JPH0570550B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for controlling the output of a welding power source in a consumable electrode type short-circuit transfer arc welding method in which short circuits and arc generation are repeated between a consumable electrode and a base material.

Prior Art Figure 1 shows the process of droplet formation and transfer in the consumable electrode type short-circuit transitional arc welding method, in which short-circuiting and arc generation are repeated alternately.
2 is a droplet formed at the tip of the welding wire 1, 3 is an arc, and 4 is a molten pool, that is, a base material. (a) is the initial short-circuit state where the droplet 2 is in contact with the molten pool 4, and b is the intermediate short-circuit state where the contact between the droplet 2 and the molten pool 4 has become reliable and the droplet 2 has moved to the molten pool 4. , (c) shows the late short circuit state where the droplet 2 moves to the molten pool 4 side and a constriction occurs in the droplet 2 between the welding wire 1 and the molten pool 4, and (d) shows the short circuit broken and a welding arc. 3 occurs, (e) is an arc generation state where the tip of welding wire 1 melts and a droplet 2 grows, (f)
1 and 2 respectively show the arc generation state immediately before the droplet 2 short-circuits with the molten pool 4, and the processes of (a) to (f) are repeated.

In conventional welding power sources used in the above-mentioned consumable electrode type short-circuit transitional arc welding method, which repeats short circuits and arc generation, output control is performed by combining a power source with approximately constant voltage characteristics and a reactor that limits the rise of current. . The waveforms of the welding current and welding voltage in this case are shown in FIG. That is, due to the short circuit between the droplet 2 at the tip of the welding wire 1 and the molten pool 4, the welding voltage rapidly decreases, and the welding current increases with a time constant determined by the reactor, external resistance, etc. Then, when the transition of the droplet 2 at the tip of the welding wire 1 to the droplet pool 4 is completed and the arc 3 is generated again, the welding voltage increases rapidly, and the welding current is determined by the external resistance including the reactor and the arc 3. decreases by a constant.

However, when the above-mentioned conventional welding power source is used, it is known that spatter occurs immediately after a short circuit and at the moment when arc 3 is generated.

This occurs when the cross-sectional area of the contact area A between the droplet 2 and the molten pool 4 immediately after the short circuit is small, as shown in Figure 1a, that is, the transfer of the droplet 2 to the molten pool 4 does not proceed. When the welding current becomes too large, the short circuit is broken and an arc 3 is generated, causing spatter. Further, as shown in FIG. 2, when the arc 3 is generated, the welding current reaches its maximum value, and the repulsive energy of the arc 3 generates spatter.

In view of the above-mentioned causes of spatter, the present inventors proposed in Japanese Patent Application No. 58-217288 a method for controlling the output of a welding power source to reduce the amount of spatter generated. This controls the welding current as shown in FIG. In other words, when the droplet 2 at the tip of the welding wire 1 short-circuits with the molten pool 4, the welding current is reduced to a low current I _D
This prevents spatter from occurring immediately after a short circuit. Furthermore, this low current I _D is maintained for a period T _D to ensure welding of the droplet 2 and the molten pool 4. After the period T _D has elapsed, the welding current is increased to a high level, the current I _SP , and the droplet 2
The transition of the liquid to the molten pool 4 is promoted. When the transition of the droplet 2 to the molten pool 4 progresses, and when a constriction occurs in the droplet 2 and a sign of the re-occurrence of the arc 3 is detected, the welding current is lowered to a low level, the current _IRA .
Reduces the energy when arcing occurs and reduces the amount of spatter. When the arc 3 is generated again, the welding current is increased to a high level current I _AP to form a droplet 2 at the tip of the welding wire 1 . Then, after the predetermined period T _AP has elapsed, the welding current is reduced to a low level current I _AB , and this current I _AB is maintained until the droplet 2 short-circuits with the droplet molten pool 4.
Conditions a, b, ... of changes in welding current shown in Fig. 3
f corresponds to the formation and transfer processes of the droplet 2 shown by a, b, . . . , f in FIG. 1 described above.

However, in the output control method of the welding power source described above, when welding is started, the droplet 2 is not formed at the tip of the welding wire 1, so when the welding wire 1 and the base metal 4 are short-circuited, , the period T _D to ensure contact between the droplet 2 and the molten pool 4 becomes meaningless. Generally, this dead time is 1 to 3 msec, and the arc start will be delayed by at least this time. Actually, since the unmelted welding wire 1 is fed during this period, the short circuit time until the tip of the welding wire 1 melts and arc occurs becomes longer.

In addition, with the conventional welding power source that outputs the welding current and welding voltage shown in Fig. 2, when starting welding,
Although the welding current rises when the unmelted welding wire 1 and the base metal 4 are short-circuited, the rate of increase in the welding current is small because it is controlled by the reactor, and therefore,
It took a long time to start the arc.

This delay in arc start had a particularly negative effect on automatic welding.

OBJECTS OF THE INVENTION The present invention has been made in view of the above circumstances, and its purpose is to provide a method for controlling the output of a welding power source that prevents a delay in arc start when starting welding.

Summary of the Invention In the consumable electrode type short-circuit transitional arc welding method in which short circuit and arc generation are repeated between the base metal and the consumable electrode being fed, an arc occurs immediately before the short circuit occurs between the base metal and the consumable electrode. Judging from the magnitude of the voltage applied between the base metal and the consumable electrode or the magnitude of the welding current, it is determined whether the base metal and the consumable electrode are short-circuited and then the welding current reaches a predetermined level. change the point at which the welding current is supplied.

Examples of the invention An embodiment of the present invention will be described below.

In an arc welding method in which short circuit and arc generation are alternately repeated between welding wire 1 and base metal 4,
The fact that a hot droplet 2 is formed at the tip of the welding wire 1 before a short circuit occurs means that an arc 3 is generated. Furthermore, if the temperature of the droplet 2 is low and the droplet 2 is in a semi-molten state before the short circuit occurs, arc breakage occurs and heating is stopped. Furthermore, if there is no droplet 2 at the tip of the welding wire 1 or if the droplet 2 has cooled down and solidified completely, it means that the arc 3 has not been generated for a long time before the short circuit occurs. . Therefore, in the present invention, when a short circuit occurs, the time point at which a predetermined level of short circuit current is supplied is changed depending on whether or not the arc 3 has occurred immediately before the short circuit. For example, when starting welding, since no arc has been generated for a long time, the welding power source should be turned on to immediately supply a high-level short-circuit current to eliminate the delay in arc start. Control.

FIG. 4 shows the configuration of a control device for carrying out the output control method of a welding power source according to the present invention, in which a welding voltage detection circuit 5 for detecting welding voltage is connected to each input terminal of a short circuit detection circuit 6 and an arc breakage detection circuit 7. connected to. The short circuit detection circuit 6 is a circuit that detects a short circuit when the voltage value supplied from the welding voltage detection circuit 5 becomes substantially 0, and the output terminal of the short circuit detection circuit 6 is connected to the first terminal of the OR circuit 8. The input terminal is connected to a first inverting input terminal of AND circuit 9 and a first input terminal of AND circuit 10, respectively. The arc breakage detection circuit 7 is a circuit that detects the occurrence of an arc when the voltage value supplied from the welding voltage detection circuit 5 exceeds a predetermined value.The output terminal of the arc breakage detection circuit 7 is connected to the OR circuit 8. The second input terminal and the second inverting input terminal of the AND circuit 9 are respectively connected. The output terminal of the OR circuit 8 is connected to the input terminal of a switch drive circuit 12 that opens and closes the switch 11.
The output terminal of the AND circuit 9 is connected to the input terminal of a switch drive circuit 14 that opens and closes the switch 13. A switch 11 and a switch 13 are connected in series between a power source that outputs a positive voltage +V and a power source that outputs a negative voltage -V. A connection point _P1 between the switch 11 and the switch 13 is connected to the first input terminal of an operational amplifier 16 via a resistor 15, and a capacitor 17 is connected between the first input terminal and the output terminal of the operational amplifier 16. Connected. Operational amplifier 16
The second input terminal of is grounded. Furthermore, the output terminal P ₂ of the operational amplifier 16 is connected to a first input terminal of the comparator 18 . The second input terminal of this comparator 18 is grounded, and the comparator 18 and the output terminal P ₃ are connected to the second input terminal of the AND circuit 10 .
The output terminal of the AND circuit 10 is the short circuit current setting circuit 1
9, the short circuit current setting circuit 19
An output terminal of the welding power source 20 is connected to an input terminal of the welding power source 20. A circuit 21 surrounded by a dashed line including the above-mentioned switches 11, 13, resistor 15, capacitor 17, operational amplifier 16 and comparator 18 constitutes a timer.

When welding progresses by alternately repeating short circuits and arc generation, when a short circuit is detected by the short circuit detection circuit 6 based on a signal indicating the welding voltage from the welding voltage detection circuit 5, the output of the short circuit detection circuit 6 becomes "High". level, the output of the OR circuit 8 becomes a "High" level, and the output of the AND circuit 9 becomes a "Low" level. Then, the switch drive circuit 12 operates and the switch 11 closes.
The switch drive circuit 14 operates and the switch 13 opens. Here, the voltage at the output terminal P ₂ of the operational amplifier 16 decreases with a time constant determined by the resistor 15 and capacitor 17. When the voltage at the terminal _P2 becomes 0V or less, the output terminal _P3 of the comparator 18 becomes "High" level. The signal at terminal _P3 is input to the short-circuit current setting circuit 19 via the AND circuit 10, and the short-circuit current setting circuit 19 outputs a signal to the welding power source 20 to output a short-circuit current that is at a high level at the time of a short circuit. is input. A short circuit current is then supplied to the welding wire 1.

When a short circuit and arc breakage do not occur, that is, when an arc occurs, the outputs of the short circuit detection circuit 6 and the arc breakage detection circuit 7 are originally at "Low" level, and the output of the OR circuit 8 is The level becomes "Low", and the output of the AND circuit 9 becomes "High" level. Then, the switch drive circuit 12 operates to open the switch 11, and the switch drive circuit 14 operates to close the switch 13.
Therefore, the output terminal P ₂ of the operational amplifier 16 maintains a positive voltage, the output terminal P ₃ of the comparator 18 becomes a “Low” level, and the output of the AND circuit 10 is at a “Low” level and the short circuit current setting circuit No signal is input from 19 to the welding power source 20 for outputting a short circuit current.

When arc breakage occurs during arc generation, the arc breakage detection circuit 7 detects the arc breakage, the output of the arc breakage detection circuit 7 becomes "High" level, and the output of the OR circuit 8 becomes "High" level. At the same time, the output of the AND circuit 9 becomes "Low" level. Then, the switch drive circuit 12 operates, the switch 11 closes, and the switch drive circuit 14 closes.
operates, the switch 13 opens, and the operational amplifier 16
The voltage at output terminal P ₂ of resistor 15 and capacitor 1
It decreases with a time constant determined by 7. If the voltage at terminal P ₂ is
When the voltage falls below 0V, the output terminal _P3 of the comparator 18 becomes "High" level.After that, when the droplet 2 at the tip of the welding wire 1 short-circuits with the molten pool 4, the output terminal of the short circuit detection circuit 6 becomes "High" level. level, the output of the OR circuit 8 continues to be at the “High” level, the output of the AND circuit 10 is set to the “High” level, the short circuit current setting circuit 19 is operated, and a short circuit current is output to the welding power source 20. Input the signal to Here, the welding power source 20 supplies a short circuit current to the welding wire 1.

Before welding starts, since the arc 3 is not generated, the arc breakage detection circuit 7 is activated, the output of the OR circuit 8 is "High" level, and the output of the AND circuit 9 is "Low" level. be. The switch 11 is closed by the switch drive circuit 12, and the switch 13 is opened by the switch drive circuit 14. Therefore, the output terminal P ₂ of the operational amplifier 16 is at a negative voltage, and the output terminal P ₃ of the comparator 18 is at the "High" level.
In this state, when welding wire 1 and base metal 4 are short-circuited to start an arc, short-circuit detection circuit 6 is activated, and the output terminal of short-circuit detection circuit 6 becomes "High" level. And circuit 10
The output becomes "High" level, the short-circuit current setting circuit 19 operates, and a signal for outputting a short-circuit current to the welding power source 20 is input, and the welding power source 20 outputs a high-level short-circuit current. do. That is, at the time of arc start, welding wire 1
When short-circuited to the base material 4, a high-level short-circuit current is immediately supplied. Then, a droplet 2 is formed at the tip of the welding wire 1 in a short time, and an arc 3 is generated by the breakage of the droplet 2.

Figure 5 shows how the short circuit current rises during a short circuit; at arc start, the short circuit current rises immediately when a short circuit occurs, and during steady welding, the short circuit current rises after a certain period of time after the short circuit occurs. Furthermore, when a conventional welding power source is used, the rate of increase in short circuit current is low.

In the above embodiment, short circuits and arc breaks are detected by detecting changes in welding voltage, but short circuits and arc breaks are detected by detecting welding current,
By using a welding current detector that outputs the detected value as a voltage, it can be implemented with the circuit shown in FIG. 4 of the above embodiment.

Furthermore, welding methods for carrying out the present invention include methods in which droplets are short-circuited during welding, such as those using CO ₂ or MIG shielding gas, and non-gas earth welding that does not use shielding gas.

Effects of the Invention As explained above, in the present invention, depending on whether or not an arc occurs immediately before a short circuit occurs between the base material and the consumable electrode, By changing the point at which a predetermined level of welding current is supplied, if an arc has not occurred immediately before a short circuit occurs, a high level of welding current is supplied immediately after a short circuit occurs, eliminating the delay in arc start. can do.

[Brief explanation of the drawing]

Figure 1 shows the process of droplet formation and migration, Figure 2 shows the waveforms of welding current and welding voltage when using a conventional welding power source, and Figure 3 shows how to reduce the amount of spatter. FIG. 4 is a block diagram showing the configuration of a control device for carrying out the method for controlling the output of a welding power source according to the present invention, and FIG. It is a figure which shows the state of the rise of the short circuit current in FIG. DESCRIPTION OF SYMBOLS 1... Welding wire, 3... Arc, 4... Base metal (molten pool), 5... Welding voltage detection circuit, 6... Short circuit detection circuit, 7... Arc break detection circuit, 19...
Short-circuit current setting circuit, 20... Welding power source, 21...
timer.

Claims (1)

[Scope of Claims] 1. A welding power source output control method for a consumable electrode type short-circuit transitional arc welding method in which short circuits and arc generation are repeated between the consumable electrode and the base material that are fed, wherein the consumable electrode and the base metal The voltage applied between them is detected and the presence or absence of the occurrence of the short circuit and the occurrence of the arc are detected from the magnitude of the voltage, and when the occurrence of the short circuit is detected, the occurrence of the arc before the occurrence of the short circuit is detected. A method for controlling the output of a welding power source, characterized in that when there is no short circuit, a predetermined level of welding current is supplied to the consumable electrode more quickly than when an arc occurs before a short circuit occurs. 2. The output control method for a welding power source according to claim 1, wherein the presence or absence of the occurrence of the arc before the occurrence of the short circuit is determined based on the magnitude of the welding current.