Double shield tig welding method

Abstract

To provide a double shield tig welding method that energizes an AC welding current Iw which suppresses occurrence of a blow hole.SOLUTION: A double shield tig welding method using a welding torch having an inner nozzle jetting an inner gas and an outer nozzle jetting an outer gas energizes an AC welding current Iw formed of an electrode negative polarity current during an electrode negative polarity period at times t1 to t4 and an electrode positive polarity current during an electrode positive polarity period at times t4 to t7, and performs welding, wherein the peak value of the electrode positive polarity current Iw at times t4 to t7 is set to be larger than the peak value of the electrode negative polarity current Iw at times t1 to t4. A second electrode positive polarity current at times t5 to t6 is a pulse waveform formed of the peak current during a peak period and the base current during a base period.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a double shielded TIG welding method in which welding is performed by passing an alternating current welding current.

Background Art

[0002] A double shielded TIG welding method is commonly used in which a welding torch having an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used, and welding is performed by passing an alternating current welding current formed from an electrode negative polarity current during the electrode negative polarity period and an electrode positive polarity current during the 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] The alternating current TIG welding method is used for welding metals such as aluminum, aluminum alloys, and magnesium on the surface of which an oxide film is formed. This is because the oxide film is removed by the cleaning action due to the application of the electrode positive polarity current to perform good welding.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the double-shielded TIG welding method performed by passing an alternating welding current, there is a problem that blowholes may occur. In particular, blowholes are likely to occur when welding while inserting a filler wire.

[0007] Therefore, an object of the present invention is to suppress the generation of blowholes in a double-shielded TIG welding method performed by passing an alternating welding current.

Means for Solving the Problems

[0008] In order to solve the above-described problems, the invention according to claim 1 is using a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, in a double-shielded TIG welding method of welding by passing an alternating 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, setting the peak value of the electrode positive-polarity current to a value larger than the peak value of the electrode negative-polarity current, which is a double-shielded TIG welding method characterized by the above.

[0009] The invention according to claim 2 is the electrode positive-polarity current includes a pulse waveform formed from a peak current during a peak period and a base current during a base period, which is the double-shielded TIG welding method according to claim 1, characterized by the above.

[0010] The invention according to claim 3 is the period of the pulse waveform of the electrode positive-polarity current is set in the range of 0.3 ms to 1 ms, which is the double-shielded TIG welding method according to claim 2, characterized by the above.

[0011] The invention according to claim 4 is The electrode positive polarity current is formed from 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, 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, which is the double-shielded TIG welding method according to any one of claims 1 to 3.

[0012] The invention of claim 5 is the electrode negative polarity current is formed from the first electrode negative polarity current during the first electrode negative polarity period and the second electrode negative polarity current during the 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, which is the double-shielded TIG welding method according to claim 4.

Effect of the Invention

[0013] According to the double-shielded TIG welding method performed by energizing an alternating welding current according to the present invention, the generation of blow holes can be suppressed and good welding quality can be obtained.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] FIG. 1 is a block diagram of a welding apparatus for implementing a double shield tig welding method according to an embodiment of the present invention. Hereinafter, each block will be described with reference to the figure.

[0017] The welding torch WT mainly includes an electrode 1, an inner nozzle 4 surrounding it, 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.

[0018] When the start switch ON is turned on, it outputs a start signal On that becomes a high level, and when it is turned off, it becomes a low level. This start switch ON is a torch switch provided on the welding torch WT. Also, a start signal On may be output from the robot control device.

[0019] 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.

[0020] The first electrode positive polarity current setting circuit IP1R outputs a first electrode positive polarity current setting signal Ip1r having a predetermined positive value.

[0021] The second electrode positive polarity current setting circuit IP2R outputs a second electrode positive polarity current setting signal Ip2r having a pulse waveform formed from a predetermined peak current having a predetermined positive value during a predetermined peak period and a predetermined base current having a predetermined positive value during a predetermined base period. 1) The value of the first electrode positive polarity current setting signal Ip1r is set to a value smaller than the peak value (peak current) of the second electrode positive polarity current setting signal Ip2r. 2) The peak value (peak current) of the second electrode positive polarity current setting signal Ip2r is set to a value larger than the peak value of the second electrode negative polarity current setting signal In1r. 3) The second electrode positive polarity current setting signal Ip2r has a pulse waveform, and its period is set in the range of 0.3 ms to 1 ms.

[0022] The inner gas flow rate setting circuit FIR takes the above-mentioned second electrode negative polarity current setting signal In2r as an 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 the inner gas setting function is shown below. Fir = (In2r - 75) / 50 + 3.5 (Equation (1)) However, it is in the range of 75 ≤ In2r ≤ 150. When In2r < 75, it has the same value as In2r = 75, and when In2r > 150, it has the same value as In2r = 150. Thus, the larger the value of the second electrode negative polarity current setting signal In2r, the larger the value of the inner gas flow rate setting signal Fir.

[0023] The inner gas flow rate regulator CI is a commonly used mass flow controller. Taking the above-mentioned start signal On and the above-mentioned inner gas flow rate setting signal Fir as inputs, when the start signal On becomes High level, the flow rate Fi of the inner gas 7 from the inner gas cylinder 6 is adjusted to the value determined by the inner gas flow rate setting signal Fir and ejected.

[0024] The outer gas flow rate setting circuit FOR takes the above-mentioned second electrode negative polarity current setting signal In2r as an input, inputs the second electrode negative polarity current setting signal In2r [A] into 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 (Equation (2)) However, it is in the range of 75 ≦ In2r ≦ 150. When In2r < 75, it has the same value as In2r = 75, and when In2r > 150, it has the same value as In2r = 150. Thus, the larger the value of the second electrode minus-polarity current setting signal In2r, the larger the value of the outer gas flow rate setting signal For.

[0025] The outer gas flow regulator CO is a commonly used mass flow controller. Taking the above start signal On and the above outer gas flow rate 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 the value determined by the outer gas flow rate setting signal For and ejects it.

[0026] The inner gas 7 flows through the passage inside the inner nozzle 4. Also, the outer gas 9 flows through the passage between the outside of the inner nozzle 4 and the inside of the outer nozzle 5. Inert gases such as argon and helium are used for the inner gas 7 and the outer gas 9.

[0027] 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.

[0028] The first electrode minus-polarity period setting circuit TN1R takes the above voltage detection signal Vd as an input, measures the period until the variation of the voltage detection signal Vd during this period converges, and outputs a predetermined first electrode minus-polarity period setting signal Tn1r. The second electrode minus-polarity period setting circuit TN2R outputs a predetermined second electrode minus-polarity period setting signal Tn2r.

[0029] The first electrode plus-polarity period setting circuit TP1R takes the above voltage detection signal Vd as an input, measures the period until the variation of the voltage detection signal Vd during this period converges, and outputs a predetermined first electrode plus-polarity period setting signal Tp1r. The second electrode plus-polarity period setting circuit TP2R outputs a predetermined second electrode plus-polarity period setting signal Tp2r.

[0030] The current setting circuit IR takes the above-mentioned first electrode negative polarity period setting signal Tn1r, the above-mentioned second electrode negative polarity period setting signal Tn2r, the above-mentioned first electrode positive polarity period setting signal Tp1r, the above-mentioned second electrode positive polarity period setting signal Tp2r, the above-mentioned first electrode negative polarity current setting signal In1r, the above-mentioned second electrode negative polarity current setting signal In2r, the above-mentioned first electrode positive polarity current setting signal Ip1r, the above-mentioned second electrode positive polarity current setting signal Ip2r, and the above-mentioned current detection signal Id as inputs, 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) Subsequently, a current setting signal Ir with 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) Subsequently, a current setting signal Ir with 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, a low-level polarity switching signal Snp is output. 7) Repeat the processes of 1) to 6) above.

[0031] The welding power source PS takes 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 as inputs. When the start signal On becomes High level, a high-frequency high voltage is applied between the electrode 1 and the base material 2. When the arc 3 is generated, the output of the welding current Iw and the welding voltage Vw with the current value set by the current setting signal Ir and the power source polarity set by the polarity switching signal Snp is started, and when the start signal On becomes Low level, the output is stopped. Although not shown in the figure, the welding power source PS is connected to a commercial AC power source such as three-phase 200V, and includes a primary rectification circuit that rectifies the commercial AC power source to DC, a capacitor that smoothes the rectified DC, a primary-side 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 rectification circuit that rectifies the stepped-down high-frequency AC to DC, a reactor that smoothes the rectified DC, a secondary-side inverter circuit that switches the smoothed DC to the electrode negative polarity EN or the electrode positive polarity EP according to the 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 become equal, and a drive circuit that drives the primary-side inverter circuit based on the output of the modulation circuit.

[0032] Figure 2 is a timing chart of each signal in the welding apparatus shown in Figure 1 showing the double-shielded tig welding method according to an embodiment of the present invention. In the figure, (A) shows the time change of the welding current Iw, (B) shows the time change of the welding voltage Vw, and (C) shows the time change of the polarity switching signal Snp. Hereinafter, the operation during welding will be described with reference to the figure.

[0033] The welding current Iw shown in Figure (A) and the welding voltage Vw shown in Figure (B) show waveforms of the electrode negative polarity EN above 0 and waveforms of the electrode positive polarity EP below 0. In the following, the magnitudes of the values of the welding current Iw and the welding voltage Vw are described by the magnitudes of their absolute values regardless of the electrode negative polarity EN and the electrode positive polarity EP.

[0034] Inner gas and outer gas (not shown) are ejected into the arc generation section. The flow rate FI of the inner gas is a value calculated by inputting the negative-polarity current In2 of the second electrode into the above-described formula (1). The flow rate Fo of the outer gas is a value calculated by inputting the negative-polarity current In2 of the second electrode into the above-described formula (2).

[0035] (1) Explanation of the operation during the negative electrode polarity period Ten Immediately before time t1, as shown in Fig. (A), the welding current Iw decreases from the negative-value second electrode positive-polarity current Ip2 to a predetermined polarity switching current value of negative value. At time t1, when the welding current Iw becomes equal to the polarity switching current value as shown in Fig. (A), as shown in Fig. (C), the polarity switching signal Snp changes from the Low level to the High level and shifts to the negative electrode polarity period Ten. In response to this, as shown in Fig. (A), the welding current Iw sharply changes from the negative-value polarity switching current value to a positive-value predetermined first electrode negative-polarity current value In1. As shown in Fig. (B), the welding voltage Vw has a waveform similar to the current waveform and changes from a negative voltage value to a positive voltage value.

[0036] During the first electrode negative polarity period Tn1 from time t1 to t2, as shown in Fig. (A), the welding current Iw becomes the first electrode negative polarity current value In1. As shown in Fig. (B), the welding voltage Vw fluctuates during this period, and the fluctuation converges immediately before time t2. This fluctuation of the welding voltage Vw is because the arc generation state at the time of polarity switching is in a transient state. In the double shielded TIG welding method in which inner gas and outer gas flow, compared with the normal TIG welding method in which only shielding gas flows, turbulent flow is likely to occur due to the difference in the flow rates of both gases. When the arc generation state is in a transient state, the fluctuation is large, so turbulent flow is 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 turbulent flow 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 turbulent flow. Therefore, the first electrode negative polarity period Tn1 is set to the period until the fluctuation of the welding voltage Vw converges during this period. For example, the absolute value of the polarity switching current value is set to 50 A. The reason for decreasing the welding current Iw to the polarity switching current value and switching the polarity is to prevent the secondary side inverter circuit in the welding power source PS in Fig. 1 from malfunctioning due to the surge voltage at the time of switching.

[0037] During the predetermined second electrode negative polarity period Tn2 from time t2 to t3, as shown in Fig. (A), the welding current Iw increases to the second electrode negative polarity current value In2. As shown in Fig. (B), the welding voltage Vw becomes a larger value than during the first electrode negative polarity period Tn1. Since the melting of the base material is promoted during this period, it becomes the main period of welding.

[0038] At time t3, when the second electrode negative polarity period Tn2 ends, as shown in Fig. (A), the welding current Iw decreases with a slope and becomes the polarity switching current value at time t4. 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.

[0039] (2) Explanation of the operation during the electrode positive polarity period Tep At time t4, as shown in Fig. (A), when the welding current Iw becomes equal to the polarity switching current value, as shown in Fig. (C), the polarity switching signal Snp changes to the Low level and shifts to the electrode positive polarity period Tep. In response to this, as shown in Fig. (A), the welding current Iw sharply changes from the positive polarity switching current value to the predetermined first electrode positive polarity current value Ip1 of a negative value. As shown in Fig. (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.

[0040] During the first electrode positive polarity period Tp1 from time t4 to t5, as shown in Fig. (A), the welding current Iw becomes the first electrode positive polarity current value Ip1. As shown in Fig. (B), the welding voltage Vw fluctuates during this period, and the fluctuation converges immediately before time t5. This fluctuation of the welding voltage Vw is because the formation state of the cathode spots formed for obtaining the oxide film is in a transient state. In the double shielded TIG welding method in which the inner gas and the outer gas flow, compared with the normal TIG welding method in which only the shielding gas flows, turbulent flow is likely to occur due to the difference in the flow rates of both gases. When the formation state of the cathode spots is in a transient state, the fluctuation is large, so turbulent flow is likely to occur. The generation state of this turbulent flow becomes more intense when switching to the electrode positive polarity EP than when switching the above-mentioned polarity to the electrode negative polarity EN. Therefore, by making the first electrode positive polarity current value Ip1 a small value, the fluctuation of the arc generation state is suppressed and the generation of turbulent flow is prevented. As a result, it is possible to suppress the incomplete shielding state of the arc and the generation of blowholes due to the generation of turbulent flow. Therefore, the first electrode negative polarity period Tp1 is set to the period until the fluctuation of the welding voltage Vw converges during this period.

[0041] During the predetermined second electrode positive polarity period Tp2 from time t5 to t6, as shown in Fig. (A), the welding current Iw increases to the second electrode positive polarity current value Ip2. As shown in Fig. (B), 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.

[0042] The positive current Ip2 of the second electrode is set by the positive current setting signal Ip2r of the second electrode shown in FIG. 1. The positive current Ip2 of the second electrode has a pulse waveform formed from a predetermined peak current during a predetermined peak period and a predetermined base current during a predetermined base period. 1) The value of the positive current Ip1 of the first electrode is set to a value smaller than the peak value (peak current) of the positive current Ip2 of the second electrode. 2) The peak value (peak current) of the positive current Ip2 of the second electrode is set to a value larger than the peak value of the negative current In1 of the second electrode. 3) The period of the pulse waveform of the positive current Ip2 of the second electrode is set in the range of 0.3 ms to 1 ms.

[0043] At time t6, when the positive period Tp2 of the second electrode 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.

[0044] Numerical examples of each parameter are shown below. In1 = 60 A, In2 = 150 A Ten = 10 ms, Tn1 = 0.5 ms Ip1 = 60 A Ip2 peak current = 200 A, base current = 100 A, pulse period = 0.3 ms to 1 ms Tep = 3 ms, Tp1 = 0.3 ms

[0045] The effects of the present embodiment will be described below. According to this embodiment, the peak value of the electrode positive polarity current is set to be 50 A or more greater than the peak value of the electrode negative polarity current. By doing so, the removal region of the oxide film due to the cleaning action of the electrode positive polarity current becomes wider. As a result, the generation of blowholes caused by insufficient removal of the oxide film can be suppressed. In particular, when welding while inserting a filler wire, the removal of the oxide film on the surface of the filler wire is insufficient and blowholes are likely to occur. However, in this embodiment, the generation of blowholes can be suppressed even in such a case.

[0046] More preferably, according to this embodiment, the electrode positive polarity current includes a pulse waveform formed from the peak current during the peak period and the base current during the base period. When the electrode positive polarity current is a pulse waveform, the removal region of the oxide film due to the cleaning action becomes even wider compared to the case of a DC waveform. As a result, the generation of blowholes caused by insufficient removal of the oxide film can be more effectively suppressed.

[0047] More preferably, according to this embodiment, the period of the pulse waveform of the electrode positive polarity current is set in the range of 0.3 ms to 1 ms. When the period of the pulse waveform of the electrode positive polarity current is within the above range, the removal region of the oxide film due to the cleaning action can be made the widest. As a result, the generation of blowholes caused by insufficient removal of the oxide film can be further more effectively suppressed.

[0048] More preferably, according to this embodiment, the electrode plus-polarity current is formed from the first electrode plus-polarity current during the first electrode plus-polarity period and the second electrode plus-polarity current during the second electrode plus-polarity period. The value of the first electrode plus-polarity current is 20% to 60% of the peak value of the second electrode plus-polarity current, and the first electrode plus-polarity period is 5% to 30% of the electrode plus-polarity period. Even more preferably, the value of the first electrode plus-polarity current is 30% to 50% of the peak value of the second electrode plus-polarity current, and the first electrode plus-polarity period is 10% to 20% of the electrode plus-polarity period. When the electrode polarity is switched to the plus-polarity, the formation state of the cathode spots formed for obtaining the oxide film becomes a transient state. In the double-shielded TIG welding method in which the inner gas and the outer gas flow, turbulent flow is likely to occur due to the difference in the flow rates of both gases as compared with the normal TIG welding method in which only the shielding gas flows. When the formation state of the cathode spots is in a transient state, the arc generation state fluctuates greatly, so turbulent flow is likely to occur. The generation state of this turbulent flow becomes more intense when switching to the electrode plus-polarity than when switching the polarity to the electrode minus-polarity. Therefore, by at least reducing the value of the first electrode plus-polarity current, the fluctuation of the arc generation state is suppressed and the generation of turbulent flow 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 turbulent flow. The value of the second electrode plus-polarity current is set as the peak value in order to include the case of the pulse waveform.

[0049] More preferably, according to the present embodiment, the electrode negative polarity current is formed from the first electrode negative polarity current during the first electrode negative polarity period and the second electrode negative polarity current during the 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 switching to the electrode negative polarity, the arc generation state becomes a transient state. In the double shield TIG welding method in which the inner gas and the outer gas flow, turbulent flow is likely to occur due to the difference in the flow rates of both gases compared to the normal TIG welding method in which only the shielding gas flows. Since the arc generation state fluctuates, turbulent flow is likely to occur. 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 turbulent flow is prevented. As a result, it is possible to suppress the incomplete shielding state of the arc due to the generation of turbulent flow and the occurrence of blowholes. The value of the second electrode negative polarity current is set as the peak value in order to include not only the rectangular wave but also the case of a sine wave whose value changes.

[0050] More preferably, according to the present embodiment, the first electrode positive polarity period is set to a period until the fluctuation of the welding voltage converges during this period. When the fluctuation of the welding voltage converges, the fluctuation of the arc generation state converges. If the first electrode positive polarity period is too short, the generation of turbulent flow 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 until the fluctuation of the welding voltage converges, it can be set to an appropriate value.

[0051] More preferably, according to the present embodiment, the first electrode negative polarity period is set to a period until the fluctuation of the welding voltage converges during this period. When the fluctuation of the welding voltage converges, the fluctuation of the arc generation state also converges. If the first electrode negative polarity period is too short, the generation of turbulent flow cannot be sufficiently suppressed, and there is a risk of blow holes 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 until the fluctuation of the welding voltage converges, it can be set to an appropriate value.

Explanation of Signs

[0052] 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 FIR Inner Gas Flow Setting Circuit Fir Inner Gas Flow Setting Signal Fo Outer Gas Flow FOR Outer Gas Flow Setting Circuit For Outer Gas Flow 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 First 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 Positive electrode current of the first electrode IP1R Positive electrode current setting circuit of the first electrode Ip1r Positive electrode current setting signal of the first electrode Ip2 Positive electrode current of the second electrode IP2R Positive electrode current setting circuit of the second electrode Ip2r Positive electrode current setting signal of the second electrode 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 Negative polarity period of the first electrode TN1R Negative polarity period setting circuit of the first electrode Tn1r Negative polarity period setting signal of the first electrode Tn2 Negative polarity period of the second electrode TN2R Negative polarity period setting circuit of the second electrode Tn2r Negative polarity period setting signal of the second electrode Tp1 Positive polarity period of the first electrode TP1R Positive polarity period setting circuit of the first electrode Tp1r Positive polarity period setting signal of the first electrode Tp2 Positive polarity period of the second electrode TP2R Positive polarity period setting circuit of the second electrode Tp2r Positive polarity period setting signal of the second electrode VD Voltage detection circuit Vd Voltage detection signal WT Welding torch

Claims

1. Using a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, In a double shielded TIG welding method where welding is performed by passing an alternating welding current formed from the electrode negative polarity current during the electrode negative polarity period and the electrode positive polarity current during the electrode positive polarity period, Setting the peak value of the electrode positive polarity current to a value greater than the peak value of the electrode negative polarity current, A double shielded TIG welding method characterized by this.

2. The electrode positive polarity current includes a pulse waveform formed from the peak current during the peak period and the base current during the base period, The double shielded TIG welding method according to Claim 1, characterized by this.

3. The period of the pulse waveform of the electrode positive polarity current is set in the range of 0.3 ms to 1 ms, The double shielded TIG welding method according to Claim 2, characterized by this.

4. The electrode positive polarity current is formed from 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, 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, The double shielded TIG welding method according to any one of Claims 1 to 3, characterized by this.

5. The electrode negative polarity current is formed from the first electrode negative polarity current during the first electrode negative polarity period and the second electrode negative polarity current during the 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 4, characterized by this.

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