JP4965311B2 - Constriction detection control method for consumable electrode AC arc welding - Google Patents

Description

  The present invention relates to a constriction detection control method for consumable electrode AC arc welding for detecting a constriction phenomenon of droplets during a short-circuit period in consumable electrode AC arc welding to rapidly reduce the welding current and improve welding quality. .

  FIG. 5 is a diagram showing current / voltage waveforms and droplet transfer in consumable electrode arc welding in which the short-circuit period Ts and the arc period Ta are repeated. FIG. 4A shows the change over time in the welding current Iw for energizing the consumable electrode (hereinafter referred to as welding wire 1), and FIG. 4B shows the time of the welding voltage Vw applied between the welding wire 1 and the base material 2. FIG. FIGS. 3C to 3E show the transition 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 advances rapidly, and as shown to the same figure (E) at the time t3, the droplet 1a transfers from the welding wire 1 to the molten pool 2a, and the arc 3 regenerates.

  When the above-mentioned constriction phenomenon occurs, the short circuit is released after an extremely short time of about several hundred μs, and the arc 3 is regenerated. That is, this constriction phenomenon is a precursor of short circuit opening. When the constriction 1b occurs, the conduction path of the welding current Iw becomes narrow at the constricted portion, and the resistance value of the constricted portion increases. The increase in the resistance value increases as the constriction progresses and the constricted portion becomes narrower. Therefore, the occurrence and progress of the constriction phenomenon can be detected by detecting the change in resistance value between the welding wire 1 and the base material 2 during the short-circuit period Ts. This change in resistance value can be calculated by (welding voltage Vw) / (welding current Iw). Further, as described above, since the constriction occurrence time is extremely short, the change in the welding current Iw during this period is small as shown in FIG. For this reason, the occurrence of the constriction phenomenon can be detected by the change of the welding voltage Vw instead of the change of the resistance value. As a specific necking detection method, a change rate (differential value) of the resistance value or the welding voltage value Vw during the short-circuit period Ts is calculated, and the necking detection is performed when the rate of change reaches a predetermined necking detection reference value. There is a way to do. As another method, as shown in FIG. 5B, a voltage increase value ΔV from a stable short-circuit voltage value Vs before occurrence of constriction during the short-circuit period Ts is calculated, and this voltage increase value ΔV is calculated at time t2. There is a method of detecting the squeezing when the squeezing reaches a predetermined squeezing detection reference value Vtn. In the following description, a case in which the squeezing detection method is based on the above-described voltage increase value ΔV will be described, but other methods that have been proposed in the past may be used. Detection of arc reoccurrence at time t3 can be easily performed by determining that the welding voltage Vw has become equal to or greater than the short circuit / arc determination value Vta. Incidentally, the period of Vw <Vta is the short circuit period Ts, and the period of Vw ≧ Vta is the arc period Ta. The time from the occurrence of squeezing at times t2 to t3 to the reoccurrence of the arc is hereinafter referred to as a squeezing detection period Tn. When the arc is regenerated at the time t3, the welding current Iw gradually decreases after rapidly increasing as shown in FIG. 9A, and the welding voltage Vw is about several tens of volts as shown in FIG. Arc voltage value. During the arc period Ta from time t3 to t4, the tip of the welding wire 1 is melted to form a droplet 1a. Thereafter, the operation in the period from time t1 to t4 is repeated.

  In the welding with short circuit described above, when the arc regeneration current value Ia when the arc 3 is regenerated at the time t3 is a large current value, the arc force from the arc 3 to the molten pool 2a increases sharply. A large amount of spatter is generated. That is, the amount of spatter generated increases substantially in proportion to the current value Ia at the time of arc re-generation. Therefore, in order to suppress the occurrence of sputtering, it is necessary to reduce the current value Ia at the time of arc re-occurrence. As a method for this, various welding power sources have been proposed in which a constriction detection control method is added to detect the occurrence of the above-mentioned constriction phenomenon, to rapidly reduce the welding current Iw and to reduce the current value Ia at the time of arc reoccurrence. . Hereinafter, this prior art will be described.

  FIG. 6 is a block diagram of a welding power source employing a squeezing detection control method of the prior art. The welding power source PS is a general welding power source for consumable electrode arc welding. The transistor TR is inserted in series with the output, and a resistor R is connected in parallel therewith. The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The squeezing detection circuit ND receives this voltage detection signal Vd, and is set to a high level when the above-mentioned voltage rise value ΔV reaches a predetermined squeezing detection reference value Vtn during the short-circuit period Ts. When the value of the signal Vd reaches a predetermined short-circuit / arc discrimination value Vta, a squeezing detection signal Nd that is reset to a low level is output. In other words, the squeezing detection signal Nd becomes High level during the above-described squeezing detection period Tn. When the squeezing detection signal Nd is at a low level (when non-necking is detected), the driving circuit DR outputs a driving signal Dr that turns on the transistor TR. Therefore, the transistor TR is turned off when the squeezing detection signal Nd is at a high level (when squeezing is detected).

  FIG. 7 is a timing chart of each signal of the welding power source. (A) shows the welding current Iw, (B) shows the welding voltage Vw, (C) shows the squeezing detection signal Nd, and (D) shows the drive signal Dr. Hereinafter, a description will be given with reference to FIG.

  In the figure, during the period other than the squeezing detection period Tn from time t2 to t3, the squeezing detection signal Nd is at a low level as shown in FIG. The signal Dr becomes a high level. As a result, since the transistor TR is turned on, the operation is the same as that of a normal welding power source for consumable electrode arc welding.

  At time t2, as shown in FIG. 5B, it is detected that the welding voltage Vw has increased during the short-circuit period Ts and the voltage increase value ΔV has become equal to or greater than a predetermined squeezing detection reference value Vtn. If it is determined that constriction has occurred, the constriction detection signal Nd becomes High level as shown in FIG. In response to this, as shown in FIG. 4D, the drive signal Dr goes to a low level, so that the transistor TR is turned off. As a result, the resistor R is inserted into the energization path of the welding current Iw. Since the value of this resistor R is set to a value that is at least 10 times larger than the short-circuit load (several tens of mΩ), it is accumulated in the DC reactor in the welding power source and the cable reactor as shown in FIG. As a result, the welding current Iw decreases rapidly. At time t3, when the short circuit is released and the arc is regenerated, the welding voltage Vw becomes equal to or higher than a predetermined short circuit / arc discrimination value Vta as shown in FIG. By detecting this, the squeezing detection signal Nd becomes the Low level as shown in FIG. 5C, and the drive signal Dr becomes the High level as shown in FIG. As a result, the transistor TR is turned on, and normal consumable electrode arc welding is controlled. By this operation, the arc regeneration current value Ia at the time of arc regeneration (time t3) can be reduced, and the occurrence of sputtering can be suppressed.

  The above description is for the case of DC consumable electrode arc welding, but the same applies to consumable electrode AC arc welding with short circuit. A constriction detection control method for consumable electrode AC arc welding will be described below.

  FIG. 8 is a current / voltage waveform diagram showing a constriction detection control method for consumable electrode AC arc welding. (A) shows the polarity switching signal Spn, (B) shows the welding current Iw, and (C) shows the welding voltage Vw. Hereinafter, a description will be given with reference to FIG.

  The polarity switching signal Spn is at a high level during a predetermined electrode plus polarity period Tep and is at a low level during a predetermined electrode minus polarity period Ten, as shown in FIG. The output polarity of the welding power source is switched according to this polarity switching signal Spn. In FIG. 5B and FIG. 6C, the upper side from 0A or 0V indicates the electrode positive polarity EP, and the lower side indicates the electrode negative polarity EN. Moreover, unless otherwise indicated, the values of the welding current Iw and the welding voltage Vw represent absolute values in the respective polarities.

  When a short circuit occurs at time t1 during the electrode positive polarity period Tep, the welding current Iw increases as shown in FIG. 5B, and the welding voltage Vw is about several volts as shown in FIG. The short-circuit voltage value Vs becomes low. When constriction occurs in the droplet during the short-circuit period Ts, the welding voltage Vw increases and the voltage increase value ΔV reaches the constriction detection reference value Vtn at time t2, as shown in FIG. In response to this, the welding current Iw rapidly decreases as shown in FIG. Then, the arc is regenerated at time t3. Since the current value Ia at the time of this arc re-generation is a low value, the occurrence of spatter becomes very small. During the arc period Ta, as shown in FIG. 5B, the welding current Iw suddenly increases and then gradually decreases. As shown in FIG. 5C, the welding voltage Vw is an arc voltage value of several tens of volts. Become. The above operation is repeated during the electrode positive polarity period Tep. Since the electrode positive polarity period Tep is often set to about several hundred ms, the number of short circuits during one period is about several to several tens.

  At time t5, as shown in FIG. 5A, when the polarity switching signal Spn changes to the low level, the output polarity of the welding power source is switched to the electrode negative polarity EN. When a short circuit occurs at time t5 and a short circuit period Ts is reached. Similarly to the above, the welding current Iw increases and the welding voltage Vw becomes a short-circuit voltage value Vs having a low value. When the constriction occurs in the droplet at time t6, when the voltage rise value ΔV reaches the above constriction detection reference value Vtn as shown in FIG. 10C, the welding current is shown in FIG. Iw decreases rapidly. When the arc is regenerated at time t7, the welding current Iw increases rapidly as shown in FIG. 5B, and then gradually decreases. As shown in FIG. 5C, the welding voltage Vw is several tens of volts. Arc voltage value. Also in this case, since the current value Ia at the time of arc re-occurrence at time t7 is a low value, the occurrence of spatter becomes very small. The above operation is repeated during the electrode negative polarity period Ten. Since this electrode negative polarity period Ten is also set to about several hundred ms, the number of short circuits in one period is several to several tens as in the above.

  As described above, by performing constriction detection control even in consumable electrode AC arc welding, the occurrence of spatter can be significantly reduced, and high-quality welding can be achieved.

  In the squeezing detection control described above, accurately detecting the occurrence of a squeezing phenomenon is the main point of whether or not high quality welding can be achieved by greatly reducing spatter. Therefore, it is necessary to optimize the sensitivity of the necking detection (setting of the necking detection reference value Vtn) for each of various welding conditions. As welding conditions, there are a number of conditions such as the material of the workpiece, the joint, the welding posture, the wire protrusion length, the feeding speed, and the welding speed. In order to optimize the squeezing detection reference value Vtn for each of these welding conditions, as shown in FIG. 7, in the prior art, the squeezing detection period Tn or the arc regeneration current Ia is feedback-controlled so as to become a target value. A method of automatically adjusting the necking detection reference value Vtn is used. There is also a panel of a welding power source in which a constriction detection reference value Vtn adjustment knob is provided. (See Patent Documents 1 and 2 for examples of the prior art.)

JP 2004-114088 A JP 2006-281219 A

  In the constriction detection control method of the consumable electrode AC arc welding of the prior art described above, the absolute value of the AC welding voltage Vw is detected and used for constant voltage control and constriction detection control of the welding power source. This is because the processing becomes easier when a DC signal is used in the control circuit. Therefore, also in the constriction detection control method of consumable electrode AC arc welding, the constriction detection reference value Vtn for each welding condition is usually set to one value. For this reason, the same squeezing detection reference value Vtn is set for both the electrode positive polarity period Tep and the electrode negative polarity period Ten.

  However, the electrode positive polarity EP and the electrode negative polarity EN are greatly different in the formation state of the droplets and the state of occurrence of the constriction. As a result, if the squeezing detection reference value Vtn, which is the squeezing detection sensitivity, is optimized with the electrode plus polarity EP, the electrode minus polarity EN is not suitable, and vice versa. Even if the above-described method for optimizing the squeezing detection reference value Vtn is used, it is optimized for each welding condition but not for each polarity. For this. In consumable electrode AC arc welding, the effect of reducing the amount of spatter generated may not be sufficient.

  Therefore, the present invention provides a constriction detection control method for consumable electrode AC arc welding that can optimize the constriction detection sensitivity in consumable electrode AC arc welding and can maximize the effect of reducing the amount of spatter generated. With the goal.

In order to solve the above-described problem, the first invention is to alternately switch the output of the welding power source between an electrode positive polarity and an electrode negative polarity, and an arc is generated between the consumable electrode and the base material during the both polarities. In consumable electrode AC arc welding that repeats a short circuit and a short circuit state, the voltage or resistance value between the consumable electrode and the base material is a constriction phenomenon of droplets, which is a precursor to the occurrence of an arc again from the short circuit state in both polarities. A consumable electrode that controls the output so that the arc is regenerated at a low current value by rapidly reducing the welding current that is applied to the short-circuit load when this change is detected by detecting that the change has reached the squeezing detection reference value. In the constriction detection control method of AC arc welding,
The squeezing detection reference value is set to a first squeezing detection reference value during the electrode positive polarity, and a second squeezing detection reference having a value different from the absolute value of the first squeezing detection reference value during the electrode negative polarity. The constriction detection control method for consumable electrode AC arc welding is characterized in that the first and second squeezing detection reference values are set so that the welding state with the corresponding polarity is good. .

  According to a second aspect of the present invention, the absolute value of the first squeezing detection reference value is set to a value smaller than the absolute value of the second squeezing detection reference value. This is a welding necking detection control method.

  According to a third aspect of the invention, the second squeezing detection reference value is set by a predetermined function that receives the first squeezing detection reference value as input. This is a constriction detection control method for electrode AC arc welding.

  According to a fourth aspect of the present invention, the absolute value of the squeezing detection reference value is set to the absolute value of the first squeezing detection reference value and the second squeezing value during a period from when the polarity is switched until the occurrence of a short circuit reaches a predetermined number of times. The constriction detection control method for consumable electrode AC arc welding according to any one of the first to third inventions, wherein the constriction electrode is set to an intermediate value with respect to an absolute value of a detection reference value.

In a fifth aspect of the invention, a constriction detection period, which is a period from the constriction detection time point to a time point when an arc is regenerated, is detected separately for the electrode positive polarity and the electrode negative polarity,
The first squeezing detection reference value is automatically set so that a squeezing detection period in the electrode plus polarity is equal to a predetermined first squeezing detection period setting value,
The second squeezing detection reference value is automatically set so that a squeezing detection period in the negative polarity of the electrode is equal to a predetermined second squeezing detection period setting value. It is a constriction detection control method of the consumable electrode alternating current arc welding of description.

  According to the present invention, the squeezing detection control in the consumable electrode AC arc welding can be stabilized by setting the squeezing detection reference value to an appropriate value for each polarity. For this reason, in the consumable electrode AC arc welding, the amount of spatter can be greatly reduced, and high-quality welding can be performed.

  Furthermore, according to the third invention, the second squeezing detection reference value is set by a predetermined function having the first squeezing detection reference value as an input. Setting of the 2-necking detection reference value becomes easy.

  Further, according to the fourth invention, during the period from when the polarity is switched until the occurrence of the short circuit reaches a predetermined number of times, the absolute value of the squeezing detection reference value is set to the absolute value of the first squeezing detection reference value and the second value. By setting an intermediate value with the absolute value of the squeezing detection reference value, squeezing detection control can be stabilized even in a transient state at the time of polarity switching. For this reason, the sputter reduction effect is further increased.

  Furthermore, according to the fifth aspect, the first squeezing detection reference value and the second squeezing detection reference value can be always set to appropriate values by automatically setting using the squeezing detection period. Can be greatly reduced, and stable low sputter control performance can be obtained.

  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 equipped with a constriction detection control method for consumable electrode AC arc welding according to an embodiment of the present invention. Hereinafter, each circuit will be described with reference to FIG.

  The inverter circuit INV rectifies a commercial power source such as a three-phase 200V, and outputs high-frequency alternating current by performing inverter control according to a pulse width modulation signal Pwm described later. The high frequency transformer INT steps down the high frequency AC voltage to a voltage suitable for welding. Secondary rectifiers D2a to D2d rectify the stepped-down high-frequency alternating current and output positive and negative direct-current voltages. The reactor WL smoothes this DC voltage.

  The electrode positive polarity switching element PTR and the electrode negative polarity switching element NTR switch the positive / negative output to the electrode positive polarity EP or the electrode negative polarity EN. When the electrode positive polarity switching element PTR becomes conductive, the output of the welding power source becomes the electrode positive polarity EP, while when the electrode negative polarity switching element NTR becomes conductive, the output becomes the electrode negative polarity EN.

  A circuit in which the first switching element TR1 and the first resistor R1 are connected in series is connected in parallel to the electrode positive polarity switching element PTR, and further, the second switching element TR2 and the second resistor R2 are connected in series. The connected circuit is connected in parallel to the electrode negative polarity switching element NTR.

  The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 of the wire feeding device, and an arc 3 is generated between the welding wire 1 and the base material 2. A welding current Iw is supplied.

  The voltage detection circuit VD detects an AC welding voltage Vw, converts it to an absolute value, and outputs a voltage detection signal Vd. The short circuit determination circuit SD receives the voltage detection signal Vd and outputs a short circuit determination signal Sd. The squeezing detection reference value setting circuit VTN receives the short-circuit determination signal Sd and the polarity switching signal Spn from the outside, and when the polarity switching signal Spn is at a high level (electrode plus polarity EP) as will be described later with reference to FIG. A predetermined first squeezing detection reference value Vtn1 is output as a squeezing detection reference value signal Vtn. When the level is low (electrode negative polarity EN), a predetermined second squeezing detection reference value Vtn2 is used as a squeezing detection reference value signal Vtn. Output. Further, the occurrence of a short circuit is counted from the time when the polarity is switched by the short circuit determination signal Sd, and the third squeezing detection reference value Vtn3 is output as the squeezing detection reference value signal Vtn until the value reaches a predetermined number of times. To do. The third squeezing detection reference value Vtn3 is set as an intermediate value between the first squeezing detection reference value Vtn1 and the second squeezing detection reference value Vtn2, for example, Vtn3 = (Vtn1 + Vtn2) / 2. In the squeezing detection circuit ND, the voltage rise value ΔV described above is the squeezing detection reference value signal Vtn for the occurrence of the squeezing of the droplet, which is a precursor to the transition between the welding wire 1 and the base metal 2 from the short circuit state to the arc state. , And a squeezing detection signal Nd is output. In the electrode positive polarity switching element drive circuit EPD, the polarity switching signal Spn from the outside of the power source is a setting signal (High level) corresponding to the electrode positive polarity, and the above-described squeezing detection signal Nd is not output (Low). The electrode plus polarity switching element drive signal Epd for turning on the electrode plus polarity switching element PTR is output only during the level period). The electrode negative polarity switching element drive circuit END is a period (Low level) in which the polarity switching signal Spn is a setting signal (Low level) corresponding to the electrode negative polarity and the squeezing detection signal Nd is not output. The electrode minus polarity switching element drive signal End that makes the electrode minus polarity switching element NTR conductive is output only during (period).

  The first switching element driving circuit DV1 has a period (High level period) in which the polarity switching signal Spn is a setting signal (High level) corresponding to the electrode positive polarity and the squeezing detection signal Nd is output. ) Only outputs the first switching element drive signal Dv1 that makes the first switching element TR1 conductive. The second switching element drive circuit DV2 has a period (High level period) in which the polarity switching signal Spn is a setting signal (Low level) corresponding to the negative polarity of the electrode and the squeezing detection signal Nd is output. ) Only outputs the second switching element drive signal Dv2 that makes the second switching element TR2 conductive.

  Therefore, when the polarity switching signal Spn is at a high level (electrode plus polarity), the electrode plus polarity switching element PTR is in a conductive state, and the welding current Iw is in the path of PTR → welding wire 1 → base material 2 → reactor WL. Energize. When the squeezing detection signal Nd is output in this state (High level), the operation of the inverter circuit INV is stopped, the electrode positive polarity switching element PTR is turned off, and the first switching element TR1 is turned on. Make it conductive. As a result, the energy accumulated in the reactor WL is discharged through a route of R1 → TR1 → welding wire 1 → base material 2 → reactor WL. The discharge speed is substantially proportional to the value of (L / R) depending on the inductance value L [H] of the reactor WL and the resistance value R [Ω] of the first resistor R1. Usually, the internal resistance value of the power supply when the first resistor R1 is not inserted is about 0.01 to 0.05Ω. On the other hand, if the resistance value R = about 0.5Ω of the first resistor R1 is selected, the discharge rate The (current rapid deceleration) is about 10 times faster. Even when the polarity switching signal Spn is at the low level (electrode negative polarity), the current is rapidly decreased in the same manner as described above.

  The current detection circuit ID detects an AC welding current Iw, converts it to an absolute value, and outputs a current detection signal Id. The voltage setting circuit VR outputs a voltage setting signal Vr having a desired value. The current setting circuit IR outputs the current setting signal Ir for setting the welding current Iw during the short-circuit period with the squeezing detection signal Nd as an input. The current setting signal Ir has a low current value of several tens of A while the squeezing detection signal Nd is at a high level (squeezing detection period Tn). The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vr and the voltage detection signal Vd and outputs a voltage error amplification signal Ev. The current error amplification circuit EI amplifies an error between the current setting signal Ir and the current detection signal Id and outputs a current error amplification signal Ei. When the short circuit determination signal Sd is at the low level (arc period), the external characteristic switching circuit SC switches to the a side and outputs the voltage error amplification signal Ev as the error amplification signal Ea, and the high level (short circuit period). In this case, the current error amplified signal Ei is output as the error amplified signal Ea by switching to the b side. This provides constant voltage characteristics during the arc period and constant current characteristics during the short circuit period. The pulse width modulation circuit PWM receives the error amplification signal Ea as an input, and outputs a pulse width modulation signal Pwm for performing pulse width modulation control on the inverter circuit INV.

  FIG. 2 is a timing chart of each signal in the welding power supply apparatus of FIG. 1 described above. (A) shows the polarity switching signal Spn, (B) shows the welding current IW, (C) shows the welding voltage Vw, (D) shows the short circuit determination signal Sd, (E) shows the squeezing detection signal Nd, (F) shows the squeezing detection reference value signal Vtn, (G) shows the electrode positive polarity switching element drive signal Epd, (H) Represents the first switching element drive signal Dv1, FIG. 10I represents the electrode negative polarity switching element drive signal End, and FIG. 10J represents the second switching element drive signal Dv2. Numbers 1 to 3 on the waveform shown in FIG. 6F abbreviate the first squeezing detection reference value Vtn1, the second squeezing detection reference value Vtn2, and the third squeezing detection reference value Vtn3. Here, the value of the third squeezing detection reference value Vtn3 is an intermediate value between the first squeezing detection reference value Vtn1 and the second squeezing detection reference value Vtn2, and the squeezing in the first short-circuit period Ts after the polarity is switched. The value of the detection reference value signal Vtn becomes the third squeezing detection reference value Vtn3. The value of the squeezing detection reference value signal Vtn in the second and subsequent short-circuit periods Ts becomes the first squeezing detection reference value Vtn1 or the second squeezing detection reference value Vtn2 corresponding to each polarity. Hereinafter, a description will be given with reference to FIG.

(1) Operation during Electrode Plus Polarity Period Tep At time t1, as shown in (A) of the figure, when the polarity switching signal Spn changes to High level, it responds to this as shown in (G) of the figure. In addition, since the electrode positive polarity switching element drive signal Epv is output (High level), the electrode positive polarity switching element PTR becomes conductive, and the output of the welding power source becomes the electrode positive polarity EP. At this time, as shown in FIG. 5H, the first switching element drive signal Dv1 is at the low level, so the first switching element TR1 is in the OFF state. Further, as shown in FIG. 4D, since the first short-circuit determination signal Sd after switching the polarity is at a high level, the value of the squeezing detection reference value signal Vtn is as described above, as shown in FIG. The third necking detection reference value Vtn3 is obtained.

  When the voltage increase value ΔV of the welding voltage Vw reaches the value of the squeezing detection reference value signal Vtn (currently the third squeezing detection reference value Vtn3) as shown in FIG. As shown in FIG. 5E, the squeezing detection signal Nd becomes High level. In response to this, as shown in FIG. 5G, the electrode positive polarity switching element drive signal Epv is at the low level, so that the electrode positive polarity switching element PTR is turned off. At the same time, as shown in FIG. 5H, the first switching element drive signal Dv1 is output (High level), so that the first switching element TR1 becomes conductive. For this reason, as described above with reference to FIG. 1, the first resistor R1 is inserted into the electrode positive-polarity current path, so that the electrode-positive polarity current rapidly decreases to a low current value. In this state, the arc is regenerated at time t3, so that the amount of spatter generated is reduced.

  When the arc is regenerated at time t3, the short circuit determination signal Sd is at the low level (arc period Ta) as shown in FIG. In response to this, as shown in FIG. 5G, the electrode positive polarity switching element drive signal Epd is output (High level), so that the electrode positive polarity switching element PTR becomes conductive. At the same time, as shown in FIG. 5H, the first switching element drive signal Dv1 is at the low level, so that the first switching element TR1 is turned off. As shown in FIG. 5B, the welding current Iw increases rapidly when the arc is regenerated, and then gradually decreases. Further, since the first short circuit is completed at time t3, the value of the squeezing detection reference value signal Vtn becomes the first squeezing detection reference value Vtn1 as shown in FIG. This value is maintained until the positive polarity period Tep ends. During the short-circuit period Ts (time t1 to t3), the welding power source is under constant current control, so that the current set by the current setting signal Ir described above with reference to FIG. Then, during the squeezing detection period Tn from time t2 to t3, the value of the current setting signal Ir becomes a low value, so that the welding current value Iw also becomes a low value. On the other hand, during the arc period Ta (time t3 to t4), the welding power source is under constant voltage control.

  The above operation is repeated during the period from time t4 to t5. However, the value of the squeezing detection reference value signal Vtn during this period becomes the first squeezing detection reference value Vtn1, as shown in FIG.

(2) Operation in Electrode Negative Polarity Period Ten At time t5, when the polarity switching signal Spn changes to the low level as shown in FIG. 6A, the electrode positive polarity switching element is shown in FIG. Since the drive signal Epv is at the low level, the electrode positive polarity switching element PTR is turned off, and the electrode minus polarity switching element drive signal End is output (high level) as shown in FIG. The polarity switching element NTR becomes conductive, and the output of the welding power source is switched to the electrode minus polarity EN. Then, the squeezing detection reference value signal Vtn in the first short-circuit period Ts (time t5 to t7) becomes the third squeezing detection reference value Vtn3 as shown in FIG. At time t6, when the increase value ΔV of the welding voltage Vw reaches the third squeezing detection reference value Vtn3 as shown in FIG. 10C, the squeezing detection signal Nd is changed as shown in FIG. Becomes High level. In response to this, as shown in FIG. 5I, the electrode minus polarity switching element drive signal End is at the low level, so that the electrode minus polarity switching element NTR is turned off. At the same time, as shown in FIG. 6J, the second switching element drive signal Dv2 is output (High level), so that the second switching element TR2 becomes conductive. For this reason, since the second resistor R2 is inserted into the current path of the electrode negative polarity current, the current rapidly decreases and becomes a low value. In this state, when the arc is regenerated at time t7, the short circuit determination signal Sd becomes the low level as shown in FIG. In response to this, as shown in FIG. 5I, the electrode minus polarity switching element drive signal End is output, so that the electrode minus polarity switching element NTR becomes conductive. At the same time, as shown in FIG. 6J, the second switching element drive signal Dv2 is at the low level, so that the second switching element TR2 is turned off.

  When the first short-circuit period Ts ends at time t7. As shown in FIG. 5F, the value of the squeezing detection reference value signal Vtn becomes the second squeezing detection reference value Vtn2, and is maintained during the electrode minus polarity period Ten at time t9. Therefore, the value of the squeezing detection reference value signal Vtn in the second and subsequent short-circuit periods Ts becomes the second squeezing detection reference value Vtn2. The operation during the period from time t8 to t9 is the same as the operation during the period from time t5 to t8.

  FIG. 3 is a diagram exemplifying appropriate values of the squeezing detection reference value Vtn for each polarity EP and EN. In the figure, the horizontal axis indicates the feeding speed (cm / min), and the vertical axis indicates the appropriate value (V) of the squeezing detection reference value Vtn. The figure shows appropriate values of the squeezing detection reference value Vtn in each polarity when the feed speed is changed using a steel material welding wire.

  As is apparent from the figure, under the same welding conditions, the appropriate value of the squeezing detection reference value Vtn is smaller when the electrode plus polarity EP is smaller than when the electrode minus polarity EN is present. The detection sensitivity increases as the value of the squeezing detection reference value Vtn decreases. Therefore, the sensitivity of the constriction detection is set higher for the electrode plus polarity EP. This is because if the feed speed is the same, the electrode negative polarity EN has a larger average current and a larger droplet size. Furthermore, the droplet transfer at the time of electrode negative polarity EN is inferior in stability to that at the time of electrode positive polarity EP. Because of these factors, it is better to set the detection sensitivity low when the electrode has negative polarity EN.

  As described above, since the constriction formation state differs between the electrode negative polarity EP and the electrode negative polarity EN, it is necessary to set the constriction detection reference value Vtn to a different value suitable for each polarity. At that time, the squeezing detection reference value Vtn is set to be smaller (sensitivity is lower) at the time of electrode plus polarity EP. Furthermore, when the occurrence of a short circuit is within a predetermined number of times from the time of polarity switching, the squeezing detection reference value Vtn is an intermediate value between the squeezing detection reference value at the time of the electrode positive polarity EP and the squeezing detection reference value at the time of the electrode negative polarity EN. Set to. This is because the constriction formation state is in a transitional state from the time of polarity switching to the predetermined number of short circuits. That is, from the time when the electrode positive polarity EP is switched to the electrode negative polarity EN until the predetermined number of short-circuits, the constriction formation state transits transiently from the formation state at the electrode positive polarity EP to the formation state at the electrode negative polarity EN. Because it changes.

  In the above-described embodiment, the case where the third constriction detection reference value Vtn3 is used only during the first short-circuit period after polarity switching has been described. good. In FIG. 3 described above, the second squeezing detection reference value Vtn2 may be automatically set by a predetermined function when the first squeezing detection reference value Vtn1 is input. Furthermore, the squeezing detection reference values Vtn1 and Vtn2 may be automatically adjusted so that the squeezing detection period Tn or the arc regeneration occurrence current value Ia becomes the target value for each polarity. Furthermore, the value of the third squeezing detection reference value Vtn3 is set to a different value when switching from the electrode plus polarity EP to the electrode minus polarity EN and when switching from the electrode minus polarity EN to the electrode plus polarity EP. Also good. Further, a predetermined period may be used instead of the predetermined number of short circuits after polarity switching. In the present embodiment, the case of short-circuit transfer welding is exemplified as consumable electrode AC arc welding, but it can also be applied to globule transfer welding with short circuit, pulse arc welding with short circuit, spray transfer welding with short circuit, and the like. it can.

  The case where the first squeezing detection reference value Vtn1 and the second squeezing detection reference value Vtn2 are automatically set to appropriate values using the squeezing detection period tn will be described below. FIG. 4 is a block diagram of a circuit for adding this automatic setting function to the welding power source described above with reference to FIG. This figure is a circuit added to automatically set the first squeezing detection reference value Vtn1 and the second squeezing detection reference value Vtn2 shown in FIG. Hereinafter, a description will be given with reference to FIG.

  The circuit shown in the figure receives the polarity switching signal Spn and the squeezing detection signal Nd described above with reference to FIG. 1, and outputs a first squeezing detection reference value signal Vtn1 and a second squeezing detection reference value signal Vtn2. The squeezing detection period detection circuit TND receives the polarity switching signal Spn and the squeezing detection signal Nd, calculates a moving average value of the time length of the squeezing detection period in the electrode positive polarity EP, and calculates a first squeezing detection period signal Tn1. Further, a moving average value of the length of the squeezing detection period in the electrode negative polarity EN is calculated and output as a second squeezing detection period signal Tn2. Here, since the squeezing detection signal Nd is a signal that is at a high level during the squeezing detection period, the squeezing detection period can be detected by measuring the high level period.

  The first squeezing detection period setting circuit TNR1 outputs a predetermined first squeezing detection period setting signal Tnr1. The first period error amplification circuit ET1 amplifies the error between the first squeezing detection period setting signal Tnr1 and the first squeezing detection period signal Tn1, and outputs a first period error amplification signal ΔT1. The first squeezing detection reference value setting circuit VTN1 integrates the first period error amplification signal ΔT1 and outputs a first squeezing detection reference value signal Vtn1.

  The second squeezing detection period setting circuit TNR2 outputs a predetermined second squeezing detection period setting signal Tnr2. The second period error amplification circuit ET2 amplifies the error between the second squeezing detection period setting signal Tnr2 and the second squeezing detection period signal Tn2, and outputs a second period error amplification signal ΔT2. The second squeezing detection reference value setting circuit VTN2 integrates the second period error amplification signal ΔT2 and outputs a second squeezing detection reference value signal Vtn2.

  In the above, when the squeezing detection reference value is set to an appropriate value, the squeezing detection period substantially converges to a predetermined value. The convergence value of the squeezing detection period varies depending on the polarity. A target value for the squeezing detection period (first squeezing detection period setting signal Tnr1) when the electrode is positive polarity EP is set, and the squeezing detection period (first squeezing detection period signal Tn1) in the electrode positive polarity EP is set to this target value. The first squeezing detection reference value signal Vtn1 is automatically set to be equal. Similarly, a target value for the squeezing detection period (second squeezing detection period setting signal Tnr2) when the electrode has negative polarity EN is set, and the squeezing detection period (second squeezing detection period signal Tn2) in the electrode negative polarity EN is set to the second value. The necking detection reference value signal Vtn2 is automatically set.

  According to the embodiment described above, the squeezing detection control in the consumable electrode AC arc welding can be stabilized by setting the squeezing detection reference value to an appropriate value for each polarity. For this reason, in the consumable electrode AC arc welding, the amount of spatter can be greatly reduced, and high-quality welding can be performed.

  Furthermore, by setting the second squeezing detection reference value by a predetermined function that receives the first squeezing detection reference value, in addition to the above effects, the second squeezing detection reference value can be set for each welding condition. It becomes easy.

  Further, during the period from when the polarity is switched until the occurrence of the short circuit reaches a predetermined number of times, the absolute value of the squeezing detection reference value is set to the absolute value of the first squeezing detection reference value and the absolute value of the second squeezing detection reference value. By setting to the intermediate value, the squeezing detection control can be stabilized even in a transient state at the time of polarity switching. For this reason, the sputter reduction effect is further increased.

  Furthermore, since the first squeezing detection reference value and the second squeezing detection reference value can be always set to appropriate values by automatically setting using the squeezing detection period, the setting labor is greatly reduced, and Stable low spatter control performance can be obtained.

It is a block diagram of the welding power source carrying the constriction detection control method of the consumable electrode alternating current arc welding which concerns on embodiment of this invention. It is a timing chart of each signal of FIG. It is a figure which shows the appropriate value of the squeezing detection reference value in the electrode positive polarity EP and the electrode negative polarity EN. FIG. 3 is a block diagram of a circuit added to FIG. 1 for automatically setting a first squeezing detection reference value Vtn1 and a second squeezing detection reference value Vtn2 according to an embodiment of the present invention. It is a figure which shows the electric current and voltage waveform and droplet transfer state of consumable electrode arc welding in a prior art. It is a block diagram of the welding power supply carrying the constriction detection control in a prior art. It is a timing chart of each signal of FIG. It is an electric current / voltage waveform diagram which shows the constriction detection control method of consumable electrode alternating current arc welding in a prior art.

Explanation of symbols

1 welding wire 1a droplet 1b constriction 2 base material 2a molten pool 3 arc 4 welding torch 5 feed rolls D2a to D2d secondary rectifier DR drive circuit Dr drive signal DV1 first switching element drive circuit DV1 first switching element drive signal DV2 Second switching element drive circuit Dv2 Second switching element drive signal Ea Error amplification signal EI Current error amplification circuit Ei Current error amplification signal EN Electrode minus polarity END Electrode minus polarity switching element drive circuit End Electrode minus polarity switching element drive signal EP Electrode plus Polarity EPD electrode plus polarity switching element drive circuit Epd electrode plus polarity switching element drive signal ET1 first period error amplification circuit ET2 second period error amplification circuit EV voltage error amplification circuit Ev voltage error amplification signal Ia current ID upon arc regeneration Detection circuit Id Current detection signal INT High frequency transformer INV Inverter circuit IR Current setting circuit Ir Current setting signal Iw Welding current ND Necking detection circuit Nd Necking detection signal NTR Electrode negative polarity switching element PS Welding power supply PTR Electrode positive polarity switching element PWM Pulse width Modulation circuit Pwm Pulse width modulation signal R Resistor R1 First resistor R2 Second resistor SC External characteristic switching circuit SD Short circuit determination circuit Sd Short circuit determination signal Spn Polarity switching signal Ta Arc period Ten Electrode negative polarity period Tep Electrode positive polarity period Tn Constriction Detection Period Tn1 First Constriction Detection Period Signal Tn2 Second Constriction Detection Period Signal TND Constriction Detection Period Detection Circuit TNR1 First Constriction Detection Period Setting Circuit Tnr1 First Constriction Detection Period Setting Signal TNR2 Second Constriction Detection Period Setting Circuit Tnr2 2 Constriction detection Setting signal TR Transistor TR1 First switching element TR2 Second switching element Ts Short-circuit period VD Voltage detection circuit Vd Voltage detection signal VR Voltage setting circuit Vr Voltage setting signal Vs Short-circuit voltage value Vta Short-circuit / arc discrimination value VTN Constriction detection reference value setting Circuit Vtn Necking detection reference value (signal)
VTN1 first squeezing detection reference value setting circuit Vtn1 first squeezing detection reference value (signal)
VTN2 Second squeezing detection reference value setting circuit Vtn2 Second squeezing detection reference value (signal)
Vtn3 Third constriction detection reference value Vw Welding voltage WL Reactor ΔT1 First period error amplification signal ΔT2 Second period error amplification signal ΔV Voltage rise value

Claims (5)

In the consumable electrode AC arc welding in which the output of the welding power source is alternately switched between the electrode positive polarity and the electrode negative polarity and the arc generation state and the short-circuit state are repeated between the consumable electrode and the base material during both the polarities, Detecting the constriction phenomenon of the droplet, which is a precursor to the arc re-occurring from the short-circuit state during both polarities, when the change in the voltage value or resistance value between the consumable electrode and the base material reaches the constriction detection reference value, In this constriction detection control method for consumable electrode AC arc welding, which controls the output so that the arc is regenerated at a low current value by rapidly reducing the welding current flowing to the short-circuit load when this constriction phenomenon is detected.
The squeezing detection reference value is set to a first squeezing detection reference value during the electrode positive polarity, and a second squeezing detection reference having a value different from the absolute value of the first squeezing detection reference value during the electrode negative polarity. A constriction detection control method for consumable electrode AC arc welding, wherein the first and second squeezing detection reference values are set so that the welding state with a corresponding polarity is good.   2. The constriction detection control method for consumable electrode AC arc welding according to claim 1, wherein the absolute value of the first constriction detection reference value is set to a value smaller than the absolute value of the second constriction detection reference value.   3. The constriction detection control for consumable electrode AC arc welding according to claim 1, wherein the second constriction detection reference value is set by a predetermined function having the first constriction detection reference value as an input. Method.   The absolute value of the squeezing detection reference value is the absolute value of the first squeezing detection reference value and the absolute value of the second squeezing detection reference value during a period from when the polarity is switched to when the occurrence of a short circuit reaches a predetermined number of times. The constriction detection control method for consumable electrode AC arc welding according to any one of claims 1 to 3, wherein the constriction detection control method is used. Detecting a constriction detection period, which is a period from the constriction detection time to a time when the arc is regenerated, separately for the electrode positive polarity and the electrode negative polarity,
The first squeezing detection reference value is automatically set so that a squeezing detection period in the electrode plus polarity is equal to a predetermined first squeezing detection period setting value,
5. The second squeezing detection reference value is automatically set so that a squeezing detection period in the electrode negative polarity is equal to a predetermined second squeezing detection period setting value. Constriction detection control method for consumable electrode AC arc welding.

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