JP5557249B2 - Feed control method for arc welding with short circuit - Google Patents

Description

  The present invention relates to a feed control method for arc welding involving a short circuit in which a welding wire is fed forward to a base material during an arc period, and the welding wire is moved backward in a direction away from the base material during a short circuit period. .

  Examples of the arc welding method with short circuit include a carbon dioxide arc welding method, a mag welding method, and a MIG welding method. Moreover, as a droplet transfer form, there exist a short circuit transfer form, a globule transfer form with a short circuit, a spray transfer form with a short circuit, etc. In these welding methods, the welding wire is fed forward at a constant feeding speed, and welding is performed by repeating the arc period and the short-circuit period. A droplet is formed at the tip of the welding wire during the arc period, and the droplet moves during the short circuit period. In the arc welding method with short circuit, it is important to reduce the amount of spatter generated in order to obtain good welding quality. In a general arc welding method, a large welding current is applied in order to transfer droplets during a short circuit period. As a result, since the current value at the time when the droplet transfer is finished and the arc is regenerated, a large amount of spatter is generated. In order to improve this, the conventional techniques disclosed in Patent Documents 1 and 2 are used. In these prior arts, the welding wire is fed forward during the arc period, and the welding wire is fed backward during the short circuit period. Hereinafter, this prior art will be described.

  FIG. 6 is an output waveform diagram showing a feed control method for arc welding with a short circuit in the prior art. (A) shows the welding voltage Vw, (B) shows the welding current Iw, (C) shows the feed speed setting signal Fr, and (D) shows the actual welding wire tip. When the feed speed setting signal Fr and the feed speed Fs indicating the feed speed Fs are positive values, they indicate forward feed, and when they are negative values, they indicate reverse feed. Hereinafter, a description will be given with reference to FIG.

  In the figure, the period from time t1 to t2 is the (n-1) th arc period Ta (n-1), and the period from time t2 to t3 is the n-1th short-circuit period Ts (n-1). Yes, the period from time t3 to t4 is the nth arc period Ta (n), and the period from time t4 to t5 is the nth short circuit period Ts (n).

  During the arc period Ta (n-1) from time t1 to t2, the value of the feed speed setting signal Fr becomes a predetermined positive forward feed speed setting value Ffr as shown in FIG. As shown in FIG. 4D, the feeding speed Fs becomes the forward feeding speed Ffs. As shown in FIG. 3A, the welding voltage Vw has an arc voltage value of several tens of volts. As shown in FIG. 5B, the welding current Iw is a current value determined by the forward feed speed Ffs and the arc load because the welding power source is controlled at a constant voltage. Therefore, the welding current Iw has a waveform that varies with the variation of the arc load. During this arc period Ta (n-1), the tip of the welding wire melts to form droplets.

  When the droplet formed at the tip of the welding wire comes into contact with the molten pool at time t2, a short-circuit state occurs. In the short circuit state, the welding voltage Vw decreases to a short circuit voltage value of several volts as shown in FIG. It is determined that the welding voltage Vw is less than the threshold value, and occurrence of a short circuit is determined. This threshold is set to about 10-15V. When the occurrence of a short circuit is determined, the welding power source is switched to constant current control, and as shown in FIG. 5B, the short circuit current Is is set to a small current value during a predetermined short circuit initial period Tsi from time t2 to t21. It is maintained and increases in a curved line during a predetermined short-circuit current increase period Tsu of times t21 to t23, and decreases with a slope during a short-circuit current decrease period Tsd from time t23 to time t3 when an arc is generated. At the same time t2, as shown in FIG. 5C, the feed speed setting signal Fr is switched to a reverse feed speed setting value Frr having a predetermined negative value. In response to this, as shown in FIG. 4D, the feed speed Fs passes through 0 from the positive forward feed speed Ffs during the period from the time t2 to the time t22, and the negative value reverses. The feed speed changes to Frs. That is, when the short-circuit occurs at the time t2, the feeding speed Fs at the tip of the welding wire is decelerated from the forward feeding speed Ffs to 0, accelerates by reversing the feeding direction, and reaches the backward feeding speed Frs at the time t22. . Therefore, the period from time t2 to t22 is referred to as a feeding reversal period. This feed reversal period is about 2 ms when a servo motor having good responsiveness is used as the feed motor, the length of the welding torch is shortened to several tens of centimeters, and the friction of the feed path is reduced. In the figure, the time t22 at which the feed speed Fs becomes the reverse feed speed Frs is in the above-described short-circuit current increasing period Tsu. After time t22, the backward feeding at the backward feeding speed Frs is continued. As a result, the tip of the welding wire gradually moves away from the molten pool. When the contact state with the molten pool is eliminated at time t3, the arc is regenerated. The initial short-circuit period Tsi is set to about 0.5 to 2 ms by experiment according to welding conditions. Said short circuit current increase period Tsu is set to about 2-6 ms by experiment according to welding conditions. The short circuit current value Is during the short circuit initial period Tsi is set to about several tens of A. The maximum value of the short circuit current Is during the short circuit current increase period Tsu is set to a value close to the welding current average value. The short-circuit initial period Tsi is provided in order to lead the contact between the droplet and the molten pool to a stable short-circuit state. The reason why the short-circuit current Is is increased is not to promote detachment by forming a constriction by applying an electromagnetic pinch force to the droplet as in general consumable electrode arc welding, but during the short-circuit period Ts. This is also to ensure heating by Joule heat. Therefore, the maximum value of the short-circuit current Is is about 400 to 500 A in general consumable electrode arc welding, but is about 150 to 250 A in the figure. Since the arc is regenerated by the backward feeding, each short-circuit period becomes a substantially constant value. Therefore, both values are set so that the addition point of Tsi + Tsu is shorter by about 1 ms than the time length of the short-circuit period. This is because the short-circuit current reduction period Tsd is secured for about 1 ms so that the short-circuit current Is can be reduced to a small value by the time of arc re-occurrence at time t3. The decrease rate of the short circuit current Is during the short circuit current decrease period Tsd is determined by the resistance value of the short circuit negative, the inductance value of the current path from the welding power source, and the resistance value. This decrease rate is about 150 A / ms. Therefore, if the maximum value of the short-circuit current Is at time t23 is 200 A and the short-circuit current reduction period Tsd is 1 ms as described above, the current value at time t3 is as small as 50 A. When the current value at the time of arc re-generation becomes a small value, the occurrence of spatter is reduced. For example, to give numerical examples, Tsi = 1 ms, Tsu = 3 ms, and Tsd = 1 ms. In this case, the short-circuit period Ts = 5 ms.

  When the arc is regenerated at time t3, the welding voltage Vw increases to an arc voltage value of about several tens of volts as shown in FIG. When it is determined that the welding voltage Vw has become equal to or higher than the threshold value and the reoccurrence of the arc is determined, the feed speed setting signal Fr is the forward feed speed set value Ffr as shown in FIG. Can be switched to. In response to this, as shown in FIG. 4D, the feed speed Fs is changed from the reverse feed speed Frs to the forward feed speed Ffs during the feed reversal period from time t3 to t31. Change. At time t3, as shown in FIG. 5B, the welding power source is switched to constant voltage control, so that the welding current Iw increases to a current value determined by the forward feed speed Ffs and the arc load.

  The same applies to the n-th arc period Ta (n) and the short-circuit period Ts (n). In the feed control method shown in the figure, since the current value at the time of arc re-occurrence at time t3 is a small value, the amount of spatter generation is reduced. Moreover, since the arc can be reliably regenerated by performing the backward feeding during the short circuit period, the stability of the welding state is improved.

JP 2004-298924 A JP 2007-216268 A

  In FIG. 6 described above, the welding current value and the time length of the arc period Ta vary due to irregular movement of the weld pool, fluctuation of the height of the welding torch (wire protrusion length), fluctuation of the arc length, and the like. Yes. If both values fluctuate, the size of the droplet formed during the arc period Ta will fluctuate. When the size of the droplet varies, the time required to transfer the droplet during the short-circuit period Ts varies, so the time length of the short-circuit period Ts varies. If the time length of the short-circuit period Ts varies, the time length of the arc period Ta also varies under the influence. Therefore, in the above-described prior art, in order to further improve the welding quality, it is necessary to suppress the fluctuation of the short-circuit period with respect to the fluctuation of the size of the droplet formed during the arc period.

  Therefore, an object of the present invention is to provide a feed control method for arc welding with a short circuit that can suppress the variation of the short circuit period even if the size of the droplet formed during the arc period varies. To do.

In order to solve the above-described problems, the invention of claim 1
In the feed control method of arc welding with a short circuit that feeds the welding wire forward to the base material during the arc period and reversely feeds the welding wire away from the base material during the short circuit period,
The feeding speed of the backward feeding is set by a backward feeding speed calculation function by inputting an index correlating with the size of the droplet at the start of each short-circuit period. Is preset for each section divided into a plurality of sections,
This is a feed control method for arc welding accompanied by a short circuit.

In the invention of claim 2, the index is a time length of the immediately preceding arc period.
The feed control method for arc welding with short circuit according to claim 1.

In the invention of claim 3, the index is an integral value of the welding current in the immediately preceding arc period.
The feed control method for arc welding with short circuit according to claim 1.

In the invention of claim 4, the index is a moving average value of the time length of the arc period.
The feed control method for arc welding with short circuit according to claim 1.

In the invention of claim 5, the index is a moving average value of integrated values of the welding current in the arc period.
The feed control method for arc welding with short circuit according to claim 1.

The invention of claim 6 continues the forward feeding until a predetermined short-circuit initial period elapses from the time when the short-circuit period starts.
The feed control method of arc welding with a short circuit according to any one of claims 1 to 5.

The invention according to claim 7 continues the backward feeding until a predetermined arc initial period elapses from the time when the arc period starts.
The feed control method for arc welding with a short circuit according to any one of claims 1 to 6.

  According to the present invention, the backward feeding speed is changed according to an index correlated with the droplet size at the start of each short-circuit period. For this reason, even if the size of the droplets varies, fluctuations in the short-circuit period can be suppressed, so that the droplet transfer state is stabilized and the welding quality is improved. As the above index, from the time length of the immediately preceding arc period, the integrated value of the welding current in the immediately preceding arc period, the moving average value of the time length of the arc period or the moving average value of the integrated value of the welding current in the arc period Select one to use.

In Embodiment 1 of this invention, it is a figure which illustrates the change of the reverse feed speed Frs when the index value Hd is the time length of the arc period Ta, or its moving average value. In Embodiment 1 of this invention, it is a figure which illustrates the change of the reverse feed speed Frs when the index value Hd is the electric current integral value S in the arc period Ta, or its moving average value. It is a block diagram of the welding power supply which concerns on Embodiment 1 of this invention. It is an output waveform diagram which shows the feed control method of arc welding with the short circuit which concerns on Embodiment 2 of this invention. It is a block diagram of the welding power supply which concerns on Embodiment 2 of this invention. It is an output waveform diagram which shows the feed control method of arc welding with a short circuit in a prior art.

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

[Embodiment 1]
The invention according to Embodiment 1 changes the backward feeding speed Frs in FIG. 6 described above according to an index correlated with the size of the droplet at the start of each short-circuit period. That is, an index value that is substantially proportional to the size of the droplet at the start of each short-circuit period is calculated, and the reverse feed speed Frs is changed based on this index value. Since the index value is large when the size of the droplet is large, the backward feeding speed Frs is increased to prevent the short-circuit period Ts from increasing. Conversely, when the index value is small, the size of the droplet is small, so the backward feeding speed Frs is slowed to suppress the short circuit period Ts from being shortened.

As the index value Hd correlated with the size of the droplet at the start of the n-th short-circuit period Ts (n), one of the following four is selected and used.
(1) Hd = Ts (n)
Let the time length Ta (n) of the arc period immediately before the n-th short-circuit period Ts (n) be the index value Hd. As the time length of the immediately preceding arc period is longer, the size of the droplet increases.
(2) Hd = S (n) = ∫Iw · dt
The nth integrated current value S (n) is a value obtained by integrating the welding current Iw during the arc period Ta (n). Since the size of the droplet formed is substantially proportional to the welding current value Iw and the time length Ta (n) of the arc period, the current integrated value S (n) is substantially proportional to the size of the droplet.
(3) Hd = (Ta (n−m + 1) +... + Ta (n)) / m
m is a positive integer and represents the number of moving averages. This index value Hd is a value obtained by moving average the arc period of the above item (1). By taking the moving average value, the change in the reverse feed speed Frs is smoothed.
(4) Hd = (S (n−m + 1) +... + S (n)) / m
m is a positive integer and represents the number of moving averages. This index value Hd is a value obtained by moving and averaging the current integrated value of the above item (2). By taking the moving average value, the change in the reverse feed speed Frs is smoothed.

  FIG. 1 is a diagram exemplifying a change in the reverse feed speed Frs when the index value Hd is the arc period Ta in the items (1) and (3). In the figure, the horizontal axis indicates the arc period Ta (ms), and the vertical axis indicates the reverse feed speed Frs (m / min). In the figure, the welding method is a carbon dioxide arc welding method, the diameter of the welding wire is 1.2 mm, and the average value of the welding current is 180A. As shown in the figure, when 0 ≦ Ta <5, Frs = 20, and when 5 ≦ Ta <15, the reverse feed speed Frs increases from 20 to 60, and 15 ≦ Ta. At this time, the reverse feed speed Frs is 60. That is, the reverse feed speed Frs increases as the arc period Ta increases. The relationship shown in the figure is referred to as a first reverse feed speed calculation function. In the figure, the change pattern may be curved, stepped, or the like. This first reverse feed speed calculation function is calculated by experiment according to the welding method, the diameter of the welding wire, the welding current average value, and the like. Examples of the welding method include a carbon dioxide arc welding method, a mag welding method, and a MIG welding method. The diameter of the welding wire includes 0.9 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, and the like. As the welding current average value, the function is set in a plurality of sections such as less than 100A, 100 to 150A, 150 to 200A, 200 to 250A, 250A or more.

  FIG. 2 is a diagram exemplifying a change in the reverse feed speed Frs when the index value Hd is the current integrated value S of the above items (2) and (4). In the figure, the horizontal axis represents the current integration value S (ms · A), and the vertical axis represents the reverse feed speed Frs (m / min). In the figure, the welding method is a carbon dioxide arc welding method, the diameter of the welding wire is 1.2 mm, and the average value of the welding current is 180A. As shown in the figure, when 0 ≦ S <1250, Frs = 20, and when 1250 ≦ S <3750, the reverse feed speed Frs increases from 20 to 60 and increases to 3750 ≦ S. At this time, the reverse feed speed Frs is 60. That is, the reverse feed speed Frs increases as the current integrated value S increases. The relationship shown in the figure is called a second reverse feed speed calculation function. In the figure, the change pattern may be curved, stepped, or the like. This second reverse feed speed calculation function is calculated by experiment according to the welding method, the diameter of the welding wire, the welding current average value, and the like. Examples of the welding method include a carbon dioxide arc welding method, a mag welding method, and a MIG welding method. The diameter of the welding wire includes 0.9 mm, 1.0 mm, 1.2 mm, 1.4 mm, 1.6 mm, and the like. As the welding current average value, the function is set in a plurality of sections such as less than 100A, 100 to 150A, 150 to 200A, 200 to 250A, 250A or more.

  FIG. 3 is a block diagram of a welding power source for carrying out the feeding control method according to Embodiment 1 of the present invention described above. Hereinafter, each circuit will be described with reference to FIG.

  The power supply main circuit PM receives a commercial AC power supply (not shown) such as three-phase 200V as input and performs output control by inverter control according to a drive signal Dv described later, and outputs a welding voltage Vw and a welding current Iw suitable for welding. To do. Although not shown, this power main circuit PM has a primary rectifier circuit that rectifies commercial AC power, a capacitor that smoothes the rectified direct current, and an inverter that converts the smoothed direct current into high frequency alternating current according to the drive signal Dv. The circuit includes a high-frequency transformer that steps down the high-frequency alternating current to a voltage value suitable for arc welding, a secondary rectifier circuit that rectifies the stepped-down high-frequency alternating current, and a reactor that smoothes the rectified direct current. The welding wire 1 is fed through the welding torch 4 by the rotation of the feeding roll 5 directly connected to the feeding motor WM, and an arc 3 is generated between the welding wire 1 and the base material 2.

  The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The short circuit determination circuit SD receives the voltage detection signal Vd as an input, determines a short circuit period and an arc period based on the value, and outputs a short circuit determination signal Sd which is at a high level during the short circuit period and is at a low level during the arc period. To do.

  The index value calculation circuit HD receives the short-circuit determination signal Sd and the current detection signal Id as inputs, and corresponds to the above-described items (1) to (4) every time the short-circuit determination signal Sd changes to a high level. A value is calculated and output as an index value signal Hd. That is, the index value signal Hd includes (1) the arc period Ta (n) immediately before, (2) the current integrated value S (n) during the arc period immediately before, (3) the moving average value of the arc period, (4 ) Select and calculate one from the moving average value of the current integral value.

  The reverse feed speed setting circuit FRR receives the index value signal Hd as an input and calculates based on a predetermined first reverse feed speed calculation function or second reverse feed speed calculation function corresponding to the index value signal Hd. The reverse feed speed setting signal Frr is output. That is, when the index value signal Hd is the index of the above item (1) or (3), the first reverse feed speed calculation function illustrated in FIG. 1 is selected and the reverse feed speed setting signal is selected. The value of Frr is calculated. When the index value signal Hd is the index of the above item (2) or (4), the second reverse feed speed calculation function exemplified in FIG. 2 is selected and the reverse feed speed setting signal is selected. The value of Frr is calculated. The forward feed speed setting circuit FFR outputs a predetermined forward feed speed setting signal Ffr. The feed speed setting switching circuit SF receives the short circuit determination signal Sd as described above, and switches to the b side when the short circuit determination signal Sd is at the low level (arc period), and sends the forward feed speed setting signal Ffr. It outputs as the feed speed setting signal Fr, and when it is at the High level (short circuit period), it switches to the a side and outputs the reverse feed speed setting signal Frr as the feed speed setting signal Fr. The feed control circuit FC outputs a feed control signal Fc for feeding the welding wire to the feed motor WM in accordance with the feed speed setting signal Fr. Therefore, as shown in FIG. 6 described above, during the arc period from time t1 to t2, the value of the feed speed setting signal Fr becomes the value of the forward feed speed setting signal Ffr, and the feed speed Fs is the forward feed speed. Ffs. Further, during the short-circuit period from time t2 to t3, the value of the feeding speed setting signal Fr becomes the value of the backward feeding speed setting signal Frr, and the feeding speed Fs becomes the backward feeding speed Frs.

  The short-circuit current setting circuit ISR takes the short-circuit determination signal Sd as an input and becomes a small current value during a predetermined short-circuit initial period Tsi from the time when the short-circuit determination signal Sd becomes High level (short-circuit period), and continues to be determined in advance. The short-circuit current setting signal Isr is output in a curved line during the short-circuit current increase period Tsu and decreases after the short-circuit current increase period Tsu has elapsed. The arc voltage setting circuit VAR outputs a predetermined arc voltage setting signal Var for setting the arc voltage during the arc period. The current error amplification circuit EI amplifies an error between the short circuit current setting signal Isr and the current detection signal Id, and outputs a current error amplification signal Ei. The voltage error amplification circuit EV amplifies an error between the arc voltage setting signal Var and the voltage detection signal Vd, and outputs a voltage error amplification signal Ev. The external characteristic switching circuit SP switches to the b side when the short circuit determination signal Sd is at the low level (arc period), outputs the voltage error amplification signal Ev as the error amplification signal Ea, and is at the high level (short circuit period). ), The current error amplification signal Ei is output as the error amplification signal Ea. Therefore, constant voltage control is performed during the arc period, and constant current control is performed during the short circuit period. The drive circuit DV performs pulse width modulation control according to the error amplification signal Ea, and outputs a drive signal Dv for driving the inverter circuit.

  According to the first embodiment described above, the backward feeding speed is changed according to the index correlated with the droplet size at the start of each short-circuit period. For this reason, even if the size of the droplets varies, fluctuations in the short-circuit period can be suppressed, so that the droplet transfer state is stabilized and the welding quality is improved. As the above index, from the time length of the immediately preceding arc period, the integrated value of the welding current in the immediately preceding arc period, the moving average value of the time length of the arc period or the moving average value of the integrated value of the welding current in the arc period Select one to use.

[Embodiment 2]
In the invention according to the second embodiment, in the above-described first embodiment, the forward feeding is continued until the short-circuit initial period Tsi elapses after the short-circuit period Ts starts, and the arc period Ta starts. Until the predetermined arc initial period Tai passes, the reverse feed is continued. Hereinafter, the second embodiment will be described.

  FIG. 4 is an output waveform diagram showing a feed control method for arc welding with a short circuit according to Embodiment 2 of the present invention. (A) shows the welding voltage Vw, (B) shows the welding current Iw, (C) shows the feed speed setting signal Fr, and (D) shows the actual welding wire tip. The feeding speed Fs is shown. This figure corresponds to FIG. 6 described above, and the description of the same operation is omitted. In FIG. 6, an arc initial period Tai is added to FIG. Hereinafter, a description will be given with reference to FIG.

  In the figure, the period from time t1 to t2 is the (n-1) th arc period Ta (n-1), and the period from time t2 to t3 is the n-1th short-circuit period Ts (n-1). Yes, the period from time t3 to t4 is the nth arc period Ta (n), and the period from time t4 to t5 is the nth short circuit period Ts (n).

  During the arc period Ta (n-1) excluding the arc initial period Tai at times t1 and t2, the value of the feed speed setting signal Fr is a forward positive feed value determined in advance as shown in FIG. The feed speed set value Ffr is obtained, and the feed speed Fs becomes the forward feed speed Ffs as shown in FIG. As shown in FIG. 3A, the welding voltage Vw has an arc voltage value of several tens of volts. As shown in FIG. 5B, the welding current Iw is a current value determined by the forward feed speed Ffs and the arc load because the welding power source is controlled at a constant voltage. Therefore, the welding current Iw has a waveform that varies with the variation of the arc load. During this arc period Ta (n-1), the tip of the welding wire melts to form droplets.

  When the droplet formed at the tip of the welding wire comes into contact with the molten pool at time t2, a short-circuit state occurs. In the short circuit state, the welding voltage Vw decreases to a short circuit voltage value of several volts as shown in FIG. It is determined that the welding voltage Vw is less than the threshold value, and occurrence of a short circuit is determined. When the occurrence of a short circuit is determined, the welding power source is switched to constant current control, and as shown in FIG. 5B, the short circuit current Is is set to a small current value during a predetermined short circuit initial period Tsi from time t2 to t21. It is maintained and increases in a curved line during a predetermined short-circuit current increase period Tsu of times t21 to t23, and decreases with a slope during a short-circuit current decrease period Tsd from time t23 to time t3 when an arc is generated. However, as shown in FIG. 5C, the feed speed setting signal Fr is different from the first embodiment until the forward feed speed set value Ffr until time t21 when the predetermined short-circuit initial period Tsi elapses. Therefore, as shown in FIG. 4D, the feeding speed Fs remains the forward feeding speed Ffs. At time t21, as shown in FIG. 5C, the feed speed setting signal Fr is switched to a reverse feed speed set value Frr having a predetermined negative value. In response to this, as shown in FIG. 4D, the feeding speed Fs passes through 0 from the forward feed speed Ffs having a positive value during the period from the time t21 to the time t22. The feed speed changes to Frs. That is, the feed speed Fs at the tip of the welding wire remains at the forward feed speed Ffs from the time when the short circuit occurs at time t2 until the initial short circuit period Tsi elapses, and when the initial short circuit period Tsi ends at time t21. It decelerates from the forward feed speed Ffs to zero, reverses the feed direction and accelerates to reach the reverse feed speed Frs at time t22. Therefore, the period from time t21 to t22 is the feed reversal period. After time t22, the backward feeding at the backward feeding speed Frs is continued. As a result, the tip of the welding wire gradually moves away from the molten pool. When the contact state with the molten pool is eliminated at time t3, the arc is regenerated. The method of setting the change pattern of the short-circuit initial period Tsi, the short-circuit current increase period Tsu, and the short-circuit current Is is the same as that in FIG. However, unlike the first embodiment, the timing of entering the reverse feed is delayed until the end of the short-circuit initial period Tsi, and the short-circuit period becomes longer by that amount, so the short-circuit current increase period Tsu is set longer by that amount. There is a need. The reverse feed speed setting value Frr (reverse feed speed Frs) is changed according to an index correlated with the droplet size at the start time of each short-circuit period, as in the first embodiment. The reason why the forward feeding is continued during the initial short-circuit period Tsi is to more reliably lead to a stable short-circuit state. During the short-circuit initial period Tsi, the forward feed is continued at the same forward feed speed Ffs as during the arc period Ta, but even if the forward feed speed Ffs different from the arc period Ta is set independently. good. Furthermore, the short-circuit initial period Tsi for maintaining the short-circuit current Is at a small current value and the short-circuit initial period Tsi for continuing forward feeding even when the short-circuit is entered may be set independently.

  When the arc is regenerated at time t3, the welding voltage Vw increases to an arc voltage value of about several tens of volts as shown in FIG. It is determined that the welding voltage Vw is equal to or higher than the threshold value, and the reoccurrence of the arc is determined. When the occurrence of the arc is determined, the welding power source is switched to constant voltage control as shown in FIG. On the other hand, until a predetermined arc initial period Tai passes from time t3, the feed speed setting signal Fr remains at the reverse feed speed set value Frr as shown in FIG. As shown in D), the feeding speed Fs continues the backward feeding at the backward feeding speed Frs. The arc length is gradually increased by continuing the backward feeding. At time t31, the feed speed setting signal Fr is switched to the forward feed speed setting value Ffr as shown in FIG. In response to this, as shown in FIG. 4D, the feed speed Fs is changed from the reverse feed speed Frs to the forward feed speed Ffs during the feed reversal period from time t31 to t32. Change. The arc initial period Tai is provided for the purpose of increasing the arc length in order to prevent a short circuit from occurring again immediately after the arc is regenerated. This arc initial period Tai is set to about 0.5 to 3 ms. This set value is determined to an appropriate value by experiment according to the welding method, the diameter of the welding wire, the welding current average value, and the like. Further, constant current control may be continued during the arc initial period Tai to increase the welding current Iw.

  FIG. 5 is a block diagram of a welding power source for carrying out the feeding control method according to the second embodiment of the present invention described above. In the figure, the same blocks as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof is omitted. In FIG. 3, a reverse feed period circuit TR indicated by a broken line in FIG. 3 is added, and the feed speed setting switching circuit SF of FIG. 3 is replaced with a second feed speed setting switching circuit SF2 indicated by a broken line. Hereinafter, these circuits will be described with reference to FIG.

  The reverse feed period circuit TR receives the short-circuit determination signal Sd as input, delays the timing at which the short-circuit determination signal Sd changes to the high level by a predetermined short-circuit initial period Tsi, and the short-circuit determination signal Sd is at the low level. The reverse feed period signal Tr is output by delaying the timing to change to OFF by a predetermined arc initial period Tai. Therefore, the backward feed period signal Tr is a signal that is at a high level during the backward feed period of time t21 to t31 in FIG. The second feed speed setting switching circuit SF2 receives the reverse feed period signal Tr described above, and switches to the b side when the reverse feed period signal Tr is at the low level (forward feed period). The speed setting signal Ffr is output as the feeding speed setting signal Fr. When the level is high (reverse feeding period), the speed is switched to the a side, and the backward feeding speed setting signal Frr is output as the feeding speed setting signal Fr.

  In the above description, the case where both the short-circuit initial period Tsi and the arc initial period Tai are provided has been described, but only one of them may be provided. Further, as described above, the constant current control period may be a period of the short circuit period Ts + the arc initial period Tai. Further, the arc initial period for continuing the reverse feed and the arc initial period for continuing the constant current control may be set as different time lengths.

  According to the second embodiment described above, the forward feeding is continued until the predetermined short-circuit initial period elapses from the time when the short-circuit period starts, and the predetermined arc initial period elapses from the time when the arc period starts. Continue to move backwards until you do. Thereby, in addition to the effect of Embodiment 1, when a short circuit occurs, it can be led to a reliable short circuit state, and when the arc is regenerated, the re-short circuit can be prevented. For this reason, a welding state can be made more stable.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll DV Drive circuit Dv Drive signal Ea Error amplification signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal FC Feed control circuit Fc Feed control signal FFR Forward feed speed setting circuit Ffr Forward feed speed setting (value / signal)
Ffs Forward feed speed Fr Feed speed setting signal FRR Reverse feed speed setting circuit Frr Reverse feed speed setting (value / signal)
Frs Reverse feed speed Fs Feed speed HD Index value calculation circuit Hd Index value (signal)
ID Current detection circuit Id Current detection signal Is Short-circuit current value ISR Short-circuit current setting circuit Isr Short-circuit current setting signal Iw Welding current PM Power supply main circuit S Current integration value SD Short-circuit determination circuit Sd Short-circuit determination signal SF Feeding speed setting switching circuit SF2 2 Feeding speed setting switching circuit SP External characteristic switching circuit Ta Arc period Tai Arc initial period TR Reverse feed period circuit Tr Reverse feed period signal Ts Short circuit period Tsd Short circuit current decrease period Tsi Short circuit initial period Tsu Short circuit current increase period VAR Arc Voltage setting circuit Var Arc voltage setting signal VD Voltage detection circuit Vd Voltage detection signal Vw Welding voltage WM Feeding motor

Claims (7)

In the feed control method of arc welding with a short circuit that feeds the welding wire forward to the base material during the arc period and reversely feeds the welding wire away from the base material during the short circuit period,
The feeding speed of the backward feeding is set by a backward feeding speed calculation function by inputting an index correlating with the size of the droplet at the start of each short-circuit period. Is preset for each section divided into a plurality of sections,
A feed control method for arc welding accompanied by a short circuit. The indicator is the time length of the immediately preceding arc period;
The feed control method of arc welding with a short circuit according to claim 1. The indicator is an integral value of the welding current in the immediately preceding arc period.
The feed control method of arc welding with a short circuit according to claim 1. The indicator is a moving average value of the time length of the arc period.
The feed control method of arc welding with a short circuit according to claim 1. The index is a moving average value of integral values of welding current in the arc period,
The feed control method of arc welding with a short circuit according to claim 1. Continue the forward feeding until a predetermined short-circuit initial period elapses from the time when the short-circuit period starts,
The feed control method for arc welding with short circuit according to any one of claims 1 to 5. Continue the reverse feed until a predetermined arc initial period elapses from the time when the arc period starts,
The feed control method for arc welding accompanied by a short circuit according to any one of claims 1 to 6.

Images