Pulse arc welding control method

Abstract

To reduce generation of spatter at the time of high-speed welding in consumable electrode pulse arc welding.SOLUTION: In a pulse arc welding control method, a welding wire is fed, electrification of a welding current Iw formed of a peak current during a predetermined peak period of time t11 to t12 and a base current during a predetermined base period of time t13 to t2 is repeated, at least the peak current is controlled to perform arc length control, and, when the welding wire and a base material are short-circuited, electrification with a short circuit current is performed to perform welding. In the method, a value correlating with a time length of short circuit of t21 to t26 per unit time is calculated, and a time length of the base period of time t13 to t2 is changed on the basis of the correlated value. The correlated value is an occurrence frequency of long-period short circuit with a time length of short circuit equal to or greater than a reference time.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for controlling pulse arc welding performed by feeding a welding wire. [Background technology]

[0002] In consumable electrode pulsed arc welding, welding is performed by repeatedly feeding the welding wire and outputting a peak period with a peak current and a peak voltage, and a base period with a base current and a base voltage. The peak current is set to a large current value of about 500A, which is equal to or higher than the critical current value, and the welding wire is melted to form and transfer droplets. The base current is set to about 50A, which is less than the critical current value, and the welding wire is hardly melted. When the welding current value exceeds the critical current value, the droplet transfer state becomes a spray transfer state. In pulsed arc welding, it is important to maintain a one-pulse-cycle one-droplet transfer state, in which one droplet is transferred by passing one peak current, in order to obtain a high-quality weld bead with little spatter.

[0003] In pulse arc welding, if the welding voltage is set so that the arc length is at an appropriate value, the tip of the welding wire melts when the peak current is applied, forming a droplet, which transfers to the molten pool in a spray state immediately after the peak current is no longer applied. When the droplet transfers to the molten pool, the tip of the droplet often comes into contact with the molten pool, causing a micro-short circuit of about 0.5 ms or less. However, this micro-short circuit does not occur when the droplet transfers due to a short circuit, as in carbon dioxide arc welding, but rather occurs when the droplet simply comes into contact with the molten pool during the spray transfer process. For this reason, there is no need to control the micro-short circuit by increasing the welding current or other means to release the short circuit, and the micro-short circuit is automatically released.

[0004] When performing high-speed welding with a welding speed of about 1 m / min or more, in order to improve the welding quality, it is necessary to set the welding voltage low so that the arc length becomes short. When the arc length becomes short, normal short circuits of 0.5 ms or more in addition to micro short circuits occur. In normal short circuits, the molten droplet is in a state of short-circuit transfer, and a large amount of spatter is generated when the short circuit is released. In the invention of Patent Document 1, in pulsed arc welding for performing high-speed welding, when a normal short circuit occurs, the welding current is increased at a rising speed slower than the rising speed of the peak current, and when the constriction of the molten droplet is detected, the welding current is decreased.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In pulsed arc welding for performing high-speed welding, in the conventional short-circuit welding current control, the spatter reduction effect is not sufficient, and further reduction of spatter has been desired. In particular, when many long short circuits of 5 ms or more occur, there is a problem that large spatter is generated and the welding quality deteriorates.

[0007] Therefore, an object of the present invention is to provide an arc welding control method capable of reducing the generation of spatter during high-speed welding by pulsed arc welding.

Means for Solving the Problems

[0008] In order to solve the above-described problems, the invention of claim 1 is feeding a welding wire, repeating energization of a peak current during a predetermined peak period and a base current during a predetermined base period, and controlling at least the peak current to perform arc length control, In a pulse arc welding control method in which a short-circuit current is passed to perform welding when the welding wire and the base material are short-circuited, a value correlated with the time length of the short circuit per unit time is calculated, and the time length of the base period is changed based on the correlated value, which is a pulse arc welding control method characterized by the above.

[0009] The invention according to claim 2 is wherein the correlated value is an average value of the time length of the short circuit, which is the pulse arc welding control method according to claim 1, characterized by the above.

[0010] The invention according to claim 3 is wherein the correlated value is the occurrence frequency of a long-term short circuit in which the time length of the short circuit is equal to or longer than a reference time, which is the pulse arc welding control method according to claim 1, characterized by the above.

[0011] The invention according to claim 4 is controlling the peak value of the short-circuit current based on the correlated value, which is the pulse arc welding control method according to any one of claims 1 to 3, characterized by the above.

Effect of the Invention

[0012] According to the pulse arc welding control method according to the present invention, the generation of spatter can be reduced during high-speed welding. In particular, the generation of spatter can be reduced even when a long-term short circuit occurs.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Embodiment for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] FIG. 1 is a block diagram of a welding power source for implementing a pulse arc welding control method according to an embodiment of the present invention. Hereinafter, each block will be described with reference to the figure.

[0016] The main power circuit MC takes a commercial power supply (not shown) such as 3-phase 200V as an input, performs output control such as inverter control according to a current error amplification signal Ei described later, and outputs an output voltage suitable for welding.

[0017] The reactor WL smoothes the output of the main power circuit MC.

[0018] The welding wire 1 is fed through the welding torch 4 by the rotation of a feeding roll 5 coupled to a wire feeding motor (not shown), and an arc 3 is generated between the welding wire 1 and the base material 2. A welding voltage Vw is applied between a power supply tip (not shown) in the welding torch 4 and the base material 2, and a welding current Iw flows.

[0019] The voltage detection circuit VD detects the above welding voltage Vw and outputs a voltage detection signal Vd. The voltage averaging circuit VAV averages the above voltage detection signal Vd and outputs a voltage average signal Vav. The voltage setting circuit VR outputs a voltage setting signal Vr with a desired value.

[0020] The voltage error amplification circuit EV amplifies the error between the above voltage setting signal Vr and the above voltage average signal Vav and outputs a voltage error amplification signal Ev.

[0021] The current modulation circuit IC performs current modulation control by PI control or PID control based on the above voltage error amplification signal Ev, and outputs a peak current setting signal Ipr and a base current setting signal Ibr. By this circuit, the peak current setting signal Ipr and the base current setting signal Ibr are controlled so that the voltage average signal Vav becomes equal to the voltage setting signal Vr, and as a result, arc length control is performed. It is also possible to perform current modulation control only on the peak current setting signal Ipr. In this case, the base current setting signal Ibr is set to a predetermined value.

[0022] The peak current rise speed setting circuit SUR outputs a predetermined peak current rise speed setting signal Sur. The peak current fall speed setting circuit SDR outputs a predetermined peak current fall speed setting signal Sdr.

[0023] The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr.

[0024] The base period setting circuit TBR takes as an input the short-circuit time correlation value signal Tsd described later, substitutes the short-circuit time correlation value signal Tsd into a predetermined base period calculation function, and outputs the calculated value as the base period setting signal Tbr. The base period calculation function is a function that becomes longer as the value of the short-circuit time correlation value signal Tsd increases.

[0025] The current setting circuit IR takes as inputs the above peak current setting signal Ipr, the above base current setting signal Ibr, the above peak current rise speed setting signal Sur, the above peak current fall speed setting signal Sdr, the above peak period setting signal Tpr, and the above base period setting signal Tbr, performs the following processing, and outputs a current setting signal Ir. 1) Outputs a current setting signal Ir that increases by the value of the peak current rise speed setting signal Sur from the value of the base current setting signal Ibr. 2) Then, when the value of the current setting signal Ir reaches the value of the peak current setting signal Ipr, maintains that value for the duration of the peak period setting signal Tpr. 3) Then, an output current setting signal Ir is output, which decreases from the value of the peak current setting signal Ipr by the value of the peak current decay rate setting signal Sdr. 4) Then, when the value of the current setting signal Ir becomes equal to the value of the base current setting signal Ibr, that value is maintained for the duration of the base period setting signal Tbr. 5) Repeat the above 1) to 4).

[0026] The short - circuit discrimination signal SD takes the above voltage detection signal Vd as an input. When this value is less than the short - circuit discrimination value (about 10V), it is determined that it is a short - circuit period and becomes High level. Otherwise, it is determined that it is an arc period and becomes Low level, and outputs a short - circuit discrimination signal Sd.

[0027] The short - circuit time correlation value calculation circuit TSD takes the above short - circuit discrimination signal Sd as an input, and calculates a value correlated with the short - circuit time per unit time by the following process 1) or 2), and outputs a short - circuit time correlation value signal Tsd. The unit time is set to about 0.1 to 1 second. About 10 to 100 short - circuits occur per unit time. 1) For each unit time, the average value of the short - circuit time when the short - circuit discrimination signal Sd is High level is output as the short - circuit time correlation value signal Tsd [ms]. 2) For each unit time, the occurrence frequency of long - term short - circuits where the short - circuit time when the short - circuit discrimination signal Sd is High level is equal to or longer than a predetermined reference time (for example, 5ms) is output as the short - circuit time correlation value signal Tsd [%]. For example, the occurrence frequency is the percentage of the number of long - term short - circuits occurring per unit time in the total number of short - circuits. Or, the number of long - term short - circuits occurring per unit time may be used as the short - circuit time correlation value signal Tsd [times].

[0028] The first rising speed setting circuit S1R takes the above short - circuit time correlation value signal Tsd as an input, substitutes the short - circuit time correlation value signal Tsd into a predetermined first rising speed calculation function, and outputs the calculated value as the first rising speed setting signal S1r. The first rising speed calculation function is a function that becomes larger as the value of the short - circuit time correlation value signal Tsd becomes larger.

[0029] The second rising speed setting circuit S2R outputs a predetermined second rising speed setting signal S2r. The value of the second rising speed setting signal S2r is set to a value smaller than the value of the above-mentioned first rising speed setting signal S1r.

[0030] The current-limiting resistor R is inserted between the above-mentioned reactor WL and the welding torch 4. The value of this current-limiting resistor R is set to a value more than 50 times larger (about 0.5 to 3 Ω) than the short-circuit load (about 0.01 to 0.03 Ω). When this current-limiting resistor R is inserted into the energization path, the energy accumulated in the reactor WL and the reactor of the external cable is rapidly discharged.

[0031] The transistor TR is connected in parallel with the above-mentioned current-limiting resistor R and is controlled to be turned on or off according to a drive signal Dr described later.

[0032] The constriction detection circuit ND takes the above-mentioned short-circuit discrimination signal Sd, the above-mentioned voltage detection signal Vd, and the above-mentioned current detection signal Id as inputs. When the voltage rise value of the voltage detection signal Vd when the short-circuit discrimination signal Sd is at the High level (short-circuit period) reaches the reference value, it determines that the formation state of the constriction has reached the reference state and becomes High level, and becomes Low level when the short-circuit discrimination signal Sd changes to the Low level (arc period), and outputs a constriction detection signal Nd. Also, the constriction detection signal Nd may be changed to High level when the differential value of the voltage detection signal Vd during the short-circuit period reaches the corresponding reference value. Further, the resistance value of the droplet may be calculated by dividing the value of the voltage detection signal Vd by the value of the current detection signal Id, and the constriction detection signal Nd may be changed to High level when the differential value of this resistance value reaches the corresponding reference value.

[0033] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr. The current comparison circuit CM takes this low-level current setting signal Ilr and the above-mentioned current detection signal Id as inputs, and outputs a current comparison signal Cm that becomes High level when Id < Ilr and becomes Low level when Id ≧ Ilr.

[0034] The drive circuit DR takes the above current comparison signal Cm and the above constriction detection signal Nd as inputs, and outputs a drive signal Dr that changes to a low level when the constriction detection signal Nd changes to a high level, and then changes to a high level when the current comparison signal Cm changes to a high level, to the base terminal of the above transistor TR. Therefore, when constriction is detected, this drive signal Dr becomes low level, the transistor TR turns off, and the current limiting resistor R is inserted into the energization path, so the welding current Iw flowing through the short-circuit load rapidly decreases. And when the value of the rapidly decreasing welding current Iw decreases to the value of the low-level current setting signal Ilr, the drive signal Dr becomes high level, the transistor TR turns on, so the current limiting resistor R is short-circuited and returns to the normal state.

[0035] The buckling current value setting signal ITR takes the above short-circuit time correlation value signal Tsd as an input, substitutes the short-circuit time correlation value signal Tsd into a predetermined buckling current value calculation function, and outputs the calculated value as the buckling current value setting signal Itr. The calculation function is a function that becomes a larger value as the value of the short-circuit time correlation value signal Tsd increases.

[0036] The short-circuit current setting circuit ISR takes the above short-circuit discrimination signal Sd, the above low-level current setting signal Ilr, the above constriction detection signal Nd, the above first rising speed setting signal S1r, the above second rising speed setting signal S2r, and the above buckling current value setting signal Itr as inputs, performs the following processing, and outputs the short-circuit current setting signal Isr. 1) When the short-circuit discrimination signal Sd changes to a high level (short-circuit period), the short-circuit current setting signal Isr that becomes a predetermined initial current setting value during a predetermined initial period is output. The initial current setting value is set to be equal to or less than the value of the above base current setting signal Ibr. 2) Thereafter, the value of the short-circuit current setting signal Isr increases by the value of the first rising speed setting signal S1r from the above initial current setting value. 3) Thereafter, when the value of the short-circuit current setting signal Isr reaches the value of the buckling current value setting signal Itr, it increases by the value of the second rising speed setting signal S2r. 4) Then, when the constriction detection signal Nd changes to the High level, a short-circuit current setting signal Isr having a value of the low-level current setting signal Ilr is output.

[0037] The current control setting circuit ICR takes the above short-circuit discrimination signal Sd, the above current setting signal Ir, and the above short-circuit current setting signal Isr as inputs. When the short-circuit discrimination signal Sd is at the Low level (arc period), it outputs the current setting signal Ir as the current control setting signal Icr. When the short-circuit discrimination signal Sd is at the High level (short-circuit period), it outputs the short-circuit current setting signal Isr as the current control setting signal Icr.

[0038] The current detection circuit ID detects the above welding current Iw and outputs a current detection signal Id.

[0039] The current error amplification circuit EI amplifies the error between the above current control setting signal Icr and the above current detection signal Id and outputs a current error amplification signal Ei.

[0040] FIG. 2 is a timing chart of each signal in the welding power source shown in FIG. 1, which shows a pulse arc welding control method according to an embodiment of the present invention. In the figure, (A) shows the time change of the welding current Iw, (B) shows the time change of the welding voltage Vw, (C) shows the time change of the short-circuit discrimination signal Sd, (D) shows the time change of the constriction detection signal Nd, and (E) shows the time change of the drive signal Dr. Hereinafter, the operations of each signal will be described with reference to this figure.

[0041] This figure shows the case where the welding voltage is set low and the arc length is set short for high-speed welding. This figure shows waveforms of two cycles. The first cycle is the case where a micro short circuit occurs, and the second cycle is the case where a normal short circuit in which a droplet migrates occurs. Although the welding wire is not shown, it is fed at a constant speed.

[0042] (1) Explanation of the operation in the first cycle As shown in FIG. (A), during the rising period from time t1 to t11, the welding current Iw increases from the base current Ib by the value of the peak current rising speed setting signal Sur in FIG. 1. During the peak period from time t11 to t12, it becomes the peak current value. During the falling period from time t12 to t13, it decreases by the value of the peak current falling speed setting signal Sdr in FIG. 1. During the base period from time t13 to t2, it becomes the base current value. The above base current value is set by the base current setting signal Ibr in FIG. 1, the above peak current value is set by the peak current setting signal Ipr in FIG. 1, the above peak period is set by the peak period setting signal Tpr in FIG. 1, and the above base period is set by the base period setting signal Tbr in FIG. 1. As shown in FIG. (B), the welding voltage Vw becomes a voltage value proportional to the arc length and has a waveform similar to the current waveform. The peak current rising speed and the peak current falling speed are set so that the formation state of the droplet is stable. The peak current value and the base current value are modulated and controlled so that the average value of the welding voltage Vw becomes equal to the value of the voltage setting signal Vr in FIG. 1, and the arc length is controlled. For example, the peak current value is modulated and controlled in the range of about 400 to 600 A, the peak period is set to 1.2 ms, the base current value is modulated and controlled in the range of about 30 to 100 A, and the base period varies in the range of about 2 to 7 ms. The peak current rising speed is set in the range of 400 to 600 A / ms, and the peak current falling speed is set in the range of 300 to 500 A / ms. The welding state is most stable when both speeds are set within the above ranges.

[0043] The short-circuit time correlation value calculation circuit TSD in FIG. 1 performs the following processing 1) or 2) to calculate a value correlated with the short-circuit time per unit time and outputs a short-circuit time correlation value signal Tsd. The unit time is set to about 0.1 to 1 second. About 10 to 100 short circuits occur per unit time. 1) Every unit time, the average value of the short-circuit time when the short-circuit discrimination signal Sd is at the High level is output as the short-circuit time correlation value signal Tsd [ms]. 2) Output the occurrence frequency of long-term short circuits where the short-circuit discrimination signal Sd is at a high level for a short-circuit time equal to or longer than a predetermined reference time (e.g., 5 ms) per unit time as a short-circuit time correlation value signal Tsd [%]. For example, the occurrence frequency is the percentage of the number of long-term short circuits occurring per unit time in the total number of short circuits.

[0044] The base period is set as follows. By the base period setting circuit TBR in FIG. 1, the value calculated by substituting the short-circuit time correlation value signal Tsd into a predetermined base period calculation function is set as the base period setting signal Tbr. The base period calculation function is a function that becomes longer as the value of the short-circuit time correlation value signal Tsd increases. An example of the base period calculation function is shown below. 1) When the short-circuit time correlation value signal Tsd [ms] is the average value of the short-circuit time STbr [ms]=Tb0+(Tsd - 3) Tb0 is the reference base period and is a value predetermined corresponding to the feeding speed of the welding wire. When Tsd ≤ 3 ms, Tbr = Tb0, and when Tsd = 5 ms, tTbr is the value obtained by adding 2 ms to Tb0. 2) When the short-circuit time correlation value signal Tsd [%] is the occurrence frequency of long-term short circuits Tbr [ms]=Tb0 + 0.1×Tsd However, when Tsd ≥ 20%, it is set to the same value as Tsd = 20%. When Tsd = 5%, Tbr is the value obtained by adding 0.5 ms to Tb0, and when Tsd = 20%, it is the value obtained by adding 2 ms to Tb0.

[0045] In the first cycle, a micro short circuit occurs during the period from time t14 to t15 in the base period. The micro short circuit is a short circuit of 0.5 ms or less, and many short circuits of about 0.1 ms occur. The micro short circuit occurs when the tip of the droplet contacts the molten pool for a very short time during the process of the droplet formed by the energization of the peak current migrating in a spray state. Therefore, in the case of a micro short circuit, the droplet does not migrate by short circuit but always migrates by spray. For this reason, as shown in Fig. (A), the welding current Iw is controlled to an initial current value below the base current value during the micro short circuit period, thereby suppressing the generation of spatter. As shown in Fig. (B), the welding voltage Vw becomes a short circuit voltage value of several volts. As shown in Fig. (C), the short circuit discrimination signal Sd becomes a high level. As shown in Fig. (D), the necking detection signal Nd remains at a low level because no necking of the droplet is detected during the micro short circuit. For this reason, as shown in Fig. (E), the drive signal Dr remains at a high level, the transistor in Fig. 1 is turned on, and the current reducing resistor R in Fig. 1 is in a short-circuited state.

[0046] (2) Explanation of the operation in the second cycle A description will be given of points different from the first period. In the second period, this is a case where normal short circuits occur in which droplets undergo short-circuit transfer during the period from time t21 to t26 during the base period. Since the arc length is set to be short, normal short circuits sometimes occur. When a short circuit occurs at time t21, as shown in Fig. (B) of the same figure, the welding voltage Vw rapidly decreases to a short-circuit voltage value of several volts, and as shown in Fig. (C) of the same figure, the short-circuit discrimination signal Sd changes to the High level. In response to this, as shown in Fig. (A) of the same figure, a short-circuit current controlled by the short-circuit current setting signal Isr in Fig. 1 is energized. During a predetermined initial period from time t21 to t22, the short-circuit current becomes a predetermined initial current value. The initial period is set to about 0.5 ms. The initial current value is set to be equal to or less than the base current value as described above. Subsequently, during the first period from time t22 to t23, the short-circuit current increases by the value of the first rising speed setting signal S1r in Fig. 1. Subsequently, when the value of the short-circuit current reaches the value of the bend current value setting signal Itr in Fig. 1, it increases by the value of the second rising speed setting signal S2r in Fig. 1. The value of the second rising speed setting signal S2r is set to be less than the value of the first rising speed setting signal S1r. For example, the value of the second rising speed setting signal S2r is set to 200 A / ms.

[0047] The first rising speed setting circuit S1R substitutes the above short-circuit time correlation value signal Tsd into a predetermined first rising speed calculation function and sets the calculated value as the first rising speed setting signal S1r. The first rising speed calculation function is a function that becomes a larger value as the value of the short-circuit time correlation value signal Tsd becomes larger. An example of the first rising speed calculation function is shown below. 1) When the short-circuit time correlation value signal Tsd [ms] is the average value of the short-circuit time S1r [A / ms] = 500 + 100 × (Tsd - 3) When Tsd ≤ 3 ms, S1r = 500 A / ms, and when Tsd = 5 ms, S1r = 700 A / ms. 2) When the short-circuit time correlation value signal Tsd [%] is the occurrence frequency of long-term short circuits S1r [A / ms] = 500 + 10 × Tsd However, when Tsd ≧ 20%, it shall be set to the same value as Tsd = 20%. When Tsd = 5%, S1r = 550 A / ms, and when Tsd = 20%, S1r = 700 A / ms.

[0048] The buckling current value setting circuit ITR substitutes the above short-circuit time correlation value signal Tsd into a predetermined buckling current value calculation function, and sets the calculated value as the buckling current value setting signal Itr. The first rising speed calculation function is a function that becomes a larger value as the value of the short-circuit time correlation value signal Tsd increases. An example of the first rising speed calculation function is shown below. 1) When the short-circuit time correlation value signal Tsd [ms] is the average value of the short-circuit time Itr [A] = 200 + 50 × (Tsd - 3) When Tsd ≦ 3 ms, Itr = 200 A, and when Tsd = 5 ms, Itr = 300 A. 2) When the short-circuit time correlation value signal Tsd [%] is the occurrence frequency of long-term short circuits Itr [A] = 200 + 5 × Tsd However, when Tsd ≧ 20%, it shall be set to the same value as Tsd = 20%. When Tsd = 5%, Itr = 225 A, and when Tsd = 20%, Itr = 300 A.

[0049] As shown in FIG. (B), the welding voltage Vw rises during the second period when the rising speed of the short-circuit current becomes slow. This is because the pinch force due to the short-circuit current gradually forms a constriction in the droplet. After the voltage rise value of the welding voltage Vw reaches the reference value, it is determined that the constriction formation state has reached the reference state. At time t24, as shown in FIG. (D), the constriction detection signal Nd changes to the High level. In response to this, as shown in FIG. (E), the drive signal Dr becomes the Low level, and the transistor TR in FIG. 1 is turned off, so the current-reducing resistor R in FIG. 1 is inserted into the conduction path. At the same time, the value of the short-circuit current setting signal Isr in FIG. 1 becomes smaller than the value of the low-level current setting signal Ilr. For this reason, as shown in FIG. (A), the short-circuit current rapidly decreases to a low-level current value (about 70 A). At the time t25 when the short-circuit current decreases to the low-level current value, as shown in FIG. (E), the drive signal Dr returns to the High level, so the transistor TR is turned on and the current-reducing resistor R is short-circuited. As shown in FIG. (A), the short-circuit current maintains the low-level current value until the time t26 when the arc reoccurs because the short-circuit current setting signal Isr remains the low-level current setting signal Ilr. Therefore, the transistor TR is turned off only during the period from when the constriction detection signal Nd changes to the High level until the short-circuit current decreases to the low-level current value. As shown in FIG. (B), the welding voltage Vw once decreases and then rapidly increases because the short-circuit current becomes smaller. Since the current value at the time of arc reoccurrence can be reduced by constriction detection control, spatter generation can be reduced.

[0050] When an arc is generated at time t26, as shown in FIG. (B), the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, and as shown in FIG. (C), the short-circuit discrimination signal Sd changes to the Low level (arc period). In response to this, as shown in FIG. (A), the welding current Iw changes to the base current value. At the same time, as shown in FIG. (D), the constriction detection signal Nd also returns to the Low level.

[0051] The base period of the second cycle is also set based on the short-circuit time correlation value signal Tsd in the same manner as the first cycle described above.

[0052] In the above-described embodiment, the first rising speed setting signal S1r and the bending current value setting signal Itr are changed based on the short-circuit time correlation value signal Tsd, but only one of them may be changed. Further, the second rising speed setting signal S2r may be changed based on the short-circuit time correlation value signal Tsd.

[0053] Hereinafter, the operation and effect of this embodiment will be described. According to this embodiment, a value correlated with the time length of a short circuit per unit time is calculated, and the time length of the base period is changed based on the correlated value. In pulsed arc welding for performing high-speed welding, in the short-circuit welding current control of the prior art, the spatter reduction effect is not sufficient, and further reduction of spatter has been desired. In particular, when many long-term short circuits of 5 ms or more occur, there is a problem that large spatter is generated and the welding quality deteriorates. In this embodiment, a state in which many long-term short circuits occur is detected by a value correlated with the short-circuit time. That is, the value correlated with the short-circuit time increases as the number of long-term short circuits increases. When energization of the next peak current is started in a long-term short-circuit state, the short-circuit state is forcibly released and large spatter is generated. In this embodiment, control is performed such that the base period becomes longer as the value correlated with the short-circuit time increases. By doing so, it is possible to suppress the start of energization of the next peak current in a long-term short-circuit state. As a result, generation of spatter can be reduced even during high-speed welding.

[0054] More preferably, according to this embodiment, the correlated value is the average value of the time length of the short circuit. As the number of long-term short circuits increases, the average value of the time length of the short circuit (short-circuit time) per unit time increases. Therefore, the occurrence state of long-term short circuits can be detected by the average value of the short-circuit time.

[0055] More preferably, according to the present embodiment, the correlated value is the occurrence frequency of a long-term short circuit in which the time length of the short circuit is equal to or longer than a reference time. The more frequently long-term short circuits occur, the higher the occurrence frequency of long-term short circuits per unit time. Therefore, the occurrence state of long-term short circuits can be detected based on the occurrence frequency of long-term short circuits.

[0056] More preferably, according to the present embodiment, the peak value of the short-circuit current is controlled based on the correlated value. In the present embodiment, the control is performed such that the peak value of the short-circuit current increases as the value correlated with the short-circuit time increases. When the peak value of the short-circuit current increases, the short circuit is released earlier, so that the occurrence of long-term short circuits can be reduced. As a result, the generation of spatter can be reduced even during high-speed welding.

[0057] More preferably, according to the present embodiment, the short-circuit current includes a first period in which it increases at a first rising speed and a second period in which it increases at a second rising speed lower than the first rising speed, and the peak value is controlled by changing the first rising speed. The peak value of the short-circuit current is controlled by changing the first rising speed according to the value correlated with the short-circuit time. In this way, when long-term short circuits occur frequently, the first rising speed increases, so that the peak value of the short-circuit current increases. When the peak value of the short-circuit current increases, the short circuit is released earlier, so that the occurrence of long-term short circuits can be reduced.

[0058] More preferably, according to the present embodiment, the short-circuit current includes a first period in which it increases at a first rising speed and a second period in which it increases at a second rising speed lower than the first rising speed, and when the value of the short-circuit current reaches the bend current value, it shifts from the first period to the second period, and the peak value is controlled by changing the bend current value. In this way, when long-term short circuits occur frequently, the bend current value increases, so that the peak value of the short-circuit current increases. When the peak value of the short-circuit current increases, the short circuit is released earlier, so that the occurrence of long-term short circuits can be reduced.

Description of Reference Numerals

[0059] 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feeding roll CM Current comparison circuit Cm Current comparison signal DR Drive circuit Dr Drive signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal Ib Base current Ibr Base current setting signal IC Current modulation circuit ICR Current control setting circuit Icr Current control setting signal ID Current detection circuit Id Current detection signal ILR Low-level current setting circuit Ilr Low-level current setting signal Ip Peak current Ipr Peak current setting signal IR Current setting circuit Ir Current setting signal ISR Short-circuit current setting circuit Isr Short-circuit current setting signal ITR Buckling current value setting circuit Itr Buckling current value setting signal Iw Welding current MC Power main circuit ND Necking detection circuit Nd Necking detection signal R Current-reducing resistor S1R First rising speed setting circuit S1r First rising speed setting signal S2R Second rising speed setting circuit S2r Second rising speed setting signal SD Short-circuit discrimination circuit Sd Short-circuit discrimination signal SDR Peak Current Decay Rate Setting Circuit Sdr Peak Current Decay Rate Setting Signal SUR Peak Current Rise Rate Setting Circuit Sur Peak Current Rise Rate Setting Signal TBR Base Period Setting Circuit Tbr Base Period Setting Signal TPR Peak Period Setting Circuit Tpr Peak Period Setting Signal TR Transistor TSD Short-Circuit Time Correlation Value Calculation Circuit Tsd Short-Circuit Time Correlation Value Signal VAV Voltage Averaging Circuit Vav Voltage Average Signal VD Voltage Detection Circuit Vd Voltage Detection Signal VR Voltage Setting Circuit Vr Voltage Setting Signal Vw Welding Voltage WL Reactor

Claims

1. feeding a welding wire, repeating energization of a peak current during a predetermined peak period and a base current during a predetermined base period, and performing arc length control by controlling at least the peak current, in a pulsed arc welding control method of energizing a short-circuit current for welding when the welding wire and the base material are short-circuited, calculating a value correlated with the time length of the short circuit per unit time, changing the time length of the base period based on the correlated value, A pulsed arc welding control method characterized by this.

2. The correlated value is an average value of the time length of the short circuit, The pulsed arc welding control method according to claim 1, characterized by this.

3. The correlated value is the occurrence frequency of a long-term short circuit in which the time length of the short circuit is equal to or longer than a reference time, The pulsed arc welding control method according to claim 1, characterized by this.

4. Controlling the peak value of the short-circuit current based on the correlated value, The pulsed arc welding control method according to any one of claims 1 to 3, characterized by this.

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