JP2024037473A - Arc welding control method - Google Patents

Abstract

[Problem] To perform welding with a wide gap tolerance and prevent burn-through even for steel materials with a plate thickness of 1 mm or less in consumable electrode arc welding. [Solution] A method of controlling arc welding in which a welding wire is fed, a short circuit period and an arc period are repeated, the arc period includes a first arc period from time t4 to t61 and a subsequent second arc period from time t61 to t62, a welding current Iw is supplied by constant current control during the first arc period, and a welding current Iw is supplied by constant voltage control during the second arc period, in which the first arc period has electrode negative polarity EN and the second arc period has electrode positive polarity EP, and during the first arc period, a welding current Iw having a pulse waveform formed from a base current and a peak current is supplied. [Selected Figure] Figure 2

Description

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

Inventions such as Patent Documents 1 and 2 are commonly used to weld thin plates with high quality by reducing heat input to the base material.
In the AC pulsed arc welding method according to Patent Document 1, a welding wire is fed, and the peak current and base current are applied during the electrode positive polarity period, and the electrode negative polarity current is applied during the electrode negative polarity period in one cycle. Welding is performed by repeating as follows. In this AC pulsed 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. can. Therefore, low heat input welding is possible, and high quality thin plate welding can be performed.

In the welding method according to Patent Document 2, welding is performed by feeding a welding wire and alternately switching a period of performing pulsed arc welding and a period of performing short-circuit transition arc welding. In this welding method, heat input to the base metal can be controlled by adjusting the ratio between the pulse arc welding period and the short-circuit transfer arc welding period. This makes it possible to perform low heat input welding and high-quality thin plate welding.

International Publication WO2018/079345 Publication JP 2021-53649 Publication

In the automobile industry, steel sheets are increasingly being made thinner in order to reduce the weight of vehicle bodies with the aim of improving fuel efficiency. When the steel material becomes thinner, problems such as burn-through occur during welding and it becomes difficult to form a bead due to the gap at the joint. When conventional AC pulse arc welding is applied to a thin plate, when the plate thickness is 1 mm or less, the problems of burn-through and narrow gap tolerance cannot be solved.

Therefore, an object of the present invention is to provide an arc welding control method that can prevent burn-through and perform welding with a wide gap tolerance even on steel materials with a plate thickness of 1 mm or less. do.

In order to solve the above-mentioned problem, the invention of claim 1:
Feed the welding wire, repeat the short circuit period and the arc period,
The arc period includes a first arc period and a second arc period following it, in which the welding current is applied by constant current control during the first arc period, and the welding current is applied by constant voltage control during the second arc period. In the arc welding control method for welding by applying current,
The first arc period has a negative electrode polarity, and the second arc period has a positive electrode polarity,
During the first arc period, the welding current is applied with a pulse waveform formed from a base current and a peak current;
This is an arc welding control method characterized by the following.

The invention of claim 2 is:
Switching the polarity while the base current is energized during the first arc period to transition to a second arc period;
The arc welding control method according to claim 1, characterized in that:

The invention of claim 3 is:
The welding current during the first arc period is adjusted so that the electrode negative polarity current ratio, which is the ratio of the welding current during the first arc period to the average value of the welding current, is in the range of 40% to 70%. set,
The arc welding control method according to claim 1 or 2, characterized in that:

The invention of claim 4 is:
The welding wire is fed backward during the short circuit period and forward fed during the arc period,
The arc welding control method according to claim 1 or 2, characterized in that:

The invention of claim 5 is:
Detecting a constriction of a droplet formed on the welding wire during the short circuit period and reducing the welding current, and then transitioning to the first arc period;
The arc welding control method according to claim 1 or 2, characterized in that:

According to the present invention, it is possible to prevent burn-through and perform welding with a wide gap tolerance even on steel materials with a plate thickness of 1 mm or less.

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. 2 is a timing chart of each signal in the arc welding apparatus of FIG. 1 illustrating an arc welding control method according to an embodiment of the present invention.

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

FIG. 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 the figure, a circuit for applying a high voltage of several hundred volts for a short period of time between the welding wire 1 and the base material 2 is omitted in order to facilitate polarity switching. Each block will be explained below with reference to the same figure.

The power control circuit PM receives a commercial power source (not shown) such as a three-phase 200V power source, performs output control by inverter control, etc. according to an error amplification signal Ea, which will be described later, and changes the polarity between the electrodes and the positive polarity EP by a polarity switching signal Dr, which will be described later. The welding voltage Vw and welding current Iw are output between the welding wire 1 and the base metal 2 by switching the electrode negative polarity EN. Although not shown, this power control circuit PM is driven by a primary rectifier that rectifies commercial power, a smoothing capacitor that smoothes the rectified DC, and the above-mentioned error amplification signal Ea that converts the smoothed DC into high-frequency AC. A high-frequency transformer that steps down high-frequency AC to a voltage value suitable for welding, a secondary rectifier that rectifies the stepped-down high-frequency AC to DC, a reactor that smoothes the rectified DC, and a high-frequency transformer that steps down high-frequency AC to a voltage value suitable for welding. It is equipped with a secondary inverter circuit that converts the alternating current to several tens to several hundreds of Hz based on the polarity switching signal Dr.

The feed motor WM receives a feed control signal Fc, which will be described later, as an input, and feeds the welding wire 1 at a feed speed Fw by alternately repeating forward feed and reverse feed. Further, as is generally the case, the welding wire 1 may be fed at a constant speed at a predetermined speed. A motor with fast transient response is used as the feed motor WM. In order to speed up the rate of change in 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. Further, two feeding motors WM may be used to form a push-pull feeding system.

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

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 amplification circuit EV receives the above voltage setting signal Vr and the above voltage detection signal Vd as input, amplifies the error between both values, and outputs a voltage error amplification signal Ev.

The short-circuit discrimination circuit SD inputs the above-mentioned voltage detection signal Vd, and when this value is less than a predetermined short-circuit discrimination value (approximately 10V), it determines that there is a short-circuit period and becomes High level; It determines that it is in the arcing period and outputs a short circuit determination signal Sd that goes to Low level.

The normal feed acceleration period setting circuit TSUR outputs a predetermined normal feed acceleration period setting signal Tsur.

The normal feed deceleration period setting circuit TSDR outputs a predetermined normal feed deceleration period setting signal Tsdr.

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

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

The normal feed peak value setting circuit WSR outputs a predetermined normal feed 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 has 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, and the above-mentioned forward feed deceleration period setting signal Trdr. The forward feed peak value setting signal Wsr, the above reverse feed peak value setting signal Wrr, and the above short circuit determination signal Sd are inputted, and a feed speed pattern generated by the following processing is output as a feed speed setting signal Fr. When this feeding speed setting signal Fr is 0 or more, it is a forward feeding period, and when it is less than 0, it is a reverse feeding period.
1) During the normal feed acceleration period Tsu determined by the normal feed acceleration period setting signal Tsur, a feed speed setting signal Fr is output that accelerates from 0 to a positive forward feed peak value Wsp determined by the normal feed peak value setting signal Wsr. .
2) Subsequently, during the normal feed peak period Tsp, the feed speed setting signal Fr is output to maintain the above-mentioned normal feed peak value Wsp.
3) When the short circuit determination signal Sd changes from Low level (arc period) to High level (short circuit period), it shifts to the normal feed deceleration period Tsd determined by the normal feed deceleration period setting signal Tsdr, and from the above normal feed peak value Wsp. Outputs a feed speed setting signal Fr that decelerates to 0.
4) Subsequently, during the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur, the feed rate setting signal Fr is accelerated from 0 to a negative reverse feed peak value Wrp determined by the reverse feed peak value setting signal Wrr. Output.
5) Subsequently, during the reverse feed peak period Trp, a feed speed setting signal Fr is output to maintain the above-mentioned reverse feed peak value Wrp.
6) When the short circuit determination signal Sd changes from High level (short circuit period) to Low level (arc period), it shifts to the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr, and from the above reverse feed peak value Wrp. Outputs a feed speed setting signal Fr that decelerates to 0.
7) By repeating steps 1) to 6) above, a feeding speed setting signal Fr having a feeding pattern that changes in the form of a positive and negative trapezoidal wave is generated.

The feed control circuit FC inputs the above feed speed setting signal Fr and generates a feed control signal Fc for feeding the welding wire 1 at a feed speed Fw corresponding to the value of the feed speed setting signal Fr. Output to the above feed motor WM.

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

The constriction detection circuit ND inputs the short circuit determination signal Sd, the voltage detection signal Vd, and the current detection signal Id, and detects the voltage detection signal Vd when the short circuit determination signal Sd is at a high level (short circuit period). When the voltage rise value reaches the constriction detection reference value, it is determined that a constriction has been formed, and the constriction detection signal Nd becomes High level, and when the short circuit determination signal Sd changes to Low level (arc period), the constriction detection signal Nd becomes Low level. Output. Further, the constriction detection signal Nd may be changed to High level at the time when the differential value of the voltage detection signal Vd during the short-circuit period reaches the corresponding constriction detection reference value. Furthermore, the resistance value of the droplet is calculated by dividing the value of the voltage detection signal Vd by the value of the current detection signal Id, and when the differential value of this resistance value reaches the corresponding waist detection reference value, a waist detection signal is sent. Alternatively, Nd may be changed to a high level. Furthermore, the constriction detection signal Nd may be changed to High level by estimating that a constriction has been formed when a predetermined period of time has elapsed since the short circuit determination signal Sd changed to High level (short circuit period).

The short circuit current setting circuit ISR receives the above short circuit discrimination signal Sd, the above low level current setting signal Ilr, and the above constriction detection signal Nd, 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 High level (short circuit), a short circuit current setting signal Isr having a predetermined initial current setting value is output.
2) Thereafter, the short-circuit current setting signal Isr is outputted, which increases at a predetermined short-circuit slope and maintains the value when it reaches a predetermined short-circuit peak value.
3) After that, when the constriction detection signal Nd changes to High level (constriction detection), the short-circuit current setting signal Isr having the value of the low-level current setting signal Ilr is output.

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

The first arc period circuit STA1 inputs the short circuit determination signal Sd and the first arc period setting signal Ta1r, and starts the first arc period setting signal from the time when the short circuit determination signal Sd changes to Low level (arc period). During the first arc period Ta1 set by Ta1r, the first arc period signal Sta1 which is at High level is output.

The first arc current setting circuit IA1R inputs the first arc period signal Sta1 and starts the first arc period signal Sta1 from the time when the first arc period signal Sta1 changes to High level and a predetermined delay period Tc has elapsed. During the period in which Sta1 changes to Low level, the predetermined base current setting value during the predetermined base period and the predetermined peak current setting value during the predetermined peak period are repeated for one cycle or more, and then the base current A first arc current setting signal Ia1r, which is a set value, is output.

The third arc period circuit STA3 inputs the above-mentioned short circuit determination signal Sd and becomes High level when a predetermined current drop time Td has elapsed from the time when the short circuit determination signal Sd changed to Low level (arc period). Then, when the short circuit determination signal Sd becomes High level (short circuit period), the third arc period signal Sta3 that becomes Low level is output.

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

The current control setting circuit ICR includes the above short circuit determination signal Sd, the above low level current setting signal Ilr, the above short circuit current setting signal Isr, the above first arc period signal Sta1, the above third arc period signal Sta3, and the above The first arc current setting signal Ia1r and the third arc current setting signal Ia3r described above are input, the following processing is performed, and a current control setting signal Icr is output.
1) During the above delay period Tc from the time when the short circuit determination signal Sd changes to Low level (arc period) and the first arc period signal Sta1 changes to High level, the current becomes the value of the low level current setting signal Ilr. Outputs control setting signal Icr.
2) After that, a current control setting signal Icr having the value of the first arc current setting signal Ia1r is output.
3) During the period from the time when the first arc period signal Sta1 changes to Low level until the third arc period signal Sta3 changes to Low level (second arc period and third arc period), the third arc current setting is A current control setting signal Icr having the value of the signal Ia3r is output.
4) When the short circuit determination signal Sd is at 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 amplification circuit EI receives the above current control setting signal Icr and the above current detection signal Id, amplifies the error between both values, and outputs a current error amplified signal Ei.

The power supply characteristic switching circuit SW receives the current error amplification signal Ei, the voltage error amplification signal Ev, the first arc period signal Sta1, and the third arc period signal Sta3 as input, and performs the following processing, Outputs an error amplified signal Ea.
1) During the second arc period Ta2 until the first arc period signal Sta1 changes to Low level and the third arc period signal Sta3 changes to High level, the voltage error amplification signal Ev is output as the error amplification signal Ea. .
2) During other periods, the current error amplification signal Ei is output as the error amplification signal Ea.
With this circuit, the characteristics of the welding power source are constant current characteristics during the short circuit period, the first arc period Ta1, and the third arc period Ta3, and are constant voltage characteristics during the second arc period Ta2.

The polarity switching circuit DR inputs the above current detection signal Id, the above low level current setting signal Ilr and the above first arc period signal Sta1, and the value of the current detection signal Id is decreased by the waist detection, and the low level current is set. The polarity changes to High level (electrode negative polarity EN) during the period when it is equal to the value of the setting signal Ilr, and then returns to Low level (electrode positive polarity EP) when the first arc period signal Sta1 changes to Low level. Outputs the switching signal Dr.

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

When the feeding speed Fw shown in FIG. 2 (A) is a positive value, it indicates a forward feeding state in which the welding wire 1 is fed forward toward the base material 2, and when it is a negative value, it is separated from the base material 2. This shows a reverse feeding state in which the paper is fed backwards in the direction in which it is fed. The feed rate Fw is controlled by the value of the feed rate setting signal Fr output from the feed rate setting circuit FR of FIG. The feeding speed Fw is a normal feed acceleration period Tsu determined by the normal feed acceleration period setting signal Tsur in FIG. 1, a normal feed peak period Tsp that continues until a short circuit occurs, and a normal feed speed determined by the normal feed deceleration period setting signal Tsdr in FIG. A feed deceleration period Tsd, a reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur in FIG. 1, a reverse feed peak period Trp that continues until an arc occurs, and a reverse feed determined by the reverse feed deceleration period setting signal Trdr in FIG. It is formed from the deceleration period Trd. Further, 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. As a result, the feed rate setting signal Fr has a feed pattern that changes in the shape of a substantially trapezoidal wave of positive and negative values. When the welding current Iw shown in the same figure (B) and the welding voltage Vw shown in the same figure (C) are positive values, they indicate the waveforms for the electrode positive polarity EP, and when they are negative values, they indicate the waveforms for the electrode negative polarity EN. The waveform when .

[Operation during the short circuit period from time t1 to t4]
Until the middle of the short-circuit period, the polarity switching signal Dr is at a low level, as shown in FIG. Therefore, during the short-circuit period, the welding current Iw shown in FIG. 5B and the welding voltage Vw shown in FIG. When a short circuit occurs at time t1 during the forward feed peak period Tsp, the welding voltage Vw suddenly decreases to a short circuit voltage value of several volts, as shown in (D) of the same figure, as shown in (C) of the same figure. The short circuit determination signal Sd changes to High level (short circuit period). In response to this, a transition is made to a predetermined normal feed deceleration period Tsd from time t1 to t2, and the feeding speed Fw is decelerated from the above normal feed peak value Wsp to 0, as shown in FIG. .

As shown in FIG. 3A, the feed rate Fw enters a predetermined reverse feed acceleration period Tru from time t2 to t3, and accelerates from 0 to the above-mentioned reverse feed peak value Wrp. During this period, the short circuit period continues.

When the reverse feed acceleration period Tru ends at time t3, the feed rate Fw enters the reverse feed peak period Trp and reaches the above-mentioned reverse feed peak value Wrp, as shown in FIG. The reverse feed peak period Trp continues until an arc occurs at time t4. Therefore, the period from time t1 to t4 becomes a short circuit period.

As shown in FIG. 1B, the welding current Iw during the short-circuit period from time t1 to t4 is constant-current controlled to the value of the short-circuit current setting signal Isr shown in FIG.

As shown in FIG. 3B, the welding current Iw during the short circuit period from time t1 to t4 has a predetermined initial current value during the predetermined initial period. Thereafter, the welding current Iw increases at a predetermined short-circuit slope, and when it reaches a predetermined short-circuit peak value, it maintains that value. The above initial period is about 0.5 ms, the initial current value is about 40 A, the slope at the time of short circuit is about 300 A/ms, and the peak value at the time of short circuit is about 340 A.

As shown in FIG. 3C, the welding voltage Vw increases from around the point where the welding current Iw reaches its peak value at the time of short circuit. This is because a constriction is gradually formed in the droplet at the tip of the welding wire 1 due to the reverse feeding of the welding wire 1 and the action of the pinch force due to the welding current Iw.

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

At time t32 when the welding current Iw is at a low level current value, the polarity switching signal Dr changes from Low level to High level as shown in FIG. Switches to polarity EN. In response to this, the welding current Iw changes from a positive low-level current value to a negative low-level current value, as shown in FIG. Similarly, as shown in FIG. 3C, the welding voltage Vw changes from a positive short-circuit voltage value to a negative short-circuit voltage value. Switching to the negative electrode polarity EN is performed during a period in which the value of the welding current Iw decreases due to waist detection and becomes equal to the value of the low-level current setting value. Therefore, the constriction is detected at time t31, and the electrode polarity is switched to negative polarity EN during the period from the time when the welding current Iw decreases to a low level current value until time t51 when an arc occurs and the delay period Tc ends. It will be done. In this way, since the polarity is switched when the welding current Iw is a small value, application of a problematic surge voltage to the transistors forming the 2 o'clock side inverter circuit is suppressed, and failure of the transistors is prevented. be able to.

At time t4, when the constriction progresses due to the reverse feeding of the welding wire and an arc is generated, the welding voltage Vw rapidly increases to a negative arc voltage value of several tens of V, as shown in FIG. As shown in FIG. 3D, the short circuit determination signal Sd changes to Low level (arc period). In response to this, the constriction detection signal Nd changes to Low level, as shown in FIG. At the same time, as shown in FIG. 3E, 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, the polarity switching signal Dr remains at the High level, as shown in FIG. Furthermore, constant current control continues during the first arc period Ta1.

At the same time, the period from time t4 to time t5 becomes a predetermined reverse feed deceleration period Trd. As shown in FIG. 3A, the feeding speed Fw is decelerated from the above-mentioned reverse feeding peak value Wrp to 0.

When the reverse deceleration period Trd ends at time t5, a transition begins to a predetermined forward acceleration period Tsu from time t5 to t6. During this normal feed acceleration period Tsu, as shown in FIG. 2A, the feeding speed Fw accelerates from 0 to the above normal feed peak value Wsp. During this period, the arc period continues.

When the normal feed acceleration period Tsu ends at time t6, the feeding speed Fw enters the normal feed peak period Tsp and reaches the above-mentioned normal feed peak value Wsp, as shown in FIG. The arc period continues during this period as well. The forward transmission peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to t7 becomes an arc period. Then, when a short circuit occurs, the operation returns to time t1.

As shown in the figure (B), the welding current Iw takes the value of the low-level current setting signal Ilr in FIG. 1 during a predetermined delay period Tc from time t4.

When the delay period Tc ends at time t51, the welding current Iw during the first arc period up to time t61 is set by the first arc current setting signal Ia1r in FIG. 1, as shown in FIG. This becomes the first arc current Ia1. The first arc current Ia1 repeats a pulse waveform formed from a predetermined base current during a predetermined base period and a predetermined peak current during a predetermined peak period for one period or more, and then becomes the base current. . In the figure, a case of a two-cycle pulse waveform is illustrated. By starting the first arc current Ia1 from a base current with a small current value, it is possible to prevent the arc length from rapidly increasing immediately after the arc occurs, thereby preventing the arc generation state from becoming unstable. Furthermore, the state of arc generation in the negative electrode polarity EN is more unstable than in the electrode positive polarity EP. Therefore, when the first arc current Ia1 has a pulse waveform, the rigidity of the arc becomes higher than when the first arc current Ia1 has a constant value DC waveform, and the stability of the arc can be improved. Furthermore, by making the first arc current Ia1 a pulse waveform, the amount of melting of the welding wire can be increased compared to when the first arc current Ia1 is a constant value DC waveform. Then, the first arc current Ia1 is terminated by supplying the base current. In this way, the electrode polarity is switched to the positive polarity EP while the base current having a small current value is flowing, and as described above, the transistors forming the secondary side inverter circuit can be protected from surge voltage. As shown in FIG. 3C, the welding voltage Vw also has a waveform similar to the welding current Iw.

When the first arc period Ta1 ends at time t61, the polarity switching signal Dr changes to Low level as shown in FIG. In response to this, the welding current Iw takes on a positive value, as shown in FIG. 4(B), and the welding voltage Vw also takes a positive value, as shown in FIG. 2(C). 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 the same figure (B), the second arc current Ia2 has a value according to the arc load, and as shown in the same figure (C), the welding voltage Vw is a value controlled by the voltage setting signal Vr of Fig. 1. becomes. By controlling this second arc period Ta2 at a constant voltage, the arc length is controlled to an appropriate value. As described above, when the electrode has negative polarity EN, the arc generation state tends to become unstable. For this reason, when arc length control is performed with the electrode negative polarity EN, the performance for maintaining the arc length at an appropriate value is inferior to when it is performed with the electrode positive polarity EP. Therefore, it is preferable to control the arc length using the electrode positive polarity EP.

At time t62, when a predetermined current drop time Td has elapsed from arc occurrence time t4, the third arc period signal Sta3 changes to High level, as shown in FIG. The period from this point to 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 continues to be at the Low level, as shown in FIG. During the third arc period Ta3, constant current control is performed. As shown in FIG. 3B, a predetermined third arc current Ia3 determined by the third arc current setting signal Ia3r in FIG. 1 is applied. As shown in the same figure (C), the welding voltage Vw becomes a value determined by the current value and the arc load. By setting the third arc current value Ia3 immediately before a short circuit to a small value, it is possible to guide the occurrence of a short circuit and suppress the occurrence of spatter when a short circuit occurs. This third arc period may not be provided. In that case, the first arc period and the second arc period constitute an arc period.

Numerical examples of each of the above parameters are shown below.
Welding wire: 1.2mm mild steel, shielding gas: 80% argon + 20% carbon dioxide
Average welding current: 170A, average welding voltage: 17V, average feeding speed: 9m/min
Forward feed peak value: 30m/min, reverse feed peak value: -40m/min
Short circuit period (not specified value): 3ms, arc period (not specified value): 7ms
Delay period: 0.5ms, 1st arc period: 4ms,
Base current: 150A, peak current: 250A, 2nd arc period repeated for 3 cycles: 2.5ms
3rd arc period (not a predetermined value): 0.5ms, current drop time: 6.5ms
Low level current value: 50A, 3rd arc current value: 50A,

If the ratio of the first arc current Ia1 of the electrode negative polarity EN to the average value of the welding current is defined as the electrode negative polarity current ratio ren (%), it can be defined by the following formula.
Ren=(∫|Ia1|・dt/∫|Iw|・dt)×100
However, each integration is performed during one cycle of the short circuit period and the arc period.
In the case of the numerical example mentioned above, the electrode negative polarity current ratio Ren=50%.

The effects of this embodiment will be explained below.
According to this embodiment, the electrode has negative polarity during the first arc period, the electrode has positive polarity during the second arc period, and a welding current with a pulse waveform formed from a base current and a peak current is applied during the first arc period. do. Thereby, during the first arc period, the electrode polarity is negative EN, so it is possible to increase the amount of melting of the welding wire while reducing the heat input to the base metal. Furthermore, the state of arc generation in the negative electrode polarity EN is more unstable than in the electrode positive polarity EP. Therefore, by making the first arc current a pulse waveform, the rigidity of the arc becomes higher than when the first arc current has a constant value DC waveform, and the stability of the arc can be improved. Furthermore, by making the first arc current a pulse waveform, the amount of melting of the welding wire can be further increased compared to when the first arc current is a constant DC waveform. As a result, in this embodiment, it is possible to prevent burn-through and perform welding with a wide gap tolerance even on steel materials with a plate thickness of 1 mm or less.

More preferably, according to the present embodiment, the polarity is switched while the base current is flowing during the first arc period, and the transition is made to the second arc period. In this way, the electrode polarity is switched to the positive polarity EP while the base current having a small current value is flowing, and the transistors constituting the secondary side inverter circuit can be protected from surge voltage.

More preferably, according to the present embodiment, the electrode negative polarity current ratio, which is the ratio of the welding current during the first arc period to the average value of the welding current, is in the range of 40% to 70%. Set the welding current during the arc period. The welding current (first arc current) for the first arc period is set by setting the base period, base current, peak period, peak current, and repetition period. When the electrode negative polarity current ratio is set within the above range, it is possible to prevent burn-through and perform welding with a wide gap tolerance even on steel materials with a plate thickness of 1 mm or less. If the electrode negative polarity current ratio is less than 40%, the heat input to the steel material will increase, and burn-through may occur when welding plates with a thickness of 1 mm or less. When the electrode negative polarity current ratio exceeds 70%, the welding condition becomes unstable and it becomes difficult to form a good bead.

More preferably, according to the present embodiment, the welding wire is fed backward during the short circuit period and forward fed during the arc period. In this way, the repetition period of the short circuit period and the arc period is stabilized, so that the heat input to the base metal becomes uniform and the welding quality is improved.

More preferably, according to the present embodiment, the constriction of a droplet formed on the welding wire during the short-circuit period is detected and the welding current is reduced, and then the first arc period is started. In this way, the current value at the time of arc generation can be reduced, so the amount of spatter generated can be reduced. Furthermore, since the current value when switching to the negative electrode polarity EN can be reduced, the transistors forming the secondary side inverter circuit can be protected from surge voltage.

1 welding wire
2 Base material
3 arc
4 welding torch
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 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 3 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 Ren Electrode negative polarity current ratio 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 supply 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 Forward 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 (5)

Feed the welding wire, repeat the short circuit period and the arc period,
The arc period includes a first arc period and a second arc period following it, in which the welding current is applied by constant current control during the first arc period, and the welding current is applied by constant voltage control during the second arc period. In the arc welding control method for welding by applying current,
The first arc period has a negative electrode polarity, and the second arc period has a positive electrode polarity,
During the first arc period, the welding current is applied with a pulse waveform formed from a base current and a peak current;
An arc welding control method characterized by: Switching the polarity while the base current is energized during the first arc period to transition to a second arc period;
The arc welding control method according to claim 1, characterized in that: The welding current during the first arc period is adjusted so that the electrode negative polarity current ratio, which is the ratio of the welding current during the first arc period to the average value of the welding current, is in the range of 40% to 70%. set,
The arc welding control method according to claim 1 or 2, characterized in that: The welding wire is fed backward during the short circuit period and forward fed during the arc period,
The arc welding control method according to claim 1 or 2, characterized in that: Detecting a constriction of a droplet formed on the welding wire during the short circuit period and reducing the welding current, and then transitioning to the first arc period;
The arc welding control method according to claim 1 or 2, characterized in that:

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