JP2002178145A - Arc start control method and welding power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the bead appearance of an arc start part becomes bad because time is spent for the shift from an initial arc 3a to a stationary arc 3b, in an arc start control method wherein a welding wire 1 is advanced to an object 2 to be welded when a welding start signal St is inputted, an initial current Is of a small current value is made to flow at a time point when the welding wire 1 comes into contact with the object 2 to be welded and also the welding wire 1 is withdrawn from the object 2 to be welded to feed, the welding wire 1 is advanced again at a stationary speed Wfs and also a stationary welding current Iw is made to flow when the welding wire 1 leaves the object 2 to be welded by the withdrawal feeding and the initial arc 3a is generated. SOLUTION: In the arc start control method, withdrawal feeding is continued even after the initial arc 3a is generated, and advance feeding is performed again at a time when a distance Lw between the wire tip and the object to be welded reaches a withdrawing distance setting value Ls which is decided so as to become nearly equal to the arc length Lwc of the stationary arc 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a consumable electrode gas shielded arc welding system in which a welding wire is fed forward and backward by a wire feed motor capable of forward and reverse rotation to start an arc. It relates to a start control method.

[0002]

2. Description of the Related Art A wire feed motor is rotated forward to feed a welding wire forward to a workpiece, and when it is determined that the welding wire has come into contact with the workpiece, the wire feeding motor is rotated in a reverse direction. The welding wire is fed backward, and at the same time, an initial current Is having a small current value is supplied. When an initial arc is generated by the feeding backward, the welding wire is fed forward again at a constant feed speed Wfs, and at the same time, a steady feed is performed. Conventionally, an arc start control method of consumable electrode gas shielded arc welding in which a welding current Iw is supplied to start an arc is known. Hereinafter, this conventional arc start control method will be described with reference to FIGS.

FIG. 2 is a schematic diagram showing a welding wire feeding system. The welding wire 1 is fed through the welding torch 4 by a feed roll 5a directly connected to the wire feed motor WM. When the wire feed motor WM rotates forward, the welding wire 1 is fed forward to the workpiece 2, and when the wire feed motor WM rotates reversely, the welding wire 1 is fed backward from the workpiece 2. The welding voltage Vw from the welding power supply PS is supplied to the welding wire by the contact tip 4a attached to the tip of the welding torch 4. The shortest distance between the tip of the welding wire 1 and the work 2 is the distance Lw [mm] between the wire tip and the work.

FIG. 3 is a block diagram of a welding power supply for implementing the above-described conventional arc start control method. Hereinafter, each circuit block will be described with reference to FIG.

The voltage detection circuit VD detects a welding voltage Vw and outputs a voltage detection signal Vd. The short-circuit / arc discrimination circuit SA receives the voltage detection signal Vd as input and outputs a short-circuit signal when the welding wire 1 and the workpiece 2 are in contact with each other, an arc generation signal when an arc is generated, It is output as a short circuit / arc determination signal Sa. Delay circuit DT
Is a delay signal Dt which becomes High level for a predetermined delay time Td, triggered by the change of the short-circuit / arc determination signal Sa from the short-circuit signal to the arc generation signal.
Is output.

[0006] The steady feed speed setting circuit WS outputs a steady feed speed setting signal Ws. The feed control circuit FC
When a welding start signal St is input from outside, the welding wire 1 is forwardly fed to the workpiece 2 at an initial feed speed Wfi corresponding to a predetermined initial feed speed set value Wi, and then the short circuit described above is performed. When the / arc discrimination signal Sa becomes a short-circuit signal, the welding wire 1 is fed backward from the work piece 2 at the backward feeding speed Wfr corresponding to the predetermined backward feeding speed set value Wr, and subsequently the above-described operation is performed. When the output of the delay signal Dt ends, the feed control signal Fc for feeding the welding wire 1 forward to the workpiece 2 again at the steady feed speed Wfs corresponding to the steady feed speed setting signal Ws is sent to the workpiece 2 again. Output. The wire feed motor WM is
As described above in the description of FIG. 2, the welding wire 1 is fed forward or backward in accordance with the feed control signal Fc.

The voltage setting circuit VS outputs a voltage setting signal Vs for setting the welding voltage Vw of the welding power supply PS. The output control circuit INV receives commercial power as an input,
A welding voltage Vw and a welding current Iw suitable for maintaining the arc 3 stably by inverter control, thyristor phase control, and the like are output. The output control circuit INV has a constant current characteristic in which an initial current Is having a predetermined small current value is supplied from the time when the welding start signal St is input from the outside to the time when the output of the delay signal Dt ends. Alternatively, a drooping characteristic is formed, and thereafter, a constant voltage characteristic corresponding to the above-described voltage setting signal Vs for applying a steady welding current Iw corresponding to the value of the above-described steady feeding speed setting signal Ws is formed.

FIG. 4 shows the welding power supply device PS described in FIG.
3 is a timing chart of each signal of FIG. FIG. 7A shows the time change of the welding start signal St, and FIG. 7B shows the time change of the feed control signal Fc, and FIG.
Indicates a time change of the short circuit / arc discrimination signal Sa,
FIG. 3D shows the time change of the delay signal Dt, FIG. 3E shows the time change of the welding current Iw, and FIG. 3F shows the change of the distance Lw between the wire tip and the workpiece. The time change is shown, and FIGS. (G1) to (G5) show the feeding state of the welding wire 1 at each time. Hereinafter, description will be made with reference to FIG.

[0009] At time t1 at time t1 to t2, when a welding start signal St is externally input as shown in FIG. 1A, a feed control signal Fc is output as shown in FIG. Is a positive initial feed speed set value Wi, and as shown in FIG.
Is fed forward to the workpiece 2 at the initial feed rate Wfi. When the feed control signal Fc has a positive value, forward feed is performed, and when the feed control signal Fc has a negative value, reverse feed is performed. At the same time, as described above in the description of FIG. 3, the output control circuit INV forms a constant current characteristic or a drooping characteristic, and applies a no-load voltage (not shown) as the welding voltage Vw. next,
During the period from time t1 to t2,
As shown in FIG. 4F, the distance Lw between the wire tip and the workpiece is gradually reduced.

[0010] Period from time t2 to t3 At time t2, when the welding wire 1 comes into contact with the workpiece 2 by forward feeding as shown in FIG. 2G, a short circuit occurs as shown in FIG. The / arc discrimination signal Sa changes to a short circuit signal (High level). When the short-circuit / arc discrimination signal Sa changes to a short-circuit signal, the feed control signal Fc becomes a negative backward feed speed set value Wr, as shown in FIG. 2, the sheet is fed backward at the backward feeding speed Wfr. At the same time, the initial current Is having a small current value flows due to the constant current characteristic or the drooping characteristic described above in FIG. The reason for setting the value of the initial current Is to a small current value of about 50 [A] is to prevent the welding wire 1 from being melted by the initial current Is and welded to the workpiece 2. Next, during the period from the time t2 to the time t3, the welding wire 1 is fed backward, but the response delay time of the forward / reverse reversal of the wire feeding motor WM described above with reference to FIG. The welding wire 1 and the workpiece 2 remain in contact with each other due to the time required for the backward feeding of the play due to the bending. Therefore, as shown in FIG. 5F, the distance Lw between the tip of the wire and the workpiece remains 0 [mm] during this period.

[0011] At time t3, at time t3, when the welding wire 1 and the workpiece 2 are not brought into contact with each other due to the backward feeding as shown in FIG. 3G, the initial current Is is supplied. An initial arc 3a occurs. It is determined that the initial arc 3a has occurred, and as shown in FIG.
a changes from the short-circuit signal (High level) to the arc generation signal (Low level). With this change as a trigger, the delay signal Dt is output (High) during a predetermined delay time Td (time t3 to t4) as shown in FIG.
Level). During the backward feeding time Tr from time t3 to time t4 when the delay signal Dt is output, FIG.
As shown in (2), the backward feeding is continued while the initial arc occurrence state 3a is maintained. Therefore, FIG.
As shown in (1), the distance Lw between the tip of the wire and the workpiece becomes gradually longer.

[0012] At time t4, at time t4, when the output of the delay signal Dt is completed as shown in FIG. 3D, the transmission control signal Fc becomes positive as shown in FIG. Value steady feed rate setting signal Ws
Thus, the welding wire 1 is again fed forward to the workpiece 2 at a constant feed speed Wfs. At the same time, as described above in the description of FIG. 3, the output control circuit INV forms a constant voltage characteristic and supplies a large steady welding current Iw corresponding to the steady feeding speed Wfs. Further, as shown in FIG. 4F, the distance Lw between the wire tip and the workpiece is set at time t4.
Distance between the tip of the wire and the work to be welded during re-feeding
From wt [mm], at the time t5 after the convergence time Tc1 [s] elapses due to the application of the steady welding current Iw, a steady arc length (steady distance between the wire tip and the workpiece) Lwc.
It converges to [mm]. Accordingly, during this period, the state shifts from the initial arc generation state 3a shown in FIG. (G4) to the steady arc generation state 3b shown in FIG.

[0013]

The above-described prior art arc start control method has the following two problems to be solved for smoothly shifting from the initial arc generation state to the steady arc generation state. First Problem to be Solved As described above with reference to FIG. 4, during the period of the backward feeding at the backward feeding speed Wfr (time t3 to t4), the welding wire and the workpiece are not brought into contact again, In addition, it is necessary to continue the backward feeding while maintaining the initial arc generation state stably without causing arc breakage. The reason is that if re-contacting occurs after the initial arc is generated, the welding wire and the workpiece are likely to be welded to each other, so that the arc cannot be started. Also, if an arc break occurs during this period, the arc does not occur for a long time until the welding wire comes into contact with the workpiece again due to the re-advanced feeding, and as a result, the bead appearance at the arc start portion becomes poor. Because.

In order to prevent the above re-contact, it is necessary to increase the backward feeding speed Wfr in order to quickly increase the distance Lw between the wire tip and the workpiece after the initial arc is generated.
On the other hand, in order to prevent the occurrence of the arc break, the maximum value of the backward feeding speed Wfr is limited in accordance with the type of the shielding gas, the diameter of the welding wire, the thickness of the workpiece, and the like. Therefore, it is necessary to set the retreating feed speed Wfr to an appropriate value that does not cause re-contact or arc break according to the type of the shielding gas, the diameter of the welding wire, the plate thickness of the workpiece, and the like. For example, if the type of the shielding gas is carbon dioxide 10
In the case of 0 [%], arc breakage is more likely to occur than in the case of a mixed gas of carbon dioxide gas 20 [%] + argon gas 80 [%]. .

However, as described above with reference to FIG. 4, in the prior art, the delay time Td for performing the reverse feed is a constant value. Wire tip during forward feeding
The distance Lwt between the workpieces changes. Due to this change, when the difference between the wire tip-to-be-welded distance Lwt and the steady arc length Lwc at the time of the re-forward feeding becomes large, the convergence time required for the transition from the initial arc generating state to the steady arc generating state. Since Tc1 is long, there is a problem that the bead appearance at the arc start portion is deteriorated.

Second Problem to be Solved The steady-state arc length Lwc shown in FIG. 4F described above depends on the type of the shield gas, the steady-state feed speed Wfs, the plate thickness of the workpiece, and the like. It is set to an appropriate value by the voltage setting signal Vs. Therefore, in order to shorten the convergence time Tc1 required for transition from the initial arc generation state to the steady arc generation state and improve the bead appearance at the arc start portion,
Depending on the type of the shielding gas, the steady feed speed Wfs, the thickness of the work to be welded, and the like, the distance between the wire tip and the work to be welded is determined so that the difference from the steady arc length Lwc is reduced. It is necessary to control the distance Lwt to an appropriate value.

However, in the prior art, when the backward feeding speed Wfr is determined to be an appropriate value for the reason described above, the delay time Td is a constant value. The distance Lwt between objects becomes a constant value and cannot be controlled to an arbitrary value. Therefore, in the prior art, even if the setting of the steady arc length Lwc changes, the distance Lwt between the wire tip and the work to be welded at the time of re-advancing feeding cannot be controlled in accordance with the change. There is a problem that it is impossible to prevent the bead appearance at the arc start portion from being deteriorated due to a large convergence time Tc1 due to the large convergence time.

[0018]

According to the first aspect of the present invention, as shown in FIGS. 5 and 6, when a welding start signal St is input, a welding wire 1 is forwardly fed to a workpiece 2. Then, when the welding wire 1 comes into contact with the workpiece 2, an initial current Is having a predetermined small current value is supplied from the welding power supply device PS and the welding wire 1 is fed backward from the workpiece 2. When the welding wire 1 is separated from the workpiece 2 by the backward feeding, an initial arc 3a in which the initial current Is flows is generated, and the initial arc generation state 3a is generated.
Continue the backward feeding while maintaining
When the inter-workpiece distance Lw reaches a predetermined retreat distance set value Ls, the welding wire 1 is again forward-fed to the to-be-welded article 2 at a predetermined steady-state feed speed Wfs, and the above-mentioned steady-state operation is performed. This is an arc start control method for consumable electrode gas shielded arc welding in which a steady welding current Iw corresponding to the feed speed Wfs is applied to smoothly transition from the initial arc generation state 3a to the steady arc generation state 3b.

As shown in FIG. 7, in the invention of claim 2 at the time of filing, the distance Lw between the tip of the wire and the workpiece reaches the retreat distance set value Ls by the retraction feed described in claim 1 of the filing application. 2. The arc start control according to claim 1, wherein the determination is made based on the fact that the welding wire retreat distance Lr obtained by integrating the reciprocating feed rate Wfr from the point of occurrence of the initial arc has reached the retreat distance set value Ls. Is the way.

As shown in FIG. 8, in the invention of claim 3 at the time of filing, the distance Lw between the tip of the wire and the workpiece reaches the retreat distance set value Ls due to the retraction feed described in claim 1 of the filing application. This means that the backward feed time Tr from the initial arc occurrence time is determined by the backward feed time set value Ls and the backward feed feed speed set value Wr.
The arc start control method according to claim 1 at the time of filing of the application, wherein the method is determined by the fact that the temperature has reached the limit.

According to the invention of claim 4 at the time of filing, as shown in FIG. 9, the distance Lw between the tip of the wire and the workpiece reaches the retreat distance set value Ls due to the retraction feed described in claim 1 of the filing application. The welding voltage value Vw in the initial arc generation state.
Is an arc start control method according to claim 1 at the time of application, wherein the determination is made based on reaching a setback voltage set value Vrs determined in correspondence with the setback distance Ls and the set value Is of the initial current.

As shown in FIGS. 5 and 6, the invention of claim 5 at the time of filing applies a wire feed motor WM for feeding the welding wire 1 forward or backward from the work 2 to be welded. When,
A short circuit / arc determining circuit SA for outputting a short circuit signal when the welding wire 1 and the workpiece 2 are in contact with each other and outputting an arc generating signal as a short circuit / arc determining signal Sa when an arc is generated; Distance between tip and work piece Lw
Is equal to a predetermined value of the retreat distance setting signal Ls, a distance discriminating circuit LD that outputs a distance match signal Ld, and when a welding start signal St is input, the welding wire 1 is forwarded to the workpiece 2. And the short-circuit / arc discrimination signal Sa
When the signal becomes a short-circuit signal, the welding wire 1 is fed back from the workpiece 2 and when the distance matching signal Ld is output, the welding wire 1 is fed at a predetermined steady-state feeding speed Wfs. A predetermined small current is supplied between the time when the welding start signal St is input and the time when the distance coincidence signal Ld is output from the retreat distance feeding control circuit FCR for feeding the workpiece 2 forward again. From the output control circuit INV, which forms a constant current characteristic or a drooping characteristic for supplying the initial current Is of a value, and thereafter forms a constant voltage characteristic for supplying a steady welding current Iw corresponding to the steady feeding speed Wfs. When the welding start signal St is inputted, the welding wire 1 is fed forward, and when the short-circuit / arc discrimination signal Sa becomes a short-circuit signal, the initial current Is is supplied and the welding wire 1 is supplied. 1 When the welding wire 1 is separated from the workpiece 2 by the backward feeding, an initial arc 3a through which the initial current Is flows is generated, and the initial arc generating state 3a is maintained. The reverse feed is continued, and when the distance matching signal Ld is output, the welding wire 1 is again fed forward at a steady feeding speed Wfs and the steady welding current Iw is supplied, thereby setting the initial arc. A welding power supply PS for consumable electrode gas shielded arc welding that smoothly transitions from the generation state 3a to a steady arc generation state 3b.

As shown in FIG. 7, the invention of claim 6 at the time of filing is a distance discriminating circuit LD according to claim 5 at the time of filing.
Is the feed speed Wfr of the reverse feed from the point of occurrence of the initial arc.
The welding power supply device PS according to claim 5 at the time of filing, which is a feed speed integration circuit IW that outputs a distance matching signal Ld when the welding wire retreat distance Lr obtained by integrating the above reaches the value of the retreat distance setting signal Ls.

As shown in FIG. 8, the invention of claim 7 at the time of filing is a distance discriminating circuit LD according to claim 5 at the time of filing.
Is the reverse feed time Tr from the point of occurrence of the initial arc, the reverse distance setting signal Ls and the reverse speed feed speed setting value Wr.
The welding power supply device PS according to claim 5 at the time of filing, which is a backward feeding timer circuit TR that outputs a distance coincidence signal Ld when the value of the backward feeding time setting signal Trs determined according to the above is reached.

As shown in FIG. 9, the invention of claim 8 at the time of filing applies a distance discriminating circuit LD according to claim 5 at the time of filing.
Outputs the distance match signal Ld when the welding voltage value Vw in the initial arc occurrence state 3a reaches the value of the retreat distance voltage setting signal Vrs determined according to the retreat distance setting signal Ls and the initial current set value Is. A welding power supply PS according to claim 5 at the time of filing, which is a voltage comparison circuit CM.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One example of an embodiment of the present invention is shown in FIG.
Is input, the welding wire 1 is forwardly fed to the workpiece 2, and when the welding wire 1 comes into contact with the workpiece 2, an initial current Is having a predetermined small current value is supplied to the welding power supply device P.
When the welding wire 1 is separated from the workpiece 2 by the backward feeding, the welding wire 1 is separated from the workpiece 2 by the backward feeding. The backward feeding is continued while the generated initial arc generating state 3a is maintained, and the welding wire 1 is moved when the distance Lw between the wire tip and the workpiece reaches a predetermined retracting distance set value Ls. The forward arc is again fed to the workpiece 2 at a predetermined steady-state feed speed Wfs, and a steady-state welding current Iw corresponding to the steady-state feed speed Wfs is supplied.
This is an arc start control method for consumable electrode gas shielded arc welding that smoothly transitions from a to a steady arc generation state 3b.

[0027]

[Embodiment 1] The invention of Embodiment 1 described below corresponds to the inventions of Claims 1 and 5 at the time of filing. According to the invention of the first embodiment, the distance Lwt between the tip of the wire and the workpiece at the time of re-feeding can be set to an appropriate value corresponding to the steady arc length Lwc by a retreat distance setting signal Ls described later. . Hereinafter, the invention of the first embodiment will be described.

FIG. 5 is a block diagram of a welding power supply device for implementing the arc start control method of the first embodiment.
In this figure, the same circuit blocks as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, the reverse distance setting circuit LS, the distance discriminating circuit LD, the reverse distance feed control circuit FCR, and the output control circuit INV, which are circuit blocks different from those in FIG. 3 surrounded by a dotted line, will be described with reference to FIG.

The retreat distance setting circuit LS outputs a retreat distance setting signal Ls set corresponding to the steady arc length Lwc described above with reference to FIG. The distance discrimination circuit LD outputs a distance coincidence signal Ld when the distance Lw between the wire tip and the workpiece is equal to the value of the retreat distance setting signal Ls. As a method of detecting the distance Lw between the wire tip and the workpiece,
The method described later in Examples 2 to 4, the output control circuit I described above.
When the NV is an inverter control, there is a method in which the pulse width is controlled by the PWM control, and when the NV is a thyristor phase control, a method is performed by the firing phase angle. Reverse distance feed control circuit F
CR is a welding start signal S from outside as in the case of FIG.
When t is input, the initial feed speed W corresponding to the initial feed speed set value Wi predetermined for the welding wire 1 to the workpiece 2 is predetermined.
The feed wire is fed forward by fi, and when the short-circuit / arc discrimination signal Sa becomes a short-circuit signal, the reverse feed speed Wfr corresponding to the preset reverse feed speed set value Wr from the workpiece 2 to the welding wire 1 is obtained. 3, and when the distance matching signal Ld is output, unlike the case of FIG. 3, the welding wire 1 is again fed to the workpiece 2 at a steady state corresponding to the steady feeding speed setting signal Ws. Feed control signal Fc for forward feed at feed speed Wfs
Is output. The output control circuit INV starts the distance matching signal L from the time when the welding start signal St is input from the outside.
Until the time point when d is output, a constant current characteristic or a drooping characteristic for supplying an initial current Is having a predetermined small current value is formed, and thereafter, it corresponds to the value of the above-mentioned steady feed speed setting signal Ws. A constant voltage characteristic corresponding to the voltage setting signal Vs for applying the steady welding current Iw is formed.

FIG. 6 is a timing chart of each signal in the welding power supply device PS of the first embodiment. FIG. 6A shows the time change of the welding start signal St, and FIG. 6B shows the time change of the feed control signal Fc.
FIG. 9C shows the time change of the short circuit / arc discrimination signal Sa, FIG. 9D shows the time change of the distance matching signal Ld, and FIG. 10E shows the time change of the welding current Iw. (F) shows the distance L between the tip of the wire and the workpiece.
The graph (G1) to (G5) show the feeding state of the welding wire 1 at each time.
The operation in the period from time t1 to time t3 in FIG. 9 is the same as the operation at the same time in FIG. Hereinafter, time t4 in FIG. 4 corresponding to time t4 in FIG.
1 and the operation at time t51 in FIG. 4 corresponding to time t5 in FIG. 4 will be described with reference to FIG.

At the time t41 from the time t41 to the time t51, as shown in FIG. 4F, the distance Lw between the tip of the wire and the work to be welded by the backward feeding at the backward feeding speed Wfr is set to the above-mentioned backward distance setting signal. When the value becomes equal to the value of Ls, as shown in FIG.
Is output (High level). When the distance matching signal Ld is output, the feed control signal Fc becomes the value of the steady feed speed setting signal Ws, as shown in FIG.
The welding wire 1 is again fed forward to the workpiece 2 at a steady feed rate Wfs. At the same time, the output control circuit INV described above with reference to FIG. 5 forms a constant voltage characteristic, and supplies a steady welding current Iw having a large current value corresponding to the steady feed speed Wfs. Further, as shown in FIG. 4F, the distance Lw between the wire tip and the work to be welded is equal to the value of the retreat distance setting signal Ls at time t41, and the wire tip and the work to be welded at the time of re-forward feeding. The distance becomes Lwt [mm], and at time t51, it becomes the steady arc length Lwc [mm]. At this time, as described above, since the retreat distance setting signal Ls is set to a value substantially equal to the steady arc length Lwc, the distance Lwt between the wire tip and the work to be welded at the time of the re-forward feeding is set to the value described above. Is smaller than the steady arc length Lwc of FIG.
Is shorter than the convergence time Tc1 in the prior art. Therefore, from the initial arc generation state 3a shown in FIG. (G4) to the steady arc generation state 3 shown in FIG.
b smoothly transitions in a short time.

[Embodiment 2] The invention of Embodiment 2 described below corresponds to the inventions of Claims 2 and 6 at the time of filing. The invention of the second embodiment is based on the fact that the distance Lw between the tip of the wire and the workpiece reaches the value of the retreat distance setting signal Ls due to the retreat feed described in the description of the first embodiment. This is an arc start control method according to the first embodiment in which the welding wire retreat distance Lr obtained by integrating the feed speed Wfr of the retraction feed reaches the above-described retreat distance set value Ls. Hereinafter, the invention of the second embodiment will be described.

FIG. 7 is a block diagram of a welding power supply device for implementing the arc start control method of the second embodiment.
In this figure, the same circuit blocks as those in FIG. 5 described above are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, the feeding speed detecting circuit WD and the feeding speed integrating circuit IW, which are circuit blocks different from those in FIG. 5 surrounded by a dotted line, will be described with reference to FIG.

The feed speed detecting circuit WD detects the feed speed Wf and outputs a feed speed detection signal Wd. As the detection method, a method of attaching an encoder to the wire feed motor WM and detecting the output signal of the encoder with an encoder,
A method of detecting by the armature voltage of the wire feed motor WM proportional to the feed speed Wf is commonly used. The feed speed integration circuit IW is a circuit that replaces the distance determination circuit LD described above with reference to FIG. 5, and is used during the reverse feed period from the time when the short circuit / arc determination signal Sa changes from the short circuit signal to the arc generation signal. When the welding wire retreat distance Lr obtained by integrating the above-described feed speed detection signal Wd reaches the value of the retreat distance setting signal Ls, a distance coincidence signal Ld is output. The integral value of the backward feed speed Wfr from the above-described initial arc occurrence time (the time when the short circuit / arc discrimination signal Sa changes from the short circuit signal to the arc occurrence signal) is determined by the welding wire regardless of the set value of the backward feed speed Wfr. Is the distance Lw between the wire tip and the work to be welded, which is the retreat distance. In addition, the timing chart of each signal in the welding power supply device PS of the above-described second embodiment is the same as that in FIG.

[Third Embodiment] The invention of a third embodiment described below corresponds to the third and seventh inventions at the time of filing. According to the invention of the third embodiment, the fact that the distance Lw between the wire tip and the workpiece reaches the value of the retreat distance setting signal Ls due to the retreat feed described above in the description of the first embodiment from the time of the initial arc occurrence. The arc start control according to the first embodiment, which is determined based on the fact that a later-described reverse feed time Tr has reached a value of a reverse feed time setting signal Trs determined according to the reverse distance setting signal Ls and the reverse feed speed setting value Wr. Is the way. Hereinafter, the invention of the third embodiment will be described.

FIG. 8 is a block diagram of a welding power supply device for implementing the arc start control method of the third embodiment.
In this figure, the same circuit blocks as those in FIG. 5 described above are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, the reverse feed time setting circuit TRS and the reverse feed timer circuit TR, which are circuit blocks different from those in FIG.
Will be described with reference to FIG.

The reverse feed time setting circuit TRS outputs a reverse feed time setting signal Trs determined according to the reverse distance setting signal Ls and the reverse feed speed setting value Wr. This correspondence is Trs [s] = Ls [mm] / Wr [mm / s].
The backward feed timer circuit TR is a circuit that replaces the distance determining circuit LD described above with reference to FIG. 5, and the backward feed time Tr from the time when the short-circuit / arc determining signal Sa changes from the short-circuit signal to the arc generating signal. , The backward feed time setting signal T
When the value of rs is reached, the distance matching signal Ld is output. Therefore, the output time point of the distance coincidence signal Ld is the time point at which the distance Lwt between the tip of the wire and the workpiece at the time of re-forward feeding becomes equal to the value of the retreat distance setting signal Ls. A timing chart of each signal in the welding power supply device PS of the third embodiment is the same as that in FIG.

[Embodiment 4] The invention of Embodiment 4 described below corresponds to the inventions of Claims 4 and 8 at the time of filing. In the invention of the fourth embodiment, the fact that the distance Lw between the tip of the wire and the work to be welded has reached the value of the retreat distance setting signal Ls by the retreat feed described in the description of the first embodiment is made in the initial arc generation state. This is an arc start control method according to the first embodiment in which the welding voltage value Vw is determined based on reaching a retreat distance voltage set value Vrs, which will be described later, which is determined according to the retreat distance setting signal Ls and the initial current set value Is. Hereinafter, the invention of the fourth embodiment will be described.

FIG. 9 is a block diagram of a welding power supply device for implementing the arc start control method of the fourth embodiment.
In this figure, the same circuit blocks as those in FIG. 5 described above are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, the backward distance voltage setting circuit VRS and the voltage comparison circuit CM, which are circuit blocks different from those in FIG. 5 surrounded by a dotted line, will be described with reference to FIG.

The retreat distance voltage setting circuit VRS outputs a retreat distance setting signal Vrs determined according to the retreat distance setting signal Ls and the initial current set value Is. Here, if the value of the current supplied to the arc is constant, the arc length and the welding voltage value Vw are in a proportional relationship. Therefore, the welding voltage value Vw when the arc length of the initial arc (the distance Lw between the tip of the wire and the work to be welded) to which the initial current Is flows is equal to the value of the predetermined retreat distance setting signal Ls is set to the retreat distance voltage setting. Set as the value of signal Vrs. The voltage comparison circuit CM is shown in FIG.
A circuit that replaces the distance determination circuit LD described above.
When the welding voltage value Vw when the short circuit / arc discrimination signal Sa is the arc generation signal reaches the value of the retreat distance voltage setting signal Vrs, the distance matching signal Ld is output. Therefore, the output time point of the distance coincidence signal Ld is the time point at which the distance Lwt between the wire tip and the work to be welded at the time of re-forward feeding becomes equal to the value of the retreat distance setting signal Ls. In addition, the timing chart of each signal in the welding power supply device PS of the above-described fourth embodiment is the same as that of FIG. When the power supply characteristic at the time of energization of the initial current Is is the drooping characteristic, the fact that the distance Lw between the tip of the wire and the work to be welded reaches the value of the retreat distance setting signal Ls due to the retreat feed described above indicates that the initial arc is generated. The determination can also be made based on the fact that the welding current value Iw in the state has reached the retreat distance current set value determined according to the retreat distance setting signal Ls.

[0041]

According to the present invention, even if the backward feeding speed Wfr changes according to the kind of the shielding gas, the diameter of the welding wire, the plate thickness of the work to be welded, etc., the wire tip and the wire at the time of the re-forward feeding are changed. Since the inter-weld distance Lwt is controlled to be equal to the predetermined retreat distance set value Ls, the transition from the initial arc generation state to the steady arc generation state is performed by the retreat feed speed W.
Even if fr changes, the bead appearance at the arc start portion is always good, as a result, the operation is smoothly performed in a fixed short time. Further, in the present invention, the wire tip and
Since the distance Lwt between the workpieces is controlled to be equal to the receding distance set value Ls which is substantially equal to the steady arc length Lwc, the type of the shielding gas, the steady feed speed Wfs, the thickness of the workpiece, etc. Even if the steady-state arc length Lwc, which is set to an appropriate value by the voltage setting signal Vs, changes smoothly from the initial arcing state to the steady-state arcing state in a short period of time, the arc start portion The bead appearance is always good.

[Brief description of the drawings]

FIG. 1 is a block diagram of a welding power supply device illustrating an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a welding wire feeding system.

FIG. 3 is a block diagram of a conventional device.

FIG. 4 is a timing chart of each signal of the conventional device.

FIG. 5 is a block diagram of the welding power supply device according to the first embodiment.

FIG. 6 is a timing chart of the first embodiment.

FIG. 7 is a block diagram of a welding power supply device according to a second embodiment.

FIG. 8 is a block diagram of a welding power supply device according to a third embodiment.

FIG. 9 is a block diagram of a welding power supply device according to a fourth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Workpiece 3a Initial arc (generating state) 3b Steady arc (generating state) 4 Welding torch 4a Contact tip 5a Feeding roll of wire feeder CM Voltage comparing circuit DT Delay circuit Dt Delay signal FC Sending Control circuit Fc Feed control signal FCR Retreat distance feed control circuit INV Output control circuit Is Initial current (value / set value) IW Feed speed integration circuit Ld Distance match signal LD Distance discriminating circuit Lr Welding wire retreat distance LS Retreat distance setting Circuit Ls Retreat distance setting (signal) Lw Distance between wire tip and work piece Lwc Steady arc length (steady distance between wire tip and work piece) Lwt Distance between wire tip and work piece when feeding forward again PS Weld power supply SA Short circuit / arc determination circuit Sa Short circuit / arc determination signal St Weld start signal Tc Convergence time Td Delay (Set value) TR Reverse feed timer circuit Tr Reverse feed time Trs Reverse feed time setting (value / signal) TRS Reverse feed time setting circuit VD Voltage detection circuit Vd Voltage detection signal Vrs Reverse distance voltage setting (value / Signal) VRS Reverse distance voltage setting circuit VS Voltage setting circuit Vs Voltage setting signal Vw Welding voltage (value) WD Feed speed detection circuit Wd Feed speed detection signal Wf Feed speed Wfi Initial feed speed Wfr Reverse feed speed Wfs Steady Feed speed Wi Initial feed speed set value WM Wire feed motor Wr Reverse feed speed set value WS Steady feed speed setting circuit Ws Steady feed speed set signal

Claims (8)

[Claims] When a welding start signal is input, a welding wire is fed forward to an object to be welded, and when the welding wire comes into contact with the object to be welded, an initial current having a predetermined small current value is supplied to a welding power source. When the welding wire is separated from the work to be welded and the welding wire is separated from the work to be welded and the welding wire is separated from the work to be welded, an initial arc through which the initial current flows is generated and the initial arc is generated. The backward feeding is continued while the occurrence state is maintained, and when the distance between the wire tip and the workpiece reaches a predetermined backward distance setting value, the welding wire is again fed at a predetermined steady feeding speed. A consumable electrode gas that moves forward from the initial arcing state to a steady arcing state by applying a steady welding current corresponding to the steady feeding speed while feeding the workpiece forward. Arc start control method for shielded arc welding. 2. The fact that the distance between the tip of the wire and the workpiece to be welded has reached the retreat distance set value by the retreat feed, and the welding wire retreat distance obtained by integrating the feed speed of the retreat feed from the time of the initial arc occurrence, 2. The arc start control method according to claim 1, wherein the determination is made based on the fact that the reverse distance set value has been reached. 3. The fact that the distance between the tip of the wire and the workpiece to be welded has reached the retreat distance set value by the retreat feed is determined by the time of the retreat feed from the time when the initial arc is generated. 2. The arc start control method according to claim 1, wherein the determination is made when the reverse feed time set value determined according to the feed speed set value is reached. 4. The fact that the distance between the tip of the wire and the workpiece to be welded has reached the retreat distance set value due to retreat feed, the welding voltage value in the initial arc occurrence state is set to the retreat distance set value and the initial current set value. 2. The arc start control method according to claim 1, wherein the determination is made based on reaching a setback distance voltage set value correspondingly determined. 5. A wire feed motor for feeding a welding wire forward or backward from an object to be welded, and a short-circuit signal when the welding wire and the object to be welded are in contact with each other. A short-circuit / arc determining circuit that outputs an arc generating signal as a short-circuit / arc determining signal when an arc is generated;
A distance discrimination circuit that outputs a distance coincidence signal when the distance between the wire tip and the workpiece is equal to a value of a predetermined retreat distance setting signal; and when a welding start signal is input, the welding wire is connected to the workpiece. The welding wire is fed back from the workpiece when the short-circuit / arc discrimination signal becomes a short-circuit signal when the short-circuit / arc discrimination signal becomes a short-circuit signal, and the welding wire is predetermined when the distance matching signal is output. A retreat distance feed control circuit for feeding forward again to the workpiece at a steady feed speed,
From the time when the welding start signal is input to the time when the distance coincidence signal is output, a constant current characteristic or a drooping characteristic for applying an initial current of a predetermined small current value is formed, and thereafter, the steady state characteristic is formed. And an output control circuit for forming a constant voltage characteristic for supplying a steady welding current corresponding to the feeding speed. When the welding start signal is input, the welding wire is fed forward and the short circuit / arc is formed. At the time when the discrimination signal becomes a short-circuit signal, the initial current is supplied and the welding wire is fed backward, and the initial current is supplied when the welding wire is separated from the workpiece by the backward feeding. Is generated, the backward feeding is continued while maintaining the initial arc generating state, and when the distance coincidence signal is output, the welding wire is fed forward at a steady feeding speed again. A welding power supply for consumable electrode gas shielded arc welding in which the steady welding current is supplied to the electrode to smoothly transition from the initial arcing state to a steady arcing state. 6. A feed for outputting a distance coincidence signal when the welding wire retreat distance obtained by integrating the feed speed of the retreat feed from the point of occurrence of the initial arc reaches the value of the retreat distance setting signal. The welding power supply device according to claim 5, which is a speed integration circuit. 7. A distance discriminating circuit sets a value of a reverse feed time setting signal determined in accordance with a reverse distance setting signal and a feed speed set value of the reverse feed from the time of initial arc occurrence. 6. The welding power supply device according to claim 5, wherein the reverse power supply timer circuit outputs a distance coincidence signal when reaching. 8. A distance matching signal when a distance discriminating circuit reaches a value of a retreat distance setting signal determined in accordance with a retreat distance setting signal and a setting value of an initial current in a state where an initial arc is generated. 6. The welding power supply device according to claim 5, wherein the voltage comparison circuit outputs a voltage.