Polarity control method for pulsed arc welding

Abstract

To reduce occurrence of sputter at the time of high-speed welding by pulse arc welding.SOLUTION: In a polarity control method in pulse arc welding, in which welding wire is fed, peak currents Ip and base currents Ib are distributed at an electrode plus polarity EP, short-circuit currents are distributed when the welding wire and a base material are short-circuited, and then the short-circuit currents are reduced to generate an arc for welding when constriction of weld droplets is detected (Nd), output polarity is switched from electrode plus polarity EP to electrode minus polarity EN, when the short circuit lasts for a reference time or more at a time t22. After the constriction is detected (Nd) at the electrode minus polarity EN and the short-circuit currents are reduced, the output polarity is returned to the electrode plus polarity EP at a time t25.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for controlling the polarity of pulsed arc welding performed by feeding a welding wire.

Background Art

[0002] In consumable electrode pulsed arc welding, welding is performed by repeatedly feeding a welding wire and outputting a peak current and a peak voltage with electrode positive polarity during a peak period, and outputting a base current and a base voltage during a base period. The peak current is set to a large current value of about 500 A that is equal to or higher than the critical current value, and the welding wire is melted to form and transfer droplets. The base current is set to about 50 A that is less than the critical current value, and the welding wire hardly melts. When the welding current value becomes equal to or higher than the critical current value, the transfer and carrying of droplets becomes a spray transfer state. In pulsed arc welding, it is important to maintain a state of one droplet transfer per one pulse cycle, in which one droplet is transferred by one energization of the peak current, in order to obtain a high-quality weld bead with less spatter generation.

[0003] In pulsed arc welding, when the welding voltage is set so that the arc length becomes an appropriate value, the tip of the welding wire is melted to form a droplet during the energization of the peak current, and the droplet transfers to the molten pool in a spray state immediately after the energization of the peak current ends. When the droplet transfers to the molten pool, the tip of the droplet often contacts the molten pool and a micro short circuit of about 0.5 ms or less occurs. However, this micro short circuit is not a situation where the droplet transfers due to a short circuit as in carbon dioxide arc welding, but rather the droplet only contacts the molten pool during the process of spray transfer. Therefore, it is not necessary to perform control to解除 the short circuit, such as increasing the welding current, for the micro short circuit, and the micro short circuit is automatically解除.

[0004] When performing high-speed welding with a welding speed of approximately 1 m / min or more, it is necessary to set the welding voltage low to shorten the arc length in order to improve welding quality. When the arc length is shortened, normal short circuits of 0.5 ms or more occur in addition to minute short circuits. In a normal short circuit, the molten droplet moves to the short circuit state, and a lot of spatter is generated when the short circuit is released. In the invention of Patent Document 1, in pulsed arc welding for high-speed welding, when a normal short circuit occurs, the welding current is increased at a rise speed slower than the rise speed of the peak current, and when a constriction of the molten droplet is detected, the welding current is decreased. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 3844004 [Overview of the project] [Problems that the invention aims to solve]

[0006] In pulsed arc welding, a high-speed welding process, conventional short-circuit welding current control techniques do not sufficiently reduce spatter, and further spatter reduction is desired. This is because long-term short circuits, which are longer than typical short circuits, occasionally occur, resulting in a large amount of spatter.

[0007] Therefore, the present invention aims to provide a method for controlling the polarity of pulsed arc welding that can reduce the generation of spatter during high-speed welding by pulsed arc welding. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the invention of claim 1 provides a welding wire, and energizes the electrode with positive polarity and a peak current and a base current, In a pulsed arc welding polarity control method in which a short-circuit current is applied when the welding wire and the base material are short-circuited, and then the short-circuit current is reduced to generate an arc and perform welding when a constriction of the molten droplet is detected, If the aforementioned short-circuit current is applied but no constriction is formed by the reference time, The output polarity is switched from the positive polarity of the electrode to the negative polarity of the electrode to promote the formation of the constriction, and when the constriction is detected thereafter, the short-circuit current is reduced to generate the arc. This is a method for controlling the polarity of pulsed arc welding, characterized by the following features.

[0009] The invention of claim 2 is, After detecting the constriction while the electrode is negatively polarized and the short-circuit current decreases, the electrode is returned to positive polarity. The method for controlling the polarity of pulsed arc welding according to feature 1.

[0010] The invention of claim 3 is, After the arc occurs, the electrode is returned to its positive polarity. The method for controlling the polarity of pulsed arc welding according to feature 1. [Effects of the Invention]

[0011] According to the present invention, spatter generation can be reduced during high-speed welding by pulsed arc welding. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram of a welding power supply for implementing the pulsed arc welding polarity control method according to Embodiment 1 of the present invention. [Figure 2] Figure 1 shows a timing chart of each signal in the welding power supply, illustrating a polarity control method for pulsed arc welding according to Embodiment 1 of the present invention. [Figure 3] Figure 1 shows a timing chart of each signal in the welding power supply, illustrating a polarity control method for pulsed arc welding according to Embodiment 2 of the present invention. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the drawings.

[0014] [Embodiment 1] FIG. 1 is a block diagram of a welding power source for implementing a method for controlling the polarity of pulsed arc welding according to Embodiment 1 of the present invention. Hereinafter, each block will be described with reference to the figure.

[0015] The main power circuit MC takes a commercial power supply (not shown) such as 3-phase 200V as an input, performs output control by inverter control or the like according to a current error amplification signal Ei described later, and switches between an electrode positive polarity EP and an electrode negative polarity EN by a polarity switching signal Dr described later to output a welding voltage Vw and a welding current Iw between the welding wire 1 and the base material 2. Although not shown, this main power circuit MC includes a primary rectifier for rectifying the commercial power supply, a smoothing capacitor for smoothing the rectified DC, an inverter circuit driven by a current error amplification signal Ei for converting the smoothed DC into a high-frequency AC, a high-frequency transformer for stepping down the high-frequency AC to a voltage value suitable for welding, a secondary rectifier for rectifying the stepped-down high-frequency AC into DC, a reactor for smoothing the rectified DC, and a secondary-side inverter circuit for switching the polarity based on the polarity switching signal Dr.

[0016] The welding wire 1 is fed through the welding torch 4 by the rotation of a feed roll 5 coupled to a wire feed 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 a power supply tip (not shown) in the welding torch 4 and the base material 2, and a welding current Iw flows through.

[0017] The voltage detection circuit VD detects the absolute value of the above welding voltage Vw and outputs a voltage detection signal Vd. The voltage averaging circuit VAV averages the above voltage detection signal Vd and outputs a voltage average signal Vav. The voltage setting circuit VR outputs a predetermined voltage setting signal Vr.

[0018] The voltage error amplification circuit EV amplifies the error between the above voltage setting signal Vr and the above voltage average signal Vav and outputs a voltage error amplification signal Ev.

[0019] The V / F converter VF outputs a pulse period signal Tf having a period corresponding to the voltage error amplification signal Ev described above. This pulse period signal Tf is a signal that determines one period of the peak period and the base period.

[0020] The peak current rising speed setting circuit SUR outputs a predetermined peak current rising speed setting signal Sur. The peak current falling speed setting circuit SDR outputs a predetermined peak current falling speed setting signal Sdr.

[0021] The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr.

[0022] The base current setting circuit IBR outputs a predetermined base current setting signal Ibr. The peak current setting circuit IPR outputs a predetermined peak current setting signal Ipr. The peak current setting signal Ipr is set to about 400 to 600 A according to the diameter, material, feeding speed, etc. of the welding wire.

[0023] The current setting circuit IR takes the above base current setting signal Ibr, the above peak current setting signal Ipr, the above pulse period signal Tf, the above peak current rising speed setting signal Sur, the above peak current falling speed setting signal Sdr, and the above peak period setting signal Tpr as inputs, performs the following processing, and outputs a current setting signal Ir. 1) When the pulse period signal Tf changes to the High level for a short time, a current setting signal Ir that increases from the value of the base current setting signal Ibr by the value of the peak current rising speed setting signal Sur is output. 2) After that, when the value of the current setting signal Ir reaches the value of the peak current setting signal Ipr, that value is maintained for the duration of the peak period setting signal Tpr. 3) After that, a current setting signal Ir that decreases from the value of the peak current setting signal Ipr by the value of the peak current falling speed setting signal Sdr is output. 4) After that, when the value of the current setting signal Ir becomes equal to the value of the base current setting signal Ibr, that value is maintained. 5) Repeat the above 1) to 4).

[0024] The short-circuit detection signal SD takes the above-mentioned voltage detection signal Vd as input and outputs a short-circuit detection signal Sd that is High level when this value is less than the short-circuit detection value (approximately 10V), and Low level when it is greater than or equal to the arc period.

[0025] The constriction detection circuit ND takes the above-mentioned short-circuit discrimination signal Sd and the above-mentioned voltage detection signal Vd as inputs and outputs a constriction detection signal Nd that becomes high level when the rise value or rate of rise of the voltage detection signal Vd reaches a reference value while the short-circuit discrimination signal Sd is at a high level (short-circuit period), determining that the constriction formation state has reached the reference state, and becoming low level when the short-circuit discrimination signal Sd changes to a low level (arc period).

[0026] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr. The current comparison circuit CM takes this low-level current setting signal Ilr and the current detection signal Id (described later) as input and outputs a current comparison signal Cm that is high level when the value of the current detection signal Id is less than or equal to the value of the low-level current setting signal Ilr, and low level when it exceeds that value.

[0027] The reference time setting circuit TSR outputs a predetermined reference time setting signal Tsr.

[0028] The polarity switching circuit DR takes the above-mentioned short-circuit detection signal Sd, current comparison signal Cm, and reference time setting signal Tsr as inputs, and changes to a high level (electrode negative polarity EN) when the elapsed time from the point in time when the short-circuit detection signal Sd changes to a high level (short-circuit period) is equal to or greater than the value of the reference time setting signal Tsr. Subsequently, a polarity switching signal Dr is output, which returns to a low level (electrode positive polarity EP) with a delay from the point when the current comparison signal Cm changes to a high level or when the short-circuit detection signal Sd changes to a low level (arc period).

[0029] The short-circuit current setting circuit ISR takes the above-mentioned short-circuit detection signal Sd, low-level current setting signal Ilr, constriction detection signal Nd, and reference time setting signal Tsr as inputs, performs the following processing, and outputs the short-circuit current setting signal Isr. 1) When the short-circuit detection signal Sd changes to a high level (short-circuit period), a short-circuit current setting signal Isr is output for a predetermined initial period, which is set to a predetermined initial current setting value. The initial current setting value is set to be less than or equal to the value of the base current setting signal Ibr mentioned above. 2) Subsequently, the value of the short-circuit current setting signal Isr increases with a slope from the initial current setting value described above, and when it reaches the predetermined electrode positive polarity current setting value, it maintains that value. 3) Subsequently, when the short-circuit period exceeds the value of the reference time setting signal Tsr, the value of the short-circuit current setting signal Isr becomes the predetermined negative electrode polarity current setting value. 4) Subsequently, when the constriction detection signal Nd changes to a high level, a short-circuit current setting signal Isr, which is equal to the value of the low-level current setting signal Ilr, is output.

[0030] The current control setting circuit ICR takes the above-mentioned short-circuit detection signal Sd, current setting signal Ir, and short-circuit current setting signal Isr as inputs. When the short-circuit detection signal Sd is at a low level (arc period), it outputs the current setting signal Ir as the current control setting signal Icr. When the short-circuit detection signal Sd is at a high level (short-circuit period), it outputs the short-circuit current setting signal Isr as the current control setting signal Icr.

[0031] The current detection circuit ID detects the absolute value of the welding current Iw mentioned above and outputs a current detection signal Id.

[0032] The current error amplification circuit EI amplifies the error between the current control setting signal Icr and the current detection signal Id, and outputs a current error amplification signal Ei.

[0033] Figure 2 is a timing chart of each signal in the welding power supply of Figure 1, showing the polarity control method for pulse arc welding according to Embodiment 1 of the present invention. Figure (A) shows the time change of the welding current Iw, Figure (B) shows the time change of the welding voltage Vw, Figure (C) shows the time change of the short-circuit detection signal Sd, Figure (D) shows the time change of the necking detection signal Nd, and Figure (E) shows the time change of the polarity switching signal Dr. The operation of each signal will be explained below with reference to the figure.

[0034] The figure shows the case where the welding voltage is set low and the arc length is set short in order to perform high-speed welding. The figure shows two waveforms; the first cycle is when a normal short circuit occurs for a period of less than the reference time, and the second cycle is when a long-term short circuit occurs for a period of longer than the reference time. In the figure, the welding current Iw shown in (A) and the welding voltage Vw shown in (B) are positive electrode polarity EP above 0 and negative electrode polarity EN below 0. The welding wire is not shown but is fed at a constant speed.

[0035] (1) Explanation of the operation of the first cycle As shown in Figure (A), the welding current Iw increases from the base current Ib to the value of the peak current rise rate setting signal Sur in Figure 1 during the rise period from time t1 to t11, reaches the peak current value during the peak period from time t11 to t12, decreases to the value of the peak current fall rate setting signal Sdr in Figure 1 during the fall period from time t12 to t13, and reaches the base current value during the base period from time t13 to t2. The above base current value is set by the base current setting signal Ibr in Figure 1, the above peak current value is set by the peak current setting signal Ipr in Figure 1, and the above peak period is set by the peak period setting signal Tpr in Figure 1. As shown in Figure (B), the welding voltage Vw is a voltage value proportional to the arc length and has a waveform similar to the current waveform. The peak current value and peak period are set so that one droplet transfer occurs per pulse period. The peak current rise rate and peak current fall rate are set so that the droplet formation state is stable. The pulse period from time t1 to t2 is feedback-controlled so that the average value of the welding voltage Vw is equal to the value of the voltage setting signal Vr in Figure 1, thereby controlling the arc length. For example, the peak current value is set to 550A, the peak duration is set to 1.2ms, and the base current value is set to 50A. The peak current rise speed is set to a range of approximately 400 to 600 A / ms, and the peak current fall speed is set to a range of approximately 300 to 500 A / ms. The most stable welding state is achieved when both speeds are set within the above ranges.

[0036] In the first cycle, a normal short circuit occurs during the period from time t14 to t18 in the base period, which is shorter than the reference time. In the figure, a normal short circuit occurs occasionally because the arc length is set to be short. During the first cycle from time t1 to t2, as shown in the figure (E), the polarity switching signal Dr remains at a low level, so the output polarity of the welding power supply is the electrode positive polarity EP.

[0037] At time t14, when a short circuit occurs, as shown in Figure (B), the welding voltage Vw rapidly decreases to a short-circuit voltage of a few volts, and as shown in Figure (C), the short-circuit detection signal Sd changes to a high level. In response to this, as shown in Figure (A), a short-circuit current controlled by the short-circuit current setting signal Isr in Figure 1 is supplied. During the predetermined initial period from time t14 to t15, the short-circuit current is set to a predetermined initial current value. As described above, the initial current value is set to be less than or equal to the base current value. Subsequently, from time t15, the short-circuit current increases with a slope from the initial current value, and once it reaches a predetermined electrode positive polarity current value, it maintains that value. As shown in Figure (B), the welding voltage Vw increases during the period when the electrode positive polarity current is supplied. This is because a constriction is gradually formed in the molten droplet due to the pinch force caused by the short-circuit current. Subsequently, when the voltage rise of the welding voltage Vw reaches the reference value, it is determined that the neck formation state has reached the reference state, and at time t16, as shown in Figure (D), the neck detection signal Nd changes to a high level. In response to this, the value of the short-circuit current setting signal Isr in Figure 1 decreases to the value of the low-level current setting signal Ilr. For this reason, as shown in Figure (A), the short-circuit current rapidly decreases to the low-level current value at time t17. Then, as shown in Figure (A), since the short-circuit current setting signal Isr remains at the low-level current setting signal Ilr, the short-circuit current maintains a low-level current value until time t18 when the arc re-starts. As shown in Figure (B), the welding voltage Vw decreases once because the short-circuit current decreases, and then rapidly increases. By reducing the current value at the time of arc re-starting through neck detection control, spatter generation can be reduced. To speed up the rapid decrease rate of the welding current Iw described above, a transistor and a current-reducing resistor may be inserted in parallel in the current path. In this case, the rate of rapid deceleration can be increased by turning off the transistor during a sudden decrease and inserting a current-reducing resistor into the current-carrying circuit.

[0038] When an arc occurs at time t18, as shown in Figure (B), the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, and as shown in Figure (C), the short-circuit detection signal Sd changes to a low level (arc period). In response to this, as shown in Figure (A), the welding current Iw changes to the base current value. At the same time, as shown in Figure (D), the necking detection signal Nd also returns to a low level.

[0039] (2) Explanation of the operation of the second cycle In the second cycle, a long-term short circuit exceeding the reference time occurs during the period from time t21 to t26 in the base period. In the normal short circuit described above, a constriction is formed in less than the reference time, and the arc is re-generated with the welding current Iw at a low current value. However, in rare cases, a constriction may not be formed by the reference time due to the effects of the droplet formation state, the contact state with the molten pool, etc. In such long-term short circuits, even if the electrode positive polarity current is continued to flow, a constriction will not be formed, and the arc will be re-generated with the electrode positive polarity current flowing. As a result, a large amount of spatter is generated when the arc is re-generated, and the welding state also becomes unstable. Therefore, in Embodiment 1, when the short circuit period exceeds the reference time, the following polarity control is performed. The reference time is set by the reference time setting signal Tsr in Figure 1. The reference time is set as the time for stable constriction to form, and is set to about 4 to 6 ms.

[0040] Since the short circuit occurs at time t21 and the period from then until time t22, when the positive polarity current flows through the electrodes, is the same as the first period, the explanation will not be repeated.

[0041] As shown in Figure (A), when the reference time is reached at time t22 while the electrode positive polarity current is flowing, the polarity switching signal Dr changes from a low level to a high level, as shown in Figure (E), and the output polarity of the welding power supply switches to the electrode negative polarity EN. In response to this, as shown in Figure (A), the welding current Iw switches from a positive electrode positive polarity current to a predetermined negative electrode negative polarity current. At the same time, as shown in Figure (B), the welding voltage Vw also switches from a positive short-circuit voltage value to a negative short-circuit voltage value.

[0042] Then, during the period when the electrode negative polarity current is flowing, the welding voltage Vw rises, as shown in Figure (B). This is because the polarity of the welding current Iw becomes the electrode negative polarity EN, which promotes the formation of a neck. Subsequently, when the voltage rise of the welding voltage Vw reaches the reference value, it is determined that the neck formation state has reached the reference state, and at time t23, as shown in Figure (D), the neck detection signal Nd changes to a high level. In response to this, the value of the short-circuit current setting signal Isr in Figure 1 decreases to the value of the low-level current setting signal Ilr. For this reason, as shown in Figure (A), the short-circuit current rapidly decreases to the low-level current value at time t24.

[0043] At time t25, after a constriction is detected in the electrode negative polarity EN and the short-circuit current decreases, the polarity switching signal Dr changes from a high level to a low level, as shown in Figure (E), so the output polarity of the welding power supply switches to the electrode positive polarity EP. In response to this, as shown in Figure (A), the welding current Iw switches from a negative low-level current value to a positive low-level current value. At the same time, as shown in Figure (B), the welding voltage Vw also switches from a negative short-circuit voltage value to a positive short-circuit voltage value.

[0044] When an arc occurs at time t26, as shown in Figure (B), the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, and as shown in Figure (C), the short-circuit detection signal Sd changes to a low level (arc period). In response to this, as shown in Figure (A), the welding current Iw changes to the base current value. At the same time, as shown in Figure (D), the necking detection signal Nd also returns to a low level.

[0045] For example, the positive electrode current is set to 200A, and the negative electrode current is set to 300A.

[0046] According to Embodiment 1, when a short circuit lasts for a specified time or longer, the output polarity is switched from the positive electrode polarity to the negative electrode polarity. In this way, even if a long-term short circuit occurs that lasts longer than the specified time, switching to the negative electrode polarity EN promotes the formation of a neck, and reliable detection of the neck becomes possible. As a result, even if a long-term short circuit occurs, the current value when the arc is regenerated can be reduced, thereby suppressing the generation of spatter and maintaining a stable welding state.

[0047] Furthermore, according to Embodiment 1, after detecting a constriction while the electrode is negatively polarized and the short-circuit current decreases, the electrode is switched back to positive polarity. In this way, the polarity can be switched while the current value is small, so a stable short-circuit state can be maintained before the arc is re-generated. As a result, the welding state after the arc is re-generated can be stabilized.

[0048] [Embodiment 2] In Embodiment 2, the electrode polarity is returned to positive after the arc is generated.

[0049] The block diagram of the welding power supply for implementing the pulse arc welding polarity control method according to Embodiment 2 of the present invention is the same as that of Figure 1.

[0050] Figure 3 is a timing chart of each signal in the welding power supply of Figure 1, showing the polarity control method for pulse arc welding according to Embodiment 2 of the present invention. Figure (A) shows the time change of the welding current Iw, Figure (B) shows the time change of the welding voltage Vw, Figure (C) shows the time change of the short-circuit detection signal Sd, Figure (D) shows the time change of the constriction detection signal Nd, and Figure (E) shows the time change of the polarity switching signal Dr. In this figure, the operation during the period from time t1 to t24 is the same as in Figure 2, so the explanation will not be repeated. Hereinafter, the operation from time t24 onwards, which differs from that in Figure 2, will be explained with reference to this figure.

[0051] When an arc occurs at time t26, as shown in Figure (B), the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, and as shown in Figure (C), the short-circuit detection signal Sd changes to a low level (arc period). In response to this, as shown in Figure (A), the welding current Iw changes to the base current value. At the same time, as shown in Figure (D), the necking detection signal Nd also returns to a low level.

[0052] At time t27, after the arc is generated at time t26, as shown in Figure (E), the polarity switching signal Dr changes from a high level to a low level, so the output polarity of the welding power supply switches to the electrode positive polarity EP. In response to this, as shown in Figure (A), the welding current Iw switches from a negative base current value to a positive base current value. At the same time, as shown in Figure (B), the welding voltage Vw also switches from a negative arc voltage value to a positive arc voltage value.

[0053] According to Embodiment 2, the electrode polarity is returned to positive after the arc is generated. In this way, the polarity can be switched while the current value is small, so the welding state after arc regeneration can be stabilized. [Explanation of Symbols]

[0054] 1. Welding wire 2 Base material 3 Arc 4. Welding torch 5 Feeding Roll CM current comparison circuit Cm current comparison signal DR polarity switching circuit Dr polarity switching signal EI Current Error Amplifier Circuit Ei Current Error Amplification Signal EV voltage error amplification circuit Ev Voltage Error Amplification Signal Ib Base current IBR Base Current Setting Circuit Ibr Base current setting signal ICR Current Control Setting Circuit Icr current control setting signal ID Current Detection Circuit Id Current detection signal ILR Low-Level Current Setting Circuit Ilr Low-level current setting signal Ip Peak Current IPR Peak Current Setting Circuit IPR Peak Current Setting Signal IR current setting circuit Ir current setting signal ISR Short-Circuit Current Setting Circuit ISR short-circuit current setting signal Iw welding current MC power supply main circuit ND (Narrowing) Waistline Detection Circuit Nd constriction detection signal SD Short Circuit Detection Circuit Sd short-circuit detection signal SDR Peak Current Fall Speed ​​Setting Circuit Sdr Peak Current Fall Speed ​​Setting Signal SUR Peak Current Rise Speed ​​Setting Circuit Sur Peak current rise speed setting signal Tf pulse period signal TPR Peak Period Setting Circuit Tpr Peak Period Setting Signal TSR Reference Time Setting Circuit Tsr reference time setting signal VAV Voltage Averaging Circuit Vav voltage averaged signal VD Voltage Detection Circuit Vd voltage detection signal VF V / F Converter VR voltage setting circuit Vr voltage setting signal Vw welding voltage

Claims

1. The welding wire is fed, and the peak current and base current are applied with the electrode in positive polarity. In a pulsed arc welding polarity control method in which a short-circuit current is applied when the welding wire and the base material are short-circuited, and then the short-circuit current is reduced to generate an arc and perform welding when a constriction of the molten droplet is detected, If a constriction is not formed by the reference time even when the aforementioned short-circuit current is applied, the output polarity is switched from the positive polarity of the electrode to the negative polarity of the electrode to promote the formation of the constriction, and when the constriction is detected thereafter, the short-circuit current is reduced to generate the arc. A method for controlling the polarity of pulsed arc welding, characterized by the features described above.

2. After detecting the constriction while the electrode is negatively polarized and the short-circuit current decreases, the electrode is returned to positive polarity. The method for controlling the polarity of pulsed arc welding according to feature 1.

3. After the arc occurs, the electrode is returned to its positive polarity. The method for controlling the polarity of pulsed arc welding according to feature 1.

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