JPS6144597B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of gas-shielded arc welding a butt groove of Al or Al alloy (hereinafter referred to as Al alloy) in a horizontal position.

Horizontal welding of Al alloys is considered to be a very problematic welding method due to the metallurgical and physical characteristics described below.

(1) The melting point of the oxide film covering the surface of the Al alloy is much higher than that of the base metal. Therefore, to the extent that it is in contact with the molten base metal, the oxide film is difficult to melt and is likely to cause welding defects such as cold traps and poor fusion. That is, in order to perform good welding, it is necessary to apply arc force directly to the surface of the base metal.

(2) The thermal conductivity of Al alloys is better than that of steel, and the heat retained in the molten metal is quickly diffused into the base metal, which promotes the defects mentioned in (1).

(3) In horizontal welding, the ability to hold molten metal on the lower groove surface is small, and there is a limit to the weight of molten metal per pass. Therefore, overall welding work with low heat input is forced.

(4) As soon as the Al alloy on the upper groove surface melts, it begins to droop, so the unmelted base metal is exposed on the upper side, and the base metal on the lower groove surface is exposed as described in (1). The molten metal appears to be protected and protects the base metal from arc forces (this is referred to herein as the cushion effect). That is, the base material of the upper groove is directly affected by the arc force, and the penetration depth is greatly unbalanced between the upper and lower parts.

Based on these considerations, in conventional horizontal Al alloy welding, the groove angle is set sufficiently large.
Measures were taken to reduce the amount of molten metal by suppressing the welding current, and to strictly control welding conditions such as the insertion angle of the consumable electrode, target position, and welding speed. Therefore, the welding efficiency is extremely poor, and some kind of improvement is desired, and the following measures have been proposed.

Special Publication No. 51-263831 does not form a groove on the upper side,
This method forms a groove only on the lower side, which seems to be effective in eliminating welding defects, but requires more severe control than before to prevent sagging of molten metal. Therefore, although the effect of increasing the welding current is touted, it is not enough to significantly reduce the number of welding passes, and moreover, it forces the welder to face upward, so it is not necessarily recommended.

In addition, Japanese Patent Publication No. 52-36940 achieved a reduction in the number of passes by making the groove shape as narrow as possible and oscillating the tip of the consumable electrode in the direction of the plate thickness, and the work procedure for each pass was almost reduced. Coupled with the fact that they can be made identical, it is recommended as a highly efficient means. However, in connection with the narrowing of the groove spacing, the tolerance range of the groove dimensions has become narrower, and there are problems when applying it to actual structures.

The present invention has been made with attention to these circumstances, and has a wide tolerance for errors in groove preparation, is easy to perform welding, can be welded with high efficiency, and is highly reliable. The purpose is to provide a welding method that allows a welded joint to be obtained.

That is, in the present invention, when performing horizontal butt gas shield arc welding of Al or Al alloy by making the angle formed by the consumable electrode and the molten pool surface on the forward side in the welding progress direction larger than 90 degrees, the tip of the electrode is opened. The gist is that the welding current is increased in the vicinity of the turning point on the lower groove surface side during the swinging process to perform welding while swinging in the tip width direction.

The welding conditions of the present invention will be explained below based on the drawings.

Figure 1 is a vertical cross-sectional view showing a horizontally welded joint;
2 is a horizontal sectional view showing the upper part of the same, and corresponds to the sectional view taken along the line - in FIG. 1. However, FIG. 2 shows a ready-made bead 7 and a molten pool 9 formed at the back of the groove. In these figures, an upper base material 1a and a lower base material 1b made of an Al alloy are butted together through a groove portion as shown by A. On the other hand, an electrode wire 2 protrudes from a current-carrying chip equipped with an external shield nozzle 4 and an internal shield nozzle 5, and is inserted toward the back of the groove A to generate an arc 8.

The reason why the angle θ on the front side in the welding progress direction formed by the electrode wire 2 and the surface of the molten pool 9 is set to be larger than 90 degrees is as follows.

(1) By setting θ>90°, the arc 8 precedes the molten pool 9 and directly hits the surface of the base material, and its cleaning action removes the high melting point oxide film on the surface of the base material.

(2) Arc force acts directly on the base metal surface, allowing deep penetration.

On the other hand, if θ≦90°, the arc 8 will always be directed toward the molten pool 9, making it impossible to obtain the above-mentioned cleaning action and resulting in insufficient penetration due to the cushioning effect of the molten pool.

By the way, the most important point in the present invention is that the electrode wire 2 is swung in the width direction of the groove A as shown by the arrow 6 in FIG. In other words, Fig. 3 is a longitudinal cross-sectional view showing a wide groove with a groove width exceeding 10 mm, and it is possible to obtain one-pass welding per layer using the conventional method of simply swinging in the plate thickness direction. Even if you try, it will result in an inclined bead 7 as shown in Figure 3A,
Undercuts 7a and overlaps 7b are formed, leading to welding defects. On the other hand, in the present invention, the arc spreads in the width direction of the groove due to the above-mentioned rocking, so a good bead 7 as shown in FIG. become parallel. This effect is exhibited even with a groove width of about 20 mm, and the groove width tolerance for single-layer, one-pass welding is expanded to approximately twice that of conventional welding.

The second point of the present invention resides in increasing the welding current in the vicinity of the turning point on the lower groove surface side during the swinging process in the groove width direction. In other words, the molten metal formed by the above-mentioned oscillating welding drips down toward the lower groove surface due to its gravitational action.
If the arc is simply oscillated in the width direction of the groove, the arc directed toward the lower groove surface is likely to be affected by the cushioning effect of the molten pool. On the other hand, the upper groove side is not affected by the cushioning effect and is unbalanced. Therefore, a configuration was adopted in which the welding current was increased to strengthen the arc force when the electrode wire came near the turning point on the lower groove surface side, and the molten pool was pushed back toward the rear in the welding direction. As a result, the arc force was sufficiently applied to the lower groove surface, and the above-mentioned cleaning effect was exerted and deep penetration was ensured.

Although the basic configuration of the present invention has been explained above, the embodiments thereof will be further described in detail.

First, the stroke of the wire tip in the groove width direction is less than 1/2 of the groove width (absolute value is
15 mm or less), but since the need for rocking is particularly large on the lower groove side, the center point of the rocking stroke should be moved to the lower groove side, and the rocking should be performed on the lower side as a whole. It is preferable to do so. If the rocking stroke becomes excessive, microfissure, which will be described later, is likely to occur.

Next, a front view from the direction of the arrow in Fig. 1 (see Fig. 4).
In Figure), when considering a perpendicular line H that is orthogonal to the welding line W, it is desirable to not only swing the electrode wire in the H direction, but also to take into account the swing in the W direction. The resulting swing direction is indicated by a zigzag arrow in FIG.
The angle β between this composite direction and the H direction is
It is preferable to select from the range of −45° to +45°. In Fig. 4, A is β = +45°, B is β = -
The case of 45° is shown respectively. The reason why such an embodiment is preferred is that in the case of the present invention, which aims to increase the amount of molten metal in one pass, the surface of the molten pool tends to be inclined, and the direction of rocking is directed toward this surface. By making it run along the surface, the cleaning action is strengthened and the influence of the arc force on the surface of the base material is increased.

Further, by performing such tilting and swinging, the effect of expanding the applicable postures of the method of the present invention can also be obtained. In other words, even if the weld line is inclined with respect to the horizontal direction, if the swing direction is selected according to the degree of inclination of the molten pool surface, the effects of the present invention as described above can be achieved without any dilution. It is performed as it is without. If the inclination angle β exceeds the range of ±45°, it will be difficult to avoid the cushioning action on the lower groove surface side, and the actual swing width in the groove width direction will become smaller.
The effect of the present invention is reduced. When welding a weld line with a large groove error, it is necessary to vary the swing stroke accordingly, which may cause the repeated phenomenon of bead solidification and remelting in some areas (especially at the front edge of the bead). This also caused microfission to occur inside the bead.

Next, the swing interval in the groove width direction is
It is recommended that the rate be 200 times/min or less. 200 per minute
If the speed exceeds the rotation speed, the arc will be dragged in the swinging direction and spatter will occur frequently due to arc instability, which is not preferable.

Next, the angle α (the angle between the electrode wire 2 and the lower groove surface) shown in FIG. 1 will be described.
The shape of the horizontal groove to which the present invention is applied is I
It doesn't matter what shape, rectangular shape, V shape, U shape, etc., but considering the improvement of welding work efficiency and the reduction of materials,
It is desirable that the groove angle is 30 degrees or less. On the other hand, the above-mentioned angle α is set to the optimum value each time depending on the lamination method of the groove shape, but is generally selected from within the range of 0 to 40 degrees. That is, if the angle exceeds 40 degrees, the surface of the weld bead will be formed to be significantly inclined with respect to the welded material, making it difficult to hold the molten metal during the next pass of lamination. Further, since the shield nozzle is also tilted greatly with respect to the surface of the base material, a problem arises in that the supply of shield gas to the inside of the groove tends to be insufficient. If the angle is less than 0 degrees, that is, if the electrode wire is oriented toward the upper groove surface, the influence of the arc force on the lower groove surface becomes weak, resulting in poor penetration.

Next, we will discuss the increase in welding current near the turning point on the lower groove surface side. The amount of increase in welding current can be determined according to the base current, but at least
An increased current of 50A or more is recommended. Regarding the base current, from the viewpoint of work efficiency, the higher the welding current, the more effective it is, and generally a welding current of 250A or more is used. Therefore, the welding current near the turning point is 300A or more. Al
In welding alloys, it is desired to prevent the occurrence of puckering, so a current below puckering should be used. The puckering current varies depending on the diameter of the electrode wire and shielding conditions, but
When welding with a 2.4mmφ wire under He shielding conditions, the current is 450A, so there are no particular disadvantages as long as the current is within the above recommended current range.

By the way, as a method of increasing the welding current near the turning point, the following means are adopted. The first method is as shown in FIG. 5, in which the lower groove surface is formed or arranged to be inclined, and the electrode swing width S in the groove width direction is adjusted to the lower groove surface. Set it so that it straddles the back corner C. When a welding power source with constant voltage characteristics is used under such conditions, the "arc length self-maintenance phenomenon in consumable electrode feeding type gas shielded arc welding" occurs advantageously for the present invention. That is, the electrode wire 2m that was initially in the state M
However, when it swings downward and enters the N state, the tip of the electrode wire 2n retreats as shown in the figure, but if you observe the progress in minute time units, you will notice that the arc first appears on the groove surface. thrust occurs, and the arc length is lm
It is shortened like →ln→. Therefore, the arc voltage is Em
→ En, and as is clear from the current-voltage relationship diagram shown in Figure 6, the welding current increases as Im → In. The protruding length of the electrode wire is Lm→
During this process, the electrode wire tip behaves as if it were swinging in the thickness direction of the base material, and the arc moves along the lower groove surface and opens. Gives a deep blend to the tip. When adopting this method, if the above angle α is less than 0 degrees, the arc will burn back along the lower groove surface, and if it exceeds 40 degrees, the swing width (in the groove width direction) will be considerably reduced. Unless it is made large, the above-mentioned current increasing effect cannot be obtained and this is not practical. Therefore, in I-shaped groove welding, the angle α becomes small and it becomes difficult to employ the first method, so the second method as described below is employed. In other words, the tip of the electrode wire is set so that it does not go beyond the inner corner C of the groove and swings above the inner corner C, and when it approaches the inner corner C, the arc voltage and welding This is a method of switching the current from Em to En and Im to In as described above. Since such switching is performed by setting switching conditions in advance, the welding conditions can be managed extremely accurately, and if it is desired to add swinging in the plate thickness direction, it can be controlled independently. Therefore, it is possible to change the welding conditions while reviewing the bead condition in the previous pass, and fine-grained welding can be performed.

FIG. 7 is a graph showing the relationship between the swing width of the electrode wire (in the groove width direction) and the current change in the first method, and FIG. 8 is a corresponding graph in the second method. The swing locus shown in the upper part of FIGS. 7 and 8 is seen from the direction of the arrow in FIG. 3. Note that T indicates the welding time during which a large current is applied.

Although there are no particular restrictions on the shielding gas used in carrying out the present invention, Ar has a specific gravity approximately 1.7 times that of air, so it is superior to He in terms of shielding performance. However, since He has a larger potential gradient, He is preferable for performing large heat input welding to deepen penetration, and also has the advantage of being able to increase welding speed. Therefore, it is practical to use a mixed gas of Ar+He depending on the purpose.

9 and 10 are examples of lamination in the present invention,
A to D in FIG. 9 are progress charts showing the V-groove lamination procedure, and in FIG. 10, A shows the case where the groove width is narrow, and B shows the case where the groove width is wide. In each figure, the upper and lower electrode wires represent the upper and lower limits of swing, respectively. Regarding the pass on the lower groove side in FIG. 10B, it is preferable that the aiming angle of the electrode wire be the same as in FIG. 10A.

Since the present invention is constructed as described above, Al
When performing gas-shielded arc lateral welding on butt grooves of alloys, it is possible to improve welding efficiency and to obtain good penetration into the groove surface, especially the lower groove surface.

Next, examples of the present invention will be shown.

Test material: Al alloy A5083-O material Plate thickness 70mm Welding wire: Al-MIG welding wire 2.4mmφ JIS 5183-WY Shielding gas: Ar double shield Inside 20/min Outside 40/min Groove shape: Fig. 11 Welding conditions : Welding current 280A←→350A Welding voltage 29V←→33V Swing conditions Groove width direction (β=0°) Swing width 5 to 8 mm Number of swings 80 times/min Torch angle θ=100° α=10° comparison Example Welding current 280~300A (unspecified) Welding voltage 29~30V (unspecified) Oscillation conditions Only in the plate thickness direction Oscillation width 10mm Number of oscillations 80 times/min Torch angle θ=100゜ α=10゜ Obtained The macro cross-section of the welded part is as shown in Reference Photo 1 (invention) and Reference Photo 2 (comparative example). In the former case, penetration is sufficient and a nugget shape is obtained at the back corner on the lower groove side, whereas in the latter case, penetration is insufficient and poor fusion occurs.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of the weld, Figure 2 is a horizontal cross-section, Figure 3 is a vertical cross-section of the joint, Figure 4 is a front view showing progress during welding, and Figure 5 is a cross-sectional view of the electrode wire. 6 is a current/voltage relationship diagram, 7 and 8 are graphs showing the relationship between the oscillation width of the electrode wire and current change, and 9 and 10 are lamination explanatory diagrams. 1
FIG. 1 is a longitudinal sectional view showing the groove shape of the example. 2... Electrode wire, 6... Oscillating direction, 7... Bead, 9... Molten pool.

Claims (1)

[Claims] 1. In a method of performing horizontal butt gas shielded arc welding of Al or Al alloy by making the angle formed by the consumable electrode and the molten pool surface on the forward side in the welding progress direction larger than 90 degrees, the tip of the electrode is in the groove width direction. 1. A horizontal butt gas-shielded arc welding method for Al or Al alloy, characterized in that the welding is performed by increasing the welding current near the turning point on the lower groove surface side during the rocking process.