JP2014042939A - Ac pulse arc welding control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent bead external shape when high-speed welding is carried out with an electrode minus polarity current ratio set to a large value in AC pulse arc welding using a flux-cored wire.SOLUTION: A method includes: feeding a flux-cored wire; supplying an electrode minus polarity base current in an electrode minus polarity base period; then supplying an electrode minus polarity peak current Ipn in an electrode minus polarity peak period Tpn; and then supplying an electrode plus polarity peak current in an electrode plus polarity peak period, one cycle of supplying those welding currents Iw being repeated. An oscillation frequency fs of the electrode minus polarity peak current Ipn is set to be higher as a welding speed is faster. Consequently, the oscillation frequency fs becomes higher as the welding speed becomes faster, so droplets which move increase in number and decrease in size, so that an excellent bead external shape can be obtained.

Description

  The present invention relates to an AC pulse arc welding control method capable of obtaining a stable welding state even when an electrode negative polarity current ratio is set to a large value.

  In AC pulse arc welding, welding is performed by repeating the energization of the peak current and base current during the electrode positive polarity period and the energization of the base current during the electrode negative polarity period as one cycle. In this AC pulse arc welding, by adjusting the electrode negative polarity period, the electrode negative polarity current ratio, which is the ratio of the current in the electrode negative polarity period to the average value of the welding current, is changed, and the heat input to the base metal is changed. Can be controlled. For this reason, low heat input welding is possible, and high-quality thin plate welding can be performed. Further, by changing the electrode negative polarity current ratio, the bead shape such as the penetration depth and the surplus height can be optimized according to the workpiece. Usually, the electrode negative polarity current ratio is used in the range of about 0 to 30%. Here, the electrode negative polarity current ratio of 0% means DC pulse arc welding with electrode positive polarity.

  Depending on the workpiece, it may be necessary to form a bead shape with a small dilution rate with a small melted portion and a large surplus portion. For example, in the thin plate welding of steel materials, there is a case where a workpiece having a large gap in the welded joint portion is welded at high speed. In such a case, a bead shape with a small dilution rate is required to fill the gap with molten metal and reduce the penetration. In order to form such a bead shape, it is necessary to set the electrode minus polarity current ratio to 30% or more, which is a value larger than the normal range. Sometimes it may be necessary to set a value exceeding 50%. In such a case, an AC pulse arc welding method is used in which welding is performed with one cycle of energization of the peak current and base current during the electrode plus polarity period and the energization of the peak current and base current during the electrode minus polarity period. Has been. Hereinafter, this conventional technique (see Patent Document 1) will be described. In the following description, the welding current and the welding voltage during the electrode negative polarity period are negative values, but when the magnitude of the value is described, it means the magnitude of the absolute value.

  FIG. 4 is a waveform diagram of a welding current Iw showing an AC pulse arc welding control method in the prior art. In the figure, the upper side from 0A shows the electrode positive polarity EP, and the lower side shows the electrode negative polarity EN. This figure shows a case where the electrode negative polarity current ratio is set larger than the normal range (about 0 to 30%). In order to prevent arc break at the time of polarity switching, a high voltage (not shown) of about 200 V is applied between the welding wire and the base material for a short time at the time of polarity switching. Hereinafter, a description will be given with reference to FIG.

  During the electrode minus polarity base period Tbn from time t1 to t2, an electrode minus polarity base current Ibn less than the critical value is applied. During the electrode minus polarity peak period Tpn from time t2 to t3, the electrode minus polarity peak current Ipn having a larger average value than the electrode minus polarity base current Ibn is applied. The polarity is reversed at time t3. During the electrode positive polarity peak period Tp from time t3 to t4, the electrode positive polarity peak current Ip greater than the critical value is applied. During the electrode positive polarity base period Tb from time t4 to t5, the electrode positive polarity base current Ib less than the critical value is applied. Times t5 to t6 again become the electrode negative polarity base period Tbn, times t6 to t7 again become the electrode negative polarity peak period Tpn, and times t7 to t8 again become the electrode positive polarity peak period Tp. The period from time t1 to t5 is one pulse period Tf. Further, the period from time t1 to t3 becomes the electrode negative polarity period Ten. The electrode positive polarity base period Tb may be deleted. In this case, electrode negative polarity base period Tbn → electrode negative polarity peak period Tpn → electrode positive polarity peak period Tp → electrode negative polarity base period Tbn is repeated.

The electrode positive polarity peak period Tp, the electrode positive polarity peak current Ip, the electrode negative polarity peak period Tpn, the electrode negative polarity peak current Ipn, the electrode negative polarity base current Ibn, and the electrode positive polarity. The base current Ib is set to an appropriate value in advance. Further, the length of the pulse period Tf is feedback-controlled (arc length control) so that the average value of the absolute values of the welding voltage becomes equal to a predetermined voltage setting value. In order to change the pulse period Tf, the electrode plus polarity base period Tb or the electrode minus polarity base period Tbn is changed by the feedback control. When the electrode positive polarity base period Tb changes by feedback control, the electrode negative polarity base period Tbn is set to an appropriate value in advance. Conversely, when the electrode negative polarity base period Tbn changes by feedback control, the electrode positive polarity base period Tb is set to an appropriate value in advance. In the figure, the electrode negative polarity current ratio Ren is as follows.
Ren = ((Tpn · | Ipn | + Tbn · | Ibn |) / (Tp · Ip + Tpn · | Ipn | + Tbn · | Ibn | + Tb · Ib)) × 100

  When the welding wire is made of iron and the shield gas is a mixed gas of 80% Ar + 20% CO2, the setting values of the parameters are as follows, for example. Tp = 1.7 ms, Ip = 450 A, Tpn = 2.0 to 10.0 ms, Ipn = 200 to 500 A, Ib = 60 A, Ibn = 60 A. When Tbn is feedback-controlled, Tb = 0 to 4.0 ms. When Tb = 0, there is no electrode positive polarity base period. The range of Tbn to be feedback controlled is about 10 to 1 ms.

  This figure shows a case where the rising and falling edges of the electrode positive polarity peak current Ip and the electrode negative polarity peak current Ipn are steep and become a rectangular wave. However, a trapezoidal wave may be formed by giving a predetermined slope to the rise and fall of these peak currents. In AC pulsed arc welding for aluminum materials, by making these peak currents a trapezoidal wave, the arc force can be weakened and the occurrence of spatter can be reduced.

  Next, formation and transfer of droplets will be described with reference to FIG. In the vicinity of the end of the electrode positive polarity peak period Tp at time t4, the droplet moves. During the electrode positive polarity base period Tb from time t4 to t5, since a small current less than the critical value is energized and the polarity is the electrode positive polarity EP, the welding wire tip melts little and the droplets are Little formed. During the electrode negative polarity base period Tbn from time t5 to t6, the tip of the welding wire is melted to form small droplets. Since the electrode negative polarity current ratio is set to be large, the electrode negative polarity base period Tbn becomes long. For this reason, even if the electrode negative polarity base current Ibn is a small current value less than the critical value, the electrode negative polarity EN promotes melting of the tip of the welding wire, so that a small droplet is formed. During the electrode negative polarity peak period Tpn from time t6 to t7, since the electrode negative polarity peak current Ipn having a large current value is energized, the droplet gradually grows and becomes larger. In the latter half of this period, the constriction is gradually formed in the droplet, but the transition is not reached because the size of the droplet is usually large. During the electrode positive polarity peak period Tp from time t7 to t8, since a large current exceeding the critical value is applied, the droplet becomes larger and a strong electromagnetic pinch force acts on the constricted portion of the droplet, resulting in a constriction. Progresses rapidly and droplets migrate. This transferred droplet size is larger than in the case of DC pulse arc welding and AC pulse arc welding with a normal electrode negative polarity current ratio. However, since this large-sized droplet is pushed toward the molten pool by a strong arc force due to the electrode plus polarity peak current Ip having a large current value, the droplet does not generate much spatter.

  As described above, when the electrode negative polarity current ratio is set to a large value, the droplets grow rapidly during the electrode negative polarity peak period Tpn, and the droplets to be transferred during the peak period. Increase in size. For this purpose, two peak periods are provided, one of which is an electrode minus polarity peak period Tpn and the other is an electrode plus polarity peak period Tp, so that a large-sized droplet is transferred. Furthermore, by changing the polarities of these two peak periods, the electrode negative polarity current ratio can be easily set to a large value.

  In the figure, when the electrode plus polarity base period Tb is changed by feedback control, the electrode minus polarity peak period Tpn, the electrode minus polarity peak current Ipn, the electrode minus polarity is changed when the electrode minus polarity current ratio is changed. This is performed by changing at least one of the base period Tbn or the electrode negative polarity base current Ibn. When the electrode negative polarity base period Tbn is changed by feedback control, the electrode negative polarity peak period Tpn, the electrode negative polarity peak current Ipn or the electrode negative polarity base current Ibn is changed. This is done by changing at least one. Here, in order to set the electrode negative polarity current ratio to be larger than the normal range, it is desirable to adjust the electrode negative polarity peak period Tpn or at least one of the electrode negative polarity peak current Ipn. .

In the figure, the electrode negative polarity peak current Ipn is a constant value, but by oscillating it in a rectangular wave shape or the like, the following operational effects can be obtained.
(1) If the electrode negative polarity current ratio is set larger than the normal range, the arc rigidity tends to be weakened. On the other hand, when the electrode negative polarity peak current Ipn is vibrated, the rigidity of the arc becomes strong and the workability is improved.
(2) When the electrode negative polarity peak current Ipn is not oscillating, sometimes the constriction of the droplet during the electrode negative polarity peak period Tpn is not sufficient. If it will be in such a state, the case where a droplet cannot transfer during the following electrode positive polarity peak period Tp will arise. On the other hand, when the electrode negative polarity peak current Ipn is oscillating, the lifting force acting on the droplet also changes strongly, so that the droplet oscillates up and down. For this reason, the formation of the constriction of the droplet is promoted, and the droplet can be surely transferred in the next electrode positive polarity peak period Tp, and the good dissolution in the one-pulse period 1 droplet transfer state can be achieved. The droplet transfer state can be maintained with a higher probability.

JP 2010-234441 A

  As described above, in the AC pulse arc welding of Patent Document 1 in which a solid wire is used as the welding wire, the droplet at the tip of the welding wire gradually increases during the electrode minus polarity base period Tbn, and the electrode minus polarity peak period Tpn. As you enter, it grows and grows rapidly. At this time, when the electrode negative polarity peak current Ipn is vibrated, the droplet grows and grows while vibrating up and down, and the constriction of the droplet gradually forms. Then, when the electrode positive polarity peak period Tp is entered, the droplet continues to grow and the constriction of the droplet proceeds rapidly, and the droplet smoothly moves to the molten pool near the end of the period. When the growth and transfer of droplets are performed in this cycle, the droplet transfer state is one pulse period, so that a stable welding state with less spattering is obtained.

  When the flux-cored wire is used as the welding wire and the AC pulse arc welding of Patent Document 1 is performed, the droplet transfer state does not become one pulse cycle one droplet transfer state. A plurality of droplets move substantially in synchronization with the oscillation cycle of the electrode negative polarity peak current Ipn, and one droplet moves due to the electrode positive polarity peak current Ip. The droplet size due to the electrode negative polarity peak current Ipn is smaller than the droplet size due to the electrode positive polarity peak current Ip. The droplet transfer state is caused by the composition component of the flux-cored wire. In such a droplet transfer state, small-sized droplets stably transfer, so that the amount of spatter generated is reduced and a good bead appearance can be obtained.

  However, when AC pulse arc welding using flux-cored wire is used for high-speed welding with a welding speed of 100 cm / min or more, the formation of the beads cannot follow the welding speed, and the bead appearance deteriorates. Arise. For this reason, production efficiency could not be improved.

  Therefore, in the present invention, a good bead appearance is obtained even when high-speed welding is performed in AC pulse arc welding in which the electrode negative polarity current ratio using a flux-cored wire is larger than the normal range (0 to 30%). An object of the present invention is to provide an AC pulsed arc welding control method that can be used.

In order to solve the above-described problem, the invention of claim 1 is configured to feed the flux-cored wire at a predetermined feeding speed and to pass an electrode minus polarity base current less than a critical value during the electrode minus polarity base period. Then, during the electrode negative polarity peak period, an oscillating electrode negative polarity peak current whose average value is larger than the electrode negative polarity base current is energized. In the AC pulse arc welding control method in which a positive polarity peak current is applied and welding is performed by repeating the application of these welding currents as one cycle,
The vibration frequency of the electrode negative polarity peak current is set by a predetermined function with the welding speed as an input,
An AC pulse arc welding control method characterized by the above.

In the invention of claim 2, the function is a function in which the vibration frequency is increased as the welding speed is increased.
The alternating-current pulse arc welding control method according to claim 1.

According to a third aspect of the present invention, the function is such that the vibration frequency is a constant value when the welding speed is less than a predetermined reference speed, and the welding speed is increased when the welding speed exceeds the reference speed. As a result, the vibration frequency is a function that increases.
The alternating-current pulse arc welding control method according to claim 1.

  The invention of claim 4 is characterized in that, following the electrode plus polarity peak period, an electrode plus polarity base period for passing an electrode plus polarity base current less than a critical value is provided to form one cycle. 4. The AC pulse arc welding control method according to any one of items 3 to 3.

  According to the present invention, as the welding speed is increased, the vibration frequency of the electrode negative polarity peak current is increased, so that the number of droplets to be transferred is increased and the size thereof is reduced. Will be formed. As a result, in the present invention, a good bead appearance is achieved even when high-speed welding is performed in AC pulse arc welding in which the electrode negative polarity current ratio using the flux-cored wire is larger than the normal range (0 to 30%). Can be obtained.

In the AC pulse arc welding control method according to the embodiment of the present invention, it is a welding current waveform diagram showing the vibration waveform of the electrode minus polarity peak current Ipn. In FIG. 1, it is a figure which shows the example of the function which calculates the vibration frequency fs by inputting the welding speed Ws. It is a block diagram of the welding power source for implementing the alternating current pulse arc welding control method concerning an embodiment of the invention. It is an electric current waveform diagram in the alternating current pulse arc welding of a prior art.

  Embodiments of the present invention will be described below with reference to the drawings.

  The welding current waveform of the AC pulse arc welding control method according to the embodiment of the present invention is the same as that in FIG. 4 described above. That is, the electrode negative polarity base period Tbn → the electrode negative polarity peak period Tpn → the electrode positive polarity peak period Tp → the electrode positive polarity base period Tb is set to one pulse period Tf, and the electrode negative polarity base period Tbn → electrode negative polarity peak The period Tpn → the electrode positive polarity peak period Tp may be set to one pulse period Tf. However, in this embodiment, a flux-cored wire is used as the welding wire. Furthermore, in the present embodiment, as described above, the electrode negative polarity peak current Ipn vibrates, and the vibration frequency is automatically calculated and set by a predetermined function using the welding speed as an input. The

  The setting values of each parameter of the welding current waveform when the welding wire is a flux cored wire with a diameter of 1.2 mm for steel and the type of shielding gas is a mixed gas of carbon dioxide and argon are as follows, for example: become. Tp = 1.5 ms, Ip = 430 A, Tpn = 2.0 to 10.0 ms, Ipn = 200 to 500 A, Ib = 60 A, Ibn = 60 A. When Tbn is feedback-controlled, Tb = 0 to 4.0 ms. When Tb = 0, there is no electrode positive polarity base period. The range of Tbn to be feedback controlled is about 10 to 1 ms. Hereinafter, the vibration waveform of the electrode negative polarity peak current Ipn will be described.

  FIG. 1 is a welding current waveform diagram showing a vibration waveform of electrode negative polarity peak current Ipn in the AC pulse arc welding control method according to the embodiment of the present invention. The welding current waveform in the other periods is the same as that in FIG. 4 described above. In the figure, the period before time t2 becomes the electrode minus polarity base period Tbn, and the period after time t3 becomes the electrode plus polarity peak period Tp with the polarity reversed. Hereinafter, a description will be given with reference to FIG.

  At time t2, the electrode negative polarity base period Tbn is switched to the electrode negative polarity peak period Tpn, and the electrode negative polarity peak current Ipn starts energization. As shown in the figure, the electrode negative polarity peak current Ipn has a waveform oscillating in a rectangular waveform having a center current value of Ipc [A], an amplitude of W [A], and a vibration period of Ts [ms]. The period from time t2 to t22 is the vibration period Ts, and the reciprocal thereof is the vibration frequency fs = 1 / Ts [Hz]. Therefore, Ipc + (W / 2) is energized during the period from time t2 to t21, and Ipc− (W / 2) is energized during the period from time t21 to t22. Here, when the duty is (maximum value (Ipc + (W / 2)) energization period / vibration period Ts) × 100 [%], the duty is 50% in FIG. In the figure, the electrode negative polarity peak current Ipn oscillates over five periods during the electrode negative polarity peak period Tpn from time t2 to t3. In this example, the amplitude W is a constant value.

  The setting range of the amplitude W is about 100 to 300 A, and is set to a value at which the flux-cored wire moves to the droplet substantially in synchronization with the vibration period Ts. The vibration frequency fs is calculated and set by a predetermined function using the welding speed as an input. The setting range of the vibration frequency fs is about 0.5 to 2.0 kHz. This function will be described later with reference to FIG.

  The figure shows the case where the electrode negative polarity peak current Ipn vibrates in a rectangular wave shape, but it may also vibrate in a sine wave, triangular wave or sawtooth wave shape. In addition, the amplitude W may change so as to decrease with the passage of time during the electrode negative polarity peak period Tpn from time t2 to t3.

  The droplet transfer during the electrode negative polarity peak period Tpn is performed substantially in synchronization with the vibration period Ts. Therefore, in the case of the same figure, since it vibrates over 5 periods, five droplets will transfer. Then, the droplet grows and becomes larger during the electrode positive polarity peak period Tp, and one droplet moves near the end of the period. The size of the droplet that moves during the electrode minus polarity peak period Tpn is smaller than the size of the droplet that moves near the end of the electrode plus polarity peak period Tp.

  FIG. 2 is a diagram illustrating an example of a function that calculates the vibration frequency fs with the above-described welding speed Ws as an input. The horizontal axis of the figure shows the welding speed Ws (cm / min), and the range is 30 to 150 cm / min. The vertical axis represents the vibration frequency fs (kHz), and the range is 0 to 2.0 kHz. The figure shows an example of two functions. The first example is a function L1 indicated by a solid line, and the second example is a function L2 indicated by a broken line. Hereinafter, a description will be given with reference to FIG.

  The function L1 is fs = 1.0 kHz when Ws = 30 cm / min, and the vibration frequency fs increases linearly as the welding speed Ws increases, and fs = 1.5 kHz when Ws = 100 cm / min. As the welding speed Ws further increases, the vibration frequency fs increases linearly, and when Ws = 150 cm / min, fs = 2.0 kHz.

  The function L2 has a constant value of fs = 1.25 kHz when Ws = 30 to 100 cm / min, fs = 1.25 kHz when Ws = 100 cm / min, and the vibration frequency fs increases as the welding speed Ws increases. It increases linearly, and when Ws = 150 cm / min, fs = 2.0 kHz.

  The function L1 is a function that increases the vibration frequency fs as the welding speed Ws increases. In particular, the function is set so that the change rate of the vibration frequency fs when the welding speed Ws is equal to or higher than a predetermined reference speed ft is larger than the change rate when the welding speed Ws is less than the predetermined reference speed ft. In the figure, the reference speed ft = 100 cm / min. That is, the reference speed ft is a threshold value that classifies whether or not high-speed welding is performed. The function L2 is a function in which the vibration frequency fs is a constant value when the welding speed Ws is less than the reference speed ft, and when the welding speed Ws is equal to or higher than the reference speed ft, the vibration frequency fs increases as the welding speed Ws increases. is there. In the figure, a portion that changes linearly may be changed to a curved shape.

  As described above, the droplet moves substantially in synchronization with the oscillation period Ts of the electrode negative polarity peak current Ipn. Therefore, when the vibration frequency fs is increased, even if the time length of the electrode negative polarity peak period Tpn is the same, the number of transferred droplets increases and the size of the droplets decreases. For this reason, when the vibration frequency fs is increased as the welding speed Ws is increased, the number of droplets to be transferred is increased and the size is reduced, so that the bead formation becomes smooth and the bead appearance is improved. In particular, when high-speed welding is performed at a reference speed ft = 100 cm / min or more, this effect is remarkable. In the case of low-speed welding at a speed lower than the reference speed ft, the bead appearance is not so bad even if the vibration frequency fs is a constant value. However, if the vibration frequency fs is too high in the case of low speed welding, the bead appearance is worsened. This is because, when the vibration frequency is too high during low-speed welding, the arc length becomes short, the arc spread is insufficient, and the bead appearance is deteriorated. Therefore, in the case of low speed welding, the vibration frequency fs may be a constant value, but the value should not be set as high as during high speed welding. On the other hand, when the vibration frequency fs is changed according to the welding speed Ws in the range of high-speed welding, the bead appearance is clearly improved.

  FIG. 3 is a block diagram of a welding power source for carrying out the AC pulse arc welding control method according to the embodiment of the present invention. The figure shows a case where the electrode negative polarity base period Tbn is changed by feedback control and the electrode positive polarity base period Tb is a predetermined value. In the figure, the high voltage application circuit at the time of switching the polarity is omitted. Hereinafter, each block will be described with reference to FIG.

  The inverter circuit INV receives an AC commercial power supply (not shown) such as a three-phase 200V as an input, performs inverter control by rectifying and smoothing a DC voltage by pulse width modulation control using a current error amplification signal Ei, which will be described later, and high-frequency AC Is output. The inverter transformer INT steps down the high-frequency AC voltage to a voltage value suitable for arc welding. The secondary rectifiers D2a to D2d rectify the stepped-down high-frequency alternating current into direct current. The electrode plus polarity transistor PTR is turned on by an electrode plus polarity drive signal Pd described later. At this time, the output of the welding power source becomes the electrode plus polarity EP. The electrode minus polarity transistor NTR is turned on by an electrode minus polarity drive signal Nd described later, and at this time, the output of the welding power source becomes the electrode minus polarity EN. The reactor WL smooths the rippled output. The welding wire 1 is fed through the welding torch 4 by the rotation of the feed roll 5 coupled to the wire feed motor WM, and an arc 3 is generated between the base metal 2 and the welding wire 1. A welding voltage Vw is applied between the welding wire 1 and the base material 2, and a welding current Iw is conducted.

  The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The voltage averaging circuit VAV averages the absolute value of the voltage detection signal Vd and outputs a voltage average value signal Vav. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vr and the voltage average value signal Vav, and outputs a voltage error amplification signal Ev. The voltage / frequency conversion circuit VF converts the signal into a signal having a frequency proportional to the voltage error amplification signal Ev, and outputs a pulse period signal Tf that becomes High level for a short time for each frequency. This pulse cycle signal Tf is a trigger signal that becomes a high level for a short time every pulse cycle.

  The electrode positive polarity peak period setting circuit TPR outputs a predetermined electrode positive polarity peak period setting signal Tpr. The electrode negative polarity peak period setting circuit TPNR outputs a predetermined electrode negative polarity peak period setting signal Tpnr. The electrode plus polarity base period setting circuit TBR outputs a predetermined electrode plus polarity base period setting signal Tbr. The timer circuit TM receives the pulse period signal Tf, the electrode plus polarity peak period setting signal Tpr, the electrode minus polarity peak period setting signal Tpnr, and the electrode plus polarity base period setting signal Tbr as inputs, and outputs a pulse period. Each time the signal Tf changes to the high level for a short time, the value becomes 1 during the period determined by the electrode minus polarity peak period setting signal Tpnr, and subsequently the value becomes during the period determined by the electrode plus polarity peak period setting signal Tpr. Then, the timer signal Tm is output, which becomes 3 during the period determined by the electrode positive polarity base period setting signal Tbr, and becomes 4 during the subsequent electrode negative polarity base period.

  The center current setting circuit IPCR outputs a center current setting signal Ipcr for setting the center current value of the vibration waveform of the electrode minus polarity peak current. The amplitude setting circuit WR outputs a predetermined amplitude setting signal Wr.

  The vibration frequency setting circuit FSR receives the welding speed signal Ws from the external robot controller RC and outputs a vibration frequency setting signal fsr calculated by a predetermined function. This function is described above in FIG. When using a self-propelled carriage without using a robot as means for moving the welding torch 4, a welding speed signal Ws from the self-propelled carriage may be input.

  The electrode negative polarity peak current setting circuit IPNR has the center current setting signal Ipcr, the amplitude setting signal Wr and the vibration frequency setting signal fsr as inputs, and the amplitude setting signal with the value of the center current setting signal Ipcr as the center value. An electrode negative polarity peak current setting signal Ipnr that vibrates in a rectangular waveform with a period determined by the amplitude determined by Wr and the reciprocal of the vibration frequency setting signal fsr is output.

  The electrode positive polarity peak current setting circuit IPR outputs a predetermined electrode positive polarity peak current setting signal Ipr. The electrode negative polarity base current setting circuit IBNR outputs a predetermined electrode negative polarity base current setting signal Ibnr. The electrode positive polarity base current setting circuit IBR outputs a predetermined electrode positive polarity base current setting signal Ibr. The switching circuit SW includes the timer signal Tm, the electrode positive polarity peak current setting signal Ipr, the electrode negative polarity peak current setting signal Ipnr, the electrode negative polarity base current setting signal Ibnr, and the electrode positive polarity base. When the current setting signal Ibr is input, the electrode negative polarity peak current setting signal Ipnr is output as the current setting signal Ir when the timer signal Tm = 1, and the electrode positive polarity peak current setting signal Ipr is set when the timer signal Tm = 2. When the timer signal Tm = 3, the electrode positive polarity base current setting signal Ibr is output as the current setting signal Ir. When the timer signal Tm = 4, the electrode negative polarity base current setting signal Ibnr is output as the current setting signal Ir. Output as. The current detection circuit ID detects the absolute value of the welding current Iw and outputs a current detection signal Id. The current error amplification circuit EI amplifies an error between the current setting signal Ir and the current detection signal Id, and outputs a current error amplification signal Ei.

  The drive circuit DV receives the timer signal Tm, and outputs an electrode minus polarity drive signal Nd when the timer signal Tm = 1 or 4, and outputs an electrode plus polarity drive signal Pd when the timer signal Tm = 2 or 3. To do. Accordingly, the electrode negative polarity base period and the electrode negative polarity peak period become the electrode negative polarity, and the electrode positive polarity peak period and the electrode positive polarity base period become the electrode positive polarity. The feeding speed setting circuit FR outputs a predetermined feeding speed setting signal Fr. The feed control circuit FC receives this feed speed setting signal Fr, and feeds a feed control signal Fc for feeding the welding wire 1 at a feed speed corresponding to the value to the wire feed motor WM. Output.

  In the figure, when the electrode plus polarity base period Tb is deleted, the above electrode plus polarity base period setting signal Tbr = 0 may be set.

  According to the above-described embodiment, the vibration frequency of the electrode negative polarity peak current is set by a predetermined function using the welding speed as an input. This function is a function in which the vibration frequency increases as the welding speed increases. In this way, as the welding speed increases, the vibration frequency of the electrode negative polarity peak current increases, so the number of droplets that migrate increases and the size decreases, so that a good bead is formed. Will come to be. As a result, in this embodiment, a good bead can be obtained even in high-speed welding in AC pulse arc welding in which the electrode negative polarity current ratio using a flux-cored wire is larger than the normal range (0 to 30%). Appearance can be obtained.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll D2a-D2d Secondary rectifier DV Drive circuit EI Current error amplification circuit Ei Current error amplification signal EN Electrode minus polarity EP Electrode plus polarity EV Voltage error amplification circuit Ev Voltage error Amplified signal FC Feed control circuit Fc Feed control signal FR Feed speed setting circuit Fr Feed speed setting signal fs Vibration frequency FSR Vibration frequency setting circuit fsr Vibration frequency setting signal ft Reference speed Ib Electrode positive polarity Base current Ibn Electrode negative polarity Base current IBNR Electrode minus polarity base current setting circuit Ibnr Electrode minus polarity base current setting signal IBR Electrode plus polarity base current setting circuit Ibr Electrode plus polarity base current setting signal ID Current detection circuit Id Current detection signal INT Inverter transformer INV Inverter circuit Ip Electrode The Polarity peak current IPCR Center current setting circuit Ipcr Center current setting signal Ipn Electrode minus polarity peak current IPNR Electrode minus polarity peak current setting circuit Ipnr Electrode minus polarity peak current setting signal IPR Electrode plus polarity peak current setting circuit Ipr Electrode plus polarity peak current Setting signal Ir Current setting signal Iw Welding current L1, L2 Function Nd Electrode minus polarity drive signal NTR Electrode minus polarity transistor Pd Electrode plus polarity drive signal PTR Electrode plus polarity transistor RC Robot controller Ren Electrode Negative polarity current ratio SW Switching circuit Tb Electrode Positive polarity base period Tbn Electrode minus polarity base period TBR Electrode plus polarity base period setting circuit Tbr Electrode plus polarity base period setting signal Ten Electrode minus polarity period Tf Pulse period (signal)
TM timer circuit Tm timer signal Tp electrode plus polarity peak period Tpn electrode minus polarity peak period TPNR electrode minus polarity peak period setting circuit Tpnr electrode minus polarity peak period setting signal TPR electrode plus polarity peak period setting circuit Tpr electrode plus polarity peak period setting signal Ts Vibration period VAV Voltage averaging circuit Vav Voltage average value signal VD Voltage detection circuit Vd Voltage detection signal VF Voltage / frequency conversion circuit VR Voltage setting circuit Vr Voltage setting signal Vw Welding voltage W Amplitude WL Reactor WM Wire feed motor WR Amplitude setting Circuit Wr Amplitude setting signal Ws Welding speed (signal)

Claims (4)

While feeding the flux-cored wire at a predetermined feeding speed, the electrode minus polarity base current less than the critical value is applied during the electrode minus polarity base period, and the average value is continuously applied during the electrode minus polarity peak period. An oscillating electrode minus polarity peak current having a value larger than the minus polarity base current is applied, and then an electrode plus polarity peak current exceeding the critical value is energized during the electrode plus polarity peak period. In the AC pulse arc welding control method of performing welding repeatedly as a cycle,
The vibration frequency of the electrode negative polarity peak current is set by a predetermined function with the welding speed as an input,
AC pulse arc welding control method characterized by the above. The function is a function in which the vibration frequency increases as the welding speed increases.
The AC pulse arc welding control method according to claim 1, wherein: The function is that when the welding speed is less than a predetermined reference speed, the vibration frequency becomes a constant value, and when the welding speed is equal to or higher than the reference speed, the vibration frequency increases as the welding speed increases. Is a function,
The AC pulse arc welding control method according to claim 1, wherein:   4. The electrode positive polarity base period for passing an electrode positive polarity base current less than a critical value following the electrode positive polarity peak period is set to one cycle, according to claim 1. The AC pulse arc welding control method described.

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