Double shield TIG welding method and double shield TIG welding apparatus

Abstract

To obtain excellent welding quality by suppressing the occurrence of arc interruption at the start of welding in a double shield TIG welding method.SOLUTION: When arc interruption is determined at the time t3 during the initial period from the time t3 to the time t4 from the time of generation of the arc at the time t31, the flow volume Fo of the outer gas during the initial period is reduced to a reduced flow volume value.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a double-shielded TIG welding method and a double-shielded TIG welding apparatus. [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] In the double-shielded TIG welding method, arc interruption occurs at the start of welding, resulting in poor weld quality. This is particularly likely to occur when welding aluminum, aluminum alloys, magnesium, etc.

[0005] Therefore, an object of the present invention is to provide a double-shielded TIG welding method and apparatus that can suppress the occurrence of arc interruption, for example, at the start of welding, and thereby obtain good welding quality. [Means for solving the problem]

[0006] A double-shield TIG welding method provided by a first aspect of the present invention is a double-shield TIG welding method in which an arc is generated and welding is performed using a welding torch equipped with an inner nozzle that sprays inner gas and an outer nozzle that sprays outer gas, characterized in that when arc interruption is detected during an initial period from the time the arc is generated, the flow rate of the outer gas during the initial period is reduced to a reduced flow rate value.

[0007] As an example, the double-shielded TIG welding method of the present invention is characterized in that an AC welding voltage formed from an electrode negative polarity voltage during an electrode negative polarity period and an electrode positive polarity voltage during an electrode positive polarity period is output, and the value of the reduced flow rate value is set based on the electrode positive polarity voltage during the initial period.

[0008] As an example, the double-shielded TIG welding method of the present invention is characterized in that once the flow rate of the outer gas during the initial period reaches the reduced flow rate value, it is set to the reduced flow rate value in subsequent welding regardless of whether the arc has been interrupted.

[0009] As an example, the double-shielded TIG welding method of the present invention is characterized in that the initial period is set to a period until the molten pool is formed in a steady state.

[0010] As an example, the double-shielded TIG welding method of the present invention is characterized in that during the initial 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.

[0011] A double-shielded TIG welding apparatus provided according to a second aspect of the present invention is a double-shielded TIG welding apparatus that uses a welding torch equipped with an inner nozzle that sprays inner gas and an outer nozzle that sprays outer gas to generate an arc and weld, and is characterized in that when arc interruption is detected during an initial period from the time the arc is generated, the double-shielded TIG welding apparatus reduces the flow rate of the outer gas during the initial period to a reduced flow rate value. [Effects of the Invention]

[0012] According to the above configuration, for example, in a double-shielded TIG welding method and a double-shielded TIG welding apparatus, arc interruption at the start of welding can be suppressed, thereby achieving good welding quality. [Brief explanation 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. [Figure 2] FIG. 2 is a current-voltage waveform diagram in a double-shield 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

[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 figure shows a double-shielded TIG welding method in which an AC welding current Iw is applied, which 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. An AC welding voltage Vw, which is formed from an electrode negative polarity voltage and an electrode positive polarity voltage, is applied between the electrode 1 and the base material 2. The double-shielded TIG welding method in which an AC welding current Iw is applied is used to weld aluminum, aluminum alloys, magnesium, etc.

[0017] 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.

[0018] 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.

[0019] The current detection circuit ID detects the welding current Iw, converts it into an absolute value, and outputs a current detection signal Id.

[0020] The arc occurrence determination circuit AD receives the current detection signal Id as input, and outputs an arc occurrence determination signal Ad that goes to High level when the value of the current detection signal Id is equal to or greater than the current conduction determination value (approximately 5 A), and goes to Low level when the value of the current detection signal Id is less than the current conduction determination value, determining that no arc is occurring.

[0021] The initial period setting circuit TIR outputs a predetermined initial period setting signal Tir, which is set to the period from when the arc 3 is generated until the molten pool is formed in a steady state.

[0022] The period determination circuit TP receives the torch switch signal On, the arc occurrence determination signal Ad, and the initial period setting signal Tir 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 the initial period set by the initial period setting signal Tir 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.

[0023] The arc interruption determination circuit BD receives the period determination signal Tp and the arc occurrence determination signal Ad as inputs, and outputs an arc interruption determination signal Bd that goes to a high level when the arc occurrence determination signal Ad goes to a low level (no arc occurring) when the period determination signal Tp=3 (initial period). Once the arc interruption determination signal Bd goes to a high level, it will maintain that state in subsequent welding processes unless the welding conditions, such as the welding current, change.

[0024] 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。

[0025] 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。

[0026] 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.

[0027] 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.

[0028] The electrode positive polarity voltage detection circuit VPD receives a voltage detection signal Vd (described later) and a polarity switching signal Snp (described later), and outputs the instantaneous value or average value of the voltage detection signal Vd when the polarity switching signal Snp is at a low level (electrode positive polarity EP) as an electrode positive polarity voltage detection signal Vpd.

[0029] The initial-period outer gas flow rate setting circuit FOIR receives the steady-state outer gas flow rate setting signal Focr, the arc interruption detection signal Bd, and the electrode positive polarity voltage detection signal Vpd as inputs. When the arc interruption detection signal Bd is at a low level, the initial-period outer gas flow rate setting circuit FOIR outputs a steady-state outer gas flow rate setting signal Focr. When the arc interruption detection signal Bd is at a high level, the initial-period outer gas flow rate setting circuit FOIR outputs a reduced outer gas flow rate value obtained by multiplying the steady-state outer gas flow rate setting signal Focr by a reduction rate set according to the value of the electrode positive polarity voltage detection signal Vpd. Therefore, the initial-period outer gas flow rate setting signal Foir maintains the steady-state outer gas flow rate setting signal Focr until arc interruption is detected during the initial period. If arc interruption is detected during the initial period, the initial-period outer gas flow rate setting signal Foir decreases to the reduced outer gas flow rate value obtained by multiplying the steady-state outer gas flow rate setting signal Focr by the reduction rate. Once the reduced outer gas flow rate value is reached, the initial-period outer gas flow rate setting signal Foir maintains the reduced outer gas flow rate value even if arc interruption is not detected during subsequent welding. The decrease rate becomes smaller as the value of the electrode positive polarity voltage detection signal Vpd becomes larger than a predetermined reference voltage value, and falls within a range of approximately 0.7 to 0.9. That is, the decrease rate of the outer gas flow rate becomes smaller as the value of the electrode positive polarity voltage detection signal Vpd becomes larger than the reference voltage value.

[0030] The flow rate reduction inner gas flow rate setting circuit FIIR receives the outer gas flow rate setting signal For (described later) 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 is within ±20% of the outer gas flow rate. Fiir=For×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 When the outer gas flow rate setting signal For = 5.5 l / min and the steady-state inner gas flow rate setting signal Ficr = 3.5 l / min, when K = 0.8, the flow rate reduced inner gas flow rate setting signal Fiir = 0.75 l / min. When K = 1.0, the flow rate reduced inner gas flow rate setting signal Fiir = 0.94 l / min. When K = 1.2, the flow rate reduced inner gas flow rate setting signal Fiir = 1.12 l / min. (2) When the second electrode negative polarity current setting signal In2r=150A When the outer gas flow rate setting signal For = 7 l / min and the steady-state inner gas flow rate setting signal Ficr = 5 l / min, when K = 0.8, the flow rate reduced inner gas flow rate setting signal Fiir = 0.95 l / min. When K = 1.0, the flow rate reduced inner gas flow rate setting signal Fiir = 1.2 l / min. When K = 1.2, the flow rate reduced inner gas flow rate setting signal Fiir = 1.42 l / min.

[0031] The preflow inner gas flow rate setting circuit FIPR outputs a predetermined preflow inner gas flow rate setting signal Fipr, where the preflow inner gas flow rate setting signal Fipr is smaller than the steady inner gas flow rate setting signal Ficr, and the preflow inner gas flow rate setting signal Fipr may be equal to the flow rate reduced inner gas flow rate setting signal Fiir.

[0032] The inner gas flow rate setting circuit FIR receives the period discrimination signal Tp, the preflow inner gas flow rate setting signal Fipr, the flow rate reduction inner gas flow rate setting signal Fiir, and the steady-state inner gas flow rate setting signal Ficr as inputs, performs the following processing, and outputs the inner gas flow rate setting signal Fir. 1) When the period discrimination signal Tp=2 (pre-flow period), the value of the pre-flow 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), the inner gas flow rate setting signal Fir is output, which increases over time from the value of the flow rate reduction inner gas flow rate setting signal Fiir to the value of the steady inner gas flow rate setting signal Ficr. Here, the value may be switched to the value of the steady inner gas flow rate setting signal Ficr when the initial period ends. 4) When the period discrimination signal Tp=5 (crater treatment period), the value of the flow velocity 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 (after-flow 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.

[0033] 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.

[0034] The outer gas flow rate setting circuit FOR receives the period discrimination signal Tp, the steady-state outer gas flow rate setting signal Focr, and the initial-period outer gas flow rate setting signal Foir 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), the value of the initial-period outer gas flow rate setting signal Foir when the period discrimination signal Tp=3 (initial period), and the value of the steady-state outer gas flow rate setting signal Focr when the period discrimination signal Tp=4-6. Here, the preflow outer gas flow rate value is preferably set to a value larger than the value of the steady-state 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, the value of the initial-period outer gas flow rate setting signal Foir during the initial period, and the value of the steady-state outer gas flow rate setting signal Focr during the steady welding period, the crater treatment period, and the post-flow period.

[0035] 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.

[0036] 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.

[0037] The voltage detection circuit VD detects the welding voltage Vw, converts it into an absolute value, and outputs a voltage detection signal Vd.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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 applies a high-frequency high voltage between the electrode 1 and the base material 2 when the period discrimination signal Tp changes to 1 and the preflow period has elapsed. When an arc 3 is generated, the welding power source PS outputs a welding current Iw and a 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 when the period discrimination signal Tp=3 to 5 (initial period, steady-state welding period, and crater treatment period), 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.

[0042] 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 of the welding current Iw, (B) in the figure shows the change over time of the welding voltage Vw, and (C) in the figure shows the change over time of the polarity switching signal Snp. The operation of each waveform will be explained below with reference to the figure.

[0043] 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.

[0044] [Operation explanation for the 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 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] [Explanation of the operation 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.

[0049] 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.

[0050] 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.

[0051] At time t16, when the second electrode positive polarity period Tp2 ends, as shown in (A) of the same figure, the welding current Iw decreases at a slope and reaches the polarity switching current value at time t17. The slope is determined by the inductance value of the current path through which the welding current Iw flows. As shown in (B) of the same figure, the welding voltage Vw also decreases. After this, the operation returns to the operation at time t11.

[0052] During the electrode positive polarity period Tep from time t14 to t17, the oxide film is removed by the cleaning action. In order to obtain good welding quality, it is necessary to properly form the cleaning width. The cleaning width correlates with the average value of the welding voltage Vw (electrode positive polarity voltage) during the electrode positive polarity period Tep. Therefore, the average value of the electrode positive polarity voltage at which the cleaning width is appropriate is preset as the reference voltage value, and by detecting the average value of the electrode positive polarity voltage during welding and comparing it with the reference voltage value, it is possible to determine whether the cleaning width is appropriate. The cleaning action is mainly performed during the second electrode positive polarity period Tp2 from time t15 to t16. For this purpose, instead of the average value of the electrode positive polarity voltage, the instantaneous value or average value of the welding voltage Vw (second electrode positive polarity voltage) during the second electrode positive polarity period Tp2 may be used.

[0053] 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.

[0054] 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

[0055] Figure 3 is a timing chart of each signal in the welding apparatus of Figure 1 showing the double shielded tig welding method according to an embodiment of the present invention. (A) of the figure shows the time change of the torch switch signal On, (B) of the figure shows the time change of the outer gas flow rate Fo (l / min), (C) of the figure shows the time change of the inner gas flow rate Fi (l / min), (D) of the figure shows the time change of the average welding current value Iav which is the average value of the absolute value of the welding current Iw shown in Figure 2, (E) of the figure shows the time change of the arc generation discrimination signal Ad, and (F) of the figure shows the time change of the arc interruption discrimination signal Bd. Hereinafter, the operation of each signal will be described with reference to the figure.

[0056] [Operation during the preflow 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.

[0057] 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.

[0058] 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.

[0059] [Initial period behavior] When the preflow period ends at time t3, 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 an arc 3 in FIG. 1, and as shown in FIG. 1(D), the flow of the welding current average value Iav begins. The waveforms of the welding current Iw and welding voltage Vw become those shown in FIG. 2 above. At time t3, when the flow of the welding current Iw determines that an arc has occurred, the arc occurrence determination signal Ad changes to a high level as shown in FIG. 1(E). Welding begins at time t3.

[0060] When the arc occurrence determination signal Ad changes to a high level, the period determination signal Tp in FIG. 1 changes to 3, and the system transitions to a predetermined initial period from time t3 to t4. As shown in FIG. 1(B), the outer gas flow rate Fo during the initial period is determined by the initial period outer gas flow rate setting signal Foir in FIG. 1. Because no arc interruption occurs during the period from time t3 to t31, the arc interruption determination signal Bd is at a low level, as shown in FIG. 1(F). Therefore, the value of the initial period outer gas flow rate setting signal Foir is the value of the steady outer gas flow rate setting signal Focr in FIG. 1. The value of the steady outer gas flow rate setting signal Focr is a value calculated by substituting the value of the second electrode negative polarity current setting signal In2r in FIG. 1 into the above-mentioned equation (2).

[0061] At time t31, when the cleaning width becomes too wide, the arc length becomes too long, and arc interruption occurs, as shown in FIG. 1(D), the welding current average value Iav becomes 0 A. In response to this, as shown in FIG. 1(E), the arc occurrence determination signal Ad becomes low level, and as shown in FIG. 1(F), the arc interruption determination signal Bd changes to high level. As a result, at time t31, as shown in FIG. 1(B), the outer gas flow rate Fo decreases to the reduced outer gas flow rate value. The reduced outer gas flow rate value is the value obtained by multiplying the value of the steady outer gas flow rate setting signal Focr by the reduction rate set in accordance with the value of the electrode positive polarity voltage detection signal Vpd in FIG. 1.

[0062] At time t32, approximately 0.1 seconds after time t31, a high-frequency high voltage is applied between the electrode 1 and the base material 2, re-strikes the arc 3, and the welding current average value Iav begins to flow, as shown in (D) of the figure. In response to this, as shown in (E) of the figure, the arc occurrence determination signal Ad changes to a high level. As shown in (F) of the figure, the arc interruption determination signal Bd remains at a high level. As shown in (B) of the figure, the outer gas flow rate Fo remains at the reduced outer gas flow rate value during the remaining initial period from time t32 to t4. Because the outer gas flow rate Fo is reduced, the cleaning width narrows and becomes the appropriate value, so arc interruption does not occur again. Once the reduced outer gas flow rate value is reached, the outer gas flow rate Fo remains at the reduced outer gas flow rate value during subsequent welding, even if arc interruption is not determined.

[0063] As shown in FIG. 1C, the inner gas flow rate Fi during the initial period is determined by the flow rate reduction inner gas flow rate setting signal Fiir shown in FIG. 1. This flow rate reduction inner gas flow rate setting signal Fiir is calculated by substituting the value of the outer gas flow rate setting signal For shown in FIG. 1 into the above-mentioned equation (3). Therefore, since For = Focr during the period from time t3 to t31, the value is calculated by substituting the value of the steady outer gas flow rate setting signal Focr into equation (3). Since For = the reduced outer gas flow rate during the period from time t31 to t4, it is reduced to the value calculated by substituting this value into 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 approximately 1 to 5 seconds.

[0064] [Operation during steady welding period] When the initial period ends at time t4, the period determination signal Tp in FIG. 1 changes to Tp=4, and the steady-state welding period begins. As shown in FIG. 1B, the outer gas flow rate Fo becomes the value of the steady-state outer gas flow rate setting signal Focr. 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.

[0065] 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.

[0066] [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.

[0067] [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.

[0068] [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.

[0069] The effects of this embodiment are described below. According to this embodiment, if arc interruption is detected during the initial period from the generation of the arc, the flow rate of the outer gas during the initial period is reduced to a reduced flow rate value. Immediately after the generation of the arc at the start of welding, the weld pool is in the process of formation, so the cleaning width becomes too wide, the arc length becomes long, and arc interruption is likely to occur. Arc interruption deteriorates welding quality. In this embodiment, if arc interruption is detected during the initial period from the generation of the arc, the flow rate of the outer gas during the initial period is reduced to a reduced flow rate value to narrow the excessively wide cleaning width. Reducing the flow rate of the outer gas narrows the cleaning width, thereby suppressing arc interruption. As a result, this embodiment can suppress arc interruption at the start of welding and achieve good welding quality.

[0070] More preferably, according to this embodiment, an AC welding voltage formed from an electrode negative polarity voltage during the electrode negative polarity period and an electrode positive polarity voltage during the electrode positive polarity period is output, and the reduced flow rate value is set based on the electrode positive polarity voltage during the initial period. The cleaning action is performed by the action of the electrode positive polarity period. The cleaning width correlates with the instantaneous or average value of the electrode positive polarity voltage. Therefore, if the reduced flow rate value of the outer gas during the initial period is set based on the electrode positive polarity voltage, the cleaning width can be controlled to an appropriate value. As a result, this embodiment can improve the welding quality of the welding start portion.

[0071] More preferably, according to this embodiment, once the flow rate of the outer gas during the initial period reaches the reduced flow rate value, it is set to the reduced flow rate value in subsequent welding operations regardless of whether arc interruption has occurred. Once arc interruption occurs during the initial period, there is a high possibility that arc interruption will also occur in subsequent welding operations. Therefore, in this embodiment, once arc interruption has been detected and the flow rate of the outer gas has been set to the reduced flow rate value, the flow rate of the outer gas is set to the reduced flow rate value in subsequent welding operations regardless of whether arc interruption has occurred. In this way, arc interruption can be suppressed in subsequent welding operations after arc interruption has been detected, thereby further improving the welding quality at the start of welding.

[0072] More preferably, according to this embodiment, the initial period is set to the period until the weld pool is formed in a steady state. As described above, arc interruption occurs immediately after arc generation because the cleaning width becomes too wide as the weld pool is in the process of forming. Therefore, in this embodiment, by setting the initial period, in which arc interruption is likely to occur, to the period until the weld pool is formed in a steady state, arc interruption during the initial period can be suppressed. Furthermore, during the steady welding period after the initial period, the flow rate of the outer gas returns from the reduced flow rate value to the original flow rate value, so that the cleaning width during the steady welding period can be set to an appropriate value, thereby achieving good welding quality.

[0073] More preferably, according to this embodiment, during the initial period, 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 arc generation, 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.

[0074] More preferably, according to this embodiment, the after-flow is set so that the flow rate of the inner gas is such that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas. During the after-flow period, the welding state is in a transitional state because the arc has been extinguished. In the double-shield TIG welding method, when the welding state is in a transitional state, the gas flow becomes turbulent, causing a problem of oxidation of the electrode tip. In this embodiment, the generation of turbulence is suppressed by setting the flow rate of the inner gas during the after-flow period so that the flow rate of the inner gas is within ±20% of the flow rate of the outer gas. As a result, this embodiment can suppress the problem of oxidation of the electrode tip, which leads to poor welding quality in subsequent welding.

[0075] 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 flow rate of the inner gas is within ±20% of the flow rate of the outer gas. 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 the double-shield TIG welding method, when the welding state enters a transient state, the gas flow becomes turbulent, which can easily cause blowholes. In this embodiment, 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 during the crater treatment period, thereby suppressing the occurrence of turbulence. As a result, this embodiment can prevent blowholes from occurring in the crater portion, which can lead to poor welding quality.

[0076] Furthermore, according to this embodiment, in a double-shield TIG welding apparatus that uses a welding torch equipped with an inner nozzle that sprays inner gas and an outer nozzle that sprays outer gas to generate an arc and perform welding, when the double-shield TIG welding apparatus detects an arc interruption during the initial period from the point of arc generation, it reduces the flow rate of the outer gas during the initial period to a reduced flow rate value. This double-shield TIG welding apparatus achieves the above-mentioned effects. [Explanation of symbols]

[0077] 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, BD: Arc interruption determination circuit, Bd: Arc interruption 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 reduction indicator inner gas flow rate setting circuit, Fiir: flow rate reduced inner gas flow rate setting 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, FOIR: initial period outer gas flow rate setting circuit, Foir: initial period 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 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, Ip 2r: 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 source, Snp: Polarity switching signal, Ten: Electrode negative polarity period, Tep: Electrode positive polarity period, TIR: Initial period setting circuit, Tir: Initial period setting signal, 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, VPD: electrode positive polarity voltage detection circuit, Vpd: electrode positive polarity voltage detection signal, WT: welding torch,

Claims

1. In a double-shielded TIG welding method, an arc is generated and welding is performed using a welding torch equipped with an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas, a double-shielded TIG welding method, characterized in that when an arc interruption is detected during an initial period from the time the arc is generated, the flow rate of the outer gas during the initial period is reduced to a reduced flow rate value.

2. 2. The double-shielded TIG welding method according to claim 1, wherein an AC welding voltage formed from an electrode negative polarity voltage during an electrode negative polarity period and an electrode positive polarity voltage during an electrode positive polarity period is output, and the value of the reduced flow rate value is set based on the electrode positive polarity voltage during the initial period.

3. 3. The double-shielded TIG welding method according to claim 1, wherein once the flow rate of the outer gas during the initial period reaches the reduced flow rate value, the flow rate is set to the reduced flow rate value in subsequent welding regardless of whether the arc has been interrupted.

4. 3. The double-shielded TIG welding method according to claim 1, wherein the initial period is set to a period until the molten pool is formed in a steady state.

5. 3. The double shield TIG welding method according to claim 1, wherein during the initial 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.

6. In a double-shielded TIG welding device, a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas is used to generate an arc for welding, The double shielded TIG welding device is characterized in that, when an arc interruption is detected during an initial period from the time the arc is generated, the flow rate of the outer gas during the initial period is reduced to a reduced flow rate value.

Images