阅读说明：本技术 一种基于变化离焦量的不等强度激光冲击加工方法 (Variable-defocusing-amount-based unequal-strength laser shock processing method ) 是由 卢国鑫 于 2021-08-11 设计创作，主要内容包括：本发明公开一种基于变化离焦量的不等强度激光冲击加工方法,包括将待加工构件根据厚度划分为不敏感区域和敏感区域；根据不敏感区域的目标强化效果确定所需的脉冲激光参数；根据敏感区域最小厚度位置的目标强化效果和所述脉冲激光参数确定所需的激光离焦量；根据不敏感区域的厚度、敏感区域厚度以及敏感区域最小厚度位置确定的激光离焦量,得到待加工构件任一厚度位置的激光离焦量；根据待加工构件任一厚度位置的激光离焦量对待加工构件进行不同厚度位置的不等强度激光冲击加工处理。采用非单一离焦量的脉冲激光加工方式,针对待加工构件具有不同截面厚度的部位设定不同的激光光束离焦量,使待加工构件不同部位获得不同强度的激光冲击作用效果。(The invention discloses an unequal strength laser shock processing method based on variable defocusing amount, which comprises the steps of dividing a member to be processed into an insensitive area and a sensitive area according to the thickness; determining required pulse laser parameters according to the target strengthening effect of the insensitive region; determining the required laser defocusing amount according to the target strengthening effect of the minimum thickness position of the sensitive area and the pulse laser parameters; obtaining the laser defocusing amount of any thickness position of the member to be processed according to the thickness of the insensitive region, the thickness of the sensitive region and the laser defocusing amount determined by the minimum thickness position of the sensitive region; and carrying out unequal-strength laser shock processing on the member to be processed at different thickness positions according to the defocusing amount of the laser at any thickness position of the member to be processed. The pulse laser processing mode with non-single defocusing amount is adopted, different defocusing amounts of laser beams are set for parts of the to-be-processed member with different section thicknesses, and different parts of the to-be-processed member obtain laser impact effects with different intensities.)

1. A variable-defocus-amount-based unequal-intensity laser shock processing method is characterized by comprising the following steps:

dividing a component to be processed into an insensitive area and a sensitive area according to the thickness;

determining required pulse laser parameters according to the target strengthening effect of the insensitive region;

determining the defocusing amount of laser required by the sensitive area according to the target strengthening effect of the minimum thickness position of the sensitive area and the pulse laser parameters;

obtaining the laser defocusing amount of any thickness position of the member to be processed according to the thickness of the insensitive region, the thickness of the sensitive region and the laser defocusing amount determined by the minimum thickness position of the sensitive region;

and carrying out unequal-strength laser shock processing on the member to be processed at different thickness positions according to the defocusing amount of the laser at any thickness position of the member to be processed.

2. The unequal-strength laser shock processing method based on the varying defocus amount according to claim 1, wherein the required pulsed laser parameters are determined according to the target strengthening effect of the insensitive region, and comprise: laser energy and pulse width of the vertical incidence pulse laser.

3. The variable defocus-based variable intensity laser shock processing method as claimed in claim 1, wherein the target enhancement effect refers to the residual stress field intensity, including the surface residual stress magnitude and the residual stress distribution depth.

4. The variable defocus-based variable intensity laser shock processing method as claimed in claim 1, wherein the laser defocus of the pulse laser beam corresponding to the specific cross-sectional thickness position of the member to be processed is determined by a linear interpolation method.

5. The variable defocus-based laser shock processing method with unequal intensity as claimed in claim 1, wherein the defocus of the laser at any thickness position of the member to be processed isWherein, X_maxCritical thickness of the insensitive region, X_minThe minimum thickness of the sensitive area is defined, A is the thickness of any thickness position, and n is the laser defocusing amount determined by the minimum thickness position of the sensitive area.

6. The unequal-strength laser shock processing method based on the variable defocus amount according to claim 1, wherein during the unequal-strength laser shock processing, the spot overlapping rate of the laser beam irradiation area is determined, and the unequal-strength laser shock processing is performed according to the laser defocus amount and the spot overlapping rate of any thickness position of the member to be processed.

7. The variable defocus-based variable intensity laser shock processing method as claimed in claim 6, wherein the spot overlap ratio is a ratio of a length of a connecting line of intersection points of adjacent circular spots to an average value of diameters of the adjacent circular spots.

8. The unequal-intensity laser shock processing method based on the variable defocus amount according to claim 1, wherein the laser defocus amount is changed by adjusting a relative distance between any thickness position of the member to be processed and the laser emitting device during the unequal-intensity laser shock processing.

9. The variable defocus-based variable intensity laser shock processing method as claimed in claim 1, wherein the member to be processed is divided into an insensitive region and a sensitive region according to the thickness, a critical thickness is set, and the region with the thickness greater than or equal to the critical thickness is the insensitive region, otherwise, the sensitive region is set.

10. The variable defocus-based unequal intensity laser shock processing method of claim 1, wherein the laser defocus is a positive defocus value or a negative defocus value.

Technical Field

The invention relates to the technical field of laser shock, in particular to an unequal strength laser shock processing method based on variable defocusing amount.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

Parts in the key fields of aeroengine blades and the like have the harsh service requirements of long service life and high reliability, and the fatigue life of materials is prolonged by introducing residual compressive stress or changing the microstructure state by different surface strengthening technologies. Compared with the traditional mechanical shot peening method, the laser shock method has the technical advantages of cleanness, no pollution and capability of introducing residual compressive stress field distribution with larger depth in the material, and becomes a preferred method for surface strengthening of parts such as blades and the like.

The blade member has a shape characteristic that the thickness distribution of the cross section is uneven, the wall of the middle part is thick, and the wall of the edge is thin. If the conventional laser impact process method is adopted to carry out strengthening treatment on the variable cross-section thickness part, the probability of macroscopic deformation of the edge part of the material is increased. At present, researchers have proposed specific methods for realizing unequal strength processing and 'shape-property' coordinated regulation and control of variable cross-section thickness type components by changing the thickness of an absorption layer, changing laser parameters, changing the incident angle of a light beam and the like. However, the above solutions all achieve the goal of unequal strength reinforcement by changing the laser beam conditions and applying additional coating materials, and how to achieve unequal strength surface reinforcement of a variable cross-section thickness member without changing the beam conditions and without additional coating materials is a problem to be solved by the skilled person.

Disclosure of Invention

In order to solve the problems, the invention provides an unequal-strength laser shock processing method based on variable defocusing amount, which adopts a pulse laser processing mode with non-single defocusing amount, sets different defocusing amounts of laser beams aiming at parts of a member to be processed with different section thicknesses, and enables different parts of the member to be processed to obtain laser shock effect effects with different strengths.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a varying defocus-based unequal intensity laser shock processing method, including:

dividing a component to be processed into an insensitive area and a sensitive area according to the thickness;

determining required pulse laser parameters according to the target strengthening effect of the insensitive region;

determining the laser defocusing amount required by the minimum thickness position of the sensitive area according to the target strengthening effect of the sensitive area and the pulse laser parameters;

obtaining the laser defocusing amount of any thickness position of the member to be processed according to the thickness of the insensitive region, the thickness of the sensitive region and the laser defocusing amount determined by the minimum thickness position of the sensitive region;

and carrying out unequal-strength laser shock processing on the member to be processed at different thickness positions according to the defocusing amount of the laser at any thickness position of the member to be processed.

As an alternative embodiment, the required pulsed laser parameters are determined according to the target enhancement effect of the insensitive region, and the required pulsed laser parameters include: laser energy and pulse width of the vertical incidence pulse laser.

As an alternative embodiment, the target strengthening effect refers to the residual stress field strength, and the main indicators include the surface residual stress magnitude and the residual stress distribution depth.

As an alternative embodiment, the laser defocusing amount of the pulse laser beam corresponding to the specific section thickness position of the component to be processed is determined by a linear interpolation method.

As an alternative embodiment, the defocusing amount of the laser at any thickness position of the member to be processed is as follows:

wherein, X_maxCritical thickness of the insensitive region, X_minIs the minimum thickness of the sensitive area, A is the thickness of any thickness position, and n is the minimum thickness of the edge section of the component in the determined sensitive area (namely X)_min) The laser defocusing amount of the thin-wall region.

It should be noted that any thickness described in the present invention refers to the thickness of any position of the region where defocus selection is required, that is, only refers to the thickness of any position of the sensitive region where laser surface treatment with variable intensity is required.

As an alternative embodiment, during the unequal intensity laser shock processing, the spot overlapping rate of the laser beam irradiation area is determined, and the unequal intensity laser shock processing is performed according to the laser defocusing amount and the spot overlapping rate of any thickness position of the member to be processed.

In an alternative embodiment, the spot overlap ratio is the ratio of the length of the connecting line of the intersection points of the adjacent circular spots to the average value of the diameters of the adjacent circular spots.

As an alternative embodiment, when the laser shock processing is carried out with unequal intensity, the defocusing amount of the laser is changed by adjusting the relative distance between any thickness position of the component to be processed and the laser emitting device.

As an alternative embodiment, the component to be processed is divided into a non-sensitive area and a sensitive area according to the thickness, a critical thickness is set, and the area with the thickness greater than or equal to the critical thickness is the non-sensitive area, and is the sensitive area otherwise.

In the present invention, the critical thickness is a thickness insensitive region which becomes a laser shock when the cross-sectional thickness of the member to be processed exceeds the thickness value, that is, the minimum thickness of the insensitive region.

As an alternative embodiment, the laser defocus amount is a positive defocus amount or a negative defocus amount.

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

the method determines the physical condition of the beam irradiation area by the defocusing amount of the laser beam, adopts a pulse laser processing mode of non-single defocusing amount, changes the defocusing amount of the laser at different positions of the variable cross-section thickness member by adjusting the relative distance between the variable cross-section thickness member and a laser emitting device in real time to obtain different laser energy densities, and obtains the processing effect matched with the thickness of the variable cross-section thickness member at different positions on the surface under the action of different shock wave pressures.

According to the method, different laser beam defocusing amounts are set for different cross-section thickness parts of the variable cross-section thickness component, so that different cross-section thickness areas obtain laser impact effects with different intensities, the different cross-section thickness areas obtain residual stress distribution characteristics matched with the shape size and the mechanical property, and the macroscopic deformation of the thin-wall part of the variable cross-section thickness component caused by the same laser beam defocusing amount is avoided, and the size control of the component to be processed is influenced.

Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is a schematic view of an exemplary component having varying cross-sectional characteristics with different regions having different thickness profiles;

FIG. 2 is a schematic representation of a shape feature of an aircraft engine blade component; wherein, 1 is the edge part of the blade; 2 is the middle part of the blade;

FIG. 3 is a schematic illustration of a prior art laser shock method for a variable cross-sectional thickness component; wherein 3 is a pulse laser beam with the same defocusing amount; 4, a variable cross-section thickness component to be processed;

FIG. 4 is a schematic diagram of the relative positions of the laser beam and the surface of the member to be processed under the positive and negative defocusing conditions provided in embodiment 1 of the present invention;

FIG. 5 is a schematic view of the processing method of laser shock with different intensities provided in example 1 of the present invention; wherein, 5 is laser beams in different defocusing states irradiated on different positions of the surface of the member to be processed; 6 is a member to be processed with the characteristic of variable section thickness; 7 is the irradiation area of the laser beam with larger positive defocusing amount at the thin-wall part; 8 is an irradiation area of the laser beam with smaller positive defocusing amount at the relatively thicker section part;

fig. 6 shows the surface strengthening effect of the pulsed laser with the laser beam in the varying defocused state in the areas with different cross-sectional thicknesses provided in embodiment 1 of the present invention; wherein 11 is the residual stress field distribution of the thin-wall region; 12 is the residual stress field distribution of the thick-wall region;

fig. 7 shows the surface strengthening effect of the pulse laser with non-defocused laser beams in the areas with different cross-sectional thicknesses provided in embodiment 1 of the present invention; wherein 9 is the residual stress field distribution and the generated macroscopic deformation of the thin-wall region; the residual stress field distribution of the thick-walled region is 10.

The specific implementation mode is as follows:

the invention is further described with reference to the following figures and examples.

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, and it should be understood that the terms "comprises" and "comprising", and any variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

The embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

Example 1

During laser shock processing, the size of the shock wave applied to the surface of the material is directly determined by the energy density of the laser beam. The laser energy density is the laser energy received by the surface of the material in unit time and unit area, and when the irradiation area of the laser beam changes, the laser energy density inevitably changes correspondingly. The laser beam adopted by the laser impact surface treatment belongs to a converged beam, namely the irradiation area of the focusing position of the laser beam represents the minimum spot size, and the larger the distance deviating from the focal point of the beam, the larger the irradiation area of the laser beam.

Fig. 1-2 show a typical component with variable cross-section characteristics, an aeroengine blade component, having different regions with different thickness distributions, wherein the blade edge portion 1 generally has a smaller thickness and is required to have a relatively lower machining strength during laser impact, and the blade middle portion 2 generally has a larger thickness and is required to have a relatively higher machining strength during laser impact; in the prior art, when the laser shock treatment is carried out on the variable cross-section shape component, the surface of the component to be processed is acted by the pulse laser beam with the same defocusing amount, and the pulse laser beam 3 with the same defocusing amount is applied to the variable cross-section thickness component 4 to be processed as shown in fig. 3.

The embodiment provides a variable-defocusing-amount-based unequal-strength laser shock processing method aiming at a variable-section-thickness component with the maximum thickness difference value of different parts not less than 3mm, and adopts a pulse laser processing mode with non-single defocusing amount to set different defocusing amounts of laser beams aiming at the parts of the component to be processed with different section thicknesses, so that different parts of the component to be processed obtain different-strength laser shock effect effects; the method comprises the following specific steps:

dividing a component to be processed into an insensitive area and a sensitive area according to the thickness;

determining required pulse laser parameters according to the target strengthening effect of the insensitive region;

determining the laser defocusing amount required by the minimum thickness position of the sensitive area according to the target strengthening effect of the sensitive area and the pulse laser parameters;

obtaining the laser defocusing amount of any thickness position of the member to be processed according to the thickness of the insensitive region, the thickness of the sensitive region and the laser defocusing amount determined by the minimum thickness position of the sensitive region;

and carrying out unequal-strength laser shock processing on the member to be processed at different thickness positions according to the defocusing amount of the laser at any thickness position of the member to be processed.

Specifically, the physical condition of the irradiation area of the laser beam is determined by the defocusing amount of the laser beam, the defocusing amount of the laser beam is changed by adjusting the relative distance between the variable cross-section thickness component and the laser emitting device in real time, different laser energy densities are obtained by changing the defocusing amount of the laser beam at different positions of the variable cross-section thickness component, and then under the action of different shock wave pressures, different positions of the surface of the material obtain the processing effect matched with the thickness of the material. The method is specifically divided into the following steps:

s1: determining a thickness insensitive area of the member to be processed to laser impact according to the thickness;

the thickness insensitive region of the laser impact refers to: and the laser shock wave penetration phenomenon does not occur in the laser shock process, and the laser shock processing device has a region with relatively consistent distribution state of the residual compressive stress field.

In the embodiment, the critical thickness is set, and the area with the thickness greater than or equal to the critical thickness is a thickness insensitive area, otherwise, the area is a thickness sensitive area; in the embodiment, the areas of the to-be-processed component with the thickness of more than or equal to 3mm are all the thickness insensitive areas impacted by the laser.

It should be noted that in order to more accurately represent the extent of the thickness insensitive region, a skilled person can accurately quantify the specific thickness of the laser shock insensitive region by comparing the laser shock effects of different thicknesses of the component to be machined.

S2: determining a target strengthening effect of a laser impact thickness insensitive region and pulse laser parameters required for realizing the effect;

the step requires determining a target strengthening effect of a thicker region of the variable cross-section thickness member, and determining a required laser shock treatment process according to the target strengthening effect to obtain pulse laser parameters required for realizing the target strengthening effect.

Preferably, the desired pulsed laser parameters refer to laser energy, pulse width, etc. of the normally incident pulsed laser that can achieve the targeted enhancement effect.

The pulsed laser is used for surface treatment of the material without defocusing of the laser beam and the surface of the material, that is, the focal position of the pulsed laser is located on the surface of the material to be treated.

S3: determining the minimum thickness part (thickness X) in the sensitive area of the member to be processed_min) The target strengthening effect and the positive defocus amount value of the pulse laser required for realizing the effect;

this step requires determining the target reinforcement effect of the thinnest zone of the variable section thickness member; the thinnest area of the variable cross-section thickness component is generally located at the edge of the component, and the area generally has a small target reinforcing effect of a relatively thick area in order to keep the shape and the size of the edge thin wall and mechanical properties coordinated.

It should be noted that the target strengthening effect mainly refers to the residual stress field strength, etc., including the magnitude of the surface residual stress, the depth of the residual stress distribution, etc.

This step also requires determining the positive defocus amount value required to achieve the target enhancement effect; because the target strengthening effect of the edge thin-wall area of the variable cross-section component is lower than that of the thickness insensitive area, the thickness sensitive area opposite to the thickness insensitive area weakens the actual laser impact strength born by the variable cross-section component to different degrees by changing the positive defocusing amount of the laser beam relative to the material surface.

In the present embodiment, the positive defocus value required for the edge thin-wall region to achieve the target enhancement effect is determined to be nmm.

It should be noted that, in the present embodiment, the maximum shock wave intensity induced by the pulsed laser is received by the material surface under the condition that the laser beam and the material surface are not out of focus by default; when the laser beam is out of focus with the surface of the material, the intensity of the laser shock wave received by the surface of the material is reduced.

It should be noted that, in the present embodiment, the impact effect reduction corresponding to the positive defocus amount variation is used as a basic principle to realize the laser impact surface processing of different intensities of the material, but a skilled person may also select the impact effect reduction corresponding to the negative defocus amount variation as the basic principle to realize the laser impact surface processing of different intensities of the material according to specific processing conditions, as shown in fig. 4, the laser beam and the material surface are in a relative position schematic diagram under the positive and negative defocus conditions.

S4: determining the overlapping rate of light spots impacted by laser, and calculating the positive defocusing amount of the laser required by any thickness position of the variable cross-section component;

this step requires that the specific thickness of the laser shock insensitive region has been determined to be 3mm, or that the skilled person has determined the structure to be machined by experimental meansThe specific thickness of the laser shock insensitive region of the part is X_maxmm; taking the specific thickness of the insensitive area of the determined member to be processed as X_maxmm, minimum thickness X in sensitive area_minmm, the positive defocus value of any position with the thickness of A of the variable cross-section component is

S5: carrying out laser shock treatment on the variable cross-section thickness component needing unequal strength laser shock treatment by adopting the laser defocusing amount and the light spot lap ratio of any thickness position of the component to be processed;

the clamping of the member to be processed and the coating of the material of the absorption layer and the constraint layer are already completed by default before the step is carried out; as shown in fig. 5, the laser shock processing is performed on the parts with different thicknesses of the member to be processed by using the pulse laser beams with different positive defocusing amounts, and the parts with different thicknesses of the member to be processed have different laser irradiation areas in the pulse laser shock process in different defocusing states.

In this embodiment, the overlap ratio of the laser spots at different positions of the variable cross-section thickness member is determined by the skilled person from practical machining experience, on the principle that the spots of the same or different sizes overlap such that the material surface is completely covered by the impact area. In this embodiment, the ratio of the length of the connection line of the intersection points of adjacent circular spots to the average value of the diameters of adjacent circular spots is defined as the spot overlapping ratio of the laser beam irradiation area.

The embodiment takes the processing of an aircraft engine blade component as an example, and describes the implementation process of the unequal-intensity laser shock processing method of the variable cross-section thickness component based on the variable defocusing amount.

(1) Based on actual processing experience, the regions of the to-be-processed member with the thickness larger than 3mm are determined to be insensitive regions of laser impact thickness, and when the thickness of the to-be-processed material is considered to be more than 3mm, the penetrating phenomenon of pulse laser shock waves can not occur, and meanwhile, the whole deformation of the to-be-processed material can not be caused.

(2) According to a processing target of a region with the section thickness of a member to be processed being more than 3mm and needing to introduce 0.6mm residual stress depth distribution, determining parameters of a vertically incident defocusing-free laser beam selected by a pulse laser strengthening process as follows: laser energy 4J, pulse width 18ns, beam diameter 1.2 mm.

(3) According to a processing target needing to introduce 0.2mm residual stress depth distribution in an area with the section thickness of a member to be processed being about 1mm, through a comparison test of a plurality of groups of variable positive defocusing amount numerical values, the parameters of the laser beam selected by the pulse laser strengthening process are determined as follows: when the laser energy is 4J, the pulse width is 18ns, and the beam diameter is 1.2mm, the positive defocusing amount value of the laser beam is 1.8mm (relative to the positive defocusing amount value of 0 under the condition that the laser beam is not defocused).

(4) The method determines the positive defocusing amount value of the corresponding pulse laser beam at the specific section thickness part through a linear interpolation relation;

for example, when the thickness of the edge cross section is 1mm and the corresponding positive defocus amount of the pulse laser is 1.8mm, the thickness of the middle cross section is 3mm and the corresponding positive defocus amount of the pulse laser is 0, the portion with the cross section thickness of 2mm in the two position interval can be determined to have the corresponding positive defocus amount of the pulse laser of about 0.9 mm.

(5) Determining that the overlapping rate of light spots of laser beams with the same size is 30%, the overlapping rate of light spots of laser beams with different sizes is 40%, and defining the ratio of the length of the connecting line of the intersection points of adjacent circular light spots to the average value of the diameters of the adjacent circular light spots as the overlapping rate of the light spots of the laser beam irradiation area;

the determined positive defocusing amount of the corresponding laser beams at different parts is adopted to perform laser shock treatment on the variable cross-section thickness component needing unequal-intensity laser shock treatment, unequal-intensity laser shock surface treatment of the variable cross-section characteristic component to be processed based on the variable radiation area in the variable defocusing state is completed, and the residual stress distribution characteristics of the variable cross-section thickness area matched with the shape size and the mechanical property shown in figure 6 are obtained in the different cross-section thickness areas.

In addition, if the laser defocusing state is uniformly set to be the non-defocusing state in the process of processing the variable-section-thickness component by adopting the laser shock in the non-fixed defocusing state, the component to be processed can easily form the surface processing effect as shown in fig. 7, namely, the thin-wall part of the edge of the component to be processed bears the same laser shock pressure as the thicker section area, the macroscopic deformation of the thin-wall part is caused, and the dimensional control of the component to be processed is influenced.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.