JP7569722B2 - Arc welding equipment - Google Patents

Description

The present invention relates to an arc welding device that feeds a welding wire and welds by repeating short circuit periods and arc periods.

In typical consumable electrode arc welding, the welding wire, which is a consumable electrode, is fed at a constant speed and an arc is generated between the welding wire and the base material to perform welding. In consumable electrode arc welding, the welding wire and the base material often enter a welding state in which short-circuit periods and arc periods alternate.

To improve welding quality, a constriction detection control is commonly used in which, if a constriction of the droplet is detected during a short circuit, the welding current is reduced to a low current level and the arc is re-sparked. Constriction detection control can significantly reduce the generation of spatter, resulting in high-quality welding results. To perform this constriction detection control, it is necessary to accurately detect the state of the constriction of the droplet from the voltage at the arc generation point. For this reason, a dedicated detection wire is wired to the base material and the welding torch to detect the voltage at the arc generation point. However, wiring this detection wire is time-consuming. Furthermore, since the welding torch moves during welding, the detection wire may break, causing problems. Furthermore, when welding large structures, it is difficult to detect the voltage at the arc generation point.

In order to solve the above problem, in the invention of Patent Document 1, when a predetermined reference time has elapsed from the start of the short circuit, it is assumed that the formation state of the droplet necking has reached the reference state, and the welding current is reduced. In this way, there is no need to detect the voltage of the arc generation part, and therefore no need to wire a detection line. However, in this control, the problem is what value to set the reference time to. Since the formation state of the droplet necking varies depending on various welding conditions such as the material of the welding wire, the type of shielding gas, the welding current, the welding voltage, the welding speed, the welding position, and the wire extension length, it is difficult to set an appropriate reference time in advance by experiment. If the reference time is shorter than the appropriate value, the welding current is reduced at a time when the droplet formation state is not yet sufficient, so the timing of the re-ignition of the arc is delayed and the welding state becomes unstable. Conversely, if the reference time is longer than the appropriate value, the arc is re-ignited at a time when the welding current has not yet been reduced sufficiently, resulting in a large amount of spatter. Therefore, in the conventional technology, setting the reference time to an appropriate value is excessive.

Patent No. 5974984

The present invention aims to provide an arc welding device that can perform high-quality welding with minimal spatter under various welding conditions without detecting the voltage at the arc generating point.

In order to solve the above-mentioned problems, the invention of claim 1 comprises:
a feed motor that feeds the welding wire;
a short circuit determination unit that determines that a short circuit period exists between the welding wire and the base metal and outputs a short circuit determination signal;
a current reduction timer unit which receives the short circuit determination signal as an input and outputs a current reduction signal when a reference time has elapsed from the start point of the short circuit period;
a power control unit that supplies a welding voltage and a welding current between the welding wire and the base material to repeat the short circuit period and the arc period, and reduces the welding current to transition to the arc period when the current reduction signal is input during the short circuit period;
In an arc welding device comprising:
an average short circuit duration calculation unit which receives the short circuit determination signal as an input, calculates an average short circuit duration for every 3 to 10 periods , and outputs an average short circuit duration calculation signal;
a reference time setting unit that automatically sets the reference time based on the average short circuit duration calculation signal that changes every time a short circuit occurs during welding under various welding conditions ;
The arc welding device further comprises:

The invention of claim 2 is as follows:
the reference time setting unit sets a value obtained by subtracting a predetermined time from the value of the average short circuit duration calculation signal as the reference time.
2. The arc welding device according to claim 1 .

The invention of claim 3 is as follows:
the feed motor feeds the welding wire in a forward direction during the arc period and in a reverse direction during the short circuit period;
3. The arc welding apparatus according to claim 1 or 2.

The arc welding device of the present invention can perform high-quality welding with minimal spatter under various welding conditions without detecting the voltage at the arc generating point.

1 is a block diagram of an arc welding device according to an embodiment of the present invention. 2 is a timing chart of each signal in the arc welding device of FIG. 1 .

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

Figure 1 is a block diagram of an arc welding device according to an embodiment of the present invention. Each block will be explained below with reference to the figure.

The power control unit PM receives a commercial power supply (not shown) such as a three-phase 200V power supply, performs output control such as inverter control according to an error amplification signal Ea described below, and outputs an output voltage E to supply an output terminal voltage Vw and a welding current Iw between the welding wire 1 and the base material 2. Although not shown, the power control unit PM includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smoothes the rectified DC, an inverter circuit driven by the error amplification signal Ea described above that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for welding, and a secondary rectifier that rectifies the stepped-down high-frequency AC into DC.

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

The feed motor WM receives a feed control signal Fc (described later) as input and alternates between forward and reverse feed to feed the welding wire 1 at a feed speed Fw. Forward feed means forward feeding of the welding wire in a direction approaching the base material, and reverse feed means backward feeding away from the base material. A motor with fast transient response is used for the feed motor WM. In order to speed up the rate of change of the feed speed Fw of the welding wire 1 and the reversal of the feed direction, the feed motor WM may be installed near the tip of the welding torch 4. In some cases, two feed motors WM are used to create a push-pull type feed system.

The welding wire 1 is fed through the welding torch 4 by the rotation of the feed roll 5 connected to the feed motor WM, and an arc 3 is generated between the base material 2 and the welding wire 1. An output terminal voltage Vw is applied between the power feed tip (not shown) in the welding torch 4 and the base material 2, and a welding current Iw flows. Shielding gas (not shown) is sprayed from the tip of the welding torch 4.

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 inputs, amplifies the error between the output voltage setting signal Er(+) and the output voltage detection signal Ed(-), and outputs the 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 voltage Vw between the output terminals of the welding power source and outputs a voltage detection signal Vd. The short circuit determination circuit SD receives the voltage detection signal Vd and outputs a short circuit determination signal Sd that goes to High level when this value is less than a predetermined short circuit determination value (approximately 10 V) and determines that the short circuit is in progress, and goes to Low level when this value is equal to or greater than this and determines that the arc is in progress.

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

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

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

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

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

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

The feed speed setting circuit FR receives the forward feed acceleration period setting signal Tsur, the forward feed deceleration period setting signal Tsdr, the reverse feed acceleration period setting signal Trur, the reverse feed deceleration period setting signal Trdr, the forward feed peak value setting signal Wsr, the reverse feed peak value setting signal Wrr and the short circuit determination signal Sd as inputs, and outputs a feed speed pattern generated by the following process as a feed speed setting signal Fr. When this feed speed setting signal Fr is 0 or more, it is a forward feed period, and when it is less than 0, it is a reverse feed period.
1) During the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur, the feed speed setting signal Fr is output for accelerating from 0 to the forward feed peak value Wsp, which is a positive value determined by the forward feed peak value setting signal Wsr.
2) Subsequently, during the forward feed peak period Tsp, the feed speed setting signal Fr for maintaining the forward feed peak value Wsp is output.
3) When the short circuit detection signal Sd changes from a low level (arc period) to a high level (short circuit period), the process moves to a forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr, and the feed speed setting signal Fr is output to decelerate the feed speed from the forward feed peak value Wsp to 0.
4) Subsequently, during the reverse acceleration period Tru determined by the reverse acceleration period setting signal Trur, the feed speed setting signal Fr is output for accelerating from 0 to the reverse peak value Wrp, which is a negative value determined by the reverse peak value setting signal Wrr.
5) Subsequently, during the reverse feed peak period Trp, the feed speed setting signal Fr for maintaining the reverse feed 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 begins, and the feed speed setting signal Fr for decelerating the feed speed from the reverse feed peak value Wrp to 0 is output.
7) By repeating the above steps 1) to 6), a feed speed setting signal Fr is generated having a feed pattern that changes like a positive and negative trapezoidal wave.

The feed control circuit FC receives the feed speed setting signal Fr as an input and outputs a feed control signal Fc to the feed motor WM to feed the welding wire 1 at a feed speed Fw that corresponds 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 this current-reducing resistor R is set to a value (approximately 0.5 to 3 Ω) that is 50 times larger than the short-circuit load (approximately 0.01 to 0.03 Ω). When this current-reducing resistor R is inserted into the current path, the energy stored in the reactor WL and the reactor of the external cable is suddenly discharged.

The transistor TR is connected in parallel with the current reducing resistor R and is controlled to be turned on or off according to the drive signal Dr described below.

The average short circuit duration calculation circuit TSA takes the above-mentioned short circuit determination signal Sd as input, calculates a moving average of the short circuit duration during which the short circuit determination signal Sd is at a high level (short circuit duration) over a specified period, and outputs the average short circuit duration calculation signal Tsa. The above-mentioned specified period is the period during which a short circuit occurs, and is set to approximately 3 to 10 periods. Therefore, each time a short circuit occurs, the average value of the short circuit duration for the specified period immediately preceding it is calculated.

The reference time setting circuit TNR receives the average short circuit duration calculation signal Tsa as input, subtracts a predetermined time from the value of the average short circuit duration calculation signal Tsa, and outputs a reference time setting signal Tnr. The predetermined time is set to, for example, about 1 ms. The state of the neck formation is in the reference state a predetermined time before the short circuit ends and the arc re-strikes. If the welding current is reduced at this timing, the welding current will reach the desired low-level current value at the point when the arc re-strikes.

The current reduction timer circuit ND receives the above short circuit determination signal Sd and the above reference time setting signal Tnr as inputs, and outputs a current reduction signal Nd that goes to a high level for a short time when the short circuit determination signal Sd is at a high level (short circuit period) and the elapsed time from when it changed to a high level reaches the reference time Tn determined by the reference time setting signal Tnr.

The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr. The current comparison circuit CM receives this low-level current setting signal Ilr and the current detection signal Id as inputs, and outputs a current comparison signal Cm that goes to a high level when Id<Ilr and a low level when Id≧Ilr.

The drive circuit DR receives the current comparison signal Cm and the current reduction signal Nd as inputs, and outputs a drive signal Dr to the base terminal of the transistor TR. The drive signal Dr changes to a low level when the current reduction signal Nd changes to a high level, and then changes to a high level when the current comparison signal Cm changes to a high level. Therefore, when a constriction is detected, the drive signal Dr goes to a low level, the transistor TR is turned off, and the current reduction resistor R is inserted in the current path, so that the welding current Iw passing through the short-circuit load is suddenly reduced. Then, when the value of the suddenly reduced welding current Iw decreases to the value of the low-level current setting signal Ilr, the drive signal Dr goes to a high level, the transistor TR is turned on, and the current reduction resistor R is short-circuited and returns to the normal state.

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

The first arc period circuit STA1 receives the above short circuit determination signal Sd and the above first arc period setting signal Ta1r as inputs, and outputs a first arc period signal Sta1 that is at a high level during the first arc period Ta1 that is predetermined by the first arc period setting signal Ta1r from the point in time when the short circuit determination signal Sd changes to a low level (arc period) and a predetermined delay period Tc has elapsed.

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

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

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

The current control setting circuit ICR receives as inputs the short circuit determination signal Sd, the low level current setting signal Ilr, the current reduction signal Nd, the first arc period signal Sta1, the third arc period signal Sta3, the first arc current setting signal Ia1r, and the third arc current setting signal Ia3r, performs the following processing, and outputs the current control setting signal Icr.
1) During the delay period from the point when the short circuit determination signal Sd changes to a low level (arc period) until the first arc period signal Sta1 changes to a high level, a current control setting signal Icr having the value of the low-level current setting signal Ilr is output.
2) Thereafter, when first arc period signal Sta1 is at a high level (first arc period), current control setting signal Icr which becomes first arc current setting signal Ia1r is output.
3) During the period from the point when the first arc period signal Sta1 changes to low level to the point when the third arc period signal Sta3 changes to low level (the second arc period and third arc period), a current control setting signal Icr which becomes the third arc current setting signal Ia3r is output.
4) When the short circuit determination signal Sd changes to a high level (short circuit period), a predetermined initial current setting value is output during a predetermined initial period, and thereafter, a current control setting signal Icr is output which rises with a predetermined short circuit slope to a predetermined short circuit peak setting value and maintains that value.
5) Thereafter, when the current decrease signal Nd changes to a high level, the current control setting signal Icr having the value of the low-level current setting signal Ilr is output.

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

The power supply characteristics switching circuit SW receives the current error amplified signal Ei, the voltage error amplified signal Ev, the first arc period signal Sta1, and the third arc period signal Sta3 as inputs, performs the following processing, and outputs an error amplified signal Ea.
1) During the second arc period Ta2 from when first arc period signal Sta1 changes to low level until third arc period signal Sta3 changes to high level, voltage error amplified signal Ev is output as error amplified signal Ea.
2) During the other periods, the current error amplified signal Ei is output as the error amplified signal Ea.
This circuit causes the welding power supply to have constant current characteristics during the short circuit period, delay period, first arc period Ta1 and third arc period Ta3, and constant voltage characteristics during second arc period Ta2.

Figure 2 is a timing chart of each signal in the arc welding device of Figure 1. Figure 2 (A) shows the change over time in the feed speed Fw, Figure 2 (B) shows the change over time in the welding current Iw, Figure 2 (C) shows the change over time in the voltage Vw between the output terminals, Figure 2 (D) shows the change over time in the short circuit determination signal Sd, Figure 2 (E) shows the change over time in the first arc period signal Sta1, Figure 2 (F) shows the change over time in the third arc period signal Sta3, and Figure 2 (G) shows the change over time in the current reduction signal Nd. The operation of each signal will be explained below with reference to the figure.

The feed speed Fw shown in FIG. 1A is controlled by the value of the feed speed setting signal Fr output from the feed speed setting circuit FR in FIG. 1. The feed speed Fw is formed by the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur in FIG. 1, the forward feed peak period Tsp that continues until a short circuit occurs, the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr in FIG. 1, the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Trur in FIG. 1, the reverse feed peak period Trp that continues until an arc occurs, and the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr in FIG. 1. Furthermore, the forward feed peak value Wsp is determined by the forward feed peak value setting signal Wsr in FIG. 1, and the reverse feed peak value Wrp is determined by the reverse feed peak value setting signal Wrr in FIG. 1. As a result, the feed speed setting signal Fr becomes a feed pattern that changes in a substantially trapezoidal wave shape between positive and negative.

[Operation during the short circuit period from time t1 to t4]
When a short circuit occurs at time t1 during the forward feed peak period Tsp, as shown in Fig. 1C, the voltage Vw between the output terminals drops sharply to a short circuit voltage value of several volts, and the short circuit determination signal Sd changes to a high level (short circuit period) as shown in Fig. 1D. In response to this, the system transitions to a predetermined forward feed deceleration period Tsd from time t1 to t2, and the feed speed Fw decelerates from the forward feed peak value Wsp to 0 as shown in Fig. 1A. For example, the forward feed deceleration period Tsd is set to 1 ms.

As shown in FIG. 1A, the feed speed Fw enters a predetermined reverse acceleration period Tru between times t2 and t3, and accelerates from 0 to the reverse peak value Wrp. During this period, the short circuit period continues. For example, the reverse acceleration period Tru is set to 1 ms.

When the reverse feed acceleration period Tru ends at time t3, as shown in FIG. 1A, the feed speed Fw enters the reverse feed peak period Trp and becomes the reverse feed peak value Wrp described above. The reverse feed peak period Trp continues until an arc occurs at time t4. Therefore, the period from time t1 to t4 is the short circuit period. The reverse feed peak period Trp is not a predetermined value, but is about 3 ms. For example, the reverse feed peak value Wrp is set to -40 m/min.

As shown in FIG. 1B, the welding current Iw during the short circuit period from time t1 to t4 is a predetermined initial current value during a predetermined initial period. Thereafter, the welding current Iw rises at a predetermined short circuit slope, and when it reaches a predetermined short circuit peak value, it maintains that value.

As shown in FIG. 1C, the voltage Vw between the output terminals rises from the point where the welding current Iw reaches its peak value during a short circuit. This is because a constriction gradually forms in the droplet at the tip of the welding wire 1 due to the reverse feed of the welding wire 1 and the pinching force caused by the welding current Iw.

When the elapsed time from the start of the short circuit period at time t1 reaches the reference time Tn, it is estimated that the state of the necking has reached the reference state, and the current decrease signal Nd changes to a high level for a short time at time t31, as shown in FIG. 1(G). The reference time Tn is set by the reference time setting signal Tnr in FIG. 1. Furthermore, the reference time setting signal Tnr is set as a value obtained by subtracting a predetermined time from the value of the average short circuit period calculation signal Tsa in FIG. 1. The average short circuit period calculation signal Tsa is calculated by taking a moving average of the short circuit period over a predetermined period. For example, if the short circuit from time t1 is the mth short circuit, the predetermined period is 3, and the short circuit periods during the predetermined period are Ts(m-3), Ts(m-2), and Ts(m-1), the reference time setting signal Tsa(m) during the mth short circuit period is calculated as follows.
Tsa(m)=(Ts(m-3)+Ts(m-2)+Ts(m-1))/3
The short circuit time is a substantially constant value for each of various welding conditions. Therefore, by calculating the average short circuit time, the short circuit time under the current welding conditions can be estimated. Then, by subtracting a predetermined time from this average short circuit time to set the reference time Tm, it can be estimated that the state of necking is in the reference state a predetermined time before the short circuit ends and the arc re-strikes. For example, the value of the average short circuit time calculation signal Tsa is about 5 ms, the predetermined time is 0.5 ms, and the reference time Tn is about 4.5 ms. In this manner, the reference time Tn can be automatically set to an appropriate value under various welding conditions.

At time t31, as shown in FIG. 1(G), in response to the current reduction signal Nd becoming high level for a short time, the drive signal Dr in FIG. 1 becomes low level, so that the transistor TR in FIG. 1 is turned off and the current reduction resistor R in FIG. 1 is inserted into the current path. At the same time, the current control setting signal Icr in FIG. 1 becomes small to the value of the low-level current setting signal Ilr. For this reason, as shown in FIG. 1(B), the welding current Iw suddenly decreases from the peak value at the time of short circuit to the low-level current value. Then, when the welding current Iw decreases to the low-level current value, the drive signal Dr returns to the high level, so that the transistor TR becomes on and the current reduction resistor R is short-circuited. As shown in FIG. 1(B), the welding current Iw maintains the low-level current value until a predetermined delay period Tc has elapsed since the arc re-ignition, because the current control setting signal Icr remains the low-level current setting signal Ilr. Therefore, the transistor TR is in the off state only during the period from when the current reduction signal Nd changes to a high level until the welding current Iw decreases to a low-level current value. As shown in FIG. 1C, the voltage Vw between the output terminals decreases once as the welding current Iw decreases, and then rises sharply. The above-mentioned parameters are set to the following values, for example: initial current = 40 A, initial period = 0.5 ms, short circuit slope = 180 A/ms, short circuit peak value = 400 A, low level current value = 50 A, delay period Tc = 1 ms.

[Operation during arc period from time t4 to t7]
At time t4, when the pinching force caused by the reverse feed of the welding wire and the flow of the welding current Iw causes the necking to progress and an arc to be generated, as shown in Fig. 1C, the voltage Vw between the output terminals rapidly increases to an arc voltage value of several tens of volts, and the short circuit determination signal Sd changes to a low level (arc period) as shown in Fig. 1D. In response to this, the system transitions to a predetermined reverse feed deceleration period Trd from time t4 to t5, and the feed speed Fw decelerates from the reverse feed peak value Wrp to 0 as shown in Fig. 1A. For example, the reverse feed deceleration period Trd is set to 1 ms.

When the reverse feed deceleration period Trd ends at time t5, a predetermined forward feed acceleration period Tsu begins from time t5 to t6. During this forward feed acceleration period Tsu, as shown in FIG. 1A, the feed speed Fw accelerates from 0 to the forward feed peak value Wsp. During this period, the arc period continues. For example, the forward feed acceleration period Tsu is set to 1 ms.

When the forward acceleration period Tsu ends at time t6, as shown in FIG. 1A, the feed speed Fw enters the forward peak period Tsp and reaches the forward peak value Wsp described above. The arc period continues during this period. The forward peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to t7 is the arc period. When a short circuit occurs, the operation returns to that at time t1. The forward peak period Tsp is not a predetermined value, but is about 5 ms. For example, the forward peak value Wsp is set to 60 m/min.

When an arc is generated at time t4, as shown in FIG. 1C, the voltage Vw between the output terminals increases rapidly to an arc voltage value of several tens of volts. On the other hand, as shown in FIG. 1B, the welding current Iw continues to have a low current value from time t4 until the delay period Tc. This is because if the current value is increased immediately after the arc is generated, the reverse feed of the welding wire and the melting of the welding wire by the welding current will be added together, causing the arc length to increase rapidly and possibly resulting in an unstable welding state.

When the delay period Tc ends at time t51 during the forward acceleration period Tsu, as shown in FIG. 1(E), the first arc period signal Sta1 changes to a high level, and a predetermined first arc period Ta1 from time t51 to t61 begins. Constant current control continues during this first arc period Ta1, and as shown in FIG. 1(B), a predetermined first arc current Ia1 determined by the first arc current setting signal Ia1r in FIG. 1 flows. As shown in FIG. 1(C), the output terminal voltage Vw becomes a large value determined by the current value and arc load. For example, the delay period Tc is about 1 ms, the first arc period Ta1 is about 1 ms, and the first arc current Ia1 is about 400 A.

At time t62, when a predetermined current drop time Td has elapsed from the arc generation time t4, the third arc period signal Sta3 changes to a high level, as shown in FIG. 1F. The period from time t61 to t62 is the second arc period Ta2. During this second arc period Ta2, constant voltage control is performed. As shown in FIG. 1B, the second arc current Ia2 varies depending on the arc load, but is smaller than the first arc current Ia1 and larger than the third arc current Ia3. In other words, the output is controlled so that Ia1>Ia2>Ia3. As shown in FIG. 1C, the output terminal voltage Vw is controlled to a predetermined value by constant voltage control, and is an intermediate value between the voltage value of the first arc period Ta1 and the voltage value of the third arc period Ta3. The second arc period Ta2 is not a predetermined value, but is about 4.5 ms.

The period from time t62 when the third arc period signal Sta3 changes to a high level to time t7 when a short circuit occurs is the third arc period Ta3. Constant current control is performed during this third arc period Ta3. As shown in FIG. 1B, a predetermined third arc current Ia3 determined by the third arc current setting signal Ia3r in FIG. 1 flows. As shown in FIG. 1C, the output terminal voltage Vw is a value determined by the current value and the arc load. For example, the third arc current Ia3 is set to 60 A. The third arc period Ta3 is not a predetermined value, but is about 0.5 ms.

In the above embodiment, the welding wire is fed forward during the arc period and fed backward during the short circuit period, but it may be fed at a constant speed throughout the entire period.

The arc welding device according to the present embodiment described above includes an average short circuit time calculation unit that receives a short circuit determination signal, calculates an average short circuit time at a predetermined cycle, and outputs an average short circuit time calculation signal, and a reference time setting unit that sets a reference time based on the average short circuit time calculation signal. In this embodiment, the reference time that determines the timing to reduce the welding current by estimating that the necking state has reached the reference state is automatically set based on the average short circuit time. For this reason, the reference time can be automatically set to an appropriate value according to various welding conditions. As a result, in this embodiment, high-quality welding with little spatter can be performed under various welding conditions without detecting the voltage of the arc generation part.

Furthermore, according to this embodiment, it is preferable that the reference time setting unit sets the reference time to a value obtained by subtracting a predetermined time from the value of the average short circuit duration calculation signal. In this way, the welding current can be brought to a low level current value just before the arc re-strikes, thereby reducing the amount of spatter and facilitating the transition to the arc period.

Furthermore, according to this embodiment, it is preferable that the feed motor feeds the welding wire in the forward direction during the arc period and in the reverse direction during the short circuit period. When forward and reverse feed control of the welding wire is performed, the variation in the short circuit time is smaller than when constant speed feed control is performed. This improves the accuracy of estimating the state of necking formation based on the reference time. As a result, the amount of spatter generated can be further reduced.

1 Welding wire
2. Base material
3. Arc
4. Welding torch
5 Feed roll CM Current comparison circuit Cm Current comparison signal DR Drive circuit Dr Drive signal E Output voltage Ea Error amplification signal ED Output voltage detection circuit Ed Output voltage detection signal EI Current error amplification circuit Ei Current error amplification signal ER Output voltage setting circuit Er Output voltage setting signal EV Voltage error amplification circuit Ev Voltage error amplification signal FC Feed control circuit Fc Feed control signal FR Feed speed setting circuit Fr Feed speed setting signal Fw Feed speed Ia1 First arc current IA1R First arc current setting circuit Ia1r First arc current setting signal Ia2 Second arc current Ia3 Third arc current IA3R Third arc current setting circuit Ia3r Third arc current setting signal ICR Current control setting circuit Icr Current control setting signal ID Current detection circuit Id Current detection signal ILR Low level current setting circuit Ilr Low level current setting signal Iw Welding current ND Current reduction timer circuit Nd Current reduction signal PM Power control unit R Current reducing resistor SD Short circuit determination circuit Sd Short circuit determination signal STA1 First arc period circuit Sta1 First arc period signal STA3 Third arc period circuit Sta3 Third arc period signal SW Power supply characteristics changeover circuit Tc Delay period TA1R First arc period setting circuit Ta1r First arc period setting signal Td Current fall time Tn Reference time TNR Reference time setting circuit Tnr Reference time setting signal TR Transistor Trd Reverse feed deceleration period TRDR Reverse feed deceleration period setting circuit Trdr Reverse feed deceleration period setting signal Trp Reverse feed peak period Tru Reverse feed acceleration period TRUR Reverse feed acceleration period setting circuit Trur Reverse feed acceleration period setting signal TSA Average short circuit duration calculation circuit Tsa Average short circuit duration calculation signal Tsd Forward feed deceleration period TSDR Forward feed deceleration period setting circuit Tsdr Forward feed deceleration period setting signal Tsp Forward feed peak period Tsu Forward feed acceleration period TSUR Forward feed acceleration period setting circuit Tsur Forward feed acceleration period setting signal VD Voltage detection circuit Vd Voltage detection signal Vw Voltage between output terminals WL Reactor WM Feeding motor Wrp Reverse feed peak value WRR Reverse feed peak value setting circuit Wrr Reverse feed peak value setting signal Wsp Forward feed peak value WSR Forward feed peak value setting circuit Wsr Forward feed peak value setting signal

Claims (3)

a feed motor that feeds the welding wire;
a short circuit determination unit that determines that a short circuit period exists between the welding wire and the base metal and outputs a short circuit determination signal;
a current reduction timer unit which receives the short circuit determination signal as an input and outputs a current reduction signal when a reference time has elapsed from the start point of the short circuit period;
a power control unit that supplies a welding voltage and a welding current between the welding wire and the base material to repeat the short circuit period and the arc period, and reduces the welding current to transition to the arc period when the current reduction signal is input during the short circuit period;
In an arc welding device comprising:
an average short circuit duration calculation unit which receives the short circuit determination signal as an input, calculates an average short circuit duration for every 3 to 10 periods , and outputs an average short circuit duration calculation signal;
a reference time setting unit that automatically sets the reference time based on the average short circuit duration calculation signal that changes every time a short circuit occurs during welding under various welding conditions ;
The arc welding device further comprises: the reference time setting unit sets a value obtained by subtracting a predetermined time from the value of the average short circuit duration calculation signal as the reference time.
2. The arc welding apparatus according to claim 1 . the feed motor feeds the welding wire in a forward direction during the arc period and in a reverse direction during the short circuit period;
3. The arc welding apparatus according to claim 1 or 2.

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