JP3219360B2 - AC self-shielded arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-shielded arc welding method in which welding is performed using a small-diameter flux-cored wire, and relates to a long wire protruding length in which a large droplet is formed at the tip of the wire. The present invention relates to an AC self-shielded arc welding method capable of performing welding while stabilizing an arc 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 require external supply of a shielding gas or a flux for preventing deterioration of the performance of a weld metal due to solid solution of nitrogen in the atmosphere into a molten metal. It is a welding method that can perform welding even if it is a flux cored wire that contains a component that fixes nitrogen that has entered the molten metal and a component that generates gas around the arc to prevent nitrogen from entering, in the flux. This is a welding method in which welding is performed using a consumable electrode (welding wire).

[0003] The self-shielded arc welding method has been mainly used in field welding of thick steel plates outdoors where strong winds are not available and shield gas cannot be used, such as field welding of steel pipe piles. In this case, the wire for self-shielding welding has a wire diameter (wire diameter) of 2.4,
A welding wire having a large diameter exceeding 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 manual welding of z) is used.

On the other hand, recently, the simplicity of the self-shielded arc welding method has attracted attention in the field of thin steel plates having a thickness of about 0.6 to 3.2 mm, such as automobiles, houses, agricultural equipment, and lightweight steel frames. And self-shielding welding wires for thin plate welding are also commercially available. In such a self-shielded arc welding of a thin steel plate, the current value is 8
Since a low current of about 0 to 250 A is used and welding is performed not only in downward welding but also in all positions such as vertical welding and horizontal welding, a thin welding wire having a wire diameter (wire diameter) of 2 mm or less is used. Is used.

[0005] In self-shielded arc welding using this small-diameter welding wire, a DC welding power source having a constant voltage characteristic generally used for ordinary consumable electrode type gas shielded arc welding is used as a welding power source. The electrical connection with the welding power source is made positive by connecting the welding wire to the cathode and the base material to the anode, and generating a positive polarity arc between the welding wire and the base material to perform welding. I have.
Conversely, as is well-known, a method in which a welding wire is used as an anode and a base material is used as a cathode is called reverse polarity.

[0006] A wire diameter of 2 mm or less, particularly a wire diameter of 1.4.
When performing self-shielded arc welding with a positive polarity arc using a welding wire with a small diameter of less than 1 mm, an arc instability phenomenon may occur if the length of the wire protrudes so long that a large droplet is formed at the tip of the wire. Had occurred. This arc instability phenomenon means that even if the wire feed speed and the wire protrusion length (the 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 becomes longer or shorter periodically, 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 appropriate wire protrusion length is 10 to 15 mm. When the wire protrusion length is 15 mm, the occurrence of arc instability due to arc length variation is extremely small. When it is set to about 30 mm, an arc instability phenomenon in which the arc length varies greatly occurs.

[0007]

The occurrence of arc instability due to such variations in arc length causes weld bead defects such as undercuts of weld beads and irregularities in weld bead width. Furthermore, the function of the gas generating component and the nitrogen fixing component contained in the flux in the welding wire is weakened, and the function as a self-shielding wire cannot be exhibited.
Pore defects occur and the toughness of the weld metal deteriorates, thereby deteriorating the performance of the weld joint. 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 position welding such as vertical and sideways welding and welding of complicated shaped workpieces where the welding torch is difficult to enter. It is often longer than the value, and there is a limit to the application of self-shielded arc welding using thin welding wire to thin plate welding.

The present invention has been made in view of the above circumstances, and when performing self-shielded arc welding using a small-diameter self-shielded welding wire, a large droplet is formed at the tip of the wire. Even with a long wire overhang length, the arc can be stabilized without causing arc instability due to fluctuations in the arc length, and welding with less spatter can be performed. 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]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to an alternating current system in which welding is performed by alternately repeating a period in which a welding wire is used as a cathode and a period in which the welding wire is used as an anode. In the self-shielded arc welding method,
Assuming that the time ratio of the welding wire to be the cathode in one AC cycle is the EN ratio , the wire protrusion length during welding is detected.
Then , an EN ratio is determined and set in a range of 50% or more and 90% or less according to the detected wire protrusion length , and the output of a welding power source is controlled so as to achieve the set EN ratio to perform welding. It is characterized by performing.

According to a second aspect of the present invention, in the alternating current self-shielding arc welding method according to the first aspect, the EN ratio is set so as to decrease as the wire protrusion length increases when the wire diameter is the same. In the case of the wire protrusion length, the length is set so as to decrease as the wire diameter decreases.

[0011]

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

In the case where the length of the wire protruding is proper (about 15 mm) in the conventional positive polarity, the droplet moves in a fine and small particle-like spray form. The cathode spot is generated at the unmelted portion of the wire tip and moves around irregularly and at high speed in the circumferential direction of the wire, but the unmelted portion of the wire tip is located at a certain value above the molten pool. Therefore, the arc length is substantially constant macroscopically, and the arc is stable (see FIG. 4).

On the other hand, if the length of the wire protruding in the conventional positive polarity is too long (about 30 mm), a large droplet is formed at the tip of the wire, and the droplet transfer mode is a globular transfer. The cathode spot generated on the droplet surface at the wire tip is
It does not always occur at the bottom of the droplet, which is the shortest with respect to the surface of the molten pool, but also occurs at the top of the droplet, as shown in FIG. Then, when a cathode spot is generated above the droplet, this triggers the macro-arc length instability to occur continuously. The lower part of FIG. 9 shows a waveform obtained by recording a welding current waveform at the time of occurrence of an arc instability phenomenon due to an arc length variation with a waveform recorder and tracing the same. Average welding current is 150A
As shown in FIG. 9, an arc unstable phenomenon occurs, and the welding current fluctuates periodically. Once the arc instability phenomenon occurs, it continues in this manner periodically.

On the other hand, when the polarity is reversed and the length of the wire protruding in the reverse polarity is increased (about 30 m).
In (m), although a large droplet is formed at the wire tip to cause a globular transition, as shown in FIG. 6, an arc is generated between the lowermost portion of the droplet at the wire tip and the molten pool, resulting in a macroscopic phenomenon. Has an almost constant arc length. However, the amount of spatter generated is very large, and large droplets may be directly sputtered, resulting in poor welding workability. In addition, when the wire protrusion length is short (about 15 mm) in the reverse polarity,
Similarly, large droplets are formed at the tip of the wire, and spatter occurs frequently.

The difference in the droplet size 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 speed (wire feeding speed) when the wire protrusion length is about 15 mm, and FIG. 8 is the diagram showing the welding current and the wire melting speed (wire feeding speed) when the wire protrusion length is about 30 mm. FIG. In both figures, “white circles” indicate the case of positive polarity, and “black circles” indicate the case of reverse polarity.

In self-shielded arc welding with positive polarity, if the wire protrusion length is short and the wire melting rate is low, extra droplets are unlikely to be formed at the wire tip, and the cathode spot is the unmelted portion at the wire tip. That is, it occurs at the hoop portion of the welding wire. Since the cathode spot is preferentially generated from the presence of an oxide having a low ionization voltage, it is considered that the wire hoop portion covered with the oxide is a stable generation point of the cathode spot. .

On the other hand, when the wire protrusion length is increased, the wire melting speed increases with the same welding current,
It is considered that when the melting is excessive, a large droplet is formed at the tip of the wire. When a large droplet is formed, the wire hoop part moves away from the molten pool, and since there is little oxide with a low ionization voltage on the surface of the droplet, the cathode spot seeks the oxide and melts. Irregular movement around the drop surface results in an unstable arc length.
The wire melting rate in the positive polarity is smaller than that of the opposite polarity in which a large droplet is formed when the wire protrusion length is short as shown in FIG. As the protrusion length becomes longer, the wire melting speed of the opposite polarity becomes almost the same, and the point that a large droplet is formed is also the same as the opposite polarity.

From the above, it is considered that in the positive self-shielded arc welding using a small-diameter welding wire, 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.

If the wire protrusion length is long, the wire melting speed increases, and a large droplet is formed at the tip of the wire.
The cathode spot moves around the droplet surface in search of oxides with low ionization voltage. When the cathode spot moves to the upper part of the droplet, the arc does not occur between the surface of the molten pool and the lowermost part of the droplet, which is the shortest, and the arc length becomes longer. When the arc length is increased, the welding power source having a constant voltage characteristic operates to control the arc length by the welding power source to keep the arc length (arc voltage) constant, and the welding current starts to decrease. 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, a cathode spot is formed at the wire hoop portion, resulting in a short arc length. The self-control of the arc length by the welding power source works,
The welding current increases. As the welding current increases, the wire melting rate further increases, and the welding wire burns up rapidly, forming a large droplet at the tip of the wire.

From the mechanism of occurrence of such an arc instability phenomenon, in order to stabilize the arc at a long wire projection length where a large droplet is formed at the tip of the wire, a cathode spot formed on the surface of the droplet is required. It has been found that stabilization of is important. As described above, in the case of the reverse polarity using the welding wire as the anode, an arc is generated between the lowest part of the droplet at the tip of the wire and the molten pool, and the arc is stable. However, in the case of the opposite polarity, there is a problem that the droplets are large and large spatters frequently occur.

Therefore, focusing on AC welding (bipolar welding), which is considered to have both positive polarity and opposite polarity characteristics, the time ratio at which the welding wire becomes a cathode in one AC cycle is defined as EN.
Using a small-diameter welding wire and a wire protrusion length such that a large droplet is formed at the wire tip,
The N ratio was changed and AC self-shielded arc welding was performed. As a result, by setting the EN ratio in the range of more than 50% and less than 90% in accordance with the wire protrusion length, the arc length is kept constant during the period of the reverse polarity, so that the arc instability phenomenon only in the positive polarity can be prevented. Generation can be prevented, spatter is less generated, and arc-stabilized alternating-current self-shielded arc welding can be performed. Incidentally, a period for the welding wire in an alternating current one period a cathode and T _SP, when the period for the welding wire and the anode and T _RP, an EN ratio = _{[T SP / (T SP + T} RP) ] × 100% .

The EN ratio is 50% or less, ie, T
_{When RP} ≧ T _SP , the occurrence of spatter increases. On the other hand, if the EN ratio exceeds 90% at a long wire protrusion length at which a large droplet is formed at the tip of the wire, the reverse polarity ratio is too small to prevent the occurrence of arc instability.

Then, as the wire protrusion length increases, the wire melting rate increases and the droplet formed at the wire tip gradually increases, and the cathode spot moves more irregularly on the droplet surface. The ratio is preferably set so as to decrease as the wire protrusion length increases in the case of the same wire diameter, and to increase the ratio of the reverse polarity period for keeping the arc length constant. Using a self-shielding welding wire having a wire diameter of 1.2 mm, which is a typical example of a small diameter, the relationship between the wire protrusion length and the EN ratio was examined. 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 EN in which the arc instability phenomenon is eliminated with an increase in the wire projection length.
The ratio becomes smaller. "Arc stable region" in FIG.
Is an area where there is no arc instability due to arc length fluctuation, the arc is stabilized, and the occurrence of spatter is small,
The “spatter-prone region” is a region where the influence of the opposite polarity is too strong and spatter frequently occurs. In the case of a wire diameter of 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 can be seen 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 eliminated, but spatters occur frequently, which is not practical.

FIG. 10 is a diagram showing the protruding length of the wire at which the arc instability phenomenon occurs at each wire diameter in DC positive polarity self-shielded arc welding using a small-diameter wire. FIG. 10 shows the results obtained by performing downward bead-on-plate welding with a welding current of 150 A and a self-shielding welding wire. In the figure, the marks ◎ and ○ indicate that the arc is stable, and the marks △ indicate that the arc instability occurs occasionally. A cross indicates that the arc unstable phenomenon occurs frequently, and a cross with two crosses indicates a state in which welding is impossible.

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

[0029]

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

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

As shown in FIG. 1, in the conventional self-shielded arc welding using only positive polarity (EN ratio: 100%), when the wire protrusion length exceeds 25 mm, an arc instability occurs and the welding current varies. Becomes larger.

On the other hand, the EN ratio of the present invention 75%
In the case of (1), if the wire protrusion length at which a large droplet is formed at the tip of the wire is 25 mm or 30 mm, the occurrence of the arc instability phenomenon can be reliably prevented, and the occurrence of spatter is small.
Also, even at 35 mm, the fluctuation of the welding current is small, and the arc is relatively stable. When the wire protrusion length was 40 mm, an arc instability occurred.

On the other hand, when the EN ratio out of the range of the present invention is 50,
%, 25% and 0%, there is no occurrence of arc instability, but many spatters are generated, and welding workability is extremely poor.

Next, wire diameters of 1.1 mm, 1.2 mm,
Using three types of 1.4 mm self-shielding welding wires having different wire diameters, the relationship between the wire protrusion length and the optimum EN ratio at each wire diameter was determined. Figure 2 shows the result.
Shown in As the wire diameter becomes smaller, the rate of increase in the wire melting rate due to the increase in the wire protrusion length increases, so that the EN ratio is reduced as the wire diameter decreases in the case of the same wire protrusion length. By setting, it was possible to stabilize the arc without causing the arc instability phenomenon and perform welding with less generation of spatter.

In the above embodiment, the wire protrusion length is known in advance.
If it is necessary to detect the wire protrusion length during welding, the following may be performed. 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, the function is determined as a function of the welding wire diameter and the wire protrusion length so as to decrease as the wire diameter decreases, and this function is input in advance to, for example, an EN ratio setting device.

At the time of welding, a wire diameter d _{D to be} used is used.
Is manually input to the EN ratio setting device by the welder, the wire protrusion length during welding is automatically detected, and the detected value L _D is input to the EN ratio setting device, and the detected value is input to the EN ratio setting device. By applying the used wire diameter d _D and the wire protrusion length detection value L _D to the function, an EN ratio corresponding to the d _D and L _D is determined and set, so that the set EN ratio is obtained. The output of the welding power source may be controlled. And for the detection of the wire protrusion length,
In a welding power source with constant voltage characteristics, the welding current decreases when the wire protrusion length is longer than the set value, and on the contrary, the welding current increases when the wire extension length is shorter than the set value. A known means for detecting the wire protrusion length based on the increase or decrease of the welding current detection value may be employed.

[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 is connected to the cathode. Since the time ratio is set to an EN ratio, and the EN ratio is set within a predetermined range in accordance with the length of the protruding wire, welding is performed. Self-shielded arc using a small-diameter welding wire can stabilize the arc without causing arc instability due to arc length fluctuations, and generate less spatter, even at the wire protrusion length. The application of welding to thin plate welding can be expanded.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 A welding wire having a wire diameter of 1.2 mm is used, and a wire protrusion length is set at intervals of 5 mm from 10 to 40 mm.
When self-shielded arc welding is set in stages,
It is a figure which shows the welding current waveform (when EN ratio was 75%, 50%, and 25%, it rectified to direct current).

FIG. 2 shows the wire protrusion length and optimum E for each wire diameter.
It is a figure showing the relation 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 when the wire diameter is 1.2 mm, the polarity is positive, and the wire protrusion length is about 15 mm.

FIG. 5 is a schematic view showing a welding phenomenon when the wire diameter is 1.2 mm, the polarity is positive, and the wire protrusion length is about 30 mm.

FIG. 6 is a schematic diagram showing a welding phenomenon in a case where a wire diameter is 1.2 mm, and a wire protrusion length is about 30 mm with reverse polarity.

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

FIG. 8 shows a wire diameter of 1.2 mm and a wire protrusion length of about 3
It is a figure which shows the relationship between the welding current at 0 mm, and a wire melting speed (wire feeding speed).

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

FIG. 10 is a view showing a wire protrusion length at which arc instability occurs at each wire diameter in DC positive polarity self-shielded arc welding with a small diameter wire.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-254396 (JP, A) JP-A-1-215468 (JP, A) JP-A-58-112653 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B23K 9/073 B23K 9/00

Claims (2)

(57) [Claims] In an AC self-shielded arc welding method in which welding is performed by alternately repeating a period in which a welding wire is used as a cathode and a period in which the welding wire is used as an anode, the time ratio in which the welding wire becomes a cathode in one AC cycle is determined. Assuming the EN ratio , the wire protrusion length during welding is detected, and the detected
It is characterized in that the EN ratio is determined and set in the range of 50% to 90% corresponding to the set wire protrusion length , and welding is performed by controlling the output of a welding power source so as to achieve the set EN ratio. AC self-shielded arc welding method. 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 to decrease as the wire diameter decreases in the case of the same wire protrusion length. The AC self-shielding arc welding method according to claim 1, wherein the setting is performed.