Arc welding control method

Abstract

To perform high-quality welding of a thin plate having a large gap in a weld joint part, in consumable electrode arc-welding.SOLUTION: In an arc welding control method, a welding wire is fed and a short-circuit period and an arc period are repeated, and the arc period comprises a first arc period Ta1 of times t4-t61 and a second arc period Ta2 of times t61-t62 following the first arc period, where welding currents are carried by constant current control in the first arc period Ta1 and the welding currents are carried by constant voltage control in the second arc period Ta2 so as to perform welding. An electrode is set to have a minus polarity in the first arc period Ta1, and an electrode is set to have a plus polarity in the period other than the first arc period. At a time when the first arc period starts or at a time which is delayed from the time when the first arc period starts, the electrode with the plus polarity is switched to the electrode with the minus polarity.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an arc welding control method performed by feeding a welding wire.

Background Art

[0002] Inventions such as Patent Documents 1 and 2 are commonly used to reduce the heat input to the base material and weld thin plates with high quality. In the alternating current pulse arc welding method according to Patent Document 1, welding is performed by feeding a welding wire and repeating, as one cycle, the energization of the peak current and the base current during the electrode positive polarity period and the energization of the electrode negative polarity current during the electrode negative polarity period. In this alternating current pulse arc welding, by adjusting the electrode negative polarity period, the electrode negative polarity ratio, which is the time ratio of the electrode negative polarity period in one cycle, can be changed to control the heat input to the base material. For this reason, low heat input welding becomes possible, and high-quality thin plate welding can be performed.

[0003] In the welding method according to Patent Document 2, welding is performed by feeding a welding wire and alternately switching between a period of performing pulse arc welding and a period of performing short-circuit transfer arc welding. In this welding method, heat input control to the base material can be performed by adjusting the ratio between the period of pulse arc welding and the period of short-circuit transfer arc welding. For this reason, low heat input welding becomes possible, and high-quality thin plate welding can be performed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In thin plate welding, when there is a gap in the welded joint, it is necessary to form a bead shape with a small dilution rate that reduces the penetration and increases the reinforcement. However, with the conventional welding methods described in Patent Documents 1, 2, etc., it has been difficult to weld thin plates with large gaps with high quality.

[0006] Therefore, an object of the present invention is to provide an arc welding control method capable of performing high-quality welding on a thin plate having a large gap in the welded joint.

Means for Solving the Problems

[0007] In order to solve the above-described problems, the invention according to claim 1 is feeding a welding wire and repeating a short-circuit period and an arc period, wherein the arc period includes a first arc period and a second arc period following the first arc period, the first arc period energizes a welding current by constant current control, and the second arc period energizes the welding current by constant voltage control to perform welding, in an arc welding control method, making the first arc period have an electrode negative polarity and other periods have an electrode positive polarity, which is an arc welding control method characterized by this.

[0008] The invention according to claim 2 is switching to the electrode negative polarity at the time when the first arc period is started or at a time delayed therefrom, which is the arc welding control method according to claim 1, characterized by this.

[0009] The invention according to claim 3 is switching to the electrode negative polarity during the short-circuit period, which is the arc welding control method according to claim 1, characterized by this.

[0010] The invention according to claim 4 is when switching the polarity, performing it in a state where the absolute value of the welding current is equal to or less than a reference value, The arc welding control method according to any one of claims 1 to 3, characterized in that

[0011] The invention of claim 5 is During the short - circuit period, the welding wire is reversely fed, and during the arc period, it is forward - fed. The arc welding control method according to any one of claims 1 to 4, characterized in that

Advantages of the Invention

[0012] According to the present invention, high - quality welding can be performed on thin plates having a large gap at the welded joint.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] FIG. 1 is a block diagram of an arc welding apparatus for implementing the arc welding control method according to an embodiment of the present invention. In the figure, a circuit for applying a high voltage of several hundred volts between the welding wire 1 and the base material 2 for a short time to smooth the polarity switching is omitted. Hereinafter, each block will be described with reference to the figure.

[0016] The power control circuit PM takes a commercial power supply (not shown) such as three-phase 200V as input, performs output control by inverter control or the like according to the error amplification signal Ea described later, and switches between the electrode positive polarity EP and the electrode negative polarity EN by the polarity switching signal Dr described later to output a welding voltage Vw and a welding current Iw between the welding wire 1 and the base material 2. Although not shown, this power control circuit PM includes a primary rectifier for rectifying the commercial power supply, a smoothing capacitor for smoothing the rectified direct current, an inverter circuit driven by the above-described error amplification signal Ea for converting the smoothed direct current into a high-frequency alternating current, a high-frequency transformer for stepping down the high-frequency alternating current to a voltage value suitable for welding, a secondary rectifier for rectifying the stepped-down high-frequency alternating current into a direct current, a reactor for smoothing the rectified direct current, and a secondary-side inverter circuit for converting the smoothed direct current into an alternating current of several tens to several hundreds of Hz based on the above-described polarity switching signal Dr.

[0017] The feeding motor WM takes the feeding control signal Fc described later as input, and alternately repeats forward feeding and reverse feeding to feed the welding wire 1 at a feeding speed Fw. Also, as is common, the welding wire 1 may be fed at a constant speed at a predetermined speed. A motor with fast transient responsiveness is used for the feeding motor WM. In order to increase the change rate of the feeding speed Fw of the welding wire 1 and the reversal of the feeding direction, the feeding motor WM may be installed near the tip of the welding torch 4. Also, there are cases where two feeding motors WM are used to form a push-pull type feeding system.

[0018] The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 coupled to the above-described feeding motor WM, and an arc 3 is generated between the welding wire 1 and the base material 2. A welding voltage Vw is applied between the welding wire 1 and the base material 2, and a welding current Iw flows. For the welding wire 1, a steel wire, an aluminum wire, or the like is used. Shielding gas (not shown) is ejected from the tip of the welding torch 4.

[0019] The current detection circuit ID detects the absolute value of the above-described welding current Iw and outputs a current detection signal Id.

[0020] The voltage detection circuit VD detects the absolute value of the above welding voltage Vw and outputs a voltage detection signal Vd. The voltage setting circuit VR outputs a voltage setting signal Vr for setting the welding voltage Vw during the second arc period.

[0021] The voltage error amplification circuit EV takes the above voltage setting signal Vr and the above voltage detection signal Vd as inputs, amplifies the error between the two values, and outputs a voltage error amplification signal Ev.

[0022] The short-circuit discrimination circuit SD takes the above voltage detection signal Vd as an input. When this value is less than a predetermined short-circuit discrimination value (about 10V), it discriminates that it is in the short-circuit period and becomes High level, and when it is more than that, it discriminates that it is in the arc period and outputs a short-circuit discrimination signal Sd that becomes Low level.

[0023] The forward feed acceleration period setting circuit TSUR outputs a predetermined forward feed acceleration period setting signal Tsur.

[0024] The forward feed deceleration period setting circuit TSDR outputs a predetermined forward feed deceleration period setting signal Tsdr.

[0025] The reverse feed acceleration period setting circuit TRUR outputs a predetermined reverse feed acceleration period setting signal Trur.

[0026] The reverse feed deceleration period setting circuit TRDR outputs a predetermined reverse feed deceleration period setting signal Trdr.

[0027] The forward feed peak value setting circuit WSR outputs a predetermined forward feed peak value setting signal Wsr.

[0028] The reverse feed peak value setting circuit WRR outputs a predetermined reverse feed peak value setting signal Wrr.

[0029] The feed speed setting circuit FR takes as inputs the above-mentioned forward feed acceleration period setting signal Tsur, the above-mentioned forward feed deceleration period setting signal Tsdr, the above-mentioned reverse feed acceleration period setting signal Trur, the above-mentioned reverse feed deceleration period setting signal Trdr, the above-mentioned forward feed peak value setting signal Wsr, the above-mentioned reverse feed peak value setting signal Wrr, and the above-mentioned short-circuit discrimination signal Sd, and outputs, as the feed speed setting signal Fr, a feed speed pattern generated by the following processing. When this feed speed setting signal Fr is 0 or more, it is the forward feed period, and when it is less than 0, it is the reverse feed period. 1) During the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur, it outputs a feed speed setting signal Fr that accelerates from 0 to the positive forward feed peak value Wsp determined by the forward feed peak value setting signal Wsr. 2) Subsequently, during the forward feed peak period Tsp, it outputs a feed speed setting signal Fr that maintains the above-mentioned forward feed peak value Wsp. 3) When the short-circuit discrimination signal Sd changes from the Low level (arc period) to the High level (short-circuit period), it shifts to the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr, and outputs a feed speed setting signal Fr that decelerates from the above-mentioned forward feed peak value Wsp to 0. 4) Subsequently, during the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur, it outputs a feed speed setting signal Fr that accelerates from 0 to the negative reverse feed peak value Wrp determined by the reverse feed peak value setting signal Wrr. 5) Subsequently, during the reverse feed peak period Trp, it outputs a feed speed setting signal Fr that maintains the above-mentioned reverse feed peak value Wrp. 6) When the short-circuit discrimination signal Sd changes from the High level (short-circuit period) to the Low level (arc period), it shifts to the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr, and outputs a feed speed setting signal Fr that decelerates from the above-mentioned reverse feed peak value Wrp to 0. 7) By repeating the above 1) to 6), a feed speed setting signal Fr with a feed pattern that changes in a positive and negative trapezoidal wave shape is generated.

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

[0031] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr.

[0032] The short-circuit current setting circuit ISR outputs a predetermined short-circuit current setting signal Isr.

[0033] The first arc period setting circuit TA1R outputs a predetermined first arc period setting signal Ta1r.

[0034] The first arc period circuit STA1 takes the above short-circuit discrimination signal Sd and the above first arc period setting signal Ta1r as inputs, and outputs a first arc period signal Sta1 that becomes high level during a predetermined first arc period Ta1 from the time when the short-circuit discrimination signal Sd changes to the low level (arc period) according to the first arc period setting signal Ta1r.

[0035] The first arc current setting circuit IA1R outputs a predetermined first arc current setting signal Ia1r.

[0036] The third arc period circuit STA3 takes the above short-circuit discrimination signal Sd as an input, becomes high level at the time when a predetermined current drop time Td has elapsed from the time when the short-circuit discrimination signal Sd changes to the low level (arc period), and then becomes low level when the short-circuit discrimination signal Sd becomes high level (short-circuit period), and outputs a third arc period signal Sta3.

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

[0038] The current control setting circuit ICR takes the above short - circuit discrimination signal Sd, the above low - level current setting signal Ilr, the above short - circuit current setting signal Isr, the above first arc period signal Sta1, the above third arc period signal Sta3, the above first arc current setting signal Ia1r, and the above third arc current setting signal Ia3r as inputs, performs the following processes, and outputs a current control setting signal Icr. 1) During a predetermined delay period Tc from the time when the short - circuit discrimination signal Sd changes to the Low level (arc period) and the first arc period signal Sta1 changes to the High level, a current control setting signal Icr having the value of the low - level current setting signal Ilr is output. 2) Thereafter, a current control setting signal Icr having the value of the first arc current setting signal Ia1r is output. 3) Thereafter, the current control setting signal Icr is output while decreasing it to a predetermined switching current value. 4) During the period from the time when the first arc period signal Sta1 changes to the Low level until the third arc period signal Sta3 changes to the Low level (the second arc period and the third arc period), a current control setting signal Icr having the value of the third arc current setting signal Ia3r is output. 5) When the short - circuit discrimination signal Sd is at the High level (short - circuit period), a current control setting signal Icr having the value of the short - circuit current setting signal Isr is output.

[0039] The current error amplification circuit EI takes the above current control setting signal Icr and the above current detection signal Id as inputs, amplifies the error between the two values, and outputs a current error amplification signal Ei.

[0040] The power supply characteristic switching circuit SW takes the above current error amplification signal Ei, the above voltage error amplification signal Ev, the above first arc period signal Sta1, and the above third arc period signal Sta3 as inputs, performs the following processes, and outputs an error amplification signal Ea. 1) During the second arc period Ta2 from the time when the first arc period signal Sta1 changes to the Low level until the third arc period signal Sta3 changes to the High level, the voltage error amplification signal Ev is output as the error amplification signal Ea. 2) During other periods, the current error amplification signal Ei is output as the error amplification signal Ea. With this circuit, the characteristics of the welding power source become constant current characteristics during the short - circuit period, the first arc period Ta1, and the third arc period Ta3, and become constant voltage characteristics during the second arc period Ta2.

[0041] The polarity switching circuit DR takes the above - mentioned first arc period signal Sta1 and the above - mentioned short - circuit discrimination signal Sd as inputs, performs any one of the following processes 1) to 3), and outputs a polarity switching signal Dr. When the polarity switching signal Dr is at a high level, the output of the welding power source is the electrode negative polarity EN, and when it is at a low level, it is the electrode positive polarity EP. 1) When the first arc period signal Sta1 changes to a high level, it outputs a polarity switching signal Dr that changes to a high level (electrode negative polarity EN) and changes to a low level (electrode positive polarity EP) when it changes to a low level. 2) When the first arc period signal Sta1 changes to a high level and the above - mentioned delay period Tc elapses, it outputs a polarity switching signal Dr that changes to a high level (electrode negative polarity EN) and changes to a low level (electrode positive polarity EP) when it changes to a low level. 3) When a predetermined period elapses after the short - circuit discrimination signal Sd changes to a high level (short - circuit period), it outputs a polarity switching signal Dr that changes to a high level (electrode negative polarity EN), and changes to a low level (electrode positive polarity EP) when the first arc period signal Sta1 changes to a low level.

[0042] Figure 2 is a timing chart of each signal in the arc welding apparatus of Figure 1 showing the arc welding control method according to an embodiment of the present invention. In the figure, (A) shows the time change of the feeding speed Fw, (B) shows the time change of the welding current Iw, (C) shows the time change of the welding voltage Vw, (D) shows the time change of the short - circuit discrimination signal Sd, (E) shows the time change of the first arc period signal Sta1, (F) shows the time change of the third arc period signal Sta3, and (G) shows the time change of the polarity switching signal Dr. Hereinafter, the operations of each signal will be described with reference to this figure.

[0043] The wire feed speed Fw shown in FIG. (A) indicates a forward feed state in which the welding wire 1 is fed forward toward the base material 2 when the value is positive, and a reverse feed state in which it is fed backward in a direction away from the base material 2 when the value is negative. The wire feed speed Fw is controlled by the value of the wire feed speed setting signal Fr output from the wire feed speed setting circuit FR in FIG. 1. The wire feed speed Fw consists of a forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur in FIG. 1, a forward feed peak period Tsp that continues until a short circuit occurs, a forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr in FIG. 1, a reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur in FIG. 1, a reverse feed peak period Trp that continues until an arc is generated, and a reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr in FIG. 1. Furthermore, the forward feed peak value Wsp is determined by the forward feed peak value setting signal Wsr in FIG. 1, and the reverse feed peak value Wrp is determined by the reverse feed peak value setting signal Wrr in FIG. 1. As a result, the wire feed speed setting signal Fr has a feed pattern that changes in a substantially trapezoidal wave shape with positive and negative values. The welding current Iw shown in FIG. (B) and the welding voltage Vw shown in FIG. (C) indicate waveforms when the electrode is in the positive polarity EP when the value is positive, and waveforms when the electrode is in the negative polarity EN when the value is negative.

[0044] [Operation during the short circuit period from time t1 to t4] During the short circuit period, as shown in FIG. (G), since the polarity switching signal Dr is at the Low level, the output of the welding power source has the electrode positive polarity EP. Therefore, during the short circuit period, the welding current Iw shown in FIG. (B) and the welding voltage Vw shown in FIG. (C) have positive values. When a short circuit occurs at time t1 during the forward feed peak period Tsp, as shown in FIG. (C), the welding voltage Vw rapidly decreases to a short circuit voltage value of several volts, so as shown in FIG. (D), the short circuit discrimination signal Sd changes to the High level (short circuit period). In response to this, it shifts to a predetermined forward feed deceleration period Tsd from time t1 to t2, and as shown in FIG. (A), the wire feed speed Fw decelerates from the above forward feed peak value Wsp to 0.

[0045] As shown in Fig. (A), the feeding speed Fw enters the predetermined reverse feeding acceleration period Tru from time t2 to t3 and accelerates from 0 to the above reverse feeding peak value Wrp. During this period, the short - circuit period continues.

[0046] When the reverse feeding acceleration period Tru ends at time t3, as shown in Fig. (A), the feeding speed Fw enters the reverse feeding peak period Trp and reaches the above reverse feeding peak value Wrp. The reverse feeding peak period Trp continues until an arc occurs at time t4. Therefore, the period from time t1 to t4 is the short - circuit period.

[0047] As shown in Fig. (B), during the short - circuit period from time t1 to t4, the instantaneous value of the welding current Iw is controlled to a constant current according to the value of the short - circuit current setting signal Isr in Fig. 1. The value of this short - circuit current setting signal Isr is set to be equal to or less than the average value of the welding current Iw. The average value of the welding current Iw is approximately determined by the average value of the feeding speed Fw. Preferably, the value of the short - circuit current setting signal Isr is set to 100 A or less, and more preferably 70 A or less. In this way, by controlling the welding current Iw during the short - circuit period to a small current value, the generation of spatter during short - circuit is suppressed, and the smooth absorption of the droplet into the molten pool is promoted. Furthermore, since the value of the welding current Iw at the time of arc re - generation can be made smaller without performing necking detection control as in the prior art, the generation of spatter associated with arc re - generation can be significantly reduced. In the present embodiment, since necking detection control is not performed, a detection line for detecting the voltage of the arc generation part is unnecessary. In the prior art, the instantaneous value of the welding current Iw during the short - circuit period has a maximum value of 400 A or more. This is because in order to release the short - circuit state, it was necessary to pass a large current and form a neck in the droplet by the pinch force. In contrast, in the present embodiment, by reversely feeding the welding wire at high speed, a neck can be formed and the short - circuit state can be released without relying on the pinch force. For this reason, in the present embodiment, the welding current Iw during the short - circuit period can be made smaller than in the prior art.

[0048] [Operation during the arc period from time t4 to t7] At time t4, when necking progresses due to reverse feeding of the welding wire and an arc is generated, as shown in Fig. (C), the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts. Therefore, as shown in Fig. (D), the short-circuit discrimination signal Sd changes to the Low level (arc period). In response to this, as shown in Fig. (E), the first arc period signal Sta1 changes to the High level, and the period from time t4 to t61 becomes the predetermined first arc period Ta1. The first arc period Ta1 is set by the first arc period setting signal Ta1r in Fig. 1. During the first arc period Ta1, constant current control is performed. At the same time, it shifts to the predetermined reverse feeding deceleration period Trd from time t4 to t5, and as shown in Fig. (A), the feeding speed Fw decelerates from the above reverse feeding peak value Wrp to 0.

[0049] When the reverse feeding deceleration period Trd ends at time t5, it shifts to the predetermined forward feeding acceleration period Tsu from time t5 to t6. During this forward feeding acceleration period Tsu, as shown in Fig. (A), the feeding speed Fw accelerates from 0 to the above forward feeding peak value Wsp. The arc period continues during this period.

[0050] When the forward feeding acceleration period Tsu ends at time t6, as shown in Fig. (A), the feeding speed Fw enters the forward feeding peak period Tsp and reaches the above forward feeding peak value Wsp. The arc period continues during this period. The forward feeding peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to t7 becomes the arc period. When a short circuit occurs, it returns to the operation at time t1.

[0051] When an arc is generated at time t4, as shown in Fig. (C), the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts. On the other hand, as shown in Fig. (B), the welding current Iw becomes the value of the low level current setting signal Ilr in Fig. 1 during the predetermined delay period Tc from time t4. This is because if the current value is increased immediately after the arc is generated, the melting of the welding wire due to the reverse feeding of the welding wire and the welding current is added, and the arc length may rapidly increase, resulting in an unstable welding state. This delay period Tc may be set to 0.

[0052] At time t51 during the forward acceleration period Tsu, when the delay period Tc ends, as shown in Fig. (G), the polarity switching signal Dr changes to the High level, and the output of the welding power source becomes the electrode negative polarity EN. When the delay period Tc = 0, at time t4, it becomes the electrode negative polarity EN. In response to this, as shown in Fig. (B), the welding current Iw becomes a low-level current value with a negative value, and as shown in Fig. (C), the welding voltage Vw also becomes an arc voltage value with a negative value. As shown in Fig. (B), the welding current Iw increases from time t51 and maintains the first arc current value Ia1 set by the first arc current setting signal Ia1r, and then decreases to a predetermined switching current value at time t61. As shown in Fig. (C), the welding voltage Vw also has a waveform similar to that of the welding current Iw. The reason for decreasing the welding current Iw to a switching current value of about 50 to 100 A is as follows. If the current value at the time of polarity switching is large, a surge voltage that poses a problem may be applied to the transistor constituting the secondary-side inverter circuit of the power control circuit PM in Fig. 1 and cause it to be destroyed. This is to prevent this.

[0053] When the first arc period Ta1 ends at time t61, as shown in Fig. (G), the polarity switching signal Dr changes to the Low level, and the output of the welding power source becomes the electrode positive polarity EP. In response to this, as shown in Fig. (B), the welding current Iw becomes a switching current value with a positive value, and as shown in Fig. (C), the welding voltage Vw also becomes an arc voltage value with a positive value. The period from time t61 to t62 becomes the second arc period Ta2, and the welding power source is switched to constant voltage control. As shown in Fig. (B), the second arc current Ia2 becomes a value corresponding to the arc load, and as shown in Fig. (C), the welding voltage Vw becomes a value controlled by the voltage setting signal Vr in Fig. 1. By controlling this second arc period Ta2 under constant voltage control, the arc length is controlled to an appropriate value.

[0054] At time t62, when a predetermined current drop time Td has elapsed since the arc generation time t4, as shown in FIG. (F), the third arc period signal Sta3 changes to the High level. The period from this point until the time t7 when the next short circuit occurs becomes the third arc period Ta3. During the third arc period Ta3, as shown in FIG. (G), since the polarity switching signal Dr continues at the Low level, the output of the welding power source becomes the electrode positive polarity EP. During the third arc period Ta3, constant current control is performed. As shown in FIG. (B), a predetermined third arc current Ia3 determined by the third arc current setting signal Ia3r in FIG. 1 is energized. As shown in FIG. (C), the welding voltage Vw becomes a value determined by the current value and the arc load. By making the third arc current value Ia3 immediately before the short circuit a small value, the occurrence of the short circuit can be induced, and the generation of spatter at the time of short circuit occurrence can be suppressed.

[0055] Numerical examples of the above parameters are shown below. Short circuit period (not a predetermined value): 3 ms, arc period (not a predetermined value): 4 ms, delay period Tc (predetermined value): 0.5 ms, first arc period Ta1 (predetermined value): 1.5 ms, second arc period Ta2 (not a predetermined value): 2 ms, third arc period Ta3 (not a predetermined value): 0.5 ms, current drop time (predetermined value): 3.5 ms, low level current value (predetermined value): 50 A, first arc current value Ia1 (predetermined value): -150 A, third arc current value Ia3 (predetermined value): 50 A, forward peak value Wsp (predetermined value): 30 m / min, reverse peak value Wrp (predetermined value): -25 m / min,

[0056] In the above-described embodiment, the first arc period is the electrode negative polarity EN, and the other periods are the electrode positive polarity EP. Thereby, during the first arc period, since it is the electrode negative polarity EN, heat input to the base material can be reduced, and the droplet formed on the welding wire can be enlarged. When the size of the droplet becomes large, a large gap can be filled with the droplet. As a result, high-quality welding can be performed on a thin plate having a large gap at the welded joint portion.

[0057] FIG. 3 is a timing chart of each signal in the arc welding apparatus shown in FIG. 1, which shows an arc welding control method according to an embodiment of the present invention different from that in FIG. 2. In the figure, (A) shows the time change of the feeding speed Fw, (B) shows the time change of the welding current Iw, (C) shows the time change of the welding voltage Vw, (D) shows the time change of the short-circuit discrimination signal Sd, (E) shows the time change of the first arc period signal Sta1, (F) shows the time change of the third arc period signal Sta3, and (G) shows the time change of the polarity switching signal Dr. In this figure, the operation during the period from time t3 to t61 is different from that in FIG. 2, and the operation during other periods is the same. Hereinafter, with reference to this figure, the operation different from that in FIG. 2 will be described.

[0058] Regarding the operation of the feeding speed Fw shown in FIG. (A) of this figure, since it is the same as that in FIG. 2, the description will not be repeated.

[0059] At time t31 when a predetermined period has elapsed since the start of the short-circuit period at time t1, as shown in FIG. (G) of this figure, since the polarity switching signal Dr changes from the Low level to the High level, the output of the welding power source switches to the electrode negative polarity EN. In response to this, as shown in FIG. (B) of this figure, the welding current Iw changes from the short-circuit current value of a positive value to the short-circuit current value of a negative value. Similarly, as shown in FIG. (C) of this figure, the welding voltage Vw changes from the short-circuit voltage value of a positive value to the short-circuit voltage value of a negative value. The above-mentioned predetermined period is set to about 1 to 2.5 ms because the short-circuit period is 3 ms or more in order to switch the polarity in the middle of the short-circuit period. Since it takes about 1 ms after the start of the short-circuit period for the droplet and the molten pool to reach a stable short-circuit state, it is desirable to switch the polarity after this time has elapsed.

[0060] At time t4, when necking progresses due to reverse feeding of the welding wire and an arc is generated, as shown in Fig. (C) of the same figure, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts with a negative value. Therefore, as shown in Fig. (D) of the same figure, the short-circuit discrimination signal Sd changes to the Low level (arc period). In response to this, as shown in Fig. (E) of the same figure, the first arc period signal Sta1 changes to the High level, and the period from time t4 to t61 becomes the predetermined first arc period Ta1. During the first arc period, as shown in Fig. (G) of the same figure, since the polarity switching signal Dr remains at the High level, the output of the welding power source continues with the electrode negative polarity EN. Furthermore, constant current control continues during the first arc period Ta1. As shown in Fig. (B) of the same figure, the welding current Iw becomes the value of the low-level current setting signal Ilr in Fig. 1 during the predetermined delay period Tc from time t4.

[0061] At time t51, when the delay period Tc ends, as shown in Fig. (B) of the same figure, the welding current Iw increases from time t51 and maintains the first arc current value Ia1 set by the first arc current setting signal Ia1r. After that, it decreases so as to become the predetermined switching current value at time t61. As shown in Fig. (C) of the same figure, the welding voltage Vw also has a waveform similar to that of the welding current Iw.

[0062] When the first arc period Ta1 ends at time t61, as shown in Fig. (G) of the same figure, the polarity switching signal Dr changes to the Low level, and the output of the welding power source becomes the electrode positive polarity EP. In response to this, as shown in Fig. (B) of the same figure, the welding current Iw becomes the positive switching current value, and as shown in Fig. (C) of the same figure, the welding voltage Vw also becomes the positive arc voltage value. The period from time t61 to t62 becomes the second arc period Ta2, and the welding power source is switched to constant voltage control. The subsequent operations are the same as those in Fig. 2, so the description will not be repeated.

[0063] As described above, when the polarity is switched during the short-circuit period, no arc is generated, so there is no arc interruption, and the polarity can be switched smoothly.

Explanation of symbols

[0064] 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feeding roll DR Polarity switching circuit Dr Polarity switching signal Ea Error amplification signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal FC Feeding control circuit Fc Feeding control signal FR Feeding speed setting circuit Fr Feeding speed setting signal Fw Feeding speed Ia1 First arc current IA1R First arc current setting circuit Ia1r First arc current setting signal Ia2 Second arc current Ia3 Third arc current IA3R Third arc current setting circuit Ia3r Third 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 ISR Short-circuit current setting circuit Isr Short-circuit current setting signal Iw Welding current PM Power control circuit SD Short-circuit discrimination circuit Sd Short-circuit discrimination signal STA1 First arc period circuit Sta1 First arc period signal STA3 Third arc period circuit Sta3 Third arc period signal SW Power characteristic switching circuit TA1R First arc period setting circuit Ta1r First arc period setting signal Tc Delay period Td Current drop time Trd Reverse feed deceleration period TRDR Reverse feed deceleration period setting circuit Trdr Reverse feed deceleration period setting signal Trp Reverse feed peak period Tru Reverse feed acceleration period TRUR Reverse feed acceleration period setting circuit Trur Reverse feed acceleration period setting signal Tsd Forward feed deceleration period TSDR Forward feed deceleration period setting circuit Tsdr Forward feed deceleration period setting signal Tsp Forward feed peak period Tsu Forward feed 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 feed peak value WRR Reverse feed peak value setting circuit Wrr Reverse feed peak value setting signal Wsp Forward feed peak value WSR Forward feed peak value setting circuit Wsr Forward feed peak value setting signal

Claims

Claim 1 A welding wire is fed, and a short - circuit period and an arc period are repeated. The arc period includes a first arc period and a subsequent second arc period. In the arc welding control method, in the first arc period, a welding current is passed by constant - current control, and in the second arc period, the welding current is passed by constant - voltage control for welding. The first arc period has an electrode - negative polarity, and the other periods have an electrode - positive polarity. An arc welding control method characterized by the above. Claim 2 Switch to the electrode - negative polarity at the start of the first arc period or at a time delayed therefrom. The arc welding control method according to claim 1, characterized by the above. Claim 3 Switch to the electrode - negative polarity during the short - circuit period. The arc welding control method according to claim 1, characterized by the above. Claim 4 When switching the polarity, it is performed in a state where the absolute value of the welding current is less than or equal to a reference value. The arc welding control method according to any one of claims 1 to 3, characterized by the above. Claim 5 The welding wire is fed reversely during the short - circuit period and fed forward during the arc period. The arc welding control method according to any one of claims 1 to 4, characterized by the above.

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