JPH10249531A - Mag welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a MAG welding method which surely executes welding of an initial layer at the welding beginning position in the case of executing an uranami welding and which improves the welding quality of the welding beginning position. SOLUTION: In this MAG welding method to execute uranami welding of mutual base materials 1 formed with welding grooves 2, welding is started toward the reverse direction to the welding advancing direction X from a welding starting position 6, after welding a prescribed distance, it reversed to the real welding advancing direction X, and the welding heat input when welding the back side range 7 in the direction opposite to the welding advancing direction X is set smaller than that of the welding starting position 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a MAG welding method in which a base material having a welding groove formed therein is back-side welded.

[0002]

2. Description of the Related Art Heretofore, in the case of performing rim welding using this type of MAG welding method, it is necessary to form a good rim welding and not to cause poor fusion to a welding groove side surface. In addition, it is necessary to start welding under welding conditions that can obtain a predetermined heat input. Particularly, at the welding start position, the base material itself to be joined is in a low temperature state, so that heat input by welding is easily diffused. For this reason, in order to ensure the formation of an undercut from the welding start position, welding may be performed using welding conditions with increased welding current and voltage in order to secure a large heat input at the start of welding.

[0003]

However, if the welding heat input is set to a large value as described above, a backwash can be formed stably, while increasing the welding heat input can be achieved by increasing the amount of metal deposited in the welding groove. , That is, the amount of the deposited metal. At the welding start position, even if the backwash is completely formed, the heat of the weld bead is easily diffused to the surrounding base material because the temperature of the base material has not yet been sufficiently increased.
The weld bead is cooled rapidly. As a result, the weld bead solidifies without being sufficiently fused with both sides of the weld groove, and the cross-sectional shape of the weld bead becomes convex near the center as shown in the figure, and the weld bead near the boundary with the weld groove. The groove surface and the bead surface have an acute angle. When the next second layer is welded from above, a welding groove having a small welding groove angle is formed near the boundary between the welding bead and the welding groove surface. The welding arc of the layer welding does not reach the bottom of the “weld groove”, which causes welding defects such as slag entrainment and poor fusion. For this reason, the working efficiency is lowered such that it is necessary to grind the convex portion of the weld bead using a grinder or the like before welding the second layer. In addition, when performing multi-layer fill welding in a left-right direction from a single welding start position, the above-described welding for reliably forming a back seam is performed twice at one welding start position. Become. In this case, the amount of the deposited metal at the welding start position surely increases.
Therefore, even if a weld bead appearance that does not cause a weld defect is obtained, it is necessary to remove excess weld metal by a grinder treatment or the like, and the working efficiency is also poor. As described above, the conventional MAG welding method may cause various inconveniences, and there is still room for improvement.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to surely perform the first layer welding at the welding start position when performing Uranami welding, and to improve the welding quality at the welding start position. It is an object of the present invention to provide a MAG welding method.

[0005]

Means for achieving the above object of the present invention will be described with reference to the example shown in FIG. (Means 1) According to the MAG welding method of the present invention, as described in claim 1, welding is started from the welding start position 6 in the direction opposite to the welding advancing direction X, and after welding a predetermined distance, the original The present invention is characterized in that the heat input is reversed in the welding progress direction X and the welding heat input when the rear region 7 in the direction opposite to the welding progress direction X is welded to the welding start position 6 is reduced. (Operation / Effect) According to the present means, uranami welding can be performed in welding performed from the welding start position in the direction opposite to the welding progress direction. However, since the welding heat input is set to be small, the welding bead formed by welding in the opposite direction becomes convex toward the welding electrode. However, the subsequent welding in the original welding direction can re-melt the convex weld bead. In other words, even if welding defects such as poor fusion occur in the welding in the opposite direction, welding in the original welding direction re-melts the welding defects. Obtainable. In addition, by welding in the original welding direction, the convex portion of the weld bead formed by welding in the opposite direction is also flattened, so that a beautiful weld bead can be obtained. Further, in the rear region where these reciprocating weldings are performed, the welding heat input is reduced, so that the build-up amount does not become excessive, and time and effort such as removing excess weld metal during welding of the second and subsequent layers. It does not occur.

(Means 2) In the MAG welding method of the present invention,
As described in claim 2, the welding current and the welding voltage can be set low in order to reduce the welding heat input when welding the rear region 7. (Operation / Effect) With this means, especially when performing automatic welding, the conditions before and after the change of the welding conditions may be input to a welding control device or the like in advance, and in general, the welding build-up amount may be reduced. Since the most influential is the welding current value, it is also possible to easily adjust the welding build-up amount during welding.

(Means 3) In the MAG welding method according to the present invention, the welding speed is set to be high in order to reduce the heat input when welding the rear region 7 as described above. You may. (Operation / Effect) This means is convenient especially when performing semi-automatic welding. In the case of semi-automatic welding, the operator himself can change the feed speed of the welding torch, so that an appropriate welding bead can be formed while visually checking the build-up amount.

(Means 4) According to the MAG welding method of the present invention, as described in claim 4, in the rear area 7 in the area where lap welding is performed after reversing the welding direction X, the welding direction is May be oscillated in a direction intersecting with the welding electrode. (Operation / Effect) By means of this means, for example, the welding electrode is swung so that the arc of the lap welding in the original direction passes over the concave portion on both sides of the weld bead formed by welding in the opposite direction. Even if welding in the opposite direction produces welding defects such as poor fusion or slag entrapment on both sides of the weld bead, these welding defects can be re-melted to form a sound weld bead. In addition, the weld bead width of the lap welding can be positively increased, and a beautiful weld bead shape can be obtained.

In the description of the means for solving the above problems, reference is made to the drawings and, in order to facilitate comparison with the drawings, the reference numerals are used, but the invention is limited to the means shown in the accompanying drawings. Not something.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

As one of the embodiments using the MAG welding method of the present invention, a butt welding between flat plates is performed by using a welding groove 2.
FIGS. 1 and 2 show an example in which an object is sorted in the opposite direction from the middle of the process.
Shown in Hereinafter, the flat plate is referred to as a base material 1. In the present embodiment, in particular, the first layer is subjected to uranami welding, and the second and subsequent layers are subjected to full penetration welding over the entire thickness of the base material 1 by ordinary multi-layer welding. The base material 1 may use any material as long as the MAG welding method can be applied. In the present embodiment, ordinary steel is welded. Welding groove 2
Has a welding groove angle 2a as shown in FIG. 1, for example.
Is a V-shaped welding groove of about 35 degrees, and the root gap 2b is 0 to 2 mm. The root face 2c has a thickness of 0 to 1 mm in order to surely perform backwash welding. Backing money shall not be used. The welding electrode 3 is a consumable type, for example, a welding wire of 1.2 to 1.6 mmφ is used. The polarity is
The welding electrode 3 is a positive electrode, and the base material 1 is a negative electrode. As the shielding gas 4, a CO ₂ gas, a mixed gas of a CO ₂ gas and an argon gas, or the like is used. Regarding the welding conditions, the conditions at the start of welding and the conditions after the welding has transitioned to the steady state are different.

FIG. 2 shows a state of formation of a weld bead 5 when the above-described welding groove 2 is welded by using the MAG welding method of the present invention.
(A) to (f). In particular, in the first layer welding, it is necessary to form the surface shape of the welding bead 5 facing the welding electrode 3 appropriately, as well as to surely perform the backside welding. However, at the start of welding, the temperature of the base material 1 is not sufficiently increased, so that the heat input by welding is rapidly diffused into the base material 1, and the weld bead 5 is rapidly cooled. As a result, the penetration of the weld bead 5 into the welding groove 2 on both sides becomes insufficient, which causes welding defects such as poor fusion. Also, even when no fusion failure has occurred,
Since the molten metal transferred to the base material 1 solidifies rapidly,
As shown in (a), the surface of the weld bead 5 has a convex shape. For this reason, both end faces in the width direction of the welding bead 5 and the welding groove 2 form an acute angle, and the welding of the next layer is in the same state as performing the narrow welding groove welding, and the welding bead is formed. At the boundary position between the welding groove 5 and the welding groove 2, welding defects such as insufficient penetration may be caused. Therefore, the MA of the present invention
In the G welding method, as shown in FIG. 2A, first, reverse welding is started from the welding start position 6 in a direction opposite to the welding progress direction X, and after welding a predetermined distance, the original welding progress direction X The welding current and voltage during the reciprocating welding are set small so that the forward welding is performed in reverse and the build-up amount in the rear region 7 where the reciprocating welding is performed is not excessive. Specifically, for example, the welding current is set to 50 A, the welding voltage is set to 15 to 20 V, the welding speed is set to about 200 mm / min, and the welding groove 2 is reciprocally welded over a length of 20 to 30 mm. This situation is shown in FIGS. In this case, the main purposes of the reverse welding are to form a sound backwash bead 5a and to heat the base material 1. The welding bead 5 of the backward welding has a convex shape as shown in FIG. 2A, but the shape of the welding bead 5 is flattened by the subsequent forward welding. That is, the base metal 1 near the welded portion is formed by the reverse welding.
Has been preheated, and the welding bead 5 formed by the reverse welding still has a high temperature. For this reason, although the heat input of the forward welding is small, the convex portion of the weld bead 5 formed by the backward welding is easily re-melted by the forward welding.
Then, the re-melted metal surely fuses with the weld groove 2 already heated, and becomes a healthy weld bead 5 having a flat surface as shown in FIG. When performing forward welding of the reciprocating welding, the welding electrode 3 may be swung. That is, by oscillating the welding electrode 3 so that the welding arc 8 passes over the concave portions located on both sides of the welding bead 5 formed by the backward welding, welding defects such as defective fusion and slag entrapment in the backward welding are temporarily provided. Even if the welding has occurred, these welding defect portions can be re-melted to form a sound welding bead 5. Further, the width of the weld bead 5 in forward welding can be positively increased, and a beautifully shaped weld bead 5 can be obtained. The swing of the welding electrode 3 may be performed automatically or manually.
After the welding electrode 3 reaches the welding start position 6 again, the welding is performed while changing to the normal initial layer welding conditions. Specifically, the welding current is changed to 200 A, the welding voltage is changed to 18 to 22 V, and the welding speed is changed to about 200 mm / min. As shown in FIG. 2C, the surface of the welding bead 5 formed here facing the welding electrode 3 has a planar shape. That is, in the first layer welding after the reciprocating welding is completed and the normal welding conditions are transferred, the rear part of the periphery of the molten pool 9 in the welding traveling direction X, that is, the newly formed weld bead 5 is still at a high temperature. It is in. Therefore, the molten metal in the weld pool 9 receives the heat of the weld bead 5 and receives the welding groove 2 on both sides.
Can be surely fused. In addition, since the heat input of the weld bead 5 formed under the normal welding conditions is larger than that of the backward welding, the cooling rate of the weld bead 5 under the normal welding conditions is also reduced, and the welding bead 5 is flattened. A weld bead 5 having a surface shape can be obtained.

Since the reciprocating welding is performed by lowering the welding current and the like, the welding build-up amount of the portion concerned is, as apparent from the comparison between (b) and (c) of FIG. Less than the welded portion. However, the shortage of the build-up amount here is added by reciprocating welding when welding the remaining half of the welding groove 2 in distributed welding, and as a result, the same build-up as other initial layer welded parts The amount is obtained. As shown in FIGS. 2 (d), (e), and (f), in the reciprocating welding of the remaining half of the distributed welding, the welding is performed near the turning point of the preceding reciprocating welding, that is, near the end of the preceding welding bead 5. Start. As a result, reciprocating welding is further performed on the previous reciprocating welded portion, so that approximately the same build-up amount as that of a normal welded portion can be obtained.

In the welding of the second and subsequent layers, whether or not the reciprocating welding is performed is determined according to the working condition. For example, when performing the welding of the second and subsequent layers continuously after the initial layer welding, the base material 1 has sufficient heat. Therefore, even if reciprocating welding is not performed at the start of welding, the welding bead 5
Are sufficiently fused with the weld groove 2 to obtain a beautiful weld bead 5 having a flat surface shape. On the other hand, when the temperature of the base material 1 has decreased after a long time has elapsed after the end of the initial layer welding, the shape of the weld bead 5 at the welding restart position is adjusted by performing the reciprocating welding. Can be.

As described above, by using the MAG welding method of the present invention, it is possible to reliably perform the first layer welding at the welding start position when performing Uranami welding, and to improve the welding quality at the welding start position. .

[Brief description of the drawings]

FIG. 1 is a three-view drawing of a welding groove used in the MAG welding method of the present invention.

FIG. 2 is an explanatory view showing a state of formation of a weld bead in the MAG welding method of the present invention.

FIG. 3 is an explanatory view showing a state of formation of a weld bead in the MAG welding method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 base material 2 welding groove 6 welding start position 7 rear area X welding progress direction

Claims (4)

[Claims] In a MAG welding method for welding a base material having a welding groove formed therein, a welding is started from a welding start position in a direction opposite to a welding progress direction, and after a predetermined distance is welded. A MAG that reverses to the original welding direction and sets a small welding heat input when welding a rear region opposite to the welding direction with respect to the welding start position.
Welding method. 2. The MAG welding method according to claim 1, wherein the welding heat input is reduced by setting a welding current and a welding voltage for welding the rear region low. 3. The welding heat input is reduced by setting a high welding speed when welding the rear region.
3. The MAG welding method according to 1. 4. The welding electrode according to claim 1, wherein the welding electrode is swung in a direction intersecting with the welding progress direction in a region where lap welding is performed after reversing the welding progress direction in the rear region. MAG welding method.