JP2006075890A - Method for controlling welding current in pulsed arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve weldability by making a peak rising characteristic U controllable at a curved desired value, in pulsed arc welding in which a peak current Ip corresponding to a peak current set value Ips is energized during a peak period Tp and in which a base current Ib corresponding to a base current set value Ibs is energized during a base period Tb. <P>SOLUTION: This is a method for controlling a welding current in pulsed arc welding in which a peak current rising characteristic constant Nu of a positive integer is set preliminarily, in which a current set value Is(k) is computed, for each control period ΔT of a very short time during the peak period Tp, using Is(k)=Is(k-1)+[Ips-Is(k-1)]/Nu, provided that k=1, 2(Tp/ΔT) and Is(0)=Ibs, and in which the rising characteristic of the peak current Ip during the peak period Tp is controlled at the curved desired value using the current set value Is(k). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a welding current control method for pulse arc welding that can improve welding performance by controlling the rising characteristic or falling characteristic of a peak current into a curve having a desired value.

[Prior Art 1 (Patent Document 1)]
FIG. 7 is a current / voltage waveform diagram of consumable electrode type pulse arc welding, where FIG. 7 (A) shows the change over time of the welding current Iw energizing the arc, and FIG. The time change of the welding voltage Vw applied to is shown. Hereinafter, a description will be given with reference to FIG.

  As shown in FIG. 6A, during the peak rising period Tu from time t1 to t2, a transition current rising from the base current Ib to the peak current Ip is energized, and then during the peak period Tp from time t2 to t3. The peak current Ip is energized, and subsequently, during the peak fall period Td from time t3 to t4, a transition current falling from the peak current Ip to the base current Ib is energized. The base current Ib is energized during the base period Tb from t4 to t5. In general, since a welding power source for pulse arc welding is controlled at a constant current, the current set value Is for each period changes and the welding current for each period energizes. In response to the energization of the welding current, a transition voltage rising from the base voltage Vb to the peak voltage Vp is applied during the peak rising period Tu as shown in FIG. During the peak period Tp, the peak voltage Vp is applied, and subsequently, during the peak fall period Td, a transition voltage falling from the peak voltage Vp to the base voltage Vb is applied. Subsequently, the base voltage Vb is applied during the base period Tb. The welding is performed by repeating the period from the time t1 to the time t5 as one pulse period Tf. By the way, in order to maintain the arc length during welding at an appropriate value, as shown in FIG. 5B, the above pulse is set so that the average value of the welding voltage Vw becomes substantially equal to the predetermined voltage setting value Vs. The period Tf is feedback controlled. Therefore, waveform parameters (Tu, Tp, Td, Ip, Ib) other than the pulse period Tf are set in advance.

  When the peak rising period Tu and the peak falling period Td are set long, the arc has a shape in which the base is widened, the concentration of the arc is weakened, the spread of the arc is widened, the arc force is weakened, and soft arc characteristics are obtained. Become. For this reason, it is suitable for posture welding and has an effect of suppressing the occurrence of undercut. On the other hand, when the peak rising period Tu and the peak falling period Td are set short, the arc has a narrow base, the arc concentration becomes strong, the arc spread becomes narrow, the arc force becomes strong, and the hard arc characteristics. become. For this reason, there is an effect of increasing the penetration depth. In addition to the above effects, since the workability of welding varies depending on the arc characteristics, a skilled welding operator often adjusts the arc characteristics to suit his / her preference and performs welding.

[Prior Art 2 (Patent Document 2)]
FIG. 8 is a block diagram of a welding power source according to Prior Art 2. The DC power supply E is a rectified commercial AC power supply such as a three-phase 200V. The inverter circuit INV is a full bridge circuit composed of a plurality of switching elements and converts direct current to high frequency alternating current. The transformer Tr steps down the high frequency alternating current to a voltage value suitable for welding. The rectifiers D1 and D2 rectify the stepped-down high-frequency alternating current into direct current. The reactor WL smoothes a rippled direct current. The above-described circuit constitutes the power supply main circuit PM. The welding wire 1 is fed at a predetermined feeding speed, and the welding voltage Vw and the welding current Iw are output from the power supply main circuit PM, so that the arc 3 between the welding wire 1 and the base material 2 is output. Will occur.

  The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The pulse generation circuit PG outputs a current setting signal Is that becomes the peak current set value Ips during the peak period Tp and becomes the base current set value Ibs during the base period Tb. The current error amplification circuit EI amplifies the error between the current setting signal Is and the current detection signal Id and outputs a current error amplification signal ΔI. Thus, constant current control is performed. The reactor WL is provided with a secondary winding, and a current differential signal di / dt is output from the secondary winding. The second current error amplifier circuit EI2 amplifies an error between the current error amplification signal ΔI and the current differential signal di / dt and outputs a current control signal Isc. The drive circuit DR outputs a drive signal Dr for controlling the inverter circuit INV according to the current control signal Isc.

  FIG. 9 is a waveform diagram of the welding current Iw according to the conventional technique 2. In the figure, a rectangular wave indicated by a dotted line is a virtual waveform of the welding current Iw corresponding to the current setting signal Is described above with reference to FIG. That is, since the peak rising period and the peak falling period are short, it becomes a substantially rectangular wave, and the peak current Ip and the base current Ib are energized.

  On the other hand, as described above with reference to FIG. 8, by using the current differential signal di / dt for control, the rising of the peak current Ip changes in a curved line as indicated by U1. Similarly, as indicated by D1, the fall of the peak current Ip also changes in a curve. In the prior art 2, the peak current Ip rises in a curved shape during the peak period Tp and smoothly converges to the peak current set value Ips. Further, during the peak falling period Td included in the base period Tb, the peak current Ip falls in a curved shape and smoothly converges to the base current set value Ibs.

  In the prior art 2, the rising and falling characteristics of the peak current do not change linearly and converge smoothly in a curved line as in the prior art 1, and therefore arc instability due to overshoot and undershoot is unlikely to occur. . Furthermore, the generation of spatter and dust is reduced.

JP 2003-285163 A Japanese Patent Laid-Open No. 62-192264

  In the prior art 2, if the rising characteristic or falling characteristic of the peak current can be changed to a desired value. The effect of the prior art 1 can be added to the effect of the prior art 2 described above. That is, the arc instability can be suppressed and the generation of spatter and dust can be suppressed by changing the rising or falling of the peak current in a curved line as in the prior art 2. Further, the arc characteristic can be adjusted by changing the rising characteristic or falling characteristic of the peak current to a desired value as in the prior art 1. That is, in FIG. 9 described above, the peak current rising characteristic can be set to a desired value such as U1, I2, etc., and the peak current falling characteristic can be set to a desired value such as D1, D2, etc. It is an object of the present invention.

  In Prior Art 2, it is difficult to adjust the rising characteristic or falling characteristic of the peak current. The reason is as follows. That is, in FIG. 8 described above, the rising characteristic or falling characteristic of the peak current is determined by the value of the current differential signal di / dt. However, since this value is determined by the secondary winding of the reactor WL, it is difficult to adjust it to an arbitrary value. As an improvement, a method of obtaining a current differential signal di / dt by newly providing a current differentiating circuit and differentiating the current detection signal Id by the current differentiating circuit is conceivable. In this case, the value of the current differential signal di / dt can be adjusted by adjusting the differential gain of the current differentiating circuit which is an electronic circuit. However, in this case, since the external inductance value changes when the length of the welding cable for wiring the welding power source, the welding torch and the base material, the routing method, etc., the value of the current differential signal also changes, As a result, there arises a problem that the rising characteristic or falling characteristic of the peak current deviates from a desired value.

  Therefore, the present invention provides a welding current control method for pulse arc welding that can change the rising characteristic or falling characteristic of the peak current in a curved shape and adjust it to a desired value.

In order to solve the above-described problem, the first invention supplies a peak current Ip corresponding to the peak current set value Ips during the peak period Tp and a base current corresponding to the base current set value Ibs during the base period Tb. In the welding current control method of pulse arc welding in which Ib is energized and welded,
A positive integer peak current rising characteristic constant Nu is set in advance, and during the peak period Tp, the current set value Is (k) is set to Is (k) = Is (k-1) + [ Ips−Is (k−1)] / Nu, where k = 1, 2... (Tp / ΔT) and Is (0) = Ibs, and the peak period Tp depends on the current set value Is (k). It is a welding current control method of pulse arc welding characterized in that the rising characteristic of the peak current Ip is controlled to a curved desired value.

In the second aspect of the invention, the peak current Ip corresponding to the peak current set value Ips is energized during the peak period Tp, and the base current Ib corresponding to the base current set value Ibs is energized and welded during the base period Tb. In the welding current control method of pulse arc welding,
A positive integer peak current falling characteristic constant Nd is set in advance, and a peak falling period Td is set in advance from the start of the base period Tb. During this peak falling period Td, every minute control time ΔT is set. The current set value Is (k) is calculated by Is (k) = Is (k−1) + [Ibs−Is (k−1)] / Nd, where k = 1, 2... (Td / ΔT) and Is (0) = Ips, and the pulse arc welding is characterized in that the falling characteristic of the peak current Ip during the peak falling period Td is controlled to a curved desired value by the current set value Is (k). This is a welding current control method.

  According to the first aspect of the invention, by calculating the current setting value Is (k) during the peak period by a predetermined calculation, the curve-shaped peak current rising characteristic having a desired value corresponding to the peak current rising characteristic constant Nu is obtained. Obtainable. For this reason, the arc characteristic can be adjusted to a desired value. Furthermore, since the rising characteristics converge smoothly in a curved line, the arc stability can be improved and the occurrence of spatter and dust can be reduced.

  According to the second aspect of the present invention, by calculating the current set value Is (k) during the peak fall period by a predetermined calculation, a curved peak current having a desired value corresponding to the peak current fall characteristic constant Nd is obtained. Falling characteristics can be obtained. For this reason, the arc characteristic can be adjusted to a desired value. Furthermore, since the falling characteristic smoothly converges in a curved line, the arc stability can be improved and the occurrence of spatter and dust can be reduced.

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

[Embodiment 1]
FIG. 1 is a time change diagram of a current setting value showing a method for controlling the rising characteristic of the peak current to a desired value according to the first embodiment of the present invention. In the figure, the peak period Tp is preset in the range of about 0.7 to 3 ms, and the control period ΔT of minute time is set to 50 μs, for example. Therefore, the control described below is performed every control period ΔT. Assuming that the start time of the peak period Tp is 0 and a number is assigned for each control cycle ΔT and the number of elapsed times is k (positive integer), 0 ≦ k ≦ (Tp / ΔT) during the peak period Tp. For example, when Tp = 2 ms and ΔT = 50 μs, k = 0, 1, 2, 3,. Furthermore, the peak current set value is Ips, and the base current set value is Ibs.

Here, a peak current rising characteristic constant Nu which is a positive integer is set as a parameter for setting the rising characteristic of the peak current. The current set value Is (k) at each elapsed time number k is calculated by the following equation.
Is (0) = Ibs
Is (1) = Is (0) + [Ips−Is (0)] / Nu
...
Is (k) = Is (k-1) + [Ips-Is (k-1)] / Nu (1) Formula ...
Is (Tp / ΔT) = Is (Tp / ΔT−1) + [Ips−Is (Tp / ΔT−1)] / Nu

  A peak current rising characteristic having a desired value indicated by U is set by the peak current rising characteristic constant Nu, and the welding current is controlled to the peak current rising characteristic by the current set value Is (k). FIG. 2 is a diagram showing a change in the peak current rising characteristic when the peak current rising characteristic constant Nu is changed. The horizontal axis represents the number of elapsed times k, and the vertical axis represents the welding current value. In this figure, the base current set value Ibs = 50 A, the peak current set value Ips = 450 A, the control period ΔT = 50 μs, and the maximum value 40 of k, so the peak period Tp = 2 ms. As shown in the figure, when the peak current rising characteristic constant Nu is changed to 2, 4, and 8, the peak current rising characteristic has a gentle curve. Therefore, by adjusting the peak current rising characteristic constant Nu, a peak current rising characteristic having a desired value can be obtained. Here, the peak current rising characteristic constant Nu may be a positive integer, but a numerical value that satisfies the current set value Is (Tp / ΔT) ≈Ips at the end of the peak period Tp may be limited as a maximum value. That is, when the peak current rising characteristic constant Nu exceeds the maximum value, Is (Tp / ΔT) <Ips.

  FIG. 3 is a block diagram of a welding power source for carrying out the welding current control method of pulse arc welding according to the first embodiment. Hereinafter, each block will be described with reference to FIG.

  As described above with reference to FIG. 8, the power supply main circuit PM receives the commercial AC power supply, performs output control by inverter control according to a drive signal Dr described later, and outputs a welding voltage Vw and a welding current Iw. The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The voltage average value calculation circuit VDA calculates the average value of the voltage detection signal Vd and outputs the voltage average value signal Vda. The voltage setting circuit VS outputs a voltage setting signal Vs having a desired value. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vs and the voltage average value signal Vda and outputs a voltage error amplification signal ΔV. The V / F converter circuit VF has a frequency proportional to the voltage error amplification signal ΔV, and outputs a pulse period signal Tf that becomes a high level for a short time every one period.

  The peak period setting circuit TPS outputs a predetermined peak period setting signal Tps. The timer circuit TM outputs a timer signal Tm that is at a high level for a period determined by the peak period setting signal Tps from the time when the pulse period signal Tf changes to a high level. That is, the timer signal Tm is a signal that is at a high level during the peak period and is at a low level during the base period.

  The peak current rising characteristic constant setting circuit NU outputs a peak current rising characteristic constant signal Nu having a desired value. 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 current setting circuit IS receives the peak current setting signal Ips, the base current setting signal Ibs, and the peak current rising characteristic constant signal Nu, and when the timer signal Tm is at a high level (peak period), the above-described ( 1) Perform an operation based on the equation and output a current setting signal Is (k).

  When the timer signal Tm is at the high level (peak period), the switching circuit SW switches to the a side and outputs the current setting signal Is (k) as the current control signal Isc. When the timer signal Tm is at the low level (base period) ) Switches to the b side and outputs the base current setting signal Ibs as the current control signal Isc. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The current error amplification circuit EI amplifies the error between the current control signal Isc and the current detection signal Id and outputs a current error amplification signal Ei. The drive circuit DR outputs a drive signal Dr for driving the inverter of the power supply main circuit PM in accordance with the current error amplification signal Ei. Constant current control is performed by this circuit.

[Embodiment 2]
FIG. 4 is a time change diagram of the current setting value showing a method for controlling the falling characteristic of the peak current to a desired value according to the second embodiment of the present invention. In the figure, the base period Tb is variably controlled so that the average value of the welding voltage becomes substantially equal to the voltage setting value as described above with reference to FIG. The peak falling period Td is preset to a predetermined value from the start time of the base period Tb, and the value is in a range of about 0.5 to 3 ms. The minute time control cycle ΔT is set to 50 μs, for example. Therefore, the control described below is performed every control period ΔT. When the start time of the peak falling period Td is set to 0 and a number is assigned for each control period ΔT and the number of elapsed times k (a positive integer), 0 ≦ k ≦ (Td / ΔT) is satisfied during the peak falling period Td. . For example, when Td = 2 ms and ΔT = 50 μs, k = 0, 1, 2, 3,. Furthermore, the peak current set value is Ips, and the base current set value is Ibs.

Here, a peak current falling characteristic constant Nd which is a positive integer is set as a parameter for setting the falling characteristic of the peak current. The current set value Is (k) at each elapsed time number k is calculated by the following equation.
Is (0) = Ips
Is (1) = Is (0) + [Ibs−Is (0)] / Nd
...
Is (k) = Is (k-1) + [Ibs-Is (k-1)] / Nd (2) Formula ...
Is (Td / ΔT) = Is (Td / ΔT−1) + [Ibs−Is (Td / ΔT−1)] / Nd

  A peak current falling characteristic having a desired value indicated by D is set by the peak current falling characteristic constant Nd, and the welding current is controlled to the peak current falling characteristic by the current setting signal Is (k). FIG. 5 is a diagram showing a change in the peak current falling characteristic when the peak current falling characteristic constant Nd is changed. The horizontal axis represents the number of elapsed times k, and the vertical axis represents the welding current value. In this figure, the base current set value Ibs = 50 A, the peak current set value Ips = 450 A, the control cycle ΔT = 50 μs, and the maximum value 40 of k, so the peak falling period Td = 2 ms. As shown in the figure, when the peak current falling characteristic constant Nd is changed to 2, 4, and 8, the peak current falling characteristic has a gradual change. Therefore, a peak current falling characteristic having a desired value can be obtained by adjusting the peak current falling characteristic constant Nd. Here, the peak current falling characteristic constant Nd may be a positive integer, but the numerical value at which the current set value Is (Td / ΔT) ≈Ibs at the end of the peak falling period Td is limited as a maximum value. Also good. That is, when the peak current falling characteristic constant Nd exceeds this maximum value, Is (Td / ΔT)> Ibs.

  In the arithmetic expression described above, Is (0) = Ips. However, the current value at the end of the peak period may not substantially converge to the peak current set value Ips. Assuming such a case, Is (0) may be set to the current value at the end of the peak period.

  FIG. 6 is a block diagram of a welding power source for carrying out the welding current control method of pulse arc welding according to the second embodiment. In the figure, the same blocks as those in FIG. 3 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. 3 will be described with reference to FIG.

  The peak current falling characteristic constant setting circuit ND outputs a peak current falling characteristic constant signal Nd having a desired value. The peak falling period setting circuit TDS outputs a predetermined peak falling period setting signal Tds. The peak falling period timer circuit TTD outputs a peak falling period timer signal Ttd which becomes a High level only during a period determined by the peak falling period setting signal Tds from the time when the timer signal Tm changes to the Low level (base period). To do. The second current setting circuit IS2 receives the peak current setting signal Ips, the base current setting signal Ibs, and the peak current falling characteristic constant signal Nd, and when the peak falling period timer signal Ttd is at a high level (peak falling). (Period) is calculated based on the above-described equation (2), and the current setting signal Is (k) is output.

  In the above, by performing both of the first and second embodiments, the rising characteristics and the falling characteristics of the peak current can be controlled to the desired values. Further, as shown in the above formulas (1) and (2), the calculation of the current set value Is (k) uses only integer addition, subtraction, and division, and includes floating point calculations. Absent. For this reason, the load when computing by the microprocessor is reduced, and the processing speed is also increased.

It is a time change figure of electric current set value Is (k) which shows the welding current control method of pulse arc welding concerning Embodiment 1 of the present invention. FIG. 6 is a diagram showing a change in peak current rising characteristic when the peak current rising characteristic constant Nu is changed in the first embodiment. 1 is a block diagram of a welding power source according to Embodiment 1. FIG. It is a time change figure of electric current set value Is (k) which shows the welding current control method of pulse arc welding concerning Embodiment 2 of the present invention. It is a figure which shows the change of the peak current falling characteristic when changing the peak current falling characteristic constant Nd in Embodiment 2. FIG. 6 is a block diagram of a welding power source according to Embodiment 2. FIG. It is a wave form diagram of welding current Iw and welding voltage Vw in pulse arc welding of prior art 1. It is a block diagram of the welding power supply concerning the prior art 2. It is a wave form diagram of welding current Iw in pulse arc welding of conventional technology 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc D1, D2 Rectifier di / dt Current differential signal DR Drive circuit Dr Drive signal E DC power supply EI Current error amplification circuit Ei Current error amplification signal EI2 Second current error amplification circuit EV Voltage error amplification circuit Ib Base current IBS Base current setting circuit Ibs Base current setting (value / signal)
ID Current detection circuit Id Current detection signal INV Inverter circuit Ip Peak current IPS Peak current setting circuit Ips Peak current setting (value / signal)
IS Current setting circuit Is Current setting (value / signal)
IS2 Second current setting circuit Isc Current control signal Iw Welding current

Nd Peak current falling characteristic constant (signal)
ND Peak current falling characteristic constant setting circuit Nu Peak current rising characteristic constant (signal)
NU peak current rising characteristic constant setting circuit PG pulse generation circuit PM power supply main circuit SW switching circuit Tb base period Td peak falling period TDS peak falling period setting circuit Tds peak falling period setting signal Tf pulse period (signal)
TM timer circuit Tm timer signal Tp peak period TPS peak period setting circuit Tps peak period setting signal Tr transformer TTD peak falling period timer circuit Ttd peak falling period timer signal Tu peak rising period Vb base voltage VD voltage detection circuit Vd voltage detection signal VDA voltage average value calculation circuit Vda voltage average value signal VF V / F converter circuit Vp peak voltage VS voltage setting circuit Vs voltage setting (value / signal)
Vw Welding voltage WL Reactor ΔI Current error amplification signal ΔT Control period ΔV Voltage error amplification signal

Claims (2)

A welding current control method of pulse arc welding in which a peak current Ip corresponding to the peak current set value Ips is supplied during the peak period Tp and a base current Ib corresponding to the base current set value Ibs is supplied during welding during the base period Tb. In
A positive integer peak current rising characteristic constant Nu is set in advance, and during the peak period Tp, the current set value Is (k) is set to Is (k) = Is (k-1) + [ Ips−Is (k−1)] / Nu, where k = 1, 2... (Tp / ΔT) and Is (0) = Ibs, and the peak period Tp depends on the current set value Is (k). A welding current control method for pulse arc welding, wherein the rising characteristic of the peak current Ip is controlled to a desired value having a curved shape. A welding current control method of pulse arc welding in which a peak current Ip corresponding to the peak current set value Ips is supplied during the peak period Tp and a base current Ib corresponding to the base current set value Ibs is supplied during the base period Tb. In
A positive integer peak current falling characteristic constant Nd is set in advance, and a peak falling period Td is set in advance from the start of the base period Tb. During this peak falling period Td, every minute control time ΔT is set. The current set value Is (k) is calculated by Is (k) = Is (k−1) + [Ibs−Is (k−1)] / Nd, where k = 1, 2... (Td / ΔT) and Is (0) = Ips, and the pulse arc welding is characterized in that the falling characteristic of the peak current Ip during the peak falling period Td is controlled to a curved desired value by the current set value Is (k). Welding current control method.

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