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 rise 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, feeding speed Fw of the welding wire is set to a forward feeding value in an initial period of time after arc-start at times of t2-t4, the feeding speed Fw is switched between a forward feeding peak value and a backward feeding peak value in a regular period of time after the initial period ends at the time of t4 and the feeding speed is set to the backward feeding peak value in the base period of times of t7-t8.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 state 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 fed in a forward direction during an initial period after arc start, and the forward and reverse feeds of the welding wire are repeated during a steady period after the initial period ends, and the welding wire is fed in a reverse direction at least during the base period.

[0008] As an example, the pulse arc welding control method of the present invention is characterized in that the value of the peak current during the initial period is greater than the value of the peak current during the steady period.

[0009] As an example, the pulse arc welding control method of the present invention is characterized in that an average value of the welding wire feed rate during the steady period is set to a value equal to the feed rate during the initial period.

[0010] As an example, the pulse arc welding control method of the present invention is characterized in that the feed speed during the steady period 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.

[0011] As an example, the pulse arc welding control method of the present invention is characterized in that the change period 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. [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 current detection circuit ID detects the welding current Iw and outputs a welding current detection signal Id.

[0021] The hot start period circuit STH receives the welding current detection signal Id as input, and when the value of the welding current detection signal Id reaches or exceeds the current flow determination value (approximately 10 A), determines that an arc start has begun and outputs a hot start period signal Sth that goes to a high level, and then returns to a low level after a predetermined hot start period has elapsed.

[0022] The initial period circuit STI receives the welding current detection signal Id as input, and when the value of the welding current detection signal Id reaches or exceeds the current flow determination value (approximately 10 A), determines that an arc start has begun and outputs an initial period signal Sti that goes to a high level, and then returns to a low level after a predetermined initial period has elapsed.

[0023] The hot start period current setting circuit IHR receives the hot start period signal Sth as an input, and outputs a hot start period current setting signal Ihr which becomes a predetermined hot start peak current value when the hot start period signal Sth changes to a high level, and which becomes a predetermined hot start base current value when the predetermined hot start peak period has elapsed.

[0024] 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.

[0025] The welding voltage setting circuit VR receives the initial period signal Sti as an input and outputs a welding voltage setting signal Vr that is a predetermined first welding voltage set value when the initial period signal Sti is at a high level (initial period) and a predetermined second welding voltage set value when the initial period signal Sti is at a low level (steady period). Here, the first welding voltage set value is greater than the second welding voltage set value.

[0026] The voltage error amplifier 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 amplified signal Ev.

[0027] 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.

[0028] 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.

[0029] 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%.

[0030] 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.

[0031] 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.

[0032] The current control setting circuit ICR receives the hot start period current setting signal Ihr, the welding current setting signal Ir, and the hot start period signal Sth as inputs, and outputs the hot start period current setting signal Ihr as the current control setting signal Icr when the hot start period signal Sth is at a high level, and outputs the welding current setting signal Ir as the current control setting signal Icr when the hot start period signal Sth is at a low level.

[0033] The current error amplifier circuit EI amplifies the error between the current control setting signal Icr(+) and the welding current detection signal Id(-) and outputs a current error amplified signal Ei. The drive circuit DV receives this current error amplified signal Ei and an activation signal On from a robot control device RC (described later), and performs PWM modulation control based on the current error amplified signal Ei when the activation signal On is at a high level (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 at a low level (welding stops).

[0034] 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.

[0035] 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%.

[0036] 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%.

[0037] The initial period feed rate setting circuit FIR outputs an initial period feed rate setting signal Fir having a predetermined positive value.

[0038] 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.

[0039] The feed speed control setting circuit FCR receives the above-mentioned initial period feed speed setting signal Fir, the above-mentioned feed speed setting signal Fr, the above-mentioned initial period signal Sti, and a start signal On described later, performs the following processing, and outputs the feed speed control setting signal Fcr. 1) When the start signal On becomes high level, a feed speed control setting signal Fcr is output, which becomes a predetermined slow-down feed speed. 2) After that, when the initial period signal Sti becomes high level, the initial period feed speed setting signal Fir is output as the feed speed control setting signal Fcr. 3) After that, when the initial period signal Sti becomes low level, the feed speed setting signal Fr is output as the feed speed control setting signal Fcr.

[0040] The feed control circuit FC receives as input the feed speed control setting signal Fcr and a start signal On from the robot control device RC, which will be 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 control setting signal Fcr 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.

[0041] The robot control device RC moves a robot (not shown) in accordance with a work program that has been taught to it in advance, and outputs a start signal On that commands the start or stop of welding.

[0042] 2 is a timing chart of each signal in the welding apparatus 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 the welding current Iw, (B) in FIG. 2 shows the change over time in the welding voltage Vw, and (C) in FIG. 2 shows the change over time in the welding wire feed rate Fw. Note that the vertical and horizontal axes of the timing charts in each figure have been appropriately enlarged or reduced for ease of understanding, and the waveforms shown have been simplified, exaggerated, or emphasized for ease of understanding. The operation of each signal will now be described with reference to the figures.

[0043] The feed speed Fw shown in Figure 1(C) indicates a forward feed state in which the material is fed forward in the 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 the direction away from the base material when it is a negative value below 0.

[0044] (1) Operation during the slow-down feeding period from time t1 to time t2 At time t1, when the start signal On in FIG. 1 changes to a high level, welding begins. In response to this, as shown in FIG. 1(B), the welding voltage Vw becomes a no-load voltage value, which is a maximum voltage value of about 80 V. As shown in FIG. 1(C), the feed speed Fw becomes a slow, predetermined slow-down feed speed of about 1 m / min, and the welding wire is fed forward. As shown in FIG. 1(A), the welding current Iw is not flowing and is 0 A.

[0045] (2) Operation during the hot start period from time t2 to t3 At time t2, an arc is generated when the tip of the welding wire contacts the base metal, and the arc start begins. As shown in Figure 1(A), a predetermined hot start peak current is applied during a predetermined hot start peak period from time t2 to t21. Thereafter, a predetermined hot start base current is applied during a predetermined hot start base period from time t21 to t3. As shown in Figure 1(B), the welding voltage Vw reaches an arc voltage value of several tens of volts during the period from time t2 to t21, and then reaches an arc voltage value lower than the previous period during the period from time t21 to t3. As shown in Figure 1(C), the feed speed Fw accelerates to the value of the initial period feed speed setting signal Fir in Figure 1. By applying a high hot start peak current, an arc is generated instantly when the tip of the welding wire contacts the base metal, and the arc length is increased to the appropriate value. The hot start peak period is set to approximately 10 ms, and the hot start peak current is set to approximately 500 A. The hot start base period is set to about 10 ms, and the hot start base current is set to about 50 A.

[0046] (3) Operation during the initial period from time t2 to time t4 From time t3, during a peak rise period Tu, as shown in FIG. 1A, a peak rise current Iu is supplied, which increases from a base current Ib that is subject to current modulation control to a peak current Ip that is subject to current modulation control, and as shown in FIG. 1B, a peak rise voltage is applied between the welding wire and the base metal, which increases from a base voltage Vb to a peak voltage Vp. Subsequently, during a peak period Tp, as shown in FIG. 1A, a peak current Ip is supplied, which is subject to current modulation control, and as shown in FIG. 1B, a peak voltage Vp is applied between the welding wire and the base metal. Subsequently, during a peak fall period Tk, as shown in FIG. 1A, a peak fall current Ik is supplied, which decreases from a peak current Ip that is subject to current modulation control to a base current Ib that is subject to current modulation control, and as shown in FIG. 1B, a peak fall voltage is applied between the welding wire and the base metal. Subsequently, during the base period Tb, as shown in FIG. 1(A), a base current Ib is supplied, which is modulated, and as shown in FIG. 1(B), a base voltage Vb is applied between the welding wire and the base metal. The peak current Ip and base current Ib are modulated so that the average value of the welding voltage Vw is equal to the predetermined value of the welding voltage setting signal Vr in FIG. 1. This allows arc length control to maintain the arc length at an appropriate value. As shown in FIG. 1(C), the feed rate Fw during the initial period from time t2 to t4 is the value of the initial period feed rate setting signal Fir in FIG. 1, and the welding wire is fed forward at a constant feed rate. The initial period is the period during which the welding state transitions from a transient state after arc start to a steady state, and is set to approximately 50 to 200 ms. In FIG. 1(B), two cycles of the current waveform are depicted during the period from time t3 to t4, but in reality, approximately 10 to 40 cycles are included. The peak rise period Tu is set by the peak rise period setting signal Tur in FIG. 1. The peak period Tp is set by the peak period setting signal Tpr in FIG. 1. The peak fall period Tk is set by the peak fall period setting signal Tkr in FIG. 1. The base period Tb is set by the base period setting signal Tbr in FIG. 1. The peak current Ip is set by the peak current setting signal Ipr in FIG. 1. The base current Ib is set by the base current setting signal Ibr in FIG. 1.

[0047] (4) Operation during the steady state period after time t4 When the initial period ends at time t4, during a predetermined peak rise period Tu from time t4 to t5, 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 t4 to t41, as shown in FIG. 1C, the feed speed Fw changes from a positive value of the initial period feed speed (reverse feed peak value Wr from the next cycle onward) 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 rising transition period Tfu is set by the rising transition period setting signal Tfur in Fig. 1. The backward transmission peak value Wr is set by the backward transmission peak value setting signal Wrr in Fig. 1. The forward transmission peak value Ws is set by the forward transmission peak value setting signal Wsr in Fig. 1.

[0048] During a predetermined peak period Tp from time t5 to t6, as shown in Fig. 1A, a peak current Ip is supplied by current modulation control, and as shown in Fig. 1B, a peak voltage Vp is applied between the welding wire and the base metal. During the period from time t41 to t6, as shown in Fig. 1C, the feed speed Fw is equal to the forward feed peak value Ws.

[0049] During a predetermined peak fall period Tk from time t6 to t7, 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. During a predetermined fall change period Tfk from time t6 to t61, 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 fall change period Tfk is set by the fall change period setting signal Tfkr of FIG. 1.

[0050] During a predetermined base period Tb from time t7 to t8, as shown in (A) of the figure, a base current Ib that is current modulation controlled is supplied, and as shown in (B) of the figure, a base voltage Vb is applied between the welding wire and the base metal. During the period from time t61 to t8, as shown in (C) of the figure, the feeding speed Fw is equal to the reverse feeding peak value Wr. Therefore, the welding wire is fed in the reverse direction at least during the base period Tb.

[0051] The pulse frequency Pf, which is the reciprocal of the pulse period from time t4 to t8 in the steady period after the initial period ends, 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.

[0052] Numerical examples of the above parameters are shown below. Tu=1ms, Tp=1.5ms, Tk=1ms, Pf=100~350Hz Ip (initial period) = 450 to 550 A, Ip (steady state period) = 350 to 450 A Ib=50~150A Tfu=0.4~0.9ms, Tfk=0.4~0.9ms Fir=8m / min, Ws=50m / min, Wr=-20m / min

[0053] 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 increases from a base current value to a peak current value during a peak rise period, passing a peak current during a peak period, passing a peak fall current that decreases 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 cycle. In this method, the welding wire is fed forward during an initial period after arc start, and the welding wire is fed forward and backward repeatedly during a steady period after the initial period ends, with the welding wire being fed backward at least during the base period. During the steady period after the initial period ends, a droplet is formed at the tip of the welding wire by the peak current fed during the peak period. By feeding the welding wire backward during the subsequent base period, an upward force is continuously applied to the droplet throughout the base period, thereby ensuring reliable droplet transfer to the weld pool. As a result, even if the welding condition fluctuates, a one-droplet-per-pulse-cycle transfer state can be consistently maintained, thereby achieving good welding quality. Furthermore, in this embodiment, the welding wire is fed in the forward direction during the initial period after the arc starts. During the initial period, the welding state is in a transitional state after the arc starts. Therefore, if the welding wire is fed in the forward direction and in the reverse direction repeatedly, the welding state may become unstable. For this reason, by feeding the welding wire in the forward direction at a constant feed rate during the initial period, it is possible to prevent the welding state from becoming unstable.

[0054] More preferably, according to this embodiment, the peak current value during the initial period is greater than the peak current value during the steady period. During the initial period, the welding state is in a transient state after arc start, so by setting the peak current value to a value greater than that during the steady period, a one-pulse-cycle, one-droplet-transfer state can be reliably achieved. To set the peak current value during the initial period to a value greater than that during the steady period, the value of the welding voltage setting signal Vr in FIG. 1 is set to a value greater during the initial period than that during the steady period. In this way, the peak current value during the initial period can be set to a value greater than that during the steady period by current modulation control.

[0055] More preferably, according to this embodiment, the average value of the welding wire feed rate during the steady period is set to a value equal to the feed rate during the initial period. In this way, the wire deposition amount can be made equal between the initial period and the steady period, thereby making the bead appearance uniform. In order to make the average value of the feed rate during the steady period equal to the feed rate during the initial period, the forward feed peak value and / or the reverse phase peak value may be adjusted.

[0056] More preferably, according to this embodiment, the welding wire feed speed during the steady period starts to change from the reverse feed peak value to the 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. 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, it is possible to reliably form a droplet of an appropriate size 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 droplet, thereby reliably detaching the droplet and transferring it to the molten pool.

[0057] More preferably, in this embodiment, the change period from the forward feed peak to the reverse feed peak is 40% to 90% of the peak fall period. By increasing the rate of change of the feed speed by setting the period to 90% or less, the upward force acting on the droplet can be further strengthened, thereby more reliably separating the droplet and transferring it to the molten pool. The reason for setting the period to 40% or more is that if the rate of change of the feed speed is too large, the feed state becomes unstable.

[0058] 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.

[0059] More preferably, according to this embodiment, arc length control is performed by modulating at least the peak current during the steady period. 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, resulting in a change in the average feed rate. Pulse width modulation control changes the peak period of forward feed, resulting in a change in the average feed rate. Therefore, except for current modulation control, the pulse period changes from moment to moment, resulting in a corresponding change in the average feed rate. 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. This configuration, according to this embodiment, can prevent fluctuations in the average feed rate, which can result in variations in the bead appearance and penetration shape. [Explanation of symbols]

[0060] 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, FCR: feed speed control setting circuit, Fcr: feed speed control setting signal, FIR: initial period feed speed setting circuit, Fir: initial period feed speed setting 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, ICR : Current control setting circuit, Icr: Current control setting signal, ID: Welding current detection circuit, Id: Welding current detection signal, IHR: Hot start period current setting circuit, Ihr: Hot start period current setting 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, STH: Hot hot start period circuit, Sth: hot start period signal, STI: initial period circuit, Sti: initial period signal, Tb: base period, TBR: base period setting circuit, Tbr: base period setting signal, Tfk: falling edge change period, TFKR: falling edge change period setting circuit, Tfkr: falling edge change period setting signal, Tfu: rising edge change period, TFUR: rising edge change period setting circuit, Tfur: rising edge change period setting signal, Tk: peak falling edge period, TKR: peak falling edge period setting circuit, Tkr: peak falling edge period setting signal, Tm: timer signal, Tp: peak period, TPR: peak period Setting circuit, Tpr: Peak period setting signal, Tu: Peak rise period, TUR: Peak rise 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 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 arc welding control method comprising: feeding the welding wire forward during an initial period after arc start; repeating the forward and reverse feeding of the welding wire during a steady period after the initial period ends; and feeding the welding wire backward during at least the base period.

2. 2. The pulse arc welding control method according to claim 1, wherein the value of the peak current during the initial period is greater than the value of the peak current during the steady period.

3. 3. The pulse arc welding control method according to claim 2, wherein an average value of the welding wire feed speed during the steady period is set to a value equal to the feed speed during the initial period.

4. 4. The pulse arc welding control method according to claim 1, wherein the feed speed during the steady period 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.

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

Images