KR20160084292A - Arc start control method of pulse arc welding - Google Patents

Abstract

In pulse arc welding, it is possible to suppress the phenomenon that the arc length generated at the time of arc start is rapidly lengthened to stabilize the welding state.
During the transient period Tk after arc-start, the transient peak current Ipk in which the normal peak current Ipc is decreased and the normal base current Ipc in which the normal peak current Ipc is reduced are used in the arc- Transmitting the transient base current Ibk with Ibc increased. The transient period Tk is set based on the time when the welding wire is fed by a distance corresponding to the wire protrusion length, and the transient peak current Ipk is set based on the unit length resistance value of the welding wire. As a result, the transient peak current Ipk decreases, thereby suppressing the abnormal heating of the welding wire and suppressing the occurrence of a phenomenon in which the arc length is rapidly lengthened.

Description

TECHNICAL FIELD [0001] The present invention relates to an arc start control method for pulsed arc welding,

The present invention relates to an arc start control method for pulse arc welding in which a welding wire is fed and a normal peak current during a peak period and a normal base current during a peak period during one welding period are energized and welded with one pulse period.

A consumable electrode type pulse arc welding method is widely used in which a welding wire is fed at a constant speed and an arc is generated by welding a pulse current having a peak current during a peak period and a base current during a base period in one pulse period . This pulse arc welding method can perform high-quality welding with a small amount of spatter generated for various metal materials such as steel, stainless steel and aluminum with high efficiency.

Fig. 7 is a current / voltage waveform diagram during normal welding in consumable electrode type pulse arc welding. Fig. Fig. 7A shows the waveform of the welding current Iw that energizes the arc, and Fig. 7B shows the waveform of the welding voltage Vw applied between the welding wire and the base material. This will be described below with reference to Fig.

During the peak period Tp of the time t1 to t2, as shown in Fig. 7 (A), the peak current Ip set to the normal peak current value higher than the threshold value is energized to rise with the inclination, As shown in Fig. 7 (B), a peak voltage Vp that rises with an inclination and is proportional to the arc length is applied. During the base period Tb from time t2 to time t3, as shown in Fig. 7A, the base current Ib set to the normal base current value lower than the threshold value is energized because the capacitor is lowered with the inclination and no volume is formed, As shown in Fig. 7 (B), the base voltage Vb having a slope falls and is proportional to the arc length. Welding is repeatedly performed at times t1 to t3 as one pulse period Tf.

The waveform parameters in the case where the welding wire is a metal-based cored wire having a diameter of 1.2 mm for stainless steel are, for example, as follows. The peak period Tp = 2.0 ms including the peak current Ip = 450 A, the rising period Tf = 3.0 to 10.0 ms, the base current Ib = 50 A, the rising period and the falling period = 0.5 ms.

During the peak period Tp, the tip of the welding wire is melted and the volume grows, and a constriction due to the pinching force is gradually formed on the volume. Then, at time t21 after the welding current Iw falls and converges to the base current Ib, the volume shifts to the fusing point. In this transition, the volume becomes elongated and elongated in shape and comes into contact with the fused paper. At this time, a short-time (in most cases, less than 0.2 ms) short-circuit occurs. Therefore, as shown in Fig. 7 (B), at time t21, the welding voltage Vw becomes approximately 0 V and a short circuit occurs. As shown in Fig. 7 (A), the welding current Iw increases after a predetermined time from the time t21 at which the short circuit occurs, and returns to the normal value at the time t22 when the short circuit ends. The predetermined time is about 0.1 ms. The reason for increasing the welding current Iw is to return to the arcing state by releasing the short-circuit at an early stage.

In consumable electrode arc welding including pulse arc welding, it is important to maintain the arc length during welding at an appropriate value in order to obtain a good welding quality. This arc length control is performed as follows. The average value Vav of the welding voltage shown in FIG. 7 (B) is approximately proportional to the average arc length. Accordingly, the welding voltage average value Vav is detected, and the welding voltage average value Vav is equal to the welding voltage setting value Vr (not shown) set to a value corresponding to an appropriate average arc length. Control) or the peak period Tp (pulse width modulation control) according to the feedback control.

In the frequency modulation control, the peak period Tp, the peak current Ip, and the base current Ib become waveform parameters and set to predetermined values. Then, the pulse period Tf (base period Tb) is feedback-controlled.

In the pulse width modulation control, the peak current Ip, the pulse period Tf, and the base current Ib become waveform parameters and set to predetermined values. Then, the peak period (pulse width) Tp is feedback-controlled.

The welding voltage average value Vav is detected by detecting the welding voltage Vw and passing it through a low-pass filter (cutoff frequency of about 1 to 10 Hz).

In each modulation control, the waveform parameter is set to an appropriate value such that a so-called one-pulse-period-1 volumetric transition state in which one volume shifts in one pulse period.

According to the invention of Patent Document 1, in the pulse arc welding, the slope of the peak current is made gentler than that in the main welding during a predetermined period from the generation of the arc. As a result, it is possible to suppress the arc interruption by suppressing self-migration at the time of arc start.

Japanese Patent No. 3003673

In the pulse arc welding, during the transient period after arc start, the arc length suddenly becomes suddenly long and the welding state becomes unstable occasionally. In addition, since the arc length becomes very long, there is a case where arc cutting or welding to a power supply chip may be caused.

It is therefore an object of the present invention to provide an arc start control method of pulse arc welding capable of suppressing a sudden and prolonged increase in arc length during a transient period after arc start, thereby achieving a stable welding state.

In order to solve the above-mentioned problems, the invention of claim 1 is characterized in that the welding wire is fed, and during the normal welding period, a pulse for welding by energizing a welding current for setting a steady peak current during a peak period and a steady- A method for controlling an arc start of an arc welding, the method comprising the steps of: during a transient period after arc start, a transient peak current in which the steady peak current is reduced by a predetermined decreasing value and a transient base current in which the steady- Wherein the pulse arc welding is an arc start control method.

The invention of claim 2 is the arc start control method of pulse arc welding according to claim 1, wherein the reduction value is set based on a unit length resistance value of the welding wire.

According to a third aspect of the present invention, when the arc length control is the frequency modulation control, the increase value is set so that a difference between an average value of the pulse periods during the transient period and an average value of the pulse periods during the normal welding period is less than a predetermined value Wherein the pulse arc welding is an arc start control method according to claim 1 or 2.

According to the invention of claim 4, when the arc length control is the pulse width modulation control, the increase value is set so that the difference between the average value of the peak period during the transient period and the average value of the peak period during the normal welding period becomes less than the predetermined value Arc arc welding control method according to claim 1 or 2.

The invention according to claim 5 is the arc start control method for pulse arc welding according to any one of claims 1 to 4, wherein the transient period is set to a predetermined period.

The invention according to claim 6 is characterized in that the transient period is set based on a time when the welding wire is fed by a distance corresponding to the wire protrusion length after the arc start, Arc start control method of arc welding.

The invention according to claim 7 is characterized in that, during the transient period, the feeding speed of the welding wire is set to be higher than the feeding speed during the normal welding period, and the arc start control of pulse arc welding according to any one of claims 1 to 6 Method.

According to the present invention, since the peak current value is reduced, even if the welding wire is damaged, there is no case of reaching an abnormal heating state, so that it is possible to suppress the occurrence of a phenomenon in which the arc length rapidly becomes long. In addition, since the average value of the pulse period or the peak period is made smaller than the predetermined value during the transient period and the normal welding period, the welding state in both periods can be maintained well.

1 is a timing chart for explaining an arc start control method for pulse arc welding according to the first embodiment of the present invention.
Fig. 2 is a diagram showing the relationship between the reduction value? D [A] shown on the ordinate and the unit length resistance value Rw [m? / Mm] of the welding wire shown in the abscissa.
3 is a block diagram of a welding power source for implementing an arc start control method for pulse arc welding according to the first embodiment of the present invention.
4 is a block diagram of a welding power source for implementing an arc start control method of pulse arc welding according to a second embodiment of the present invention.
5 is a timing chart for explaining an arc start control method of pulse arc welding according to a third embodiment of the present invention.
6 is a block diagram of a welding power source for implementing an arc start control method of pulse arc welding according to a third embodiment of the present invention.
Fig. 7 is a general current / voltage waveform diagram in consumable electrode type pulse arc welding in the prior art; Fig.

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

[First Embodiment]

The invention of the first embodiment energizes a peak current in which the steady peak current value is reduced by a predetermined decrease value and a base current in which the steady base current value is increased by a predetermined increase value during the transient period after the arc start. The transient period is set to a predetermined period.

1 is a timing chart for explaining an arc start control method for pulse arc welding according to the first embodiment of the present invention. Fig. 1 (A) shows a time variation of the welding start signal St, Fig. 1 (B) shows a time variation of the feeding speed Fw, 1 (D) shows the time variation of the welding voltage Vw, and FIG. 1 (E) shows the time variation of the transient time signal Stk. In Fig. 1, the description of the same operation as that of Fig. 7 described above is not repeated. Hereinafter, a description will be given with reference to Fig.

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

At the 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. As a result, as shown in Fig. 1 (C), the hot start current Ih (about 500 A) of the predetermined large current value is energized during the predetermined hot start period Th of the time t2 to t3. As shown in FIG. 1 (D), the welding voltage Vw rapidly decreases from a time t2 to a short-circuit voltage value of several V during a short short circuit, and when an arc 3 occurs, . When the welding current Iw starts to be energized at the time t2, the feeding speed Fw is accelerated with the inclination and converged to the predetermined feeding speed Fwc at time t7 as shown in Fig. 1 (B). Similarly, when energization of the welding current Iw is started at the time t2, the transient period signal Stk is set to the high level as shown in (E) of Fig. 1, and is reset to the Low level at the time t10 after the lapse of the predetermined period. The period in which the transient period signal Stk is at the High level becomes the transient period Tk.

When the hot start period Th ends at the time t3, the predetermined transient base current Ibk is energized as shown in Fig. 1 (C) during the period from the time t3 to t4, and as shown in Fig. 1 (D) , The transient base voltage Vbk proportional to the arc length is applied.

As shown in Fig. 1 (C), a predetermined transient peak current Ipk is energized during the predetermined peak period Tp from time t4 to t5, and as shown in Fig. 1 (D), a transient The peak voltage Vpk is applied. During the base period Tb of time t5 to t6, as shown in Fig. 1 (C), the transitional base current Ibk is energized and the transient base voltage Vbk is applied as shown in Fig. 1 (D) do. As described above, the pulse cycle Tf (base period Tb) is feedback-controlled (frequency modulation control) such that the average value of the welding voltage Vw during the pulse period Tf from time t4 to t6 becomes equal to the predetermined welding voltage setting signal Vr.

The operation of the pulse cycle Tf of the times t6 to t8, the pulse cycle Tf of the times t8 to t9, and the pulse cycle Tf of the times t9 to t11 is the same as the operation of the pulse cycle Tf of the time t4 to t6. At time t7 in the pulse period Tf from time t6 to time t8, the feed rate Fw converges to the normal feed rate Fwc as shown in Fig. 1 (B). Further, at the time t10 in the pulse period Tf from time t9 to t11, the predetermined period has ended, so that the transient period signal Stk is changed to Low level as shown in Fig. 1 (E). The slope period of the feeding speed Fw of time t2 to t7 is about 50 ms. In Fig. 1, waveforms for two cycles are plotted during this slope period, but actually it is about 10 to 20 cycles. The transient period Tk of time t2 to t10 is set in the range of about 100 to 500 ms. In Fig. 1, waveforms corresponding to four cycles are drawn in this transient period Tk, but actually, the waveforms are about 10 to 100 cycles.

Since the transient period signal Stk shown in FIG. 1 (E) is at the Low level from the pulse period Tf of the time t11 to t13, the normal welding operation is performed. During the above-mentioned peak period Tp from time t11 to time t12, as shown in Fig. 1 (C), a predetermined peak peak current Ipc is energized, and as shown in Fig. 1 (D) The peak voltage Vpc is applied. As shown in Fig. 1 (C), during the base period Tb from time t12 to time t13, a predetermined normal base current Ibc is energized, and as shown in Fig. 1 (D) Vbc is applied. As described above, the pulse cycle Tf (base period Tb) is feedback-controlled (frequency modulation control) such that the average value of the welding voltage Vw during the pulse period Tf from time t11 to time t13 becomes equal to the predetermined welding voltage setting signal Vr. During the subsequent normal welding period, the above-described operation is repeated.

The transient peak current Ipk is set to a value obtained by reducing the value of the normal peak current Ipc by a predetermined reduction value? D. The transient base current Ibk is set to a value obtained by increasing the value of the above-mentioned normal base current Ibc by a predetermined increase value? U. The normal peak current Ipc is a value that is equal to or larger than a threshold value and is set to a range in which the volume transition state is set to one pulse period 1. The normal base current Ibc is a value less than the threshold value and is set to a range in which no volume is formed during the base period Tb. The transient peak current Ipk is a value equal to or larger than the threshold value, but is reduced by the reduction value? D, so that the transient peak current Ipk is often set to the multiple pulse period 1 volumetric transition state. The transient base current Ibk is set to a value less than the threshold value, but is increased by the increment value? U, so that the volume is often small in the base period Tb.

The arc state at the time when the arc length rapidly became long during the transient period Tk after arc start was observed using a high-speed camera. When the arc length is in the normal state, the arc 3 is generated from the volume formed at the lower end of the wire protruding portion. The phenomenon that the arc length became prolonged suddenly was fused at the intermediate position of the wire projection portion, and it was determined that the arc 3 was generated from the terminal end portion. The reason for melting at the intermediate position of the wire protruding portion is that the wire 1 at the melting end position is damaged, and thus it is discriminated that the wire 1 is abnormally heated and fused. The reason for the damage of the welding wire 1 is that when the feed speed Fw is reduced and feeding is stopped at the end of the last welding, the inner surface of the feeding chip contacts with the welding wire 1, This is because the welding wire 1 may be damaged by arcing or the like. Also, when the feed speed Fw is accelerated during the arc start, the welding wire 1 may be damaged in the same manner. In order to feed the damaged welding wire 1 to the intermediate position of the wire protruding portion in the power supply chip, it takes about 100 to 500 ms after arc start. For this reason, the phenomenon that the arc length is rapidly lengthened tends to occur in a range of about 100 to 500 ms after arc start. However, even if the welding wire 1 is damaged, if the resistance value per unit length (hereinafter, referred to as a unit length resistance value) of the welding wire 1 is small, abnormal heating hardly occurs, The phenomenon of rapid lengthening becomes difficult to occur.

Therefore, in order to suppress the occurrence of the phenomenon that the arc length is rapidly lengthened, damage to the welding wire in the power supply chip is prevented or abnormal heating is prevented. Since it is difficult to prevent damage to the welding wire 1, measures to prevent abnormal heating will be performed. The abnormal heating is caused by energizing a peak current of a large current value to the damaged portion of the welding wire. Therefore, during the transient period Tk after the arc start, the excessive peak current Ipk in which the normal peak current Ipc is reduced by the decrease value? D is energized to prevent the abnormal heating. However, the transient peak current Ipk becomes closer to the normal peak current Ipc, that is, the smaller the decrease value? D, the better the volumetric transient state. In other words, when the reduction value? D is increased, the volume transition state is slightly deteriorated, so that the sputter is increased. Therefore, the decrease value? D is preferably set to the minimum value within a range in which the phenomenon that the arc length is not prolonged rapidly occurs. The abnormal heating is more likely to occur when the unit length resistance value of the welding wire is larger. Therefore, it is preferable that the appropriate value of the reduction value? D is changed according to the unit length resistance value of the welding wire 1. [ This relationship will be described later in Fig.

Since the transient peak current Ipk is smaller than the normal peak current Ipc, the average value of the pulse period Tf during the transient period Tk becomes longer than the average value of the pulse period Tf during the normal welding period. If the pulse cycle Tf becomes longer, the welding state becomes somewhat unstable. The reason why the pulse period Tf changes is due to the frequency modulation control described above. In order to make the average value of the pulse period Tf during the transient period Tk equal to the average value of the pulse period Tf during the normal welding period, the transient base current Ibk may be made larger than the normal base current Ibc. Therefore, the transient base current Ibk is set to a value obtained by increasing the normal base current Ibc by the increment value? U. Therefore, the increment value? U is set so that the difference between the average value of the pulse cycle Tf during the transient period Tk and the average value of the pulse cycle Tf during the normal welding period becomes less than the predetermined value after the transient peak current Ipk is set. The predetermined value is about 10%.

When the arc length control is the pulse width modulation control, the pulse period Tf becomes a fixed value, and the peak period (pulse width) Tp is feedback-controlled. Therefore, the transient base current Ibk (increase value? U) may be set so that the difference between the transient period Tk and the average value of the peak period Tp in the normal welding period becomes less than a predetermined value.

Fig. 2 is a diagram showing the relationship between the reduction value? D [A] shown on the ordinate and the unit length resistance value Rw [m? / Mm] of the welding wire shown on the abscissa.

As shown in Fig. 2,? D = 0 in the range of Rw <0.03. This is because, since the unit length resistance value Rw of the welding wire is small, abnormal heating does not occur even if the welding wire is damaged. When the material of the welding wire is aluminum, it falls within this range.

In the range of Rw? 0.03, the straight line is the upper right side. That is, the larger the unit length resistance value Rw, the larger the decrease value? D. In the case of a mild steel solid wire having a diameter of 1.2 mm, Rw = 0.09, and? D = 10A. In the case of a mild steel solid wire having a diameter of 0.9 mm, Rw = 0.16 and? D = 20A. In the case of a stainless steel solid wire having a diameter of 1.2 mm, Rw = 0.65, and? D = 80A. In the case of a metal-based core wire made of stainless steel having a diameter of 1.2 mm, Rw = 0.85, and? D = 100A.

Fig. 3 is a block diagram of a welding power source for carrying out the arc start control method of pulse arc welding according to the first embodiment of the present invention described above with reference to Fig. 1; Hereinafter, each block will be described with reference to FIG.

The power main circuit PM receives a commercial power source (not shown) such as three-phase 200V, and performs output control by inverter control in accordance with a drive signal Dv to be described later, and outputs a welding current Iw and a welding voltage Vw. The power main circuit PM includes a primary rectifier for rectifying a commercial power source, a capacitor for smoothing a rectified DC current, an inverter circuit for converting a smoothed direct current into a high frequency AC in accordance with the drive signal Dv described above, A secondary rectifier for rectifying the rectified high frequency AC, and a reactor for smoothing the rectified DC.

The welding wire 1 is wound around the wire reel 1a. The welding wire 1 is fed in the welding torch 4 at the feeding speed Fw by the rotation of the feeding roll 5 coupled to the wire feeding motor WM and the arc 3 is generated between the welding torch 4 and the base material 2 Welding is performed. The welding current Iw is energized in the arc 3 and the welding voltage Vw is applied between the feed chip (not shown) and the base material 2 in the welding torch 4. [

The welding voltage detection circuit VD detects the welding voltage Vw and outputs the welding voltage detection signal Vd. The welding voltage average value calculation circuit VAV receives the welding voltage detection signal Vd as an input and passes it through a low pass filter to average the welding voltage average signal Vav and output 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 the voltage error amplification signal Ev.

The voltage / frequency conversion circuit VF receives the voltage error amplification signal Ev as described above, and outputs a pulse period signal Tf having a frequency corresponding to the value of the voltage error amplification signal Ev. This pulse periodic signal Tf is a signal which becomes a high level for a short time every pulse cycle.

The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr. The timer circuit TM receives the above-mentioned peak period setting signal Tpr and the above-mentioned pulse period signal Tf and outputs only the period determined by the peak period setting signal Tpr to the High level every time the pulse period signal Tf changes to the High level And outputs the timer signal Tm. Therefore, when this timer signal Tm is at a high level, it is a peak period, and when it is at a low level, it is a base period.

The welding start circuit ST outputs a welding start signal St which becomes a high level when the welding power source is started. The welding start circuit ST corresponds to a start switch of the welding torch 4, a PLC for controlling the welding process, a robot control device, and the like.

The welding current detection circuit ID detects the welding current Iw and outputs the welding current detection signal Id. The current energization discrimination circuit CD receives the above-mentioned current detection signal Id and outputs a current energization discrimination signal Cd which is high level when it is judged that the welding current Iw is energized when this value is equal to or higher than the threshold value (about 10 A).

The hot start period circuit STH receives the current energization discrimination signal Cd as described above and outputs a hot start period signal Sth which becomes a high level during a predetermined hot start period Th from the time when the current energization discrimination signal Cd changes to the high level . The hot start current setting circuit IHR outputs a predetermined hot start current setting signal Ihr.

The welding wire selection circuit WS selects the combination of the material and the diameter of the welding wire to be used, and outputs the welding wire selection signal Ws. For example, when a mild steel solid wire having a diameter of 1.2 mm is selected, Ws = 1, and when a mild steel solid wire having a diameter of 0.9 mm is selected, Ws = 2, and when a stainless steel metal- Ws = 3.

The unit length resistance value setting circuit RWR reads the unit length resistance value of the welding wire corresponding to the welding wire selection signal Ws from the built-in database by using the welding wire selection signal Ws as described above, And outputs a signal Rwr.

The reduction value setting circuit? DR receives the unit length resistance value setting signal Rwr as described above, and outputs a reduction value setting signal? Dr calculated based on the above-described relational expression in FIG.

The welding current average value setting circuit IR outputs a predetermined welding current average value setting signal Ir.

The normal peak current setting circuit IPCR outputs a predetermined normal peak current setting signal Ipcr. The normal base current setting circuit IBCR outputs a predetermined normal base current setting signal Ibcr.

The transient peak current setting circuit IPKR inputs the normal peak current setting signal Ipcr and the reduction value setting signal? Dr as described above, subtracts the reduction value setting signal? Dr from the normal peak current setting signal Ipcr, Output as Ipkr.

The normal welding period pulse cycle calculating circuit TFC receives the welding current average value setting signal Ir, the peak period setting signal Tpr, the normal peak current setting signal Ipcr, and the normal base current setting signal Ibcr described above and outputs Tfc = (Tpr · (Ipcr-Ibcr)) / (Ir-Ibcr) and outputs a normal welding period pulse period signal Tfc.

The transient base current setting circuit IBKR receives the welding current average value setting signal Ir, the normal welding period pulse period signal Tfc, the peak period setting signal Tpr and the transient peak current setting signal Ipkr described above, (Tfc, Ir-Tpr, Ipkr) / (Tfc-Tpr) and outputs it as the transient base current setting signal Ibkr.

The transient period circuit STK receives the above-described current energization discrimination signal Cd and outputs a transient period signal Stk which becomes a high level from the time when the current energization discrimination signal Cd is changed to the High level (energized) until a predetermined period elapses do.

The peak current setting circuit IPR receives as inputs the transient period signal Stk, the transient peak current setting signal Ipkr and the normal peak current setting signal Ipcr, and when the transient period signal Stk is at the High level (transient period) The peak current setting signal Ipkr is output as the peak current setting signal Ipr and the normal peak current setting signal Ipcr is outputted as the peak current setting signal Ipr when Stk = Low level (normal welding period).

The base current setting circuit IBR receives as inputs the transient period signal Stk, the transient base current setting signal Ibkr and the normal base current setting signal Ibcr, and when the transient period signal Stk is at the High level (transient period) Outputs the base current setting signal Ibkr as the base current setting signal Ibr and outputs the normal base current setting signal Ibcr as the base current setting signal Ibr when Stk = Low level (normal welding period).

The switching circuit SW is supplied with the hot start period signal Sth, the timer signal Tm, the hot start current setting signal Ihr, the peak current setting signal Ipr, and the base current setting signal Ibr described above, When the period signal Sth is at the High level, the hot start current setting signal Ihr is outputted as the current control setting signal Icr. When the hot start period signal Sth is at the Low level and the timer signal Tm is at the High level, And outputs the base current setting signal Ibr as the current control setting signal Icr when the hot start period signal Sth is at the Low level and the timer signal Tm is at the Low level.

The current error amplification circuit EI amplifies the error between the current control setting signal Icr and the welding current detection signal Id described above and outputs the current error amplification signal Ei. The drive circuit DV receives the current error amplification signal Ei and the welding start signal St as input and performs PWM control when the welding start signal St is at a high level and drives the inverter circuit of the power main circuit PM And outputs the drive signal Dv.

The feed rate setting circuit FR receives the above described welding current average value setting signal Ir and calculates a feed rate setting signal Fr corresponding to the value of the welding current average value setting signal Ir in accordance with a pre- And outputs it.

The feed control circuit FC receives the above feed rate setting signal Fr, the welding start signal St and the current energization discrimination signal Cd. When the welding start signal St becomes a high level, the feeding control circuit FC feeds the welding wire When the current energization discrimination signal Cd changes to the high level, it is accelerated at a predetermined inclination to output the feed wire control signal Fc at the feed speed Fw determined by the feed rate setting signal Fr, To the wire feed motor WM as described above.

Fig. 3 shows a case where the arc length control method is frequency modulation control. In the case of the pulse width modulation control, the pulse period signal Tf may be set to a predetermined value, and the peak period setting signal Tpr may be feedback-controlled based on the voltage error amplification signal Ev. At this time, the transitional base current setting signal Ibkr may be set so that the difference between the average value of the peak periods during the transient period and the average value of the peak periods during the normal welding period is less than the predetermined value.

According to the first embodiment described above, during the transient period after the arc start, the transient base current is increased by increasing the transient peak current and the steady-state base current by the predetermined increase value by reducing the steady-state peak current by the predetermined decrease value. The reduction value is set based on the unit length resistance value of the welding wire. When the arc length control is the frequency modulation control, the increase value is set such that the difference between the average value of the pulse period during the transient period and the average value of the pulse period during the normal welding period becomes less than the predetermined value. When the arc length control is the pulse width modulation control, the increase value is set such that the difference between the average value of the peak periods during the transient period and the average value of the peak periods during the normal welding period is less than the predetermined value. The transient period is set to a predetermined period. Thus, in the present embodiment, since the peak current value is reduced, even if the welding wire is damaged, there is no case where the abnormal heating state is reached, so that the occurrence of the phenomenon that the arc length is rapidly lengthened can be suppressed. In addition, since the average value of the pulse period or the peak period during the transient period and the normal welding period becomes a difference smaller than the predetermined value, it is possible to maintain a good welding state in both periods.

[Second Embodiment]

The invention of the second embodiment is that the transient period is set based on the time when the welding wire is fed by a distance equivalent to the wire protruding length after arc-starting.

Fig. 4 is a block diagram of a welding power source for implementing an arc start control method for pulse arc welding according to the second embodiment. Fig. Fig. 4 corresponds to Fig. 3 described above, and the same reference numerals are assigned to the same blocks, and description thereof is not repeated. Fig. 4 is a circuit diagram of the feed-through distance setting circuit LWR, the feeding distance setting circuit LR, and the feeding distance calculating circuit LD in Fig. 3, in which the feeding tip end / parent material distance setting circuit LWR, the feeding period length calculating circuit LD, and the second transient period circuit STK2 will be. Hereinafter, these blocks will be described with reference to FIG.

The feed chip tip / parent material distance setting circuit LWR outputs a predetermined feed tip end / parent material distance setting signal Lwr. The feed distance setting circuit LR receives the feed tip end-to-parent material distance setting signal Lwr as input, subtracts a predetermined arc length set value from this value, calculates a wire projection length, And outputs it as the feed distance setting signal Lr. The arc length set value is an average arc length during welding, which is about 3 mm. The margin rate is set to about 120%. For example, in the case of Lwr = 20 mm, Lr = (20-3) 1.2 = 20.4 mm.

The feeding distance calculation circuit LD receives the feeding speed detection signal Fd from the wire feeding motor WM and the current conduction discrimination signal Cd as described above so that the current conduction discrimination signal Cd changes to High level The feed-forward speed detection signal Fd is integrated from the time when the detection signal Fd is converged at the normal feed-back speed after completion of the acceleration, and the feed-in distance is calculated and outputted as the feed-in distance calculation signal Ld.

The second transient period circuit STK2 receives the above-described current energization discrimination signal Cd, the above-described feed-distance setting signal Lr and the above-mentioned feed-in distance calculation signal Ld, and when the current energization discrimination signal Cd changes to High level And outputs a transient period signal Stk which is reset to the Low level when the value of the feeding distance calculation signal Ld reaches the value of the feeding distance setting signal Lr.

The timing chart for explaining the arc start control method of the pulse arc welding according to the second embodiment of the present invention is the same as that of Fig. 1 described above, and therefore description thereof will not be repeated. However, only the transition timing from the High level to the Low level of the transient period signal Stk shown in Fig. 1 (E) is different. That is, the end timing of the transient period Tk is different. In the first embodiment, the timing is the end timing when a predetermined period elapses from the start of the transient period Tk. On the other hand, in the second embodiment, the end timing is determined by the following processing.

1) As shown in Fig. 1 (B), the feeding speed Fw is integrated from the time t7 at which the feeding speed Fw (feeding speed detection signal Fd) converges at the normal feeding speed to calculate the feeding distance calculation signal Ld.

2) At time t10 when the value of the feed distance calculation signal Ld reaches the value of the feed distance setting signal Lr, the transient period signal Stk is changed to Low level as shown in Fig. 1 (E).

As described above, the welding wire is damaged when accelerating the feed speed Fw at the time of decelerating the feed speed Fw at the end of the last welding and at the time of arc start at this time. Therefore, the last timing of the damage is the time t7 at which the acceleration state ends. Therefore, from the last timing in which the damage is likely to be received by the above 1), the distance to which the damaged portion is fed is calculated. It is determined from the above 2) that the feed distance calculation signal Ld reaches the feed distance setting signal Lr obtained by multiplying the wire protrusion length by the margin rate.

According to the second embodiment described above, the transient period is set based on the time when the welding wire is fed by a distance equivalent to the wire projection length after arc-starting. Thus, in addition to the effects of the first embodiment, the following effects are exhibited. That is, in the present embodiment, since the transient period can be automatically set to the optimum value, it is not necessary to conduct an experiment to set the transient period to an appropriate value for various welding conditions. Therefore, production preparation becomes efficient. Further, since the transient period is always set to the optimum value, it is possible to quickly converge to the normal welding state.

[Third embodiment]

The invention of the third embodiment is to increase the feeding speed of the welding wire to be higher than the feeding speed during the normal welding period during the transient period described above.

5 is a timing chart for explaining an arc start control method for pulse arc welding according to the third embodiment of the present invention. 5 (A) shows the time variation of the welding start signal St, Fig. 5 (B) shows the time variation of the feed rate Fw, Fig. 5 5 (D) shows the time variation of the welding voltage Vw, and FIG. 5 (E) shows the time variation of the transient time signal Stk. Fig. 5 corresponds to Fig. 1 described above, and only the operation of the feeding speed Fw shown in Fig. 5 (B) is different. That is, in FIG. 1, the feeding speed Fw is constant during the transient period Tk and during the normal welding period. On the other hand, in Fig. 5, different feeding speeds are obtained. Hereinafter, the operation of the feeding speed Fw will be described with reference to FIG.

When the welding current Iw starts to be energized at the time t2, the feeding speed Fw is accelerated with the inclination as shown in Fig. 5B, and converged to the transient feeding speed Fwk predetermined at the time t7. At the time t10, since the predetermined period has ended, the transient period signal Stk is changed to the Low level and the transient period Tk is ended as shown in (E) of Fig. 5, and the normal welding period is reached. During the normal welding period from time t10, as shown in Fig. 5B, the feeding speed Fw is switched to the predetermined normal feeding speed Fwc. The transient feeding rate Fwk is set to a value higher than the normal feeding speed Fwc and is set to about 110 to 130% of the normal feeding speed Fwc.

During the transient period, the peak current and the base current are set to values deviating from the optimum value in order to suppress the occurrence of the phenomenon that the arc length is rapidly lengthened. Therefore, the volume transition state during the transient period is somewhat worse than during the normal welding period in which the optimum value is set. In this embodiment, since the feeding speed during the transient period is increased, the transient period can be set shorter. As a result, the welding quality can be improved as compared with the first embodiment.

Fig. 6 is a block diagram of a welding power source for carrying out the arc start control method for pulse arc welding according to the third embodiment of the present invention described above with reference to Fig. 5. Fig. Fig. 6 corresponds to Fig. 3 described above, and the same reference numerals are assigned to the same blocks, and description thereof is not repeated. Fig. 6 shows a modification of the feeding speed setting circuit FR of Fig. 3 by the normal feeding speed setting circuit FCR and the second feeding speed setting circuit FR2. Hereinafter, this block will be described with reference to FIG.

The normal feeding speed setting circuit FCR receives the welding current average value setting signal Ir as described above and sets the normal feeding speed setting corresponding to the value of the welding current average value setting signal Ir in accordance with a pre- And calculates and outputs the signal Fcr.

The second feeding speed setting circuit FR2 receives the transient period signal Stk and the normal feeding speed setting signal Fcr as described above. When the transient period signal Stk is at the Low level, the normal feeding speed setting signal Fcr is set to the feeding speed setting signal Fr And outputs the transient period feeding speed when the value of the normal feeding speed setting signal Fcr is increased by a predetermined value when the level is at the high level as the feeding speed setting signal Fr.

The present embodiment is based on the first embodiment, but the same is true on the basis of the second embodiment.

According to the above-described third embodiment, during the transient period, the feeding speed of the welding wire is made faster than during the normal welding period. Thus, in addition to the effects of the first and second embodiments, the following effects are exhibited. That is, in this embodiment, since the feeding speed during the transient period is accelerated, the phenomenon that the arc length is rapidly prolonged occurs in the early stage. Therefore, the transient period can be set to be shorter, and the welding quality can be further improved.

1: welding wire
1a: Wire reel
2: base material
3: arc
4: welding torch
5: Feed roll
CD: current conduction discrimination circuit
Cd: current energization discrimination signal
DV: drive circuit
Dv: drive signal
EI: Current error amplifying circuit
Ei: current error amplified signal
EV: voltage error amplifier circuit
Ev: Voltage error amplified signal
FC: feed control circuit
Fc: feed control signal
FCR: Normal feed rate setting circuit
Fcr: Normal feed speed setting signal
Fd: Feeding speed detection signal
FR: feed rate setting circuit
Fr: feed rate setting signal
FR2: 2nd feeding speed setting circuit
Fw: feed rate
Fwc: Normal Feed Rate
Fwk: transit period feed rate
Ib: Base current
Ibc: Normal base current
IBCR: Normal base current setting circuit
Ibcr: Normal base current setting signal
Ibk: transient base current
IBKR: Transient base current setting circuit
Ibkr: Transient base current setting signal
IBR: Base current setting circuit
Ibr: base current setting signal
Icr: current control 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: normal peak current
IPCR: Normal peak current setting circuit
Ipcr: Normal peak current setting signal
Ipk: transient peak current
IPKR: Transient peak current setting circuit
Ipkr: Transient peak current setting signal
IPR: Peak current setting circuit
Ipr: Peak current setting signal
IR: welding current average value setting circuit
Ir: welding current average value setting signal
Iw: welding current
LD: feed distance calculation circuit
Ld: Signal to calculate feed distance
LR: Feeding distance setting circuit
Lr: Feeding distance setting signal
LWR: Feeding chip tip / base material distance setting circuit
Lwr: Signal for setting the distance between the tip of the feed chip and the parent material
PM: Power main circuit
Rw: unit length resistance value
RWR: Unit length resistance value setting circuit
Rwr: Unit length resistance value setting signal
ST: welding start circuit
St: welding start signal
STH: Hot start period circuit
Sth: Hot start period signal
STK: transient period circuit
Stk: transient signal
STK2: Second transient period circuit
SW: switching circuit
Tb: Base period
Tf: Pulse period (signal)
TFC: normal welding period pulse cycle calculating circuit
Tfc: Normal welding period Pulse period signal
Th: Hot start period
Tk: transient period
TM: Timer circuit
Tm: Timer signal
Tp: peak period
TPR: peak period setting circuit
Tpr: peak period setting signal
VAV: welding voltage average value calculating circuit
Vav: Welding voltage mean value (signal)
Vb: base voltage
Vbc: Normal base voltage
Vbk: transient base voltage
VD: Welding voltage detection circuit
Vd: welding voltage detection signal
VF: voltage / frequency conversion circuit
Vp: peak voltage
Vpc: normal peak voltage
Vpk: transient peak voltage
VR: welding voltage setting circuit
Vr: welding voltage setting signal
Vw: welding voltage
WM: Wire feed motor
WS: Welding wire selection circuit
Ws: welding wire selection signal
D: Decrease value
ΔDR: Decreasing value setting circuit
? Dr: Decrease value setting signal
Δu: increment value

Claims (7)

A method of controlling an arc start of a pulse arc welding in which a welding wire is fed and welded in such a manner that a normal peak current during a peak period and a normal base current during a base period are made one pulse period during a normal welding period,
Characterized in that during the transient period after arc start, a transient peak current in which the steady peak current is reduced by a predetermined decreasing value and a transient base current in which the steady base current is increased by a predetermined increase value is energized. Arc start control method. The method according to claim 1,
Wherein the reduction value is set based on a unit length resistance value of the welding wire. 3. The method according to claim 1 or 2,
Wherein when the arc length control is a frequency modulation control, the increase value is set so that a difference between an average value of the pulse periods during the transitional period and an average value of the pulse periods during the normal welding period becomes less than a predetermined value. Arc start control method of arc welding. 3. The method according to claim 1 or 2,
Wherein when the arc length control is a pulse width modulation control, the increase value is set such that a difference between an average value of the peak periods during the transient period and an average value of the peak periods during the normal welding period is less than a predetermined value. Arc start control method for pulse arc welding. 3. The method according to claim 1 or 2,
Wherein the transient period is set to a predetermined period. 3. The method according to claim 1 or 2,
Wherein the transient period is set based on a time when the welding wire is fed by a distance corresponding to the wire protrusion length after the arc start. 3. The method according to claim 1 or 2,
Wherein the feeding speed of the welding wire is made higher than the feeding speed during the normal welding period during the transient period.

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