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

Abstract

In a double-shielded TIG welding method, the objective is to obtain an appropriate penetration depth according to the joint shape by setting simple welding conditions. [Solution] In a double-shielded TIG welding method that uses a welding torch equipped with an inner nozzle for ejecting inner gas Fi and an outer nozzle for ejecting outer gas Fo, and generates an arc by applying a welding current Iav, the setting value of the inner gas flow velocity is set according to the welding current Iav and the joint shape, and the flow rate Fi of the inner gas is set using the setting value of the inner gas flow velocity as input.

Description

Technical Field

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

Background Art

[0002] A double shield 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 shield tig welding method, the rigidity of the arc can be increased by ejecting the inner gas at a flow rate about 2.5 to 5 times faster than the flow rate of the outer gas. For this reason, in the double shield 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 shield tig welding method, when the joint shapes such as butt joints, fillet lap joints, and T-joint fillets are different, the appropriate penetration depth values are different. For this reason, in the prior art, in order to obtain an appropriate penetration depth according to the joint shape, it is necessary to determine conditions such as the welding current and the welding speed by performing a large number of test welds. As a result, in the prior art, there is a problem that the pre-welding preparation takes time and the work efficiency is reduced.

[0006] Therefore, the present invention aims to provide a double-shielded TIG welding method and a double-shielded TIG welding apparatus that can obtain an appropriate penetration depth according to the joint shape by setting simple welding conditions, for example. [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 a set value for the flow velocity of the inner gas is set according to the welding current and the joint shape, and the flow rate of the inner gas is set using the set value for the flow velocity of the inner gas as input.

[0008] As an example, the double-shielded TIG welding method of the present invention is characterized by correcting the set value of the flow velocity of the inner gas according to the forward angle of the welding torch.

[0009] As an example, the double-shielded TIG welding method of the present invention is characterized by providing notification of the set value of the flow velocity of the inner gas.

[0010] As an example, the double-shielded TIG welding method of the present invention is characterized by setting the flow rate of the inner gas by taking the inner diameter of the inner nozzle and the flow velocity of the inner gas as input values.

[0011] As an example, the double-shielded TIG welding method of the present invention is characterized in that the set value of the flow velocity of the inner gas is set to a different value during the initial period after arc generation and / or during the crater processing period than during the steady-state welding period.

[0012] A double-shielded TIG welding apparatus provided by a second aspect of the present invention is characterized by setting a set value for the flow velocity of the inner gas according to the welding current and the joint shape, and setting the flow rate of the inner gas using the set value for the flow velocity of the inner gas as input. [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, an appropriate penetration depth according to the joint shape can be obtained by setting simple welding conditions, thereby improving the welding quality. [Brief explanation of the drawing]

[0014] [Figure 1] This is a block diagram of a double-shielded TIG welding apparatus according to an embodiment of the present invention. [Figure 2] This is a current and voltage waveform diagram for a double-shielded TIG welding method according to an embodiment of the present invention. [Figure 3] 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 according to an embodiment of the present invention. Each block will be described below with reference to this figure.

[0017] The figure shows a double-shielded TIG welding method in which an alternating current Iw is applied, formed from the negative electrode current during the negative electrode polarity period and the positive electrode current during the positive electrode polarity period. This double-shielded TIG welding method, using an alternating current Iw, is used for welding aluminum, aluminum alloys, magnesium, and the like.

[0018] The welding torch WT mainly includes an electrode 1, an inner nozzle 4 surrounding it, and an outer nozzle 5 surrounding the inner nozzle 4. For the electrode 1, a tungsten electrode or the like is used. For example, the inner diameter of the inner nozzle 4 has a plurality of types such as 4 mm, 5 mm, 6 mm, etc., and the inner diameter of the outer nozzle 5 is 13 mm.

[0019] The torch switch circuit ON is a torch switch mounted on the welding torch WT, and outputs a torch switch signal On that becomes High level when the welding operator turns it on and becomes Low level when it is turned off.

[0020] 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 takes the above current detection signal Id as an input, and when the value of the current detection signal Id is equal to or greater than the energization discrimination value (about 5 A), it discriminates that an arc has occurred and outputs an arc generation discrimination signal Ad that becomes High level.

[0021] 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 processing, and outputs a period discrimination signal Tp. When welding is completed, the period discrimination signal Tp = 0. 1) When the torch switch signal On changes to High level, the period discrimination signal Tp = 1 (preflow period start) is output. 2) When a predetermined delay time Td has elapsed from the time when Tp changes to 1, the period discrimination signal Tp = 2 (inner gas ejection start) is output. 3) When a predetermined preflow period has elapsed from the time when Tp changes to 1 and the arc generation discrimination signal Ad changes to High level, the period discrimination signal Tp = 3 (initial period start) is output. 4) When a predetermined initial period has elapsed from the time when Tp changes to 3, Tp = 4 (steady welding period start) is output. 5) Thereafter, when the torch switch signal On changes to Low level and then changes to High level again, Tp = 5 (crater treatment period start) is output. 6) After that, when the torch switch signal On changes to the Low level again, a period discrimination signal Tp = 6 (afterflow period start) is output. 7) When a predetermined afterflow period elapses, a period discrimination signal Tp = 0 (welding end state) is output.

[0022] The first electrode negative polarity current setting circuit IN1R outputs a first electrode negative polarity current setting signal In1r with a predetermined positive value. The second electrode negative polarity current setting circuit IN2R outputs a second electrode negative polarity current setting signal In2r with a predetermined positive value. Here, In1r < In2r.

[0023] The first electrode positive polarity current setting circuit IP1R outputs a first electrode positive polarity current setting signal Ip1r with a predetermined positive value. The second electrode positive polarity current setting circuit IP2R outputs a second electrode positive polarity current setting signal Ip2r with a predetermined positive value. Here, Ip1r < Ip2r.

[0024] When the welder selects the joint shape of the base material 2, the joint shape setting circuit JR outputs a joint shape setting signal Jr whose value becomes 1 for a butt joint, 2 for an overlap fillet joint, and 3 for a T-fillet joint.

[0025] When the welder inputs the forward angle of the welding torch WT during construction, the forward angle setting circuit AFR outputs that value as a forward angle setting signal Afr. The forward angle setting signal Afr is an integer value in the range of 0 to 30 degrees.

[0026] When the welder inputs the inner nozzle inner diameter of the inner nozzle to be used, the inner nozzle inner diameter setting circuit DR outputs it as an inner nozzle inner diameter setting signal Dr. For example, the values of the inner nozzle inner diameter setting signal Dr are 4 mm, 5 mm, and 6 mm.

[0027] The inner gas flow velocity setting circuit SIR takes the second electrode negative polarity current setting signal In2r, the joint shape setting signal Jr, and the advance angle setting signal Afr as inputs, performs the following processes 1) and 2), and outputs the inner gas flow velocity setting signal Sir. 1) The second electrode negative polarity current setting signal In2r[A] and the joint shape setting signal Jr are input to the following predetermined inner gas flow velocity setting function to calculate the inner gas flow velocity setting signal Sir[cm / s]. Sir=(In2r-75)×2+270+Jr×30 (1) formula However, this is within the range of 75 ≤ In2r ≤ 150, and if In2r < 75, it is equivalent to In2r = 75, and if In2r > 150, it is equivalent to In2r = 150. For example, when In2r=75A and Jr=1 (butt joint), Sir=300cm / s; when In2r=75A and Jr=2 (lap fillet joint), Sir=330cm / s; when In2r=75A and Jr=3 (T-fillet joint), Sir=360cm / s; when In2r=150A and Jr=1 (butt joint), Sir=450cm / s; when In2r=150A and Jr=2 (lap fillet joint), Sir=480cm / s; and when In2r=150A and Jr=3 (T-fillet joint), Sir=510cm / 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. 2) The value of the inner gas flow velocity setting signal Sir calculated in 1) above is corrected by Sir × (1 + Afr × 0.3 × 0.01) and output as the inner gas flow velocity setting signal Sir. For example, the value of the inner gas flow velocity setting signal Sir is the uncorrected value when Afr = 0 degrees, and the value is increased by 9% when Afr = 30 degrees. The greater the advance angle setting signal Afr, the shallower the penetration depth. Therefore, the value of the inner gas flow velocity setting signal Sir is increased as the advance angle setting signal Afr increases to suppress the shallowing of the penetration depth.

[0028] The inner gas flow rate notification circuit DP takes the above-mentioned inner gas flow rate setting signal Sir as input and displays its value on an LCD display or the like.

[0029] The steady-state inner gas flow rate setting circuit FICR takes the inner nozzle diameter setting signal Dr [mm] and the 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 inner diameter of the inner nozzle is the value of the inner nozzle diameter setting signal Dr. Ficr=(Sir×(Dr / 2)×(Dr / 2)×3.14×0.01×60) / 1000 (2) formula 1) When Dr=5mm, Ficr=3.5l / min when Sir=300cm / s, and Ficr=5.3l / min when Sir=450cm / s. 2) When Dr=4mm, Ficr=2.3l / min when Sir=300cm / s, and Ficr=3.4l / min when Sir=450cm / s. 3) When Dr=6mm, Ficr=5.1l / min when Sir=300cm / s, and Ficr=7.6l / min when Sir=450cm / s.

[0030] 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.

[0031] The low-flow-rate reduction inner gas flow rate setting circuit FIIR takes the above inner nozzle inner diameter setting signal Dr [mm] as an input, inputs it into the following function, and outputs the calculated value as the low-flow-rate reduction inner gas flow rate setting signal Fiir [l / min]. The function is a function that calculates the value of the low-flow-rate reduction inner gas flow rate setting signal Fiir such that when the inner diameter of the inner nozzle is the value of the inner nozzle inner diameter setting signal Dr, the flow rate of the inner gas is within ±20% of the flow rate of the outer gas. Here, when the flow rate of the outer gas is 8 l / min, the flow rate is 118 cm / s. Fiir=(118×(Dr / 2)×(Dr / 2)×3.14×0.01×60) / 1000 Equation (3) 1) When Dr = 5 mm, Fiir = 1.4 l / min ± 20%. 2) When Dr = 4 mm, Fiir = 0.9 l / min ± 20%. 3) When Dr = 6 mm, Fiir = 2.0 l / min ± 20%.

[0032] The preflow inner gas flow rate setting circuit FIPR outputs a predetermined preflow inner gas flow rate setting signal Fipr. Here, Fipr < Ficr, and it may be set that Fipr = Fiir.

[0033] The inner gas flow rate setting circuit FIR takes the above period discrimination signal Tp, the above preflow inner gas flow rate setting signal Fipr, the above low-flow-rate reduction inner gas flow rate setting signal Fiir, and the above 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 (preflow period), the value of the preflow inner gas flow rate setting signal Fipr is output as the inner gas flow rate setting signal Fir. 2) When the period discrimination signal Tp = 3 (initial period), the value of the low-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-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. The second electrode positive polarity period setting circuit TP2R outputs a predetermined second electrode positive polarity period setting signal Tp2r.

[0041] 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.

[0042] 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.

[0043] Figure 2 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.

[0044] 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.

[0045] (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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] (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.

[0050] 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.

[0051] 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.

[0052] At time t16, when the second electrode positive polarity period Tp2 ends, the welding current Iw decreases in a slope, as shown in Figure (A), 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 Figure (B), the welding voltage Vw also decreases. From this point onward, the operation returns to that at time t11.

[0053] The figure shows the case of the balanced waveform of In2 = Ip2, but there may also be 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 sine wave case.

[0054] Numerical examples of each parameter are shown below. In1 = 60 A, In2 = 150 A, Ten = 10 ms, Tn1 = 0.5 ms, Ip1 = 60 A, Ip2 = 150 A, Tep = 3 ms, Tp1 = 0.3 ms

[0055] Figure 3 is a timing chart of each signal in the double-shielded tig welding apparatus shown in FIG. 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 welding current average value Iav which is the average value of the absolute value of the welding current Iw shown in FIG. 2, and (E) of the figure shows the time change of the arc generation discrimination signal Ad. 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 welder turns on the torch switch provided on the welding torch WT in FIG. 1, as shown in (A) of the figure, the torch switch signal On changes to the High level. In response to this, the period discrimination signal Tp in FIG. 1 changes to 1, and the preflow period starts. At the same time, the ejection of the outer gas is started by the outer gas flow rate regulator CO in FIG. 1. As shown in (B) of the figure, 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. The preflow outer gas flow rate value is preferably set to a value larger than the value of the steady outer gas flow rate setting signal Focr in FIG. 1.

[0057] 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 velocity reduction inner gas flow rate setting signal Fiir in Figure 1.

[0058] 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.

[0059] [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.

[0060] 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 flow rate reduction inner gas flow rate setting signal Fiir in Figure 1. This flow rate reduction inner gas flow rate setting signal Fiir is calculated by substituting the value of the inner nozzle diameter setting signal Dr in Figure 1 into equation (3) above. In other words, 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. Since the flow velocity of the inner gas during the steady-state welding period is about 2.5 to 5 times that of the outer gas, the flow velocity is slowed down by reducing the inner gas flow rate Fi during the initial period. For example, the initial period is set to 500 ms.

[0061] [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 process 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 diameter setting signal Dr and the inner gas flow velocity setting signal Sir in Figure 1 into equation (2) above. The inner nozzle diameter setting signal Dr can be any of three types, for example, 4 mm, 5 mm, or 6 mm. The value of the inner gas flow velocity setting signal Sir is calculated by substituting the values ​​of the second electrode negative polarity current setting signal In2r in Figure 1 and the joint shape setting signal Jr in Figure 1 into equation (1) above, and then correcting the value of the advance angle setting signal Afr in Figure 1. 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, and also increases as the joint shape (joint shape setting signal Jr) changes from a butt joint to a lap fillet joint and then to a T-fillet joint. Furthermore, the value of the inner gas flow velocity setting signal Sir increases as the advance angle of the welding torch WT (advance angle setting signal Afr) increases. This allows the desired penetration depth to be obtained even when the joint shape and advance angle change. The value of the steady-state inner gas flow rate setting signal Ficr is set to a value appropriate for each inner diameter, even when the inner nozzle is replaced with one of a different inner diameter, so the desired penetration depth, work efficiency, etc., can be obtained. As described above, the inner gas flow velocity during the steady-state welding period is about 2.5 to 5 times faster than the outer gas flow velocity. By ejecting high-speed inner gas, the rigidity of the arc can be increased, so the penetration can be deepened and the welding speed can be increased. For example, the period during which the inner gas flow rate Fi increases over time is set to 200 ms.

[0062] 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.

[0063] [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 5 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.

[0064] [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 5 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.

[0065] [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.

[0066] 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.

[0067] The effects of this embodiment are described below. According to this embodiment, the inner gas flow rate is set according to the welding current and joint shape, and the inner gas flow rate is set using the inner gas flow rate as input. In double-shielded TIG welding, the appropriate penetration depth differs depending on the joint shape, such as butt joints, lap fillet joints, and T-fillet joints. In this embodiment, the inner gas flow rate is automatically set according to the welding current and joint shape, and the inner gas flow rate is set so that the set flow rate is achieved. The penetration depth correlates with the inner gas flow rate. Therefore, in this embodiment, since the inner gas flow rate is automatically set to a value corresponding to the joint shape, the penetration depth can be optimized by setting simple welding conditions.

[0068] More preferably, according to this embodiment, the set value of the inner gas flow velocity is corrected according to the advance angle of the welding torch. When the advance angle increases, the penetration depth becomes shallower. Therefore, in this embodiment, the penetration depth is optimized by correcting the inner gas flow velocity according to the advance angle.

[0069] More preferably, according to this embodiment, the set value of the inner gas flow rate is notified. By managing the notification information of the set value of the inner gas flow rate, the penetration depth can be controlled, and thus the welding quality can be controlled.

[0070] More preferably, according to this embodiment, the flow rate of the inner gas is set by inputting the inner diameter of the inner nozzle and the flow velocity of the inner gas. In this way, even if inner nozzles with different inner diameters are used, the flow velocity of the inner gas can be controlled to the set value, so that an appropriate penetration depth can be obtained according to the joint shape.

[0071] More preferably, according to this embodiment, the inner gas flow rate setting value is set to a different value during the initial period after arc generation and / or during the crater processing period than during the steady-state welding period. The desired state of arc rigidity during the initial period and the crater processing period is different from that during the steady-state welding period. Therefore, in this embodiment, the inner gas flow rate setting value for setting the arc rigidity is set to a different value during the initial period and / or during the crater processing period than during the steady-state welding period. In this way, the arc rigidity during the initial period and / or the crater processing period can be set to the desired state, thereby improving the welding quality.

[0072] Furthermore, according to this embodiment, the double-shielded TIG welding apparatus sets the inner gas flow rate according to the welding current and joint shape, and sets the inner gas flow rate using the inner gas flow rate as input. The double-shielded TIG welding apparatus according to this embodiment provides the above-mentioned effects. [Explanation of Symbols]

[0073] 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, AFR: Forward angle setting circuit, Afr: Forward angle setting signal, AD: Arc generation discrimination circuit, Ad: Arc generation discrimination signal, CI: Inner gas flow regulator, CO: Outer gas flow regulator, DP: Inner gas flow rate notification circuit, DR: Inner nozzle inner diameter setting circuit, Dr: Inner nozzle inner diameter setting signal, EN: Electrode negative polarity, EP: Electrode positive polarity, Fi: Inner gas flow rate, FICR : Steady-state inner gas flow rate setting circuit, Ficr: Steady-state 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, Fo: Outer gas flow rate, FOCR: Steady-state outer gas flow rate setting circuit, Focr: Steady-state outer gas flow rate setting signal, FOR: Outer gas flow rate setting circuit, For: Outer gas flow rate setting signal, Ia v: Average welding current, 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, JR: Joint shape setting circuit, Jr: Joint shape setting signal, 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 setting a set value for the flow velocity of the inner gas according to the welding current and the joint shape, and setting the flow rate of the inner gas using the set value for the flow velocity of the inner gas as input.

2. The double-shielded TIG welding method according to claim 1, characterized in that the set value of the flow velocity of the inner gas is corrected according to the forward angle of the welding torch.

3. The double-shielded TIG welding method according to claim 1 or 2, characterized in that it provides notification of the set value of the flow velocity of the inner gas.

4. The double-shielded TIG welding method according to claim 1 or 2, characterized in that the flow rate of the inner gas is set by inputting the inner diameter of the inner nozzle and the flow velocity of the inner gas.

5. The double-shielded TIG welding method according to claim 1 or 2, characterized in that the set value of the inner gas flow velocity is set to a different value during the initial period after arc generation and / or during the crater processing period than during the steady-state welding period.

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, The double-shielded TIG welding apparatus is characterized by setting a set value for the flow velocity of the inner gas according to the welding current and the joint shape, and setting the flow rate of the inner gas using the set value for the flow velocity of the inner gas as input.

Images