JPS5940549B2 - DC TIG welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC TIG welding method that enables high-speed welding in all positions, especially in the vertical position, while preventing magnetic blow.

Although TIG welding is recommended as a welding method for large structures, it also has the following drawbacks.

1. If the welding speed is increased too much, insufficient preheating of the base metal will result in poor fusion between the base metal and the weld metal.

2. DC TIG arcs are easily affected by surrounding magnetic fields due to magnetization and shape changes of the welded materials.

As a result, magnetic blowing is often experienced, especially when deflected onto a prefabricated bead, resulting in poor fusion or reduced welding speed due to insufficient preheating of the base metal, or remelting of the bead, especially in the latter case. Welding in a standing or upward position may even cause the bead to fall off. From this point of view, we first proposed Japanese Patent Application No. 53-60523, and succeeded in overcoming the above-mentioned drawbacks by making reverse use of the magnetic blowing phenomenon.

The gist of the proposed method is that (A) a DC power source is installed between the non-consumable electrode and the base metal, and between the filler metal and the base metal, (B) the direction of the current flowing through these is When the consumable electrode is in the leading position, the direction is in the opposite direction (B) When the filler metal is in the leading position, it is in the same direction, and (C) These direct the arc forward along the welding progress line. This is shown in FIG. 1, taking the case of case B)-1 (a) as an example.

That is, the direction of welding progress is indicated by arrow W, the shield gas cup 5 and tungsten electrode 2 are on the leading side, and the filler metal 6 is on the leading side.
follows the trailing side while being fed in the direction of arrow Y. 3
is an arc, 4 is a bead, and 7 is a molten pool, but when the tungsten electrode 2 is of DC positive polarity as shown in the example,
The filler metal 6 side is used as an anode (the base metal 1 side is used as a cathode).

When the DC polarity is reversed, these relationships are reversed. As a result, the directions of the currents in the electrode 2 and the filler metal 6 become opposite, and the electromagnetic forces generated by these currents and magnetic fields repel each other according to Fleming's left-hand rule. Similarly, the arc column is deflected in a direction away from the filler metal 6, that is, in the welding progress direction. The adoption of the above means paved the way for faster DC TIG welding, and furthermore, in order to sweep the above-mentioned arc forward along the welding progress line, the energization to the filler metal was changed to a pulsating current. A welding method was also proposed (Japanese Patent Application No. 53-133004).

Therefore, the drawbacks of DC TIG welding have been solved and its application to large structures has increased, but when performing all-position welding,
In particular, the following problems were encountered with vertical advancement welding. Fig. 2 is a corresponding diagram when the welding method shown in Fig. 1 is applied to the vertical position, but except for the angle formed between the front surface of the molten pool 7 and the base metal, there is no substantial difference from that in Fig. 1. do not have. However, the filler metal 6 must not be in contact with the electrode 2 and the gas cup 5;
Also, even if there is no contact, it must not contaminate the electrode 2, so an appropriate angle (
θ, ). Then, the filler metal 6 is inserted into the melt pool 7 as shown in the figure, but the surface of the melt pool 7 seen from the feeding direction of the filler metal 6 is extremely small in the vertical position, and moreover, the surface directly below it is extremely small. Since there is a final bead 4' in the semi-solidified or solidified stage, accidents such as the filler metal 6 hitting or getting caught on the bead 4' are likely to occur. These accidents may force welding to be interrupted, or even if they do not cause welding to be interrupted, they may form scratches or dents on the bead surface, leading to welding defects. The above-mentioned accidents are not limited to the vertical position, but can also occur when the feed rate of the filler metal is high, and it has been found that this will become a bottleneck in the generalization of the inventions of the earlier applications. Ivy. The present invention has been made in view of these circumstances, and aims to establish a DC TIG welding method that does not have the above-mentioned drawbacks.

That is, the present invention provides the above-mentioned DC TIG welding method in which the leading side is a non-consumable electrode and the trailing side is a filler metal, while keeping the non-consumable electrode in a forward tilted position. The gist is that each current flowing in the opposite direction is formed. The configuration and effects of the present invention will be described below based on drawings showing examples, but the following examples merely describe typical embodiments, and in addition to the embodiments described in the claims, the previous embodiments, Modifications in accordance with the spirit described below do not depart from the technical scope of the present invention.

First, FIG. 3 shows an example of application of the present invention in upward welding in a vertical position, in which the electrode 2 and shield gas cup 5 are tilted forward in the direction of the welding force, so A considerable margin is formed in the space above (on the right side in the figure) the molten pool 7 formed on the rear side.

Therefore, although the surface of the molten pool 7 viewed from the feeding direction of the filler metal 6 is quite narrow as described above, the angle at which the filler metal 6 is raised from the surface of the base metal 1, that is, the angle of the base metal 1 It can be fed from an angle fairly close to perpendicular to the surface. That is, the intersection angle formed by the electrode 2 and the filler metal 6 is θ1 as described above.
In addition, when the forward inclination angle of the electrode 2 is θ2, the intersection angle between the filler metal 6 and the surface of the welded side base metal 1 is θ3, and the intersection angle between the surface of the molten pool 7 and the surface of the welded side base metal 1 is θ4. , θ1 has a limit, and in order to increase θ3 (more specifically, to satisfy θ3>θ4), θ2 must be decreased. Thus, one of the essential requirements in the present invention is defined as θ2 minus 90 degrees, and a more preferable condition is θ2≦85 degrees. By the way, as mentioned above, there is a limit to reducing θ1, but from the viewpoint of the general size of the shield gas cup 5 and stable feedability of the filler metal 6, the lower limit of θ1 is practically 2.
It is thought to be around 0 degrees.

However, if θ1 is made too large, θ3 may not be able to be made large enough even though a forward leaning posture of θ2<90 degrees is provided, and θ3≦θ4. In that case, the risk of contact between the filler metal 6 and the final bead 4' is secondary.
Since it is larger than the case shown in the figure, the upper limit of θ1 is 60.
It was determined as degree. However, the above numerical limitations may be changed depending on the viscosity of the melt pool. In the present invention, since the electrode 2 is held in the forward tilted position as described above, the arc 3 is originally formed in the direction of the molten pool 7, which is substantially the same as the magnetic blowing state described as a drawback of the prior art. This not only hinders the improvement of welding speed, but also heats the molten pool 7 and becomes a cause of burn-through defects in the vertical position.

However, the second point of the present invention is to reverse the direction of direct current flowing through the electrode 2 and the filler metal 6, so that the electromagnetic forces generated near the arc repel each other as described above. The arc column can be deflected forward. That is, when welding is carried out under constant welding current conditions, the greater the forward inclination angle of the electrode 1, the greater the electromagnetic force acting on the arc column, so the amount of current applied to the filler metal 6 depends on the magnitude of θ2. It is desirable to control the
Although stable feeding of the filler metal 6 was guaranteed by the above method,
The method of the present invention is not only effective for welding in a vertical position as illustrated, but is also useful for welding in any position, and is widely applicable to welding in all positions, single welding in a horizontal position, single welding in a horizontal position, etc. Applicable.

In this way, it was possible to effectively prevent magnetic blowing during DC TIG welding and improve the welding speed.
It is recommended to use the arc sweeping method proposed in 3-133004. That is, when the welding speed is increased, proholes are more likely to occur, and some countermeasure is desired. Further, although the filler metal of the present invention is energized as described above, the filler metal itself is not heated because it is not the so-called hot wire method itself. Therefore, if the tip of the filler metal becomes detached from the molten pool for some reason, there is a risk that it will subsequently be fed onto the solidified bead. There is an arc weeping method as a means to solve these problems, but in the above-mentioned prior invention, the electromagnetic force is strong and weak by applying electricity to the filler metal in a pulsating manner without using mechanical means. (Weakness includes zero) is proposed. This method utilizes the high flexibility of TIG arc,
If the current flowing through the filler metal is made weaker (or zero), the arc that was deflected forward can be pulled back in the direction of the filler metal, and conversely, if it is made stronger, it will be deflected forward again. In the present invention, the proposed method can be adopted almost as is, but the pulsating flow pattern shown in FIG. 4 is exemplified. In addition, welding state explanatory diagram F shown on the right side of Fig. 4,
G shows the case of horizontal position welding, and for the sake of understanding, the molten pool, weld bead, shield gas cup, etc. are omitted. In Figure 4, the pulsating flow pattern is shown on the left side A-E.
In particular, for A and D, the arc deflection states F and G at this time are shown on the right side. That is, AC is alternately energized and de-energized, and the de-energized time limit of C is almost equal to zero. In addition, in D and E, the filler metal is constantly energized, and pulsating currents are formed by alternating between high energization (Ah) and low energization (Al). Note that (Th) indicates the time interval during which a large current is flowing, and (Tl) indicates the time interval during which a small current is flowing (or no current is flowing), and the deflection state of the arc column at each stage is You can understand that it changes depending on the amount of current. Note that E is a case where the current changes minutely in both time periods, and such a case is also included in the embodiment of the present invention. As described above, by selecting various values of (Ah), (Al), (Th), and (Tl), the weeping width (weeping angle) and the weeping cycle can be freely adjusted, and the weeping progress or Each behavior at both ends of the amplitude is also
Can be freely adjusted by changing the current value. For example, when welding circumferential butt weld lines of pipes in sequence in upward, sideways, and downward positions, the direction of gravity relative to the weld pool changes moment by moment, and the optimal weeping pattern is selected at each time. This is one of the significant effects of the present invention. In addition, in general single-sided back wave welding, when abnormalities are encountered along the welding line, such as fluctuations in the groove root gap, misalignment, or errors in the root face, the TIG current value is varied in response. However, the temperature and shape of the arc, as well as the size of the molten pool, etc., vary accordingly.

Therefore, it is necessary to change the melting rate of the filler metal, and the TI
The current value of the G arc and the feeding speed of the filler metal had to be synchronized. However, this adjustment is extremely complicated;
It is very convenient that the above-mentioned abnormality can be dealt with simply by changing the amount of current applied to the filler metal as in the above method. Some examples of such measures will be explained below. (1) For example, when welding according to the pattern shown in FIG. 4A, if the root face suddenly becomes thicker, the back bead at that part becomes difficult to come out as it is. Therefore, when the current value indicated by (Ah) is adjusted to be even larger, the forward deflection angle of the arc column increases, and the arc directly acts on the groove root surface of the unwelded portion in the forward direction. As a result, the root portion is sufficiently melted and the back bead is sufficiently formed. (2
) In the same case as above, if the time limit for energizing the filler metal is lengthened, the time that the arc is directed forward becomes longer and sufficient penetration can still be obtained.

(3) In the same case as above, there is a method of combining measures (1) and (2). (4) In the same case as above, change to the pattern shown in FIG. 2 D and E, and if necessary, make (Ah) higher.

(5) In the above (4), there is a method of using the means of (2) in combination.

(6) A combination of the above (4) and (5) may be used.

(7) In addition, if various fine adjustments are made in accordance with these, several further embodiments can be considered. Regarding the situation of the materials to be welded,
In addition to these, it may be necessary to consider welding when the groove is wide.

At this time, the electrode 2 itself must be turned on in a direction that intersects the welding progress line, so the filler metal must also be turned on in a direction that intersects the welding progress line. Note that the on-rate pattern is not limited. By the way, in the scope of the present invention, the arc is deflected forward even during the above-mentioned on-rate in principle, but the present invention also includes control methods in which the deflection is interrupted, relaxed, or strengthened as modified examples of implementation. 5th to 8th
The figures explain these. Figure 5 shows the intersection A of the base metal 1 and backing metal 8 when welding in the I groove, and Figure 6 shows the intersection B of the base metal 1. When aiming and welding (8!
(indicates a backing material), Fig. 7 shows when welding is aimed at the intersection C between the base metal 1 and weld bead 4, and Fig. 8 shows when welding is aimed at the intersection D between the weld beads 4 in addition to the above C. When welding such an intersection, the above-mentioned on-rate welding is often performed regardless of whether it is downward, vertical, horizontal, upward, etc. However, among the on-rate paths, the base metal 1, weld bead 4, and backing metal 8 must be preheated particularly carefully at each intersection A-
It is D. Therefore, it is extremely useful to particularly increase the amount of current applied to the filler metal at the stage when the TIG arc aims at the above-mentioned intersection, and to tilt the arc sufficiently forward.As one of the preferred embodiments of the present invention, Recommended. In addition, in areas other than the intersection A-D, the amount of forward deflection may be reduced, and in some cases, it is also possible to stop the deflection by cutting off the current to the filler metal, and these can be combined with the above-mentioned weeping. Even better welding can be achieved by carrying out the welding process. Since the present invention is configured as described above, it has become possible to perform high-speed welding in all positions when performing DC TIG arc welding.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the basic concept of deflecting the TIG arc forward, Fig. 2 is an explanatory diagram showing problems in vertical position welding, Fig. 3 is an explanatory diagram showing an embodiment of the present invention, and Fig. 4 is an explanatory diagram showing the basic concept of deflecting the TIG arc forward. Figure 5 is an explanatory diagram showing means for weeping the arc.
Figures 8 to 8 are explanatory diagrams showing locations where arc deflection is particularly required when turning on the torch. 1... Base material, 2... Tungsten electrode, 3... Arc, 4... Bead, 6...
...Filler metal.

Claims (1)

[Scope of Claims] 1. A DC TIG in which both the non-consumable electrode and the filler metal are connected to a DC power source, and the non-consumable electrode is placed in front in the direction of welding progress, and the filler metal is supplied from a rear position. A direct current TIG welding method characterized in that the non-consumable electrode is kept in a forward-inclined position while the directions of current flowing through the non-consumable electrode and the filler metal are opposite to each other. 2. In claim 1, a direct current T whose intersection angle with the base material in the forward-inclined position of the non-consumable electrode is 85 degrees or less
IG welding method. 3. The DC TIG welding method according to claim 1 or 2, in which the intersection angle between the non-consumable electrode and the filler metal is 60 degrees or less. 4. The DC TIG welding method according to claim 1, 2 or 3, in which the arc is weaved along the welding progress line by applying a pulsating current to the filler metal. 5. A DC TIG welding method according to claim 4, in which the pulsating current to the filler metal is carried out by alternating periods in which the current is energized and periods in which it is not energized. 6. The direct current TIG welding method according to claim 4, in which the pulsating current to the filler metal is carried out by alternating time periods in which a relatively large current is passed and times in which a relatively small current is passed. 7. A DC TIG welding method according to claims 1 to 5 or 6, in which the non-consumable electrode and the filler metal are oscillated in a direction intersecting a welding progress line. 8 In claim 7, the welding target position is
TIG welding in which the amount of current applied to the filler metal is increased at intersections between base metals, intersections between preceding weld metals, intersections between base metals and preceding weld metals, and intersections between base metals and backing metals. Law.