second feed rate that is greater than the first feed rate.

2. An AC arc welding method as claimed in claim 1, characterized in that during the first welding period and the positive polarity period of the second welding period, a base current and a peak current having an absolute value greater than that of the base current are alternately passed through the welding wire.

3. An AC arc welding method according to claim 1, characterized in that the short circuit welding period is the reverse polarity period.

4. An AC arc welding method according to claim 1, characterized in that the short circuit welding period is the positive polarity period.

5. An AC arc welding method as claimed in claim 1, characterized in that, during the short circuit welding period, the welding wire feed rate is reduced from the second feed rate, the welding wire is then fed in a reverse direction away from the base metal, and the welding wire is then fed in a forward direction to maintain the first feed rate.

6. An AC arc welding method as claimed in claim 1, characterized in that the welding period includes a period in which the second welding periods are successive, and at the transition from one second welding period to the next, the feed rate of the welding wire is increased to change to the second feed rate.

7. An AC arc welding method as claimed in claim 1, characterized in that the ratio of the first welding period to the second welding period included in the welding period is changed in response to a change in the shape or material of the base metal.

8. An AC arc welding method as claimed in claim 7, characterized in that, when the base metal is welded along a predetermined weld line and the heat input to the base metal is made smaller in one section of the weld line than in other sections, the proportion of the first welding period included in the welding period is made smaller in the one section than in the other sections.

9. An AC arc welding method as claimed in claim 1, characterized in that, when the base material is welded along a predetermined weld line, the ratio of the first welding period to the second welding period included in the welding period can be changed at every predetermined distance along the weld line, or every predetermined period, or every predetermined teaching point on the weld line.

10. An arc welding apparatus comprising at least a welding power source that supplies a welding current to a welding wire, a welding torch that holds the welding wire, a wire feeder that feeds the welding wire in a forward direction toward a base metal or in a reverse direction away from the base metal, and a control unit that controls the output of the welding power source and the operation of the wire feeder, wherein the base metal is welded by flowing the welding current through the welding wire such that a welding period including a first welding period and a second welding period includes a reverse polarity period in which the welding wire is a positive electrode and the base metal is a negative electrode and a positive polarity period in which the welding wire is a negative electrode and the base metal is a positive electrode, and when the second welding period includes a short circuit welding period and the positive polarity period, the control unit: controls the operation of the wire feeder so that the welding wire is forward fed at a first feed rate toward the base metal in the first welding period, and controls the welding current output from the welding power source so that arc welding in the reverse polarity period and arc welding in the positive polarity period are performed alternately; the operation of the wire feeding device is controlled so that, during the short circuit welding period, the welding wire is short-circuited to the base material and then the short circuit between the welding wire and the base material is released; and, at a transition from the first welding period to the second welding period, the operation of the wire feeding device is controlled so that the feeding amount of the welding wire is changed to a second feeding amount that is greater than the first feeding amount.

11. An arc welding apparatus as claimed in claim 10, characterized in that, during each of the first welding period and the positive polarity period of the second welding period, the control unit controls the welding current output from the welding power source so that a base current and a peak current having an absolute value greater than that of the base current flow alternately through the welding wire.

12. The arc welding device according to claim 10, wherein the control unit controls the welding current output from the welding power source so that the short circuit welding period coincides with the reverse polarity period.

13. The arc welding device according to claim 10, wherein the control unit controls the welding current output from the welding power source so that the short circuit welding period coincides with the positive polarity period.

14. An arc welding apparatus as defined in claim 10, characterized in that the control unit controls the operation of the wire feeding device so as to reduce the feeding rate of the welding wire from the second feeding rate, feed the welding wire in a reverse direction away from the base material, and then feed the welding wire in a forward direction, and then maintain the welding wire at the first feeding rate.

15. An arc welding apparatus as claimed in claim 10, characterized in that, when the welding period includes a period in which the second welding period is continuous, the control unit controls the operation of the wire feeding device to increase the amount of welding wire fed at the transition from one second welding period to the next second welding period, so as to achieve the second feeding amount.

16. An arc welding apparatus as claimed in claim 10, characterized in that the control unit is configured to be able to change the ratio of the first welding period to the second welding period included in the welding period in response to changes in the shape or material of the base metal.

17. An arc welding apparatus as claimed in claim 16, characterized in that, when the base material is welded along a predetermined weld line and the heat input to the base material is made smaller in one section of the weld line than in other sections, the control unit makes the proportion of the first welding period included in the welding period smaller in the one section than in the other sections.

18. An arc welding apparatus as defined in claim 10, characterized in that, when the base material is welded along a predetermined welding line, the control unit is configured to be able to change the ratio of the first welding period and the second welding period included in the welding period at predetermined distances along the welding line, or at predetermined intervals, or at predetermined teaching points on the welding line.