JP2012071310A - Method of detecting/controlling constriction in consumable electrode arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly regenerate an arc even when any constriction of droplets is mistakenly detected in a consumable electrode arc welding.SOLUTION: In a method of detecting/controlling constriction in the consumable electrode arc welding, the constriction of droplets which is a fore-running phenomenon of arc regeneration from a short-circuit state is detected by the fact that the change in the voltage Vw or the resistance Vw/Iw between a welding wire and a base material reaches the constriction detection reference value, the arc is regenerated (t3) while the welding current Iw to be conducted to a short-circuit load from the constriction detection time (t2) is reduced, and the welding current is increased when the arc is regenerated. It is discriminated to be (t21) mistaken detection when the elapsed time from the constriction detection time (t2) reaches the reference time Tt before arc is regenerated, the welding wire is allowed to the retraction feed Frr, and separated from the base material to smoothly regenerate (t3) the arc. When the arc is regenerated, the welding wire is returned to the advance feed Ffr.

Description

  The present invention relates to a constriction detection control method of consumable electrode arc welding for detecting a constriction phenomenon of a droplet during a short circuit period and reducing welding current to improve welding quality.

  FIG. 5 is a diagram showing current / voltage waveforms and droplet transfer in consumable electrode arc welding in which the short-circuit period Ts and the arc period Ta are repeated. FIG. 4A shows the change over time of the welding current Iw for energizing the consumable electrode (hereinafter referred to as welding wire 1), and FIG. 4B shows the welding voltage applied between the welding wire 1 and the base material 2. The time change of Vw is shown, The figure (C)-(E) shows the mode of the transfer of the droplet 1a. Hereinafter, a description will be given with reference to FIG.

  During the short-circuit period Ts from time t1 to t3, the droplet 1a at the tip of the welding wire 1 is short-circuited with the base material 2, and as shown in FIG. As shown in B), since the welding voltage Vw is in a short circuit state, the welding voltage Vw becomes a low value of about several volts. As shown in FIG. 5C, the droplet 1a comes into contact with the base material 2 at a time t1 to enter a short circuit state. Thereafter, as shown in FIG. 4D, a constriction 1b is generated at the upper part of the droplet 1a by an electromagnetic pinch force generated by a welding current Iw for energizing the droplet 1a. This electromagnetic pinch force increases in proportion to the value of the welding current Iw. Therefore, by increasing the welding current Iw, the electromagnetic pinch force is increased and the formation of the constriction 1b is promoted. And this constriction 1b advances rapidly, and as shown to the same figure (E) at the time t3, the droplet 1a transfers from the welding wire 1 to the molten pool 2a, and the arc 3 regenerates.

  When the above-mentioned constriction phenomenon occurs, the short circuit is released after a short time of about several hundred μs, and the arc 3 is regenerated. That is, this constriction phenomenon is a precursor of short circuit opening. When the constriction 1b occurs, the conduction path of the welding current Iw 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, by detecting a change in resistance value between the welding wire 1 and the base material 2 during the short-circuit period Ts, it is possible to detect the occurrence and progress of the necking phenomenon. This change in resistance value can be calculated by dividing the welding voltage Vw by the welding current Iw. Further, the change in resistance value after the formation of the constriction is larger than the change in the welding current Iw during the short-circuit period Ts. For this reason, the occurrence of the constriction phenomenon can be detected by the change of the welding voltage Vw instead of the change of the resistance value. As a specific necking detection method, the rate of change (differential value) of the resistance value or the welding voltage value Vw during the short-circuit period Ts is calculated, and the necking is achieved by reaching the predetermined necking detection reference value Vtn. There is a way to detect. As another method, as shown in FIG. 5B, a voltage increase value ΔV from a stable short-circuit voltage value Vs before occurrence of constriction during the short-circuit period Ts is calculated, and this voltage increase value ΔV is calculated at time t2. There is a method of detecting the squeezing when the squeezing reaches a predetermined squeezing detection reference value Vtn. In the following description, a case in which the squeezing detection method is based on the above-described voltage increase value ΔV will be described, but other methods that have been proposed in the past may be used. Detection of arc re-occurrence at time t3 can be easily performed by determining that the welding voltage Vw has become equal to or greater than the arc determination value Vta. Incidentally, the period of Vw <Vta is the short circuit period Ts, and the period of Vw ≧ Vta is the arc period Ta. The time from the occurrence of squeezing at times t2 to t3 to the reoccurrence of the arc is hereinafter referred to as squeezing detection time Tn. When the arc is regenerated at the time t3, the welding current Iw gradually decreases as shown in FIG. 5A, and the welding voltage Vw is about 20-30V as shown in FIG. become. Therefore, the arc discrimination value Vta is set to about 10 to 15V. During the arc period Ta from time t3 to t4, the tip of the welding wire 1 is melted to form a droplet 1a. Thereafter, the operation in the period from time t1 to t4 is repeated.

  Examples of the consumable electrode arc welding that repeats the short-circuit period Ts and the arc period Ta include carbon dioxide arc welding, mag welding, MIG welding, and pulse arc welding with short-circuiting. In the case of carbon dioxide arc welding, mag welding, and MIG welding, the droplet transfer mode is a short-circuit transfer mode in a current region of less than about 200 A, and a globule transfer mode when the current value increases. In the case of pulse arc welding, the droplet transfer mode is a spray transfer mode. Also in these globule transfer forms and spray transfer forms, when performing high-speed welding or the like, the arc length is set short, so that a short circuit occurs. Therefore, in order to open this short circuit, the constriction 1b is formed as described above.

  In the welding with short circuit described above, when the arc regeneration current value Ia when the arc 3 is regenerated at the time t3 is a large current value, the arc force from the arc 3 to the molten pool 2a increases sharply. A large amount of spatter is generated. That is, the amount of spatter generated increases substantially in proportion to the current value Ia at the time of arc re-generation. For this reason, in order to suppress generation | occurrence | production of a sputter | spatter, it is necessary to make small this electric current value Ia at the time of arc regeneration. As a method for this purpose, various welding power sources have been proposed in which a constriction detection control method for detecting the occurrence of the above-described constriction phenomenon and reducing the welding current Iw to reduce the current value Ia at the time of arc re-generation is added. . Hereinafter, this conventional technique (for example, refer to Patent Document 1) will be described.

  FIG. 6 is a block diagram of a welding apparatus equipped with a conventional necking detection control method. The welding power source PS is a general welding power source for consumable electrode arc welding, outputs a welding voltage Vw and a welding current Iw, and rotates the feeding motor WM in response to a feeding speed setting signal Fr described later. A feed control signal Fc for control is output to the feed motor WM. The transistor TR is inserted in series with the output, and a current reducing resistor R is connected in parallel therewith. The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 coupled to the feeding motor WM, and an arc 3 is generated between the welding wire 1 and the base material 2. The feeding speed setting circuit FR outputs a predetermined feeding speed setting signal Fr for setting the feeding speed of the welding wire 1 to the welding power source PS. The welding wire 1 is fed forward at a feeding speed determined by a feeding speed setting signal Fr.

  The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The squeezing detection reference value setting circuit VTN outputs a squeezing detection reference value signal Vtn. The squeezing detection circuit ND receives the squeezing detection reference value signal Vtn, the voltage detection signal Vd, and the current detection signal Id, and the voltage increase value ΔV during the short circuit period is converted into the squeezing detection reference value signal Vtn as described above. The squeezing detection signal Nd that becomes the Low level is output when the arc is regenerated and the value of the voltage detection signal Vd becomes equal to or greater than the arc discrimination value Vta. Therefore, the squeezing detection time Tn is a period during which the squeezing detection signal Nd is at a high level. As described above, the squeezing detection signal Nd may be changed to a high level when the differential value of the voltage detection signal Vd during the short circuit period reaches the value of the squeezing detection reference value signal Vtn. Further, the resistance value of the droplet is calculated by dividing the value of the voltage detection signal Vd by the value of the current detection signal Id, and when the differential value of the resistance value reaches the value of the squeezing detection reference value signal Vtn, the squeezing is detected. The signal Nd may be changed to a high level. When the squeezing detection signal Nd is at a low level (when non-necking is detected), the driving circuit DR outputs a driving signal Dr that turns on the transistor TR. Therefore, the transistor TR is turned off when the squeezing detection signal Nd is at a high level (when squeezing is detected).

  FIG. 7 is a timing chart of each signal of the welding apparatus. (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 the time change of the drive signal Dr. Hereinafter, a description will be given with reference to FIG.

  In the figure, during a period other than the squeezing detection time Tn from time t2 to t3, as shown in FIG. 10C, the squeezing detection signal Nd is at the low level, and as shown in FIG. The signal Dr becomes a high level. As a result, since the transistor TR is turned on, the operation is the same as that of a welding apparatus for normal consumable electrode arc welding.

At time t2, as shown in FIG. 5B, it is detected that the welding voltage Vw has increased during the short-circuit period Ts and the voltage increase value ΔV has become equal to or greater than a predetermined squeezing detection reference value Vtn. If it is determined that constriction has occurred, the constriction detection signal Nd becomes High level as shown in FIG. In response to this, as shown in FIG. 4D, the drive signal Dr goes to a low level, so that the transistor TR is turned off. As a result, the current reducing resistor R is inserted into the current path of the welding current Iw. The value of the current reducing resistor R is a short-circuit load (0.01 to 0.03Ω).
Is set to a value (approximately 0.5 to 3Ω) that is at least 10 times greater than (approx.). 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 rapidly decreases to a small current value as shown in FIG. Here, assuming that the output voltage of the welding power source PS is 50V and the current reducing resistor R is 1Ω, the small current value is 50A. When the short circuit is released and the arc is regenerated at time t3, the welding voltage Vw becomes equal to or higher than a predetermined arc discrimination value Vta as shown in FIG. By detecting this, the squeezing detection signal Nd becomes the Low level as shown in FIG. 5C, and the drive signal Dr becomes the High level as shown in FIG. As a result, the transistor TR is turned on, and normal consumable electrode arc welding is controlled. When the arc is regenerated and the transistor TR is turned on at time t3, the welding current Iw increases to a predetermined high level and then converges to a value determined by the feeding speed, as shown in FIG. To do. By this operation, the arc regeneration current value Ia at the time of arc regeneration (time t3) can be reduced, so that the occurrence of sputtering can be suppressed. As a means for rapidly reducing the welding current Iw when the constriction is detected, the method for inserting the current reducing resistor R into the energizing path has been described above. As another means, a capacitor is connected in parallel between the output terminals of the welding apparatus via a switching element, and when the constriction is detected, the switching element is turned on and a discharge current is supplied from the capacitor to rapidly reduce the welding current Iw. There is also a method (see, for example, Patent Document 2).

  In the above-described constriction detection control method, it is important to accurately detect the occurrence of constriction in order to increase the effect of suppressing the amount of spatter generated. The occurrence of the constriction and the state of progress thereof vary depending on the welding conditions such as the type of shielding gas, the type of welding wire, the weld joint, the feeding speed of the welding wire, and the welding posture. For this reason, it is necessary to optimize the sensitivity for detecting the occurrence of constriction according to the welding conditions. The squeezing detection sensitivity can be adjusted by increasing or decreasing the squeezing detection reference value Vtn. That is, when the squeezing detection reference value Vtn is increased, the sensitivity is lowered, and conversely, when it is decreased, the sensitivity is increased. If the squeezing detection reference value Vtn is too large, the sensitivity will be too low, and the squeezing detection time Tn will be too short, and the welding current cannot be reduced sufficiently until the arc is regenerated. The effect is reduced. Conversely, if the squeezing detection reference value Vtn is too small, the sensitivity will be too high, and the above-described squeezing detection time Tn will be too long and the arc will not reoccur, making the welding state unstable. Therefore, it can be said that the squeezing detection time Tn is in the range of about 50 to 1000 μs when the squeezing detection reference value Vtn is set to an appropriate value.

  As described above, the squeezing detection reference value Vtn is set to an appropriate value according to the welding conditions. However, even if the squeezing detection reference value Vtn is optimized due to fluctuation factors such as fluctuations in the feeding speed, irregular movement of the molten pool, and variations in droplet shape, the squeezing detection time Tn varies. When the range of this variation is about 50 to 1000 μs as described above, there is not much adverse effect on the occurrence of spatter and the stability of the welded state. Moreover, even if the constriction detection time Tn occasionally becomes less than 50 μs, it is only a slight increase in spatter and is not a big problem. On the other hand, when the squeezing detection time Tn exceeds 1000 μs, particularly 2000 μs or more, the welding state becomes unstable, and the arc may not be regenerated. For this reason, if the arc has not regenerated even if the elapsed time from the point of detection of the constriction reaches the reference time, the constriction progresses by increasing the electromagnetic pinch force by increasing the welding current Iw. Compensation control is commonly used to promote and reinitiate arcs. Hereinafter, the compensation control (for example, see Patent Document 3) will be described.

  FIG. 8 is a timing chart of each signal corresponding to FIG. 7 described above for explaining compensation control. (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 the time change of the drive signal Dr. In the figure, the operations other than the operation during the period from time t21 to t3 are the same as those in FIG. The operation during the period from time t21 to t3 will be described below with reference to FIG.

  When the elapsed time t from the squeezing detection time at the time t2 reaches the reference time Tt at the time t21, the welding voltage Vw is less than the arc discrimination value Vta as shown in FIG. It has not reoccurred. For this purpose, the drive signal Dr is changed to a high level as shown in FIG. When the drive signal Dr becomes high level, the transistor TR in FIG. 6 is turned on, so that the welding current Iw increases to a predetermined value as shown in FIG. As the welding current Iw increases, the electromagnetic pinch force also increases, so that the progress of the constriction is promoted and the arc is regenerated at time t3. When the arc is regenerated at time t3, the welding voltage Vw becomes an arc voltage value equal to or higher than the arc discriminating value Vta as shown in FIG. 5B, and the welding current Iw is as shown in FIG. After that, it gradually decreases and converges to a steady value. As shown in FIG. 6C, the squeezing detection signal Nd is at a high level from the time of squeezing detection at time t2 until the occurrence of an arc again at time t3. As shown in FIG. 4D, the drive signal Dr becomes High level from time t21. The reference time Tt is set to about 1000 μs.

JP 2006-281219 A JP 2005-288540 A JP 2006-116585 A

  As described above, the welding state is prevented from becoming unstable by increasing the welding current when the arc has not regenerated even when the elapsed time from the necking detection time reaches the reference time. . However, when such compensation control is performed, as shown in FIG. 8A, since the current value when the arc is regenerated at time t3 becomes a large value, large spatters are generated. . In addition, since the period during which the current is decreased (the period from the time t2 to t21) is long, the temperature of the molten pool and the droplets is lowered. Therefore, even if the current is increased, the arc is not smoothly regenerated. In addition, the appearance of the weld bead may be deteriorated.

  Therefore, in the present invention, when the arc has not regenerated even if the elapsed time from the time of detection of the constriction has reached the reference time, the arc can be regenerated smoothly without increasing the generation of spatter. An object of the present invention is to provide a constriction detection control method for electrode arc welding.

In order to solve the above-described problem, the invention of claim 1 is a consumable electrode arc welding in which a welding wire is fed forward from a welding torch and an arc generation state and a short-circuit state are repeated between the welding wire and the base material. In this case, the constriction of the droplet, which is a precursor to the occurrence of the arc again from the short-circuit state, is detected when the change in the voltage value or resistance value between the welding wire and the base metal reaches the constriction detection reference value, In the constriction detection control method for consumable electrode arc welding, where the arc is regenerated with the welding current flowing to the short-circuit load decreased from the time of detection of the constriction, and the welding current is increased when the arc is regenerated,
When the elapsed time from the necking detection time reaches a predetermined reference time before the arc is regenerated, the arc is regenerated by moving the welding wire backward and pulling it away from the base metal. Then, the backward movement is stopped,
This is a constriction detection control method for consumable electrode arc welding.

The invention of claim 2 delays the increase of the welding current and the stoppage of the backward movement by a predetermined delay time from the arc re-occurrence point.
The constriction detection control method for consumable electrode arc welding according to claim 1.

The invention of claim 3 is that the backward movement is the backward feeding of the welding wire, and the stop of the backward movement is to stop the backward feeding and return to the forward feeding.
The constriction detection control method for consumable electrode arc welding according to any one of claims 1 to 2.

According to a fourth aspect of the invention, the backward movement is to raise the torch height by moving the welding torch backward, and after the stoppage of the backward movement, the welding torch is moved forward to restore the torch height. Back to
The constriction detection control method for consumable electrode arc welding according to any one of claims 1 to 2.

  According to the present invention, when the elapsed time from the necking detection time reaches the reference time before the arc is regenerated, the arc is regenerated by moving the welding wire backward and pulling it away from the base material. As a result, the arc can be reliably regenerated with a small current value, and the arc can be smoothly regenerated without increasing the generation of spatter.

It is a block diagram of the welding apparatus for implementing the constriction detection control method of consumable electrode arc welding which concerns on Embodiment 1 of this invention. It is a timing chart of each signal in the welding apparatus of FIG. It is a block diagram of the welding apparatus for enforcing the constriction detection control method of consumable electrode arc welding which concerns on Embodiment 2 of this invention. It is a timing chart of each signal in the welding apparatus of FIG. In a prior art, it is a figure which shows the electric current and voltage waveform and droplet transfer in consumable electrode arc welding which repeats the short circuit period Ts and the arc period Ta. It is a block diagram of the welding apparatus carrying the necking detection control method of a prior art. It is a timing chart of each signal in the welding apparatus of FIG. It is a timing chart of each signal corresponding to above-mentioned FIG. 7 for demonstrating the compensation control in a prior art.

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

[Embodiment 1]
In the invention according to the first embodiment, when the elapsed time t from the squeezing detection time reaches a predetermined reference time Tt before the arc is regenerated, the welding wire is moved backward and pulled away from the base material. The arc is regenerated with the small current value maintained, and when the arc is regenerated, the backward movement is stopped. In the first embodiment, the welding wire is moved backward by backward feeding. Therefore, the stop of the backward movement means that the backward feeding is stopped and returned to the normal forward feeding. Hereinafter, the first embodiment will be described.

  1 is a block diagram of a welding apparatus for carrying out a constriction detection control method for consumable electrode arc welding according to Embodiment 1 of the present invention. In the figure, the same blocks as those in FIG. 6 described above are denoted by the same reference numerals, and description thereof is omitted. In the figure, a delay circuit NDD indicated by a broken line is added, the drive circuit DR shown in FIG. 6 is replaced with a second drive circuit DR2 indicated by a broken line, a backward movement control circuit RC indicated by a broken line is added, and the feeding circuit shown in FIG. The speed setting circuit FR is replaced with a second feeding speed setting circuit FR2 indicated by a broken line. Hereinafter, these blocks will be described with reference to FIG.

  The delay circuit NDD receives the squeezing detection signal Nd and outputs a squeezing detection delay signal Ndd obtained by delaying this signal by a predetermined delay time Td. This squeezing detection delay signal Ndd is a signal that becomes High level at the time of squeezing detection, and becomes Low level when it is delayed by the delay time Td from the time when the arc is regenerated. The second drive circuit DR2 receives the squeezing detection delay signal Ndd, and when this signal is at a high level (squeezing detection period), the second driving circuit DR2 stops the driving signal Dr to turn off the transistor TR, and the low level (non-squeezing detection). (Period), the drive signal Dr is output to turn on the transistor TR.

  The backward movement control circuit RC receives the above-described squeezing detection signal Nd and the above-described squeezing detection delay signal Ndd, and a predetermined reference time Tt has elapsed since the squeezing detection signal Nd becomes a high level (squeezing detection period). When it is still at the High level, the backward movement control signal Rc is set to the High level, and when the squeezing detection delay signal Ndd changes to the Low level, the backward movement control signal Rc is reset to the Low level. Therefore, the backward movement control signal Rc becomes High level when the arc has not regenerated when the elapsed time from the point of detection of the squeezing reaches the reference time Tt, and the delay time Td from the time when the arc reoccurs. It is a signal that becomes Low level when it is delayed by a certain amount. The second feed speed setting circuit FR2 receives the reverse movement control signal Rc as an input, and when this signal is at the Low level, the forward feed speed set value Ffr having a predetermined positive value is used as the feed speed setting signal Fr. When the output is high level, a reverse feed speed setting value Frr having a predetermined negative value is output as a feed speed setting signal Fr. The welding power source PS receives a feed speed setting signal Fr and outputs a feed control signal Fc for feeding forward the welding wire 1 when the value of this signal is the forward feed speed set value Ffr. When the feed speed setting value Frr is set, a feed control signal Fc for feeding the welding wire 1 backward is output.

  FIG. 2 is a timing chart of each signal of the welding apparatus described above with reference to 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 the time change of the drive signal Dr, FIG. 9E shows the time change of the squeezing detection delay signal Ndd, FIG. 8F shows the time change of the backward movement control signal Rc, and FIG. Indicates the time change of the feed speed setting signal Fr. This figure is a timing chart in the case where the arc is not regenerated even when the elapsed time from the necking detection time reaches the reference time Tt. This figure corresponds to FIG. 7 and FIG. 8 described above, and the operation during the period from time t21 to t31 is different. Since the operation is the same except for this period, the description is omitted. Hereinafter, different operation periods will be described with reference to FIG.

  When the constriction is detected at time t2, the constriction detection signal Nd changes to the high level as shown in FIG. 10C, and in response to this, as shown in FIG. Ndd also changes to a high level. When the squeezing detection delay signal Ndd changes to the high level, as shown in FIG. 4D, the drive signal Dr changes to the low level, so that the transistor TR is turned off, and the current reducing resistor R enters the current path. Will be inserted. For this reason, the welding current Iw decreases to a small current value (about 10 to 100 A) as shown in FIG. The method for detecting the constriction is the same as that of the above-described prior art. Further, the value of the current reducing resistor R is the same as that of the above-described conventional technology.

  As shown in FIG. 10C, at the time t21 when the elapsed time reaches the reference time Tt from the time when the squeezing detection signal Nd changes to the high level (squeezing detection time), as shown in FIG. The movement control signal Rc becomes High level. In response to this, as shown in FIG. 5G, the feed speed setting signal Fr is a predetermined negative value of the reverse feed speed from a predetermined positive value of the forward feed speed setting value Ffr. The setting value Frr is switched, and the welding wire is fed backward in a direction away from the base material. When the welding wire is separated from the base material by the backward feeding at time t3, the arc is regenerated. When the arc is regenerated, the welding voltage Vw rapidly rises to an arc voltage value equal to or higher than the arc determination value Vta as shown in FIG. Since the value of the welding current Iw at the time of arc re-occurrence at time t3 remains as a small current value as shown in FIG. In addition, since the arc is generated by pulling the wire tip away from the base material by the backward feeding, stable arc regeneration can be realized.

  As shown in FIG. 4B, when it is determined that the value of the welding voltage Vw has become equal to or greater than the arc determination value Vta at time t3, and the reoccurrence of the arc is determined, as shown in FIG. The squeezing detection signal Nd changes to the low level. Then, as shown in FIG. 9E, the squeezing detection delay signal Ndd is off-delayed by the delay time Td from the time t3, and becomes the low level at the time t31. In response to this, at time t31, as shown in FIG. 4D, the drive signal Dr changes to the high level, so that the transistor TR is turned on and the current reducing resistor R is short-circuited. In response to this, the welding current Iw increases to a high level as shown in FIG. At the same time, at time t31, the reverse movement control signal Rc becomes low level as shown in (F). Therefore, as shown in (G) of FIG. The feed speed setting value Frr is switched to a positive forward feed speed setting value Ffr, so that the welding wire is fed forward as usual.

  The above operation is organized as follows. As shown in FIG. 6A, the welding current Iw decreases from the time of detection of squeezing at time t2, and is maintained at a small current value until the time when the arc is regenerated and the delay time Td has elapsed at time t3. The As shown in FIG. 5G, the welding wire is switched to backward feeding at time t21 when the elapsed time from the time of detecting the neck at time t2 reaches the reference time Tt, and advanced at time t31 after the delay time Td has elapsed. Returned to delivery.

  The reference time Tt is set to about 500 to 1500 μs. The reference time Tt is set to an appropriate value by experiment according to the average value of the welding current, the type of shield gas, the type of welding wire, and the like. This is because the variation in time from the detection of the necking until the arc is regenerated varies depending on the welding conditions. The reference time Tt is set to a larger value as the variation becomes larger. The delay time Td is set to about 0 to 2000 μs. Td = 0 is a case where no delay is performed. In the first embodiment, the delay time Td may be set to zero. The reason for providing this delay time Td is as follows. That is, since the arc length is very short immediately after the re-occurrence of the arc, a re-short circuit may occur due to the weld pool vibration, the welding wire feed vibration, or the like. When the re-short circuit occurs, spatter occurs and the welding state becomes unstable. Therefore, the reverse feed is maintained even after the arc is regenerated, and the welding current is maintained at a small current value, thereby preventing the occurrence of a re-short circuit. The delay time Td is set to an appropriate value by experiment according to the average value of the welding current, the weld joint, the welding speed, and the like. This is because the likelihood of re-short circuiting varies depending on the welding conditions. The forward feed speed setting value Ffr is set to an appropriate value according to the thickness of the base metal, the weld joint, the welding speed, etc., as in general consumable electrode arc welding. The setting range is about 2 to 20 m / min. The reverse feed speed set value Frr is set to about 30 to 50 m / min so that the arc is regenerated as soon as possible after the start of reverse feed. Further, in order to quickly switch from forward feed to backward feed and from backward feed to forward feed, it is desirable to use a servo motor or the like having good transient response as the feed motor WM. Furthermore, since the transient response is improved as the length from the feed motor WM to the tip of the welding torch is shorter, it is preferably 2 m or less, and preferably 1 m or less.

  In the first embodiment, the timing chart in the normal case where the arc is regenerated before the elapsed time from the point of detection of the neck reaches the reference time Tt is substantially the same as that in FIG. That is, the backward feeding of the welding wire is not performed, and only the forward feeding at a constant speed is performed. However, the timing at which the welding current Iw starts to increase is after the delay time Td has elapsed.

  According to the first embodiment described above, when the elapsed time from the necking detection time reaches the reference time before the arc is regenerated, the arc is regenerated by moving the welding wire backward and pulling it away from the base material. Let As a result, the arc can be reliably regenerated with a small current value, and the arc can be smoothly regenerated without increasing the generation of spatter. Furthermore, since the backward feeding of the welding wire is performed only when the elapsed time from the time of detection of the constriction reaches the reference time, the frequency of performing the backward feeding in the number of short circuits is low. For this reason, since an excessive load is not imposed on the feeding motor, the reliability of the feeding motor is also increased.

[Embodiment 2]
As in the first embodiment, the invention according to the second embodiment moves the welding wire backward when the elapsed time t from the necking detection time reaches a predetermined reference time Tt before the arc is regenerated. Thus, the arc is regenerated in the state of the small current value by being separated from the base material, and when the arc is regenerated, the backward movement is stopped. In the second embodiment, the welding wire is moved backward by moving the welding torch backward to increase the torch height Lt. Then, after stopping the backward movement, the welding torch is moved forward to return the torch height Lt to the original height. During the backward movement, the forward feeding of the welding wire is continued. Hereinafter, the second embodiment will be described.

  FIG. 3 is a block diagram of a welding apparatus for carrying out a constriction detection control method for consumable electrode arc welding according to Embodiment 2 of the present invention. In this figure, the same blocks as those in FIGS. 6 and 1 described above are denoted by the same reference numerals, and description thereof is omitted. In FIG. 1, a robot controller RCE and a robot body RM indicated by broken lines are added to FIG. 1, and the backward movement control circuit RC shown in FIG. 1 is replaced by a second backward movement control circuit RC2 indicated by broken lines. The second feed speed setting circuit FR2 is replaced with a third feed speed setting circuit FR3 indicated by a broken line. Hereinafter, these blocks will be described with reference to FIG.

  The second backward movement control circuit RC2 receives the squeezing detection signal Nd and the squeezing detection delay signal Ndd, and when a predetermined reference time Tt elapses from when the squeezing detection signal Nd becomes a high level (squeezing detection period). When it is still at the High level, the backward movement control signal Rc is set to the High level, and when the squeezing detection delay signal Ndd changes to the Low level, the backward movement control signal Rc is reset to the Low level, and this backward movement control is performed. The signal Rc is output to the third feed speed setting circuit FR3 and the robot controller RCE. Therefore, the backward movement control signal Rc becomes High level when the arc has not regenerated when the elapsed time from the point of detection of the squeezing reaches the reference time Tt, and the delay time Td from the time when the arc reoccurs. It is a signal that becomes Low level when it is delayed by a certain amount. The third feed speed setting circuit FR3 receives the reverse movement control signal Rc as an input, and when this signal is at the Low level, the forward feed speed set value Ffr having a predetermined positive value is used as the feed speed setting signal Fr. When it is at the High level, the second forward feed speed setting value Ffr2 having a predetermined value of 0 or more is outputted as the feed speed setting signal Fr. Here, 0 ≦ Ffr2 ≦ Ffr. That is, the second feed speed setting value Ffr2 is set to the same value as or smaller than the forward feed speed setting value Ffr, which is the feed speed during steady welding. The welding power source PS receives a feed speed setting signal Fr, and when the value of this signal is the forward feed speed set value Ffr, the welding power source PS feeds the welding wire 1 forward at a feed speed corresponding to that value. The feed control signal Fc is output, and when the second forward feed speed setting value Ffr2, the feed control signal for feeding forward (including feeding stop) the welding wire 1 at the feed speed corresponding to that value. Output Fc.

  The robot control apparatus RCE outputs the operation control signal Mc for moving the welding torch 4 attached to the robot body RM according to a work program created in advance to the robot body RM, with the reverse movement control signal Rc described above as an input. . In normal welding, the welding torch 4 is maintained at a predetermined welding speed while maintaining the distance between the tip of the power feed tip and the base material 2 (hereinafter referred to as torch height Lt) at a predetermined reference height Lt0. Move along the weld line. However, in the present embodiment, the welding torch 4 moves backward along the weld line, and moves backward in the direction in which the torch height Lt increases when the backward movement control signal Rc changes to the high level. When the level changes to the Low level, the torch height Lt moves forward and returns to the reference height Lt0. Details of this operation will be described in detail with reference to FIG. When the welding torch 4 has a forward or backward angle, the torch height Lt is measured in the wire feed direction. The robot body RM is an articulated manipulator, and a plurality of attached servo motors are driven by the operation control signal Mc. A feeding device including a feeding motor WM and a welding torch 4 are mounted on the robot body RM.

  FIG. 4 is a timing chart of each signal of the welding apparatus described above with reference to 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 the time change of the drive signal Dr, FIG. 9E shows the time change of the squeezing detection delay signal Ndd, FIG. 8F shows the time change of the backward movement control signal Rc, and FIG. Represents the time change of the feed speed setting signal Fr, and FIG. 5H shows the time change of the torch height Lt. This figure is a timing chart in the case where the arc is not regenerated even when the elapsed time from the necking detection time reaches the reference time Tt. This figure corresponds to FIG. 1 described above, and the torch height Lt in FIG. 1 differs from FIG. 1 in the operation during the period from time t21 to t32. Since the operation during the period other than this period is the same, the description for the same period is omitted. Hereinafter, different operation periods will be described with reference to FIG.

  When the constriction is detected at time t2, the constriction detection signal Nd changes to the high level as shown in FIG. 10C, and in response to this, as shown in FIG. Ndd also changes to a high level. When the squeezing detection delay signal Ndd changes to the high level, as shown in FIG. 4D, the drive signal Dr changes to the low level, so that the transistor TR is turned off, and the current reducing resistor R enters the current path. Will be inserted. For this reason, the welding current Iw decreases to a small current value (about 10 to 100 A) as shown in FIG. The method for detecting the constriction is the same as that of the above-described prior art. Further, the value of the current reducing resistor R is the same as that of the above-described conventional technology.

  As shown in FIG. 10C, at the time t21 when the elapsed time reaches the reference time Tt from the time when the squeezing detection signal Nd changes to the high level (squeezing detection time), as shown in FIG. The movement control signal Rc becomes High level. In response to this, as shown in FIG. 5G, the feed speed setting signal Fr is set to a second positive forward feed value having a predetermined positive value from a forward feed speed setting value Ffr having a predetermined positive value. It switches to the speed set value Ffr2, and the welding wire continues forward feeding (including feeding stop). In the figure, since the case of Ffr2 <Ffr is shown, the feeding speed of the forward feeding of the welding wire is reduced. At the same time, at time t21, the robot controller RCE starts the backward movement of the welding torch, so that the torch height Lt gradually increases from the reference height Lt0 so far as shown in FIG. Here, the speed at which the welding torch is moved backward is set to be faster than the second forward feed speed setting value Ffr2. In this way, the wire tip moves backward.

  At time t3, when the welding wire is separated from the base metal by the backward movement of the welding torch, the arc is regenerated. When the arc is regenerated, the welding voltage Vw rapidly rises to an arc voltage value equal to or higher than the arc determination value Vta as shown in FIG. Since the value of the welding current Iw at the time of arc re-occurrence at time t3 remains as a small current value as shown in FIG. Further, since the arc is generated by pulling the wire tip away from the base metal by the backward movement of the welding torch, stable arc regeneration can be realized.

  As shown in FIG. 4B, when it is determined that the value of the welding voltage Vw has become equal to or greater than the arc determination value Vta at time t3, and the reoccurrence of the arc is determined, as shown in FIG. The squeezing detection signal Nd changes to the low level. Then, as shown in FIG. 9E, the squeezing detection delay signal Ndd is off-delayed by the delay time Td from the time t3, and becomes the low level at the time t31. In response to this, at time t31, as shown in FIG. 4D, the drive signal Dr changes to the high level, so that the transistor TR is turned on and the current reducing resistor R is short-circuited. In response to this, the welding current Iw increases to a high level as shown in FIG. At the same time, at time t31, as shown in FIG. 5F, the reverse movement control signal Rc is at the low level, so that the feed speed setting signal Fr has a positive value as shown in FIG. 2. The forward feed speed setting value Ffr2 is switched to the positive forward feed speed setting value Ffr. As a result, the welding wire is fed forward at a steady feeding speed (forward feeding speed set value Ffr). At the same time, at time t31, the robot controller RCE starts the forward movement of the welding torch, so that the torch height Lt gradually decreases as shown in FIG. Then, as shown in FIG. 5H, when the torch height Lt returns to the reference height Lt0 (time t32), the forward movement of the welding torch stops. However, as described above, the welding torch moves along the welding line regardless of the backward movement or forward movement of the welding torch. The forward movement and backward movement of the welding torch are performed so as to move up and down in the wire feeding direction.

  The above operation is organized as follows. As shown in FIG. 6A, the welding current Iw decreases from the time of detection of squeezing at time t2, and is maintained at a small current value until the time when the arc is regenerated and the delay time Td has elapsed at time t3. The As shown in FIG. 5G, the welding wire is switched to the second forward feed speed at time t21 when the elapsed time from the time of detecting the neck at time t2 reaches the reference time Tt, and the time after the delay time Td has elapsed. At t31, the forward feeding speed (steady feeding speed) is restored. As shown in FIG. 11H, the torch height Lt starts to move backward at time t21 when the elapsed time from the time of detection of the neck at time t2 reaches the reference time Tt, and at time t31 after the lapse of the delay time Td. The forward movement starts and returns to the reference height Lt0 at time t32.

  The method for setting the reference time Tt, the delay time Td, and the forward feed speed setting value Ffr is the same as in the first embodiment. The speed of the backward movement of the welding torch is set to an appropriate value by experiment in the range of about 30 to 70 m / min in order to shorten the time from time t21 to t3 so that the arc is regenerated quickly. (Reverse movement speed of wire tip) = (Reverse movement speed of welding torch) − (Second forward feed speed). Therefore, when the forward feed speed setting value Ffr is a large value, the second forward feed speed setting value Ffr2 is set to a value smaller than Ffr, so that the speed of the backward movement of the wire tip is increased and the arc is increased. Can be regenerated quickly. The second forward feed speed setting value Ffr2 is set in the range of 0 ≦ Ffr2 ≦ Ffr. That is, when the second forward feed speed setting value Ffr2 is set to 0, the feed is stopped, and when it is set to the same value as Ffr, the second forward feed speed set value Ffr2 is fed at a constant value of the forward feed speed setting value Ffr during welding. It will be. The speed of forward movement of the welding torch is set to an appropriate value by experiment within a range of about 1 to 5 m / min. (Speed of forward movement of wire tip) = (forward feed speed) + (speed of forward movement of welding torch). Therefore, if the speed of forward movement of the welding torch is too fast, the speed of forward movement of the wire tip becomes too fast and the arc state becomes unstable. The speed of the forward movement of the welding torch is determined so that the arc state does not become unstable while shortening the time from time t31 to t32 to quickly converge to the steady state.

  In the second embodiment, the timing chart in the normal case where the arc is regenerated before the elapsed time from the point of detection of the neck reaches the reference time Tt is substantially the same as that in FIG. That is, the welding wire is not switched to the second feeding speed, and only forward feeding at a constant speed is performed. The backward movement and forward movement of the welding torch are not performed. However, the timing at which the welding current Iw starts to increase is after the delay time Td has elapsed.

  According to the second embodiment described above, the same effect as that of the first embodiment can be obtained by performing the backward movement of the welding wire by the backward movement of the welding torch. Since the welding torch is moved backward by the robot, it is not necessary to use a feed motor with excellent transient response as in the first embodiment, and the cost is low. Furthermore, since it is not necessary to shorten the length of the welding torch as in the first embodiment, workability is improved.

1 welding wire 1a droplet 1b constriction 2 base material 2a molten pool 3 arc 4 welding torch 5 feed roll DR drive circuit Dr drive signal DR2 second drive circuit Fc feed control signal Ffr forward feed speed set value Ffr2 second forward Feeding speed setting value FR Feeding speed setting circuit Fr Feeding speed setting signal FR2 Second feeding speed setting circuit FR3 Third feeding speed setting circuit Frr Reverse feeding speed setting value Ia Current value ID when arc is regenerated ID Current detection Circuit Id Current detection signal Iw Welding current LT Torch height (distance between tip of feed tip and base material)
Lt0 Reference height ND Constriction detection circuit Nd Constriction detection signal NDD Delay circuit Ndd Constriction detection delay signal PS Welding power supply R Current reducing resistor RC Reverse movement control circuit Rc Reverse movement control signal RC2 Second reverse movement control circuit RCE Robot controller RM Robot body t Elapsed time Ta Arc period Td Delay time Tn Constriction detection time TR Transistor Ts Short circuit period Tt Reference time VD Voltage detection circuit Vd Voltage detection signal Vs Short circuit voltage value Vta Arc discrimination value VTN Constriction detection reference value setting circuit Vtn Constriction detection standard Value (signal)
Vw Welding voltage WM Feed motor ΔV Voltage rise value

Claims (4)

In consumable electrode arc welding in which the welding wire is fed forward from the welding torch and the arc generation state and the short-circuit state are repeated between the welding wire and the base metal, this is a precursor phenomenon in which the arc is regenerated from the short-circuit state. Necking of the droplet was detected when the voltage or resistance change between the welding wire and the base metal reached the squeezing detection reference value, and the welding current applied to the short-circuit load was reduced from this squeezing detection point. In the constriction detection control method for consumable electrode arc welding, where the arc is regenerated in the state and the welding current is increased when the arc is regenerated,
When the elapsed time from the necking detection time reaches a predetermined reference time before the arc is regenerated, the arc is regenerated by moving the welding wire backward and pulling it away from the base metal. Then, the backward movement is stopped,
A constriction detection control method for consumable electrode arc welding. Delaying the increase of the welding current and the stoppage of the backward movement by a predetermined delay time from the arc re-occurrence point,
The constriction detection control method of consumable electrode arc welding according to claim 1. The backward movement is a backward feeding of the welding wire, and the stop of the backward movement is to stop the backward feeding and return to the forward feeding.
The constriction detection control method of consumable electrode arc welding according to any one of claims 1 to 2. The backward movement is to raise the torch height by moving the welding torch backward, and after the stoppage of the backward movement, the welding torch is moved forward to restore the torch height.
The constriction detection control method of consumable electrode arc welding according to any one of claims 1 to 2.

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