Multi-beam laser shock peening method for reinforcing rib metal structure

Abstract

The application provides a method for multi-beam laser shock peening of a stiffener metal structure, comprising the following steps: using two or more laser processing beams to perform bilateral synchronous laser shock peening on the transition zones on both sides of the stiffener of the stiffener metal structure; and using at least one laser processing beam to perform laser shock peening on the non-stiffener surface of the stiffener metal structure; wherein the laser shock peening on the non-stiffener surface is performed before or after the bilateral synchronous laser shock peening on the transition zones on both sides. The application can introduce a deep, uniform and reasonably distributed residual compressive stress layer in the key area of the stiffener structure, significantly inhibit the initiation and propagation of fatigue cracks, minimize the deformation of the workpiece caused by the strengthening process, and improve the reliability and consistency of the strengthening effect.

Description

Technical Field

[0001] This invention relates to the field of laser shock stabilization technology, and more specifically, to a multi-beam laser shock stabilization method for reinforcing metal structures. Background Technology

[0002] Stiffening ribs are widely used in manufacturing, particularly in metal structural components such as wall panels and frame beams. In thin-walled structures, stiffening ribs significantly improve the overall deformation resistance of parts. However, stress concentration occurs in the transition zone between the stiffener and the substrate (typically the fillet radius or weld). Under fatigue loading conditions, this transition zone is prone to premature fatigue cracking, posing a significant risk of fatigue fracture. Laser shock peening (LSP) utilizes the plasma shock wave effect generated by the laser pulse energy of a nanosecond laser acting on the material surface, creating a residual compressive stress distribution. This surface strengthening technique can significantly improve the fatigue performance of metal parts. Currently, stiffened metal structural components are increasingly adopting LSP to enhance their fatigue resistance. The main process involves performing LSP on both sides of the stiffener's radius (R-zone). LSP primarily utilizes the residual compressive stress formed on the surface of the transition zone (fillet radius or weld) between the stiffener and the substrate to inhibit crack initiation and delay crack propagation, thereby improving fatigue performance.

[0003] Laser shock peening inevitably induces plastic strain on the surface of parts, causing plastic extension in the strengthened zone and resulting in deformation. Existing laser shock peening methods for stiffened metal structures employ a sequential strengthening approach on both sides of the transition zone. After strengthening one side of the transition zone, the stiffened metal structure deforms, inevitably leading to a redistribution of residual stress on the strengthened surface. When the other side of the transition zone is strengthened, the stiffened metal structure deforms again, again resulting in a redistribution of residual stress on the strengthened surface. Therefore, existing laser shock peening methods cannot effectively control residual stress and structural deformation. Summary of the Invention

[0004] (a) Technical problems to be solved The technical problem to be solved by this invention is that existing laser shock peening methods cannot effectively control residual stress and structural deformation.

[0005] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a multi-beam laser shock peening method for reinforcing metal structures with stiffeners, comprising the following steps: Provide at least three independent laser processing beams. These beams can be generated by multiple lasers, or by a single laser splitting the beam using a beam splitting system, and are equipped with independent or collaborative control systems to adjust their paths, focus, and beam output timing; Two or more laser processing beams are used to perform bilateral synchronous laser shock blasting on the transition zone on both sides of the stiffener of the metal structural component. Specifically, a first number of laser processing beams are used to perform bilateral synchronous laser shock blasting on the transition zone on both sides of the stiffener (i.e., the R-zone or weld area where stress concentration is most severe). The first number is even and not less than two to ensure that both sides can be acted on simultaneously. Synchronous strengthening means applying laser shock to corresponding or designated points on both sides in the same or staggered but closely related time sequence, so that the plastic deformation effects generated on both sides mutually restrain and cancel each other out, thereby fundamentally suppressing the torsional deformation caused by unilateral sequential strengthening.

[0006] Furthermore, laser shock peening is performed on the non-reinforcing surface (i.e., the usual "back side" or non-stiffening plate surface) of the reinforcing metal structure using at least one laser processing beam; this step aims to introduce a certain residual compressive stress into the non-reinforcing surface to coordinate with the compressive stress distribution in the transition zone, further balance the overall stress state, and adjust the stress distribution of the surface as needed.

[0007] Specifically, the laser shock strengthening of the non-reinforcing rib surface is performed before or after the bilateral synchronous laser shock strengthening in the transition zone on both sides.

[0008] Preferably, the transition zone includes region A and region B. The laser shock peening range of the transition zone on each side of the reinforcing rib is divided into region A, closer to the substrate, and region B, closer to the reinforcing rib, by the angle bisector of the angle between the center plane of the reinforcing rib and the non-reinforcing rib surface. The non-reinforcing rib surface includes region C and region D. Region C is located within the projection area of ​​the reinforcing rib, and region D is located on both sides of region C. This partitioning allows for the application of differentiated process parameters based on the geometric characteristics and stress patterns of different regions.

[0009] Preferably, when performing bilateral synchronous laser shock peening on region A, the laser processing beams used on both sides employ identical process parameters and spot paths, and the strengthening spots on both sides are symmetrically distributed relative to the center plane of the reinforcing rib. This strict symmetrical operation aims to ensure that the shock wave pressure, plastic deformation, and induced instantaneous bending moment generated in regions A on both sides are equal in magnitude and opposite in direction, thereby maximizing the cancellation of deformation effects.

[0010] Preferably, the laser power density enhanced in region A is I A The pulse width is τ AIts actual reinforcement range completely covers area A, and the portion extending beyond the boundary of area A is less than 50% of the thickness of the reinforcing rib. Preferably, the laser power density for laser shock enhancement of region C is: I C Pulse width is τ C The laser power density for laser shock enhancement of region D is I D Pulse width is τ D And satisfy: I D ≤ I C ≤ I A ,and τ D ≤ τ C ≤ τ A Specifically, when strengthening regions C and D, the process parameters follow the aforementioned gradient design principle. This means that the impact strength (reflected in power density and energy) decreases from the root of the transition zone (region A), where stress concentration is most severe, to the substrate region far from the reinforcing rib (region D). This design ensures sufficient strengthening of critical areas, smooths the stress gradient in the transition zone, avoids new stress concentration points at abrupt parameter changes, and makes the residual stress distribution in the entire strengthened region more reasonable and stable.

[0011] Preferably, when performing bilateral synchronous laser shock blasting on region B, the same process parameters and different spot paths are used on both sides. Multiple strengthening units are arranged along the length of the reinforcing rib metal structure. Each strengthening unit consists of two adjacent spots on one side of the reinforcing rib along its length and two adjacent spots mirror-distributed on the other side. For each strengthening unit, the two non-mirror-distributed spots on both sides of the reinforcing rib are first synchronously strengthened, and then the remaining two spots within the same strengthening unit are synchronously strengthened. This process is repeated for all strengthening units. Specifically, during strengthening, instead of simultaneously impacting two mirror-symmetrical points on both sides, two non-mirror-symmetrical points within a unit (e.g., the first point on the left and the second point on the right) are first synchronously impacted, and then the remaining two points within the unit (the second point on the left and the first point on the right) are synchronously impacted. This "interlaced synchronous within a unit" strategy ensures the overall synchronicity of bilateral strengthening to control macroscopic deformation, and also disperses the instantaneous impact load through microscopic impact point misalignment, which helps to generate a more uniform residual compressive stress field and may reduce stress concentration.

[0012] Preferably, the reinforcement range of regions C and D does not exceed the projection range of regions A and B on the non-reinforcing rib surface.

[0013] Preferably, when performing bilateral synchronous laser shock blasting on areas A and / or B, the central axis of the laser processing beam is controlled to be perpendicular to the tangential plane at the center of the blasting spot, and the size of the blasting spot is controlled so that the angle between all tangential planes within the area covered by the blasting spot in a single shock is no greater than 30°. This ensures uniform laser energy incidence and that the plasma shock wave acts perpendicularly on the material surface, resulting in a uniform and consistent blasting effect, and avoids energy loss or pressure field asymmetry caused by oblique incidence.

[0014] Preferably, when performing laser shock peening on areas A, B, C, and D, the same absorption layer medium and constraint layer medium are used. Specifically, to simplify the process and ensure consistency, it is recommended to use the same type and thickness of absorption layer medium (such as special black paint or aluminum foil) and constraint layer medium (usually a flowing water curtain or transparent covering layer) when performing laser shock peening on areas A, B, C, and D.

[0015] Preferably, the beam angle of the laser processing beam relative to the reinforcing metal structure and the position of the strengthening spot are adjusted by moving the laser processing beam (e.g., a robotic arm), moving the reinforcing metal structure (e.g., a CNC rotary table), or by making the laser processing beam and the reinforcing metal structure move in tandem. The final residual stress distribution on the surface of the part can be precisely controlled by comprehensively adjusting parameters such as laser power density, pulse width, spot overlap rate, and coverage in each region.

[0016] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: 1. This invention employs dual-sided synchronous laser shock blasting to strengthen the transition zone on both sides of the reinforcing rib, causing the instantaneous deformation trends generated on both sides during strengthening to cancel each other out. This significantly reduces the overall bending deformation caused by sequential strengthening on one side. Combined with the orderly strengthening of the non-reinforcing rib surface, the overall stress state is further balanced, ensuring reliable control of the shape accuracy of the strengthened workpiece and reducing or even eliminating subsequent straightening processes.

[0017] 2. In this invention, synchronous strengthening avoids the problem of repeated redistribution of residual stress caused by sequential strengthening. Combining the strictly symmetrical strengthening of area A, the unitized staggered strengthening of area B, and the parametric gradient design of the non-reinforcing rib surface, the residual compressive stress layer ultimately formed on the surface of the part is more uniformly distributed, with a more reasonable gradient and more controllable magnitude. The critical area (transition zone) can obtain a sufficiently deep compressive stress, and the stress transition with adjacent areas is smooth, effectively improving the stability and anti-relaxation ability of the residual stress field.

[0018] 3. In this invention, due to the small deformation and high-quality, controllable residual stress field, the fatigue life improvement effect of the stiffened metal structural components treated by the method of this invention is more significant and consistent. The initiation and propagation of fatigue cracks in the stress concentration zone are more effectively suppressed, thereby greatly improving the safety, reliability, and service life of the structural components during service.

[0019] 4. The method of this invention clearly defines the process principles of partitioning, synchronization, and parameter coordination, with clear logic and ease of programming implementation. It can be adapted to multi-beam laser processing systems and industrial robots or CNC machine tools to achieve efficient, automated, and standardized processing of complex curved surface stiffening structures (such as aircraft frames and wing panels), and has good engineering application prospects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the reinforcing rib metal structural component provided in an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of the state of laser shock strengthening of region A provided in an embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram of the state of laser shock strengthening of region B provided in an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram showing the positional relationship between the laser beam and the reinforcing metal structural component provided in an embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram of the state of laser shock strengthening of regions C and D provided in an embodiment of the present invention.

[0026] Figure 6 This is a schematic diagram illustrating the implementation state of the multi-beam laser shock strengthening method for reinforcing metal structures provided in this embodiment of the invention.

[0027] The labels for the attached figures are as follows: 1. Substrate; 2. Reinforcing rib; 3. First transition R region; 4. Second transition R region; 5. Non-reinforcing rib surface; 6. Reinforcing rib center surface; 7. First angle bisector; 8. Second angle bisector; 9. First laser beam; 10. Second laser beam; 11. Third laser beam; 12. Reinforcing unit; 13. First reinforcing spot; 14. Second reinforcing spot; 15. Third reinforcing spot; 16. Fourth reinforcing spot. Detailed Implementation

[0028] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0029] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0030] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0031] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: like Figure 1 As shown, this embodiment takes a typical T-shaped reinforcing rib metal structural component as an example. This structural component includes a base plate 1 and a reinforcing rib 2 perpendicular to the base plate 1. The connection between the reinforcing rib 2 and the base plate 1 is a rounded transition, forming a first transition R region 3 and a second transition R region 4. The plane opposite to the reinforcing rib 2 is the non-reinforcing rib surface 5. The center surface 6 of the reinforcing rib is the symmetry plane of the structure.

[0032] like Figure 6 As shown, this embodiment uses three independent pulsed lasers (or one laser in conjunction with a beam splitting and delay system) to generate three laser processing beams: the first laser beam 9, the second laser beam 10, and the third laser beam 11. The workpiece is clamped on a CNC worktable capable of multi-axis linkage.

[0033] The specific implementation steps of this invention are as follows: S1. Before laser shock peening, the boundaries of each zone are first determined based on the three-dimensional model.

[0034] In the first transition R region 3, a first angle bisector 7 is formed between the reinforcing rib center surface 6 and the non-reinforcing rib surface 5, dividing the reinforcement range of the first transition R region 3 into region A near the substrate 1 and region B near the reinforcing rib 2.

[0035] Similarly, within the second transition zone R4, zones A and B are divided.

[0036] On the non-reinforcing rib surface 5, the projection area of ​​the reinforcing rib 2 is designated as area C, and the areas on both sides of area C are designated as area D.

[0037] S2. In this embodiment, the non-reinforcing rib surface 5 is strengthened first to pre-set a basic pressure field.

[0038] The unreinforced surface 5 is scanned and strengthened using a third laser beam 11. For example... Figure 5 As shown, region C is first strengthened. The laser shock strengthening parameters for region C are as follows: a square laser spot with a size of 3 mm × 3 mm, a laser pulse width of 15 ns, and a laser power density of 8 GW / cm². 2 The overlap rate of light spots is 10%.

[0039] Subsequently, regions D on both sides of region C were strengthened using the following laser shock strengthening parameters: a square laser spot of 3 mm × 3 mm, a laser pulse width of 15 ns, and a laser power density of 6 GW / cm². 2 The overlap rate of the light spots is 10%. The reinforcement range is controlled within the outer contour of the projection of areas A and B on the non-reinforcing rib surface 5.

[0040] During the strengthening process, water (deionized water) is kept flowing stably as a constraint layer to form a deionized water film of uniform thickness, and aluminum foil tape is pasted on the surface of the workpiece as an absorption layer.

[0041] S3. This step is the core, using the first laser beam 9 and the second laser beam 10 to work synchronously.

[0042] Symmetrical synchronous reinforcement in area A (such as...) Figure 2 (as shown) The A region of the first transition R region 3 and the A region of the second transition R region 4 are enhanced synchronously and mirror-symmetrically. The first laser beam 9 and the second laser beam 10 use identical process parameters: a square laser spot size of 3 mm × 3 mm, a laser pulse width of 15 ns, and a laser power density of 7 GW / cm². 2 The overlap rate of light spots is 10%.

[0043] The beam paths of the two beams are strictly mirror-symmetrical about the central plane 6 of the reinforcing rib. The computer control system ensures that the two beams simultaneously impact symmetrical positions in area A on both sides.

[0044] The reinforcement path must completely cover area A on both sides. The actual light spot path can extend slightly to substrate 1 and reinforcing rib 2, but the extension amount is controlled within 30% of the thickness of reinforcing rib 2.

[0045] like Figure 4 As shown, when impacting the curved surface of region A, by adjusting the incident angle of beams 9 and 10 or the workpiece posture, it is ensured that the central axis of the beam is always basically perpendicular to the local surface tangent plane at the impact point (shown by the dotted line in the figure), and the normal change angle of the curved surface area covered by a single beam spot is less than 30°.

[0046] Unitized interleaved synchronous reinforcement in area B (e.g.) Figure 3 (as shown) After strengthening region A, strengthening is performed on region B of the first transition R region 3 and region B of the second transition R region 4. At this time, the first laser beam 9 and the second laser beam 10 still use the same process parameters: a square laser spot with a size of 3 mm × 3 mm, a laser pulse width of 15 ns, and a laser power density of 7 GW / cm². 2 The overlap rate of the light spot is 10%, but it may differ from the parameters of area A.

[0047] Region B is divided into multiple reinforcing units 12 along the length of the reinforcing rib. For example... Figure 3 As shown, an enhancement unit 12 includes a first enhancement spot 13 and a second enhancement spot 14 that are adjacent along the length direction in region B of the first transition R region 3, and a third enhancement spot 15 and a fourth enhancement spot 16 that are mirror-symmetrical to it in region B of the second transition R region 4.

[0048] The enhanced sequence is not mirror synchronization, but interleaved synchronization: First, the control system controls the first laser beam 9 to form a first enhanced spot 13 to enhance the impact on region B of the first transition R region 3, while simultaneously controlling the second laser beam 10 to form a fourth enhanced spot 16 to enhance the impact on region B of the second transition R region 4. This completes the synchronous impact.

[0049] Then, within the same strengthening unit 12, the first laser beam 9 moves to form a second strengthening spot 14 to strengthen the impact on region B of the first transition R region 3, and the second laser beam 10 moves to form a third strengthening spot 15 to strengthen the impact on region B of the second transition R region 4, thus performing a second synchronous impact.

[0050] At this point, one enhancement unit 12 is complete. The system controls the laser beam to move to the next enhancement unit, repeating the above interleaved synchronization process until the enhancement of the entire B area is completed.

[0051] During the above process, the absorber layer and the confinement layer media remain unchanged. By adjusting the laser output, beam scanning speed and path, parameters such as power density, pulse width (by adjusting the laser), and beam overlap rate in each region can be flexibly controlled, thereby achieving precise control over the depth and distribution of the final residual stress field.

[0052] The advantages of this invention are as follows: Through the above steps, the strengthening of the transition zones on both sides maintains a high degree of synchronicity (complete synchronization in zone A, staggered synchronization within the unit of zone B), ensuring that the deformation torques generated by the impact on both sides are canceled out in real time, and the cumulative deformation of the workpiece during the entire strengthening process is minimal. The pre-strengthening of the non-reinforcing rib surface and the design of gradient parameters further optimize the overall stress balance. The final workpiece not only obtains a deep and stable residual compressive stress layer in the first transition zone R3 and the second transition zone R4, effectively improving fatigue performance, but also maintains excellent shape accuracy such as straightness and flatness, requiring little or no straightening.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for multi-beam laser shock strengthening of reinforcing rib metal structures, characterized in that, Includes the following steps: Using two or more laser processing beams, dual-sided synchronous laser shock strengthening is carried out on the transition area on both sides of the stiffener of the metal structural component. Furthermore, laser shock peening is performed on the non-reinforcing surface of the reinforcing metal structural member using at least one laser processing beam; Specifically, the laser shock strengthening of the non-reinforcing rib surface is performed before or after the bilateral synchronous laser shock strengthening in the transition zone on both sides.

2. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 1, characterized in that, The transition zone includes region A and region B. The laser shock strengthening range of the transition zone on each side of the reinforcing rib is divided into region A, which is closer to the substrate, and region B, which is closer to the reinforcing rib, by the bisector of the angle between the center plane of the reinforcing rib and the non-reinforcing rib. The non-reinforcing surface includes region C and region D. Region C is located within the projection area of ​​the reinforcing rib, and region D is located on both sides of region C.

3. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 2, characterized in that, When performing dual-sided synchronous laser shock strengthening on region A, the laser processing beams used on both sides adopt the same process parameters and spot paths, and the strengthening spots on both sides are symmetrically distributed relative to the center plane of the reinforcing rib.

4. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 3, characterized in that, The laser power density enhanced in region A is I A The pulse width is τ A Its actual reinforcement range completely covers area A, and the part that extends beyond the boundary of area A is less than 50% of the thickness of the reinforcing rib.

5. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 4, characterized in that, The laser power density for laser shock enhancement of region C is: I C Pulse width is τ C The laser power density for laser shock enhancement of region D is I D Pulse width is τ D And satisfy: I D ≤ I C ≤ I A ,and τ D ≤ τ C ≤ τ A .

6. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 2, characterized in that, When performing dual-sided synchronous laser shock strengthening on region B, the same process parameters and different spot paths are used on both sides; Multiple reinforcing units are arranged along the length of the reinforcing rib metal structure. Each reinforcing unit consists of two adjacent light spots on one side of the reinforcing rib along its length and two adjacent light spots mirrored on the other side. For each of the strengthening units, the two non-mirror-distributed light spots on both sides of the reinforcing rib are first strengthened synchronously, and then the remaining two light spots in the same strengthening unit are strengthened synchronously. The strengthening of all strengthening units is completed in this order.

7. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 2, characterized in that, The reinforcement range of regions C and D does not exceed the projection range of regions A and B on the non-reinforcing rib surface.

8. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 2, characterized in that, When performing bilateral synchronous laser shock enhancement on areas A and / or B, the central axis of the laser processing beam is controlled to be perpendicular to the tangent plane at the center of the enhancement spot, and the size of the enhancement spot is controlled so that the angle between all tangent planes within the area covered by the enhancement spot in a single shock is no greater than 30°.

9. The multi-beam laser shock blasting method for reinforcing rib metal structures as described in claim 2, characterized in that, When performing laser shock strengthening on regions A, B, C, and D, the same absorption layer medium and constraint layer medium are used.

10. The multi-beam laser shock peening method for reinforcing rib metal structures as described in claim 1, characterized in that, By moving the laser processing beam, moving the reinforcing metal structure, or moving the laser processing beam and the reinforcing metal structure together, the beam angle of the laser processing beam relative to the reinforcing metal structure and the position of the strengthening spot can be adjusted.

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