Double-shielded TIG welding method and double-shielded TIG welding apparatus

Abstract

To suppress the occurrence of blowholes during welding in a double-shielded TIG welding method. [Solution] In a double-shielded TIG welding method using a welding torch WT equipped with an inner nozzle 4 for ejecting inner gas 7 and an outer nozzle 4 for ejecting outer gas 9, welding is performed by applying a welding current Iw to generate an arc 3, wherein the cross-sectional shape of the inner nozzle 4 is made elliptical, and welding is performed with the major axis of the ellipse in the welding direction.

Description

Technical Field

[0001] The present invention relates to a double-shielded tig welding method and a double-shielded tig welding apparatus.

Background Art

[0002] A double-shielded tig welding method is commonly used in which a welding torch having an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used, and a welding current is passed to generate an arc for welding (see, for example, Patent Document 1). As the inner gas and the outer gas, an inert gas such as argon or helium is used.

[0003] In the double-shielded tig welding method, the stiffness of the arc can be increased by ejecting an inner gas at a flow rate about 2.5 to 4 times faster than the flow rate of the outer gas. For this reason, in the double-shielded tig welding method, the penetration can be increased and the welding speed can also be increased, so that the welding operation can be made more efficient.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the double-shielded tig welding method, there is a problem that blowholes may occur during welding and the welding quality may deteriorate. In particular, this problem becomes prominent when welding is performed by inserting a filler wire at the welding start portion.

[0006] Therefore, the present invention aims to provide a double-shielded TIG welding method and a double-shielded TIG welding apparatus that can suppress the occurrence of blowholes during welding and obtain good welding quality. [Means for solving the problem]

[0007] A double-shielded TIG welding method provided by a first aspect of the present invention is a double-shielded TIG welding method that uses a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, and generates an arc by applying a welding current to perform welding, characterized in that the cross-sectional shape of the inner nozzle is elliptical, and welding is performed with the major axis of the elliptical shape as the welding direction.

[0008] As an example, the double-shielded TIG welding method of the present invention is characterized in that the ratio of the major axis to the minor axis of the elliptical shape is 1.2 or more and 2.0 or less.

[0009] As an example, the double-shielded TIG welding method of the present invention is characterized in that the welding torch is set to an advanced angle during the initial period after arc generation.

[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 increases as the advance angle increases.

[0011] As an example, the double-shielded TIG welding method of the present invention is characterized in that, during the initial period, the flow velocity of the inner gas is kept within ±20% of the flow velocity of the outer gas.

[0012] A double-shielded TIG welding apparatus provided by a second aspect of the present invention is a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, which generates an arc by applying a welding current to perform welding, characterized in that the cross-sectional shape of the inner nozzle is elliptical, and welding is performed with the major axis of the elliptical shape as the welding direction. [Effects of the Invention]

[0013] According to the above configuration, for example, with regard to a double-shielded TIG welding method and a double-shielded TIG welding apparatus, it is possible to suppress the occurrence of blowholes during welding and obtain good welding quality. [Brief explanation of the drawing]

[0014] [Figure 1] This is a block diagram of a double-shielded TIG welding apparatus for implementing a double-shielded TIG welding method according to an embodiment of the present invention. [Figure 2] This figure shows the cross-sectional shape of the inner nozzle according to an embodiment of the present invention. [Figure 3] This is a current and voltage waveform diagram for a double-shielded TIG welding method according to an embodiment of the present invention. [Figure 4] Figure 1 shows a timing chart of each signal in a double-shielded TIG welding apparatus illustrating a double-shielded TIG welding method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below with reference to the drawings.

[0016] Figure 1 is a block diagram of a double-shielded TIG welding apparatus for implementing a double-shielded TIG welding method according to an embodiment of the present invention. Each block will be described below with reference to the same figure.

[0017] This is a case of a double shielded tig welding method in which an alternating current welding current Iw formed from an electrode minus polarity current during an electrode minus polarity period and an electrode plus polarity current during an electrode plus polarity period is energized. The double shielded tig welding method performed by energizing the alternating current welding current Iw is used for welding aluminum, aluminum alloys, magnesium, etc.

[0018] The welding torch WT mainly includes an electrode 1, an inner nozzle 4 surrounding it, and an outer nozzle 5 surrounding it. A tungsten electrode or the like is used for the electrode 1. The inner diameter of the outer nozzle 5 is, for example, 13 mm.

[0019] As shown in FIG. 2, the cross-sectional shape of the inner nozzle 4 is an elliptical shape. In this specification, the "cross-sectional shape of the inner nozzle 4" means the shape of the cross-section when the inner surface of the inner nozzle 4 is cut by a plane perpendicular to the direction in which the inner nozzle 4 extends. Welding is performed while holding the welding torch WT so that the major axis direction of the elliptical shape is in the welding direction. The ratio of the major axis to the minor axis of the elliptical shape is 1.2 or more and 2.0 or less, and more preferably 1.4 or more and 1.8 or less. For example, the elliptical shape has a major axis length of 5 mm, 6 mm, or 8 mm and a minor axis length of 4 mm.

[0020] The torch switch circuit ON is a torch switch attached to the welding torch WT, and outputs a torch switch signal On that becomes High level when the welding operator turns it on and Low level when it is turned off.

[0021] The current detection circuit ID detects the welding current Iw, converts it to an absolute value, and outputs a current detection signal Id. The arc generation discrimination circuit AD inputs the above current detection signal Id, and when the value of the current detection signal Id is equal to or greater than a conduction discrimination value (about 5 A), it discriminates that an arc has occurred and outputs an arc generation discrimination signal Ad that becomes High level.

[0022] The period discrimination circuit TP takes the above torch switch signal On and the above arc generation discrimination signal Ad as inputs, performs the following processes, and outputs a period discrimination signal Tp. When welding has ended, the period discrimination signal Tp = 0. 1) When the torch switch signal On changes to the High level, it outputs a period discrimination signal Tp = 1 (preflow period start). 2) When a predetermined delay time Td has elapsed since the time when Tp changed to 1, it outputs a period discrimination signal Tp = 2 (inner gas ejection start). 3) When a predetermined preflow period has elapsed since the time when Tp changed to 1 and the arc generation discrimination signal Ad changes to the High level, it outputs a period discrimination signal Tp = 3 (initial period start). 4) When a predetermined initial period has elapsed since the time when Tp changed to 3, it outputs Tp = 4 (steady welding period start). 5) Thereafter, when the torch switch signal On changes to the Low level and then changes to the High level again, it outputs Tp = 5 (crater treatment period start). 6) Thereafter, when the torch switch signal On changes to the Low level again, it outputs a period discrimination signal Tp = 6 (afterflow period start). 7) When a predetermined afterflow period has elapsed, it outputs a period discrimination signal Tp = 0 (welding end state).

[0023] The first electrode minus polarity current setting circuit IN1R outputs a first electrode minus polarity current setting signal In1r with a predetermined positive value. The second electrode minus polarity current setting circuit IN2R outputs a second electrode minus polarity current setting signal In2r with a predetermined positive value. Here, In1r < In2r.

[0024] The first electrode plus polarity current setting circuit IP1R outputs a first electrode plus polarity current setting signal Ip1r with a predetermined positive value. The second electrode plus polarity current setting circuit IP2R outputs a second electrode plus polarity current setting signal Ip2r with a predetermined positive value. Here, Ip1r < Ip2r.

[0025] The inner nozzle long axis setting circuit DR takes the length of the elliptical long axis of the inner nozzle used by the welder as input and outputs it as an inner nozzle long axis setting signal Dr. For example, the values ​​of the inner nozzle long axis setting signal Dr are 5 mm, 6 mm, or 8 mm. The length of the short axis is 4 mm.

[0026] The inner gas velocity setting circuit SIR takes the second electrode negative polarity current setting signal In2r as input and outputs the value calculated by inputting the second electrode negative polarity current setting signal In2r[A] into the following predetermined inner gas velocity setting function as the inner gas velocity setting signal Sir[cm / s]. An example of the inner gas velocity setting function is shown below. Sir=(In2r-75)×2+300 (1) formula However, this is within the range of 75 ≤ In2r ≤ 150, where In2r < 75 is the same value as In2r = 75, and In2r > 150 is the same value as In2r = 150. For example, when In2r = 75A, Sir = 300 cm / s, and when In2r = 150A, Sir = 450 cm / s. As a result, the value of the inner gas flow velocity setting signal Sir increases as the value of the second electrode negative polarity current setting signal In2r increases. Instead of the second electrode negative polarity current setting signal In2r, the average value of the absolute value of the welding current Iw or the average value during the electrode negative polarity period may be used.

[0027] The steady-state inner gas flow rate setting circuit FICR takes the above-mentioned inner nozzle long axis setting signal Dr [mm] and the above-mentioned inner gas flow velocity setting signal Sir [cm / s] as inputs, inputs both values ​​into the following predetermined steady-state inner gas flow rate setting function, and outputs the calculated value as the steady-state inner gas flow rate setting signal Ficr [l / min]. The steady-state inner gas flow rate setting function is shown below. The steady-state inner gas flow rate setting function is a function that calculates the value of the steady-state inner gas flow rate setting signal Ficr such that the inner gas flow velocity is the value of the inner gas flow velocity setting signal Sir when the length of the long axis of the elliptical shape of the inner nozzle 4 is the value of the inner nozzle long axis setting signal Dr, and the length of the short axis is 4 mm. Ficr=(Sir×(Dr / 2)×2×3.14×0.01×60) / 1000 (2) formula 1) When Dr=5mm, Ficr=2.8l / min when Sir=300cm / s, and Ficr=4.2l / min when Sir=450cm / s. 2) When Dr=6mm, Ficr=3.4l / min when Sir=300cm / s, and Ficr=5.1l / min when Sir=450cm / s. 3) When Dr = 8 mm, Ficr = 4.5 l / min when Sir = 300 cm / s, and Ficr = 6.8 l / min when Sir = 450 cm / s.

[0028] The steady-state outer gas flow rate setting circuit FOCR outputs a predetermined steady-state outer gas flow rate setting signal Focr. For example, the steady-state outer gas flow rate setting signal Focr is set to 8 l / min. At this time, the outer gas flow velocity is approximately 120 cm / s.

[0029] The flow velocity reduction inner gas flow rate setting circuit FIIR takes the inner nozzle long axis setting signal Dr[mm] as input and outputs the value calculated by inputting it into the function shown below as the flow velocity reduction inner gas flow rate setting signal Fiir[l / min]. The function calculates the value of the flow velocity reduction inner gas flow rate setting signal Fiir when the length of the long axis of the elliptical shape of the inner nozzle 4 is the value of the inner nozzle long axis setting signal Dr, and the length of the short axis is 4 mm, so that the flow velocity of the inner gas is equal to the flow velocity of the outer gas. Here, if the flow rate of the outer gas is 8 l / min, the flow velocity will be approximately 120 cm / s as described above. Fiir=(120×(Dr / 2)×2×3.14×0.01×60) / 1000 (3) formula 1) When Dr=5mm, Fiir=1.1l / min. 2) When Dr = 6 mm, Fiir = 1.4 l / min. 3) When Dr = 8 mm, Fiir = 1.8 l / min.

[0030] The advancing angle setting circuit AFR takes the above-mentioned period discrimination signal Tp as an input. When the period discrimination signal Tp = 1 to 3 (pre-flow period, initial period), it becomes a predetermined initial advancing angle setting value, and when the period discrimination signal Tp = 4 to 6 (steady welding period, crater treatment period, after-flow period), it outputs an advancing angle setting signal Afr that becomes a predetermined steady advancing angle setting value. The advancing angle setting signal Afr is set within the range of 0 to 40 degrees. The initial advancing angle setting value is set to a value larger than the steady advancing angle setting value. For example, the initial advancing angle setting value is 30 degrees, and the steady advancing angle setting value is 0 degrees.

[0031] The initial period inner gas flow rate setting circuit FISR takes the above-mentioned flow rate reduction inner gas flow rate setting signal Fiir and the above-mentioned advancing angle setting signal Afr as inputs, inputs them into the function shown below, and outputs the calculated value as the initial period inner gas flow rate setting signal Fisr. Fisr = Fiir × (0.8 + Afr × 0.01) (Equation (4)) Here, when Afr = 0, Fisr = Fiir × 0.8, and when Afr = 40, Fisr = Fiir × 1.2. The value of the flow rate reduction inner gas flow rate setting signal Fiir is a value at which the flow rate of the inner gas becomes equal to the flow rate of the outer gas. The value of the advancing angle setting signal Afr is within the range of 0 to 40 degrees as described above. As a result, the value of the initial period inner gas flow rate setting signal Fisr is a value at which the flow rate of the inner gas is within ±20% of the flow rate of the outer gas, and the larger the value of the advancing angle setting signal Afr, the larger the value.

[0032] The pre-flow inner gas flow rate setting circuit FIPR outputs a predetermined pre-flow inner gas flow rate setting signal Fipr. Here, Fipr < Ficr, and Fipr may be Fisr or Fiir.

[0033] The inner gas flow rate setting circuit FIR takes the above-mentioned period discrimination signal Tp, pre-flow inner gas flow rate setting signal Fipr, initial period inner gas flow rate setting signal Fisr, velocity reduction inner gas flow rate setting signal Fiir, and 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 initial period inner gas flow rate setting signal Fisr is output as the inner gas flow rate setting signal Fir. 3) When the period discrimination signal Tp=4 (steady-state welding period), the inner gas flow rate setting signal Fir is output, which increases over time to the value of the steady-state inner gas flow rate setting signal Ficr and maintains that value. Alternatively, the value may be switched to the steady-state inner gas flow rate setting signal Ficr when the initial period ends. 4) When the period discrimination signal Tp=5 (crater processing 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 velocity reduction inner gas flow rate setting signal Fiir is output as the inner gas flow rate setting signal Fir.

[0034] The inner gas flow regulator CI is a known mass flow controller that takes the above-mentioned period discrimination signal Tp and the above-mentioned 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 during the period discrimination signal Tp = 2 to 6, and then ejects it. Therefore, the ejection of the inner gas 7 begins when the torch switch is turned ON and the pre-flow period begins, after a delay time Td has elapsed, and the ejection stops when the after-flow period ends.

[0035] The outer gas flow rate setting circuit FOR takes the above-mentioned period discrimination signal Tp and the above-mentioned steady-state outer gas flow rate setting signal Focr as inputs and outputs an outer gas flow rate setting signal For which the pre-flow outer gas flow rate value is predetermined when the period discrimination signal Tp = 1 to 2 (pre-flow period), and the value of the steady-state outer gas flow rate setting signal Focr is obtained when the period discrimination signal Tp = 3 to 6. Here, it is desirable that the pre-flow 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. As a result, the outer gas flow rate Fo is the pre-flow outer gas flow rate value during the pre-flow period, and the value of the steady-state outer gas flow rate setting signal Focr is obtained during the initial period, steady-state welding period, crater processing period, and after-flow period.

[0036] The outer gas flow regulator CO is a known mass flow controller that takes the above-mentioned period determination signal Tp and the above-mentioned 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 determination signal Tp = 1 to 6, and then ejects it. Therefore, the outer gas 9 is ejected during the pre-flow period, initial period, steady-state welding period, crater processing period, and after-flow period.

[0037] Inner gas 7 flows through the passage inside inner nozzle 4. Outer gas 9 flows through the passage outside inner nozzle 4 and inside outer nozzle 5. Inert gases such as argon and helium are used for inner gas 7 and outer gas 9.

[0038] The voltage detection circuit VD detects the welding voltage Vw, converts it to an absolute value, and outputs a voltage detection signal Vd.

[0039] The first electrode negative polarity period setting circuit TN1R takes the above-mentioned voltage detection signal Vd as input, measures the period until the fluctuation of the voltage detection signal Vd during this period 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.

[0040] The first electrode positive polarity period setting circuit TP1R takes the above-mentioned voltage detection signal Vd as input, measures the period until the fluctuation of the voltage detection signal Vd during this period converges, and outputs a predetermined first electrode positive polarity period setting signal Tp1r.

[0041] The second electrode positive polarity period setting circuit TP2R takes the above period discrimination signal Tp as input and outputs a second electrode positive polarity period setting signal Tp2r, which sets the initial second electrode positive polarity period setting value to a predetermined value when the period discrimination signal Tp = 1 to 3, and the steady-state second electrode positive polarity period setting value to a predetermined value when the period discrimination signal Tp = 4 to 6. Here, the initial second electrode positive polarity period setting value is a larger value than the steady-state second electrode positive polarity period setting value. Also, the electrode negative polarity period ratio (%) is the time ratio of the electrode negative polarity period to the period of electrode negative polarity in one cycle. For this reason, the electrode negative polarity period ratio is smaller during the initial period than during the steady-state welding period.

[0042] The current setting circuit IR takes the above-mentioned first electrode negative polarity period setting signal Tn1r, second electrode negative polarity period setting signal Tn2r, first electrode positive polarity period setting signal Tp1r, second electrode positive polarity period setting signal Tp2r, first electrode negative polarity current setting signal In1r, second electrode negative polarity current setting signal In2r, first electrode positive polarity current setting signal Ip1r, second electrode positive polarity current setting signal Ip2r, and current detection signal Id as input, 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, which is 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, which is determined by the second electrode negative polarity period setting signal Tn2r, the second electrode negative polarity current setting signal In2r is output as the current setting signal Ir. During this period, a high-level polarity switching signal Snp is output. 3) Next, a current setting signal Ir with a predetermined polarity switching current value is output and maintained until the value of the current detection signal Id drops to the polarity switching current value. During this period, a high-level polarity switching signal Snp is output. 4) Subsequently, during the first electrode positive polarity period Tp1, which is 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, which is determined by the second electrode positive polarity period setting signal Tp2r, the second electrode positive polarity current setting signal Ip2r is output as the current setting signal Ir. During this period, a low-level polarity switching signal Snp is output. 6) Next, a current setting signal Ir for the polarity switching current value is output and maintained until the value of the current detection signal Id drops to the polarity switching current value. During this period, a low-level polarity switching signal Snp is output. 7) Repeat steps 1) to 6) above.

[0043] The welding power supply PS takes the above-mentioned period determination signal Tp, current setting signal Ir, current detection signal Id, and polarity switching signal Snp as inputs. When the period determination signal Tp is 3 to 5 (initial period, steady welding period, and crater processing period), it applies a high-frequency high voltage between electrode 1 and base material 2. When arc 3 is generated, it outputs a welding current Iw and welding voltage Vw with the current value set by the current setting signal Ir and the power supply polarity set by the polarity switching signal Snp. When the period determination signal Tp is 6 (after-flow period), it stops outputting. The welding power supply PS, although not shown in the diagram, is connected to a commercial AC power supply such as 3-phase 200V and includes a primary rectifier circuit that rectifies the commercial AC power supply to DC, a capacitor that smooths the rectified DC, a primary inverter circuit that converts the smoothed DC to high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage 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 according to 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.

[0044] The welder sets the advance angle of the welding torch WT to the initial advance angle setting value during the initial period, and to a steady-state advance angle setting value smaller than the initial advance angle setting value during the steady-state welding period and crater processing period, and performs welding while inserting the filler wire 10 into the arc 3. For example, the advance angle is set to 30 degrees during the initial period and to 0 degrees during the steady-state welding period. Although not shown in the illustration, in welding using a welding robot, the welding torch WT is held by the robot. In this case, the robot sets the welding torch WT to an advance angle and inserts the filler wire 10 from the filler wire feeder into the arc 3 to perform welding.

[0045] Figure 3 is a current-voltage waveform diagram in a double-shielded TIG welding method according to an embodiment of the present invention. Figure (A) shows the time variation of the welding current Iw, Figure (B) shows the time variation of the welding voltage Vw, and Figure (C) shows the time variation of the polarity switching signal Snp. The operation of each waveform will be explained below with reference to the figure.

[0046] In Figure (A), the welding current Iw, and in Figure (B), the welding voltage Vw, above 0 represent the waveform for a negative electrode polarity (EN), and below 0 represent the waveform for a positive electrode polarity (EP). In the following, the magnitude of the welding current Iw and welding voltage Vw is described in terms of their absolute values, regardless of whether they represent a negative electrode polarity (EN) or a positive electrode polarity (EP). Inner gas and outer gas, not shown in the figures, are ejected to the arc generation area.

[0047] (1) Explanation of operation of the negative electrode period Ten Just before time t11, as shown in Figure (A), the welding current Iw decreases from a negative value, the second electrode positive polarity current value Ip2, to a predetermined negative polarity switching current value. At time t11, as shown in Figure (A), when the welding current Iw becomes equal to the polarity switching current value, as shown in Figure (C), the polarity switching signal Snp changes from a low level to a high level, transitioning to the electrode negative polarity period Ten. In response to this, as shown in Figure (A), the welding current Iw changes sharply from a negative value, the polarity switching current value, to a predetermined positive value, the first electrode negative polarity current value In1. As shown in Figure (B), the welding voltage Vw takes on a waveform similar to the current waveform and changes from a negative voltage value to a positive voltage value.

[0048] During the first electrode negative polarity period Tn1 from time t11 to t12, as shown in Figure (A), the welding current Iw becomes the first electrode negative polarity current value In1. As shown in Figure (B), the welding voltage Vw fluctuates during this period, and the fluctuation converges just before time t12. This fluctuation in welding voltage Vw is because the arc generation state is transient during polarity switching. In the double-shielded TIG welding method, which uses both inner and outer gases, turbulence is more likely to occur compared to the normal TIG welding method which uses only shielding gas, due to the difference in flow velocity between the two gases. Turbulence is more likely to occur when the arc generation state is transient because the fluctuations are large. Therefore, by setting the first electrode negative polarity current value In1 to a small value, fluctuations in the arc generation state are suppressed, and the generation of turbulence is prevented. As a result, it is possible to suppress the occurrence of blowholes, which can result from incomplete arc shielding due to the generation of turbulence. Therefore, the first electrode negative polarity period Tn1 is set to the period until the fluctuation of the welding voltage Vw converges during this period. For example, the absolute value of the polarity switching current is set to 50A. The reason for reducing the welding current Iw to the polarity switching current value and switching the polarity is to prevent the secondary inverter circuit in the welding power supply PS in Figure 1 from failing due to the surge voltage during switching.

[0049] During the predetermined second electrode negative polarity period Tn2 from time t12 to t13, as shown in Figure (A), the welding current Iw increases to the second electrode negative polarity current value In2. As shown in Figure (B), the welding voltage Vw becomes greater than during the first electrode negative polarity period Tn1. Since the melting of the base material is accelerated during this period, it becomes the main welding period.

[0050] At time t13, when the second electrode negative polarity period Tn2 ends, the welding current Iw decreases in a slope, as shown in Figure (A), and becomes the polarity switching current value at time t14. The slope is determined by the inductance value of the current path of the welding current Iw. As shown in Figure (B), the welding voltage Vw also decreases.

[0051] (2) Operation of the positive electrode period Tep At time t14, as shown in Figure (A), when the welding current Iw becomes equal to the polarity switching current value, as shown in Figure (C), the polarity switching signal Snp changes to a low level, and the electrode transitions to the positive polarity period Tep. In response to this, as shown in Figure (A), the welding current Iw changes abruptly from the positive polarity switching current value to a predetermined negative first electrode positive polarity current value Ip1. As shown in Figure (B), the welding voltage Vw takes on a waveform similar to the current waveform and changes from a positive voltage value to a negative voltage value.

[0052] During the first electrode positive polarity period Tp1 from time t14 to t15, as shown in Figure (A), the welding current Iw becomes the first electrode positive polarity current value Ip1. As shown in Figure (B), the welding voltage Vw fluctuates during this period, and the fluctuation converges just before time t15. This fluctuation in welding voltage Vw is because the formation state of the cathode point, which is formed to obtain the oxide film, is in a transient state. In the double-shielded TIG welding method, which uses both inner and outer gases, turbulence is more likely to occur compared to the normal TIG welding method which uses only shielding gas, due to the difference in flow velocity between the two gases. Turbulence is more likely to occur when the cathode point formation state is in a transient state because the fluctuations are large. This turbulence is more intense when switching to electrode positive polarity EP than when switching to electrode negative polarity EN. Therefore, by setting the first electrode positive polarity current value Ip1 to a small value, fluctuations in the arc generation state are suppressed, and the generation of turbulence is prevented. As a result, the generation of turbulence can suppress the occurrence of blowholes, which can result from incomplete arc shielding. Therefore, the first electrode positive polarity period Tp1 is set to the period during which the fluctuations in the welding voltage Vw converge.

[0053] During the predetermined second electrode positive polarity period Tp2 from time t15 to t16, as shown in Figure (A), the welding current Iw increases to the second electrode positive polarity current value Ip2. As shown in Figure (B), the welding voltage Vw becomes greater than during the first electrode positive polarity period Tp1. The oxide film is removed mainly by the cleaning action during this period.

[0054] At time t16, when the second electrode positive polarity period Tp2 ends, as shown in FIG. (A), the welding current Iw decreases with a slope and becomes the polarity switching current value at time t17. The slope is determined by the inductance value of the current path of the welding current Iw. As shown in FIG. (B), the welding voltage Vw also decreases. Thereafter, the operation returns to that at time t11.

[0055] As described above, since the electrode negative polarity period ratio (%) is the time ratio of the electrode negative polarity period in one cycle, it is calculated by the operation of (Ten / (Ten+Tep))×100. Since the value of the second electrode positive polarity period Tp2 is larger during the initial period than during the steady welding period, the electrode negative polarity period ratio during the initial period is smaller than that during the steady welding period. Since the cleaning effect becomes larger as the electrode negative polarity period ratio becomes smaller, the cleaning effect during the initial period is larger than that during the steady welding period.

[0056] The figure shows the case of the balanced waveform of In2 = Ip2, but there may also be a case of an unbalanced waveform of In2 < Ip2. Also, the figure shows the case where the current waveform is a substantially rectangular wave, but there may also be a case of a sine wave.

[0057] Numerical examples of each parameter are shown below. In1 = 60A, In2 = 150A, Ten = 10ms, Tn1 = 0.5ms, Ip1 = 60A, Ip2 = 150A, Tep = 3 - 5ms, Tp1 = 0.3ms

[0058] Figure 4 is a timing chart of each signal in the double-shielded TIG welding apparatus shown in Figure 1, illustrating a double-shielded TIG welding method according to an embodiment of the present invention. Figure (A) shows the time variation of the torch switch signal On, Figure (B) shows the time variation of the outer gas flow rate Fo (l / min), Figure (C) shows the time variation of the inner gas flow rate Fi (l / min), Figure (D) shows the time variation of the average welding current Iav, which is the average of the absolute values ​​of the welding current Iw shown in Figure 2, Figure (E) shows the time variation of the arc generation discrimination signal Ad, and Figure (F) shows the advance angle setting signal Afr [degrees]. The operation of each signal will be explained below with reference to the same figure.

[0059] As described above, in this embodiment, the cross-sectional shape of the inner nozzle 4 in Figure 1 is elliptical. Welding is performed by holding the welding torch so that the major axis of the ellipse is in the welding direction. When welding is performed with the inner nozzle 4 having an elliptical cross-sectional shape and the major axis of the ellipse being in the welding direction, the inner gas and outer gas are ejected in the forward direction of the arc generation part. As a result, a sufficient cleaning action is performed to remove the oxide film from the base material and filler wire, so that the occurrence of blowholes during welding can be suppressed. Furthermore, since the length of the minor axis of the inner nozzle, which is perpendicular to the welding direction, is short, the rigidity of the arc can be strengthened.

[0060] As shown in Figure (F), the advance angle setting signal Afr is in the range of 0 to 40 degrees, as described above, and the waveform height is displayed according to the value. In this figure, the value of the advance angle setting signal Afr is 30 degrees during the pre-flow period and initial period from time t1 to t4, and 0 degrees during the steady-state welding period, crater processing period and after-flow period thereafter.

[0061] [Preflow Period Operation] At time t1, when the welder turns on the torch switch on the welding torch WT in Figure 1, the torch switch signal On changes to a High level, as shown in Figure (A). In response, the period discrimination signal Tp in Figure 1 changes to 1, and the system transitions to the pre-flow period. Simultaneously, the outer gas flow regulator CO in Figure 1 starts ejecting the outer gas. As shown in Figure (B), the outer gas flow rate Fo becomes a predetermined pre-flow outer gas flow rate value determined by the outer gas flow rate setting signal For in Figure 1. It is desirable that the pre-flow 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 Figure 1.

[0062] At time t2, after a predetermined delay time Td has elapsed from time t1, the period discrimination signal Tp in Figure 1 changes to 2. In response to this, the inner gas injection is started by the inner gas flow regulator CI in Figure 1. As shown in Figure (C), the inner gas flow rate Fi is determined by the pre-flow inner gas flow rate setting signal Fipr in Figure 1. The value of the pre-flow 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 Figure 1, and may be equal to the value of the initial period inner gas flow rate setting signal Fisr in Figure 1.

[0063] During the pre-flow period, the inner gas is ejected after the outer gas. In this way, the inner gas is ejected while the surrounding area is shielded by the ejection of the outer gas, so the inner gas does not entrain the surrounding air, and the welding can be brought to a steady state quickly. For this reason, in this embodiment, the pre-flow time can be shortened by about 50% compared to the conventional technology in which the ejection of the outer gas and inner gas is started simultaneously. Therefore, in this embodiment, sufficient shielding can be ensured even if the pre-flow time at the start of welding is set short, so work efficiency can be increased and the consumption of expensive inert gas can be reduced. For example, in the conventional technology, the pre-flow period had to be set to about 6 seconds, but in this embodiment it can be set to about 3 seconds.

[0064] [Initial operation] At time t3, when the preflow period ends and the period discrimination signal Tp=3 in Figure 1 changes, the welding power supply PS in Figure 1 applies a high-frequency high voltage between the electrode 1 and the base material 2 in Figure 1, generating the arc 3 in Figure 1, and the average welding current Iav is applied, as shown in Figure (D). The waveforms of the welding current Iw and welding voltage Vw, which are not shown, are the waveforms shown in Figure 2 above. At time t3, when the generation of an arc is determined by the application of the welding current Iw, the arc generation discrimination signal Ad changes to a high level, as shown in Figure (E). At time t3, as shown in Figure (B), the outer gas flow rate Fo becomes the value determined by the steady-state outer gas flow rate setting signal Focr in Figure 1. Then, welding starts from time t3.

[0065] When the arc generation detection signal Ad changes to a high level, the system transitions to a predetermined initial period from time t3 to t4. As shown in Figure (C), the inner gas flow rate Fi is determined by the initial period inner gas flow rate setting signal Fisr shown in Figure 1. This initial period inner gas flow rate setting signal Fisr is calculated by substituting the values ​​of the velocity reduction inner gas flow rate setting signal Fiir and the advance angle setting signal Afr shown in Figure 1 into equation (4) above. The value of the velocity reduction inner gas flow rate setting signal Fiir is the value at which the velocity of the inner gas becomes equal to the velocity of the outer gas. The value of the advance angle setting signal Afr is in the range of 0 to 40 degrees, as described above. As a result, the inner gas flow rate Fi during the initial period is a value at which the velocity of the inner gas is within ±20% of the velocity of the outer gas, and it increases as the value of the advance angle setting signal Afr increases. During steady-state welding, the inner gas flow rate is approximately 2.5 to 4 times that of the outer gas flow rate. Therefore, the inner gas flow rate Fi is reduced during the initial period to slow down the flow rate. For example, the initial period is set to 500 ms.

[0066] As shown in Figure (F), the value of the advance angle setting signal Afr during the initial period is a predetermined initial advance angle setting value. The initial advance angle setting value is preferably in the range of 10 to 40 degrees, and more preferably in the range of 15 to 35 degrees. When welding is performed with the welding torch at an advance angle, the inner gas and outer gas are ejected in the forward direction of the arc generation part. As a result, a sufficient cleaning action is performed to remove the oxide film from the base material and filler wire, so that the occurrence of blowholes at the start of the weld can be suppressed. Furthermore, the inner gas flow rate Fi during the initial period is set so that the flow velocity of the inner gas is within ±20% of the flow velocity of the outer gas. If the difference between the flow velocity of the inner gas and the flow velocity of the outer gas is large, turbulence will occur and blowholes will be more likely to occur. In this embodiment, the difference between the flow velocity of the inner gas and the flow velocity of the outer gas is within ±20%, so the occurrence of turbulence can be suppressed. Furthermore, the inner gas flow rate Fi during the initial period is set to increase as the value of the advance angle setting signal Afr increases. The larger the value of the advance angle setting signal Afr, the shallower the penetration. In this embodiment, the inner gas flow rate Fi increases as the value of the forward angle setting signal Afr increases, which can suppress the increase in flow velocity and the resulting shallower fusion.

[0067] [Operation during steady-state welding period] At time t4, when the initial period ends, the period discrimination signal Tp=4 in Figure 1 changes, and the system transitions to the steady-state welding period. As shown in Figure (C), 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 Figure 1. The value of this steady-state inner gas flow rate setting signal Ficr is calculated by substituting the values ​​of both the inner nozzle long axis setting signal Dr and the inner gas flow velocity setting signal Sir in Figure 1 into equation (2) above. The inner nozzle long axis setting signal Dr can be any of three types, for example, 5 mm, 6 mm, or 8 mm. The value of the inner gas flow velocity setting signal Sir is calculated by substituting the value of the second electrode negative polarity current setting signal In2r in Figure 1 into equation (1) above. The value of the inner gas flow velocity setting signal Sir increases as the welding current (second electrode negative polarity current setting signal In2r) increases. The value of the steady-state inner gas flow rate setting signal Ficr is set to a value appropriate for each type of inner nozzle, even when the inner nozzle has a different elliptical shape, thus enabling the acquisition of desired penetration depth, work efficiency, etc. As mentioned above, the inner gas flow rate during steady-state welding is approximately 2.5 to 4 times faster than the outer gas flow rate. By ejecting high-speed inner gas, the rigidity of the arc can be increased, allowing for 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.

[0068] As shown in Figure (F), the value of the advance angle setting signal Afr during the steady-state welding period becomes a predetermined steady-state advance angle setting value. The steady-state advance angle setting value is smaller than the initial advance angle setting value mentioned above. Reducing the advance angle allows for deeper penetration and improves work efficiency.

[0069] If the welder turns off the torch switch at time t41, which is in the middle of the steady welding period from time t4 to t5, the torch switch signal On changes to a Low level, as shown in Figure (A), but the steady welding period described above is maintained.

[0070] [Operation during crater processing period] When the welder turns the torch switch back on at time t5, the torch switch signal On changes to a High level, as shown in Figure (A). In response, the period discrimination signal Tp=5 in Figure 1 changes, and the crater processing period begins. As shown in Figure (B), the outer gas flow rate Fo is the same as during the steady-state welding period. As shown in Figure (C), 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 processing period is set so that the flow velocity of the inner gas is within ±20% of the flow velocity of the outer gas. Since the flow velocity of the inner gas during the steady-state welding period is about 2.5 to 4 times that of the outer gas, the flow velocity is slowed down by reducing the inner gas flow rate Fi during the crater processing period. As shown in Figure (D), the average welding current Iav is smaller than during the steady-state welding period.

[0071] [Operation during the after-flow period] When the welder turns the torch switch off again at time t6, the torch switch signal On changes to a Low level, as shown in Figure (A), and the period discrimination signal Tp=6 in Figure 1 changes, transitioning to the after-flow period. In response, the welding power supply PS in Figure 1 stops outputting, the arc is extinguished, and the average welding current Iav becomes 0A, as shown in Figure (D). As shown in Figure (B), the outer gas flow rate Fo is the same value as during the steady-state welding period. As shown in Figure (C), the inner gas flow rate Fi is a value 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 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. Since the flow rate of the inner gas during the steady-state welding period is about 2.5 to 4 times that of the outer gas, the flow rate of the inner gas is reduced during the after-flow period to slow down the flow rate.

[0072] [Welding complete] At time t7, when the after-flow period ends, the period discrimination signal Tp in Figure 1 changes to 0. In response, as shown in Figure (B), the outer gas flow rate Fo becomes 0 and ejection stops. Also, as shown in Figure (C), the inner gas flow rate Fi becomes 0 and ejection stops. This completes the welding process.

[0073] In the embodiments described above, a case where a crater treatment period is provided after the steady-state welding period was explained, but the crater treatment period may be omitted. Also, in the embodiments described above, the case where the welding current is AC was explained, but it can also be applied to DC current and pulsed current.

[0074] The effects of this embodiment will now be explained. According to this embodiment, in a double-shielded TIG welding method that uses a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, and generates an arc by applying a welding current, the cross-sectional shape of the inner nozzle is made elliptical, and welding is performed with the major axis of the ellipse in the welding direction. Conventional double-shielded TIG welding methods have the problem of blowholes occurring during welding, resulting in poor welding quality. In this embodiment, the cross-sectional shape of the inner nozzle is made elliptical, and welding is performed with the major axis of the ellipse in the welding direction, so that the inner gas and outer gas are ejected in the forward direction of the arc generation part. As a result, a sufficient cleaning action is performed to remove the oxide film from the base material and filler wire, so that the occurrence of blowholes during welding can be suppressed. Furthermore, since the length of the short axis of the inner nozzle, which is perpendicular to the welding direction, is short, the rigidity of the arc can be increased. As a result, penetration can be increased, and the welding speed can be increased.

[0075] More preferably, according to this embodiment, the ratio of the major axis to the minor axis of the ellipse is 1.2 or more and 2.0 or less. When the ratio of the major axis to the minor axis is less than 1.2, the ejection of inner gas and outer gas forward from the arc generation part is reduced, resulting in insufficient cleaning action, and thus the effect of suppressing the occurrence of blowholes is reduced. When the ratio of the major axis to the minor axis is greater than 2.0, the rigidity of the arc is weakened, so the effects unique to the double-shielded TIG welding method, such as being able to achieve deeper penetration and a faster welding speed, are reduced. More preferably, the ratio of the major axis to the minor axis is 1.4 or more and 1.8 or less.

[0076] More preferably, according to this embodiment, the welding torch is set to an advanced angle during the initial period after arc generation. When welding is performed with the welding torch set to an advanced angle, the inner gas and outer gas are ejected in the forward direction of the arc generation area. For this reason, in this embodiment, a sufficient cleaning action is performed to remove the oxide film from the base material and filler wire, so that the occurrence of blowholes at the start of the weld can be suppressed.

[0077] More preferably, according to this embodiment, the flow rate of the inner gas is increased as the advance angle increases during the initial period. Dissolution becomes shallower as the advance angle increases. In this embodiment, since the flow rate of the inner gas is increased as the advance angle increases, the flow velocity of the inner gas increases, and as a result, the shallow dissolution can be suppressed.

[0078] More preferably, according to this embodiment, the flow velocity of the inner gas is kept within ±20% of the flow velocity of the outer gas during the initial period. During the initial period, the arc generation state is transient, so if the difference between the flow velocity of the inner gas and the flow velocity of the outer gas is large, turbulence will occur, resulting in insufficient shielding and making blowholes more likely to occur. In this embodiment, the difference between the flow velocity of the inner gas and the flow velocity of the outer gas is kept within ±20%, so the generation of turbulence can be suppressed. As a result, the occurrence of blowholes caused by turbulence during the initial period can be suppressed.

[0079] More preferably, according to this embodiment, the advance angle is made smaller during the steady-state welding period than during the initial period. A smaller advance angle results in deeper penetration and improved work efficiency. In this embodiment, by making the advance angle smaller during the steady-state welding period, deep penetration welding can be performed efficiently.

[0080] More preferably, according to this embodiment, an alternating welding current formed from a negative electrode polarity period and a positive electrode polarity period is applied, and the ratio of the negative electrode polarity period is made smaller during the initial period than during the steady-state welding period. The cleaning action is performed during the positive electrode polarity period. For this reason, as the ratio of the negative electrode polarity period decreases, the ratio of the positive electrode polarity period increases, and the cleaning action becomes larger. In this embodiment, by decreasing the ratio of the negative electrode polarity period during the initial period and increasing the cleaning action, the oxide film on the base material and filler wire is sufficiently removed. As a result, the occurrence of blowholes at the welding start can be suppressed more reliably.

[0081] More preferably, according to this embodiment, the flow rate is controlled so that the flow velocity of the inner gas reaches a predetermined value according to the cross-sectional area of ​​the inner nozzle. When the cross-sectional area of ​​the inner nozzle changes, the rigidity of the arc changes, causing fluctuations in the penetration depth and reducing work efficiency. In this embodiment, by controlling the flow rate so that the flow velocity of the inner gas reaches a predetermined value according to the cross-sectional area of ​​the inner nozzle, the rigidity of the arc can be maintained in an appropriate state, thereby obtaining the desired penetration depth, work efficiency, etc.

[0082] Furthermore, according to this embodiment, in a double-shielded TIG welding apparatus that uses a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, and generates an arc by applying a welding current for welding, the cross-sectional shape of the inner nozzle is made elliptical, and welding is performed with the major axis of the ellipse oriented in the welding direction. The double-shielded TIG welding apparatus according to this embodiment provides the above-mentioned effects. [Explanation of Symbols]

[0083] 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, 10: Filler wire, AD: Arc generation discrimination circuit, Ad: Arc generation discrimination signal, AFR: Forward angle setting circuit, Afr: Forward angle setting signal, CI: Inner gas flow regulator, CO: Outer gas flow regulator, DR: Inner nozzle long axis setting circuit, Dr: Inner nozzle long axis setting signal, EN: Electrode negative polarity, EP: Electrode positive polarity, Fi: Inner gas flow rate, FICR: Steady-state input Inner gas flow rate setting circuit, Ficr: steady inner gas flow rate setting signal, FIIR: velocity reduction inner gas flow rate setting circuit, Fiir: velocity reduction inner gas flow rate setting signal, FIPR: pre-flow inner gas flow rate setting circuit, Fipr: pre-flow inner gas flow rate setting signal, FIR: inner gas flow rate setting circuit, Fir: inner gas flow rate setting signal, FISR: initial period inner gas flow rate setting circuit, Fisr: initial period 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 Constant 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, 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, SIR: Inner gas flow rate setting circuit, Sir: Inner gas flow rate setting signal, 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. In a double-shielded TIG welding method that uses a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, and generates an arc by applying a welding current, A double-shielded TIG welding method characterized by making the cross-sectional shape of the inner nozzle elliptical and performing welding with the major axis of the elliptical shape as the welding direction.

2. The double-shielded TIG welding method according to claim 1, characterized in that the ratio of the major axis to the minor axis of the elliptical shape is 1.2 or more and 2.0 or less.

3. The double-shielded TIG welding method according to claim 1 or 2, characterized in that the welding torch is set to an advanced angle during the initial period after arc generation.

4. The double-shielded TIG welding method according to claim 3, characterized in that the flow rate of the inner gas is increased as the advance angle increases during the initial period.

5. The double-shielded TIG welding method according to claim 3, characterized in that during the initial period, 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 apparatus that uses a welding torch equipped with an inner nozzle for ejecting inner gas and an outer nozzle for ejecting outer gas, and generates an arc by applying a welding current, A double-shielded TIG welding apparatus characterized by having an elliptical cross-sectional shape for the inner nozzle and performing welding with the major axis of the elliptical shape as the welding direction.

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