Method for controlling arc start in pulsed arc welding

Abstract

To improve transient responsiveness until an arc length after arc start converges to a proper value in pulsed arc welding that performs output control by current modulation control for changing peak current.SOLUTION: In a method for controlling arc start in pulsed arc welding that repeats electric conduction of peak current Ip during a peak period Tp and base current Ib during a base period Tb as one pulse period Tf and performs output control by current modulation control for changing at least the peak current Ip, output control is performed by pulse period modulation control for changing a pulse period Tf during a transitional period of time t3 to t4 after arc start, and output control is performed by current modulation control during a steady period after the time t4.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an arc start control method for pulse arc welding. [Background technology]

[0002] A consumable electrode pulsed arc welding method is widely used in which a welding wire is fed and a welding current having a peak current during a peak period and a base current during a base period as one pulse cycle is passed through to weld.

[0003] In order to perform good pulse arc welding, it is important to maintain the arc length at an appropriate value. In order to maintain the arc length at an appropriate value, the following output control is performed. The arc length is approximately proportional to the welding voltage average value. For this purpose, the welding voltage average value is detected, and output control is performed to change the welding current average value so that this detected value is equal to the welding voltage set value corresponding to the appropriate arc length. When the welding voltage average value is greater than the welding voltage set value, the arc length is longer than the appropriate value, so the welding current average value is reduced to reduce the wire melting rate and shorten the arc length. On the other hand, when the welding voltage average value is smaller than the welding voltage set value, the arc length is shorter than the appropriate value, so the welding current average value is increased to increase the wire melting rate and lengthen the arc length.

[0004] In the above, in order to change the welding current average value, at least one of the peak period, base period, peak current, and base current is changed. In particular, current modulation control, which fixes the peak period and base period to a predetermined value and changes the welding current average value by changing the peak current or the base current in addition to the peak period, has the following characteristics (see, for example, Patent Document 1). In pulse arc welding, the arc is deflected during the base period in which a base current of a small current value is passed due to a phenomenon called magnetic blow, and the welding state is likely to become unstable. In current modulation control, the base period is a fixed value and does not become a transiently long period, so the welding state is less likely to become unstable due to magnetic blow. In addition, in multi-electrode pulse arc welding, in which welding is performed while simultaneously generating arcs by placing multiple welding wires adjacent to each other, the passing of peak currents is synchronized in order to suppress instability of the welding state due to interference between the arcs. In order to achieve this synchronization, it is desirable to use current modulation control in which the peak period and the base period are constant values. Furthermore, the weldability is improved by synchronizing the weaving of the welding torch with the peak period (weaving welding), and current modulation control is also advantageous in such cases. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5429790 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in current modulation control, output control is performed by varying at least the peak current. If the peak current becomes too large, the arc force becomes strong, resulting in poor bead appearance. On the other hand, if the peak current becomes too small, droplet transfer becomes unstable, resulting in an unstable welding state. For this reason, upper and lower limits are set for the range of change in the peak current. As a result, the amount of change in the operation amount (peak current) is limited during the transient response of the feedback system, which can result in poor transient response. In particular, with current modulation control, there is a problem in that it takes a long time for the arc length to converge to an appropriate value due to poor transient response after the arc starts.

[0007] Therefore, an object of the present invention is to provide an arc start control method for pulse arc welding that can improve transient response after arc start, at least when output control is performed by current modulation control that changes the peak current. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the invention of claim 1 comprises: The peak current during the peak period and the base current during the base period are repeated as one pulse period. In a method for controlling an arc start in pulse arc welding, an output control is performed by current modulation control that changes at least the peak current, During a transient period after the arc start, the output control is performed by a pulse period modulation control that changes the pulse period. The present invention relates to a method for controlling an arc start in pulse arc welding.

[0009] The invention of claim 2 is as follows: The transition period is set to a predetermined period or a period until the change in the pulse period is converged. 2. The method for controlling an arc start in pulse arc welding according to claim 1,

[0010] The invention of claim 3 is as follows: setting the pulse period of the current modulation control to the pulse period at the end of the transient period; 3. The method for controlling an arc start in pulse arc welding according to claim 1 or 2. Effect of the Invention

[0011] According to the method for controlling an arc start in pulse arc welding according to the present invention, it is possible to improve the transient response after the arc start at least in the case where output control is performed by current modulation control that changes the peak current. [Brief description of the drawings]

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

[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 power source for carrying out an arc start control method for pulse arc welding according to an embodiment of the present invention. Each block will be described below with reference to the diagram.

[0015] The power supply main circuit PM receives a commercial power supply (not shown) such as a three-phase 200V commercial power supply, performs output control by inverter control in accordance with a drive signal Dv described below, and outputs a welding current Iw and a welding voltage Vw. Although not shown, the power supply main circuit PM includes a primary rectifier that rectifies the 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, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for arc welding, a secondary rectifier that rectifies the stepped-down high-frequency AC, and a reactor that smoothes the rectified DC.

[0016] The welding wire 1 is wound around a wire reel 1a. The welding wire 1 is fed through a welding torch 4 at a feed speed Fw by the rotation of a feed roll 5 coupled to a wire feed motor WM, and an arc 3 is generated between the welding wire 1 and a base material 2 to perform welding. A welding current Iw flows through the arc 3, and a welding voltage Vw is applied between a power feed tip (not shown) in the welding torch 4 and the base material 2.

[0017] The welding voltage detection circuit VD detects the welding voltage Vw and outputs a welding voltage detection signal Vd. The welding voltage average calculation circuit VAV receives the welding voltage detection signal Vd, averages it 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 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 amplification signal Ev.

[0018] The rising period setting circuit TUR outputs a predetermined rising period setting signal Tur. The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr. The falling period setting circuit TDR outputs a predetermined falling period setting signal Tdr.

[0019] The pulse period modulation circuit VF receives the voltage error amplified signal Ev and outputs a pulse period signal Tf having a frequency corresponding to the value of the voltage error amplified signal Ev. The pulse period signal Tf is a signal that goes to a high level for a short period of time every pulse period. This circuit changes the pulse period signal Tf so that the value of the welding voltage average signal Vav becomes equal to the value of the welding voltage setting signal Vr.

[0020] The peak current setting circuit IPR outputs a predetermined peak current setting signal Ipr, and the base current setting circuit IBR outputs a predetermined base current setting signal Ibr.

[0021] The transitional period current setting circuit ITR receives as input the pulse period signal Tf, the rise period setting signal Tur, the peak period setting signal Tpr, the fall period setting signal Tdr, the peak current setting signal Ipr, and the base current setting signal Ibr, and repeats the following processes 1) to 4) each time the pulse period signal Tf becomes High level for a short period of time, to output a transitional period current setting signal Itr having a pulsed waveform. 1) During the rising period Tu determined by the rising period setting signal Tur, a transition period current setting signal Itr that rises from the value of the base current setting signal Ibr to the value of the peak current setting signal Ipr is output. 2) Subsequently, during the peak period Tp determined by the peak period setting signal Tpr, a transition period current setting signal Itr having the value of the peak current setting signal Ipr is output. 3) Subsequently, during the falling period Td determined by the falling period setting signal Tdr, a transition period current setting signal Itr is outputted which falls from the value of the peak current setting signal Ipr to the value of the base current setting signal Ibr. 4) Subsequently, during the base period Tb until the pulse period signal Tf changes to a high level, the transition period current setting signal Itr having the value of the base current setting signal Ibr is output.

[0022] The pulse cycle setting circuit TFR receives a transitional period signal Stt (described later) as input, and outputs a pulse cycle setting signal Tfr that represents the time interval during which the pulse cycle signal Tf is at a high level for a short period of time when the transitional period signal Stt changes from a high level to a low level. This circuit sets the pulse cycle in the current modulation control to the pulse cycle at the end of the transitional period Tt.

[0023] The current modulation circuit VI receives the voltage error amplified signal Ev, the peak current setting signal Ipr, and the base current setting signal Ibr as inputs, calculates a peak current modulation signal Ipc=Ipr+∫Ev dt, limits it to a predetermined range of change and outputs it, and calculates a base current modulation signal Ibc=Ibr+∫Ev dt, limits it to a predetermined range of change and outputs it. This circuit changes the peak current modulation signal Ipc and the base current modulation signal Ibc so that the value of the welding voltage average signal Vav becomes equal to the value of the welding voltage setting signal Vr.

[0024] The steady-state period current setting circuit ICR receives as input the pulse period setting signal Tfr, the rising period setting signal Tur, the peak period setting signal Tpr, the falling period setting signal Tdr, the peak current modulation signal Ipc, and the base current modulation signal Ibc, and outputs the steady-state period current setting signal Icr having a pulsed waveform by repeating the following processes 1) to 4). 1) During the rising period Tu determined by the rising period setting signal Tur, the steady-state period current setting signal Icr that rises from the value of the base current modulation signal Ibc to the value of the peak current modulation signal Ipc is output. 2) Subsequently, during the peak period Tp determined by the peak period setting signal Tpr, the steady-state period current setting signal Icr having the value of the peak current modulation signal Ipc is output. 3) Subsequently, during the falling period Td determined by the falling period setting signal Tdr, the steady period current setting signal Icr is output, which falls from the value of the peak current modulation signal Ipc to the value of the base current modulation signal Ibc. 4) Subsequently, during the base period Tb until the time elapsed from 1) reaches the value of the pulse cycle setting signal Tfr, the steady-state period current setting signal Icr having the value of the base current modulation signal Ibc is output.

[0025] The welding start circuit ST outputs a welding start signal St that goes to a high level when starting up the welding power source. This welding start circuit ST is a torch switch attached to the welding torch 4. When a welding robot is used, the signal is output from a robot control device.

[0026] The welding current detection circuit ID detects the above welding current Iw and outputs a welding current detection signal Id. The current flow discrimination circuit CD receives the above welding current detection signal Id, and when this signal is equal to or greater than a threshold value (approximately 10 A), determines that the welding current Iw is flowing and outputs a high-level current flow discrimination signal Cd.

[0027] The hot start period circuit STH receives the current flow discrimination signal Cd as an input and outputs a hot start period signal Sth that is at a High level during a predetermined hot start period Th from the time when the current flow discrimination signal Cd changes to a High level.

[0028] The transition period circuit STT receives the hot start period signal Sth and the pulse period signal Tf as input, performs either the following process 1) or 2), and outputs a transition period signal Stt. 1) A transition period signal Stt that is at a High level is output during a transition period Tt from the time when the hot start period signal Sth changes to a Low level until a predetermined period has elapsed. The predetermined period is set in advance through experiments to a period until the arc length converges at the time of arc start. 2) A transition period signal Stt that is at a high level is output during a transition period Tt from the time when the hot start period signal Sth changes to a low level until the time interval during which the pulse period signal Tf is at a high level for a short period of time converges within a predetermined change range.

[0029] The hot start current setting circuit IHR outputs a predetermined hot start current setting signal Ihr.

[0030] The current setting circuit IR receives the welding start signal St, the hot start period signal Sth, the transient period signal Stt, the hot start current setting signal Ihr, the transient period current setting signal Itr, and the steady period current setting signal Icr as inputs, performs the following processing, and outputs a current setting signal Ir. 1) During the slow-down feed speed period from when the welding start signal St changes to high level until the hot start period signal Sth changes to low level and during the hot start period Th, the hot start current setting signal Ihr is output as the current setting signal Ir. 2) Thereafter, during the transition period Tt when the transition period signal Stt is at a high level, the transition period current setting signal Itr is output as the current setting signal Ir. 3) After that, when the transition period signal Stt becomes low level, the steady period Tc begins, and the steady period current setting signal Icr is output as the current setting signal Ir.

[0031] The current error amplifier circuit EI amplifies the error between the current setting signal Ir and the welding current detection signal Id and outputs a current error amplified signal Ei. The drive circuit DV receives the current error amplified signal Ei and the welding start signal St, and performs pulse width control when the welding start signal St is at a high level, and outputs a drive signal Dv for driving the inverter circuit of the main power supply circuit PM.

[0032] The steady-state feed speed setting circuit FCR outputs a steady-state feed speed setting signal Fcr for setting the feed speed during the steady period.

[0033] The feed speed setting circuit FR receives the welding start signal St, the current flow determination signal Cd, and the steady feed speed setting signal Fcr as inputs, performs the following processing, and outputs a feed speed setting signal Fr. 1) When the welding start signal St goes to high level, a feed speed setting signal Fr which becomes a predetermined slow-down feed speed is output. 2) After that, when the current energization discrimination signal Cd changes to a high level, the feed speed setting signal Fr is output, which accelerates the feed speed from the slow-down feed speed to the value of the steady-state feed speed setting signal Fcr.

[0034] The feed control circuit WC receives the feed speed setting signal Fr and the welding start signal St as inputs, and when the welding start signal St goes to a high level, outputs a feed control signal Wc to the wire feed motor WM for feeding the welding wire 1 at a feed speed Fw determined by the feed speed setting signal Fr.

[0035] Fig. 2 is a timing chart of each signal in the welding power source of Fig. 1, which illustrates the method for controlling the arc start of pulse arc welding according to the embodiment of the present invention. Fig. 2(A) shows the change over time of the welding start signal St, Fig. 2(B) shows the change over time of the feed speed Fw, Fig. 2(C) shows the change over time of the welding current Iw, Fig. 2(D) shows the change over time of the welding voltage Vw, and Fig. 2(E) shows the change over time of the transient period signal Stt. The operation of each signal will be explained below with reference to the figure.

[0036] (1) Slow-down feeding speed period At time t1, as shown in Fig. 1(A), when the welding start signal St changes to a high level (welding starts), the welding power source is started, as shown in Fig. 1(B), feeding of the welding wire 1 at a predetermined slow-down feed speed is started, and as shown in Fig. 1(D), a no-load voltage is applied between the welding wire 1 and the base material 2. The slow-down feed speed is set to a slow speed of about 1 m / min.

[0037] (2) Hot Start Period Th At time t2, when the tip of the welding wire 1 comes into contact with the base material 2, an arc 3 is generated after a short short circuit. In response to this, as shown in FIG. 1B, the feed speed Fw accelerates from the slow-down feed speed to the steady feed speed determined by the steady feed speed setting signal Fcr of FIG. 1. As shown in FIG. 1C, a hot start current Ih (about 450 A) having a predetermined large current value is passed during a predetermined hot start period Th (about 5 ms) from time t2 to t3. As shown in FIG. 1D, the welding voltage Vw is rapidly reduced to a short circuit voltage value of several volts during the short short circuit from time t2, and increases to an arc voltage value of several tens of volts until time t3 when the arc 3 is generated.

[0038] (3)Transition period Tt When the hot start period Th ends at time t3, as shown in FIG. 1(E), the transition period signal Stt becomes High level during the period from time t3 to t4, and the transition period Tk begins. The end point of the transition period Tt at time t4 is the time when a predetermined period has elapsed, or the time when the change in the pulse period, which is the time interval during which the pulse period signal Tf in FIG. 1 becomes High level for a short time, converges within a predetermined change range. As shown in FIG. 1(B), the feed speed Fw maintains a steady feed speed. As shown in FIG. 1(C), the welding current Iw rises from a predetermined base current Ib to a predetermined peak current Ip during a predetermined rise period Tu, becomes the peak current Ip during a predetermined peak period Tp, falls from the peak current Ip to the base current Ib during a predetermined fall period Td, and becomes the base current Ib during a base period Tb until the pulse period signal Tf in FIG. 1 becomes High level for a short time. During the transient period Tt, output control is performed by pulse period modulation control. Therefore, the rising period Tu set by the rising period setting signal Tur in FIG. 1, the base current Ib set by the base current setting signal Ibr in FIG. 1, the peak current Ip set by the peak current setting signal Ipr in FIG. 1, the peak period Tp set by the peak period setting signal Tpr in FIG. 1, and the falling period Td set by the falling period setting signal Tdr in FIG. 1 are fixed values. Then, the pulse period Tf is feedback controlled so that the welding voltage average value signal Vav in FIG. 1 is equal to the predetermined welding voltage setting signal Vr. In the figure, three pulse periods are included in the transient period Tt. In reality, the transient period Tt is about 100 ms, so that about 10 pulse periods are included. For example, the rising period Tu is set to 1 ms, the peak period Tp is set to 1.2 ms, and the falling period Td is set to 1 ms. The base current Ib is set to 50 A, which is less than the critical current value, and the peak current Ip is set to 500 A, which is greater than or equal to the critical current value. As shown in FIG. 1D, the welding voltage Vw has a value of several tens of volts and a waveform similar to that of the welding current Iw.

[0039] (4) Steady-state period Tc When the transient period Tt ends at time t4, as shown in FIG. 1E, the transient period signal Stt changes to a low level, and the period transitions to the steady state period Tc. As shown in FIG. 1B, the feed speed Fw maintains the steady state feed speed. As shown in FIG. 1C, the welding current Iw rises from a base current Ib, which is controlled by current modulation control, to a peak current Ip, which is controlled by current modulation control, during a predetermined rise period Tu, and becomes the peak current Ip during a predetermined peak period Tp, and falls from the peak current Ip to the base current Ib during a predetermined fall period Td, and becomes the base current Ib during a base period Tb until the predetermined pulse period is reached. During the steady state period Tc, output control is performed by current modulation control. Therefore, the rising period Tu set by the rising period setting signal Tur in FIG. 1, the peak period Tp set by the peak period setting signal Tpr in FIG. 1, the falling period Td set by the falling period setting signal Tdr in FIG. 1, and the pulse period set by the pulse period setting signal Tfr in FIG. 1 are fixed values. Then, the peak current Ip and the base current Ib are feedback controlled so that the welding voltage average value signal Vav in FIG. 1 is equal to the predetermined welding voltage setting signal Vr. Here, only the peak current Ip may be current-modulated. However, the peak current Ip and the base current Ib are limited within a predetermined change range. For example, the change range of the peak current Ip is equal to or greater than the critical current value, and is in the range of 400 to 600 A. The change range of the base current Ib is less than the critical current value, and is in the range of 30 to 100 A. Also, the rising period Tu is set to 1 ms, the peak period Tp to 1.2 ms, and the falling period Td to 1 ms. The pulse period is set to the time length of the pulse period immediately before the end of the transition period Tt. As shown in FIG. 1D, the welding voltage Vw has a value of several tens of volts and a waveform similar to that of the welding current Iw.

[0040] The effects of this embodiment will be described below. According to the present embodiment, in the arc start control method for pulse arc welding in which output control is performed by current modulation control that changes at least the peak current, output control is performed by pulse period modulation control that changes the pulse period during the transient period after the arc start. In the current modulation control, output control is performed by changing at least the peak current. If the peak current becomes too large, the arc force becomes strong and the bead appearance becomes poor. On the other hand, if the peak current becomes too small, the droplet transfer becomes unstable and the welding state becomes unstable. For this reason, an upper limit value and a lower limit value are set in the change range of the peak current. As a result, the change amount of the operation amount (peak current) is limited during the transient response of the feedback system, and the transient response may become poor. In particular, in the current modulation control, there is a problem that it takes a long time for the arc length to converge to an appropriate value because the transient response after the arc start is poor. In contrast, in the pulse period modulation control, there is no need to set a limit on the change range of the pulse period. Therefore, by performing output control by pulse modulation control during the transient period after the arc start, the transient response after the arc start can be improved and the arc length can be quickly converged to an appropriate value. During the steady period, current modulation control can provide more advantageous welding than pulse period modulation control, as described below. In pulse arc welding, the arc is deflected during the base period in which a base current of a small current value is applied due to a phenomenon called magnetic blow, and the welding state is likely to become unstable. In current modulation control, the base period is a fixed value and does not become a transiently long period, so the welding state is less likely to become unstable due to magnetic blow. In multi-electrode pulse arc welding, in which multiple welding wires are adjacent to each other and arcs are generated simultaneously while welding, the application of peak currents is synchronized to suppress instability of the welding state due to interference between the arcs. In order to achieve this synchronization, it is desirable to use current modulation control in which the peak period and the base period are constant values. Furthermore, the weaving of the welding torch is synchronized with the peak period to improve weldability (weaving welding), and current modulation control is also advantageous in such cases.

[0041] More preferably, according to this embodiment, the transition period is set to a predetermined period or a period until the change in the pulse period converges. When the change in the pulse period due to the pulse period modulation control has almost ceased, the transition period is ended and control is shifted to the current modulation control. In this way, the transition period during which the pulse period modulation control is performed can be set to the minimum necessary, so that the above-mentioned advantageous welding using the current modulation control can be started early.

[0042] More preferably, according to this embodiment, the pulse period of the current modulation control is set to the pulse period at the end of the transition period. By setting the pulse period, which is a fixed value in the current modulation control, to a value to which the pulse period has converged by the pulse period modulation control, it is possible to make a smooth transition from the pulse period modulation control to the current modulation control. [Explanation of symbols]

[0043] 1 Welding wire 1a Wire reel 2 Base material 3. Arc 4. Welding torch 5 Feeding roll CD current determination circuit Cd Current discrimination signal DV driver circuit Dv drive signal EI Current Error Amplifier Circuit Ei Current error amplification signal EV voltage error amplifier circuit Ev Voltage error amplified signal FCR Steady feeding speed setting circuit Fcr Steady feeding speed setting signal FR feed speed setting circuit Fr feed speed setting signal Fw Feed speed Ib Base current Ibc Base current modulation signal IBR base current setting circuit Ibr Base current setting signal ICR Steady-state current setting circuit Icr Steady-state current setting signal ID Welding current detection circuit Id Welding current detection signal Ih Hot start current IHR Hot start current setting circuit Ihr Hot start current setting signal Ip Peak current Ipc Peak current modulation signal IPR Peak current setting circuit Ipr Peak current setting signal IR current setting circuit Ir Current setting signal ITR transient period current setting circuit Itr Transient period current setting signal Iw Welding current PM power supply main circuit ST Welding Start Circuit St Welding start signal STH Hot start period circuit Sth Hot start period signal STT transient period circuit Stt transient period signal Tb Base period Tc Steady state period Td Falling period TDR Falling period setting circuit Tdr Falling period setting signal Tf Pulse periodic signal TFR pulse period setting circuit Tfr Pulse period setting signal Th Hot Start Period Tp peak period TPR peak period setting circuit Tpr Peak period setting signal Tt transient period Tu Rise Period TUR Rising period setting circuit Tur Rising period setting signal VAV Welding voltage average calculation circuit Vav Welding voltage average value signal VD Welding voltage detection circuit Vd Welding voltage detection signal VF Pulse period modulation circuit VI Current Modulation Circuit VR welding voltage setting circuit Vr Welding voltage setting signal Vw welding voltage WC feed control circuit Wc feed control signal WM Wire feed motor

Claims

1. The peak current during the peak period and the base current during the base period are repeated as one pulse period. In a method for controlling an arc start in pulse arc welding, an output control is performed by current modulation control that changes at least the peak current, During a transient period after the arc start, the output control is performed by a pulse period modulation control that changes the pulse period.

1. A method for controlling an arc start in pulse arc welding.

2. The transition period is set to a predetermined period or a period until the change in the pulse period is converged.

2. The method for controlling an arc start in pulse arc welding according to claim 1.

3. setting the pulse period of the current modulation control to the pulse period at the end of the transient period; 3. The method for controlling an arc start in pulse arc welding according to claim 1 or 2.

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