JPH0736958B2 - Double gas shield metal arc welding method - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a double gas shield metal arc welding method. More specifically, it is generally known as a so-called MAG (MAG) welding method which is an arc welding method in which carbon dioxide gas or a mixed gas of carbon dioxide gas and an inert gas such as argon is used as a shield gas and a welding wire is used as an electrode. In the method, the shield gas supply is divided into two, at least an inert gas is provided around the welding tip, and further carbon dioxide gas (carbon dioxide) is annularly provided outside the welding tip, that is, a MAGCI welding in general. Method or a DMAG welding method.

[0002]

2. Description of the Related Art Double gas shield metal arc welding method (hereinafter referred to as MAGCI or DMAG welding method)
This was the first MAGCI welding method to be offered to the market by Lomen Heller in West Germany in 1979, and Alexander Bünzel manufactured and sold the welding torch. A schematic diagram of this welding process and nozzle is shown in FIGS. 1 and 2, respectively.

In FIG. 1, 1 is a reel, 2 is a welding wire, 3 is a captire and a conduit, 4 is a double nozzle welding torch, 5 is a base metal, 6 is a welding power source, 7 is a moving carriage, 8
Is an inert gas container such as argon or helium, 9 is a carbon dioxide gas container, and 10 is an active gas container such as oxygen, hydrogen or carbon dioxide gas. Further, in FIG. 2, 11 is an outer nozzle, 12 is an inner nozzle, 13 is an outer gas distributor, 14 is a contact tip, 15 is a droplet, 16 is a molten pool, and 17 is an arc.

However, during practical use of the welding process, the spatter that is generated adheres to the nozzle.
The gas flow rate of the outer nozzle changed, stable welding became impossible, it could not be used continuously, and it was forced to abandon sales without being accepted by the market. Then, Nagoya University of Masumoto, by Kutsuna et al., Is again research is performed for the reduction of sputtering, the announcement of the results over two degrees in 1988 and 1989, the prospect of practical use has been built. The main contents of the result are: (1) Welding parameters (especially arc voltage and welding current) are properly adjusted (30V / 30
0 A) By selecting, and (2) by selecting the flow rate ratio of argon of the inner nozzle gas and carbon dioxide gas of the outer nozzle gas to be an appropriate value (28%) or more, stable droplet spray transfer is performed. , Low spatter, and
(3) By changing the welding wire from the solid wire to the flux cored wire, the result of lower spatter is obtained.

As a result of these achievements, the amount of spatter can be reduced more than ever, and the "normal MAG welding" (80% argon +
Compared with the mixed gas shielded metal arc welding method using a mixed gas of 20% carbon dioxide gas) and the carbon dioxide gas arc welding method, the welding result was equal to or better than that of the carbon dioxide arc welding method.

At the time of the invention of MAGCI, since the rigorous examination of the welding conditions and the quantitative evaluation of the spatter were incomplete as described above, sufficient measures could be taken and stable droplet transfer could be maintained in the practical stage. It is thought that it could not be done.

The present inventors have further studied the results at Nagoya University, and recently, especially in welding robots and automation, stable operation and improvement of operation rate, and strict low spatter regarding product appearance, labor workability, etc. When,
Furthermore, it is necessary to ensure stable maintenance of this low sputter state over time, that is, technology that meets today's practical requirements, and, instead of argon as the inner nozzle gas, use argon instead of helium and / or oxygen, hydrogen, etc. By using the mixed gas with the active gas added, the experimental research on the technology to improve the quality of the welded part and the remarkable welding productivity due to the lower spatter and the increased penetration than the conventional DMAG welding method. The goal was to realize it as a practical technology in a wider market.

The major technical features of the DMAG welding method are the following three points.

(1) Argon, which is the inner nozzle gas, or a mixed gas of argon and helium, acts on the arc region and stabilizes the formation, separation and migration of droplets. Specifically, spray transfer is performed by reducing the diameter of the droplets and steadily moving away in the axial direction, and also prevents the occurrence of spatter caused by a short circuit between the welding wire and the molten pool.

(2) When helium, oxygen, or hydrogen is added to the inner nozzle gas in addition to argon, the arc is concentrated and the penetration depth can be expected to increase.

(3) Carbon dioxide gas, which is the outer nozzle gas, effectively prevents the mixture of the atmosphere, and partially acts on the molten pool to physically and metallurgically affect the penetration of the welded portion, etc. Control mechanical properties and quality.

That is, the gas of each of the inner and outer nozzles individually and intensively acts on the droplet forming / separating portion, the atmosphere and the molten pool, and the effect thereof is appropriately and efficiently exhibited. In the welding method using a mixed gas of argon and carbon dioxide, which is called the above-mentioned method, the amount of the inert gas such as expensive argon or helium is not only reduced but also the shielding gas is significantly reduced as compared with the case where the above two areas are acted on average. The effect of is superior. Therefore, excellent results can be obtained with respect to reduction of the amount of spatter generated, mechanical properties of the welded portion, welding defects, and the like.

[0013]

However, in order to ensure that such characteristics are exhibited, both the arc region and the molten pool have appropriate gas compositions, and they maintain stable conditions over time. Needs to be done. For that purpose, the gas discharged from the inner and outer nozzles must be mixed to have a constant composition and should not vary with time. In other words, if this fluctuates, stability of droplet transfer, spatter generation,
The mechanical properties of the welded part fluctuate, and the stability cannot be obtained.

The main factors that determine the gas composition are the mutual relationship of the flow conditions of the gas flow of the inner and outer nozzles, the distance between the nozzle and the arc area, the distance between the nozzle and the molten pool, etc., when a fixed nozzle is used. Mutual relationship.

[0015] These have not been sufficiently conducted in the conventional research, and they are only slightly exemplified as the proper values for the total gas amount and the ratio of argon / carbon dioxide gas.
The mechanism and quantitative examination of the action effect of gas have not been sufficiently done. Therefore, a general-purpose method for determining the optimum welding conditions such as gas flow rate has not been found. In order to bring out the excellent features of DMAG as a practical technique, it is necessary to clarify these.

The problem to be solved in the practical technique of the DMAG welding method is to achieve a strict low spatter which can be applied to robot welding etc., and to achieve stable welding with excellent welding quality. , The mechanism of the double gas shield is clarified, and (1) a method for universally determining the proper gas flow rate and composition regardless of the type of inner and outer nozzle gas, (2) between the nozzle and the arc region and the molten pool It is to develop the technology such as the method of determining the proper relationship position of.

[0017]

The double gas shield metal arc welding method of the present invention uses a welding torch having a double nozzle to generate a stable arc between an electrode and a welded joint to form a molten pool. In order to protect from the atmosphere and to control the physical properties of the molten pool at the same time, it is necessary to flow carbon dioxide gas to the outer nozzle and inert gas or a mixed gas with a small amount of active gas added to the inner nozzle at the same time. A double gas shield metal arc welding method including: (a)
The flow rate of carbon dioxide gas flowing through the outer nozzle is at room temperature and atmospheric pressure.
Within the range of 10 to 25 liters / minute, (b) the flow rate of the inert gas flowing through the inner nozzle or the mixed gas obtained by adding a small amount of the inert gas to the inert gas is 4 to 18 liters at room temperature and atmospheric pressure. / Min, and (c) the gas flow of both the inner and outer nozzles is in the laminar flow region, and the flow condition at both nozzle ends is Reynolds number Re = DUρ / μ (D: equivalent flow path diameter at nozzle end) , U: gas flow velocity at the nozzle end, ρ: density of the gas at room temperature and atmospheric pressure, μ: viscosity of the gas at room temperature and atmospheric pressure, and the difference in Reynolds number between the inner and outer nozzle ends (ΔRe = Outer nozzle Re
-The gas flow rate of each nozzle is set so that Re) of the inner nozzle is in the range of 0 to 500.

[0018]

[Operation] In the case of the double gas shield, the nozzle structure is such that the inner nozzle gas mainly flows toward the arc region forming droplets and the outer nozzle gas flows so as to act on the molten pool. . The state of this gas flow is schematically shown in FIG.

At the tip of the nozzle, as shown in FIG. 3, the outer surface of each of the contact tip and the inner nozzle is tapered so that the inner tip and the outer nozzle gas are both focused in the axial direction. It flows to connect. Both gases are in a laminar flow state, and the contact time is extremely short, on the order of milliseconds.
Even in the vicinity of the high temperature plasma arc, they do not mutually diffuse and do not mix with each other. On the other hand, although the shape of the gas flow itself can be slightly changed depending on the degree of the gas flow condition, in the case of the double gas shield, the flow condition of the outer nozzle gas is usually superior to that of the inner nozzle gas. As shown in, the outer nozzle gas enters inside in the vicinity of the arc region. Therefore, the ratio of the amounts of both gases reaching the arc region changes variously depending on the distance between the nozzle tip and the arc region or the difference in the flow state of the outer nozzle gas and the inner nozzle gas. This pattern is shown in Figure 4.
7 to 7 schematically show typical examples.

FIG. 4 shows the case where the flow condition of the outer nozzle gas is extremely larger than that of the inner nozzle gas, and the inner nozzle gas hardly reaches the arc and the outer nozzle gas becomes dominant. FIG. 5 shows the case where the difference in the flow conditions is small, the inner nozzle gas reaches the arc sufficiently, and the outer nozzle gas slightly affects the arc. Unlike FIG. 4 to FIG. 5, FIG. 6 is a case where the inner nozzle gas has a better flow condition than the outer nozzle gas and almost only the inner nozzle gas reaches the arc region. Furthermore, Fig. 7 shows the case where the distance from the nozzle to the arc region is significantly increased. Normally, the flow condition of the outer nozzle gas is better, so the mixing point of both gases does not reach the arc, so almost all of the arc If it is affected by the outer nozzle gas.

The gas reaching these arc regions is immediately ionized in high temperature plasma. For example, when the inner nozzle is argon and the outer nozzle is carbon dioxide gas, usually Ar ions, O
It becomes ions, CO molecules, and electrons, and at this stage, both gases are mixed. The abundance and state in these arc regions greatly affect the state of droplet formation and separation. Therefore, in order to obtain a desirable stable spray transfer and a spatter-free state, the composition of the shield gas in the arc region must be appropriate and the welding parameters must be adapted to the arc voltage, welding current, etc., corresponding thereto.

As described above, the shield gas flows are laminar, and the composition of the gas reaching the arc region changes depending on the difference in the flow conditions, but the condition at the nozzle tip is the decisive factor for this flow condition. . Generally, what controls the flow condition of a fluid is the flow velocity, the density, the viscosity of the fluid and the equivalent diameter of the flow path. In fluid dynamics, the flow condition is a dimensionless quantity Reynolds number Re = DUρ / μ (D: equivalent diameter ,
U: flow velocity, ρ: density, μ: viscosity). Therefore, by using the Re number, the flow state can be expressed in a unified manner regardless of the type of gas, and further, the difference in the Re number at the nozzle tip portion between the outer nozzle gas and the inner nozzle gas (hereinafter referred to as ΔRe) is used. Therefore, the composition of the mixed gas in the arc region can be inferred. In fact, it is known that when the welding parameters are properly selected, there is a certain relationship between the shield gas composition and the droplet transfer morphology. For example, when welding steel using a mixed gas of argon and carbon dioxide, the arc is unstable with pure argon, but a small oxygen potential, for example, 2% oxygen (volume%, and so on). (Expressed in volume%) improves the stability of the arc by reducing the mobility of the arc root as well as promoting the ionization of oxygen due to the lower ionization potential of oxygen than argon. That is, a small amount of oxygen is necessary for arc stability. However, when the oxygen content exceeds 5%, short circuit transfer and globular transfer occur conversely with the increase, which causes arc instability and spatter increase. Carbon dioxide has the same effect, and is 3-5.
% Addition is good for arc stability, but if it is 8 to 10% or more, the arc becomes unstable and spatter increases. Furthermore, if the carbon dioxide gas is 30% or more, no matter how much the current is increased, it will not be a spray transfer and an unstable arc similar to carbon dioxide welding,
It becomes a state of very much spatter. On the other hand, a high carbon dioxide composition is preferable from the viewpoint of improved penetration and gas cost. In the case of a single nozzle, in practice, a "normal mag" mixture gas with an intermediate carbon dioxide composition of about 15 to 20% is used. The "welding method" is commonly used.

In short, when welding is performed by adopting appropriate welding parameters according to the type and composition of the shield gas, controlling the amount of spatter means controlling the amount of carbon dioxide gas mixed in the arc region. It will be. From the above, it was inferred that ΔRe and the carbon dioxide composition in the arc region were proportional, and that the carbon dioxide composition was proportional to the sputter amount. Therefore, assuming that ΔRe and the sputter amount were proportional, this relationship was experimentally determined. As a result of the investigation, it was possible to obtain a very significant correlation and to obtain a result of extremely low spatter which was not available in the past, and at the same time, to maintain this continuously and stably, regarding the outer nozzle flow rate and the relational position with respect to the base material of the nozzle. I found a way to decide the conditions. Next, this will be specifically shown in Examples.

[0024]

【Example】

Example 1 Carbon dioxide gas was used as the outer nozzle gas, argon was used as the inner nozzle gas, the flow rate of the inner and outer nozzle gases was changed, and welding of the bead-on-plate was performed with welding parameters such that the most stable droplet transfer was obtained. The amount of adhered spatter was measured. At the same time, we photographed the droplet transfer with a high-speed stationary camera and recorded the waveform of the arc voltage welding current, and observed the droplet transfer situation. The welding conditions were as follows.

Welding conditions Welding wire: Solid wire 1.2mmφ DD50S Base material: SM-50A 12mm thickness Arc voltage / welding current: 30V / 300A Welding speed: 400 mm / min Welding time: 3 minutes Welding torch: Bunzel double Gas shield nozzle Distance between tip and base material: 18mm Respective flow rate of both inner and outer nozzle gas Re
FIG. 8 is a graph showing the number of nozzles sputtered and the value obtained by subtracting the Re number of the argon stream from the Re number of the carbon dioxide stream. The numerical values used for the calculation are shown in Table 1.

[0026]

[Table 1]

Also, the equivalent diameter of the double gas shield channel is such that the outer nozzle is an annular channel of 18 mmφ and 11 mmφ, and Deq =
18-11 = 7 mm, the inner nozzle is an annular passage of 8.5 mmφ and 4 mmφ, and Deq = 8.5-4 = 4.5 mm.

As is clear from FIG. 8, ΔRe is approximately 100.
The amount of nozzle spatter becomes the minimum around, and the amount of spatter relatively increases as ΔRe increases. On the other hand, when ΔRe is negative, that is, when the flow condition of argon in the inner nozzle is superior, the sputter amount is increasing. As described above, these indicate that as the flow of carbon dioxide in the outer nozzle increases, the amount of carbon dioxide mixed in the arc region increases almost proportionally, and the nozzle spatter amount increases. When the situation becomes worse than that of argon, it is considered that spatter is generated due to the instability observed in the arc of pure argon.

When ΔRe = 120, the amount of spatter is 0.0088.
Very low spatter results of gram / min were obtained.
This is an excellent result, which is an order of magnitude different from the lowest value of 0.06 g / min obtained in the previous studies. In the middle region of ΔRe (400 to 800), there are variations such as when the amount of spatter is low and when it is high. Among them, when ΔRe is 400 to 500, there are variations, but it is in a relatively low sputter range, but Δ
When Re is 700 to 800, there are variations up to very high places. This is because the carbon dioxide composition in the arc region is estimated to be about 12 to 22% when ΔRe is in the range of 400 to 800, short-circuit transfer and spray transfer coexist, and even slight fluctuations in the carbon dioxide composition are subtle in the droplet transfer mode. It is shown that there is a change over time during welding because it is in the range where changes occur in. However, among these, in the low carbon dioxide gas range close to 10% composition, the spray transfer is the main and the spatter amount and its fluctuation are small. On the other hand, when observing the current waveforms recorded at the same time, for ΔRe 100 to 200, regular and clean waveforms showing spray transfer continue (see FIG. 9), but
At ΔRe = 400 to 800, an unstable waveform showing an instantaneous short circuit as shown in Fig. 10 was observed to coexist with the above spray transfer waveform over time, which supports the reasoning for the above variation. There is. When ΔRe is 1000 or more, the carbon dioxide gas arc clearly occurs and excessive spatter is generated.

Under the condition that the outer nozzle is 18 l / min of carbon dioxide gas and the inner nozzle is 7 l / min of argon,
ΔRe = 750, but in the previous research results, this droplet transfer mode was found to be a mixed gas with a single nozzle (80% Ar + 20
% CO ₂ ), the carbon dioxide gas in the arc region in the case of ΔRe = 750 is assumed to be mixed from the outer nozzle so as to be 20%. If proportional to ΔRe, ΔRe = 120
Carbon dioxide is estimated to be about 4%, and ΔRe = 400 is estimated to be about 12%.

These are also confirmed from the observation result of the droplet transfer morphology, and the above inference can be proved. Therefore, ΔRe is 0 to 500, preferably 100 to 40
It is clear that stable welding with very low spatter can be obtained by setting the flow rate so that it becomes zero.

In the case of ΔRe = 120, the nozzle gas flow rate in the outer nozzle was 13 liters / minute of carbon dioxide gas and the inner nozzle was 7 liters / minute of argon. Considering this as an average mixed gas composition, carbon dioxide gas 65 %, Argon 35%, and if this composition is used for a single nozzle, the state of extremely high spatter is obviously the same as carbon dioxide welding. In the case of the double nozzle, as described above, the composition of carbon dioxide gas 4% and argon 96% is estimated in the droplet transfer region, resulting in extremely good droplet transfer and extremely low spatter. Therefore, in order to obtain the same state as this with the single nozzle system, it is necessary to use about 2.7 times the amount of argon so that it can be easily understood from the above composition value, which is a great advantage from the viewpoint of gas cost.

The welding current is usually preferably in the range of 150 to 800 amps, and the arc voltage is in the range of (I / 50 + 20) to (I / 50 + 37) (I: welding current expressed in amps). Is preferred.

Example 2 Carbon dioxide gas was used as the outer nozzle gas, a mixed gas of argon and helium was used as the inner nozzle gas, the flow rates of the inner and outer nozzle gases were changed, and the bead-on-plate was welded with the same welding parameters as in Example 1, The amount of spatter adhering to the nozzle was measured. The composition of the inner nozzle gas was 4Ar / 3He. FIG. 11 is a graph showing the correspondence between ΔRe and the nozzle sputter amount in the same manner as in Example 1. As is clear from FIG. 11, even in the case of the mixed gas of argon and helium, as in the case of only argon (Example 1), a clear proportional relationship is recognized between ΔRe and the nozzle sputter amount. In this case as well, in the intermediate region of ΔRe, as in the case of only argon, there is a large variation in the nozzle sputter amount, indicating that there is a problem in steadiness. Further, in the case of this embodiment, the relatively low ΔRe
However, the amount of spatter is about twice that of the case of using argon only, but this is because the arc voltage of 30 V adopted in this experiment is insufficient because of the presence of helium, which has a high ionization potential. This is because the arc was slightly unstable because spray transfer was not obtained. The purpose of the present example is to find out that the same relationship exists in the case of a mixed gas of argon and helium as in the case of argon alone.

Example 3 It was confirmed from the above Examples 1 and 2 that the same relationship of ΔRe, nozzle sputter amount and droplet transfer was obtained regardless of the type of the inner nozzle gas. It was confirmed that when the mixed gas of argon and helium was used for the inner nozzle, if the optimum parameters were adopted, the low sputterability could be obtained more than the case of only argon. The welding conditions were as follows.

Welding conditions Shield gas: outer nozzle carbon dioxide gas 15 l / min, inner nozzle 7.5 l / min Argon +2.5 l / min Helium arc voltage: 34-40 V Welding current: 300-500 A Welding speed: 500 mm / min Welding time: 1 minute Chip-base metal distance: 20 mm The bead-on-plate was welded in the same manner as in Example 1 under other conditions. Further, the wire feed amount was increased to change the deposition amount, and an appropriate voltage / current combination was selected accordingly to maintain a preferable droplet transfer. The results of the nozzle sputter amount are shown in Table 2.

[0037]

[Table 2]

In this example, based on the preferable range of ΔRe found in Examples 1 and 2, the shield gas composition and flow rate were selected in consideration of the preferable shield gas composition in terms of welding quality characteristics. It was 360.

Comparing the values of the amount of sputtering in Table 2 with the results of Example 2, as can be seen from FIG. 11, in the case of ΔRe = 360, it clearly decreased to about 1/3.

This is because stable droplet transfer was obtained by adopting appropriate parameters as described above. On the other hand, also in comparison with FIG. 8 showing the result of Example 1, the amount of spatter is reduced to about 60% in the vicinity of ΔRe = 360. This is because, as a result of the high heat input due to the addition of helium, the droplet size is further reduced and the scattered spatter is reduced. In Examples 1 and 2, the deposition amount was constant, but in this Example, the deposition amount was changed stepwise and was increased up to about 1.9 times. You can see that you got the result.

In this case, the gas composition in the arc region is estimated to be about 70% Ar + 23% He + 8% CO _2, which is almost the same as the composition suitable for mild steel.

Example 4 Carbon dioxide gas was used for the outer nozzle, and a mixed gas of argon, helium and oxygen was used for the inner nozzle, and welding was performed under the same conditions as in Example 2 with appropriate welding parameters. The results are shown in Table 3.

[0043]

[Table 3]

In this embodiment, ΔRe of the shield gas flow is 40
It is in the range of 0 to 500, but if the proper voltage is selected, the same ΔRe
In the case of the inner nozzle gas argon (Example 1), the nozzle sputter amount was reduced to about 1/3, and a mixed gas of argon and helium (Example 3) was used.
Even when compared with the estimated value when ΔRe is the same, the decrease is about 1/2 (see FIG. 11). In addition to the effect of helium described in Example 3, this is a current value that must be exceeded in order to reduce the surface tension of the droplet due to oxygen, reduce the droplet diameter, and obtain spray transfer. This is because the droplet transfer becomes more stable due to a decrease in the "transition current," etc., and thus scattered spatter is greatly reduced.

In this example, 0.1 liter / min of oxygen was added to the inert gas.
It was found that the amount of sputter was reduced when at least one of 0.1 to 5% oxygen and 0.1 to 3% hydrogen was added as an active gas.

Example 5 Carbon dioxide gas was used for the outer nozzle and a mixed gas of argon, helium and carbon dioxide gas was used for the inner nozzle, and the same welding as in Example 2 was performed. The results are shown in Table 4.

[0047]

[Table 4]

In this example, an extremely high sputter amount was recorded in all cases, which means that the ΔRe of the shield gas flow was
Although it is low at 420 or less, the carbon dioxide gas from the outer nozzle and the carbon dioxide gas in the inner nozzle are added together, and the carbon dioxide composition in the arc region becomes high. For example, if the shielding gas is 1 liter / min for the outer nozzle and 6 liter / min for the inner nozzle (4 argon / 3 helium) + 1 liter / min for carbon dioxide, the carbon dioxide composition in the arc region is about 23. A high value is estimated as%. If the hypothetical ΔRe is calculated assuming that all the carbon dioxide gas in the inner nozzle is mixed in from the outer nozzle, it becomes 790, which is the same as in the high ΔRe state.
If e is used, the relationship between ΔRe and the amount of nozzle sputter is the same as in the other embodiments.

Further, in the present embodiment, the carbon dioxide gas flow rate of the outer nozzle gas is kept low at 11 liters / minute to reduce ΔRe. However, in order to further reduce ΔRe, it is necessary to reduce this flow rate to the atmosphere. It also affects the shield of. Therefore, putting carbon dioxide into the inner nozzle is not preferable in terms of spatter measures, and it is appropriate to control the composition of carbon dioxide in the arc region by controlling the amount of carbon dioxide mixed in the arc region depending on the amount of carbon dioxide in the outer nozzle. is there.

Embodiment 6 In Embodiments 1 to 5, the nozzles and the base material were in the same relational position, and both were arranged so that both gas flows from the nozzle were focused in the arc region. In this embodiment, the relational position is changed and the droplet transfer state and the spattering when the nozzle is farther from the base material are described.

The welding conditions are exactly the same as in Example 1, and the relational positions between the nozzle and the base material are shown in FIG. 8 in comparison between Example 1 and Example 6.

By changing the combination of the inner and outer gas flow rates, Δ
The result of welding over a wide range of Re is shown in FIG. 8 by a dotted line in comparison with Example 1.

As is clear from FIG. 8, in this embodiment, Δ
Regardless of Re, the amount of spatter is constant at a relatively low level, which is completely different from those of Examples 1 to 5.
In any of the examples, the arc region was separated from the mixing point of both nozzle gas flows, and an excessive carbon dioxide gas state or a pure argon state was generated, and the arc became extremely unstable and spatter increased. However, the amount of spatter is comparatively low in both cases, because the distance from the arc start position to the nozzle is 13 mm (20 mm) for the inner nozzle and 5 mm (13 mm) for the outer nozzle. It is thought to have decreased. The instability of droplet transfer can also be supported by the fact that the recorded current waveform shows an irregular waveform indicating many short circuits. Increasing the distance to the base material in order to reduce the nozzle adhesion amount is not preferable considering the effect of blocking the arc region from the atmosphere and the effect of gas to the molten pool, and is usually 10 to 15 mm. . Therefore, it is preferable to keep the distance between the outer nozzle end and the base material to be 15 to 20 mm. On the other hand, considering the effect of the gas on the arc region, it is not preferable that the inner nozzle is too far apart, and the distance between the inner nozzle and the base material is preferably 15 to 25 mm, considering the structural dimensions of the nozzle. In the distance between the tip and the base metal
18-23 mm is preferable.

[0054]

As described above, in the double gas shield metal arc welding of the present invention, the difference ΔRe between the Re of the outer nozzle gas and the Re of the inner nozzle gas is set to fall within the range of 0 to 500. Therefore, it is possible to obtain an effect that a state of an extremely low sputter amount can be stably and continuously achieved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a welding apparatus used in a welding method of the present invention.

FIG. 2 is a schematic sectional view of a DMAG welding torch.

FIG. 3 is an explanatory view of the vicinity of the nozzle tip in the DMAG welding method.

FIG. 4 is an explanatory diagram of the vicinity of the nozzle tip when ΔRe is large.

FIG. 5 is an explanatory diagram of the vicinity of the nozzle tip when ΔRe is small.

FIG. 6 is an explanatory diagram in the vicinity of the nozzle tip when ΔRe has a negative value.

FIG. 7 is an explanatory diagram of the vicinity of the nozzle tip when the distance between the nozzle and the base material is excessive.

FIG. 8 is a graph showing the relationship between ΔRe and the amount of nozzle sputtering in Example 1.

FIG. 9 is a graph showing a current waveform when ΔRe is in the range of 100 to 200 in Example 1.

10 is a graph showing a current waveform when ΔRe is 400 to 800 in Example 1. FIG.

FIG. 11 is a graph showing the relationship between ΔRe and the amount of nozzle sputtering in Example 2.

[Explanation of symbols]

 2 Welding wire 4 Double nozzle welding torch 5, 20 Base metal 11 Outer nozzle 12 Inner nozzle 15 Droplet 16 Molten pool 17 Arc 18 Carbon dioxide flow

Claims (6)

[Claims] 1. A welding torch having a double nozzle is used to generate a stable arc between an electrode and a welded joint to protect the molten pool from the atmosphere and to control the physical properties of the molten pool at the same time. A double gas shielded metal arc welding method comprising simultaneously flowing carbon dioxide gas to the outer nozzle and inert gas or a mixed gas containing a small amount of active gas added to the inner nozzle at the same time. The flow rate of carbon dioxide gas flowing through the nozzle is within a range of 10 to 25 liters / minute at room temperature and atmospheric pressure, and (b) the inert gas flowing through the nozzle or a mixture of the inert gas and a small amount of active gas added. The gas flow rate is within the range of 4 to 18 liters / minute at room temperature and atmospheric pressure, and (c) the gas flow of both the inner and outer nozzles is in the laminar flow region, and the flow condition at the end of both nozzles is Reynolds number Re. = DUρ / μ D: flow path equivalent diameter at nozzle end, U: gas flow velocity at nozzle end, ρ: density of gas at room temperature and atmospheric pressure, μ: viscosity of gas at room temperature and atmospheric pressure, both inside and outside Reynolds number difference at nozzle end ΔRe = Re at outer nozzle end-Re at inner nozzle end is set so that the gas flow rate of each nozzle is in the range of 0 to 500. Double gas shield. Metal arc welding method. 2. The welding method according to claim 1, wherein the ΔRe is in the range of 100 to 400. 3. The welding method according to claim 1, wherein the welding current is in the range of 150 to 800 amperes. 4. The arc voltage is (I / 50 + 20) to (I / 50).
The welding method according to claim 1 or 2, wherein the range is +37) (I: welding current expressed in amperes). 5. The mixed gas flowing through the inner nozzle is an inert gas to which at least one of 0.1 to 5% by volume of oxygen and 0.1 to 3% by volume of hydrogen is added as an active gas. 2. The welding method described in 2. 6. The distance between the outer nozzle end and the welding base metal is 15 to 20 m.
The welding method according to claim 1 or 2, wherein m and the distance between the inner nozzle end and the welding base material are set to 15 to 25 mm.