JP4847082B2 - Welding power supply with current suddenly decreasing function when detecting constriction - Google Patents

Description

  The present invention detects the constriction phenomenon of droplets, which is a precursor to the occurrence of short-circuiting and arc re-generation in short-circuit transfer welding such as carbon dioxide arc welding and mag welding, thereby rapidly reducing the welding current and suppressing spattering. Therefore, the present invention relates to an improvement in a welding power source with a function of rapidly reducing current at the time of detection of constriction.

  FIG. 4 is a diagram showing current / voltage waveforms and droplet transfer in consumable electrode gas shielded arc welding (hereinafter referred to as short-circuit transfer welding) in which the short-circuit period Ts and the arc period Ta are repeated. FIG. 4A shows the time variation of the welding current Iw for energizing the consumable electrode (hereinafter referred to as the welding wire 1), and FIG. 4B shows the time change of the welding voltage Vw between the welding wire 1 and the base material 2. (C)-(E) show the state of transfer of the droplet 1a. Hereinafter, a description will be given with reference to FIG.

  During the short-circuit period Ts from time t1 to t3, the droplet 1a at the tip of the welding wire 1 is short-circuited with the base material 2, and as shown in FIG. As shown in B), since the welding voltage Vw is in a short circuit state, the welding voltage Vw becomes a low value of about several volts. As shown in FIG. 5C, the droplet 1a comes into contact with the base material 2 at a time t1 to enter a short circuit state. Thereafter, as shown in FIG. 4D, a constriction 1b is generated at the upper part of the droplet 1a by an electromagnetic pinch force generated by a welding current Iw for energizing the droplet 1a. And this constriction 1b progresses rapidly, and as shown to the same figure (E) at the time t3, the droplet 1a will detach | leave from the welding wire 1 to the molten pool 2a, and the arc 3 will generate | occur | produce again. When this constriction occurs, the short circuit is opened after an extremely short time of several hundred μs, and the arc 3 is regenerated. That is, the constriction phenomenon 1b becomes a precursor phenomenon of short circuit opening. When the constriction 1b occurs, the energization path of the welding current Iw becomes narrow at the constricted portion, and the resistance value r of the energization path increases. The increase value of the resistance value r increases as the constriction 1b progresses. Since the resistance value can be calculated by r = Vw / Iw, the progress of the constriction 1b can be detected by detecting the increase in the resistance value r. Further, since the constriction occurrence period from time t2 to t3 is an extremely short time as described above, the welding current Iw can be regarded as a substantially constant value during this period as shown in FIG. For this reason, the increase in the resistance value r as the constriction progresses appears as an increase in the welding voltage Vw, as shown in FIG. Therefore, it is possible to detect the occurrence of constriction by determining that the welding voltage value Vw has risen above the reference increase value Vu.

  In short-circuit transfer welding, since a large current is applied when the arc 3 is regenerated at time t3, the pressure (arc force) from the arc 3 to the molten pool 2a becomes very large, and a large amount of spatter is generated. To do. That is, the amount of spatter generated increases substantially in proportion to the value of the welding current Iw when the arc is regenerated. Therefore, in order to suppress the occurrence of spatter, it is necessary to reduce the current value when the arc is regenerated. As a method for this purpose, a welding power source has been conventionally proposed in which a constriction phenomenon is detected and the welding current Iw is suddenly reduced to reduce the current value at the time of arc re-generation, and a current reduction function at the time of constriction detection is added (for example, (See Patent Documents 1 and 2). Hereinafter, this prior art will be described.

  FIG. 5 is a block diagram of a welding power source with a current suddenly decreasing function at the time of squeezing detection in the prior art. Hereinafter, each circuit block will be described with reference to FIG.

  The power supply main circuit MC is the same as the power supply main circuit for general consumable electrode gas shielded arc welding, and performs output control by inverter control, thyristor phase control, etc. with a commercial power supply as input, and outputs the output voltage and output current Io. Output. A discharge circuit composed of a series circuit of a capacitor C and a discharge switching element TRD is connected between the + terminal and the − terminal of the power supply main circuit MC. The discharge current Id from this discharge circuit is energized in the direction opposite to the welding current Iw during the squeezing detection period. The capacity of the capacitor C is such that a discharge current Id that is slightly smaller than the welding current value Iw at the time of squeezing detection shown at time t2 in FIG. 4 is energized, and that the discharge current Id has a substantially peak value when the arc is regenerated. Set. Next, a charging circuit comprising a series circuit of a charging power source E and a charging switching element TRC is connected in parallel with the capacitor C.

  The squeezing detection circuit ND receives the welding voltage Vw, detects the occurrence of squeezing of the droplets as the voltage rises, and outputs a squeezing detection signal Nd that assumes a high level. As described above, the constriction detection may be performed by detecting an increase in the resistance value r. The charge / discharge drive circuit DR receives the squeezing detection signal Nd and turns off the charging switching element TRC when the squeezing detection signal Nd becomes a high level, or when a predetermined time has elapsed since then. Then, the charging drive signal Drc for turning on the charging switching element TRC is output. At the same time, the charging / discharging drive circuit DR receives the squeezing detection signal Nd as an input, and turns on the discharging switching element TRD when the squeezing detection signal Nd becomes a high level. When the time has elapsed, a discharge drive signal Drd for turning off the discharge switching element TRD is output.

  The constriction detection circuit ND may be included in the charge / discharge drive circuit DR. Further, the charge / discharge drive circuit DR including the discharge circuit, the charging circuit, and the squeezing detection circuit ND is defined as a squeezing-detected current rapid decrease unit CD indicated by a one-dot chain line. The welding power supply with a current rapid decrease function at the time of constriction detection is a welding power supply for general consumable electrode gas shield arc welding in which the current rapid decrease unit CD at the time of constriction detection is incorporated.

  FIG. 6 is a timing chart of each signal in the welding power supply with a current sudden decrease function at the time of detecting the squeezing. (A) is the welding current Iw, (B) is the welding voltage Vw, (C) is the squeezing detection signal Nd, (D) is the charge drive signal Drc (E) ) Shows the discharge drive signal Drd, (F) shows the discharge current Id, and (G) shows the time change of the capacitor voltage Vc. Hereinafter, a description will be given with reference to FIG.

  In the same figure, except for the period of time t2 to t3 and time t5 to t6, the squeezing detection signal Nd is at the low level as shown in FIG. For this reason, as shown in FIG. 5E, the discharge drive signal Drd is at a low level and the discharge switching element TRD is turned off, so that the welding current Iw is as shown in FIG. This is the same as the welding power source for normal consumable electrode gas shield arc welding.

  At time t2, as shown in FIG. 4B, when it is determined that the welding voltage Vw has increased during the short-circuit period Ts and has become the reference increase value Vu or more and it is determined that constriction has occurred in the droplet, As shown in FIG. 5C, the squeezing detection signal Nd becomes High level. In response to this, as shown in FIG. 4D, the charging drive signal Drc is at the low level, so that the charging switching element TRC is turned off. At the same time, as shown in FIG. 5E, the discharge drive signal Drd is at a high level, so that the discharge switching element TRD is turned on. Therefore, as shown in FIG. 5F, the discharge current Id is supplied from the capacitor C in the opposite direction to the welding current Iw shown in FIG. As indicated by the dotted lines at time t2 to t3 in FIG. 6A, the output current Io is reduced only slightly in a short time due to the action of a large value DC reactor in the power supply main circuit MC. Since the value obtained by subtracting the discharge current Id from the output current Io is the welding current Iw, the welding current Iw = Io−Id rapidly decreases. At time t3, when the short circuit is opened and the arc is regenerated, the welding voltage Vw changes to the arc voltage value as shown in FIG. When this is detected, the squeezing detection signal Nd returns to the low level as shown in FIG. 8C, and the charging drive signal Drc becomes the high level as shown in FIG. Therefore, as shown in FIG. 5G, the capacitor voltage Vc is charged by the charging power source E and gradually increases. At the same time, as shown in FIG. 5E, the discharge drive signal Drd is at the low level, so that the discharge switching element TRD is turned off. For this reason, the discharge current Id is interrupted as shown in FIG. 5F, so that the welding current Iw becomes the output current Io and the welding current Iw increases as shown in FIG. By this operation, the current value at the time of arc reoccurrence (time t3) can be reduced, and the occurrence of sputtering can be suppressed.

JP-A-1-170582 JP-A-4-284972

  FIG. 7 is a timing chart corresponding to FIG. 6 described above for explaining the problem. In the same figure, since it is the same as that of FIG. 6 except the period of time t1-t3, a different point is demonstrated.

  As shown in FIG. 6A, when the short-circuit period Ts from time t1 to time t3 is shortened, the welding current value Iw (= output current value Io2) at time t2 is greater than the output current value Io in FIG. Becomes smaller. As described above, the welding current value when the squeezing detection signal Nd at time t2 to t3 is at the high level is Iw = Io2−Id. The value of the discharge current Id shown in FIG. 9F is determined by the value of the capacitor voltage Vc shown in FIG. In the prior art, since the capacitor voltage Vc is a constant value, the discharge current Id is also a constant value. However, the output current value Io2 varies depending on the length of the short circuit period Ts, the short circuit load state, the ripple of the welding current, and the like. As a result, when Io2 ≦ Id, the welding current Iw becomes zero or negative at time t3, and arc re-generation fails. Failure to regenerate the arc results in arc breakage and poor weld quality. On the contrary, if the short-circuit period Ts becomes longer and Io2 becomes considerably larger than Id, the current value at the time of arc re-occurrence increases, and the sputter reduction effect decreases.

  Therefore, the present invention provides a welding power source with a function of rapidly reducing the current at the time of squeezing detection, which can reduce the current value at the time of arc re-occurrence to a substantially predetermined small value even if the output current value Io at the time of squeezing detection changes.

In order to solve the above-described problems, a first invention is a welding power source used for consumable electrode gas shield arc welding in which a short circuit period in which a welding current increases and an arc period in which the welding current decreases are repeated. Welding with a rapid current reduction function at the time of squeezing detection that suppresses the occurrence of spatter by detecting the constriction phenomenon of the droplet at the tip of the consumable electrode, which is a precursor to the occurrence of an arc after being opened, and rapidly reducing the welding current passing through the short-circuit load. In power supply
A discharge circuit comprising a series circuit of a capacitor and a discharge switching element provided between two output terminals of the welding power source;
A charging circuit comprising a series circuit of a charging power source and a charging switching element provided in parallel with the capacitor;
The discharge circuit and the charging circuit are connected so that the discharge current from the capacitor to the load is energized in the direction opposite to the output current from the welding power source,
When the occurrence of the constriction phenomenon is detected during the short-circuit period, the charging switching element is turned off and the discharging switching element is turned on to pass the discharge current from the discharge circuit to the short-circuit load, thereby rapidly reducing the welding current. Then, when it is detected that the short circuit is opened and the arc is regenerated or when a predetermined time has elapsed, the discharging switching element is turned off to stop discharging, and the chopper control by the charging switching element is performed. A charging / discharging drive circuit that controls the charging voltage value to the capacitor to a predetermined initial charging voltage value during the arc period and to a value proportional to the increase in the welding current value during the subsequent short circuit period. This is a welding power source with a function of suddenly reducing current when detecting constriction.

  According to a second aspect of the present invention, there is provided a welding power source with a function of rapidly reducing current at the time of squeezing detection, wherein the initial charging voltage value described in the first aspect of the invention is changed according to the feed rate of the consumable electrode.

  According to the first aspect of the invention, since the discharge current suitable for the welding current value at the time of squeezing can be applied by charging the capacitor voltage to a value proportional to the welding current value during the short circuit period, squeezing detection The welding current value at the time of arc re-occurrence can be reduced to a substantially predetermined small value without being affected by variations in the welding current value at the time. For this reason, it is always possible to significantly reduce the occurrence of spatter, and the welding quality can be greatly improved. In particular, the effect of the present invention is significant in a thyristor phase control welding power source having a large variation in the welding current value at the time of detection of squeezing due to a large welding current ripple during the short circuit period.

  According to the second aspect of the invention, by changing the initial charging voltage value, which is the capacitor voltage value at the time of occurrence of the short circuit, according to the wire feed speed, the capacitor voltage value is quickly changed to the welding current value immediately after the occurrence of the short circuit. It can be charged to a proportional value. For this reason, the effect of the said 1st invention can be heightened more. The reason for this is that the initial charge voltage value is always set to a value close to the target charge voltage value proportional to the welding current value at the time of occurrence of the short-circuit as described above, so that it can quickly converge to the target charge voltage value. Because it can.

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

  FIG. 1 is a block diagram of a welding power source with a current suddenly decreasing function at the time of detection of squeezing according to an embodiment of the present invention. In the figure, the same blocks as those in FIG. Hereinafter, blocks indicated by dotted lines different from those in FIG. 5 will be described.

  The short-circuit / arc discrimination circuit SD discriminates between the short-circuit period and the arc period with the welding voltage Vw as an input, and outputs a short-circuit / arc discrimination signal Sd that is high level during the short-circuit period and low level during the arc period. The welding current detector IWD detects the welding current Iw and outputs a welding current detection signal Iwd. The capacitor voltage detection circuit VCD detects the charging voltage value of the capacitor C and outputs a capacitor voltage detection signal Vcd. The second charging / discharging drive circuit DR2 receives the short-circuit / arc discrimination signal Sd, the welding current detection signal Iwd, the capacitor voltage detection signal Vcd, and the squeezing detection signal Nd, and discharges the squeezing detection signal Nd during the high level period. A discharge driving signal Drd for turning on the switching element TRD for output, and a charge driving signal for controlling the charging switching element TRC in the off state while the squeezing detection signal Nd is in the high level period and chopper-controlling in the period in the low level. Drc is output. Details of the chopper control will be described later.

  FIG. 2 is a detailed block diagram of the above-described second charge / discharge drive circuit DR2. The discharge drive circuit DRD outputs a discharge drive signal Drd that turns on the discharge switching element TRD when the squeezing detection signal Nd is at a high level. The capacitor voltage setting circuit VCR receives the welding current detection signal Iwd and outputs a capacitor voltage setting signal Vcr = α · Iwd. α is a predetermined coefficient. The initial charging voltage setting circuit VCIR outputs a predetermined initial charging voltage setting signal Vcir. The switching circuit SW switches to the a side when the short circuit / arc determination signal Sd is at the low level (arc), and outputs the initial charge voltage setting signal Vcir as the voltage setting signal Vr, and when it is at the high level (short circuit). Switching to the b side outputs the capacitor voltage setting signal Vcr as the voltage setting signal Vr. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vr and the capacitor voltage detection signal Vcd and outputs a voltage error amplification signal Ev. The logical negation circuit NOT logically negates the squeezing detection signal Nd and outputs a logical negation signal Not. Therefore, this logical negation signal Not is a signal that is at a high level during a period other than the squeezing detection period. When the logic negation signal Not is at a high level, the pulse width modulation circuit PWM outputs the pulse width modulation signal Pwm with the voltage error amplification signal Ev as an input. The charge drive circuit DRC receives this pulse width modulation signal Pwm and outputs a charge drive signal Drc for pulse width modulation control of the charging switching element TRC.

  FIG. 3 is a timing chart of each signal in the welding power supply with a current sudden decrease function at the time of squeezing detection described above with reference to FIGS. 1 and 2. (A) is the welding current Iw, (B) is the welding voltage Vw, (C) is the squeezing detection signal Nd, (D) is the charge drive signal Drc (E) ) Shows the discharge drive signal Drd, (F) shows the discharge current Id, and (G) shows the time change of the capacitor voltage Vc. This figure corresponds to FIG. 7 described above. Since the length of the short-circuit period Ts varies, the current values Io2 and Io3 at the time of squeezing detection (time t2 and t5) are shown in FIG. This is a case of different values. Hereinafter, a description will be given with reference to FIG.

  During the arc period Ta from time t0 to t2, the constriction detection signal Nd is at the low level as shown in FIG. 10C, and therefore the discharge drive signal Drd is at the low level as shown in FIG. Then, the discharge switching element TRD is turned off. On the other hand, as shown in FIG. 4D, the charging drive signal Drc becomes a pulse width modulation control signal, and the charging switching element TRC has the capacitor voltage Vc shown in FIG. 4G equal to the value of the initial charging voltage setting signal Vcir. The chopper is controlled to be equal.

  During the short-circuit period Ts from time t1 to t2, the squeezing detection signal Nd is at the low level as shown in FIG. 5C, and therefore the discharge drive signal Drd is at the low level as shown in FIG. The discharge switching element TRD remains off. On the other hand, as shown in FIG. 4D, the charging drive signal Drc becomes a pulse width modulation control signal, and the charging switching element TRC has the capacitor voltage Vc shown in FIG. 4G equal to the value of the capacitor voltage setting signal Vcr. The chopper is controlled as follows. Since this capacitor voltage setting signal is Vcr = α · Iwd, the capacitor voltage Vc during this period becomes a value proportional to the welding current value Iw shown in FIG. 5A, and the capacitor voltage value Vc at time t2 is The value is proportional to the output current Io2. Similarly, the capacitor voltage value Vc at time t5 is a value proportional to the output current Io3.

  During the period from the time t2 to the time t3, as shown in FIG. 6C, the squeezing detection signal Nd is at a high level, so that the discharge drive signal Drd is at a high level as shown in FIG. The discharge switching element TRD is turned on. On the other hand, as shown in FIG. 4D, the charging drive signal Drc is at the low level, and the charging switching element TRC is turned off. As a result, as shown in FIG. 5F, the discharge current Id corresponding to the output current Io2 shown in FIG. For this reason, as shown in FIG. 5A, the welding current value Iw = Io2−Id at the time of the arc re-occurrence at time t3 becomes a substantially predetermined small value. Similarly, at the time of arc reoccurrence at time t6, the current value at the time of arc reoccurrence becomes a substantially predetermined small value. Therefore, even if the welding current value at the time of detection of squeezing varies, the current value at the time of arc re-occurrence can be reduced to a substantially predetermined small value by changing the capacitor voltage value Vc to an appropriate value.

  The value of the initial charging voltage setting signal Vcir is set to be approximately equal to the welding current value at the time of occurrence of the short circuit at time t1. However, since the welding current value at the time of occurrence of the short circuit varies greatly depending on the wire feeding speed (average welding current value), it is necessary to change the value of the initial charging voltage setting signal Vcir according to the wire feeding speed. Further, when the arc is regenerated at time t3, the discharging switching element TRD is turned off and the chopper control of the charging switching element TRC is started. This timing is determined after a predetermined time (1 ms or less) has elapsed from the arc regenerating. It may be delayed. This is because, depending on the welding conditions, the spatter may be further reduced by delaying. As described above, the variation in the welding current value at the time of detecting the necking is caused by fluctuations in the length of the short circuit period, the short circuit load state, the ripple of the welding current, and the like. Therefore, when the output control method of the welding power source is the thyristor phase control, the above-described variation is large, and thus the effect of the present invention is remarkable.

It is a block diagram of the welding power supply with an electric current rapid decrease function at the time of a necking detection concerning an embodiment of the invention. FIG. 3 is a detailed block diagram of a second charge / discharge drive circuit DR2 in FIG. It is a timing chart of each signal in the welding power supply of FIG. It is a figure which shows the electric current and voltage waveform and droplet transfer of short circuit transfer welding. It is a block diagram of the welding power supply with an electric current sudden decrease function at the time of a constriction detection in a prior art. It is a timing chart of each signal in the welding power supply of FIG. 7 is a timing chart corresponding to FIG. 6 for explaining a problem.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Welding wire 1a Droplet 1b Constriction 2 Base material 2a Weld pool 3 Arc C Capacitor CD Current reduction unit when constriction is detected DR Charge / discharge drive circuit DR2 Second charge / discharge drive circuit DRC Charge drive circuit DRc Charge drive signal DRD Discharge drive circuit Drd Discharge drive signal E Charging power supply EV Voltage error amplification circuit Ev Voltage error amplification signal Id Discharge current Io Output current Iw Welding current IWD Welding current detector Iwd Welding current detection signal MC Power supply main circuit ND Constriction detection circuit Nd Constriction detection signal NOT Logic Negative circuit Not logic negative signal PWM pulse width modulation circuit Pwm pulse width modulation signal r resistance value SD short circuit / arc discrimination circuit Sd short circuit / arc discrimination signal SW switching circuit Ta arc period TRC switching element TRD for charging switching element Ts short circuit period Vc Capacitor voltage VCD Condensate Voltage detection circuit Vcd Capacitor voltage detection signal VCIR Initial charging voltage setting circuit Vcir Initial charging voltage setting signal VCR Capacitor voltage setting circuit Vcr Capacitor voltage setting signal Vr Voltage setting signal Vu Reference increase value Vw Welding voltage

Claims (2)

A consumable electrode gas shield arc welding power source that repeats a short-circuit period in which the welding current increases and an arc period in which the welding current decreases, and a consumable electrode tip that is a precursor to the arc being regenerated by opening the short-circuit In a welding power source with a current reduction function at the time of constriction detection, which suppresses the occurrence of spatter by detecting the constriction phenomenon of droplets and rapidly reducing the welding current passing through the short-circuit load.
A discharge circuit comprising a series circuit of a capacitor and a discharge switching element provided between two output terminals of the welding power source;
A charging circuit comprising a series circuit of a charging power source and a charging switching element provided in parallel with the capacitor;
The discharge circuit and the charging circuit are connected so that the discharge current from the capacitor to the load is energized in the direction opposite to the output current from the welding power source,
When the occurrence of the constriction phenomenon is detected during the short-circuit period, the charging switching element is turned off and the discharging switching element is turned on to pass the discharge current from the discharge circuit to the short-circuit load, thereby rapidly reducing the welding current. Then, when it is detected that the short circuit is opened and the arc is regenerated or when a predetermined time has elapsed, the discharging switching element is turned off to stop discharging, and the chopper control by the charging switching element is performed. A charging / discharging drive circuit that controls the charging voltage value to the capacitor to a predetermined initial charging voltage value during the arc period and to a value proportional to the increase in the welding current value during the subsequent short circuit period. A welding power supply with a function of sudden current reduction when detecting constriction. A welding power source with a function of rapidly reducing current at the time of constriction detection, wherein the initial charging voltage value according to claim 1 is changed in accordance with a feeding speed of a consumable electrode.

Images