JP2014014835A - Constriction detection time current control method of consumable electrode arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occurrence of spatter caused by vibration of a molten pool, in a constriction detection time current control method for quickly reducing a welding current by detecting constriction of a droplet in a short-circuit period.SOLUTION: When detecting the constriction of the droplet, a welding current Iw energized to a short-circuit load is reduced, and is maintained at a low constriction current value Im, and when an arc is regenerated, the welding current Iw is raised up to a high arc current value Ih from the low constriction current value Im by imparting an inclination S to the welding current Iw when a delay period Td passes. This inclination S in a front half part and a rear half par is a value different from in an intermediate part, and is set so that the inclination of the front half part and the rear half part is a value smaller than the inclination of the intermediate part. Thus, transfer to an inclination period Tu from the constriction current Im and transfer to the high arc current Ih from the inclination period Tu become smooth, and the molten pool is not vibrated when arc force is suddenly changed, so that the occurrence of spatter can be reduced.

Description

  The present invention relates to a current control method for detecting constriction in consumable electrode arc welding, in which a constriction phenomenon of droplets is detected during a short-circuit period, and the welding current is rapidly reduced just before the reoccurrence of arc to reduce the occurrence of spatter.

  In consumable electrode arc welding that repeats the arc generation state and short circuit state between the consumable electrode (welding wire) and the base metal, the constriction electrode of the droplet constriction phenomenon, which is a precursor to the occurrence of an arc again from the short circuit state・ Detected by changes in the voltage value or resistance value between the base metals, and when this squeezing phenomenon is detected, the welding current flowing through the short-circuit load is reduced and maintained at a low squeezing current value. A current control method at the time of constriction detection of consumable electrode arc welding in which the welding current is ramped from the low constriction current value to a high arc current value at the time when the delay period has elapsed and the arc load is energized is widely used. . This method is mainly applied to consumable electrode arc welding of steel materials. As the consumable electrode arc welding, carbon dioxide arc welding, mag welding, pulse mag welding, AC pulse mag welding, or the like is used. As a transfer form of the droplet, a short circuit transfer form, a globule transfer form with a short circuit, a spray transfer form with a short circuit, and the like are applied.

  When the droplet at the tip of the welding wire formed during the arc period comes into contact with the base material and is short-circuited, a short-circuit current having a large current value is passed through the droplet. Necking occurs at the top of the droplet due to the pinch force caused by this short-circuit current. And this constriction progresses rapidly, the droplets are detached from the welding wire to the molten pool, and the arc is regenerated. When this constriction occurs, the short circuit is opened after an extremely short time of about several hundreds μs, and the arc is regenerated. In other words, this constriction phenomenon is a precursor of arc reoccurrence. When the constriction occurs, the current path of the short-circuit current becomes narrow at the constricted portion, and the resistance value of the constricted portion increases. The increase in the resistance value increases as the constriction progresses and the constricted portion becomes narrower. Therefore, the occurrence of the constriction phenomenon can be detected by detecting a change in resistance value between the welding wire and the base material during the short circuit period. This change in resistance value can be calculated by dividing the welding voltage by the welding current. In addition, when the short-circuit current during the period in which the constriction occurs can be regarded as a substantially constant value, the occurrence of the constriction phenomenon can be detected by the change in the welding voltage instead of the change in the resistance value. As a specific squeezing detection method, by calculating the rate of change (differential value) of the resistance value or welding voltage value during the short circuit period, it is determined that this rate of change has reached a predetermined squeezing detection reference value. Constriction detection is performed. As a second method, a voltage rise value from a stable short-circuit voltage value before the occurrence of constriction during the short-circuit period is detected, and it is determined that the voltage rise value has reached a predetermined constriction detection reference value. Constriction detection is performed.

  According to the invention of Patent Document 1, the change in the arc force is softened by giving a predetermined inclination to the welding current that is raised from the low current value to the high arc current value after the arc is regenerated. In this way, since the vibration of the molten pool due to the arc force is reduced, the generation of spatter due to the vibration of the molten pool can be reduced. Furthermore, since the vibration of the molten pool is reduced, it is possible to suppress the occurrence of a re-short circuit immediately after the arc is regenerated.

Japanese Patent No. 4875311

  As described above, in the prior art, the arc force change is softened by giving a predetermined slope to the welding current that is increased from a low squeezing current value to a high arc current value after the arc is regenerated. The vibration of the molten pool due to the force is reduced, and the occurrence of spatter due to the vibration of the molten pool can be reduced. In order to further reduce the generation of spatter, observation of the arc generation portion with a high-speed camera revealed the following. That is, there is a period during which the vibration of the weld pool increases during the increase in the welding current from the low current value to the high arc current value, and sputtering occurs during that period. This part of the period is a period in which the low current value shifts to a rising slope and a period in which the rising slope shifts to a high arc current value.

  In view of this, the present invention provides a current control method for detecting constriction in consumable electrode arc welding that can reduce spatter generated during a rising slope from a low constriction current value to a high arc current value after arc reoccurrence. Objective.

In order to solve the above-described problem, the invention of claim 1 is consumable electrode arc welding in which an arc generation state and a short-circuit state are repeated between a consumable electrode and a base material, and the arc is regenerated from the short-circuit state. The constriction phenomenon of droplets, which is a precursor phenomenon, is detected by a change in the voltage value or resistance value between the consumable electrode and the base material, and when this constriction phenomenon is detected, the welding current flowing to the short-circuit load is reduced to lower the constriction current value. When the arc is regenerated, the welding current is ramped up from the low constriction current value to a high arc current value at that time or when a delay period has elapsed from that point, and the consumable electrode arc welding is performed. In the current control method when detecting constriction,
The inclination of the first half part and the second half part is different from that of the intermediate part, and the inclination of the first half part and the second half part is smaller than the inclination of the intermediate part.
This is a current control method for detecting constriction in consumable electrode arc welding.

According to a second aspect of the present invention, the slope of the first half portion is a value that continuously changes from 0 to the slope of the intermediate portion, and the slope of the second half portion is a value that continuously changes from the slope of the intermediate portion to 0. Is,
2. The current control method according to claim 1, wherein the constriction detection of consumable electrode arc welding is detected.

In the invention of claim 3, the period lengths of the first half part, the middle part and the second half part are the same.
The current control method according to claim 1 or 2, wherein the constriction detection of consumable electrode arc welding is detected.

In the invention of claim 4, the inclination of the intermediate portion changes according to the feeding speed.
The current control method for constriction detection of consumable electrode arc welding according to any one of claims 1 to 3.

  According to the present invention, it is possible to smoothly shift from a low current to a middle portion having a large slope through a first half portion having a small slope. Similarly, it is possible to smoothly shift from a middle portion having a large slope to a high arc current through a second half portion having a small slope. For this reason, the slope of the welding current does not change suddenly, and the arc force does not change suddenly to vibrate the molten pool, so that the generation of spatter can be further reduced.

It is a block diagram of the welding power supply for implementing the current control method at the time of the constriction detection of consumable electrode arc welding which concerns on embodiment of this invention. It is a timing chart of each signal in the welding power supply of FIG. In FIG. 2, it is a figure which shows the change of the value of the electric current setting signal Ir with respect to the elapsed time t in the constant current characteristic period of the time t2-t5.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of a welding power source for carrying out a current control method during constriction detection in consumable electrode arc welding according to an embodiment of the present invention. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit MC receives a commercial power supply (not shown) such as three-phase 200V, performs output control such as inverter control and chopper control according to an error amplification signal Ea described later, and outputs an output voltage Vo and a welding current Iw. To do. The parallel circuit of the transistor TR and the resistor R is inserted into the energization path, and as will be described later, when the constriction is detected, the transistor TR is turned off and energized through the resistor R to rapidly reduce the welding current Iw. The welding wire 1 is fed at a constant speed by a feed motor (not shown), and a welding voltage Vw is applied to the base material 2 to generate an arc 3.

  The squeezing detection circuit ND receives the welding voltage Vw and outputs a squeezing detection signal Nd that changes to a low level when the squeezing is detected by the above-described squeezing detection method and returns to a high level when an arc is regenerated. As described above, the resistance value of the droplet may be calculated by dividing the welding voltage Vw by the welding current Iw, and the constriction may be detected by the change in the resistance value. The drive circuit DR outputs a drive signal Dr that turns off the transistor TR only when the squeezing detection signal Nd is at a low level. That is, since the resistor R is inserted into the current path during the constriction detection period Tn, the current path resistance value is 10 times or more larger than the short-circuit load (about 0.01 to 0.03Ω) (about 0.5 to 3Ω). )become. For this reason, the energy accumulated in the DC reactor in the welding power source and the reactor of the cable is suddenly discharged, and the welding current Iw decreases rapidly. Since the transistor TR is in an on state during a period other than the constriction detection period Tn, the resistor R is short-circuited to have the same configuration as that of a normal welding power source.

  The delay period setting circuit TDR outputs a predetermined delay period setting signal Tdr. The rising period setting circuit TUR outputs a predetermined rising period setting signal Tur. The low current setting circuit IMR outputs a predetermined low current setting signal Imr. The high arc current setting circuit IHR outputs a predetermined high arc current setting signal Ihr. The inclination locus storage circuit SM outputs a predetermined inclination locus storage signal Sm, which will be described later with reference to FIG. The feed speed setting circuit FR outputs a feed speed setting signal Fr for setting the feed speed of the welding wire 1. The squeezing detection current slope control circuit NSC includes the delay period setting signal Tdr, the rising period setting signal Tur, the low squeezing current setting signal Imr, the high arc current setting signal Ihr, and the squeezing detection signal Nd. Then, the above-described inclination trajectory storage signal Sm and the above-described feed speed setting signal Fr are input, and the processes shown in FIGS. 2 and 3 to be described later are performed to output the power supply characteristic switching signal Sw and the current setting signal Ir.

  The voltage setting circuit VR outputs a predetermined voltage setting signal Vr. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The voltage detection circuit VD detects the output voltage Vo and outputs a voltage detection signal Vd. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vr and the voltage detection signal Vd, and outputs a voltage error amplification signal Ev. The current error amplification circuit EI amplifies an error between the current setting signal Ir and the current detection signal Id, and outputs a current error amplification signal Ei. The power supply characteristic switching circuit SW receives the power supply characteristic switching signal Sw as an input, and switches to the b side during the squeezing detection period Tn + delay period Td + rise period Tu, which will be described later with reference to FIG. 2, and error-amplifies the current error amplification signal Ei. The signal Ea is output, and during the other periods, the voltage is switched to the a side and the voltage error amplified signal Ev is output as the error amplified signal Ea. Therefore, the period switched to the a side is a constant current characteristic period, and the period switched to the b side is a constant voltage characteristic period.

  FIG. 2 is a timing chart of each signal in the welding power source of FIG. (A) shows the time change of the welding current Iw, (B) shows the time change of the welding voltage Vw, (C) shows the time change of the squeezing detection signal Nd, (D) ) Shows a time change of the power supply characteristic switching signal Sw, and FIG. 9E shows a time change of the current setting signal Ir. Hereinafter, a description will be given with reference to FIG.

  In the figure, a period other than the constant current characteristic period at times t2 to t5 is a constant voltage characteristic period. During this constant voltage characteristic period, the transistor TR is in an on state, so that it has the same current / voltage waveform as in the case of general consumable electrode arc welding.

  When the droplet at the tip of the welding wire and the base material are short-circuited at time t1, the welding voltage Vw rapidly decreases to a short-circuit voltage value of several volts as shown in FIG. In addition, the welding current Iw gradually increases. As the welding current Iw increases, a pinch force acts on the droplet to form a constriction at the top of the droplet.

  When the constriction progresses and the voltage rise value ΔV reaches the constriction detection reference value Vtn at time t2 as shown in FIG. 5B, the constriction detection signal Nd becomes high level as shown in FIG. Changes from low to low level. In response to this, as shown in FIG. 4D, the power supply characteristic switching signal Sw is changed to the low level, and the power supply characteristic is switched to the constant current characteristic. At the same time, since the transistor TR is turned off and the resistor R is inserted into the energization path, the welding current Iw is rapidly decreased and kept at the current value Im as shown in FIG.

  If the constriction further progresses and the arc is regenerated at time t3, the welding voltage Vw reaches the short circuit / arc discriminating value Vta as shown in FIG. 5B, so that the constriction occurs as shown in FIG. The detection signal Nd changes to the high level. During a predetermined delay period Td from time t3 to time t4, the current setting signal Ir is low and maintains a value determined by the current setting signal Imr, as shown in FIG. For this reason, the welding current Iw is low and the current value Im is maintained as shown in FIG. When the arc is regenerated at time t3, the welding current value is low and the current value Im, so that the arc force at the time of droplet detachment becomes weak and the occurrence of spatter is suppressed. Further, a predetermined delay period Td from the time when the arc is regenerated at time t3 to time t4 is provided, and during this delay period Td, the current setting signal Ir = Imr is maintained as shown in FIG. This waits for the vibration of the molten pool to settle due to the influence of the droplets transferred to the molten pool. Since the welding current Iw is increased in the next process after the vibration of the molten pool has subsided, the change in the arc force due to the current change and the vibration of the molten pool do not resonate to generate spatter. In many cases, the delay period Td is determined depending on the welding conditions. The delay period Td is about 0 to 1 ms.

  When the delay period Td ends at time t4, the current setting signal Ir rises with a slope characteristic determined by the slope trajectory memory signal Sm from the value of the squeezing current setting signal Imr, as shown in FIG. The value of the high arc current setting signal Ihr is reached at time t5 when the rising period Tu ends. As will be described later with reference to FIG. 3, the slope locus storage signal Sm has a slope different from that of the intermediate portion in the first half portion and the latter half portion, and the slope of the first half portion and the latter half portion is smaller than the slope of the intermediate portion. In response to this, as shown in FIG. 5A, the welding current Iw is low and rises from the squeezing current value Im by the slope characteristic S, and reaches the high arc current value Ih at time t5. The rising period Tu from time t4 to t5 is about 1 ms, the low current value Im is about several tens of A, and the high arc current value Ih is about several hundred A.

  When the rising period Tu ends at time t5, as shown in FIG. 4D, the power supply characteristic switching signal Sw changes to a high level, so that the welding power supply has a constant voltage characteristic. As shown in FIG. 3A, the welding current Iw changes according to the arc load and gradually decreases after maintaining a value substantially equal to the high arc current value Ih for a short time after time t5. As shown in FIG. 5B, the welding voltage Vw gradually decreases and converges to the value of the voltage setting signal Vr.

  FIG. 3 is a diagram showing a change in the value of the current setting signal Ir with respect to the elapsed time t in the constant current characteristic period from time t2 to t5 in FIG. 2 described above. In the figure, during the squeezing detection period Tn from time t2 to t3 and during the delay period Td from time t3 to t4, the current setting signal Ir = Imr (low squeezing current setting signal). During the subsequent rising period Tu from time t4 to t5, the current setting signal Ir rises from the value of the squeezing current setting signal Imr to a polygonal line or a curve of the slope characteristics L1 to L2 set by the slope trajectory memory signal Sm. Thus, the value of the high arc current setting signal Ihr is reached at time t5.

  The slope characteristic L1 indicated by the broken line is formed by three broken lines of the first half part, the middle part and the second half part. The slopes of the first half and the second half are smaller than the slope of the middle part. In the figure, the period lengths of the first half part, the middle part and the second half part have the same value. The period length of the first half part and the second half part is in a range of about −50 to 0% of the period length of the intermediate part.

  The slope characteristic L2 shown in practice also changes in a curved manner in the first half part, the middle part and the second half part. The slope of the first half is a value that continuously changes from the slope 0 of the narrow current setting signal Imr to the slope of the middle portion. The slope of the latter half is a value that continuously changes from the slope of the middle part to the slope 0 of the high arc current setting signal Ihr.

  These inclination characteristics are stored in advance in the inclination trajectory storage circuit SM. The inclination of the intermediate portion is changed so as to increase in proportion to the value of the feed speed setting signal Fr, that is, the welding current average value. When the welding current average value is increased, the inclination is increased to promptly increase the welding current Iw, thereby preventing the arc heat from becoming insufficient. It is desirable to switch the inclination of the intermediate part depending on the welding method, welding speed, welded joint, base material, and the like. The inclination of the intermediate portion is about 50 to 100 A / 100 μs. The inclination of the first half part and the second half part is about 50% of the inclination of the middle part. When the inclination of the portion changes in a curved line, the average value of the continuously changing inclination becomes these numerical values.

  According to the above-described embodiment, the slope is increased from the low current value to the high arc current value, and this slope is different from the middle part in the first half part and the second half part. The slope is smaller than the slope of the middle part. In this way, it is possible to smoothly shift from a low current to a middle portion having a large slope through a first half portion having a small slope. Similarly, it is possible to smoothly shift from a middle portion having a large slope to a high arc current through a second half portion having a small slope. For this reason, the slope of the welding current does not change suddenly, and the arc force does not change suddenly to vibrate the molten pool, so that the generation of spatter can be further reduced.

  In the above-described embodiment, the case where the slope characteristic during the rising period Tu is generated by controlling the current setting signal Ir under the constant current characteristic has been described. As another method, the ramp characteristics may be generated by electronic reactor control, which is a known technique, with constant voltage characteristics during the rising period Tu. In this case, the gain of the electronic reactor control may be increased in order to reduce the inclination of the first half portion and the latter half portion of the inclination characteristic, and the gain of the electronic reactor control may be reduced in order to increase the inclination of the intermediate portion.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc DR Drive circuit Dr Drive signal Ea Error amplification signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit EV Voltage error amplification signal FR Feeding speed setting circuit Fr Feeding speed setting signal ID current detection circuit Id current detection signal Ih high arc current value IHR high arc current setting circuit Ihr high arc current setting signal Im low constriction current value IMR low constriction current setting circuit Imr low constriction current setting signal Ir current setting signal Iw welding current L1 , L2 Inclination characteristic MC Power supply main circuit ND Constriction detection circuit Nd Constriction detection signal NSC Constriction detection current inclination control circuit R Resistor S Inclination characteristic SM Inclination locus storage circuit Sm Inclination locus storage signal SW Power supply characteristic switching circuit Sw Power supply characteristic switching signal t Elapsed time Td Delay period TDR Delay period setting circuit Tdr Delay period setting signal No. Tn Necking detection period TR Transistor Tu Rising period TUR Rising period setting circuit Tur Rising period setting signal VD Voltage detection circuit Vd Voltage detection signal Vo Output voltage VR Voltage setting circuit Vr Voltage setting signal Vta Short circuit / arc discrimination value Vtn Constriction detection reference value Vw Welding voltage ΔV Voltage rise value

Claims (4)

In consumable electrode arc welding where the arc generation state and short circuit state are repeated between the consumable electrode and the base material, the constriction phenomenon of droplets, which is a precursor to the arc re-occurring from the short circuit state, is observed between the consumable electrode and the base material. Detected by a change in the voltage value or resistance value of this, and when this squeezing phenomenon is detected, the welding current flowing to the short-circuit load is reduced and maintained at a low squeezing current value, and when the arc is regenerated, at that time or after that a delay period has elapsed In the current control method at the time of constriction detection of consumable electrode arc welding in which the welding current is ramped up from the low constriction current value to a high arc current value at a time point and the arc load is energized,
The inclination of the first half part and the second half part is different from that of the intermediate part, and the inclination of the first half part and the second half part is smaller than the inclination of the intermediate part.
A current control method for detecting a constriction in consumable electrode arc welding. The slope of the first half portion is a value that continuously changes from 0 to the slope of the intermediate portion, and the slope of the second half portion is a value that continuously changes from the slope of the intermediate portion to 0.
The current control method for detecting constriction in consumable electrode arc welding according to claim 1. The first half part, the middle part and the second half part have the same period length,
The current control method at the time of constriction detection of consumable electrode arc welding according to claim 1 or 2. The slope of the intermediate portion changes according to the feeding speed.
The current control method at the time of constriction detection of consumable electrode arc welding according to any one of claims 1 to 3.

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