JPH0890265A - Tube manufacturing method by laser beam welding - Google Patents

Abstract

PURPOSE: To form an excellent weld zone free from blow holes or weld metal solidification cracks by increasing the molten pool both in width and length so that the molten flow formed by the preceding keyhole may be blocked by the succeeding keyhole to make the peripheral flow, and promoting the removal of bubbles therefrom. CONSTITUTION: A first laser beam B1 to form a keyhole H1 through a base metal 7 and a second laser beam B2 to form a keyhole H2 of the depth of at least 30% that of the base metal 7 are continuously arranged in the welding direction and at the position where these laser beams are separated from each other so that the keyholes H1, H2 are not overlapped each other. The welding is achieved while irradiating the second laser beam B2 in the molten pool 4 formed by the first laser beam, and the upper reinforcement 6 is formed on the weld zone to collect the bubbles 3 present in the molten pool 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for manufacturing a pipe by laser welding.

[0002]

2. Description of the Related Art Conventionally, a high-frequency preheating laser pipe manufacturing method including high-frequency heating (preheating) + laser welding has been carried out as a method for manufacturing high-quality welded pipes. In this pipe manufacturing method, a laser can be directly irradiated with high density into the thick wall through a through hole formed in a molten pool called a keyhole. As a result, uniform inner and outer surfaces can be welded, which is suitable for high-speed welding.
Particularly in the welding of a material having a relatively thin wall, a very good weld having no defects can be obtained.

However, when the wall thickness is large (depending on the type of steel, it exceeds 6 mm, for example), defects such as blowholes and solidification cracks are likely to occur in the welded portion. The generation mechanism of these defects will be described with reference to the drawings.

FIGS. 15 (a) to 15 (c) are explanatory views of the mechanism of generation of a welding defect, which are all cut surfaces in the longitudinal direction when the laser beam 101 is relatively moving in the direction of the arrow (from right to left in the drawing). is there. The base material 102 is, for example, a steel plate having a thickness of 12 mm. FIG. 1A is a diagram showing a drop of molten metal, and a keyhole 104 is formed through the tip of a molten pool 103 formed by melting with a laser beam 101.
4 also has a depth of about 12 mm, which is the same as the base metal, and keyhole 1
It is easy for part of the molten metal to fall into the area 04. Note that 105
... (... indicates a plurality, the same applies hereinafter) is a bubble, 106
Is a solidification portion, and 107 is a blow hole formed by bubbles contained during solidification.

(B) shows that the laser beam 101 directly irradiates a part of the molten metal dropped in the keyhole 104. In (c), a part of the molten metal evaporates explosively and forms bubbles 105 ... And cavities 105a ... The above processes (a) to (c) are repeated in this order or in any order to generate the bubbles 105, and there is no problem if these bubbles 105 are released to the outside of the metal before the molten metal solidifies, but in reality, Are partially left behind to form the blow holes 107.

Further, since the keyhole fluctuates unstablely, the shape of the molten pool also becomes unstable, and a solidification delay part 110 is often generated. This causes a swelling bead cross section as shown in FIG.
9 may occur. FIG. 16 shows the bead after solidification, and the bead has blowholes 107 and solidification cracks 109.
Is formed. An attempt was made to improve elimination of the bubbles 105 by preheating the end portion (welded portion) of the base material, but the effect could not be expected. In addition, deposits such as rolling oil also cause blowholes 107 to occur.

Therefore, the following methods have been proposed as countermeasures against defects such as blowholes and solidification cracks. First method: A deoxidizer is added to the molten pool to suppress the generation of bubbles. Second method: the method proposed in Japanese Patent Laid-Open No. 60-240395, and as shown in FIG.
With the laser beam, the corner of the end of the molten metal is dropped to enlarge the opening of the keyhole, promoting the discharge of metal vapor and preventing the generation of blowholes. Third method: a method proposed in Japanese Patent Laid-Open No. Hei 1-99789, in which a laser beam is simultaneously irradiated from the outer surface and the inner surface of the pipe, and the bead width is narrowed because single-side welding is changed to double-sided welding. It is possible to do.

[0008]

However, although the above-mentioned first method can prevent blowholes due to oxidation when air is involved, the formation of blowholes due to unstable keyholes and solidification cracking occur. Can not be expected to be effective. In the second method, the keyhole is formed by the first laser beam as in the embodiment, but the keyhole is not formed by the second laser beam. That is, the second laser beam has a low output, and the irradiation target is only in the vicinity of the outer peripheral surface of the tube. Then, for welding thicker than 6 mm, the second laser beam acts only on the very upper part of the keyhole, most of the keyhole remains narrow, and bubble escape is improved. Blowholes are generated without this. Also,
In the third method, laser irradiation (laser passage formation, irradiation position alignment, spatter and fume discharge) on the inner surface of the tube is extremely difficult, and occurs when an optical path is formed by mirror reflection as in the embodiment. Fume, water vapor, etc. interfere with light transmission, making it difficult to put into practical use.

[0009]

Therefore, the inventors of the present invention, from a practical point of view, decided to use single-sided laser welding from the outer surface of the pipe as the welding method, and this welding method is capable of processing thick walls of more than 6 mm without welding defects. I repeated research to find out. As a result, it was confirmed that by irradiating the molten pool with two laser beams, the width and the length of the molten pool can be increased, the escape of bubbles can be promoted, and the occurrence of blowholes and solidification cracks can be prevented. Further, it has been found that a good welded portion can be easily obtained by interposing the above-mentioned bubbles in the upper bulge and cutting the bulged portion later.

Specifically, (claim 1) a flat metal strip is formed into a tubular shape by bending, and both ends of the tubular metal strip facing each other are pressed against each other by a squeeze roll, and the butted portion is laser beam. The welding and the post-treatment are performed in the following steps before welding. First step: the laser beam is composed of a laser beam capable of forming a keyhole penetrating the pipe wall thickness and a laser beam capable of forming a keyhole having a depth of at least 30% of the pipe wall thickness. These two laser beams are arranged side by side in the welding direction in this order or in the reverse order and at positions separated from each other so that the keyholes do not overlap each other, and are placed in the molten pool formed by the preceding laser beams. Welding process in which welding is performed while irradiating a laser beam of a row, and an upper bulge is formed at the welded portion in order to collect air bubbles existing in the molten pool. Second step: a step of removing the upper overfill.

(Claim 2) The pressing force of the squeeze roll is increased so that the height of the upper surplus is at least 0.5 mm.

(Claim 3) Prior to the first step, opposite ends of the tubular metal strip are preheated to at least 700 ° C. by a high frequency heating means.

(Claim 4) The upper sill is cut off with a cutting tool.

[0014]

The operation of the present invention will be described with reference to the drawings. 1A to 1D show the first laser beam output of 20 k.
W, second laser beam output is 20 kW, preheating temperature is 1
Wall thickness of 12 mm at 200 ° C and pipe making speed of 7 m / min
FIG. 7 is an operation diagram when the pipe of FIG. In (a), the first laser beam B1 penetrates to the inner surface of the base material 7
The keyhole H1 is formed. Since the keyhole H1 is unstable like the conventional method, a large number of bubbles 3 are generated behind. Then, by irradiating the second laser beam B2 to the rear side to form the second keyhole H2, the bubbles 3
Can be satisfactorily discharged. The action of the second laser beam B2 includes a first action and a second action described below.

The first action is an action of trapping (capturing) the bubbles 3 generated in the first keyhole H1 and reducing the number of bubbles in the molten pool 4. At this time, air bubbles are also generated in the keyhole H2, but since the laser beam B2 is applied to the high-temperature molten pool 4, there is a sufficient energy margin, and the second keyhole H2 is the first keyhole. It becomes larger than H1. If the keyhole H2 is large,
The molten metal dropped into the keyhole H2 is the laser beam B2
Therefore, the rate of direct irradiation becomes small, and the generation of the bubbles 3 becomes minute.

The second action is, as shown in (b), that the second keyhole H2 blocks the backward flow from the first keyhole H1 to create a peripheral flow, and the width and length of the molten pool 4 are both increased. It is the action of expanding. When the molten pool 4 becomes wider, the bubbles in the molten pool 4 are more likely to float and are less likely to be trapped by the lateral solidified wall surfaces 5 and 5. Further, the molten pool 4 becomes longer, so that the bubbles for discharging the bubbles are increased. I can get time.

By the above-mentioned first and second actions, the bubbles 3 are sufficiently discharged before solidification, or they are concentrated on the upper bulge 6 as shown in (c). Regarding solidification cracking, even if the keyhole is unstable because the molten pool is large, all this fluctuation is absorbed by the molten pool, so solidification is performed stably and a local delay in solidification occurs. No, there is no concern about solidification cracking. As shown in (d), the upper weld 6 (see (c)) including the bubbles (blowholes) 3 is cut off to obtain a good weld 8 having substantially the same width and no defects.

The irradiation position of the second laser beam B2 of the present invention is within the molten pool 4 formed by the first laser beam B1 and the keyhole H1 formed by the first laser beam B1. It is characterized by being located further back. The reason for specifying the irradiation position of the second laser beam B2 as described above is as follows. When the irradiation position of the second laser beam B2 is outside the molten pool 4 formed by the first laser beam B1, welding of the conventional method is performed again after the molten pool 4 is solidified, and the conventional defects are eliminated. I can't solve it. Further, the irradiation position of the second laser beam B2 is
If it is too close, the keyhole H1 formed by the first laser beam B1 is irradiated, and most of the irradiation energy is blown through, which is not preferable.

2A to 2D, the first laser beam output is 20 kW and the second laser beam output is 10 kW.
FIG. 7 is an operation diagram when a pipe having a wall thickness of 12 mm is welded at a preheating temperature of 1200 ° C. and a pipe forming speed of 7 m / min.
In (a), the first laser beam B1 penetrates to the inner surface to form a first keyhole H1, and this keyhole H1 is formed.
A large number of bubbles 3 are generated in the rear of the, and the second keyhole H2 in the rear traps these bubbles 3, and
Since a wide and long molten pool 4 is formed as shown in (b), the bubbles easily rise and are completely discharged or collected in the upper swell. Since the molten pool 4 is large, there is no risk of solidification cracking. As shown in (c), the bubbles 3 remain in the upper bulge 6, and if the upper bulge 6 is cut off, a good welded portion 8 shown in (d) can be obtained. As shown in (a), since the rear laser beam B2 has a relatively low output, the keyhole H2 is not penetrated, and the energy of the laser beam is much heat input above the wall thickness. In this case, the cross section of the bead has a shape in which the upper side is slightly widened as shown in (d).

If the keyhole H2 is not penetrated and is too shallow, the trapping effect of the bubble 3 and the expanding action of the molten pool 4 are weakened, and the desired effect may not be obtained. Therefore, the appropriate depth of the keyhole was investigated. FIG. 3 is an explanatory diagram of transmission X-ray photography according to the present invention, in which an X-ray source 11 is arranged on one side of the welded portion 8 and an X-ray camera 12 is arranged on the other side, and the X-rays of the welded portion 8 before solidification are arranged. A photograph was prepared and the keyhole depth was determined from this X-ray photograph.

Further, samples were taken from the welded portion 8 at a pitch of 50 mm, and the samples were subjected to an optical microscope to count blow holes having a diameter of 10 μm or more. The number of target cross sections of the microscope is 200. FIG. 4 is a correlation diagram of the second keyhole depth and the number of blowholes according to the present invention. The horizontal axis is the second keyhole depth divided by the base metal thickness, and 100% is Indicates penetration. In addition, the vertical axis is the above 200
It is the number of blow holes per cross section, which is the average of cross sections. In the figure, ● indicates that solidification cracking occurred, and ○ indicates that solidification cracking did not occur. As is clear from the figure, if the second keyhole depth is 30% or more, the number of blowholes is 0 "zero", and there is no fear of solidification cracking. Therefore, one of the keyholes should have a thickness of 30% or more. From this, it is understood that the first keyhole may be penetrated and the second keyhole may have a thickness of 30% or more. Alternatively, there is a possibility that the second keyhole may be penetrated and the first keyhole may be 30% or more of the wall thickness. This will be described below.

5A to 5D, the first laser beam output is 10 kW and the second laser beam output is 20 kW.
FIG. 7 is an operation diagram when a pipe having a wall thickness of 12 mm is welded at a preheating temperature of 1200 ° C. and a pipe forming speed of 7 m / min.
In (a), since the first laser beam B1 does not penetrate to the inner surface and is relatively shallow, the number of bubbles generated is small. The rear keyhole H2 penetrates to the inner surface and traps the bubbles 3 generated in the front keyhole H1, (b)
Since a wide and long molten pool 4 is formed as shown in (3), the bubbles 3 easily rise and are completely discharged or collected in the upper surplus 6. Since the molten pool 4 is large, there is no risk of solidification cracking. As shown in (c), the bubbles 3 remain in the upper bulge 6, and if the upper bulge 6 is cut off, a good welded portion 8 shown in (d) can be obtained.

The above keyhole depth depends on the laser beam output. Therefore, the relationship between the laser output and the keyhole depth was investigated. FIG. 6 is a correlation diagram of the welding speed and the keyhole depth with the laser output according to the present invention as a parameter. The horizontal axis represents the welding speed V (m / min) and the vertical axis represents the keyhole depth Kd (mm). is there. When data was plotted on this graph when the laser output was set to 3, 5, 10, and 20 kW, it was confirmed that the smaller the welding speed and the larger the laser output, the larger the keyhole depth. Then, it was found from the multiple regression calculation of the data that the keyhole depth Kd is inversely proportional to the square root of the welding speed V. This relationship is shown by the following formula.

[0024]

[Equation 1]

That is, the keyhole depth Kd is directly proportional to the laser output coefficient C. FIG. 7 is a correlation diagram between the laser output P and the laser output coefficient C, and shows the table in the equation 1, where 1 is set between the laser output P and the laser output coefficient C.
It can be seen that there is a linear relationship. This relationship is shown by an equation, and the expression C is substituted into the equation. The keyhole depth Kd can be easily calculated from the equation.

[0026]

[Equation 2]

By the way, the inventors of the present invention have long been researching a composite technology welding method that combines high-frequency preheating and laser beam welding, and study whether or not preheating can be applied to the present invention. I found that. This will be described below. FIG. 8 is a correlation diagram between the preheating temperature and the specific keyhole depth according to the present invention, where the horizontal axis represents the preheating temperature T of the welded portion and the vertical axis represents the preheating without keyhole depth Kd0 of 1.0. The specific keyhole depth Kd / Kd0, which indicates the keyhole depth Kd with preheating, is shown. Preheating has the same effect as increasing the laser heat input, so the higher the preheating temperature, the deeper the keyhole can be.

From the figure, the relationship between the preheating temperature and the keyhole depth is obtained by multiple regression calculation, and the expression is obtained by substituting the expression for Kd0.

[0029]

(Equation 3)

Appropriate conditions for the first and second laser beams may be derived from equations. Since the second laser beam is always sprayed on the molten metal, the formula on the (T ≧ Tm) side is used.

The characteristic feature of the present invention is to collect residual bubbles in the upper part of the upper layer. Therefore, the height dimension of the upper overfill is important. 9 (a) to 9 (d) are conceptual diagrams of the upper sill, and FIG. 9 (a) is a sill 6 having a relatively small height h1, and the sill 6 is too small to accommodate the bubbles 3. , (B), a part of the bubbles 3 becomes blow holes after the extra cut and remains in the welded portion 8, which is not preferable. (C) is the surplus 6 of sufficient height h2, and since all the bubbles 3 are accommodated in the surplus 6, as shown in (d), there is a concern that blowholes will remain in the welded portion 8 after excision of the surplus. There is no. Extra height h2
If the height h2 can be maintained, a sound weld 8
Will be obtained. Then, in (c), when the upper bulge 6 was examined in detail with a microscope, it was found that almost all bubbles (blowholes) 3 having a diameter of 0.4 mm or more were in contact with the lower surface of the outer surface of the upper bulge 6. I understood.

FIG. 10 is a frequency distribution chart of blowholes, where the horizontal axis represents the diameter of blowholes and the vertical axis represents the number of blowholes (thousands). This frequency distribution chart was created under the following conditions. Pipe outer diameter: 609.6 mm Wall thickness: 9 mm, 12 mm, 15 mm Preheating temperature: 0 ° C., 800 ° C., 1200 ° C. First beam output / second beam output: 20 kW / 10 kW, 20 kW / 20 kW, 10 kW / 20 kW Welding speed: 3-10m / min Upset: None Number of samples: 10000 randomly selected cross-sections

From the figure, it can be seen that the practical maximum diameter of the blowhole is 0.5 mm, and it is sufficient if the upper surplus height h2 is 0.5 mm or more. However, it is difficult to manage the excess in submillimeter units in an actual pipe manufacturing line. Therefore, the present inventors have devised a technique of substituting the upset amount.

The upset amount is the difference between the peripheral length of the pipe before welding and the peripheral length of the pipe after welding, and is generated by pressing with a squeeze roll. Specifically, the upset amount is 1 to 2
Set to mm. 0.5m even if an error of 0.5mm is expected
This is because a surplus of m can be secured.

FIG. 11 is a correlation diagram of preheating temperature and squeeze roll pressure according to the present invention. The vertical axis shows the ratio of squeeze roll pressure with preheat when the squeeze roll pressure without preheating is 1.0. Since the welded part is preheated and softened, the upset can be formed with a small pressing force. It was found that when the preheating temperature was 700 ° C. or higher, the squeeze roll pressure was small, and conversely, when the preheating temperature was less than 700 ° C., the preheating effect was small. Therefore, the preheating temperature is preferably 700 ° C. or higher from the viewpoint of upset molding.

[0036]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 12 is a schematic view of a laser welding pipe forming apparatus according to the present invention. A laser welding pipe forming apparatus 20 is a roll type pipe forming apparatus 21 for gradually bending a flat metal strip W into a tubular shape.
A high-frequency heating means 22, a laser welding machine 23, a squeeze roll 24, and a cutting means 25.

FIG. 13 is a plan view of a laser welding machine and an accessory device according to the present invention. The laser welding machine 23 has a first welding torch 23a and a second welding torch 23b juxtaposed in the welding direction. , The contact tip 22 of the high-frequency heating means 22 on the upstream side of these welding torches 23a, 23b.
a and 22a are arranged. 22b is a high frequency oscillator,
The contact tips 22a, 22a fed from the high frequency oscillator 22b are the end portions W of the metal strip W before laser welding.
1, a contact for energizing W1. The contact tip 22a is an example, and may be, for example, an annular coil for induction heating.

FIG. 14 is a side view of a laser welding machine and an accessory device according to the present invention. The cutting means 25 comprises, for example, a cutting tool 25a, a tool holder 25b, a slider 25c and a horizontal bed 25d, which is held by the tool holder 25b. The upper tool 6 of the welded portion is cut by the cutting tool 25a thus cut. Depending on the conditions, the weld may become extremely hard martensite. At this time, the horizontal bed 25
The cutting tool 2 is moved by moving the slider 25c on the d.
5a may be brought close to the welding torch 23a and cut before being completely hardened. Therefore, the cutting tool 25a can move along the welding direction. The cutting tool 25a may be a tool capable of grinding metal, such as a cutting tool, a milling cutter, or a milling cutter.

As described above, in the laser welding pipe forming apparatus 20 according to the present invention, the flat type metal strip W is formed into a tubular shape by the roll type pipe forming apparatus 21, and the tubular metal is formed by the high frequency heating means 22. Heat the opposite ends of the strip and squeeze roll 2
The opposite end portions are pressed against each other with 4, 24, and the butted portions are laser-welded with a laser welding machine 23.
A welded pipe of good quality is manufactured by cutting off the extra portion 6 of the welded portion at a.

A comparative experiment between the technique of the present invention and the conventional technique was carried out using the above laser welding pipe forming apparatus 20. As a result, evaluation and consideration will be described below. The test material (base material) is the low carbon steel shown in Table 1, and its melting point is 1500 ° C.

[0041]

[Table 1]

Examples 1 to 4 and Comparative Examples 1 to 5: A base material having the above composition and a wall thickness of 9 mm was pipe-formed by the laser welding pipe-making apparatus 20 to an outer diameter of 609.6 mm. The number of blowholes was measured by the above method. Also, 20 randomly selected 500 mm length test parts (total 10 m)
An ultrasonic flaw detection test was conducted on those samples, and those in which cracks were detected at one or more locations were “solid” cracks, and those in which no cracks were detected were “none”. The results are shown in Table 2, and the part marked with ● indicates the failure factor.

[0043]

[Table 2]

In Examples 1 to 4, the first beam output is 20 kW,
The second beam output is 20 kW and the preheating temperature is 0 ℃, 0 ℃,
The temperature was set to 800 ° C. and 1200 ° C., and although there were only 2 (locations) blow holes in Example 1 (5 (locations or more) failed), the welded portion was satisfactory without solidification cracking.

In Comparative Examples 1 to 4, the first beam output is 20 kW,
It was normal 1-beam welding with the second beam output of 0 kW, and solidification cracking was observed and it was unacceptable. In Comparative Example 5, the first beam output was 20 kW and the second beam output was 2 kW. Although the effect of the second beam was recognized, the number of blowholes was as large as 7, and the test was rejected.

Quantitative examination of Comparative Example 5 will be tried using the above formula. The first keyhole depth is Kd1, and this Kd1 is laser output P = 20 kW and preheating temperature T = 120.
Calculated from 0 ° C, pipe making speed = 18 m / min, and
The second keyhole depth is Kd2, and this Kd2 is calculated from the laser output P = 2 kW, the preheating temperature Tm = 1500 ° C., and the pipe-making speed = 18 m / min.

[0047]

[Equation 4]

Since the base material has a thickness of 9 mm, Kd1 indicates penetration, while Kd2 is 25.3% (← 2.28 ÷).
9 × 100). Since Kd2 is less than 30%,
It can be seen from FIG. 4 that solidification cracking does not occur but blowholes do occur, which is in good agreement with the results in Table 2.

Examples 5 to 15 and Comparative Examples 6 to 13: A base material having a wall thickness of 12 mm was made into a tube having an outer diameter of 609.6 mm by the laser welding pipe making apparatus 20 and the number of blow holes and solidification cracking were measured. .

[0050]

[Table 3]

In Examples 5 to 15, the first beam output / second beam output was set to 20 kW / 20 kW, 20 kW / 10 kW or 10 kW / 20 kW, and the number of blow holes was zero or within an allowable value, and solidification cracking occurred. There is no good. Comparative Examples 6 to 12 have a first beam output of 20 kW and a second beam output of 0 kW, and since they are conventional 1-beam welding methods, solidification cracking is recognized and they are unacceptable. Comparative Example 1
No. 3 had a first beam output of 4 kW and a second beam output of 20 kW. When the first beam output was calculated by the above formula, the keyhole depth was 3.14 mm, which was less than 30%, and the number of blowholes was large, which was unacceptable. It was

Examples 16-24 and Comparative Examples 14-19:
A base material having a wall thickness of 15 mm was made into a pipe having an outer diameter of 609.6 mm by the laser welding pipe making apparatus 20, and the number of blow holes and solidification cracking were measured.

[0053]

[Table 4]

In Examples 16 to 24, the first beam output / second
Beam power 20kW / 20kW, 20kW / 10kW
Alternatively, it is set to 10 kW / 20 kW, the number of blowholes is zero or within an allowable value, and solidification cracking is satisfactory.

In Comparative Examples 14 to 17, the first beam output is 20k.
The second beam output was 0 kW at W, and since it was the conventional 1-beam welding method, solidification cracking was recognized and it was unacceptable. Comparative Example 18 has a first beam output of 20 kW and a second beam output of 3 k
When the second beam output was calculated by the above formula, the keyhole depth was less than 30%, and the number of blowholes was large and solidification cracking was also recognized, and the result was unacceptable. In Comparative Example 19, the first beam output was 4 kW and the second beam output was 20 kW, and when the first beam output was calculated by the above formula, the keyhole depth was less than 30%, and the number of blowholes was large, resulting in failure.

[0056]

The present invention has the following effects due to the above configuration. The laser-welded pipe manufacturing method according to claim 1, wherein two laser beams are arranged side by side in the welding direction, one penetrates the base metal, and the other reaches the keyhole to a depth of at least 30% of the wall thickness. Since both beams are arranged at appropriate intervals,
Both the width and the length of the molten pool are designed to reduce the bubbles generated in the previous keyhole by the latter keyhole, and additionally to prevent the molten flow formed by the former keyhole from being blocked by the latter keyhole and becoming a peripheral flow. Enlarges, promotes bubble escape, and forms good welds without blowholes or solidification cracks. Also,
Even if air bubbles remain, the air bubbles are collected in the upper part of the heap, so that there is little adverse effect on the welded portion.

In the laser welding pipe manufacturing method of the second aspect, the height of the upper squeeze roll is maintained at 0.5 mm or more by adjusting the pressing force of the squeeze roll, and the pressing force of the squeeze roll is easily controlled. Therefore, the management of the upper bulge is extremely easy and the pipe manufacturing method is simple.

According to a third aspect of the present invention, there is provided a method for producing a laser-welded pipe by using a high-frequency heating means for at least 700 before welding a portion to be welded by laser.
It is preheated to ℃. By preheating, the pressing force of the squeeze roll is reduced and the amount of upset can be easily earned, so the equipment is not burdened.

In the laser-welded pipe manufacturing method according to the fourth aspect, since the upper swell containing the air bubbles is cut off, a sound weld portion without blowholes can be obtained.

[Brief description of drawings]

FIG. 1 shows a first laser beam output of 20 k according to the present invention.
W, second laser beam output is 20 kW, preheating temperature is 1
Wall thickness of 12 mm at 200 ° C and pipe making speed of 7 m / min
Of action when welding pipes

FIG. 2 shows a first laser beam output of 20 k according to the present invention.
W, second laser beam output is 10 kW, preheating temperature is 1
Wall thickness of 12 mm at 200 ° C and pipe making speed of 7 m / min
Of action when welding pipes

FIG. 3 is an explanatory diagram of transmission X-ray photography according to the present invention.

FIG. 4 is a correlation diagram of the second keyhole depth and the number of blowholes according to the present invention.

FIG. 5 shows a first laser beam output of 10 k according to the present invention.
W, second laser beam output is 20 kW, preheating temperature is 1
Wall thickness of 12 mm at 200 ° C and pipe making speed of 7 m / min
Of action when welding pipes

FIG. 6 is a correlation diagram of the welding speed and the keyhole depth with the laser output according to the present invention as a parameter.

FIG. 7 is a correlation diagram of laser output and laser output coefficient C according to the present invention.

FIG. 8 is a correlation diagram of preheating temperature and specific keyhole depth according to the present invention.

FIG. 9 is a conceptual diagram of an upper sill according to the present invention.

FIG. 10 is a frequency distribution diagram of blowholes according to the present invention.

FIG. 11 is a correlation diagram between preheating temperature and squeeze roll pressure according to the present invention.

FIG. 12 is a schematic view of a laser welding pipe manufacturing apparatus according to the present invention.

FIG. 13 is a plan view of a laser welding machine and an accessory device according to the present invention.

FIG. 14 is a side view of a laser welding machine and an accessory device according to the present invention.

FIG. 15 is an explanatory view of a conventional welding defect generation mechanism.

FIG. 16 is a sectional view of a welding bead including a conventional welding defect.

[Explanation of symbols]

3 ... Bubbles, 4 ... Molten pool, 5 ... Solidification wall surface, 6 ... Upper swell,
7 ... Base material, 8 ... Welded part, 20 ... Laser welding pipe making device, 2
DESCRIPTION OF SYMBOLS 1 ... Roll-type tube forming device, 22 ... High frequency heating means, 23
… Laser welders, 23a, 23b… Welding torches, 24…
Squeeze roll, 25 ... Cutting means, B1 ... First laser beam, B2 ... Second laser beam, H1 ... First keyhole, H2 ... Second keyhole, W ... Metal band, W1 ...
Both ends facing each other.

Claims (4)

[Claims] 1. A flat metal strip is formed into a tubular shape by bending, opposite end portions of the tubular metal strip are pressed against each other with a squeeze roll, and the butted portion is welded with a laser beam in the following steps. A laser welding pipe manufacturing method characterized in that welding and post-treatment are carried out. First step: the laser beam is composed of a laser beam capable of forming a keyhole penetrating the pipe wall thickness and a laser beam capable of forming a keyhole having a depth of at least 30% of the pipe wall thickness. These two laser beams are arranged side by side in the welding direction in this order or in the reverse order and at positions separated from each other so that the keyholes do not overlap each other, and are placed in the molten pool formed by the preceding laser beams. Welding process in which welding is performed while irradiating a laser beam of a row, and an upper bulge is formed at the welded portion in order to collect air bubbles existing in the molten pool. Second step: a step of removing the upper overfill. 2. The laser welding pipe manufacturing method according to claim 1, wherein the height of the upper ridge is at least 0.5 mm by increasing the pressure of the squeeze roll. 3. Prior to the first step, the opposite ends of the tubular metal band are opposed by at least 70 by high frequency heating means.
The laser welding pipe manufacturing method according to claim 2, wherein preheating is performed at 0 ° C. 4. The laser welding pipe manufacturing method according to claim 1, wherein the upper sill is cut off with a cutting tool.