Laser peening apparatus and laser peening method

Abstract

To provide a laser peening device and a laser peening method capable of applying compressive stress to an inner surface of a hole, one end of which is sealed.SOLUTION: A laser peening device 50 performs laser peening to an inner surface of a hole 20, one end of which is sealed, and which is a processing target. The laser peening device comprises: a laser generator 1 which emits a pulse laser beam 2; a laser beam transmission mechanism 21 which transmits the pulse laser beam 2 emitted from the laser generator 1, to the surface of the hole 20 being the processing target; and a fluid supply mechanism 6 for supplying fluid 18 into the hole 20. The laser peening device is characterized in using, as the laser beam transmission mechanism 21, an end cap fiber 22 comprising an optical fiber 40 fusion-spliced with an end cap 41 having a light receiving area on an incident side larger than a cross-sectional area of the optical fiber 40.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a laser peening apparatus and a laser peening method for applying compressive stress.

Background Art

[0002] The surface of a material is likely to be a starting point for the occurrence of fatigue fracture, stress corrosion cracking, etc. Therefore, by applying compressive residual stress to the vicinity of the surface of the material and suppressing the generation and progression of cracks, the fatigue fracture resistance and stress corrosion cracking resistance of the material can be improved.

[0003] For example, in order to apply compressive residual stress to the surface of the cooling water passage (water cooling hole) of a mold, shot peening may be performed on the surface of the cooling water passage.

[0004] Also, a compressive stress application mechanism using laser peening is also used. Laser peening is a technique for applying compressive residual stress to the surface of a construction target. A pulsed laser is irradiated onto the construction target to generate and expand plasma. Due to the mechanical reaction of this expansion, the vicinity of the surface of the construction target is compressed and stress remains. In laser peening, by adjusting construction conditions such as the energy of the laser beam and the irradiation area, the magnitude of the compressive residual stress and the depth of application can be controlled. Furthermore, by combining an optical fiber and an irradiation head, construction on narrow parts such as the turbine blade implantation part and the inner surface of a pipe becomes possible.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0006] In laser peening, a pulsed laser is irradiated onto the surface of the object to be treated to generate an ablation plasma. The pressure of this plasma causes plastic deformation on the surface of the object, thereby applying compressive stress.

[0007] For example, if the inner diameter of a cooling hole sealed at one end is sufficiently large, it is possible to irradiate the inside with laser light. However, cooling holes are generally small in diameter, such as φ10 mm or less, making it difficult to insert an irradiation head or optical system for laser peening into them. Furthermore, if an irradiation head designed for the inner surface of a pipe is used, while laser peening can be performed on the sides of the cooling hole, the bottom surface of the cooling hole cannot be irradiated with laser light, making stress relief impossible.

[0008] One possible method for irradiating the bottom surface of a cooling hole with a laser is to use a focusing lens installed outside the cooling hole to focus the laser beam onto the bottom surface of the cooling hole. However, if the diameter of the cooling hole is small or the depth of the cooling hole is deep, the laser beam may interfere with the cooling hole, making it impossible to irradiate the bottom surface of the cooling hole with a laser beam that has the required energy and spot diameter. [Means for solving the problem]

[0009] The laser peening apparatus according to the embodiment is a laser peening apparatus that performs laser peening on the inner surface of a hole in a workpiece which is sealed at one end, and comprises a laser oscillator that emits pulsed laser light, a laser light transmission mechanism that transmits the pulsed laser light emitted from the laser oscillator to the surface of the hole in the workpiece, and a fluid supply mechanism for supplying fluid to the inside of the hole, characterized in that the laser light transmission mechanism uses an end cap fiber in which an end cap with a light-receiving area on the incident side that is larger than the cross-sectional area of ​​the optical fiber is fused to the optical fiber.

[0010] Furthermore, the laser peening method according to the embodiment is an end cap fiber, in which an end cap with a light-receiving area on the incident side is fused to an optical fiber, and the end cap fiber has a light-receiving area on the incident side that is larger than the cross-sectional area of ​​the optical fiber. The end cap fiber is provided with a fiber tip protection mechanism at the tip of the end cap fiber facing the inner surface of a hole in a workpiece, which is sealed at one end, to protect the end cap fiber from shock waves, and a liquid is sealed and placed as an intermediate layer between the tip of the end cap fiber and the fiber tip protection mechanism. By irradiating the optical fiber with laser light and changing its position and angle, the position from which the laser light is emitted from the tip of the optical fiber can be freely controlled. The surface of the workpiece This method is characterized by performing laser peening. [Effects of the Invention]

[0011] Embodiments of the present invention have been made to solve the above-mentioned problems, and aim to provide a laser peening apparatus and a laser peening method that can apply compressive stress to the inner surface of a hole that is sealed at one end. [Brief explanation of the drawing]

[0012] [Figure 1] A conceptual diagram showing the laser peening apparatus according to the first embodiment being used in a hole that has one end sealed. [Figure 2] The images show the laser peening device of this embodiment inserted into a hole. (a) is a side cross-sectional view showing the end cap fiber positioned at the center of the hole, (b) is a side cross-sectional view showing the entire laser peening device moved in parallel, and (c) is a side cross-sectional view showing the entire laser peening device tilted with respect to the central axis of the hole. [Figure 3]This is a side cross-sectional view showing the process of bending the end cap fiber in the laser peening apparatus of this embodiment and observing the application to the side of the hole from the side. [Figure 4] The images show the bottom of the hole as viewed from above. (a) is a plan view showing the end cap fiber positioned at the center of the hole, (b) is a plan view showing the entire laser peening apparatus moved in parallel, (c) is a plan view showing the entire laser peening apparatus tilted relative to the central axis of the hole, and (d) is a plan view showing the end cap fiber in the laser peening apparatus bent. [Figure 5] The images show a side view of the structure at the tip of the laser light transmission mechanism. (a) is a plan view showing the laser beam being irradiated onto the workpiece from the tip of the end cap fiber, and (b) to (d) are plan views showing modified examples of the tip of the end cap fiber. [Figure 6] (a) is a side cross-sectional view showing an end cap fiber, and (b) is a side cross-sectional view showing a modified example of the end cap fiber. [Modes for carrying out the invention]

[0013] (First Embodiment) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 is a configuration diagram of a laser peening apparatus 50 according to the first embodiment of the present invention, and shows a cross-sectional view of the laser peening apparatus 50 of the present invention inserted into the cooling hole.

[0014] This laser peening apparatus 50 and laser peening method perform laser peening on the inner surface of a hole, such as a cooling hole 20 provided in a mold, which has one end sealed and has a diameter of, for example, several millimeters to more than ten millimeters (particularly about 3 mm to 10 mm).

[0015] As shown in Fig. 1, the laser peening device 50 is composed of a laser oscillator 1, a laser light transmission mechanism 21, a condenser lens unit 5, a fluid supply mechanism 6, a cover 10, a fluid storage mechanism 12, a suction mechanism 11, an end cap fiber 22, a protection mechanism 26, etc. Fig. 1 shows a state in which the protection mechanism 26 housing the end cap fiber 22 is inserted into a cooling hole 20 with one end sealed.

[0016] In this way, the outer diameter of the protection mechanism 26 is set smaller than the inner diameter of the cooling hole 20. The laser light transmission mechanism 21 has at least two mirrors for reflecting the laser light 2. For example, in the configuration shown in Fig. 1, the first mirror 3 has an external position confirmation mechanism 9, and the second mirror 4 has a drive mechanism (not shown) for changing the irradiation angle of the laser light 2.

[0017] The laser oscillator 1 oscillates (emits) pulsed laser light for laser peening. The wavelength and pulse width of this pulsed laser light can be appropriately selected. For example, using a Nd:YAG laser, pulsed laser light with a wavelength of 1064 nm or 532 nm and a pulse width of several ns to several tens of ns can be emitted. By selecting the wavelength of the pulsed laser light according to the light absorption characteristics of the fluid 18, the energy loss of the laser light can be reduced.

[0018] For example, when the fluid 18 contained in the fluid supply mechanism 6 is water, the laser light 2 can be irradiated with an energy loss of about 0.5% by using a laser with a wavelength of 532 nm. Also, even when a laser with a wavelength of 1064 nm is used, depending on the transmission distance in water, the energy absorbed by water, for example, if 50% is absorbed, twice the pulse energy can be irradiated.

[0019] The laser beam 2 emitted from the laser oscillator 1 is incident on the end cap fiber 22 via the laser beam transmission mechanism 21 and the focusing lens unit 5 provided inside the housing 25, and the laser beam 2 emitted from the tip of the end cap fiber 22 is irradiated onto the inner surface of the cooling hole 20. As described above, the laser beam transmission mechanism 21 is equipped with at least two mirrors, a first mirror 3 and a second mirror 4, and the incident position on the end cap fiber 22 can be adjusted by changing the angle of the second mirror 4, for example, so that the laser beam 2 can be irradiated onto a predetermined position on the inner surface of the cooling hole 20, such as the side or bottom surface.

[0020] Furthermore, a beam intensity adjustment unit 24 can be placed inside the housing 25 in front of the focusing lens unit 5 as needed. This beam intensity adjustment unit 24 is preferably a laser homogenizer composed of a diffractive optical element or a cylindrical array, and has the function of making the intensity distribution of laser light, which has a high central peak intensity such as a Gaussian distribution, uniform, and can reduce damage to the end cap fiber 22 when the intensity of the laser light 2 is strong.

[0021] Furthermore, for example, the laser light transmission mechanism 21 can be equipped with an attenuator 17, which can control the pulse energy irradiated onto the cooling holes 20 to a predetermined intensity, and, in combination with a control device (not shown), can close the shutter 16 and stop construction if the pulse energy falls below a predetermined value.

[0022] As shown in Figure 6(a), the end cap fiber 22 is constructed by fusing a cylindrical member called an end cap 41 to an optical fiber 40 via a joint 43. While a cylindrical member is preferable for the end cap 41 of the end cap fiber 22 as shown in Figure 6(a), a conical cone rod 42 is also acceptable as long as the light-receiving area on the laser beam 2 incidence side is larger than the cross-sectional area of ​​the optical fiber 40 and can be joined by fusion via the joint 43, in order to reduce damage to the laser beam 2 incidence side.

[0023] In the end cap fiber 22, the diameter of the optical fiber 40 is preferably φ0.4 to 1.0 mm, and it is sufficient to ensure a power density that generates an ablation plasma 13 with a diameter of φ0.6 to φ1.5 mm when the laser beam 2 irradiated from the tip of the optical fiber is projected onto the workpiece surface.

[0024] Furthermore, if the end cap 41 has a diameter of approximately φ5 to 10 mm at the laser beam incidence point, laser transmission is possible without damaging the end cap fiber 22. For example, if an end cap fiber 22 is used in which an optical fiber 40 with a core diameter of φ1.0 mm and a length of 7 m is fused to an end cap 41 with a diameter of φ8 mm and a length of 5 mm, when a laser beam 2 with a pulse energy of 160 mJ is incident from the end cap 41, 130 mJ of laser beam is emitted from the exit end of the fiber 40, and laser transmission can be achieved with a transmission efficiency of approximately 80%, including losses due to end-face reflections of the end cap 41 and the optical fiber 40.

[0025] A protective mechanism 26 can be provided on the outer circumference of the end cap fiber 22 to protect the optical fiber 40 of the end cap fiber 22 from damage when it is inserted into the cooling hole 20. Furthermore, the outer diameter of the protective mechanism 26 can be adjusted according to the outer diameter of the optical fiber 40. For example, when using an end cap fiber 22 made of an optical fiber 40 with a core diameter of φ1.0 mm, the outer diameter of the optical fiber 40, including the buffer layer (not shown) and the covering, is about φ3 mm, so the outer diameter of the fiber tip protective mechanism (hereinafter referred to as the protective mechanism) 26 can be reduced to about φ6 mm.

[0026] The spot diameter used in laser peening can be changed depending on the material of the object to be treated (inner surface of the cooling hole 20) and the residual stress introduced. For example, in the configuration shown in Figure 1, a laser beam of a predetermined spot diameter can be irradiated by changing the distance from the end cap fiber 22 to the laser irradiation position. However, since the laser beam 2 irradiated from the end cap fiber 22 spreads with the numerical aperture (NA) inherent to the optical fiber, it is applicable as long as conditions can be met to irradiate a laser beam 2 that generates ablation plasma 13 with a spot diameter greater than or equal to the diameter of the optical fiber 40.

[0027] In laser peening, an ablation plasma 13 is generated on the surface of the object to be treated, and compressive stress is applied by causing plastic deformation of the material due to the plasma pressure. At that time, a fluid 18 such as water is required to confine the plasma, but because the cooling holes 20 are narrow, even if one tries to supply the fluid 18 into the cooling holes 20 using a pump or the like, cavitation occurs or there are areas where the fluid 18 is not supplied, making stable treatment impossible.

[0028] The laser peening apparatus 50 of this embodiment includes an opening / closing unit 7 for controlling the inflow of fluid 18 into the cover 10, and a cover 10 that uses a suction mechanism 11 to create a negative pressure state inside the cooling hole 20. When the laser peening apparatus 50 of this embodiment is installed in the cooling hole 20 and the opening / closing unit 7 is closed, the inside of the cooling hole 20 is sucked using the suction mechanism 11, the inside of the cover 10 becomes a negative pressure state as shown in Figure 2, and any bubbles 14 and debris remaining inside the cooling hole 20 can be removed in advance.

[0029] In this state, when the opening / closing unit 7 is opened, the internal pressure is negative, so the fluid 18 inside the fluid supply mechanism 6 is drawn up, and the fluid 18 can be stably supplied to the inside of the cooling hole 20 through the fluid transmission mechanism 8 in the direction shown in the fluid flow 19, as shown in Figure 3. Furthermore, if the inner diameter of the cooling hole 20 is small and it is difficult to supply the fluid 18 to the inside of the cooling hole 20, a check valve (not shown) can be placed in the protective mechanism 26 so as to cover the cooling hole 20, thereby allowing the fluid 18 inside the cooling hole 20 to be preferentially discharged.

[0030] Here, water is preferable as the fluid 18. For example, using a pulsed laser with a wavelength of 532 nm allows for laser peening with virtually no transmission loss in water. Furthermore, using fluid 18 such as water mixed with a rust inhibitor or ammonia water allows for laser peening while suppressing rust formation on the object to be treated. Alkaline ionized water or rust-preventive oil may also be used.

[0031] This embodiment can be equipped with a position confirmation mechanism 9, which can measure the distance from the tip of the laser light transmission mechanism 21 (the tip of the end cap fiber 22) to the laser irradiation position of the cooling hole 20. As the position confirmation mechanism 9, for example, a laser rangefinder can be used, and the position can be identified by measuring the laser light reflected from the laser light transmission mechanism 21 and the laser light reflected from the cooling hole 20, respectively, so that the position of the laser light transmission mechanism 21 inside the cooling hole 20 can be recognized from the outside. As the position confirmation mechanism 9, the laser rangefinder is not limited to a laser rangefinder; methods using other light sources such as sound waves or optical sensors, or methods such as checking an image of the tip of the laser light transmission mechanism 21 with a camera may also be used. Furthermore, even if the tip of the laser light transmission mechanism 21 is equipped with a fiber tip protection mechanism 23 as shown in Figure 5(b), the position can still be identified by the method described above.

[0032] Then, based on the distance from the tip of the end cap fiber 22 or the tip of the fiber tip protection mechanism 23 to the laser irradiation position measured by the position confirmation mechanism 9, the end cap fiber 22 can be moved by the drive mechanism operating unit 28, etc., to change the focal position of the laser beam 2 and irradiate a laser beam 2 with a predetermined spot diameter.

[0033] When the shutter 16 is opened, the laser beam 2 reaches the bottom of the cooling hole 20, as shown in Figure 1, making laser peening possible. The method for performing laser peening on the bottom surface of the cooling hole 20 will be explained with reference to Figures 2 to 4.

[0034] Figures 2 and 3 show side cross-sectional views of the laser peening apparatus 50 of this embodiment inserted into the cooling hole 20. Figure 4 is a cross-sectional view of the bottom of the cooling hole 20 as seen from above.

[0035] In this embodiment, the laser light transmission mechanism 21 is equipped with a protective mechanism 26 and a drive mechanism 27 on the outer circumference of the optical fiber 40, preventing damage to the laser light transmission mechanism 21 by contact when it is inserted into a cooling hole 20 or the like. Furthermore, as shown in Figure 3, the angle of the optical fiber 40 at the tip of the laser light transmission mechanism 21 can be changed by using the drive mechanism 27.

[0036] For example, a bellows-shaped flexible tube can be used as the drive mechanism 27, and a wire (not shown) can be placed between the laser light transmission mechanism 21, the protection mechanism 26, and the drive mechanism 27, with the drive mechanism 27 and the drive mechanism operating unit 28 shown in Figure 1 connected by this wire. The angle of the tip of the laser light transmission mechanism 21 can be changed by pulling the wire (not shown) towards the drive mechanism operating unit 28. Preferably, the drive mechanism operating unit 28 is equipped with a motor for extending and retracting the wire (not shown) and a sensor for measuring the position of the wire, and it is possible to control the tilt angle of the laser light transmission mechanism 21 by the length of the wire extended or retracted. Furthermore, by providing the drive mechanism operating unit 28 with a rotation mechanism that rotates in the axial direction of the end cap fiber 22, laser peening can be performed over a wider area.

[0037] Figure 2(a) shows the end cap fiber 22 positioned at the center of the cooling hole 20. As shown in Figures 2(a) and 4(a), the laser beam 2 is irradiated onto the center of the bottom surface of the cooling hole 20, which is the same as the laser peening workable area 30. When the entire laser peening apparatus is moved in parallel, it becomes as shown in Figure 2(b), and the laser beam 2 can be moved from the center of the cooling hole 20 to the area where the drive mechanism 27 contacts the side surface of the cooling hole 20. By rotating the end cap fiber 22 with respect to the central axis of the cooling hole 20 using the drive mechanism operating unit 28, it becomes possible to perform laser peening on the central part of the cooling hole 20 around the laser peening workable area shown in Figure 4(a), as shown in the laser peening workable area 30 in Figure 4(b).

[0038] Next, when the entire end cap fiber 22 is tilted with respect to the central axis of the cooling hole 20, it becomes as shown in Figure 2(c). By rotating the end cap fiber 22 with respect to the central axis of the cooling hole 20 using the drive mechanism operating unit 28, the laser peening area 30 becomes even wider than in the case of Figure 2(b), as shown in Figure 4(c). Furthermore, when the end cap fiber 22 is bent by the drive mechanism 27, it becomes as shown in Figure 3, and the movable range of the laser beam 2 becomes even wider, making it possible to perform laser peening on the entire bottom and sides of the cooling hole 20, as shown in Figure 4(d). In addition, by moving the entire end cap fiber 22 upward with respect to the central axis of the cooling hole 20, it becomes possible to perform laser peening on the sides of the cooling hole 20.

[0039] Furthermore, if the laser peening application area 30 deviates from being perpendicular to the irradiation angle of the laser beam 2, the spot diameter of the laser beam 2 will become elliptical. However, since the same peening effect as a circle with an equivalent area can be obtained, this can be addressed by controlling the focal length.

[0040] As shown in Figure 1, the fluid 18 drawn in by the suction mechanism 11 is stored in the fluid storage mechanism 12. The stored fluid 18 can be returned to the fluid supply mechanism 6 using a pump (not shown), allowing the fluid 18 to be circulated and reused. The fluid 18 drawn into the fluid storage mechanism 12 from the cooling holes 20 using the suction mechanism 11 contains bubbles 14 associated with laser peening and small metal fragments (not shown) generated from the ablation plasma 13. Therefore, when circulating the fluid back into the fluid supply mechanism 6, it is desirable to filter it using a filter (not shown).

[0041] Furthermore, if bubbles 14 generated during laser peening remain in the fluid 18 and the next pulse laser is irradiated, energy loss may occur as the laser light 2 is irradiated onto the remaining bubbles 14, potentially leading to unstable peening. The laser peening apparatus 50 of this embodiment is equipped with a bubble confirmation mechanism 15 for checking images of the inside of the protection mechanism 26 and the laser irradiation position via a first mirror 3 provided in the laser light transmission mechanism 21.

[0042] According to the laser peening apparatus and laser peening method of the embodiment described above, compressive stress can be applied to the inner surface of a cooling hole 20 or the like, which is difficult to access and has one end sealed. Furthermore, if the position and depth of the cooling hole 20 of the object to be treated, as well as the laser peening treatment area, are known in advance, the focal length and movement pattern of the focusing lens unit 5 can be programmed using a control device (not shown), and by combining movement to the laser irradiation position, irradiation of the laser beam 2, and confirmation of remaining bubbles using the bubble confirmation mechanism 15 according to the frequency of the laser oscillator 1, it becomes possible to automatically perform laser peening on the bottom of a narrow cooling hole 20.

[0043] (Second Embodiment) A second embodiment will be described using Figure 5. Figure 5 is a conceptual diagram showing the structure of the tip of the laser light transmission mechanism as observed from the side, illustrating the situation in which laser peening is performed by irradiating the workpiece 31 with laser light 2 from the laser transmission mechanism 21 in the fluid 18.

[0044] In Figure 5(a), when a high-power laser beam 2 is irradiated onto the workpiece 31, the laser beam 2 is absorbed by the workpiece 31, and when it reaches an energy level above a certain threshold, the workpiece 31 vaporizes and an ablation plasma 13 is generated.

[0045] When the end cap fiber 22 used as the laser light transmission mechanism 21 is a quartz fiber, the laser light 2 propagates through the fluid 18 while spreading at a divergence angle NA = 0.2 inherent to quartz. For example, if the core diameter of the optical fiber 40 in the end cap fiber 22 is φ1.0 mm, when laser light 2 with a wavelength of 532 nm and pulse energy of 40 mJ is irradiated from the optical fiber 40 into water and onto a nickel-based alloy Alloy 600 placed as the workpiece 31, the beam diameter of the laser light 2 expands to about φ1.1 mm at a position 2 mm away from the tip, but due to the high energy density, an ablation plasma 13 is generated.

[0046] In the laser peening process, the ablation plasma 13 is contained by the pressure of the fluid 18, generating a shock wave 32. This shock wave 32 causes plastic deformation in the workpiece 31, forming compressive stress near the surface. Here, the shock wave 32 propagates not only to the workpiece 31 but also into the fluid 18, and some of it reaches the end cap fiber 22. When a quartz fiber is used as the end cap fiber 22, as shown in Figure 5(a), the shock wave 32 generated by the ablation plasma 13 reaches the end cap fiber 22, and may be damaged by its high impact force.

[0047] On the other hand, in this embodiment, as shown in Figure 5(b), a fiber tip protection mechanism 23 is provided at the tip of the laser light transmission mechanism 21, and even when the aforementioned shock wave 32 arrives, it is possible to prevent damage due to its high shock resistance. The fiber tip protection mechanism 23 is preferably made of sapphire, and since sapphire has high laser light transmittance, transmission loss will hardly occur when, for example, quartz is used for the end cap fiber 22 or tapered fiber. Here, the fiber tip protection mechanism 23 can be arranged with the end cap fiber 22 by optical contact (a technique for joining two highly polished prisms without using adhesive), but a structure with the same function can be made by fusing it with the end cap fiber 22.

[0048] Furthermore, as shown in Figure 5(c), the present invention also allows for the use of a structure in which liquid 33 is sealed and placed between the end cap fiber 22 and the fiber tip protection mechanism 23. Sealing and placing liquid 33 has the advantage of eliminating the need for a polishing process to form the surface accuracy required for optical contact, and also eliminating the need for fusion bonding. Water is preferred as the liquid 33, and with laser light of a wavelength of 532 nm, transmission loss is almost eliminated and changes in refractive index can be kept small.

[0049] Furthermore, in this embodiment, as shown in Figure 5(d), a collimating lens unit 29 that parallelizes the laser beam can be provided instead of the fiber tip protection mechanism 23. When a quartz fiber such as an end cap fiber or tapered fiber is used as the laser light transmission mechanism 21, the laser light 2 emitted from the tip of the optical fiber 40 propagates while expanding at the divergence angle NA = 0.2 inherent to quartz. However, by providing the collimating lens unit 29, it becomes possible to transmit the laser light over long distances while maintaining an aperture larger than the beam diameter of the laser light 2 emitted from the end cap fiber 22.

[0050] For example, if an end cap fiber with a core diameter of φ0.8 mm at the laser beam emission end is used as the end cap fiber 22, it becomes possible to irradiate the collimating lens unit 29 with parallel light of φ0.9 mm, and the laser beam 2 can be emitted with a beam diameter of φ0.9 mm even at a position 20 mm away from the collimating lens unit 29. Therefore, as shown in Figure 5(d), laser peening can be performed without being affected by the shock wave 32 caused by the ablation plasma 13, and it becomes possible to perform processing with the same beam diameter without precisely maintaining the distance to the workpiece 31, and the tolerance range can be expanded.

[0051] These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations are possible without departing from the spirit of the invention.

[0052] These embodiments and their variations are included within the scope and essence of the invention, as well as within the scope of the claims and its equivalents. [Explanation of Symbols]

[0053] 1: Laser oscillator, 2: Laser light (pulsed laser light), 3: First mirror, 4: Second mirror, 5: Focusing lens unit, 6: Fluid supply mechanism, 7: Opening / closing unit, 8: Fluid transmission mechanism, 9: Position confirmation mechanism, 10: Cover, 11: Suction mechanism, 12: Fluid storage mechanism, 13: Ablation plasma, 14: Bubbles, 15: Bubble confirmation mechanism, 16: Shutter, 17: Attenuator, 18: Fluid, 19: Fluid flow, 20: Cooling holes, 21: 1. Laser light transmission mechanism, 22: end cap fiber, 23: fiber tip protection mechanism, 24: beam intensity adjustment unit, 25: housing, 26: protection mechanism, 27: drive mechanism, 28: drive mechanism operating unit, 29: collimating lens unit, 30: laser peening application range, 31: workpiece, 32: shock wave, 33: liquid, 40: optical fiber, 41: end cap, 42: cone rod, 43: joint, 50: laser peening device.

Claims

1. A laser peening apparatus for performing laser peening on the inner surface of a hole in a workpiece that has one end sealed, A laser oscillator that emits pulsed laser light, A laser light transmission mechanism that transmits the pulsed laser light emitted from the laser oscillator to the surface of the hole in the workpiece, A fluid supply mechanism for supplying fluid to the inside of the hole, Composed of, As the laser light transmission mechanism, an end cap fiber is used in which an end cap with a larger light-receiving area on the incident side than the cross-sectional area of ​​the optical fiber is fused to the optical fiber. The end cap fiber facing the surface of the workpiece is equipped with a fiber tip protection mechanism to protect the end cap fiber from shock waves, A laser peening apparatus characterized in that a liquid is sealed and placed as an intermediate layer between the tip of the end cap fiber and the fiber tip protection mechanism.

2. The laser peening apparatus according to claim 1, characterized in that sapphire is used as the fiber tip protection mechanism.

3. The laser peening apparatus according to claim 1, further comprising a position confirmation mechanism for measuring the distance from the tip of the fiber tip protection mechanism to the laser irradiation position, wherein the end cap fiber can be moved according to the distance from the tip of the fiber tip protection mechanism to the laser irradiation position measured by the position confirmation mechanism to change the focal position of the pulsed laser beam.

4. The laser peening apparatus according to claim 1, further comprising a drive mechanism using a flexible tube on the outer circumference of the optical fiber constituting the end cap fiber, wherein the drive mechanism changes the angle of the tip of the optical fiber by the drive mechanism operating part.

5. The laser peening apparatus according to claim 4, characterized in that the drive mechanism operating unit rotates, moves up and down, moves in parallel, and tilts the end cap fiber with respect to the central axis of the hole in the workpiece.

6. The laser peening apparatus according to claim 1, characterized in that the end cap is a cone-shaped rod whose light-receiving area on the incident side is larger than the area of ​​the junction with the optical fiber.

7. A laser peening method characterized by performing laser peening on the surface of a workpiece while freely controlling the position from which the laser beam is irradiated to the tip of an end cap fiber, the end cap fiber having an end cap with a light-receiving area on the incident side that is larger than the cross-sectional area of ​​the optical fiber, the tip of the end cap fiber facing the inner surface of a hole in a workpiece which is sealed at one end, and a fiber tip protection mechanism to protect the end cap fiber from shock waves, and a liquid sealed as an intermediate layer between the tip of the end cap fiber and the fiber tip protection mechanism, and by injecting laser light into the end cap fiber, the position and angle of the optical fiber to freely control the position from which the laser light is irradiated to the tip of the optical fiber.

Images