Consumable electrode arc welding power source

Abstract

To reduce generation of a spatter by exactly detecting a constriction of a droplet by an output terminal voltage, in consumable electrode arc welding.SOLUTION: A consumable electrode arc welding power supply comprises: a welding voltage detection part VWD for outputting a welding voltage detection signal Vwd by inputting a welding voltage Vw of an arc generation part by a detection line 5; an output terminal voltage detection part VTD for outputting an output terminal voltage detection signal Vtd by inputting a voltage VT of an output terminal of the welding power supply; a voltage detection switching part VD for outputting a signal selected from both signals as a voltage detection signal Vd with the welding voltage detection signal Vwd and the output terminal voltage detection signal Vtd as input; and a constriction detection part ND for detecting a constriction detection signal Nd by detecting a constriction of a droplet in a shortcircuit period by the voltage detection signal Vd. When the constriction detection signal Nd is detected, a welding current Iw is reduced, an arc is regenerated, and welding is started.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a consumable electrode arc welding power supply that detects the constriction of a molten droplet, which is a precursor phenomenon of re-strike of an arc during a short circuit, and reduces the welding current. [Background technology]

[0002] A constriction detection control method has been proposed for consumable electrode arc welding, which repeats short circuit periods and arc periods between the welding wire and base metal, detects constriction of a droplet, which is a precursor phenomenon of an arc re-strike during a short circuit period, and reduces the welding current and re-strikes the arc when constriction is detected (see, for example, Patent Document 1). This constriction detection control method reduces the value of the welding current when the arc re-strikes, so the amount of spatter is greatly reduced, vibration of the molten pool is reduced, and the bead appearance is improved.

[0003] When using a consumable electrode arc welding power source, the welding power source and the location where welding is performed are often far apart. In such cases, the two are connected with a welding cable to perform welding. At this time, the resistance and inductance of the welding cable are inserted into the current path. The resistance is often a small value that does not have much effect on the welding condition and can be ignored. However, the inductance will affect the welding condition if the welding cable is long, such as tens of meters.

[0004] The above-mentioned necking is usually detected based on the welding voltage during the short circuit period. However, in order to detect the welding voltage, which is the voltage at the welded point, it is necessary to wire a dedicated detection wire. Wiring a detection wire of several tens of meters takes time and effort. In addition, since the welding torch moves repeatedly, there is a risk of the detection wire breaking. Furthermore, if the detection wire is long, electromagnetic noise from the welding current flowing through the welding cable will be superimposed.

[0005] For this reason, if the necking could be detected by the output terminal voltage of the welding power source, the above problem would be solved. However, the back electromotive force due to the inductance value of the welding cable is superimposed on the output terminal voltage as noise. As a result, a large amount of noise is superimposed on the output terminal voltage. For this reason, erroneous detection occurs when necking is detected by the output terminal voltage. When erroneous detection occurs, the welding state becomes unstable and the welding quality deteriorates. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5851798 Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a consumable electrode arc welding power supply that can accurately detect a constriction based on the output terminal voltage and can obtain good welding quality. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the invention of claim 1 comprises: a welding voltage detection unit that receives a welding voltage of an arc generating portion via a detection line and outputs a welding voltage detection signal through a low-pass filter having a first cutoff frequency; a constriction detection unit that detects a constriction of a droplet during a short circuit period based on the welding voltage detection signal and outputs a constriction detection signal, a consumable electrode arc welding power source which reduces a welding current and re-generates an arc for welding when the constriction detection signal is output, an output terminal voltage detection unit which receives a voltage at an output terminal of the welding power source and outputs an output terminal voltage detection signal through a low-pass filter having a second cutoff frequency; a voltage detection switching unit which receives the welding voltage detection signal and the output terminal voltage detection signal as inputs and outputs a signal selected from both signals as a voltage detection signal, the constriction detection unit detects the constriction of the droplet during the short circuit period based on the voltage detection signal and outputs the constriction detection signal. The present invention relates to a consumable electrode arc welding power source.

[0009] The invention of claim 2 is as follows: The second cutoff frequency is less than the first cutoff frequency. 2. A consumable electrode arc welding power supply according to claim 1.

[0010] The invention of claim 3 is as follows: The second cutoff frequency is set in the range of 0.8 kHz to 5 kHz. 3. A consumable electrode arc welding power source according to claim 1 or 2.

[0011] The invention of claim 4 is as follows: a constriction detection accuracy evaluation unit that evaluates the accuracy of the constriction detection and outputs a constriction detection accuracy evaluation signal; 4. The consumable electrode arc welding power source according to claim 1, further comprising:

[0012] The invention of claim 5 is as follows: the voltage detection switching unit switches the input signal based on the constriction detection accuracy evaluation signal. 5. A consumable electrode arc welding power source according to claim 4.

[0013] The invention of claim 6 is as follows: setting the second cutoff frequency based on the constriction detection accuracy evaluation signal. 6. A consumable electrode arc welding power source according to claim 4 or 5. Effect of the Invention

[0014] According to the present invention, it is possible to accurately detect a constriction based on the output terminal voltage, and to obtain good welding quality. [Brief description of the drawings]

[0015] [Figure 1] 1 is a block diagram of a consumable electrode arc welding power supply according to an embodiment of the present invention. [Diagram 2] 2 is a timing chart of each signal in the welding power supply of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] 1 is a block diagram of a consumable electrode arc welding power source according to an embodiment of the present invention, each block of which will be described below with reference to the drawing.

[0018] 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.

[0019] The output terminal 6a of the main power supply circuit PM and the welding torch 4 are connected by a welding cable 7a, and the other output terminal 6b and the base material 2 are connected by a welding cable 7b. The length of these welding cables 7a and 7b can be up to 40m round trip. The inductance value of these welding cables 7a and 7b is L (μH). The inductance value L varies within a range of about 10 to 200μH depending on the length and installation state.

[0020] The current-down resistor R is inserted between the main power supply circuit PM and the output terminal 6a. 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.

[0021] 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.

[0022] The welding voltage detection circuit VWD receives the welding voltage Vw at the arc generation point via detection line 5 and outputs a welding voltage detection signal Vwd through a low-pass filter with a predetermined first cutoff frequency. The welding voltage Vw is the voltage between the power contact tip and the base metal. In some cases, the voltage is detected from the conductive part of the feeder FD or welding torch 4 instead of the power contact tip. To improve the accuracy of necking detection, it is desirable that the welding voltage Vw is the voltage at a position as close as possible to the arc generation point. The detection line 5 is wired to detect the welding voltage Vw.

[0023] The output terminal voltage detection circuit VTD receives the output terminal voltage Vt between the output terminals 6a and 6b, and outputs an output terminal voltage detection signal Vtd through a low-pass filter with a second cutoff frequency that is determined in advance. The second cutoff frequency is lower than the first cutoff frequency.

[0024] A welding current detection circuit ID detects the above-mentioned welding current Iw and outputs a welding current detection signal Id.

[0025] The voltage detection switching circuit VD receives the welding voltage detection signal Vwd and the output terminal voltage detection signal Vtd as inputs, and outputs the welding voltage detection signal Vwd or the output terminal voltage detection signal Vtd selected by the welding operator by switching a switch or the like as the voltage detection signal Vd.

[0026] The short circuit determination circuit SD receives the voltage detection signal Vd as input, and when this value is less than a predetermined short circuit / arc determination value Vta (approximately 10 V), it determines that the device is in a short circuit period and outputs a short circuit determination signal Sd that goes to a High level, and when this value is equal to or greater than this value, it determines that the device is in an arc period and outputs a Low level short circuit determination signal Sd.

[0027] 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.

[0028] The squeezing detection circuit ND receives the squeezing detection reference value signal Vtn, the short circuit determination signal Sd, the voltage detection signal Vd, and the welding current detection signal Id as inputs, and outputs a squeezing detection signal Nd that determines that the formation state of the squeezing of the droplet has reached a reference state when the voltage rise value of the 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). In addition, the squeezing detection signal Nd may be changed to a high level when the differential value of the voltage detection signal Vd during the short circuit period reaches the value of the squeezing detection reference value signal Vtn corresponding thereto. Furthermore, the value of the 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.

[0029] The squeezing time detection circuit TND receives the squeezing detection signal Nd, detects the squeezing time Tn at which the squeezing detection signal Nd becomes high level, and outputs the squeezing time detection signal Tnd. The squeezing time Tn is the time from when the squeezing is detected during the short circuit period until the arc re-strikes. If the squeezing time Tn is shorter than the appropriate value, the value of the welding current Iw at the time of the arc re-strike cannot be reduced to a sufficiently small value, resulting in spatters. On the other hand, if the squeezing time Tn is longer than the appropriate value, the low-level current value Il continues for a long time, resulting in an unstable welding state. Therefore, when the squeezing time Tn is within the appropriate range, the squeezing detection control is operating properly.

[0030] The squeezing detection accuracy evaluation circuit NA receives the short circuit determination signal Sd and the squeezing time detection signal Tnd, performs the following processing, and outputs a squeezing detection accuracy evaluation signal Na, the value of which is displayed on a liquid crystal panel or the like. 1) The total number of short circuits that have occurred during welding is counted in response to the short circuit discrimination signal Sd. 2) During welding, count the number of proper constriction times when the value of the constriction time detection signal Tnd is within a predetermined appropriate range. 3) Calculate (number of proper constriction times / total number of short circuits) × 100 (%) and output it as the constriction detection accuracy evaluation signal Na. Here, the appropriate range is, for example, 0.1 to 0.5 ms. The larger the value of the constriction detection accuracy evaluation signal Na, the higher the accuracy of constriction detection. Also, the constriction detection accuracy evaluation signal Na may be output based on the difference value between the average value of the constriction time detection signal Tnd and the target value, the value of the welding current detection signal Id at the time of short circuit release, etc.

[0031] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr.

[0032] The current comparison circuit CM takes the above low-level current setting signal Ilr and the above welding current detection signal Id as inputs, and outputs a current comparison signal Cm that becomes High level when Id < Ilr and becomes Low level when Id ≧ Ilr.

[0033] The drive circuit DR takes the above current comparison signal Cm and the above constriction detection signal Nd as inputs, and outputs a drive signal Dr to the base terminal of the above transistor TR that changes to Low level when the constriction detection signal Nd changes to High level, and then changes to High level when the current comparison signal Cm changes to High level. Therefore, this drive signal Dr becomes Low level when constriction is detected, the transistor TR becomes off, and the current reduction resistor R is inserted into the energization path, so the welding current Iw passing through the short circuit load rapidly decreases. And when the value of the rapidly decreased welding current Iw decreases to the value of the low-level current setting signal Ilr, the drive signal Dr becomes High level, the transistor TR becomes on, so the current reduction 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.

[0034] The current control setting circuit ICR receives the short circuit determination signal Sd, the low level current setting signal Ilr, and the constriction detection signal Nd as inputs, performs the following processing, and outputs a current control setting signal Icr. 1) During a predetermined initial period from the time when the short circuit determination signal Sd changes to a high level (short circuit), a predetermined initial current setting value is output as the current control setting signal Icr. 2) Thereafter, 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 then maintained at that value. 3) When the squeezing detection signal Nd 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. 4) When the short circuit determination 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 with a predetermined arcing slope, and is maintained at that value.

[0035] 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.

[0036] 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 voltage detection signal Vd, amplifies the error between the voltage setting signal Vr(+) and the voltage detection signal Vd(-), and outputs a voltage error amplification signal Ev.

[0037] 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.

[0038] 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.

[0039] Figure 2 is a timing chart of each signal in the welding power source of Figure 1. Figure 2(A) shows the change over time of the welding current Iw, Figure 2(B) shows the change over time of the welding voltage Vw, Figure 2(C) shows the change over time of the squeezing detection signal Nd, Figure 2(D) shows the change over time of the drive signal Dr, Figure 2(E) shows the change over time of the short circuit determination signal Sd, and Figure 2(F) shows the change over time of the current control setting signal Icr. The operation of each signal will be explained below with reference to the figure.

[0040] The welding voltage Vw shown in Fig. 1B or the output terminal voltage Vt (not shown) is switched between the welding voltage detection signal Vwd and the output terminal voltage detection signal Vtd by the welding operator and output as the voltage detection signal Vd in Fig. 1. As described above, the welding voltage detection signal Vwd is a signal obtained by inputting the welding voltage Vw of the arc generating part via the detection line 5 and passing it through a low-pass filter with a first cutoff frequency. The output terminal voltage detection signal Vtd is a signal obtained by inputting the output terminal voltage Vt of the welding power source and passing it through a low-pass filter with a second cutoff frequency.

[0041] (1) Operation from the occurrence of a short circuit at time t1 to the detection of a constriction 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. Then, it is determined that the value of the voltage detection signal Vd in FIG. 1 is less than the short circuit / arc determination value Vta, and as shown in FIG. 1E, the short circuit determination signal Sd changes from a low level to a high level. In response to this, as shown in FIG. 1F, the current control setting signal Icr changes from a predetermined high level current setting value at time t1 to a predetermined initial current setting value, which is a small value. During the predetermined initial period from time t1 to t11, the current setting value is the above-mentioned initial current setting value, during the period from time t11 to t12, the current rises at a predetermined short circuit slope, and during the period from time t12 to t2, the current setting value is the predetermined peak setting value. During the short circuit period, the welding current Iw is controlled to a value corresponding to the current control setting signal Icr, since the constant current control is performed as described above. For this reason, as shown in FIG. 1A, the welding current Iw decreases from the welding current value during the arc period at time t1, becomes the initial current value during the initial period from time t1 to t11, rises at a short-circuit slope during the period from time t11 to t12, and becomes the peak value during the period from time t12 to t2. As shown in FIG. 1C, the squeezing detection signal Nd becomes High level during the squeezing time Tn from time t2 to t3 described later, and becomes Low level during the other period. As shown in FIG. 1D, the drive signal Dr becomes Low level during the period from time t2 to t21 described later, and becomes High level during the other period. Therefore, during the period before time t2 in FIG. 1, the drive signal Dr becomes High level, and the transistor TR in FIG. 1 is turned on, so that the current reducing resistor R is short-circuited and becomes the same state as a normal consumable electrode arc welding power source. For example, the initial period is about 1 ms, the initial current value is about 50A, the short-circuit slope is about 400A / ms, and the peak value is about 450A.

[0042] As shown in FIG. 1B, the welding voltage Vw rises from about time t12 when the welding current Iw reaches its peak value. This is because a constriction gradually forms in the droplet. This change in the welding voltage Vw is detected by the voltage detection signal Vd. The period from time t12 is the period in which the constriction is detected.

[0043] (2) Operation from the time when the constriction is detected 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 rise value ΔV of the voltage detection signal Vd from the voltage value during the initial period becomes equal to the predetermined squeezing detection reference value Vtn, so that a squeezing is detected. As shown in FIG. 1C, the squeezing detection signal Nd changes to a high level. In response to this, as shown in FIG. 1D, the drive signal Dr becomes a low level, so that the transistor TR in FIG. 1 is turned off and the current reducing resistor R is inserted in the current path. At the same time, as shown in FIG. 1F, the current control setting signal Icr decreases to the value of the low-level current setting signal Ilr. As a result, as shown in FIG. 1A, the welding current Iw suddenly decreases from the peak value. Then, at time t21, when the welding current Iw decreases to the low-level current value Il, as shown in FIG. 1D, 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 short-circuited. As a result, as shown in Fig. 1A, the welding current Iw maintains the low-level current value Il from time t21 until time t3 when the arc is re-strike. Therefore, the transistor TR is in the off state only during the period from when the constriction is detected at time t2 until the welding current Iw decreases to the low-level current value Il at time t21. As shown in Fig. 1B, the welding voltage Vw decreases once from time t2 and then suddenly increases as the welding current Iw decreases.

[0044] Here, the squeezing detection accuracy evaluation circuit NA in Fig. 1 calculates the ratio of the number of times when the squeezing time Tn from time t2 to t3 was within a predetermined appropriate range to the total number of short circuits at the end of welding, and outputs it as a squeezing detection accuracy evaluation signal Na (%). The larger this value, the more normally the squeezing detection control is operating without erroneous detection.

[0045] (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 arc 3 is re-struck at time t3, as shown in FIG. 1B, welding voltage Vw increases rapidly and the value of voltage detection signal Vd becomes equal to or greater than short circuit / arc discrimination value Vta. The period from time t3 to t31 corresponds to a predetermined delay period Td (approximately 1 ms). As shown in FIG. 1F, the value of current control setting signal Icr remains at low-level current setting signal value Ilr until time 31. Then, the period from time t31 to t4 corresponds to a predetermined high current period (approximately 2 ms). The value of current control setting signal Icr increases from time t31, and when it reaches the high-level current setting value (approximately 400 A), it is maintained at that value. Since the welding power source is under constant current control from when the arc re-strikes at time t3 until the delay period Td and the high current period have elapsed at time t4, 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 from time t31 until it reaches a high level current value, which it maintains 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. As shown in FIG. 1C, the squeezing detection signal Nd changes to a low level since the arc re-strikes at time t3.

[0046] (4) Operation during the arc period from the end of the high current period 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 a high level current value in response to the arc load. Similarly, as shown in FIG. 1B, the welding voltage Vw gradually decreases from a high level voltage value.

[0047] The setting of the first cutoff frequency will be described. When a detection line is wired to the arc generating portion and the welding voltage detection signal Vwd is selected by the voltage setting switching circuit VD of FIG. 1, the welding voltage detection signal Vwd is not superimposed with a back electromotive force due to the inductance of the welding cable. On the other hand, electromagnetic noise from the welding current Iw passing through the welding cable is superimposed on the welding voltage detection signal Vwd. This electromagnetic noise has a lower noise intensity and a higher frequency than the back electromotive force. Therefore, in order to remove this electromagnetic noise, the first cutoff frequency is set to about 10 kHz. As a result, even when welding is performed with the welding cable having a round trip length of 40 m, which is the maximum length actually used, the squeezing detection accuracy evaluation signal Na is almost 100%, and squeezing detection works without erroneous detection.

[0048] Next, the setting of the second cutoff frequency will be described. When the detection line is not wired to the arc generating portion and the output terminal voltage detection signal Vtd is selected by the voltage setting switching circuit VD of FIG. 1, the counter electromotive voltage due to the inductance of the welding cable is superimposed on the output terminal voltage detection signal Vtd. In order to remove this counter electromotive voltage, the second cutoff frequency is set in the range of 0.8 kHz to 5 kHz. When the second cutoff frequency is set in this way, when welding is performed with the welding cable having a length of 30 m or less, which is the most commonly used length, the necking detection accuracy evaluation signal Na is 80% or more. When the second cutoff frequency is less than 0.8 kHz, noise due to the counter electromotive voltage is removed, but the minute increase in short circuit voltage accompanying necking formation is smoothed, and the detection accuracy decreases. On the other hand, when the second cutoff frequency exceeds 5 kHz, the counter electromotive voltage increases the number of false detections of necking, and the accuracy decreases. When the necking detection accuracy evaluation signal Na is 80% or more, the generation of spatter is reduced and the welding state is stable. When the second cutoff frequency is less than 80%, the number of false detections increases and the welding state is easily unstable. Furthermore, it is more preferable to set the second cutoff frequency in the range of 1 kHz to 3 kHz. By setting it in this manner, the constriction detection accuracy evaluation signal Na becomes 90% or more, and the occurrence of spatters is further reduced.

[0049] The effects of this embodiment will be described below. According to this embodiment, the device further includes a voltage detection switching unit which receives a welding voltage detection signal and an output terminal voltage detection signal as inputs and outputs a signal selected from the two signals as a voltage detection signal, and the constriction detection unit detects constriction of the droplet during the short circuit period using the voltage detection signal and outputs a constriction detection signal. 1) During welding, the welding operator first operates the voltage detection switching circuit to select the output terminal voltage detection signal to be output as the voltage detection signal, without wiring the detection wire. 2) Welding is carried out, and the state of spatter generation and the stability of the weld condition are observed and evaluated. If the conditions are good, welding is continued in this state. 3) If the above evaluation is poor, wire the detection wire and operate the voltage detection switching circuit to select the welding voltage detection signal to be output as the voltage detection signal. Then, perform welding in this state. In this way, in many cases, the constriction detection control can be effectively operated without wiring a detection wire. As a result, in this embodiment, at many construction sites, the constriction can be accurately detected by the output terminal voltage without wiring a detection wire, and good welding quality can be obtained.

[0050] More preferably, according to this embodiment, the second cutoff frequency for the output terminal voltage detection signal is lower than the first cutoff frequency for the welding voltage detection signal. In this way, the back electromotive force due to the inductance of the welding cable can be removed from the output terminal voltage detection signal, so that the squeezing detection control can be performed without erroneous detection.

[0051] More preferably, according to this embodiment, the second cutoff frequency is set in the range of 0.8 kHz to 5 kHz. In this way, the back electromotive force due to the inductance of the welding cable can be removed from the output terminal voltage detection signal, and the voltage rise accompanying the formation of a constriction can be accurately detected, thereby improving the accuracy of constriction detection.

[0052] More preferably, according to this embodiment, there is provided a constriction detection accuracy evaluation section which evaluates the accuracy of constriction detection and outputs a constriction detection accuracy evaluation signal, thereby making it possible to evaluate the accuracy of constriction detection as objective data.

[0053] More preferably, according to this embodiment, the voltage detection switching unit switches the input signal based on the squeezing detection accuracy evaluation signal. In the above, switching between the output terminal voltage detection signal and the welding voltage detection signal was performed based on observation and evaluation by the welding operator. However, in this manner, the squeezing detection accuracy can be evaluated as objective data, so that the voltage detection method can be switched appropriately.

[0054] More preferably, according to this embodiment, the second cut-off frequency is set based on the constriction detection accuracy evaluation signal. In this way, the second cut-off frequency can be optimized based on the value of the constriction detection accuracy evaluation signal, thereby improving the accuracy of constriction detection. [Explanation of symbols]

[0055] 1 Welding wire 2 Base material 3. Arc 4. Welding torch 5 Detection Line 6a, 6b output terminals 7a, 7b Welding cable 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 Narrowing Detection Accuracy Evaluation Circuit Na Constriction detection accuracy evaluation signal ND Constriction Detection Circuit Nd Constriction detection signal PM power supply main circuit R Current reducing resistor SD Short circuit detection circuit Sd Short circuit detection signal SW control switching circuit Td Delay Period TND Neck Time Detection Circuit Tnd Neck time detection signal TR Transistor VD voltage detection switching circuit Vd Voltage detection signal VR voltage setting circuit Vr Voltage setting signal Vt Output terminal voltage Vta short circuit / arc discrimination value VTD Output terminal voltage detection circuit Vtd Output terminal voltage detection signal VTN Constriction detection reference value setting circuit Vtn Constriction detection reference value (signal) Vw welding voltage VWD Welding voltage detection circuit Vwd Welding voltage detection signal ΔV Voltage increase value

Claims

1. a welding voltage detection unit that receives a welding voltage of an arc generating portion via a detection line and outputs a welding voltage detection signal through a low-pass filter having a first cutoff frequency; a constriction detection unit that detects a constriction of a droplet during a short circuit period based on the welding voltage detection signal and outputs a constriction detection signal, a consumable electrode arc welding power source which reduces a welding current and re-generates an arc for welding when the constriction detection signal is output, an output terminal voltage detection unit which receives a voltage at an output terminal of the welding power supply and outputs an output terminal voltage detection signal through a low-pass filter having a second cutoff frequency; a voltage detection switching unit which receives the welding voltage detection signal and the output terminal voltage detection signal as inputs and outputs a signal selected from both signals as a voltage detection signal, the constriction detection unit detects the constriction of the droplet during the short circuit period based on the voltage detection signal and outputs the constriction detection signal.

1. A consumable electrode arc welding power source comprising:

2. the second cutoff frequency is less than the first cutoff frequency; 2. A consumable electrode arc welding power supply as defined in claim 1.

3. The second cutoff frequency is set in the range of 0.8 kHz to 5 kHz.

3. A consumable electrode arc welding power source according to claim 1 or 2.

4. a constriction detection accuracy evaluation unit that evaluates the accuracy of the constriction detection and outputs a constriction detection accuracy evaluation signal; 4. The consumable electrode arc welding power source according to claim 1, further comprising:

5. the voltage detection switching unit switches the input signal based on the constriction detection accuracy evaluation signal.

5. A consumable electrode arc welding power supply as claimed in claim 4.

6. setting the second cutoff frequency based on the constriction detection accuracy evaluation signal; 6. A consumable electrode arc welding power source according to claim 4 or 5.

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