CN108546818B - One-side laser shot peening method for thin-walled structural parts - Google Patents

Abstract

The invention provides a single-side laser shot peening strengthening method of a thin-wall structural member, which comprises the following steps: s1, performing thickness analysis on the thin-wall structural part, and screening N characteristic thickness values; s2, determining the optimal spot size of each thickness of the thin-wall structural member; s3, determining a laser shot blasting path of the thin-wall structural member; s4, performing laser peening on the thin-wall structural member by the laser peening path of the step S3; when the thin-wall structural part is an equal-thickness thin-wall structural part, N is 1; when the thin-wall structural part is a variable-thickness thin-wall structural part, N is more than or equal to 2. Compared with the prior art, the invention has the following beneficial effects: 1. deformation control is realized only through optimization of process parameters without an external clamp or a gasket, so that the universality of the method is improved; 2. residual compressive stress can be obtained on both sides of the thin-wall structure only through single-side laser shot peening strengthening, and the applicability to strengthening of complex structures is improved.

Description

One-side laser shot peening method for thin-walled structural parts

technical field

The invention relates to the field of mechanical manufacturing, and in particular, to a single-side laser shot peening process method for thin-walled structures, which does not rely on external fixtures or gaskets, and only optimizes process parameters to make the edge of aero-engine turbine blades, etc. The variable-thickness and thin-walled structures are subjected to single-side laser shot peening while achieving deformation control.

Background technique

During the service process of aero-engine, the blade edge of the blade is easily affected by foreign object damage and high-cycle fatigue, resulting in fatigue failure. Laser shot peening technology is an effective method to strengthen the surface of aero-engine blades and improve the anti-fatigue and anti-foreign body impact damage performance of the blades. However, the thickness of the blade edge is only 0.4 to 0.6 mm, which is a typical thin-walled structure with variable thickness. The deformation of the blade edge is always accompanied by laser shot peening, and these deformations will affect the aerodynamic performance of the blade. Therefore, it is necessary to establish a laser shot peening process method of variable-thickness thin-walled structure, which can reduce its distortion while achieving strengthening.

An existing solution is to control the deformation by double-sided laser shock. The double-sided impact is divided into double-sided synchronous and double-sided asynchronous. Due to the symmetry of the load, there is no deformation in theory. However, due to the superposition of stress waves in the middle of the sample, there is a risk of internal cracks. Moreover, the complexity of the optical path and the difficulty of control are also increased due to the need for bilateral simultaneous shocks. The double-sided asynchronous impact does not have the problem of superposition of stress waves, and the deformation can be effectively controlled for the flat plate, but the problem of uncontrollable deformation occurs for some twisted blades. Moreover, for workpieces such as blisks that are mutually shielded to a certain extent, the optical path is not fully accessible, and it becomes more difficult to achieve bilateral impact. Therefore, the present invention provides a process method for single-side laser shot peening.

The invention with application number 201310224538.6 discloses a method and device for laser impacting aircraft turbine blades, which suppress deformation by designing flexible clamps and gaskets that match the shape of the blade, and optimize process parameters to achieve deformation control. However, the invention needs to design a fixture separately for blades of different shapes, the system is complicated, and the versatility is not enough. In addition, the invention with application number 201310040844.4 discloses a combined method and device for laser shock treatment of engine blades. By controlling the residual stress field of the blade, the method of increasing the smooth transition area between the strengthened and unstrengthened areas is used to achieve improved performance. For the purpose of blade fatigue life, the invention does not involve the control of blade deformation. In addition, the invention with application number 201710065831.0 discloses a method for double-sided asynchronous laser shock strengthening of the leading edge of a turbine blade, and the invention with application number 201710065820.2 discloses a method for double-sided synchronous laser shock strengthening of the leading edge of a turbine blade, The deformation control is achieved by double-sided laser shot peening, but the double-sided optical path system increases the complexity of the system structure and the difficulty of programming. The light guide system is additionally designed to achieve laser shot peening on both sides. In addition, the invention with the application number EP02250594.5 discloses a double-sided synchronous laser shot peening method for an integral blisk. By using two obliquely incident laser beams and adjusting the posture of the integral blisk, an elliptical spot shape is used. The laser shot peening on both sides of the blade is carried out, but it also has the problems of complex structure and difficult programming control.

To sum up, none of the existing laser shot peening methods for aero-engine turbine blade edges with variable thickness and thin-walled structures does not have a single-side laser shot peening deformation that is completely optimized by process parameters without external fixtures. Control Method. Therefore, there is an urgent need for a deformation control method that can adapt to the laser shot peening of variable-thickness thin-walled structures.

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, the present invention provides a single-side laser shot peening process method for a thin-walled structure, which can make the process parameters optimized and single-side laser shot peening without the aid of external fixtures or gaskets. Thin-walled structures such as blade edges of aero-engine turbine blades are strengthened while deformation control is achieved.

The present invention is achieved through the following technical solutions:

The invention provides a single-side laser shot peening method for thin-walled structures, which comprises the following steps:

S1. Perform thickness analysis on thin-walled structural parts, and screen out N characteristic thickness values;

S2. Determine the optimal spot size at different thicknesses of thin-walled structural parts;

S3. Determine the laser shot peening path of the thin-walled structural parts;

S4, performing laser peening on the thin-walled structural member with the laser peening path described in step S3;

Wherein, when the thin-walled structural member is an equal-thickness thin-walled structural member, N=1; when the thin-walled structural member is a variable-thickness thin-walled structural member, N≥2.

As a preferred solution, the method for thickness analysis is: performing thickness analysis on a three-dimensional digital model of a thin-walled structural part or performing thickness measurement on a solid part with a thickness gauge.

As a preferred solution, the method for determining the optimal spot size is:

A single-thickness knife-edge specimen is selected for single-side laser shot peening that does not pass the spot size. The change curve of the end of the knife-edge specimen obtained by laser shot peening with different spot sizes is the intersection of the change curve and the zero displacement line. That is, the optimal spot size corresponding to the thickness.

As a preferred solution, the knife-edge test piece includes a test piece main body and a first step portion integrally formed with the test piece main body, a pressure plate is provided on each side surface of the test piece main body, and the upper surface of the pressure plate is The upper surfaces of the first step portion are flush to form a second step portion, the thickness of the first step portion is 3 to 4 times the thickness of the main body of the specimen, and the two step portions ensure that the maximum deformation point of the knife-edge specimen is at There is no step surface at the tip of the blade.

As a preferred solution, the method for determining the laser peening path is:

The N characteristic thickness values and their corresponding optimal spot sizes are fitted into a curve d=f(t). According to the optimal spot sizes corresponding to different thickness values, single-side laser shot peening is performed on all strengthened areas, where , d is the optimal spot size, and t is the thickness of the impact point.

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

1. Without external fixtures or gaskets, deformation control is only achieved through the optimization of process parameters, which improves the versatility of the method;

2. The residual compressive stress can be obtained on both sides of the thin-walled structure only by single-side laser shot peening, which improves the applicability of complex structure strengthening;

3. The knife-edge specimens constrained on both sides make the maximum deformation after laser shot peening concentrated on the knife-edge, which is convenient for measurement, and the method of unilateral bolt tightening reduces the processing difficulty and experimental cost;

4. The commonly used thin-walled structural material is TC4 or TC17 titanium alloy. For the characteristic thickness and corresponding material for which the optimal spot size has been obtained, there is no need to repeat the experiment to determine the optimal spot size;

5. Those skilled in the art generally think that the spot size only affects the efficiency of laser shot peening, and the process parameters are often optimized by changing the pulse energy. The invention determines the non-deformable equilibrium point by reducing the spot size, and solves the technical problem that the non-deformable equilibrium point cannot be found by changing the pulse energy for a beam spot with a diameter of 4 mm.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

Fig. 1 is the knife edge test piece provided by the present invention and the shot peening path measurement path schematic diagram;

Fig. 2 is the top view of the knife edge test piece used in the present invention;

Fig. 3 is the side view of the knife edge test piece used in the present invention;

Fig. 4 is the relation curve of the deformation and the spot size of the 0.5mm thick TC4 titanium alloy specimen in the present invention after 7.96GW/cm ² power density laser shot peening;

Fig. 5 is the relation curve of the residual stress and the spot size of the 0.5mm thick TC4 titanium alloy specimen in the present invention after 7.96GW/cm ² power density laser shot peening;

Fig. 6 is the relation curve of optimal spot size and impact point thickness in the present invention;

7 is a schematic diagram of the spot size and the path of laser peening in the present invention;

In the figure: 1, light spot; 2, shot peening path; 3, shot peening area; 4, pressure plate; 5, bolt; 6, nut; 7, deformation measurement path; 8, first step part;

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

1 is a schematic diagram of a knife-edge test piece and a shot peening path measurement path provided by the present invention. The knife-edge test piece includes a test piece main body 9 and a first step portion 8 integrally formed with the test piece main body 9. The two sides of the test piece main body 9 Each surface is fixed with a pressure plate 4 through bolts 5 and nuts 6. The upper surface of the pressure plate 4 is flush with the upper surface of the first step portion 8 to form a second step portion. The thickness of the first step portion 8 is the main body of the specimen. 9 is 3 to 4 times the thickness, and the two stepped parts ensure that the maximum deformation point of the knife edge specimen is at the tip of the knife without the stepped surface.

The shot peening area 3 is close to the end point of the knife edge, the shot peening path 2 is carried out from the inside to the outside, and the shape of the light spot 1 is a circle. According to the deformation measurement path 7, the knife-edge specimens before and after shot peening are measured, and the end displacement is obtained with the step surface as the benchmark. One embodiment of the device needs to implement single-side laser shot peening on the thin-walled structure, so as to ensure that there is residual compressive stress on both sides of the workpiece, and at the same time make it almost not deformed.

Figures 2 to 3 are schematic diagrams of the structure of the knife-edge test piece used in the present invention, which are thin-walled test pieces of uniform thickness with stepped bodies on both sides. The thickness of the knife-edge is selected as a single characteristic thickness value, and the stepped surface is used as the boundary constraint and measurement benchmark. 3 to 4 times larger than the knife edge.

The workflow of the embodiment is as follows:

Step 1: Use UG software to analyze the thickness of the three-dimensional model of the workpiece, and evenly select 100 points on its surface to obtain 100 thickness values, and screen out the maximum value, the minimum value and the value with the highest frequency as the three characteristic thickness values. (eg 0.4mm, 0.5mm, 0.6mm).

Step 2: Prepare 10 knife-edge specimens with three thicknesses. For one of the specimen groups with thickness (eg 0.5mm), under the condition of a certain (eg 7.96GW/cm ² ) pulse power density, by changing the diameter of the through hole of the special aperture, four spot sizes (eg diameter 0.6 mm, 0.8mm, 1.0mm, and 1.2mm) to laser shot peening the specimen to obtain the corresponding deformation value, which is connected into a curve. The intersection of the curve and the zero displacement line is the optimal spot size (such as diameter) under the thickness. 1.03mm), as shown in Figure 4. Figure 5 shows the measured values of residual stress on both sides of the knife-edge specimen after unilateral laser shot peening with different spot sizes.

Select another two specimen groups with thickness (eg 0.4mm and 0.6mm) to repeat the above process to obtain the other two corresponding optimal spot size values (eg diameter 0.79mm and 1.25mm).

Step 3: Fit the three characteristic thickness values and the corresponding optimal spot size into a curve d=f(t), as shown in FIG. 6 . According to the optimal spot size corresponding to different thickness values, single-side laser shot peening is performed on all strengthened areas, as shown in Figure 7.

Among them, d is the optimal spot size, and t is the thickness value of the impact point.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various variations or modifications within the scope of the claims, which do not affect the essential content of the present invention.

Claims (4)

1. a single-side laser shot peening method for thin-walled structural parts, is characterized in that, comprises the steps: S1. Perform thickness analysis on thin-walled structural parts, and screen out N characteristic thickness values; S2. Determine the optimal spot size at each thickness of the thin-walled structural member; the method for determining the optimal spot size is: select a single-thickness knife-edge specimen, and perform single-side laser shot peening with different spot sizes. The change curve of the end displacement of the knife-edge specimen obtained by laser shot peening, the intersection of the change curve and the zero displacement line is the optimal spot size corresponding to the thickness; S3. Determine the laser shot peening path of the thin-walled structural parts; S4, performing laser peening on the thin-walled structural member with the laser peening path described in step S3; Wherein, when the thin-walled structural member is an equal-thickness thin-walled structural member, N=1; when the thin-walled structural member is a variable-thickness thin-walled structural member, N≥2. 2. The single-side laser shot peening method for thin-walled structural parts according to claim 1, wherein the method for thickness analysis is: performing a thickness analysis on a three-dimensional digital model of a thin-walled structural part or performing a thickness analysis on a solid The thickness of the piece is measured with a thickness gauge. 3. The single-side laser shot peening method for thin-walled structural parts according to claim 1, wherein the knife-edge test piece comprises a test piece main body and a first step portion integrally formed with the test piece main body, Each side surface of the main body of the test piece is provided with a pressing plate, and the upper surface of the pressing plate is flush with the upper surface of the first step portion to form a second step portion, and the thickness of the first step portion is the thickness of the test piece. 3 to 4 times the thickness of the main body. 4. The single-side laser shot peening method for thin-walled structural parts as claimed in claim 1, wherein the method for determining the laser shot peening path is: The N characteristic thickness values and their corresponding optimal spot sizes are fitted into a curve d=f(t). According to the optimal spot sizes corresponding to different thickness values, single-side laser shot peening is performed on all strengthened areas, where , d is the optimal spot size, and t is the thickness of the impact point.

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