WO2019062427A1

WO2019062427A1 - Method with variable pulse width and controllable residual stress for laser shock peening of blades

Info

Publication number: WO2019062427A1
Application number: PCT/CN2018/102597
Authority: WO
Inventors: 张永康; 张峥
Original assignee: 广东工业大学
Priority date: 2017-09-30
Filing date: 2018-08-28
Publication date: 2019-04-04
Also published as: CN107858500B; CN107858500A

Abstract

A method with variable pulse width and controllable residual stress for laser shock peening of blades. The pulse width of a nanosecond pulse laser is set according to the structural features of a blade, so as to control the penetration depth of an induced shock wave in the blade, thereby controlling the distribution depth of a generated residual stress, and finally realizing consistent matching of residual stress distributions and structural features in different regions of the blade, thereby both strengthening and preserving the shape of the blade. The method achieves full thickness residual compressive stress distribution of blade edges (air intake and exhaust edges), eliminates blade root stress concentration without macroscopic deformation, and is suitable for performing laser shock peening processing on aviation turbofan engine fans and various grades of titanium alloy compressor blades.

Description

Blade laser shot peening method for variable pulse width controllable residual stress

Technical field

The invention relates to the field of laser shot peening surface strengthening technology, in particular to a blade laser shot peening method with variable pulse width controllable residual stress.

Background technique

Laser Shock Peening (LSP) is an efficient surface strengthening technology that uses the mechanical effects of laser shock waves to form high amplitude residual compressive stress and microstructure changes on the surface of metal materials, and suppresses crack initiation by introducing residual pressure. And expansion to increase the fatigue strength and life of the component, which has been widely used in the blade manufacturing process of American aircraft engines.

Aeroengine fans or compressor blades have large spans and thin walls (lengths of 20 to 800 mm, wall thickness of 0.5 to 2 mm), and have complex curved shapes and varying cross sections, which are typical weak rigid thin walls. member. In the laser shot peening, the introduction of high amplitude residual stress faces the following common basic problems: the residual compressive stress field and the blade dimensional stability problem caused by shot peening and the consistency effect of the strengthening effect of the variable cross-sectional structure thickness.

In order to solve the above problems, the Chinese patent CN105002349A "a method of uniformly polarizing a multi-layered interlaced laser beam to uniformly strengthen the blade" uses an adjacent spot to be in close contact with each other to perform inter-layer interlaced impact of multiple variable spots, the first of which The large spot is mainly used for laser impact to produce a deep residual stress layer, while the second and third layer staggered impact is used to eliminate the spot boundary effect and reduce the roughness of the machined surface. However, this method only changes the spot size and the overlap ratio, and does not regulate the laser energy and pulse width that affect the residual stress distribution characteristics. Therefore, the method can only uniformize the stress distribution of the laser shot peening within a specific layer depth range, and cannot guarantee Shape accuracy.

Chinese patent CN103205545 A "A laser shock treatment engine blade combination method and device" adjusts the distance between the focusing mirror and the blade to adjust the spot size, realizes power density adjustment, and makes the residual compressive stress and untreated area of the blade edge surface smooth. transition. The method essentially changes the power density of laser peening, so it can only regulate the generation of residual stress amplitude, can not control the depth of stress distribution, and can not control the shape accuracy, and the power density has a constraint relationship with the spot size, and is adopted for thin-walled blades. Large spots can cause spot boundary effects, affecting dimensional accuracy and surface quality.

Chinese patent CN104862468 A "Method for improving the life of turbine blades based on laser double-sided impact technology" uses gradient lap joint to impact the root of the blade to make the distribution of residual stress field tend to be gentle, using laser double-sided impact to avoid single-sided laser shock The deformation and destruction of the blade, while the impact makes the force on both sides of the blade the same. However, this method only optimizes the lap ratio parameters. In essence, the laser energy and pulse width parameters that affect the residual stress characteristics are not set. Therefore, it is difficult to precisely control the amplitude and depth of stress distribution, and there is no blade strengthening and protection. Shape process requirements.

Therefore, it is extremely important to match the consistency of the residual stress field and structural characteristics of the laser shot peening during the laser shot peening process and to solve the technical problems of dimensional precision control and residual stress characteristic control.

technical problem

The main object of the present invention is to propose a blade laser shot peening method with variable pulse width controllable residual stress, aiming at improving the consistency matching of the residual stress field and structural characteristics of the laser shot peening of the blade, and solving the dimensional precision control and residual stress characteristics. Technical issues of control.

Technical solution

In order to achieve the above object, the present invention provides a blade laser shot peening method with variable pulse width controllable residual stress, which sets a nanosecond pulse laser pulse width based on the blade structure characteristics to control the penetration of the induced shock wave in the blade. The depth, in turn, controls the distribution depth of the generated residual stresses, and the residual stress distribution in different regions of the blade is matched with the structural features.

Preferably, the blade laser shot peening method for variable pulse width controllable residual stress of the present invention comprises the following steps:

S1: short pulse width is set according to the thickness of the leaf edge and the rigidity is weak, and the full thickness compressive stress distribution is realized by the shallow depth residual compressive stress layer and the multi-layer shot peening superposition;

S2: the thickness of the transition zone from the leaf edge to the blade body is gradually increased, the variable pulse width is proportional to the thickness of the section, and the number of shots is reduced, and the stress of the treated area to the untreated area is smoothly transitioned;

S3: Short-pulse laser peening parameters are set at the root of the blade, and the multi-layer shot peening of the shallow residual compressive stress is used to eliminate stress concentration and avoid macroscopic torsional deformation of the blade.

Preferably, the laser pulse width, the penetration depth of the induced shock wave in the blade, and the distribution depth of the generated residual stress are positively correlated.

Preferably, short pulse laser shot peening is used to produce a shallower residual compressive stress distribution while maintaining a structural shape that does not change.

Preferably, a deeper stress distribution is achieved by superimposing the residual compressive stress by multilayer shot peening.

The technical scheme of the present invention controls the penetration depth of the induced shock wave in the blade by setting the pulse width of the nanosecond pulse laser based on the blade structure characteristics, thereby controlling the distribution depth of the generated residual stress, and finally realizing the residual stress distribution of different regions of the blade and Consistent matching of structural features to achieve the dual purpose of strengthening and conformal.

Beneficial effect

The invention can realize the residual compressive stress distribution of the full thickness of the leaf edge (inlet and exhaust side), eliminate the stress concentration of the blade root without macroscopic deformation, and is suitable for the laser shot peening treatment of the fan of the aviation turbofan engine and the titanium alloy blade of each compressor. .

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and those skilled in the art can obtain other drawings according to the structures shown in the drawings without any creative work.

1 is a characteristic diagram of a shock wave induced by a 16 ns pulse width according to an embodiment of the present invention;

2 is a diagram showing a shock wave characteristic induced by a pulse width of 8 ns according to an embodiment of the present invention;

3 is a view showing a laser peening area of a blade according to an embodiment of the present invention;

4 is a schematic view of short pulse laser peening at the edge of the embodiment of the present invention;

Figure 5 is a schematic view showing the blasting of the leaf edge to the blade body transition zone according to an embodiment of the present invention;

Figure 6 is a schematic view of a blade root laser peening according to an embodiment of the present invention.

Description of the reference numerals:

1:16ns pulse width induced shock wave;

2:8 ns pulse width induced shock wave;

3: test piece;

4: Induced shock wave:

5: blade;

6: intake side;

7: exhaust side;

8: Ye Gen;

9: blade cross section;

10: thick residual residual stress distribution;

11: the transition zone of the leaf body;

12: Rounded corners.

The implementation, functional features, and advantages of the present invention will be further described in conjunction with the embodiments.

Embodiments of the invention

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

It should be noted that if there is a directional indication (such as up, down, left, right, front, back, ...) in the embodiment of the present invention, the directional indication is only used to explain in a certain posture (as shown in the drawing) The relative positional relationship between the components, the motion situation, and the like, if the specific posture changes, the directional indication also changes accordingly.

In addition, if there is a description relating to "first", "second", etc. in the embodiments of the present invention, the description of the "first", "second", etc. is used for descriptive purposes only, and is not to be construed as an Its relative importance or implicit indication of the number of technical features indicated. Thus, features defining "first" and "second" may include at least one of the features, either explicitly or implicitly. In addition, the technical solutions between the various embodiments may be combined with each other, but must be based on the realization of those skilled in the art, and when the combination of the technical solutions is contradictory or impossible to implement, it should be considered that the combination of the technical solutions does not exist. It is also within the scope of protection required by the present invention.

The invention provides a blade laser shot peening method with variable pulse width controllable residual stress. The method sets the nanosecond pulse laser pulse width based on the blade structure characteristics, controls the penetration depth of the induced shock wave in the blade, and then controls the generation. The distribution depth of the residual stress is such that the residual stress distribution in different regions of the blade is matched with the structural features.

Specifically, the blade laser shot peening method for variable pulse width controllable residual stress of the present invention comprises the following steps:

Example

The selection of the power density of the nanosecond pulse laser peening is related to the material to be processed and the processing area. The blade of the embodiment of the invention is a titanium alloy blade of material TC4 or TC17, and the power density of the laser peening is selected to be 5-7 GW/cm ² , according to the laser power density formula I=E/(S×t), where E is a laser single Pulse energy, S is the spot area, and t is the laser pulse width. The laser single pulse energy E affects the amplitude of the residual stress, and the laser pulse width t affects the distribution depth of the residual stress.

The working principle of the blade laser peening method for variable pulse width controllable residual stress in the technical solution of the present invention is that the laser pulse width, the penetration depth of the induced shock wave in the blade, and the distribution depth of the residual stress are positively correlated. The short-pulse laser shot peening is used to produce a shallower residual compressive stress distribution while maintaining the shape of the structure. The residual stress is superimposed by multi-layer shot peening to achieve a deeper stress distribution.

In Fig. 1, when the input laser pulse width is 16 ns, the penetration depth of the shock wave 1 induced by the 16 ns pulse width in the thickness direction of the test piece 3 is as shown in Fig. 1. In Fig. 2, when the input laser pulse width is 8 ns, the penetration depth of the shock wave 2 induced by the 8 ns pulse width in the thickness direction of the test piece 3 is as shown in Fig. 2. Obviously, in the thickness direction of the test piece 3, the penetration depth of the long pulse width when the input laser pulse width is 16 ns is deeper than the short pulse width when the input laser pulse width is 8 ns.

The technical scheme of the invention sets the pulse width of the nanosecond pulse laser according to the blade structure characteristics, controls the distribution depth of the production residual stress, and finally achieves the consistency matching of the residual stress distribution and the structural features in different regions of the blade 5, and achieves the reinforcement and conformality. The dual purpose. As shown in FIG. 3, the area where the blade 5 needs to be processed includes the intake edge 6, the exhaust side 7, and the blade root 8 at the transition of the blade face and the gutter. The residual stress is achieved by setting a variable pulse width in different thickness regions. The structural features are matched.

Specifically, the steps of the blade laser shot peening method for varying the pulse width controllable residual stress of the present invention include:

Referring to FIG. 4, the corresponding short pulse width is set according to the wall thickness and the thinness of the blade edge, and the full thickness compressive stress distribution is realized by the shallow depth residual stress layer and the multi-layer shot peening. The blade cross-section 9 is unequal thickness distribution, and the inlet side 6 is treated by 8 ns short-pulse laser shot peening, which produces a shallow depth of the induced shock wave 4, and at the same time ensures shape accuracy through multi-layer superposition processing, and finally a full thickness cross section at the intake side. A thick residual stress distribution 10 is produced.

Referring to FIG. 5, the thickness of the transition zone from the leaf edge to the blade body is gradually increased, and the variable pulse width is matched with the thickness of the section to reduce the number of shots, and the stress transition from the treated area to the untreated area is achieved. The thickness of the transition from the leaf edge to the blade body is gradually increased. The laser shot peening in this region is to slow the stress gradient between the treated area and the untreated area, and maintain the residual stress strengthening effect. Therefore, the gradient pulse width is set according to the thickness of the leaf surface, the interval is [8 ns, 16 ns], and the pulse width is proportional to the thickness of the section. A gradient induced shock wave 4 is generated, and the full pressure stress distribution is gradually transformed into a relatively balanced stress distribution curve. The thick residual stress distribution 10 as shown in FIG.

Referring to Fig. 6, the short pulse laser peening parameters are set at the blade root to eliminate stress concentration by shallow residual stress multi-layer shot peening to avoid macroscopic torsional deformation of the blade. The rounded corner 12 at the leaf root of the leaf transition zone, the stress concentration caused by the sudden change of the size seriously affects the performance of the blade. The 8 ns short pulse laser peening parameters are used to form a shallow residual compressive stress layer to maintain the blade without macroscopic deformation, and then proceed. The 3-5 shot peening stacks form a strong constrained residual compressive stress, thereby improving the stress concentration of the blade root 8.

The blade laser shot peening method with variable pulse width controllable residual stress can realize the full thickness residual compressive stress distribution of the leaf edge (intake and exhaust side), eliminate the stress concentration of the blade root without macroscopic deformation, and is suitable for the aviation turbofan engine fan. Laser shot peening treatment of titanium alloy blades of various compressors.

The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the invention, and the equivalent structural transformations made by the present specification and the drawings are directly or indirectly utilized in the concept of the present invention. Other related technical fields are included in the scope of patent protection of the present invention.

Claims

A blade laser shot peening method with variable pulse width controllable residual stress, characterized in that the nanosecond pulse laser pulse width is set according to the blade structure feature, and the penetration depth of the induced shock wave in the blade is controlled, thereby controlling the generation residual The distribution depth of the stress is such that the residual stress distribution in different regions of the blade is matched with the structural features.
The blade laser shot peening method for variable pulse width controllable residual stress according to claim 1, comprising the steps of:

S1: short pulse width is set according to the thickness of the leaf edge and the rigidity is weak, and the full thickness compressive stress distribution is realized by the shallow depth residual compressive stress layer and the multi-layer shot peening superposition;

S2: the thickness of the transition zone from the leaf edge to the blade body is gradually increased, the variable pulse width is proportional to the thickness of the section, and the number of shots is reduced, and the stress of the treated area to the untreated area is smoothly transitioned;

S3: Short-pulse laser peening parameters are set at the root of the blade, and the multi-layer shot peening of the shallow residual compressive stress is used to eliminate stress concentration and avoid macroscopic torsional deformation of the blade.
A blade laser shot peening method for variable pulse width controllable residual stress according to claim 1, wherein said laser pulse width, said penetration depth of said induced shock wave in said blade, and said residual stress distribution There is a positive correlation between the three.
A blade laser shot peening method for variable pulse width controllable residual stress according to claim 1, wherein short-pulse laser shot peening is used to generate a shallower residual compressive stress distribution while maintaining a structural shape that does not change.
The blade laser shot peening method for variable pulse width controllable residual stress according to claim 1, wherein a deeper stress distribution is achieved by superimposing residual compressive stress by multi-layer shot peening.