JP7789464B2 - Arc welding control method - Google Patents

Description

The present invention relates to a method for controlling arc welding performed by feeding a welding wire.

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.

In the welding method described in Patent Document 2, welding is performed by feeding a welding wire and alternating between periods of pulse arc welding and periods of short-circuit transfer arc welding. This welding method allows for heat input control to the base material by adjusting the ratio between the pulse arc welding period and the short-circuit transfer arc welding period. This enables low-heat input welding and high-quality thin-plate welding.

International Publication No. WO2018/079345 Japanese Patent Application Laid-Open No. 2021-53649

When welding thin plates, if 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 conventional welding methods such as those described in Patent Documents 1 and 2, it was difficult to achieve high-quality welding of thin plates with large gaps.

The present invention therefore aims to provide an arc welding control method that can perform high-quality welding on thin plates with large gaps in the weld joint.

In order to solve the above-mentioned problems, the invention of claim 1 provides:
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.
The arc welding control method is characterized by the above.

The invention of claim 2 is
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:

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

The invention of claim 4 is
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 invention of claim 5 is
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 present invention enables high-quality welding of thin plates with large gaps at the weld joint.

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; 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; 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 .

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a block diagram of an arc welding device for implementing an arc welding control method according to an embodiment of the present invention. The diagram omits the circuit that applies a high voltage of several hundred volts for a short period of time between the welding wire 1 and the base material 2 to facilitate smooth polarity switching. Each block will be explained below with reference to the diagram.

The power control circuit PM receives a commercial power supply (not shown), such as a three-phase 200V power supply, as input, and performs output control using inverter control or the like in accordance with an error amplification signal Ea (described below). It switches between electrode positive polarity EP and electrode negative polarity EN in accordance with a polarity switching signal Dr (described below), 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 also 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 to high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage suitable for welding, a secondary rectifier that rectifies the stepped-down high-frequency AC to DC, a reactor that smooths the rectified DC, and a secondary inverter circuit that converts the smoothed DC to AC of several tens to several hundreds of Hz based on the polarity switching signal Dr.

The feed motor WM receives a feed control signal Fc (described below) as input, and feeds the welding wire 1 at a feed speed Fw by alternately feeding forward and backward. Alternatively, as is common, the welding wire 1 may be fed at a constant, predetermined speed. A motor with fast transient response is used for the feed motor WM. In order to speed up the rate of change of the feed speed Fw of the welding wire 1 and the reversal of the feed direction, the feed motor WM may be installed near the tip of the welding torch 4. Alternatively, two feed motors WM may be used to create a push-pull feed system.

The welding wire 1 is fed through the welding torch 4 by the rotation of the 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. The welding wire 1 may be steel wire, aluminum wire, or the like. A shielding gas (not shown) is ejected from the tip of the welding torch 4.

The current detection circuit ID detects the absolute value of the welding current Iw and outputs a current detection signal Id.

The voltage detection circuit VD detects the absolute value of the 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.

The voltage error amplifier circuit EV receives the voltage setting signal Vr and the voltage detection signal Vd as inputs, amplifies the error between the two values, and outputs the voltage error amplification signal Ev.

The short circuit determination circuit SD receives the voltage detection signal Vd as input, and outputs a short circuit determination signal Sd that goes High if this value is below a predetermined short circuit determination value (approximately 10V) and indicates that a short circuit is occurring; if this value is above that value, it determines that an arc is occurring and outputs a short circuit determination signal Sd that goes Low.

The forward acceleration period setting circuit TSUR outputs a predetermined forward acceleration period setting signal Tsuru.

The forward transmission deceleration period setting circuit TSDR outputs a predetermined forward transmission deceleration period setting signal Tsdr.

The reverse acceleration period setting circuit TRUR outputs a predetermined reverse acceleration period setting signal Trur.

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

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

The reverse transmission peak value setting circuit WRR outputs a predetermined reverse transmission peak value setting signal Wrr.

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 a forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr, and the feed speed setting signal Fr is output to decelerate the feed speed 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 reverse peak value Wrp, which is a negative value determined by the reverse peak value setting signal Wrr.
5) Subsequently, during the backward transport peak period Trp, the feed speed setting signal Fr for maintaining the above-mentioned backward transport peak value Wrp is output.
6) When the short circuit detection signal Sd changes from a high level (short circuit period) to a low level (arc period), the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr begins, and the feeding speed setting signal Fr for decelerating the reverse feed speed from the above-mentioned reverse feed peak value Wrp to 0 is output.
7) By repeating the above steps 1) to 6), a feed speed setting signal Fr is generated with a feed pattern that changes in a trapezoidal waveform between positive and negative.

The feed control circuit FC receives the feed speed setting signal Fr as 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.

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

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

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

The first arc period circuit STA1 receives the short circuit detection signal Sd and the first arc period setting signal Ta1r as inputs, and outputs a first arc period signal Sta1 that remains high during the first arc period Ta1, which is predetermined by the first arc period setting signal Ta1r, from the time the short circuit detection signal Sd changes to low level (arc period).

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

The third arc period circuit STA3 receives the short circuit detection signal Sd as input and outputs a third arc period signal Sta3 that goes high when a predetermined current drop time Td has elapsed since the short circuit detection signal Sd changed to low level (arc period), and then goes low when the short circuit detection signal Sd subsequently goes high level (short circuit period).

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

The current control setting circuit ICR receives as inputs 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 the current control setting signal Icr.
1) During a predetermined delay period Tc from the point in time when the short circuit detection signal Sd changes to a low level (arcing period) and the first arcing period signal Sta1 changes to a 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) Thereafter, 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 first arc period signal Sta1 changes to low level until third arc period signal Sta3 changes to low level (second arc period and third arc period), current control setting signal Icr having the value of third arc current setting signal Ia3r is output.
5) When the short circuit determination signal Sd is at a high level (short circuit period), a current control setting signal Icr having the value of the short circuit current setting signal Isr is output.

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

Power supply characteristics switching circuit SW receives as input 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, performs the following processing, and outputs error amplified signal Ea.
1) During the 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.

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 which changes to a high level (electrode positive polarity EP) when the first arc period signal Sta1 changes to a high level, and changes to a low level (electrode negative polarity EN) when the first arc period signal Sta1 changes to a low level.
2) When the first arc period signal Sta1 changes to a high level and the delay period Tc has elapsed, a polarity switching signal Dr is output, which changes to a high level (electrode positive polarity EP) and when the first arc period signal Sta1 changes to a low level, a polarity switching signal Dr changes to a 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).

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

The feed speed Fw shown in Figure 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 a reverse feed state in which the welding wire 1 is fed backward 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 in Figure 1. The feed speed Fw is composed of a forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur in Figure 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 Figure 1, a reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur in Figure 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 in Figure 1. Furthermore, the forward feed peak value Wsp is determined by the forward feed peak value setting signal Wsr in Figure 1, and the reverse feed peak value Wrp is determined by the reverse feed peak value setting signal Wrr in Figure 1. As a result, the feed speed setting signal Fr has a feed pattern that changes in a generally trapezoidal waveform between positive and negative. The welding current Iw shown in Figure 1(B) and the welding voltage Vw shown in Figure 1(C) show waveforms with negative electrode polarity EN when positive values are used, and waveforms with positive electrode polarity EP when negative values are used. In the following description, the values of the welding current Iw and welding voltage Vw are given in absolute values.

[Operation during the short circuit period from time t1 to time t4]
During the short-circuit period, as shown in FIG. 1G, the polarity switching signal Dr is at a low level, so the output of the welding power supply has a negative electrode polarity EN. Therefore, during the short-circuit period, the welding current Iw shown in FIG. 1B and the welding voltage Vw shown in FIG. 1C are positive values. When a short circuit occurs at time t1 during the forward feed peak period Tsp, as shown in FIG. 1C, the welding voltage Vw suddenly drops 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. 1D. 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 zero as shown in FIG. 1A.

As shown in Figure 1(A), the feed speed Fw enters a predetermined reverse acceleration period Tru from time t2 to t3, and accelerates from 0 to the reverse peak value Wrp described above. The short circuit period continues during this period.

When the reverse acceleration period Tru ends at time t3, as shown in Figure 1(A), the feed speed Fw enters the reverse peak period Trp, and reaches the reverse peak value Wrp described above. The reverse peak period Trp continues until an arc occurs at time t4. Therefore, the period from times t1 to t4 is the short-circuit period.

As shown in Figure 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 Figure 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 wire 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 low 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 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 point is not required. 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, it was necessary to pass a large current and use the resulting pinching force to form a constriction in the droplet. In contrast, in this embodiment, by reversing the welding wire at high speed, it is possible to form a constriction and release the short circuit without relying on pinching force. As a result, in this embodiment, the welding current Iw during the short circuit period can be set to a smaller value than in conventional technology.

[Operation during arc period from time t4 to t7]
At time t4, when the constriction progresses due to the reverse feed of the welding wire and an arc is generated, as shown in FIG. 1C, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, and the short-circuit determination signal Sd changes to a low level (arc period) as shown in FIG. 1D. In response to this, as shown in FIG. 1E, the first arc period signal Sta1 changes to a 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 in 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.

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

When the forward feed acceleration period Tsu ends at time t6, as shown in Figure 1A, the feed speed Fw enters the forward feed peak period Tsp and reaches the forward feed peak value Wsp mentioned above. 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 times t4 to t7 is the arc period. When a short circuit occurs, the operation returns to that at time t1.

When an arc is generated at time t4, as shown in Figure 1(C), the welding voltage Vw rises sharply to an arc voltage value of several tens of volts. Meanwhile, as shown in Figure 1(B), the welding current Iw remains at the value of the low-level current setting signal Ilr in Figure 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 due to the welding current will be combined, causing the arc length to increase rapidly and potentially resulting in an unstable welding state. This delay period Tc may also be set to 0.

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 same 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 same figure, the welding current Iw changes to a low-level negative current value, and as shown in (C) of the same figure, the welding voltage Vw also changes to a negative arc voltage value. As shown in (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. Thereafter, it decreases to the predetermined switching current value at time t61. As shown in (C) of the same figure, the welding voltage Vw also has a waveform similar to that of the welding current Iw. The reason for reducing the welding current Iw 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 can be applied to the transistors that make up the secondary inverter circuit of the power control circuit PM in Figure 1, which can cause damage, and this is to prevent this.

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

At time t62, when the predetermined current drop time Td has elapsed since the arc generation time t4, the third arc period signal Sta3 changes to high level, as shown in Figure 1(F). 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, as shown in Figure 1(G), the polarity switching signal Dr remains low, so the welding power supply output has electrode negative polarity EN. Constant current control is performed during the third arc period Ta3. As shown in Figure 1(B), a predetermined third arc current Ia3 determined by the third arc current setting signal Ia3r in Figure 1 is applied. As shown in Figure 1(C), the welding voltage Vw is a value determined by the current value and 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.

Example values for the above parameters are shown below: Short circuit period (not specified): 3 ms, Arc period (not specified): 4 ms, Delay period Tc (specified): 0.5 ms, First arc period Ta1 (specified): 1.5 ms, Second arc period Ta2 (not specified): 2 ms, Third arc period Ta3 (not specified): 0.5 ms, Current fall time (specified): 3.5 ms, Low level current value (specified): 50 A, First arc current value Ia1 (specified): 150 A, Third arc current value Ia3 (specified): 50 A, Forward transmission peak value Wsp (specified): 30 m/min, Reverse transmission peak value Wrp (specified): 25 m/min.

In the above-described embodiment, the first arc period has positive electrode polarity EP, and the other periods have negative electrode polarity EN. As a result, the electrode polarity is negative EN during periods other than the first arc period, which reduces heat input to the base material and allows larger droplets to form on the welding wire. Larger droplet sizes allow larger gaps to be filled with the droplets. As a result, high-quality welding can be performed on thin plates with large gaps in the weld joint.

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

The operation of the feed speed Fw shown in Figure 2(A) is the same as that in Figure 2, so the explanation will not be repeated.

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 Figure 1(G), and the output of the welding power supply switches to electrode positive polarity EP. In response to this, as shown in Figure 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 Figure 1(C), the welding voltage Vw changes from a positive short circuit voltage value to a negative short circuit voltage value. The above-mentioned predetermined period is set to approximately 1 to 2.5 ms, since the short circuit period is 3 ms or more, in order to switch polarity during the short circuit period. Approximately 1 ms is required from the start of the short circuit period for the droplet and molten pool to establish a stable short circuit, so it is desirable to switch polarity after this time has elapsed.

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

At time t51, when the delay period Tc ends, as shown in Figure 1(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 Figure 1(C), the welding voltage Vw also has a waveform similar to that of the welding current Iw.

When the first arc period Ta1 ends at time t61, as shown in (G) of the same 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 same figure, the welding current Iw becomes a positive switching current value, and as shown in (C) of the same 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. The operation thereafter is the same as in Figure 2, so a description will not be repeated.

As mentioned above, if you switch polarity during a short circuit, no arc is generated, so the arc does not break and the polarity can be switched smoothly.

1 welding wire
2 Base material
3. Arc
4 welding torches
5 Feed 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 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 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 determination circuit Sd Short circuit determination signal STA1 First arc period circuit Sta1 First arc period signal STA3 Third arc period circuit Sta3 Third arc period signal SW Power supply characteristics switching circuit TA1R First arc period setting circuit Ta1r First arc period setting signal Tc Delay period Td Current fall 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 transmission peak value setting signal Wsp Forward transmission peak value WSR Forward transmission peak value setting circuit Wsr Forward transmission peak value setting signal

Claims (5)

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: switching the electrode polarity to positive polarity at the start of the first arc period or at a delayed time thereafter;
2. The method for controlling arc welding according to claim 1. The electrode polarity is switched to positive polarity during the short-circuit period.
2. The method for controlling arc welding according to claim 1. 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 is a method for controlling an arc welding process. 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 is a method for controlling an arc welding process.