Arc welding control method

Abstract

To perform high-quality welding to a thin plate having a large gap in a weld joint part, in consumable electrode arc-welding.SOLUTION: In an arc welding control method, 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 distributed by constant current control in the first arc period Ta1 and the welding currents are distributed by constant voltage control in the second arc period Ta2, so as to perform welding. An electrode plus polarity is set in the first arc period Ta1, and an electrode minus polarity is set 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 minus polarity is switched to the electrode plus polarity.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for controlling arc welding performed by feeding a welding wire. [Background technology]

[0002] In order to reduce the heat input to the base material and weld thin plates with high quality, inventions such as those disclosed in Patent Documents 1 and 2 are commonly used. In the AC pulse arc welding method disclosed in Patent Document 1, welding is performed by feeding a welding wire and repeating one cycle of passing a peak current and a base current during an electrode positive polarity period and passing an electrode negative polarity current during an electrode negative polarity period. In this AC 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 metal. This enables low heat input welding and high-quality thin plate welding.

[0003] In the welding method disclosed in Patent Document 2, welding is performed by feeding a welding wire and alternating between a period of pulse arc welding and a period of short-circuit transfer arc welding. In this welding method, the heat input to the base material can be controlled by adjusting the ratio between the period of pulse arc welding and the period of short-circuit transfer arc welding. This enables low heat input welding and high-quality thin plate welding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2018 / 079345 [Patent Document 2] Patent Publication No. 2021-53649 Summary of the Invention [Problem to be solved by the invention]

[0005] In thin plate welding, when there is a gap in the weld joint, it is necessary to form a bead shape with a small dilution ratio, with a small penetration area and a large reinforcement area. However, with the conventional welding methods described in Patent Documents 1 and 2, it was 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 that can perform high-quality welding on thin plates having large gaps in the weld joint. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the invention of claim 1 is as follows: The welding wire is fed, and a short circuit period and an arc period are repeated. an arc welding control method in which the arc period comprises a first arc period and a subsequent second arc period, a welding current is supplied by constant current control during the first arc period, and a welding current is supplied by constant voltage control during the second arc period, The electrode polarity is positive during the first arc period, and the electrode polarity is negative during the other periods. The arc welding control method is characterized by the above.

[0008] The invention of claim 2 is as follows: switching the electrode polarity to positive polarity at the start of the first arc period or at a delayed time thereafter; 2. The arc welding control method according to claim 1, wherein:

[0009] The invention of claim 3 is as follows: The electrode polarity is switched to positive polarity during the short-circuit period. 2. The arc welding control method according to claim 1, wherein:

[0010] The invention of claim 4 is as follows: When switching the polarity, the absolute value of the welding current is set to a reference value or less. 4. The arc welding control method according to claim 1, wherein: the arc welding control method comprises: a step of: controlling a welding state of the arc welding;

[0011] The invention of claim 5 is as follows: the welding wire is fed in a reverse direction during the short circuit period and fed in a forward direction during the arc period; 5. The arc welding control method according to claim 1, wherein: the arc welding control method comprises: a step of: controlling a welding state of the arc welding; [Effects of the Invention]

[0012] According to the present invention, high-quality welding can be performed on thin plates having large gaps in the weld joints. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a block diagram of an arc welding apparatus for carrying out an arc welding control method according to an embodiment of the present invention; [Figure 2] 2 is a timing chart of signals in the arc welding apparatus of FIG. 1, illustrating an arc welding control method according to an embodiment of the present invention. [Figure 3] 3 is a timing chart of signals in the arc welding apparatus of FIG. 1, illustrating an arc welding control method according to an embodiment of the present invention different from that of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

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

[0015] 1 is a block diagram of an arc welding apparatus for carrying out an arc welding control method according to an embodiment of the present invention. In this diagram, a circuit for applying a high voltage of several hundred volts for a short period of time between a welding wire 1 and a base material 2 in order to facilitate polarity switching is omitted. Each block will be described below with reference to this diagram.

[0016] The power control circuit PM receives a commercial power supply (not shown) such as a three-phase 200V as an input, performs output control by inverter control or the like in accordance with an error amplification signal Ea (described later), and switches between electrode positive polarity EP and electrode negative polarity EN in accordance with a polarity switching signal Dr (described later), thereby outputting a welding voltage Vw and a welding current Iw between the welding wire 1 and the base material 2. Although not shown, the power control circuit PM includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smooths the rectified DC, an inverter circuit driven by the error amplification signal Ea that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for welding, a secondary rectifier that rectifies the stepped-down high-frequency AC into DC, a reactor that smooths the rectified DC, and a secondary-side inverter circuit that converts the smoothed DC into AC of several tens to several hundreds of Hz in accordance with the polarity switching signal Dr.

[0017] The feed motor WM receives a feed control signal Fc (described later) as an input and alternately feeds the welding wire 1 in a forward direction and a reverse direction at a feed speed Fw. Alternatively, as is common, the welding wire 1 may be fed at a constant speed determined in advance. A motor with fast transient response is used as the feed motor WM. The feed motor WM may be installed near the tip of the welding torch 4 to increase the rate of change in the feed speed Fw of the welding wire 1 and the reversal of the feed direction. Alternatively, two feed motors WM may be used to form a push-pull feed system.

[0018] The welding wire 1 is fed through the welding torch 4 by the rotation of a feed roll 5 connected to the feed 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 between the welding wire 1 and the base material 2. A steel wire, an aluminum wire, or the like is used as the welding wire 1. A 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 welding current Iw and outputs a current detection signal Id.

[0020] A voltage detection circuit VD detects the absolute value of the welding voltage Vw and outputs a voltage detection signal Vd. A 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 amplifier circuit EV receives the voltage setting signal Vr and the voltage detection signal Vd, amplifies the error between the two signals, and outputs a voltage error amplified signal Ev.

[0022] The short circuit determination circuit SD receives the voltage detection signal Vd as input, and outputs a short circuit determination signal Sd that goes to High level when this value is less than a predetermined short circuit determination value (approximately 10 V) and determines that the device is in a short circuit period, and goes to Low level when this value is equal to or greater than this value and determines that the device is in an arc period.

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

[0024] The normal transport deceleration period setting circuit TSDR outputs a predetermined normal transport deceleration period setting signal Tsdr.

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

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

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

[0028] The backward transmission peak value setting circuit WRR outputs a predetermined backward transmission peak value setting signal Wrr.

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

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

[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 receives the short circuit determination signal Sd and the first arc period setting signal Ta1r as inputs, and outputs a first arc period signal Sta1 that is at a high level from the time the short circuit determination signal Sd changes to a low level (arc period) during the first arc period Ta1 that is predetermined by 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 receives the short circuit determination signal Sd as an input, and outputs a third arc period signal Sta3 that goes to a high level when a predetermined current drop time Td has elapsed since the short circuit determination signal Sd changed to a low level (arc period), and then goes to a low level when the short circuit determination signal Sd goes to a high level (short circuit period).

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

[0038] The current control setting circuit ICR receives as input the short circuit determination 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, performs the following processing, and outputs a current control setting signal Icr. 1) During a predetermined delay period Tc from the point when the short circuit detection signal Sd changes to low level (arc period) and the first arc period signal Sta1 changes to high level, a current control setting signal Icr having the value of the low-level current setting signal Ilr is output. 2) Thereafter, the current control setting signal Icr having the value of the first arc current setting signal Ia1r is output. 3) After that, the current is decreased to a predetermined switching current value and the current control setting signal Icr is output. 4) During the period from when the first arc period signal Sta1 changes to low level until the third arc period signal Sta3 changes to low level (the second arc period and 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 determination signal Sd is at a high level (short circuit period), the current control setting signal Icr having the value of the short circuit current setting signal Isr is output.

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

[0040] The power supply characteristics switching circuit SW receives the current error amplified signal Ei, the voltage error amplified signal Ev, the first arc period signal Sta1, and the third arc period signal Sta3 as inputs, performs the following processing, and outputs an error amplified signal Ea. 1) During second arc period Ta2 from when first arc period signal Sta1 changes to low level until third arc period signal Sta3 changes to high level, voltage error amplified signal Ev is output as error amplified signal Ea. 2) During other periods, the current error amplified signal Ei is output as the error amplified signal Ea. This circuit causes the welding power supply to have constant current characteristics during the short circuit period, first arc period Ta1, and third arc period Ta3, and constant voltage characteristics during the second arc period Ta2.

[0041] The polarity switching circuit DR receives the first arc period signal Sta1 and the short circuit determination signal Sd as inputs, performs 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 has electrode positive polarity EN, and when it is at a low level, the output has electrode negative polarity EP. 1) A polarity switching signal Dr is output that changes to High level (electrode positive polarity EP) when first arc period signal Sta1 changes to High level, and changes to Low level (electrode negative polarity EN) when first arc period signal Sta1 changes to Low level. 2) When the first arc period signal Sta1 changes to high level and the delay period Tc described above has elapsed, the polarity switching signal Dr changes to high level (electrode positive polarity EP), and when it changes to low level, the polarity switching signal Dr changes to low level (electrode negative polarity EN). 3) When a predetermined period of time has elapsed since the short circuit determination signal Sd changed to a high level (short circuit period), the polarity switching signal Dr changes to a high level (electrode positive polarity EP), and when the first arc period signal Sta1 changes to a low level, the polarity switching signal Dr changes to a low level (electrode negative polarity EN).

[0042] 2 is a timing chart of signals in the arc welding apparatus of FIG. 1, illustrating an arc welding control method according to an embodiment of the present invention. (A) in FIG. 2 shows the change over time in the feed rate Fw, (B) in FIG. 2 shows the change over time in the welding current Iw, (C) in FIG. 2 shows the change over time in the welding voltage Vw, (D) in FIG. 2 shows the change over time in the short-circuit detection signal Sd, (E) in FIG. 2 shows the change over time in the first arc period signal Sta1, (F) in FIG. 2 shows the change over time in the third arc period signal Sta3, and (G) in FIG. 2 shows the change over time in the polarity switching signal Dr. The operation of each signal will be explained below with reference to the diagram.

[0043] The feed speed Fw shown in Fig. 1(A) indicates a forward feed state in which the welding wire 1 is fed forward toward the base material 2 when it is a positive value, and indicates a reverse feed state in which the welding wire 1 is fed backward in a direction away from the base material 2 when it is a negative value. The feed speed Fw is controlled by the value of the feed speed setting signal Fr output from the feed speed setting circuit FR of Fig. 1. The feed speed Fw is made up of a forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur of 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 of Fig. 1, a reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur of Fig. 1, a reverse feed peak period Trp that continues until an arc occurs, and a reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr of 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 feed speed setting signal Fr has a feed pattern that changes in a substantially trapezoidal waveform between positive and negative. The welding current Iw shown in Fig. 1(B) and the welding voltage Vw shown in Fig. 1(C) show waveforms for electrode negative polarity EN when positive values ​​are used, and waveforms for electrode positive polarity EP when negative values ​​are used. In the following description, the values ​​of the welding current Iw and welding voltage Vw are indicated as absolute values.

[0044] [Operation during the short-circuit period from time t1 to t4] During the short circuit period, as shown in FIG. 1(G), the polarity switching signal Dr is at a low level, so the output of the welding power supply has electrode negative polarity EN. Therefore, during the short circuit period, the welding current Iw shown in FIG. 1(B) and the welding voltage Vw shown in FIG. 1(C) are positive values. When a short circuit occurs at time t1 during the forward feed peak period Tsp, as shown in FIG. 1(C), the welding voltage Vw suddenly decreases to a short circuit voltage value of several volts, and the short circuit determination signal Sd changes to a high level (short circuit period) as shown in FIG. 1(D). In response to this, the system transitions to a predetermined forward feed deceleration period Tsd from time t1 to t2, and the feed speed Fw decelerates from the forward feed peak value Wsp to 0 as shown in FIG. 1(A).

[0045] As shown in Fig. 1A, the feeding speed Fw enters a predetermined backward acceleration period Tru from time t2 to t3, and accelerates from 0 to the above-mentioned backward peak value Wrp. During this period, the short circuit period continues.

[0046] When the reverse acceleration period Tru ends at time t3, as shown in (A) of the figure, the feeding speed Fw enters the reverse peak period Trp and reaches the reverse peak value Wrp. The reverse 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. 1B, the instantaneous value of the welding current Iw during the short-circuit period from time t1 to time t4 is controlled 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 a value 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 feed rate Fw. Preferably, the value of the short-circuit current setting signal Isr is set to 100 A or less, more preferably 70 A or less. By controlling the welding current Iw to a small current value during the short-circuit period in this manner, spatter generation during a short circuit is suppressed and droplets are smoothly absorbed into the molten pool. Furthermore, since the value of the welding current Iw can be reduced at the time of arc re-strike without performing constriction detection control as in the prior art, spatter generation associated with arc re-strike can be significantly reduced. In this embodiment, since constriction detection control is not performed, a detection line for detecting the voltage at the arc generation portion is not required. In the prior art, the maximum instantaneous value of the welding current Iw during the short-circuit period is 400 A or more. This is because, in order to release the short circuit state, it is necessary to pass a large current and form a constriction in the droplet by the pinching force of the current. In contrast, in the present embodiment, by feeding the welding wire in reverse at high speed, it is possible to form a constriction and release the short circuit state without relying on the pinching force. For this reason, in the present embodiment, the welding current Iw during the short circuit period can be set to a smaller value than in the prior art.

[0048] [Arc period from time t4 to t7] At time t4, when the necking progresses due to the reverse feed of the welding wire and an arc is generated, as shown in FIG. 1C, the welding voltage Vw suddenly rises to an arc voltage value of several tens of volts, and as shown in FIG. 1D, the short-circuit determination signal Sd changes to Low level (arc period). In response to this, as shown in FIG. 1E, the first arc period signal Sta1 changes to High level, and the period from time t4 to t61 becomes a predetermined first arc period Ta1. The first arc period Ta1 is set by the first arc period setting signal Ta1r of FIG. 1. Constant current control is performed during the first arc period Ta1. At the same time, the welding wire transitions to a predetermined reverse feed deceleration period Trd from time t4 to t5, and the feed speed Fw decelerates from the reverse feed peak value Wrp to 0 as shown in FIG. 1A.

[0049] When the reverse feed deceleration period Trd ends at time t5, the period transitions to a predetermined forward feed acceleration period Tsu from time t5 to time t6. During this forward feed acceleration period Tsu, as shown in Fig. 1(A), the feed speed Fw accelerates from 0 to the forward feed peak value Wsp. During this period, the arc period continues.

[0050] When the forward feed acceleration period Tsu ends at time t6, as shown in FIG. 1A, the feed speed Fw enters the forward feed peak period Tsp and reaches the forward feed peak value Wsp. The arc period 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. Then, when a short circuit occurs, the operation returns to that at time t1.

[0051] When an arc is generated at time t4, as shown in FIG. 1C, the welding voltage Vw rises sharply to an arc voltage value of several tens of volts. On the other hand, as shown in FIG. 1B, the welding current Iw remains at the value of the low-level current setting signal Ilr in FIG. 1 for a predetermined delay period Tc from time t4. This is because if the current value is increased immediately after the arc is generated, the reverse feed of the welding wire and the melting of the welding wire by the welding current will be added together, causing the arc length to increase rapidly and possibly resulting in an unstable welding state. This delay period Tc may be set to zero.

[0052] At time t51 during the forward feed acceleration period Tsu, when the delay period Tc ends, the polarity switching signal Dr changes to a high level, as shown in (G) of the figure, and the output of the welding power supply changes to electrode positive polarity EP. When the delay period Tc=0, the electrode positive polarity EP is achieved at time t4. In response to this, as shown in (B) of the figure, the welding current Iw changes to a low-level negative current value, and as shown in (C) of the figure, the welding voltage Vw also changes to a negative arc voltage value. As shown in (B) of the 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. Thereafter, it decreases to a predetermined switching current value at time t61. As shown in (C) of the figure, the welding voltage Vw also has a waveform similar to that of the welding current Iw. The reason why the welding current Iw is reduced to a switching current value of approximately 50 to 100 A is as follows. If the current value is large when switching polarity, a surge voltage may be applied to the transistors that make up the secondary inverter circuit of the power control circuit PM in Figure 1, which could cause them to be destroyed, and this is to prevent this.

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

[0054] At time t62, after a predetermined current drop time Td has elapsed since the arc occurrence time t4, the third arc period signal Sta3 changes to a high level, as shown in (F) of the figure. The period from this time until time t7, when the next short circuit occurs, is the third arc period Ta3. During the third arc period Ta3, the polarity switching signal Dr remains low, as shown in (G) of the figure, so the output of the welding power supply has electrode negative polarity EN. Constant current control is performed during the third arc period Ta3. As shown in (B) of the figure, a predetermined third arc current Ia3 determined by the third arc current setting signal Ia3r of Figure 1 is applied. As shown in (C) of the figure, the welding voltage Vw is a value determined by the current value and the arc load. By reducing the third arc current Ia3 immediately before the short circuit, a short circuit can be initiated and spatter generation during the short circuit 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 fall 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 transmission peak value Wsp (predetermined value): 30 m / min, reverse transmission peak value Wrp (predetermined value): 25 m / min,

[0056] In the above-described embodiment, the electrode polarity is positive EP during the first arc period and negative EN during other periods. This allows the electrode polarity to be negative EN during periods other than the first arc period, thereby reducing the heat input to the base metal and increasing the size of the droplets formed on the welding wire. The larger the droplet size, the larger the gap can be filled with the droplets. As a result, high-quality welding can be performed on thin plates with large gaps in the weld joint.

[0057] FIG. 3 is a timing chart of signals in the arc welding apparatus of FIG. 1, illustrating an arc welding control method according to an embodiment of the present invention different from that of FIG. 2. (A) in FIG. 3 shows the change over time in the feed rate Fw, (B) in FIG. 3 shows the change over time in the welding current Iw, (C) in FIG. 3 shows the change over time in the welding voltage Vw, (D) in FIG. 3 shows the change over time in the short-circuit determination signal Sd, (E) in FIG. 3 shows the change over time in the first arc period signal Sta1, (F) in FIG. 3 shows the change over time in the third arc period signal Sta3, and (G) in FIG. 3 shows the change over time in the polarity switching signal Dr. In FIG. 3, the operation from time t3 to t61 differs from that of FIG. 2, but the operation in the remaining periods is similar. Hereinafter, the operations different from those of FIG. 2 will be described with reference to FIG. 3.

[0058] The operation of the feed speed Fw shown in FIG. 4(A) is the same as that in FIG. 2, and therefore the description will not be repeated.

[0059] At time t31, a predetermined period of time has elapsed since the start of the short circuit period at time t1, the polarity switching signal Dr changes from low to high, as shown in FIG. 1(G), and the output of the welding power supply switches to electrode positive polarity EP. In response to this, as shown in FIG. 1(B), the welding current Iw changes from a positive short circuit current value to a negative short circuit current value. Similarly, as shown in FIG. 1(C), the welding voltage Vw changes from a positive short circuit voltage value to a negative short circuit voltage value. The predetermined period is set to approximately 1 to 2.5 ms since the short circuit period is 3 ms or longer, so that the polarity can be switched during the short circuit period. Approximately 1 ms is required from the start of the short circuit period for the droplet and the weld pool to establish a stable short circuit, so it is desirable to switch the polarity after this time has elapsed.

[0060] At time t4, the welding wire is fed backward, causing the necking to progress and an arc to be generated. As shown in FIG. 1C, the welding voltage Vw suddenly rises to a negative arc voltage value of several tens of volts. As a result, the short-circuit detection signal Sd changes to a low level (arc period) as shown in FIG. 1D. In response to this, the first arc period signal Sta1 changes to a high level as shown in FIG. 1E, and the period from time t4 to time t61 becomes the predetermined first arc period Ta1. During the first arc period, the polarity switching signal Dr remains high as shown in FIG. 1G, so the output of the welding power supply maintains the electrode negative polarity EN. Furthermore, constant current control continues during the first arc period Ta1. As shown in FIG. 1B, the welding current Iw is at the value of the low-level current setting signal Ilr in FIG. 1 from time t4 through the predetermined delay period Tc.

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

[0062] When the first arc period Ta1 ends at time t61, as shown in FIG. 2(G), the polarity switching signal Dr changes to low level, and the output of the welding power supply becomes electrode negative polarity EN. In response to this, as shown in FIG. 2(B), the welding current Iw becomes a positive switching current value, and as shown in FIG. 2(C), the welding voltage Vw also becomes a positive arc voltage value. The period from time t61 to t62 becomes the second arc period Ta2, and the welding power supply switches to constant voltage control. The operation thereafter is the same as in FIG. 2, so description thereof will not be repeated.

[0063] As described above, when the polarity is switched during the short circuit period, no arc is generated, so that the arc does not break and the polarity can be switched smoothly. [Explanation of symbols]

[0064] 1 welding wire 2 Base material 3. Arc 4 welding torches 5 Feeding roll DR polarity switching circuit Dr polarity switching signal Ea Error amplification signal EI current error amplifier circuit Ei Current error amplification signal EV voltage error amplifier circuit Ev Voltage error amplified signal FC feed control circuit Fc feed control signal FR feed speed setting circuit Fr feed speed setting signal Fw Feed speed Ia1 First arc current IA1R First arc current setting circuit Ia1r 1st arc current setting signal Ia2 Second arc current Ia3 Third arc current IA3R 3rd 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 detection circuit Sd Short circuit detection signal STA1 First arc period circuit Sta1 First arc period signal STA3 Third arc period circuit Sta3 Third arc period signal SW Power supply characteristic switching circuit TA1R First arc period setting circuit Ta1r 1st arc period setting signal Tc delay period Td Current fall time Trd Reverse feed deceleration period TRDR Reverse deceleration period setting circuit Trdr Reverse feed deceleration period setting signal Trp Backhaul Peak Period Tru Reverse acceleration period TRUR Reverse acceleration period setting circuit Trur Reverse acceleration period setting signal Tsd Forward feed deceleration period TSDR Forward feed deceleration period setting circuit Tsdr Forward feed deceleration period setting signal Tsp forward peak period Tsu forward acceleration period TSUR Forward feed acceleration period setting circuit Tsur Forward feed acceleration period setting signal VD voltage detection circuit Vd Voltage detection signal VR voltage setting circuit Vr voltage setting signal Vw welding voltage WM feed motor Wrp Reverse peak value WRR reverse transmission peak value setting circuit Wrr Reverse transmission peak value setting signal Wsp forward peak value WSR forward peak value setting circuit Wsr Forward transmission peak value setting signal

Claims

1. The welding wire is fed, and a short circuit period and an arc period are repeated. an arc welding control method in which the arc period includes a first arc period and a subsequent second arc period, a welding current is supplied by constant current control during the first arc period, and a welding current is supplied by constant voltage control during the second arc period, The electrode polarity is positive during the first arc period, and the electrode polarity is negative during the other periods.

1. An arc welding control method comprising:

2. The electrode polarity is switched to positive polarity at the time when the first arc period starts or at a time delayed therefrom.

2. The method for controlling arc welding according to claim 1.

3. The electrode polarity is switched to positive polarity during the short-circuit period.

2. The method for controlling arc welding according to claim 1.

4. When switching polarity, the absolute value of the welding current is set to a reference value or less.

4. The arc welding control method according to claim 1, wherein the arc welding control method is a method for controlling an arc welding process.

5. The welding wire is fed in reverse during the short circuit period and fed in forward direction during the arc period.

5. The arc welding control method according to claim 1, wherein the arc welding control method is a method for controlling an arc welding process.

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