Pulse arc welding control method

Abstract

To obtain excellent welding quality by always maintaining one pulse period and one droplet transfer state even when a welding state is fluctuated in consumable electrode pulse arc welding.SOLUTION: Feeding a welding wire to pass a peak rising current that increases from a value of a base current to a value of a peak current during a peak rising period, pass the peak current during a peak period, and pass a peak falling current that decreases from the value of the peak current to the value of the base current during a peak falling period; In the pulsed arc welding control method in which the base current is supplied during the base period and the welding is performed by repeating the supply of the welding current Iw as one pulse cycle, the feeding rate Fw starts changing from the forward feeding peak value to the reverse feeding peak value at a time point before the start time point (time t3) of the peak falling period, and changes to the reverse feeding peak value before the end time point (time t4) of the peak falling period.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pulse arc welding control method for feeding a welding wire to weld. [Background technology]

[0002] Pulse arc welding, which involves feeding a welding wire to weld, is used to weld steel and other materials. In pulse arc welding, the welding wire is fed, and a peak-rise current is applied during the peak-rise period, increasing from the base current value to the peak current value. The peak current is applied during the peak period, and a peak-fall current is applied during the peak-fall period, decreasing from the peak current value to the base current value. The base current is applied during the base period, and these welding currents are repeated as one pulse cycle to perform welding. In pulse arc welding, by achieving one droplet transfer per pulse cycle, spatter is reduced and a beautiful bead appearance can be achieved.

[0003] In the invention of Patent Document 1, during a predetermined period from a first point in time during the peak period to a second point in time during the base period, the welding wire feed speed is set to be slower than the feed speed at the rising point of the peak current, or the welding wire is fed in a reverse direction, i.e., in a direction away from the workpiece to be welded. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6123069 Summary of the Invention [Problem to be solved by the invention]

[0005] In pulsed arc welding, it is important to constantly maintain one droplet per pulse cycle in order to achieve good weld quality. However, with conventional pulsed arc welding, fluctuations in the welding condition can cause deviations from this one droplet per pulse cycle state, resulting in poor weld quality.

[0006] Therefore, an object of the present invention is to provide a pulse arc welding control method that can always maintain a one-droplet-per-pulse-cycle state even if the welding condition fluctuates, thereby obtaining good welding quality. [Means for solving the problem]

[0007] A pulse arc welding control method according to a first aspect of the present invention includes a pulse arc welding control method for welding by feeding a welding wire, passing a peak rise current that rises from a base current value to a peak current value during a peak rise period, passing the peak current during the peak period, passing a peak fall current that falls from the peak current value to the base current value during a peak fall period, and passing the base current during the base period, and repeating these welding currents as one pulse period, wherein the welding wire feed speed starts changing from a reverse feed peak value to a forward feed peak value at a time point a first early period before a start of the peak rise period, changes to the forward feed peak value at a time point before an end of the peak rise period, starts changing from the forward feed peak value to the reverse feed peak value at a time point a second early period before a start of the peak fall period, and changes to the reverse feed peak value at a time point before an end of the peak fall period.

[0008] As an example, the pulse arc welding control method of the present invention is characterized in that the first early period and the second early period are set to values ​​of 0.2 ms or more and 1 ms or less.

[0009] As an example, the pulse arc welding control method of the present invention is characterized in that a pulse frequency, which is the reciprocal of the pulse period, is set within a range of ±15% of the average value of the welding current.

[0010] As an example, the pulse arc welding control method of the present invention is characterized in that arc length control is performed by modulating and controlling at least the peak current. [Effects of the Invention]

[0011] According to the above configuration, for example, in relation to the pulse arc welding control method, even if the welding state fluctuates, a one-pulse-cycle, one-droplet transfer state can always be maintained, thereby obtaining good welding quality. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram of a welding device for carrying out a pulse arc welding control method according to an embodiment of the present invention. [Figure 2] 2 is a timing chart of each signal in the welding device of FIG. 1, illustrating a pulse arc welding control method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] 1 is a block diagram of a welding apparatus for carrying out a pulse arc welding control method according to an embodiment of the present invention. The welding apparatus is mainly composed of a welding power source PS, a robot control device RC, a robot (not shown), etc., all of which are enclosed by dashed lines. Each block will be described below with reference to the diagram.

[0015] The welding power source PS consists of the following blocks:

[0016] The power control circuit MC receives an AC commercial power supply (not shown) such as a three-phase 200V, performs output control such as inverter control in accordance with a drive signal Dv described below, and outputs a welding voltage Vw and welding current Iw suitable for welding. Although not shown, the power control circuit MC includes a primary rectifier circuit that rectifies the AC commercial power supply, a capacitor that smoothes the rectified DC, an inverter circuit that converts the smoothed DC into high-frequency AC in accordance with the drive signal Dv, an inverter transformer that steps down the high-frequency AC to a voltage value suitable for welding, and a secondary rectifier circuit that rectifies the stepped-down high-frequency AC.

[0017] The reactor WL is inserted between the positive output of the power control circuit MC and the welding torch 4, and smoothes the output of the power control circuit MC.

[0018] The feed motor WM is driven to rotate by a feed control signal Fc, which will be described later. The welding wire 1 is fed forward and backward through the welding torch 4 at a feed speed Fw by the rotation of a feed roll 5 connected to the feed motor WM, and an arc 3 is generated between the welding wire 1 and the base material 2. The feed motor WM and the welding torch 4 are mounted on a robot. A welding voltage Vw is applied between a power feed tip (not shown) in the welding torch 4 and the base material 2, and a welding current Iw flows.

[0019] The welding voltage detection circuit VD detects the welding voltage Vw and outputs a welding voltage detection signal Vd. The welding voltage averaging circuit VAV averages the welding voltage detection signal Vd (by passing it through a low-pass filter) and outputs a welding voltage average value signal Vav. The welding voltage setting circuit VR outputs a predetermined welding voltage setting signal Vr. The voltage error amplification circuit EV amplifies the error between the welding voltage setting signal Vr(+) and the welding voltage average value signal Vav(-) and outputs a voltage error amplification signal Ev.

[0020] The current modulation circuit IC receives the voltage error amplified signal Ev as an input, performs PI (proportional-integral) control or PID (proportional-integral-derivative) control, and outputs a peak current setting signal Ipr and a base current setting signal Ibr. This circuit performs current modulation control of the peak current setting signal Ipr and the base current setting signal Ibr so that the welding voltage average value signal Vav becomes equal to the welding voltage setting signal Vr. As a result, arc length control is performed so that the arc length is maintained at an appropriate value. It is also possible to perform current modulation control of only the peak current setting signal Ipr, and set the base current setting signal Ibr to a predetermined value.

[0021] The peak rise period setting circuit TUR outputs a predetermined peak rise period setting signal Tur, the peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr, and the peak fall period setting circuit TKR outputs a predetermined peak fall period setting signal Tkr.

[0022] The pulse frequency setting circuit PFR outputs a pulse frequency setting signal Pfr that is predetermined to meet the following condition 1) or 2). 1) The value of the pulse frequency setting signal Pfr is set within the range of 100 Hz to 350 Hz, and more preferably within the range of 150 Hz to 300 Hz. 2) The value of the pulse frequency setting signal Pfr is set within a range of ±15% of the average value of the welding current Iw, and more preferably within a range of ±10%.

[0023] The base period setting circuit TBR receives the peak rise period setting signal Tur, the peak period setting signal Tpr, the peak fall period setting signal Tkr, and the pulse frequency setting signal Pfr as inputs, calculates Tbr=(1 / Pfr)-Tur-Tpr-Tkr, and outputs the base period setting signal Tbr.

[0024] The welding current setting circuit IR receives the peak rise period setting signal Tur, the peak period setting signal Tpr, the peak fall period setting signal Tkr, the base period setting signal Tbr, the peak current setting signal Ipr, and the base current setting signal Ibr as inputs, performs the following processing, and outputs the welding current setting signal Ir and the timer signal Tm. 1) During the peak rise period Tu determined by the peak rise period setting signal Tur, a timer signal Tm=1 is output, and the peak rise current Iu, which rises from the value of the base current setting signal Ibr to the value of the peak current setting signal Ipr, is output as the welding current setting signal Ir. 2) Subsequently, during the peak period Tp determined by the peak period setting signal Tpr, the timer signal Tm=2 is output, and the peak current setting signal Ipr is output as the welding current setting signal Ir. 3) Subsequently, during the peak fall period Tk determined by the peak fall period setting signal Tkr, a timer signal Tm=3 is output, and the peak fall current Ik decreasing from the value of the peak current setting signal Ipr to the value of the base current setting signal Ibr is output as the welding current setting signal Ir. 4) Subsequently, during the base period Tb determined by the base period setting signal Tbr, the timer signal Tm=4 is output, and the base current setting signal Ibr is output as the welding current setting signal Ir. 5) Repeat steps 1) to 4) above.

[0025] The forward transmission peak value setting circuit WSR outputs a forward transmission peak value setting signal Wsr of a predetermined positive value, and the backward transmission peak value setting circuit WRR outputs a backward transmission peak value setting signal Wrr of a predetermined negative value.

[0026] The welding current detection circuit ID detects the welding current Iw and outputs a welding current detection signal Id. The current error amplifier circuit EI amplifies the error between the welding current setting signal Ir(+) and the welding current detection signal Id(-) and outputs a current error amplification signal Ei. The drive circuit DV receives the current error amplification signal Ei and an activation signal On from the robot control device RC (described later), and performs pulse width modulation control based on the current error amplification signal Ei when the activation signal On is high (welding starts) and outputs a drive signal Dv for driving the inverter circuit in the power control circuit MC, but does not output the drive signal Dv when the activation signal On is low (welding stops).

[0027] The first early period setting circuit TA1R outputs a predetermined first early period setting signal Ta1r. The second early period setting circuit TA2R outputs a predetermined second early period setting signal Ta2r. The third early period setting circuit TA3R outputs a predetermined third early period setting signal Ta3r. The fourth early period setting circuit TA4R outputs a predetermined fourth early period setting signal Ta4r.

[0028] The feeding speed setting circuit FR receives the forward feed peak value setting signal Wsr, the reverse feed peak value setting signal Wrr, the timer signal Tm, the first early period setting signal Ta1r, the second early period setting signal Ta2r, the third early period setting signal Ta3r, and the fourth early period setting signal Ta4r as inputs, performs the following processes 1) and 2), and outputs a feeding speed setting signal Fr. 1) When the period (Tpr-Ta2r) has elapsed since the timer signal changed to Tm=2 (peak period), the value of the forward feed peak value setting signal Wsr starts to change to the value of the reverse feed peak value setting signal Wrr, and when the period (Tkr-Ta4r) has elapsed since the timer signal changed to Tm=3 (peak fall period), the feed speed setting signal Fr is output, which becomes the value of the reverse feed peak value setting signal Wrr. 2) When the period (Tbr-Ta1r) has elapsed since the timer signal changed to Tm=4 (base period), the value of the reverse feed peak value setting signal Wrr starts to change to the value of the forward feed peak value setting signal Wsr, and when the period (Tur-Ta3r) has elapsed since the timer signal changed to Tm=1 (peak rise period), the feed speed setting signal Fr is output, which becomes the value of the forward feed peak value setting signal Wsr.

[0029] The feed control circuit FC receives as input the feed speed setting signal Fr and a start signal On from the robot control device RC described later, and outputs a feed control signal Fc to the feed motor WM for feeding the welding wire 1 at the value of the feed speed setting signal Fr when the start signal On is at a high level (welding start), and outputs a feed control signal Fc to the feed motor WM for stopping feeding when the start signal On is at a low level.

[0030] The robot control device RC moves a robot (not shown) in accordance with a pre-taught work program, and outputs a start signal On to command the start or stop of welding.

[0031] 2 is a timing chart of signals in the welding device of FIG. 1, illustrating a pulse arc welding control method according to an embodiment of the present invention. (A) in FIG. 2 shows the change over time in welding current Iw, (B) in FIG. 2 shows the change over time in welding voltage Vw, and (C) in FIG. 2 shows the change over time in welding wire feed speed Fw. The operation of each signal will be explained below with reference to the diagram.

[0032] The feed speed Fw shown in Figure 1(C) indicates a forward feed state in which the material is fed forward in a direction toward the base material when it is a positive value above 0, and a reverse feed state in which the material is fed backward in a direction away from the base material when it is a negative value below 0.

[0033] During a predetermined peak rise period Tu from time t1 to t2, as shown in FIG. 1A, a peak rise current Iu is supplied, which rises from a base current Ib that is current modulation controlled to a peak current Ip that is current modulation controlled, and as shown in FIG. 1B, a peak rise voltage that rises from a base voltage Vb to a peak voltage Vp is applied between the welding wire and the base metal.

[0034] As shown in FIG. 1C, the feed speed Fw starts to change from the reverse feed peak value Wr to the forward feed peak value Ws at a time period determined by the first early period setting signal Ta1r before the start of the peak rise period Tu at time t1. Then, the feed speed Fw reaches the forward feed peak value Ws at a time period determined by the third early period setting signal Ta3r before the end of the peak rise period Tu at time t2, and maintains that value. The values ​​of the first early period setting signal Ta1r and the third early period setting signal Ta3r are set to values ​​between 0.2 ms and 1 ms, more preferably between 0.5 ms and 0.8 ms. The peak rise period Tu is set by the peak rise period setting signal Tur of FIG. 1. The base current Ib is set by the base current setting signal Ibr of FIG. 1. The peak current Ip is set by the peak current setting signal Ipr of FIG. 1. The reverse feed peak value Wr is set by the reverse feed peak value setting signal Wrr of FIG. 1. The forward transmission peak value Ws is set by the forward transmission peak value setting signal Wsr in FIG.

[0035] During a predetermined peak period Tp from time t2 to t3, a peak current Ip that is modulated and controlled flows as shown in (A) of the figure, and a peak voltage Vp is applied between the welding wire and the base metal as shown in (B) of the figure. The peak period Tp is set by a peak period setting signal Tpr in FIG.

[0036] During a predetermined peak fall period Tk from time t3 to time t4, as shown in FIG. 1A, a peak fall current Ik is supplied, decreasing from a peak current Ip, which is modulated by current modulation, to a base current Ib, which is modulated by current modulation. As shown in FIG. 1B, a peak fall voltage, which decreases from a peak voltage Vp to a base voltage Vb, is applied between the welding wire and the base metal. As shown in FIG. 1C, the feed speed Fw starts to change from a forward feed peak value Ws to a reverse feed peak value Wr at a time period determined by the second early period setting signal Ta2r before the start of the peak fall period Tk at time t3. Then, the feed speed Fw reaches and maintains the reverse feed peak value Wr at a time period determined by the fourth early period setting signal Ta4r before the end of the peak fall period Tk at time t4. The values ​​of the second early period setting signal Ta2r and the fourth early period setting signal Ta4r are set to values ​​between 0.2 ms and 1 ms. More preferably, it is set to a value between 0.5 ms and 0.8 ms. The peak falling period Tk is set by the peak falling period setting signal Tkr in FIG.

[0037] During a predetermined base period Tb from time t4 to t5, a base current Ib that is modulated and controlled flows as shown in (A) of the figure, and a base voltage Vb is applied between the welding wire and the base metal as shown in (B) of the figure. The base period Tb is set by a base period setting signal Tbr of FIG.

[0038] The pulse frequency Pf, which is the reciprocal of the pulse period from time t1 to time t5, is set by the pulse frequency setting signal Pfr in FIG. 1 as follows: 1) or 2). 1) It is set in the range of 100Hz or more and 350Hz or less. 2) The welding current Iw is set within a range of ±15% of the average value.

[0039] Examples of values ​​for the above parameters are shown below: Tu=1ms, Tp=1.5ms, Tk=1ms, Pf=100-350Hz, Ip=350-450A, Ib=50-150A, Ws=50m / min, Wr=-20m / min

[0040] The effects of this embodiment will be described below. According to this embodiment, a pulse arc welding control method includes feeding a welding wire, supplying a peak rise current that increases from a base current value to a peak current value during a peak rise period, supplying the peak current during the peak period, supplying a peak fall current that decreases from the peak current value to the base current value during a peak fall period, and supplying the base current during the base period, and repeating these welding currents as one pulse period. In this method, the welding wire feed speed starts to change from a reverse feed peak value to a forward feed peak value at a time point a first early period before the start of the peak rise period, reaches the forward feed peak value at a time point before the end of the peak rise period, starts to change from the forward feed peak value to the reverse feed peak value at a time point a second early period before the start of the peak fall period, and reaches the reverse feed peak value at a time point before the end of the peak fall period. A droplet is formed at the tip of the welding wire by supplying the peak current during the peak period. During the subsequent base period, the welding wire is fed backward, allowing an upward force to be continuously applied to the droplets throughout the base period, thereby ensuring droplet transfer to the weld pool. Furthermore, the feed rate starts changing from the reverse feed peak value to the forward feed peak value at a point in time equal to the first early period before the start of the peak rise period, and is changed to the forward feed peak value at a point in time equal to the end of the peak rise period. This allows the feed rate to converge to the forward feed peak value at the start of the peak period, thereby enabling droplets of appropriate size to be formed during the peak period. Furthermore, the feed rate starts changing from the forward feed peak value to the reverse feed peak value at a point in time equal to the second early period before the start of the peak fall period, and is changed to the reverse feed peak value at a point in time equal to the end of the peak fall period. This allows the reverse feed peak value to be reached at the start of the base period, allowing a strong upward force to be applied to the droplets, ensuring droplet transfer and achieving a one-droplet-per-pulse-cycle transfer state. As a result, even if the welding condition fluctuates, the one droplet per pulse period state can always be maintained, thereby achieving good welding quality.

[0041] More preferably, in this embodiment, the first early period and the second early period are set to a value between 0.2 ms and 1 ms. If the period is shorter than 0.2 ms, the convergence of the feed speed may lag behind the convergence of the welding current, which may adversely affect the formation and detachment of droplets. If the period is longer than 1 ms, the difference between the change in the feed speed and the change in the welding current may become too great, which may adversely affect the formation and detachment of droplets.

[0042] More preferably, according to this embodiment, the pulse frequency, which is the reciprocal of the pulse period, is set within a range of ±15% of the average value of the welding current. That is, when the average value of the welding current is 100 A, the pulse frequency is set within a range of 100 Hz ±15%, when it is 150 A, the pulse frequency is set within a range of 150 Hz ±15%, and when it is 200 A, the pulse frequency is set within a range of 200 Hz ±15%. The feed rate is determined by the average value of the welding current. In current modulation control, the pulse frequency can be set independently of the average value of the welding current. For example, when the average value of the welding current is 200 A, the pulse frequency can be set to 100 Hz, 200 Hz, or 300 Hz. However, since the welding wire feed rate is determined by the average value of the welding current, the size of the droplets transferred per pulse cycle varies depending on the pulse frequency. A pulse frequency of 100 Hz results in droplets that are too large, while a pulse frequency of 300 Hz results in droplets that are too small. A pulse frequency of 200 Hz results in droplets that are the appropriate size. This requires that the pulse period be constant through current modulation control, and that the welding wire be fed forward and backward to reliably maintain one droplet transfer per pulse period. Experiments have shown that in order to consistently maintain the appropriate droplet size, it is sufficient to set the pulse frequency within ±15% of the average value of the welding current. In this way, the size of the droplets transferred during one pulse period can be more appropriately adjusted in accordance with the average value of the welding current, thereby improving welding quality.

[0043] More preferably, according to this embodiment, the arc length control is performed by modulating at least the peak current. Arc length control methods include current modulation control, which modulates at least the peak current according to this embodiment, frequency modulation control, which modulates the pulse frequency, and pulse width modulation control, which modulates the peak period. Frequency modulation control changes the base period of reverse feed, which results in a change in the average feed rate. Pulse width modulation control changes the peak period of forward feed, which results in a change in the average feed rate. Therefore, except for current modulation control, the pulse period changes from moment to moment, which causes the average feed rate to fluctuate accordingly. Therefore, in forward / reverse feed control, which repeatedly feeds the welding wire forward and backward, current modulation control is required to maintain a constant average feed rate. In this way, this embodiment can prevent fluctuations in the average feed rate, which can result in fluctuations in the bead appearance and penetration shape. [Explanation of symbols]

[0044] 1: welding wire, 2: base material, 3: arc, 4: welding torch, 5: feed roll, DV: drive circuit, Dv: drive signal, EI: current error amplifier circuit, Ei: current error amplifier signal, EV: voltage error amplifier circuit, Ev: voltage error amplifier signal, FC: feed control circuit, Fc: feed control signal, FR: feed speed setting circuit, Fr: feed speed setting signal, Fw: feed speed, Ib: base current, Ibr: base current setting signal, IC: current modulation circuit, ID: welding current detection circuit, Id: welding current detection signal, Ik: peak / fall current, Ip: peak current, Ipr: peak current setting signal, IR: welding current setting circuit, Ir: welding current setting signal, Iu: peak rise current, Iw: welding current, MC: power control circuit, On: start signal, Pf: pulse frequency, PFR: pulse frequency setting circuit, Pfr: pulse frequency setting signal, PS: welding power source, RC: robot control device, TA1R: first early period setting circuit, Ta1r: first early period setting signal, TA2R: second early period setting circuit, Ta2r: second early period setting signal, TA3R : Third early period setting circuit, Ta3r: Third early period setting signal, TA4R: Fourth early period setting circuit, Ta4r: Fourth early period setting signal, Tb: Base period, TBR: Base period setting circuit, Tbr: Base period setting signal, Tk: Peak falling period, TKR: Peak falling period setting circuit, Tkr: Peak falling period setting signal, Tm: Timer signal, Tp: Peak period, TPR: Peak period setting circuit, Tpr: Peak period setting signal, Tu: Peak rising period, TUR: Peak rising period setting circuit , Tur: Peak rise period setting signal, VAV: Welding voltage averaging circuit, Vav: Welding voltage average value signal, Vb: Base voltage, VD: Welding voltage detection circuit, Vd: Welding voltage detection signal, Vp: Peak voltage, VR: Welding voltage setting circuit, Vr: Welding voltage setting signal, Vw: Welding voltage, WL: Reactor, WM: Feed motor, Wr: Reverse feed peak value, WRR: Reverse feed peak value setting circuit, Wrr: Reverse feed peak value setting signal, Ws: Forward feed peak value, WSR: Forward feed peak value setting circuit, Wsr: Forward feed peak value setting signal

Claims

1. 1. A pulse arc welding control method for welding, comprising: feeding a welding wire; supplying a peak rise current that rises from a base current value to a peak current value during a peak rise period; supplying the peak current during the peak period; supplying a peak fall current that falls from the peak current value to the base current value during a peak fall period; and supplying the base current during the base period; and repeating the supply of these welding currents as one pulse period, the welding wire feed speed starts to change from a reverse feed peak value to a forward feed peak value at a time point a first early period before a start of the peak rise period, changes to the forward feed peak value at a time point before an end of the peak rise period, starts to change from the forward feed peak value to the reverse feed peak value at a time point a second early period before a start of the peak fall period, and changes to the reverse feed peak value at a time point before an end of the peak fall period.

2. 2. The pulse arc welding control method according to claim 1, wherein the first early period and the second early period are set to values ​​of 0.2 ms to 1 ms.

3. 3. The pulse arc welding control method according to claim 2, wherein the pulse frequency, which is the reciprocal of the pulse period, is set within a range of ±15% of the average value of the welding current.

4. 4. The pulse arc welding control method according to claim 1, wherein the arc length is controlled by modulating at least the peak current.

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