JP3605897B2 - Irradiation method using laser beam irradiation torch - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses, for example, a laser beam irradiation torch used to form a reinforcing film such as a clad portion in a predetermined range on the inner wall of a small-diameter tube such as an in-core monitor housing that is attached to penetrate a reactor pressure vessel . It relates to the irradiation method .
[0002]
[Prior art]
In general, as shown in FIG. 4, a reactor pressure vessel that forms the core of a nuclear reactor facility is formed with a through hole b in the lower mirror part a, and a small diameter tube c such as an in-core monitor housing is formed in the through hole b. Is welded through. Further, in a plant constructed relatively early, the inner wall of the small-diameter pipe c is provided with a clad portion e which is alloyed to reinforce the strength of the region in order to prevent cracks in the peripheral region of the welded portion d. May be constructed.
[0003]
As a formation method of this clad part e, first, as shown in FIG. 5, mixing in the small-diameter pipe c is, for example, Cr: 4, Ni: 4, Mo: 0.5, Fe: 1. After applying a paste clad material made of metal powder to a thickness of about 0.3 to 0.4 mm, a laser beam irradiation torch f is inserted into the small-diameter tube c as shown in FIG. The clad material is irradiated with a high energy laser beam from the laser oscillation part h as shown in FIG. 5 while the laser beam irradiation torch f is swirled helically by the swivel means g. Is melted to form an alloy with the base material of the small-diameter pipe c, and a clad portion having a thickness of about 0.2 mm is welded.
[0004]
Then, as shown in FIG. 6, the laser beam irradiation torch f is connected to a turning drive unit i for driving the turning of the laser beam irradiation torch f, and a laser beam is applied to a cylindrical body k having an optical fiber cable j at its axial center. A first convex lens l and a second convex lens m that refract B and a mirror n that reflects the laser beam B are provided, and a diffused beam emitted from the end of the optical fiber cable j is paralleled by the first convex lens l. After being refracted into a beam and refracting the parallel beam into a convergent beam by the second convex lens m, the converged beam is reflected radially outward of the cylindrical body k by the mirror n, and the small diameter tube c is irradiated from the irradiation hole o. Welding is performed by irradiating the inner wall with a focused high-energy laser beam. And, as shown in FIG. 7, the irradiation position of the laser beam by this laser beam irradiation torch 6 is to efficiently perform the melting work of the clad material by irradiation, that is, to ensure a certain irradiation area. It is controlled so that it is not the focal position of the laser beam but before and after it.
[0005]
[Problems to be solved by the invention]
Incidentally, as shown in FIG. 8, the laser beam at this irradiation position is obtained by converging the parallel beam formed by the first convex lens l as it is by the second convex lens m as shown in FIG. The beam intensity distribution has the highest peak at the center of the irradiation position, and has a sharp mountain shape that decreases rapidly toward the periphery.
[0006]
Therefore, as shown in FIG. 8, the welding beat obtained with such a laser beam also has a deep central portion and a narrow shape, so that the heat effect on the base material is large, It was also difficult to perform efficient clad construction.
[0007]
Accordingly, the present invention has been devised in order to solve the above-mentioned problems, and its purpose is to provide a novel laser capable of making the beam intensity uniform at the irradiation position and obtaining a wide and uniform welding beat. An object of the present invention is to provide an irradiation method using a beam irradiation torch.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an optical fiber cable that irradiates a high energy laser beam from an end, a first convex lens that refracts a diffused beam emitted from the optical fiber cable into a parallel beam, and converges the parallel beam. A second convex lens , and a laser beam irradiation torch having a plane portion positioned at right angles to the incident angle of the parallel beam at a central portion on the convex surface side of the second convex lens. Before and after the focal point, the laser beam is irradiated with the irradiation area of the beam being substantially the same as the area of the flat portion .
[0009]
In the present invention, as described above, the plane portion is formed in the central portion on the convex surface side of the second convex lens for converging the parallel beam obtained by the first convex lens, so that the beam intensity is substantially reduced at the central portion and its peripheral portion. A uniform laser beam can be obtained. Therefore, a uniform welding beat having a shallow depth and a wide width can be obtained by using a laser beam having such a beam intensity distribution for welding the clad material of the inner wall of the small diameter pipe. In addition, by making the area of this flat part substantially the same as the irradiation area, the beam intensity is slightly higher in the peripheral part than in the central part, and by using such a laser beam, a better welding beat can be obtained. can get.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0011]
FIG. 1 shows a laser beam irradiation torch according to the present invention. As shown in the figure, this laser beam irradiation torch accommodates an optical fiber cable 2 of about 0.8 mmφ, a first convex lens 3 and a second convex lens 4 of about 15 mmφ in a cylindrical body 1.
[0012]
The optical fiber cable 2 is fixed to the axial center portion of the cylindrical body 1, and guides the high energy laser beam B generated from the laser oscillation means described above and emits it as a diffused beam from the end portion.
[0013]
The first convex lens 3 is formed in a flat shape on the fiber cable 2 side and the other surface is processed in a convex shape, and refracts the diffused beam B1 radiated from the end of the fiber cable 2 into a parallel beam B2. Yes.
[0014]
On the other hand, the second convex lens 4 is installed so that the convex portion faces the first convex lens 3 side, and the parallel beam B2 obtained by the first convex lens 3 is refracted so as to converge and used for welding. A beam B3 is obtained. Further, as shown in FIG. 2, a circular cut portion of about 2 mmφ cut into a flat shape so as to be incident at a right angle to the incident angle of the parallel beam B2 at the central portion on the convex portion side of the second convex lens 4. 5 is formed, and the parallel beam B2 incident on the cut portion 5 is allowed to pass through without being converged. The second convex lens 4 can be moved close to and away from the first convex lens 3 so that the focal length from the first convex lens 3 can be set arbitrarily.
[0015]
Next, an irradiation method using the laser beam irradiation torch according to this embodiment will be described. As shown in FIG. 1, first, fiber-Lee bar laser beam emitted from the end portion of the cable 2 B reaches the flat surface side of the first convex lens 3 at the position of distance X becomes diffused beam B1, here When passing through, it is refracted to the axial center side of the housing 1 and becomes a parallel beam B2, then reaches the convex side of the second convex lens 4 and passes through it. At this time, the parallel beam B2 that passes through the peripheral portion of the second convex lens 4, that is, the spherical surface portion, is further refracted toward the axial center side of the housing 1 to become a convergent beam B3, and is focused at a distance Z from the second convex lens 4. However, the parallel beam B2 passing through the central cut portion 5 of the second convex lens 4 passes through the second convex lens 4 as it is in the state of the parallel beam B2, and is separated from the second convex lens 4 by a distance. The irradiation position at Y is reached.
[0016]
As shown in FIG. 3, the beam at the irradiation position obtained in this way is a parallel beam B2 having a substantially uniform beam intensity from the central part to the peripheral part, and a convergent beam B3 having a higher beam intensity at the peripheral part than at the central part. The beam intensity distribution is slightly higher at the periphery than at the center of the irradiation position, and unlike the conventional mountain shape having a large beam intensity at the center, It will disperse to form a substantially trapezoid.
[0017]
When the above-described clad construction is performed using the laser beam B having such a beam intensity distribution, the welding beat has a wide and shallow penetration as shown in FIG. become. As shown in the figure, the weld beat has a uniform depth even when a beam having a greater intensity distribution in the periphery than in the center is used. This is because a certain amount of heat escapes to the periphery of the heat input in the peripheral part, and as a result, the total amount of heat input required for melting is uniform in the central part and the peripheral part. . In the present embodiment, the area of the cut portion 5 at the center of the second convex lens 4 is preferably set substantially the same as the irradiation area at the laser beam irradiation position. That is, if the area of the cut portion 5 is too smaller than the irradiation area, the beam intensity is concentrated in the center portion. Conversely, if the area of the cut portion 5 is too large, the irradiation area of the beam also increases. This is because an ideal welding beat shape as shown in FIG.
[0018]
【The invention's effect】
In short, according to the present invention, a uniform welding beat having a shallow depth and a wide width can be easily obtained by irradiating the laser beam with the area of the plane portion being substantially the same as the irradiation area of the beam , In addition to being able to reduce the thermal influence on the base material, it exhibits excellent effects such as efficient clad execution.
[Brief description of the drawings]
FIG. 1 is a schematic view illustrating one embodiment of the present invention.
FIG. 2 is a perspective view showing a second convex lens according to the present invention.
FIG. 3 is an explanatory diagram showing a beam intensity distribution and a welding beat shape obtained by the present invention.
FIG. 4 is an explanatory view showing an outline of a conventional laser cladding method.
FIG. 5 is an explanatory view showing a process of a conventional laser cladding method. FIG. 6 is a longitudinal sectional view showing an example of a conventional laser beam irradiation torch.
FIG. 7 is an explanatory view showing a beam obtained by a conventional laser beam irradiation torch.
FIG. 8 is an explanatory diagram showing a beam intensity distribution and a welding beat shape obtained by a conventional laser beam irradiation torch.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tube 2 Optical fiber cable 3 First convex lens 4 Second convex lens 5 Plane part

Claims (1)

An optical fiber cable for irradiating a high energy laser beam from the end, a first convex lens for refracting a diffused beam emitted from the optical fiber cable into a parallel beam, and a second convex lens for converging the parallel beam , and Using a laser beam irradiation torch in which a plane portion positioned perpendicular to the incident angle of the parallel beam is formed in the central portion on the convex surface side of the biconvex lens, the irradiation area of the beam before and after the focal point of the second convex lens is An irradiation method using a laser beam irradiation torch , characterized by irradiating a laser beam with substantially the same area as a flat portion .

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