Double shield TIG welding method

Abstract

To suppress occurrence of a blow hole in a double shield TIG welding method performed by applying an AC welding current Iw.SOLUTION: A double shield TIG welding method uses a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, and performs welding by applying AC welding current Iw formed from electrode negative polarity current during an electrode negative polarity period and electrode positive polarity current during an electrode positive polarity period. In the double shield TIG welding method, electrode positive polarity current from time t4 to time t7 is composed of first electrode positive polarity current during a first electrode positive polarity period from time t4 to time t5 and second electrode positive polarity current during a second electrode positive polarity period from time t5 to time t6, a value of the first electrode positive polarity current is 20% to 60% of a peak value of the second electrode positive polarity current, and the first electrode positive polarity period is 5% to 30% of the electrode positive polarity period.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a double-shielded TIG welding method for welding by passing an AC welding current. [Background technology]

[0002] A double-shield TIG welding method is commonly used in which a welding torch equipped with an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used to pass an AC welding current formed from an electrode negative polarity current during an electrode negative polarity period and an electrode positive polarity current during an electrode positive polarity period (see, for example, Patent Document 1). As the inner gas and the outer gas, an inert gas such as argon or helium is used.

[0003] AC TIG welding is used to weld metals such as aluminum, aluminum alloys, and magnesium that have an oxide film on their surfaces. This is because the cleaning effect of passing a positive polarity current through the electrode removes the oxide film, resulting in good welding.

[0004] In the invention of Patent Document 2, in an AC TIG welding method, noise generated from the arc is reduced by providing gradients to the rise and fall of the electrode positive polarity current and the electrode negative polarity current. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-15048 A [Patent Document 2] Patent No. 4657588 Summary of the Invention [Problem to be solved by the invention]

[0006] In the double-shielded TIG welding method in which an AC welding current is passed through, there is a problem that blowholes are likely to occur due to disturbances in the gas flow when the power supply polarity is switched.

[0007] Therefore, an object of the present invention is to suppress the occurrence of blowholes in a double-shielded TIG welding method in which an AC welding current is passed through. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the invention of claim 1 comprises: A welding torch having an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used, 1. A double shield TIG welding method for welding by passing an AC welding current formed from an electrode negative polarity current during an electrode negative polarity period and an electrode positive polarity current during an electrode positive polarity period, the electrode positive polarity current is formed from a first electrode positive polarity current during a first electrode positive polarity period and a second electrode positive polarity current during a second electrode positive polarity period; the value of the first electrode positive polarity current is 20% to 60% of the peak value of the second electrode positive polarity current; The first electrode positive polarity period is 5% to 30% of the electrode positive polarity period. This is a double shielded TIG welding method characterized by the above.

[0009] The invention of claim 2 is as follows: the electrode negative polarity current is formed from a first electrode negative polarity current during a first electrode negative polarity period and a second electrode negative polarity current during a second electrode negative polarity period; the value of the first electrode negative polarity current is 20% to 60% of the peak value of the second electrode negative polarity current; The first electrode negative polarity period is 2% to 20% of the electrode negative polarity period. 2. The double shielded TIG welding method according to claim 1,

[0010] The invention of claim 3 is as follows: The first electrode positive polarity period is set to a period during which the fluctuation of the welding voltage during this period converges. 2. The double shielded TIG welding method according to claim 1,

[0011] The invention of claim 4 is as follows: The first electrode negative polarity period is set to a period during which the fluctuation of the welding voltage converges. 3. The double shielded TIG welding method according to claim 2, Effect of the Invention

[0012] According to the double shielded TIG welding method of the present invention, in which an AC welding current is applied, the occurrence of blowholes is suppressed and good weld quality can be obtained. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram of a welding apparatus for carrying out a double-shielded TIG welding method according to an embodiment of the present invention. [Diagram 2] 2 is a timing chart of each signal in the welding apparatus of FIG. 1 illustrating a double-shielded TIG welding method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] 1 is a block diagram of a welding apparatus for carrying out a double shielded TIG welding method according to an embodiment of the present invention. Each block will be described below with reference to the diagram.

[0016] The welding torch WT mainly includes an electrode 1, an inner nozzle 4 surrounding the electrode 1, and an outer nozzle 5 surrounding the inner nozzle 4. A tungsten electrode or the like is used for the electrode 1. For example, the inner diameter of the inner nozzle 4 is 5 mm, and the inner diameter of the outer nozzle 5 is 13 mm.

[0017] The start switch ON outputs a start signal On that goes to a high level when it is turned on and goes to a low level when it is turned off. This start switch ON is a torch switch provided on the welding torch WT. The start signal On may also be output from the robot control device.

[0018] The first electrode negative polarity current setting circuit IN1R outputs a first electrode negative polarity current setting signal In1r having a predetermined positive value. The second electrode negative polarity current setting circuit IN2R outputs a second electrode negative polarity current setting signal In2r having a predetermined positive value. Here, In1r <In2rである。

[0019] The first electrode positive polarity current setting circuit IP1R outputs a first electrode positive polarity current setting signal Ip1r having a predetermined positive value. The second electrode positive polarity current setting circuit IP2R outputs a second electrode positive polarity current setting signal Ip2r having a predetermined positive value. Here, Ip1r <Ip2rである。

[0020] The inner gas flow rate setting circuit FIR takes the above-mentioned second electrode negative polarity current setting signal In2r as input, inputs the second electrode negative polarity current setting signal In2r [A] into the following predetermined inner gas flow rate setting function, and outputs the calculated value as the inner gas flow rate setting signal Fir [l / min]. An example of an inner gas setting function is shown below. Fir=(In2r-75) / 50+3.5 (1) However, within the range of 75≦In2r≦150, when In2r<75, the value is the same as In2r=75, and when In2r>150, the value is the same as In2r=150. As a result, the value of the inner gas flow rate setting signal Fir increases as the value of the second electrode negative polarity current setting signal In2r increases.

[0021] The inner gas flow regulator CI is a commonly used mass flow controller that receives the above-mentioned start signal On and the above-mentioned inner gas flow setting signal Fir as inputs, and when the start signal On becomes high level, it adjusts the flow rate Fi of the inner gas 7 from the inner gas cylinder 6 to a value determined by the inner gas flow setting signal Fir and sprays it.

[0022] The outer gas flow rate setting circuit FOR receives the second electrode negative polarity current setting signal In2r as an input, inputs the second electrode negative polarity current setting signal In2r [A] to the following predetermined outer gas flow rate setting function, and outputs the calculated value as the outer gas flow rate setting signal For [l / min]. An example of the outer gas setting function is shown below. For = (In2r-75) / 50+5.5 (2) However, within the range of 75≦In2r≦150, when In2r<75, the value is the same as In2r=75, and when In2r>150, the value is the same as In2r=150. As a result, the value of the outer gas flow rate setting signal For increases as the value of the second electrode negative polarity current setting signal In2r increases.

[0023] The outer gas flow regulator CO is a commonly used mass flow controller that receives the above-mentioned start signal On and the above-mentioned outer gas flow setting signal For as inputs. When the start signal On becomes high level, it adjusts the flow rate Fo of the outer gas 9 from the outer gas cylinder 8 to a value determined by the outer gas flow setting signal For and sprays it.

[0024] An inner gas 7 flows through a passage inside the inner nozzle 4. An outer gas 9 flows through a passage outside the inner nozzle 4 and inside the outer nozzle 5. The inner gas 7 and outer gas 9 are inert gases such as argon and helium.

[0025] The current detection circuit ID detects the welding current Iw, converts it to an absolute value, and outputs a current detection signal Id. The voltage detection circuit VD detects the welding voltage Vw, converts it to an absolute value, and outputs a voltage detection signal Vd.

[0026] The first electrode negative polarity period setting circuit TN1R receives the voltage detection signal Vd, measures the period until the fluctuation of the voltage detection signal Vd converges during this period, and outputs a predetermined first electrode negative polarity period setting signal Tn1r. The second electrode negative polarity period setting circuit TN2R outputs a predetermined second electrode negative polarity period setting signal Tn2r.

[0027] The first electrode positive polarity period setting circuit TP1R receives the voltage detection signal Vd, measures the period until the fluctuation of the voltage detection signal Vd converges during this period, and outputs a predetermined first electrode positive polarity period setting signal Tp1r. The second electrode positive polarity period setting circuit TP2R outputs a predetermined second electrode positive polarity period setting signal Tp2r.

[0028] The current setting circuit IR receives as input the first electrode negative polarity period setting signal Tn1r, the second electrode negative polarity period setting signal Tn2r, the first electrode positive polarity period setting signal Tp1r, the second electrode positive polarity period setting signal Tp2r, the first electrode negative polarity current setting signal In1r, the second electrode negative polarity current setting signal In2r, the first electrode positive polarity current setting signal Ip1r, the second electrode positive polarity current setting signal Ip2r, and the current detection signal Id, performs the following processing, and outputs a current setting signal Ir and a polarity switching signal Snp. 1) During the first electrode negative polarity period Tn1 determined by the first electrode negative polarity period setting signal Tn1r, the first electrode negative polarity current setting signal In1r is output as the current setting signal Ir. During this period, a high-level polarity switching signal Snp is output. 2) Subsequently, during the second electrode negative polarity period Tn2 determined by the second electrode negative polarity period setting signal Tn2r, the second electrode negative polarity current setting signal In2r is output as the current setting signal Ir. During this period, a high-level polarity switching signal Snp is output. 3) Next, a current setting signal Ir of a predetermined polarity switching current value is output and maintained until the value of the current detection signal Id drops to the polarity switching current value. During this period, a high-level polarity switching signal Snp is output. 4) Subsequently, during the first electrode positive polarity period Tp1 determined by the first electrode positive polarity period setting signal Tp1r, the first electrode positive polarity current setting signal Ip1r is output as the current setting signal Ir. During this period, a low-level polarity switching signal Snp is output. 5) Subsequently, during the second electrode positive polarity period Tp2 determined by the second electrode positive polarity period setting signal Tp2r, the second electrode positive polarity current setting signal Ip2r is output as the current setting signal Ir. During this period, a low-level polarity switching signal Snp is output. 6) Next, the current setting signal Ir of the polarity switching current value is output and maintained until the value of the current detection signal Id drops to the polarity switching current value. During this period, the polarity switching signal Snp of low level is output. 7) Repeat steps 1) to 6) above.

[0029] The welding power supply PS receives as input the above-mentioned start signal On, the above-mentioned current setting signal Ir, the above-mentioned current detection signal Id and the above-mentioned polarity switching signal Snp, and when the start signal On goes to high level, it applies a high-frequency high voltage between the electrode 1 and the base material 2, and when an arc 3 is generated, it begins outputting the welding current Iw and welding voltage Vw of the current value set by the current setting signal Ir and the power polarity set by the polarity switching signal Snp, and stops outputting them when the start signal On goes to low level. Although not shown, the welding power source PS is connected to a commercial AC power source such as three-phase 200V, and is equipped with a primary rectifier circuit that rectifies the commercial AC power source to DC, a capacitor that smoothes the rectified DC, a primary inverter circuit that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for arc welding, a secondary rectifier circuit that rectifies the stepped-down high-frequency AC to DC, a reactor that smoothes the rectified DC, a secondary inverter circuit that switches the smoothed DC to electrode negative polarity EN or electrode positive polarity EP in accordance with a polarity switching signal Snp, a modulation circuit that performs pulse width modulation control so that the current setting signal Ir and the current detection signal Id are equal, and a drive circuit that drives the primary inverter circuit based on the output of the modulation circuit.

[0030] Fig. 2 is a timing chart of each signal in the welding device of Fig. 1, which shows the double-shielded TIG welding method according to the embodiment of the present invention. Fig. 2(A) shows the change over time of the welding current Iw, Fig. 2(B) shows the change over time of the welding voltage Vw, and Fig. 2(C) shows the change over time of the polarity switching signal Snp. The operation during welding will be described below with reference to the figures.

[0031] The welding current Iw shown in Fig. 1A and the welding voltage Vw shown in Fig. 1B show waveforms with electrode negative polarity EN above 0, and with electrode positive polarity EP below 0. In the following, the magnitudes of the welding current Iw and welding voltage Vw are described as absolute values, regardless of the electrode negative polarity EN and electrode positive polarity EP.

[0032] Inner gas and outer gas (not shown) are injected into the arc generating portion. The flow rate FI of the inner gas is calculated by inputting the second electrode negative polarity current In2 into the above-mentioned formula (1). The flow rate Fo of the outer gas is calculated by inputting the second electrode negative polarity current In2 into the above-mentioned formula (2).

[0033] (1) Operation explanation of electrode negative polarity period Ten Just before time t1, as shown in FIG. 1A, the welding current Iw drops from the second electrode positive polarity current Ip2, which is a negative value, to a predetermined negative polarity switching current value. At time t1, as shown in FIG. 1A, when the welding current Iw becomes equal to the polarity switching current value, the polarity switching signal Snp changes from a low level to a high level, as shown in FIG. 1C, and the period shifts to the electrode negative polarity period Ten. In response to this, as shown in FIG. 1A, the welding current Iw abruptly changes from the negative polarity switching current value to the first electrode negative polarity current value In1, which is a positive value, which is a predetermined value. As shown in FIG. 1B, the welding voltage Vw has a waveform similar to the current waveform, and changes from a negative voltage value to a positive voltage value.

[0034] During the first electrode negative polarity period Tn1 from time t1 to time t2, as shown in FIG. 1A, the welding current Iw is the first electrode negative polarity current value In1. As shown in FIG. 1B, the welding voltage Vw fluctuates during this period, and the fluctuation is converged just before time t2. This fluctuation of the welding voltage Vw occurs because the arc generation state at the time of polarity switching is in a transitional state. In the double shield TIG welding method in which the inner gas and the outer gas are flowed, turbulence is more likely to occur due to the difference in flow speed between the two gases compared to the normal TIG welding method in which only the shielding gas is flowed. When the arc generation state is in a transitional state, the fluctuation is large, so that turbulence is more likely to occur. Therefore, by setting the first electrode negative polarity current value In1 to a small value, the fluctuation of the arc generation state is suppressed and the generation of turbulence is prevented. As a result, it is possible to suppress the occurrence of blowholes due to the incomplete shielding state of the arc caused by the generation of turbulence. Therefore, the first electrode negative polarity period Tn1 is set to a period until the fluctuation of the welding voltage Vw is converged during this period. For example, the absolute value of the polarity switching current value is set to 50 A. The reason why the welding current Iw is lowered to the polarity switching current value to switch the polarity is to prevent the secondary inverter circuit in the welding power source PS in Figure 1 from being damaged by a surge voltage at the time of switching.

[0035] During a predetermined second electrode negative polarity period Tn2 from time t2 to t3, as shown in FIG. 1A, the welding current Iw increases to a second electrode negative polarity current value In2. As shown in FIG. 1B, the welding voltage Vw has a larger value than during the first electrode negative polarity period Tn1. During this period, melting of the base metal is promoted, and this becomes the main period of welding.

[0036] At time t3, when the second electrode negative polarity period Tn2 ends, the welding current Iw decreases with a slope as shown in FIG. 1A, and reaches the polarity switching current value at time t4. The slope is determined by the inductance value of the current path through which the welding current Iw flows. As shown in FIG. 1B, the welding voltage Vw also decreases.

[0037] (2) Operation explanation of electrode positive polarity period Tep At time t4, as shown in Fig. 1(A), when the welding current Iw becomes equal to the polarity switching current value, the polarity switching signal Snp changes to low level as shown in Fig. 1(C), and the electrode positive polarity period Tep begins. In response to this, as shown in Fig. 1(A), the welding current Iw abruptly changes from the polarity switching current value, which is a positive value, to the predetermined first electrode positive polarity current value Ip1, which is a negative value. As shown in Fig. 1(B), the welding voltage Vw has a waveform similar to the current waveform, and changes from a positive voltage value to a negative voltage value.

[0038] During the first electrode positive polarity period Tp1 from time t4 to time t5, as shown in FIG. 1A, the welding current Iw is the first electrode positive polarity current value Ip1. As shown in FIG. 1B, the welding voltage Vw fluctuates during this period, and the fluctuation converges just before time t5. This fluctuation in the welding voltage Vw occurs because the formation state of the cathode spot formed in search of the oxide film is in a transient state. In the double shield TIG welding method in which the inner gas and the outer gas are flowed, turbulence is more likely to occur due to the difference in flow speed between the two gases compared to the normal TIG welding method in which only the shielding gas is flowed. When the formation state of the cathode spot is in a transient state, the fluctuation is large, so turbulence is more likely to occur. The generation state of this turbulence is more intense when the polarity is switched to the electrode positive polarity EP than when the above-mentioned polarity is switched to the electrode negative polarity EN. Therefore, by setting the first electrode positive polarity current value Ip1 to a small value, the fluctuation in the arc generation state is suppressed, and the generation of turbulence is prevented. As a result, it is possible to suppress the occurrence of blowholes caused by an incomplete arc shielding state due to the occurrence of turbulence. Therefore, the first electrode negative polarity period Tp1 is set to a period during which the fluctuations in the welding voltage Vw converge.

[0039] During a predetermined second electrode positive polarity period Tp2 from time t5 to t6, as shown in FIG. 1A, the welding current Iw increases to a second electrode positive polarity current value Ip2. As shown in FIG. 1B, the welding voltage Vw becomes a larger value than during the first electrode positive polarity period Tp1. The oxide film is mainly removed by the cleaning action during this period.

[0040] At time t6, when the second electrode positive polarity period Tp2 ends, as shown in Fig. (A), the welding current Iw decreases with a slope and becomes the polarity switching current value at time t7. The slope is determined by the inductance value of the current path of the welding current Iw. As shown in Fig. (B), the welding voltage Vw also decreases. Thereafter, the operation returns to that at time t1.

[0041] Although the figure shows the case of the balanced waveform with In2 = Ip2, there may also be an unbalanced waveform with In2 < Ip2. Also, although the figure shows the case where the current waveform is a substantially rectangular wave, there may also be a sine wave case.

[0042] Numerical examples of each parameter are shown below. In1 = 60A, In2 = 150A Ten = 10ms, Tn1 = 0.5ms Ip1 = 60A, Ip2 = 150A Tep = 3ms, Tp1 = 0.3ms

[0043] Hereinafter, the operation and effects of the present embodiment will be described. According to this embodiment, the electrode positive polarity current is formed by the first electrode positive polarity current during the first electrode positive polarity period and the second electrode positive polarity current during the second electrode positive polarity period, and the value of the first electrode positive polarity current is 20% to 60% of the peak value of the second electrode positive polarity current, and the first electrode positive polarity period is 5% to 30% of the electrode positive polarity period. More preferably, the value of the first electrode positive polarity current is 30% to 50% of the peak value of the second electrode positive polarity current, and the first electrode positive polarity period is 10% to 20% of the electrode positive polarity period. When the electrode polarity is switched to positive polarity, the formation state of the cathode spot formed in search of the oxide film becomes a transient state. In the double shield TIG welding method in which the inner gas and the outer gas are flowed, turbulence is more likely to occur due to the difference in flow speed between the two gases than in the normal TIG welding method in which only the shield gas is flowed. When the formation state of the cathode spot is in a transient state, the arc generation state fluctuates greatly, so turbulence is more likely to occur. The occurrence of this turbulent flow is more intense when the polarity is switched to the positive electrode polarity than when the polarity is switched to the negative electrode polarity. Therefore, by setting at least the value of the first electrode positive polarity current to a small value, the fluctuation of the arc occurrence state is suppressed and the occurrence of turbulence is prevented. As a result, it is possible to suppress the occurrence of blowholes caused by the occurrence of turbulence that results in an incomplete arc shielding state. The value of the second electrode positive polarity current is set to the peak value because it includes not only square waves but also sine waves whose values ​​change.

[0044] More preferably, according to this embodiment, the electrode negative polarity current is formed from a first electrode negative polarity current during a first electrode negative polarity period and a second electrode negative polarity current during a second electrode negative polarity period, the value of the first electrode negative polarity current is 20% to 60% of the peak value of the second electrode negative polarity current, and the first electrode negative polarity period is 2% to 20% of the electrode negative polarity period. More preferably, the value of the first electrode negative polarity current is 30% to 50% of the peak value of the second electrode negative polarity current, and the first electrode negative polarity period is 3% to 10% of the electrode negative polarity period. When the electrode polarity is switched to negative polarity, the arc generation state becomes a transient state. In the double shield TIG welding method in which an inner gas and an outer gas are flowed, turbulence is more likely to occur due to the difference in flow speed between the two gases than in the normal TIG welding method in which only a shielding gas is flowed. Turbulence is more likely to occur because the arc generation state is fluctuating. Therefore, by setting the first electrode positive polarity current value to a small value, the fluctuation of the arc generation state is suppressed and the generation of turbulence is prevented. As a result, it is possible to suppress the occurrence of blowholes caused by incomplete arc shielding due to the generation of turbulence. The reason why the value of the second electrode negative polarity current is taken as the peak value is to include not only square waves but also sine waves whose values ​​change.

[0045] More preferably, according to this embodiment, the first electrode positive polarity period is set to a period during which the fluctuations in the welding voltage converge. When the fluctuations in the welding voltage converge, the fluctuations in the arc generation state converge. If the first electrode positive polarity period is too short, the generation of turbulence cannot be sufficiently suppressed, and there is a risk of blowholes occurring. On the other hand, if the first electrode positive polarity period is too long, the cleaning action becomes insufficient, and the welding quality deteriorates. Therefore, if the first electrode positive polarity period is set to a period during which the fluctuations in the welding voltage converge, it can be set to an appropriate value.

[0046] More preferably, according to this embodiment, the first electrode negative polarity period is set to a period during which the fluctuations in the welding voltage converge. When the fluctuations in the welding voltage converge, the fluctuations in the arc generation state converge. If the first electrode negative polarity period is too short, the generation of turbulence cannot be sufficiently suppressed, and there is a risk of blowholes occurring. On the other hand, if the first electrode negative polarity period is too long, the penetration becomes insufficient and the welding quality deteriorates. Therefore, if the first electrode negative polarity period is set to a period during which the fluctuations in the welding voltage converge, it can be set to an appropriate value. [Explanation of symbols]

[0047] 1 electrode 2 Base material 3. Arc 4 Inner nozzle 5 Outer nozzle 6 Inner gas cylinder 7. Inner Gas 8 Outer gas cylinder 9. Outer Gas CI Inner Gas Flow Regulator CO outer gas flow regulator EN Electrode negative polarity EP electrode positive polarity Fi Inner gas flow rate FIR inner gas flow rate setting circuit Fir inner gas flow rate setting signal Fo Outer gas flow rate FOR OUTER GAS FLOW SETTING CIRCUIT For outer gas flow rate setting signal ID Current Detection Circuit Id Current detection signal In1 First electrode negative polarity current IN1R First electrode negative polarity current setting circuit In1r 1st electrode negative polarity current setting signal In2 Second electrode negative polarity current IN2R Second electrode negative polarity current setting circuit In2r Second electrode negative polarity current setting signal Ip1 First electrode positive polarity current IP1R First electrode positive polarity current setting circuit Ip1r First electrode positive polarity current setting signal Ip2 Second electrode positive polarity current IP2R Second electrode positive polarity current setting circuit Ip2r Second electrode positive polarity current setting signal IR current setting circuit Ir Current setting signal Iw Welding current ON Start switch On Start signal PS Welding Power Source Ten electrode negative polarity period Tep electrode positive polarity period Tn1 1st electrode negative polarity period TN1R First electrode negative polarity period setting circuit Tn1r 1st electrode negative polarity period setting signal Tn2 Second electrode negative polarity period TN2R Second electrode negative polarity period setting circuit Tn2r Second electrode negative polarity period setting signal Tp1 First electrode positive polarity period TP1R First electrode positive polarity period setting circuit Tp1r 1st electrode positive polarity period setting signal Tp2 Second electrode positive polarity period TP2R Second electrode positive polarity period setting circuit Tp2r Second electrode positive polarity period setting signal VD voltage detection circuit Vd Voltage detection signal WT Welding Torch

Claims

1. A welding torch having an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used, 1. A double shield TIG welding method for welding by passing an AC welding current formed from an electrode negative polarity current during an electrode negative polarity period and an electrode positive polarity current during an electrode positive polarity period, the electrode positive polarity current is formed from a first electrode positive polarity current during a first electrode positive polarity period and a second electrode positive polarity current during a second electrode positive polarity period; the value of the first electrode positive polarity current is 20% to 60% of the peak value of the second electrode positive polarity current; The first electrode positive polarity period is 5% to 30% of the electrode positive polarity period; A double shielded TIG welding method.

2. the electrode negative polarity current is formed from a first electrode negative polarity current during a first electrode negative polarity period and a second electrode negative polarity current during a second electrode negative polarity period; the value of the first electrode negative polarity current is 20% to 60% of the peak value of the second electrode negative polarity current; The first electrode negative polarity period is 2% to 20% of the electrode negative polarity period; The double shielded TIG welding method according to claim 1 .

3. The first electrode positive polarity period is set to a period during which the fluctuation of the welding voltage during this period converges. The double shielded TIG welding method according to claim 1 .

4. The first electrode negative polarity period is set to a period during which the fluctuation of the welding voltage during this period is converged. The double shield TIG welding method according to claim 2 .

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