JP2011050981A - Output control method for pulsed arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transient responsiveness while arc stability is maintained, when an arc length is largely fluctuated in consumable electrode pulsed arc welding. <P>SOLUTION: An output control method for pulsed arc welding is disclosed in which a welding wire is fed at a first feeding speed Fs1, forming the external characteristic of the welding power source set by a first slope Ks1, a welding current reference value Is and a welding voltage reference value Vs, and forming the external characteristic by replacing the first slope Ks1 with a second slope Ks2 having a smaller value than that of the first slope when an arc length is largely fluctuated during the welding. In the method, during the period when the external characteristic is formed by the second slope Ks2, the feeding speed Fsc is varied from the first feeding speed Fs1 to the second feeding speed Fs2 so that the fluctuation of the arc length converges. The gain of the arc length control system is increased by reducing the slope, with the feeding speed variably controlled, thereby improving the transient responsiveness. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an improvement in an output control method of consumable electrode pulse arc welding that can form an external characteristic of a welding power source having a desired inclination.

  In consumable electrode pulse arc welding, it is extremely important to maintain the arc length during welding at an appropriate value in order to obtain good welding quality such as a beautiful bead appearance and uniform penetration depth. In general, the arc length is determined by the balance between the welding wire feeding speed and the melting speed by arc heat input. Therefore, the arc length is always constant when the melting rate approximately proportional to the average value of the welding current becomes equal to the feed rate. However, the feeding speed during welding varies due to fluctuations in the rotational speed of the feeding motor, fluctuations in the frictional force of the feeding path due to the routing of the welding torch cable, and the like. For this reason, the balance with the melting rate is lost, and the arc length changes. Furthermore, the arc length also fluctuates due to fluctuations in the distance between the power supply tip and the base material due to the shaking of the welding operator, irregular vibrations in the molten pool, and the like. Therefore, in order to suppress the fluctuation of the arc length due to these various fluctuation factors (hereinafter referred to as disturbance), arc length control is required which always adjusts the melting rate according to the disturbance and suppresses the change in the arc length. Become.

In consumable electrode gas shielded arc welding including consumable electrode pulse arc welding, a method of controlling the output of the external characteristics of the welding power source to a desired value is commonly used as a method for suppressing fluctuations in arc length caused by the various disturbances described above. Yes. An example of this external characteristic is shown in FIG. In the figure, the horizontal axis represents the average value Iw of the welding current passing through the welding wire, and the vertical axis represents the average value Vw of the welding voltage applied between the welding wire and the base material. The characteristic L1 is a case of a complete constant voltage characteristic with a slope Ks = 0 V / A. The characteristic L2 is a case of a constant voltage characteristic having a slope Ks = −0.1 V / A and a slope with a downward slope. Since the external characteristic can be expressed as a straight line, the external characteristic having an inclination Ks passing through the intersection point P0 between the welding current reference value Is and the welding voltage reference value Vs is expressed by the following equation.
Vw = Ks · (Iw−Is) + Vs (1)

  By the way, it has been conventionally known that the stability of arc length control (referred to as self-control action) is greatly influenced by the slope Ks of the external characteristic of the welding power source. That is, in order to stabilize the arc length against disturbance, it is necessary to control the slope Ks of the external characteristic to an appropriate value according to the welding conditions including the welding method. For example, the appropriate value of the slope Ks is in the range of about 0 to -0.03 V / A in the carbon dioxide arc welding method, and in the range of about -0.05 to -0.3 V / A in the pulse arc welding method. Therefore, in the pulse arc welding method which is the object of the present invention, in order to stabilize the arc length control, not within the characteristic L1 shown in the figure but in the range of about -0.05 to -0.3 V / A. It is necessary to form a characteristic L2 or the like having a predetermined slope Ks. By the way, changing the inclination changes the gain of the arc length control system. When the absolute value of the slope Ks decreases (when the negative value approaches 0), the gain increases. When the absolute value of the slope Ks increases (when the slope becomes steep), the gain decreases. Therefore, the arc stability is deteriorated in the pulse arc welding method unless the gain is reduced as compared with the carbon dioxide arc welding method. On the other hand, if the gain is made too small, the transient response becomes worse. For this reason, it is necessary to set an appropriate value for the slope by taking into account steady-state arc stability and transient response. Hereinafter, a conventional technique (for example, see Patent Documents 1 to 3) for forming an external characteristic having a desired inclination Ks in pulse arc welding will be described. In the following description, the value of the slope Ks means an absolute value even when not described as an absolute value. This is because, as described above, the value of the slope Ks is 0 or a negative value and does not become a positive value, so that the description is simplified.

  FIG. 5 is a current / voltage waveform diagram of pulse arc welding. FIG. 4A shows the waveform of the welding current (instantaneous value) io, and FIG. 4B shows the waveform of the welding voltage (instantaneous value) vo. Hereinafter, description will be given with reference to FIG.

(1) Peak period Tp between times t1 and t2
During the predetermined peak period Tp, a predetermined peak current Ip having a large current value is applied to transfer the welding wire to the droplet as shown in FIG. In addition, a peak voltage Vp substantially proportional to the arc length during this period is applied between the welding wire and the base material.

(2) Base period Tb between times t2 and t3
During the base period Tb determined by the output control of the welding power source described later, as shown in FIG. 5A, a predetermined base current Ib having a small current value is applied so as not to grow the droplets at the tip of the welding wire, As shown in FIG. 5B, a base voltage Vb that is substantially proportional to the arc length during this period is applied.

  Welding is performed by repeating the period from time t1 to t3, which includes the peak period Tp and the base period Tb, as one pulse period Tpb. As shown in FIG. 6A, the average value of the welding current for each pulse period Tpb is Iw. Similarly, as shown in FIG. 5B, the average value of the welding voltage for this pulse period Tpb is Vw. It becomes. Output control for forming external characteristics of the welding power source is performed by feedback control using the time length of the pulse period Tpb as an operation amount. That is, output control is performed by increasing or decreasing the pulse period Tpb with the peak period Tp as a constant value.

  As shown in FIG. 6, the welding current average value of the n-th pulse period Tpb (n) from time t (n) to t (n + 1) is Iw (n), and the welding voltage average value is Vw (n ). In FIG. 4 described above, output control is performed so that the intersection (operating point) P1 between these Iw (n) and Vw (n) is on the set characteristic L2. Hereinafter, the output control method of the welding power source for forming the external characteristic having the desired inclination Ks will be described.

With reference to the waveform diagram of the pulse arc welding described above with reference to FIG. 5, a conventional external characteristic forming method will be described. The target external characteristic to be formed is the external characteristic of the above-described equation (1). The welding current average value Iw and welding voltage average value Vw in the n-th pulse period Tpb (n) can be expressed by the following equations.
Iw = (1 / Tpb (n)) · ∫io · dt (2) Equation Vw = (1 / Tpb (n)) · ∫vo · dt (3) However, the integration is the nth time This is performed for the pulse period Tpb (n).

Substituting these equations (2) and (3) into the above equation (1) and rearranging them gives the following equation.
∫ (Ks · io−Ks · Is + Vs−vo) · dt = 0 (4) However, integration is performed during the nth pulse period Tpb (n), and as described above, Ks is an external characteristic. It is a slope, Is is a welding current reference value, and Vs is a welding voltage reference value.

Therefore, when the nth pulse cycle Tpb (n) ends, the above equation (4) is established. Here, when the left side of the above equation (4) is defined as the integral value Svb, the following equation is obtained.
Svb = ∫ (Ks · io−Ks · Is + Vs−vo) · dt (5)

  The calculation of the integral value Svb of the above equation (5) is started from the time when the nth pulse cycle Tpb (n) starts. The n-th pulse period Tpb (n) is set when the above-mentioned integral value Svb = 0 (or Svb ≧ 0) is reached during the n-th base period after the n-th predetermined peak period ends. finish. By repeating this operation, the external characteristic of the above equation (1) can be formed.

The above-described conventional external characteristic forming method is summarized and described below.
(1) The external characteristics of the target welding power source are set in advance based on the above equation (1) based on the inclination Ks, the welding current reference value Is, and the welding voltage reference value Vs.
(2) Detect welding voltage vo and welding current io during welding.
(3) Calculation of the integral value Svb = ∫ (Ks · io−Ks · Is + Vs−vo) · dt is started from the start point of the nth pulse cycle Tpb (n) based on the above equation (5).
(4) When the integrated value Svb in the nth base period Tb following the nth predetermined peak period Tp becomes zero or more (Svb ≧ 0), the nth pulse period Tpb (n ) Ends.
(5) Subsequently, the (n + 1) th pulse cycle Tpb (n + 1) is started, and the operations (3) to (4) are repeated to form desired external characteristics.

  FIG. 7 is a block diagram of a welding power source equipped with the above-described external characteristic forming method. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives a commercial power supply such as a three-phase 200 V input, performs output control by inverter control according to a current error amplification signal Ei described later, and outputs a welding current io and a welding voltage vo suitable for arc welding. This power supply main circuit PM is omitted in the drawing, but a primary rectifier for rectifying commercial power, a capacitor for smoothing the rectified direct current, an inverter circuit for converting the smoothed direct current to high frequency alternating current, and high frequency alternating current for arc welding. A high-frequency transformer that steps down the voltage to an appropriate voltage value, a secondary rectifier that rectifies the stepped-down high-frequency alternating current, a reactor that smoothes the rectified direct current, and pulse width modulation control using the current error amplification signal Ei as an input. And a driving circuit for driving the above inverter circuit. 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 current detection circuit ID detects the welding current io and outputs a current detection signal id. The voltage detection circuit VD detects the welding voltage vo and outputs a voltage detection signal vd. The welding voltage reference value setting circuit VS outputs a predetermined welding voltage reference value signal Vs. The welding current reference value setting circuit IS outputs a predetermined welding current reference value signal Is. The welding voltage average value detection circuit VA smoothes the voltage detection signal vd with a time constant of several pulse periods to several tens of pulse periods, and outputs a welding voltage average value signal Va. The difference calculation circuit DV calculates a difference between the welding voltage average value signal Va and the welding voltage reference value signal Vs, and outputs a difference signal ΔV = Va−Vs. The first inclination setting circuit KS1 outputs a first inclination setting signal Ks1 for setting the inclination of the external characteristic when the arc length varies in the normal range. The second gradient setting circuit KS2 outputs a second gradient setting signal Ks2 for setting the gradient of the external characteristic when the arc length varies greatly. The slope control setting circuit KSC compares the absolute value of the difference signal ΔV with a predetermined voltage threshold value ΔVt. When | ΔV | <ΔVt, the slope control setting circuit KSC uses the first slope setting signal Ks1 as the slope setting signal. Ks is output. When | ΔV | ≧ ΔVt, the second inclination setting signal Ks2 is output as the inclination setting signal Ks.

  The integrated value calculation circuit SVB receives the current detection signal id, the voltage detection signal vd, the welding voltage reference value signal Vs, the welding current reference value signal Is, and the inclination setting signal Ks as inputs. From the start of the pulse period, the integral calculation is performed according to the above equation (5), and the integral value signal Svb is output. The comparison circuit CM outputs a comparison signal Cm that becomes a high level for a short time when the value of the integral value signal Svb becomes zero or more. The period of the comparison signal Cm is a pulse period. The timer circuit MM outputs a timer signal Mm that is at a high level for a period determined by a predetermined peak period setting value Tps from the time when the comparison signal Cm changes to a high level. The peak period is when the timer signal Mm is at a high level, and the base period is when the timer signal Mm is at a low level.

  The peak current setting circuit IPS outputs a predetermined peak current setting signal Ips. The base current setting circuit IBS outputs a predetermined base current setting signal Ibs. The switching circuit SW switches to the a side when the timer signal Mm is at the High level and outputs the peak current setting signal Ips as the current control setting signal Ics, and switches to the b side when the timer signal Mm is at the Low level. The base current setting signal Ibs is output as the current control setting signal Ics.

  The current error amplification circuit EI amplifies an error between the current control setting signal Ics and the current detection signal id, and outputs a current error amplification signal Ei. The first feed speed setting circuit FS1 outputs a predetermined first feed speed setting signal Fs1. The feed control circuit FC receives the first feed speed setting signal Fs1 and outputs a feed control signal Fc for controlling the feed speed of the welding wire 1 to the feed motor WM. With these blocks, the welding current io as described above with reference to FIG. 5 is applied, and the external characteristics set by the above equation (1) are formed.

  The value of the welding voltage average value signal Va is substantially proportional to the arc length, and the welding voltage reference value signal Vs sets an appropriate arc length. Therefore, the absolute value of the difference signal ΔV indicates the magnitude of the arc length variation. Therefore, when the absolute value of the difference signal ΔV is less than a predetermined voltage threshold value ΔVt (| ΔV | <ΔVt), the first external characteristic of the normal inclination (the first inclination setting signal Ks1) is formed. When the absolute value of the difference signal ΔV is equal to or greater than the voltage threshold value ΔVt (| ΔV | ≧ ΔVt), the second external characteristic of the absolute value of the slope is smaller than usual (the above-described second slope setting signal Ks2). Form. The first external characteristic is set by the first inclination setting signal Ks1, the welding voltage reference value signal Vs, and the welding current reference value signal Is, and the second external characteristic is the second inclination. It is set by the setting signal Ks2, the welding voltage reference value signal Vs and the welding current reference value signal Is. | Ks1 |> | Ks2 |. Since the second external characteristic is formed when the arc length fluctuates greatly, the gain of the arc length control system is increased and the transient response is accelerated. When the variation in the arc length is small, the first external characteristic is formed, so that the gain is reduced and the arc stability is improved.

JP 2002-361417 A Japanese Patent Laid-Open No. 2005-118872 JP 2008-105095 A

  In the above-described prior art, an external characteristic having a desired slope can be formed, and when the arc length fluctuates greatly, the arc length is reduced by reducing the slope and increasing the gain to increase the transient response. Can be quickly returned to the proper range, and when the fluctuation of the arc length is small, the slope is increased to reduce the gain and to improve the steady stability.

  However, if the gradient of the external characteristic is made too small when the variation in the arc length is large, the arc stability in the transient state is deteriorated, and conversely, there is a case where the steady state is not easily converged. In other words, there is a limit to reducing the slope when the fluctuation of the arc length is large. For this reason, there is a certain limit to speeding up the transient response. In particular, when the feed rate is relatively slow (when the welding current value is in a small current range), the range in which the slope of the external characteristics can be reduced is more limited, so the transient response when the arc length varies greatly There was a problem in speeding up sex.

  Therefore, the present invention provides an output control method for pulsed arc welding that can form desired external characteristics and maintain transient stability when the arc length greatly fluctuates, while speeding up transient response. The purpose is to do.

In order to solve the above-described problems, the invention of claim 1 is directed to a welding power source that is fed by a first feeding speed and is set by a first inclination, a welding current reference value, and a welding voltage reference value. An output control method of pulse arc welding that forms and welds external characteristics,
When the arc length greatly fluctuates during welding, in the output control method of pulse arc welding in which the first inclination is replaced with a second inclination having an absolute value smaller than the absolute value of the first inclination to form external characteristics,
During the period in which the external characteristic is formed by the second inclination, the feeding speed is changed so that the fluctuation of the arc length converges from the first feeding speed to the second feeding speed.
An output control method of pulse arc welding characterized by the above.

The invention of claim 2 changes the feed speed to the second feed speed only when the first feed speed is equal to or less than the feed speed reference value.
The output control method for pulse arc welding according to claim 1, wherein:

Invention of Claim 3 discriminate | determines that the said arc length changed greatly by the absolute value of the difference of a welding voltage average value and the said welding voltage reference value becoming more than the predetermined voltage threshold value,
The output control method for pulse arc welding according to claim 1 or 2, wherein the output control method is used.

Invention of Claim 4 discriminate | determines that the said arc length changed greatly when the absolute value of the difference of a welding current average value and the said welding current reference value became more than the predetermined current threshold value,
The output control method for pulse arc welding according to claim 1 or 2, wherein the output control method is used.

  According to the present invention, when the arc length fluctuates greatly, the absolute value of the slope of the external characteristic is reduced to increase the gain of the arc length control system, and the feed speed is changed so that the arc length converges. By doing so, the transient response can be improved while maintaining the arc stability. For this reason, good welding quality can be obtained even when the arc length varies greatly.

It is a block diagram of the welding power supply which concerns on Embodiment 1 of this invention. It is a timing chart of each signal in the welding power supply of FIG. It is a block diagram of the welding power supply which concerns on Embodiment 2 of this invention. It is a figure which shows the external characteristic of the welding power supply in a prior art. It is a current and voltage waveform diagram of pulse arc welding in the prior art. It is a wave form diagram for demonstrating the relationship between the welding current average value Iw (n) of the nth pulse period in the prior art, and welding voltage average value Vw (n). It is a block diagram of the welding power source carrying the external characteristic formation method in a prior art.

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

[Embodiment 1]
FIG. 1 is a block diagram of a welding power source for carrying out an output control method of pulse arc welding according to Embodiment 1 of the present invention. In the figure, the same blocks as those in FIG. 7 described above are denoted by the same reference numerals, and description thereof is omitted. In this figure, a feed control setting circuit FSC indicated by a broken line is inserted between the first feed speed setting circuit FS1 and the feed control circuit FC of FIG. Hereinafter, this circuit will be described with reference to FIG.

The feed control setting circuit FSC receives the first feed speed setting signal Fs1 and the difference signal ΔV as input, performs the following processing, and feed speed control setting signal Fsc for performing variable speed control of the feed speed. Is output.
(1) When the absolute value of the difference signal ΔV is less than the voltage threshold value ΔVt, the value of the first feed speed setting signal Fs1 is output as the feed speed control setting signal Fsc.
(2) When the absolute value of the difference signal ΔV is equal to or greater than the voltage threshold value ΔVt and the sign of the difference signal ΔV is positive, the second feed speed setting value Fs2 = Fs1 × (1 + a) is calculated and sent. It is output as a feed speed control setting signal Fsc.
(3) When the absolute value of the difference signal ΔV is equal to or greater than the voltage threshold value ΔVt and the sign of the difference signal ΔV is negative, the second feed speed setting value Fs2 = Fs1 × (1-a) is calculated. And output as a feed speed control setting signal Fsc.
Here, a is a predetermined correction coefficient, for example, about 0.05 to 0.3. In the case of (1) above, the variation in the arc length is small, and the slope of the external characteristic is the value of the first slope setting signal Ks1. For this reason, since the gain of the arc length control system is reduced, the steady stability is improved. In this case, the feeding speed is not changed, and the value determined by the first feeding speed setting signal Fs1 remains. In the case of (2), the arc length greatly fluctuates in the direction of increasing, and the slope of the external characteristic becomes the value of the second slope setting signal Ks2. At this time, the feeding speed becomes a second feeding speed that is faster than the first feeding speed. Since the slope of the external characteristic is smaller than in the case of (1), the gain of the arc length control system is increased, and since the feeding speed is faster than in the case of (1), the arc length is shortened. Therefore, the transient response is improved and the arc length quickly converges to a steady value. In the case of (3), the arc length is greatly fluctuating in the direction of shortening, and the slope of the external characteristic becomes the value of the second slope setting signal Ks2. At this time, the feeding speed becomes a second feeding speed that is slower than the first feeding speed. Since the slope of the external characteristic is smaller than in the case of (1), the gain of the arc length control system is increased, and since the feeding speed is slower than in the case of (1), the arc length is increased. Therefore, the transient response is improved and the arc length quickly converges to a steady value. That is, as in (2) and (3), when the arc length fluctuates greatly, the slope of the external characteristics is reduced and the feed speed is changed so that the fluctuation of the arc length converges. By doing so, the transient response can be improved without making the slope of the external characteristic very small (increasing the gain). “Change the feed speed so that the fluctuation of the arc length converges” means that when the arc length greatly fluctuates in the direction of increasing the arc length, the feed speed is increased, and conversely, the arc length is shortened. If the direction is greatly fluctuated, the feeding speed will be slowed down. In the above, the correction coefficient a may be set to a different value between the case (2) and the case (3). The correction coefficient a is set to an appropriate value according to the material of the welding wire, the diameter, the welding speed, the first feeding speed, and the like.

  As described above in the section of the problem, when the value of the first feed speed setting signal Fs1 is less than or equal to the predetermined feed speed reference value Ft (in the case of a small current region), the second slope of the external characteristic is arced. Since the problem that it cannot be made very small from the viewpoint of stability becomes remarkable, there is a limit to improving the transient response. Therefore, in the feed control setting circuit FSC, when the value of the first feed speed setting signal Fs1 is equal to or less than the feed speed reference value Ft, the correction coefficient a is set to a predetermined value. When the value of the 1 feeding speed setting signal Fs1 exceeds the feeding speed reference value Ft, the correction coefficient a may be set to 0. In this way, variable speed control of the feed speed is performed when Fs1 ≦ Ft, and variable speed control of the feed speed is not performed when Fs1> Ft. The feed speed reference value Ft is set to 5 m / min (corresponding to 150 A), for example, in the case of mag pulse welding using a mild steel wire having a diameter of 1.2 mm.

  In the figure, when the difference signal ΔV is equal to or greater than the voltage threshold value ΔVt, the external characteristic is switched to the second inclination setting signal Ks2 to perform variable speed control of the feeding speed. However, two voltage threshold values may be provided so that the threshold value for switching the slope of the external characteristic and the threshold value for starting the variable speed control can be set separately.

  In high-speed welding, the arc length is generally set to be short in order to prevent the occurrence of undercut. For this reason, it does not fluctuate greatly in the direction of decreasing the arc length. Therefore, in such a case, it may be determined only that the arc length has greatly changed in the direction in which the arc length increases, and the switching of the slope of the external characteristic and the start of the variable speed control of the feeding speed may be performed.

  FIG. 2 is a timing chart of each signal in the above-described welding power source. FIG. 4A shows the change over time of the welding voltage average value signal Va, FIG. 4B shows the change over time of the inclination setting signal Ks (absolute value), and FIG. 4C shows the feed speed control setting signal. The time change of Fsc is shown. In the figure, the period from time t1 to t4 is when the arc length is greatly changed in the increasing direction, and the period from time t5 to t8 is when the arc length is greatly changed in the decreasing direction. Hereinafter, a description will be given with reference to FIG.

(1) When the arc length at times t1 to t4 changes greatly in the direction of increasing As shown in FIG. 5A, the middle broken line indicates the welding voltage reference value Vs, and the upper broken line indicates Vs + ΔVt (ΔVt is voltage Threshold), and the lower broken line indicates Vs−ΔVt. The value of welding voltage average value signal Va fluctuates in the vicinity of the middle broken line before time t1, indicating that the variation in arc length is small. When the arc length becomes longer due to disturbance at time t1, the value of the welding voltage average value signal Va rises sharply from time t1, intersects with the upper broken line at time t2, and further rises to the peak value. After that, it reverses and descends, crosses the upper broken line again at time t3, further descends and converges to the vicinity of the middle broken line at time t4. As shown in FIG. 5B, the slope setting signal Ks becomes the first slope setting signal Ks1 before the time t2, the value decreases during the period from the time t2 to the time t3, and becomes the second slope setting signal Ks2. During the period from t3 to t4, the value increases and becomes the first inclination setting signal Ks1 again. Further, as shown in FIG. 5C, the feed speed control setting signal Fsc becomes the first feed speed setting signal Fs1 before time t2, and its value increases during the period from time t2 to t3, and Fs2 = Fs1 × (1 + a), and during the period from time t3 to t4, the first feed speed setting signal Fs1 is obtained again. Therefore, during a period in which the arc length is greatly fluctuated (period t2 to t3), the absolute value of the slope of the external characteristic is reduced and the feed speed is increased to stabilize the arc. The transient response is improved while maintaining the performance.

(2) When the arc length at times t5 to t8 changes greatly in the direction of shortening As shown in FIG. 5A, the value of the welding voltage average value signal Va is the middle broken line during the period of times t4 to t5. It fluctuates in the vicinity, indicating that the variation in arc length is small. When the arc length is shortened due to disturbance at time t5, the value of the welding voltage average value signal Va decreases sharply from time t5, crosses the lower broken line at time t6, and further decreases to the minimum value. Then, it reverses and rises, crosses the lower broken line again at time t7, rises further, and converges to the vicinity of the middle broken line at time t8. As shown in FIG. 5B, the inclination setting signal Ks becomes the first inclination setting signal Ks1 during the period from the time t4 to t6, and its value becomes small during the period from the time t6 to t7. Ks2, and during the period after time t7, the value increases and becomes the first inclination setting signal Ks1 again. Further, as shown in FIG. 5C, the feed speed control setting signal Fsc becomes the first feed speed setting signal Fs1 during the period from time t4 to t6, and its value during the period from time t6 to t7. Fs2 = Fs1 × (1−a), and becomes the first feed speed setting signal Fs1 again during the period after time t7. Therefore, during a period in which the arc length greatly varies in the direction of shortening (period from time t6 to t7), the absolute value of the slope of the external characteristic is decreased and the feed speed is decreased to stabilize the arc. The transient response is improved while maintaining the performance.

  According to the first embodiment described above, when the arc length fluctuates greatly, the absolute value of the slope of the external characteristic is reduced to increase the gain of the arc length control system, and the arc length converges on the feeding speed. By changing in such a manner, the transient response can be improved while maintaining the arc stability. For this reason, even when the arc length fluctuates greatly, good welding quality can be obtained. In the first embodiment, it is determined that the arc length has greatly fluctuated by the fact that the welding voltage average value has fluctuated by a voltage threshold value from a predetermined welding voltage reference value.

[Embodiment 2]
FIG. 3 is a block diagram of a welding power source for carrying out the output control method of pulse arc welding according to Embodiment 2 of the present invention. In the figure, the same blocks as those in FIG. 1 described above are denoted by the same reference numerals, and description thereof is omitted. In the figure, the welding voltage average value detection circuit VA in FIG. 1 is replaced with a welding current average value detection circuit IA indicated by a broken line, and the difference calculation circuit DV in FIG. 1 is replaced by a current difference calculation circuit DI indicated by a broken line. 1 is replaced by a second inclination control setting circuit KSC2 indicated by a broken line, and the feeding control setting circuit FSC of FIG. 1 is replaced by a second feeding control setting circuit FSC2 indicated by a broken line. . Hereinafter, these blocks will be described with reference to FIG.

The welding current average value detection circuit IA smoothes the current detection signal id with a time constant of several pulse periods to several tens of pulse periods, and outputs a welding current average value signal Ia. The current difference calculation circuit DI calculates a deviation between the welding current average value signal Ia and the welding current reference value signal Is, and outputs a current difference signal ΔI = Ia−Is. The second slope control setting circuit KSC2 compares the absolute value of the current difference signal ΔI with a predetermined current threshold value ΔIt, and when | ΔI | <ΔIt, the first slope setting signal Ks1 is used as the slope setting signal. Ks is output, and when | ΔI | ≧ ΔIt, the second inclination setting signal Ks2 is output as the inclination setting signal Ks. The second feed control setting circuit FSC2 receives the first feed speed setting signal Fs1 and the current difference signal ΔI as described above, performs the following processing, and performs feed for variable speed control of the feed speed. A speed control setting signal Fsc is output.
(1) When the absolute value of the current difference signal ΔI is less than the current threshold value ΔIt, the value of the first feed speed setting signal Fs1 is output as the feed speed control setting signal Fsc.
(2) When the absolute value of the current difference signal ΔI is equal to or greater than the current threshold value ΔIt and the sign of the current difference signal ΔI is negative, the second feed speed setting value Fs2 = Fs1 × (1 + a) is calculated. And output as a feed speed control setting signal Fsc.
(3) When the absolute value of the current difference signal ΔI is equal to or greater than the current threshold value ΔIt and the sign of the current difference signal ΔI is positive, the second feed speed setting value Fs2 = Fs1 × (1-a) Calculate and output as a feed speed control setting signal Fsc.
However, a is a correction coefficient as in the first embodiment. When the arc length varies in the increasing direction, the value of the welding current average value signal Ia is different from the value of the welding voltage average value signal Va and changes in the decreasing direction. When the arc length varies in the direction of shortening, the value of the welding current average value signal Ia differs from the value of the welding voltage average value signal Va in a direction of increasing. Therefore, as shown in (2) above, when it is determined that the arc length has changed in the increasing direction, the sign of the current difference signal ΔI is negative. On the other hand, as shown in (3) above, when it is determined that the arc length has changed in the direction of shortening, the sign of the current difference signal ΔI is positive.

  When the arc length varies greatly, the welding current average value also varies greatly from the welding current reference value. Therefore, when the absolute value of the current difference ΔI between the value of the welding current average value signal Ia and the value of the welding current reference value signal Is is greater than or equal to a predetermined current threshold value ΔIt, the arc length varies greatly. Determine. When the arc length fluctuates greatly, the second inclination setting signal Ks2 is used as the inclination setting signal Ks, and variable speed control of the feeding speed is performed. On the other hand, when the arc length does not fluctuate greatly, the first inclination setting signal Ks1 is used as the inclination setting signal, and the variable speed control of the feeding speed is not performed.

  According to the second embodiment described above, the arc length increases or decreases greatly depending on the absolute value of the difference between the welding current average value and the predetermined welding current reference value and its sign. Can be determined. By using this discrimination, the same effect as that of the first embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll a Correction coefficient CM Comparison circuit Cm Comparison signal DI Current difference calculation circuit DV Difference calculation circuit EI Current error amplification circuit Ei Current error amplification signal FC Feed control circuit Fc Feed control signal FS1 First feed speed setting circuit Fs1 First feed speed setting signal Fs2 Second feed speed setting value FSC Feed control setting circuit Fsc Feed speed control setting signal FSC2 Second feed control setting circuit Ft Feed speed reference value IA Welding current average value detection circuit Ia Welding current average value signal Ib Base current IBS Base current setting circuit Ibs Base current setting signal Ics Current control setting signal ID Current detection circuit id Current detection signal io Welding current (instantaneous value)
Ip peak current IPS peak current setting circuit Ips peak current setting signal IS welding current reference value setting circuit Is welding current reference value (signal)
Iw welding current average value per pulse period Ks inclination setting signal KS1 first inclination setting circuit Ks1 first inclination setting signal KS2 setting circuit Ks2 setting signal KSC control setting circuit KSC2 control setting circuit L1 characteristic L2 characteristic MM timer circuit Mm timer signal n P0th intersection PM power supply main circuit Svb integral value SVB integral value calculation circuit Svb integral value signal SW switching circuit t time t1 time t1-t2 time t1-t3 time t1-t4 time t2 time t2-t3 time t3 time t3-t4 Time t4 Time t4-t5 Time t4-t6 Time t5 Time t5-t8 Time t6 Time t6-t7 Time t7 Time t8 Time Tb Base period Tp Peak period Tpb Pulse period Tps Peak period set value VA Welding voltage average value detection circuit Va Welding Voltage average value signal Vb Base voltage VD Voltage detection circuit vd Voltage detection signal vo Welding voltage V Peak voltage VS welding voltage reference value setting circuit Vs welding voltage reference value (signal)

Vw Welding voltage average value WM per pulse period Feed motor ΔI Current difference (signal)
ΔV difference (signal)
ΔVt Voltage threshold

Claims (4)

An output control method for pulse arc welding that feeds a welding wire at a first feed speed and welds by forming external characteristics of a welding power source set by a first slope, a welding current reference value, and a welding voltage reference value. There,
When the arc length greatly fluctuates during welding, in the output control method of pulse arc welding in which the first inclination is replaced with a second inclination having an absolute value smaller than the absolute value of the first inclination to form external characteristics,
During the period in which the external characteristic is formed by the second inclination, the feeding speed is changed so that the fluctuation of the arc length converges from the first feeding speed to the second feeding speed.
An output control method of pulse arc welding characterized by the above. Only when the first feed speed is equal to or less than the feed speed reference value, the feed speed is changed to the second feed speed.
The output control method of pulse arc welding according to claim 1. It is determined that the arc length has fluctuated greatly by the absolute value of the difference between the welding voltage average value and the welding voltage reference value being equal to or greater than a predetermined voltage threshold value.
The output control method of pulse arc welding according to claim 1 or 2, characterized in that. It is determined that the arc length has fluctuated greatly by the absolute value of the difference between the welding current average value and the welding current reference value being equal to or greater than a predetermined current threshold value.
The output control method of pulse arc welding according to claim 1 or 2, characterized in that.

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