A laser shock peening apparatus and method

Abstract

This invention provides a laser shock peening device and method, belonging to the field of laser shock peening technology. It can at least partially solve the problem of poor laser shock peening effect caused by insufficient utilization of laser energy in existing methods. The laser shock peening device of this invention includes a laser generating system, comprising a laser, a workpiece control system, and a beam control system. The beam control system is located between the laser generating system and the workpiece control system. The beam control system includes a beam splitter, a beam combiner, a reflector, a photodetector, and a focusing lens fixed on an optical path platform. Both the beam splitter and the beam combiner are double-sided coated lenses, each having a semi-reflective / semi-transparent surface coated with a semi-reflective / semi-transparent film and a fully transparent film. The laser shock peening process is completed by splitting a single laser beam into two or four beams, combining them through a reflector array by adding a certain time interval between the beams, and focusing the beams to irradiate the workpiece surface, thereby improving the laser shock peening effect.

Description

Technical Field

[0001] This invention belongs to the field of laser shock peening, and specifically relates to a laser shock peening device and method. Background Technology

[0002] Laser shock peening technology utilizes short-pulse (<50ns), high-power-density (GW / cm²) lasers that pass through a transparent confinement layer and act on an absorption layer covering a metal surface. Upon absorbing laser energy, the absorption layer rapidly vaporizes, generating dense, high-temperature, high-pressure plasma. Constrained by the confinement layer, the plasma continues to absorb laser energy and expands rapidly, forming a high-pressure shock wave along the laser propagation path. This causes intense plastic deformation of the metal surface, refining the metal grains and generating numerous dislocations, twins, and other microstructures, thereby improving the fatigue life of the material surface. Increasing the laser energy density can increase the peak pressure of the laser-induced shock wave, thus enhancing the laser shock peening effect.

[0003] Existing methods for increasing laser energy density generally involve reducing the spot diameter. However, a small spot diameter leads to poor stress distribution uniformity. In existing laser shock peening equipment, for a laser beam with a pulse width of tens of nanoseconds, only the first few nanoseconds reach the target surface and induce plasma. The subsequent laser energy is largely absorbed by the high-density plasma, resulting in a plasma shielding effect. This leads to suboptimal laser energy distribution and insufficient utilization, limiting the pressure and duration of the laser-induced shock wave, ultimately affecting the effectiveness of laser shock peening. Furthermore, when laser shock peening complex workpiece surfaces, the laser processing parameters are generally fixed, making it difficult or impossible to "tailor" the treatment to specific needs, thus hindering the achievement of optimal strengthening results. Summary of the Invention

[0004] The purpose of this application is to provide a laser shock peening device and method. On the one hand, it solves the technical problem of poor laser shock peening effect caused by insufficient utilization of laser energy in related technologies. On the other hand, by adjusting the number of pulses, delay interval, spot diameter, spot overlap rate, and spot scanning path in real time, different laser processing parameters are used for different processing areas on the surface of complex workpieces, thereby obtaining a better peening effect.

[0005] In a first aspect, this application provides a laser shock peening device, comprising: a laser generating system including a laser capable of emitting a laser beam; a beam control system disposed between the laser generating system and the workpiece control system, including an optical path platform and a beam splitter, a beam combiner, a reflector, a photodetector, and a focusing lens fixed on the optical path platform; the beam splitter and the beam combiner are both double-sided coated lenses, the double-sided coated lenses having a semi-reflective and semi-transparent surface coated with a semi-reflective and semi-transparent film and a fully transparent film; the beam splitter includes a first beam splitter and a second beam splitter, the beam combiner includes a first beam combiner and a second beam combiner; the first beam splitter, the first beam combiner, the second beam splitter, and the second beam combiner are sequentially spaced on the optical path platform, and the photodetector and the focusing lens are sequentially disposed on the side of the second beam combiner away from the second beam splitter; the reflector includes a first reflector group, the first reflector group including a first reflector, a second reflector, a third reflector, a fourth reflector, a fifth reflector, and a sixth reflector;

[0006] A workpiece control system includes a support platform for placing the workpiece; the workpiece control system is located on the side of the focusing lens opposite to the second beam combiner lens, and the workpiece control system includes the support platform for placing the workpiece; wherein,

[0007] When the beam-splitting surface of the first beam splitter faces the light beam and the incident angle is 45°, and the semi-reflective and semi-transparent surfaces of the first beam combiner, the second beam splitter, and the second beam combiner are parallel to each other and perpendicular to the semi-reflective and semi-transparent surface of the first beam splitter, all the light transmitted on the semi-reflective and semi-transparent surface of the first beam splitter propagates in a straight line to the focusing lens after being transmitted through the first beam combiner, the second beam splitter, and the second beam combiner. The light beam reflected from the semi-reflective and semi-transparent surface of the first beam splitter can propagate sequentially through the first reflector, the second reflector, the fifth reflector, the sixth reflector, the third reflector, and the fourth reflector to the first beam combiner, and then propagate sequentially through the reflection of the first beam combiner, the transmission of the second beam splitter, and the transmission of the second beam combiner to the focusing lens, thereby increasing the propagation path of the light beam.

[0008] In the above scheme, the laser shock strengthening equipment uses double-sided lenses with semi-reflective and fully transparent films coated on both the beam splitter and beam combiner in the beam control system. The first beam splitter splits the beam into two laser beams: one for transmission and one for reflection. The reflected laser beam has its propagation time extended by a reflecting mirror. This results in the delayed optical path through the first beam splitter and the first beam combiner being only half that through the second beam splitter and the second beam combiner. This forms two pulsed laser beams that strike the workpiece sequentially at a certain time interval. By adjusting the number of pulses and the delay interval, the problems of insufficient laser energy utilization and poor laser shock strengthening effect are solved.

[0009] In some embodiments of this application, the beam control system further includes a second mirror group, which comprises a seventh mirror, an eighth mirror, a ninth mirror, a tenth mirror, an eleventh mirror, and a twelfth mirror. When the first beam splitter and the second beam splitter are parallel to each other, and the beam splitting surfaces of their semi-reflective and semi-transparent surfaces are both facing the beam with an incident angle of 45°, and the semi-reflective and semi-transparent surfaces of the first beam combiner and the second beam combiner are parallel to each other and both perpendicular to the semi-reflective and semi-transparent surface of the first beam splitter, the light transmitted on the semi-reflective and semi-transparent surface of the first beam splitter passes through the second mirror group. After transmission through the beam combiner, a portion of the light is reflected by the second beam splitter, and then sequentially reflected by the seventh, eighth, fourth, third, sixth, fifth, second, first, ninth, tenth, first, second, fifth, sixth, third, fourth, eleventh, and twelfth mirrors before propagating to the second beam combiner and being reflected by the focusing lens.

[0010] In the above scheme, by changing the angle of the second beam splitter so that its semi-reflective and semi-transparent surface is parallel to that of the first beam splitter, the beam is split twice by the first and second beam splitters. The four laser beams are then formed by the reflector to create four pulsed laser beams that strike the workpiece sequentially at a certain time interval due to their different optical paths.

[0011] In some embodiments of this application, the first and second reflectors, the third and fourth reflectors, and the fifth and sixth reflectors are arranged in pairs, with the reflecting surfaces of each pair of reflectors perpendicular to each other. The fourth reflector ensures that the light reflected from it to the first beam combiner is perpendicular to the laser emission direction. By delaying the laser beam through the reflector array, the optical path is delayed, and the beam is combined, ultimately resulting in two or four laser pulses of equal energy striking the same location on the strengthening target.

[0012] In some embodiments of this application, a terminal control system is also included, which includes a workbench, an oscilloscope, and a computer. The oscilloscope is connected to the photoelectric probe and the computer for signal transmission. The computer can control the laser generation system and the workpiece control system to monitor, debug, and control the two systems.

[0013] In the above scheme, the computer-controlled laser generation system and workpiece control system can monitor, debug and control the entire equipment, while the photoelectric probe can also transmit the detected signals to the computer.

[0014] In some embodiments of this application, the optical path platform further includes a rotating platform for fixing each of the beam splitters, with at least the second beam splitter fixed on the rotating platform.

[0015] In the above scheme, the rotating platform can control the rotation angle of the beam splitter in order to adjust the propagation path of the beam.

[0016] In some embodiments of this application, the workpiece control system further includes a robot arm, the free end of which is fixedly mounted with the support platform.

[0017] In the above scheme, the support platform is set at the free end of the robot arm, which can adjust the position and angle of the workpiece.

[0018] In some embodiments of this application, the optical path platform further includes a through slot and a linear platform section. The linear platform section includes a linear platform body that can move away from and close to the first beam splitter within the through slot. The first reflector, the second reflector, the third reflector, and the fourth reflector are sequentially arranged on the linear platform body along the laser emission direction.

[0019] In the above scheme, a movable direct-motion platform body is set up, which can adjust the optical path of the laser reflected from the first beam splitter and the second beam splitter, thereby controlling the interval time between multiple laser beams impacting the workpiece.

[0020] In some embodiments of this application, the linear motion platform further includes a motor, a lead screw, and a light rod. The lead screw and the light rod are both mounted on the optical path platform and pass through the linear motion platform body in a direction perpendicular to the laser emission direction. The motor is capable of driving the lead screw to rotate.

[0021] In the above scheme, a lead screw and slider structure is used to adjust the linear platform body to move closer to or further away from the first beam splitter. The optical rod is used for guidance, which enables the worktable to move smoothly and avoids the linear platform body from rotating, which would cause the reflector to become unstable.

[0022] In some embodiments of this application, the linear motion platform further includes two accordion-style dustproof cloths, one side of which is connected to the linear motion platform body along a path perpendicular to the laser emission direction, and the other side is connected to the inner side of the through groove.

[0023] In the above solution, the two accordion-style dustproof cloths installed on both sides of the direct-motion platform body can ensure that the inside of the platform is clean and free of foreign objects.

[0024] Secondly, this application provides a laser shock strengthening method, which employs the aforementioned laser shock strengthening apparatus and includes the following steps:

[0025] Mapping and modeling the surface of the workpiece: including the shape, size, and material properties of different areas of the workpiece to be processed;

[0026] The laser processing parameters for different processing and strengthening areas on the workpiece surface are planned by computer: the laser processing parameters include the pulsed laser wavelength, pulse width, single pulse energy during the strengthening process, the diameter of the circular spot, the spot overlap rate, the spot scanning path, the number of pulses and the delay interval adjusted according to different processing areas;

[0027] Pre-treatment of the surface of the workpiece to be processed;

[0028] After fixing the workpiece, turn on the laser;

[0029] After the laser shock peening process is completed, remove the workpiece and turn off the laser;

[0030] When the actual laser pulse does not match the preset value, the laser pulse information is transmitted to the oscilloscope in real time through the photoelectric probe PS, and then the computer corrects the actual laser pulse in real time.

[0031] The technical solution of this application effectively increases the density and duration of laser-induced plasma by splitting the laser into two or four beams of equal energy and then impacting the target material sequentially at a certain time interval. This, in turn, increases the peak pressure and duration of the laser-induced shock wave, ultimately improving the effect and application range of laser shock strengthening. Furthermore, addressing the issue that processing parameters are generally fixed and unadjustable during laser processing, this application provides a laser shock strengthening device. By adjusting the number of pulses, delay interval, spot diameter, spot overlap rate, and spot scanning path, different processing parameters can be assigned to different processing areas, thereby achieving better strengthening effects on various surfaces to be processed. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram illustrating the principle of laser shock peening in some embodiments of this application;

[0034] Figure 2 This is a schematic diagram of the structure of the laser shock strengthening device in some embodiments of this application;

[0035] Figure 3This is a schematic diagram of the structure of the double-sided coated lens in some embodiments of this application. Figure 1 ;

[0036] Figure 4 This is a schematic diagram of the structure of the double-sided coated lens in some embodiments of this application. Figure 2 ;

[0037] Figure 5 This is a schematic diagram of the optical path platform in some embodiments of this application;

[0038] Figure 6 This is a partial structural schematic diagram of the optical path platform and the linear motion platform in some embodiments of this application;

[0039] Figure 7 This is a schematic diagram of the structure of the direct-drive platform in some embodiments of this application;

[0040] Figure 8 These are schematic diagrams of the supporting platform and workpiece structure in some embodiments of this application;

[0041] Figure 9 The amplitude factor of the single-pulse laser-induced shock wave pressure in the comparative example;

[0042] Figure 10 This refers to the dual-pulse laser-induced shock wave pressure amplitude factor in some embodiments of this application;

[0043] Figure 11 This refers to the four-pulse laser-induced shock wave pressure amplitude factor in some embodiments of this application.

[0044] The reference numerals in the detailed embodiments are as follows:

[0045] 1-Laser generating system; 11-Vibration-resistant platform; 12-Laser; 2-Beam control system; 21-Optical path platform; 211-First rotating platform; 212-Second rotating platform; 213-Directional platform body; 214-Lead screw; 215-Optical rod; 213-Cellowing dustproof cloth; 22-Double-sided coated mirror; 221-First double-sided coated mirror; 222-Second double-sided coated mirror; 23-Beam combiner; 231-First beam combiner; 232-Second beam combiner; 24-Reflector; 25-Photodetector; 26-Focusing lens; 3-Workpiece control system; 31-Bearing platform; 32-Workpiece; 33-Robot arm; 34-Energy absorption layer; 35-Energy confinement layer; 4-Terminal control system; 41-Workbench; 42-Oscilloscope; 43-Computer. Detailed Implementation

[0046] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms "comprising" and "having" and any variations thereof in the specification, claims and foregoing drawings are intended to cover non-exclusive inclusion.

[0048] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0049] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0050] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0051] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two).

[0052] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0053] For a laser beam with a pulse width of tens of nanoseconds, existing laser shock equipment only allows the first few nanoseconds of the laser to reach the target surface and induce plasma. The subsequent laser energy is largely absorbed by the high-density plasma, resulting in a plasma shielding effect. This leads to suboptimal laser energy distribution and insufficient utilization, limiting the pressure and duration of the laser-induced shock wave, ultimately affecting the laser shock strengthening effect. Therefore, the inventors improved the shock effect by using a semi-reflective, semi-transparent beam splitter and beam combiner, combined with a reflector, to sequentially impact the workpiece with multiple pulsed laser beams at regular time intervals. Furthermore, by adjusting the number of pulses, delay interval, spot diameter, spot overlap rate, and spot scanning path in real time, different laser processing parameters are applied to different processing areas on the workpiece surface, thereby achieving a better strengthening effect.

[0054] For ease of explanation, the following embodiments use a laser shock peening device according to an embodiment of this application as an example.

[0055] Reference Figures 1 to 3 A laser shock peening device includes: a laser generating system, including a laser capable of emitting a laser beam; a workpiece control system, including a support platform 31 for placing a workpiece; and a beam control system, disposed between the laser generating system and the workpiece control system, including an optical path platform 21 and a beam splitter 22, a beam combiner 23, a reflector 24, a photodetector 25, and a focusing lens 26 fixed on the optical path platform 21; the beam splitter 22 and the beam combiner 23 are both double-sided coated lenses, each having a semi-reflective and semi-transparent surface coated with a semi-reflective and semi-transparent film; the beam splitter 22 includes a first beam splitter 221 and a second beam splitter 222, and the beam combiner 23 includes a first beam combiner 232. 1. A first beam splitter 221, a first beam combiner 231, a second beam splitter 222, and a second beam combiner 232 are sequentially and spaced apart on the optical path platform 21. A photoelectric probe 25 and a focusing lens 26 are sequentially arranged on the side of the second beam combiner 232 away from the second beam splitter 222. A reflecting mirror 24 includes a first reflecting mirror group, which includes a first reflecting mirror M1, a second reflecting mirror M2, a third reflecting mirror M3, a fourth reflecting mirror M4, a fifth reflecting mirror M5, and a sixth reflecting mirror M6. A workpiece control system is located on the side of the focusing lens 26 away from the second beam combiner 232. The workpiece control system includes a support platform 31 for placing the workpiece.

[0056] When the beam splitting surface of the semi-reflective and semi-transparent surface of the first beam splitter 221 faces the beam and the incident angle is 45°, and the semi-reflective and semi-transparent surfaces of the first beam combiner 231, the second beam splitter 222, and the second beam combiner 232 are parallel to each other and perpendicular to the semi-reflective and semi-transparent surface of the first beam splitter 221, all the light transmitted through the semi-reflective and semi-transparent surface of the first beam splitter 221 is transmitted through the first beam combiner 231, the second beam splitter 222, and the second beam combiner 232 and propagates in a straight line to the focusing lens 26; the beam reflected from the semi-reflective and semi-transparent surface of the first beam splitter 221 can propagate sequentially through the first reflecting mirror M1, the second reflecting mirror M2, the fifth reflecting mirror M5, the sixth reflecting mirror M6, the third reflecting mirror M3, and the fourth reflecting mirror M4 to the first beam combiner 231, and then propagate sequentially through the reflection of the first beam combiner 231, the transmission of the second beam splitter 222, and the transmission of the second beam combiner 232 to the focusing lens 26, thereby increasing the propagation path of the beam.

[0057] Among them, the double-sided coated lens has a semi-reflective and semi-transparent film coated on one side and a fully transparent film coated on the other side. The transmission intensity and reflection intensity of the double-sided coated lens can be 50% / 50%, 60% / 40%, 70% / 30%, and 80% / 20%, respectively.

[0058] In some embodiments of this application, the beam control system further includes a second mirror group, which includes a seventh mirror m1, an eighth mirror m2, a ninth mirror m3, a tenth mirror m4, an eleventh mirror m5, and a twelfth mirror m6. When the first beam splitter 221 and the second beam splitter 222 are parallel to each other, and the beam splitting surfaces of their semi-reflective and semi-transparent surfaces are both facing the beam with an incident angle of 45°, and the semi-reflective and semi-transparent surfaces of the first beam combiner 231 and the second beam combiner 232 are parallel to each other and both are perpendicular to the semi-reflective and semi-transparent surface of the first beam splitter 221, the light transmitted through the semi-reflective and semi-transparent surface of the first beam splitter 221... After being transmitted through the first beam combiner 231, a portion is reflected by the second beam splitter 222, and then sequentially reflected by the seventh mirror m1, the eighth mirror m2, the fourth mirror M4, the third mirror M3, the sixth mirror M6, the fifth mirror M5, the second mirror M2, the first mirror M1, the ninth mirror m3, the tenth mirror m4, the first mirror M1, the second mirror M2, the fifth mirror M5, the sixth mirror M6, the third mirror M3, the fourth mirror M4, the eleventh mirror m5, and the twelfth mirror m6, before propagating to the second beam combiner 232 and being reflected by the focusing mirror 26.

[0059] The double-sided coated lens is a beam splitter with a semi-transparent and semi-reflective coating on one side and a fully transparent coating on the other. During beam splitting, the semi-transparent and semi-reflective coating faces the laser at a 45° angle; during full transparency, the fully transparent coating faces the laser at a 45° angle. When beam splitting is not required, both the first beam splitter 221 and the second beam splitter 222 operate with the fully transparent coating. When beam splitting is required once, the first beam splitter 221 operates with the semi-transparent and semi-reflective coating, and the second beam splitter 222 operates with the fully transparent coating, suitable for situations with small optical path differences. The second beam splitter 222 operates with the semi-transparent and semi-reflective coating, and the first beam splitter 221 operates with the fully transparent coating, suitable for situations with large optical path differences. When beam splitting is required twice, both the first beam splitter 221 and the second beam splitter 222 operate with the semi-transparent and semi-reflective coating.

[0060] When the transmission intensity and reflection intensity of the double-sided coated lens are both 50%, the laser energy is divided into two or four laser beams with the same energy, and they impact the target material sequentially at a certain time interval.

[0061] The working principle of a single laser shock is as follows:

[0062] The main mechanism in laser pulse-induced plasma is avalanche ionization. The electron density growth rate is: (dN_e(t)) / dt=v_i N_e(t), where the electron density N_e is a function of time t; v_i is the avalanche ionization coefficient, which is proportional to the laser intensity. Since the laser energy is divided equally, the energy of each laser pulse after beam splitting is less than the energy before beam splitting. Therefore, the plasma density generated by a single laser pulse is greater than that generated by the first pulse of a multi-pulse series. Subsequently, the plasma density decreases due to recombination losses, with a decay rate of: (dN_e(t)) / dt=-α_r〖[N_e(t)]〗^2, where α_r is the collision recombination coefficient. From the formula, it can be seen that the decay rate is proportional to the square of the electron density. Therefore, the plasma density generated by a single laser pulse decreases faster than that of the first pulse of a multi-pulse series, and the plasma density generated by a single laser pulse continues to decrease thereafter.

[0063] The working principle of time-series multi-laser pulses is as follows:

[0064] In sequential multi-pulse laser systems, after a certain interval between subsequent pulses, the plasma density of the previous pulses decreases. Some of the laser energy can penetrate the plasma and reach the target surface to induce new plasma, while some energy can re-excite the plasma generated by the previous pulses. At the same time, due to the dispersing effect of the plasma generated by the previous pulses, the subsequent plasma expands more rapidly within the previous plasma, thereby increasing the peak pressure and duration of the laser-induced shock wave, and thus effectively improving the effect and application range of laser shock enhancement.

[0065] Please refer to Figure 1The first reflecting mirror M1 and the second reflecting mirror M2, the third reflecting mirror M3 and the fourth reflecting mirror M4, and the fifth reflecting mirror M5 and the sixth reflecting mirror M6 are arranged in pairs, with the reflecting surfaces of each pair of reflecting mirrors perpendicular to each other. The fourth reflecting mirror M4 ensures that the light rays reflected from it to the first beam combiner 231 are perpendicular to the laser emission direction. The perpendicular arrangement of the pairs of reflecting mirrors causes the laser to reciprocate in a certain direction. This arrangement helps to make full use of the limited space to extend the propagation time between beams, thereby achieving the effect of each laser beam impacting the workpiece at intervals.

[0066] Taking a four-pulse laser as an example, the single-pulse laser is emitted by the laser generator. After the first beam split, the laser is divided into two pulse lasers a and b with equal energy. a travels directly from the first beam splitter 221 to the first beam combiner 231. b is reflected by M1-M2-M5-M6-M3-M4 and then combined with the previous laser to form a sequential double-pulse laser a+b. a+b undergoes a second beam split to obtain four sub-lasers with energy one-quarter that of the initial pulse laser: a1, a2, b1, and b2. a1 and b1 travel directly from the second beam splitter 222 to the second beam combiner 232. a1, emitted from the laser generator, travels directly to the second beam combiner 232 without changing direction. The beam combiner 232 requires the shortest time. After reflection by M1-M2-M5-M6-M3-M4, phase b1 is combined with a1 on the first beam combiner 231 with a path difference of one time. After reflection by m1-m2-M4-M3-M6-M5-M2-M1-m3-m4-M1-M2-M5-M6-M3-M4-m5-m6, pulsed lasers a2 and b2 are respectively combined with a1 and b1 with a2 times the path difference. They are then combined with a1 and b1 on the second beam combiner 232 to form a sequential sub-pulse a1+b1+a2+b2. The four pulses are all separated by a path difference of one time. Finally, after focusing, the workpiece is subjected to laser shot peening strengthening.

[0067] In some embodiments of this application, a terminal control system is also included. The terminal control system 4 includes a workbench 41, an oscilloscope 42, and a computer 43. The oscilloscope 42 is connected to the photoelectric probe 25 and the computer 43 respectively to transmit information. The computer 43 can control the laser generation system 1 and the workpiece control system respectively to realize the monitoring, debugging and control of the two systems.

[0068] The workpiece control system, controlled by a computer, ensures that the processing area remains perpendicular to the laser. The diameter of the circular laser spot is adjusted by regulating the gap between the workpiece surface and the focusing lens. The overlap rate and scanning path of the laser spot are adjusted by controlling the feed speed and strategy of the robotic arm in the workpiece control system. The double-sided coating mirror on the rotating platform is controlled by a computer to ultimately control the laser to be split into 1, 2, or 4 beams and then combined. The position of the reflector on the linear platform body is adjusted by controlling the rotation of the motor, which drives the lead screw to adjust the optical path difference, thereby achieving the purpose of adjusting the delay interval.

[0069] In the above scheme, the computer-controlled laser generating system 1 and workpiece control system can monitor, debug and control the entire equipment, while the photoelectric probe can also transmit the detected signals to the computer.

[0070] Optionally, the laser generating system 1 also includes a vibration-damping platform 11, on which the laser 12 is placed. The vibration-damping platform 11 reduces the influence of external factors on the optical path.

[0071] In some embodiments of this application, the optical path platform 21 further includes a rotating platform for fixing each beam splitter 22, with at least the second beam splitter 222 fixed on the rotating platform. The second beam splitter 222 is fixed on the rotating platform, and the beam from the second beam splitter 222 is controlled to be either semi-transparent / semi-reflective or fully transparent by controlling the rotating platform, thus achieving beam splitting once or twice. The optical path platform 21 also includes a drive device for driving the rotating platform to rotate; optionally, the drive device can be a motor. The rotating platform includes a first rotating platform 211 and a second rotating platform 212.

[0072] In some embodiments of this application, the workpiece control system further includes a robot arm 32, with a support platform 31 fixedly mounted on the free end of the robot arm 32. By placing the support platform at the free end of the robot arm, the position and angle of the workpiece can be adjusted.

[0073] In some embodiments of this application, the optical path platform 21 further includes a through slot and a linear motion platform section. The linear motion platform section includes a linear motion platform body 213 that can move away from and closer to the first beam splitter 221 within the through slot. The first reflector M1, the second reflector M2, the third reflector M3, and the fourth reflector M4 are sequentially arranged on the linear motion platform body 213 along the laser emission direction. The movable linear motion platform body 213 can adjust the optical path of the laser reflected from the first beam splitter and the second beam splitter, thereby controlling the interval between the successive impacts of multiple laser beams on the workpiece.

[0074] In some embodiments of this application, the linear motion platform further includes a motor (not shown), a lead screw 214, and a light rod 215. Both the lead screw 214 and the light rod 215 are mounted on the optical path platform and pass through the linear motion platform body 213 perpendicular to the laser emission direction. The motor can drive the lead screw 214 to rotate. The light rod 215 provides support and a track for the linear motion platform body, preventing the reflector from becoming unstable due to rotation of the linear motion platform body 213, thus ensuring the stability and reliability of the movement. The motor drives the lead screw 214 to rotate, thereby moving the linear motion platform body 213 to adjust the optical path difference. Optionally, there can be two light rods 215.

[0075] In some embodiments of this application, the direct-motion platform also includes two accordion-style dustproof cloths 216. One side of the accordion-style dustproof cloth 216, perpendicular to the laser emission direction, is connected to the direct-motion platform body 213, and the other side is connected to the inner side of the through groove. The two accordion-style dustproof cloths 216 installed on both sides of the direct-motion platform body 213 can ensure that the inside of the platform is clean and free of foreign objects.

[0076] Optionally, the two sides of the direct-drive platform body 213 are provided with pressure plates for fixing the free ends of the accordion-style dustproof cloth. Each pressure plate is provided with positioning pins at both ends, and the middle part of the pressure plate is fixed by multiple set screws.

[0077] Reference Figures 1 to 2 A laser shock enhancement method based on time-series multi-laser pulses is provided, wherein the method employs the aforementioned laser shock enhancement device based on time-series multi-laser pulses.

[0078] Includes the following steps:

[0079] Mapping and modeling the surface of the workpiece: including the shape, size, and material properties of different areas of the workpiece to be processed;

[0080] The laser processing parameters for different processing and strengthening areas on the workpiece surface are planned by computer: the laser processing parameters include the pulsed laser wavelength, pulse width, single pulse energy during the strengthening process, the diameter of the circular spot, the spot overlap rate, the spot scanning path, the number of pulses and the delay interval, which are adjusted according to different processing areas.

[0081] Pre-treatment of the surface of the workpiece to be processed;

[0082] After fixing the workpiece, turn on the laser;

[0083] After the laser shock peening process is completed, the workpiece is removed and the laser is turned off.

[0084] Example 1:

[0085] The original single-pulse laser energy was 2J, the laser wavelength was 1064nm, and the pulse half-width was 10ns. The laser spot focused onto the workpiece surface by the lens was 2mm. A piezoelectric thin-film sensor was fixed on the support platform as the target material, with its surface perpendicular to the laser incident direction. A 120μm thick black tape was attached to the surface as an energy absorption layer, and a 2mm thick flowing water curtain was used as an energy confinement layer. Single-point laser shot peening tests were conducted, and the variation of shock wave pressure was recorded by the piezoelectric thin-film sensor. Finally, the variation of laser-induced shock wave pressure amplitude was corrected based on the computer simulation.

[0086] Based on the principle of laser-induced plasma detonation waves, the laser pulse first reaches the energy absorption layer, inducing the generation of plasma. As the plasma density continuously increases, most of the subsequent laser energy fails to reach the energy absorption layer and is absorbed by the plasma, rapidly expanding and compressing the air outside the surface, thus forming a detonation wave. Its pressure amplitude factor is as follows: Figure 9 As shown.

[0087] The dual-pulse laser is formed by splitting the original single-pulse laser beam. The first beam splitter, 221, separates the beams, while the second beam splitter, 222, is fully transparent. The optical path difference between the two pulsed laser beams is adjusted to 10 ns by adjusting the linear motion platform. After measurement correction, the detonation wave pressure factor induced by the dual-pulse laser is as follows: Figure 10 As shown.

[0088] Based on previous dual-pulse laser experiments, the second beam splitter 222 was adjusted to a splitting mode. At this point, the two pulsed laser beams split from the original single-pulse laser were each further divided into two beams, resulting in a total of four sequentially ordered pulsed laser beams, with a 10ns interval between each pair. After testing and correction, the detonation wave pressure factor induced by the four-pulse laser was as follows: Figure 11 As shown.

[0089] The results show that sequential multi-laser pulses can effectively avoid the plasma shielding time, effectively improve the effective utilization rate of laser energy, increase the peak pressure and duration of laser-induced detonation waves, thereby improving the effect of laser shock peening process and enhancing the performance of workpieces.

[0090] Example 2:

[0091] A time-sequential multi-laser-pulse laser shock strengthening device was used on a workpiece made of 2024-T351 aerospace-grade aluminum alloy. The specific steps are as follows:

[0092] (1) Select a 2mm thick 2024-T351 plate as the example sample. Use a wire cutting machine to cut it into a rectangular sample of 40mm×20mm×2mm. Grind and polish the surface to a surface roughness of ≤0.1μm. Finally, clean the sample surface with anhydrous ethanol and blow it dry for later use.

[0093] (2) The Poisson's ratio υ = 0.33 for 2024-T351, and the dynamic yield strength σ_Y^dym = 0.311 GPa, thus obtaining the Hugoniot elastic limit of 2024-T351:

[0094]

[0095] Generally, the optimal peak shock wave pressure Pm for laser shock enhancement is around 2HEL to 2.5HEL, or 1.2 to 1.5 GPa. For single-pulse laser shock enhancement, the peak pressure is:

[0096] P_m=0.01√(α / (2α+3))√Z√(I_0)

[0097] Where I_0=4χE / (τπd^2), 2 / Z=1 / Z_1+1 / Z_2, χ=0.7, d=0.3cm, τ=10ns, α=0.1, Z_1=0.165×10^6g / (cm2·s), Z_2=1.48×10^6g / (cm2·s). To meet the peak pressure requirement, the laser energy E should be between 1.4 and 2.2J, so in this embodiment, E=1J, and the spot overlap rate is 50%, using a zigzag trajectory. Furthermore, due to the simple structure, the processing parameters are the same in each region.

[0098] (3) Since the HEL of 2024-T351 is not high, only one beam splitting is required in this embodiment. Therefore, the second motor is controlled by computer to make BS2 exit the optical path. At the same time, the third electronic control third lead screw drives the third movable platform to move, and the interval between the two pulses is adjusted to 10ns, 20ns and 30ns by controlling the optical path difference.

[0099] (4) After the entire surface to be processed has been subjected to shock strengthening, turn off the laser, tidy up the experimental equipment, and the entire time-series multi-laser pulse laser shock strengthening process is over.

[0100] Table 1 compares the residual stress under different experimental parameters, namely single-laser pulse shock strengthening and dual-laser pulse shock strengthening (pulse intervals of 10 ns, 20 ns, and 30 ns). The parameters used for all four strengthening methods are: laser pulse energy 2 J, laser pulse width 10 ns, repetition frequency 1 Hz, and spot diameter 0.3 cm. After laser shock strengthening, residual stress was tested on the strengthened area.

[0101] As can be seen from the residual stress comparison in Table 1, compared with the single-pulse laser shock strengthening method, the sequential multi-pulse laser shock strengthening method can generate greater residual compressive stress on the surface, and the larger residual compressive stress can effectively improve the fatigue life of the workpiece. The progression from short to long pulse intervals also reflects a trend where the laser-induced shock wave pressure first increases and then decreases with the increase in pulse interval. If the pulse interval is too short, the plasma density remains high, and the shielding effect remains strong. If the pulse interval is too long, the second laser beam has almost no effect on the previous plasma.

[0102] Table 1

[0103] single laser pulse 10ns 20ns 30ns Surface residual stress -241MPa -310MPa -388MPa -340MPa

[0104] Compared with the prior art, this application divides a laser beam into two or four laser beams of equal energy, and combines them by adding a certain time interval between the beams through a reflector array and focusing them to irradiate the surface of the workpiece to complete the laser shock strengthening process. The plasma induced by this process has the advantages of longer duration and higher peak density compared with a laser beam of the same energy, which in turn leads to an increase in the duration of the induced shock wave and a greater peak pressure, ultimately enhancing the effect of laser shock strengthening.

[0105] Furthermore, for complex workpiece surfaces, different laser processing parameters are applied to different areas. This includes adjusting the linear platform to control the optical path difference, adjusting the rotary platform to control the beam splitting mode, and adjusting the robotic arm to control the spot diameter, spot width, and scanning path during the laser shock stabilization process, thereby achieving better laser shock stabilization results. The actual laser pulse is monitored in real time using a photoelectric sensor (PS), and the information is returned to an oscilloscope. Finally, a computer can be used to correct any deviations from the preset laser pulse in real time.

Claims

1. A laser shock peening device, comprising: A laser generating system, including a laser capable of emitting a laser beam; A beam control system, located between the laser generating system and the workpiece control system, includes an optical path platform ((21)) and a beam splitter (22), a beam combiner (23), a reflector (24), a photodetector (25), and a focusing lens (26) fixed on the optical path platform (21). Both the beam splitter (22) and the beam combiner (23) are double-sided coated lenses, each having a semi-reflective and semi-transparent surface coated with a semi-reflective and semi-transparent film and a fully transparent film. The beam splitter (22) includes a first beam splitter (221) and a second beam splitter (222), and the beam combiner (23) includes a first beam combiner (231) and a second beam combiner (232). 32); The first beam splitter (221), the first beam combiner (231), the second beam splitter (222), and the second beam combiner (232) are sequentially and spaced apart on the optical path platform (21). The photodetector (25) and the focusing lens (26) are sequentially arranged on the side of the second beam combiner (232) away from the second beam splitter (222); The reflector (24) includes a first reflector group, which includes a first reflector (M1), a second reflector (M2), a third reflector (M3), a fourth reflector (M4), a fifth reflector (M5), and a sixth reflector (M6); The workpiece control system includes a support platform (31) for placing the workpiece; the workpiece control system is located on the side of the focusing lens (26) opposite to the second beam combiner (232), and includes the support platform (31) for placing the workpiece; wherein, When the beam-splitting surface of the first beam splitter (221) faces the beam and the incident angle is 45°, and the semi-reflective and semi-transparent surfaces of the first beam combiner (231), the second beam splitter (222), and the second beam combiner (232) are parallel to each other and perpendicular to the semi-reflective and semi-transparent surface of the first beam splitter (221), all the light transmitted on the semi-reflective and semi-transparent surface of the first beam splitter (221) propagates in a straight line to the focusing lens after being transmitted through the first beam combiner (231), the second beam splitter (222), and the second beam combiner (232). 26); The light beam reflected from the semi-reflective and semi-transparent surface of the first beam splitter (221) can propagate sequentially through the first reflector (M1), the second reflector (M2), the fifth reflector (M5), the sixth reflector (M6), the third reflector (M3), and the fourth reflector (M4) to the first beam combiner (231), and then propagate sequentially through the reflection of the first beam combiner (231), the transmission of the second beam splitter (222), and the transmission of the second beam combiner (232) to the focusing lens (26), thereby increasing the propagation path of the light beam.

2. The laser shock peening device according to claim 1, characterized in that, The beam control system further includes a second mirror group, which includes a seventh mirror (m1), an eighth mirror (m2), a ninth mirror (m3), a tenth mirror (m4), an eleventh mirror (m5), and a twelfth mirror (m6). When the first beam splitter (221) and the second beam splitter (222) are parallel to each other, and the beam splitting surfaces of their semi-reflective and semi-transparent surfaces are both facing the light beam with an incident angle of 45°, and the semi-reflective and semi-transparent surfaces of the first beam combiner (231) and the second beam combiner (232) are parallel to each other and both are perpendicular to the semi-reflective and semi-transparent surface of the first beam splitter (221), the light transmitted on the semi-reflective and semi-transparent surface of the first beam splitter (221) is transmitted through the first beam combiner (231), and part of it is reflected by the second beam splitter (222), and then sequentially passes through the seventh reflector (m1), the eighth reflector (m2), and the fourth reflector (m3). 4) The third reflector (M3), the sixth reflector (M6), the fifth reflector (M5), the second reflector (M2), the first reflector (M1), the ninth reflector (M3), the tenth reflector (M4), the first reflector (M1), the second reflector (M2), the fifth reflector (M5), the sixth reflector (M6), the third reflector (M3), the fourth reflector (M4), the eleventh reflector (M5), and the twelfth reflector (M6) reflect the light and then propagate it to the second beam combiner (232) and reflect it to the focusing lens (26).

3. The laser shock peening device according to claim 1, characterized in that, The first reflector (M1) and the second reflector (M2), the third reflector (M3) and the fourth reflector (M4), the fifth reflector (M5) and the sixth reflector (M6) are arranged in pairs and the reflecting surfaces of each pair of reflectors are perpendicular to each other. The fourth reflector (M4) is able to make the light reflected from it to the first beam combiner (231) perpendicular to the emission direction of the laser.

4. The laser shock peening device according to claim 2, characterized in that, It also includes a terminal control system, which includes a workbench (41), an oscilloscope (42), and a computer (43). The oscilloscope (42) is connected to the photoelectric probe (25) and the computer (43) respectively to transmit information. The computer (43) can control the laser generation system (1) and the workpiece control system respectively to realize the monitoring, debugging and control of the two systems.

5. The laser shock peening device according to claim 2, characterized in that, The optical path platform (21) further includes a rotating platform for fixing each of the beam splitters (22), and at least the second beam splitter (222) is fixed on the rotating platform.

6. The laser shock peening device according to claim 2, characterized in that, The workpiece control system also includes a robot (32), the free end of which is fixedly mounted with the bearing platform (31).

7. The laser shock peening device according to claim 3, characterized in that, The optical path platform (21) further includes a through slot and a linear motion platform section. The linear motion platform section includes a linear motion platform body (213) that can move away from and close to the first beam splitter (221) within the through slot. The first reflector (M1), the second reflector (M2), the third reflector (M3), and the fourth reflector (M4) are sequentially arranged on the linear motion platform body (213) along the laser emission direction.

8. The laser shock peening device according to claim 7, characterized in that, The linear motion platform also includes a motor, a lead screw (214), and a light rod (215). The lead screw (214) and the light rod (215) are both mounted on the optical path platform and pass through the linear motion platform body (213) perpendicular to the laser emission direction. The motor can drive the lead screw (214) to rotate.

9. The laser shock peening device according to claim 8, characterized in that, The linear motion platform also includes two accordion-style dustproof cloths (216), one side of which is connected to the linear motion platform body (213) perpendicular to the laser emission direction, and the other side is connected to the inner side of the through groove.

10. A laser shock peening method, wherein the method employs the laser shock peening apparatus according to any one of claims 1-9, comprising the following steps: Mapping and modeling the surface of the workpiece: including the shape, size, and material properties of different areas of the workpiece to be processed; The laser processing parameters for different processing and strengthening areas on the workpiece surface are planned by computer: the laser processing parameters include the pulsed laser wavelength, pulse width, single pulse energy during the strengthening process, the diameter of the circular spot, the spot overlap rate, the spot scanning path, the number of pulses and the delay interval adjusted according to different processing areas; Pre-treatment of the surface of the workpiece to be processed; After fixing the workpiece, turn on the laser; After the laser shock peening process is completed, remove the workpiece and turn off the laser; When the actual laser pulse does not match the preset value, the laser pulse information is transmitted to the oscilloscope in real time through the photoelectric probe PS, and then the computer corrects the actual laser pulse in real time.

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