JP2003290924A - Arc length control method in pulsed arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for accurately controlling arc length in pulsed arc welding by accurately detecting apparent arc length without being affected by voltage fluctuation. <P>SOLUTION: A stationary peak voltage is detected in a normal peak period Tpb excepting a transient peak period Tpa at the start (time t1) of a peak period Tp. Then, one or more among the base period, base current, and peak period or peak current is controlled so that the stationary peak voltage is nearly equalized to a predetermined peak voltage set value, thereby maintaining the arc length at the optimum value. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse arc in which a welding wire is fed at a constant speed, and a peak current during a peak period and a base current during a base period are repeatedly energized as one cycle. In welding, the present invention relates to an arc length control method based on the peak voltage during the peak period.

[0002]

2. Description of the Related Art In consumable electrode type arc welding, an anode spot is formed on the tip of a welding wire and a cathode spot is formed on the surface of a base metal, and an arc is generated between the anode spot and the cathode spot. To do. The distance between the anode point and the cathode point at this time is generally called the true arc length. On the other hand, the shortest distance between the tip of the welding wire and the surface of the base metal immediately below is generally called an apparent arc length (hereinafter, simply referred to as arc length). Important welding qualities such as penetration depth and bead appearance have a strong correlation with the above-mentioned apparent arc length, so in order to obtain good welding quality, the apparent arc length during welding should be maintained at an appropriate value. (Hereinafter referred to as arc length control) is important. On the other hand, the welding voltage value is substantially proportional to the true arc length. In carbon dioxide arc welding, MAG welding, etc., the cathode spot is likely to be formed on the surface of the base metal immediately below the welding wire (hereinafter referred to as the welding target position). Therefore, the true arc length and the apparent arc length are substantially Will be equal. For this,
By controlling the average value of the welding voltage to the target value, the true arc length can be controlled, and thereby the apparent arc length, which is the original purpose, can be controlled. On the contrary,
MIG used for aluminum alloy, stainless steel, etc.
In welding, the cathode spot has a property that an oxide film on the surface of the base material is likely to be formed in a portion which is not removed by the cleaning action and remains. For this reason, the cathode spot is often formed not at the welding target position but at a position apart from the welding spot where the oxide film exists. In this case,
Since the true arc length and the apparent arc length are considerably different values, precise arc length control cannot be performed by the welding voltage average value that is not proportional to the apparent arc length. In pulse MIG welding, an arc length control method using a peak voltage described below has been proposed as one of methods for solving this problem. Hereinafter, as a conventional technique, an arc length control method using the peak voltage will be described.

FIG. 1 shows the current in pulse MIG welding.
It is a voltage waveform figure, the figure (A) shows the time change of the welding current Iw, and the figure (B) shows the time change of the welding voltage Vw. 2 is a diagram showing an arc generation state during the peak period Tp shown in FIG. 2 (A) and during the base period Tb shown in FIG. 2 (B). Hereinafter, description will be given with reference to FIG.

A period from time t1 to t2 (peak period T
p) As shown in (A) of the same figure, during the peak period Tp, a peak current Ip of a critical value or more is passed, and as shown in (B) of the same figure, a peak voltage Vp is applied. The values of the peak period Tp and the peak current Ip are set so that one pulse and one droplet are transferred depending on the type of welding wire, the type of shield gas, the feed rate, and the like. Further, the rising and falling of the peak current Ip may be controlled to an appropriate value depending on the type of welding wire, the type of shield gas, the feeding speed, etc., as in the above case.

FIG. 2A shows the arc generation state during this period. Since the peak current Ip is a large current of about 300 to 600 [A], the arc 3 is likely to be formed in the wire feeding direction (arc rigidity). Therefore, the cathode spot N1 is formed near the welding target position in the wire feeding direction due to the rigidity of the arc even if the oxide film is removed. The rigidity of the arc increases in proportion to the value of the current that flows, and as described above, the peak current Ip
= 300 [A] or more, the cathode spot N1 has a property of being formed in the vicinity of the welding target position by the rigidity of the arc rather than a property of forming the cathode spot on the oxide film. Therefore, as shown in FIG. 2 (A), during the peak period Tp, an anode point is formed in the droplet 1a at the tip of the welding wire 1, and a cathode point N1 is formed in the vicinity of the welding target position immediately below it. In the meantime, the arc 3 is generated. As a result, the true arc length La1 [mm] becomes substantially equal to the apparent arc length Lb1 [mm]. Further, since the peak voltage Vp and the true arc length La1 are in a substantially proportional relationship and the true arc length La1 and the apparent arc length Lb1 are substantially equal to each other as described above, as a result, the peak voltage Vp and the apparent arc length Lb1. It has a substantially proportional relationship with the arc length Lb1. Therefore, the apparent arc length Lb1 can be controlled by controlling the arc length by the peak voltage Vp.

A period from time t2 to t3 (base period T
b) As shown in (A) of the same figure, during the base period Tb, the base current Ib is conducted, and as shown in (B) of the figure, the base voltage Vb is applied. The values of the base current Ib and the base period Tb are determined by the type of welding wire, the type of shield gas,
It is set to an appropriate value according to the feeding speed and the like.

FIG. 2B shows the arc generation state during this period. Since the base current Ib is a small current of about several tens [A], the rigidity of the arc is low, and the cathode point N2 is formed on the surface of the base material where the oxide film is not removed.
Normally, the oxide film on the surface of the base metal near the welding target position is first removed by the above-mentioned energization of the peak current Ip, so that the cathode point N2 is formed at a position distant therefrom.
Therefore, as shown in FIG. 2B, the base period Tb
In the inside, an anode point is formed on the droplet 1a, and a cathode point N2 is formed on the surface of the base metal on which the oxide film remains away from the welding target position, and the arc 3 is generated therebetween. As a result, the true arc length La2 [mm] and the apparent arc length Lb2 [mm] are considerably different values. Moreover, in order to obtain the oxide film and move the position at high speed, the cathode point N2 is formed at each time point immediately after the start of the base period Tb, at an intermediate time point, immediately before the end time, and the like. Since the position changes, the true arc length La2 also changes accordingly. Since the base voltage Vb is substantially proportional to the true arc length La2, the base voltage Vb also changes when the true arc length La2 changes. Therefore, the base voltage Vb during the base period Tb
The apparent arc length cannot be controlled by.
Further, as shown in FIG. 7B, the above-mentioned average value Vav of the welding voltage is the average value of the above-mentioned peak voltage Vp and the base voltage Vb, so that it is not proportional to the apparent arc length. It includes a varying base voltage Vb. Therefore, in pulsed MIG welding, precise arc length control cannot be performed by the average value Vav of the welding voltage.

By the way, the apparent arc length is determined by the balance between the feed rate and the melting rate, and changes depending on the difference between them. Usually, the feeding speed is constant. On the other hand,
As shown in FIG. 9A, the melting rate is the pulse period Tf.
Average value Iav of peak current Ip and base current Ib for each
Is approximately proportional to. That is, when the welding current average value Iav becomes large, the melting speed becomes faster than the feeding speed and the apparent arc length becomes long. On the contrary, when the welding current average value Iav becomes smaller, the melting speed becomes slower than the feeding speed, and the apparent arc length becomes shorter. As a method of changing the welding current average value Iav, at least one of the base period Tb, the base current Ib, the peak period Tp, and the peak current Ip may be changed. Therefore, in the arc length control method of the prior art, the base period Tb, the base current Ib, the peak period Tp, or the peak current is set so that the peak voltage Vp that is approximately proportional to the apparent arc length becomes substantially equal to the target value. Control at least one or more of Ip.

[0009]

FIG. 3 is a peak voltage waveform diagram for explaining a problem to be solved by the conventional technique. In the figure, times t1 and t2 are the times t1 in FIG. 1 described above.
And t2. Hereinafter, description will be given with reference to FIG. The peak period Tp includes a peak rising period Tup and a maximum peak period Tpp thereafter until time t2.
The welding voltage value Vw during the peak period Tp is the peak voltage V
p. In the prior art, the peak voltage serving as the feedback value for controlling the arc length is the average value of the peak voltage during the maximum peak period Tpp excluding the peak rising period Tup (hereinafter, referred to as the maximum peak voltage average value Vpp). Was used.

However, when the peak voltage during the transient period from the start of the peak period Tp at the time t1 to the time when it converges to a steady value has an ideal waveform as shown by the curve Y1, it becomes as shown by the curve Y2. There are various cases such as a large overshoot or a convergence below an ideal waveform as shown by the curve Y3. The reason for this is as follows. That is, the arc during the base period before time t1 is in the state of FIG. 2B described above, and its cathode point N2 is formed at a position away from the welding target position.
Then, the arc in the converged state during the peak period Tp after the time t1 is in the state of FIG. 2 (A) described above, and the cathode point N1 is formed near the welding target position. Therefore, depending on the position of the cathode spot before time t1 or the transient movement path of the cathode spot, the peak voltage associated therewith also shows various transient changes as shown by the curves Y1 to Y3.

At the end of the peak period Tp (time t
2) Peak period T so that the droplets move before and after
Usually, p is set. For this reason, if the droplet transfer is performed immediately before the end of the peak period Tp, the formation position of the anode point formed in the droplet will move, as shown by the curve Y4 in the figure. The peak voltage may fluctuate accordingly.

As described above, the maximum peak voltage average value V
Since pp includes transient fluctuations due to the movement of the cathode point at the start of the peak period and transient fluctuations due to the movement of the anode point during droplet transfer, there is an error in the detection of the apparent arc length. Will occur. In particular, since the voltage fluctuation value at the start of the peak period is large, it is not possible to perform precise arc length control with the maximum peak voltage average value Vpp including this.

Therefore, the present invention provides an arc length control method for pulse arc welding in which the arc length can be precisely controlled by accurately detecting the apparent arc length without being affected by voltage fluctuations. .

[0014]

The first aspect of the present invention is shown in FIGS.
, The welding wire is fed at a constant speed, the peak current Ip is supplied during the peak period TP, and the base period T is reached.
In the arc length control method of pulse arc welding in which energization of the base current Ib in b is repeatedly energized as one cycle Tf, the transient peak period Tpa in which the voltage at the start of the peak period Tp transiently changes is excluded. Steady peak period T
The steady peak voltage Vpa in pb is detected, and the base period Tb or the base current Ib is set so that the steady peak voltage value Vpa becomes substantially equal to a predetermined peak voltage set value Vps.
Alternatively, the arc length control method for pulse arc welding is characterized in that the arc length is maintained at an appropriate value by controlling at least one of the peak period Tp and the peak current Ip.

In the second aspect of the invention, as shown in FIGS. 4 and 6, the steady peak voltage value Vpa is equal to the steady peak period Tpb.
It is the arc length control method for pulse arc welding according to the first invention, which is the instantaneous value Vpc of the peak voltage at a specific point in time.

In a third aspect of the invention, as shown in FIGS. 4, 7 and 8, the steady-state peak voltage value Vpa is an average value of peak voltages during a part or all of the steady-state peak period Tpb ( Vpd or Vpb) is the arc length control method for pulse arc welding according to the first invention.

In a fourth aspect of the invention, as shown in FIGS. 4 and 6, the steady peak voltage value Vpa is equal to the steady peak period Tpb.
2 is an arc length control method for pulse arc welding according to the first aspect of the present invention, which is a moving average value Vpcr of a peak voltage instantaneous value at a specific point in time over a predetermined period in the past.

In a fifth aspect of the invention, as shown in FIGS. 4, 7 and 8, the steady-state peak voltage value Vpa is a past peak voltage average value during a part or all of the steady-state peak period Tpb. It is an arc length control method for pulse arc welding according to the first invention, which is a moving average value over a predetermined period.

The sixth aspect of the present invention is, as shown in FIGS.
The peak voltage setting value Vps is detected by detecting the number of short circuits per unit time between the welding wire and the base metal during welding, and the short circuit frequency detection value Nd is automatically set to be substantially equal to the predetermined short circuit frequency set value Ns. An arc length control method for pulse arc welding according to the first aspect of the invention, which is set.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 is a peak voltage waveform diagram corresponding to FIG. 3 described above for explaining an example of an embodiment of the present invention. The peak voltage waveform in the figure is the same as that in FIG. Hereinafter, description will be given with reference to FIG. As shown in the figure, at the start of the peak period Tp at the time t1, the peak voltage Vp during the transient peak period Tpa accompanying the movement of the cathode spot as described above is as shown by the curves Y1 to Y3. It varies greatly depending on the route. When the transient peak period Tpa elapses and the steady peak period Tpb is entered, the cathode spot is stably formed in the vicinity of the welding target position as described above with reference to FIG. The voltage Vp becomes a stable and substantially steady value (hereinafter, referred to as steady peak voltage value Vpa). Since the cathode spot is stably formed in the vicinity of the welding target position, the above-mentioned steady peak voltage value V
With pa, the apparent arc length can be accurately detected with almost no error. Therefore, the steady-state peak voltage value Vpa is detected and the preset peak voltage set value Vos is determined.
By controlling at least one of the base period Tb, the base current Ib, the peak period Tp, or the peak current Ip so as to be substantially equal to the (target value), it is possible to control to an appropriate arc length.

The following detected value can be used as the above-mentioned steady peak voltage value Vpa. Instantaneous value of steady peak voltage Vpc at a specific time point As shown in the same figure, the instantaneous value of steady peak voltage Vpc at the time when a predetermined delay time Tpc has passed from the start time of the peak period Tp is used as the steady peak voltage value Vpa. be able to. The delay time Tpc is the transient peak period Tpa.
It is set in advance so that it will be a point in the period from after the passage of time to before the voltage fluctuation due to the movement of the anode point during the droplet transfer shown in the curve Y4 occurs. For example, as shown in FIG.
It is conceivable to set it at the middle point of the maximum peak period Tpp shown in.

Steady-state peak voltage average value V during a predetermined period
pd The above term is an instantaneous value, but in order to reduce the detection error, a predetermined averaging period T after the delay time Tpc elapses.
The average value Vpd of the steady peak voltage in pd can be used as the steady peak voltage value Vpa.

The average value Vpb of the steady peak voltage during the steady peak period The period during which the peak voltage is averaged in the above term is set to the whole period of the steady peak period Tpb, that is, the average value Vpb of the steady peak voltage during the steady peak period. Is.

The moving average value of the above items to Vpc (n) is the steady-state peak voltage instantaneous value of the above item in the n-th peak period Tp (n), and the moving average value from the current cycle to the previous predetermined cycle m times. Vpcr is given by the following formula. Vpcr = (Vpc (n) + Vpc (n-1) + ... + Vpc (n-m + 1)) / m In the above equation, the steady-state peak voltage instantaneous value Vpc of each cycle is averaged with equal weight. It may be a weighted moving average value in which the weight of the value of the cycle close to the current cycle is increased. The reason for calculating the moving average value and setting it as the steady-state peak voltage value Vpa is as follows. That is, even if the cathode spot is formed in the vicinity of the welding target position during the steady peak period Tpb, the state of the molten pool, the state of the droplets, etc., fluctuate slightly in each cycle, so the apparent arc length Will also fluctuate. A moving average value is calculated in order to average this variation and detect a more accurate apparent arc length. Also, the moving average values of the above-mentioned terms and the steady-state peak voltage average values Vpd and Vpb over a predetermined period in the past can be calculated in the same manner as above.

Hereinafter, a welding power supply device for carrying out the arc length control method using the steady peak voltage Vpa described in the above items 1 to 4 will be described. FIG. 5 is a block diagram of a welding power supply device for carrying out the present invention. Hereinafter, each circuit block will be described with reference to FIG. The output control circuit INV is a commercial AC power supply (three-phase 200
[V] and the like) as an input, and a current error amplification signal E described later
According to i, output control such as inverter control and thyristor phase control is performed, and welding voltage Vw and welding current Iw for welding are output. The welding wire 1 is fed at a constant speed through the welding torch 4 by the feeding roll 5 of the wire feeding device, and the arc 3 is generated between the welding wire 1 and the base material 2. In the figure, the circuit block relating to the feeding control is omitted.

The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The steady peak voltage detection circuit VPA receives the above voltage detection signal Vd and a peak period signal Stp described later, and detects the peak voltage Vp after the passage of the transient peak period Tpa as described above with reference to FIG. The detection signal Vpa is output. The peak voltage setting circuit VPS uses a predetermined peak voltage setting signal V
Output ps. The voltage error amplification circuit EV includes the above steady peak voltage detection signal Vpa and the above peak voltage setting signal Vps.
The error between and is amplified and a voltage error amplified signal ΔV is output. The error integration circuit IV uses the above voltage error amplification signal ΔV.
Is integrated and the manipulated variable setting signal Iv is output. In the drawing, the case where the length of the base period is controlled as the operation amount of the feedback control is illustrated, and thus the operation amount setting signal Iv is expressed by the following equation. Iv = Tb = Tb0 + ΔV where Tb is the base period length of the current period, and Tb0 is the base period length of the previous period. Also, when the manipulated variable is the base current, the peak period, or the peak current, the manipulated variable setting signal Iv can be calculated in the same manner as the above equation. When the manipulated variable is in the base period Tb, the manipulated variable setting signal Iv is based on the base feedback timer circuit TB described later.
Is input to the base current setting circuit IBS described later when it is the base current Ib, is input to the peak feedback timer circuit TP described later when it is the peak period Tp, and is the peak current setting circuit described later when it is the peak current Ip. Input to IOS.

The base period timer circuit TB outputs the base period signal Stb which becomes High level for the length of time determined by the manipulated variable setting signal Iv from the time when the peak feedback signal Stp described later changes from High level to Low level. Output. The peak period timer circuit TP keeps the High level for a predetermined time period from the time when the base period signal Stb changes from the High level to the Low level.
The peak period signal Stp that is at the h level is output. Therefore, the peak period signal Stp is Hi during the peak period Tp.
It is a signal that goes to the gh level and goes to the Low level during the base period Tb.

The peak current setting circuit IPS outputs a predetermined peak current setting signal Ips. The base current setting circuit IBS outputs a predetermined base current setting signal Ibs. The current setting switching circuit SW switches to the a side when the peak period signal Stp is at the high level and outputs the peak current setting signal Ips as the current control setting signal Isc, and when it is at the low level, the base current setting signal is above. Ibs is output as the current control setting signal Isc.

The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The current error amplifier circuit EI has the above current control setting signal Isc and current detection signal Isc.
The error from d is amplified and the current error amplified signal Ei is output. By this current error amplification circuit EI, the external characteristics of the welding power source device PS are output-controlled to the constant current characteristics, and the welding current Iw corresponding to the above current control setting signal Isc is supplied.

The welding power source PS described above controls the time length of the base period Tb so that the value of the steady peak voltage detection signal Vpa becomes substantially equal to the value of the peak voltage setting signal Vps of the target value, and the apparent length is apparent. The arc length of is always maintained at a proper value.

FIG. 6 is a block diagram of the steady peak voltage detection circuit VPA of FIG. 5 when the steady peak voltage Vpa is the steady peak voltage instantaneous value Vpc of the above term. Less than,
It will be described with reference to FIG. Delay time timer circuit TPC
Outputs a delay time signal Stpc which becomes High level for a predetermined time length from the time when the peak period signal Stp changes from Low level to High level (starting point of the peak period Tp). The trigger circuit TG outputs a trigger signal Tg which becomes High level for a short time at the end of the delay time signal Stpc. The sample hold circuit S / H samples and holds the voltage detection signal Vd when the above trigger signal Tg is at the high level, and becomes the steady peak voltage instantaneous value Vpc and becomes the steady peak voltage detection signal Vd.
Output pa. Further, when calculating the moving average value described above, a moving average value calculating circuit for storing the output of the sample hold circuit S / H for a predetermined number of cycles and calculating the moving average value may be inserted.

FIG. 7 is a block diagram of the steady peak voltage detection circuit VPA of FIG. 5 when the steady peak voltage Vpa is the steady peak voltage average value Vpd of the above-mentioned term. Less than,
It will be described with reference to FIG. Delay time timer circuit TPC
Outputs a delay time signal Stpc which becomes High level for a predetermined time length from the time when the peak period signal Stp changes from Low level to High level (starting point of the peak period Tp). Averaging period timer circuit TP
The D outputs the averaging period signal Stpd which becomes High level for a predetermined period from the end point of the delay time signal Stpc. The sample hold circuit S / H samples and holds the voltage detection signal Vd when the averaging period signal Stpd is at the high level, and outputs the sample hold signal Sh. The average value calculation circuit AV calculates the average value of the plurality of sample hold signals Sh described above, and becomes the steady peak voltage average value Vpd, which is the steady peak voltage detection signal V.
Output pa. Further, when calculating the moving average value described above, a moving average value calculating circuit for storing the output of the average value calculating circuit AV for a predetermined number of cycles and calculating the moving average value may be inserted.

FIG. 8 is a block diagram of the steady peak voltage detection circuit VPA of FIG. 5 when the steady peak voltage Vpa is the steady peak voltage average value Vpb of the above term. Less than,
It will be described with reference to FIG. The on-delay circuit OD outputs a steady peak period signal Stpb by delaying the time when the peak period signal Stp changes from the Low level to the High level by a predetermined transient peak period Tpa. The sample and hold circuit S / H samples and holds the voltage detection signal Vd when the above-mentioned steady peak period signal Stpb is at the high level, and then holds the sample and hold signal Sd.
Output h. The average value calculation circuit AV calculates the average value of the plurality of sample hold signals Sh described above, and becomes the steady peak voltage average value Vpb, which is the steady peak voltage detection signal Vpa.
Is output. Further, when calculating the moving average value described above, a moving average value calculating circuit for storing the output of the average value calculating circuit AV for a predetermined number of cycles and calculating the moving average value may be inserted.

By the way, in the above-described present invention, the steady peak voltage value Vpa is detected, and the output of the welding power source device is set so that the steady peak voltage value Vpa becomes substantially equal to the peak voltage set value Vps corresponding to the target arc length. To control. That is, if you want to maintain the target arc length at an appropriate value of 4 mm,
The peak voltage setting value Vps corresponding to this target arc length is set. FIG. 9 is a diagram illustrating a relationship between the welding current average value Iav and the peak voltage setting value Vps when the target arc length is 4 mm. In the figure, the characteristic A is an aluminum-magnesium alloy (Al-M) having a diameter of 1.2 mm.
g alloy) wire, and characteristic B shows the case of an Inconel wire having a diameter of 1.2 mm. For example, in order to set the target arc length to 4 mm when the welding current average value Iav = 150 A is used by using an Al-Mg alloy wire, the peak voltage setting value Vps = 26. Must be set to 6V. Similarly, in order to set the target arc length to 4 mm when the welding current average value Iav = 200 A using the Al-Mg alloy wire, the peak voltage setting value Vps = 28 V is set as shown at point A2 in FIG. Must be set to. Further, in order to set the target arc length to 4 mm when the welding current average value Iav = 150 A is used by using Inconel wire, as shown at point B1 in the figure, the peak voltage setting value V
It is necessary to set ps = 28V. Similarly, in order to set the target arc length to 4 mm when the welding current average value Iav = 200 A using Inconel wire, the peak voltage setting value Vps = 29.4 V is set as shown at point B2 in FIG. Must be set. After setting the peak voltage setting value Vps as described above, the arc length is always maintained at the target value of 4 mm by the above-described arc length control method of the present invention.

As described above, since the peak voltage set value Vps corresponding to the target arc length differs depending on the material, diameter, welding current average value Iav, etc. of the welding wire, the peak voltage set value Vps before welding is performed. Need to be obtained by experiments, setting conditions, etc. On the other hand, in pulse arc welding, the welding wire material, diameter, and welding current average value I
Regardless of av etc., the proper (target) arc length is about 4 mm, which is almost constant. A method of automatically setting the peak voltage setting value Vps will be described below. That is, this is a method for automatically setting the peak voltage setting value Vps by utilizing the fact that the number of short circuits between the welding wire and the base material per unit time is substantially inversely proportional to the arc length. FIG. 10 is a diagram showing a short circuit count characteristic C between the arc length and the short circuit count in pulse arc welding. As indicated by point C1 in the figure, the number of short circuits when the arc length is 4 mm is 8 times / second, and as shown by point C2 in the figure, the number of short circuits is 12 times / second. Becomes Therefore, the number of short circuits per unit time may be detected during welding, and the peak voltage set value Vps may be automatically set so that the number of short circuits becomes the target number corresponding to the target arc length. Assuming that the target arc length is 4 mm, the peak voltage setting value Vps is automatically set so that the number of short circuits is 8 times / second, as indicated by point C1 in FIG. By doing so, the appropriate peak voltage setting value Vps shown in the above-mentioned FIG. 9A1 to A2 or B1 to B2 corresponding to the welding wire material, diameter, and welding current average value Iav is automatically set.

FIG. 11 is a block diagram of the welding power source device of the present invention for automatically setting the peak voltage setting value according to the number of short circuits described above. This figure is obtained by adding a circuit shown by a dotted line for automatically setting a peak voltage setting value according to the number of short circuits to the block diagram of FIG. 5 described above. In the figure,
The same circuits as those in FIG. 5 are designated by the same reference numerals, and the description of those circuits will be omitted. Hereinafter, a circuit shown by a dotted line different from that of FIG. 5 will be described with reference to FIG.

The short circuit frequency detection circuit ND has a voltage detection signal V
With d as an input, the number of short circuits per unit time is detected and a short circuit count detection signal Nd is output. Short circuit count setting circuit N
S outputs a short circuit number setting signal Ns corresponding to the target arc length. The short circuit number error amplification circuit EN amplifies an error between the short circuit number setting signal Ns and the short circuit number detection signal Nd and outputs a short circuit number error amplification signal ΔN. The short circuit number error amplified signal integration circuit IN integrates the short circuit number error amplified signal ΔN and outputs a peak voltage setting signal Vps. With these circuits, the value of the peak voltage setting signal Vps is automatically set by feedback control so that the value of the short circuit number detection signal Nd becomes equal to the value of the short circuit number setting signal Ns.

As described above, the arc length control method of the present invention exerts a great effect in pulse MIG welding, but also in pulse MAG welding, the arc length can be precisely controlled. Therefore, the present invention can be applied to the entire pulse arc welding.

[Effects] The effects of the present invention will be illustrated below.
FIG. 12 is a diagram comparing the variation range of the arc length between the present invention and the prior art in pulse MIG welding of an aluminum alloy. The welding condition is 1.2 for the welding wire.
[Mm] aluminum alloy wire (JIS A4043
This is the case where a welding material is used and the peak voltage setting value Vps is set to 27 [V]. This figure compares the variation range of the arc length during welding by performing bead-on-plate welding while keeping the torch height constant at 20 [mm]. As is clear from the figure, in the conventional technique, the variation range is large at ± 0.8 [mm]. On the other hand, in the present invention, the variation range is ± 0.2 [mm].
And it is reduced to 1/4. As described above, according to the arc length control method of the present invention, the arc length can be controlled more precisely to the target value, and the welding quality becomes good.

FIG. 13 compares arc length fluctuations as shown in FIG. 12B when the torch height is changed as shown in FIG. 12A under the same welding conditions as in FIG. FIG. This figure compares the arc length variation between the present invention and the prior art when the torch height is periodically changed within the range of 20 ± 5 [mm] as shown in FIG. Is. As is clear from the figure, in the conventional technology,
Since it is impossible to suppress the variation of the arc length due to the change of the torch height, the arc length also varies by about ± 1.2 [mm] according to the change of the torch height. On the contrary,
In the present invention, since the variation of the arc length due to the variation of the torch height can be well suppressed, the variation of the arc length is ±
It becomes 1/3 as small as 0.4 mm.

[0041]

According to the present invention, since the arc length can be controlled more precisely by controlling the arc length by the steady peak voltage Vpa in pulse arc welding, a higher quality welding result can be obtained. it can. Furthermore, by using the average value (Vpd and Vpb) of the steady peak voltage during a part or all of the steady peak period as the steady peak voltage value Vpa, the arc length detection error can be further reduced. Therefore, the arc length control becomes more stable. Furthermore, as the steady peak voltage value Vpa,
Instantaneous value of steady peak voltage Vpc, average value of steady peak voltage Vpd
Alternatively, by using the moving average value of Vpb over a predetermined period in the past, the detection error due to the variation of the arc length for each period can be more averaged, so that the arc length control becomes more stable.

Further, according to the automatic setting method of the peak voltage setting value Vps depending on the number of short circuits, in addition to the above effects, the appropriate peak voltage setting value Vps according to the material, diameter, welding current average value, etc. of the welding wire. Since it is automatically set to, it is possible to save the trouble of setting.

[Brief description of drawings]

FIG. 1 Current / voltage waveform diagram of prior art pulsed MIG welding

FIG. 2 is a peak period Tp and a base period Tb of the related art.
Arc state diagram

FIG. 3 is a conventional peak voltage waveform diagram for explaining the problem to be solved by the present invention.

FIG. 4 is a peak voltage waveform diagram for explaining the principle of the present invention.

FIG. 5 is a block diagram of a welding power source device of the present invention.

FIG. 6 is a first diagram of the steady-state peak voltage detection circuit VPA of the present invention.
Examples of

FIG. 7 is a second diagram of the steady-state peak voltage detection circuit VPA of the present invention.
Examples of

FIG. 8 is a third diagram of the steady-state peak voltage detection circuit VPA of the present invention.
Examples of

FIG. 9 is a diagram showing a relationship between a welding current average value Iav and a peak voltage setting value Vps in the present invention.

FIG. 10 is a diagram showing the relationship between the arc length and the number of short circuits in the present invention.

FIG. 11 is a block diagram of a welding power source device for automatically setting a peak voltage setting value Vps according to the number of short circuits according to the present invention.

FIG. 12 is an arc length variation comparison diagram when the torch height is constant, illustrating the effect of the present invention.

FIG. 13 is a comparison diagram of arc length fluctuations when the torch height changes, which illustrates another effect of the present invention.

[Explanation of symbols]

1 welding wire 1a Droplet 2 base material 3 arc 4 welding torch 5 feeding rolls AV average value calculation circuit EI current error amplifier circuit Ei Current error amplification signal EN Short circuit error amplifier EV voltage error amplifier circuit Iav welding current average value Ib base current IBS base current setting circuit Ibs Base current setting signal IN Short circuit error amplification signal integration circuit INV output control circuit Ip peak current IPS peak current setting circuit Ips peak current setting signal Isc current control setting signal IV error integration circuit Iv manipulated variable setting signal Iw welding current La1, La2 True arc length Lb1, Lb2 Apparent arc length N1, N2 cathode spot ND short circuit detection circuit Nd short circuit count detection signal NS short circuit count setting circuit Ns Short circuit count setting signal OD on-delay circuit PS welding power supply S / H sample and hold circuit Sh sample hold signal Stb base period signal Stp peak period signal Stpc delay time signal Stpd averaging period signal SW current setting switching circuit Tb base period TB base period timer circuit Tf pulse period TG trigger circuit Tg trigger signal Tp peak period TP peak period timer circuit Tpa transient peak period Tpb steady peak period Tpc delay time TPC delay time timer circuit TPD averaging period timer circuit Tpd averaging time Tpp maximum peak period Tup peak rising period Vav Average welding voltage Vb base voltage VD voltage detection circuit Vd voltage detection signal Vp peak voltage Vpa steady peak voltage (detection signal) VPA steady peak voltage detection circuit Vpb, Vpd Steady peak voltage average value Vpc Instantaneous peak voltage value Vpp maximum peak voltage average value VPS peak voltage setting circuit Vps peak voltage setting signal Vw welding voltage Y1 to Y4 voltage fluctuation curve ΔN Short circuit count error amplification signal ΔV Voltage error amplification signal

Claims (6)

[Claims] 1. A method for controlling an arc length of pulse arc welding, in which a welding wire is fed at a constant speed, and a peak current during a peak period and a base current during a base period are repeatedly energized as one cycle. In, the voltage at the start of the peak period detects a steady peak voltage during a steady peak period excluding a transient peak period in which the voltage transiently changes, and this steady peak voltage value is substantially equal to a preset peak voltage setting value. Arc length control method for pulse arc welding, characterized in that the arc length is maintained at an appropriate value by controlling at least one of the base period, the base current, the peak period or the peak current so that . 2. The steady peak voltage value is an instantaneous value of the peak voltage at a specific time point during the steady peak period.
An arc length control method for pulse arc welding as described. 3. The arc length control method for pulse arc welding according to claim 1, wherein the steady peak voltage value is an average value of peak voltages during a part or all of the steady peak period. 4. The arc length control method for pulse arc welding according to claim 1, wherein the steady peak voltage value is a moving average value of the instantaneous peak voltage value at a specific time point during the steady peak period over a past predetermined cycle. 5. The arc length of pulse arc welding according to claim 1, wherein the steady peak voltage value is a moving average value of peak voltage average values during a part or all of the steady peak period over a past predetermined cycle. Control method. 6. The peak voltage set value is detected by detecting the number of short circuits per unit time between the welding wire and the base material during welding,
The arc length control method for pulse arc welding according to claim 1, wherein the detected value of the number of short circuits is automatically set so as to be substantially equal to a preset value of the number of short circuits.