JP2003170273A - Arc welding method using hollow electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an arc welding method capable of performing a high efficient welding of either aluminum material or magnesium material. <P>SOLUTION: A tungsten electrode 3 is formed into a hollow pipe, a DC voltage is applied with the tungsten electrode 3 being applied as a cathode and an aluminum material 5 arranged in opposition to the tungsten electrode being applied as an anode under a vacuum environment, argon gas is supplied through the tungsten electrode 3, an arc is generated in the gas to perform a welding of the aluminum material 5. An electron temperature in the arc plasma in this case is higher than an electron temperature measured through the prior art GTA process under an atmospheric pressure. The electrons in this case flow in a certain directional characteristic toward the anode. As a result, it is possible to perform a welding operation with a positive polarity (SP) arc having the electrode 3 as a cathode in which an oxidation film (alumina) at the surface is removed, and consumption of the electrode is restricted to improve a welding operation efficiency. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc welding method using a hollow electrode in which an aluminum material or a magnesium material useful as a space structure material is used as an object to be welded.

[0002]

2. Description of the Related Art The construction of large structures in outer space has become a reality, as represented by the construction of the International Space Station (ISS), which began in November 1998.
The ISS currently under construction is assembled by mechanical joining without using welding when assembling in outer space. However, in the near future, safe and highly reliable welding technology will be required for maintenance of various infrastructures in space and construction of large structures. The characteristics of outer space are mainly the microgravity environment and the vacuum environment. Regarding the welding technique in such an environment, the electron beam welding method, which can be used even in a vacuum state, has been studied mainly, but the problem of safety etc. remains unsolved.

By the way, in general, the most extensive research
The arc welding method is used. For example, welding of aluminum alloy is usually performed by GTA (gas tungsten arc) welding. Here, this GTA welding will be briefly described. FIG. 7 schematically shows the tip structure of a welding torch used in conventional GTA welding. A solid rod-shaped tungsten electrode 23 is provided at the tip of an internal hollow welding torch 21 via a collet body 22, and a cylindrical nozzle 24 surrounding the collet body 22 is attached to the outer periphery of the lower side of the collet body 22. Has been. Welding is performed by applying a voltage between the electrode 23 and the object to be welded 25 arranged facing the electrode 23, and generating an arc between them. At this time, as shown by the solid line arrow in the figure, the torch 21 and the collet body 2 are
2 is supplied with a shield gas, for example Ar gas,
The shielding gas is jetted downward from the gas outflow hole 22a in the lower end side wall of the collet body 22 in the nozzle 24, whereby an inert gas atmosphere is formed between the tungsten electrode 23 and the object to be welded 25. As a result, welding is performed while preventing deterioration of the workpiece 25.

The materials for the space structure described above are mainly aluminum alloys and magnesium alloys. Therefore, it is conceivable to adopt the above-mentioned GTA welding as a safe welding method for the welding in space for these.

[0005]

However, when the conventional GTA welding used in the atmospheric pressure is used in a low pressure environment, as the pressure decreases, the potential gradient of the arc column decreases and the arc Becomes unstable and becomes 10 Tor
It is difficult to start the arc below r (about 1 × 10 ³ Pa). Therefore, it is difficult to generate and maintain the arc discharge in outer space as usual.

Further, in the case of welding, for example, an aluminum material by conventional GTA welding, it is necessary to perform welding by an AC arc or a reverse polarity (RP) arc in which an electrode is an anode in order to remove a surface oxide film. ing. In other words, the melting point of aluminum is 933K, whereas the melting point of the oxide film (Al ₂ O ₃ ) is about 2300K. Therefore, when welding with a positive polarity (SP) arc with the tungsten electrode 23 as the cathode, Although the aluminum itself of the material is molten, the oxide film on the surface remains as it is, which hinders the joining. Therefore, in order to remove the oxide film, the cleaning action of the cathode spots generated on the cathode surface is used, and normally an AC arc is used from the viewpoint of heat input and oxide film removal. Therefore, in conventional GTA welding,
There is a drawback that sufficient work efficiency cannot be obtained.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object thereof is arc welding using a hollow electrode capable of highly efficiently welding an aluminum material or a magnesium material under a space environment or the like. To provide a method.

[0008]

Therefore, in the arc welding method using a hollow electrode according to a first aspect of the present invention, a hollow electrode 3 is used as a cathode and an aluminum material 5 is used as an anode in a vacuum environment to apply a direct current voltage, It is characterized in that an inert gas is supplied through the electrode 3 and an arc is generated in the inert gas to weld the aluminum material 5.

As described above, when the hollow electrode 3 is used, an arc can be generated between the hollow electrode 3 and the object to be welded even under a low pressure by adjusting the flow rate of the inert gas supplied therethrough. it can. Moreover, the electron temperature in the arc plasma generated with the polarity in which the hollow electrode 3 is the cathode and the aluminum material 5 is the anode is the conventional GT under the atmospheric pressure.
Electrons having a temperature higher than the electron temperature in A welding and having high energy can be concentrated and flow into the anode surface. As a result, the oxide film on the surface of the aluminum material 5 is removed, and a deeper penetration can be obtained as compared with the conventional GTA welding under the atmosphere. Therefore, even if the object to be welded is the aluminum material 5, with the positive polarity (SP) arc using the hollow electrode 3 as the cathode as described above,
Welding can be performed without the oxide film (alumina) on the surface, so electrode wear is suppressed, and in addition, the deep penetration as described above improves welding work efficiency, and the amount of thermal deformation Is reduced and welding accuracy is improved.

In the arc welding method using a hollow electrode according to a second aspect of the present invention, a DC voltage is applied in a vacuum environment using the hollow electrode 3 as a cathode and a magnesium material as an anode, and the hollow electrode 3 is used.
It is characterized in that an inert gas is supplied through the arc and an arc is generated in the inert gas to weld the magnesium material.

Also in this case, since the arc generated in the inert gas becomes a concentrated heat source having a high heat input energy in the same manner as described above, even if the magnesium material is required to have a particularly high surface cleanliness during welding. Therefore, it is not necessary to separately perform the surface cleaning work, and therefore high quality welding can be performed with high efficiency.

An arc welding method using a hollow electrode according to claim 3 is the method according to claim 1 or 2, wherein 10 Torr
It is characterized in that the above welding is performed in a vacuum environment on the higher vacuum side.

That is, in the conventional GTA method, 10 Tor
While it was difficult to start and maintain the arc in a vacuum environment higher than r, the above method using the hollow electrode 3 can be performed in such a vacuum environment to obtain the above effects. Therefore, especially in a space environment, it can be applied as a suitable welding method with high safety and high work efficiency for aluminum materials and magnesium materials.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, specific embodiments of an arc welding method using a hollow electrode according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of the main part of a welding apparatus used for carrying out the arc welding method using the hollow electrode of the present invention. In the figure, 1 is a hollow internal welding torch, and the tip of the welding torch 1 is
A tungsten electrode 3 is provided via a collet body 2. Further, a cylindrical nozzle 4 surrounding the collet body 2 is attached to the outer periphery on the lower side.

The tungsten electrode 3 is formed in the shape of a hollow pipe. At the time of welding, as indicated by a solid arrow in the drawing, an inert gas such as Ar gas supplied from above through the welding torch 1 is blown out toward the workpiece 5 below through the hollow tungsten electrode 3. It has become so.

As described above, when a hollow pipe-shaped tungsten electrode 3 is used, and a voltage is applied between the electrode 3 and the object to be welded 5 while ejecting a small amount of inert gas through the electrode 3, a low pressure is applied. , For example, 10 Torr (≈1
It is possible to generate and maintain an arc in an inert gas atmosphere even in a vacuum environment on the higher vacuum side than x10 ³ Pa). Hereinafter, using the hollow pipe-shaped tungsten electrode 3 as described above, an arc generated under a low pressure with the tungsten electrode 3 as a cathode is used as an HCA (Ho11ow Cathode Ar).
c), the arc welding method according to the present invention in which welding is performed by using this arc is referred to as an HCA method. In order to apply this HCA method to welding of an aluminum material, an aluminum material is used as the workpiece 5. The results of various experiments will be sequentially described. These experiments were carried out by installing the welding apparatus including the above-described welding torch 1 in a vacuum chamber (not shown) connected to an exhaust pump including a rotary pump and a mechanical booster pump.

FIG. 2 is a schematic diagram showing the appearance of the discharge actually observed during the bead-on-plate welding experiment using pure aluminum (A1050) as the object to be welded. At this time, the tungsten electrode 3 has an outer diameter of 4.
A hollow tungsten electrode containing 0% and an inner diameter of 3.0 mm and containing 2% thorium oxide was used. As an inert gas, A
While flowing r gas at a flow rate of 0.167 ml / s, the valve between the vacuum chamber and the exhaust pump was adjusted to maintain the pressure in the vacuum chamber at 5 Pa.

Further, a DC voltage was applied to the tungsten electrode 3 as a cathode and an object to be welded (hereinafter also referred to as a base material) as an anode to generate an arc, and the arc current was 150A. Arc length (distance between electrode 3 and work piece) is 1
It is set to 0 mm. The size of the test piece as the object to be welded at this time is 70 mm × 150 mm × thickness 10 mm.
The welding speed is set to 5 mm / s by the method of fixing the torch and moving the base metal.

During this welding experiment, it was observed that the arc plasma 6 emitting blue light was formed in a substantially columnar shape from the electrode 3 to the base metal as shown by the broken line in the figure. On the bead surface just below the electrode, red plasma different from blue plasma was observed. This is considered to be metal vapor from the surface of the base material, and is considered to be aluminum vapor since the base material is pure aluminum (purity 99.5% or more). Further, a metallic glossy portion was observed in the bead central portion 7 shown by hatching in the figure after solidification. From these, it is considered that the oxide film on the surface of the base metal is removed immediately below the electrode during welding, and aluminum appears. When observing the appearance of the beads after such bead-on-plate welding, a metallic glossy portion having a width of about 3 mm is observed in the central portion of the bead from the welding start end to the welding end, and this metallic luster appears. The oxide film was removed from the part.

3 (a) to 3 (c) show the shape of a bead cross section (a position 70 mm from the welding start position) in a test piece obtained by performing such a bead-on-plate welding experiment. There is. In the figure (a), the arc current I = 100 A,
The figure (b) is I = 150A, the figure (c) is I = 200A.
Other conditions are the same as above.

FIGS. 6 (d) to 6 (f) show a conventional GT in the atmospheric pressure using the solid tungsten electrode shown in FIG.
It is the shape of the bead cross section in the test piece obtained by performing the same bead-on-plate welding experiment by A welding (hereinafter, referred to as the conventional GTA method). In this case, a tungsten electrode with a diameter of 3.2 mm and containing 2% cerium oxide was used, and the base material was pure aluminum (A105
0). The flow rate of Ar gas as shield gas is 16
7 ml / s, arc length and welding speed are 2 m each
m, 5 mm / s. The arc current I is set to 100 A as in the case of FIG. 9A, (d) is the same, and I = 150 A is the same (e), I = 200.
The A type is shown in FIG. In addition, the average arc voltage V measured during the experiment is additionally shown in each of FIGS.

Comparing (a)-(c) and (d)-(f) in the figure, the melting amounts of both are clearly different, and H
When CA is used, it is several times more. This difference in the amount of melting increases as the arc current increases, and when HCA is used, the back surface is melted when the arc current is 200A.

Thus, when HCA is used, the positive electrode (S) having the tungsten electrode 3 as the cathode and the base material as the anode (S
P) Despite the arc, the oxide film on the surface of the aluminum material was removed, and the melting amount was large. The reason for this is that in the HCA method, the heat input energy to the base metal is conventionally G
It is considered to be higher than that of the TA method. Thus, the Langmuir probe method is used to measure the electron density and temperature of the HCA plasma when aluminum is used for the anode. The results will be described below.

In this case, in order to measure a stable plasma, the stationary arc plasma was used as the target, not the moving plasma. The discharge conditions are the same as above, pressure 5 Pa, arc length 10 mm, gas flow rate 0.1.
67 ml / s and arc current 100A. Even when aluminum was melted by the static arc at this time, it was confirmed that pink plasma was generated from the surface of the molten pool directly below the electrode, and a metallic luster with a diameter of about 5 mm from the surface of the molten pool after the experiment. There was a surface with a mark.

FIG. 4 shows the cathode obtained by this measurement.
It is an electron density distribution between base materials (anode). In addition, on the horizontal axis of the graph, a thick line is added over the range corresponding to the size of the molten pool described above. As shown in the graph, the density distribution does not spread so much between the electrode base materials, and plasma tends to gather in the central portion near the anode surface. In addition, the maximum value of the electron density is 1.0 × 10 ²⁰ / m ³ near the arc center axis, and in the plasma by the conventional GTA method under atmospheric pressure,
Considering that it will be about 10 ²³ / m ³ just below the electrode, it is about 1/1000 of this.

FIG. 5 shows the measurement result of the electron temperature distribution.
Electron temperature distributions in the arc radius direction were measured at heights of 2, 4, 6, 8, and 9 mm from the anode. At any height, the electron temperature is the highest near the center of the arc and shows a value of about 55,000-60,000K. The temperature drops sharply in the radial direction,
It shows around 20,000K near the periphery. The arc column temperature of argon-shielded tungsten cathode / copper anode under atmospheric pressure is about 20,000K measured near the cathode regardless of the arc current. To do. Therefore, the electron temperature in HCA is much higher than that in general atmospheric pressure GTA.

The reason why the electron temperature in HCA is high can be explained as follows. That is, FIG. 6B schematically shows a potential distribution in an arc generated by the conventional GTA method under atmospheric pressure. The arc voltage V _{a in} this case is V _a = V _C + V _P + V _A where V _C : cathode drop voltage, V _P : arc column drop voltage, V
_A : Anode drop voltage.

On the other hand, in the case of HCA under a low pressure, the discharge itself penetrates into the inside of the cathode as shown in FIG. Therefore, it is necessary to consider the arc column drop voltage inside the cathode. Therefore, the arc voltage V at this time
_a is V _a = V _C + V _A + V _PE + V _PI, where V _{C is the} cathode drop voltage, V _PI is the arc column drop voltage within the cathode V _{PE is the} external arc column drop voltage, and V _{A is the} anode drop voltage. .

In this way, the arc column drop voltage V _PI in the cathode is
Is further added, the overall arc voltage rises. This appears in the arc voltage V shown in FIGS. 3 (a) to 3 (f), and the arc voltage in the HCA method ((a) to (c) in the figure) is the same as that in the conventional GTA method. The value is larger by 10 V or more than ((d) to (f) in the figure). Then, the electrons in the HCA plasma are accelerated by the electric field from the inside of the cathode, and as a result, the electrons having high energy flow toward the anode surface with directivity.

As is clear from the above description, in the HCA method, the electron temperature is high and the electrons with high energy flow toward the anode surface with directivity. Therefore, the HCA plasma serves as a concentrated heat source with a high heat input energy, and as a result, it is possible to remove the oxide film on the surface of the aluminum material, and the melting amount is higher than that in the conventional GTA method. It is possible to perform welding that is significantly larger.

The experimental results concerning the HCA welding method for aluminum, which is a promising material for space structures, have been described above. However, in order to actually use it as a space welding technique, it is further applicable to butt welding and the like. It is also necessary to consider Particularly in the case of aluminum, it is necessary to perform bonding with the oxide film removed over the entire abutting surface.

Therefore, pure aluminum (A
In addition to 1050), an aluminum alloy (A2219) that is actually used for the space shuttle is also used to perform a butt welding experiment with a plate thickness of 3 mm, which is closer to the actual welding conditions, and the radiation is applied to the joint. A transmission test and a tensile test were carried out. The results will be described below. In the welding experiment, two test pieces of 70 mm × 150 mm × thickness of 3 mm were butted against each other, and a copper plate was used as a backing for the purpose of preventing the joint from sagging and melting.

When the appearance of the welded portion after the butt experiment was observed, the width of the surface near the center of the bead was 2-, regardless of whether the material was A1050 or A2219.
A part having a metallic luster in which the oxide film was removed was formed at about 2.5 mm. Looking at the back surface, a bead width similar to that of the front surface was obtained, and a sufficient penetration state reaching the back surface was observed.

Further, as a result of a radiation transmission test of these bead portions, it was found that the welded portions were well welded without containing welding defects such as blowholes. Generally A100
In 0 series pure aluminum, it is said that blowholes are likely to occur depending on the welding conditions. When actually performing butt welding using AC GTA in the atmosphere, blowholes are confirmed at the joints. Was done. When HCA is used, the reason why the number of blowholes can be reduced is that there is almost no air entrained in the arc atmosphere due to the low pressure, and the gas flow rate is very small. There is almost no water. It is impossible to remove the dissolved hydrogen contained in the base material, but it is possible to remove the water and organic substances that have adhered to or adsorbed to the surface of the base material, which is said to be the cause of blowholes. By eliminating the supply source, the generation of blowholes can be suppressed in HCA as compared with the case of using the welding method in the atmosphere.

Next, the result of a tensile test will be described in order to investigate the joint strength of the welded portion using HCA. In the case of A1050, it was observed that not the butt portion or the bead portion was broken, but the base material was clearly broken. It is a fracture in the heat affected zone where the strength was reduced. In the case of A2219, the fracture occurred on the boundary between the bead portion and the heat affected zone.

Table 1 shows the tensile strength of each test piece obtained in the tensile test. Further, in the same table, the tensile test results of the test pieces that have been butt-welded with AC GTA at atmospheric pressure are also shown. In addition, a tensile test of the base material without welds was also conducted.
0 base metal has an average tensile strength of 115.7 MPa, A22
The tensile strength of 19 base materials was 249.6 MPa on average.

[0037]

[Table 1]

As shown in the table, the tensile strength of the welded portion when HCA was applied to A2219 was 2 on average.
It is 33.0 MPa, which is almost equal to the tensile strength of the base material, and sufficient strength is obtained. Also A105
When HCA is applied to 0, the tensile strength is 6 on average.
8.7 MPa, which is about 60% of the base material tensile strength
Has become. However, considering that the tensile strength when AC GTA is applied at atmospheric pressure is 62.8 MPa on average, the tensile strength is higher than that, and sufficient strength can be obtained at A1050. There is.

As described above, by using HCA as a heat source for aluminum welding, it is possible to perform welding with the oxide film on the surface removed even during butt welding, and further, it becomes difficult for blowholes to be included in the joint. From HCA
The welds made using the alloy have strengths equal to or higher than those of GTA welds at atmospheric pressure.

As described above, according to the HCA method,
As compared with the conventional GTA method in the atmosphere, a deep penetration of several times to ten times can be obtained, the welding work efficiency is remarkably improved, and the thermal deformation amount is reduced to improve the welding accuracy. Moreover, even if the object to be welded is an aluminum material, it is possible to perform welding in which the surface oxide film has been removed by a positive polarity (SP) arc using the tungsten electrode as a cathode. Therefore, the electrode wear is suppressed, the welding work efficiency is improved, and the welding work can be completed in a short time, so that the amount of thermal deformation is reduced and the welding accuracy is improved.

Although the specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. For example, in the above, A105 is used as the aluminum material.
Although 0 and A2219 have been described, other aluminum alloys can be used as the objects to be welded.

Furthermore, by applying the above-mentioned HCA method to the welding of the magnesium material made of magnesium or its alloy as the work to be welded, high quality welding can be performed with high efficiency welding work. That is, also in this case, the arc generated in the inert gas becomes a concentrated heat source with high heat input energy as described above, and thus, even in the case of a magnesium material that requires particularly surface cleanliness during welding, There is no need to perform a separate surface cleaning operation, and therefore good quality welding can be performed with high efficiency.

Further, in the above embodiment, the shape of the hollow tungsten electrode, the welding conditions and the like have been described by exemplifying specific numerical values, but the present invention is not limited to these numerical values. For example, for pressure conditions, 10 Torr
The above welding can be performed in a vacuum environment on the higher vacuum side than (≈1 × 10 ³ Pa). Even under such a low pressure, it is possible to start the discharge at a voltage of 1 kV or less, and most easily discharge when the ambient pressure is about 27 Pa. Further, on the vacuum side higher than 27 Pa,
It has been confirmed that the discharge start voltage depends on the gas flow rate, and an increase in the discharge start voltage can be suppressed by increasing the gas flow rate. As described above, even in a low-pressure environment where it is difficult to start or maintain an arc in the conventional GTA method, the above-described effects can be obtained by appropriately setting the welding conditions.

On the other hand, it is possible to use a gas other than Ar gas as the inert gas, and also as a non-consumable hollow electrode, in addition to tungsten containing thorium oxide,
For example, lanthanum oxide-containing tungsten, cerium oxide-containing tungsten, or a tantalum tube, zirconium, or other high melting point material having a good thermoelectron emission capability can be used.

[0045]

As described above, according to the arc welding method using the hollow electrode of the first aspect, it is possible to obtain a heat source in which the heat input energy is highly concentrated due to the polarities of the hollow electrode as the cathode and the aluminum material as the anode. As a result, the oxide film on the surface is removed and a deep penetration can be obtained. As a result, electrode consumption is suppressed and welding work efficiency is improved, and the amount of thermal deformation is reduced, and welding accuracy is improved.

Also in the arc welding method using the hollow electrode according to the second aspect, since the arc in the inert gas supplied through the hollow electrode becomes a concentrated heat source with high heat input energy, the surface cleanliness is particularly high during welding. Even for the required magnesium material, it is not necessary to separately perform a surface cleaning operation, and therefore, similar to the above, good quality welding can be performed with high efficiency.

In the arc welding method using the hollow electrode according to claim 3, the welding using the hollow electrode as described above is performed in a vacuum environment in which it is difficult to start and maintain the arc in the conventional GTA method. Since the above-mentioned effects can be obtained, it can be applied to aluminum materials and magnesium materials as a welding method having high safety and excellent work efficiency, especially in a space environment.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration of a main part of a welding apparatus used for carrying out an arc welding method of the present invention.

FIG. 2 is a perspective view schematically showing an arc column observed during a bead-on-plate welding experiment of an aluminum material using the above apparatus.

FIG. 3 is a view showing a shape of a cross section of a base metal obtained in a bead-on-plate welding experiment of an aluminum material, and FIGS. The figure which shows the shape of the cross section of the formed base material, FIG.
(F) is a figure which shows the shape of the base material respectively obtained by the conventional GTA welding method in atmospheric pressure.

FIG. 4 is a graph showing measurement results of electron density in an arc generated by using a hollow tungsten electrode as a cathode.

FIG. 5 is a graph showing measurement results of electron temperature in an arc generated by using a hollow tungsten electrode as a cathode.

6A and 6B show changes in potential along the central axis of the arc. FIG. 6A is an explanatory diagram of changes in potential in an arc generated by using a hollow tungsten electrode as a cathode, and FIG. 6B.
FIG. 6 is an explanatory diagram of a potential change in an arc generated by a conventional GTA welding method under atmospheric pressure.

FIG. 7 is a schematic cross-sectional view showing a configuration of a main part of an apparatus used in conventional GTA welding.

[Explanation of symbols]

1 welding torch 2 collet body 3 hollow electrodes 5 Workpiece (aluminum material)

Claims (3)

[Claims] 1. A hollow electrode (3) is used as a cathode in a vacuum environment,
A direct current voltage is applied using the aluminum material (5) as an anode, and an inert gas is supplied through the hollow electrode (3),
An arc welding method using a hollow electrode, wherein an arc is generated in the inert gas to weld the aluminum material (5). 2. A hollow electrode (3) is used as a cathode in a vacuum environment,
A hollow electrode characterized in that a direct current voltage is applied using a magnesium material as an anode, an inert gas is supplied through the hollow electrode (3), and an arc is generated in the inert gas to weld the magnesium material. Arc welding method using. 3. The arc welding method using a hollow electrode according to claim 1 or 2, wherein the welding is performed in a vacuum environment on a higher vacuum side than 10 Torr.