CN111906411A - Arc welding control method - Google Patents
Arc welding control method Download PDFInfo
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- CN111906411A CN111906411A CN202010252729.3A CN202010252729A CN111906411A CN 111906411 A CN111906411 A CN 111906411A CN 202010252729 A CN202010252729 A CN 202010252729A CN 111906411 A CN111906411 A CN 111906411A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/12—Automatic feeding or moving of electrodes or work for spot or seam welding or cutting
- B23K9/133—Means for feeding electrodes, e.g. drums, rolls, motors
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/10—Other electric circuits therefor; Protective circuits; Remote controls
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/10—Other electric circuits therefor; Protective circuits; Remote controls
- B23K9/1006—Power supply
- B23K9/1043—Power supply characterised by the electric circuit
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Abstract
The invention provides an arc welding control method. In the forward and reverse feeding arc welding method, the amount of spatter generated is always reduced without being affected by the viscosity of the welding wire. In an arc welding control method in which a welding wire is fed forward when an arc period is present between the welding wire and a base material, the welding wire is fed backward when a short-circuit period is present, and welding is performed by decreasing a welding current Iw to a low level current value when a constriction of a droplet of the welding wire is detected during the short-circuit period and increasing the welding current Iw from the low level current value after the arc period is started at time t4, the timing of increase of the welding current Iw is set to a time when a feed speed Fw at the time of switching from backward feed to forward feed becomes 0 (time t 5). By synchronizing the timing of increasing the welding current Iw with the point in time when the feed rate Fw becomes 0, the amount of spatter generated can be reduced without being affected by the viscosity of the welding wire.
Description
Technical Field
The present invention relates to an arc welding control method for performing welding by feeding a welding wire in a forward direction during an arc period between the welding wire and a base material and feeding the welding wire in a reverse direction during a short-circuit period.
Background
In general consumable electrode arc welding, a welding wire as a consumable electrode is fed at a fixed 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 welding quality, a forward and reverse feed arc welding method has been proposed in which welding is performed by alternately switching the feeding of a welding wire between forward feeding and reverse feeding (see, for example, patent document 1). In this forward and reverse feed arc welding method, the period of repetition of short circuits and arcs can be stabilized as compared with the conventional technique at a fixed feed speed, and therefore, the welding quality can be improved, such as reduction in the amount of spatter generated and improvement in bead appearance.
Documents of the prior art
Patent document
Patent document 1: JP patent publication No. 2018-1270
Many brands of welding wire are sold as an arc welding wire for steel materials. These welding wires also have differences in their viscosities due to their different compositions. In forward and reverse feed arc welding, if a wire having a relatively low viscosity is used, there is a problem in that the amount of spatter generated immediately after the generation of arc increases.
Disclosure of Invention
Therefore, an object of the present invention is to provide an arc welding control method capable of always reducing the amount of spatter generated in forward and reverse arc welding without being affected by the viscosity of the welding wire.
In order to solve the above-described problems, the invention according to claim 1 is an arc welding control method in which the welding wire is fed forward when an arc period is established between the welding wire and a base material, the welding wire is fed backward when a short-circuit period is established, a welding current is reduced to a low level current value when a constriction of a droplet of the welding wire is detected in the short-circuit period, and the welding current is increased from the low level current value after the arc period is started to perform welding, wherein the arc welding control method is characterized in that the timing of increasing the welding current is set to a time when a feed speed at the time of switching from the backward feed to the forward feed becomes 0.
The invention of claim 2 is the arc welding control method according to claim 1, wherein the feed speed is detected when switching from the reverse feed to the forward feed, and the timing of the increase in the welding current is set to a time when the detected feed speed becomes 0.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, in forward and reverse feed arc welding, the amount of spatter generated can always be reduced without being affected by the viscosity of the welding wire.
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 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 reference numerals
1 welding wire
2 base material
3 arc of electricity
4 welding torch
5 feed roller
CM current comparison circuit
Cm current comparison signal
DR drive circuit
Dr 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
Es (from feed motor) encoder signal
EV voltage error amplifying circuit
Ev voltage error amplified signal
FC feed control circuit
Fc feed control signal
FD feed speed detection circuit
Fd feed speed detection signal
FR feed speed setting circuit
Fr feed rate setting signal
Fw feed rate
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
Iw welding current
ND necking down detection circuitry
Nd neck detection signal
PM power main circuit
R current reducing resistor
SD short circuit discrimination circuit
Sd short circuit discrimination signal
Circuit in small current period of STD
Signal during Std small current
SW power supply characteristic switching circuit
TDR current fall time setting circuit
Tdr current falling time setting signal
TR transistor
During Trd reverse feed deceleration
TRDR reverse feeding deceleration period setting circuit
Trdr reverse feeding deceleration period setting signal
During the reverse peak feed period of Trp
During acceleration of Tru reverse feed
TRUR reverse feed acceleration period setting circuit
Trur reverse feed acceleration period setting signal
During forward feed deceleration of Tsd
TSDR forward feed deceleration period setting circuit
Tddr Forward feed deceleration period setting Signal
During Tsp positive feed peak
During acceleration of Tsu forward feed
TSUR forward feed acceleration period setting circuit
Tsur Forward feed acceleration period setting Signal
VD voltage detection circuit
Vd voltage detection signal
Vw welding voltage
WL reactor
WM feed motor
Peak reverse feed of Wrp
WRR reverse feeding peak value setting circuit
Wrr reverse feed peak setting signal
Peak Wsp forward feed
WSR forward feeding peak value setting circuit
Wsr positive feed peak setting signal
Detailed Description
Embodiments of the present invention are described below 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. Each block is described below with reference to the figure.
The power main circuit PM receives a 3-phase 200V commercial power supply (not shown) as an input, performs output control by inverter control or the like in accordance with an error amplification signal Ea described later, and outputs an output voltage E. Although not shown, the power supply main circuit PM includes: a rectifier for 1 time rectifying the commercial power; an inverter circuit driven by the error amplification signal Ea for converting the rectified dc to a high-frequency ac; the high-frequency transformer is used for reducing the high-frequency alternating current to a voltage value suitable for welding; and 2-time rectifier for rectifying the high-frequency alternating current with voltage reduction into direct current.
The reactor WL smoothes the welding current Iw. The inductance value of the reactor WL is, for example, 100 μ H.
Feed motor WM alternately repeats forward feeding and reverse feeding using a feed control signal Fc described later as an input, and feeds welding wire 1 at feed speed Fw. A motor having a high transient response 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 reverse the feeding direction, the feeding motor WM may be provided near the tip of the welding torch 4. In addition, there is a case where a push-pull type feed system is made using the feed motor WM.
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 described above, 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.
The current detection circuit ID detects the welding current Iw and outputs a current detection signal ID. 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, determines that the short circuit period is in the short circuit period when the voltage detection signal Vd is less than a predetermined short circuit determination value (about 10V), and outputs the short circuit determination signal SD at a high level, and determines that the short circuit period is in the arc period when the voltage detection signal Vd is greater than the predetermined short circuit determination value (about 10V), and outputs the short circuit determination signal SD at a low level.
The forward feed acceleration period setting circuit TSUR outputs a predetermined forward feed acceleration period setting signal TSUR.
The forward feed deceleration period setting circuit TSDR outputs a predetermined forward feed deceleration period setting signal TSDR.
The reverse feed acceleration period setting circuit TRUR outputs a predetermined reverse feed acceleration period setting signal TRUR.
The reverse feed deceleration period setting circuit TRDR outputs a predetermined reverse feed deceleration period setting signal TRDR.
The forward feeding peak value setting circuit WSR outputs a predetermined forward feeding peak value setting signal Wsr. The forward feeding peak value setting signal Wsr is set to a value corresponding to the average feeding speed (average welding current value).
The reverse feeding peak value setting circuit WRR outputs a predetermined reverse feeding peak value setting signal WRR. The reverse feeding peak value setting signal Wrr is set to a value corresponding to the average feeding speed (average welding current value).
The feed rate setting circuit FR receives the forward acceleration period setting signal Tsur, the forward deceleration period setting signal Tsdr, the reverse acceleration period setting signal Trur, the reverse deceleration period setting signal Trdr, the forward peak value setting signal Wsr, the reverse peak value setting signal Wrr, and the short-circuit discrimination signal Sd as inputs, and outputs a feed rate pattern generated by the following processing as the feed rate setting signal FR. The stop state is set when the feed rate setting signal Fr is 0, the forward feed period is set when the feed rate setting signal Fr is greater than 0, and the reverse feed period is set when the feed rate setting signal Fr is less than 0.
1) During the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur, a feed speed setting signal Fr for a forward feed peak Wsp accelerated from 0 to a positive value determined by the forward feed peak setting signal Wsr is output.
2) Next, in the forward peak feeding period Tsp, the feeding speed setting signal Fr for maintaining the above-described forward peak feeding Wsp is output.
3) When the short-circuit determination signal Sd changes from a low level (arc period) to a high level (short-circuit period), the short-circuit determination signal Sd transitions to a forward feed deceleration period Tsd specified by the forward feed deceleration period setting signal Tsdr, and a feed speed setting signal Fr for decelerating from the above-described forward feed peak Wsp to 0 is output.
4) Next, in the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur, the feed speed setting signal Fr of the reverse feed peak value Wrp accelerated from 0 to a negative value determined by the reverse feed peak value setting signal Wrr is output.
5) Next, in the backward feeding peak period Trp, the feeding speed setting signal Fr for maintaining the above-described backward feeding peak value Wrp is output.
6) When the short-circuit determination signal Sd changes from a high level (short-circuit period) to a low level (arc period), the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr is transited to, and the feed rate setting signal Fr for decelerating from the reverse feed peak value Wrp to 0 is output.
7) By repeating the above-described 1) to 6), the feed rate setting signal Fr of the feed pattern in which the positive and negative trapezoidal waves change is generated.
The feed speed detection circuit FD receives the encoder signal Es from the feed motor WM and outputs a feed speed detection signal FD.
The feed control circuit FC receives the feed speed setting signal Fr and the feed speed detection signal Fd as input, and outputs a feed control signal FC to the feed motor WM, the feed control signal FC controlling the feed speed Fw so that the value of the feed speed detection signal Fd becomes equal to the value of the feed speed setting signal Fr.
The current reducing resistor R is inserted between the reactor WL and the welding torch 4. The value of the current reducing resistor R is set to a large value (on the order of 0.5 to 3 Ω) 50 times or more the short-circuit load (on the order of 0.01 to 0.03 Ω). When the current reducing resistor R is inserted into a current path of the welding current, energy of a reactor component accumulated in the reactor WL and the welding cable is discharged suddenly.
The transistor TR is connected in parallel with the aforementioned current reducing resistor R, and is turned on or off in accordance with a drive signal Dr described later.
The neck detection circuit ND receives the short-circuit determination signal Sd, the voltage detection signal Vd, and the current detection signal Id as input, determines that the state of neck formation is in the reference state at a time point when the voltage rise value of the voltage detection signal Vd reaches the reference value when the short-circuit determination signal Sd is at the high level (short-circuit period), outputs the neck detection signal ND at the high level, and outputs the neck detection signal ND at the low level at a time point when the short-circuit determination signal Sd changes to the low level (arc period). Further, the neck detection signal Nd may be changed to the high level at a time point when the differential value of the voltage detection signal Vd during the short-circuit period reaches the reference value corresponding thereto. Further, the resistance value of the droplet may be calculated by dividing the value of the voltage detection signal Vd by the value of the current detection signal Id, and the neck detection signal Nd may be changed to a high level at a time point when the differential value of the resistance value reaches a reference value corresponding thereto.
The low level current setting circuit ILR outputs a predetermined low level current setting signal ILR. The current comparison circuit CM receives the low-level current setting signal Ilr and the current detection signal Id as input, and outputs a current comparison signal CM which becomes high when Id < Ilr and becomes low when Id ≧ Ilr.
The drive circuit DR receives the current comparison signal Cm and the neck detection signal Nd as input, outputs a drive signal DR to the base terminal of the transistor TR, changes the drive signal DR to a low level when the neck detection signal Nd changes to a high level, and then changes the drive signal DR to a high level when the current comparison signal Cm changes to a high level. Therefore, when the constriction is detected, the drive signal Dr is set to a low level, the transistor TR is turned off, and the current reducing resistor R is inserted into the conduction path of the welding current, so that the welding current Iw is rapidly reduced. When the value of welding current Iw that has been suddenly decreased decreases to the value of low-level current setting signal Ilr, drive signal Dr becomes high, and transistor TR is turned on, so that current reducing resistor R is short-circuited and returns to the normal state.
The current control setting circuit ICR receives the short circuit determination signal Sd, the low level current setting signal Ilr, and the necking detection signal Nd as input, performs the following processing, and outputs a current control setting signal ICR.
1) When the short circuit determination signal Sd is at a low level (arc period), the current control setting signal Icr which becomes the low-level current setting signal Ilr is output.
2) When the short circuit determination signal Sd changes to a high level (short circuit period), a current control setting signal Icr is output, which reaches a predetermined initial current setting value in a predetermined initial period and then ramps up to a predetermined short circuit peak setting value at the time of short circuit to maintain the value.
3) Then, when the neck detection signal Nd changes to the high level, the current control setting signal Icr that becomes the value of the low-level current setting signal Ilr is output.
The current error amplification circuit EI receives the current control setting signal Icr and the current detection signal Id, amplifies an error between the current control setting signal Icr (+) and the current detection signal Id (-) and outputs an output error amplified signal EI.
The current fall time setting circuit TDR outputs a predetermined current fall time setting signal TDR. The current drop time setting signal Tdr is set to a value corresponding to the average feed speed (average welding current value).
The small current period circuit STD receives the short circuit determination signal Sd and the current fall time setting signal Tdr as input, and outputs a small current period signal STD which becomes high at a time point after a time determined by the current fall time setting signal Tdr elapses from a time point when the short circuit determination signal Sd changes to low level (arc period), and then becomes low when the short circuit determination signal Sd becomes high level (short circuit period).
The power supply characteristic switching circuit SW receives the current error amplification signal Ei, the voltage error amplification signal Ev, the short circuit determination signal Sd, the reverse feed deceleration period setting signal Trdr, and the small current period signal Std, and performs the following processing to output an error amplification signal Ea.
1) The current error amplification signal Ei is output as the error amplification signal Ea during a period from a time point when the short circuit determination signal Sd changes to a high level (short circuit period) to a time point when the short circuit determination signal Sd changes to a low level (arc period) and a reverse feed deceleration period determined by the reverse feed deceleration period setting signal Trdr elapses.
2) In the subsequent large current arc period, the voltage error amplification signal Ev is output as the error amplification signal Ea.
3) In a low-current arc period in which the low-current period signal Std becomes a high level in the subsequent arc period, the current error amplification signal Ei is output as the error amplification signal Ea.
With this circuit, the characteristics of the welding power supply are constant current characteristics in the short circuit period, the backward feed deceleration period, and the small current arc period, and are constant voltage characteristics in the large current arc period other than these periods.
Fig. 2 is a timing chart of signals in the welding power supply of fig. 1, which shows the arc welding control method according to embodiment 1 of the present invention. In the graph, (a) shows a temporal change in the feed speed Fw, (B) shows a temporal change in the welding current Iw, (C) shows a temporal change in the welding voltage Vw, (D) shows a temporal change in the short-circuit determination signal Sd, and (E) shows a temporal change in the small-current period signal Std. The operation of each signal will be described below with reference to the figure.
The feed rate Fw shown in fig. a is controlled to the value of the feed rate setting signal FR output from the feed rate setting circuit FR in fig. 1. The feed speed Fw is formed by the following period: a forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur of fig. 1; continuing until a forward feed peak period Tsp during which a short circuit occurs; a forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr of fig. 1; a reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur of fig. 1; up to the reverse feed peak period Trp, during which arcing occurs; and a reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr of fig. 1. Further, the forward feed peak Wsp is determined by the forward feed peak setting signal Wsr of fig. 1, and the reverse feed peak Wrp is determined by the reverse feed peak setting signal Wrr of fig. 1. As a result, the feed speed setting signal Fr has a feed pattern that changes in a substantially trapezoidal wave shape with positive and negative polarities.
[ operation during short-circuit period from time t1 to t4 ]
When a short circuit occurs at time t1 in the forward feed peak period Tsp, the welding voltage Vw rapidly decreases to a short-circuit voltage value of several V as shown in (C) of the figure, and therefore the short-circuit determination signal Sd changes to a high level (short-circuit period) as shown in (D) of the figure. In response to this, the predetermined forward feed deceleration period Tsd from time t1 to t2 is transitioned to, and as shown in (a) of the figure, the feed speed Fw is decelerated from the above-described forward feed peak Wsp to 0. For example, the forward feed deceleration period Tsd is set to 1 ms.
As shown in fig. a, the feed speed Fw enters a predetermined reverse feed acceleration period Tru from time t2 to time t3, and accelerates from 0 to the above-described reverse feed peak value Wrp. In this period, the short-circuit period continues. For example, the reverse feed acceleration period Tru is set to 1 ms.
When the reverse feeding acceleration period Tru ends at time t3, the feeding speed Fw enters the reverse feeding peak period Trp as shown in fig. (a) of the drawing, and becomes the reverse feeding peak value Wrp. The reverse feed peak period Trp continues until an arc is generated at time t 4. Therefore, the period from time t1 to time t4 becomes a short-circuit period. The reverse feeding peak period Trp is not a predetermined value but is about 4 ms. For example, the reverse feed peak Wrp is set to-60 m/min.
As shown in fig. B, the welding current Iw in the short-circuit period from time t1 to time t4 reaches a predetermined initial current value in a predetermined initial period. Thereafter, the welding current Iw is ramped up at a predetermined short circuit time, and when it reaches a predetermined short circuit time peak value, the value is maintained.
As shown in fig. C, welding voltage Vw rises near the peak when welding current Iw is short-circuited. This is because the droplet at the leading end of the welding wire 1 gradually forms a neck due to the reverse feeding of the welding wire 1 and the pinch force caused by the welding current Iw.
When the voltage rise value of the welding voltage Vw reaches the reference value, it is determined that the state of formation of the neck is the reference state, and the neck detection signal Nd in fig. 1 changes to the high level.
In response to the neck detection signal Nd becoming high, the drive signal Dr of fig. 1 becomes low, and therefore the transistor TR of fig. 1 becomes off, and the current-carrying path of the welding current is inserted into the current-reducing resistor R of fig. 1. At the same time, the current control setting signal Icr in fig. 1 becomes smaller to the value of the low level current setting signal Ilr. Therefore, as shown in fig. B, the welding current Iw sharply decreases from the short-circuit peak value to a low-level current value. Then, when welding current Iw decreases to a low level current value, drive signal Dr returns to a high level, and transistor TR is turned on, thereby short-circuiting current reducing resistor R. As shown in fig. B, since the current control setting signal Icr is maintained in the low level current setting signal Ilr, the welding current Iw is maintained at the low level current value until the predetermined reverse feed deceleration period Trd elapses from the arc regeneration. Therefore, the transistor TR is turned off only during a period from a time point when the neck detection signal Nd changes to the high level to a time point when the welding current Iw decreases to a low level current value. As shown in fig. C, welding voltage Vw decreases once as welding current Iw decreases, and then rises rapidly. The above parameters are set to, for example, the following values. The initial current is 40A, the initial period is 0.5ms, the short-circuit slope is 180A/ms, the short-circuit peak value is 400A, and the low-level current value is 50A.
[ operation during arc period from time t4 to t7 ]
When the neck is advanced by the backward feeding of the welding wire and the pinching force by the energization of the welding current Iw at time t4 and an arc is generated, welding voltage Vw rapidly increases to an arc voltage value of several tens V as shown in (C) of the figure, and thus short circuit determination signal Sd changes to a low level (arc period) as shown in (D) of the figure. In response to this, the predetermined reverse feed deceleration period Trd from time t4 to time t5 is transitioned to, and as shown in (a) of the figure, the feed speed Fw is decelerated from the above-described reverse feed peak value Wrp to 0. For example, the reverse feed deceleration period Trd is set to 1 ms.
When the reverse feed deceleration period Trd ends at time t5, the transition is made to a predetermined forward feed acceleration period Tsu from time t5 to t 6. In the forward feed acceleration period Tsu, as shown in (a) of the figure, the feed speed Fw is accelerated from 0 to the above-described forward feed peak Wsp. During this period, the arc period continues. For example, the forward feed acceleration period Tsu is set to 1 ms.
When the forward feed acceleration period Tsu ends at time t6, the feed speed Fw enters the forward feed peak period Tsp as shown in fig. a, and becomes the forward feed peak. During this period, the arc period also continues. The forward feed peak period Tsp continues until a short circuit occurs at time t 7. Therefore, the period from time t4 to time t7 is an arc period. If a short circuit occurs, the operation returns to the operation at time t 1. The forward feed peak period Tsp is not a predetermined value, but is about 4 ms. For example, the forward feed peak Wsp is set to 70 m/min.
When an arc is generated at time t4, welding voltage Vw sharply increases to an arc voltage value of several tens V as shown in fig. (C) of the figure. On the other hand, as shown in fig. B, the welding current Iw continues at a low level of current during the reverse feed deceleration period Trd from time t4 to t 5. Then, from time t5, welding current Iw rapidly increases and reaches a peak value, and then gradually decreases to a large current value. Therefore, the timing (time t5) at which the welding current Iw increases after the arc is generated at time t4 is the end time point of the reverse feed deceleration period Trd at which the feed speed becomes 0 when switching from the reverse feed to the forward feed.
In the large current arc period from time t5 to time t61, the feedback control of the welding power source is performed by the voltage error amplification signal Ev in fig. 1, and therefore, the constant voltage characteristic is obtained. Therefore, the value of the welding current Iw during the large-current arc varies depending on the arc load.
At time t61 when the current drop time determined by the current drop time setting signal Tdr in fig. 1 elapses after the arc is generated at time t4, the low-current period signal Std changes to the high level as shown in (E) of the figure. In response, the welding power source switches from a constant voltage characteristic to a constant current characteristic. Therefore, as shown in fig. B, the welding current Iw is reduced to a low level current value and is maintained until time t7 when a short circuit occurs. Similarly, as shown in fig. C, welding voltage Vw also decreases. If a short circuit occurs at time t7, the small current period signal Std returns to the low level.
According to embodiment 1 described above, the timing at which the welding current is increased from the low level current value after the arc period starts is set to the timing at which the feed speed when switching from the reverse feed to the forward feed is 0. That is, the welding current increase timing is set to the end time point of the reverse feed deceleration period. When forward and reverse feed arc welding is performed using a wire having low viscosity as a wire for steel, the following welding state is achieved depending on the timing of increasing the welding current after the arc is generated.
(1) When the timing of increase of welding current is halfway during the reverse feed deceleration
In this case, the welding current is increased while the welding wire is also being fed reversely. If the welding current is increased, the front end of the welding wire is melted to form a molten drop. In a welding wire having a low viscosity, when a droplet is formed while moving in reverse, a part of the droplet is scattered as spatters. In the case of a wire having a high viscosity, spatter is not generated even when the wire is fed in a reverse direction to form a droplet.
(2) The welding current increase timing is at the end time of the backward feed deceleration period (embodiment 1)
In this case, when the feeding speed of the welding wire becomes 0, the welding current increases. If the welding current is increased, the front end of the welding wire is melted to form a molten drop. Therefore, the droplet is formed gradually in a state where the feeding speed is gradually accelerated from 0, and no spatter is generated regardless of the viscosity of the wire.
(3) When the timing of increase of welding current is halfway during forward feed acceleration
In this case, the welding current increases while the welding wire is being fed forward. Therefore, since the wire is fed forward in a state where a droplet is not formed, the probability of occurrence of a short circuit again becomes high regardless of the viscosity of the wire. If a re-short circuit occurs, the welding state becomes unstable.
Therefore, in the invention according to embodiment 1, the spatter generation amount can be always reduced without being affected by the viscosity of the wire in the forward and backward feed arc welding. In embodiment 1, the timing of increasing the welding current is set so that the feed rate becomes 0, but the increase of spattering is small even when the welding current deviates by about ± 0.2ms, and therefore, this embodiment includes this.
[ embodiment 2]
In the invention according to embodiment 2, the feed speed at the time of switching from the reverse feed to the forward feed is detected, and the timing at which the welding current is increased from the low-level current value after the arc period is started is set to be 0.
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 assigned to the same blocks, and the description thereof will not be repeated. In this figure, the power supply characteristic switching circuit SW of fig. 1 is replaced with a 2 nd power supply characteristic switching circuit SW 2. This block is explained below with reference to this figure.
The 2 nd power supply characteristic switching circuit SW2 receives the current error amplification signal Ei, the voltage error amplification signal Ev, the short circuit determination signal Sd, the feed rate detection signal Fd, and the small current period signal Std, and outputs an error amplification signal Ea by performing the following processing.
1) The current error amplification signal Ei is output as the error amplification signal Ea during a period from a time point when the short circuit determination signal Sd changes to a high level (short circuit period) to a time point when the speed detection signal Fd becomes 0 after the short circuit determination signal Sd changes to a low level (arc period).
2) In the subsequent large current arc period, the voltage error amplification signal Ev is output as the error amplification signal Ea.
3) In a low-current arc period in which the low-current period signal Std becomes a high level in the subsequent arc period, the current error amplification signal Ei is output as the error amplification signal Ea.
With this circuit, the characteristics of the welding power supply are constant current characteristics in the short-circuit period, the actually measured backward feed deceleration period, and the small-current arc period, and are constant voltage characteristics in the large-current arc period other than these periods.
The timing diagrams of the signals in fig. 3 are the same as those in fig. 2 described above, and therefore are omitted. However, the timing at which the welding current Iw increases at time t4 shown in fig. B is different. In embodiment 1, the timing of increasing the welding current from the low level current value after the start of the arc period is set to the point of time when the period determined by the predetermined reverse feeding deceleration period setting signal Trdr ends. On the other hand, in embodiment 2, the above-described increase timing is a period until the feed speed detection signal Fd becomes 0. When the feed resistance of the welding wire is small, the two are substantially the same. However, if the feed resistance is increased, the deviation between the two becomes large. Therefore, in embodiment 2, regardless of the magnitude of the feed resistance, the increase timing can be made to coincide with the time point at which the feed speed becomes 0. As a result, the amount of sputtering can be minimized.
Claims (2)
1. An arc welding control method is provided, which comprises the steps of,
feeding the wire in a forward direction during an arc period between the wire and the base material, feeding the wire in a reverse direction during a short circuit period,
if a necking of a droplet of the welding wire is detected during the short circuit, the welding current is reduced to a low level current value,
increasing the welding current from the low level current value after the arc period begins to weld,
the arc welding control method is characterized in that,
the welding current is increased at a timing when the feed speed at the time of switching from the reverse feed to the forward feed is 0.
2. The arc welding control method according to claim 1,
the feed speed at the time of switching from the reverse feed to the forward feed is detected, and the timing of increase of the welding current is set to a time when the detected feed speed becomes 0.
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