阅读说明：本技术 一种激光冲击强化方法与系统 (Laser shock peening method and system ) 是由 张文武 王玉峰 于 2019-04-26 设计创作，主要内容包括：本发明公开了一种激光冲击强化方法和系统。该方法首先形成流向工件表面待处理区域的水柱；然后将流动的吸收保护层材料注入水柱形成吸收保护层；最后,将激光束通过水柱后作用于吸收保护层,形成冲击波作用于工件表面。该方法无需预先设置吸收保护层,通过对吸收保护层材料与激光束的注入时序控制,使吸收保护层到达工件表面后将激光束射入水柱,不仅提升了处理效率,而且可用于处理形状复杂或者表面狭小的工件。(The invention discloses a laser shock peening method and a laser shock peening system. Firstly, forming a water column flowing to a region to be processed on the surface of a workpiece; then injecting the flowing absorbing protective layer material into a water column to form an absorbing protective layer; and finally, enabling the laser beam to pass through a water column and then act on the absorption protective layer to form shock waves to act on the surface of the workpiece. The method does not need to arrange an absorption protective layer in advance, and the laser beam is injected into the water column after the absorption protective layer reaches the surface of the workpiece by controlling the injection time sequence of the material of the absorption protective layer and the laser beam, so that the treatment efficiency is improved, and the method can be used for treating the workpiece with a complex shape or a narrow surface.)

1. A laser shock peening method is characterized in that: the method comprises the following steps:

(1) forming a water column flowing to a region to be processed on the surface of the workpiece;

(2) adopting a flowing medium as an absorption protective layer material; injecting the absorbing protective layer material into a water column, enabling the absorbing protective layer material to reach the surface of the workpiece through the water column, and spreading on the surface of the workpiece under the action of impact force to form an absorbing protective layer;

(3) and (3) after the step (2) is finished, the laser beam passes through the water column and then acts on the absorption protective layer to form shock waves which act on the surface of the workpiece.

2. The laser shock peening method of claim 1, wherein: the water column is a laminar water column.

3. The laser shock peening method of claim 1, wherein: the distance of one end of the water column to the surface of the workpiece is greater than 10mm, preferably greater than 50mm, more preferably greater than 100mm, most preferably greater than 500 mm.

4. The laser shock peening method of claim 1, wherein: the flow velocity of the water column is greater than 2m/s, preferably greater than 10 m/s.

5. The laser shock peening method of claim 1, wherein: setting the cross section perpendicular to the water column flow direction as the cross section, and setting the laser shock strengthening strength as I₀Laser pulse energy of E₀Laser pulse width of t_pThe diameter D is:

6. the laser shock peening method of claim 5, wherein: the predetermined laser shock peening intensity is achieved by adjusting the laser pulse energy and/or the diameter D.

7. The laser shock peening method of any one of claims 1 to 6, wherein: the absorbing protective layer material is a medium which is insoluble in water or diffuses slowly in water, and is preferably an oily ink, paint or dye.

8. A laser shock peening system is characterized in that: the device comprises a laser, an optical transmission and focusing unit, a first transmission unit, a second transmission unit, a cavity and a control unit;

Under the action of the control unit, water enters the cavity through the first transmission unit and flows out through a nozzle arranged at the end part of the cavity to form a water column; the flowing absorbing and protecting layer material enters the cavity through the second transmission unit and then flows out through the nozzle, reaches the surface of the workpiece through the water column and is spread on the surface of the workpiece under the action of impact force to form an absorbing and protecting layer; the laser emits laser, and the laser passes through the water column along the optical transmission and focusing unit and then acts on the surface of the workpiece through the absorption protective layer.

9. The laser shock peening system of claim 8, wherein: the control unit is an industrial control computer or an airborne intelligent processing terminal.

10. The laser shock peening system of claim 8, wherein: the workpiece is displaced under the action of the motion system unit.

11. The laser shock peening system of claim 8, wherein: the pulse width of the laser is less than 50 nanoseconds, preferably less than 20 nanoseconds.

12. The laser shock peening system of claim 8, wherein: the laser wavelength is 450-1200 nm, preferably 450-550 nm.

13. The laser shock peening system of any one of claims 8 to 12, wherein: the distance between the workpiece and the nozzle is greater than or equal to 5-10 times the diameter of the water column.

Technical Field

The invention relates to the technical field of laser shock peening, in particular to a laser shock peening method and a laser shock peening system.

Background

Laser shock peening is a surface treatment technique used to apply compressive stress to the surface of a workpiece. In general, the laser shock peening process is: arranging an absorption protective layer on the surface of the workpiece by methods of spraying, attaching and the like, and arranging a constraint layer on the surface of the absorption protective layer; the strong laser is focused and acts on the absorption protective layer after penetrating through the constraint layer to generate strong high-temperature high-pressure plasma, and the plasma is exploded and expanded to form a plurality of GPa (10) ⁹Pa), which is coupled into the workpiece with relative high efficiency with the aid of the constraining layer, to produce plastic deformation and compressive stress, thereby enhancing the surface hardness and wear resistance of the workpiece, improving fatigue life, etc.

The main purpose of the constraint layer in laser shock peening is to improve shock wave coupling efficiency. At present, a solid material film such as optical glass is generally used as a constraining layer, or a flexible material such as a water film with a thickness of about 0.5mm to 1mm is sprayed on the side surface of the film. In contrast, a water film is a fluid that can recover after breaking. However, the use of a water film as a constraining layer in the laser shock peening process also creates a series of problems: firstly, the effective laser energy is very sensitive to the thickness of a water film and the waviness of the water film, so that the quality of the water film is required to be controlled in the traditional laser shock peening. Secondly, the water film is easy to crack and sputter under the action of strong laser, so that the water film is polluted by optical components or electric elements, and the reliability of a process system is easy to reduce. In addition, for narrow spaces such as the root of a blisk of an aircraft engine, the bottom of a groove with a high depth-diameter ratio and the like, side water spraying cannot be effectively realized, and the application of laser shock peening treatment is limited.

In addition, in order to realize a large processing depth, a high-power laser is used in laser shock peening, the pulse energy of the laser is often more than 1J, for example, the wavelength of a typical high-power laser is generally 1064 nm, the pulse energy is 1-30J, the pulse width is 7-50 ns, and the pulse energy of green light is approximately halved relative to the wavelength of 1064 nm. The large pulse energy causes the cross-section energy distribution to be distorted, namely, peaks and valleys exist, and in severe cases, the peaks exceed the average value by more than 50%, and the spot energy is not uniform. Therefore, for a high-power laser, even if the average power of the laser is stable, the consistency of each laser pulse is difficult to guarantee, so that the phenomenon that local stress is too strong or too weak occurs when the high-power laser is used for shock peening treatment, internal stress tearing of a workpiece can be caused when the local stress is too strong, and the internal defects are difficult to detect through nondestructive detection, so that the fatigue life of the workpiece with internal cracks is not increased or reduced. Therefore, improving the uniformity of the laser spot energy is one of the important factors for obtaining a high quality laser shock peening effect. In order to improve the uniformity of laser spot energy, one method is to detect laser pulses in real time and feedback control pumping current, so that laser energy is used conservatively and the over-limit of local effects of excessive energy is avoided. Another approach is to optically shape the laser beam to make it as flat-topped as possible, i.e. to reduce the amplitude of the peaks and valleys. However, for high power lasers, these two methods are expensive and have low reliability.

In addition, in the conventional laser shock peening, an absorption protective layer needs to be arranged on the surface of a workpiece firstly, but the arrangement of the absorption protective layer on the surface of the workpiece with a complex shape and the surface of the workpiece with a narrow surface is not easy, and brings difficulty to the treatment process.

Disclosure of Invention

In view of the above technical situation, the present invention provides a laser shock peening method, including the steps of:

(1) forming a water column flowing to a region to be processed on the surface of the workpiece;

(2) adopting a flowing medium as an absorption protective layer material; injecting the absorbing protective layer material into a water column, enabling the absorbing protective layer material to reach the surface of the workpiece through the water column, and spreading on the surface of the workpiece under the action of impact force to form an absorbing protective layer;

(3) and (3) after the step (2) is finished, the laser beam passes through the water column and then acts on the absorption protective layer to form shock waves which act on the surface of the workpiece.

In order to avoid the influence of bubbles in the water column and the like on the laser transmission efficiency, the water column is preferably a laminar water column.

Preferably, the length of the water column, namely the distance between one end of the water column and the surface of the workpiece is more than 10mm, and the laser can be fully emitted for multiple times in the water column so as to improve the uniformity of light spots. As a further preference, the length of the water column is greater than 50mm, more preferably greater than 100mm, most preferably greater than 500 mm.

Preferably, the flow velocity of the water column is greater than 2m/s, more preferably greater than 10m/s, and may be greater than 20 m/s.

The cross section perpendicular to the flow direction of the water column is set as a cross section, and the cross section of the water column is not limited and comprises a circle and a non-circle. When the cross section of the water column is circular, the cross section is straightThe diameter D (in cm) is preferably determined by the laser intensity, for example, by setting the laser shock peening intensity to I₀(unit is W/cm)²) Laser pulse energy of E_p(in J) and the laser pulse width is t_p(in seconds), the diameter D is preferably:

preferably, the diameter D is less than or equal to 0.5 mm.

In addition, by adjusting the laser pulse energy and/or the diameter D, a predetermined laser shock peening intensity can be achieved.

The absorbing protective layer material is not limited, and is preferably a medium which is insoluble in water or diffuses slowly in water, and includes oily ink, paint, dye and the like.

Compared with the prior art, the invention has the following beneficial effects:

(1) in the invention, the water column is used as a constraint layer and forms a total reflection light guide in the air, so that the laser can be transmitted to the surface of a workpiece on one hand, and the uneven laser distribution can be conveniently changed into even laser distribution through multiple interface reflections through the total reflection light guide effect on the other hand, thereby improving the laser shock strengthening effect. In addition, the length and diameter of the water column can be adjusted, so that the water column can conveniently reach a narrow space part with a complicated shape.

(2) According to the invention, an absorption protective layer is not required to be arranged in advance in the region to be processed on the surface of the workpiece, but the flowing absorption protective layer material passes through the water column before the laser is injected into the water column, and the absorption protective layer material generates a diameter expansion effect under the action of impact force, so that the absorption protective layer is instantly and completely covered on the region to be processed on the surface of the workpiece to form the absorption protective layer, the processing efficiency is greatly improved, the absorption protective layer can be conveniently laid on the surfaces of various workpieces, and the absorption protective layer is particularly suitable for the surfaces of workpieces with complex shapes and the surfaces of.

(3) According to the invention, the injection time sequence of the absorption protective layer material and the laser beam is controlled, so that the laser beam is injected into the water column after the absorption protective layer reaches the surface of the workpiece, on one hand, the water column can quickly recover the optical transmission channel after the injection of the absorption protective layer material is stopped, and on the other hand, the absorption protective layer material completely covers the area to be processed on the surface of the workpiece to form the absorption protective layer, thereby avoiding the damage to the surface of the workpiece caused by the direct action of the laser.

The invention also provides a laser shock peening system, which comprises a laser, an optical transmission and focusing unit, a first transmission unit, a second transmission unit, a cavity and a control unit;

Under the action of the control unit, a water source enters the cavity through the first transmission unit and flows out through a nozzle arranged at the end part of the cavity to form a water column; the flowing absorbing and protecting layer material enters the cavity through the second transmission unit and then flows out through the nozzle, reaches the surface of the workpiece through the water column and is spread on the surface of the workpiece under the action of impact force to form an absorbing and protecting layer; the laser emits laser, and the laser passes through the water column along the optical transmission and focusing unit and then acts on the surface of the workpiece through the absorption protective layer.

The control unit can be an industrial control computer or an onboard intelligent processing terminal.

Preferably, the workpiece is displaceable by the motion system unit. The motion system unit includes, but is not limited to, a robot, a motion stage, and the like.

The workpiece material is not limited and includes metal, nonmetal, etc.

The laser is a laser which can be used for laser shock peening after being focused. Preferably, the laser has a pulse width of less than 50 nanoseconds, and more preferably, the laser has a pulse width of less than 20 nanoseconds, including picosecond and femtosecond lasers.

Preferably, the laser wavelength is selected to be capable of high-energy, long-distance and low-attenuation transmission in water. More preferably, the laser wavelength is 450-1200 nm, and more preferably, the laser is 450-550 nm blue-green light.

The optical transmission and focusing unit can be discrete optical devices such as mirrors and lenses, or can be an integrated optical system including, but not limited to, a flexible light pipe with a focusing lens at the end.

Preferably, the intensity of the laser transmission is 1-6GW/cm²。

Preferably, the spacing between the workpiece and the nozzle is equal to or greater than 5-10 times the diameter of the water column to take full advantage of the beam shaping effect of the water column light guide.

Drawings

FIG. 1 is a schematic structural diagram of a laser shock peening system in example 1 of the present invention.

Fig. 2 is a partially enlarged view of fig. 1.

FIG. 3 is a schematic diagram of a laser shock peening method in example 1 of the present invention.

FIG. 4 is a schematic structural diagram of a laser shock peening system in embodiment 2 of the present invention.

FIG. 5 is a schematic structural diagram of a laser shock peening system in embodiment 3 of the present invention.

FIG. 6 is a schematic structural diagram of a laser shock peening system in embodiment 4 of the present invention.

The reference numerals in fig. 1-6 are: 1-a laser; 2-a laser beam; 3-a mirror; 4-a focusing lens; 5-water inlet; 6, mounting a filter screen; 7-lower filter screen; 8-quartz window piece; 9-a nozzle; 10-water column; 11-a workpiece; 12-liquid absorbing protective layer material; 13-liquid absorbent protective layer material inlet; 14-a motion stage; 15-plasma; 16-shock wave; 17-a motion controller; 18-industrial control computer; 19-a container; 20-high pressure devices; 21-electromagnetic valve A; 22-a container; 23-solenoid valve B; 24-a blade; 25-a clamp; 26-an installation table; 27-a recovery water tank; 28-a robot; 29-laser a; 30-laser B; 31-a workpiece; 32-flexible transmission of laser fiber; 33-large workpieces; 34-large installation table.

Detailed Description

The present invention will be described in further detail with reference to the following examples and drawings, which are intended to facilitate the understanding of the present invention and are not intended to limit the present invention in any way.