WO2021052065A1

WO2021052065A1 - Method and apparatus for strengthening by means of kilohertz low-energy laser scanning shock

Info

Publication number: WO2021052065A1
Application number: PCT/CN2020/108527
Authority: WO
Inventors: 周留成; 李应红; 潘鑫磊; 田增; 何卫锋; 冯晓泰; 时小松
Original assignee: 中国人民解放军空军工程大学
Priority date: 2019-09-19
Filing date: 2020-08-11
Publication date: 2021-03-25
Also published as: CN110438333A; LU500167B1

Abstract

Disclosed are a method and apparatus for strengthening by means of kilohertz low-energy laser scanning shock. The method comprises the steps of: pretreatment of a workpiece, coating with an absorption and protection layer, application of a confinement layer, scanning laser shock treatment, and post-treatment of the workpiece. The apparatus comprises an optical fiber laser device (1), a process control system (2), an industrial personal computer (3), a processor (4), a sound wave acquisition device (5), a motion platform (6), and a photosensitive element (10). A high-repetition-frequency and low-energy laser is output by means of the optical fiber laser device, so that a design for a mechanical system is made very simple, the comprehensive photoelectric efficiency reaches 20% or above, the power consumption during working is significantly reduced, and operation cost is reduced. A scanning shock treatment on an area to be strengthened is performed by means of a high-speed shot flow simulating mechanical shot blasting, so as to improve the machining efficiency and solve the problem of the great difficulty of optimizing the residual stress field after strengthening. A small-light-spot and low-energy laser is used for scanning-type machining strengthening, so as to achieve wider adaptability.

Description

Kilohertz low-energy laser scanning shock strengthening method and device

Technical field

The invention relates to the technical field of surface treatment, in particular to a kilohertz low-energy laser scanning shock strengthening method and a device thereof.

Background technique

In recent years, in order to further improve the surface strengthening effect of key components in the aerospace and other fields, some new surface strengthening technologies have been developed, and the more representative one is the laser shock strengthening technology. The basic principle is to use laser-induced shock waves to act on the surface of metal parts to form residual compressive stress and change the surface structure, which greatly improves the surface quality and surface integrity, thereby significantly improving its fatigue strength and life.

technical problem

Since the existing laser shock strengthening equipment mainly uses YAG solid-state lasers, the price is expensive, and the market price is 8-10 million yuan/unit. At present, only surface treatment for aerospace components and some products with higher added value is difficult to achieve. Widespread popularity.

Secondly, since the laser trigger frequency of laser shock strengthening is generally 1-20Hz, the processing efficiency is lower compared with the high-speed and dense projectile flow used in traditional mechanical shot peening technology.

In addition, to ensure the formation of a uniform residual compressive stress field, laser shock strengthening requires precise design and control of process parameters such as pulse energy, pulse width, spot size, spot overlap, and impact path, especially for complex parts or thin-walled parts. It is difficult to optimize the residual stress field.

Technical solutions

In view of the shortcomings of the above-mentioned background technology, the present invention provides a kilohertz low-energy laser scanning shock strengthening method and device, which have the advantages of good adaptability, good strengthening effect, and green and pollution-free, and solve the problems raised by the background technology.

The present invention provides the following technical solutions: a kilohertz low-energy laser scanning shock strengthening method, including the steps:

S1. Pretreatment of the workpiece: Put the workpiece in an ultrasonic cleaning machine equipped with a constant temperature ethanol solution, and perform ultrasonic cleaning on the workpiece;

S2, coating absorption protection layer: smear absorption protection layer on the surface of the processed workpiece to absorb laser energy to generate plasma detonation waves and protect the workpiece;

S3. Apply a confinement layer: apply a uniform water confinement layer to the surface of the workpiece according to the pre-designed scanning path to confine the plasma shock wave and increase the shock wave pressure;

S4. Scanning laser shock treatment: Use high repetition frequency fiber laser to simulate the high-speed projectile flow of mechanical shot peening, and perform scanning shock treatment on the surface of the to-be-strengthened workpiece according to the pre-designed scanning path;

S5. Workpiece post-treatment: Put the strengthened work piece into an ultrasonic cleaning machine equipped with a constant temperature ethanol solution again, and perform ultrasonic cleaning on the work piece. After cleaning, it is rinsed with deionized water and dried with nitrogen.

Preferably, in the step S4, the laser energy of the high repetition frequency fiber laser is set to 50-500MJ, the pulse repetition frequency is 500-2000HZ, and the spot diameter is 0.4-0.6MM.

Preferably, the fiber laser is electrically connected to a process control system, the process control system acquires and collects plasma glow discharge information through a photosensitive element, and the process control system controls the activation of the acoustic wave acquisition device through a processor and acquires and processes Acoustic wave information received by the acoustic wave acquisition device, the process control system and the industrial computer perform information transmission, and the process control system controls the movement of the motion platform.

Preferably, an integrated laser shot peening head is installed at the bottom of the fiber laser, a ventilation hole is provided on one side of the integrated laser shot peening head, and a shot cavity is provided inside the integrated laser shot peening head, and the shot cavity A processing lens is installed in the middle of the spray chamber, and the spray cavity is connected with a constrained water chamber.

Preferably, a suitable trigger level is set in the process control system.

Preferably, standard acoustic wave characteristics are stored in the processor.

Beneficial effect

The present invention has the following beneficial effects:

1. Use fiber lasers to output high repetition frequency and low energy lasers. As a representative of the third generation of laser technology, compared with traditional YAG solid-state lasers, glass fiber manufacturing costs are low and the technology is mature. The market price of fiber lasers is 2 to 3 million/ The laser is miniaturized and intensive due to the flexibility of the fiber. In addition, the technical advantages of fiber export make the laser easily competent for various multi-dimensional and arbitrary space processing applications, making the design of the mechanical system very simple, and it is not necessary during use. Thermoelectric cooling and water cooling only need simple air cooling, and the comprehensive photoelectric efficiency is as high as 20% or more, which greatly saves power consumption during work and saves operating costs.

2. Simulating the high-speed projectile flow of mechanical shot blasting to perform scanning impact processing on the area to be strengthened, which is different from the point-by-point overlap impact in the traditional laser shock strengthening process. Through scanning impact processing, it is no longer necessary to plan the impact path, spot size, etc. in advance Parameters, only need to sweep the impact treatment for the full coverage of the strengthened area, the processing efficiency is high, and the process is simple.

3. The use of low-energy light beams to scan the surface of the material to ensure the formation of a uniform residual compressive stress field. There is no need to design and control the pulse energy, pulse width, spot size, spot overlap, impact path and other process parameters. It solves the difficult problem of optimizing the residual stress field of complex parts or thin-walled parts after strengthening.

4. In the present invention, a small spot, low-energy laser is used for scanning processing and strengthening. On the one hand, the small spot is processed accurately, and it has the unique advantages of processing complex and special-shaped components, which broadens the application range of laser shock strengthening technology. On the other hand, low-energy beams It has little effect on the surface state of the material and is suitable for precision machining parts.

Description of the drawings

Figure 1 is a schematic diagram of pulsed laser shock strengthening;

Figure 2 is the effect diagram of pulsed laser shock strengthening;

Figure 3 is a schematic diagram of the process of the method of the present invention;

Figure 4 is a schematic diagram of the device of the present invention;

Figure 5 is a schematic diagram of an integrated laser shot blasting head in the device of the present invention;

Fig. 6 is an effect diagram of enhancement of the method of the present invention;

Fig. 7 is a control flow chart of the device of the present invention.

In the figure: 1. Fiber laser; 2. Process control system; 3. Industrial computer; 4. Processor; 5. Acoustic wave acquisition equipment; 6. Motion platform; 7. Workpiece; 8. Absorption protection layer; 9. Constraint layer; 10. Photosensitive element; 11. Integrated laser shot peening head; 12. Ventilation hole; 13. Processing lens; 14. Confinement water cavity; 15. Spray cavity.

The best mode of the present invention

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

In this embodiment, the titanium alloy Ti6Al4V is strengthened. The workpiece is a rectangular thin-walled piece with a length of 45 mm, a width of 20 mm, and a thickness of 3 mm.

Please refer to Figure 3-7, a kilohertz low-energy laser scanning shock strengthening method, including the steps:

S1. Pretreatment of the workpiece 7: In this embodiment, the workpiece 7 is placed in an ultrasonic cleaning machine equipped with ethanol with a temperature of 20-24° C. and a concentration of 75-95%, the ultrasonic frequency is 40 kHz, and the cleaning is performed for 9 minutes.

S2, coating absorption protection layer 8: In this embodiment, the 120um-thick absorption protection layer 8 is coated on the surface of the workpiece 7 to be processed, which is used to absorb laser energy to generate plasma detonation waves and protect the workpiece 7, generally black Adhesive tape or aluminum foil. Aluminum foil is used in this embodiment. After coating, fix the workpiece 7 coated with the absorbing protective layer 8 on the fixture of the moving platform 6, and control the posture of the fixture through the moving platform 6, so that the workpiece 7 is integrated with the laser The positions of the shot blasting head 11 are matched;

S3. Apply a confinement layer 9: Input the previously designed area scanning strengthening path into the industrial computer 3, and apply a uniform water confinement layer to the surface of the workpiece 7 through the integrated laser shot peening head 11 to confine the plasma The shock wave will increase the shock wave pressure by more than double;

S4. Scanning laser shock treatment: Start the high repetition frequency fiber laser 1, and set the laser energy to low energy 50-500 mJ, the spot diameter is 0.42-0.6mm, and the pulse repetition frequency is 500-2000 Hz, which is used to simulate the high-speed projectile flow of mechanical shot peening to perform scanning impact treatment on the area to be strengthened, with one impact;

S5. Post-treatment of work piece 7: remove the strengthened work piece 7, remove the absorption protective layer 8 coated on the surface of the work piece 7, and put the test piece into a water solution containing ethanol at a temperature of 20-24°C and a concentration of 75-95% In the ultrasonic cleaning machine, the ultrasonic frequency is 40kHz, cleaning for 10 minutes, then rinse with deionized water for 2 minutes, and then blow dry with dry nitrogen.

Among them, the laser energy of the high repetition frequency fiber laser in step S4 is set to 50-500MJ, the pulse repetition frequency is 500-2000HZ, and the spot diameter is 0.4-0.6MM. On the one hand, the small spot is processed accurately, and it has the unique ability to handle complex shaped components. Advantages, broaden the application range of laser shock strengthening technology; on the other hand, low-energy beams have little effect on the surface state of the material, which is suitable for precision machining parts, while high frequency improves the strengthening efficiency.

Among them, the fiber laser 1 is electrically connected to the process control system 2. The process control system 2 controls the working state of the fiber laser 1. The process control system 2 acquires and collects plasma glow discharge information through the photosensitive element 10 for recording impact occurrence At the time, the process control system 2 controls the activation of the sound wave acquisition device 5 through the processor 4 and acquires and processes the sound wave information received by the sound wave acquisition device 5, and compares whether the sound wave signal activity impact state is normal, the process control system 2 and the industrial computer 3 For information transmission, the industrial computer 3 controls the process control system 2 and obtains the information of the process control system 2. The process control system 2 controls the movement of the motion platform 6, the fixture on the motion platform 6 fixes the workpiece 7, and the motion platform 6 moves the workpiece 7 is moved so that the surface of the workpiece 7 to be impacted is completely covered.

Among them, the bottom of the fiber laser 1 is equipped with an integrated laser blasting head 11, one side of the integrated laser blasting head 11 is provided with a vent 12, and the integrated laser blasting head 11 is provided with a spray cavity 15 in the middle of the spray cavity 15. The processing lens 13 is installed, and the spray cavity 15 is connected to the constrained water cavity 14. In view of the fact that the water nozzle and the laser head are separated from each other in the traditional laser shock strengthening equipment, they will block each other and affect the processing when processing complex configuration parts, the present invention proposes The water nozzle and the laser head are combined together to achieve the same output of water flow and beam. The constrained water flows in from the water inlet of the constrained water cavity 14 and part of it flows out from the water outlet of the constrained water cavity 14 to monitor the quality of the confined water. The control valve between the water cavity 14 and the spray cavity 15 controls the water flow speed. The laser beam is emitted from the laser head through the processing lens 13, and the position and size of the laser are adjusted by the moving mechanism of the processing lens 13, and it enters and exits through the vent 12 for cooling , The cleaning gas protects the laser source from pollution, improves the accuracy of laser shock strengthening, makes the laser red shock strengthening equipment miniaturized and intensive, and broadens the application range of its processing of complex configuration parts.

Wherein, a suitable trigger level is set in the process control system 2, and when the collected plasma glow discharge signal intensity is greater than the trigger level, the acoustic wave collection device 5 is triggered to work.

Among them, the processor 4 stores standard sound wave characteristics, which are used to compare the sound wave signals generated during the impact to determine whether the impact is normal.

The working principle of the present invention:

A high-sensitivity, wide-band acoustic wave acquisition device 5 is used to convert acoustic and electrical signals, monitor the characteristics of each shock wave, and compare with the data in the database. The laser is irradiated on the absorption protection layer 8 through the confinement layer 9 to absorb and protect Layer 8 forms plasma. The photosensitive element 10 collects the plasma glow discharge and uses it as an external trigger source. Set an appropriate trigger level in the process control system 2 to ensure that the acoustic wave collection device 5 can only be triggered to work when it is strengthened. The device 4 analyzes the collected acoustic wave signal and compares it with the acoustic wave characteristics obtained in the standard state, and uses the signal collected by the photosensitive element 10 as a reference to determine the propagation speed of the acoustic wave, and comprehensively obtains the real-time triggering of each laser State, the process control system 2 issues instructions based on the processing results. If the sound wave characteristics are normal, the impact will continue. If there is an abnormality, the fiber laser 1 and the motion platform 6 will be synchronously stopped, and a warning signal will be issued to indicate the abnormal state, which is carried out by the operator. Restore and record the position of the strengthening point and the abnormal situation of the process parameters at this time. When the process parameters return to normal, the operator clicks on the synchronization control to continue the strengthening.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply one of these entities or operations. There is any such actual relationship or order between. Moreover, the terms "include", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes those that are not explicitly listed Other elements of, or also include elements inherent to this process, method, article or equipment.

Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. And variations, the scope of the present invention is defined by the appended claims and their equivalents.

Claims

A kilohertz low-energy laser scanning shock strengthening method, which is characterized in that it comprises the steps of:

S1. Pretreatment of the workpiece: Put the workpiece in an ultrasonic cleaning machine equipped with a constant temperature ethanol solution, and perform ultrasonic cleaning on the workpiece;

S2, coating absorption protection layer: smear absorption protection layer on the surface of the processed workpiece to absorb laser energy to generate plasma detonation waves and protect the workpiece;

S3. Apply a confinement layer: apply a uniform water confinement layer to the surface of the workpiece according to the pre-designed scanning path to confine the plasma shock wave and increase the shock wave pressure;

S4. Scanning laser shock treatment: Use high repetition frequency fiber laser to simulate the high-speed projectile flow of mechanical shot peening, and perform scanning shock treatment on the surface of the to-be-strengthened workpiece according to the pre-designed scanning path;

S5. Workpiece post-treatment: Put the strengthened work piece into an ultrasonic cleaning machine equipped with a constant temperature ethanol solution again, and perform ultrasonic cleaning on the work piece. After cleaning, it is rinsed with deionized water and dried with nitrogen.
A kilohertz low-energy laser scanning shock strengthening method according to claim 1, wherein the laser energy of the high repetition frequency fiber laser in the step S4 is set to 50-500MJ, and the pulse repetition frequency is 500-2000HZ. The spot diameter is 0.4-0.6MM.
A kilohertz low-energy laser scanning impact strengthening device, including a fiber laser (1), a process control system (2), an industrial computer (3), a processor (4), a sound wave acquisition device (5), and a motion platform (6) And a photosensitive element (10), characterized in that: the fiber laser (1) is electrically connected to a process control system (2), and the process control system (2) acquires and collects plasma glow discharge through the photosensitive element (10) Information, the process control system (2) controls the activation of the sound wave collection device (5) through the processor (4) and acquires and processes the sound wave information received by the sound wave collection device (5), the process control system (2) and The industrial computer (3) performs information transmission, and the process control system (2) controls the movement of the motion platform (6).
A kilohertz low-energy laser scanning impact strengthening method and device according to claim 3, characterized in that: the bottom of the fiber laser (1) is equipped with an integrated laser shot blasting head (11), and the integrated laser One side of the shot blasting head (11) is provided with a vent (12), the integrated laser shot blasting head (11) is provided with a spray cavity (15) inside, and a processing lens is installed in the middle of the spray cavity (15) (13), the spray cavity (15) is connected with a constrained water cavity (14).
A kilohertz low-energy laser scanning shock strengthening method and device according to claim 3, wherein a suitable trigger level is set in the process control system (2).
A kilohertz low-energy laser scanning shock strengthening method and device according to claim 3, characterized in that: the processor (4) stores standard acoustic wave characteristics.