JP2002346847A - Peening method and apparatus by combined use of water jet and laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a peening apparatus by combined use of water jet and laser, by which a peening effect for workpiece material reaches to a wide area and a deep position. SOLUTION: The peening apparatus by combined use of water jet and laser comprises a laser irradiation head 1 for irradiating laser to a peening target region 8 of a structure located in surrounding water 7, and a nozzle head 2 which is coaxially arranged with the laser irradiation head 1 and forms cavitation jet 13 by discharging high pressure water 4 from the circumference around the laser irradiation head 1 and makes the cavitation jet 13 collide with the peening target region 8. If the laser 5 and the cavitation jet 13 are combined using this apparatus, air bubbles produced by the laser and cavitation at the peening target region 8 are radially spread with a high speed and an impact pressure region produced by rapid collapse of the air bubbles is enlarged. Therefore, the peening effect can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for treating a surface of an underwater structure to improve stress, and more particularly to a peening method and apparatus using a water jet with cavitation and a laser.

[0002]

2. Description of the Related Art Recently, new techniques have been proposed for surface treatment of underwater structures, and some of them have been put to practical use. Stress improvement of light water reactors is based on stress corrosion cracking (S
CC) is important in preventing fatigue and improving fatigue strength.As a new peening method used for surface treatment in reactor water with cooling water (moderator) for the purpose of improving stress,
There are water jet peening (WJP) method and laser peening method. Each of these methods has a feature that does not exist in the conventional shot peening method, that is, there is no need to collect solid particles called shots used in the shot peening method.

[0003] The water jet peening method is shown in FIG.
As shown in (1), high-pressure water 4 is jetted from nozzle 31 into water 7 at high speed to form water jet 13 and utilizes the intense cavitation generated therein, and the impact pressure generated when cavitation bubbles collapse. Is used for peening the processing surface 30 of the underwater structure. This method is a processing method using only water in water, and has no thermal effect on the processing surface 30, so that the base material of the material forming the processing surface 30 is not damaged, and a large area portion is not damaged. Peening is possible. It has already been applied as an actual stress improvement technology for nuclear reactors.

On the other hand, in the laser peening method, as shown in FIG. 10, plasma is instantaneously generated when a laser beam 5 is condensed and irradiated from a laser irradiation head 1 in a water 7 onto a point on a processing surface 30. (The bubbles 15 are rapidly expanded as indicated by the arrows and become bubbles 15), because the expansion of the bubbles 15 is suppressed by an inertial medium such as water, the pressure inside the bubbles 15 rises sharply. Laser peening is a stress improvement technology that compresses the crystal grains on the surface layer of the material of the structure by the shock wave pressure 33 generated by rapid contraction as shown by the arrow when this high-pressure plasma is formed, as shown in FIG. is there. Laser peening has a feature that the stress improvement effect extends to the inside of the material as compared with other methods.

[0005]

In the case of peening with a laser alone, as shown in FIGS. 10 and 11, a single bubble generated in water by a pulse laser grows and collapses, so that a single pulse shock wave is generated by the laser. Very small area where peening effect only occurs at the beam extension position
(For example, a region having a diameter of 1 to 3 mm). However, in the depth direction of the peening target material, there is a feature that it is effective to a deep region (for example, to a depth of 1 mm) as compared with other methods.

On the other hand, in the case of the water jet peening method alone using a water jet accompanied by vigorous cavitation (cavitation jet), as shown in FIG. 9, the area affected by the peening effect is overwhelmingly larger than that of laser peening. large. However, as shown in the residual stress distribution of FIG. 9, there is a problem that the stress on the central axis is low, and the effective peening range in the depth direction of the material is about 0.1 mm.

In short, the laser peening method concentrates laser energy on a small area, whereas the water jet method disperses cavitation energy over a large area.

An object of the present invention is to provide a method and an apparatus for peening with a water jet / laser, in which the peening effect extends over a wide area and to a deep position.

[0009]

In order to achieve the above-mentioned object, a peening method using a water jet and a laser according to the present invention is for treating a surface of an underwater structure. At the same time as irradiating a cavitation jet, which is a water jet accompanied by cavitation. In this peening method, it is preferable that the cavitation jet collide with the laser irradiation axis such that the central axis of the cavitation jet is coaxial, or both axes are inclined with each other and intersect at the target portion.

The operation of the peening method using water jet and laser will be described. In peening by laser, air bubbles are generated at a target portion, and the air bubbles are crushed to generate an impact pressure. The material pressure, which is the target portion, is peened by this impact pressure, but the area of effect is local and the peening effective area is small. Therefore,
If the laser is not pulsed or the laser irradiation head is not scanned vertically and horizontally at high speed, it interferes with subsequent bubbles and the effective area is not increased.

When a cavitation jet is combined with the cavitation jet, a peening effect is generated by the impact pressure action when the cavitation bubble is crushed, and at the same time, the bubble generated by the laser or the cavitation is radially pushed and spread by the shock jet, and the bubble is expanded. The area where rapid collapse occurs increases. In addition, the center of impact of the cavitation jet is a stagnation point, and the peening effect is likely to decrease.However, by irradiating the center of impact of the cavitation jet with laser, the peening effect is enhanced even at the stagnation point of the water jet. As a result, the effect can be improved flatly over the entire target region.

In order to achieve the above object, a first aspect of the present invention is provided.
Water-jet and laser peening equipment
A laser irradiation head that irradiates a laser to a target part to be subjected to surface treatment, and a high-pressure water jet is provided coaxially with the laser irradiation head from around the laser irradiation head. And a nozzle head that forms a cavitation jet and collides with a target portion.

The second water jet of the present invention
The laser-peening device is a device for surface-treating a structure in water, and is provided with a laser irradiation head for irradiating a laser to a target portion to be surface-treated, and a tilted sideways side of the laser irradiation head, and a high-pressure water-peening device. And a nozzle head for forming a cavitation jet by colliding with the target portion.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a peening apparatus using a water jet / laser according to an embodiment of the present invention; FIG. 1 is a cross-sectional view illustrating a configuration of a head unit of a peening apparatus according to an embodiment.

The peening apparatus combined with water jet and laser according to the present invention irradiates a laser to a target part of the surface treatment and collides a cavitation jet, which is a water jet accompanied by cavitation, in order to surface-treat a structure underwater. Device. Head part of this peening device (referred to as peening head)
Basically, a laser beam 5 is applied to a processing target portion 8 (a target portion to be subjected to surface treatment) on an underwater structure 6 in the surrounding water 7.
Laser irradiation head 1 for irradiating light, and laser irradiation head 1
And a nozzle head 2 for ejecting high-pressure water 4 from the periphery to form a cavitation jet 13 with cavitation and causing the cavitation jet 13 to collide with the processing target portion 8. The laser irradiation head 1 and the nozzle head 2 are coaxially combined, and at the time of peening operation, the distance (stand-off distance) between the tip of the nozzle head 2 and the processing target portion 8 is Xs.

The nozzle head 2 has a high-pressure water supply channel 12 around a laser irradiation head 1 disposed at the center of the nozzle.
And a flow formed by a contraction portion 9 whose diameter is gradually reduced from the high-pressure water supply channel 12, an annular ejection portion 10 following the contraction portion 9, and a dome-shaped enlarged cavity portion 11 formed on the outlet side of the annular ejection portion 10. It has a road. In the nozzle head 2, the high-pressure water 4 introduced from the upstream into the high-pressure water supply channel 12 is decompressed and accelerated in a radially contracting portion (restriction portion) 9, and is blown out as a water jet from an annular ejection portion 10, causing severe cavitation. Cavitation jet 13 with Enlarged cavity 11
Within, a circulating vortex 14 is created around the cavitation jet 13. This circulating vortex 14 causes unstable pressure fluctuations to be applied to the cavitation jet, and also causes cavitation nuclei
To activate the cavitation in the cavitation jet 13.

FIG. 2 is a diagram showing the entire system of the peening apparatus of the present invention. This peening apparatus includes a peening head obtained by combining the laser irradiation head 1 and the water jet nozzle head 2 described with reference to FIG. 1, a laser oscillator 21 for sending laser light to the laser irradiation head 1 through a light guide tube 22, and a laser oscillator 21. Control device 20, a pump 23 for pumping water 7 from the water having the underwater structure 6, a water tank 24 for storing the pumped water, a plunger pump for taking in the water in the water tank 24 and pressurizing it to produce high-pressure water 4. 25 and
A high-pressure water hose 26 for guiding the high-pressure water 4 to the nozzle head 2. In this peening apparatus, the laser beam 5 and the cavitation jet 13 are simultaneously irradiated and ejected, and the processing target portion is peened by the action of both.

FIG. 3 is a diagram schematically illustrating the behavior during peening in the peening apparatus of one embodiment. Irradiation of the laser beam 5 by the laser irradiation head 1 of the peening head installed in the surrounding water 7 generates bubbles at the collision portion of the laser beam 5 on the processing surface 30 of the underwater structure. Due to the bulging pressure of the bubble and the rapid contraction, an impact pressure 33 is generated at the collision portion of the laser beam 5, which performs peening (laser peening) of the processing surface 30.
At the same time as the laser beam 5, the cavitation jet 13 ejected from the nozzle head 2 violently collides with the processing surface 30 to perform peening. Cavitation jet 13
Cavitation and the radial flow after the collision cause bubbles generated by the laser
It has the effect of forcibly spreading radially along 30. For this reason, the region where the impact pressure 33 is generated is dispersed on the processing surface 30 in the radial direction (34). By using the laser and the cavitation jet together in this way, the processing target portion 8 on which the peening effectively acts is remarkably increased as compared with the case of the laser peening alone. The action of each bubble created by the laser and the cavitation jet is basically the same. That is, rapid turgor pressure and rapid contraction (crush) are repeated. According to the cavitation jet, the strong flow field created on the impingement surface is helping to make the effect of bubbles created during laser peening more effective. The effect of cavitation generated in the cavitation jet is also great, but the present invention can be regarded as jet-assisted laser peening from a different viewpoint.

FIG. 4 shows a comparison of the conventional peening with only the laser (FIGS. 10 and 11) and the embodiment according to the present invention (FIGS. 1 and 2) with respect to the peening effective area. Here, "peening effective" means that the residual stress on the surface to be processed is converted to the compression side and improved, and does not quantitatively specify the level or depth of the residual stress. The peening effective area S shown on the vertical axis was made dimensionless by dividing by the peening effective area S ^* using only the laser. Therefore, S / S ^* =
It becomes 1. On the other hand, in the case of the present invention, S / S ^* = 20
Therefore, a remarkable result can be recognized with respect to the plan of increasing the effective area of peening. As mentioned above,
This is an effect that the features of the cavitation jet are skillfully used.

FIG. 5 shows the distribution of residual stress (compression direction) in the direction of deformation generated after peening, with water jet single peening (FIG. 9) and a water jet laser according to one embodiment of the present invention (FIGS. 1 and 2). It is a graph which compared with combination peening. The compressive stress σ generated by peening was made dimensionless by dividing by the peak residual stress σ ^* of the water jet alone. Also, σ
The radius γ of the peening surface was made dimensionless by dividing by the radial distance γ ^1/2 corresponding to the radius width of ^* . Therefore, when γ = γ ^1/2 , σ = (1/2) σ ^* . As is clear from the comparison between the stress distribution 42 in the case of peening with the water jet alone and the stress distribution 43 in the case of peening with the water jet / laser of the present invention, a clear difference is recognized. Compared to peening with water jet alone, peening with water jet and laser has a residual compressive stress of 40% especially on central axis 41.
It is nearer and larger, and the "dent" of the stress distribution seen at the center of the water jet collision in the peening of the water jet alone is completely eliminated. Moreover,
The stress distribution has a high value and a flat distribution. Further, the residual stress due to peening with water jet / laser of the present invention has a large spread in the radial direction. In short, according to the method of the present invention, the distribution of the residual stress can be improved while enhancing the level of the residual stress itself.
The improvement of the distribution on the central axis 41 of the graph shown in FIG. Also, the overall improvement in residual stress is none other than the effect of simultaneous peening of the laser and the cavitation jet. From the above, the effect of implementing the present invention was confirmed.

FIG. 6 shows the penetration depth from the surface to the inside of the material when the compressive stress reaches 300 MPa.
0, 11), the peening (FIGS. 1 and 2) of the water jet alone (FIG. 9) and the combined use of the water jet and laser according to the embodiment of the present invention (FIGS. 1 and 2). In the case of laser alone peening, it is as deep as 1 mm (however, the effective area is narrow as described later), while in the case of water jet alone peening, it is as shallow as 0.1 mm (effective area is large)
On the other hand, it can be seen that the peening effect using water jet / laser does not reach the case using only the laser, but the peening effect extends to a deep portion up to four times as much as the case using only water jet. When the effect reaches this depth, it is effective for improving the fatigue strength. The reason why the effect of the peening with the combined use of the water jet and the laser is shallower than that of the peening with the laser alone is that the bubble crushing effect of the laser is dispersed in the radial direction due to the flow action of the water jet.

FIG. 7 compares the diameters of the regions where the stress is converted to the compression side and improved to a depth of 0.1 mm, which is sufficient for stress corrosion cracking (SCC). While laser peening alone is as narrow as 3 mm, a water jet has a significantly larger effective area of 30 mm in diameter. On the other hand, if combined peening like the present invention, the diameter 44mm
The effective area is approximately doubled.

FIG. 8 is a diagram showing a configuration of a peening head of a peening apparatus according to another embodiment of the present invention.
The peening head according to another embodiment includes a processing target portion 8.
A laser irradiation head 1 for irradiating a laser beam 5 to a laser beam, and a laser beam
To cavitation
And a nozzle head 2 for colliding the jet 13. The center axis 32 of the cavitation jet 13 is inclined with respect to the axis of the laser beam 5, and both axes intersect at the processing target portion 8 so as to be focused. The peening head in which the laser irradiation head 1 and the nozzle head 2 are combined adjacently as described above, and peening of the system in which the cavitation jet 13 is inclined with respect to the laser beam 5 is performed. A peening effect similar to that obtained is obtained. It is preferable that the laser irradiation axis and the center axis of the cavitation jet cross each other on the processing target portion, but strictly speaking, the present invention is not limited to this condition, and the crossing point may be shifted.

Further, the peening head according to another embodiment is easy to manufacture because the laser irradiation head 1 and the nozzle head 2 are combined side by side, and is not affected by the vibration of the nozzle portion due to the cavitation jet. On the other hand, the peening head according to one embodiment has a structure in which the laser irradiation head 1 and the nozzle head 2 are coaxially arranged and the cavitation jet 13 is blown out from around the laser irradiation head 1. Although it is compact, it also requires precision manufacturing and assembly precision and durability to overcome vibrations caused by cavitation jets.

In each of the above embodiments, the water jet
According to the peening apparatus combined with laser, the following effects can be obtained. (1) The area of the peening surface is overwhelmingly increased as compared with the peening of the laser alone. (2) The stress distribution, particularly the characteristics on the irradiation central axis, is improved as compared with the peening of the water jet alone. (3) Compared to peening with water jet alone, the effect of improving stress extends to a deeper position of the material to be peened. (4) By peening, the resistance to stress corrosion cracking (SCC) and the fatigue strength of the material are improved, and the soundness of the structure is sufficiently ensured.

[0026]

According to the present invention, it is possible to provide a peening method and apparatus using water jet and laser which have a peening effect on a material over a wide area and a deep position.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a head unit of a peening apparatus using water jet and laser according to an embodiment of the present invention.

FIG. 2 shows an entire system of a peening apparatus using water jet and laser according to an embodiment of the present invention.

FIG. 3 is a diagram schematically showing a phenomenon in the peening method using water jet and laser according to the present invention.

FIG. 4 is a graph showing test results that demonstrate the effect of the peening method according to the present invention (expansion of the effective area of peening).

FIG. 5 is a graph showing test results that demonstrate the effect of the peening method according to the present invention (increase in compressive residual stress).

FIG. 6 is a graph showing test results for demonstrating the effect (enlargement of penetration depth) of the peening method according to the present invention.

FIG. 7 is a graph showing test results that demonstrate the effect of the peening method according to the present invention (enlargement of the conversion area of compressive stress).

FIG. 8 is a diagram showing a configuration of a head unit of a peening apparatus using water jet and laser according to another embodiment of the present invention.

FIG. 9 is a diagram illustrating water jet peening as a conventional technique.

FIG. 10 is a diagram illustrating laser peening as a conventional technique.

FIG. 11 is a diagram illustrating laser peening together with FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser irradiation head 2 Nozzle head 3 Laser beam 4 High pressure water 5 Laser beam 6 Underwater structure 7 Ambient water 8 Processing target part 9 Diameter contraction part 10 Annular ejection part 11 Expansion cavity part 12 High pressure water supply channel 13 Cavitation jet 15 Bubble 16 Rapid expansion 20 Controller 21 Laser oscillator 22 Light guide tube 23 Pumping pump 24 Water tank 25 Plunger pump 26 High pressure hose 30 Work surface 31 Nozzle 32 Jet center axis 33 Impact pressure (force)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G21C 19/02 G21C 19/02 J

Claims (4)

[Claims] 1. A peening method for surface-treating a structure in water, wherein a laser beam is applied to a target portion of the surface treatment and a cavitation jet, which is a water jet accompanied by cavitation, is collided with the laser beam. Combination peening method. 2. A cavitation jet impinges on the irradiation axis of the laser so that the central axis of the cavitation jet is coaxial or such that both axes are inclined with each other and intersect at the target portion. 2. The peening method according to claim 1, wherein the peening method is used. 3. A peening apparatus for surface-treating a structure in water, comprising: a laser irradiation head for irradiating a laser to a target portion to be surface-treated; and a periphery of the laser irradiation head which is arranged coaxially with the laser irradiation head. And a nozzle head for ejecting high-pressure water from the nozzle to form a cavitation jet and impinge on the target portion. 4. A peening apparatus for surface-treating a structure in water, comprising: a laser irradiation head for irradiating a laser to a target portion to be subjected to the surface treatment; A water jet / laser peening apparatus, comprising: a nozzle head that jets out to form a cavitation jet and impinges on the target portion.