Follow-up regulation and control method for unequal-intensity laser shock peening intensity of liquid restraint layer

Abstract

The invention relates to a follow-up regulation and control method for unequal-intensity laser shock peening intensity of a liquid restraint layer, and belongs to the technical field of high-energy laser material surface engineering. The method comprises the following steps: (1) constructing a thickness-strength mapping model; (2) building a constraint type laser shock surface strengthening device, and setting a moving path of a laser beam in a to-be-processed area; (3) processing the surface of the to-be-processed material, and placing a photosensitive element on the surface of the material; and (4) state changes of different to-be-machined positions are tested in real time, and the constraint type laser shock surface strengthening device is adjusted until machining is completed. Based on real-time monitoring of the light refractive index, change data of the thickness of the deionized water restraint layer is tested and obtained, indexes such as the thickness of the deionized water restraint layer or laser energy needing to be adjusted are calculated and fed back, and unequal-intensity laser shock surface strengthening is achieved.

Description

Technical Field

[0001] The present invention relates to a follow-up regulation method for the unequal strength of laser shock peening on a liquid constraint layer, belonging to the technical field of high-energy laser material surface engineering. Background Art

[0002] Thin-walled structures such as aero-engine blades serve in harsh environments of high temperature and high load. The post-treatment of fatigue life extension of such components has important engineering significance. Compared with conventional surface strengthening processes such as mechanical shot peening, laser shock peening has a lower cold work hardening rate and is regarded as one of the most promising surface post-treatment technologies for aero high-temperature alloy material components.

[0003] When using the laser shock peening post-treatment technology to perform surface strengthening treatment on a variable-thickness thin-walled structure, if a relatively high strengthening intensity is always adopted, when the blade body of structures such as blades meets the use requirements, the edge part is extremely likely to be deformed due to overload; if a relatively low strengthening intensity is always adopted, when the edge part of structures such as blades meets the use requirements, the surface strengthening effect of the blade body part has a high probability of not meeting the strengthening requirements.

[0004] To better adapt to the unequal-thickness structural characteristics of thin-walled structures, the development of a "shape-property" collaborative unequal-strength laser shock surface strengthening process has become a problem that needs to be solved by technicians. The "shape-property" collaborative unequal-strength strengthening treatment is mainly achieved by adjusting the laser beam parameters and the characteristics of the absorption layer, constraint layer, etc. Among them, when using a deionized water constraint layer for variable-intensity laser shock treatment, inaccurate control of the deionized water thickness is very likely to cause deviations in the actual intensity and effect of laser shock. At present, technicians have achieved accurate control of the actual intensity in the laser shock of the deionized water constraint layer through physical principles such as the change of the refractive index of light. However, it is still a technical blank to achieve unequal-strength surface strengthening of complex parts through accurately variable constraint layer thickness. Based on the change law of the constraint layer thickness, it is of great importance and significance to develop a variable-intensity laser shock surface strengthening technology by using the quantitatively adjusted shock effect. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a follow-up regulation method for the unequal strength of laser shock peening on a liquid constraint layer. Based on the real-time monitoring of the refractive index of light, the change data of the deionized water constraint layer thickness is tested and obtained, and the indexes such as the deionized water constraint layer thickness or laser energy that need to be adjusted are calculated and fed back, so as to realize unequal-strength (variable-intensity) laser shock surface strengthening.

[0006] The technical solution of the present invention is as follows:

[0007] A follow-up regulation method for the unequal strength of laser shock peening on a liquid constraint layer, the steps are as follows:

[0008] (1) Construct a thickness-strength mapping model. By detecting the thickness change of thin-walled parts, determine the "shape-property" collaborative surface strengthening process requirements that adapt to the shape characteristics of the actual component, and inversely deduce the surface strengthening index of the laser shock wave intensity required at different positions on the surface of the part to be machined.

[0009] (2) Build a constrained laser shock surface strengthening device and set the moving path of the laser beam in the area to be machined.

[0010] (3) Treat the surface of the material to be machined and place a photosensitive element on the material surface.

[0011] (4) Real-time test the state changes at different positions to be machined, and adjust the constrained laser shock surface strengthening device until the machining is completed.

[0012] Preferably according to the present invention, in step (1), the thickness-strength mapping model is:

[0013] Determine the target shock wave intensity P at each position according to the component thickness distribution T(x, y) and the strengthening requirements target :

[0014] P target (x, y) = k·T(x, y) + P0 (1)

[0015] Wherein, k is the strength gradient coefficient (0.5 - 2.0 GPa / mm), and P0 is the base strength (1.0 - 3.0 GPa).

[0016] The physical meaning of the strength gradient coefficient is the change requirement of the shock wave intensity when the thickness changes by a unit. It needs to be calibrated by the material yield strength. Taking 0.5 GPa / mm as an example, if the thickness of a certain position of a variable-thickness component is 1 mm and the shock wave intensity requirement is 1.0 GPa, then for another position with a thickness change of 2 mm, the required shock wave intensity is 1.0 GPa + 0.5 GPa / mm × (2 - 1) mm = 1.5 GPa.

[0017] The physical meaning of the base strength is the shock wave intensity required at the thinnest position of the variable-thickness component. It needs to be calibrated by the material yield strength. Continuing with the above example, if 1 mm is the thickness of the thinnest position of the variable-thickness component and the base strength of the material of this component is 2.0 GPa, then the shock wave intensity requirement at the 1 mm thickness position of this component, that is, the thinnest position, is 2.0 GPa.

[0018] The strength gradient coefficient and the base strength are related to the mechanical strength properties of the component to be processed. If the material strength (such as yield strength, tensile strength, etc.) is high, the values of the base strength and the strength gradient coefficient are high. The determination of the above two indicators should also refer to the mechanical strength limit of the material to be processed, that is, the calculated shock wave strength in the thick-walled area should not be too large to avoid exceeding the strength limit of the material.

[0019] It should be noted that the specific values of the two indicators k and P0 are determined by technicians according to actual processing requirements. In actual applications, technicians should calibrate k and P0 based on experimental data;

[0020] When limiting the base strength for a specific processing scenario, the minimum thickness of the corresponding component should not be less than 1 mm. If the thinnest position of a variable-thickness component is less than 1 mm, technicians need to make special treatments based on the mechanical strength of the material and specific practical experience outside the above formula, which is not limited in the present invention.

[0021] According to the preference of the present invention, in step (2), the laser shock surface strengthening device includes a deionized water confinement layer and an absorption layer. The absorption layer is set as required. For working conditions where ablation damage on the material surface is unacceptable or the substrate reflectivity > 30%, an absorption layer is set; for working conditions where the surface quality requirement of the material is not high or the substrate reflectivity < 30%, the absorption layer is abandoned.

[0022] According to a further preference of the present invention, the back-calculation accuracy of the thickness of the deionized water confinement layer is not less than ±1 μm.

[0023] According to the preference of the present invention, in step (3), the photosensitive element is an optical fiber sensor, such as an FRI-NP FISO optical fiber refractive index sensor, which is used to monitor the change of the refractive index of the deionized water confinement layer in real time, and then obtain the thickness of the deionized water confinement layer.

[0024] According to the preference of the present invention, in step (4), the adjustment strategy of the constrained laser shock surface strengthening device includes the regulation of the thickness of the deionized water confinement layer and the regulation of the laser energy;

[0025] Based on the relationship between the thickness (h) of the deionized water confinement layer and the shock wave strength (P), under the shock wave strength limit given in step (1), it is required that P(x, y) = O target (x, y) at the laser shock position (x, y), calculate the thickness h of the deionized water confinement layer (E remains unchanged, and the shock wave strength is changed in a follow-up manner by changing the thickness of the deionized water to regulate the strengthening strength) or the laser energy E (h remains unchanged, and the shock wave strength is changed in a follow-up manner by changing the laser energy to regulate the strengthening strength);

[0026] The relationship between the thickness (h) of the deionized water confinement layer and the shock wave strength (P):

[0027] P = α·exp(-β·h)·E γ (2)

[0028] In the formula:

[0029] α: Comprehensive attenuation coefficient (unit: GPa·J -γ )(For example, select α = 3.2 GPa·J -γ , in practical applications, technicians need to calibrate more accurate coefficient values through experiments);

[0030] β: Thickness attenuation coefficient (unit: μm -1 ), reflecting the exponential attenuation of the deionized water thickness on the shock wave intensity (for example, select β = 0.05 μm -1 , in practical applications, technicians need to calibrate more accurate coefficient values through experiments);

[0031] γ: Energy nonlinear gain coefficient (dimensionless), reflecting the nonlinear contribution of laser energy to the shock wave intensity (for example, select γ = 0.5, in practical applications, technicians need to calibrate more accurate coefficient values through experiments);

[0032] E: Laser energy (2 - 10 J).

[0033] α, β, and γ must be calibrated through experiments (such as orthogonal experimental design). The present invention does not limit the determination method and process of the above parameters, and technicians can select according to the actual working conditions.

[0034] According to a further preference of the present invention, for the regulation of the deionized water confinement layer thickness: with the laser energy E fixed, the shock wave intensity is changed by adjusting the thickness of the deionized water confinement layer. When P target ≤α·E γ , the supply rate is adjusted through a flow controller to make the actual thickness (h real ) approach the target thickness (h target ):

[0035]

[0036] Example: If the shock wave intensity required at the target position is 5.0 GPa and the laser energy remains 6 J unchanged, the deionized water thickness required at this position needs to be maintained at 18.4 μm.

[0037] If P target = 5.0 GPa, α = 3.2 Gpa·J -γ , γ = 0.5, E = 6 J, then:

[0038]

[0039] Preferably according to the present invention, for laser energy regulation: the output energy of the laser is modulated by a Q-switch (adjustment accuracy ±0.2 J), and the thickness h of deionized water real is fixed. By adjusting the laser energy, the shock wave intensity is changed. When h real exceeds the adjustable range or it is inconvenient to achieve deionized water thickness regulation, when E new ≤ E max (the maximum energy of the laser), the laser energy is adjusted according to the following formula:

[0040]

[0041] Example: If the shock wave intensity required at the target position is 3.5 GPa and the thickness of deionized water remains unchanged at 50 μm, the laser energy required at this position needs to be maintained at 18.4 μm.

[0042] If P target = 3.5 GPa, h real = 50 μm, α = 3.2 GPa·J -γ , β = 0.05 μm -1 , γ = 0.5, then:

[0043]

[0044] Preferably according to the present invention, when the set thickness of deionized water is M, the laser beam propagates to the material surface in a zero defocus state. When the thickness of deionized water increases, the laser beam approaches an increasing negative defocus amount relative to the material surface; when the thickness of deionized water decreases, the laser beam approaches an increasing positive defocus amount relative to the material surface.

[0045] The present invention does not consider the laser-induced cavitation effect in the positive defocus state, or the maximum thickness of deionized water is default not to exceed the critical value of the positive defocus amount that can cause the cavitation effect. If considering the cavitation effect, those skilled in the art can set a new process according to the innovative idea described in the present invention.

[0046] The beneficial effects of the present invention are as follows:

[0047] 1. The present invention obtains the thickness of deionized water on the material surface through the principle of light refraction, transmits the deionized water thickness information in real time, and based on the shape characteristics of the component to be processed on the light beam movement path, calculates in real time the deionized water thickness or laser energy that needs to be adjusted and feeds back, and finally performs laser shock treatment with the adjusted process indicators or parameters to achieve precise processing.

[0048] 2. The present invention establishes a quantitative relationship model among the deionized water thickness (h), laser energy (E) and shock wave intensity (P) to achieve precise matching of the strengthening intensity. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic diagram of the thickness of the deionized water confinement layer that meets the requirements set at different thickness positions of the component to be processed in the present invention;

[0050] Figure 2 It is a schematic diagram of adjusting the thickness of the deionized water confinement layer after real-time detection of the thickness of the deionized water confinement layer in the present invention. The thickness of the deionized water confinement layer is adjusted to be consistent with the preset thickness of the deionized water confinement layer at the corresponding position;

[0051] Figure 3 It is a schematic diagram of laser energy compensation after real-time detection of the thickness of the deionized water confinement layer in the present invention.

[0052] Among them, 1, pulsed laser beam; 2, deionized water confinement layer; 3, absorption layer; 4, plasma; 5, shock wave pressure; 6, photosensitive element; 7, total control system; 8, PID controller; 9, laser energy control system. Specific embodiments

[0053] The present invention will be further described below through embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0054] Embodiment 1:

[0055] As Figures 1-3 shown, this embodiment provides a follow-up control method for the intensity of laser shock peening with unequal intensity of the liquid confinement layer, and the steps are as follows:

[0056] (1) Construct a thickness-intensity mapping model. By detecting the thickness change of the thin-walled part, determine the "shape-property" collaborative surface strengthening process requirements that adapt to the shape characteristics of the actual component, and inversely deduce the surface strengthening indexes of the laser shock wave intensity required at different positions on the surface of the part to be processed;

[0057] The thickness-intensity mapping model is:

[0058] According to the component thickness distribution T(x, y) and the strengthening requirements, determine the target shock wave intensity P tdrget :

[0059] P target (x, y) = k·T(x, y) + P0 (1)

[0060] Among them, k is the intensity gradient coefficient (0.5 - 2.0 GPa / mm), and P0 is the base intensity (1.0 - 3.0 GPa).

[0061] (2) Build a constrained laser shock peening device and set the moving path of the laser beam in the area to be processed;

[0062] The laser shock surface strengthening device includes a deionized water confinement layer 2 and an absorption layer 3. The absorption layer is set as required. For the working conditions where ablation damage on the material surface is unacceptable or the substrate reflectivity > 30%, the absorption layer is set; for the working conditions where the surface quality requirement of the material is not high or the substrate reflectivity < 30%, the absorption layer is abandoned. The deionized water confinement layer is formed by using a high-precision flow pump (such as Cole-Parmer Masterflex L / S) and a PID controller, dynamically adjusting the flow rate according to the real-time thickness feedback, and then adjusting the thickness to ensure that h real is tracked within ±2 μm of h target . The back-calculation accuracy of the deionized water confinement layer thickness is not less than ±1 μm.

[0063] (3) Treat the surface of the material to be processed, and place a photosensitive element 6 on the material surface; the photosensitive element 6 is an optical fiber sensor, such as an FRI-NP FISO optical fiber refractive index sensor, used to monitor the refractive index change of the deionized water confinement layer in real time, and then obtain the thickness of the deionized water confinement layer. The photosensitive element 6, the PID controller 8, and the laser energy control system 9 are all connected to the master control system 7.

[0064] (4) Real-time test the state changes at different positions to be processed, and adjust the constrained laser shock surface strengthening device until the processing is completed.

[0065] The adjustment strategy of the constrained laser shock surface strengthening device includes the regulation of the deionized water confinement layer thickness and the regulation of the laser energy;

[0066] According to the relationship between the deionized water confinement layer thickness (h) and the shock wave intensity (P), under the shock wave intensity limit given in step (1), it is required that P(x,y) = P at the laser shock position (x,y) target (x,y), calculate the deionized water confinement layer thickness h (E remains unchanged, and the shock wave intensity is changed in a follow-up manner by changing the deionized water thickness to regulate the strengthening intensity) or the laser energy E (h remains unchanged, and the shock wave intensity is changed in a follow-up manner by changing the laser energy to regulate the strengthening intensity);

[0067] The relationship between the deionized water confinement layer thickness (h) and the shock wave intensity (P):

[0068] P = α·exp(-β·h)·E γ (2)

[0069] In the formula:

[0070] α: Comprehensive attenuation coefficient (unit: GPa·J -γ )(for example, select α = 3.2 GPa·J -γ , in actual applications, technicians need to calibrate more accurate coefficient values through experiments);

[0071] β: Thickness attenuation coefficient (unit: μm -1 ), reflecting the exponential attenuation of the shock wave intensity with the thickness of deionized water (for example, select β = 0.05 μm -1 , in actual applications, technicians need to calibrate more accurate coefficient values through experiments);

[0072] γ: Energy nonlinear gain coefficient (dimensionless), reflecting the nonlinear contribution of laser energy to the shock wave intensity (for example, select γ = 0.5, in actual applications, technicians need to calibrate more accurate coefficient values through experiments);

[0073] E: Laser energy (2 - 10 J).

[0074] α, β, and γ must be calibrated through experiments (such as orthogonal experimental design). The present invention does not limit the determination methods and processes of the above parameters, and technicians can select according to the actual working conditions.

[0075] Regulation of the thickness of the deionized water confinement layer: With the laser energy E fixed, the shock wave intensity is changed by adjusting the thickness of the deionized water confinement layer. When P target ≤α·E γ , the supply rate is adjusted through a flow controller to make the actual thickness (h real ) approach the target thickness (h target ):

[0076]

[0077] Regulation of laser energy: The output energy of the laser is modulated by a Q-switch (adjustment accuracy ±0.2 J). With the thickness h of the deionized water real fixed, the shock wave intensity is changed by adjusting the laser energy. When h real exceeds the adjustable range or it is inconvenient to achieve the regulation of the deionized water thickness, when E new ≤E max (the maximum energy of the laser), the laser energy is adjusted according to the following formula:

[0078]

[0079] If the set thickness of the deionized water is M, when the laser beam propagates to the surface of the material, it is in a zero defocus state. When the thickness of the deionized water increases, the laser beam approaches an increasing negative defocus with respect to the surface of the material; when the thickness of the deionized water decreases, the laser beam approaches an increasing positive defocus with respect to the surface of the material.

[0080] Taking the non-uniform intensity laser shock surface treatment of a certain aeroengine blade (nickel-based superalloy, yield strength σ y = 800 MPa) as an example, the blade body and the blade edge have significantly different thicknesses.

[0081] Technicians accurately measure the actual thicknesses at different positions in the area to be processed of the component to be processed, determine the surface strengthening intensity or effect at different positions according to the component thickness and strengthening requirements. In the determined strengthening process, different deionized water thicknesses are required for the leaf edge part and the leaf body part, and the deionized water thickness of the leaf edge part is significantly greater than the corresponding value of the leaf body part.

[0082] Leaf body thickness T 叶身 = 2 mm, leaf edge T 叶缘 = 1 mm.

[0083] Target strength model: P target = 1.5·T + 2.0 (unit: GPa, k = 1.5 GPa / mm), O0 = 1.5 GPa).

[0084] Leaf body target strength: P 叶身 = 1.5 × 2 + 2.0 = 5.0 GPa

[0085] Leaf edge target strength: P 叶缘 = 1.5 × 1 + 2.0 = 3.5 GPa

[0086] Calibration parameters: α = 3.2 GPa·J -γ , β = 0.05 μm -1 , γ = 0.5.

[0087] Build a laser shock surface strengthening device without an absorption layer. Select deionized water as the surface constraint layer of the material, and set the moving path of the laser beam on the area to be processed on the material surface according to requirements such as process simplicity.

[0088] Place a photosensitive element on the material surface to obtain the real-time change of the deionized water thickness on the material surface. Its basic working principle is that the change in the light refraction state directly reflects the change in the deionized water thickness.

[0089] Build a signal transmission system to transmit the information such as the deionized water thickness detected by the photosensitive element in real time; based on the change in the real-time deionized water thickness and the deionized water thickness that should be at different positions determined in step (1), measure and determine the deionized water thickness that should be adjusted, and the deionized water thickness is adjusted by means of flow control.

[0090] Leaf body treatment:

[0091] P 叶身 = 5.0 GPa.

[0092] Fix E = 6 J and calculate the target thickness:

[0093]

[0094] Adjust the deionized water flow rate through the PID flow controller to ensure the real-time thickness h real is stabilized at 18.4 ± 2 μm.

[0095] Leaf edge treatment:

[0096] P 叶缘 = 3.5 GPa.

[0097] Fix E = 6 J and calculate the target thickness:

[0098]

[0099] Adjust the deionized water flow rate through the PID flow controller to ensure the real-time thickness h real is stabilized at 35.2 ± 2 μm.

[0100] After the surface treatment of the area to be processed is completed according to the established beam movement path, the impact effect on the material surface is matched with the shape characteristics of the actual component.

[0101] Example 2:

[0102] In this example, a certain aeroengine blade is used as the processing object. The blade body and the leaf edge part have significantly different thicknesses. The method described in Example 1 is used for processing. The difference is that the laser shock surface strengthening device includes an absorption layer, and the absorption layer is 3M black tape with a thickness of 200 μm;

[0103] Blade body treatment:

[0104] P 叶身 = 5.0 GPa.

[0105] Fix the deionized water thickness h = 20 μm and calculate the target laser energy:

[0106]

[0107] Adjust the laser output to 7.8 J to ensure the energy adjustment accuracy of ±0.2 J.

[0108] Leaf edge treatment:

[0109] P 叶缘 = 3.5 GPa.

[0110] Fix the deionized water thickness h = 20 μm and calculate the target laser energy:

[0111]

[0112] Adjust the laser output to 3.2 J to verify that the energy does not exceed the equipment upper limit (assuming E max = 10 J).

[0113] After the surface treatment of the area to be processed is completed according to the established beam movement path, the impact effect on the material surface matches the shape characteristics of the actual component.

[0114] Comparative Example 1:

[0115] Taking the non-uniform strength laser shock surface treatment of a certain aero-engine blade as an example in Comparative Example 1, the blade body and the blade edge part have significantly different thicknesses.

[0116] Technicians accurately measure the actual thicknesses at different positions in the area to be processed of the component to be processed, and determine the surface strengthening intensity or effect at different positions according to the component thickness and strengthening requirements. In the determined strengthening process, different deionized water thicknesses are required for the blade edge part and the blade body part, and the deionized water thickness at the blade edge part is significantly greater than the corresponding value of the blade body part.

[0117] Build a laser shock surface strengthening device without an absorption layer, and select deionized water as the constraint layer on the material surface. Set the movement path of the laser beam on the area to be processed on the material surface according to requirements such as process setting simplicity.

[0118] Using a fixed deionized water flow rate and a fixed laser energy, after the surface treatment of the area to be processed is completed according to the established beam movement path, the impact effect on the material surface cannot match the shape characteristics of the actual component.

[0119] Comparative Example 2:

[0120] Taking the non-uniform strength laser shock surface treatment of a certain aero-engine blade as an example in Comparative Example 2, the blade body and the blade edge part have significantly different thicknesses.

[0121] Technicians accurately measure the actual thicknesses at different positions in the area to be processed of the component to be processed, and determine the surface strengthening intensity or effect at different positions according to the component thickness and strengthening requirements. In the determined strengthening process, different deionized water thicknesses are required for the blade edge part and the blade body part, and the deionized water thickness at the blade edge part is significantly greater than the corresponding value of the blade body part. The deionized water flow rate that can obtain the deionized water thickness used for different positions is preset in advance.

[0122] Build a laser shock surface strengthening device without an absorption layer, and select deionized water as the constraint layer on the material surface. Set the movement path of the laser beam on the area to be processed on the material surface according to requirements such as process setting simplicity.

[0123] Using the preset deionized water flow rates at different positions to be processed and a fixed laser energy, after the surface treatment of the area to be processed is completed according to the established beam movement path, the impact effect on the material surface cannot match the shape characteristics of the actual component, but the degree of non-matching is lower than that in Comparative Example 1.

[0124] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without creative efforts within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A follow-up regulation method for the unequal strength laser shock peening intensity of a liquid constraint layer, characterized in that The steps are as follows: (1) Construct a thickness-strength mapping model. By detecting the thickness change of thin-walled parts, determine the requirements of the shape-property collaborative surface strengthening process adapted to the actual component shape characteristics, and inversely deduce the surface strengthening index of the laser shock wave intensity required at different positions on the surface of the part to be machined; (2) Build a constrained laser shock surface strengthening device and set the moving path of the laser beam in the area to be machined; (3) Treat the surface of the material to be machined and place a photosensitive element on the material surface; (4) Real-time test the state changes at different positions to be machined, and adjust the constrained laser shock surface strengthening device until the machining is completed.

2. The follow-up control method for the unequal-strength laser shock strengthening intensity facing the liquid constraint layer according to claim 1, characterized in that, In step (1), the thickness-strength mapping model is: Determine the target shock wave intensity P at each position according to the component thickness distribution T(x, y) and the strengthening requirements target : P target (x,y) = k·T(x,y) + P0 (1) where k is the strength gradient coefficient and P0 is the base strength.

3. The follow-up regulation method for non-uniform intensity laser shock strengthening intensity facing the liquid constraint layer according to claim 2, wherein In step (2), the laser shock surface strengthening device includes a deionized water constraint layer and an absorption layer. The absorption layer is set as required. For the working conditions where ablation damage on the material surface is unacceptable or the substrate reflectivity > 30%, an absorption layer is set; for the working conditions where the surface quality requirements of the material are not high or the substrate reflectivity < 30%, the absorption layer is abandoned.

4. The follow-up control method for the unequal-strength laser shock strengthening intensity facing the liquid confinement layer according to claim 3, characterized in that The back-calculation accuracy of the thickness of the deionized water constraint layer is not less than ±1 μm.

5. The follow-up control method for the unequal strength laser shock strengthening intensity facing the liquid constraint layer according to claim 4, characterized in that In step (3), the photosensitive element is an optical fiber sensor, which is used to monitor the refractive index change of the deionized water constraint layer in real time, and then obtain the thickness of the deionized water constraint layer.

6. The follow-up control method for the unequal strength laser shock strengthening intensity facing the liquid constraint layer according to claim 5, characterized in that In step (4), the adjustment strategy of the constrained laser shock surface strengthening device includes the thickness control of the deionized water constraint layer and the laser energy control; Based on the relationship between the thickness of the deionized water confinement layer and the shock wave intensity, under the shock wave intensity limit given in step (1), it is required that P(x, y) = P at the laser shock position (x, y). target (x, y), calculate the thickness h of the deionized water confinement layer or the laser energy E; The relationship between the thickness of the deionized water constraint layer and the shock wave intensity: P = α·exp(-β·h)·E γ (2) In the formula: α: Comprehensive attenuation coefficient; β: Thickness attenuation coefficient, reflecting the exponential attenuation of the shock wave intensity by the deionized water thickness; γ: Energy nonlinear gain coefficient, reflecting the nonlinear contribution of the laser energy to the shock wave intensity; E: Laser energy.

7. The follow-up control method for the unequal-strength laser shock strengthening intensity facing the liquid constraint layer according to claim 6, characterized in that In step (4), the thickness control of the deionized water confinement layer: with the laser energy E fixed, the shock wave intensity is changed by adjusting the thickness of the deionized water confinement layer. When P target ≤α·E γ is satisfied, the actual thickness is made to approach the target thickness:

8. The follow-up control method for the unequal-strength laser shock strengthening intensity facing the liquid confinement layer according to claim 7, characterized in that, In step (4), laser energy regulation: the thickness h of deionized water real is fixed, and the shock wave intensity is changed by adjusting the laser energy. When h real exceeds the adjustable range or it is inconvenient to achieve the regulation of the thickness of deionized water, in the case of E new ≤ E max , the laser energy is adjusted according to the following formula:

9. The follow-up control method for the unequal strength laser shock strengthening intensity facing the liquid constraint layer according to claim 8, characterized in that, In step (4), if the deionized water thickness is set to M, when the laser beam propagates to the material surface, it is in a zero defocus state. When the deionized water thickness increases, the laser beam approaches an increasing negative defocus amount relative to the material surface; when the deionized water thickness decreases, the laser beam approaches an increasing positive defocus amount relative to the material surface.

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