JP2008105095A - Output control method for pulsed arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transient response when the arc length makes a large change in pulsed arc welding by forming external characteristics of a welding power source which have a desired slope. <P>SOLUTION: An output control method for pulsed arc welding for forming external characteristics of the welding power source which are set by a slope Ks, a welding current reference value Is, and a welding voltage reference value Vs, is characterized by detecting an average welding voltage value Va during welding, by calculating a deviation ΔV between the average welding voltage value Va and the welding voltage reference value Vs, and by forming the external characteristics by changing the slope Ks to become smaller (from Ks1 to Ks2) when the deviation ΔV equals to or is larger than a predetermined reference value ΔVt. <P>COPYRIGHT: (C)2008,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 improve the 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. The horizontal axis of the figure is the average value Iw of the welding current passing through the welding wire, and the vertical axis is 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 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. 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 forming an external characteristic having a desired inclination Ks in pulse arc welding will be described.

  FIG. 6 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. 7, 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. 5 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. 6, 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 by 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) The calculation of the integral value Svb = ∫ (Ks · io−Ks · Is + Vs−vo) · dt is started from the start point of the n-th pulse period Tpb (n).
(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. 8 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 takes a commercial power supply such as a three-phase 200V as an input, performs output control such as inverter control and thyristor control according to a current error amplification signal Ei described later, and generates a welding current io and welding voltage vo suitable for arc welding. Output. The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 of the wire feeding device, and an arc 3 is generated between the base metal 2 and the welding wire 1.

  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 inclination setting circuit KS outputs a predetermined 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 slope setting signal Ks as input, and the above (5) An integral calculation is performed according to the equation, and an 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. By these blocks, the welding current io as described above with reference to FIG. 6 is applied.

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

  As described above, in the arc length control of the pulse arc welding, it is necessary to increase the slope Ks of the external characteristics (increase the slope of the rightward downward) as compared with the DC arc welding such as carbon dioxide arc welding. This is because the arc stability in the steady welding state is deteriorated unless the inclination Ks is increased. However, as described above, when the inclination is increased, the gain of the arc length control system is reduced, and the transient response is deteriorated. When the arc length varies in the normal range due to various disturbances, the fact that the transient response is slightly slow does not significantly affect the arc stability. However, when the arc length greatly fluctuates, since the transient response is slow, it takes time for the arc length to return to an appropriate value, and the welding quality during that period may deteriorate. In high-speed welding, posture welding, MIG pulse welding, and the like, the arc length tends to fluctuate originally, and the arc length sometimes fluctuates greatly. Therefore, in such welding, there has been a demand for pulsed arc welding which is stable in steady welding state and excellent in transient response.

  Therefore, the present invention provides an output control method for pulse arc welding that is excellent in transient response when the arc length varies greatly.

In order to solve the above-described problem, the first invention is an output control method of pulse arc welding that forms external characteristics of a welding power source set by a slope, a welding current reference value, and a welding voltage reference value.
The welding voltage average value during welding is detected, the deviation between the welding voltage average value and the welding voltage reference value is calculated, and when the deviation is equal to or larger than a predetermined reference value, the inclination is changed to be small. This is an output control method of pulse arc welding characterized by forming external characteristics.

  2nd invention changes the said reference value according to at least 1 or more of the kind of welding wire, the kind of shielding gas, or wire feeding speed, The pulse arc welding of 1st invention characterized by the above-mentioned This is an output control method.

3rd invention is the output control method of the pulse arc welding which forms the external characteristic of the welding power source set by the inclination, the welding current reference value, and the welding voltage reference value.
The welding current average value during welding is detected, and a deviation between the welding current average value and the welding current reference value is calculated. When the deviation is equal to or larger than a predetermined current deviation reference value, the inclination is reduced. It is an output control method of pulse arc welding characterized in that external characteristics are formed by changing.

  According to the present invention, when the fluctuation of the arc length is small, a normal external characteristic with a large inclination is formed to ensure steady arc stability, and when the fluctuation of the arc length is large, an external characteristic with a small inclination is formed. To make the transient response faster. For this reason, even when the arc length largely fluctuates, the arc length quickly returns to an appropriate range, so that the welding quality is improved.

  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 an embodiment of the present invention. In the figure, the same blocks as those in FIG. 8 described above are denoted by the same reference numerals, and description thereof is omitted. Hereinafter, blocks indicated by dotted lines different from those in FIG. 8 will be described.

  The welding voltage average value detection circuit VA smoothes the voltage detection signal vd with a time constant of several pulse cycles to several tens of pulse cycles, and outputs a welding voltage average value signal Va. The deviation calculation circuit DV calculates a deviation between the welding voltage average value signal Va and the welding voltage reference value signal Vs, and outputs a deviation 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 inclination control setting circuit KSC compares the deviation signal ΔV with a predetermined reference value ΔVt, and when ΔV <ΔVt, outputs the first inclination setting signal Ks1 as the inclination setting signal Ks, and ΔV ≧ When ΔVt, the second inclination setting signal Ks2 is output as the inclination setting signal Ks.

  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 value of the deviation signal ΔV indicates the magnitude of the arc length variation. Therefore, when the value of the deviation signal ΔV is less than a predetermined reference value (ΔV <ΔVt), the first external characteristic L1 having a normal inclination (first inclination Ks1) is formed, and the value of the deviation signal ΔV is equal to or greater than the reference value. When (ΔV ≧ ΔVt), the second external characteristic L2 having a smaller slope than the normal (second slope Ks2) is formed. FIG. 2 shows examples of the first external characteristic L1 and the second external characteristic L2. The first external characteristic L1 is set by the first slope Ks1, the welding voltage average value Vs and the welding current reference value Is, and the second external characteristic L2 is set by the second slope, the welding voltage average value Vs and the welding current reference value Is. Is done. | 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 fluctuation of the arc length is small, the first external characteristic is formed, so that the arc stability is good. Hereinafter, numerical examples of the first inclination Ks1 and the second inclination Ks2 are shown.

(1) Example 1
Welding wire: Diameter 1.2mm, aluminum alloy Reference value ΔVt = 1V
First slope Ks1 = −0.20V / A
Second slope Ks2 = −0.15V / A
Welding method: Migpulse welding

(2) Example 2
Welding wire: Diameter 1.2mm, mild steel Reference value ΔVt = 3V
First slope Ks1 = −0.10 V / A
Second slope Ks2 = −0.05 V / A
Welding method: Magpulse welding

  The reason why the reference value ΔVt of MIG pulse welding shown in Example 1 is smaller than the reference value ΔVt of Mag Pulse welding shown in Example 2 is because the welding voltage average value Va with respect to the arc length is different.

  FIG. 3 is a timing chart showing an output control method of pulse arc welding according to the embodiment of the present invention. FIG. 4A shows the time change of the welding voltage average value signal Va, and FIG. 4B shows the time change of the inclination setting signal Ks. Hereinafter, a description will be given with reference to FIG.

  During the period before time t1, as shown in FIG. 5A, the deviation between the value of the welding voltage average value signal Va and the value of the welding voltage reference value signal Vs is in a range less than the reference value ΔVt. As shown in FIG. 5B, the value of the inclination setting signal Ks becomes the value of the first inclination setting signal Ks1. During this period, normal external characteristics having a large inclination are formed, and steady arc stability is improved.

  During the period from the time t1 to the time t2, as shown in FIG. 4A, the deviation between the value of the welding voltage average value signal Va and the value of the welding voltage reference value signal Vs becomes equal to or larger than the reference value ΔVt. As shown in FIG. (B), the value of the inclination setting signal Ks is the value of the second inclination setting signal Ks2. Since the arc length fluctuates greatly during this period, the transient response is accelerated by reducing the slope of the external characteristics. As a result, the arc length quickly returns to an appropriate value.

  When the deviation returns below the reference value ΔVt at time t2, the value of the inclination setting signal Ks becomes the value of the first inclination setting signal Ks1.

  In the above description, the case of switching to the second external characteristic when the deviation exceeds the reference value has been described. However, when the deviation becomes greater than or equal to the reference value, it is possible to sequentially switch to a plurality of external features (second, third... Nth external characteristics) according to the deviation. The reference value ΔVt is changed to an appropriate value according to at least one of the type of welding wire, the type of shield gas, and the wire feed speed. Since the present invention can be widely applied to the consumable electrode pulse arc welding method, it is naturally applicable to the consumable electrode AC pulse arc welding method.

  According to the embodiment described above, when the fluctuation of the arc length is small, a normal external characteristic having a large inclination is formed to ensure steady arc stability, and when the fluctuation of the arc length is large, the external characteristic having a small inclination. To make transient response faster. For this reason, even when the arc length largely fluctuates, the arc length quickly returns to an appropriate range, so that the welding quality is improved.

[Embodiment 2]
FIG. 4 is a block diagram of a welding power source for carrying out the output control method of pulse arc welding according to the second embodiment different from FIG. 1 described above. In this figure, the same blocks as those in FIGS. 8 and 1 described above are denoted by the same reference numerals, and description thereof is omitted. Hereinafter, blocks indicated by dotted lines different from those in FIGS. 8 and 1 will be described.

  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 deviation 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 deviation signal ΔI = | Ia−Is |. The second inclination control setting circuit KSC2 compares the current deviation signal ΔI with a predetermined current deviation reference value ΔIt, and outputs the first inclination setting signal Ks1 as the inclination setting signal Ks when ΔI <ΔIt. When ΔI ≧ ΔIt, the second inclination setting signal Ks2 is output as the inclination setting signal Ks.

  When the value of the welding current average value signal Ia is substantially equal to the welding current reference value signal Is, the arc length is in a steady state. The value of the current deviation signal ΔI between the welding current average value signal Ia and the welding current reference value signal Is is substantially proportional to the magnitude of the arc length variation. Therefore, when the value of the current deviation signal ΔI is less than a predetermined current deviation reference value (ΔI <ΔIt), a first external characteristic L1 having a normal slope (first slope Ks1) is formed, and the value of the current deviation signal ΔI is formed. Is equal to or greater than the current deviation reference value (ΔI ≧ ΔIt), the second external characteristic L2 having a smaller slope than the normal (second slope Ks2) is formed. The external characteristics L1 and L2 are described above with reference to FIG. The above-described operation description of FIG. 3 is also substantially the same.

  According to the second embodiment described above, when the fluctuation of the arc length is small, a normal external characteristic with a large inclination is formed to ensure steady arc stability, and when the fluctuation of the arc length is large, the external with a small inclination. Form the characteristics to speed up the transient response. For this reason, even when the arc length largely fluctuates, the arc length quickly returns to an appropriate range, so that the welding quality is improved.

1 is a block diagram of a welding power source according to an embodiment of the present invention. It is a figure which illustrates the 1st external characteristic L1 and the 2nd external characteristic L2 which concern on embodiment of this invention. It is a timing chart which shows the output control method of the pulse arc welding which concerns on embodiment of this invention. It is a block diagram of the welding power supply which concerns on Embodiment 2 of this invention. It is a figure which illustrates the external characteristic in the pulse arc welding of a prior art. It is an electric current and voltage waveform figure in pulse arc welding of a prior art. It is an electric current and voltage waveform diagram which shows the output control method in the pulse arc welding of a prior art. It is a block diagram of the pulse arc welding power supply of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll CM Comparison circuit Cm Comparison signal DV Deviation calculation circuit DI Current deviation calculation circuit EI Current error amplification circuit Ei Current error amplification signal 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 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 KS inclination setting circuit Ks inclination setting signal KS1 first inclination setting circuit Ks1 first inclination setting signal KS2 second inclination setting circuit Ks2 second inclination setting signal KSC inclination control setting circuit KSC2 second inclination control setting circuit L1 First external characteristic L2 Second external characteristic MM Timer circuit Mm Timer signal PM Power supply main circuit SVB Integral value calculation circuit Svb Integral value (signal)
SW switching circuit 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 Vp Peak voltage VS Welding voltage reference value setting circuit Vs Welding voltage reference value (signal)
Vw welding voltage average value ΔI Current deviation (signal)
ΔIt Current deviation reference value ΔV Deviation (signal)
ΔVt reference value

Claims (3)

In the output control method of pulse arc welding for forming the external characteristics of the welding power source set by the inclination and the welding current reference value and the welding voltage reference value,
The welding voltage average value during welding is detected, the deviation between the welding voltage average value and the welding voltage reference value is calculated, and when the deviation is equal to or larger than a predetermined reference value, the inclination is changed to be small. An output control method for pulse arc welding, characterized in that external characteristics are formed.   2. The pulse arc welding output control method according to claim 1, wherein the reference value is changed in accordance with at least one of a type of welding wire, a type of shield gas, and a wire feed speed. In the output control method of pulse arc welding for forming the external characteristics of the welding power source set by the inclination and the welding current reference value and the welding voltage reference value,
The welding current average value during welding is detected, and a deviation between the welding current average value and the welding current reference value is calculated. When the deviation is equal to or larger than a predetermined current deviation reference value, the inclination is reduced. An output control method for pulsed arc welding, characterized in that external characteristics are formed by changing.

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