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

Abstract

This invention provides a double-shielded TIG welding method that can reduce welding costs. [Solution] The double-shielded TIG welding method uses a welding torch WT equipped with an electrode 1, an inner nozzle 4 surrounding the electrode 1, and an outer nozzle 5 surrounding the inner nozzle 4, and generates an arc 3 by applying a welding current Iw to perform welding. The inner nozzle 4 ejects an inner gas 7 containing an inert gas. The outer nozzle 5 ejects an outer gas 9 containing carbon dioxide.

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] Patent Document 1 discloses a double shielded TIG welding method 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. Each of the inner gas and the outer gas is an inert gas such as argon or helium. The inner gas prevents oxidation of the electrode included in the welding torch. The outer gas prevents oxidation of the molten metal generated in the base material. Thereby, oxidation of the electrode and the molten metal can be more effectively prevented.

[0003] However, in the double shielded TIG welding method disclosed in Patent Document 1, since both the inner gas and the outer gas are inert gases, there is a demerit that the cost related to welding becomes relatively high.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above circumstances, an object of the present invention is to provide a double shielded TIG welding method capable of reducing the cost related to welding.

Means for Solving the Problems

[0006] A double-shielded TIG welding method provided by a first aspect of the present invention uses a welding torch comprising an electrode, an inner nozzle surrounding the electrode, and an outer nozzle surrounding the inner nozzle, and performs welding by applying a welding current to generate an arc. The inner nozzle ejects an inner gas containing an inert gas. The outer nozzle ejects an outer gas containing carbon dioxide.

[0007] Preferably, in the implementation of the present invention, the inert gas includes argon.

[0008] A double-shielded TIG welding apparatus provided by a second aspect of the present invention comprises a welding torch having an electrode, an inner nozzle surrounding the electrode, and an outer nozzle surrounding the inner nozzle. The welding torch generates an arc by passing a welding current through it. The inner nozzle ejects an inner gas containing an inert gas. The outer nozzle ejects an outer gas containing carbon dioxide. [Effects of the Invention]

[0009] The configuration of the double-shielded TIG welding method according to the present invention makes it possible to reduce welding costs.

[0010] Other features and advantages of the present invention will become more apparent from the detailed description below, based on the accompanying drawings. [Brief explanation of the drawing]

[0011] [Figure 1] This is a block diagram of a double-shielded TIG welding apparatus for carrying out a double-shielded TIG welding method according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] Embodiments for carrying out the present invention will be described with reference to the attached drawings.

[0013] Based on Figure 1, a double-shielded TIG welding method according to one embodiment of the present invention will be described.

[0014] Figure 1 shows a double-shielded TIG welding method in which an AC welding current Iw, formed from the negative electrode current during the negative electrode polarity period and the positive electrode current during the positive electrode polarity period, is applied. The present invention can also be applied in the case where a DC welding current Iw, formed only from the negative electrode current during the negative electrode polarity period, is applied.

[0015] The welding torch WT comprises an electrode 1, an inner nozzle 4 surrounding the electrode 1, and an outer nozzle 5 surrounding the inner nozzle 4. Here, the direction in which the inner nozzle 4 and outer nozzle 5 surround each is around the direction in which the welding torch WT extends. The electrode 1 is a tungsten electrode or the like. The inner diameter of the inner nozzle 4 is, for example, 5 mm. The inner diameter of the outer nozzle 5 is, for example, 13 mm. However, the inner diameters of the inner nozzle 4 and outer nozzle 5 are not limited to these.

[0016] The inner nozzle 4 ejects the inner gas 7. The inner gas 7 flows through a passage surrounded by the inner nozzle 4. The inner gas 7 contains an inert gas. This inert gas is argon, helium, or a mixture of argon and helium. In addition, the inner gas 7 may also contain hydrogen in addition to argon or a mixture of argon and helium.

[0017] The outer nozzle 5 ejects the outer gas 9. The outer gas 9 is located outside the inner nozzle 4 and flows through a passage surrounded by the outer nozzle 5. The outer gas 9 contains carbon dioxide. In addition, the outer gas 9 may also contain argon.

[0018] The torch switch circuit ON is a torch switch mounted on the welding torch WT. When the welding operator turns it on, it becomes a high level, and when turned off, it outputs a torch switch signal On that becomes a low level.

[0019] 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. 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 3 has occurred and outputs an arc generation discrimination signal Ad that becomes a high level.

[0020] 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 has ended, the period discrimination signal Tp = 0. 1) When the torch switch signal On changes to a high level, it outputs a period discrimination signal Tp = 1 (preflow period start). 2) When a predetermined delay time Td has elapsed from the time when Tp changes to 1, it outputs a period discrimination signal Tp = 2 (inner gas ejection start). 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 a high level, it outputs a period discrimination signal Tp = 3 (initial period start). 4) When a predetermined initial period has elapsed from the time when Tp changes to 3, it outputs Tp = 4 (steady welding period start). 5) Thereafter, when the torch switch signal On changes to a low level and then changes to a high level again, it outputs Tp = 5 (crater treatment period start). 6) Thereafter, when the torch switch signal On changes to a 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).

[0021] The first electrode minus-polarity current setting circuit INIR 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.

[0022] 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.

[0023] The steady-state inner gas flow rate setting circuit FICR takes the above second electrode minus-polarity current setting signal In2r as an input, inputs the second electrode minus-polarity current setting signal In2r [A] 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]. An example of the steady-state inner gas flow rate setting function is shown below. Ficr = (In2r - 75) / 50 + 3.5 ··· Equation (1) However, it is in the range of 75 ≤ In2r ≤ 150. When In2r < 75, it has the same value as In2r = 75. When In2r > 150, it has the same value as In2r = 150. Thus, as the value of the second electrode minus-polarity current setting signal In2r increases, the value of the steady-state inner gas flow rate setting signal Ficr increases.

[0024] The steady-state outer gas flow rate setting circuit FOCR may take the above second electrode minus-polarity current setting signal In2r as an input, input the second electrode minus-polarity current setting signal In2r [A] into the following predetermined steady-state outer gas flow rate setting function, and output the calculated value as the steady-state outer gas flow rate setting signal Focr [L / min]. An example of the steady-state outer gas setting function is shown below. Focr = (In2r - 75) / 50 + 5.5 ··· Equation (2) However, it is in the range of 75 ≦ In2r ≦ 150. When In2r < 75, it has the same value as In2r = 75, and when In2r > 150, it has the same value as In2r = 150. Thus, the larger the value of the second electrode minus-polarity current setting signal In2r, the larger the value of the steady outer gas flow rate setting signal Focr.

[0025] The flow rate reduction inner gas flow rate setting circuit FIIR takes the above-mentioned steady outer gas flow rate setting signal Focr as an input, performs the following calculation, and outputs the flow rate reduction inner gas flow rate setting signal Fiir [L / min]. The calculation calculates the inner gas flow rate Fi such that the flow rate of the inner gas 7 during the initial period is within ±20% of the flow rate of the outer gas 9. Fiir = Focr × R × K ··· Equation (3) However, R = (cross-sectional area of the flow path of the inner gas 7 in the inner nozzle 4) / (cross-sectional area of the flow path of the outer gas 9 in the outer nozzle 5), and K is a constant between 0.8 and 1.2. The above equation will be explained with numerical examples. Assuming the inner diameter of the inner nozzle 4 = 5 mm and the inner diameter of the outer nozzle 5 = 13 mm, then (cross-sectional area of the flow path of the inner gas 7 in the inner nozzle 4) = 3.14 × 2.5 × 2.5, and (cross-sectional area of the flow path of the outer gas 9 in the outer nozzle 5) = 3.14 × (6.5 × 6.5 - 2.5 × 2.5). As a result, R = 0.17.

[0026] 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 it may be set as Fipr = Fiir.

[0027] The inner gas flow rate setting circuit FIR takes the above-mentioned period discrimination signal Tp, the above-mentioned pre-flow inner gas flow rate setting signal Fipr, the above-mentioned flow rate reduction inner gas flow rate setting signal Fiir, and the above-mentioned steady inner gas flow rate setting signal Ficr as inputs, performs the following processing, and outputs the inner gas flow rate setting signal Fir. 1) When the period discrimination signal Tp=2 (pre-flow period), the value of the pre-flow inner gas flow rate setting signal Fipr is output as the inner gas flow rate setting signal Fir. 2) When the period discrimination signal Tp=3 (initial period), the value of the flow velocity 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 value of the steady-state inner gas flow rate setting signal Ficr increases over time, and then the value of the steady-state inner gas flow rate setting signal Ficr is output as the inner gas flow rate setting signal Fir. At this point, it is also possible to switch to the value of 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.

[0028] 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 inner gas flow rate Fi of the inner gas 7 flowing out of 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 inner gas 7 starts to be ejected when the delay time Td has elapsed from the time the torch switch is turned on and the pre-flow period begins, and stops when the after-flow period ends.

[0029] 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.

[0030] 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 outer gas flow rate Fo of the outer gas 9 flowing out of the outer gas cylinder 8 to a value determined by the outer gas flow rate setting signal For during the period when 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.

[0031] The voltage detection circuit VD detects the welding voltage Vw, converts it to an absolute value, and outputs a voltage detection signal Vd.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 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.

[0036] Next, the effects and advantages of the double-shielded TIG welding method according to the present invention will be explained.

[0037] The double-shielded TIG welding method according to the present invention uses a welding torch WT equipped with an electrode 1, an inner nozzle 4 surrounding the electrode 1, and an outer nozzle 5 surrounding the inner nozzle 4, and performs welding by applying a welding current Iw to generate an arc 3. The inner nozzle 4 ejects an inner gas 7 containing an inert gas. The outer nozzle 5 ejects an outer gas 9 containing carbon dioxide. With this configuration, the generation of the arc 3 is promoted by the inner gas 7, and oxidation of the electrode 1 is prevented by the inner gas 7. In addition, oxidation of the molten metal generated in the base material 2 is prevented by the outer gas 9. In this case, the total amount of inert gas contained in the inner gas 7 and outer gas 9 can be reduced compared to conventional methods. Therefore, the configuration of the double-shielded TIG welding method according to the present invention makes it possible to reduce welding costs.

[0038] The present invention is not limited to the embodiments described above. The specific configuration of each part of the present invention can be modified in various ways. [Explanation of symbols]

[0039] 1: Electrode, 2: Base material, 3: Arc, 4: Inner nozzle, 5: Outer nozzle, 6: Inner gas cylinder, 7: Inner gas, 8: Outer gas cylinder, 9: Outer gas, AD: Arc generation discrimination circuit, Ad: Arc generation discrimination signal, CI: Inner gas flow regulator, CO: Outer gas flow regulator, 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: Flow velocity reduction inner gas flow rate setting circuit, Fiir: Flow velocity reduction inner gas flow rate setting Constant 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, Iav: 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 In2: Negative polarity current setting signal for the second electrode, IN2R: Negative polarity current setting circuit for the second electrode, In2r: Negative polarity current setting signal for the second electrode, Ip1: Positive polarity current for the first electrode, IP1R: Positive polarity current setting circuit for the first electrode, Ip1r: Positive polarity current setting signal for the first electrode, Ip2: Positive polarity current for the second electrode, IP2R: Positive polarity current setting circuit for the second electrode, Ip2r: Positive polarity current setting signal for the second electrode, IR: Current setting circuit, Ir: Current setting signal, Iw: Welding current, ON: Torch switch circuit, On: Torch switch signal, PS: Weld Power supply, Ten: Negative polarity period of the electrode, Tep: Positive polarity period of the electrode, Tn1: Negative polarity period of the first electrode, TN1R: First electrode negative polarity period setting circuit, Tn1r: First electrode negative polarity period setting signal, Tn2: Negative polarity period of the second electrode, 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: Positive polarity period of the first electrode, TP1R: First electrode positive polarity period setting circuit, Tp1r: First electrode positive polarity period setting signal, Tp2: Positive polarity period of the second electrode,TP2R: Second electrode positive polarity period setting circuit, Tp2r: Second electrode positive polarity period setting signal, VD: Voltage detection circuit, Vd: Voltage detection signal, WT: Welding torch,

Claims

1. A double-shielded TIG welding method is used, which involves using a welding torch comprising an electrode, an inner nozzle surrounding the electrode, and an outer nozzle surrounding the inner nozzle, and applying a welding current to generate an arc for welding, The inner nozzle ejects an inner gas containing an inert gas, The aforementioned outer nozzle is used in a double-shielded TIG welding method that ejects an outer gas containing carbon dioxide.

2. The double-shielded TIG welding method according to claim 1, wherein the inert gas includes argon.

3. The welding torch comprises an electrode, an inner nozzle surrounding the electrode, and an outer nozzle surrounding the inner nozzle. The welding torch generates an arc by passing a welding current through it. The inner nozzle ejects an inner gas containing an inert gas, The outer nozzle is a double-shielded TIG welding apparatus that ejects an outer gas containing carbon dioxide.

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