JPH0515986A - Welding method for manufacturing pipe utilizing laser beam - Google Patents

Abstract

PURPOSE:To increase the welding speed without increasing heat input and to maintain the performance of a weld zone at the time of manufacturing a pipe by welding by the laser beam welding process. CONSTITUTION:When band steel is formed into an open pipe shape, both end faces thereof are abutted on each other and a butt part thereof is irradiated with a laser beam and welded to manufacture the pipe, a V-shaped groove having a width (a) mm and a depth (b) mm to satisfy the following conditions of (1)-(5) is formed on the exterior side of a pipe shape of the butt part before welding and welding is performed. (conditions) (4)(a)>0, (b)>0(2)(a)/(b)>D/(f) (3)(a)/(b)<=2X(P/(v)) (4)(t-b)<=4X(P/(v)) (5)(a)<=2X(P/(x)) wherein D, (f), P, (v) and (t) denote the laser beam diameter mm before condensing, the focal distance mm of a condensing optical system, the output kw of the laser beam, the welding speed m/min and thickness mm of band steels to be welded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a welded pipe such as a stainless steel pipe or a high alloy steel pipe, and more particularly to a laser beam pipe welding process capable of producing a high speed and low heat input.

[0002]

2. Description of the Related Art As a welding method for manufacturing a welded pipe,
It is roughly classified into a fusion welding method such as TIG welding, plasma welding, and submerged arc welding, and a pressure welding method represented by ERW. The fusion welding method is advantageous in that welding defects are less likely to occur and the performance of the welded portion is excellent. Particularly, in the case of TIG welding or plasma welding, since the cleanliness of the weld metal is good, high-quality steel pipes such as stainless steel Applied in manufacturing,
On the other hand, since the welding speed is slow, there is a drawback that productivity is poor. On the other hand, ERW is extremely excellent in terms of production, contrary to the fusion welding method, but has the drawback that welding defects such as penetrators are likely to occur, so this method was applied to the production of high-grade steel pipes. In this case, the reliability of the performance of the welded portion becomes a problem.

Recently, using a laser beam of carbon dioxide gas as a welding heat source has been studied for the purpose of developing a pipe welding method having a welding speed equivalent to that of ERW and a weld portion performance equivalent to that of arc welding. It is being applied to some parts of stainless welded pipes. The welding method using a laser beam (hereinafter referred to as "laser welding method") is performed by fusion welding, so that the occurrence of defects in the welded part is suppressed, and the energy density of the heat source is higher than that of normal arc welding, resulting in less penetration. It enables deep, high-speed welding, and further reduces the total heat input, resulting in good weld performance. However, the welding speed is about 2 to 3 times as high as that of the conventional plasma welding method, and it is hard to say that it is economically advantageous in view of the price of the laser oscillator and other incidental equipment.

The inventors of the present invention have proposed a high-frequency preheating laser pipe welding method in which heating by high frequency and laser welding are combined, as disclosed in Japanese Patent Laid-Open No. 2-70379. According to this, it is about 2 compared to the laser-only welding method.
It is possible to obtain a welding speed four times or more that of the plasma welding method. However, the addition of high-frequency preheating increases the total heat input, so when applying this method to ferritic stainless steel pipes for automobiles where weldability is required and high-grade carbon steel pipes where toughness is required at welds. Becomes brittle due to increased heat input, and it becomes difficult to secure the performance of the welded part.

[0005]

DISCLOSURE OF THE INVENTION The present invention is a pipe welding for ensuring the performance of a welded portion by increasing the welding speed without increasing the heat input when producing a welded pipe by the laser welding method. The purpose is to provide a method.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to supply a strip of steel to a forming roll group, continuously form it into an open pipe shape, and pressurize it with a squeeze roll opposite to this strip. A pipe-making welding method in which both end faces of steel are butted and a laser beam such as carbon dioxide gas is applied to the butted part, and a width a ( mm) and a depth b (mm) of a substantially V-shaped notch (hereinafter referred to as "V groove") are formed and welded.

[Conditions] a> 0, b> 0 a / b> D / f a / b ≦ 2 × (P / v) t−b ≦ 4 × (P / v) a ≦ 2 × (P / v ) Where D is the laser beam diameter before focusing (mm) f is the focal length of the focusing optical system (mm) P is the laser beam output (kw) v is the welding speed (m / min) t is the welding Plate thickness of power strip (mm)

[0008]

The present inventors applied a carbon dioxide gas laser as a welding heat source when bending and butt welding a steel strip,
The performance of the welded portion was evaluated by appropriately changing the conditions of the laser beam and the butt shape.

It has been considered that the laser welding method requires a very high butt precision because the laser beam diameter is small. However, in the experiments conducted by the present inventors, some recesses or gaps were formed on the outer surface of the butt portion. It was revealed that the existence thereof does not adversely affect welding. According to the method of the present invention, the V-shaped groove is provided on the outer surface side of the tubular shape within a range that does not impair the weldability, thereby substantially reducing the plate thickness of the steel strip and increasing the welding speed.

The method of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 (a) shows the state of the workpiece to be welded during the method of the present invention, and FIG. 1 (b) shows the state of the workpiece to be welded immediately before the welding.

A material 1 to be welded having a plate thickness (wall thickness) t (mm) is formed into a tubular shape, and its end faces are abutted with each other, and a width a is formed on the outer surface side of the tubular shape.
(mm), V groove 2 of depth b (mm) is provided.

The V-grooves 2 may be provided by using the V-grooves 2 whose end faces are preliminarily processed to have the V-grooves 2 when the end faces of the steel strips are butted. By continuously cutting or forming the end face of the strip steel, by performing these treatments immediately before welding after the strip steel is formed into an open pipe shape, or by changing the roll hole shape of the forming roll. Although there is a method of obtaining the V groove 2, etc., the effect on the performance of the welded portion by the method of the present invention is the same in all cases. The V-groove 2 does not have to be exactly V-shaped, and may have some irregularities or some curvature.

FIGS. 2A and 2B show the relationship between the shape of the V groove 2 and the laser beam 3.

The above conditions will be described below with reference to the symbols in FIGS.

A> 0, b>0; In the method of the present invention, it is necessary to provide the V groove 2 at the abutting portion. That is, width a> 0 and depth b> 0. The case where the width a = 0 and the depth b = 0 is the conventional method without the V groove 2.

A / b> D / f; This formula is for a focal length f of a laser beam 3 having a beam diameter D (mm) with its optical axis aligned with the abutting portion of the strip steel end face.
When focused at (mm), laser beam 3 is V-groove 2
It is to determine whether to hit the shoulder portion 5 of the. Figure 2
(A) is the case of a / b ≦ D / f, and as is clear from the figure, the laser beam 3 hits the shoulder portion 5 of the V groove. As a result, metal plasma is generated at the shoulder portion 5, the laser beam 3 is absorbed by the plasma, and the penetration depth is reduced, which is not preferable. 2 (b) shows a / b> D / f
In this case, the laser beam 3 is concentrated on the bottom portion 6 of the V groove, and deep penetration can be efficiently obtained. That is, for high speed welding, a / b> D / f is a necessary condition.

A × b ≦ 2 × (P / v); This expression is a conditional expression for preventing under-beads (defect beads recessed from the base metal surface) on the outer surface side of the welded portion. It is necessary that the V-groove 2 is sufficiently filled with the molten metal in order not to generate the under-bead. The amount of molten metal in the V groove 2 is determined by the cross-sectional area of the V groove 2 and the amount of molten metal supplied. The cross-sectional area of the V groove 2 is represented by 1/2 (a × b). Laser beam output P (KW), welding speed v (m / m
in), the amount of molten metal is proportional to the amount of heat input (P / v), so the underbead prevention condition is a × b ≦ k × (P / v
v). However, the proportional constant is k. It has been found that it is appropriate to set the value of k to 2 from a number of experimental results described later.

T−b ≦ 4 × (P / v); By providing the V groove 2 in the abutting portion, the plate thickness that must be melted by laser is reduced to tb, and the welding speed can be increased. You can Since the penetration depth of the laser is proportional to the heat input (P / v), t−b ≦ p
A relational expression of x (P / v) is obtained. However, the proportionality constant p is set. Similar to the above k, the proportional constant, p = 4, was obtained from the results of many experiments.

A ≦ 2 × (P / v); This expression is a conditional expression for preventing undercut in the welded portion.

FIG. 3 is a view showing an undercut 4 which occurs when the width a of the V groove 2 is excessively larger than the bead width Ba. To prevent undercut 4 from occurring in the weld,
The groove width a of the V groove 2 needs to be smaller than the bead width. When the welding speed v (m / min) is constant, the bead width Ba is proportional to the heat input (P / v), so that the relational expression a ≦ q × (P / v) is obtained. However, the proportional constant is q. Said k
From the result of the experiment as well as p and p, this proportional constant, q =
I asked for 2.

Some of the results of the experiments conducted by the present inventor will be described below with reference to FIGS.

FIG. 4 shows a proper range of a and b values at a plate thickness of 3 mm and a welding speed of 6 m / min.

FIG. 5 shows a proper range of a and b values at a plate thickness of 3 mm and a welding speed of 8 m / min.

FIG. 6 shows a proper range of a and b values at a plate thickness of 3 mm and a welding speed of 12 m / min.

The experimental condition is that the beam diameter before focusing is D
= 30mm, the focal length of the mirror (parabolic mirror) is f = 150mm,
The plate thickness was t = 3 mm, the laser output was constant P = 5 kW, and the focal position was set at the bottom 6 of the V groove. The material to be welded 1 is SUS 304.

The range of a and b values for obtaining a normal bead is the shaded area in the figure which satisfies the above conditions (1) to (4). In the case of the low welding speed of 6 m / min in FIG. 4, the area of the shaded area is large and the range to which the method of the present invention can be applied is wide. Also, a =
0, b = 0, that is, a normal bead is obtained even if the V groove 2 is not provided. However, as the welding speed increases,
The appropriate range of b value is narrowed. The time when the shaded portion surrounded by the above conditional expression disappears is the limit value of the welding speed at which welding can be performed by the method of the present invention.

FIG. 7 shows an appropriate range of a and b values at a plate thickness of 2 mm and a welding speed of 8 m / min.

FIG. 8 shows a proper range of a and b values at a plate thickness of 2 mm and a welding speed of 12 m / min.

FIG. 9 shows an appropriate range of a and b values at a plate thickness of 2 mm and a welding speed of 14 m / min.

As an experimental condition, the beam diameter before focusing is D
= 30mm, the focal length of the mirror (parabolic mirror) is f = 100mm,
The plate thickness was t = 2 mm, the laser output was constant P = 4 kW, and the focal position was set at the bottom 6 of the V groove 2. The material to be welded 1
The material is SUS 304.

The range of the shaded area in these figures where a normal bead is obtained is similar to the case where the plate thickness is 3 mm,
As the welding speed increases, the appropriate range of the a and b values is narrowed and the shaded area becomes smaller. The welding speed in Fig. 7 is 8m / mi.
In the case of n, a = 0, b = 0, that is, sufficient penetration is obtained without providing the V groove 2 and a normal bead is obtained.
Figure 10 shows the appropriate range of a and b values for a plate thickness of 6 mm and a welding speed of 3 m / min.

FIG. 11 shows an appropriate range of a and b values at a plate thickness of 6 mm and a welding speed of 5 m / min.

As an experimental condition, the beam diameter before focusing is D
= 30mm, the focal length of the mirror (parabolic mirror) is f = 150mm,
The plate thickness was t = 6 mm, the laser output was constant at P = 5 kW, and the focal position was set at the bottom 6 of the V groove 2. The material to be welded 1
The material is SUS 304.

Even when the plate thickness is 6 mm, the same tendency as the result when the plate thickness is 3 mm or 2 mm is shown. At the welding speed of 3 m / min shown in FIG. 10, a normal bead can be obtained without providing the V groove 2, whereas at the welding speed of 5 m / min shown in FIG. 11, the normal bead is obtained. I can't get a bead.
In other words, with the method of the present invention, the welding speed is 5 m / mi.
Can speed up to about n.

The above is the result of studying SUS 304. It was confirmed that in the case of carbon steel or ferritic stainless steel, if the above conditional expression is satisfied, a normal bead can be obtained as in the case of SUS 304. ..

[0037]

Example A carbon dioxide gas laser oscillator with a maximum output of 5 kw was used as a welding heat source, the beam diameter before focusing was set to 30 mm, and the focus position was set to the bottom of the V groove, and a butt welding test was conducted.

The welds were evaluated by visual observation of the bead shape and, for stainless steel, at the Charpy impact test transition temperature of the weld.

Table 1 shows the material of the strip steel used as the material to be welded,
There are three types of component values, A, B, and C. A is austenitic stainless steel, B is ferritic stainless steel, and C is 50 kg class low alloy steel.

[0040]

[Table 1]

Table 2 shows the results obtained by conducting experiments under various conditions.

[0042]

[Table 2]

No. 1, 2, 9, 10, 12, 13, 20, 21 are V
This is a conventional example performed without grooves, and Nos. 4 to 7 and 15
-18 are comparative examples, and others are examples of the present invention.

No. 1 welding speed 6 for A steel with a plate thickness of 3 mm
m / min is the limit speed of the conventional method, and No. 2 welding speed is 7
At m / min, insufficient penetration occurred. However, N of the present invention example
o.3 welding speed 8m / min and No. 8 welding speed 12m / m
As in the case of in, by appropriately providing the V groove, the welding speed can be increased. As is clear from FIG. 5, No. 4 is a case where a / b> D / f was not satisfied, and the laser beam was not concentrated at the bottom of the V groove, resulting in insufficient penetration.

No. 5 is a case where a × b ≦ 2 × (P / v) was not satisfied, and the molten metal was insufficient and undercut occurred. No. 6 is a case where t−b ≦ 4 × (P / v) was not satisfied, and insufficient penetration occurred due to the shallow groove. No. 7 is a case where a ≦ 2 × (P / v) was not satisfied, and the groove width was too wide and undercut occurred.

Nos. 9 to 11 are results when the plate thickness is 6 mm. In the conventional method, the limit speed of 3 m / min of No. 6 is
In the method of the present invention, it was improved to 5 m / min like No. 11.

Nos. 12 to 19 are results of ferritic stainless steel having a plate thickness of 2 mm. Although the speeding up of welding by the method of the present invention is the same as in the case of the plate thickness of 3 mm, not only the speeding up of welding was achieved, but also the heat input coefficient was reduced and the Charpy property of the welded portion was improved. It was

Nos. 20 to 22 are cases of low alloy steel, and the effects were exactly the same as those of ferritic stainless steel.

[0049]

By performing the method of the present invention in a pipe welding method using a laser beam, a significantly high speed can be achieved, and at the same time, the toughness of the welded portion is improved by the low heat input. As a result, a high-performance welded steel pipe can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a V-groove shape before welding.

FIG. 2 is a diagram showing a relationship between a and b values and a laser beam path.

FIG. 3 is a view showing a bead shape when the V groove width is excessively large.

FIG. 4 is a diagram showing appropriate ranges of a and b values at a plate thickness of 3 mm and a welding speed of 6 m / min.

FIG. 5 is a diagram showing appropriate ranges of a and b values at a plate thickness of 3 mm and a welding speed of 8 m / min.

FIG. 6 is a diagram showing appropriate ranges of a and b values at a plate thickness of 3 mm and a welding speed of 12 m / min.

FIG. 7 is a diagram showing appropriate ranges of a and b values at a plate thickness of 6 mm and a welding speed of 3 m / min.

FIG. 8 is a diagram showing a proper range of a and b values at a plate thickness of 6 mm and a welding speed of 5 m / min.

FIG. 9 is a diagram showing appropriate ranges of a and b values at a plate thickness of 2 mm and a welding speed of 8 m / min.

FIG. 10 is a diagram showing appropriate ranges of a and b values at a plate thickness of 2 mm and a welding speed of 12 m / min.

FIG. 11 is a diagram showing appropriate ranges of a and b values at a plate thickness of 2 mm and a welding speed of 14 m / min.

Claims (1)

Claims: 1. A steel strip is supplied to a forming roll group and continuously formed into an open pipe shape, and pressure is applied by a squeeze roll provided oppositely, and both end faces of this steel strip are butted. A pipe manufacturing welding method of irradiating a laser beam to the butt portion, wherein a width a (mm) and a depth b (mm) satisfying all of the following conditions on the outer surface side of the pipe shape of the butt portion before welding: (3) A method for producing a pipe by laser, which comprises forming a V groove and welding. [Condition] a> 0, b> 0 a / b> D / f a / b ≦ 2 × (P / v) t−b ≦ 4 × (P / v) a ≦ 2 × (P / v) where , D is the diameter of the laser beam before focusing (mm) f is the focal length of the focusing optical system (mm) P is the output of the laser beam (kw) v is the welding speed (m / min) t is the steel strip to be welded Board thickness (mm)