JPH0696195B2 - MIG circumference welding method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a MIG circumferential welding method used for manufacturing containers, pipes, automobile wheels and the like.

[Prior Art] In circumferential welding by the conventional MIG (Metal inert gas) method, an arc is formed with a constant current from the start of welding to a steady state.

In this case, since the temperature of the base metal is low at the start of welding, the melting of the groove wall and the penetration into the groove bottom are insufficient. For this reason, as shown in FIG.
In, in contrast to the stationary part, a convex bead 2 is formed,
At the bead start portion 3, the bead is rapidly rising.

[Problems to be Solved by the Invention] However, in the circumferential welding, when the electrode makes one round and returns to the welding start portion 1, the convex bead 2 at this start is formed.
This start part 1
At, a welding defect occurs.

Further, in the welding start portion 1, blowholes frequently occur due to factors such as poor shielding, disturbance of the arc under the initial condition, and disturbance of the shield due to the disturbance. In circumferential welding, if the welding electrode goes around and the welding bead rides on the start part and the beads overlap, part of the bead at the start of welding is remelted and the blow hole rises, sometimes deviating from the welding part. is there. However, most of the blowholes formed at the start portion at the start of welding remain and are found as defects by X-ray inspection.

In the case of discontinuous welding, such a defect in the arc welding start portion may be removed by cutting the start portion, but in the case of circumferential welding, such means cannot be taken.

In TIG (Tungsten inert gas) welding, the arc current value and the amount of filler metal can be controlled independently. For this reason, the supply speed of the filler material can be controlled regardless of the current value, so that the above-mentioned welding defect in the bead overlapping portion does not pose a problem. On the other hand, in MIG welding, since the arc current value and the filler material (electrode) supply rate are substantially proportional to each other, it is difficult to control the bead for preventing the welding defect.

The present invention has been made in view of such circumstances, and MI
An object of the present invention is to provide a MIG circumferential welding method capable of avoiding a welding defect such as a blowhole at an arc welding start portion in the circumferential welding by G and obtaining a sound weld portion in the entire region.

[Means for Solving Problems] A MIG circumferential welding method according to the present invention is a MIG circumferential welding method of circumferentially welding an aluminum material by the MIG method, which is a starting step for 0.5 seconds or more after starting arc welding. And, having a steady process of welding with a steady current, the current at the start of the arc in the starting process is 0.8 times or less of the steady current, the arc current during the period of the starting process was set lower than the current of the steady process. It is characterized by

[Operation] In the present invention, after starting the arc welding, a period of 0.5 seconds or more is set as the starting step, and the arc current in this starting step is set to be lower than the arc current in the steady step. In addition, the current at the start of the arc in the starting process
Since it is 0.8 times or less, the bead at the welding start part is small. Therefore, when the electrode goes around once and a new bead overlaps the bead at the welding start portion, most of the lower bead is remelted and the groove wall is also melted. Therefore, the blowhole existing in the bead at the start portion floats and is removed from the welded portion.

Embodiments Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a graph showing the time variation of the arc current, with the horizontal axis representing time and the vertical axis representing arc current.

As shown in FIG. 1, the present invention has a starting step for a predetermined time T from the starting point ts of arc welding, and a steady step following this starting step. In the steady process, MIG welding proceeds with a constant steady current Ic as in the conventional case, while in the start process, arc welding proceeds with a current value lower than this steady current. In this starting step, as the time change pattern of the arc current, as shown in FIG. 1, mainly four types of patterns I to IV can be considered. In other words, from the current Is at the start of welding, which is lower than the steady current Ic, the current rises along an upwardly convex curve pattern (Pattern I), linearly increases the current (Pattern II), and projects downward There is a case where the current rises along the curve pattern (pattern III) and a case where the welding start current Is is constant and the current rises momentarily when the welding proceeds to the steady process (pattern IV).

The present invention solves the above-mentioned drawbacks of the prior art by reducing the bead of the arc start portion.
That is, the problem of the conventional technique occurs because the bead at the arc start portion is large. FIG. 2 (a) shows a groove shape, but when the groove portion is arc-welded, conventionally, as shown in FIG. 2 (b), a groove is formed at the overlapping portion (start portion) of the bead. Insufficient penetration 4 occurs on the tip bottom, and insufficient melting 5 of the groove wall occurs on it. In other words, in the groove, the width of the upper bead to be overlapped later is wider than the width of the bead at the start of welding (lower), so it is difficult to remelt the first bead by the heat of the latter bead, The groove wall also has a structure that does not easily melt. However, if the width of the bead (lower bead) at the start of welding is sufficiently narrow, most of the bead can be remelted by the later bead (upper bead) and the groove wall is also melted. .

If the current value is lowered in order to reduce the bead at the start of the arc, the disturbance of the arc due to the initial condition and the disturbance of the shield based on this are reduced. This reduces blowholes. Furthermore, since the bead itself is small, the absolute amount of blowholes (amount of hydrogen gas) contained in this bead is small. Therefore, when the former bead (lower bead) is remelted by the later bead (upper bead), the blowhole is floated and removed, and in addition, the blowhole is diffused into the upper bead and the blowhole is reduced. To do.

For this reason, in the present invention, the bead at the arc start portion is reduced to eliminate the welding defect at the arc start portion. Specifically, the starting step of MIG arc welding is carried out according to the change patterns (I to IV) of the arc current shown in FIG. The current change pattern in this starting step is preferably I, II or III. Aluminum has a very large amount of welding. For this reason, when the IV pattern is adopted, the bead abruptly changes when the process shifts from the starting process to the steady process, so that insufficient fusion of the groove wall and blow holes are likely to occur in this transition region. For this reason, it is preferable to set the current change pattern in the starting step to that shown by the pattern I, II or III in FIG.

The predetermined time T of the starting step is preferably set to 0.5 seconds or more. FIG. 3 is a graph showing the relationship between the predetermined time T and the number of blowholes, with the horizontal axis representing the predetermined time T and the vertical axis representing the average number of blowholes in the welding start portion within 50 mm from the welding start point. Is. The data in this graph is from a welding test using the groove shown in FIG. The base material is A6061TD-T6, which is a cylinder with a wall thickness of 4.5 mm and an outer diameter of 120 mm. This base material was welded using the pattern II in FIG. 1 under the conditions of a current of 230 A and a welding speed of 60 cm / min. Five inspection numbers were taken for each condition, and the bead overlapping portion was X-ray inspected to measure the number of blow holes on the film. Welding start current Is is 185A and 120A. As is clear from this figure, when the time T is 0.5 seconds or more, the number of blowholes is remarkably reduced at any start current. Therefore, the time T of the starting process is secured for 0.5 seconds or more.

Next, the relationship between the start current Is and the steady current Ic will be described. When the start current Is is close to the steady current Ic,
The bead is hard to be small, and it is difficult to obtain the effect of the present invention. Therefore, the ratio Is / Ic between the start current Is and the steady current Ic is set to 0.8 or less. FIG. 5 is a graph showing the relationship between the ratio Is / Ic on the horizontal axis and the number of X-ray grade 2 rejected products on the vertical axis. Also,
FIG. 6 is a graph showing the relationship between the ratio Is / Ic on the horizontal axis and the leakage failure rate due to circumferential welding on the vertical axis. The data shown in these graphs are obtained using two types of containers (A, B) having the groove shape shown in FIG. The material used is A5083-O with a thickness of 5.5 mm for container A and 3.0 mm for container B, with a diameter of 1.6 m.
m A5183-WY wire electrode was used. And the following first
Under the welding conditions shown in the table, welding was performed by changing the current in the pattern II in FIG.

With 30 inspections for each welding condition, the number of X-ray grade 2 rejected products and the leakage failure rate were measured. As a result, as is clear from FIGS. 5 and 6, the number of rejected products and the leakage defect rate are 0 when the ratio Is / Ic is 0.8 or less, while the ratio Is / Ic is If it exceeds 0.8, the defect occurrence rate of both containers A and B sharply increases. Therefore, the current Is at the start of arc welding is preferably 0.8 or less of the steady current Ic.

The minimum value of the current Is at the start of arc welding depends on the electrode wire diameter, but may be any current that can sustain the arc at the electrode diameter used. Also,
The above description is for the case where welding is completed in one pass, but when finishing in multiple passes, the effect of the present invention can be obtained by welding under each condition of the conditions specified in the present invention. it can.

Next, examples of MIG circumference welding under the conditions specified in the present invention will be described together with comparative examples that deviate from the specified range.

First, the results of welding aluminum wheels will be described. The material was A5052-O and a 1.6 mm diameter A5356-WY wire electrode was used. The groove shape is as shown in FIG. Two kinds of steady current Ic are set, 240A is energized when the welding speed is 60cm / min, and 270A when the welding speed is 75cm / min.
Energized. Other welding conditions of this welding test are shown in Table 2 below together with the results of the airtightness investigation.

In Table 2, the airtightness is the number of pieces that have passed the airtightness test divided by the total number of inspection objects. As is clear from Table 2, the airtightness is low in the case of the comparative example in which either the current ratio Is / Ic or the predetermined time T deviates from the invention of the present application, whereas in the case of the example of the present invention, The airtightness is high and 100% of the products have passed.

Next, the result of welding the aluminum container will be described. The material is A6061TD-T6 and A6061 forged product, 1.6m
An m5 diameter A5356-WY wire electrode was used. The groove shape is as shown in FIG. The steady current Ic is 145Å and the welding speed is 65 cm / min. Other welding conditions of this welding test and the results of airtightness and X-ray inspection are shown in Table 3 below.

In Table 3, the X-ray inspection is the number of products that have passed the JIS2 class X-ray inspection divided by the total number of inspection objects.
As is clear from Table 3, in this welding test as well, in the case of the examples falling within the range defined by the present invention, both the airtightness and the X-ray inspection show a pass rate of 100%.

EFFECTS OF THE INVENTION According to the present invention, it is possible to eliminate the blowhole defect at the welding start portion in the circumferential welding where the beads are overlapped with each other, and it is possible to manufacture a product with high airtightness without insufficient fusion. it can.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph of a current change pattern showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are schematic diagrams for explaining defects in a bead overlapping portion, and FIG. Is a graph showing the relationship between the predetermined time T and the blowhole, FIG. 4 is a view showing the groove shape, FIG. 5 is a graph showing the relationship between the current ratio Is / Ic and the number of X-ray inspection failures, FIG. 6 is a graph showing the relationship between the current ratio Is / Ic and the leakage failure rate, FIGS. 7 to 9 are views showing the groove shape, and FIG. 10 is a schematic view showing a conventional welding start portion. is there. 1; welding start part, 2; convex bead, 3; bead start part, 4;
Insufficient penetration, 5; Insufficient melting of groove wall

Claims (2)

[Claims] 1. In the MIG circumferential welding method of circumferentially welding aluminum aluminum material by the MIG method, 0.5 after starting arc welding.
Starting step over a period of more than a second, and has a steady step of welding with a steady current, the current at the start of the arc in the starting step is 0.8 times or less of the steady current, the arc current during the period of the starting step. A MIG circumference welding method characterized in that the current is set to be lower than that in the steady process. 2. The MI according to claim 1, wherein the arc current in the starting step gradually increases.
G circumference welding method.