Method for detecting and controlling necking in consumable electrode arc welding

Abstract

To provide a constriction detection control method for consumable electrode arc welding that improves accuracy of constriction detection.SOLUTION: A constriction detection control method for consumable electrode arc welding detects droplet constriction, that is a sign phenomenon that arc occurs again during short circuit at a time t2, and outputs a constriction detection signal Nd, and when the constriction detection signal Nd is outputted, decreases welding current Iw to regenerate arc. In the method, a standard detection time of a lapse time from a start point of the short circuit period until the constriction detection signal Nd is outputted is set, and a standard waveform of a welding voltage Vw during a prescribed period during the short circuit period is set. When a tolerance between the detected waveform and the standard waveform of the welding voltage Vw during the prescribed period is a reference value or less, a constriction estimation signal Ns is outputted at a time point when the standard detection time has lapsed or at a time point when a delay detection time has lapsed from the aforesaid time point, and when the constriction detection signal Nd or the constriction estimation signal Ns is outputted, the welding current Iw is decreased.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a constriction detection and control method for consumable electrode arc welding, which detects the constriction of a droplet, which is a precursor phenomenon of re-ignition of an arc during a short circuit period, and reduces the welding current. [Background technology]

[0002] A constriction detection and control method has been proposed for consumable electrode arc welding, in which short circuit periods and arc periods are repeated between the welding wire and base metal, and constriction of a droplet, which is a precursor phenomenon for an arc to be re-striked during a short circuit period, is detected, and the welding current is reduced and the arc is re-striked when constriction is detected (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5851798 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional consumable electrode arc welding constriction detection control method, the welding current value when the arc re-strikes during the short circuit period is reduced by the constriction detection control, so the amount of spatter is significantly reduced, the vibration of the molten pool is reduced, and the bead appearance is improved. However, since the progression of the constriction formed in the droplet varies, there is a certain probability that the detection of the constriction will fail.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a method for controlling the detection of a constriction in consumable electrode arc welding, which is capable of improving the accuracy of detecting a constriction. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the invention of claim 1 comprises: A short circuit period and an arc period are repeated between the welding wire and the base metal, and during the short circuit period, the constriction of the droplet, which is a precursor phenomenon of the re-ignition of the arc, is observed. When the increase or differential value of the welding voltage reaches the reference value, a constriction detection control method for consumable electrode arc welding, comprising: detecting a constriction and outputting a constriction detection signal; and reducing a welding current and re-igniting an arc when the constriction detection signal is output, A standard detection time is set as the elapsed time from the start of the short circuit period until the squeezing detection signal is output, and a predetermined period from the start of the short circuit period to the standard detection time is set as the standard detection time. The above Set the standard waveform of the welding voltage, When an error between the detected waveform of the welding voltage during the predetermined period and the standard waveform is equal to or smaller than a reference value, a squeezing estimation signal is output at a time point when the standard detection time has elapsed or at a time point when a delayed detection time has elapsed from that time point, When the constriction detection signal is not output, When the constriction estimation signal is output, the welding current is reduced. The present invention relates to a method for detecting and controlling a constriction in consumable electrode arc welding.

[0007] The invention of claim 2 is as follows: The standard detection time is set by calculating an average value of the elapsed time until the squeezing detection signal is output, The standard waveform is set by calculating an average value of the detected waveform of the welding voltage during the predetermined period when the squeezing detection signal is output. 2. The method for detecting and controlling a constriction in consumable electrode arc welding according to claim 1. Effect of the Invention

[0008] According to the present invention, in a constriction detection control method for consumable electrode arc welding, it is possible to improve the precision of constriction detection. [Brief description of the drawings]

[0009] [Figure 1] 1 is a block diagram of a welding power source for implementing a method for detecting and controlling a constriction in consumable electrode arc welding according to an embodiment of the present invention. [Diagram 2]2 is a timing chart of each signal in the welding power source of FIG. 1, illustrating a method for controlling detection of a constriction in consumable electrode arc welding according to an embodiment of the present invention. [Diagram 3] FIG. 11 is a waveform diagram of the welding voltage Vw when a squeezing detection signal Nd is output during a short circuit period. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] 1 is a block diagram of a welding power source for carrying out a method for detecting and controlling a constriction in consumable electrode arc welding according to an embodiment of the present invention. Each block will be described below with reference to the diagram.

[0012] The power supply main circuit PM receives a commercial power supply (not shown) such as 3-phase 200V as an input, performs output control such as inverter control according to an error amplified signal Ea described below, and outputs a welding voltage Vw and a welding current Iw. Although not shown, the power supply main circuit PM includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smoothes the rectified DC, an inverter circuit that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for welding, a secondary rectifier that rectifies the stepped-down high-frequency AC into DC, a reactor that smoothes the rectified DC, a modulation circuit that receives the error amplified signal Ea as an input and performs pulse-width modulation control, and an inverter drive circuit that receives a pulse-width modulation control signal as an input and drives the switching elements of the inverter circuit.

[0013] The current-down resistor R is inserted between the main power supply circuit PM and the welding torch 4. The value of this current-down resistor R is set to a value (about 0.5 to 3 Ω) that is 50 times or more larger than the short-circuit load (about 0.01 to 0.03 Ω). Therefore, when the current-down resistor R is inserted into the current path by the constriction detection control, the energy stored in the DC reactor in the welding power supply and the reactor of the external cable is suddenly discharged. The transistor TR is connected in parallel with the current-down resistor R, and is controlled to be turned on or off according to a drive signal Dr described later.

[0014] Welding wire 1 is fed through welding torch 4 by a wire feeder FD, and an arc 3 is generated between the welding wire 1 and base metal 2. A welding voltage Vw is applied between a power feed tip (not shown) in welding torch 4 and base metal 2, and a welding current Iw flows between the power feed tip and base metal 2.

[0015] A welding current detection circuit ID detects the above-mentioned welding current Iw and outputs a welding current detection signal Id.

[0016] The welding voltage detection circuit VD detects the above-mentioned welding voltage Vw and outputs a welding voltage detection signal Vd.

[0017] The short circuit determination circuit SD receives the above-mentioned welding voltage detection signal Vd as input, and outputs a short circuit determination signal Sd that goes to High level when this value is less than a predetermined short circuit / arc determination value Vta (approximately 10 V) and determines that the circuit is in a short circuit period, and goes to Low level when this value is equal to or greater than this value and determines that the circuit is in an arc period.

[0018] The squeezing detection reference value setting circuit VTN outputs a predetermined squeezing detection reference value signal Vtn. The value of this squeezing detection reference value signal Vtn is set to an appropriate value according to welding conditions such as the welding method, the feed speed, the material and diameter of the welding wire 1, etc.

[0019] The squeezing detection circuit ND receives the squeezing detection reference value signal Vtn, the short circuit determination signal Sd, the welding voltage detection signal Vd, and the welding current detection signal Id as inputs, and outputs a squeezing detection signal Nd that determines that a squeezing has been formed when the voltage rise value of the welding voltage detection signal Vd reaches the value of the squeezing detection reference value signal Vtn when the short circuit determination signal Sd is at a high level (short circuit period) and becomes a high level, and becomes a low level when the short circuit determination signal Sd changes to a low level (arc period). The squeezing detection signal Nd may be changed to a high level when the differential value of the welding voltage detection signal Vd during the short circuit period reaches the value of the squeezing detection reference value signal Vtn corresponding thereto. Furthermore, the value of the welding voltage detection signal Vd may be divided by the value of the welding current detection signal Id to calculate the resistance value of the droplet, and the squeezing detection signal Nd may be changed to a high level when the differential value of this resistance value reaches the value of the squeezing detection reference value signal Vtn corresponding thereto.

[0020] The standard detection time setting circuit TSR receives the short circuit determination signal Sd, the welding voltage detection signal Vd, and the squeezing detection signal Nd as inputs, detects the elapsed time from when the short circuit determination signal Sd changes to a High level (short circuit period) until the squeezing detection signal Nd changes to a High level, calculates the average value of the elapsed time, and outputs the standard detection time setting signal Tsr. This setting is performed by a preliminary test, while prohibiting the squeezing estimation signal Ns, which will be described later, from going to a High level.

[0021] The standard waveform setting circuit WSR receives the short circuit discrimination signal Sd, the welding voltage detection signal Vd, the squeezing detection signal Nd, the standard detection time setting signal Tsr, and a period signal St described later as inputs, detects and stores the welding voltage detection signal Vd during a predetermined period when the squeezing detection signal Nd becomes high level at predetermined sampling intervals (about 10 to 100 μs), averages the stored time series data (excluding data after the squeezing detection signal Nd becomes high level) at corresponding time points, and outputs the standard waveform setting signal Wsr. This setting is performed by a preliminary test, with the squeezing estimation signal Ns described later prohibited from becoming high level. The above-mentioned specified periods are: 1) the period from the start of the initial period (period signal St=1) to the start of the short circuit period (short circuit discrimination signal Sd is at a high level) until the standard detection time Ts determined by the standard detection time setting signal Tsr has elapsed; 2) the period from the start of the current rise period (period signal St=2) to the start of the short circuit period until the standard detection time Ts has elapsed; 3) the period from the start of the peak current period of the short circuit period (period signal St=3) to the start of the short circuit period until the standard detection time Ts has elapsed.

[0022] The constriction estimation circuit NS receives as input the standard detection time setting signal Tsr, the standard waveform setting signal Wsr, the welding voltage detection signal Vd, the short circuit discrimination signal Sd and the period signal St described later, and when the error between the welding voltage detection signal Vd and the standard waveform Ws set by the standard waveform setting signal Wsr during the specified period during the short circuit period when the short circuit discrimination signal Sd is at a high level is below a reference value, it outputs a constriction estimation signal Ns which goes to a high level when the standard detection time Ts set by the standard detection time setting signal Tsr has elapsed from the start of the short circuit period or after a predetermined delay detection time from that time, and returns to a low level when the short circuit discrimination signal Sd changes to a low level (arc period). The error between the welding voltage detection signal Vd and the standard waveform Ws is calculated by integrating the error between the value of the welding voltage detection signal Vd and the value of the standard waveform Ws corresponding to that time for each sampling period mentioned above from the start of the predetermined period.

[0023] The squeezing signal generating circuit NA receives the squeezing detection signal Nd and the squeezing estimation signal Ns, performs a logical OR on both signals, and outputs a squeezing signal Na. As a result, when the squeezing detection signal Nd or the squeezing estimation signal Ns changes to a high level, the squeezing signal Na becomes a high level, and squeezing detection control is performed.

[0024] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr.

[0025] The current comparison circuit CM takes the above-mentioned low-level current setting signal Ilr and the above-mentioned welding current detection signal Id as inputs, and outputs a current comparison signal Cm that becomes High level when Id < Ilr and Low level when Id ≧ Ilr.

[0026] The drive circuit DR takes the above-mentioned current comparison signal Cm and the above-mentioned constriction signal Na as inputs, changes to Low level when the constriction signal Na changes to High level, and then changes to High level when the current comparison signal Cm changes to High level, and outputs a drive signal Dr to the base terminal of the above-mentioned transistor TR. Therefore, this drive signal Dr becomes Low level when the constriction signal Na becomes High level, the transistor TR turns off, and the current limiting resistor R is inserted into the energization path, so the welding current Iw flowing through the short-circuit load rapidly decreases. Then, when the value of the rapidly decreasing welding current Iw decreases to the value of the low-level current setting signal Ilr, the drive signal Dr becomes High level and the transistor TR turns on, so the current limiting resistor R is short-circuited and returns to the normal state. As a result, the welding current Iw maintains the value of the low-level current setting signal Ilr.

[0027] The current control setting circuit ICR takes the above-mentioned short-circuit discrimination signal Sd, the above-mentioned low-level current setting signal Ilr, and the above-mentioned constriction signal Na as inputs, performs the following processing, and outputs a current control setting signal Icr and a period signal St. 1) During a predetermined initial period from the time when the short-circuit discrimination signal Sd changes to High level (short circuit), the value of the current control setting signal Icr is set to a predetermined initial current setting value, and the period signal St = 1 is output. 2) During the subsequent current increase period, the value of the current control setting signal Icr is increased from the above-mentioned initial current setting value to a predetermined peak setting value at a predetermined short-circuit slope, and the period signal St = 2 is output. 3) During the subsequent peak current period, the value of the current control setting signal Icr is adjusted to the above-mentioned peak setting value, and the period signal St = 3 is output. 4) When the squeezing signal Na changes to a high level (squeezing detected), the value of the current control setting signal Icr is switched to and maintained at the value of the low-level current setting signal Ilr, and a period signal St=4 is output. 5) After the short circuit detection signal Sd changes to a low level (arcing period) and a predetermined delay period Td has elapsed, the current control setting signal Icr is increased to a predetermined high-level current setting value at a predetermined arcing slope, and is maintained at that value.

[0028] The current error amplifier circuit EI amplifies the error between the current control setting signal Icr(+) and the welding current detection signal Id(-), and outputs a current error amplified signal Ei.

[0029] The voltage setting circuit VR outputs a predetermined voltage setting signal Vr for setting the welding voltage during the arc period. The voltage error amplifier circuit EV receives the voltage setting signal Vr and the welding voltage detection signal Vd, amplifies the error between the voltage setting signal Vr(+) and the welding voltage detection signal Vd(-), and outputs a voltage error amplification signal Ev.

[0030] The control switching circuit SW receives the current error amplified signal Ei, the voltage error amplified signal Ev, and the short circuit determination signal Sd as inputs, and outputs the current error amplified signal Ei as the error amplified signal Ea during the period from when the short circuit determination signal Sd changes to a high level (short circuit) until when the short circuit determination signal Sd changes to a low level (arc period) and the delay period and the high current period have elapsed, and outputs the voltage error amplified signal Ev as the error amplified signal Ea during the other periods. This circuit provides constant current control during the short circuit period + delay period Td + high current period, and constant voltage control during the other arc periods.

[0031] The feed speed setting circuit FR outputs a predetermined feed speed setting signal Fr. The feed control circuit FC receives the feed speed setting signal Fr and outputs a feed control signal Fc to the feeder FD for feeding the welding wire 1 at a feed speed corresponding to the set value.

[0032] Fig. 2 is a timing chart of each signal in the welding power source of Fig. 1, which illustrates a method for controlling squeezing detection in consumable electrode arc welding according to an embodiment of the present invention. Fig. 2(A) shows the change over time in welding current Iw, Fig. 2(B) shows the change over time in welding voltage Vw, Fig. 2(C) shows the change over time in squeezing detection signal Nd, Fig. 2(D) shows the change over time in drive signal Dr, Fig. 2(E) shows the change over time in squeezing estimation signal Ns, and Fig. 2(F) shows the change over time in squeezing signal Na. Below, the operation of each signal will be explained with reference to the figure.

[0033] In the figure, the squeezing detection signal Nd is at a high level during a short circuit period from time t1 to t3, and the squeezing estimation signal Ns is at a high level during a short circuit period from time t5 to t7.

[0034] (1) Operation from the occurrence of a short circuit at time t1 to the time when the squeezing detection signal Nd becomes high level at time t2 When the welding wire 1 comes into contact with the base material 2 at time t1, a short circuit period is entered, and as shown in FIG. 1B, the welding voltage Vw is rapidly reduced to a short circuit voltage value of about several volts. When it is determined that the welding voltage Vw is less than the short circuit / arc determination value Vta, the short circuit determination signal Sd in FIG. 1 changes from a low level to a high level. As shown in FIG. 1A, the welding current Iw decreases from the welding current value of the arc period at time t1, becomes a predetermined initial current value during a predetermined initial period from time t1 to t11, rises at a predetermined short circuit slope during a current rise period from time t11 to t12, and becomes a predetermined peak current value during a peak current period from time t12 to t2. As shown in FIG. 1C, the squeezing detection signal Nd becomes a high level during a period from time t2 to t3 described later, and becomes a low level during the other periods. As shown in FIG. 1D, the drive signal Dr becomes a low level during a period from time t2 to t21 described later, and becomes a high level during the other periods. Therefore, during the period before time t2 in the figure, the drive signal Dr is at a high level, and the transistor TR in Figure 2 is turned on, so that the current-reducing resistor R is short-circuited and the state is the same as that of a normal consumable electrode arc welding power supply. For example, the above initial period is about 1 ms, the initial current value is about 50 A, the short-circuit slope is about 400 A / ms, and the peak value is about 450 A.

[0035] As shown in Fig. 1B, the welding voltage Vw increases from about time t12 when the welding current Iw reaches its peak current value. This is because a constriction gradually forms in the droplet. The period from time t12 is the period during which the constriction is detected. During this period during which the welding current Iw is detected, as shown in Fig. 1A, the welding current Iw is approximately constant at its peak value.

[0036] (2) Operation from the time when the squeezing detection signal Nd changes to a high level at time t2 to the time when the arc re-strikes at time t3 At time t2, as shown in FIG. 1B, the welding voltage Vw rises and the voltage increase ΔV from the voltage value during the initial period becomes equal to the predetermined squeezing detection reference value Vtn, and thus a squeezing is detected. As shown in FIG. 1C, the squeezing detection signal Nd changes to a high level. As a result, as shown in FIG. 1F, the squeezing signal Na changes to a high level. In this case, as shown in FIG. 1E, the squeezing estimation signal Ns remains at a low level. In response to this, as shown in FIG. 1D, the drive signal Dr goes to a low level, so that the transistor TR in FIG. 1 is turned off and the current reducing resistor R is inserted into the current path. As a result, as shown in FIG. 1A, the welding current Iw suddenly decreases from the peak current value. Then, at time t21, when the welding current Iw decreases to the low-level current value Il set by the low-level current setting signal Ilr, as shown in FIG. 1(D), the drive signal Dr returns to a high level, so that the transistor TR in FIG. 1 is turned on and the current reducing resistor R is shorted. As a result, as shown in FIG. 1(A), the welding current Iw maintains the low-level current value Il from time t21 to time t3 when the arc is re-striked. Therefore, the transistor TR is in the off state only during the period from when the constriction signal Na changes to a high level at time t2 until when the welding current Iw decreases to the low-level current value Il at time t21. As shown in FIG. 1(B), the welding voltage Vw decreases once from time t2 as the welding current Iw decreases, and then rises sharply.

[0037] (3) Operation from the re-ignition of the arc at time t3 until the end of the delay period Td and the end of the high current period at time t4 When the arc 3 re-strikes at time t3, as shown in FIG. 1B, the value of the welding voltage Vw becomes equal to or greater than the short circuit / arc discrimination value Vta. The period from time t3 to t31 is a predetermined delay period Td, and the period from time t31 to t4 is a predetermined high current period. The welding power source is under constant current control from the time the arc re-strikes at time t3 until time t4 when the delay period Td and the high current period have elapsed. Therefore, as shown in FIG. 1A, the welding current Iw is at a low level current value Il during the delay period Td from time t3 to t31, and increases at an arc-time slope from time t31. When it reaches a high level current value, it maintains that value until time t4. As shown in FIG. 1B, the welding voltage Vw is at an arc voltage value during the delay period Td from time t3 to t31, and is at a higher high level voltage value during the high current period from time t31 to t4. At time t3, an arc re-strikes, and the squeezing detection signal Nd shown in FIG. 1C and the squeezing signal Na shown in FIG. 1F return to low level. For example, the delay period Td is about 1 ms, the arcing slope is about 300 A / ms, the high-level current value is about 350 A, and the high-current period is about 2 ms.

[0038] (4) Operation during the arc period from the end of the high current at time t4 to the occurrence of the next short circuit at time t5 When the high current period ends at time t4, the welding power source is switched from constant current control to constant voltage control. As a result, as shown in FIG. 1A, the welding current Iw gradually decreases from the high-level current value. Similarly, as shown in FIG. 1B, the welding voltage Vw gradually decreases from the high-level voltage value.

[0039] The operation from the occurrence of a short circuit at time t5 to the time t6 when the squeezing estimation signal Ns goes to a high level is similar to the operation from time t1 to t2 described above, and therefore a description thereof will be omitted.

[0040] (5) Operation from the time when the necking estimation signal Ns changes to a high level at time t6 to the time when the arc re-strikes at time t7 At time t5, the time elapsed since the short circuit period reaches the standard detection time Ts set by the standard detection time setting signal Tsr in FIG. 1, and the error between the welding voltage detection signal Vd in FIG. 1 and the standard waveform Ws set by the standard waveform setting signal Wsr in FIG. 1 during a predetermined period is equal to or less than the reference value, so that the squeezing estimation signal Ns changes to a high level as shown in FIG. 1(E). As a result, as shown in FIG. 1(F), the squeezing signal Na changes to a high level. In this case, as shown in FIG. 1(C), the squeezing detection signal Nd remains at a low level. The subsequent operations are the same as those from time t2 to t3 described above, and therefore will not be described. In the case of the short circuit period from time t5, even at time t6 when the standard detection time Ts has elapsed, the voltage increase value ΔV of the welding voltage Vw has not yet reached the squeezing detection reference value Vtn. On the other hand, since the error between the welding voltage detection signal Vd and the standard waveform Ws during a predetermined period is equal to or less than the reference value, it can be estimated that the squeezing is progressing. Therefore, by setting the squeezing estimation signal Ns to a High level at this time and operating the squeezing detection control, an arc can be re-stimulated with the welding current Iw being small. In this way, the accuracy of squeezing detection can be improved. In the above, the squeezing estimation signal Ns becomes High level when the standard detection time Ts at time t5 has elapsed, but it may also become High level when a predetermined delayed detection time has elapsed from that time. The accuracy of squeezing detection can be further improved by adjusting this delayed detection time. For example, the standard detection time Ts is about 3.5 ms and the delayed detection time is about 0.5 ms.

[0041] The above-mentioned predetermined period is set, for example, as follows. 1) The period from the start of the initial period to the end of the standard detection time Ts from the start of the short circuit period. 2) The period from the start of the current rise period to the start of the short circuit period until the standard detection time Ts has elapsed. 3) The period from the start of the peak current period of the short circuit to the elapse of the standard detection time Ts from the start of the short circuit period.

[0042] The error between the welding voltage detection signal Vd and the standard waveform Ws is calculated by accumulating the error between the value of the welding voltage detection signal Vd and the value of the standard waveform Ws corresponding to that time for each predetermined sampling period (approximately 10 to 100 μs) from the start of a specified period.

[0043] 3 is a waveform diagram of the welding voltage Vw when the squeezing detection signal Nd is output during a short circuit period. Hereinafter, a method of setting a standard waveform and a method of calculating an error between the detected waveform of the welding voltage Vw will be described with reference to the diagram.

[0044] In the figure, a short circuit occurs at time t1, and an arc is re-ignited at time t5. The period from time t1 to t2 is the initial period, the period from time t2 to t3 is the current rise period, and the period from time t3 to t4 is the peak current period. At time t4, the squeezing detection signal Nd becomes a high level. When a short circuit occurs at time t1, as shown in the figure, the welding voltage Vw steeply drops from an arc voltage value of several tens of volts to a short circuit voltage value of several volts. During the initial period from time t1 to t2, the welding current Iw becomes a small current value of about 50 A. Accordingly, as shown in the figure, the welding voltage Vw becomes the smallest short circuit voltage value. During the current rise period from time t2 to t3, the welding current Iw rises from 50 A to 450 A. Accordingly, as shown in the figure, the welding voltage Vw also rises. During the peak current period from time t3 to t4, the welding current Iw becomes a peak current value of 450 A. As shown in the figure, the welding voltage Vw gradually rises as the constriction of the droplet progresses. At time t4, the voltage increase from the initial period reaches the constriction detection reference value, and the constriction detection signal Nd becomes high level. As a result, the welding current Iw drops sharply to about 50 A. In response, as shown in the figure, the welding voltage Vw also drops sharply to a small value. When the arc re-strikes at time t5, as shown in the figure, the welding voltage Vw rises sharply to the arc voltage value.

[0045] A method for setting the standard detection time Ts will be described below. The time elapsed from the start time t1 of the short circuit period to the time t4 when the squeezing detection signal Nd changes to a high level is detected. The average value of the detected elapsed times from the start of welding is calculated to set the standard detection time Ts.

[0046] Next, a method for setting the standard waveform Ws will be described. For example, the standard detection time Ts is 3.5 ms, the sampling period is 0.1 ms, the initial period is 1 ms, the current rise period is 1 ms, and the predetermined period is the period from the start point t3 of the peak current period until the standard detection time Ts has elapsed. In the figure, it is assumed that the n-th squeezing detection signal Nd is output during a short circuit period, and the elapsed time until the squeezing detection signal Nd becomes high level (the period from time t1 to t4) is 3.7 ms. The sampled values ​​of the welding voltage detection signal Vd during the 1.7 ms period from time t3 to t4 are as follows: Vd(n,0)…Vd(n,17) Here, since the standard detection time Ts=3.5 ms, Vd(n,0) to Vd(n,15) excluding the initial period and the current rise period are stored. Then, the standard waveform Ws is set as follows. Standard value of Vd(0) = average value of Vd(1,0)~Vd(n,0) … Standard value of Vd(15) = average value of Vd(1,15) to Vd(n,15) As a result, the standard waveform Ws is formed from 16 points of time-series data from the standard value Vd(0) to the standard value Vd(15).

[0047] Next, a method for calculating the error between the standard waveform Ws and the welding voltage detection signal Vd will be described. During the m-th short circuit period, the sampled values ​​of the welding voltage detection signal Vd during a predetermined period are as follows: Vd(m,0)…Vd(n,15) And the error for each sample is: Error of Vd(0) = |Vd(m,0)-standard value of Vd(0)| … Error of Vd(15) = |Vd(m,15)-standard value of Vd(15)| As a result, the error is calculated as follows: Error=Error of Vd(0)+...+Error of Vd(15).

[0048] According to the above-described embodiment, a standard detection time is set as the elapsed time from the start of the short circuit period until the squeezing detection signal is output, a standard waveform of the welding voltage during a predetermined period from the start of the short circuit period to the standard detection time is set, and when the error between the detected waveform of the welding voltage during the predetermined period and the standard waveform is equal to or less than a reference value, a squeezing estimation signal is output at the time when the standard detection time has elapsed or at the time when the delayed detection time has elapsed from that time, and the welding current is reduced when the squeezing detection signal or the squeezing estimation signal is output. Even when the standard detection time has elapsed, in a state in which the voltage rise value of the welding voltage has not reached the squeezing detection reference value, it can be estimated that the squeezing is progressing when the error between the welding voltage detection signal and the standard waveform during the predetermined period is equal to or less than the reference value. Therefore, by setting the squeezing estimation signal to a High level at this time and operating the squeezing detection control, an arc can be regenerated with a small value of the welding current. In this way, the accuracy of the squeezing detection can be improved. In addition, by providing a delayed detection time and adjusting it according to the welding conditions, the accuracy of the squeezing detection can be further improved.

[0049] Furthermore, according to this embodiment, the standard detection time is set by calculating the average value of the elapsed time until the squeezing detection signal is output, and the standard waveform is set by calculating the average value of the detected waveform of the welding voltage during a predetermined period when the squeezing detection signal is output. In this manner, the standard detection time and the standard waveform can be automatically set to appropriate values. Therefore, in this embodiment, the effort of setting can be eliminated, and appropriate values ​​are set according to various welding conditions, thereby further improving the accuracy of squeezing detection. [Explanation of symbols]

[0050] 1 Welding wire 2 Base material 3. Arc 4. Welding torch CM current comparison circuit Cm current comparison signal DR drive circuit Dr Drive signal Ea Error amplification signal EI Current Error Amplifier Circuit Ei Current error amplification signal EV voltage error amplifier circuit Ev Voltage error amplified signal FC feed control circuit Fc feed control signal FD feeder FR feed speed setting circuit Fr feed speed setting signal ICR Current control setting circuit Icr Current control setting signal ID Welding current detection circuit Id Welding current detection signal Il Low level current value ILR Low level current setting circuit Ilr Low level current setting signal Iw Welding current NA Constriction Signal Generator Circuit Na constriction signal ND Constriction Detection Circuit Nd Constriction detection signal NS Constriction Estimation Circuit Ns Estimated necking signal PM power supply main circuit R Current reducing resistor SD Short circuit detection circuit Sd Short circuit detection signal St period signal SW control switching circuit Td Delay Period TR Transistor Ts Standard detection time TSR Standard detection time setting circuit Tsr Standard detection time setting signal VD Welding voltage detection circuit Vd Welding voltage detection signal VR voltage setting circuit Vr Voltage setting signal Vta short circuit / arc discrimination value VTN Constriction detection reference value setting circuit Vtn Constriction detection reference value (signal) Vw welding voltage Ws standard waveform WSR standard waveform setting circuit Wsr standard waveform setting signal ΔV Voltage increase value

Claims

1. A constriction detection and control method for consumable electrode arc welding, the method comprising the steps of: repeating a short circuit period and an arc period between a welding wire and a base metal; detecting a constriction of a droplet, which is a precursor phenomenon of an arc being re-striked during the short circuit period, when an increase or differential value of a welding voltage reaches a reference value; outputting a constriction detection signal; and reducing a welding current and re-striking an arc when the constriction detection signal is output, the method comprising the steps of: A standard detection time is set as an elapsed time from the start of the short circuit period until the squeezing detection signal is output, and a standard waveform of the welding voltage during a predetermined period from the start of the short circuit period to the standard detection time is set; when an error between the detected waveform of the welding voltage during the predetermined period and the standard waveform is equal to or less than a reference value, a squeezing estimation signal is output at a time point when the standard detection time has elapsed or at a time point when a delayed detection time has elapsed from that time point, and when the squeezing detection signal is not being output and the squeezing estimation signal is output, the welding current is reduced.

4. A method for detecting and controlling a constriction in consumable electrode arc welding.

2. The standard detection time is set by calculating an average value of the elapsed time until the squeezing detection signal is output, The standard waveform is set by calculating an average value of the detected waveform of the welding voltage during the predetermined period when the squeezing detection signal is output.

2. The method for detecting and controlling a constriction in consumable electrode arc welding according to claim 1.

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