CN115635166A - Arc welding control method - Google Patents

Abstract

The invention provides an arc welding control method, which can perform good arc starting even under the condition that the adhesion state of slag is serious in forward and reverse feeding arc welding. In the arc welding control method, when welding is started, forward and reverse feeding control is performed in which a feeding speed (Fw) is alternately switched between a forward feeding period and a reverse feeding period in an initial period (Ti) from a feeding start time of a welding wire to an energization start time of a welding current, and when a state determined that slag is not removed continues in the initial period (Ti) and a determination signal (Hd) changes to a high level at a time (t 5), an amplitude and/or an average value of the feeding speed (Fw) is increased in the initial period (Ti) thereafter, thereby enhancing an impact of a collision between the welding wire and a base material. This increases the slag removal effect. The determination is made based on whether the elapsed time of the initial period (Ti) is equal to or longer than a reference time or the torque of the feed motor is equal to or longer than a reference torque.

Description

Arc welding control method

Technical Field

The present invention relates to an arc welding control method for performing forward/reverse feed control for alternately switching a feed speed between a forward feed period and a reverse feed period in an initial period from a feed start timing of a welding wire to a current application start timing of a welding current when welding is started.

Background

In general consumable electrode arc welding, a welding wire as a consumable electrode is fed at a constant speed, and an arc is generated between the welding wire and a base material to perform welding. In consumable electrode arc welding, a welding wire and a base material are often in a welding state in which a short-circuit period and an arc period are alternately repeated.

In order to further improve the welding quality, the following arc welding control method is used: welding is performed by performing forward/reverse feeding control in which the feeding speed of the welding wire is alternately switched between a forward feeding period and a reverse feeding period, and a short circuit period and an arc period are generated. Here, the forward feeding is feeding the welding wire in a direction close to the base material, and the backward feeding is feeding the welding wire in a direction opposite to the forward feeding (a direction in which the welding wire is separated from the base material).

However, in consumable electrode arc welding, an insulator called slag (slag) may adhere to a tip end portion of a welding wire at the end of welding. Slag is produced by chemical reaction of components contained in the wire. The adhesion state of slag varies depending on the welding conditions such as the type of welding wire, the average welding current value, and the welding posture. When the next arc starting is performed in a state where the slag is adhered to the tip of the welding wire, the slag is an insulator even if the welding wire is in contact with the base material, and therefore, the arc is not generated, and the arc starting is not performed. The same applies to arc welding based on forward and reverse feed control.

Patent document 1 discloses a method for improving an arc start failure due to slag in forward and reverse feed control arc welding. In the invention of patent document 1, the forward and reverse feeding control is performed also in the initial period from the start of feeding of the welding wire to the energization of the welding current at the start of welding. Thus, since slag adheres to the wire tip, when the welding current is not applied even if the wire tip is in contact with the base material, the collision between the wire tip and the base material is repeated. In the invention of patent document 1, the slag at the tip of the wire is removed by repetition of the collision, and an arc is generated.

Prior art documents

Patent document

Patent document 1: japanese patent No. 6593923

Problems to be solved by the invention

In the above-described conventional technique, by performing forward and reverse feeding control during the initial period, even if slag adheres to the wire tip, the slag is removed and an arc is generated while the wire tip and the base material repeatedly collide several times. However, when the adhesion state of slag is severe, the arc may not be generated even though the tip of the wire collides with the base material several times.

Disclosure of Invention

Therefore, an object of the present invention is to provide an arc welding control method capable of reliably starting an arc even when the adhesion state of slag is severe.

Means for solving the problem

In order to solve the above problems, the invention of claim 1 is an arc welding control method for performing forward/reverse feeding control in which a feeding speed is alternately switched between a forward feeding period and a reverse feeding period in an initial period from a feeding start timing of a welding wire to a energization start timing of a welding current at the start of welding,

if it is determined that the state in which slag is not removed continues during the initial period, the amplitude and/or average value of the feed rate is increased during the initial period thereafter.

The 2 nd aspect of the invention provides the arc welding control method according to the 1 st aspect of the invention, wherein the determination is made based on an elapsed time of the initial period being equal to or longer than a reference time.

The 3 rd aspect of the invention provides the arc welding control method according to the 1 st aspect of the invention, wherein the determination is made based on a torque of the feed motor becoming equal to or greater than a reference torque during the initial period.

Effect of the invention

According to the arc welding control method of the present invention, even when the adhesion state of slag is severe, arc start can be reliably performed.

Drawings

Fig. 1 is a block diagram of a welding power supply for implementing an arc welding control method according to embodiment 1 of the present invention.

Fig. 2 is a timing chart of signals at the start of welding in the welding power supply of fig. 1, which shows the arc welding control method according to embodiment 1 of the present invention.

Fig. 3 is a block diagram of a welding power supply for implementing the arc welding control method according to embodiment 2 of the present invention.

-description of symbols-

1. Welding wire

2. Base material

3. Electric arc

4. Welding torch

5. Feed roller

CD current electrifying judging circuit

Cd current power-on discrimination signal

DIR initial time ratio setting circuit

Dir initial time ratio setting signal

DV drive circuit

Dv drive signal

E output voltage

Ea error amplified signal

ED output voltage detection circuit

Ed output voltage detection signal

EI current error amplifying circuit

Ei current error amplified signal

ER output voltage setting circuit

Er output voltage setting signal

EV voltage error amplifying circuit

Ev voltage error amplified signal

FC feed control circuit

Fc feed control signal

Feed speed setting circuit during FCR stable welding

Feed rate setting signal during stable Fcr welding

FIR initial period feed speed setting circuit

Fin initial period feed speed setting signal

FR feed speed setting circuit

Fr feed rate setting signal

Frc stabilized reverse feed peak

FRCR stable reverse feeding peak value setting circuit

Frcr stable reverse feeding peak value setting signal

Fri initial reverse feed peak

FRIR initial reverse feeding peak value setting circuit

Frir initial reverse feeding peak value setting signal

Fsc stable forward feed peak

FSCR stable forward feeding peak value setting circuit

Fscr stable forward feeding peak value setting signal

Initial forward feed peak of Fsi

FSIR initial forward feed peak setting circuit

Fsir initial forward feed peak setting signal

FW feed speed

HD discrimination circuit

Hd discrimination signal

HD2 nd discrimination circuit

ID current detection circuit

Id current detection signal

IHR hot start current setting circuit

Ihr Hot Start Current setting Signal

IMD motor current detection circuit

Imd motor current detection signal

Iw welding current

Distance between front end of Lw welding wire and base metal

PM power main circuit

SD short circuit discrimination circuit

Sd short circuit discrimination signal

Initial frequency of Si

SIR initial frequency setting circuit

Sir initial frequency setting signal

ST welding start circuit

St welding start signal

STI initial period timer circuit

Sti initial period timer signal

SW power supply characteristic switching circuit

Tc Stable soldering period

Initial period of Ti

VD voltage detection circuit

Vd voltage detection signal

Vw welding voltage

WL reactor

WM feed motor.

Detailed Description

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

[ embodiment 1]

Fig. 1 is a block diagram of a welding power supply for implementing an arc welding control method according to embodiment 1 of the present invention. Hereinafter, each block will be described with reference to the drawing.

The power main circuit PM receives a three-phase 200V commercial power supply (not shown) as an input, performs output control by inverter control or the like based on a drive signal Dv to be described later, and outputs an output voltage E. Although not shown, the power supply main circuit PM includes: a primary rectifier that rectifies the commercial power source, a smoothing capacitor that smoothes the rectified direct current, an inverter circuit that converts the smoothed direct current into a high-frequency alternating current and is driven by the above-described drive signal Dv, a high-frequency transformer that steps down the high-frequency alternating current to a voltage value suitable for welding, and a secondary rectifier that rectifies the stepped-down high-frequency alternating current into direct current.

The reactor WL smoothes the output voltage E. The inductance value of the reactor WL is, for example, 100 μ H.

Feeding motor WM alternately switches between a forward feeding period and a reverse feeding period using a feeding control signal Fc described later as an input, and feeds welding wire 1 at a feeding speed Fw. A motor having excellent transient characteristics is used for the feed motor WM. In order to increase the rate of change of the feeding speed Fw of the welding wire 1 and the reversal of the feeding direction, there is a case where the feeding motor WM is provided near the front end of the welding torch 4. Further, there is also a case where two feed motors WM are used as a push-pull type feed system.

Welding wire 1 is fed into welding torch 4 by rotation of feed roller 5 coupled to feed motor WM described above, and arc 3 is generated between welding wire and base material 2. A welding voltage Vw is applied between a power feeding chip (not shown) in the welding torch 4 and the base material 2, and a welding current Iw is applied.

The output voltage setting circuit ER outputs a predetermined output voltage setting signal ER. The output voltage detection circuit ED detects and smoothes the output voltage E, and outputs an output voltage detection signal ED.

The voltage error amplifier circuit EV receives the output voltage setting signal Er and the output voltage detection signal Ed as input signals, amplifies an error between the output voltage setting signal Er (+) and the output voltage detection signal Ed (-) and outputs a voltage error amplification signal EV. By this circuit, the welding power supply is subjected to constant voltage control.

The warm-start current setting circuit IHR outputs a predetermined warm-start current setting signal IHR. The current detection circuit ID detects the welding current Iw and outputs a current detection signal ID.

The current error amplifier circuit EI receives the hot start current setting signal Ihr and the current detection signal Id, amplifies an error between the hot start current setting signal Ihr (+) and the current detection signal Id (-) and outputs a current error amplification signal EI. With this circuit, the welding power source is controlled to be constant current during the period in which the hot start current is supplied (hot start period).

The current-application determination circuit CD receives the current detection signal Id as an input, determines that the welding current Iw is applied when the current detection signal Id is equal to or greater than a threshold value (about 10A), and outputs a high-level current-application determination signal CD.

The power supply characteristic switching circuit SW receives the current error amplification signal Ei, the voltage error amplification signal Ev, and the current conduction determination signal Cd as inputs, outputs the current error amplification signal Ei as an error amplification signal Ea during a predetermined warm-up period from a time when the current conduction determination signal Cd changes to a high level (conduction), and outputs the voltage error amplification signal Ev as an error amplification signal Ea during the other periods.

The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal VD. The short circuit determination circuit SD receives the voltage detection signal Vd as an input, and outputs a short circuit determination signal SD that determines that the short circuit period is a short circuit period and becomes high when the value of the voltage detection signal Vd is lower than a short circuit determination value (about 10V), and that determines that the short circuit period is an arc period and becomes low when the value is equal to or higher than the short circuit determination value (about 10V).

The welding start circuit ST outputs a welding start signal ST at a high level when the welding power supply is started. The welding start circuit ST corresponds to a start switch of the welding torch 4, a control device of the welding process, a robot control device in the case of using a welding robot, and the like.

The drive circuit DV receives the error amplification signal Ea and the welding start signal St as input, performs PWM modulation control based on the error amplification signal Ea when the welding start signal St is at a high level (welding start), and outputs a drive signal DV for driving the inverter circuit in the power supply main circuit PM.

The initial period timer circuit STI receives the welding start signal St and the current application determination signal Cd as input, and outputs an initial period timer signal STI that is at a high level when the welding start signal St changes to a high level (welding start) and at a low level when the current application determination signal Cd changes to a high level (application).

The determination circuit HD receives the initial period timer signal Sti as an input, and outputs a determination signal HD which becomes high when an elapsed time from a time point when the initial period timer signal Sti changes to high level (initial period) is equal to or longer than a reference time, and becomes low when the initial period timer signal Sti changes to low level. The reference time is set to a time from a time point when feeding of wire 1 is started (a start time point of the initial period) until the tip of wire 1 collides with base material 2 repeatedly a plurality of times. Therefore, the timing at which the determination signal Hd changes to the high level is a case where the state in which the slag is not removed continues even if the tip of the welding wire 1 repeatedly collides with the base material 2 a plurality of times. The time until welding wire 1 and base material 2 first collide is, for example, about 0.5 seconds. The time for repeating the collision 50 times is, for example, about 0.5 second. In this case, the reference time is set to 0.5+0.5=1.0 seconds. In practice, the initial time is set to about 0.5 to 2.0 seconds.

The steady forward feed peak value setting circuit FSCR outputs a steady forward feed peak value setting signal FSCR determined in advance. The stabilized backfeed peak value setting circuit FRCR outputs a predetermined stabilized backfeed peak value setting signal FRCR.

The stable welding period feed speed setting circuit FCR receives the short-circuit discrimination signal Sd, the stable forward feed peak value setting signal Fscr, and the stable backward feed peak value setting signal Frcr as input, switches the forward feed period and the backward feed period based on the short-circuit discrimination signal Sd, and outputs a stable welding period feed speed setting signal FCR of a trapezoidal wave formed by a stable forward feed peak value Fsc determined based on the stable forward feed peak value setting signal Fscr and a stable backward feed peak value Frc determined based on the stable backward feed peak value setting signal Frc. The feed speed setting signal Fcr during stable welding is detailed in fig. 2.

The initial forward feed peak value setting circuit FSIR receives the above-described discrimination signal Hd as an input, and outputs an initial forward feed peak value setting signal FSIR which becomes a predetermined standard value when the discrimination signal Hd is at a low level and becomes a predetermined increased value when the discrimination signal Hd is at a high level. Standard value < added value. Therefore, when the value is switched to the increased value, the value of the initial forward feed peak value setting signal Fsir increases, and the amplitude of the feed speed Fw increases.

The initial reverse feeding peak value setting circuit FRIR receives the above-described discrimination signal Hd as an input, and outputs an initial reverse feeding peak value setting signal FRIR which becomes a predetermined standard value when the discrimination signal Hd is at a low level and becomes a predetermined increment value when the discrimination signal Hd is at a high level. Standard value < added value. Therefore, when the initial reverse feed peak value setting signal Frir is switched to the increased value, the absolute value of the initial reverse feed peak value setting signal Frir increases, and the amplitude of the feed speed Fw increases.

The initial frequency setting circuit SIR receives the above-described discrimination signal Hd as an input, and outputs an initial frequency setting signal SIR that becomes a predetermined standard value when the discrimination signal Hd is at a low level and becomes a predetermined increased value when the discrimination signal Hd is at a high level. The initial frequency setting signal Sir is a signal for setting the frequency of the forward feed period and the reverse feed period in the switching initial period. Standard value < added value. Therefore, if the value is switched to the increased value, the value of the initial frequency setting signal Sir is increased.

The initial time ratio setting circuit DIR receives the above-described discrimination signal Hd as an input, and outputs an initial time ratio setting signal DIR which becomes a predetermined standard value when the discrimination signal Hd is at a low level and becomes a predetermined increment value when the discrimination signal Hd is at a high level. The initial time ratio setting signal Dir sets the time ratio of the forward feeding period to the reverse feeding period in the initial period. Time ratio = (time length of forward feeding period)/(time length of forward feeding period + reverse feeding period). That is, the time ratio of the forward feed period in 1 cycle determined by the reciprocal 1/Sir of the initial frequency setting signal Sir is set. Therefore, the time length during forward feed = Dir/Sir, and the time length during reverse feed = (1-Dir)/Sir. In the above, the standard value < the added value. As a result, when the value is switched to the increased value, the average value of the feed speed Fw increases because the ratio of the forward feed period increases.

The initial period feed speed setting circuit FIR receives the initial forward feed peak value setting signal Fsir, the initial backward feed peak value setting signal Frir, the initial frequency setting signal Sir, and the initial time ratio setting signal Dir as inputs, and outputs a trapezoidal wave initial period feed speed setting signal FIR which determines the forward feed period and the backward feed period based on the initial frequency setting signal Sir and the initial time ratio setting signal Dir, determines the initial forward feed peak value Fsi based on the initial forward feed peak value setting signal Fsir, and determines the initial backward feed peak value Fri based on the initial backward feed peak value setting signal Frir. The initial period feed speed setting signal Fir is detailed in fig. 2.

The feed rate setting circuit FR receives the steady welding period feed rate setting signal Fcr, the initial period feed rate setting signal Fir, and the initial period timer signal Sti as inputs, outputs the initial period feed rate setting signal Fir as the feed rate setting signal FR in an initial period in which the initial period timer signal Sti is at a high level, and outputs the steady welding period feed rate setting signal Fcr as the feed rate setting signal FR in a steady welding period in which the initial period timer signal Sti is at a low level.

The feed control circuit FC receives the welding start signal St and the feed speed setting signal Fr as input signals, and outputs 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 to the feed motor WM when the welding start signal St is at a high level (start of welding).

Fig. 2 is a timing chart of signals at the start of welding in the welding power supply of fig. 1, which shows the arc welding control method according to embodiment 1 of the present invention. Fig. a shows a time change of the welding start signal St, fig. B shows a time change of the feed speed Fw, fig. C shows a time change of the welding current Iw, fig. D shows a time change of the welding voltage Vw, fig. E shows a time change of the current conduction determination signal Cd, fig. F shows a time change of the short circuit determination signal Sd, fig. G shows a time change of the initial period timer signal Sti, fig. H shows a time change of the wire tip/base material distance Lw, which is a distance between the wire tip and the base material surface, and fig. I shows a time change of the determination signal Hd. The operation of each signal at the start of welding will be described below with reference to this drawing.

As shown in fig. B, the feed speed Fw is a forward feed period above 0 and a reverse feed period below 0. The feed rate Fw is controlled by the initial period feed rate setting signal Fir in fig. 1 in the initial period Ti, and the forward feed period and the reverse feed period are switched at a predetermined frequency. On the other hand, the feed speed Fw is controlled by the steady welding period feed speed setting signal Fcr in fig. 1 during the steady welding period Tc, and the forward feed period and the reverse feed period are switched in synchronization with the short circuit period and the arc period. The feed speed Fw changes in a trapezoidal wave shape. The average value of the feed speed Fw is positive, and the wire 1 is fed forward on average.

At time t1 when welding starts, the tip of wire 1 is separated from the surface of base material 2, and thus, as shown in fig. (H), wire tip/base material distance Lw is a positive value. The value of Lw at time t1 is about 2 to 20 mm. A period from a time t1 when the welding start signal St is at a high level shown in fig. a to a time t7 when the current application determination signal Cd is at a high level shown in fig. E is an initial period Ti, and the subsequent period is a stable welding period Tc.

[ operation of initial period Ti from time t1 to t7 ]

At time t1, when welding start signal St changes to high level (welding start) as shown in fig. a, initial period timer signal Sti changes to high level to start initial period Ti as shown in fig. G. At the same time, since the welding power source is activated, welding voltage Vw is a no-load voltage value of the maximum output voltage value (about 70V) as shown in (D) of the figure. Since the tip of welding wire 1 is separated from the surface of base material 2, welding current Iw is not applied as shown in fig. (C) of the drawing. At the same time, as shown in fig. B, feeding of the welding wire 1 is started.

As shown in fig. B, forward and reverse feed control is performed in which a forward feed period and a reverse feed period are alternately repeated at a predetermined initial frequency Si [ Hz ] with respect to the feed rate Fw in the initial period Ti. The initial frequency Si is set by a standard value (about 100 Hz) of the initial frequency setting signal Sir shown in fig. 1. The forward feed period and the reverse feed period in the initial period are set by the reference values of the initial frequency setting signal Sir and the reference value (about 55%) of the initial time ratio setting signal Dir in fig. 1.

The feed rate Fw in the forward feed period from time t1 to time t2 is accelerated at a predetermined rate of change from 0, and is maintained at the predetermined initial forward feed peak value Fsi, and is decelerated at a predetermined rate of change to 0 after the predetermined period has elapsed. The initial forward feed peak value Fsi is set by a standard value (about 25 m/min) of the initial forward feed peak value setting signal Fsir of fig. 1. The feed rate Fw in the backward feed period from time t2 to time t3 is accelerated at a predetermined rate of change from 0, and is maintained at a predetermined negative initial backward feed peak value Fri, and is decelerated at a predetermined rate of change to 0 when a predetermined period elapses. The initial reverse feeding peak value Fri is set by a standard value (-21 m/min or so) of the initial reverse feeding peak value setting signal Frir in fig. 1. The period from time t1 to t3 is 1 cycle, and is the reciprocal 1/Si of the initial frequency Si.

As shown in fig. H, the wire tip/base material distance Lw gradually becomes shorter in the forward feeding period from time t1 to time t2, and gradually becomes longer in the reverse feeding period from time t2 to time t 3. However, the value of Lw at time t3 is shorter than the value of Lw at time t 1. This is because the waveform parameters are adjusted so that the average value of the feed speed Fw per cycle is a positive value. The same operations as described above are repeated in the period from time t3 to t 4. In the figure, 2 cycle parts from time t1 to t4 are depicted, but in reality, this period is several tens of cycles until the first collision occurs.

As shown in fig. B, when the tip of wire 1 comes into contact with (collides with) the surface of base material 2 at time 41 in the forward feeding period from time t4 to t42, wire tip/base material distance Lw =0 as shown in fig. H. However, the slag adheres to the tip of the welding wire 1, and therefore, the welding wire is in a non-conductive contact state. Therefore, as shown in fig. C, welding current Iw is not applied, and as shown in fig. D, welding voltage Vw is still at the no-load voltage value. The wire tip/base material distance Lw during the forward feeding period from time t41 to t42 is still 0. In the subsequent reverse feeding period from time t42 to time t5, the wire tip/base material distance Lw gradually increases from 0. In the figure, one cycle is depicted from time t4 to t5, but in reality, this period is several tens of cycles. In addition, since there is play in the feeding path also in the short-circuiting period of welding wire 1 and base material 2, the waveform of feeding speed Fw in this period is still a trapezoidal wave. When slag adheres little or hardly, an arc is often generated by first or several times of collision between welding wire 1 and base material 2.

At time t5, when the elapsed time from the start time of the initial period Ti at time t1 is equal to or longer than a predetermined reference time, as shown in (I) of the figure, it is determined that the state in which slag is not removed continues and the determination signal Hd changes to the high level. Accordingly, as shown in fig. B, the waveform parameter of the feed rate Fw changes as follows, and the amplitude and/or the average value increases by about 1.2 to 1.5 times. The initial forward feeding peak value Fsi increases to the increased value of the initial forward feeding peak value setting signal Fsir of fig. 1, the initial backward feeding peak value Fri increases to the increased value of the initial backward feeding peak value setting signal Frir of fig. 1, the initial frequency Si increases to the increased value of the initial frequency setting signal Sir of fig. 1, and the initial time ratio Di increases to the increased value of the initial time ratio setting signal Dir of fig. 1. These waveform parameters need not all be increased to an increased value, but at least one change may be an increased value so that the amplitude and/or average value of the feed speed Fw is increased. As shown in fig. B, when the tip of wire 1 comes into contact with (collides with) the surface of base material 2 at time 51 in the forward feed period from time t5 to time t52, wire tip/base material distance Lw =0 as shown in fig. H. However, since slag adheres to the tip of the welding wire 1, the non-conductive contact state continues. Therefore, as shown in fig. C, welding current Iw is not applied, and as shown in fig. D, welding voltage Vw remains at the no-load voltage value. The wire tip/base material distance Lw in the forward feeding period from time t51 to t52 remains 0. In the subsequent backward feeding period from time t52 to time t6, the wire tip/base material distance Lw gradually increases from 0. In the figure, one cycle is depicted from time t5 to t6, but in practice, this period is several cycles to several tens of cycles until the arc is generated. During this period, since the amplitude and/or the average value of the feed rate Fw increases, the impact at the time of collision between the tip of welding wire 1 and base material 2 becomes strong, and the slag removing effect increases. As a result, even when the adhesion state of the slag is relatively severe, the slag can be effectively removed. However, in this way, stress of the feed motor WM shown in fig. 1 may increase and the life may be shortened. Therefore, the amplitude and/or average value of the feed speed Fw is not increased from the first time, and is increased only when the reference time elapses. When the adhesion state of the slag is severe, an arc is often generated by a plurality of collisions until the reference time elapses.

As shown in fig. B, when the tip of wire 1 comes into contact with (collides with) the surface of base material 2 again at time t7 in the forward feeding period from time t6, wire tip/base material distance Lw =0 as shown in fig. H. Since the slag adhering to the tip of the welding wire 1 is scraped off and removed by the collision until the previous cycle, the current contact is in an on-contact state (short-circuit state). Therefore, welding current Iw starts to be supplied as shown in fig. C, and welding voltage Vw decreases from the no-load voltage value to a short-circuit voltage value of several V as shown in fig. D. Accordingly, at time t7, since the current-carrying determination signal Cd becomes high (carrying) as shown in (E) of the figure, the initial period timer signal Sti changes to low as shown in (G) of the figure, and the initial period Ti ends. At the same time, as shown in (I) of the figure, the discrimination signal Hd also changes to the low level. At time t7, as shown in fig. F, the short determination signal Sd becomes high (short circuit).

[ operation of Stable welding period Tc after time t7 ]

When the short-circuit state is established at time t7, welding current Iw having a predetermined hot start current value (about 200 to 500A) is applied as shown in fig. C. The hot start current is supplied during a predetermined hot start period from time t7 to t 91.

At time t8 when a predetermined delay period has elapsed since the current application determination signal Cd changed to the high level at time t7, the feed speed Fw is switched from the forward feed to the backward feed as shown in (B) of the figure, and is rapidly accelerated to and maintained at the predetermined steady backward feed peak value Frc. The delay period is set to about 1 to 10 ms. The delay period may be set to 0 so as not to delay. This delay is provided to smoothly generate an initial arc when welding wire 1 contacts base material 2.

When the arc 3 is generated by the above-described energization of the hot start current at time t9, the welding voltage Vw rapidly increases to an arc voltage value of several tens V as shown in (D) of the figure, and accordingly, the short circuit determination signal Sd changes to a low level (arc) as shown in (F) of the figure. When the short circuit determination signal Sd changes to a low level (arc) in the reverse feeding peak period, the feeding speed Fw starts to transition to the forward feeding period as shown in (B) of the figure. The feed rate Fw is decelerated at a predetermined rate of change from time t9 to become 0 at time t 10. At time t91 during the reverse feed deceleration, as shown in (C) of the figure, the welding current Iw is reduced from the hot start current value to an arc current value that varies according to the arc load. As described above, since the warm-up period from time t7 to time t91 is a predetermined value, it is not determined which period the feed speed Fw is in at the time when the warm-up period ends. The period from time t9 to t11 is an arc period.

The forward feed period is advanced from time t10, accelerated from 0 at a predetermined rate of change, and maintained at a predetermined steady forward feed peak value Fsc. When a short circuit occurs at time t11 in the forward feed peak period, welding voltage Vw rapidly decreases to a short-circuit voltage value of several V as shown in (D) of the figure, and short-circuit determination signal Sd changes to a high level (short circuit) as shown in (F) of the figure. Accordingly, as shown in (B) of the figure, the feed speed Fw starts to transition to the reverse feed period. The feed rate Fw is decelerated to 0 at a predetermined rate of change in the period from time t11 to t 12. As shown in fig. C, the welding current Iw gradually increases during the short circuit period from time t11 to time t 13.

The backward feed period is started from time t12, and the acceleration is accelerated from 0 at a predetermined rate of change, and the value is maintained when the steady backward feed peak value Frc reaches a predetermined value. When an arc is generated by the backward feeding at time t13, welding voltage Vw rapidly increases to an arc voltage value of several tens V as shown in fig. D, and short circuit determination signal Sd changes to a low level (arc) as shown in fig. F. Accordingly, as shown in (B) of the figure, the feed speed Fw starts to transit to the forward feed period. The feed speed Fw is reduced at a predetermined rate of change to 0 during the period from time t13 to t 14. As shown in (C) of the figure, the welding current Iw gradually decreases during the arc period.

The change in the wire tip/base material distance Lw is as follows. First, lw =0 from time t7 when the conductive state (short-circuit state) is established to time t9 when an arc is generated. In the reverse feed deceleration period from time t9 to t10, the value of Lw gradually increases from 0. In the forward feed period from time t10 to t11, the value of Lw becomes shorter and 0. During the period from time t11 to t13, lw is still 0. During the reverse feed deceleration period from time t13 to t14, the value Lw gradually increases.

According to embodiment 1, when the state in which it is determined that slag is not removed continues in the initial period, the amplitude and/or the average value of the feed rate is increased in the subsequent initial period. The determination is performed based on the elapsed time of the initial period being equal to or longer than the reference time. Since the adhesion state of slag is severe, there is a case where no arc is generated even if the collision of the welding wire with the base material is repeated several times. In the present embodiment, when such a state is determined, the amplitude and/or the average value of the feed rate is increased to increase the impact of collision and increase the slag removal effect. As a result, in the present embodiment, even when the adhesion state of the slag is severe, the arc starting can be reliably performed.

[ embodiment 2]

The invention of embodiment 2 is to determine the timing at which the amplitude and/or average value of the feed speed is increased in the initial period based on the torque of the feed motor becoming equal to or greater than the reference torque.

Fig. 3 is a block diagram of a welding power supply for implementing the arc welding control method according to embodiment 2 of the present invention. This figure corresponds to fig. 1 described above, and the same reference numerals are given to the same blocks, and the description thereof will not be repeated. In this figure, a motor current detection circuit IMD is added to fig. 1, and the discrimination circuit HD of fig. 1 is replaced with a 2 nd discrimination circuit HD2. These blocks will be described below with reference to the drawing.

The motor current detection circuit IMD detects a motor current of the feed motor WM and outputs a motor current detection signal IMD. Since the motor current detection signal Imd is in a proportional relationship with the torque of the feed motor WM, the torque is detected.

The 2 nd discrimination circuit HD2 receives the initial period timer signal Sti and the motor current detection signal Imd, performs the following process (1) or (2), and outputs a discrimination signal HD.

(1) When the initial period timer signal Sti is at a high level, the collision between the welding wire 1 and the base material 2 is determined based on the change in the value of the motor current detection signal Imd to a reference current value (reference torque) or more. Then, a determination signal Hd is output which becomes high when a predetermined time (about 0.5 to 1.5 seconds) has elapsed from the determination of the first collision, and becomes low when the initial period timer signal Sti changes to low.

(2) When the initial period timer signal Sti is at a high level, the collision between the welding wire 1 and the base material 2 is determined based on the change in the value of the motor current detection signal Imd to a reference current value (reference torque) or more. Then, a determination signal Hd is output which becomes high when the number of times of determination of collision reaches a predetermined number (about 50 to 150 times) and becomes low when the initial period timer signal Sti changes to low.

The timing chart of each signal in fig. 3 is the same as that in fig. 2 described above, and therefore is omitted. However, the point that the determination at time t5 when the determination signal Hd becomes high level is determined by the 2 nd determination circuit Hd2 is different.

According to embodiment 2 described above, in the initial period, the determination of the timing at which the amplitude and/or the average value of the feed speed is increased is performed based on the torque of the feed motor becoming equal to or greater than the reference torque. In this way, even if the welding wire collides with the base material a predetermined number of times but no arc is generated, the amplitude and/or average value of the feeding speed is increased, and therefore, the stress on the feeding motor can be suppressed to the minimum necessary. Further, since the variation in time to the first collision due to the variation in the wire tip/base metal distance at the start of feeding is not affected, the time required for starting the arc can be shortened, and productivity can be improved.

Claims (3)

1. An arc welding control method for performing forward/reverse feed control in which a feed speed is alternately switched between a forward feed period and a reverse feed period in an initial period from a feed start timing of a welding wire to an energization start timing of a welding current at the start of welding,

if it is determined that the state in which slag is not removed continues during the initial period, the amplitude and/or the average value of the feed rate is increased during the initial period thereafter.

2. The arc welding control method according to claim 1,

the determination is performed based on the elapsed time of the initial period being equal to or longer than a reference time.

3. The arc welding control method according to claim 1,

the determination is performed based on the torque of the feed motor becoming equal to or greater than the reference torque during the initial period.

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