Ac consumable electrode arc welding control method

Abstract

To obtain essential welding quality by preventing occurrences of welding defects, such as burn through and defective weld penetration, when performing the weaving weld of a lap fillet joint and a butt joint, different in plate thickness, in an AC consumable electrode arc welding method.SOLUTION: An AC consumable electrode arc welding control method in which an electrode polarity is periodically switched between an electrode positive polarity period and an electrode negative polarity period, each of which includes a plurality of cycles of a short-circuit period and an arc period, and a welding torch is welded while woven so as to cross a boundary line between a first workpiece and a second workpiece, comprises: when the first workpiece is thinner than the second workpiece, welding the first workpiece from time t4 to time t7, in the electrode negative polarity period in which a weld current Iw and a weld voltage Vw are negative values, and welding the second workpiece from time t1 to time t4, in the electrode-positive polarity period in which the weld current Iw and the weld voltage Vw are positive values.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for controlling AC consumable electrode arc welding in which a short circuit period and an arc period are repeated between a welding wire and a workpiece, and the electrode polarity is periodically switched between an electrode positive polarity period and an electrode negative polarity period. [Background technology]

[0002] An AC consumable electrode arc welding method is commonly used in which welding is performed by periodically switching the electrode polarity between an electrode positive polarity period and an electrode negative polarity period including a plurality of cycles of short circuit periods and arc periods (see, for example, Patent Document 1).

[0003] In addition, welding may be performed while weaving the welding torch so as to cross the boundary line between the first workpiece and the second workpiece. Patent Document 2 discloses an invention in which a change in welding conditions is synchronized with the weaving operation of the welding torch. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6601870 [Patent Document 2] Patent No. 4958630 Summary of the Invention [Problem to be solved by the invention]

[0005] Weaving welding is used when welding lap fillet joints and butt joints formed from a first workpiece and a second workpiece having different plate thicknesses. However, there is a problem that the thinner plate side melts through, causing welding defects.

[0006] Therefore, an object of the present invention is to provide a method for controlling AC consumable electrode arc welding that can suppress the occurrence of welding defects such as burn-through and poor penetration and obtain sufficient welding quality when weaving lap fillet joints and butt joints having different plate thicknesses. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the invention of claim 1 comprises: A short circuit period and an arc period are repeated between the welding wire and the base metal, cyclically switching the electrode polarity between an electrode positive polarity period and an electrode negative polarity period including a plurality of cycles of the short circuit period and the arc period; 1. A method for controlling AC consumable electrode arc welding in which a welding torch is weaved across a boundary line between a first workpiece and a second workpiece, the method comprising: When the first workpiece is thinner than the second workpiece, the first workpiece is welded in the electrode negative polarity period, and the second workpiece is welded in the electrode positive polarity period. The present invention relates to a method for controlling AC consumable electrode arc welding.

[0008] The invention of claim 2 is as follows: The switching between the electrode negative polarity period and the electrode positive polarity period is performed at a point when the welding torch passes over a weld line. 2. The method for controlling AC consumable electrode arc welding according to claim 1, wherein:

[0009] The invention of claim 3 is as follows: The switching between the electrode negative polarity period and the electrode positive polarity period is performed during the short circuit period after the welding torch has passed over the weld line. 2. The method for controlling AC consumable electrode arc welding according to claim 1, wherein: Effect of the Invention

[0010] According to the AC consumable electrode arc welding control method of the present invention, when weaving welding lap fillet joints and butt joints having different plate thicknesses, the occurrence of welding defects such as burn-through and poor penetration can be suppressed, thereby achieving sufficient welding quality. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram of a welding power source for implementing an AC consumable electrode arc welding control method according to an embodiment of the present invention. [Diagram 2] 2 is a timing chart of each signal in the welding power source of FIG. 1 , illustrating a method for controlling AC consumable electrode arc welding according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 1 is a block diagram of a welding power source for carrying out a method for controlling AC consumable electrode arc welding according to an embodiment of the present invention. Each block will be described below with reference to the diagram.

[0014] The power supply main circuit PM receives a commercial power supply (not shown) such as a three-phase 200V power supply, an error amplified signal Ea (described later) and a polarity switching signal Spn (described later), performs output control based on the error amplified signal Ea by a primary inverter circuit, switches the electrode polarity between electrode positive polarity EP and electrode negative polarity EN based on the polarity switching signal Spn by a secondary inverter circuit, and outputs an AC welding voltage Vw and welding current Iw. Although not shown, the power supply main circuit PM includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smoothes the rectified DC, a primary inverter circuit driven by the error amplified signal Ea that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for welding, a secondary rectifier that rectifies the stepped-down high-frequency AC into DC, a reactor that smooths the rectified DC, and a secondary inverter circuit driven by the polarity switching signal Spn that converts the smoothed DC into an AC output.

[0015] The feed motor WM receives a feed control signal Fc, which will be described later, and alternates between forward and reverse feed to feed the welding wire 1 at a feed speed Fw. A motor with fast transient response is used for the feed motor WM. In order to increase the rate of change of the feed speed Fw of the welding wire 1 and the reversal of the feed direction, the feed motor WM may be installed near the tip of the welding torch 4. Also, two feed motors WM may be used to form a push-pull type feed system.

[0016] The welding wire 1 is fed through the welding torch 4 by the rotation of a feed roll 5 coupled to the above-mentioned feed motor WM, and an arc 3 is generated between the workpiece 2 and the welding wire 1. An AC welding voltage Vw is applied between a power feed tip (not shown) in the welding torch 4 and the workpiece 2, and an AC welding current Iw flows through the workpiece 2. A shielding gas (not shown) is ejected from the tip of the welding torch 4. As the shielding gas, carbon dioxide gas, a mixed gas of carbon dioxide gas and argon gas, a mixed gas of oxygen and argon gas, or the like is used.

[0017] Work 2 is a lap fillet joint or a butt joint formed from a first work and a second work. In the case of a lap fillet joint, the first member and the second member are overlapped, and the first work, which is only the first member, is made of a thinner plate than the second work, which is made of the first member and the second member. In the case of a butt joint, it is formed from the first work of the first member and the second work of the second member, and the first work is made of a thinner plate than the second work.

[0018] The robot RM is equipped with the above-mentioned feed motor WM and the above-mentioned welding torch 4, and moves the position of the torch tip by receiving a movement control signal Rc, which will be described later, as an input.

[0019] The robot control device RC outputs a movement control signal Rc for moving the torch tip position along the weld line while weaving according to the stored teaching data, and outputs a weaving position signal Pw of the torch tip position. Weaving is performed in a direction perpendicular to the weld line. The weaving position signal Pw is a signal that is at a high level when the torch tip position is on the right half cycle (second work) from the weld line, and is at a low level when it is on the left half cycle (first work).

[0020] The voltage setting circuit VR outputs a predetermined voltage setting signal Vr for setting the welding voltage Vw during the second arc period in the electrode positive polarity period. The voltage detection circuit VD detects the welding voltage Vw, converts it to an absolute value, and outputs a voltage detection signal Vd. The short circuit determination circuit SD receives the voltage detection signal Vd as input, and outputs a short circuit determination signal Sd that goes to High level when this value is less than a predetermined short circuit determination value (approximately 10 V) and determines that a short circuit period is occurring, and goes to Low level when this value is equal to or greater than this value and determines that an arc period is occurring.

[0021] The voltage error amplifier circuit EV receives the voltage setting signal Vr and the voltage detection signal Vd, amplifies the error between the two signals, and outputs a voltage error amplified signal Ev.

[0022] A current detection circuit ID detects the above-mentioned welding current Iw, converts it into an absolute value, and outputs a current detection signal Id.

[0023] The forward acceleration period setting circuit TSUR receives a polarity switching signal Spn (described later) as an input, and outputs a forward acceleration period setting signal Tsur which becomes a predetermined electrode positive polarity forward acceleration period when the polarity switching signal Spn is at a high level (electrode positive polarity period), and becomes a predetermined electrode negative polarity forward acceleration period when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, the electrode negative polarity forward acceleration period is set to a period shorter than the electrode positive polarity forward acceleration period.

[0024] The forward feed deceleration period setting circuit TSDR receives a polarity switching signal Spn (described later) as an input, and outputs a forward feed deceleration period setting signal Tsdr which sets a predetermined electrode positive polarity forward feed deceleration period when the polarity switching signal Spn is at a high level (electrode positive polarity period), and sets a predetermined electrode negative polarity forward feed deceleration period when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, the electrode negative polarity forward feed deceleration period is set to a period shorter than the electrode positive polarity forward feed deceleration period.

[0025] The reverse acceleration period setting circuit TRUR receives a polarity switching signal Spn (described later) as an input, and outputs a reverse acceleration period setting signal Trur which becomes a predetermined electrode positive polarity reverse acceleration period when the polarity switching signal Spn is at a high level (electrode positive polarity period), and becomes a predetermined electrode negative polarity reverse acceleration period when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, the electrode negative polarity reverse acceleration period is set to a period shorter than the electrode positive polarity reverse acceleration period.

[0026] The reverse deceleration period setting circuit TRDR receives a polarity switching signal Spn (described later) as an input, and outputs a reverse deceleration period setting signal Trdr which sets a predetermined electrode positive polarity reverse deceleration period when the polarity switching signal Spn is at a high level (electrode positive polarity period), and sets a predetermined electrode negative polarity reverse deceleration period when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, the electrode negative polarity reverse deceleration period is set to a period shorter than the electrode positive polarity reverse deceleration period.

[0027] The positive feed peak value setting circuit WSR receives a polarity switching signal Spn (described later) as an input, and outputs a positive feed peak value setting signal Wsr which becomes a predetermined electrode positive polarity positive feed peak value when the polarity switching signal Spn is at a high level (electrode positive polarity period), and becomes a predetermined electrode negative polarity positive feed peak value when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, the absolute value of the electrode negative polarity positive feed peak value is set to a value larger than the absolute value of the electrode positive polarity positive feed peak value.

[0028] The reverse peak value setting circuit WRR receives a polarity switching signal Spn (described later) as an input, and outputs a reverse peak value setting signal Wrr which is a predetermined electrode positive polarity reverse peak value when the polarity switching signal Spn is at a high level (electrode positive polarity period), and is a predetermined electrode negative polarity reverse peak value when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, the absolute value of the electrode negative polarity reverse peak value is set to a value larger than the absolute value of the electrode positive polarity reverse peak value.

[0029] The feed speed setting circuit FR receives the forward feed acceleration period setting signal Tsur, the forward feed deceleration period setting signal Tsdr, the reverse feed acceleration period setting signal Trur, the reverse feed deceleration period setting signal Trdr, the forward feed peak value setting signal Wsr, the reverse feed peak value setting signal Wrr, and the short circuit determination signal Sd as inputs, and outputs a feed speed pattern generated by the following process as a feed speed setting signal Fr. When this feed speed setting signal Fr is 0 or more, it is a forward feed period, and when it is less than 0, it is a reverse feed period. 1) During the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur, a feed speed setting signal Fr is output that accelerates from 0 to the forward feed peak value Wsp, which is a positive value determined by the forward feed peak value setting signal Wsr. 2) Subsequently, during the forward feed peak period Tsp, the feed speed setting signal Fr for maintaining the forward feed peak value Wsp is output. 3) When the short circuit discrimination signal Sd changes from a low level (arc period) to a high level (short circuit period), the process transitions to the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr, and the feed speed setting signal Fr is output, which decelerates the feed speed from the forward feed peak value Wsp to 0. 4) Subsequently, during the reverse acceleration period Tru determined by the reverse acceleration period setting signal Trur, a feed speed setting signal Fr is output which accelerates from 0 to the reverse peak value Wrp, which is a negative value determined by the reverse peak value setting signal Wrr. 5) Subsequently, during the backward transport peak period Trp, the feed speed setting signal Fr for maintaining the above-mentioned backward transport peak value Wrp is output. 6) When the short circuit detection signal Sd changes from a high level (short circuit period) to a low level (arc period), the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr begins, and the feed speed setting signal Fr is output, which decelerates the reverse feed speed from the above-mentioned reverse feed peak value Wrp to 0. 7) By repeating the above steps 1) to 6), a feed speed setting signal Fr is generated having a feed pattern that changes like a positive and negative trapezoidal wave.

[0030] The feed control circuit FC receives the feed speed setting signal Fr as an input and outputs a feed control signal Fc to the feed motor WM for feeding the welding wire 1 at a feed speed Fw corresponding to the value of the feed speed setting signal Fr.

[0031] The constriction detection circuit ND takes the above short - circuit discrimination signal Sd, the above voltage detection signal Vd, and the above current detection signal Id as inputs. When the short - circuit discrimination signal Sd is at the High level (short - circuit period), when the voltage rise value of the voltage detection signal Vd reaches the reference value, it determines that the constriction formation state has reached the reference state and becomes High level, and outputs a constriction detection signal Nd that becomes Low level when the short - circuit discrimination signal Sd changes to the Low level (arc period). Also, the constriction detection signal Nd may be changed to High level when the differential value of the voltage detection signal Vd during the short - circuit period reaches the corresponding reference value. Further, the value of the voltage detection signal Vd is divided by the value of the current detection signal Id to calculate the resistance value of the droplet, and the constriction detection signal Nd may be changed to High level when the differential value of this resistance value reaches the corresponding reference value.

[0032] The low - level current setting circuit ILR outputs a predetermined low - level current setting signal Ilr. The current comparison circuit CM takes this low - level current setting signal Ilr and the above current detection signal Id as inputs, and outputs a current comparison signal Cm that becomes High level when Id < Ilr and becomes Low level when Id ≧ Ilr.

[0033] The first arc current setting circuit IA1R takes the polarity switching signal Spn described later as an input. When the polarity switching signal Spn is at the High level, it becomes a predetermined electrode - positive - polarity first arc current value, and when the polarity switching signal Spn is at the Low level, it outputs a first arc current setting signal Ia1r that becomes a predetermined electrode - negative - polarity first arc current value. Here, the electrode - positive - polarity first arc current value > the electrode - negative - polarity first arc current value.

[0034] The electrode - negative - polarity second arc current setting circuit IA2R outputs a predetermined electrode - negative - polarity second arc current setting signal Ia2r. The electrode - negative - polarity second arc current setting signal Ia2r is a value that decreases with time during the second arc period in the electrode - negative - polarity period.

[0035] The current drop time setting circuit TDR receives as input the first arc current setting signal Ia1r and a polarity switching signal Spn described later, and outputs a current drop time setting signal Tdr which becomes a predetermined electrode positive polarity current drop time when the polarity switching signal Spn is at a High level, and which becomes an electrode negative polarity current drop time which changes depending on the electrode negative polarity first arc current value of the first arc current setting signal Ia1r when the polarity switching signal Spn is at a Low level.

[0036] The third arc period circuit STA3 receives as input the above-mentioned short circuit determination signal Sd and the above-mentioned current drop time setting signal Tdr, and outputs a third arc period signal Sta3 which goes to a High level when the current drop time Td determined by the current drop time setting signal Tdr has elapsed from the time when the short circuit determination signal Sd changes to a Low level (arc period), and which goes to a Low level when the short circuit determination signal Sd subsequently goes to a High level (short circuit period).

[0037] The third arc current setting circuit IA3R outputs a predetermined third arc current setting signal Ia3r.

[0038] The electrode positive polarity rise rate setting circuit SPR outputs a predetermined electrode positive polarity rise rate setting signal Spr [A / ms]. The electrode negative polarity rise rate setting circuit SNR receives the first arc current setting signal Ia1r and outputs an electrode negative polarity rise rate setting signal Snr [A / ms] calculated by a predetermined rise rate setting function. 1) Snr <Sprである。 2) Snr is 50% or less of Spr, and more preferably 30% or less. 3) The Snr is set in the range of 50 to 500 A / ms, and more preferably in the range of 50 to 200 A / ms. 4) Snr is a function of Ia1r, and the larger Ia1r is, the smaller Snr is. For example, when Ia1r varies in the range of 300 to 400 A, the function sets Snr at Ia1r=400 to a value 20% smaller than when Ia1r=300.

[0039] The rise rate setting circuit SR receives as input the electrode positive polarity rise rate setting signal Spr, the electrode negative polarity rise rate setting signal Snr, and a polarity switching signal Spn described below, and outputs the electrode positive polarity rise rate setting signal Spr as the rise rate setting signal Sr when the polarity switching signal Spn is at a High level, and outputs the electrode negative polarity rise rate setting signal Snr as the rise rate setting signal Sr when the polarity switching signal Spn is at a Low level.

[0040] The polarity switching circuit SPN receives the weaving position signal Pw and the short circuit determination signal Sd, performs the following processing, and outputs a polarity switching signal Spn. 1) When the weaving position signal Pw changes to a high level and then the short circuit determination signal Sd becomes a high level (short circuit period), the polarity switching signal Spn is changed to a high level (electrode positive polarity period) and output. Therefore, the electrode positive polarity period is when the torch tip position is half a revolution to the right of the weld line and is on the second workpiece, which is a thick plate. Here, the polarity switching signal Spn may be changed to a high level at the point when the weaving position signal Pw changes to a high level. 2) When the weaving position signal Pw changes to a low level and then the short circuit determination signal Sd becomes a high level (short circuit period), the polarity switching signal Spn is changed to a low level (electrode negative polarity period) and output. Therefore, the electrode negative polarity period is when the torch tip position is half a revolution to the left of the weld line and is on the first workpiece, which is a thin plate. Here, the polarity switching signal Spn may be changed to a low level at the point when the weaving position signal Pw changes to a low level.

[0041] The current control setting circuit ICR receives as inputs the short circuit determination signal Sd, the low level current setting signal Ilr, the constriction detection signal Nd, the third arc period signal Sta3, the first arc current setting signal Ia1r, the third arc current setting signal Ia3r, the rate of rise setting signal Sr, and the electrode negative polarity second arc current setting signal Ia2r, performs the following processing, and outputs a current control setting signal Icr and a first arc period signal Sta1. 1) During a predetermined delay period Tc from the time when the short circuit determination signal Sd changes to a low level (arcing period), a current control setting signal Icr having the value of the low-level current setting signal Ilr is output. 2) When the delay period Tc ends, a current control setting signal Icr is output, which rises from the value of the low-level current setting signal Ilr to the value of the first arc current setting signal Ia1r at a rise rate determined by the rise rate setting signal Sr. This period becomes the first arc period Ta1, and the first arc period signal Sta1 is output at a High level. 3) Thereafter, during second arc period Ta2 until third arc period signal Sta3 attains High level, current control setting signal Icr which becomes electrode negative polarity second arc current setting signal Ia2r is output. 4) Thereafter, during the third arc period Ta3 until the short circuit determination signal Sd changes to a low level (arc period), the current control setting signal Icr which becomes the third arc current setting signal Ia3r is output. 5) When the short circuit determination signal Sd changes to a high level (short circuit period), a predetermined initial current setting value is set during a predetermined initial period, and thereafter a current control setting signal Icr is output which rises with a predetermined short circuit slope to a predetermined short circuit peak setting value and maintains that value. 6) Thereafter, when the squeezing detection signal Nd changes to a high level, the current control setting signal Icr having the value of the low-level current setting signal Ilr is output.

[0042] The current error amplifier circuit EI receives the current control setting signal Icr and the current detection signal Id, amplifies the error between the two values, and outputs a current error amplified signal Ei.

[0043] The power supply characteristics switching circuit SW receives as inputs the current error amplified signal Ei, the voltage error amplified signal Ev, the first arc period signal Sta1, the third arc period signal Sta3, and the polarity switching signal Spn, performs the following processing, and outputs an error amplified signal Ea. 1) During the second arc period Ta2 during which the polarity switching signal Spn is at a high level (electrode positive polarity EP) and the first arc period signal Sta1 changes to a low level and the third arc period signal Sta3 changes to a high level, the voltage error amplified signal Ev is output as the error amplified signal Ea. 2) During the other periods, the current error amplified signal Ei is output as the error amplified signal Ea. This circuit causes the welding power source to have constant current characteristics during the short circuit period, delay period, first arc period Ta1, second arc period Ta2 and third arc period Ta3 during the electrode negative polarity period, and constant voltage characteristics during the second arc period Ta2 during the electrode positive polarity period. Therefore, during the electrode positive polarity period, the output is controlled by constant voltage control for at least a part of the arc period, and during the electrode negative polarity period, the output is controlled by constant current control for the entire arc period.

[0044] Fig. 2 is a timing chart of each signal in the welding power source of Fig. 1, which shows the AC consumable electrode arc welding control method according to the embodiment of the present invention. Fig. 2(A) shows the time change of the feed speed Fw, Fig. 2(B) shows the time change of the welding current Iw, Fig. 2(C) shows the time change of the welding voltage Vw, Fig. 2(D) shows the time change of the short circuit discrimination signal Sd, Fig. 2(E) shows the time change of the first arc period signal Sta1, Fig. 2(F) shows the time change of the third arc period signal Sta3, Fig. 2(G) shows the time change of the polarity switching signal Spn, Fig. 2(H) shows the time change of the squeezing detection signal Nd, and Fig. 2(I) shows the time change of the weaving position signal Pw. The operation of each signal will be described below with reference to Fig. 2.

[0045] The feed speed Fw shown in FIG. 1(A) is a forward feed period in which the welding wire is fed toward the workpiece when it is above 0, and a reverse feed period in which the welding wire is fed away from the workpiece when it is below 0. The welding current Iw shown in FIG. 1(B) and the welding voltage Vw shown in FIG. 1(C) indicate the electrode positive polarity EP when it is above 0, and the electrode negative polarity EN when it is below 0. The magnitudes of the values ​​of the feed speed Fw, welding current Iw, and welding voltage Vw indicate the magnitudes of their absolute values. For example, when the feed speed Fw is in a reverse feed state, the value increases, which means that the absolute value increases. Similarly, when the welding current Iw and welding voltage Vw are in the electrode negative polarity period Ten, the value increases, which means that the absolute value increases. The polarity switching signal Spn shown in FIG. 1(G) controls the secondary side inverter circuit in the power supply main circuit PM of FIG. 1, and when it is at a High level, it is the electrode positive polarity period Tep, and when it is at a Low level, it is the electrode negative polarity period Ten.

[0046] In the figure, the electrode positive polarity period Tep is the period from time t1 to t4, and the electrode negative polarity period Ten is the period from time t4 to t7. The length of time of the electrode positive polarity period Tep is the period during which the weaving position signal Pw shown in FIG. (I) is at a High level or the period until a short circuit occurs plus that. The length of time of the electrode negative polarity period Ten is the period during which the weaving position signal Pw shown in FIG. (I) is at a Low level or the period until a short circuit occurs plus that. Since the weaving frequency is about 1 to 20 Hz, the electrode positive polarity period Tep and the electrode negative polarity period Ten are in the range of about 25 ms to 500 ms. Therefore, the short circuit period and the arc period include at least three cycles.

[0047] (1) Operation of the electrode positive polarity period Tep At time t0, which is the short circuit period of the electrode negative polarity period Ten, the polarity switching signal Spn is at low level, as shown in FIG. 1(G). As shown in FIG. 1(A), the feed speed Fw is at the electrode negative polarity reverse feed peak value. As shown in FIG. 1(B), the welding current IW is at a negative initial current value. As shown in FIG. 1(C), the welding voltage Vw is at a short circuit voltage value of several V, which is a negative value. As shown in FIG. 1(D), the short circuit discrimination signal Sd is at high level (short circuit period).

[0048] At time t0, when the torch tip position passes over the weld line from the first workpiece of a thin plate and enters the second workpiece of a thick plate by weaving, the weaving position signal Pw changes to a high level as shown in FIG. 1(I). In response to this, at time t1 during the short circuit period, as shown in FIG. 1(G), the polarity switching signal Spn changes to a high level, and the electrode positive polarity period Tep begins. In response to this, as shown in FIG. 1(A), the feed speed Fw is accelerated to the electrode positive polarity reverse feed peak value. As shown in FIG. 1(B), the welding current Iw is constant current controlled during the short circuit period and changes to a positive initial current value. As shown in FIG. 1(C), the welding voltage Vw changes to a positive short circuit voltage value. The timing at which the polarity switching signal Spn changes to a high level at time t1 is during the short circuit period, and is immediately after the short circuit occurs or when a predetermined period (about 1 ms) has elapsed since then.

[0049] After that, when the predetermined initial period ends, as shown in FIG. 1B, the welding current Iw rises at a predetermined short-circuit slope, and when it reaches the short-circuit peak value, it maintains that value. As shown in FIG. 1C, the welding voltage Vw rises from the point where the welding current Iw reaches the short-circuit peak value. This is because a constriction is gradually formed in the droplet at the tip of the welding wire 1 due to the reverse feed of the welding wire 1 and the pinch force caused by the welding current Iw. When the voltage rise value of the welding voltage Vw thereafter reaches the reference value, it is determined that the constriction has reached the reference state, and the constriction detection signal Nd changes to a high level as shown in FIG. 1H. In response to this, the current control setting signal Icr in FIG. 1 decreases to the value of the low-level current setting signal Ilr. As a result, as shown in FIG. 1B, the welding current Iw suddenly decreases from the short-circuit peak value to the low-level current value. Then, when the welding current Iw decreases to the low-level current value, as shown in FIG. 1B, the welding current Iw maintains the low-level current value until a predetermined delay period Tc has elapsed since the arc re-strikes, because the current control setting signal Icr remains the low-level current setting signal Ilr. In order to speed up the rapid reduction rate of the welding current Iw when a constriction is detected, it is desirable to add a circuit in which a resistor and a switching inhibition are connected in parallel to the current path of the welding current Iw. Until a constriction is detected, the switching inhibition is turned on to short-circuit the resistor to set the normal state, and when a constriction is detected, the switching inhibition is turned off to insert a resistor into the current path, thereby speeding up the rapid reduction rate. For example, the initial period is set to 1 ms, the initial current value is set to 50 A, the short-circuit slope is set to 400 A / ms, the short-circuit peak value is set to 450 A, and the low-level current value is set to 50 A. As shown in FIG. 1H, the constriction detection signal Nd returns to a low level when an arc re-strikes at time t2.

[0050] At time t2, when the pinch force caused by the reverse feed of the welding wire and the passage of the welding current Iw causes the constriction to progress and an arc to occur, as shown in FIG. 1C, the welding voltage Vw rapidly rises to an arc voltage value of several tens of volts, and the short circuit determination signal Sd changes to a low level (arc period) as shown in FIG. 1D. In response to this, as shown in FIG. 1A, the feed speed Fw starts switching from the electrode positive polarity reverse feed peak value to the electrode positive polarity forward feed peak value. The switching period from the electrode positive polarity reverse feed peak value to the electrode positive polarity forward feed peak value is the combined period of the electrode positive polarity reverse feed deceleration period and the electrode positive polarity forward feed acceleration period in FIG. 1. For example, the electrode positive polarity reverse feed period and the electrode positive polarity forward feed acceleration period are set to 1 ms. During the predetermined delay period Tc from time t2 to t21, as shown in FIG. 1B, the welding current Iw is maintained at a low level current value by constant current control. As shown in FIG. 1C, the welding voltage Vw becomes an arc voltage value. For example, the electrode positive polarity forward feed peak value is set to 50 m / min, and the electrode positive polarity reverse feed peak value is set to -30 m / min. The delay period Tc is set to about 0 to 0.5 ms. When Tc=0, the delay period Tc is deleted.

[0051] At time t21, when the delay period Tc ends, the first arc period signal Sta1 changes to a high level as shown in FIG. 1(E). In response to this, as shown in FIG. 1(B), the welding current Iw increases from a low level current value to an electrode positive polarity first arc current value determined by the first arc current setting signal Ia1r in FIG. 1 at an increase rate determined by the electrode positive polarity increase rate setting signal Spr in FIG. 1 by constant current control. At time t22, when the welding current Iw increases to the electrode positive polarity first arc current value, as shown in FIG. 1(E), the first arc period signal Sta1 changes to a low level and the first arc period ends. As shown in FIG. 1(C), the welding voltage Vw also increases with a slope. The electrode positive polarity increase rate is set to about 500 to 1000 a / ms, and the electrode positive polarity first arc current value is set to about 400 to 500 A.

[0052] At time t23, when the electrode positive polarity current fall time Td determined by the current fall time setting signal Tdr in FIG. 1 has elapsed from the arc generation time t2, the third arc period signal Sta3 changes to a high level as shown in FIG. 1(F). The period from time t22 to t23 is the second arc period Ta2. During this second arc period Ta2, the arc length is maintained at an appropriate value by constant voltage control. As shown in FIG. 1(B), the welding current Iw gradually falls. As shown in FIG. 1(C), the welding voltage Vw is controlled by constant voltage control and gradually falls. For example, the electrode positive polarity current fall time Td is set to 6 ms. The second arc period Ta2 is not a predetermined value, but is about 5 ms.

[0053] The period from time t23 when the third arc period signal Sta3 changes to a high level to time t3 when a short circuit occurs is the third arc period Ta3. Constant current control is performed during this third arc period Ta3. As shown in FIG. 1B, the welding current Iw is a value determined by the third arc current setting signal Ia3r in FIG. 1. As shown in FIG. 1C, the welding voltage Vw is a value smaller than that of the second arc period. For example, the third arc current is set to 50A. The third arc period Ta3 is not a predetermined value, but is about 1 ms. The welding current Iw is set to a small value so that the next short circuit occurs early. When a short circuit occurs at time t3, the short circuit discrimination signal Sd changes to a high level as shown in FIG. 1D. In response to this, as shown in FIG. 1A, the feed speed Fw starts to switch from the electrode positive polarity forward feed peak value to the electrode positive polarity reverse feed peak value. The switching period from the electrode positive polarity forward feed peak value to the electrode positive polarity reverse feed peak value is the combined period of the electrode positive polarity forward feed deceleration period and the electrode positive polarity reverse feed acceleration period in Fig. 1. For example, the electrode positive polarity forward feed period and the electrode positive polarity reverse feed acceleration period are set to 1 ms.

[0054] The period from time t3 to t4 is again a short circuit period, which is followed by an arc period. The operation during this period is the same as that described above, and therefore will not be described repeatedly.

[0055] (2) Operation of the electrode negative polarity period Tem At time t31 in the middle of the third arc period Ta3 during the electrode positive polarity period Tep, when the torch tip position passes over the weld line from the second workpiece of thick plate by weaving and enters the first workpiece of thin plate, the weaving position signal Pw changes to a low level as shown in FIG. 1(I). Then, when a short circuit occurs at time t4, the welding voltage Vw becomes a short circuit voltage value of a positive value as shown in FIG. 1(C), and the short circuit discrimination signal Sd changes to a high level as shown in FIG. 1(D). In response to this, the polarity switching signal Spn changes to a low level as shown in FIG. 1(G), and the electrode negative polarity period Ten is entered. In response to this, the feed speed Fw changes from the electrode positive polarity forward feed peak value to the electrode negative polarity reverse feed peak value as shown in FIG. 1(A). As shown in FIG. 1(B), the welding current Iw is constant current controlled during the short circuit period and changes to a negative initial current value. As shown in FIG. 1(C), the welding voltage Vw changes to a short circuit voltage value of a negative value. The timing at which the polarity switching signal Spn changes to low level at time t4 is during the short circuit period, and is either immediately after the short circuit occurs or when a predetermined period (approximately 1 ms) has elapsed since the occurrence of the short circuit.

[0056] After that, when the predetermined initial period ends, as shown in FIG. 1B, the welding current Iw rises at a predetermined short-circuit slope, and when it reaches the short-circuit peak value, it maintains that value. As shown in FIG. 1C, the welding voltage Vw rises from the point where the welding current Iw reaches the short-circuit peak value. This is because a constriction is gradually formed in the droplet at the tip of the welding wire 1 due to the reverse feed of the welding wire 1 and the pinch force caused by the welding current Iw. When the voltage rise value of the welding voltage Vw thereafter reaches the reference value, it is determined that the constriction has reached the reference state, and the constriction detection signal Nd changes to a high level as shown in FIG. 1H. In response to this, the current control setting signal Icr in FIG. 1 decreases to the value of the low-level current setting signal Ilr. As a result, as shown in FIG. 1B, the welding current Iw suddenly decreases from the short-circuit peak value to the low-level current value. Then, when the welding current Iw decreases to the low-level current value, as shown in FIG. 1B, the welding current Iw maintains the low-level current value until a predetermined delay period Tc has elapsed since the arc re-strikes, because the current control setting signal Icr remains the low-level current setting signal Ilr. The initial period, initial current value, short-circuit slope, short-circuit peak value, and low-level current value may be set to the same values ​​as those during the electrode positive polarity period, or may be set to different values ​​in consideration of the characteristics of the electrode negative polarity. As shown in FIG. 1H, the squeezing detection signal Nd returns to a low level when the arc re-strikes at time t5.

[0057] At time t5, when the pinch force caused by the reverse feed of the welding wire and the passage of the welding current Iw causes the constriction to progress and an arc to occur, as shown in FIG. 1C, the welding voltage Vw rapidly rises to an arc voltage value of several tens of volts, and the short circuit determination signal Sd changes to a low level (arc period) as shown in FIG. 1D. In response to this, as shown in FIG. 1A, the feed speed Fw starts to switch from the electrode negative polarity reverse feed peak value to the electrode negative polarity forward feed peak value. The switching period from the electrode negative polarity reverse feed peak value to the electrode negative polarity forward feed peak value is the combined period of the electrode negative polarity reverse feed deceleration period and the electrode negative polarity forward feed acceleration period in FIG. 1. For example, the electrode negative polarity reverse feed period and the electrode negative polarity forward feed acceleration period are set to 0.5 ms. Therefore, the switching period from the reverse feed peak value to the forward feed peak value is set to a period shorter during the electrode negative polarity period than during the electrode positive polarity period. During a predetermined delay period Tc from time t5 to t51, as shown in FIG. 1B, the welding current Iw is maintained at a low level current value by constant current control. As shown in FIG. 1C, the welding voltage Vw becomes an arc voltage value. For example, the electrode negative polarity forward feed peak value is set to 80 m / min, and the electrode negative polarity reverse feed peak value is set to -50 m / min. The average value of the feed speed Fw during the electrode negative polarity period Ten is larger than that during the electrode positive polarity period Tep. This is to make the average value of the welding current Iw in both periods approximately the same. The delay period Tc is set to about 0 to 0.5 ms, similar to the electrode positive polarity period Tep. When Tc=0, the delay period Tc is deleted.

[0058] At time t51, when the delay period Tc ends, the first arc period signal Sta1 changes to a high level as shown in FIG. 1(E). In response to this, as shown in FIG. 1(B), the welding current Iw increases from a low level current value to an electrode negative polarity first arc current value determined by the first arc current setting signal Ia1r in FIG. 1 at an increase rate determined by the electrode negative polarity increase rate setting signal Snr in FIG. 1 by constant current control. At time t52, when the welding current Iw increases to the electrode negative polarity first arc current value, as shown in FIG. 1(E), the first arc period signal Sta1 changes to a low level and the first arc period ends. As shown in FIG. 1(C), the welding voltage Vw also increases with a slope. The electrode negative polarity increase rate is set to about 50 to 500 a / ms, and the electrode negative polarity first arc current value is set to about 300 to 400 A, which is smaller than the electrode positive polarity first arc current value.

[0059] At time t53, when the electrode negative polarity current fall time Td determined by the current fall time setting signal Tdr in FIG. 1 has elapsed from the arc generation time t5, the third arc period signal Sta3 changes to a high level as shown in FIG. 1(F). The period from time t52 to t53 is the second arc period Ta2. During this second arc period Ta2, unlike during the electrode positive polarity period Tep, constant current control is performed with the electrode negative polarity second arc current setting signal Ia2r in FIG. 1 as a target value. As shown in FIG. 1(B), the welding current Iw becomes a value about 50A smaller than the electrode negative polarity first arc current value at time t52, and has a waveform that falls over time until time t53. Therefore, the relationship is electrode negative polarity first arc current value>electrode negative polarity second arc current>electrode negative polarity third arc current. As shown in FIG. 1(C), the welding voltage Vw also gradually falls. For example, the electrode negative polarity current fall time Td is set to 5 ms. The second arc period Ta2 is about 4 ms, although it is not a predetermined value. Here, the electrode negative polarity first arc current value, which is the maximum value of the welding current Iw during the first arc period Ta1, is set to a value smaller than the electrode positive polarity first arc current value.

[0060] The period from time t53 when the third arc period signal Sta3 changes to a high level to time t6 when a short circuit occurs is the third arc period Ta3. During this third arc period Ta3, constant current control is performed. As shown in FIG. 1B, the welding current Iw is a value determined by the third arc current setting signal Ia3r in FIG. 1. As shown in FIG. 1C, the welding voltage Vw is a value smaller than that of the second arc period. For example, the third arc current is set to 50A. The third arc period Ta3 is not a predetermined value, but is about 1 ms. As described above, the welding current Iw is set to a small value so that the next short circuit occurs early. When a short circuit occurs at time t6, the short circuit discrimination signal Sd changes to a high level as shown in FIG. 1D. In response to this, as shown in FIG. 1A, the feed speed Fw starts to switch from the electrode negative polarity forward feed peak value to the electrode negative polarity reverse feed peak value. The switching period from the electrode negative polarity forward feed peak value to the electrode negative polarity reverse feed peak value is the sum of the electrode negative polarity forward feed deceleration period and the electrode negative polarity reverse feed acceleration period in Fig. 1. For example, the electrode negative polarity forward feed period and the electrode negative polarity reverse feed acceleration period are set to 0.5 ms. Therefore, the switching period from the forward feed peak value to the reverse feed peak value is set to a shorter period during the electrode negative polarity period than during the electrode positive polarity period.

[0061] The period from time t6 to t7 is again a short circuit period, which is followed by an arc period. The operation during this period is the same as that described above, and therefore will not be described repeatedly. At time t61 during the third arc period Ta3, when the torch tip position passes over the weld line from the first workpiece made of a thin plate and enters the second workpiece made of a thick plate by weaving, the weaving position signal Pw changes to a high level as shown in FIG. 1(I). Then, when a short circuit occurs at time t7, the welding voltage Vw becomes a negative short circuit voltage value as shown in FIG. 1(C), and the short circuit discrimination signal Sd changes to a high level as shown in FIG. 1(D). In response to this, the polarity switching signal Spn changes to a high level as shown in FIG. 1(G), and the electrode positive polarity period Tep begins. The operation after this is the same as that after time t1.

[0062] In the figure, the increase in the welding current Iw from time t21 to t22 and from time t51 to t52 is shown as a straight line, but it may also be shown as a curved increase. In this case, the magnitude of the increase rate is compared based on the maximum increase rate of the curve. A curved increase may mean that the increase rate decreases or increases over time.

[0063] The effects of this embodiment will be described below. According to this embodiment, when the first workpiece is thinner than the second workpiece, the first workpiece is welded in the electrode negative polarity period, and the second workpiece is welded in the electrode positive polarity period. During the electrode negative polarity period, the heat input from the arc to the workpiece is smaller than during the electrode positive polarity period. Therefore, by welding the first workpiece, which is a thin plate, in the electrode negative polarity period where the heat input is small, the occurrence of burn-through can be suppressed. By welding the second workpiece, which is a thick plate, in the electrode positive polarity period where the heat input is large, sufficient penetration can be obtained, and the occurrence of poor penetration can be suppressed. As a result, in this embodiment, when weaving lap fillet joints and butt joints with different plate thicknesses, the occurrence of welding defects such as burn-through and poor penetration can be suppressed, and satisfactory welding quality can be obtained.

[0064] More preferably, according to this embodiment, the switching between the electrode negative polarity period and the electrode positive polarity period is performed when the welding torch passes over the weld line. In addition to the case where the boundary between the first workpiece and the second workpiece is taught as the weld line, there are cases where the weld line is taught by shifting it from the association line. In such cases, good welding quality can be obtained by switching between the two periods over the weld line.

[0065] More preferably, according to this embodiment, the switching between the electrode negative polarity period and the electrode positive polarity period is performed during the short circuit period after the welding torch has passed over the weld line. By switching between the two periods during the short circuit period, it is possible to prevent the welding state from becoming unstable due to the occurrence of arc interruption.

[0066] More preferably, according to this embodiment, the absolute value of the peak value of the forward feed and the absolute value of the peak value of the reverse feed are set to values ​​larger during the electrode negative polarity period than during the electrode positive polarity period. During the electrode negative polarity period, the melting speed of the welding wire is higher than during the electrode positive polarity period, so the arc length is longer and the arc period is likely to be longer. If the arc period is longer, a short circuit occurs in a state in which the droplet at the tip of the welding wire has grown large, making the welding state unstable and increasing the occurrence of spatter. In this embodiment, the absolute value of the peak value of the forward feed and the absolute value of the peak value of the reverse feed are set to values ​​larger during the electrode negative polarity period than during the electrode positive polarity period. In this way, the forward feed peak value during the arc period in the electrode negative polarity period is larger, so the arc period can be shortened. As a result, a short circuit can be generated before the droplet grows large, so that the welding state can be suppressed from becoming unstable.

[0067] More preferably, according to this embodiment, during the electrode positive polarity period, the output is controlled by constant voltage control for at least a part of the arc period, and during the electrode negative polarity period, the output is controlled by constant current control for the entire arc period. During the electrode positive polarity period, the arc length can be detected by the value of the welding voltage during the arc period. For this reason, during the electrode positive polarity period, the arc length can be controlled to an appropriate value by constant voltage control for a part of the arc period (second arc period), and the welding state can be maintained stably. However, during the electrode negative polarity period, the arc length cannot be detected by the value of the welding voltage during the arc period. This is because, during the electrode negative polarity period, the position of the cathode point formed at the tip of the welding wire moves unstably, and the proportional relationship between the welding voltage and the arc length is lost. For this reason, even if the arc length is maintained at an appropriate value by constant voltage control for a part of the arc period during the electrode negative polarity period, as in the electrode positive polarity period, the welding state is rather unstable because the value of the welding voltage does not detect the arc length. Therefore, in this embodiment, during the electrode positive polarity period, constant voltage control is performed for at least a part of the arc period, thereby maintaining the arc length at an appropriate value and stabilizing the welding state. Furthermore, in this embodiment, constant current control is performed for the entire arc period during the electrode negative polarity period, thereby preventing the welding state from becoming unstable due to low voltage control. As a result, in this embodiment, the welding state during the electrode negative polarity period can be stabilized and the welding quality can be improved.

[0068] More preferably, according to this embodiment, the arc period is formed of a first arc period, a second arc period, and a third arc period, and the welding current during the first arc period rises from a low level current value with a slope, and the rate of rise of the slope is set to a smaller value during the electrode negative polarity period than during the electrode positive polarity period. During the electrode positive polarity period, the rate of rise is set to a larger value, so that the welding current is quickly raised to the first arc current value. This ensures sufficient heat input to the workpiece, and promotes melting of the welding wire to form appropriate droplets. During the electrode negative polarity period, the melting rate of the welding wire is higher than during the electrode positive polarity period due to differences in arc characteristics, even if the same welding current is applied. For this reason, if the rate of rise during the electrode negative polarity period is set to the same value as during the electrode positive polarity period, the melting of the welding wire is rapidly promoted, the droplets grow rapidly, and a lot of spatter is generated. Therefore, by setting the rate of rise to a smaller value during the electrode negative polarity period than during the electrode positive polarity period, the melting rate of the welding wire can be slowed down, and the growth of the droplets can be mitigated. As a result, in this embodiment, the occurrence of spatters can be suppressed and the welding condition can be stabilized.

[0069] More preferably, according to this embodiment, the arc period is formed of a first arc period, a second arc period, and a third arc period, and the maximum value of the welding current during the first arc period (first arc current value) is set to a smaller value during the electrode negative polarity period than during the electrode positive polarity period. By setting the first arc current value to a larger value during the electrode positive polarity period, sufficient heat input to the workpiece can be ensured and melting of the welding wire can be promoted to form appropriate droplets. During the electrode negative polarity period, the melting rate of the welding wire is higher than that during the electrode positive polarity period due to differences in arc characteristics, even if the same welding current is applied. For this reason, if the first arc current value during the electrode negative polarity period is set to the same value as that during the electrode positive polarity period, melting of the welding wire is rapidly promoted, the droplets grow rapidly, and a lot of spatter is generated. Therefore, by setting the first arc current value during the electrode negative polarity period to a smaller value than that during the electrode positive polarity period, the melting rate of the welding wire can be slowed down and the growth of the droplets can be mitigated. As a result, in this embodiment, the generation of spatter can be suppressed and the welding state can be stabilized.

[0070] More preferably, according to this embodiment, the rate of rise during the electrode negative polarity period is set to a smaller value as the first arc current value is larger. The first arc current value is set to be larger within a range of about 300 to 400 A as the average value of the welding current is larger, taking into account the heat input to the workpiece. If the rate of rise is kept the same even if the setting of the first arc current value during the electrode negative polarity period is increased, the droplets will grow excessively and spatter will occur. To prevent this, the rate of rise is set to be smaller as the first arc current value is increased. As a result, the occurrence of spatter can be suppressed even if the first arc current value is increased. [Explanation of symbols]

[0071] 1 Welding wire 2 Work 3. Arc 4. Welding torch 5 Feeding roll CM current comparison circuit Cm current comparison signal Ea Error amplification signal EI Current Error Amplifier Circuit Ei Current error amplification signal EV voltage error amplifier circuit Ev Voltage error amplified signal FC feed control circuit Fc feed control signal FR feed speed setting circuit Fr feed speed setting signal Fw Feed speed IA1R First arc current setting circuit Ia1r 1st arc current setting signal IA2R Electrode negative polarity second arc current setting circuit Ia2r Electrode negative polarity second arc current setting signal IA3R 3rd arc current setting circuit Ia3r 3rd arc current setting signal ICR Current control setting circuit Icr Current control setting signal ID Current Detection Circuit Id Current detection signal ILR Low level current setting circuit Ilr Low level current setting signal Iw Welding current ND Constriction Detection Circuit Nd Constriction detection signal PM power supply main circuit Pw Weaving position signal RC robot controller Rc Movement control signal RM Robot SD Short circuit detection circuit Sd Short circuit detection signal SNR electrode negative polarity rise rate setting circuit Snr Electrode negative polarity rise rate setting signal SPN polarity switching circuit SPN polarity switching signal SPR electrode positive polarity rise rate setting circuit Spr electrode positive polarity rise rate setting signal SR Rise Rate Setting Circuit Sr Climb rate setting signal Sta1 First arc period signal STA3 3rd arc period circuit Sta3 3rd arc period signal SW Power supply characteristic switching circuit Tc delay period Td Current fall time TDR current fall time setting circuit Tdr Current fall time setting signal Trd Reverse feed deceleration period TRDR Reverse deceleration period setting circuit Trdr Reverse feed deceleration period setting signal Trp Backward Peak Period Tru Reverse acceleration period TRUR Reverse acceleration period setting circuit Trur Reverse acceleration period setting signal Tsd Forward feed deceleration period TSDR Forward feed deceleration period setting circuit Tsdr Forward feed deceleration period setting signal Tsp Peak forwarding period Tsu forward acceleration period TSUR Forward feed acceleration period setting circuit Tsur Forward feed acceleration period setting signal VD voltage detection circuit Vd Voltage detection signal VR voltage setting circuit Vr Voltage setting signal Vw Welding voltage WM Feed motor Wrp Reverse peak value WRR Back-transmission peak value setting circuit Wrr Reverse transmission peak value setting signal Wsp forward peak value WSR forward peak value setting circuit Wsr Positive transmission peak value setting signal

Claims

1. A short circuit period and an arc period are repeated between the welding wire and the base metal, cyclically switching the electrode polarity between an electrode positive polarity period and an electrode negative polarity period including a plurality of cycles of the short circuit period and the arc period; 1. A method for controlling AC consumable electrode arc welding in which a welding torch is weaved across a boundary line between a first workpiece and a second workpiece, the method comprising: When the first workpiece is a thinner plate than the second workpiece, the welding of the first workpiece is performed in the electrode negative polarity period, and the welding of the second workpiece is performed in the electrode positive polarity period.

2. A method for controlling AC consumable electrode arc welding.

2. The switching between the electrode negative polarity period and the electrode positive polarity period is performed at a point when the welding torch passes over a weld line.

2. The method of claim 1, wherein the AC consumable electrode arc welding is performed in a controlled manner.

3. The switching between the electrode negative polarity period and the electrode positive polarity period is performed during the short circuit period after the welding torch has passed over the weld line.

2. The method of claim 1, wherein the AC consumable electrode arc welding is performed in a controlled manner.

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