JP2012232312A - Welding current control method during short circuit period - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve favorable welding quality in arc welding of a consumable electrode even when an angle of advance of a welding torch is large.SOLUTION: When short circuit occurs, a welding current Iw is reduced and maintained at an initial current value Ii, and when an initial period Ti has elapsed, the welding current Iw is increased to a first slope K1, and, when the welding current Iw reaches a reference value Ic, the welding current Iw is increased until arc occurs again at a second slope K2 which is a value smaller than the first slope K1. A welding current value Ia at the time of occurrence of the short circuit is detected, a current difference integral value Si=∫(Ia-Iw)/dt in the initial period Ti is calculated, and the above reference value Ic is automatically set based on this current difference integral value Si. By this means, because the reference value Ic is adjusted to a proper value by the current difference integral value Si which correlates with a size of a droplet, it is possible to achieve favorable welding quality even when the angle of advance is large.

Description

  The present invention relates to a welding current control method for a short-circuit period for improving a droplet transfer state in consumable electrode arc welding in which a short-circuit period and an arc period are alternately repeated.

  Consumable electrode arc welding, in which welding wire is fed at a constant speed and welding is performed using carbon dioxide gas, argon gas, a mixed gas of carbon dioxide gas and argon gas, etc. as the shielding gas, can achieve high quality. It is widely used because it is easy to automate. In this arc welding, welding is often performed by alternately repeating a short-circuit period and an arc period between a welding wire and a base material. During the arc period, the tip of the welding wire melts to form droplets, and during the short circuit period, the droplets move to the molten pool. In order to form a good weld bead and reduce the amount of spatter generated, it is important to control the welding current during the short-circuit period to an appropriate value so that droplet transfer can be performed smoothly. Hereinafter, the welding current control method in the short circuit period in the prior art will be described (for example, see Patent Document 1).

  FIG. 3 is a voltage / current waveform diagram of consumable electrode arc welding in the prior art. FIG. 4A shows the change over time of the welding voltage Vw applied between the welding wire and the base material, and FIG. 4B shows the change over time of the welding current Iw energized from the welding wire to the base material. . Hereinafter, a description will be given with reference to FIG.

  In the figure, time t1 to t2 is a short circuit period Ts, and time t2 to t3 is an arc period. The short circuit period Ts and the arc period Ta are alternately repeated. When the droplet formed at the tip of the welding wire comes into contact with the molten pool at time t1, a short-circuit state occurs. In the short circuit state, the welding voltage Vw rapidly drops to a short circuit voltage value of about several volts as shown in FIG. As shown in FIG. 5B, the welding current Iw decreases with a slope to a predetermined initial current value Ii, and maintains that value during a predetermined initial period Ti from time t1 to t11. When the initial period Ti ends at time t11, the welding current Iw rapidly rises to a predetermined peak value as shown in FIG. 5B, and maintains that value until time t2 when the arc is regenerated.

  When the arc is regenerated at time t2, the welding voltage Vw rapidly increases to an arc voltage value of about several tens of volts as shown in FIG. As shown in FIG. 5B, the welding current Iw decreases slightly until the next short-circuit occurs after it suddenly decreases slightly when the arc is regenerated.

  Next, the transition state of the droplets will be described. The reason why the welding current Iw is maintained at a small initial current value Ii during the initial period Ti from the time when the short circuit occurs is to make the contact state between the droplet and the molten pool more reliable. Immediately after the occurrence of the short-circuit, a part of the bottom of the droplet is in contact with the molten pool. If the welding current Iw is large in this state, the contact state is released without the droplet moving and the arc is generated. It will occur again, and the stable droplet transfer state will be inhibited. By increasing the welding current Iw from the time t11 when the initial period Ti ends, a pinch force is applied to the droplet, causing a constriction at the upper portion of the droplet, and the droplet is smoothly transferred to the molten pool. At the time when the arc is regenerated at time t2, the tip of the welding wire is not melted. As the arc period Ta proceeds, the tip of the welding wire is gradually melted by heat from the arc and Joule heat to form droplets.

  In order to stabilize the droplet transfer state, it is important to optimize the setting of the peak value of the welding current Iw during the short-circuit period Ts. If this peak value is smaller than the appropriate value, the pinch force acting on the droplets becomes weak, so the time for transferring the droplets becomes long and the welding state becomes unstable. Conversely, when the peak value is larger than the appropriate value, the amount of spatter generated increases. Therefore, the peak value is set to an appropriate value according to the type of shield gas, the material of the welding wire, the diameter, the feeding speed, and the like.

Japanese Patent Publication No. 4-407

  As described above, in order to stabilize the droplet transfer state, it is necessary to set the peak value of the welding current during the short circuit period to an appropriate value according to the welding conditions. When the advancing angle of the welding torch is as small as about 0 to 10 °, by optimizing this peak value according to the welding conditions, it is possible to reduce the amount of spatter generation and form a good weld bead. . However, if the advancing angle is increased to 20 ° or 30 ° with the peak value kept at a small advancing angle, the amount of spatter generated increases. If the peak value is reduced in order to reduce the amount of spatter generated, a long short circuit exceeding 10 ms sometimes occurs and the welding state becomes unstable. That is, when the advance angle is increased to 20 ° or more, there is a problem in that it is impossible to achieve both a reduction in spatter generation and a stable welding state regardless of the peak value set in the prior art. there were. Therefore, in the prior art, select whether to give priority to the stability of the welded state at the expense of the amount of spatter generated, or select whether to sacrifice the stability of the welded state to give priority to a small amount of spatter generated, The peak value was set.

  Therefore, the present invention provides a welding current control method during a short-circuit period that can reduce the amount of spatter generated and maintain good welding state stability even when the advance angle of the welding torch is large. For the purpose.

In order to solve the above-described problem, the invention of claim 1 is an arc welding in which a welding wire is fed and a short circuit period and an arc period are alternately repeated.
When a short circuit occurs, the welding current Iw is decreased and maintained to a predetermined initial current value Ii, and when a predetermined initial period Ti has elapsed from the time of the occurrence of the short circuit, the welding current is increased at a predetermined first slope, In the welding current control method for a short-circuit period in which welding is performed by increasing the welding current at a predetermined second slope having a value smaller than the first slope until the arc is regenerated when the welding current reaches a reference value Ic. ,
The welding current value Ia at the time of the occurrence of the short circuit is detected, the current difference integrated value Si = ∫ (Ia−Iw) · dt during the initial period Ti is calculated, and the reference value Ic is set to the current difference integrated value Si. Automatically set based on the
It is the welding current control method of the short circuit period characterized by this.

The invention of claim 2 limits the reference value Ic to a predetermined range.
The welding current control method for a short circuit period according to claim 1.

The invention of claim 3 is automatically set as the reference value Ic = G · Si (where G is a predetermined constant).
The welding current control method for a short circuit period according to claim 1 or 2.

In the invention of claim 4, it is assumed that the welding current Iw = Ii during the initial period Ti, and the current difference integral value Si = Ｉ (Ia−Ii) · dt = (Ia−Ii) · Ti,
It is a welding current control method of the short circuit period of any one of Claims 1-3 characterized by the above-mentioned.

According to a fifth aspect of the present invention, the multiplication value Ii · Ti = 0 of the initial current value Ii and the initial period Ti is set, and the current difference integral value Si = (Ia−Ii) · Ti = Ia · Ti. ,
The welding current control method for a short-circuit period according to claim 4.

  According to the present invention, when a short circuit occurs, the welding current is reduced and maintained at a small initial current value during the initial period, and thereafter the welding current is increased at the first slope, and the welding current reaches the reference value. Then, the welding current is increased until the arc is regenerated at a second slope that is gentler than the first slope. Then, the reference value is automatically set based on the current difference integral value during the initial period. Thereby, when the welding state is in a steady state, the reference value is automatically set to a small value, so that the amount of spatter generated is reduced. When the droplet formation state fluctuates due to a disturbance, the reference value is automatically set to a large value, so that the welding state can be prevented from becoming unstable. Therefore, even when the advancing angle of the welding torch is large, it is possible to perform welding with a small amount of spatter generation and good stability in the welding state.

It is a voltage and current waveform diagram showing a welding current control method during a short circuit period according to an embodiment of the present invention. It is a block diagram of the welding power supply for enforcing the welding current control method of the short circuit period concerning embodiment of this invention. It is a voltage and electric current waveform diagram of consumable electrode arc welding in a prior art.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a voltage / current waveform diagram showing a welding current control method during a short-circuit period according to an embodiment of the present invention. 3A shows the change over time of the welding voltage Vw, and FIG. 3B shows the change over time of the welding current Iw. This figure corresponds to FIG. 3 described above. A description of the above will be omitted and will be described below with reference to FIG.

  In the figure, times t1 to t2 indicate a short circuit period Ts, and times t2 to t3 indicate an arc period Ta. The short circuit period Ts and the arc period Ta are alternately repeated.

  When the droplet formed at the tip of the welding wire comes into contact with the molten pool at time t1, a short-circuit state occurs. In the short circuit state, the welding voltage Vw rapidly drops to a short circuit voltage value of about several volts as shown in FIG. As shown in FIG. 2B, the welding current Iw decreases with a slope from the current value Ia at the time of occurrence of a short circuit to a predetermined initial current value Ii, and during a predetermined initial period Ti from time t1 to t11. Maintains that value. The inclination when the welding current Iw decreases is determined by the resistance value and inductance value of the current path of the welding current Iw. That is, the inclination changes depending on the length of the cable connecting the welding power source, the welding torch, and the base material. The longer the cable, the slower the slope. Further, the current value Ia at the time of occurrence of the short circuit is substantially proportional to the length of the arc period Ta before the occurrence of the short circuit. This is because the welding current Iw during the arc period Ta gradually decreases as the arc period Ta proceeds. Since the size of the droplet formed during the arc period Ta is approximately proportional to the length of the arc period Ta, it can be said that the size of the droplet is approximately inversely proportional to the current value Ia when a short circuit occurs.

  When the initial period Ti ends at time t11, the welding current Iw rises at a predetermined first slope K1 to a predetermined reference value Ic, as shown in FIG. When the welding current Iw reaches the reference value Ic, the welding current Iw continues to rise until time t2 when the arc is regenerated at a second slope K2 that is set to a value that is gentler than the first slope K1. . The method for automatically setting the reference value Ic will be described later.

  When the arc is regenerated at time t2, the welding voltage Vw rapidly increases to an arc voltage value of about several tens of volts as shown in FIG. As shown in FIG. 5B, the welding current Iw decreases slightly until the next short-circuit occurs after it suddenly decreases slightly when the arc is regenerated.

  Also in this figure, the reason for maintaining the welding current Iw at a small value by providing the initial period Ti is to prevent arc re-occurrence immediately after the occurrence of a short circuit and lead to a reliable short circuit state. After the initial period Ti ends, the welding current Iw rapidly rises to the reference value Ic with the fast first slope K1. This reference value Ic corresponds to the peak value of the prior art. This reference value Ic is set to a value smaller than the peak value of the prior art. Thereafter, the welding current Iw increases with a gentle second slope K2. Since the rising period at the second slope K2 is provided, the reference value Ic can be set to a small value.

The reference value Ic is automatically set as follows. The current difference integral value Si (A · ms) during the initial period Ti is defined as follows.
Si = ∫ (Ia−Iw) · dt (1) where the integration is performed during the initial period Ti (ms). Ia is the current value when a short circuit occurs.
Then, the reference value Ic is automatically set as follows.
Ic = G · Si (2) where G is a predetermined constant.

  The reason why the reference value Ic is automatically set based on the current difference integral value Si is as follows. As described above, the reference value Ic corresponds to the peak value of the prior art, and the reference value Ic is set to be smaller than the peak value in order to reduce the amount of spatter generated when the advance angle is large. The For this reason, the welding state may become unstable. The case where the welding state becomes unstable is when the droplet formation state is not sufficient at the time when the short circuit occurs. In such a case, the reference value Ic is set to release the short circuit state stably. It needs to be bigger. As described above, the current value Ia at the occurrence of a short circuit and the size of the droplet are inversely proportional. When the current value Ia at the time of occurrence of a short circuit is large, the current difference integrated value Si is also increased, and the reference value Ic is also increased. This means that the reference value Ic is optimized according to the size of the droplet when a short circuit occurs.

  Furthermore, since the welding current Iw is maintained at a small value during the initial period Ti, the temperature of the droplets is lowered. Therefore, compared with the case where the current value Ia at the time of occurrence of a short circuit is maintained as it is, the amount of heat lost by reducing the current value is substantially proportional to the current difference integral value Si. Therefore, when the amount of virtual heat lost during the initial period Ti increases, the current difference integral value Si also increases, and as a result, the reference value Ic also increases. This means that the reference value Ic is optimized according to the virtual heat amount lost during the initial period Ti.

  Variations in the size of the droplets at the time of occurrence of a short circuit sometimes occur due to variations in the torch height, feeding speed, etc. (variations due to disturbance). When such a change occurs, the welding state becomes unstable. Therefore, in order to suppress this, the reference value Ic is optimized according to the current difference integrated value Si. In a steady state in which no fluctuation occurs, the size of the droplet at the time when the short circuit occurs is substantially constant. From this, the constant G in the above equation (2) is determined so that the reference value Ic when the size of the droplet at the time of occurrence of the short circuit is the normal size is smaller than the peak value of the prior art. Yes.

As shown at time t <b> 1 in FIG. 5B, the welding current Iw has a slope and decreases to the initial current value Ii when the short-circuit state is reached. As described above, the slope at which the welding current Iw decreases is determined by the resistance value and inductance value of the current path. Therefore, as the cable connecting the welding power source, the welding torch, and the base material becomes longer, the current decreasing slope becomes gentler. When the total value of the cable length is as short as 10 m or less, the current decreasing slope becomes steep. In such a case, it can be considered that the welding current Iw = Ii during the initial period Ti. At this time, the above equation (1) becomes the following equation.
Si = ∫ (Ia−Iw) · dt = (Ia−Ii) · Ti (11) Further, when the initial current value Ii is set to be as small as 30 A or less, it is assumed that Ii = 0, and the above equation Is as follows.
Si = Ia · Ti (12) Therefore, the current difference integral value Si can be calculated by the formula (1), the formula (11), or the formula (12).

In the above equation (2), an upper limit value and a lower limit value of the reference value Ic may be provided in order to limit the calculated reference value Ic within a predetermined range. Further, the following equation may be used instead of the equation (2).
Ic = a · Si + b (21) Formula Ic = c · Si · Si + d · Si + e (22) where a to e are constants.

  Examples of numerical values of the above set values are as follows. In MAG welding using a mixed gas of 80% argon gas and 20% carbon dioxide gas as the shielding gas, a steel wire with a diameter of 1.2 mm is used as the welding wire, and the feeding speed is 3.5 m / min (average welding current) 150A). The values are as follows: initial period Ti = 1 ms, initial current Ii = 50 A, first slope K1 = 200 A / ms, second slope K2 = 50 A / ms, and constant G = 3. Here, consider a case where the current difference integral value Si is calculated by the above equation (11). When there is no change in the torch height, the feeding speed, etc., the size of the droplet is substantially constant, so that the current value Ia at the time of occurrence of a short circuit is about 100A. Then, the current difference integral value Si = (100−50) · 1 = 50 is obtained from the equation (11). Substituting this into equation (2) yields the reference value Ic = 3 · 50 = 150A. Since the peak value of the prior art is about 400 A, it can be seen that this reference value Ic is small. Next, when fluctuations in the torch height, feeding speed, etc. occur and the size of the droplets decreases and the current value Ia = 150 A at the occurrence of a short circuit increases, the current difference integral value Si = (150−50 ) · 1 = 100. As a result, the reference value Ic = 3 · 100 = 300 A, and by increasing the welding current Iw during the short-circuit period, the short-circuit period is prevented from becoming longer and the stability of the welding state is maintained. Further, when fluctuations in the torch height, feed speed, etc. occur and the size of the droplet increases and the current value Ia = 70 A when the short-circuit occurs, the current difference integral value Si = (70-50)・ 1 = 20. As a result, the reference value Ic = 3 · 20 = 60 A, and the welding current Iw during the short circuit period is reduced. This suppresses generation of spatter that increases when the droplet is large. Here, the upper limit value may be set to 400A, the lower limit value may be set to 100A, and the change range of the reference value Ic may be limited to 100 to 400A.

  Each of the above set locations, initial period Ti, initial current value Ii, first slope K1, second slope K2, constant G, and upper and lower limits of reference value Ic are the type of shield gas, the material of the welding wire, and the diameter. Depending on the feeding speed, etc., an appropriate value is set by experiment.

  FIG. 2 is a block diagram of a welding power source for implementing the above-described welding current control method during the short-circuit period according to the embodiment of the present invention. Hereinafter, each block will be described with reference to FIG.

  The power supply main circuit PM receives a commercial power supply (not shown) such as three-phase 200 V, performs output control such as inverter control according to an error amplification signal Ea described later, and outputs a welding voltage Vw and a welding current Iw. This power supply main circuit PM is omitted in the drawing, but a primary rectifier that rectifies commercial power, a smoothing capacitor that smoothes the rectified direct current, an inverter circuit that converts the smoothed direct current to high frequency alternating current, and high frequency alternating current for welding A high-frequency transformer that steps down to a suitable voltage value, a secondary rectifier that rectifies the stepped-down high-frequency alternating current into direct current, a reactor that smoothes the rectified direct current, a modulation circuit that performs pulse width modulation control using the error amplification signal Ea as an input, The drive circuit is configured to drive the switching element of the inverter circuit using the pulse width modulation control signal as an input.

  The welding wire 1 is fed through the welding torch 4 by the rotation of a feeding roll 5 coupled to a feeding motor (not shown), and an arc 3 is generated between the welding wire 1 and the base material 2. A welding voltage Vw is applied between the welding wire 1 and the base material 2, and a welding current Iw is passed through the arc 3. In the figure, the circuit for controlling the feeding of the welding wire is not shown.

  The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr.

  The short circuit determination circuit SD receives the voltage detection signal Vd as described above, and outputs a short circuit determination signal Sd that is at a high level when the value is less than a predetermined threshold value. The threshold is set to about 10V. The initial period setting circuit TIR outputs a predetermined initial period setting signal Tir. The initial current setting circuit IIR outputs a predetermined initial current setting signal Iir. The first inclination setting circuit KR1 outputs a predetermined first inclination setting signal Kr1. The second inclination setting circuit KR2 outputs a predetermined second inclination setting signal Kr2. The constant setting circuit GR outputs a predetermined constant setting signal Gr.

  The short-circuit occurrence current value detection circuit IAD receives the current detection signal Id and the short-circuit determination signal Sd as inputs, and calculates the value of the current detection signal Id when the short-circuit determination signal Sd changes to a high level (short circuit). Output as a current value detection signal Iad when a short circuit occurs. The current difference integration circuit SI receives the current value detection signal Iad upon occurrence of a short circuit, the current detection signal Id, the short circuit determination signal Sd, and the initial period setting signal Tir as inputs, and is based on the above equation (1). Then, during the period determined by the initial period setting signal Tir from the time when the short circuit determination signal Sd changes to the High level (short circuit), Si = ∫ (Iad−Id) · dt is integrated and output as the current difference integration signal Si. . Instead of the equation (1), as described above, the current difference integration signal Si may be calculated using the equation (11) or the equation (12). The reference value setting circuit ICR receives the current difference integration signal Si and the constant setting signal Gr, and calculates and outputs the reference value setting signal Icr = Gr · Si based on the above-described equation (2). Here, instead of the expression (2), the above-described expression (21) or (22) may be used.

The current setting circuit IR includes the initial period setting signal Tir, the initial current setting signal Iir, the first inclination setting signal Kr1, the second inclination setting signal Kr2, the reference value setting signal Icr, The following processing is performed with the short-circuit determination signal Sd as an input, and the current setting signal Ir is output.
1) The initial current setting signal Iir is output as the current setting signal Ir during a period determined by the initial period setting signal Tir from the time when the short circuit determination signal Sd changes to the High level (short circuit).
2) Thereafter, the value of the current setting signal Ir is increased from the value of the initial current setting signal Iir with a slope determined by the first slope setting signal Kr1.
3) When the value of the current setting signal Ir becomes equal to the reference value setting signal Icr, the value of the current setting signal Ir is increased at a slope determined by the second slope setting signal Kr2. This increase continues until the short circuit determination signal Sd changes to the low level (arc).
4) When the short circuit determination signal Sd changes to Low level (arc), the value of the current setting signal Ir at that time is held.

  The current error amplification circuit EI amplifies an error between the current setting signal Ir (+) and the current detection signal Id (−) and outputs a current error amplification signal Ei. The voltage error amplification circuit EV amplifies an error between the voltage setting signal Vr (+) and the voltage detection signal Vd (−) and outputs a voltage error amplification signal Ev. The control switching circuit SW receives the current error amplification signal Ei, the voltage error amplification signal Ev, and the short circuit determination signal Sd, and when the short circuit determination signal Sd is at a high level (short circuit), the current error amplification signal Ei. Is output as the error amplification signal Ea, and when the level is low (arc), the voltage error amplification signal Ev is output as the error amplification signal Ea. This circuit provides constant current control during the short circuit period and constant voltage control during the arc period.

  According to the above-described embodiment, when a short-circuit state occurs, the welding current is decreased and maintained at a small initial current value during the initial period, and thereafter, the welding current is increased at the first slope, and the welding current becomes the reference value. When the value is reached, the welding current is increased until the arc is regenerated at a second slope that is gentler than the first slope. Then, the reference value is automatically set based on the current difference integral value during the initial period. Thereby, when the welding state is in a steady state, the reference value is automatically set to a small value, so that the amount of spatter generated is reduced. When the droplet formation state fluctuates due to a disturbance, the reference value is automatically set to a large value, so that the welding state can be prevented from becoming unstable. Therefore, even when the advancing angle of the welding torch is large, it is possible to perform welding with a small amount of spatter generation and good stability in the welding state.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feed roll Ea Error amplification signal EI Current error amplification circuit Ei Current error amplification signal EV Voltage error amplification circuit Ev Voltage error amplification signal G Constant GR Constant setting circuit Gr Constant setting signal Ia Current value IAD at occurrence of short circuit Current value detection circuit Iad at occurrence of short circuit Current value detection signal Ic at occurrence of short circuit Reference value ICR Reference value setting circuit Icr Reference value setting signal ID Current detection circuit Id Current detection signal Ii Initial current value IIR Initial current setting Circuit Iir Initial current setting signal IR Current setting circuit Ir Current setting signal Iw Welding current K1 First inclination K2 Second inclination KR1 First inclination setting circuit Kr1 First inclination setting signal KR2 Second inclination setting circuit Kr2 Second inclination setting signal PM Power supply main circuit SD Short circuit determination circuit Sd Short circuit determination signal SI Current difference integration circuit Si Current difference integration (value / signal)
SW control switching circuit Ta Arc period Ti Initial period TIR Initial period setting circuit Tir Initial period setting signal Ts Short circuit period VD Voltage detection circuit Vd Voltage detection signal VR Voltage setting circuit Vr Voltage setting signal Vw Welding voltage

Claims (5)

In the arc welding where the welding wire is fed and the short circuit period and the arc period are alternately repeated,
When a short circuit occurs, the welding current Iw is decreased and maintained to a predetermined initial current value Ii, and when a predetermined initial period Ti has elapsed from the time of the occurrence of the short circuit, the welding current is increased at a predetermined first slope, In the welding current control method for a short-circuit period in which welding is performed by increasing the welding current at a predetermined second slope having a value smaller than the first slope until the arc is regenerated when the welding current reaches a reference value Ic. ,
The welding current value Ia at the time of the occurrence of the short circuit is detected, the current difference integrated value Si = ∫ (Ia−Iw) · dt during the initial period Ti is calculated, and the reference value Ic is set to the current difference integrated value Si. Automatically set based on the
A method for controlling a welding current during a short-circuit period. Limiting the reference value Ic to a predetermined range;
The welding current control method for a short-circuit period according to claim 1. It is automatically set as the reference value Ic = G · Si (where G is a predetermined constant),
The welding current control method for a short circuit period according to claim 1 or 2. The welding current Iw during the initial period Ti is assumed to be Ii, and the current difference integral value Si = ∫ (Ia−Ii) · dt = (Ia−Ii) · Ti,
The welding current control method for a short-circuit period according to any one of claims 1 to 3. The product of the initial current value Ii and the initial period Ti is Ii · Ti = 0, and the current difference integral value Si = (Ia−Ii) · Ti = Ia · Ti.
The welding current control method for a short circuit period according to claim 4.

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