JPH08309532A - Ac self-shield arc welding method - Google Patents

Abstract

PURPOSE: To stabilize an arc without causing the unstable phenomenon of the arc due to the variation of arc length even when a wire has long projecting length and a large droplet is formed at the tip part of the wire and to execute welding with spatter hardly caused, at the time of executing an self-shield arc welding by using the small diameter self-shield welding wire. CONSTITUTION: In the Ac self-shield arc welding method for executing welding alternately and repeatedly between a period of using the welding wire as a cathode and that of using the welding wire as an anode, at the time of defining an EN ratio for the ratio of time of using the welding wire as a cathode in an AC one period, this EN ratio is set in the range of >50% to <90% corresponding to the wire projecting length to execute the welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-shielding arc welding method in which welding is performed using a flux-cored wire having a small diameter, and even in the case of a long wire protrusion length in which a large droplet is formed at the tip of the wire, The present invention relates to an AC self-shielding arc welding method capable of stabilizing an arc and performing welding without causing an arc instability phenomenon due to an arc length variation.

[0002]

2. Description of the Related Art As is well known, the self-shielded arc welding method does not supply a shielding gas or flux from the outside to prevent the performance deterioration of the weld metal due to the solid solution of nitrogen in the atmosphere into the molten metal. Even if it is a welding method that can perform welding, a flux-cored wire that contains a component that fixes nitrogen that has infiltrated molten metal and a component that generates gas around the arc and prevents nitrogen from entering, is used. This is a welding method in which welding is performed by using as a consumable electrode (welding wire).

The self-shielding arc welding method has been mainly used in the field welding of steel plates, such as in-situ welding in the field, where the steel plate is thick and the wind is strong and the shielding gas cannot be used. In this case, the wire for self-shield welding has a wire diameter (wire diameter) of 2.4,
Welding wire with a diameter larger than 2 mm such as 3.2 mm is used, and the welding power source is a commercial frequency (50 or 60H).
The AC welding power source for hand welding of z) is used.

On the other hand, recently, in the field of thin steel plates having a plate thickness of about 0.6 to 3.2 mm, such as automobiles, houses, agricultural machinery, and lightweight steel frames, the simplicity of the self-shielding arc welding method has been attracting attention. The wire for self-shielding welding for thin plate welding is also commercially available. In such self-shielding arc welding of thin steel plates, the current value is 8
Welding wire with a small diameter of 2 mm or less because it uses a low current of 0 to 250 A and performs welding not only downward welding but also vertical welding, horizontal welding, etc. Is used.

In the self-shielded arc welding using the thin welding wire, a direct-current welding power source having a constant voltage characteristic used for ordinary consumable electrode type gas shielded arc welding is generally used as a welding power source. , The electrical connection with the welding power source is such that the welding wire is connected to the cathode and the base metal is connected to the positive polarity, and the positive arc is generated between the welding wire and the base metal to perform welding. There is.
As is well known, on the contrary, the one in which the welding wire is the anode and the base material is the cathode is called reverse polarity.

Wire diameter 2 mm or less, especially wire diameter 1.4
When performing self-shielded arc welding with a positive polarity arc using a welding wire with a small diameter of less than or equal to mm, the arc instability phenomenon may occur when the wire has a long protruding length such that a large droplet is formed at the tip of the wire. Had occurred. This arc instability phenomenon means that if the wire feed rate and the wire protrusion length (distance between the base metal surface and the tip of the welding tip) are maintained at constant values, if the wire protrusion length is long, the arc length Is a phenomenon that periodically becomes longer or shorter, and in a remarkable case, the arc length may fluctuate by 10 mm or more. For example, when the wire diameter is 1.2 mm, the proper wire protrusion length is 10 to 15 mm, and when the wire protrusion length is 15 mm, the occurrence of the arc instability phenomenon due to the arc length variation is extremely small, but the wire protrusion length is When it is set to about 30 mm, an arc instability phenomenon occurs in which the arc length fluctuates greatly.

[0007]

When the arc instability phenomenon due to the variation of the arc length occurs, it causes welding bead defects such as undercut of the welding bead and uneven welding bead width. Furthermore, the function of the gas generating component and nitrogen fixing component contained in the flux in the welding wire is weakened, and the function as a self-shielding wire cannot be exhibited,
Porosity defects occur and the toughness of the weld metal deteriorates, and the performance of the welded joint deteriorates. For this reason,
In semi-automatic welding where hand shake is likely to occur due to manual operation of the welding torch, the wire protrusion length is appropriate for difficult posture welding such as vertical or horizontal orientation, or welding of objects with complicated shapes in which the welding torch is difficult to enter. It is often longer than this value, and there is a limit to the application of self-shielded arc welding using a thin welding wire to thin plate welding.

The present invention has been made in view of the above circumstances, and when performing self-shielding arc welding using a small-diameter self-shielding welding wire, a large droplet is formed at the tip of the wire. Even with a long wire protrusion length, the arc can be stabilized without causing the arc instability phenomenon due to the arc length variation, and welding with less spatter can be performed, which enables self-shielding using a thin welding wire. An object of the present invention is to provide an AC self-shielding arc welding method capable of expanding the application of arc welding to thin plate welding.

[0009]

In order to achieve the above object, the invention of claim 1 is an alternating current for alternately repeating a period in which the welding wire serves as a cathode and a period in which the welding wire serves as an anode. In the self-shielded arc welding method,
Assuming that the time ratio of the welding wire becoming a cathode in one cycle of AC is the EN ratio, the EN ratio is set in the range of 50% to 90% in accordance with the protruding length of the wire and welding is performed. Is.

According to a second aspect of the present invention, in the AC self-shielding arc welding method according to the first aspect, the EN ratio is set to be smaller as the wire protrusion length increases in the case of the same wire diameter, and the same. In the case of the wire protrusion length, it is set so that it becomes smaller as the wire diameter becomes smaller.

[0011]

The present inventors first investigated the mechanism of occurrence of the aforementioned arc instability phenomenon that occurs when the protruding length of the wire increases in self-shielded arc welding using a welding wire having a small diameter. Welding was performed using a typical self-shielding welding wire with a wire diameter of 1.2 mm, and the self-shielding arc welding phenomenon was imaged and observed with a high-speed camera, and as a result, the following was found. 4 to 6 are schematic diagrams sketching the welding phenomenon captured by a high-speed camera.

When the wire protrusion length is appropriate (about 15 mm) in the conventional positive polarity, the droplets are finely divided into small particles and are transferred into a spray form. The cathode spot is generated in the unmelted portion of the wire tip and moves irregularly and at high speed in the wire circumferential direction, but the unmelted portion of the wire tip is located above the molten pool by a certain value. Therefore, the arc length is almost constant macroscopically and the arc is stable (see FIG. 4).

On the other hand, in the conventional positive polarity, when the wire protrusion length is too long (about 30 mm), a large droplet is formed at the tip of the wire, and the droplet transfer form becomes globular transfer. The cathode spot generated on the surface of the droplet at the wire tip is
It does not always occur at the bottom of the droplet, which is shortest with respect to the surface of the molten pool, but also occurs at the top of the droplet, as shown in FIG. When a cathode spot is generated on the upper part of the droplet, this triggers a macroscopic arc length instability. In the lower part of FIG. 9, a welding current waveform at the time of occurrence of an arc instability phenomenon due to an arc length variation is recorded by a waveform recorder and traced. Average welding current is 150A
As shown in FIG. 9, an arc instability phenomenon occurs and the welding current fluctuates periodically. Once the arc instability phenomenon occurs, it will continue in this manner periodically.

On the other hand, when the polarity is reversed and the wire protrusion length is increased in the reverse polarity (about 30 m).
In m), a large droplet is formed at the tip of the wire, which causes globuler transition, but as shown in FIG. 6, an arc is generated between the lowermost portion of the droplet at the tip of the wire and the molten pool, and a macroscopic phenomenon occurs. The arc length is almost constant. However, since the amount of spatter generated is very large and large droplets may spatter as they are, welding workability is poor. Even if the wire protrusion length is short (approx. 15 mm) in reverse polarity,
Similarly, a large droplet is formed at the tip of the wire, and spatter frequently occurs.

The difference in the size of the droplet due to the length of the wire protrusion in the positive polarity can be explained by the difference in the wire melting rate due to the difference in the wire protrusion length. FIG. 7 is a diagram showing the relationship between the welding current and the wire melting rate (wire feeding rate) when the wire protrusion length is about 15 mm, and FIG. 8 is the welding current and the wire melting rate (wire feeding rate) when the wire protrusion length is about 30 mm. It is a figure which shows the relationship with (feed rate). In both figures, “white circles” indicate the case of positive polarity, and “black circles” indicate the case of opposite polarity.

In the positive polarity self-shielding arc welding, when the protruding length of the wire is short and the wire melting speed is small, it is difficult to form extra droplets at the tip of the wire, and the cathode spot is the unmelted portion of the wire tip. That is, it occurs in the hoop part of the welding wire. Further, since the cathode spot is preferentially generated from the presence of the oxide having a low ionization voltage, the wire hoop portion covered with the oxide is considered to be a stable generation spot of the cathode spot. .

On the other hand, if the protruding length of the wire increases, the wire melting rate increases with the same welding current.
It is considered that when the melting is excessive, large droplets are formed at the tip of the wire. If large droplets are formed, the wire hoop part will move away from the molten pool, and since there are few oxides with a low ionization voltage on the droplet surface, the cathode spot will be sought by the oxide. It moves around the surface of the drop irregularly, resulting in an unstable arc length.
It should be noted that the wire melting rate in the positive polarity is smaller than that of the reverse polarity in which large droplets are formed when the wire protrusion length is short as shown in FIG. 7, and as shown in FIG. As the protruding length becomes longer, the wire melting speed becomes almost the same as that of the opposite polarity, and the point that large droplets are formed is also the same as that of the opposite polarity.

From the above, it is considered that in positive polarity self-shielding arc welding using a welding wire having a small diameter, an arc instability phenomenon due to an arc length variation occurs in the following process. FIG. 9 is a diagram for explaining the arc instability phenomenon.

When the wire protrusion length is long, the wire melting rate increases, and a large droplet is formed at the wire tip.
The cathode spot moves around the surface of the droplet in search of an oxide having a low ionization voltage. When the cathode spot moves to the upper part of the droplet, the arc is not generated between the surface of the molten pool and the lowermost part of the droplet, which is the shortest, and the arc length increases. When the arc length becomes longer, the welding power source having a constant voltage characteristic operates to control the arc length (arc voltage) at a constant level by the self-control action of the arc length, and the welding current starts to decrease. Then, since the welding wire is fed at a constant speed, the droplet at the tip of the wire approaches the molten pool.

When the droplet at the tip of the wire separates, the cathode spot is formed at the wire hoop portion and the arc length becomes short. The self-control function of the arc length by the welding power source works,
Welding current increases. When the welding current increases, the wire melting rate also increases, the welding wire burns up rapidly, and large droplets are formed at the tip of the wire.

In order to stabilize the arc in such a long wire protrusion length that a large droplet is formed at the tip of the wire, the cathode spot formed on the surface of the droplet can be stabilized from the mechanism of generating the arc instability phenomenon. It turned out that stabilization of is important. As described above, in the reverse polarity in which the welding wire serves as the anode, an arc is generated between the lowest portion of the droplet at the tip of the wire and the molten pool, and the arc is stable. However, in the case of the reverse polarity, there is a problem that the droplets are large and large-sized spatters frequently occur.

Therefore, focusing on AC welding (bipolar welding), which is considered to have both positive polarity and reverse polarity characteristics, the time ratio of the welding wire becoming a cathode in one AC cycle is EN.
A welding wire with a small diameter is used as the ratio, and the wire protrusion length E is such that a large droplet is formed at the wire tip.
Alternating N ratio, AC self-shield arc welding was performed. As a result, by setting the EN ratio in the range of more than 50% and less than 90% corresponding to the wire protrusion length, the arc length is made constant during the period of the opposite polarity, and thereby the arc instability phenomenon in the positive polarity only occurs. It is possible to prevent the generation of spatter, the generation of spatter is small, and it is possible to perform AC self-shielded arc welding in which the arc is stabilized. When the period in which the welding wire is the cathode in one cycle of alternating current is T _SP and the period in which the welding wire is the anode is T _RP , EN ratio = [T _SP / (T _SP + T _RP )] × 100%. .

The EN ratio is 50% or less, that is, T
_{When RP} ≧ T _SP , spatter is often generated. On the other hand, if the EN ratio exceeds 90% in a long wire protrusion length such that a large droplet is formed at the wire tip, the ratio of reverse polarity is too small to prevent the arc instability phenomenon from occurring.

Then, as the wire protrusion length increases, the wire melting rate increases, and the droplets formed on the tip of the wire gradually become larger, and the cathode spots move more irregularly on the droplet surface. In the case of the same wire diameter, the ratio is set to be smaller as the wire protruding length is increased, and the ratio of the reverse polarity period for keeping the arc length constant is preferably increased. Using a self-shielding welding wire having a wire diameter of 1.2 mm, which is a representative of small diameters, the relationship between the wire protrusion length and the EN ratio was investigated. The results are shown in Table 1 and FIG. The AC frequency is about 5
0 Hz.

[0025]

[Table 1]

As shown in Table 1 and FIG. 3, the arc instability phenomenon is eliminated as the wire protrusion length increases.
The ratio becomes smaller. "Arc stable region" in Fig. 3
Is an area where there is no arc instability due to fluctuations in arc length, the arc is stable, and spatter is less likely to occur.
The "sputtering-prone region" is a region where spatter occurs frequently due to the influence of the opposite polarity being too strong. When the wire diameter is 1.2 mm, the wire protrusion length at which a large droplet is formed at the wire tip is about 20 mm or more, and as shown in FIG. 3, if the wire protrusion length is in the range of 15 to 30 mm, It is understood that the EN ratio may be set to 75%. When the wire protrusion length is 40 mm, if the EN ratio is 50%, the arc instability phenomenon can be resolved, but spatter is often generated, which is not practical.

FIG. 10 is a diagram showing the wire protrusion length at which an arc instability phenomenon occurs at each wire diameter in DC positive polarity self-shielding arc welding with a thin wire. FIG. 10 is obtained by performing downward bead-on-plate welding with a welding current of 150 A using a self-shielding welding wire. In the figure, the ⊚ and ○ marks indicate that the arc is stable, and the Δ mark indicate that the arc instability phenomenon sometimes occurs. Moreover, the x mark indicates that the arc instability phenomenon occurs frequently, and the x mark indicates that the welding is impossible.

As can be seen from FIG. 10, as the wire diameter becomes smaller, the degree of increase in the wire melting rate due to the increase in the wire protrusion length increases, so that the arc instability occurs at a shorter wire protrusion length. The phenomenon will occur. Therefore, it is preferable to set the EN ratio to be smaller as the wire diameter is smaller in the case of the same wire protrusion length.

[0029]

Embodiments of the present invention will be described below.
As the welding power source, an inverter type welding power source having a constant voltage characteristic and capable of arbitrarily setting the EN ratio was used.

A wire for self-shielding welding having a wire diameter of 1.2 mm was used, and the wire protrusion length was set at intervals of 5 mm from 10 to 40 mm. At each wire protrusion length, the EN ratio was 100% (positive polarity only). ), 75
%, 50%, 25%, and 0% (reverse polarity only) were set in five stages and downward bead-on-plate welding was performed to investigate the arc instability phenomenon and the generation state of spatter. The frequency is about 50 Hz and the welding current is about 120A. In order to catch the fluctuation of the welding current caused by the arc instability phenomenon, the detected AC welding current signal was rectified into a direct current, which was recorded through a low-pass filter with a cutoff frequency of 10 Hz. The results are shown in Fig. 1.

As shown in FIG. 1, in the conventional self-shielding arc welding using only positive polarity (EN ratio: 100%), when the wire protrusion length is 25 mm or more, an arc instability phenomenon occurs and the welding current fluctuates. Grows larger.

On the other hand, the EN ratio of the present invention is 75%.
In this case, when the wire protrusion lengths in which large droplets are formed at the wire tip are 25 mm and 30 mm, the arc instability phenomenon can be reliably prevented and the spatter is less likely to occur.
Further, the variation of the welding current is small even at 35 mm, and the arc is relatively stable. An arc instability phenomenon occurred when the wire protrusion length was 40 mm.

On the other hand, the EN ratio outside the range of the present invention is 50.
%, 25%, and 0%, although the arc instability phenomenon did not occur, spatter often occurred and the welding workability was extremely poor.

Next, wire diameters of 1.1 mm, 1.2 mm,
Using three types of self-shielding welding wires having different wire diameters of 1.4 mm, the relationship between the wire protrusion length and the optimum EN ratio at each wire diameter was obtained. The result is shown in Figure 2.
Shown in The smaller the wire diameter, the greater the degree of increase in the wire melting rate due to the increase in the wire protrusion length. Therefore, in the case of the same wire protrusion length, the EN ratio decreases as the wire diameter decreases. By setting it, it was possible to stabilize the arc without causing an arc instability phenomenon and to perform welding with less spatter.

In the above embodiment, the wire protrusion length is known in advance, but when the method of the present invention is carried out,
When it is necessary to detect the protruding length of the wire during welding, the following may be done. EN ratio exceeds 50% 9
In the range of 0% or less, in the case of the same wire diameter, it becomes smaller as the wire protrusion length increases, and
In the case of the same wire protrusion length, it is determined as a function of the welding wire diameter and the wire protrusion length so that it becomes smaller as the wire diameter becomes smaller, and this function is input in advance to, for example, an EN ratio setting device.

When welding, the diameter of the wire used d _D
For, the welder manually inputs the wire protrusion length during welding into the EN ratio setting device, and automatically detects the wire protrusion length during welding and inputs the detected value L _D into the EN ratio setting device. , The used wire diameter d _D and the wire protrusion length detection value L _D are applied to the function to obtain and set the EN ratios corresponding to the d _D and L _{D so} that the set EN ratio is obtained. The output of the welding power source should be controlled. And for the detection of the wire protrusion length,
With a constant voltage welding power source, the welding current decreases when the wire protrusion length is longer than the set value, and conversely, the welding current increases when the wire protrusion length is shorter than the set value.Therefore, use this characteristic. A publicly known means for detecting the protruding length of the wire based on the increase / decrease in the detected value of the welding current may be adopted.

[0037]

As described above, according to the AC self-shielding arc welding method of the present invention, when performing self-shielding arc welding using a small-diameter self-shielding welding wire, the welding wire in one AC cycle becomes the cathode. The time ratio is defined as the EN ratio, and the EN ratio is set within a predetermined range corresponding to the wire protrusion length to perform welding, so that a long droplet that forms a large droplet at the tip of the wire is used. Even with the wire protrusion length, the arc can be stabilized without causing the arc instability phenomenon due to the arc length variation, and welding with less spatter can be performed. This makes it possible to perform self-shielding arc using a thin welding wire. The application of welding to thin plate welding can be expanded.

[Brief description of drawings]

FIG. 1 uses a welding wire with a wire diameter of 1.2 mm and sets the wire protrusion length from 10 to 40 mm in 5 mm pitches, and the EN ratio is 5 at each wire protrusion length.
When set to the stage and self-shielded arc welding,
It is a figure which shows a welding current waveform (rectified | straightened to DC when EN ratio is 75%, 50%, and 25%).

[Fig. 2] Wire protrusion length and optimum E for each wire diameter
It is a figure which shows the relationship with N ratio.

FIG. 3 is a diagram showing an arc stable region and the like when the wire protrusion length and the EN ratio are changed in self-shielded arc welding using a wire having a wire diameter of 1.2 mm.

FIG. 4 is a schematic diagram showing a welding phenomenon in the case where the wire diameter is 1.2 mm, the wire protrusion length is about 15 mm with positive polarity.

FIG. 5 is a schematic diagram showing a welding phenomenon in the case where the wire diameter is 1.2 mm, the wire protrusion length is about 30 mm with positive polarity.

FIG. 6 is a schematic diagram showing a welding phenomenon in the case where the wire diameter is 1.2 mm, the wire protrusion length is approximately 30 mm in the opposite polarity.

FIG. 7: Wire diameter 1.2 mm, wire protrusion length is about 1
It is a figure which shows the relationship between the welding current in 5 mm, and a wire fusion speed (wire feeding speed).

FIG. 8: Wire diameter 1.2 mm, wire protrusion length is about 3
It is a figure which shows the relationship between the welding current in 0 mm, and a wire fusion speed (wire feed speed).

FIG. 9 is a diagram for explaining an arc instability phenomenon.

FIG. 10 is a diagram showing a wire protrusion length at which an arc instability phenomenon occurs in each wire diameter in DC positive polarity self-shielding arc welding with a thin wire.

Claims (2)

[Claims] 1. In an AC self-shielding arc welding method in which a welding wire is used as a cathode and a welding wire is used as an anode alternately and alternately, welding is performed. If the EN ratio is set, the EN ratio is 50% corresponding to the wire protrusion length.
An AC self-shielding arc welding method, characterized in that welding is performed in a range of over 90%. 2. The EN ratio is set so as to decrease as the wire protrusion length increases in the case of the same wire diameter, and decreases as the wire diameter decreases in the case of the same wire protrusion length. The method according to claim 1, wherein the method is set.