Double shield tig welding method

Abstract

To provide a double shield tig welding method capable of suppressing worsening of welding quality in a transient state caused by the change of a welding state.SOLUTION: This double shield tig welding method uses a welding torch provided with an inner nozzle for jetting out an inner gas and an outer nozzle for jetting out an outer gas, generates an arc after pre-flowing (time t1-t3) of the inner gas Fi and the outer gas Fo at the time of starting welding, energizes welding current Iav to execute welding, executes after-flowing of the inner gas and the outer gas after arc-extinguishing at the time of ending the welding, and then ends the welding. During the after-flowing period at time t6 and t7, a flow rate Fi of the inner gas is set so that a flow velocity of the inner gas can be within ±20% of that of the outer gas.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a double-shielded TIG welding method. [Background technology]

[0002] A double-shielded 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 a welding current through the welding torch (see, for example, Patent Document 1). As the inner gas and the outer gas, an inert gas such as argon or helium is used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-15628 Summary of the Invention [Problem to be solved by the invention]

[0004] The double-shielded TIG welding method has a problem in that the welding quality deteriorates due to turbulence in the gas flow when the welding condition changes and the welding condition is in a transitional state, especially when welding aluminum, aluminum alloys, magnesium, etc.

[0005] Therefore, an object of the present invention is to provide a double-shielded TIG welding method that can prevent deterioration of welding quality, for example, when the welding condition changes and enters a transient state. [Means for solving the problem]

[0006] A double-shielded TIG welding method provided by a first aspect of the present invention uses a welding torch equipped with an inner nozzle for spraying inner gas and an outer nozzle for spraying outer gas, and at the start of welding, pre-flow of the inner gas and the outer gas is performed, then an arc is generated and a welding current is passed to transition to a steady-state welding period, and at the end of welding, the arc is extinguished and then after-flow of the inner gas and the outer gas is performed to complete the welding, characterized in that the after-flow sets the flow rate of the inner gas so that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas.

[0007] As an example, the double-shielded TIG welding method of the present invention is characterized in that a crater treatment period is set after the steady-state welding period, and during the crater treatment period, the flow rate of the inner gas is set so that the flow velocity of the inner gas is within ±20% of the flow velocity of the outer gas.

[0008] As an example, the double-shielded TIG welding method of the present invention is characterized in that, during the initial period from the time the arc is generated, the flow rate of the inner gas is set so that the flow velocity of the inner gas is within ±20% of the flow velocity of the outer gas.

[0009] As an example, in the double-shielded TIG welding method of the present invention, the welding current is 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, 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. [Effects of the Invention]

[0010] According to the above configuration, for example, in a double-shielded TIG welding method, it is possible to prevent the welding quality from deteriorating when the welding state changes and is in a transitional state. [Brief explanation of the drawings]

[0011] [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. [Figure 2] FIG. 2 is a current-voltage waveform diagram in a double-shielded TIG welding method according to an embodiment of the present invention. [Figure 3] 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 INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0013] 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.

[0014] The figure shows the case of a double-shielded TIG welding method using an AC welding current Iw formed from a negative electrode polarity current during the negative electrode polarity period and a positive electrode polarity current during the positive electrode polarity period. The double-shielded TIG welding method using an AC welding current Iw is used for welding aluminum, aluminum alloys, magnesium, etc.

[0015] The welding torch WT mainly comprises 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 as 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.

[0016] The torch switch circuit ON is a torch switch attached to the welding torch WT, and outputs a torch switch signal On that goes to a high level when the welding operator turns it on, and goes to a low level when the welding operator turns it off.

[0017] The current detection circuit ID detects the welding current Iw, converts it into an absolute value, and outputs a current detection signal Id. The arc occurrence determination circuit AD receives the current detection signal Id as input, and when the value of the current detection signal Id is equal to or greater than the current flow determination value (approximately 5 A), determines that an arc has occurred and outputs an arc occurrence determination signal Ad that goes high.

[0018] The period determination circuit TP receives the torch switch signal On and the arc occurrence determination signal Ad as inputs, performs the following processing, and outputs a period determination signal Tp. When welding has ended, the period determination signal Tp=0. 1) When the torch switch signal On changes to high level, the period discrimination signal Tp=1 (pre-flow period start) is output. 2) When a predetermined delay time Td has elapsed since the time Tp changed to 1, a period discrimination signal Tp=2 (inner gas ejection start) is output. 3) When a predetermined preflow period has elapsed since Tp=1 and the arc occurrence determination signal Ad has changed to high level, a period determination signal Tp=3 (initial period start) is output. 4) When a predetermined initial period has elapsed since the time when Tp changed to Tp=3, Tp=4 (start of steady welding period) is output. 5) After that, when the torch switch signal On changes to low level and then changes to high level again, Tp=5 (start of crater processing period) is output. 6) After that, when the torch switch signal On changes to low level again, the period discrimination signal Tp=6 (start of afterflow period) is output. 7) When a predetermined after-flow period has elapsed, a period determination signal Tp=0 (welding end state) is output.

[0019] The first electrode negative polarity current setting circuit IN1R outputs a first electrode negative polarity current setting signal In1r of a predetermined positive value. The second electrode negative polarity current setting circuit IN2R outputs a second electrode negative polarity current setting signal In2r of a predetermined positive value. Here, In1r <In2rである。

[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. 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。

[0021] The steady inner gas flow rate setting circuit FICR receives the 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 steady inner gas flow rate setting function, and outputs the calculated value as the steady inner gas flow rate setting signal Ficr [l / min]. An example of the steady inner gas flow rate setting function is shown below. Ficr = (In2r - 75) / 50 + 3.5 (1) However, the range is 75≦In2r≦150, and if In2r<75, the value is the same as In2r=75, and if In2r>150, the value is the same as In2r=150. As a result, the value of the steady inner gas flow rate setting signal Ficr increases as the value of the second electrode negative polarity current setting signal In2r increases.

[0022] The steady outer gas flow rate setting circuit FOCR receives the 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 steady outer gas flow rate setting function, and outputs the calculated value as the steady outer gas flow rate setting signal Focr [l / min]. An example of the steady outer gas flow rate setting function is shown below. Focr=(In2r-75) / 50+5.5 (2) Formula However, the range is 75≦In2r≦150, and if In2r<75, the value is the same as In2r=75, and if In2r>150, the value is the same as In2r=150. As a result, the value of the steady outer gas flow rate setting signal Focr increases as the value of the second electrode negative polarity current setting signal In2r increases.

[0023] The flow rate reduction inner gas flow rate setting circuit FIIR receives the steady outer gas flow rate setting signal Focr as input, performs the following calculation, and outputs the flow rate reduction inner gas flow rate setting signal Fiir. The calculation calculates the inner gas flow rate at which the inner gas flow rate during the initial period is within ±20% of the outer gas flow rate. Fiir=Focr×R×K (3) where R = (cross-sectional area of ​​the flow path of the inner gas 7 in the inner nozzle 4) / (cross-sectional area of ​​the flow path of the outer gas 9 in the outer nozzle 5), and K is a constant between 0.8 and 1.2. The above formula will be explained using a numerical example. If the inner diameter of the inner nozzle 4 is 5 mm and the inner diameter of the outer nozzle 5 is 13 mm, then (cross-sectional area of ​​the flow path of the inner gas 7 in the inner nozzle 4) = 3.14 × 2.5 × 2.5, and (cross-sectional area of ​​the flow path of the outer gas 9 in the outer nozzle 5) = 3.14 × (6.5 × 6.5 - 2.5 × 2.5). As a result, R = 0.17. (1) When the second electrode negative polarity current setting signal In2r=75A The steady outer gas flow rate is Focr = 5.5 l / min, and the steady inner gas flow rate is Ficr = 3.5 l / min. Here, when K = 0.8, the flow rate reduction inner gas flow rate Fiir = 0.75 l / min. When K = 1.0, the flow rate reduction inner gas flow rate Fiir = 0.94 l / min. When K = 1.2, the flow rate reduction inner gas flow rate Fiir = 1.12 l / min. (2) When the second electrode negative polarity current setting signal In2r=150A The steady outer gas flow rate Focr = 7 l / min and the steady inner gas flow rate Ficr = 5 l / min. Here, when K = 0.8, the flow rate reduction inner gas flow rate Fiir = 0.95 l / min. When K = 1.0, the flow rate reduction inner gas flow rate Fiir = 1.2 l / min. When K = 1.2, the flow rate reduction inner gas flow rate Fiir = 1.42 l / min.

[0024] The preflow inner gas flow rate setting circuit FIPR outputs a predetermined preflow inner gas flow rate setting signal Fipr. Here, Fipr < Ficr, and it is also possible that Fipr = Fiir.

[0025] The inner gas flow rate setting circuit FIR takes the above period discrimination signal Tp, the above preflow inner gas flow rate setting signal Fipr, the above flow rate reduction inner gas flow rate setting signal Fiir, and the above steady inner gas flow rate setting signal Ficr as inputs, performs the following processing, and outputs an inner gas flow rate setting signal Fir. 1) When the period discrimination signal Tp = 2 (preflow period), the value of the preflow inner gas flow rate setting signal Fipr is output as the inner gas flow rate setting signal Fir. 2) When the period discrimination signal Tp = 3 (initial period), the value of the flow rate reduction inner gas flow rate setting signal Fiir is output as the inner gas flow rate setting signal Fir. 3) When the period discrimination signal Tp = 4 (steady welding period), an inner gas flow rate setting signal Fir that increases over time to the value of the steady inner gas flow rate setting signal Ficr is output. Here, it is also possible to switch to the value of the steady inner gas flow rate setting signal Ficr at the end of the initial period. 4) When the period discrimination signal Tp = 5 (crater processing period), the value of the flow rate reduction inner gas flow rate setting signal Fiir is output as the inner gas flow rate setting signal Fir. 5) When the period discrimination signal Tp = 6 (afterflow period), the value of the flow rate reduction inner gas flow rate setting signal Fiir is output as the inner gas flow rate setting signal Fir.

[0026] The inner gas flow regulator CI is a known mass flow controller, and receives the period discrimination signal Tp and the inner gas flow rate setting signal Fir as inputs, and 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 rate setting signal Fir and sprays it during the period of the period discrimination signal Tp = 2 to 6. Therefore, spraying of the inner gas 7 begins when the delay time Td has elapsed from the time the torch switch is turned on and the pre-flow period begins, and spraying stops when the after-flow period ends.

[0027] The outer gas flow rate setting circuit FOR receives the period discrimination signal Tp and the steady outer gas flow rate setting signal Focr as inputs, and outputs an outer gas flow rate setting signal For that is a predetermined preflow outer gas flow rate value when the period discrimination signal Tp=1-2 (preflow period), and that is the value of the steady outer gas flow rate setting signal Focr when the period discrimination signal Tp=3-6. Here, the preflow outer gas flow rate value is preferably set to a value larger than the value of the steady outer gas flow rate setting signal Focr. As a result, the outer gas flow rate Fo is the preflow outer gas flow rate value during the preflow period, and is the value of the steady outer gas flow rate setting signal Focr during the initial period, steady welding period, crater treatment period, and post-flow period.

[0028] The outer gas flow regulator CO is a known mass flow controller, which receives the period discrimination signal Tp and the outer gas flow rate setting signal For as inputs, and 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 rate setting signal For during the period of the period discrimination signal Tp=1 to 6, and then ejects the outer gas 9. Therefore, the outer gas 9 is ejected during the pre-flow period, the initial period, the steady welding period, the crater treatment period, and the after-flow period.

[0029] 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.

[0030] The voltage detection circuit VD detects the welding voltage Vw, converts it into an absolute value, and outputs a voltage detection signal Vd.

[0031] 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, 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.

[0032] 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, 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.

[0033] The current setting circuit IR receives 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 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, the polarity switching signal Snp is output at a high level. 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, the polarity switching signal Snp is output at a low level. 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 is output at a low level. 7) Repeat steps 1) to 6) above.

[0034] The welding power source PS receives the period discrimination signal Tp, the current setting signal Ir, the current detection signal Id, and the polarity switching signal Snp as inputs, and when the period discrimination signal Tp=3 to 5 (initial period, steady welding period, and crater treatment period), applies a high-frequency high voltage between the electrode 1 and the base material 2, and when an arc 3 is generated, outputs a welding current Iw and a welding voltage Vw of the current value set by the current setting signal Ir and the power supply polarity set by the polarity switching signal Snp, and stops outputting when the period discrimination signal Tp=6 (afterflow period). Although not shown, the welding power source PS is connected to a commercial AC power source such as a three-phase 200V power source, and is equipped with a primary rectifier circuit that rectifies the commercial AC power source to DC, a capacitor that smooths 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 smooths 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.

[0035] 2 is a current and voltage waveform diagram for a double-shielded TIG welding method according to an embodiment of the present invention. (A) in the figure shows the change over time in the welding current Iw, (B) in the figure shows the change over time in the welding voltage Vw, and (C) in the figure shows the change over time in the polarity switching signal Snp. Operation during steady welding will now be described with reference to the figures.

[0036] The welding current Iw shown in Figure 1(A) and the welding voltage Vw shown in Figure 1(B) 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 stated as absolute values, regardless of electrode negative polarity EN or electrode positive polarity EP.

[0037] 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 setting signal In2r into the above-mentioned equation (1). The flow rate Fo of the outer gas is calculated by inputting the second electrode negative polarity current setting signal In2r into the above-mentioned equation (2).

[0038] (1) Operation explanation of electrode negative polarity period Ten Just before time t11, as shown in FIG. 1A, the welding current Iw decreases from the negative second electrode positive polarity current value Ip2 to the predetermined negative polarity switching current value. At time t11, 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 low to high, as shown in FIG. 1C, and the system transitions 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 In1 to the predetermined positive first electrode negative polarity current value In1. As shown in FIG. 1B, the welding voltage Vw assumes a waveform similar to the current waveform and changes from a negative voltage value to a positive voltage value.

[0039] During the first electrode negative polarity period Tn1 from time t11 to time t12, as shown in Figure 1A, the welding current Iw is set to the first electrode negative polarity current value In1. As shown in Figure 1B, the welding voltage Vw fluctuates during this period, converging just before time t12. This fluctuation in the welding voltage Vw occurs because the arc generation state is in a transient state when the polarity is switched. In a double-shielded TIG welding method using inner and outer gases, turbulence is more likely to occur due to the difference in flow speed between the two gases than in a conventional TIG welding method using only shielding gas. When the arc generation state is in a transient state, fluctuations are large, making turbulence more likely to occur. Therefore, by setting the first electrode negative polarity current value In1 to a small value, fluctuations in the arc generation state are suppressed, preventing turbulence. As a result, the generation of turbulence can cause incomplete arc shielding, thereby preventing blowholes. Therefore, the first electrode negative polarity period Tn1 is set to a period during which the fluctuations in the welding voltage Vw converge. For example, the absolute value of the polarity switching current value is set to 50 A. The reason for switching the polarity by decreasing the welding current Iw to the polarity switching current value is to prevent the secondary inverter circuit in the welding power source PS in FIG. 1 from being damaged by a surge voltage that occurs during switching.

[0040] During a predetermined second electrode negative polarity period Tn2 from time t12 to t13, as shown in (A) of the figure, the welding current Iw increases to a second electrode negative polarity current value In2. As shown in (B) of the figure, the welding voltage Vw becomes 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 welding period.

[0041] At time t13, when the second electrode negative polarity period Tn2 ends, the welding current Iw decreases at a slope as shown in (A) of the figure, and reaches the polarity switching current value at time t14. The slope is determined by the inductance value of the current path through which the welding current Iw flows. The welding voltage Vw also decreases as shown in (B) of the figure.

[0042] (2) Operation explanation of the electrode positive polarity period Tep At time t14, as shown in (A) of the figure, 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 (C) of the figure, and the electrode positive polarity period Tep begins. In response to this, as shown in (A) of the figure, the welding current Iw abruptly changes from the positive polarity switching current value to the predetermined negative first electrode positive polarity current value Ip1. As shown in (B) of the figure, the welding voltage Vw assumes a waveform similar to the current waveform and changes from a positive voltage value to a negative voltage value.

[0043] During the first electrode positive polarity period Tp1 from time t14 to time t15, as shown in Figure 1A, the welding current Iw is set to the first electrode positive polarity current value Ip1. As shown in Figure 1B, the welding voltage Vw fluctuates during this period, converging just before time t15. This fluctuation in the welding voltage Vw occurs because the cathode spot formation state, which is formed to form an oxide film, is in a transient state. In a double-shield TIG welding method using inner and outer gases, turbulence is more likely to occur due to the difference in flow speed between the two gases than in a conventional TIG welding method using only shielding gas. When the cathode spot formation state is in a transient state, fluctuations are large, making turbulence more likely to occur. This turbulence is more severe when switching the polarity to the electrode positive polarity EP than when switching to the electrode negative polarity EN. Therefore, by reducing the first electrode positive polarity current value Ip1, fluctuations in the arc generation state are suppressed and turbulence is prevented. As a result, it is possible to prevent blowholes from occurring due to incomplete arc shielding caused by the generation of turbulence. Therefore, the first electrode positive polarity period Tp1 is set to a period during which fluctuations in the welding voltage Vw converge.

[0044] During a predetermined second electrode positive polarity period Tp2 from time t15 to t16, 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 larger than during the first electrode positive polarity period Tp1. The oxide film is mainly removed by the cleaning action during this period.

[0045] At time t16, when the second electrode positive polarity period Tp2 ends, as shown in Fig. (A) of the same figure, the welding current Iw decreases with a slope and becomes the polarity switching current value at time t17. The slope is determined by the inductance value of the current path of the welding current Iw. As shown in Fig. (B) of the same figure, the welding voltage Vw also decreases. Thereafter, the operation returns to that at time t11.

[0046] The figure shows the case of the balanced waveform where In2 = Ip2, but there may also be an unbalanced waveform where In2 < Ip2. Also, the figure shows the case where the current waveform is a substantially rectangular wave, but there may also be a sine wave case.

[0047] 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

[0048] Fig. 3 is a timing chart of each signal in the welding apparatus of Fig. 1 showing the double - shielded tig welding method according to an embodiment of the present invention. Fig. (A) of the same figure shows the time change of the torch switch signal On, Fig. (B) shows the time change of the outer gas flow rate Fo (l / min), Fig. (C) shows the time change of the inner gas flow rate Fi (l / min), Fig. (D) shows the time change of the average value of the absolute value of the welding current Iw shown in Fig. 2, which is the average welding current value Iav, and Fig. (E) shows the time change of the arc generation discrimination signal Ad. Hereinafter, the operations of each signal will be described with reference to the same figure.

[0049] [Operation during the pre - flow period] At time t1, when the welding operator turns on the torch switch provided on the welding torch WT shown in FIG. 1, the torch switch signal On changes to a high level, as shown in FIG. 1(A). In response to this, the period determination signal Tp in FIG. 1 changes to 1, and the preflow period begins. At the same time, the outer gas flow regulator CO in FIG. 1 starts to eject outer gas. As shown in FIG. 1(B), the outer gas flow rate Fo becomes a predetermined preflow outer gas flow rate value determined by the outer gas flow rate setting signal For in FIG. 1. It is desirable that the preflow outer gas flow rate value be set to a value greater than the value of the steady-state outer gas flow rate setting signal Focr in FIG. 1.

[0050] At time t2, when a predetermined delay time Td has elapsed since time t1, the period discrimination signal Tp in FIG. 1 changes to Tp=2. In response to this, the inner gas flow regulator CI in FIG. 1 starts to eject the inner gas. As shown in FIG. 1(C), the inner gas flow rate Fi becomes a value determined by the preflow inner gas flow rate setting signal Fipr in FIG. 1. The value of the preflow inner gas flow rate setting signal Fipr is preferably smaller than the value of the steady-state inner gas flow rate setting signal Ficr in FIG. 1, and may be equal to the value of the flow rate reduction inner gas flow rate setting signal Fiir in FIG. 1.

[0051] During the preflow period, the inner gas is ejected after the outer gas is ejected. In this manner, the inner gas is started to be ejected while the surroundings are shielded by the outer gas, so the inner gas does not entrain the surrounding air, and the steady state can be quickly reached. Therefore, in this embodiment, the preflow time can be shortened by about 50% compared to the conventional technology in which the outer gas and inner gas are simultaneously ejected. Therefore, in this embodiment, sufficient shielding can be ensured even if the preflow time at the start of welding is set short, thereby improving work efficiency and reducing the consumption of expensive inert gas. For example, while the conventional technology required the preflow period to be set to about 6 seconds, this embodiment can be set to about 3 seconds.

[0052] [Initial period behavior] At time t3, the preflow period ends and the period determination signal Tp in FIG. 1 changes to 3. The welding power source PS in FIG. 1 applies a high-frequency high voltage between the electrode 1 and the base material 2 in FIG. 1, generating the arc 3 in FIG. 1. As shown in FIG. 1(D), the flow of the average welding current Iav begins. The waveforms of the welding current Iw and welding voltage Vw become those shown in FIG. 2. At time t3, the flow of the welding current Iw determines the occurrence of an arc, and the arc occurrence determination signal Ad changes to a high level as shown in FIG. 1(E). At time t3, as shown in FIG. 1(B), the outer gas flow rate Fo becomes a value determined by the steady-state outer gas flow rate setting signal Focr in FIG. 1. The value of the steady-state outer gas flow rate setting signal Focr is calculated by substituting the value of the second electrode negative polarity current setting signal In2r in FIG. 1 into the above-described equation (2). Then, welding begins at time t3.

[0053] When the arc occurrence determination signal Ad changes to a high level, the process transitions to a predetermined initial period from time t3 to t4. As shown in FIG. 1C, the inner gas flow rate Fi is determined by the flow rate reduction inner gas flow rate setting signal Fiir of FIG. 1. This flow rate reduction inner gas flow rate setting signal Fiir is calculated by substituting the value of the steady outer gas flow rate setting signal Focr of FIG. 1 into the above-mentioned equation (3). In other words, the inner gas flow rate Fi during the initial period is set so that the inner gas flow rate is within ±20% of the outer gas flow rate. Since the inner gas flow rate during the steady welding period is approximately four times the outer gas flow rate, the inner gas flow rate Fi during the initial period is reduced to slow the flow rate. For example, the initial period is set to 500 ms.

[0054] [Operation during steady welding period] When the initial period ends at time t4, the period determination signal Tp in FIG. 1 changes to 4, and the steady-state welding period begins. As shown in FIG. 1C, the inner gas flow rate Fi increases over time to a value determined by the steady-state inner gas flow rate setting signal Ficr in FIG. 1. The value of this steady-state inner gas flow rate setting signal Ficr is calculated by substituting the value of the second electrode negative polarity current setting signal In2r in FIG. 1 into the above-mentioned equation (1). As mentioned above, the inner gas flow rate during the steady-state welding period is approximately four times faster than the outer gas flow rate. By ejecting inner gas at a high speed, the arc stiffness can be increased, thereby achieving deeper penetration and faster welding speeds. For example, the period during which the inner gas flow rate Fi increases over time is set to 200 ms.

[0055] At time t41 during the steady welding period from time t4 to t5, when the welding operator turns off the torch switch, the torch switch signal On changes to low level as shown in the same figure (A), but the steady welding period described above is maintained as is.

[0056] [Crater processing period operation] At time t5, the welder turns the torch switch on again, as shown in Figure 1A. The torch switch signal On changes to a high level. In response, the period determination signal Tp in Figure 1 changes to 5, signaling the transition to the crater treatment period. As shown in Figure 1B, the outer gas flow rate Fo remains the same as during the steady welding period. As shown in Figure 1C, the inner gas flow rate Fi is determined by the flow rate reduction inner gas flow rate setting signal Fiir in Figure 1. Therefore, the inner gas flow rate Fi during the crater treatment period is set so that the inner gas flow rate is within ±20% of the outer gas flow rate. Because the inner gas flow rate during the steady welding period is approximately four times the outer gas flow rate, the inner gas flow rate Fi is reduced during the crater treatment period to slow the flow rate. As shown in Figure 1D, the welding current average Iav becomes smaller than during the steady welding period.

[0057] [Afterflow period operation] At time t6, the welder turns the torch switch off again. As shown in (A) of the figure, the torch switch signal On changes to low level, and the period determination signal Tp of FIG. 1 changes to 6, transitioning to the after-flow period. In response to this, the welding power source PS of FIG. 1 stops output, the arc is extinguished, and the welding current average value Iav becomes 0 A, as shown in (D) of the figure. As shown in (B) of the figure, the outer gas flow rate Fo remains the same as during the steady welding period. As shown in (C) of the figure, the inner gas flow rate Fi becomes a value determined by the flow rate reduction inner gas flow rate setting signal Fiir of FIG. 1. Therefore, the inner gas flow rate Fi during the after-flow period is set so that the inner gas flow rate is within ±20% of the outer gas flow rate. Because the inner gas flow rate during the steady welding period is approximately four times the outer gas flow rate, the inner gas flow rate Fi during the after-flow period is reduced to slow the flow rate.

[0058] [Weld End] At time t7, when the after-flow period ends, the period discrimination signal Tp in FIG. 1 changes to Tp=0. In response to this, as shown in FIG. 1(B), the outer gas flow rate Fo becomes 0 and jetting stops. Also, as shown in FIG. 1(C), the inner gas flow rate Fi becomes 0 and jetting stops. This ends welding.

[0059] In the above-described embodiment, the case where a crater treatment period is provided after a steady welding period has been described, but the crater treatment period may be omitted. Also, in the above-described embodiment, the welding current is an AC current, but the present invention can also be applied to DC current and pulse current.

[0060] The effects of this embodiment are described below. According to this embodiment, the after-flow setting is performed by setting the flow rate of the inner gas so that the inner gas flow rate is within ±20% of the outer gas flow rate. In conventional techniques, the inner gas flow rate is set during steady-state welding so that the inner gas flow rate is approximately four times faster than the outer gas flow rate. This allows the high-speed inner gas to be ejected, increasing the arc rigidity, deepening penetration, and increasing the welding speed. In conventional techniques, the steady-state welding state continues during the after-flow setting. However, during the after-flow setting, the arc is extinguished, causing the welding state to enter a transient state. In double-shielded TIG welding methods, when the welding state enters a transient state, turbulence in the gas flow can cause the electrode tip to oxidize. This occurs because the flow rates of the inner and outer gases differ significantly during the transient arc generation state, resulting in turbulence and incomplete shielding. In this embodiment, the flow rate of the inner gas during the after-flow period is set so that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas, thereby suppressing the occurrence of turbulence. As a result, this embodiment can suppress the problem of the electrode tip being oxidized, which leads to poor welding quality in subsequent welding. In order to further suppress the occurrence of turbulence, it is more preferable to set the flow rate of the inner gas so that the flow rate of the inner gas is equal to the flow rate of the outer gas.

[0061] More preferably, according to this embodiment, a crater treatment period is provided after the steady welding period, and during the crater treatment period, the flow rate of the inner gas is set so that the inner gas flow rate is within ±20% of the outer gas flow rate. In conventional technology, the steady welding period continues during the crater treatment period. However, during the crater treatment period, the welding current average value decreases, causing the welding state to enter a transient state. In double-shield TIG welding methods, when the welding state enters a transient state, the gas flow becomes turbulent, which can easily cause blowholes. This is because when the arc generation state is in a transient state, the flow rates of the inner and outer gases differ significantly, causing turbulence and resulting in incomplete shielding. In this embodiment, the flow rate of the inner gas during the crater treatment period is set so that the inner gas flow rate is within ±20% of the outer gas flow rate, thereby suppressing turbulence. As a result, this embodiment can prevent blowholes from occurring and deteriorating welding quality. In order to further suppress the occurrence of turbulence, it is more preferable to set the flow rate of the inner gas so that the flow velocity of the inner gas is equal to the flow velocity of the outer gas.

[0062] More preferably, according to this embodiment, during the initial period from the time the arc is generated, the flow rate of the inner gas is set so that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas. In the double-shield TIG welding method, when the arc generation state is in a transient state at the start of welding, there is a problem in that blowholes are likely to occur due to turbulence in the gas flow. This is because, when the arc generation state is in a transient state, the flow rates of the inner gas and outer gas differ significantly, generating turbulence and resulting in incomplete arc shielding. In this embodiment, during the initial period after the arc is generated, the flow rate of the inner gas is set so that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas, thereby suppressing the occurrence of turbulence. As a result, this embodiment can suppress the occurrence of blowholes at the start of welding. To further suppress the occurrence of turbulence, it is more preferable to set the flow rate of the inner gas so that the flow rates of the inner gas and outer gas are equal.

[0063] More preferably, according to this embodiment, the welding current is 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. The electrode positive polarity current is formed from a first electrode positive polarity current during the first electrode positive polarity period and a 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. 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. When the electrode polarity is switched to positive polarity, the formation state of cathode spots formed to form an oxide film becomes transient. In a 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 a conventional TIG welding method in which only shielding gas is flowed. When the formation state of cathode spots is transient, turbulence is more likely to occur due to large fluctuations in the arc generation state. This turbulence occurs more severely when the polarity is switched to positive electrode polarity than when it is switched to negative electrode polarity. Therefore, by setting at least the value of the first electrode positive polarity current to a small value, fluctuations in the arc generation state are suppressed and turbulence is prevented. As a result, it is possible to prevent blowholes from occurring due to incomplete arc shielding caused by turbulence. 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. [Explanation of symbols]

[0064] 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, AD: Arc occurrence determination circuit, Ad: Arc occurrence determination signal, CI: Inner gas flow regulator, CO: Outer gas flow regulator, EN: Electrode negative polarity, EP: Electrode positive polarity, Fi: Inner gas flow, FICR: Steady inner gas flow rate setting circuit, Ficr: Steady inner gas flow rate setting signal, FIIR: Flow rate reduced inner gas flow rate setting circuit, Fiir: Flow rate reduced inner gas flow rate setting constant signal, FIPR: preflow inner gas flow rate setting circuit, Fipr: preflow inner gas flow rate setting signal, FIR: inner gas flow rate setting circuit, Fir: inner gas flow rate setting signal, Fo: outer gas flow rate, FOCR: steady outer gas flow rate setting circuit, Focr: steady outer gas flow rate setting signal, FOR: outer gas flow rate setting circuit, For: outer gas flow rate setting signal, Iav: welding current average value, 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 Polarity 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: Torch switch circuit, On: Torch switch signal, PS: Welding power supply, Ten: electrode negative polarity period, Tep: electrode positive polarity period, Tn1: first electrode negative polarity period, TN1R: first electrode negative polarity period setting circuit, Tn1r: first 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, TP: period discrimination circuit, Tp: period discrimination signal, Tp1: first electrode positive polarity period, TP1R: first electrode positive polarity period setting circuit, Tp1r: first 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 double-shielded 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 at the start of welding, pre-flow of the inner gas and the outer gas is performed, then an arc is generated and a welding current is passed to transition to a steady welding period, and at the end of welding, the arc is extinguished and then after-flow of the inner gas and the outer gas is performed to finish welding, A double shield TIG welding method, characterized in that the afterflow is set so that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas.

2. 2. The double-shielded TIG welding method according to claim 1, characterized in that a crater treatment period is provided after the steady-state welding period, and during the crater treatment period, the flow rate of the inner gas is set so that the flow velocity of the inner gas is within ±20% of the flow velocity of the outer gas.

3. A double-shielded TIG welding method as described in claim 1 or 2, characterized in that during the initial period from the time the arc is generated, the flow rate of the inner gas is set so that the flow velocity of the inner gas is within ±20% of the flow velocity of the outer gas.

4. 3. The double-shielded TIG welding method according to claim 1, wherein the welding current is 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, and a value of the first electrode positive polarity current is 20% to 60% of a peak value of the second electrode positive polarity current.

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