WO2020215596A1

WO2020215596A1 - Laser shock strengthening method and system

Info

Publication number: WO2020215596A1
Application number: PCT/CN2019/106162
Authority: WO
Inventors: 张文武; 王玉峰
Original assignee: 中国科学院宁波材料技术与工程研究所
Priority date: 2019-04-26
Filing date: 2019-09-17
Publication date: 2020-10-29
Also published as: CN111850284B; CN111850284A

Abstract

A laser shock strengthening method and a system. The method comprises: first forming a water column (10) flowing towards an area to be processed on the surface of a workpiece (11); then injecting a flowing adsorption protective layer material (12) into the water column (10) to from an adsorption protective layer; and finally, acting a laser beam (2) to the adsorption protective layer after passing through the water column (10), and forming a shock wave to act on the surface of the workpiece (11). The method does not need to provide the adsorption protective layer in advance; by means of time sequence control of the adsorption protective layer material (12) and the laser beam (2), and enabling the adsorption protective layer to inject the laser beam (2) to the water column (10) after reaching the surface of the workpiece (11), the processing efficiency is improved, and the method can be used for processing the workpiece (11) having a complex shape or a narrow surface.

Description

Laser shock strengthening method and system

Technical field

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

Background technique

Laser shock strengthening is a surface treatment technology used to treat the surface of workpieces with compressive stress. Generally, the laser shock strengthening process is: to install an absorption protection layer on the surface of the workpiece by spraying, attaching, etc., and set a constraining layer on the surface of the absorption protection layer; strong laser focus passes through the constraining layer and acts on the absorption protection layer to generate strong high temperature and high pressure Plasma, the plasma explodes and expands, forming several shock waves of GPa (10 ⁹ Pa). With the aid of the confinement layer, the shock waves are relatively efficiently coupled into the workpiece to produce plastic deformation and compressive stress, thereby enhancing the surface hardness and wear resistance of the workpiece Performance, improve fatigue life, etc.

The main purpose of the confinement layer in laser shock strengthening is to improve the shock wave coupling efficiency. At present, a solid material film such as optical glass is generally used as the constraining layer, or a flexible material such as a water film with a thickness of about 0.5mm-1mm is sprayed on the side as the constraining layer. In contrast, the water film is fluid, which can be restored after being broken. However, in the laser shock strengthening process, the use of water film as a constraining layer also produces a series of problems: First, the effective laser energy is very sensitive to the thickness of the water film and the ripple of the water film. Therefore, the traditional laser shock strengthening requires the control of the water film quality. Ideally, the water film maintains the same thickness during the entire treatment and is in a stable state, but in the actual treatment process, the water film is difficult to maintain a stable state, especially on the surface of complex workpieces, workpiece edges or corners. Secondly, the water film is prone to bursting and sputtering under the action of a strong laser, thereby contaminating optical components or electrical components, and easily reducing the reliability of the process system. In addition, for narrow spaces, such as the root of the blisk of an aircraft engine, the bottom of the groove with high depth to diameter ratio, etc., side water spraying cannot be effectively achieved, resulting in limited application of laser shock strengthening treatment.

In addition, in order to achieve a large processing depth, high-power lasers are used in laser shock strengthening, and their pulse energy often exceeds 1J. For example, the wavelength of a typical high-power laser is generally 1064 nanometers, the pulse energy is 1-30J, and the pulse width is 7 -50 nanoseconds, the green pulse energy is roughly halved relative to the 1064 nanometer wavelength. Such large pulse energy often results in distortion of the cross-sectional energy distribution, that is, there are peaks and valleys. In severe cases, the peaks will exceed the average value by more than 50%, and the spot energy is uneven. Therefore, for high-power lasers, even if the average power of the laser is stable, the consistency of each laser pulse is difficult to guarantee, resulting in the phenomenon of local stress being too strong or too weak when using high-power lasers for impact strengthening. When the local stress is too strong, it may cause internal stress tearing of the workpiece, and such internal defects are difficult to detect through non-destructive testing, resulting in the fatigue life of the workpiece with internal cracks not increasing but decreasing. Therefore, improving the uniformity of laser spot energy is one of the important factors for obtaining high-quality laser shock strengthening effects. In order to improve the uniformity of the laser spot energy, one method is to detect the laser pulse in real time and feedback to control the pump current, so as to use the laser energy conservatively to avoid excessive local effects of excessive energy. Another method is to optically shape the laser beam to make the laser beam flat top as much as possible, that is, 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 current laser shock strengthening, it is first necessary to provide an absorption protection layer on the surface of the workpiece, but it is not easy to provide an absorption protection layer on the surface of a workpiece with a complex shape and a surface of a workpiece with a narrow surface, which brings difficulties to the processing process.

Summary of the invention

In view of the foregoing technical status, the present invention provides a laser shock strengthening method, which includes the following steps:

(1) Form a water column flowing to the area to be treated on the surface of the workpiece;

(2) Use a flowing medium as the material of the absorption protection layer; inject the absorption protection layer material into the water column, and the absorption protection layer material reaches the surface of the workpiece through the water column, and expands on the surface of the workpiece under the impact force to form an absorption protection layer;

(3) After step (2) is completed, the laser beam passes through the water column and acts on the absorption protection layer to form a shock wave and act on the surface of the workpiece.

In order to prevent the presence of bubbles in the water column from affecting the laser transmission efficiency, the water column is preferably a laminar flow water column.

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

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

The cross section perpendicular to the flow direction of the water column is a cross section, and the cross section of the water column is not limited, including circular and non-circular. When the cross-section of the water column is circular, the cross-sectional diameter D (in cm) is preferably determined by the laser intensity, for example, the laser shock strengthening intensity is set to I ₀ (in W/cm ² ), and the laser pulse energy is E _p (unit is J), laser pulse width is t _p (unit is second), 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 diameter D, a predetermined laser shock strengthening intensity can be achieved.

The material of the absorption protection layer is not limited, and it is preferably a medium that is insoluble in water or diffuses slowly in water, including oily ink, paint, dye, and the like.

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

(1) In the present invention, the water column is used as the confinement layer, and the water column forms a total reflection light guide in the air. On the one hand, the laser can be transmitted to the surface of the workpiece, and on the other hand, the uneven laser distribution can be easily distributed through the total reflection light guide effect. Through multiple interface reflections, it becomes a uniform laser distribution, thereby improving the laser shock strengthening effect. In addition, the length and diameter of the water column can be adjusted, so the water column can easily reach the narrow and complicated space parts.

(2) In the present invention, there is no need to pre-install an absorption protection layer on the surface of the workpiece to be treated, but the flowing absorption protection layer material is passed through the water column before the laser is injected into the water column, and the absorption protection layer material produces a diameter expansion under the impact force Effect, so as to instantly completely cover the area to be treated on the surface of the workpiece to form an absorbing protective layer, which not only greatly improves the processing efficiency, but also can easily lay the absorbing protective layer on the surface of various workpieces, especially suitable for the surface of the workpiece with complex shapes and The surface of the workpiece with a narrow surface.

(3) In the present invention, by controlling the injection timing of the absorption protection layer material and the laser beam, the laser beam is injected into the water column after the absorption protection layer reaches the surface of the workpiece. On the one hand, the water column will quickly restore the light after the absorption protection layer material is stopped. The transmission channel, on the other hand, the absorption protection layer material completely covers the area to be treated on the surface of the workpiece to form an absorption protection layer, thereby avoiding damage to the surface of the workpiece due to the direct action of the laser.

The present invention also provides a laser shock strengthening system, including 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, the water source enters the cavity through the first transmission unit, and flows out through the nozzle arranged at the end of the cavity to form a water column; the flowing absorption protection layer material enters the cavity through the second transmission unit and flows out through the nozzle. It reaches the surface of the workpiece through the water column, and expands on the surface of the workpiece under the action of the impact force to form an absorption protection layer; the laser emits a 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 protection layer.

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

Preferably, the workpiece can be displaced under the action of the motion system unit. The motion system unit includes, but is not limited to, a robot, a motion table, and the like.

The workpiece material is not limited, including metal, non-metal, etc.

The laser refers to a laser that can be used for laser shock strengthening after focusing. Preferably, the pulse width of the laser is less than 50 nanoseconds. As a further preference, the pulse width of the laser is less than 20 nanoseconds, including picosecond and femtosecond lasers.

Preferably, the laser wavelength is selected to be a laser wavelength capable of high-energy, long-distance, and low-attenuation transmission in water. As a further preference, the laser has a wavelength of 450-1200 nanometers, more preferably a blue-green light of 450-550 nanometers.

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

Preferably, the intensity of laser transmission is 1-6 GW/cm ² .

Preferably, the distance between the workpiece and the nozzle is equal to or greater than 5-10 times the diameter of the water column, so as to make full use of the beam shaping effect of the water column light guide.

Description of the drawings

FIG. 1 is a schematic diagram of the structure of the laser shock strengthening system in Embodiment 1 of the present invention.

Fig. 2 is a partial enlarged view of Fig. 1.

3 is a schematic diagram of the laser shock strengthening method in Example 1 of the present invention.

4 is a schematic diagram of the structure of the laser shock strengthening system in Embodiment 2 of the present invention.

5 is a schematic diagram of the structure of the laser shock strengthening system in Embodiment 3 of the present invention.

6 is a schematic diagram of the structure of the laser shock strengthening system in Embodiment 4 of the present invention.

The reference signs in Figure 1-6 are: 1-laser; 2-laser beam; 3-reflector; 4-focus lens; 5-water inlet; 6-upper filter; 7-lower filter; 8-quartz Window; 9-nozzle; 10-water column; 11-workpiece; 12-liquid absorption protection layer material; 13-liquid absorption protection layer material inlet; 14-motion table; 15-plasma; 16-shock wave; 17-motion control 18-industrial computer; 19-container; 20-high-pressure device; 21-solenoid valve A; 22-container; 23-solenoid valve B; 24-blade; 25-fixture; 26-installation table; 27-recovery pool; 28-robot; 29-laser A; 30-laser B; 31-workpiece; 32-laser optical fiber flexible transmission; 33-large work piece; 34-large mounting table.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the drawings. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

Example 1:

As shown in Fig. 1, the laser shock strengthening system as shown in Fig. 1, includes a laser 1, an optical transmission and focusing unit, a first transmission unit, a second transmission unit, a cavity with nozzles at the bottom, and a control unit.

In this embodiment, the optical transmission and focusing unit includes a mirror 3, a focusing lens 4, and a quartz window 8.

In this embodiment, the first transmission unit includes a high-pressure device 20, a water bucket 22, a solenoid valve B 23, a water inlet 5, an upper filter screen 6 and a lower filter screen 7.

In this embodiment, the second transmission unit includes a high-pressure device 20, a liquid absorption protective layer material container 22, and a solenoid valve A 21.

In this embodiment, the control unit is an industrial control computer 18.

In this embodiment, the laser shock strengthening system also includes a motion system unit, which includes a motion controller 17 and a motion table 14 that carries a workpiece. Under the action of the control unit, the motion controller controls the motion table to move to make the workpiece 11 Located directly below the water column 10.

As shown in Figures 2 and 3, the method for laser shock strengthening using the laser shock strengthening system includes the following steps:

(1) Under the action of the industrial control computer 18, the motion controller 17 controls the motion table 14 to move so that the area to be processed of the workpiece 11 is located directly below the nozzle 9.

(2) Under the action of the industrial control computer 18, the solenoid valve A23 is opened. Under the action of the high pressure device 20, the water in the container 22 enters the cavity through the water inlet 5, the upper filter screen 6 and the lower filter screen 7, and passes through the The nozzle 9 at the bottom of the cavity flows out to form a laminar water column 10.

(3) Under the action of the industrial control computer 18, the solenoid valve B 21 is opened. Under the action of the high-pressure device 20, the liquid absorption protective layer material 12 in the container 19 flows into the cavity, flows out through the nozzle 9, and reaches through the laminar water column 10 The surface of the workpiece 11 expands on the surface of the workpiece 11 under the impact force to form an absorption protection layer.

(4) As shown in Figures 2 and 3, the laser 1 emits a high-energy pulsed laser beam 2, and the laser beam 2 is transmitted along the optical path, enters the cavity through the mirror 3, focusing lens 4, and transparent quartz window 8, and is coupled into the layer through the nozzle 9. The flowing water column 10 propagates through the total reflection of the laminar water column 10, and the laser energy becomes sufficiently uniform and contacts the processing area of the workpiece 11 through the absorbing protective layer, and the shock wave 16 forming the plasma 15 acts on the processing area of the workpiece.

(5) Repeat the above steps (1) to (4) to complete the processing of the workpiece.

Example 2:

In this embodiment, the workpiece is a titanium alloy aero engine blade 24.

In this embodiment, the laser shock strengthening system is basically the same as the first embodiment. The difference is that as shown in FIG. 4, the motion system unit includes a clamp 25 and a six-degree-of-freedom robot 28. Under the action of the industrial control computer 18, the workpiece 24 is clamped by the clamp 25, and is displaced under the action of the six-degree-of-freedom robot 28, so that the workpiece 24 is located to the right of the nozzle. Under the action of the high-pressure device, the water in the container passes through the water inlet, The upper filter screen and the lower filter screen enter the cavity and flow out through a nozzle arranged at the right end of the cavity to form a horizontal laminar water column. A recovery pool 27 is provided under the workpiece to receive the falling water droplets.

Example 3:

In this embodiment, the workpiece is a large workpiece 33 installed on a large mounting table 34.

In this embodiment, the laser shock strengthening system is basically the same as the embodiment 1, except that as shown in FIG. 5, the laser is transmitted from the laser to the optical transmission and focusing unit through the flexible light guide arm 32. In addition, the cavity, focusing lens, quartz window, upper filter screen, lower filter screen and the like in the embodiment 1 are clamped by a six-degree-of-freedom robot 28 and displaced under the action of the industrial control computer 18.

Example 4:

In this embodiment, the laser shock strengthening system is basically the same as that of Embodiment 3, except that as shown in FIG. 6, two systems are used to perform laser shock strengthening on the workpiece 31.

The above-mentioned embodiments describe the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Anything done within the scope of the principles of the present invention Any modification, supplement or substitution in a similar manner shall be included in the protection scope of the present invention.

Claims

A laser shock strengthening method is characterized in that it comprises the following steps:

(1) Form a water column flowing to the area to be treated on the surface of the workpiece;

(2) Use a flowing medium as the material of the absorption protection layer; inject the absorption protection layer material into the water column, and the absorption protection layer material reaches the surface of the workpiece through the water column, and expands on the surface of the workpiece under the impact force to form an absorption protection layer;

(3) After step (2) is completed, the laser beam passes through the water column and acts on the absorption protection layer to form a shock wave and act on the surface of the workpiece.
The laser shock strengthening method of claim 1, wherein the water column is a laminar water column.
The laser shock strengthening method according to claim 1, wherein the distance from one end of the water column to the surface of the workpiece is greater than 10 mm, preferably greater than 50 mm, more preferably greater than 100 mm, and most preferably greater than 500 mm.
The laser shock strengthening method of claim 1, wherein the flow velocity of the water column is greater than 2 m/s, preferably greater than 10 m/s.
The laser shock strengthening method according to claim 1, wherein the cross section perpendicular to the flow direction of the water column is a cross section. When the cross section of the water column is circular, the diameter of the cross section is D, and the laser shock strengthening strength is set to I 0 , The laser pulse energy is E 0 , the laser pulse width is t p , and the diameter D is:
The laser shock strengthening method according to claim 5, wherein the predetermined laser shock strengthening intensity is achieved by adjusting the laser pulse energy and/or diameter D.
The laser shock strengthening method according to any one of claims 1 to 6, characterized in that: the absorption protection layer material is a medium that is insoluble in water or diffuses slowly in water, preferably oil-based ink, paint, or dye.
A laser shock strengthening system, which is characterized by: comprising 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 transfer unit, and flows out through the nozzle provided at the end of the cavity to form a water column; the flowing absorption and protection layer material enters the cavity through the second transfer unit and flows out through the nozzle. It reaches the surface of the workpiece through the water column, and expands on the surface of the workpiece under the action of the impact force to form an absorption protection layer; the laser emits a 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 protection layer.
8. The laser shock strengthening system according to claim 8, wherein the control unit is an industrial control computer or an airborne intelligent processing terminal.
The laser shock strengthening system of claim 8, wherein the workpiece is displaced under the action of the motion system unit.
8. The laser shock enhancement system of claim 8, wherein the pulse width of the laser is less than 50 nanoseconds, preferably less than 20 nanoseconds.
8. The laser shock strengthening system according to claim 8, wherein the laser wavelength is 450-1200 nanometers, preferably 450-550 nanometers.
The laser shock strengthening system according to 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.