JP2024081869A - Double shielded TIG welding method - Google Patents

Abstract

[Problem] To improve arc startability in a double-shielded TIG welding method. [Solution] In a double-shielded TIG welding method in which a welding torch equipped with an inner nozzle for spraying inner gas and an outer nozzle for spraying outer gas is used, and an arc is generated and a welding current Iw is passed to perform welding after preflow of the inner gas and outer gas is performed at the start of welding, the flow rate Fi of the inner gas is made smaller during a predetermined period including at least the period from the time preflow ends (time t3) to the time the arc is generated (time t31) or the time when the initial period has elapsed since then (time t32) than during the subsequent period. [Selected Figure] Figure 2

Description

The present invention relates to a double shielded TIG welding method.

A double-shielded TIG welding method is commonly used, in which welding is performed using a welding torch equipped with an inner nozzle that ejects an inner gas and an outer nozzle that ejects an outer gas (see, for example, Patent Document 1). Inert gases such as argon and helium are used as the inner and outer gases.

JP 2020-15048 A

Double-shielded TIG welding has the problem of poor stability when the arc is generated because the gas flow speed around the electrode is faster than in normal single-shielded TIG welding. In other words, double-shielded TIG welding can cause phenomena such as poor arc generation and poor stability after the arc is generated, as it fluctuates. This phenomenon is particularly noticeable when the welding current is a small current value of around 100A or less.

The present invention aims to provide a double-shielded TIG welding method that can improve stability during arc generation.

In order to solve the above-mentioned problems, the invention of claim 1 comprises:
A welding torch having an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used,
In a double shield TIG welding method, an arc is generated after preflowing the inner gas and the outer gas at the start of welding, and a welding current is applied to weld the material,
the flow rate of the inner gas is made smaller during a predetermined period including at least a period from the end of the preflow to a period from the occurrence of the arc or a period after the occurrence of the initial period than during a subsequent period;
This is a double shielded TIG welding method characterized by the above.

The invention of claim 2 is as follows:
The start time of the predetermined period is set to a time when the ejection of the inner gas during the preflow starts.
2. The double shielded TIG welding method according to claim 1 .

The invention of claim 3 is as follows:
The flow rate of the inner gas during the predetermined period is set to 50% or less of that during the subsequent period.
3. The double shielded TIG welding method according to claim 1 or 2.

The invention of claim 4 is as follows:
The flow rate of the inner gas during the predetermined period is changed in accordance with the value of the welding current.
3. The double shielded TIG welding method according to claim 1 or 2.

The invention of claim 5 is as follows:
The preflow ejects the inner gas after ejecting the outer gas.
3. The double shielded TIG welding method according to claim 1 or 2.

The double-shielded TIG welding method of the present invention can improve stability when an arc is generated.

1 is a block diagram of a welding apparatus for carrying out a double shielded TIG welding method according to an embodiment of the present invention. 2 is a timing chart of each signal in the welding apparatus of FIG. 1 , illustrating a double-shielded TIG welding method according to an embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a block diagram of a welding device for carrying out a double-shielded TIG welding method according to an embodiment of the present invention. Each block will be described below with reference to the figure.

The welding torch WT mainly comprises an electrode 1, an inner nozzle 4 surrounding it, and an outer nozzle 5 surrounding the inner nozzle 4. A tungsten electrode or the like is used for the electrode 1.

The welding start circuit ON outputs a welding start signal ON that goes to a high level when welding begins. This welding start circuit ON is a torch switch provided on the welding torch WT. In addition, when a welding robot is used, the welding start circuit ON may be provided in a robot control device (not shown).

The current setting circuit IR outputs a predetermined current setting signal Ir to set the value of the welding current Iw.

The preflow period circuit TP receives the above-mentioned welding start signal On as an input and outputs a preflow period signal Tp that remains at a high level until a predetermined preflow period has elapsed from the time the welding start signal On changes to a high level.

The inner gas ejection start circuit TI receives the preflow period signal Tp as input and outputs an inner gas ejection start signal Ti that goes to high level for a short period of time a predetermined delay time Td has elapsed since the preflow period signal Tp changed to high level. The delay time Td is shorter than the preflow period Tp.

The arc generation determination circuit AD detects the welding current Iw, and when the welding current Iw is flowing, it determines that an arc 3 is being generated and outputs an arc generation signal Ad that goes to high level.

The inner gas flow rate setting circuit FIR receives the preflow period signal Tp, the inner gas ejection start signal Ti, the arc generation signal Ad, and the current setting signal Ir as inputs, and outputs an inner gas flow rate setting signal Fir that becomes a predefined preflow inner gas flow rate value when the preflow period signal Tp changes to a high level, and becomes a predefined inner gas flow rate value determined according to the current setting signal Ir during the subsequent predetermined period, and thereafter becomes a predefined main welding inner gas flow rate value. The above-mentioned predetermined period is a period including at least the period from the end of the preflow to the time when the arc is generated or the time when the initial period has elapsed since the end of the preflow. The start of the predetermined period may also be the start of the ejection of the inner gas during the preflow. The predetermined period inner gas flow rate value is preferably set to 50% or less of the main welding inner gas flow rate value. More preferably, it is set to 30% or less. The predetermined period inner gas flow rate value may be set to 0. The predetermined period inner gas flow rate value is set according to the current setting signal Ir, and is set to be larger as the value of the current setting signal Ir increases. For example, when Ir≦50A, it is 0.5 l/min, when 50A<Ir≦100A, it is 1 l/min, and when 100A<Ir, it is 1.5 l/min. Also, for example, the pre-flow inner gas flow rate is 4 l/min, and the main welding inner gas flow rate is 5 l/min. Specific periods of the predetermined period are shown in 1) to 4) below.
1) The predetermined period is defined as the period from the end of the preflow period when the preflow period signal Tp changes to a low level to the arc generation time when the arc generation signal Ad changes to a high level.
2) The predetermined period is defined as the period from the end of the preflow period when the preflow period signal Tp changes to low level to the time when a predetermined initial period has elapsed since the arc generation signal Ad changes to high level.
3) The predetermined period is defined as the period from the start of the inner gas ejection when the inner gas ejection start signal Ti changes to a high level for a short period of time to the occurrence of an arc when the arc occurrence signal Ad changes to a high level.
4) The specified period is defined as the period from the start of the inner gas ejection when the inner gas ejection start signal Ti changes to a high level for a short period of time to the time when a predetermined initial period has elapsed since the arc generation signal Ad changes to a high level.

The inner gas flow regulator CI is a known gas flow controller or the like, and receives the above-mentioned welding start signal On, the above-mentioned inner gas ejection start signal Ti, and the above-mentioned inner gas flow rate setting signal Fir as inputs. During the period from when the inner gas ejection start signal To changes to a high level for a short period of time until the welding start signal On changes to a low level and a predetermined after-flow time has elapsed, the flow rate Fi of the inner gas 7 from the inner gas cylinder 6 is adjusted to a value determined by the inner gas flow rate setting signal Fir and ejected.

The outer gas flow rate setting circuit FOR receives the preflow period signal Tp as input, and outputs an outer gas flow rate setting signal For that is a predetermined preflow outer gas flow rate value when the preflow period signal Tp is at a high level, and is a predetermined main welding outer gas flow rate value when the preflow period signal Tp is at a low level. Here, it is desirable to set the preflow outer gas flow rate value to a value greater than the main welding outer gas flow rate value.

The outer gas flow regulator CO is a known gas flow controller or the like, and receives the above-mentioned welding start signal On, the above-mentioned preflow period signal Tp, and the above-mentioned outer gas flow setting signal For as input. During the period from when the welding start signal On changes to a high level to when the welding start signal On changes to a low level, the flow rate Fo of the outer gas 9 from the outer gas cylinder 8 is adjusted to a value determined by the outer gas flow setting signal For and sprayed.

An inner gas 7 flows through the passage inside the inner nozzle 4. An outer gas 9 flows through the passage outside the inner nozzle 4 and inside the outer nozzle 5. Inert gases such as argon and helium are used for the inner gas 7 and outer gas 9. The arc 3 is generated with the electrode 1 serving as the negative electrode and the base material 2 serving as the positive electrode.

The welding power source PS receives the above welding start signal On, the above preflow period signal Tp, and the above current setting signal Ir as inputs. When the welding start signal On goes high and the preflow period signal Tp goes low, it applies a high-frequency high voltage between the electrode 1 and the base material 2, and when an arc 3 is generated, it starts outputting the welding current Iw set by the current setting signal Ir, and when the welding start signal On goes low, it stops outputting the welding current Iw.

Figure 2 is a timing chart of each signal in the welding device of Figure 1, which shows a double-shielded TIG welding method according to an embodiment of the present invention. Figure (A) shows the change over time of the welding start signal On, Figure (B) shows the change over time of the preflow period signal Tp, Figure (C) shows the change over time of the inner gas ejection start signal Ti, Figure (D) shows the change over time of the outer gas flow rate Fo (liters/minute), Figure (E) shows the change over time of the inner gas flow rate Fi (liters/minute), Figure (F) shows the change over time of the welding current Iw, and Figure (G) shows the change over time of the arc generation signal Ad. Below, the operation at the start and end of welding will be explained with reference to the figures.

At time t1, when the welding operator turns on the torch switch provided on the welding torch WT in FIG. 1, the welding start signal On changes to a high level, as shown in FIG. 1 (A). In response to this, as shown in FIG. 1 (B), the preflow period signal Tp becomes a high level. At the same time, the outer gas starts to be ejected by the outer gas flow regulator CO in FIG. 1. As shown in FIG. 1 (D), 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.

At time t2, when a predetermined delay time Td has elapsed from time t1, the inner gas ejection start signal Ti goes to high level for a short period of time, as shown in FIG. 1C. In response to this, the ejection of the inner gas is started by the inner gas flow regulator CI in FIG. 1. As shown in FIG. 1E, the inner gas flow rate Fi becomes a predetermined pre-flow inner gas flow rate value determined by the inner gas flow rate setting signal Fir in FIG. 1.

At time t3, as shown in FIG. 1B, when the preflow period signal Tp becomes low level and the preflow period ends, as shown in FIG. 1D, the outer gas flow rate Fo becomes the actual welding outer gas flow rate value determined by the outer gas flow rate setting signal For in FIG. 1. At the same time, as shown in FIG. 1E, the inner gas flow rate Fi decreases to the predetermined period inner gas flow rate value during the predetermined period determined by the inner gas flow rate setting signal Fir in FIG. 1. The predetermined period is set to be a period including at least the period from the time t3 when the preflow ends to the time t31 when the arc occurs or the time t32 when the initial period has elapsed since then. The start time of the predetermined period may also be the time t2 when the inner gas starts to be ejected during the preflow. It is preferable that the predetermined period inner gas flow rate value is 50% or less of the actual welding inner gas flow rate value. It is even more preferable that it is 30% or less. The predetermined period inner gas flow rate value may be 0. The predetermined period inner gas flow rate value is set according to the current setting signal Ir in FIG. 1, and is set to be larger as the value of the current setting signal Ir increases. For example, when Ir≦50A, it is 0.5 l/min, when 50A<Ir≦100A, it is 1 l/min, and when 100A<Ir, it is 1.5 l/min. Also, for example, the pre-flow inner gas flow value is 4 l/min, and the main welding inner gas flow value is 5 l/min. Specific periods of the predetermined period are shown in 1) to 4) below. The figure shows the case of 2) as an example.
1) The predetermined period is defined as the period from the end time t3 of the preflow period when the preflow period signal Tp changes to low level to the arc generation time t31 when the arc generation signal Ad changes to high level.
2) The predetermined period is defined as the period from the end of the preflow period, time t3, when the preflow period signal Tp changes to low level, to time t32, when a predetermined initial period has elapsed since the arc generation signal Ad changes to high level.
3) The predetermined period is defined as the period from inner gas ejection start time t2, when the inner gas ejection start signal Ti changes to a high level for a short period of time, to arc occurrence time t31, when the arc occurrence signal Ad changes to a high level.
4) The specified period is defined as the period from the inner gas ejection start time t2, when the inner gas ejection start signal Ti changes to a high level for a short period of time, to a time t32, when a predetermined initial period has elapsed since the arc generation signal Ad changed to a high level.

At the same time, at time t3, the welding power source PS in FIG. 1 applies a high-frequency high voltage between the electrode 1 and the base material 2 in FIG. 1. Then, at time t31, an arc 3 is generated, and as shown in FIG. 1 (F), the flow of the welding current Iw begins. In response to this, as shown in FIG. 1 (G), the arc generation signal Ad changes to a high level. At time t32, when a predetermined initial period has elapsed from time t31, as shown in FIG. 1 (E), the inner gas flow rate Fi increases to the actual welding inner gas flow rate value determined by the inner gas flow rate setting signal Fir in FIG. 1. At this time, a slope of several hundred ms may be provided to increase the flow rate. The initial period is the period from when the arc 3 is generated until a stable state is reached. For example, it is set to 500 ms. The period during which the high-frequency high voltage is applied from time t3 to time t31 is about several tens to several hundred ms. To generate an arc, a high-voltage pulse of several kV may be applied instead of the high-frequency high voltage. In this way, welding is started.

According to the present embodiment described above, the flow rate of the inner gas is set smaller during a predetermined period, including at least the period from the end of preflow to the time when an arc occurs or the time when an initial period has elapsed since then, than during the subsequent period. In this way, the inner gas flow rate is set to be small during the period when high frequency high voltage is applied and the period until an arc occurs and becomes stable, so the flow rate of the gas around the electrode is slowed. As a result, the generation of an arc and the stability during the arc generation are improved.

More preferably, according to this embodiment, the start of the predetermined period is set to the start of the ejection of the inner gas during preflow. In this way, the flow rate of the inner gas is reduced before the high-frequency high voltage is applied, so the time from the start of application of the high-frequency high voltage to the generation of an arc can be shortened. As a result, workability is improved.

More preferably, according to this embodiment, the flow rate of the inner gas during a predetermined period is set to 50% or less of that during the subsequent period. In this way, the arc generation and stability during arc generation can be improved. It is even more preferable to set it to 30% or less. In this way, the arc generation and stability during arc generation can be improved.

More preferably, according to this embodiment, the flow rate of the inner gas during the specified period is changed according to the value of the welding current. In this way, the arc generation and stability during arc generation can be always improved regardless of the value of the welding current. By increasing the flow rate of the inner gas during the specified period as the value of the welding current increases, the arc generation state can be stabilized during the transition period from the specified period to the subsequent steady welding period.

According to the present embodiment described above, during the preflow period, the outer gas is ejected, followed by the inner gas. In this way, the ejection of the inner gas is started while the surroundings are shielded by the ejection of the outer gas, so that the inner gas does not entrain the surrounding air, and the steady state can be quickly converged to. For this reason, in this embodiment, the preflow time can be shortened to about 50% compared to the conventional technology in which the ejection of the outer gas and the inner gas is started at the same time. Therefore, in this embodiment, sufficient shielding can be ensured even if the preflow time at the start of welding is set short, so that the work efficiency can be improved and the consumption of expensive inert gas can be reduced. For example, in the conventional technology, it was necessary to set the preflow period to about 6 seconds, but in this embodiment, it can be set to about 3 seconds.

Furthermore, it is desirable to set the time during which only the outer gas is ejected from time t1 to t2 to be longer than the time during which the inner gas is ejected from time t2 to t3. In this way, it is possible to more reliably prevent the inner gas from entraining air, and therefore it is possible to set the preflow time even shorter.

Furthermore, it is desirable to set the inner gas flow rate Fi smaller during the preflow period than during the actual welding period after the end of the preflow period. In this way, the inner gas ejection state can be brought to a steady state more quickly, so that the preflow time can be set even shorter.

Furthermore, it is desirable to set the outer gas flow rate Fo to be greater during the preflow period than during the actual welding period after the end of the preflow period. In this way, the inner gas ejection state can be brought to a steady state more quickly, so that the preflow time can be set even shorter.

When the welding operator turns off the torch switch at time t4, the welding start signal On changes to low level, as shown in FIG. 1(A). In response to this, as shown in FIG. 1(F), the flow of the welding current Iw stops. This causes the arc 3 to be extinguished, as shown in FIG. 1(G), and the arc generation signal Ad goes low level. At the same time, as shown in FIG. 1(D), the outer gas flow rate Fo becomes 0, and the ejection of the outer gas stops.

At time t5, when a predetermined after-flow period has elapsed since time t4, the inner gas flow rate Fi becomes 0, as shown in FIG. 1(E), and the ejection of the inner gas stops. The after-flow time is set to about 7 seconds.

In the conventional technology, both the outer gas and the inner gas are ejected during the afterflow period. In contrast, in this embodiment, only the inner gas is ejected. The function of the afterflow is to shield the electrode and molten pool from the air until they are cooled. To achieve this function, it is sufficient to eject only the inner gas. In this way, the consumption of expensive inert gas can be reduced.

Numerical examples of the above parameters are shown below.
Welding torch WT: Welding torch equipped with a double shield nozzle with an inner nozzle inner diameter of 5 mm and an outer nozzle inner diameter of 13 mm Electrode 1: Tungsten electrode with a diameter of 3.2 mm Outer gas and inner gas: 100% argon gas Base material 2: Butt joint of mild steel with a plate thickness of 2.3 mm Welding current Iw: 150 A, welding speed: 30 cm/min
Outer gas flow rate Fo: Preflow period 12 l/min, main welding period 10 l/min
Inner gas flow rate Fi: Preflow period 4 l/min, Predetermined period 1.5 l/min, Main welding period 5 l/min
Preflow period: 3 seconds (the inner gas starts to jet 2 seconds after the outer gas starts to jet, and the arc occurs 1.1 seconds after that).
Afterflow period: 7 seconds

REFERENCE SIGNS LIST 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 determination circuit Ad Arc generation signal CI Inner gas flow regulator CO Outer gas flow regulator Fi Inner gas flow rate FIR Inner gas flow rate setting circuit Fir Inner gas flow rate setting signal Fo Outer gas flow rate FOR Outer gas flow rate setting circuit For Outer gas flow rate setting signal IR Current setting circuit Ir Current setting signal Iw Welding current ON Welding start circuit On Welding start signal PS Welding power source TI Inner gas jet start circuit Ti Inner gas jet start signal TP Preflow period circuit Tp Preflow period signal WT Welding torch

Claims (5)

A welding torch having an inner nozzle for ejecting an inner gas and an outer nozzle for ejecting an outer gas is used,
In a double shield TIG welding method, an arc is generated after preflowing the inner gas and the outer gas at the start of welding, and a welding current is applied to weld the material,
the flow rate of the inner gas is made smaller during a predetermined period including at least a period from the end of the preflow to a period from the occurrence of the arc or a period after the occurrence of the initial period than during a subsequent period;
A double shielded TIG welding method. The start time of the predetermined period is set to a time when the ejection of the inner gas during the preflow starts.
The double shield TIG welding method according to claim 1 . The flow rate of the inner gas during the predetermined period is set to 50% or less of that during the subsequent period.
3. The double shielded TIG welding method according to claim 1 or 2. The flow rate of the inner gas during the predetermined period is changed in accordance with the value of the welding current.
3. The double shielded TIG welding method according to claim 1 or 2. The preflow ejects the inner gas after ejecting the outer gas.
3. The double shielded TIG welding method according to claim 1 or 2.

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