JP2022029879A - Extremely narrow groove submerged arc welding method and extremely narrow groove submerged arc welding apparatus - Google Patents

Abstract

To provide a welding method and a welding apparatus by an algorithm for controlling a welding condition of not causing a welding failure with respect to fluctuations during welding, and a torch targeting position, in an extremely narrow groove SAW.SOLUTION: A bead width WB and a welding cross section area AR when the same material as a welding object is subjected to bead-on plate welding are measured. Heat input HG to a groove wall during welding is represented using weld input heat Q, the bead width WB and a distance L between a torch and a groove wall. A generalized distance R between a surface of a molten pool at a torch targeting position and a corner part of a groove bottom is represented by using the welding cross section area AR and the distance L. In an HG-R plane, display of presence/absence of welding defects during groove welding that has been experimentally determined is plotted, and a determination line based on the presence/absence of the welding defects in the groove wall is drawn. A welding condition is set so that a region has less welding defects than the determination line, and groove welding is performed.SELECTED DRAWING: Figure 30

Description

The present invention relates to an ultra-narrow groove submerged arc welding method and an ultra-narrow groove submerged arc welding apparatus.

Submerged arc welding (SAW) is often used for butt welding of thick plates and extra-thick plates in large steel structures such as pressure vessels because of its high welding efficiency and high quality. When welding a thick plate or an extra-thick plate with SAW, it is necessary to widen the groove angle to about 30 ° in order to prevent welding defects such as poor fusion (Lack of fusion: LF). However, if the groove angle is wide, the required welding cross-sectional area increases, and it takes a long time to complete the welding by laminating the weld beads.

On the other hand, in the narrow groove SAW where the groove angle is 1 to 3 ° and the root width is narrowed, the required welding cross-sectional area is reduced, and the welding time can be expected to be shortened. Some research and development has been carried out on the narrow groove SAW. In recent years, by setting the groove angle to almost 0 ° and the groove width to 18 mm or less, the extremely narrow plate to be welded is laminated from the first layer to the last layer of the weld bead in one layer and one pass. Research on groove SAW is also underway.

In 1-layer 1-pass construction, it is necessary to melt the groove walls on both sides in 1 pass, but the corners of the groove bottom are difficult to heat directly with arc plasma, and heat is easily diffused. It is difficult to melt and fusion failure is likely to occur. In addition, if the groove is narrowed, the slag will not naturally separate after welding, making it difficult to remove it. If undercut occurs on the groove wall, slag will stick to it, and if it cannot be removed sufficiently, it will cause slag entrainment. In order to prevent these welding defects, it is necessary to select welding conditions that give a welded portion shape that does not cause undercut while melting the groove walls on both sides. However, the range of welding conditions and torch target positions where defects do not occur, that is, proper welding conditions is narrow. Since the range of appropriate welding conditions is narrow, the groove width and torch aiming position change due to fluctuations during welding (changes in groove width, device operation deviation, etc.), and welding conditions that do not originally cause defects. But sudden defects can occur.

On the other hand, in recent years, a large-capacity welding power supply capable of digital waveform control has been developed, and the stability and reproducibility of the output are improved compared to the conventional movable iron core type, and the EN ratio, frequency, phase difference, etc. are improved. , The output waveform can be controlled more precisely. For example, the feed rate of the welded wire, that is, the welded cross-sectional area can be controlled by the EN ratio. As described above, in the digital waveform control power supply, the shape of the welded portion can be controlled by parameters such as the EN ratio, and it can be expected to prevent welding defects such as fusion failure and undercut in the ultra-narrow groove SAW.

On the other hand, as known techniques, there are those described in Patent Document 1 and Patent Document 2. Of these, Patent Document 1 describes a device that automatically performs left-right copying and vertical copying with respect to a welded line. According to this device, it is possible to automatically follow the torch aiming position with respect to the change in the groove shape. Patent Document 2 describes a welding method using an algorithm that formulates the bead shape at the time of laminating from the bead cross-sectional height and the welded cross-sectional area and determines the torch target position of each layer.

Japanese Unexamined Patent Publication No. 63-30175 Special Fair 6-75787 Gazette

However, in the case described in Patent Document 1, since the welding conditions cannot be optimized for the fluctuation during welding, welding defects occur in the one-layer, one-pass construction. The one described in Patent Document 2 does not correspond to 1-layer 1-pass construction, and only the torch aiming position is determined for the input welding conditions, so that the welding conditions are optimized for fluctuations during welding. Can not.

Therefore, the present invention solves such a problem and provides a welding method and a welding apparatus based on an algorithm for controlling the welding conditions, the torch aiming position, and the welding conditions in which welding defects do not occur due to fluctuations during welding in an extremely narrow groove SAW. The purpose is to get.

In order to achieve this object, the ultra-narrow groove submerged arc welding method of the present invention is used.
Under predetermined welding conditions, bead-on-plate welding is performed on the same material as the object to be welded, and the bead width _WB and welding cross-sectional area _AR at the time of the bead-on-plate welding are measured.
Welding heat input Q is obtained from the above welding conditions.
The heat input _HG to the groove wall at the time of welding is expressed by using the welding heat input Q, the bead width _WB , and the distance L between the torch and the groove wall.
The generalized distance _R from the surface of the molten pool to the corner of the groove bottom at the torch target position is expressed using the welding cross-sectional area AR and the distance L between the torch and the groove wall.
An experimentally obtained display of the presence or absence of fusion failure during groove welding was plotted on the _HG -R plane formed by the heat input _HG and the distance R.
A judgment line based on the presence or absence of fusion failure on the groove wall is drawn on the _HGR plane on which the display of the presence or absence of fusion failure during groove welding is plotted.
It is characterized in that groove welding is performed by setting welding conditions so as to be a region where there is no fusion defect from the determination line.

By doing so, it is possible to perform ultra-narrow groove submerged arc welding while preventing fusion defects from occurring.

According to the ultra-narrow groove submerged arc welding method of the present invention, the heat input _HG to the groove wall at the time of welding is the difference between the welding heat input Q, the bead width _WB and the distance L between the torch and the groove wall ( It is preferably expressed as a product of _WB -L).

Further, according to the ultra-narrow groove submerged arc welding method of the present invention, the distance R from the surface of the molten pool to the corner of the groove bottom at the torch target position is the distance _R between the torch and the groove wall, and the welding cross-sectional area AR is the distance L between the torch and the groove wall. It is preferable to express it as the sum of the power of the divided product (AR / _L ) and the power of the torch-groove wall distance L.

Further, according to the ultra-narrow groove submerged arc welding method of the present invention, the torch-groove wall distance L is measured at the time of groove welding, and the measured torch-groove wall distance L is subject to welding defects. It is preferable to set welding conditions within an appropriate range that does not occur.

Further, according to the ultra-narrow groove submerged arc welding method of the present invention, it is possible to control at least one of the EN ratio, the welding current, the voltage, and the welding speed as the welding conditions at the time of groove welding. Suitable.

The ultra-narrow groove submerged arc welding apparatus of the present invention is provided with a digital welding power source, and this digital welding power source can set and change the set values of the EN ratio, the welding current, and the voltage. It is characterized by.

With such a device, it is possible to obtain an apparatus capable of performing welding without causing fusion defects based on the method of the present invention.

According to the ultra-narrow groove submerged arc welding apparatus of the present invention, it is preferable to have a moving device for moving the torch in a direction orthogonal to the welding line direction in order to adjust the distance L between the torch and the groove wall. ..

With such a thing, when a deviation occurs in the torch aiming position, the deviation can be corrected.

According to the present invention, even when the groove width fluctuates during welding, ultra-narrow groove submerged arc welding can be performed while preventing fusion defects from occurring.

It is a figure which shows the good melting state when the submerged arc welding is performed to the narrow groove. It is a figure which shows the state which the fusion defect occurred in the corner part when the submerged arc welding was performed to the narrow groove. It is a figure which shows the state which the undercut occurred in the groove wall when the submerged arc welding was performed to the narrow groove. It is a figure which shows the experimental apparatus for observing the occurrence state of a welding defect. It is a figure which shows the macro test result of the cross section of a welded part at the value of each root width _WB . It is a figure which shows the relationship between the bead height h and the penetration depth D. It is a figure which shows the relationship between the root width _WR , the bead height h, and the penetration depth D. It is a figure which shows the macro test result of the cross section of a welded part at each torch aiming position P. It is a figure explaining the relationship between the torch aiming position P, the bead height h, and the penetration depth D. It is a figure which shows the relationship between the torch aiming position P, the bead height h, and the penetration depth D. It is a figure which shows the distance L between a torch and a groove wall. It is a figure which shows the relationship between the distance L between a torch and a groove wall and the melting area _AG in a groove wall. It is a figure which shows the relationship between the distance L between a torch and a groove wall and the melting width _WG at a groove wall. It is a figure which shows the relationship between "L + _WG " and "L" derived from FIG. It is a figure which shows the relationship between "L + _WG " and "L" derived from FIG. It is a figure which shows the relationship between "L + _WG " and "L" derived from FIG. It is a figure which shows the relationship between "L + _WG " and "L" derived from FIG. It is a figure which shows the formation state of the molten pool in arc welding. It is a figure which shows the formation state of the molten pool in arc welding. It is a figure which shows the formation state of the molten pool in arc welding. It is a figure which shows the formation state of the molten pool in arc welding. It is a figure which shows the state of the heat input in the very narrow groove submerged arc welding. It is a figure explaining the distance from the surface of a molten pool to the corner part of the groove bottom. It is a figure which shows the heat input _HG to a groove wall, the ^square r2 of a distance, and the determination result of fusion failure LF in groove welding. It is a figure which plotted the distance L between a torch and a groove wall in the figure which shows the heat input _HG to a groove wall, the ^square r2 of a distance, and the determination result of the fusion failure LF in groove welding. In the figure showing the heat input _HG to the groove wall and the ^squared r2 of the distance and the determination result of the fusion failure LF in the groove welding, the distance L between the torch and the groove wall when the heat input amount Q changes is shown. It is a plotted figure. The figure showing the heat input _HG to the groove wall and the ^squared r2 of the distance and the determination result of the fusion failure LF in the groove welding shows the distance L between the torch and the groove wall when the bead width _WB changes. It is the figure which plotted. In the figure showing the heat input _HG to the groove wall and the ^squared r2 of the distance and the determination result of the fusion failure LF in the groove welding, the distance between the torch and the groove wall when the welding cross-sectional area _AR changes. It is the figure which plotted L. Example of fusion failure judgment model at the time of ultra-narrow groove welding when the horizontal axis is the heat input _HG to the groove wall and the vertical axis is the generalized distance R from the surface of the molten pool to the corner of the groove bottom. It is a figure which shows. FIG. 29 is a diagram in which the distance L between the torch and the groove wall is plotted. FIG. 29 is a diagram plotting the distance _L between the torch and the groove wall when the welding cross-sectional area AR changes. FIG. 29 is a diagram plotting the distance L between the torch and the groove wall when the amount of heat input Q changes. FIG. 29 is a diagram plotting the distance L between the torch and the groove wall when the bead width _WB changes. It is a figure which shows the ultra-narrow groove submerged arc welding apparatus of embodiment of this invention. It is a figure which shows the flow of the welding process using the welding apparatus of FIG. 34.

The present invention has been completed on the basis of experimental techniques. Hereinafter, the present invention will be described in detail with reference to the experimental method.

1 to 3 show a situation when submerged arc welding is performed on a narrow groove. Here, 11 is the groove wall of the groove, 12 is the groove bottom, 13 is the corner portion of the groove bottom, _WR is the root width, that is, the distance between the groove walls 11 and 11, and 14 is the molten pool. Of these, FIG. 1 shows a good molten state. That is, the groove wall 11, the groove bottom 12, and the corner portion 13 are each melted to an appropriate depth. On the other hand, FIG. 2 shows a state in which poor fusion LF occurs at the corner portion 13. FIG. 3 shows a state in which an undercut 15 is generated on the groove wall 11 on the right side in the figure.

[experiment]
Weld defects are expected to be affected by the root width _WR shown in FIGS. 1 to 3 and the position of the welding torch in the direction of the torch target position P, that is, the root width _WR . Therefore, in order to evaluate the effect of the change between the root width _WR and the torch target position P on the welding defect, groove welding was performed with a single torch. Welding defects were determined under each welding condition, and the bead height h and the penetration depth D were measured. In addition, bead-on-plate welding was also performed to compare the shape of the welded portion with that at the time of groove welding. In order to create a fusion failure judgment model from the obtained results, bead-on-plate welding was performed using a single torch and a tandem torch under welding conditions in which the bead width _WB and the welded cross-sectional area _AR were changed. The bead width _WB and the welded cross-sectional area _AR under the welding conditions were measured. Next, groove welding was performed under those welding conditions, and fusion failure was determined.

The outline of the experimental apparatus used is shown in FIG. FIG. 4 shows an apparatus configuration for groove welding with a tandem torch, 16 and 17 are the welding torch, 18 is a carriage for moving the welding torches 16 and 17, and 19 is a feeder of the welding wire. Is a welding power source. As the welding power source 20, a welding power source 20 capable of digital waveform control was used. Reference numeral 21 is a test piece, and the material of the test piece 21 was _21/4 Cr ^- 1Mo steel. In order to simulate the extremely narrow groove in groove welding, a pair of materials having a length of 400 mm, a width of 70 mm, and a plate thickness of 30 mm constituting the test piece 21 are divided into a pair of materials having a length of 400 mm and a width of w (different dimensions). A test piece having a groove angle of 0 ° and a groove depth of 20 mm was prepared by sandwiching an insert material 24 having a thickness of 25 mm. A water-cooled copper plate 22 was installed on the side surface of the test piece so that the cooling rate of the groove test piece would be the same as that of the large steel structure. In addition, a strong back 23 was attached to suppress deformation during welding. The arrow 25 indicates the welding direction. The preheating and interpass temperatures were 200 to 250 ° C., and no post-heat treatment was performed. In the bead-on-plate welding, a flat plate test piece having a length of 400 mm, a width of 70 mm, and a plate thickness of 20 mm was used. Welding wires and flux used were equivalent to JIS Z3183 S642-2CM. Various experimental conditions were adopted, but in order to make the welding phenomenon easy to understand, a single electrode single torch was used, and the torch angle was set to 0 ° (vertical). Welding conditions are a square wave with an EN ratio (ratio of negative current in alternating current) 0.5, welding current 600A, welding voltage 33V, welding speed 30cm / min, CTWD (Contact Tip to Work Distance) 30mm as "reference conditions". And said. By changing the width w of the above-mentioned insert material, the root width _WR was changed at _WR = 8 to 18 mm. The torch aiming position P was changed in the range of 1 to 3 mm in the direction orthogonal to the welding line direction, with the position of the center of the groove being 0 mm.

In the experiment, a single torch or a tandem torch with two electrodes arranged in series, which is assumed in the implementation work, was used. The electrode angle was 0 ° for the single torch, 0 ° for the leading electrode and 15 ° for the trailing electrode in the tandem torch. The torch spacing in the tandem torch was set to 15 mm. Welding conditions are EN ratio 0.0 to 1.0, welding current 400 to 800 A, voltage 20 to 40 V, welding speed 30 to 43 cm / min (single torch), 60 to 81 cm / min (tandem torch). I changed each of them. The CTWD was constant at 30 mm. The root width _WR of the groove test piece was 14 mm, and the torch aiming position P was 0 mm.

For the results of bead-on-plate welding and groove welding, a macro test was conducted on the weld section to confirm the shape of the weld, and the bead width _WB and welding cross-section area _AR were measured. The test position was a position 100 mm or more away from the welding start position and the welding end position, which are the welding steady portions.

[Experimental result]
In order to evaluate the effect of the root width _WR on welding defects, the root width _WB is set to 8 to 8 to the above-mentioned reference conditions (EN ratio 0.5, welding current 600A, voltage 33V, welding speed 30cm / min). It was varied in the range of 18 mm. FIG. 5 shows the macro test results of the cross section of the welded portion at each route width _WB value. The aiming position of the torch is constant at P = 0 mm. FIG. 5 also shows the results of bead-on-plate welding under the same conditions. When the root width _WR = 8 mm, no fusion failure occurred, but both wall surfaces of the groove were largely melted and undercut occurred. The slag stuck to the undercut portion and could not be removed. When the root width _WR = 12 to 15 mm, a good welded portion was obtained in which neither undercut nor fusion failure occurred. When the root width _WR = 16 mm, the groove wall on one side (left side in the figure) melted, but the other side (right side in the figure) did not melt and the fusion was poor, and the slag could not be removed. When the root width _WR = 18 mm, both wall surfaces did not melt and fusion was poor, and slag could not be removed at the weld toes on both sides. At this root width _WR = 18 mm, the root width _WR was smaller (18 mm) compared to the bead width _WB (about 26.5 mm) on the bead-on plate, but the groove wall did not melt.

Next, the height at which the weld metal is welded from the groove bottom at the torch target position P (bead height h) and the depth at which the weld metal is welded from the groove bottom to the base metal side (penetration depth D). Was evaluated. These relationships are shown in FIG. Here, 28 is a welding torch and 29 is a welding wire. FIG. 7 shows the relationship between the root width _WR , the bead height h, and the penetration depth D. Since the welding conditions are the same, the welded cross-sectional area does not change, but the bead height h becomes lower as the root width _WR becomes wider, and becomes almost constant when _WR = 12 mm or more. On the other hand, the penetration depth D was the shallowest when the root width _WR = 8 mm, became deeper when the root width _WR was widened, and became constant when the root width _WR = 14 mm or more.

In order to evaluate the effect of the torch aiming position P on the welding defect, the torch aiming position P is changed from 0 to 3 mm under the above reference conditions for the test piece having the root width _WR = 14 mm in which the welding defect did not occur. rice field. FIG. 8 shows the macro test results of the cross section of the welded portion at each torch aiming position P. In the cross section of the welded portion shown in FIG. 8, the right side from the groove center is defined as the positive direction of the torch aiming position P. In the range of the torch aiming position P = 1 to 2 mm, the shape of the welded portion was biased in either direction (right side), but no welding defect occurred. On the other hand, when P = 3 mm, the groove wall on the side where the torch was separated did not melt, and a fusion defective LF occurred. On the other hand, on the side where the torch 28 shown in FIG. 6 was approached, the groove wall was melted in a wide range, undercut occurred, and the slag could not be removed. The relationship between the torch target position P, the bead height h, and the penetration depth D is shown in FIGS. 9 and 10. The bead height h and the penetration depth D are values immediately below the torch target position P. In the range of the torch aiming position P = 0 to 2 mm, no change was observed between the bead height h and the penetration depth D even if the size of the torch aiming position P fluctuated. On the other hand, when the torch aiming position P = 3 mm, both the bead height h and the penetration depth D became large.

[Creation of fusion failure judgment model]
(Condition of distance L between torch and groove wall to prevent welding defects)
From the above experimental results, it was found that the welding defect is affected by the root width _WR and the torch aiming position P. When the values of the route width _WR and the torch aiming position P change, the distance between the welded torch and the groove wall changes. That is, the relationship between the route width _WR and the torch aiming position P can be expressed by the torch-groove wall distance L shown in FIG. In FIGS. 5 and 8, since the groove wall was excessively melted and gouged to cause undercut, it is considered that there is a correlation between the undercut and the area where the groove wall is melted. Here, the area melted by the groove wall (the area that appears when the cross section is displayed as shown in FIGS. 5 and 8) is defined as _AG (see FIG. 12). Further, as described above, poor fusion LF during groove welding is likely to occur at the corner portion 13 of the groove bottom. That is, it is considered that the more the welding condition is such that the groove wall is greatly melted, the more the fusion defective LF can be prevented. Here, the width (melting depth) melted from the corner portion 13 to the groove wall side at the groove bottom is defined as _WG . Under the above-mentioned reference conditions (EN ratio 0.5, welding current 600A, voltage 33V, welding speed 30cm / min), the melting area A is changed under the condition that the melting width _WG and the torch target position P at the groove wall are changed. The result of measuring _G is shown in FIG. FIG. 13 shows the results of measuring the melting width _WG under the same conditions. These measurement results both represent those measured separately on the left and right groove walls. The legends are good (〇), undercut occurs (Δ), and fusion failure LF occurs (×), respectively. As shown in FIG. 12, when the distance L between the torch and the groove wall became small, the molten area _AG increased, and when L = 4 mm in which undercut occurred, the molten area _AG became 30 mm ² or more. Further, as shown in FIG. 13, the melting width _WG at the groove wall becomes maximum at the torch-groove wall distance L = 5 to 6 mm, and decreases as the torch-groove wall distance L becomes larger. , _WG = 0 mm, fusion failure LF occurred. From the above, when the distance L between the torch and the groove wall becomes small under the same welding conditions, undercut is likely to occur and the melting width _WG at the groove wall decreases. On the other hand, if the distance L between the torch and the groove wall is too large, the groove bottom cannot be sufficiently melted, resulting in poor fusion LF. That is, under the above-mentioned reference conditions, the range of the distance L between the torch and the groove wall that prevents welding defects in the extremely narrow groove SAW is 4 <L ≦ 7.5 mm.

(Influence factor on poor fusion LF)
As shown in FIG. 13, the melting width _WG at the groove wall became maximum at the distance L between the torch and the groove wall = 5 to 6 mm, and decreased as L became larger. Here, from the bead width _WB in bead-on-plate welding and the melt width _WG in the groove wall, the influence of the groove wall on the weld shape is considered. The relationship between “L + _WG ” and “L” derived from FIG. 13 is shown in FIGS. 14 to 17. Since undercut occurs when L ≦ 4 mm, L ≧ 4 mm was targeted. In FIG. 14, ◯ indicates no fusion failure LF, and × indicates that fusion failure occurred. "L + _WG " is the width melted at the groove bottom, and indicates how much was melted in the width direction of the groove groove. In the range of L + _WG > L, a good welded portion with no fusion defect LF is obtained.

In FIG. 14, it is divided into three regions, “region (a)”, “region (b)”, and “region (c)” along the direction of the horizontal axis. Here, considering the bead width _WB at the time of bead-on-plate welding, the region (a) is a region where _WB / 2 ≦ L, and here, as shown in FIG. 15, the torch with respect to the bead width _WB . -Because the distance L between the groove walls is large and therefore the groove wall is far from the torch target position P, the bead width _WB is almost the same as the bead-on-plate welding. That is, L + _WG = _WB / 2, resulting in a poor fusion LF. The region (b) is 7.5 mm <L < _WB / 2, and as shown in FIG. 16, the distance L between the torch and the groove wall is smaller than the bead width, but the groove wall cannot be melted. , Poor fusion LF occurs. Compared to bead-on-plate welding, groove welding tends to diffuse heat, so the groove wall is less likely to melt. The region (c) is a region where the distance L between the torch and the groove wall is small, 4 mm ≦ L ≦ 7.5 mm. In this region, a sufficient amount of heat is transferred from the welding torch to the groove wall, so that the groove wall is melted as shown in FIG. Therefore, L + _WG > L, and no fusion failure LF occurs.

However, as shown in FIG. 13, when the distance between the torch and the groove wall was L = 4 mm, which was smaller than L = 5 mm, the melting width _WG at the groove wall decreased. L = 4 mm is the case where the root width _WR = 8 mm in FIG. 7 and the case where the torch aiming position P = 3 mm in FIG. In either case, the bead height h is increased and the penetration depth D is decreased. On the other hand, the sum of the bead height h and the penetration depth D directly under the torch aiming position was almost constant regardless of the route width _WR and the torch aiming position P.

In arc welding, as shown in FIGS. 18 and 19, the molten pool 14 is in a state where the force that pushes the molten pool 14 downward by the arc force 32 based on the arc 31 and the position head 33 of the molten metal generated by gravity are balanced. Is formed. In a narrow groove where the root width is narrow, the position head 33 of the molten metal becomes larger than the arc force 32, and the preceding phenomenon of the molten metal (the molten metal rises greatly on the surface of the molten pool directly under the arc, and heat is input by the arc. Does not reach the bottom of the groove) is likely to occur. In FIGS. 7 and 10, no difference was observed in the sum of the bead height h and the penetration depth D at each route width _WR and route aiming position P, because the arc force proportional to the square of the welding current was not observed. It is probable that 32 became stronger. Therefore, when the bead height h increases immediately below the torch aiming position, the force that pushes the molten pool 14 downward and the position head 33 are balanced at a position higher than the groove bottom 12 of the groove (FIGS. 20 and 21). As a result, it is considered that the distance between the arc plasma and the groove wall (particularly the corner portion 13 of the groove bottom) becomes long, so that sufficient heating cannot be performed, and the melting width _WG at the groove wall decreases. Therefore, in order to prevent poor fusion LF, it is necessary to reduce the distance L between the torch and the groove wall and the bead height h so that the distance between the welding torch 28 and the corner portion 13 of the groove bottom does not become long. ..

[Welding condition range without welding defects]
(Fusion failure judgment model)
The range of the torch-weld wall distance L (4 mm <L ≦ 7.5 mm) in which welding defects do not occur as shown in FIGS. 11 to 13 is the above-mentioned reference conditions (EN ratio 0.5, welding current 600 A,). This is the result under a voltage of 33 V and a welding speed of 30 cm / min). On the other hand, when the welding conditions change, the shape of the welded portion changes, and in particular, the poorly fused LF is easily affected by the welding conditions. In general, it is necessary to carry out a large number of experiments in order to select a condition range for preventing fusion failure LF for various welding conditions. However, in the present invention, a model for determining the conditions for preventing fusion failure LF in the ultra-narrow groove SAW was created from the experimental results by bead-on-plate welding.

That is, from the above consideration, the cause of the poor fusion LF in the ultra-narrow groove SAW is that the amount of heat transferred from the arc to the groove wall decreases. That is, how much heat is input during welding and how widely the amount of heat input is transported are important. When the welding current I [A], the welding voltage V [V], and the welding speed v [cm / min] are used, the welding heat input Q [kJ / mm] is calculated by the following equation (1).

Q = I x V x 60 / (v x 10) x 1/1000 (1)

Here, in the case of welding conditions where the welding heat input is Q and the bead width in bead-on-plate welding is _WB , it is considered that the welding heat input Q is administered within the range of the bead width _WB . At this time, in the ultra-narrow groove SAW under the same conditions, as shown in FIG. 22, Q / 2 receives heat when considering half of the welded portion, and this is administered to the range of _WB / 2 on one side. At this time, if the groove wall is located at a position separated by L (distance between the torch and the groove wall) from the arc plasma which is the heat source, the amount of heat transferred to the groove wall is _WB / 2-L. .. This is defined by the following equation (2) as the heat input _HG [kJ / mm · mm] to the groove wall. At this time, the heat input by the arc has a Gaussian distribution, the molten pool temperature becomes maximum just below the target position of the torch, and becomes lower as it becomes closer to the end of the molten pool, but for simplicity, the heat input in the bead width direction is uniform. Suppose there is.

_HG = Q / 2 ( _WB / 2-L) (2)

Another cause of poor fusion is an increase in bead height h. When the bead height h increases, the distance from the arc plasma to the corner portion of the groove bottom becomes long, and this corner portion cannot be sufficiently heated. Here, for the bead height h [mm] of the molten pool at the time of the ultra-narrow groove SAW, the welding cross-sectional area AR [mm ² ] in the bead-on-plate welding and the distance _L between the torch and the groove wall are used. It is expressed by the following equation (3).

h = _AR / 2L (3)

Assuming that the surface of the molten pool at the torch target position is the origin, the square r ² of the distance from this origin to the corner of the groove bottom is as follows using the bead height h and the distance L between the torch and the groove wall. It is represented by the equation (4) (FIG. 23).

r ² = h ² + L ² (4)

A judgment model was created using the _HG calculated by the equation (2) and the r ² calculated by the equation (4) as parameters affecting the occurrence of the fusion defective LF. In order to change _HG and _r ² , bead-on-plate welding is performed under different welding conditions of bead width _WB and welding cross-sectional area AR, and bead width _WB and welding cross-sectional area _AR under each welding condition. Was measured. Next, groove welding was performed under those welding conditions, and it was determined whether or not fusion defect LF was generated. The experimental method and the shape of the test piece were as described above. Further, the root width _WR of the groove test piece was 14 mm, the torch aiming position P = 0 mm, and the distance between the torch and the groove wall L = 7 mm, which were constant.

The bead width _WB and the welded cross-sectional area _AR calculated under each welding condition are the ^squared r2 of the heat input _HG and the distance to the groove wall, and the determination result of the fusion failure LF in the groove welding. It is shown in FIG. The legend is no fusion failure (〇), fusion failure on one groove wall (◇), and fusion failure on both side groove walls (×). The larger the _HG value on the horizontal axis, the larger the welding heat input to the groove wall, and the larger the value of r2 ^on the vertical axis, the farther the heat source and the corner of the groove bottom are. In FIG. 24, for example, when compared under the same conditions of r ² = 70 mm ² , fusion failure LF occurred on the groove walls on both sides at _HG = 0.8 kJ / mm · mm, but _HG = 12.5 kJ /. No fusion failure LF occurred under the condition of mm · mm or more. In other words, it can be said that the larger the _HG is, the less likely it is that poor fusion LF will occur. Further, when compared under the same conditions of _HG = 10 kJ / mm · mm, fusion failure LF occurred at the groove wall on one side at r ² = 75 mm ² , but fusion failure LF did not occur at r ² = 63 mm ² . rice field. That is, it can be said that there is a limit value of the square r ² of the distance at which the fusion failure LF does not occur for each heat input _HG to the groove wall. As shown in FIG. 24, from the bead width _WB and the welded cross-sectional area AR obtained by bead-on-plate welding, the heat input _HG to the groove wall and the square _r ² of the distance are derived, and the fusion failure LF is derived. I was able to find the judgment conditions for.

FIG. 25 shows the measurement results of the melting width (melting depth) _WG of the groove under each welding condition. The darker the color and the lower the brightness, the larger the _WG . The melting width _WG here is an average value at both groove walls. _WG = 0 mm under the condition of poor fusion LF on both sides, and _WG = 0.1 to 0.3 mm under the condition of poor fusion LF on one side, which were small values. On the other hand, under the condition that no fusion failure LF occurred, the value was _WG = 0.3 mm or more. Further, when the heat input _HG to the groove wall became large and the ^squared r2 of the distance became small, the melting width increased to _WG = 0.9 mm.

[Distance L between torch and groove wall that does not cause fusion failure]
As described above, under the reference conditions (EN ratio 0.5, welding current 600A, voltage 33V, welding speed 30cm / min), the range of the distance L between the torch and the groove wall where welding defects do not occur (4mm < L ≦ 7.5 mm) could be obtained. However, this is a reference condition, and if the welding conditions change, the range of the distance L between the torch and the groove wall where welding defects do not occur also changes. Therefore, in the following, the influence of the torch-groove wall distance L is evaluated on the fusion defect determination model, and the range of the torch-groove wall distance L where fusion failure does not occur according to the welding conditions is determined from the model. do.

The torch-groove wall distance L, as shown in FIG. 13, is plotted in FIG. 25. In FIG. 25, the legend is good (●), undercut (▲), poor fusion (◆) on one side of the groove groove, and poor fusion (×) on both sides of the groove groove. From the above equations (2) and (4), the influence of the 1 / L term ² is small in the range of L> 4 mm, so when L is changed on the judgment model, the shape becomes almost a quadratic curve. In the above experiment, as shown in FIG. 13, the maximum was achieved at the melting width _WG = 1.5 mm at L = 5 to 6 mm, and no fusion failure occurred at that time. However, as L became larger than this, _WG decreased, and fusion failure occurred on one side of the groove groove at L = 8 mm and on both sides of the groove groove at L = 9 mm. Further, at L = 4 mm, no fusion failure occurred, but the melting width _WG decreased. Comparing these experimental results with the judgment model, on the judgment model, R ² was minimized at L = 5 to 6 mm, and _WG was plotted in a large region, and it was judged that fusion failure did not occur. On the other hand, as L becomes larger than this range, the heat input _HG to the groove wall decreases, the ^squared r2 of the distance increases, and the _WG is plotted in a small region, where L = 8 mm or more. It was judged that the fusion was poor. On the other hand, when the distance between the torch and the groove wall is L = 4 mm, the heat input _HG to the groove wall increases, but the ^squared r2 of the distance also increases, and the plot shows the region where the _WG is small (the fusion failure side). ) Was approached. From the above, the experimental results in which L was changed and the results of the determination model were in agreement. By using the created judgment model, it was possible to calculate the range of L in which fusion failure does not occur.

Using the determination model, the range of the torch-groove wall distance L corresponding to the welding conditions was determined. From the experimental results, under the above-mentioned reference conditions, the bead width _WB = 26.5 mm and the welding cross-sectional area _AR = 64.6 mm ² . Further, from the formula (1), the heat input amount Q = 4.0 kJ / mm. In arc welding, the bead width and the weld cross-sectional area are proportional to the heat input to the weld, so it is difficult to change only the respective values. On the other hand, as described above, when the digital waveform control power supply is used, the welding cross-sectional area _AR can be changed by about ± 20% with a constant welding heat input depending on the EN ratio. Therefore, the shape of the welded portion is changed from the reference condition by setting the range in which the heat input Q, the bead width _WB , and the welding cross-sectional area _AR can be changed independently by the digital waveform control power supply to ± 20%, and each torch. -The values of the heat input _HG to the groove wall and the ^squared r2 of the distance at the distance L between the groove walls were calculated. The plots of the results on the judgment model are shown in FIGS. 26 to 28. Here, under the condition that the heat input amount Q or the bead width _WB is small, the curve shifts to the left as a whole, and the range of L where the fusion defective LF does not occur is narrowed to 5 mm ≦ L ≦ 6 mm. On the other hand, under the condition that these are large, the curve shifts to the right side, and fusion failure does not occur in 4 mm ≦ L ≦ 7.5 mm (FIGS. 26 and 27). Under the condition that the welded cross-sectional area _AR is small, the curve shifts downward as a whole, and no fusion failure LF occurs when 4 mm < _L ≦ 7.5 mm, whereas under the condition that the welded cross-sectional area AR is large, the upper side. In any L, fusion failure occurs (FIG. 28). As described above, by using the judgment model, the appropriate welding condition range at the ultra-narrow groove SAW and the corresponding range from the heat input amount Q, bead width _WB , and welding cross-sectional area _AR in bead-on-plate welding. It is possible to determine the range of L. Further, when the heat input Q and the bead width _WB are increased and the welding cross-sectional area _AR is decreased to shift the curve to the lower right on the judgment model, the torch-groove wall where fusion failure does not occur. The range of the distance L can be expanded.

[Generalization]
The above equation (2) can be generalized and rewritten as follows.

_HG = C1 x Q (C2 x _WB -L) (2a)

That is, _HG can be expressed by the product of Q and ( _WB −L). In this formula (2a), C1 can be an arbitrary number, and C2 can be an arbitrary number in the range of 0.5 ≦ C2 ≦ 1.

Further, the above equation (4) can be generalized and rewritten as follows after substituting the equation (3).

_R = (AR / L) ^C3 + (L) ^C3 (4a)

R is a generalized distance from the surface of the molten pool to the corner of the groove bottom, and is the power of (AR / L) and the power of ( _L ) as shown in equation (4a). It can be expressed as a sum. C3 can be any number in the range 0 <C3 <5.

In FIG. 29, the horizontal axis is the heat input _HG to the groove wall, and the vertical axis is the distance R from the surface of the molten pool as the origin to the corner of the groove bottom, and C1 = 1 and C2 = 0. 5. This is an example of a fusion defect determination model at the time of extremely narrow groove welding when C3 = 1. Similar to the case of FIG. 24, if it is below the determination line shown by the broken line, no fusion failure occurs, and if it is above the determination line, fusion failure occurs. In FIG. 29, the determination line was obtained by the least squares method from the result of partial fusion failure and the result of fusion failure in the experimental results. The determination line can also be obtained by another appropriate method.

To repeat the above, the bead width _WB and the welded cross-sectional area _AR are uniquely obtained depending on the welding conditions. On the other hand, the distance L between the torch and the groove wall may always change due to fluctuations during welding. For example, when only _L changes under the conditions of bead width _WB = 26.5 mm and welding cross-sectional area AR = 64.6 mm ² , it is represented by a solid line in FIG. 30 on the fusion defect determination model. become. Here, similarly, fusion failure does not occur in the range of L = 4 to 7.5 mm, but fusion failure occurs when L is 8 mm or more. In FIG. 30, L = 8 mm is almost on the determination line, so that the fusion is poor.

FIG. 31 shows a state of determination of fusion failure when only the welding cross-sectional area _AR is changed under the above conditions. Here, under the condition of welding cross-sectional area AR = 77.4 mm ^{2, the range is L = 4 to 7 mm, and under the condition of AR = 64.6 mm 2} _, ^the range is _L = 4 to 7.5 mm. Under the condition of AR = 51.7 mm ² , no fusion failure occurs in the range of _L = 4 to 8 mm.

In this way, for the torch-groove wall distance L that fluctuates during welding, the welding conditions are always controlled so as to be below the judgment line on the judgment model, thereby reliably preventing fusion defects. Can be done.

FIG. 32 shows a state of fusion failure determination under welding conditions in which only the heat input amount Q is similarly changed. Here, under the condition of Q = 4.8 kJ / mm, the range is L = 4 to 8 mm, and under the condition of Q = 4.0 kJ / mm, the range is L = 4 to 7.5 mm, and further, Q = 3. Under the condition of .2 kJ / mm, it is judged that fusion failure does not occur in the range of L = 4 to 7 mm.

FIG. 33 shows a state of fusion failure determination under welding conditions in which only the bead width _WB is similarly changed. Here, under the condition of _WB = 32.0 mm, the range is L = 4 to 9 mm, and under the condition of _WB = 26.5 mm, the range is L = 4 to 7.5 mm, and further, _WB = 21. Under the condition of 0 mm, it is judged that no fusion failure occurs in the range of L = 4 to 6 mm.

[Welding equipment]
FIG. 34 shows an ultranarrow groove submerged arc welding apparatus according to an embodiment of the present invention. Here, 41 is a welding target, and 42 is a welding torch having a single torch structure. By mounting the welding torch 42 on the traveling carriage 43, the welding torch 42 can move in the welding direction 45 along the length direction of the ultra-narrow groove 44 provided in the welding target 41. The welding torch 42 is configured to be attached to the uniaxial slider 46 so that the position can be adjusted in the width direction of the extremely narrow groove 44. Reference numeral 47 is a laser sensor, which is integrated with the welding torch 42 and is configured to be moved in the width direction of the ultra-narrow groove 44 together with the welding torch 42 by the uniaxial slider 46. Then, the laser sensor 47 recognizes the extremely narrow groove 44 in front of the welded portion, and measures the current position of the torch 42 and the distances L ₁ and L ₂ from the torch 42 to the left and right groove walls. Further, in FIG. 34, 48 is a digital welding power supply, and 49 is a control device (PC). The control device 49 has an algorithm in which the bead width _WB and the welding cross-sectional area _AR under each welding condition are stored in advance as a database, and the following processes 1 and 2 are performed.

That is, in the process 1, the control device 49 selects the conditions that do not cause fusion failure from the fusion failure determination model based on the measured distances L ₁ and L ₂ , and applies the welding power supply 48 to the welding power supply 48, the EN ratio, and the welding current. , The voltage value is instructed, and the welding speed value is instructed to the traveling carriage 43.

In the process 2, the control device 49 uses the uniaxial slider 46 to weld the torch 42 so that the target position of the torch 42 is always the center of the groove (L ₁ = L ₂ ) and L ₁ , L ₂ > 4 mm. The amount of movement ΔL of is determined. That is, the control device 49 instructs the 1-axis slider 46 as the difference between the current torch aiming position and the target aiming position as the movement amount, so that the torch aiming position is always controlled to be appropriate.

It is appropriate that the welding conditions controlled by the digital welding power supply 48 are in the following range. That is, it is appropriate to set the EN ratio: 0.0 to 1.0, the welding current: 400 to 800 [A], the welding voltage: 20 to 40 [V], and the welding speed: 30 to 81 [cm / min]. be.

[Welding flow]
The welding process using the welding apparatus of FIG. 34 will be described with reference to the flowchart of FIG. If the process is started in step S11 of FIG. 35, first, in step S12, the data of the groove 44 of the welding target 41 is acquired by the laser sensor 47 of FIG. 34. The data acquired by the laser sensor 47 is sent to the control device 49, and the control device 49 acquires the data of the distances L ₁ and L ₂ from the torch 42 to the left and right groove walls in step S13. Then, in step S14, the control device 49 determines whether or not fusion failure occurs under the conditions of the acquired data of the distances L1 and _L2 by using the above _- mentioned fusion failure determination model.

If it is determined in step S14 that a fusion defect occurs, the welding conditions are changed, that is, new welding conditions are selected in step S15. Then, in response to the selection result, in step S16, it is determined whether or not the EN ratio to be set in the welding power supply 48 has changed. When there is a change, the control device 49 controls the welding power supply 48 to change the set value of the EN ratio (step S17). If the EN ratio setting value is not changed in step S16 or the EN ratio setting value is changed in the welding power supply 48 in step S17, then, in step S18, the setting value is set in the welding power supply 48. It is determined if there has been a change in the welding current to be done. When there is a change, the control device 49 controls the welding power source 48 to change the set value of the welding current (step S19). If the set value of the welding current is not changed in step S18 or the set value of the current in the welding power supply 48 is changed in step S19, then the setting value is set in the welding power supply 48 in step S20. It is determined if there has been a change in the voltage to be taken. When there is a change, the control device 49 controls the welding power supply 48 to change the set value of the voltage (step S21). If there is no change in the voltage set value in step S20 or if the voltage set value in the welding power supply 48 is changed in step S21, then the voltage set value is set in the traveling carriage 43 in step S22. It is determined whether there has been a change in the expected welding speed. When there is a change, the control device 49 controls to change the moving speed of the traveling carriage 43, that is, the set value of the moving amount (step S23).

As a result of determination in step S22 when the welding speed is not changed, in step S23 when the set value of the movement amount of the traveling carriage 43 is changed, and in step S14 described above using the fusion defect determination model. When it is determined that no fusion failure occurs, in step S24, it is determined by the control device 49 whether L ₁ and L ₂ are equal from the data of the distances L ₁ and L ₂ acquired in step S13. Will be done. If it is determined that L ₁ and L ₂ are equal, the process returns to step S12, and the subsequent steps are repeated. If it is determined that L ₁ and L ₂ are not equal, in step S25, the control device 49 instructs the uniaxial slider 46 to move the corresponding movement amount ΔL so as to make them equal. When the uniaxial slider 46 moves the welding torch 42 by the amount of movement ΔL so that L ₁ and L ₂ become equal, the process returns to step S12 in the same manner, and the subsequent steps are repeated.

The degree of influence of each of the above welding parameters will be described. When the EN ratio becomes large, the bead width _WB at the time of bead-on-plate welding decreases, and the welding cross-sectional area _AR increases. As the welding current increases, both the bead width _WB and the welded cross-sectional area _AR increase. As the voltage increases, the bead width _WB increases but the welded cross-sectional area _AR does not change. As the welding speed increases, the bead width _WB decreases slightly and the welding cross-sectional area _AR decreases.

41 Welding target 42 Welding torch 43 Traveling carriage 46 1-axis slider 47 Laser sensor 48 Digital welding device 49 Control device _WB Bead width AR Welding cross-sectional area _L Welding cross section distance Q Welding heat input _HG To groove wall Heat input R Generalized distance from the surface of the molten pool to the corner of the bottom of the groove

Claims (8)

Under predetermined welding conditions, bead-on-plate welding is performed on the same material as the object to be welded, and the bead width _WB and welding cross-sectional area _AR at the time of the bead-on-plate welding are measured.
Welding heat input Q is obtained from the above welding conditions.
The heat input _HG to the groove wall at the time of welding is expressed by using the welding heat input Q, the bead width _WB , and the distance L between the torch and the groove wall.
The generalized distance _R from the surface of the molten pool to the corner of the groove bottom at the torch target position is expressed using the welding cross-sectional area AR and the distance L between the torch and the groove wall.
An experimentally obtained display of the presence or absence of fusion failure during groove welding was plotted on the _HG -R plane formed by the heat input _HG and the distance R.
A judgment line based on the presence or absence of fusion failure on the groove wall is drawn on the _HGR plane on which the display of the presence or absence of fusion failure during groove welding is plotted.
An ultra-narrow groove submerged arc welding method characterized in that groove welding is performed by setting welding conditions so that the region is free from fusion defects from the determination line. The feature is that the heat input _HG to the groove wall at the time of welding is expressed by the product of the welding heat input Q and the difference between the bead width _WB and the distance L between the torch and the groove wall ( _WB -L). The ultra-narrow groove submerged arc welding method according to claim 1. The power R of the distance R from the surface of the molten pool to the corner of the groove bottom at the torch target position divided by the distance L between the torch and the groove wall (AR / _L ) and the _torch- The ultra-narrow groove submerged arc welding method according to claim 1 or 2, wherein the distance L between the groove walls is expressed as a sum of powers. The feature is that the distance L between the torch and the groove wall is measured at the time of groove welding, and the welded conditions within the appropriate range where welding defects do not occur are set for the measured distance L between the torch and the groove wall. The ultra-narrow groove submerged arc welding method according to any one of claims 1 to 3. The invention according to any one of claims 1 to 4, wherein at least one of an EN ratio, a welding current, a voltage, and a welding speed as welding conditions at the time of groove welding is controlled. Ultra-narrow groove submerged arc welding method. A welding apparatus for carrying out the ultra-narrow groove submerged arc welding method according to any one of claims 1 to 5, comprising a digital welding power source, and the digital welding power source is EN. An ultra-narrow groove submerged arc welding apparatus characterized in that the set values of ratio, welding current, and voltage can be set and changed. The ultra-narrow groove submerged arc welding apparatus according to claim 6, further comprising a moving device for moving the torch in a direction orthogonal to the welding line direction in order to adjust the distance L between the torch and the groove wall. The ultra-narrow groove submerged arc welding apparatus according to claim 6 or 7, further comprising a sensor for acquiring data about the groove before welding.

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