JP2012011407A - Method for manufacturing welding joint and welding device for executing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding control means allowing a heat input amount not to fluctuate even when a groove sectional area fluctuates when manufacturing a welding joint formed of a steel plate with a plate thickness of >50 mm without using a specified expensive instrument.SOLUTION: When welding is carried out at a constant voltage by moving upward a truck mounted with a welding torch along a groove of a steel plate and two electrode vertical electrogas arc welding is carried out by controlling the truck to move upward following ascending speed of a melt pool based on a welding current, the welding torch is mounted on the truck so as to be moved, the moving speed of the truck is measured, and difference between the moving speed and reference welding speed preliminarily set is calculated for each constant interval. When there is difference, the welding torch is moved upward or downward with a constant distance to change the length of the protrusion of the welding wire, wire feeding speed is changed corresponding to the change of the welding current to control the welding current so as to become constant, and the ascending speed of the melt pool is made to coincide with the reference welding speed to allow heat input during welding to be constant so that welding is carried out.

Description

  The present invention relates to the manufacture of a welded joint using two-electrode vertical electrogas arc welding, and in particular, a welded joint capable of obtaining a high-toughness welded joint by suppressing fluctuations in heat input relative to groove shape fluctuations. The present invention relates to a manufacturing method and an apparatus for carrying out the method.

  In recent years, with the increase in the size of steel structures, steel sheets with higher thickness and higher strength have been used for the construction of steel structures. There is a demand for higher efficiency, higher quality, and higher strength welded joints.

Conventionally, for vertical welding of thick steel plates, the electrogas arc welding method (EGW method) capable of high-efficiency one-pass welding has been frequently used. A thick steel plate has been used, and it has become difficult to obtain a sound weld and sufficient joint characteristics by the conventional EGW method in one pass.
For this reason, based on the EGW method, a two-electrode vertical electrogas welding method shown in Patent Documents 1 and 2 has been developed for the purpose of stabilizing the penetration of the weld and further improving the welding efficiency.
However, in recent years, extra-thick steel plates of more than 50 mm, particularly 70 mm or more have been used in container ships, etc., and there has been a tendency for heat input to steel materials to become even greater heat input, ensuring toughness of welded joints. Difficult situations have come to be seen.

Here, with reference to FIG. 1, the manufacturing method of the welded joint by automatic welding using the two-electrode vertical electrogas welding method is demonstrated.
In the two-electrode vertical electrogas welding, the two flux-cored welding wires 3 and 3 are supplied to the groove 2 extending in the vertical direction of the two steel plates 1 and 1 arranged in the vertical direction while facing upward. Welding is performed.
In order to automatically perform welding, the first and second welding torches 4 and 5 for supporting and guiding the welding wires 3 and 3 are supported and guided by the rail 7 attached along the groove 2 and are raised. 6 is installed. In order to prevent the molten pool from flowing out during welding, a water-cooled copper metal 8 rising together with the carriage 6 is provided on the groove surface side, and a backing material 9 made of ceramics is provided on the groove back side. Be placed.
In addition to the welding torch, the carriage is equipped with a driving device that swings the welding torch, a driving device for the carriage, and a control device for them.

  The first and second welding torches 4 and 5 are connected to welding power sources 12 and 13, respectively, and a constant voltage is supplied between the welding wire and the steel plate guided by the welding torches. For example, the welding power sources 12 and 13 are connected such that a positive polarity voltage is supplied to the welding wire on the back surface side and a reverse polarity voltage is supplied to the welding wire on the front surface side. A current detecting means 14 is interposed between the welding power source 13 connected to the welding torch 5 on the surface side and the steel plate 1. The operations of the wire feeding devices 10 and 11, the traveling device of the carriage, and the welding power source are controlled by the welding control device 15.

In welding, the welding wires 3 and 3 are respectively supplied at a constant speed. Further, the cart 6 is based on a command from the welding control device 15 so as to run at a low speed running according to the reference welding speed and at a high speed running speed that recovers when the running of the cart is delayed. It is controlled by the cart traveling control means 16.
As welding progresses, a molten pool is formed in the groove, and the carriage 6 first rises at a low speed. When the traveling speed of the trolley is increasing at a low speed, the rising speed of the molten pool surface (hereinafter sometimes referred to as the molten metal surface) is set to be slightly higher than the rising speed of the trolley. Therefore, since the surface of the molten pool gradually approaches the tip of the welding torch, the length of the wire protruding from the welding tip of the welding torches 4 and 5 becomes short, and the welding current value increases.
Thereafter, when the welding current value exceeds a predetermined value, the welding control device 15 instructs the carriage travel control means 16 to cause the carriage 6 to travel at a high speed. Then, when the carriage 6 rises at a high speed, the tip of the welding torch is separated from the molten metal surface again, the protruding length of the wire becomes longer, and the welding current value becomes a predetermined value or less, the welding controller 15 sends the carriage traveling control means. A command for running the carriage at a low speed is output to 16, and the carriage 6 rises at a low speed.
By repeating this operation, the welding torch can be raised following the rise of the molten pool while maintaining the welding current within a predetermined range, and the molten metal surface and the tip of the welding torch And the protruding length of the wire is controlled to be substantially constant.

According to the method for manufacturing a welded joint using such a welding control method, since welding can be automatically performed using two welding torches, even when a thick base metal is welded, Further, since the penetration of each part of the groove side is good and the welding speed is high, the work efficiency can be improved.
However, when a welded joint of a steel plate having a larger thickness, particularly a steel plate having a thickness of more than 50 mm, is manufactured by welding using the conventional welding control method as described above, it is in the middle of the groove portion where the steel plate is formed. In addition, when there is a portion where the groove cross-sectional area fluctuates due to work accuracy such as a route gap, the following problem has arisen.

For example, when there is a part where the groove width is wider than the reference width in the middle, when the carriage reaches that part, the feeding speed of the welding wire is controlled to be constant, so the rising speed of the molten pool decreases. It becomes like this. As a result, the time of the low-speed traveling period of the bogie is longer than that when the portion having the reference width is welded. For this reason, the welding speed of the location falls and the amount of heat input becomes large.
Thick plate welding is basically welding with a large heat input, but at locations where the groove width increases, the increase in heat input due to the decrease in welding speed is further superimposed, so The heat becomes excessive, the width of the weld heat affected zone increases, and the toughness of the welded joint cannot be ensured.
On the other hand, when there is a narrow groove in the middle, the heat input becomes conversely too small and the strength of the welded joint becomes excessive. Even in this case, the toughness of the welded joint cannot be ensured.

Under these circumstances, to produce a welded joint with assured toughness, the amount of deposited metal per unit time changes according to the groove cross-sectional area without changing the welding speed even if the groove width varies. It is necessary to make it.
As a means for that, it is conceivable to detect a groove shape such as a groove width and a groove angle, and control the wire supply speed according to the detected groove shape, but this is a disturbance in the welding environment. There are many factors, and it is difficult to accurately detect the groove shape in real time, and there is a problem that it is expensive.
Also, as a method of controlling the amount of deposited metal that can be implemented at low cost using the characteristics of arc welding, when the welding current value changes due to factors such as the shape change of the work piece, it automatically responds accordingly. It is also known from Patent Document 3 that the wire feed speed is changed to always make the weld bead of a constant size. Conventionally, the heat input is kept constant simultaneously with the formation of a uniform weld bead. There was no particular consideration for making it.

JP-A-10-118771 Japanese Patent Laid-Open No. 11-285826 JP-A 63-295062

  Therefore, in the present invention, particularly when manufacturing a welded joint of a thick steel plate having a plate thickness exceeding 50 mm using the electrogas arc welding method, even if the groove cross-sectional area varies, the welding heat input does not vary. It is an object of the present invention to provide a high-toughness welded joint by providing the control means without using expensive special equipment.

  In the conventional two-electrode vertical electrogas arc welding method, as described above, the welding speed follows the rise of the molten pool, and as the groove cross-sectional area increases, the molten pool rise speed (that is, the welding speed) increases accordingly. ) Slows down and heat input increases. This is considered to be because there is no mechanism for changing the wire feeding amount (that is, the wire feeding speed) in accordance with the rising speed of the molten pool.

Therefore, the inventors have made the welding speed constant so that the wire feeding speed can be changed according to the rising speed of the molten pool when manufacturing a welded joint using two-electrode vertical electrogas arc welding, A method for keeping the heat input constant even when the groove cross-sectional area fluctuated was investigated.
As a result, if the rise speed of the molten pool changes, if the wire protrusion length of the welding torch is forcibly changed and the wire feed speed is changed and controlled accordingly, the rise speed of the molten pool surface Was found to be consistent with the reference welding speed, and the heat input in the longitudinal direction of the groove can be made constant while keeping the welding speed constant.
The gist of the present invention thus made is as follows.

(1) A carriage equipped with two welding torches is raised along the groove of the steel sheet to be welded and welding is performed at a constant voltage, and the carriage is brought to the rising speed of the molten pool based on the welding current. A method of manufacturing a welded joint by performing two-electrode vertical electrogas arc welding with control to follow and rise,
The welding torch is attached to a carriage so that the welding torch can be moved along the welding direction, the movement speed of the carriage is measured, and a difference from a preset reference welding speed is calculated at regular intervals. In some cases, the welding torch is raised or lowered by a certain distance to change the protruding length of the welding wire, and the welding current is made constant by changing the wire feeding speed according to the change in welding current generated at that time. A method for manufacturing a welded joint, characterized in that two-electrode vertical electrogas arc welding is performed with the heat input during welding kept constant by matching the ascending speed of the molten pool with the reference welding speed.
(2) The method for manufacturing a welded joint according to (1), wherein a steel plate having a thickness of more than 50 mm is welded.
(3) Welding that mounts two welding torches and supplies a constant voltage between the carriage that rises along the groove of the steel sheet to be welded and the welding wire and the steel sheet guided by each welding torch. A power source, a welding wire feeding means, a current detection means for detecting a welding current, and a traveling speed of the carriage is controlled based on the detected welding current so that the carriage rises following the rising speed of the molten pool. A two-electrode vertical electrogas arc welding device having a dolly traveling speed control means,
The welding apparatus further supports the welding torch and is attached to the carriage so that the welding torch can be moved up and down along the traveling direction of the carriage, the moving speed measuring means of the carriage, and at regular intervals. Calculating the speed difference between the moving speed of the carriage and a preset reference welding speed, and determining whether the speed difference is within a set range; and when the speed difference exceeds the set value The welding torch support base is controlled to be raised or lowered by a certain distance, and the welding wire feeding speed is controlled so that the welding current changed at that time becomes a preset value. A two-electrode vertical electrogas arc welding apparatus for carrying out the method for manufacturing a welded joint according to (1) or (2).

  In the two-electrode electrogas welding method for thick steel plates, even if the groove cross-sectional area varies, a welding control means that does not change the heat input amount can be provided without using expensive special equipment. In particular, a welded joint having excellent toughness can be obtained even in welding thick steel plates having a thickness exceeding 50 mm.

It is a figure for demonstrating the apparatus used for implementation of the manufacturing method of the conventional welding joint by 2 electrode standing electrogas arc welding, and its manufacturing method. It is a figure for demonstrating the apparatus used for implementation of the manufacturing method of the welding joint of this invention by 2 electrode standing electrogas arc welding, and its manufacturing method. It is a figure for demonstrating the control flow used with the two-electrode standing electrogas arc welding method of this invention. It is a figure which shows one example of the groove | channel used in the Example. It is a figure which shows the other example of the groove | channel used in the Example. It is a figure which shows the collection position of the test piece in an Example.

In manufacturing a welded joint using two-electrode vertical electrogas arc welding, the inventors have made it possible to change the wire feeding speed according to the rising speed of the molten pool, to keep the welding speed constant, A method for keeping the heat input constant even when the cross-sectional area fluctuated was studied.
In order to make the heat input constant, the reference welding speed is set in advance, the difference between the melting pool ascending speed (actual welding speed) and the reference welding speed is detected, and the difference is detected It is necessary to change the feed rate of the welding wire so that the rising speed of the molten pool matches the reference welding speed.

Therefore, in the present invention, as described above, when controlling the rise of the carriage 6 to follow the rise of the molten metal surface based on the welding current, the rising speed of the carriage is calculated at regular intervals, The difference between the ascending speed and the standard welding speed is calculated.
Further, the welding torch support base 18 is attached so that the two welding torches 4 and 5 can move within a predetermined range with respect to the carriage 6, and a certain difference is detected between the rising speed of the carriage and the reference welding speed. If this happens, the welding torch is moved either up or down to forcibly change the protruding length of the wire. Then, since a welding current changes according to it, it controls so that a wire feed speed is changed and a welding current returns to the preset fixed value. Thereby, the rising speed of the molten metal surface is made to coincide with the reference welding speed.

Hereinafter, an example of such an embodiment of the present invention will be described with reference to FIGS.
The present invention basically has two welding torches 4 and 5 mounted on the same way as shown in FIG. 1, and a carriage 6 rising along the groove 2 of the steel plate 1 to be welded, Welding power sources 10 and 11 for supplying a constant voltage between the welding wires 3 and 4 guided by the welding torches 4 and 5 and the steel plate 1, welding wire feeding means, and current detection means 14 for detecting welding current. And a command for the carriage traveling speed control means 16 for controlling the traveling speed of the carriage, and a command for the carriage traveling speed control means 16 so that the carriage 6 rises following the rising speed of the molten pool based on the detected welding current. A two-electrode vertical electrogas arc welding is performed using a welding device comprising a welding control device 15 for outputting.

Further, in the present invention, in order to make the heat input constant, as shown in FIG. 2A, the welding torch is attached to a welding torch support base 18 that moves in the direction of the arrow along the traveling direction of the carriage.
The welding torch support base 18 is attached to the carriage so as to move up and down within a certain range, and is raised or lowered by a certain distance by a drive mechanism such as a screw mechanism or a cylinder device. In FIG. 2, the support stand drive means 19 using a cylinder apparatus is shown. The operation of the support base drive means 19 is controlled by the support base drive control means 20.

  And as shown in FIG.2 (b), while providing the measurement means 21 which measures the moving speed of the trolley | bogie 6 during welding, the output of the measurement means 21 is received, and whenever a trolley moves a fixed distance, A calculating means 22 for calculating a speed difference between the moving speed of the carriage and a preset reference welding speed and determining whether the calculated speed difference is within a setting range; and the speed difference exceeds a set value. If the welding torch support control means 20 outputs a command to raise or lower the welding torch support base 18 by a certain distance, a welding current that changes as the welding torch rises or falls is detected. The welding control apparatus 1 having a control means 23 for outputting a command for accelerating or decelerating the wire feed speed to the welding wire feed control means 17 so that the welding current becomes a preset value. The provided to to perform welding by using thus configured apparatus.

In addition, while maintaining constant voltage, it can have welding, and has a control function which controls a wire feed speed according to the change of welding current, and makes welding current become a preset value. The welding power sources 12 and 13 and the welding control device 15 are realized by using a commercially available welding device having a digital inverter control type welding power source (for example, DAIHEN Digital Auto DM500 (registered trademark)). be able to.
In addition, in the conventional constant voltage inverter welding power source, the above-described control function is realized by separately adding a constant current control mechanism disclosed in Japanese Patent Application Laid-Open No. 2007-190594, Japanese Patent No. 3886029, and the like. Can do.

  Next, with respect to an aspect in which welding is performed so as to maintain a constant heat input using the welding apparatus configured as described above, a case where the groove cross-sectional area is wide and a case where the groove cross-sectional area is narrow are illustrated in FIG. And it demonstrates in detail using FIG.

First, a case where the groove cross-sectional area is large will be described.
When welding is started, similarly to the conventional case described above, the welding torches 4 and 5 on the carriage 6 rise to the molten metal surface at a speed that matches the reference welding speed set in advance before starting welding. Follow and start rising. As the carriage 6 rises, the movement distance of the carriage is measured, and the calculation means 22 calculates the raising speed (actual welding speed) of the carriage every time the carriage rises at a fixed interval, and the rising speed and the reference welding speed. And the difference is calculated. When the groove cross-sectional area is constant according to the standard, there is no difference between the actual welding speed and the set welding speed, so that welding proceeds at the welding speed.

  When the welding torch reaches a location where the groove cross-sectional area is wider than the reference, the rising speed of the molten metal surface becomes slower than the set welding speed. For this reason, the calculating means 22 determines that the rising speed of the carriage is slower than the set welding speed (the difference between the two is smaller than 0). In that case, the control means 23 outputs a command to raise the welding torch relative to the carriage to the support base drive control means 20. If it does so, in the welding using the power supply of a constant voltage characteristic, the protrusion length of the wire from the tip of a welding torch will increase, and welding current will fall. Therefore, the control means 23 outputs a command to increase the wire feed speed to the wire feed control means 17 in accordance with the decrease in the welding current so that the welding current becomes a predetermined constant value. To do. Thereby, the wire supply amount increases and the rising speed of the hot water surface also increases. As a result, the welding torch also rises following the faster rise speed.

  Next, when the welding torch reaches a portion having a narrow groove sectional area, the rising speed of the molten metal surface becomes faster than the set welding speed. For this reason, the rising speed of the carriage is determined to be faster than the set welding speed (the difference between the two is greater than 0). If it is determined to be fast, the welding torch is lowered with respect to the carriage as opposed to the wide area. If it does so, the protrusion length of the wire from a chip | tip will become short, and a welding current will increase. Therefore, the feeding speed of the welding wire is decreased according to the increase in the welding current so that the welding current becomes a predetermined constant value. Thereby, the amount of wire supply decreases and the rising speed of the hot water surface also decreases. As a result, the welding torch also rises following the slow rise speed.

  When the above control operation is repeated at predetermined intervals, the actual welding speed is detected and repeated until it converges to the set welding speed, and welding at the set welding speed becomes possible. Return to.

  The amount of movement of the welding torch in one control operation is suitably in the range of 1 mm or more and 5 mm or less. The reason is that when the amount of movement of the welding torch is less than 1 mm, the amount of change is too small and the time required to reach the set welding speed becomes long. On the other hand, when the moving amount of the welding torch exceeds 5 mm, the control for adjusting the welding speed is excessively performed, so that the appropriate welding speed is exceeded, for example, from a welding speed that is too slow to a welding speed that is too fast ( This is because the welding speed may change extremely.

  When the range in which the groove cross-sectional area increases is continuously long (or vice versa), the welding torch reaches the upper end (lower end) of the movable range. In order to avoid this, it is preferable that the stroke length that the torch can move has a length of ± 10 mm or more from the reference position. The upper limit value of the stroke length is not particularly limited and may be appropriately determined from the viewpoint of facility operability. However, a stroke length of ± 50 mm (100 mm in total length) from the reference position is sufficient.

It should be noted that the actual welding speed is compared with the target welding speed to determine whether the speed is fast or slow by calculating a moving average in a range where the bead length is 10 cm or less, preferably 5 cm or less. . The reason is that the depth of the molten pool in the welding direction is about 8 cm. There is no particular lower limit value for the bead length with respect to the welding speed determination. However, repeating the determination of 1 mm or less increases the control load and is not practical.
In addition, in the figure, whether the speed is fast or slow is determined based on 0 as a difference between the actual welding speed and the target welding speed. Judges whether the difference exceeds the range.

As described above, in the present invention, a welded joint welded with a constant heat input can be manufactured even if the groove cross-sectional area varies.
In the manufacturing method of the present invention, heat input is not limited even when the groove shape is deformed due to thermal deformation during welding, not only when the root gap or the like fluctuates due to the work accuracy described above. It is possible to perform welding while maintaining a certain state.

  In addition, although it does not specify in particular above, it cannot be overemphasized that feeding of two welding wires is controlled simultaneously. Further, the polarity of the two welding wires and the method for detecting the welding current are not limited to those described with reference to FIGS. 1 and 2 and can be appropriately changed.

Next, the feasibility and effects of the present invention will be further described using examples.
Using the test steel materials and welding wires shown in Table 1, vertical electroslag welding with two electrodes was carried out under the welding conditions shown in Table 2 to produce welded joints.
The test steel used was a steel material conforming to the standard of KE47-H steel defined by the Japan Maritime Association, and the welding wire was a 1.6 mmφ flux cored wire conforming to KEW63Y47 defined by the Japan Maritime Association.

As shown in FIG. 4 and FIG. 5, prepare a weld specimen with a changed root gap and a weld specimen with a changed groove angle, and rise along the groove as shown in FIGS. A welding device with two welding torches and a water-cooled copper alloy attached to the front side of the groove surface of the specimen is attached to the trolley, and a ceramic refractory backing material is attached to the rear surface of the groove. Electro-slag welding was performed. At that time, carbon dioxide gas was used as the shielding gas.
In the welding according to the present invention, two welding torches are attached so as to be movable within a predetermined range in parallel with the traveling direction of the carriage, and a certain difference is detected between the rising speed of the carriage and the reference welding speed. In this case, move the welding torch either up or down to forcibly change the protruding length of the wire, and change the welding current forcibly to a constant value by changing the wire feed speed. A method of controlling to return is adopted. In addition, the movement of the torch to be moved up and down by one control was 2 mm, and the welding speed was determined as a moving average speed every 10 mm to determine a difference from the target welding speed.
On the other hand, in the welding of the comparative example, the welding torch is not moved up and down like the example of the present invention, the wire feeding speed is set to a constant speed, and the rising speed of the carriage is switched in two steps according to the welding current. Adopted.

FIG. 6B shows a tensile test piece (JIS A2 round bar test piece) in the manner shown in FIG. 6A from the weld metal parts of sections A to G in the welded joint of the welded test specimen after welding. Charpy specimens (2 mm V notch, 10 mm full size) were collected in the same manner.
In addition, since 10 cm before and after the change part (for example, the boundary of A and B) where a groove shape changes in the welding length direction is an unstable region, specimen collection is not performed from the part.
And the tension test and the Charpy test were implemented using the extract | collected test piece.

Next, the obtained test results were evaluated according to the following evaluation criteria.
First, the yield strength (YP), tensile strength (TS), and Charpy test results of the test specimens collected from A to G of the individual weld specimens were evaluated according to the following criteria.
YP: 400 MPa or more was regarded as acceptable.
TS: 600 MPa or more was regarded as acceptable.
Charpy test; absorbed energy at −20 ° C. was determined to be 50 J or more.
Furthermore, in one welding test body, what satisfied the above pass / fail criteria at all sampling positions from A to E or F to G was regarded as acceptable. Conversely, a test specimen that did not satisfy the criteria at any one position was rejected.
Table 3 shows the evaluation results.

In the example of the present invention, as a result of controlling the wire feed speed so that the amount of deposited metal corresponding to the groove width can be obtained, even if the groove gap and groove angle of the groove fluctuate, the welding speed is constant. Since welding is performed, there is no fluctuation in heat input for each groove, and the characteristics of the weld metal hardly change, and a stable weld joint is obtained.
In the examples examined in the present invention, the welding was converged to a predetermined welding speed within about 80 seconds after the start of welding, and thereafter welding was performed at the set target welding speed. Even in the existing welding method, a bead of about 10 cm from the start of welding is usually deleted as an unstable region, and the convergence time in the present invention is considered to have no problem in practice.

On the other hand, in the comparative example, since the existing two-electrode vertical electrogas welding control for switching the traveling speed of the carriage to two stages was performed, the welding speed followed the rise in the molten pool surface. As a result, the welding speed was too high in the portion A having a groove root gap of 8 mm, and the heat input was excessively reduced in the 70 mm-thick steel sheet, resulting in a welded joint with excessive strength and deteriorated toughness.
In addition, the welding speed is slow at the D portion with a root gap of 14 mm and the E portion with 16 mm, and the increase in heat input due to the use of an extremely thick steel plate of 70 mm overlaps with the increase in heat input due to the wide root gap. As a result, the required hardenability could not be ensured, resulting in a welded joint in which both the tensile strength and Charpy impact absorption energy of the weld metal deteriorated.

  As described above, when the present invention is used, a welded joint having always stable toughness can be manufactured without being influenced by fluctuations in the groove shape, and thus the value in the industry is extremely high.

1 Steel plate (workpiece)
2 Groove 3 Welding wire 4 First welding torch 5 Second welding torch 6 Rail 7 Carriage 8 Copper metal 9 Backing material 10, 11 Wire feeding device 12, 13 Welding power supply 14 Current detecting means 15 Welding control device 16 Carriage Travel Control Means 17 Wire Feed Control Means 18 Welding Torch Support Base 19 Welding Torch Support Base Drive Device 20 Support Base Drive Control Means 21 Cart Movement Speed Measuring Means 22 Calculation Means 23 Control Means

Claims (3)

The carriage carrying two welding torches is raised along the groove of the steel plate to be welded and welding is performed at a constant voltage, and the carriage follows the rising speed of the molten pool based on the welding current. A method of manufacturing a welded joint by performing two-electrode vertical electrogas arc welding with control to rise,
The welding torch is attached to a carriage so that the welding torch can be moved along the welding direction, the movement speed of the carriage is measured, and a difference from a preset reference welding speed is calculated at regular intervals. In some cases, the welding torch is raised or lowered by a certain distance to change the protruding length of the welding wire, and the welding current is made constant by changing the wire feeding speed according to the change in welding current generated at that time. A method for manufacturing a welded joint, characterized in that two-electrode vertical electrogas arc welding is performed with the heat input during welding kept constant by matching the ascending speed of the molten pool with the reference welding speed.   The method for manufacturing a welded joint according to claim 1, wherein a steel plate having a thickness of more than 50 mm is welded. A carriage that carries two welding torches and rises along the groove of the steel sheet to be welded; a welding power source that supplies a constant voltage between the welding wire and the steel sheet guided by each welding torch; Welding wire feeding means, current detection means for detecting welding current, and cart running for controlling the running speed of the cart so that the cart rises following the rising speed of the molten pool based on the detected welding current A two-electrode vertical electrogas arc welding apparatus having a speed control means,
The welding apparatus further supports the welding torch and is attached to the carriage so that the welding torch can be moved up and down along the traveling direction of the carriage, the moving speed measuring means of the carriage, and at regular intervals. Calculating the speed difference between the moving speed of the carriage and a preset reference welding speed, and determining whether the speed difference is within a set range; and when the speed difference exceeds the set value The welding torch support base is controlled to be raised or lowered by a certain distance, and the welding wire feeding speed is controlled so that the welding current changed at that time becomes a preset value. A two-electrode vertical electrogas arc welding apparatus for carrying out the method for manufacturing a welded joint according to claim 1 or 2, further comprising a control unit configured to be within a set range.

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