JP2001001141A - Consumable electrode type bipolar arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the shape of a cross-section in the bead width direction by changing the polarity of a welding power supply so that the polarity becomes a reversed polarity at an oscillating tip part and the polarity becomes a straight polarity in an oscillating center part, and making a wire feed speed increase at the time of the straight polarity while synchronizing with the change of the polarity. SOLUTION: At the time of oscillating welding torches 2 in the groove width direction by using an AC welding power supply whose polarity ratio is changeable, by changing the polarity of the welding power supply so that the polarity becomes a reversed polarity at an oscillating tip part A and so that the polarity becomes a straight polarity in an oscillating center part B, and by making a wire feed speed synchronize with the change of the polarity, the wire feed speed is increased at the time of the straight polarity. Preferably without changing a welding current value, and by changing the time ratio of the polarity of the welding power supply so that the time ratio of the straight polarity becomes 30% or below at the oscillating tip part A and that becomes 50% or over in the oscillating center part B, the wire feed speed is increased when the time ratio of the straight polarity is 50% or over.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to flat plate butt welding,
More particularly, the present invention relates to a consumable electrode type bipolar arc welding method suitable for one-sided reverse welding with a gap.

[0002]

2. Description of the Related Art Gas metal arc welding is generally performed with the opposite polarity (bar plus) with the torch side plus and the base material side minus as shown in the left diagram of FIG. In the welding of the opposite polarity, there is a characteristic that the metal penetrates deeply into the base material and the amount of wire fusion is small. Therefore, in the case of a thin plate, etc., the welding current (heat input) tends to be larger than the plate thickness. In such a case, the center in the bead width direction becomes concave, and burn-through occurs in the center in the bead width direction. There is a possibility that there will be.
Particularly, in a joint having a gap G due to a joint error as shown in FIG. 4A, there is a tendency that burn-through as shown in FIG. In the case of backside butt welding with a gap, rocking is performed to ensure penetration at both side walls of the groove. However, if the gap is large as shown in FIG. Poor fusion LF at both ends of front wall
Is easier to do.

On the other hand, as shown in the right figure of FIG. 3, in welding with a positive polarity (minus rod) with the torch side minus and the base material plus, the penetration into the base material is shallow and the amount of wire fusion is large. Has characteristics. Accordingly, as shown in FIG. 4 (d), in the backside butt welding, the center in the bead width direction becomes convex,
Although it is advantageous for burn-through, poor penetration tends to occur,
It has not been put to practical use except in special cases. That is, in the backside butt welding, it is necessary to prevent burn-through at the center and ensure penetration at both side walls.

[0004] When performing covered arc welding, the welding operator swings the tip of the welding rod as necessary to obtain a good welding joint. At the time of this swing, the welding current is switched between high and low by an AC arc welding machine, the high current time zone is set at the swing end, and the low current time zone is set at the swing center, and the bead width is set. While preventing burnout at the center of the direction,
Japanese Patent Application Laid-Open No. Sho 53-54152 proposes that welding defects such as poor fusion with a groove surface can be reduced.
Hereinafter, this is referred to as a first conventional example).

Further, in a consumable electrode type bipolar arc welding method in which a DC voltage is applied between a consumable electrode and a base material to generate an arc by inverting the polarity of the consumable electrode, a reverse polarity (rod plus) arc is used. The ratio is made higher than that of the main welding at the start of welding, and after the start of welding, the reverse polarity ratio is reduced over a predetermined period to shift to the main welding, thereby improving the shape of the weld bead at the start of welding, There has also been proposed a device which solves the problems of poor fusion and discontinuity of beads (Japanese Patent Laid-Open No. 1-192482: hereinafter referred to as a second conventional example).

[0006]

The welding current is switched between high and low levels, and the high current time zone is set at the swing end and the low current time zone is set at the swing center. In the above-mentioned first conventional example, which is capable of preventing burn-through and reducing welding defects such as poor fusion with a groove surface, two power supplies including transformers are provided to reduce the welding current value. Since the height is switched between two levels, there is a problem that it is difficult to obtain an overfill, the center in the bead width direction is concave, and the desired welding cannot be performed in one pass, and re-welding is required.

Further, the ratio of the reverse polarity (bar plus) arc is made higher at the start of welding than in the main welding, and after the welding is started, the reverse polarity ratio is reduced over a predetermined period to shift to the main welding. Improves the shape of the weld bead at the start of welding,
In the above-mentioned second conventional example in which the problem of poor fusion and the discontinuity of the bead is solved, the main purpose is to improve the discontinuity of the bead in the direction of the welding line. It did not reverse the polarity of the consumable electrode for each swing and did not improve the shape of the cross section in the bead width direction.

In any case, there has hitherto been no idea of improving the shape of the cross section in the bead width direction by focusing on the characteristics of welding with positive polarity (minus the rod).

The technical problem of the present invention is to positively utilize the characteristics of welding with a positive polarity (minus a rod) and to invert the polarity of a consumable electrode for each swing, thereby obtaining a cross section in the bead width direction. In order to improve the shape of the object.

[0010]

According to a consumable electrode type bipolar arc welding method according to the first aspect of the present invention, when the welding torch is swung in the groove width direction by using an AC welding power source, a swing end is provided. The polarity of the welding power source is changed so that the polarity becomes reverse polarity at the part and the polarity becomes positive at the center of the oscillation, and the wire feeding speed is synchronized with the change in polarity to change the polarity. It is characterized by being enlarged.

Further, in the consumable electrode type bipolar arc welding method according to claim 2 of the present invention, when the welding torch is swung in the groove width direction using a welding power source capable of changing the polarity ratio,
The welding power source is changed without changing the welding current value so that the positive time ratio is 30% or less at the swing end and the positive time ratio is 50% or more at the swing center. The present invention is characterized in that the polarity time ratio is changed and the wire feeding speed is increased in synchronization with the polarity change when the positive polarity time ratio is 50% or more.

Further, the consumable electrode type bipolar arc welding method according to claim 3 of the present invention is characterized in that when a welding torch is swung in a groove width direction using a welding power source whose polarity ratio can be varied.
The current ratio of the polarity of the welding power source is changed so that the current ratio of the positive polarity at the swing end is 30% or less and the current ratio of the positive polarity at the center of the swing is 50% or more. It is characterized in that the wire feeding speed is increased when the current ratio of the positive polarity is 50% or more in synchronization with the change in the polarity.

The consumable electrode type bipolar arc welding method according to claim 4 of the present invention is characterized in that when a welding torch is swung in a groove width direction by using a welding power source having a variable polarity ratio,
The polarity of the polarity of the welding power source is set such that the ratio of the current × time of the positive polarity at the swing end is 30% or less and the ratio of the current × time of the positive polarity is 50% or more at the center of the swing. The current / time ratio is changed, and the wire feeding speed is synchronized with the polarity change to increase the current / time ratio when the positive current / time ratio is 50% or more.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A consumable electrode type bipolar arc welding method according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a schematic diagram showing a relationship between a swing position of a wire tip and a polarity change by a consumable electrode type bipolar arc welding method according to the present embodiment. In the figure, 1 is a base material, 2 is a welding torch, 3 is a groove, G is a gap, A is a swing end, and B is a swing center.

Generally, the oscillation cycle is up to 5 Hz, and most of them are about 0.4 to 2 Hz. The stop time at the swing end is about 0.1 to 0.5 seconds. A welding power supply device capable of changing the polarity ratio in accordance with such a swing cycle is used. The principle of changing the polarity ratio is shown in FIGS. FIG. 2 (a)
Indicates the principle of changing the polarity ratio by the time ratio. The current value (absolute value) at the time of positive polarity and reverse polarity is the same, and the ratio between the time of positive polarity and the time of reverse polarity in one cycle. To change the polarity ratio. FIG. 2 (b)
Indicates the principle of changing the polarity ratio according to the current ratio, and the time of the positive polarity and the reverse polarity in one cycle is the same, and the polarity ratio fluctuates according to the ratio between the current value of the positive polarity and the current value of the reverse polarity. It is to let. FIG. 2C shows the principle of changing the polarity ratio by the ratio of current × time.
The polarity ratio is varied by the ratio of the integrated value of the current value of the positive polarity × time and the integrated value of the current value of the opposite polarity × time in the cycle. In each case, the polarity ratio is set to 80% reverse polarity and 20% positive polarity.

Table 1 below summarizes the results of experiments performed on the consumable electrode type bipolar arc welding method of this embodiment under various welding conditions and the results of experiments of a comparative example. Here, the plate thickness of the base material was 9 mm, the groove shape was a V groove, the groove angle was set to 40 °, and the gap G was set to 4 mm.

[0017]

[Table 1]

The first embodiment corresponds to claim 1.
The polarity is set so that the polarity is opposite at the swing end A and the polarity is positive at the swing center B. The second embodiment corresponds to claim 2, wherein the time ratio of the positive polarity at the swing end portion A is 30% or less (0% in this case), and the time ratio of the positive polarity at the swing center portion B is 50%. This is set so as to be above (here, 60%). In the third embodiment, the positive current ratio at the swing end A is 30% or less (here, 0%), and the positive current ratio at the swing center B is 50%. This is set so as to be above (here, 60%). The fourth embodiment corresponds to claim 4, wherein the ratio of the positive current × time at the oscillating end portion A is 30% or less (0% in this case), and the positive current × times at the oscillating center portion B. The time ratio is set so as to be 50% or more (here, 60%). In Examples 1 to 4, the wire feeding speed was set at 10.5 m / min at the swing end, 11.8 m / min or 12.6 m / min at the swing center, and set higher than the swing end. In Comparative Example 1, the polarity was not reversed, and the polarity was set to be reversed in all regions. In Comparative Example 2, positive polarity was set in all regions without inverting the polarity. The welding speeds of Examples 1 to 4 were 25 cm / min, 24 cm / min,
The welding speeds of Comparative Examples 1 and 2 were set to 22 cm / min and 27 cm / min, respectively. Further, in each of the examples and the comparative examples, the wire diameter was set to 1.2 mm, the oscillation frequency was set to 0.5 Hz, the end stop time was set to 0.4 second, and 80% Ar + 20% CO ₂ was used as a shielding gas.

As is clear from Table 1, the bead shape (cross section in the width direction) was good in each of the examples, and it was possible to ensure penetration of the groove root portion even when the gap width was wide. Comparative Example 1 in which reverse polarity is set in all regions
In Example 2, burn-through occurred, and in Comparative Example 2 in which positive polarity was set in all regions, poor penetration occurred.

[0020]

As described above, according to the present invention, the swing ratio is reduced at the swing end portion, that is, the polarity is reversed, and the swing ratio is increased at the swing center portion. Since the polarity of the consumable electrode is reversed every time of the swing, the characteristics of each polarity are effectively utilized, the burn-out at the center of the bead width direction is prevented, and the penetration at both side walls can be secured. It became easy. For this reason, the shape of the cross section in the bead width direction has been improved, and penetration of the groove root portion can be ensured even when the gap width is widened.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a relationship between a swing position of a wire tip and a polarity change by a consumable electrode type bipolar arc welding method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a principle of changing a polarity ratio.

FIG. 3 is an explanatory diagram of characteristics of reverse polarity welding and positive polarity welding.

FIG. 4 is an explanatory diagram of a problem caused by various welding power supply systems.

[Explanation of symbols]

 1 Base Material 2 Welding Torch 3 Groove A Swing End B Swing Center G Gap

Claims (4)

[Claims] When the welding torch is swung in the groove width direction using an AC welding power source, the polarity is opposite at the swing end and the polarity is positive at the swing center. A consumable electrode type bipolar arc welding method characterized by changing the polarity of a welding power source and synchronizing the wire feeding speed with the change in polarity to increase the polarity at the time of positive polarity. 2. When the welding torch is swung in the groove width direction by using a welding power source capable of changing the polarity ratio, the time ratio of the positive polarity at the swing end is 30% or less, and The welding current value is not changed so that the time ratio of the polarity of the welding power source is changed, and the wire feeding speed is synchronized with the change of the polarity so that the time ratio of the positive polarity at the swing center becomes 50% or more. The consumable electrode type bipolar arc welding method characterized by increasing the time when the positive polarity time ratio is 50% or more. 3. When the welding torch is swung in the groove width direction by using a welding power source capable of changing the polarity ratio, the current ratio of the positive polarity at the swing end is 30% or less, and The current ratio of the polarity of the welding power source is changed so that the current ratio of the positive polarity is 50% or more at the center of the swing, and the current ratio of the positive polarity is 50% by synchronizing the wire feeding speed with the change of the polarity. A consumable electrode type bipolar arc welding method characterized by increasing the above-mentioned time. 4. When the welding torch is swung in the groove width direction using a welding power source capable of changing the polarity ratio, the ratio of the positive current × time at the swing end is 30% or less. In addition, the ratio of the current × time of the polarity of the welding power source is changed so that the ratio of the current × time of the positive polarity becomes 50% or more at the center of the oscillation, and the wire feeding speed is synchronized with the change of the polarity. The consumable electrode type bipolar arc welding method characterized in that the consumable electrode type bipolar arc welding method is increased when the positive current × time ratio is 50% or more.