Arc welding control method

Abstract

To carry out high-quality arc welding for a thin plate having a large gap in a welding joint in consumable electrode arc-welding.SOLUTION: An arc-welding control method comprises: feeding a welding wire (Fw); repeating a short-circuit period and an arc period; reducing, when droplet constriction is detected during the short-circuit period, welding current to a low-level current value to change to the arc period. The arc period includes a first arc period and a subsequent second arc period. The welding current is energized through constant current control in the first arc period. The welding current is energized to perform welding through the constant current control in the second arc period. An electrode minus polarity is switched to an electrode plus polarity at time t32 when welding current Iw in the short-circuit period is in the state of the low-level current value. At time t61, the polarity is returned to the electrode minus polarity when the first arc period ends.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 those in 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 of 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 of claim 1 is feeding a welding wire, repeating a short circuit period and an arc period, when detecting the constriction of the molten droplet during the short circuit period, reducing the welding current to a low level current value and shifting to the arc period, the arc period includes a first arc period and a second arc period following it, the first arc period energizes the welding current by constant current control, and the second arc period energizes the welding current by constant voltage control to perform welding. In the arc welding control method, switching from the electrode negative polarity to the electrode positive polarity in the state of the low level current value during the short circuit period, and returning to the electrode negative polarity when the first arc period ends, which is an arc welding control method characterized by the above.

[0008] The invention of claim 2 is 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, which is the arc welding control method according to claim 1, characterized by the above.

[0009] The invention of claim 3 is feeding the welding wire reversely during the short circuit period and feeding it forward during the arc period, which is the arc welding control method according to any one of claims 1 to 2, characterized by the above.

Advantages of the Invention

[0010] According to the present invention, high-quality welding can be performed on a thin plate having a large gap in a welded joint portion.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

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

[0013] FIG. 1 is a block diagram of an arc welding apparatus for implementing an 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.

[0014] 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 an error amplification signal Ea described later, and switches between an electrode positive polarity EP and an electrode negative polarity EN by a 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 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.

[0015] The feeding motor WM takes a 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, generally, the welding wire 1 may be fed at a predetermined speed in a constant speed feeding manner. 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 may be a case where two feeding motors WM are used to form a push-pull type feeding system.

[0016] The welding wire 1 is fed through the welding torch 4 by the rotation of a 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 is energized. For the welding wire 1, a steel wire, an aluminum wire, etc. are used. Shielding gas (not shown) is ejected from the tip of the welding torch 4.

[0017] The current detection circuit ID detects the absolute value of the above-described welding current Iw and outputs a current detection signal Id.

[0018] 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.

[0019] 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.

[0020] 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. Otherwise, it discriminates that it is in the arc period and outputs a short-circuit discrimination signal Sd that becomes Low level.

[0021] The forward feed acceleration period setting circuit TSUR outputs a predetermined forward feed acceleration period setting signal Tsur.

[0022] The forward feed deceleration period setting circuit TSDR outputs a predetermined forward feed deceleration period setting signal Tsdr.

[0023] The reverse feed acceleration period setting circuit TRUR outputs a predetermined reverse feed acceleration period setting signal Trur.

[0024] The reverse feed deceleration period setting circuit TRDR outputs a predetermined reverse feed deceleration period setting signal Trdr.

[0025] The forward feed peak value setting circuit WSR outputs a predetermined forward feed peak value setting signal Wsr.

[0026] The reverse feed peak value setting circuit WRR outputs a predetermined reverse feed peak value setting signal Wrr.

[0027] 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 positive and negative trapezoidal wave-shaped change feed pattern is generated.

[0028] 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.

[0029] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr.

[0030] The necking detection circuit ND takes the above short-circuit discrimination signal Sd, the above voltage detection signal Vd, and the above current detection signal Id as inputs. When the voltage rise value of the voltage detection signal Vd reaches the necking detection reference value when the short-circuit discrimination signal Sd is at the High level (short-circuit period), it determines that a necking is formed and becomes High level, and outputs a necking detection signal Nd that becomes Low level when the short-circuit discrimination signal Sd changes to the Low level (arc period). Also, the necking 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 necking detection reference value. Further, the resistance value of the droplet may be calculated by dividing the value of the voltage detection signal Vd by the value of the current detection signal Id, and the necking detection signal Nd may be changed to High level when the differential value of this resistance value reaches the corresponding necking detection reference value. Further, the necking detection signal Nd may be changed to High level by estimating that a necking is formed when a predetermined period has elapsed since the short-circuit discrimination signal Sd changed to the High level (short-circuit period).

[0031] The short-circuit current setting circuit ISR takes the above short-circuit discrimination signal Sd, the above low-level current setting signal Ilr, and the above necking detection signal Nd as inputs, performs the following processing, and outputs a short-circuit current setting signal Isr. 1) During a predetermined initial period from the time when the short-circuit discrimination signal Sd changes to the High level (short-circuit), it outputs a short-circuit current setting signal Isr that becomes a predetermined initial current setting value. 2) After that, it outputs a short-circuit current setting signal Isr that rises at a predetermined short-circuit slope, maintains the value when it reaches a predetermined short-circuit peak value. 3) After that, when the constriction detection signal Nd changes to the High level (constriction detected), a short-circuit current setting signal Isr having a value of the low-level current setting signal Ilr is output.

[0032] The first arc period setting circuit TA1R outputs a predetermined first arc period setting signal Ta1r.

[0033] The first arc period circuit STA1 takes the short-circuit discrimination signal Sd and the first arc period setting signal Ta1r as inputs, and outputs a first arc period signal Sta1 that becomes High level during the first arc period Ta1 set by the first arc period setting signal Ta1r from the time when the short-circuit discrimination signal Sd changes to the Low level (arc period).

[0034] The first arc current setting circuit IA1R outputs a predetermined first arc current setting signal Ia1r.

[0035] The third arc period circuit STA3 takes the 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.

[0036] The third arc current setting circuit IA3R outputs a predetermined third arc current setting signal Ia3r.

[0037] The current control setting circuit ICR takes the short-circuit discrimination signal Sd, the low-level current setting signal Ilr, the short-circuit current setting signal Isr, the first arc period signal Sta1, the third arc period signal Sta3, the first arc current setting signal Ia1r, and the third arc current setting signal Ia3r as inputs, performs the following processing, and outputs a current control setting signal Icr. 1) 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, during a predetermined delay period Tc, a current control setting signal Icr having a value of the low-level current setting signal Ilr is output. 2) Thereafter, a current control setting signal Icr having a value of the first arc current setting signal Ia1r is output. 3) Thereafter, the current control setting signal Icr is output while decreasing 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 a 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 a value of the short-circuit current setting signal Isr is output.

[0038] 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.

[0039] 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 processing, 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 supply 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.

[0040] The polarity switching circuit DR takes the above current detection signal Id, the above low-level current setting signal Ilr, and the above first arc period signal Sta1 as inputs, and changes to the High level (electrode positive polarity EP) when the value of the current detection signal Id decreases and becomes equal to the value of the low-level current setting signal Ilr. Then, when the first arc period signal Sta1 changes to the Low level, it outputs a polarity switching signal Dr that returns to the Low level (electrode negative polarity EN).

[0041] Figure 2 is a timing chart of each signal in the arc welding apparatus shown in Figure 1, which shows an 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, (G) shows the time change of the polarity switching signal Dr, and (H) shows the time change of the constriction detection signal Nd. Hereinafter, the operations of each signal will be described with reference to this figure.

[0042] The wire feeding speed Fw shown in Fig. (A) indicates a forward feeding state where the welding wire 1 advances towards the base material 2 when it is a positive value, and a reverse feeding state where it retreats in a direction away from the base material 2 when it is a negative value. The wire feeding speed Fw is controlled by the value of the wire feeding speed setting signal Fr output from the wire feeding speed setting circuit FR in Fig. 1. The wire feeding speed Fw consists of a forward feeding acceleration period Tsu determined by the forward feeding acceleration period setting signal Tsur in Fig. 1, a forward feeding peak period Tsp that continues until a short circuit occurs, a forward feeding deceleration period Tsd determined by the forward feeding deceleration period setting signal Tsdr in Fig. 1, a reverse feeding acceleration period Tru determined by the reverse feeding acceleration period setting signal Trur in Fig. 1, a reverse feeding peak period Trp that continues until an arc is generated, and a reverse feeding deceleration period Trd determined by the reverse feeding deceleration period setting signal Trdr in Fig. 1. Furthermore, the forward feeding peak value Wsp is determined by the forward feeding peak value setting signal Wsr in Fig. 1, and the reverse feeding peak value Wrp is determined by the reverse feeding peak value setting signal Wrr in Fig. 1. As a result, the wire feeding speed setting signal Fr has a feeding 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 negative polarity EN when they are positive values, and waveforms when the electrode is in the positive polarity EP when they are negative values. In the following description, when describing the values of the welding current Iw and the welding voltage Vw, their absolute values are shown.

[0043] [Operation during the short circuit period from time t1 to t4] Until halfway through 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 is in the electrode negative polarity EN. 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 feeding peak period Tsp, as shown in Fig. (C), the welding voltage Vw rapidly decreases to a short circuit voltage value of several volts. As a result, 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 the predetermined forward feeding deceleration period Tsd from time t1 to t2, and as shown in Fig. (A), the wire feeding speed Fw decelerates from the above forward feeding peak value Wsp to 0.

[0044] As shown in Fig. (A), the feeding speed Fw enters the predetermined reverse feed acceleration period Tru from time t2 to t3 and accelerates from 0 to the above reverse feed peak value Wrp. During this period, the short - circuit period continues.

[0045] When the reverse feed acceleration period Tru ends at time t3, as shown in Fig. (A), the feeding speed Fw enters the reverse feed peak period Trp and reaches the above reverse feed peak value Wrp. The reverse feed peak period Trp continues until an arc occurs at time t4. Therefore, the period from time t1 to t4 is the short - circuit period.

[0046] As shown in Fig. (B), during the short - circuit period from time t1 to t4, 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.

[0047] As shown in Fig. (B), during the short - circuit period from time t1 to t4, the welding current Iw becomes a predetermined initial current value during a predetermined initial period. Thereafter, the welding current Iw rises at a predetermined short - circuit slope, and when it reaches a predetermined short - circuit peak value, it maintains that value. The above - mentioned initial period is about 0.5 ms, the initial current value is about 40 A, the short - circuit slope is about 260 A / ms, and the short - circuit peak value is about 300 A.

[0048] As shown in Fig. (C), the welding voltage Vw starts to rise when the welding current Iw reaches the short - circuit peak value. This is because due to the reverse feed of the welding wire 1 and the action of the pinch force by the welding current Iw, a constriction is gradually formed in the droplet at the tip of the welding wire 1.

[0049] After the voltage rise value of the welding voltage Vw reaches the constriction detection reference value, it is determined that the formation state of the constriction has reached the reference state. As shown in Fig. (H) of the same figure, at time t31, the constriction detection signal Nd changes to the High level. In response to this, as shown in Fig. 1, the short-circuit current setting signal Isr of Fig. 1 decreases to the value of the low-level current setting signal Ilr. For this reason, as shown in Fig. (B) of the same figure, the welding current Iw rapidly decreases from the short-circuit peak value to the low-level current value. In order to make the rapid decrease of the above-mentioned welding current Iw faster, a current-limiting resistor may be inserted into the energization path. In this case, except when rapidly decreasing, it is short-circuited by a transistor connected in parallel with the current-limiting resistor.

[0050] At time t32 when the welding current Iw is in the state of the low-level current value, as shown in Fig. (G) of the same 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 positive polarity EP. In response to this, as shown in Fig. (B) of the same figure, the welding current Iw changes from the low-level current value of a positive value to the low-level current value of a negative value. Similarly, as shown in Fig. (C) of the same 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.

[0051] At time t4, when the constriction progresses due to the 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 the arc voltage value of several tens of V of 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. (H) of the same figure, the constriction detection signal Nd changes to the Low level. At the same time, 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, the polarity switching signal Dr remains at the High level, so 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.

[0052] Meanwhile, the period from time t4 to t5 is a predetermined reverse feed deceleration period Trd. As shown in Fig. (A) of the same figure, the feed rate Fw decelerates from the above-mentioned reverse feed peak value Wrp to 0.

[0053] When the reverse feed deceleration period Trd ends at time t5, it shifts to a predetermined forward feed acceleration period Tsu from time t5 to t6. During this forward feed acceleration period Tsu, as shown in Fig. (A) of the same figure, the feed rate Fw accelerates from 0 to the above-mentioned forward feed peak value Wsp. The arc period continues during this period.

[0054] When the forward feed acceleration period Tsu ends at time t6, as shown in Fig. (A) of the same figure, the feed rate Fw enters the forward feed peak period Tsp and becomes the above-mentioned forward feed peak value Wsp. The arc period also continues during this period. The forward feed peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to t7 is the arc period. And when a short circuit occurs, it returns to the operation at time t1.

[0055] 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.

[0056] 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, and then decreases to a 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.

[0057] 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 negative polarity EN. In response to this, as shown in Fig. (B), the welding current Iw becomes the switching current value of a positive value, and as shown in Fig. (C), the welding voltage Vw also becomes the arc voltage value of 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 the second arc period Ta2 under constant voltage control, the arc length is controlled to an appropriate value.

[0058] At time t62, when a predetermined current drop time Td has elapsed from 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.

[0059] 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 feed peak value Wsp (predetermined value): 30 m / min, reverse feed peak value Wrp (predetermined value): -25 m / min,

[0060] The effects of the present embodiment will be described below. According to the present embodiment, a welding wire is fed, a short - circuit period and an arc period are repeated, and when the constriction of the droplet is detected during the short - circuit period, the welding current is decreased to a low - level current value and shifted to the arc period. The arc period includes a first arc period and a subsequent second arc period. In the first arc period, the welding current is energized by constant - current control, and in the second arc period, the welding current is energized by constant - voltage control for welding. In the arc - welding control method, during the short - circuit period, the polarity is switched from the electrode - negative polarity to the electrode - positive polarity in the state of the low - level current value, and when the first arc period ends, it returns to the electrode - negative polarity. Therefore, the first arc period is set as the electrode - positive polarity EP, and the other periods are set as the electrode - negative polarity EN. Thereby, during the periods other than the first arc period, since it is the electrode - negative polarity EN, the 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 by the droplet. As a result, high - quality welding can be performed on a thin plate having a large gap at the welded joint. Further, when the polarity is switched during the short - circuit period, since no arc is generated, no arc interruption occurs, and the polarity can be switched smoothly. Also, 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, causing a failure. In the present embodiment, since the polarity is switched in the state of the low - level current value, the generation of the surge voltage can be suppressed, and the failure of the transistor can be prevented.

[0061] More preferably, according to the present embodiment, 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. In the present embodiment, the current value at the time when the first arc period ends is made small. Thereby, as described above, the surge voltage applied to the transistor of the secondary - side inverter circuit can be made small, so that the failure of the transistor can be prevented.

[0062] More preferably, according to the present embodiment, the welding wire is reversely fed during the short-circuit period and forward fed during the arc period. By doing so, the repetition cycle of the short-circuit period and the arc period is stabilized, so that the heat input to the base material becomes uniform and the welding quality is improved.

Explanation of Signs

[0063] 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 ND Constriction detection circuit Nd Constriction detection signal 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

1. Feed a welding wire, repeat a short - circuit period and an arc period, When detecting the constriction of the droplet during the short - circuit period, reduce the welding current to a low - level current value and shift to the arc period, The arc period includes a first arc period and a subsequent second arc period. In the arc - welding control method, the first arc period energizes the welding current by constant - current control, and the second arc period energizes the welding current by constant - voltage control for welding, During the short - circuit period, switch from electrode - negative polarity to electrode - positive polarity in the state of the low - level current value, and return to electrode - negative polarity when the first arc period ends, An arc - welding control method characterized by the above.

2. When switching the polarity, perform it 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 claim 1, characterized by the above.

3. Reverse - feed the welding wire during the short - circuit period and forward - feed it during the arc period, The arc - welding control method according to any one of claims 1 to 2, characterized by the above.

Images