Pulse-arc welding control method

Abstract

To obtain an excellent welding quality by regularly maintaining a one-pulse period one droplet transfer state even when a welding state varies, in consumable electrode pulse-arc welding.SOLUTION: In a pulse-arc welding control method, in which a welding wire is fed, peak rising currents which increase from a value of base currents to a value of peak currents are distributed in a peak rising period of time, the peak currents are distributed in a peak period of time, peak falling currents, which fall from the value of the peak currents to the value of the base currents, are distributed in a peak falling period of time, the base currents are distributed in a base period of time, and the welding currents Iw are repeatedly distributed in a first pulse period to perform welding, the welding wire is repeatedly fed forward and fed backward at feeding speed Fw, where the wire is fed backward at least in the base period of time of t4-t5 and pulse frequencies that are reciprocals of a pulse period of times of t1-t5 are set in a range of 100 Hz or more and 350 Hz or less.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 period state even if the welding condition fluctuates, thereby obtaining good welding quality. [Means for solving the problem]

[0007] A pulse arc welding control method provided 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 a base period, and repeating these welding currents as one pulse period, wherein the welding wire is repeatedly fed forward and backward, the backward feed is performed at least during the base period, and a pulse frequency, which is the reciprocal of the pulse period, is set in a range of 100 Hz to 350 Hz.

[0008] As an example, the pulse arc welding control method of the present invention is characterized in that the pulse frequency is set within a range of ±15% of the average value of the welding current.

[0009] As an example, the welding wire feed speed starts to change from a reverse feed peak value to a forward feed peak value at the start of the peak rise period, and starts to change from the forward feed peak value to the reverse feed peak value at the start of the peak fall period.

[0010] As an example, the period during which the peak value changes from the forward transmission peak value to the backward transmission peak value is 40% or more and 90% or less of the peak falling period.

[0011] As an example, the arc length is controlled by modulating at least the peak current. [Effects of the Invention]

[0012] 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]

[0013] [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

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

[0015] 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.

[0016] The welding power source PS consists of the following blocks:

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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%.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 PWM 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).

[0028] The rising transition period setting circuit TFUR outputs a predetermined rising transition period setting signal Tfur. The value of the rising transition period setting signal Tfur is set to a value between 40% and 90% of the peak rising transition period setting signal Tur, and more preferably, to a value between 50% and 80%.

[0029] The falling transition period setting circuit TFKR outputs a predetermined falling transition period setting signal Tfkr. The value of the falling transition period setting signal Tfkr is set to a value between 40% and 90% of the peak falling transition period setting signal Tkr, and more preferably, to a value between 50% and 80%.

[0030] The feeding speed setting circuit FR receives the forward feeding peak value setting signal Wsr, the reverse feeding peak value setting signal Wrr, the timer signal Tm, the rising change period setting signal Tfur, and the falling change period setting signal Tfkr as inputs, performs the following processing, and outputs a feeding speed setting signal Fr. 1) During the rising change period Tfu determined by the rising change period setting signal Tfur from the start of the peak rising period Tu of the timer signal Tm=1, the feeding speed setting signal Fr that changes from the value of the reverse feeding peak value setting signal Wrr to the value of the forward feeding peak value setting signal Wsr is output. 2) Subsequently, the forward feed peak value setting signal Wsr is output as the feed speed setting signal Fr. 3) Subsequently, during the falling change period Tfk determined by the falling change period setting signal Tfkr from the start of the peak falling period Tk of the timer signal Tm=3, the feeding speed setting signal Fr is output, which changes from the value of the forward feed peak value setting signal Wsr to the value of the reverse feed peak value setting signal Wrr. 4) Subsequently, the reverse feed peak value setting signal Wrr is output as the feed speed setting signal Fr. 5) Repeat steps 1) to 4) above.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 increases from a base current Ib, which is subjected to current modulation control, to a peak current Ip, which is also subjected to current modulation control. As shown in FIG. 1B, a peak rise voltage, which increases from a base voltage Vb to a peak voltage Vp, is applied between the welding wire and the base metal. During a predetermined rise change period Tfu from time t1 to t11, as shown in FIG. 1C, the feed speed Fw changes from a reverse feed peak value Wr to a forward feed peak value Ws. The start of the rise change period Tfu is synchronized with the start of the peak rise period Tu. The rise change period Tfu is a period from 40% to 90% of the peak rise period Tu. More preferably, it is a period from 50% to 80%. 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 rising change period Tfu is set by the rising change period setting signal Tfur of FIG. 1. The reverse transmission peak value Wr is set by the reverse transmission 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 of FIG. 1.

[0036] During a predetermined peak period Tp from time t2 to t3, as shown in FIG. 1(A), a peak current Ip is supplied by current modulation control, and as shown in FIG. 1(B), a peak voltage Vp is applied between the welding wire and the base metal. During the period from time t11 to t3, as shown in FIG. 1(C), the feed rate Fw is equal to the forward feed peak value Ws. The peak period Tp is set by the peak period setting signal Tpr in FIG. 1.

[0037] During a predetermined peak fall period Tk from time t3 to t4, as shown in FIG. 1A, a peak fall current Ik is supplied, decreasing from a peak current Ip under current modulation control to a base current Ib under current modulation control. As shown in FIG. 1B, a peak fall voltage Vp decreases from a peak voltage Vp to a base voltage Vb, and is applied between the welding wire and the base metal. During a predetermined fall change period Tfk from time t3 to t31, as shown in FIG. 1C, the feed speed Fw changes from a forward feed peak value Ws to a reverse feed peak value Wr. The start of the fall change period Tfk is synchronized with the start of the peak fall period Tk. The fall change period Tfk is a period of 40% to 90% of the peak fall period Tk, and more preferably, a period of 50% to 80%. The peak fall period Tk is set by the peak fall period setting signal Tkr shown in FIG. 1. The falling transition period Tfk is set by the falling transition period setting signal Tfkr in FIG.

[0038] During a predetermined base period Tb from time t4 to t5, as shown in FIG. 1(A), a base current Ib that is current modulation controlled is supplied, and as shown in FIG. 1(B), a base voltage Vb is applied between the welding wire and the base metal. During the period from time t31 to t5, as shown in FIG. 1(C), the feed speed Fw is equal to the reverse feed peak value Wr. Therefore, the welding wire is fed in reverse at least during the base period Tb. The base period Tb is set by the base period setting signal Tbr in FIG. 1.

[0039] 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 to 350Hz. 2) The welding current Iw is set within a range of ±15% of the average value.

[0040] Numerical examples of the above parameters are shown below. Tu=1ms, Tp=1.5ms, Tk=1ms, Pf=100~350Hz Ip=350~450A, Ib=50~150A Tfu=0.4~0.9ms, Tfk=0.4~0.9ms Ws=50m / min, Wr=-20m / min

[0041] The effects of this embodiment are described below. According to this embodiment, a pulse arc welding control method includes 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 a 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 a base current during a base period. These welding currents are repeated as one pulse period. In this method, the welding wire is fed forward and backward repeatedly, and is fed backward at least during the base period. A pulse frequency, which is the reciprocal of the pulse period, is set in the range of 100 Hz to 350 Hz. A droplet is formed at the tip of the welding wire by passing the peak current during the peak period. By feeding the welding wire backward during the following base period, an upward force is continuously applied to the droplet throughout the base period, thereby ensuring that the droplet is transferred to the molten pool. As a result, even if the welding condition fluctuates, a one-pulse-period, one-droplet-transfer state can be consistently maintained, resulting in excellent welding quality. Furthermore, by setting the pulse frequency in the range of 100 Hz to 350 Hz, the size of the droplets transferred during one pulse period can be made appropriate, thereby improving the welding quality.

[0042] More preferably, according to this embodiment, the pulse frequency 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 the average value of the welding current is 150 A, the pulse frequency is set within a range of 150 Hz ±15%, and when the average value of the welding current 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 an appropriate droplet 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 welding wire feed speed starts changing from the reverse feed peak value to the forward feed peak value at the start of the peak rise period, and starts changing from the forward feed peak value to the reverse feed peak value at the start of the peak fall period. By synchronizing the start of the peak rise period with the start of the change from the reverse feed peak value to the forward feed peak value, droplets of appropriate size can be reliably formed during the peak period. Furthermore, by synchronizing the start of the peak fall period with the start of the change from the forward feed peak value to the reverse feed peak value, a strong upward force can be applied to the droplets, making it possible to more reliably maintain a one-droplet-per-pulse-cycle state.

[0044] More preferably, according to this embodiment, the change period from the forward feed peak value to the reverse feed peak value is 40% to 90% of the peak fall period. By setting the period to 90% or less and increasing the rate of change of the feed speed, the upward force acting on the droplets can be further strengthened, and the one droplet transfer state per one pulse period can be more reliably maintained. The reason for setting it to 40% or more is that if the rate of change of the feed speed is too large, the feed state becomes unstable.

[0045] 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]

[0046] 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, Tb: Base period, TBR: Base period setting circuit, Tbr: Base period setting signal, Tfk: Fall change period, T FKR: Falling transition period setting circuit, Tfkr: Falling transition period setting signal, Tfu: Rising transition period, TFUR: Rising transition period setting circuit, Tfur: Rising transition 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 rising 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, a pulse frequency, which is the reciprocal of the pulse period, set in a range of 100 Hz to 350 Hz.

2. 2. The pulse arc welding control method according to claim 1, wherein the pulse frequency is set within a range of ±15% of the average value of the welding current.

3. 3. The pulse arc welding control method according to claim 1, wherein the welding wire feed speed starts to change from a reverse feed peak value to a forward feed peak value at a start of the peak rise period, and starts to change from the forward feed peak value to the reverse feed peak value at a start of the peak fall period.

4. 4. The pulse arc welding control method according to claim 3, wherein a period during which the pulse changes from the forward feed peak value to the reverse feed peak value is 40% or more and 90% or less of the peak fall period.

5. 4. The pulse arc welding control method according to claim 3, wherein the arc length is controlled by modulating at least the peak current.

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