Ultrafast laser partition impact strengthening method and device for thin-wall covered edge of composite blade

Abstract

The invention discloses an ultrafast laser partition impact strengthening method and device for a thin-wall covered edge of a composite blade. According to the method, the surface of the thin-wall covered edge is strengthened by utilizing the characteristics of instantaneous high pressure of shock waves induced by ultrafast laser and accurate and controllable propagation depth, and meanwhile, according to the thickness characteristics of different areas of the covered edge, laser with different pulse widths is selected to carry out partitioned strengthening treatment, so that accurate regulation and control of a surface residual stress field are realized on the premise of inhibiting deformation; the problem of cooperative control of surface strengthening deformation and a stress field of the thin-wall edge covering structure is solved. According to the thickness characteristics of different areas of the edge covering structure, based on the principle that the shorter the laser pulse width is, the shallower the shock wave propagation depth is, the shallow the depth of a residual stress field influence layer is and the edge covering structure is not prone to deformation, a femtosecond / picosecond pulse width laser combined shock peening method is provided, and femtosecond laser shock is adopted in a thin-wall area; femtosecond laser or picosecond laser with relatively long pulse width is adopted for impact in a wall thickness area, and precise regulation and control of a surface stress field are achieved on the premise of restraining thin-wall wrapping edge deformation.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrafast laser surface modification, and specifically relates to a method and device for ultrafast laser partitioned impact strengthening of thin-walled edge wrapping of composite blades. Background Art

[0002] Composite blades are one of the key technologies for advanced high-bypass turbofan engines to achieve weight reduction and efficiency improvement. In order to prevent the leading edge of composite blades from delaminating and debonding during use and to improve the ability to resist bird strikes, the leading edge of the blades is generally protected by a titanium alloy metal edging structure. Since the edging structure is ultra-thin (the minimum wall thickness of the side wall is 0.38mm and the maximum wall thickness is 0.57mm), the fatigue resistance reserve is insufficient, and high-cycle fatigue fractures are prone to occur during service, damaging the engine and seriously threatening flight safety. It is urgently needed to be strengthened. However, the surface strengthening methods currently explored, such as mechanical shot peening and nanosecond laser shock, have prominent practical problems such as easy deformation during processing and disordered stress field distribution when applied to the thin-walled edging structure, and have certain limitations. Therefore, exploring a new surface strengthening method that can achieve precise control of the surface residual stress field while suppressing the deformation of the edging structure, thereby improving the fatigue resistance, has become the key to solving this problem. Summary of the invention

[0003] The purpose of the present invention is to provide a method and device for ultrafast laser zoned shock strengthening of thin-walled edge of composite blades in order to solve the above-mentioned problems.

[0004] The technical solution adopted by the present invention is as follows: an ultrafast laser partitioned impact strengthening device for thin-walled edge wrapping of composite blades, the device comprising: a mechanical arm, a scanning galvanometer, an optical path system, an ultrafast laser, a central control, an industrial camera, an ultrafast laser beam and a test piece; A test piece is arranged at the lower end of the robotic arm, an ultrafast laser is arranged at the output end of the central control, an optical path system is arranged at one end of the ultrafast laser, a scanning galvanometer is arranged at one end of the optical path system, an ultrafast laser beam is arranged inside the scanning galvanometer, and an industrial camera is arranged at the bottom of the scanning galvanometer.

[0005] In a preferred embodiment, the method comprises the following steps: S1: Pre-treat the hemming structure by placing it in an alcohol solution for ultrasonic cleaning for 10 minutes to remove surface oil stains, residues and other defects, and then dry it for later use; S2: Clamp the edge structure onto the robotic arm, use an industrial camera to perform multi-view scanning and imaging of the edge structure, obtain the size information of the edge structure, perform three-dimensional stereo reconstruction of the edge structure based on a deep learning method, and obtain a three-dimensional model of the edge structure; S3: Based on the three-dimensional model of the hemming structure, the range of the area to be strengthened is calibrated, the critical angle threshold of the partition is set, and the strengthening area is divided into partitions a1, a2... The control system matches the process database according to the size information of the three-dimensional model of the strengthening area, and automatically generates reference laser processing parameters for each partition, including laser pulse width, energy, moving path, etc.; S4: The operator can flexibly adjust the reference laser processing parameters provided by the system, and start processing after determining the strengthening process. The robot arm is visually guided based on the industrial camera target detection method. During the processing, the robot arm drives the edge to move to the processing starting point of each partition, and the scanning galvanometer system completes the scanning and strengthening processing of each partition; S5: After strengthening, the edge structure is post-processed, the edge is removed and ultrasonically cleaned in an alcohol solution for 10 minutes, and then dried for standby use.

[0006] In a preferred embodiment, in step S2, using an industrial camera to perform multi-view scanning imaging of the edge wrapping structure includes the following steps: S1: Use an industrial camera to shoot the edge structure from different angles to obtain a multi-view RGB image; S2: Search for corresponding points, extract features and match them respectively, optimize the matching based on geometric conditions, and establish a scene graph; S3: Perform incremental reconstruction, perform triangulation in the initialization state, estimate the pose and perform BA optimization; S4: Match the sparse point cloud with the cloud camera pose to obtain a thin-walled 3D stereo model.

[0007] In a preferred embodiment, in step S3, the present invention proposes a continuous surface partitioning robot-galvanometer collaborative strengthening method for the dimensional characteristics of the thin-walled hemming surface, that is, taking a certain angle α as the critical value, the hemming surface is divided into a number of sub-areas 1, 2, ..., n, etc. The movement of the laser beam between the sub-areas is moved by the robot driving components, and the laser beam remains stationary. When processing each sub-area, a scanning galvanometer is used to uniformly scan and strengthen the area, and the robot remains stationary. The entire surface is processed through the collaborative cooperation between the robot arm and the galvanometer, which ensures the uniformity and consistency of the laser scanning within the critical angle threshold α during the processing.

[0008] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: In the present invention, the surface of the thin-walled edge is strengthened by utilizing the characteristics of ultrafast laser-induced shock waves with instantaneous high pressure and precisely controllable propagation depth. At the same time, based on the principle that the shorter the laser pulse width, the shallower the shock wave propagation depth, the shallower the depth of the residual stress field influence layer, and the less prone to deformation, lasers with different pulse widths are selected for zoned strengthening according to the thickness characteristics of different areas of the edge. That is, femtosecond laser shock is used in thin-walled areas, and relatively long-pulse femtosecond laser or picosecond laser shock is used in thick-walled areas. This achieves precise control of the surface residual stress field while suppressing deformation, thereby effectively solving the problem of coordinated control of surface strengthening deformation and stress field of thin-walled edge structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the ultrafast laser shock zoning strengthening process of thin-walled edge wrapping of the present invention; Figure 2 It is a schematic diagram of the three-dimensional reconstruction process of thin-wall hemming based on multi-view imaging in the present invention; Figure 3 It is a schematic diagram of the ultrafast laser surface strengthening device in the present invention; Figure 4 Schematic diagram of variable pulse width ultrafast laser shock zoning strengthening of thin-walled edge-wrapped structure in the present invention; Figure 5 It is a schematic diagram of the coordinated strengthening of the curved thin-walled edge structure partitioned mechanical arm and the galvanometer in the present invention; Figure 6 This is the residual stress distribution diagram in the depth direction of the thin-wall hemming after strengthening in the present invention; Figure 7 It is the residual stress distribution diagram of the hemming surface after strengthening in the present invention; Markings in the figure: 1-robot arm; 2-scanning galvanometer; 3-optical system; 4-ultrafast laser; 5-central controller; 6-industrial camera; 7-ultrafast laser beam; 8-test piece. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0011] Reference Figure 1-7 , a method for ultrafast laser partitioned impact strengthening of thin-walled edge of composite blades Figure 1 As shown, it mainly includes the following steps: S1: Pre-treat the hemming structure by placing it in an alcohol solution for ultrasonic cleaning for 10 minutes to remove surface oil stains, residues and other defects, and then dry it for later use; S2: Clamp the edge structure onto the robotic arm, use an industrial camera to perform multi-view scanning and imaging of the edge structure, obtain the size information of the edge structure, perform three-dimensional stereo reconstruction of the edge structure based on a deep learning method, and obtain a three-dimensional model of the edge structure; S3: Based on the three-dimensional model of the hemming structure, the range of the area to be strengthened is calibrated, the critical angle threshold of the partition is set, and the strengthening area is divided into partitions a1, a2... The control system matches the process database according to the size information of the three-dimensional model of the strengthening area, and automatically generates reference laser processing parameters for each partition, including laser pulse width, energy, moving path, etc.; S4: The operator can flexibly adjust the reference laser processing parameters provided by the system, and start processing after determining the strengthening process. The robot arm is visually guided based on the industrial camera target detection method. During the processing, the robot arm drives the edge to move to the processing starting point of each partition, and the scanning galvanometer system completes the scanning and strengthening processing of each partition; S5: After strengthening, the edge structure is post-processed, the edge is removed and ultrasonically cleaned in an alcohol solution for 10 minutes, and then dried for standby use.

[0012] Among them, the 3D reconstruction process of thin-wall hemming based on multi-view imaging of industrial cameras is as follows: Figure 2 As shown, it mainly includes the following steps: S1: Use an industrial camera to shoot the edge structure from different angles to obtain a multi-view RGB image; S2: Search for corresponding points, extract features and match them respectively, optimize the matching based on geometric conditions, and establish a scene graph; S3: Perform incremental reconstruction, perform triangulation in the initialization state, estimate the pose and perform BA optimization; S4: Match the sparse point cloud with the cloud camera pose to obtain a thin-walled 3D stereo model.

[0013] The present invention proposes an ultrafast laser shock strengthening device for thin-walled edge wrapping of composite blades. Figure 3As shown, it includes 1-mechanical arm 1, scanning galvanometer 2, optical path system 3, ultrafast laser 4, central controller 5, industrial camera and other subsystems 6. The ultrafast laser 4 can emit 7 ultrafast laser beams with variable pulse width from femtosecond to picosecond, and can flexibly set laser parameters such as laser energy and repetition rate. The emitted ultrafast laser enters the scanning galvanometer 2 after being shaped and path adjusted by 3-optical path system. The scanning galvanometer can realize high-precision displacement control of ultrafast laser, which is used for strengthening processing on the surface of the test piece 8. The industrial camera 6 is used to capture the size and depth information of the test piece 8 for three-dimensional reconstruction, and can provide visual guidance information for the mechanical arm during the processing. 1-mechanical arm, scanning galvanometer 2, ultrafast laser 4 and industrial camera 6 realize functions such as three-dimensional reconstruction of the test piece 8, strengthening area zoning planning, automatic zoning process planning, and mechanical arm visual guidance under the coordinated control of the central controller 5, and have automated and intelligent processing capabilities.

[0014] In order to effectively control the deformation of thin-wall hemming during the strengthening process, the present invention proposes a partition strengthening method, including variable pulse width laser partition strengthening and continuous surface partition strengthening, wherein the variable pulse width ultrafast laser shock partition strengthening method is as follows: Figure 4 As shown in the figure, according to the thickness characteristics of different areas of the edge structure, based on the principle that the shorter the laser pulse width, the shallower the shock wave propagation depth, the shallower the depth of the residual stress field influence layer, and the less likely it is to deform, a method of using femtosecond / picosecond pulse width laser combined shock strengthening is proposed, that is, femtosecond laser shock is used in thin wall areas, and long pulse width femtosecond laser or picosecond laser shock is used in thick wall areas, so as to achieve precise control of the surface stress field while suppressing the deformation of the thin wall edge.

[0015] In view of the dimensional characteristics of thin-walled hemming surfaces, the present invention proposes a continuous surface partitioning robot-galvanometer collaborative strengthening method, that is, taking a certain angle α as the critical value, the hemming surface is divided into a number of sub-areas 1, 2, ..., n, etc. The movement of the laser beam between the sub-areas is carried out by the robot arm driving the components to move, and the laser beam remains stationary. When processing each sub-area, a scanning galvanometer is used to uniformly scan and strengthen the area, and the robot arm remains stationary. The entire surface is processed through the collaborative cooperation between the robot arm and the galvanometer, ensuring the uniformity and consistency of the laser scanning within the critical angle threshold α during the processing process.

[0016] The method and device proposed in the present invention are described in detail below by taking TC4 titanium alloy hemming as an example to verify the effectiveness of the present invention.

[0017] First, the TC4 titanium alloy hemming structure was placed in an alcohol solution for ultrasonic cleaning for 10 minutes to remove surface oil and residues, and then dried. Then the hemming was clamped on the robotic arm, and multi-view imaging was performed through an industrial camera to obtain a three-dimensional model of the hemming structure. The strengthening area is the entire surface of the hemming structure, and the strengthening sub-area division is set with a critical angle threshold of 5°, and the entire surface is divided into several sub-areas. For each sub-area, the area with a wall thickness of 0.3-0.5 mm is treated with a femtosecond laser, the laser spot diameter is 40 μm, the laser power density is controlled at 50 TW / cm2, the spot overlap rate is 50%, and the laser moving path is a "Z" shape; the area with a wall thickness of more than 0.5 mm is treated with a picosecond laser, the laser spot diameter is 40 μm, the laser power density is controlled at 20 TW / cm2, the spot overlap rate is 50%, and the laser moving path is a "Z" shape. Therefore, the entire surface of the hemming structure is divided into several sub-areas, and each sub-area corresponds to matching process parameters. After that, the strengthening treatment is carried out. The position of the processing starting point is determined based on the visual guidance method. The processing of each sub-area is completed by the coordinated control of the robot arm and the galvanometer. The robot arm is responsible for the movement between the sub-areas, and the galvanometer is responsible for the scanning processing of the laser in each sub-area. The two are carried out alternately and coordinated to complete the uniform processing of the entire surface. During the processing, the industrial camera monitors the processing process in real time. If there is inconsistency in the processing area or disorder in the processing sequence, the signal is transmitted to the central controller in time to issue a stop processing instruction. After the processing is completed, the hemming structure is removed and placed in an alcohol solution for ultrasonic cleaning for 10 minutes to remove the surface processing residues, and then dried for residual stress and deformation testing.

[0018] The residual stress test uses X-ray diffraction to test the residual stress on the surface and in the depth direction after strengthening. The results are as follows: Figure 7 As shown in the figure, it can be seen that the residual compressive stress value of the surface after strengthening is about 400 MPa, and the depth of the residual compressive stress influence layer in the depth direction is about 200 μm. In addition, the deformation of the hemming after strengthening meets the design requirements. It shows that the method and device proposed in the present invention can better realize the coordinated control of the deformation and stress field of the thin-walled hemming structure and achieve the expected purpose.

[0019] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0020] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultrafast laser partitioned impact strengthening device for thin-walled edge wrapping of composite blades, characterized by: The device comprises: a mechanical arm (1), a scanning galvanometer (2), an optical path system (3), an ultrafast laser (4), a central control (5), an industrial camera (6), an ultrafast laser beam (7) and a test piece (8); A test piece (8) is arranged at the lower end of the mechanical arm (1), an ultrafast laser (4) is arranged at the output end of the central control (5), an optical path system (3) is arranged at one end of the ultrafast laser (4), a scanning galvanometer (2) is arranged at one end of the optical path system (3), an ultrafast laser beam (7) is arranged inside the scanning galvanometer (2), and an industrial camera (6) is arranged at the bottom of the scanning galvanometer (2).

2. The method for ultrafast laser partitioned impact strengthening of thin-walled edge of composite blades according to claim 1, characterized in that: The method comprises the following steps: S1: Pre-treat the hemming structure by placing it in an alcohol solution for ultrasonic cleaning for 10 minutes to remove surface oil stains, residues and other defects, and then dry it for later use; S2: Clamp the edge structure onto the robotic arm, use an industrial camera to perform multi-view scanning and imaging of the edge structure, obtain the size information of the edge structure, perform three-dimensional stereo reconstruction of the edge structure based on a deep learning method, and obtain a three-dimensional model of the edge structure; S3: Based on the three-dimensional model of the hemming structure, the range of the area to be strengthened is calibrated, the critical angle threshold of the partition is set, and the strengthening area is divided into partitions a1, a2... The control system matches the process database according to the size information of the three-dimensional model of the strengthening area, and automatically generates reference laser processing parameters for each partition, including laser pulse width, energy, moving path, etc.; S4: The operator can flexibly adjust the reference laser processing parameters provided by the system. After determining the strengthening process, the processing begins. The robot arm is visually guided based on the industrial camera target detection method. During the processing, the robot arm drives the hemming to move to the processing starting point of each partition, and the scanning galvanometer system completes the scanning strengthening processing of each partition. S5: After strengthening, the edge structure is post-processed, the edge is removed and ultrasonically cleaned in an alcohol solution for 10 minutes, and then dried for standby use.

3. The method for ultrafast laser partitioned impact strengthening of thin-walled edge of composite blades according to claim 1, characterized in that: In step S2, using an industrial camera to perform multi-view scanning imaging of the edge structure includes the following steps: S1: Use an industrial camera to shoot the edge structure from different angles to obtain a multi-view RGB image; S2: Search for corresponding points, extract features and match them respectively, optimize the matching based on geometric conditions, and establish a scene graph; S3: Perform incremental reconstruction, perform triangulation in the initialization state, estimate the pose and perform BA optimization; S4: Match the sparse point cloud with the cloud camera pose to obtain a thin-walled 3D stereo model.

4. The method for ultrafast laser partitioned impact strengthening of thin-walled edge of composite blades according to claim 1, characterized in that: In the step S3, the present invention proposes a continuous surface partitioning robot-galvanometer collaborative strengthening method for the size characteristics of the thin-walled hemming surface, that is, taking a certain angle α as the critical value, the hemming surface is divided into a number of sub-areas 1, 2, ..., n, etc., and the movement of the laser beam between the sub-areas is carried out by the robot driving parts, and the laser beam remains stationary. When processing each sub-area, a scanning galvanometer is used to uniformly scan and strengthen the area, and the robot remains stationary. The entire surface is processed through the collaborative cooperation between the robot arm and the galvanometer, which ensures the uniformity and consistency of the laser scanning within the critical angle threshold α during the processing.

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