Ac consumable electrode arc welding control method

Abstract

To smoothly switch an electrode polarity in an AC consumable electrode arc welding method.SOLUTION: An AC consumable electrode arc welding control method includes: repeating a short-circuit period and an arc period between a welding wire and a base material; starting switching of a feed speed Fw of the welding wire from a forward-feed peak value to a backward-feed peak value in the short-circuit period; starting the switching of it from the backward-feed peak value to the forward-feed peak value in the arc period; and welding by periodically switching an electrode polarity between an electrode positive-polarity period Tep including the short-circuit period and the arc period of a plurality of cycles and an electrode negative-polarity period Ten; wherein the switching of the electrode polarity is performed during a forward-feed deceleration period (a period from time t0 to time t1 and a period from time t4 to time t41) in which the feed speed Fw is decelerated from the forward feed peak value to 0.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for controlling AC consumable electrode arc welding in which short-circuit periods and arc periods are repeated between a welding wire and a base metal, and welding is performed by periodically switching the electrode polarity between a positive electrode polarity period and a negative electrode 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). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6601870 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional AC consumable electrode arc welding method, the electrode polarity is switched during the short circuit period. This is because switching the electrode polarity during the arc period may cause arc interruption and deteriorate the welding quality. However, when switching the electrode polarity during the short circuit period, an arc may suddenly occur due to irregular movements of the droplets and the molten pool. When this occurs, the electrode polarity is not smoothly changed, the welding state becomes unstable, and the welding quality deteriorates.

[0005] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a method for controlling AC consumable electrode arc welding, which allows electrode polarity to be switched smoothly at all times. [Means for solving the problem]

[0006] 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, a welding wire feed speed is switched from a forward feed peak value to a reverse feed peak value during the short circuit period, and is switched from the reverse feed peak value to the forward feed peak value during the arc period; 1. A method for controlling AC consumable electrode arc welding in which electrode polarity is periodically switched 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, The electrode polarity is switched during the short circuit period and at a time when the feed speed starts to decelerate from the forward feed peak value and a delay period has elapsed; The delay period is set to a period before the feed rate is decelerated to zero. The present invention relates to a method for controlling AC consumable electrode arc welding.

[0007] The invention of claim 2 is as follows: The electrode polarity is switched by extending the state in which the feed speed is decelerated to 0. 2. The method for controlling AC consumable electrode arc welding according to claim 1, wherein: Effect of the Invention

[0008] According to the method for controlling AC consumable electrode arc welding of the present invention, electrode polarity can be switched smoothly at all times, thereby improving the welding quality. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram of a welding power source for carrying out a method for controlling AC consumable electrode arc welding according to a first embodiment of the present invention. [Diagram 2] 2 is a timing chart of each signal in the welding power source of FIG. 1, illustrating the AC consumable electrode arc welding control method according to the first embodiment of the present invention. [Diagram 3]FIG. 11 is a block diagram of a welding power source for carrying out an AC consumable electrode arc welding control method according to a second embodiment of the present invention. [Figure 4] 5 is a timing chart of each signal in the welding power source of FIG. 3, illustrating a method for controlling AC consumable electrode arc welding according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] [Embodiment 1] 1 is a block diagram of a welding power source for carrying out a method for controlling AC consumable electrode arc welding according to a first embodiment of the present invention. Each block will be described below with reference to the diagram.

[0012] 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 Sw 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.

[0013] 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.

[0014] 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 welding wire 1 and the base material 2. An AC welding voltage Vw is applied between a power feed tip (not shown) in the welding torch 4 and the base material 2, and an AC welding current Iw flows through the wire. 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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, it is preferable that the electrode negative polarity forward acceleration period is set to a period shorter than the electrode positive polarity forward acceleration period.

[0019] 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, it is preferable that the electrode negative polarity forward feed deceleration period is set to a period shorter than the electrode positive polarity forward feed deceleration period.

[0020] 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 is a predetermined electrode positive polarity reverse acceleration period when the polarity switching signal Spn is at a high level (electrode positive polarity period), and is a predetermined electrode negative polarity reverse acceleration period when the polarity switching signal Spn is at a low level (electrode negative polarity period). Here, it is preferable that the electrode negative polarity reverse acceleration period is set to a period shorter than the electrode positive polarity reverse acceleration period.

[0021] 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, it is preferable that the electrode negative polarity reverse deceleration period is set to a period shorter than the electrode positive polarity reverse deceleration period.

[0022] 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, it is preferable that 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.

[0023] 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, it is preferable that 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.

[0024] 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, and outputs a feed speed pattern generated by the following process as a feed speed setting signal Fr, and further outputs a forward feed deceleration period signal Stsd. When the 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), a forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr is entered, and a feed speed setting signal Fr is output for decelerating the feed speed from the forward feed peak value Wsp to 0. During this forward feed deceleration period Tsd, a forward feed deceleration period signal Stsd that is at a high level is output. 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.

[0025] 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.

[0026] The constriction detection circuit ND takes the above-mentioned short-circuit discrimination signal Sd, the above-mentioned voltage detection signal Vd, and the above-mentioned 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 formation state of the constriction 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 may be 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.

[0027] 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-mentioned 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.

[0028] 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, it is preferable that the electrode positive polarity first arc current value > the electrode negative polarity first arc current value.

[0029] 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.

[0030] 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.

[0031] 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).

[0032] The third arc current setting circuit IA3R outputs a predetermined third arc current setting signal Ia3r.

[0033] 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.

[0034] 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.

[0035] The electrode positive polarity period setting circuit TPR outputs a predetermined electrode positive polarity period setting signal Tpr, and the electrode negative polarity period setting circuit TNR outputs a predetermined electrode negative polarity period setting signal Tnr.

[0036] The polarity switching circuit SPN receives the electrode positive polarity period setting signal Tpr, the electrode negative polarity period setting signal Tnr, and the forward transport deceleration period signal Stsd, performs the following processing, and outputs a polarity switching signal Spn. 1) A period determined by the electrode positive polarity period setting signal Tpr has elapsed since the polarity switching signal Spn changed to a high level. Thereafter, when the forward transport deceleration period signal Stsd changes to a high level and a predetermined delay period has elapsed, the polarity switching signal Spn is changed to a low level (electrode negative polarity period) and output. It is more preferable that the timing for changing the polarity switching signal Spn to a low level (electrode negative polarity period) is during the period from when the forward transport deceleration period signal Stsd changes to a high level (start point) and a predetermined delay period has elapsed until when the forward transport deceleration period signal Stsd changes to a low level (end point). The delay period is set to a period shorter than the forward transport deceleration period. 2) When a period determined by the electrode negative polarity period setting signal Tnr has elapsed since the polarity switching signal Spn changed to a low level, and then when the forward transport deceleration period signal Stsd has changed to a high level and a predetermined delay period has elapsed, the polarity switching signal Spn is changed to a high level (electrode positive polarity period) and output. It is more preferable that the timing for changing the polarity switching signal Spn to a high level (electrode positive polarity period) is during the period from when the forward transport deceleration period signal Stsd has changed to a high level (start point) and a predetermined delay period has elapsed until when the forward transport deceleration period signal Stsd has changed to a low level (end point). The delay period is set to a period shorter than the forward transport deceleration period.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Fig. 2 is a timing chart of each signal in the welding power source of Fig. 1 showing the AC consumable electrode arc welding control method according to the first 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 determination 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 forward feed deceleration period signal Stsd. Hereinafter, the operation of each signal will be described with reference to the figure.

[0041] The feed speed Fw shown in FIG. 1(A) is a forward feed period in which the welding wire is fed in a direction toward the base metal when it is above 0, and a reverse feed period in which the welding wire is fed in a direction away from the base metal 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 electrode positive polarity EP when it is above 0, and 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 an 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.

[0042] In the figure, the electrode positive polarity period Tep is a period from time t1 to t4, and the electrode negative polarity period Ten is a period from time t4 to t7. The electrode positive polarity period Tep is a period obtained by adding a period from when a short circuit occurs and a forward deceleration period starts to when a predetermined delay period has elapsed to the value of the electrode positive polarity period setting signal Tpr in FIG. 1. The electrode negative polarity period Ten is a period obtained by adding a period from when a short circuit occurs and a forward deceleration period starts to when a predetermined delay period has elapsed to the value of the electrode negative polarity period setting signal Tnr in FIG. 1. Since the AC frequency is set to a range of 0.1 to 30 Hz and the duty is set to a range of about 20 to 80%, the electrode positive polarity period Tep and the electrode negative polarity period Ten are set to a range of about 7 ms to 8 seconds. Each period includes a short circuit period and an arc period of multiple cycles. For example, when the AC frequency is 10 Hz and the duty is 50%, Tep=50 ms and Ten=50 ms. In this case, the cycle of the short circuit / arc period is about 10 ms, so that each period contains five cycles of the short circuit / arc period.

[0043] (1) Operation of the electrode positive polarity period Tep At time t0, as shown in FIG. 1(G), the polarity switching signal Spn is at low level (electrode negative polarity period Ten), and this is the point in time when a short circuit occurs after the period determined by the electrode negative polarity period setting signal Tnr in FIG. 1 has elapsed. At time t0, as shown in FIG. 1(A), the feed speed Fw is at the electrode negative polarity positive 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).

[0044] At time t0, as shown in FIG. 1(I), the forward feed deceleration period signal Stsd becomes High level, and as shown in FIG. 1(A), the feed speed Fw decelerates from the electrode negative polarity peak value to 0. Thereafter, the feed speed Fw enters the reverse feed acceleration period, and accelerates from 0 to the electrode positive polarity forward feed peak value. At time t1, when a predetermined delay period has elapsed from the start point of the forward feed deceleration period at time t0, as shown in FIG. 1(G), the polarity switching signal Spn changes to High level, and the electrode positive polarity period Tep is entered. 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 High level at time t1 is during the short circuit period and during the forward feed deceleration period in which the feed speed Fw decelerates from the forward feed peak value to 0. It is more preferable that the timing at which the polarity switching signal Spn changes to a high level at time t1 is within the period from the start of the normal transport deceleration period until the end of the normal transport deceleration period.

[0045] When the predetermined initial period ends near the end of the forward feed deceleration period, 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, the welding current Iw suddenly decreases from the short-circuit peak value to the low-level current value as shown in FIG. 1B. 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 re-strike of the arc, because the current control setting signal Icr remains the low-level current setting signal Ilr. In order to speed up the rapid reduction in 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 out the resistor and maintain 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 in the rate of decrease. For example, the forward deceleration period is set to 0.5 ms, the reverse acceleration period is set to 0.5 ms, the delay period for switching the electrode polarity is set to 0.2 ms, the initial period is set to 0.5 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. 1(H), the squeezing detection signal Nd returns to a low level when an arc re-strikes at time t2.

[0046] 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 reverse feed deceleration period and the forward feed acceleration period in FIG. 1. For example, the reverse feed deceleration period and the forward feed acceleration period are set to 0.5 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.

[0047] 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.

[0048] 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.

[0049] 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 0.5 ms.

[0050] 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.

[0051] (2) Operation of the electrode negative polarity period Tem At time t31 in the middle of the third arc period Ta3 in the electrode positive polarity period Tep, a period determined by the electrode positive polarity period setting signal Tpr in FIG. 1 from time t1 passes. Then, when a short circuit occurs at time t4, the welding voltage Vw becomes a positive 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). At time t4, as shown in FIG. 1(A), the feed speed Fw is in a state of the electrode positive polarity forward feed peak value. At time t4, as shown in FIG. 1(I), the forward feed deceleration period signal Stsd becomes a high level, and the feed speed Fw decelerates from the electrode positive polarity forward feed peak value to 0 as shown in FIG. 1(A). After that, the feed speed Fw enters a reverse feed acceleration period, and accelerates from 0 to the electrode negative polarity forward feed peak value. At time t41, when a predetermined delay period has elapsed from the start of the forward feed deceleration period at time t4, as shown in FIG. 1G, the polarity switching signal Spn changes to a low level, and the electrode transitions to a negative polarity period Ten. As shown in FIG. 1B, the welding current Iw is controlled to be a constant current during the short circuit period, and changes to a negative initial current value. As shown in FIG. 1C, the welding voltage Vw changes to a negative short circuit voltage value. The timing at which the polarity switching signal Spn changes to a low level at time t41 is during the short circuit period and during the forward feed deceleration period in which the feed speed Fw decelerates from the forward feed peak value to 0. It is more preferable that the timing at which the polarity switching signal Spn changes to a low level at time t41 is during a period from the start of the forward feed deceleration period and the delay to the end of the forward feed deceleration period.

[0052] When the predetermined initial period ends near the end of the forward deceleration period, 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, the welding current Iw suddenly decreases from the short-circuit peak value to the low-level current value as shown in FIG. 1B. 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.

[0053] 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 necking 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 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 reverse feed deceleration period and the forward feed acceleration period in FIG. 1. During the 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 greater than that during the electrode positive polarity period Tep. This is to make the average values ​​of the welding current Iw in both periods approximately the same. The delay period Tc is set to approximately 0 to 0.5 ms, similar to the electrode positive polarity period Tep. When Tc=0, the delay period Tc is deleted.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The period from time t6 to t7 is again a short circuit period, and thereafter, an arc period. The operation during this period is the same as that described above, and therefore the description thereof will not be repeated. At time t61 in the middle of the third arc period Ta3, a period determined by the electrode negative polarity period setting signal Tnr in FIG. 1 from time t4 passes. Then, when a short circuit occurs at time t7, as shown in FIG. 1(C), the welding voltage Vw becomes a short circuit voltage value of a negative value, and as shown in FIG. 1(D), the short circuit discrimination signal Sd changes to a high level. At time t7, as shown in FIG. 1(I), the forward feed deceleration period signal Stsd becomes a high level, and as shown in FIG. 1(A), the feed speed Fw decelerates from the electrode negative polarity peak value to 0. Thereafter, the feed speed Fw enters a reverse feed acceleration period, and accelerates from 0 to the electrode positive polarity forward feed peak value. At time t71, when a predetermined delay period has elapsed from the start of the forward transport deceleration period at time t7, as shown in FIG. 11(G), the polarity switching signal Spn changes to a high level, and the electrode positive polarity period Tep begins. The subsequent operations are the same as those after time t1.

[0058] 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.

[0059] [Embodiment 2] Fig. 3 is a block diagram of a welding power source for carrying out an AC consumable electrode arc welding control method according to a second embodiment of the present invention. In the figure, the same blocks as those in Fig. 1 are given the same reference numerals, and their description will not be repeated. In the figure, an initial period setting circuit TIR is added to Fig. 1, the feed speed setting circuit FR in Fig. 1 is replaced with a second feed speed setting circuit FR2, and the polarity switching circuit SPN in Fig. 1 is replaced with a second polarity switching circuit SPN2. These blocks will be described below with reference to the figure.

[0060] The initial period setting circuit TIR receives the normal feed deceleration period setting signal Tsdr and outputs a predetermined initial period setting signal Tir having a value longer than this value.

[0061] The second feed speed setting circuit FR2 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, the short circuit determination signal Sd, and the initial period setting signal Tir as inputs, and outputs a feed speed pattern generated by the following process as a feed speed setting signal Fr, and further outputs an initial period end signal Sti. 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) Next, the feeding speed setting signal Fr=0 is output from the time when the short circuit detection signal Sd changes to a high level until the initial period set by the initial period setting signal Tir ends, and then, when the initial period ends, the initial period end signal Sti that goes to a high level for a short period is output. 5) After the initial period ends, during the reverse acceleration period Tru determined by the reverse acceleration period setting signal Trur, a feed speed setting signal Fr is output that accelerates from 0 to the reverse peak value Wrp, which is a negative value determined by the reverse peak value setting signal Wrr. 6) 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. 7) 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. 8) By repeating the above steps 1) to 7), a feed speed setting signal Fr is generated having a feed pattern that changes in a positive and negative trapezoidal wave shape.

[0062] The second polarity switching circuit SPN2 receives the electrode positive polarity period setting signal Tpr, the electrode negative polarity period setting signal Tnr, and the initial period end signal Sti as inputs, performs the following processing, and outputs a polarity switching signal Spn. 1) After a period determined by the electrode positive polarity period setting signal Tpr has elapsed since the polarity switching signal Spn changed to a high level, when the initial period end signal Sti then changes to a high level for a short period of time, the polarity switching signal Spn is changed to a low level (electrode negative polarity period) and output. 2) After a period determined by the electrode negative polarity period setting signal Tnr has elapsed since the polarity switching signal Spn changed to a low level, when the initial period end signal Sti then changes to a high level for a short period of time, the polarity switching signal Spn is changed to a high level (electrode positive polarity period) and output.

[0063] FIG. 4 is a timing chart of each signal in the welding power source of FIG. 3 showing the AC consumable electrode arc welding control method according to the second embodiment of the present invention. FIG. 4(A) shows the time change of the feed speed Fw, FIG. 4(B) shows the time change of the welding current Iw, FIG. 4(C) shows the time change of the welding voltage Vw, FIG. 4(D) shows the time change of the short circuit discrimination signal Sd, FIG. 4(E) shows the time change of the first arc period signal Sta1, FIG. 4(F) shows the time change of the third arc period signal Sta3, FIG. 4(G) shows the time change of the polarity switching signal Spn, FIG. 4(H) shows the time change of the squeezing detection signal Nd, and FIG. 4(I) shows the time change of the initial period end signal Sti. In FIG. 4, the same operations as those in FIG. 2 will not be described again. In FIG. 4(I), the forward feed deceleration period signal Stsd in FIG. 2 is replaced with the initial period end signal Sti. Hereinafter, operations different from those in FIG. 2 will be described with reference to FIG.

[0064] In the figure, the initial period is set to a value longer than the forward transport deceleration period. 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 electrode positive polarity period Tep is the period obtained by adding the period from when a short circuit occurs until the initial period ends to the value of the electrode positive polarity period setting signal Tpr in FIG. 1. The electrode negative polarity period Ten is the period obtained by adding the period from when a short circuit occurs until the initial period ends to the value of the electrode negative polarity period setting signal Tnr in FIG. 1.

[0065] At time t0, as shown in FIG. 1D, when the short circuit discrimination signal Sd changes to a high level, a forward feed deceleration period is entered, and as shown in FIG. 1A, the feed speed Fw decelerates from the electrode negative polarity peak value to 0. Thereafter, as shown in FIG. 1I, the feed speed Fw is extended and maintained at 0 until the initial period end signal Sti becomes high for a short time at time t1. When the initial period end signal Sti becomes high for a short time at time t1, the polarity switching signal Spn changes to high level as shown in FIG. 1G, and the electrode positive polarity period Tep is entered. The feed speed Fw enters a reverse feed acceleration period at time t1, and accelerates from 0 to the electrode positive polarity forward feed peak value. When the initial period ends at time t1, 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.

[0066] At time t4, as shown in FIG. 1D, when the short circuit discrimination signal Sd changes to a high level, a forward feed deceleration period is entered, and as shown in FIG. 1A, the feed speed Fw decelerates from the electrode positive polarity peak value to 0. Thereafter, as shown in FIG. 1I, the feed speed Fw is extended and maintained at 0 until the initial period end signal Sti becomes high level for a short time at time t41. When the initial period end signal Sti becomes high level for a short time at time t41, the polarity switching signal Spn changes to low level as shown in FIG. 1G, and the electrode negative polarity period Ten is entered. The feed speed Fw enters a reverse feed acceleration period at time t41, and accelerates from 0 to the electrode negative polarity forward feed peak value. When the initial period ends at time t41, as shown in FIG. 1B, the welding current Iw increases at a predetermined short circuit slope, and when it reaches the short circuit peak value, it maintains that value.

[0067] The effects of this embodiment will be described below. According to the first embodiment, the electrode polarity is switched during the short circuit period and at a point in time when the feed speed starts to decelerate from the forward feed peak value and the delay period has elapsed, and the delay period is set to a period before the feed speed is decelerated to 0. In the conventional technology, the electrode polarity is switched during the short circuit period. This is because switching the electrode polarity during the arc period may cause an arc interruption, which deteriorates the welding quality. However, when switching the electrode polarity during the short circuit period, an arc may suddenly occur due to irregular movements of the droplets and the molten pool. When such a state occurs, the electrode polarity is not smoothly changed, the welding state becomes unstable, and the welding quality deteriorates. In contrast, in the first embodiment, the electrode polarity is switched during the short circuit period and at a point in time when the feed speed starts to decelerate from the forward feed peak value and the delay period has elapsed, and the delay period is set to a period before the feed speed is decelerated to 0. In this way, the welding wire is fed forward during the delay period and pushed into the molten pool, reducing the possibility that the short circuit is suddenly released and an arc occurs when the electrode polarity is switched. When the forward feed deceleration period ends and the reverse feed acceleration period begins, the welding wire is fed backward and pulled up from the molten pool, increasing the possibility that an arc will suddenly occur. For this reason, the delay period is set to a period before the feed speed is decelerated to 0. At the moment the feed speed becomes 0, an arc may also suddenly occur, so the delay period is set to a period before that. As a result, in the first embodiment, the electrode polarity can be switched smoothly, and the welding quality can be improved.

[0068] More preferably, according to the second embodiment, the electrode polarity is switched by extending the period in which the feed speed is decelerated to zero. In this way, the welding wire is fed forward and pushed into the molten pool during the period in which the feed speed is decelerated, so that the short circuit state becomes more solid. Furthermore, since the feed speed is held at zero, a solid short circuit state is maintained, and the possibility of the short circuit being suddenly released and an arc being generated when the electrode polarity is switched can be greatly reduced.

[0069] More preferably, according to the first 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 prevented from becoming unstable.

[0070] More preferably, according to the first embodiment, the average value of the welding wire feed speed is set to a value greater during the electrode negative polarity period than during the electrode positive polarity period. In this way, the average value of the welding current can be set to approximately the same value during the electrode negative polarity period and during the electrode positive polarity period. As a result, the bead appearance can be improved.

[0071] More preferably, according to the first 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 stably maintained. 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.

[0072] More preferably, according to the first 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 base metal, 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.

[0073] More preferably, according to the first 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 base metal 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.

[0074] More preferably, according to the first embodiment, the rate of increase of the welding current during the first arc period is set to 50% or less during the electrode negative polarity period compared to the electrode positive polarity period. More preferably, it is set to 30% or less. In this way, the melting speed of the welding wire during the electrode negative polarity period can be optimized, and stable droplets can be formed. As a result, the generation of spatter can be reduced, and the welding state can be more stabilized.

[0075] More preferably, according to the first 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 consideration the heat input to the base metal. If the rate of rise is kept the same even when 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 when the first arc current value is increased. [Explanation of symbols]

[0076] 1 Welding wire 2 Base material 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 FR2 2nd feed speed setting circuit Fw Feeding 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 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 SPN2 2nd polarity switching circuit 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 Sti Initial period end signal Stsd Forward feed deceleration 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 TIR initial period setting circuit Tir Initial period setting signal TNR Electrode negative polarity period setting circuit Tnr Electrode negative polarity period setting signal TPR electrode positive polarity period setting circuit Tpr electrode positive polarity period 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, a welding wire feed speed is switched from a forward feed peak value to a reverse feed peak value during the short circuit period, and is switched from the reverse feed peak value to the forward feed peak value during the arc period; 1. A method for controlling AC consumable electrode arc welding in which electrode polarity is periodically switched 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, The electrode polarity is switched during the short circuit period and at a time when the feed speed starts to decelerate from the forward feed peak value and a delay period has elapsed; The delay period is set to a period before the feed rate is decelerated to zero.

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

2. The electrode polarity is switched while the feeding speed is decelerated to 0.

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

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