JP2007075827A - Method of detecting/controlling constriction in consumable electrode arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve accuracy of detecting constriction of a droplet in a method of detecting and controlling constriction, a method in which spatters are reduced by detecting the constriction and rapidly decreasing a welding current Iw immediately before regeneration of arc. <P>SOLUTION: In the method of detecting/controlling constriction in consumable electrode arc welding, the constriction of a droplet as a symptom of regeneration of arc from a short circuit state Ts is detected by a change Δr in a resistance value between a consumable electrode and a base material reaching a predetermined reference value rt for the detection of the constriction. In the method, when this constriction phenomenon is detected (Nd=High), a welding current Iw flowing to a short-circuit load is rapidly reduced, with the output controlled so that the arc is regenerated in the state of a low current value. The method is characterized in that the derivation of the welding current Iw in the short-circuit state Ts is computed and that the constriction is detected by the reference computed value rtc for the detection of the constriction, i.e., a value obtained by deducting this current derivation dIw/dt from the reference value rt for the detection of the constriction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a constriction detection control method of consumable electrode arc welding for detecting a constriction phenomenon of a droplet during a short-circuiting period and rapidly reducing a welding current to improve welding quality.

  FIG. 4 is a waveform diagram showing a constriction detection control method in consumable electrode arc welding in which the short-circuit period Ts and the arc period Ta are repeated. (A) of the droplet shows the constriction detection signal Nd, (B) shows the welding voltage Vw, (C) shows the welding current Iw, and (D) shows the resistance of the droplet. The change rate [Delta] r = dr / dt shows the time change, and FIGS. (E1) to (E3) show the transition state of the droplets. This figure shows a case where a thyristor phase control welding power source is used. As shown in FIGS. 5B and 5C, the welding voltage Vw and the welding current Iw are commercial frequencies (50 Hz or 60 Hz) in the case of full-wave rectification control. A large ripple having a frequency six times that of) is superimposed. Hereinafter, a description will be given with reference to FIG.

  During the arc period Ta between times t1 and t2, the welding voltage Vw becomes an arc voltage value of several tens of volts as shown in FIG. 5B, and as shown in FIG. The average current value corresponds to the feed speed.

  At time t2, as shown in FIG. 5E1, when the droplet 1a formed at the tip of the welding wire 1 contacts the base material 2 during the arc period Ta, the short circuit period Ts starts. When the short-circuit period Ts starts, the welding voltage Vw becomes a short-circuit voltage value of several V as shown in FIG. 5B, and the welding current Iw increases with time as shown in FIG. The electromagnetic pinch force due to this current application acts on the droplet 1a, and a constricted portion 1b is generated in the droplet 1a as shown in FIG. As this constriction 1b advances, as shown in FIG. 3E3, the droplet 1a moves to the molten pool 2a, and the arc 3 is regenerated at time t3. Therefore, the occurrence of the constriction 1b is a precursor of the arc reoccurrence, and the arc often reoccurs several hundred μs after the occurrence of the constriction 1b.

  As described above, when the constriction 1b occurs, the energization path of the welding current Iw becomes narrow at the constricted portion 1b, and thus the resistance value r of the energization path increases. This resistance value r rapidly increases as the constriction 1b progresses. FIG. 4D shows the waveform of the rate of change Δr = dr / dt = d (Vw / Iw) / dt of the resistance value r. As the constriction 1b progresses, the resistance value change rate Δr rapidly increases. When it is determined at time t21 that this value Δr has exceeded a predetermined squeezing detection reference value rt, the squeezing detection signal Nd becomes High level as shown in FIG. In response to this, the welding current value Iw is rapidly reduced as shown in FIG. A special circuit for this sudden decrease will be described later with reference to FIG. Since the welding current value Iw at the time when the arc is generated at time t3 is a low value, the occurrence of spatter is greatly reduced. This is because most of the spatter occurs when the arc is regenerated, and the amount generated is proportional to the magnitude of the current value when the arc is regenerated. Therefore, the constriction detection control method for consumable electrode arc welding is to detect the progress of the constriction 1b based on the resistance value change rate Δr during the short-circuit period, to rapidly reduce the welding current Iw, and to reduce the current value when the arc is regenerated. This significantly reduces the generation of spatter. The squeezing detection signal Nd is at a high level during the squeezing detection time Tn from the squeezing detection time at time t21 to the arc re-occurrence time at time t3.

  FIG. 5 is a block diagram of a welding apparatus that employs the above-described constriction detection control method. The welding power source PS is a general thyristor phase control 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. The resistance value of the resistor R is set to a value that is 10 times or more the load resistance value of several tens of mΩ during the short-circuit period. The transistor TR is turned off only during a period in which the squeezing detection signal Nd is at a high level (squeezing detection time Tn) in FIG. 4A described above, and the resistor R is inserted in the current conduction path. During the squeezing detection time Tn, when the resistor R is inserted after the output of the welding power source is stopped, the resistance value of the energization path becomes more than 10 times larger, so the energy stored in the large reactor inside the power source Is suddenly discharged and the welding current Iw decreases rapidly.

  The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The resistance value change rate calculation circuit ΔR receives the voltage detection signal Vd and the current detection signal Id and calculates the resistance value change rate signal Δr = d (Vd / Id) / dt. The squeezing detection circuit ND compares the resistance value change rate signal Δr with a predetermined squeezing detection reference value rt, and outputs a squeezing detection signal Nd that becomes a high level when Δr> rt. The drive circuit DR receives the squeezing detection signal Nd as an input, and outputs a drive signal Dr that turns on the transistor TR when the squeezing detection signal Nd is at a low level. When the transistor TR is in the on state, the resistor R is short-circuited, so that the normal operation of only the welding power source PS is performed.

  In the above-described constriction detection control method, it is important to accurately detect the occurrence of constriction. One of the important factors that determine the accuracy of the squeezing detection is whether the squeezing detection reference value rt is set to an appropriate value. The appropriate value of the squeezing detection reference value rt varies depending on welding conditions such as the welding method, the type of welding wire, and the wire feed speed. For this reason, it is necessary to perform a welding test in advance for each of various welding conditions to obtain an appropriate value. Conventionally, a method for automatically setting the squeezing detection reference value rt has been proposed. In this prior art, the squeezing detection reference value rt is automatically set so that the squeezing detection time Tn described above with reference to FIG. If the squeezing detection time Tn is too short, the arc is regenerated before the welding current Iw can be lowered to a low value, and the spatter reduction effect is reduced. Conversely, if the squeezing detection time Tn becomes too long, the possibility of false detection of squeezing detection increases, and if the current is rapidly reduced in this state, the welding state becomes unstable. Therefore, when the squeezing detection time Tn becomes an appropriate value (several hundreds of μs), there is no false detection of squeezing detection, and the current value at the time of arc re-generation becomes low, so that sputtering is greatly reduced. See Patent Documents 1 and 2 for the related art described above.

JP 59-206159 A JP-A-1-205875

  As shown in FIG. 4D, the rising curve P1 of the resistance value change rate Δr immediately before the squeezing detection signal Nd becomes high level at time t21 is a change curve of the welding current Iw shown in FIG. It is greatly influenced by P2. This is because the ascending curve P1 rises as the constriction progresses, and the constriction speed is greatly affected by the current value. The larger the rate of increase of the current change curve P2, the faster the constriction speed, and the ascending curve P1 rises rapidly. On the contrary, when the increase rate of the current change curve P2 becomes minus (decrease), the speed of constriction progresses and the ascending curve P1 rises gently. Even if the squeezing detection reference value rt is set so that the squeezing detection time Tn becomes an appropriate value according to the conventional technique, the squeezing detection time Tn varies due to a change in the welding current Iw when the squeezing occurs. This is because, in the prior art, the squeezing detection reference value rt is determined by the squeezing detection time Tn in the previous short-circuit period, but the squeezing detection time Tn changes due to the current change during the short-circuit period. This change in the welding current during the short-circuit period also occurs in the inverter-controlled welding power source, but becomes large particularly in a thyristor phase-controlled welding power source having a large ripple. Therefore, the thyristor phase control welding power source has a problem that the variation in the squeezing detection time Tn becomes large and the effect of reducing the spatter becomes small.

  FIG. 6 is a waveform diagram showing variation in the squeezing detection time Tn accompanying the above-described change in the welding current. This figure corresponds to FIG. 4 described above. As shown in FIG. 10C, the rate of increase in the current change curve P4 at the occurrence of constriction is large. Therefore, as shown in FIG. Become. For this reason, the arc is regenerated immediately after the resistance value change rate Δr reaches the squeezing detection reference value rt. As a result, as shown in FIG. 5C, there is no time for rapidly reducing the welding current Iw, and it is not possible to reduce spatter. On the contrary, when the current change at the time of occurrence of the constriction is in a decreasing state, the constriction detection time Tn becomes too long and the welding state may become unstable.

  Therefore, the present invention provides a constriction detection control method for consumable electrode arc welding that can accurately detect constriction without being affected by a change in current when the constriction occurs.

In order to solve the above-described problems, a first invention is a consumable electrode arc welding in which an arc generation state and a short circuit state are repeated between a consumable electrode and a base material, and a sign that an arc is regenerated from the short circuit state. The phenomenon of droplet constriction, which is a phenomenon, is detected when the change in the resistance value between the consumable electrode and the base material reaches a predetermined squeezing detection reference value. In the constriction detection control method for consumable electrode arc welding, the output is controlled so that the arc is regenerated in a state where the current is rapidly reduced and the current is low.
The constriction detection control method for consumable electrode arc welding, wherein the constriction detection reference value is corrected in accordance with a rate of change of the welding current during the short circuit state.

  In the second invention, the squeezing detection reference value described in the first invention is corrected by differentiating the welding current to calculate a current differential value and subtracting the current differential value from the squeezing detection reference value. This is a constriction detection control method for consumable electrode arc welding.

  According to the present invention described above, the squeezing detection reference value for detecting the squeezing is corrected according to the change rate of the welding current, thereby compensating for a decrease in squeezing detection accuracy caused by a change in the welding current when the squeezing occurs. As a result, it is possible to realize a highly accurate necking detection. For this reason, when applied to a thyristor phase control power supply with a large change (ripple) in the welding current, it is possible to improve the accuracy of detecting a particularly large neck. When the accuracy of detecting the neck is improved, the current value at the time of arc re-occurrence can be surely lowered, so that the occurrence of spatter is greatly reduced and the welding quality is greatly improved.

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

  FIG. 1 is a waveform diagram showing a constriction detection control method for consumable electrode arc welding according to an embodiment of the present invention. (A) of the figure shows the squeezing detection signal Nd, (B) shows the welding voltage Vw, (C) shows the welding current Iw, (D) shows the resistance value change rate Δr and squeezing detection reference calculation. The time change of the value rtc is shown. Differences from FIG. 4 will be described.

  The squeezing detection reference calculation value rtc shown in FIG. 4D is calculated by rtc = rt−G · (dIw / dt). Here, rt is a predetermined squeezing detection reference value, dIw / dt is a differential value of the welding current Iw, and G is a positive amplification factor. As shown in FIG. 4D, when the constriction occurs, the resistance value change rate Δr increases. At this time, as shown in FIG. 6C, since the change in the welding current Iw is in the increasing direction, the current differential value G · (dIw / dt)> 0 and the squeezing detection reference calculated value rtc <rt. . That is, the constriction detection level is lowered. As a result, at time t21, as shown in FIG. 9A, the squeezing detection signal Nd becomes High level. In response to this, the welding current Iw decreases rapidly as shown in FIG. This figure shows the case where the welding current Iw at the time of occurrence of the constriction increases as in the case of FIG. 6 described above, but the constriction detection can be accurately performed in this embodiment.

  FIG. 2 is a waveform diagram when the current change at the time of occurrence of the constriction is in a decreasing state, unlike FIG. 1 described above. As shown in FIG. 1C, the change in the welding current Iw when constriction occurs is in a decreasing direction unlike FIG. For this reason, the current differential value G · (dIw / dt) <0, and the squeezing detection reference calculated value rtc> rt as shown in FIG. As described above, when the change in the welding current Iw is in the decreasing direction, the progress speed of the constriction also becomes slow. For this reason, by setting the squeezing detection reference calculated value rtc higher than the squeezing detection reference value rt, the squeezing detection timing is delayed so that the squeezing detection time Tn becomes substantially an appropriate value.

  As described above with reference to FIGS. 1 and 2, by correcting the squeezing detection reference calculation value rtc in accordance with the rate of change of the welding current Iw when squeezing occurs, it is always accurate without being affected by the change in the welding current Iw. Constriction detection can be performed. This is apparent from the fact that the squeezing detection time Tn in FIGS. 1 and 2 is a substantially constant value even though the current change is different. As a result, spatter generation is greatly reduced, and high-quality welding is possible.

  FIG. 3 is a block diagram of a welding apparatus for implementing the above-described constriction detection control method for consumable electrode arc welding. In the figure, the same blocks as those in FIG. 5 described above are denoted by the same reference numerals, and description thereof is omitted. Hereinafter, blocks indicated by dotted lines different from those in FIG. 5 will be described.

  The current differentiating circuit BI differentiates the current detection signal Id and outputs a current differential signal Bi = G · (dIw / dt). Here, G is a predetermined positive amplification factor. The squeezing detection reference calculation circuit RTC subtracts the current differential signal Bi from a predetermined squeezing detection reference value rt, and outputs a squeezing detection reference calculation value signal rtc = rt−Bi. Constriction detection is performed using the squeezing detection reference calculated value signal rtc as a threshold value.

  In the above, the method of subtracting the current differential signal is exemplified as a method of correcting the squeezing detection reference calculation value based on the current change rate at the time of occurrence of squeezing. In addition to this, the current change rate may be divided into several stages according to the value, and a squeezing detection reference calculation value corresponding to the several stages may be determined in advance.

It is a wave form diagram which shows the constriction detection control method of the consumable electrode arc welding which concerns on embodiment of this invention. It is a wave form diagram different from FIG. 1 which shows the constriction detection control method of the consumable electrode arc welding which concerns on embodiment of this invention. It is a block diagram of the welding apparatus for implementing the constriction detection control method of the consumable electrode arc welding which concerns on embodiment of this invention. It is a wave form diagram which shows the constriction detection control method of the consumable electrode arc welding of a prior art. It is a block diagram of the welding apparatus for implementing the constriction detection control method of consumable electrode arc welding of a prior art. It is a wave form diagram which shows the subject of a prior art.

Explanation of symbols

1 welding wire 1a droplet 1b constriction 2 base material 2a molten pool 3 arc BI current differentiation circuit Bi current differentiation signal DR drive circuit Dr drive signal G gain ID current detection circuit Id current detection signal Iw welding current ND constriction detection circuit Nd Detection signal P1, P3 Ascending curve P2, P4 Current change curve PS Welding power supply R Resistor r Resistance value between consumable electrode and base material rt Constriction detection reference value RTC Constriction detection standard calculation circuit rtc Constriction detection standard calculation value (signal)
Ta Arc period Tn Constriction detection time TR Transistor Ts Short circuit period VD Voltage detection circuit Vd Voltage detection signal Vw Welding voltage ΔR Resistance value change rate calculation circuit Δr Resistance value change rate (signal)

Claims (2)

In consumable electrode arc welding where the arc generation state and short circuit state are repeated between the consumable electrode and the base material, the constriction phenomenon of droplets, which is a precursor to the arc re-occurring from the short circuit state, is observed between the consumable electrode and the base material. This is detected when the resistance value of the coil reaches a predetermined squeezing detection reference value, and when this squeezing phenomenon is detected, the welding current applied to the short-circuit load is rapidly reduced so that the arc is regenerated with a low current value. In the constriction detection control method of consumable electrode arc welding that controls the output to
A constriction detection control method for consumable electrode arc welding, wherein the constriction detection reference value is corrected in accordance with a rate of change of the welding current during the short circuit state. The squeezing detection reference value correction according to claim 1, wherein the squeezing detection reference value is a correction for differentiating the welding current to calculate a current differential value and subtracting the current differential value from the squeezing detection reference value. Neck detection control method for electrode arc welding.

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