Laser shock peening method for realizing uniform stress distribution

Abstract

The invention relates to a laser shock peening method for realizing uniform stress distribution, which is characterized in that shock waves generated by laser beams are spread in a metal material to promote plastic deformation of the material, so that the use performance of a product is improved. However, in the machining process, defects such as stress concentration, cracks and air holes influence the use performance of products, and according to the method, the spreading and acting modes of shock waves in the material are changed by changing the laser moving path so as to optimize the residual stress distribution situation in the metal material. Specifically, the method adopts an interlaced point impact and cyclic loading mode. By means of the method, rapid collision of two adjacent shock waves can be avoided, and the shock waves can be effectively spread in the metal material. Besides, the cyclic loading mode enables the surface of the sample to reach the required lap joint rate by means of multi-time interval point impact, and compared with a method that striking areas are mutually overlapped, the mode can effectively avoid the stress concentration phenomenon caused by stress accumulation. Meanwhile, the same position is affected by shock waves generated by nearby positions for multiple times, so that the effective residual stress is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material surface strengthening, and more specifically is a laser shock strengthening path for improving the stress distribution on the surface of metal materials. Background Art

[0002] Metal materials play a vital role in modern industry. They are not only the basic pillars of aerospace, automobile manufacturing, power equipment and other fields, but also show unique value in various high-tech applications. Due to their excellent strength, high temperature resistance and excellent chemical stability, metal materials can withstand extreme working environments and ensure the stable operation and long-term durability of equipment. With the continuous advancement of science and technology and the continuous improvement of industrial needs, the performance requirements of metal materials are also getting higher and higher. The performance of metal materials is crucial to the service life and performance of the entire system. Laser shock strengthening is an effective surface treatment technology. It mainly acts on the absorption layer of the metal surface through the constraint layer. The absorption layer forms a high-temperature and high-pressure plasma. Under the action of the constraint layer, the plasma forms a high-pressure shock wave and propagates into the metal material. The force effect of the shock wave is used to cause plastic deformation on the surface of the material, so that the microstructure of the material surface changes, and at the same time, favorable residual stress is generated in the impact area, which can effectively change the physical properties, corrosion resistance and mechanical properties of the metal material. At present, laser strengthening technology has defects such as pores, cracks and stress concentration. The above problems are mainly solved by adjusting the laser processing parameters. However, the effect of this method is not obvious, and it is easy to affect the effect of impact strengthening; at present, the commonly used laser shock strengthening method is to overlap each striking area and sequentially cover the surface to be processed. However, there are some problems with this processing path. First, the shock wave inside the metal material will quickly collide with the shock wave generated by the next laser shock, resulting in the energy cancellation between the two shock waves, which cannot effectively affect the impact position and the surrounding area, resulting in energy waste. Secondly, since the overlap of each laser shock area will lead to the accumulation of stress, stress concentration will occur during laser irradiation, which will affect the performance of the metal sample.

[0003] Therefore, in order to solve the above problems, this invention proposes a laser shock strengthening path of point-by-point impact, and achieves the required overlap rate by cyclic loading. Point-by-point impact provides sufficient space for the shock wave generated by laser strengthening to propagate effectively inside the metal material, and the same position is affected multiple times by the shock wave generated at nearby positions, thereby increasing the effective residual stress. At the same time, the cyclic loading method can avoid the stress concentration problem caused by stress accumulation, thereby effectively adjusting the distribution of residual stress in the metal material. Summary of the invention

[0004] The purpose of the present invention is to provide a laser shock peening method for achieving uniform stress distribution in view of the problems such as stress concentration in the existing laser shock peening process. During the laser shock peening process, the material surface is subjected to point impact and cyclic loading. Each point impact allows the shock wave to effectively propagate inside the material. The cyclic loading is performed through multiple point impacts until the overlap rate requirement is met. This method allows the shock wave to fully propagate in the material and avoids stress concentration caused by stress accumulation.

[0005] A laser shock peening method for achieving uniform stress distribution, the method comprising the following steps:

[0006] Step 1, placing the prepared metal sample in the laser processing system;

[0007] Step 2: Set the laser processing parameters, set the impact strengthening path according to the overlap rate, and start processing the metal sample.

[0008] Preferably, the types of metal samples described in step 1 include stainless steel, nickel-based alloys, aluminum alloys, titanium alloys and alloy steels, and the preparation work includes polishing the surface, selecting the impact area, and setting a constraint layer and an absorption layer.

[0009] Preferably, the laser processing system described in step one includes a laser generator, a beam shaping system, a control system, a robot arm control system and an auxiliary device.

[0010] Preferably, in the laser processing system described in step one, the laser is a pulsed laser.

[0011] Preferably, the laser processing parameters described in step 2 are: laser wavelength 193-2940nm, power 10-109W / cm2, pulse width 15fs-1000ns, processing frequency 1Hz-10MHz, overlap rate 30%-70%, impact number 1-10 times, the constraint layer includes water layer, K9 glass, air constraint layer, water film and K9 glass composite layer, and the absorption layer includes aluminum foil, black tape, and carbon powder.

[0012] Preferably, in the laser processing parameters described in step 2, if the number of impact strengthening is not 1, the starting point and the end point are changed between two impact strengthenings.

[0013] Preferably, the impact strengthening path described in step 2 includes multiple cycles of loading, and the overlap rate requirement is met through multiple cycles of loading. Each cycle of loading includes a number of impacts at intervals, and the number of impacts at intervals is determined by the distance the light spot moves each time and the overlap rate.

[0014] Preferably, in the impact strengthening path described in step 2, during each point impact process, the moving distance of the light spot should not be less than the diameter of the light spot. The starting positions of two adjacent columns of light spots should be different, and the moving distance of the light spot is not necessarily the same as the distance between two adjacent columns.

[0015] Preferably, each cyclic loading of the impact strengthening path in step 2 needs to include multiple point-interval impacts, and multiple impact strengthenings are completed to impact harden the surface of the high-temperature alloy in sequence. Multiple cyclic loading is repeated according to the overlap rate requirements, and the starting position of each cyclic loading should be different to ensure that the overlap rate requirements are met.

[0016] The laser shock strengthening method for achieving uniform stress distribution described in the present invention proposes a solution for adjusting the laser shock path to solve the problems of cracks, pores and stress concentration that occur during the laser shock strengthening process. Compared with the traditional laser strengthening path, the advantages of the present invention are:

[0017] 1. The method of the present invention can provide sufficient space for the shock wave generated by laser strengthening to achieve effective propagation of the shock wave in the metal material, so that the shock wave can have an effective impact on the position near the laser action point, thereby increasing the residual stress of the metal material;

[0018] 2. The method of the present invention can avoid stress concentration caused by stress accumulation through cyclic loading, make stress distribution more uniform, and improve the performance of metal materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Laser shock peening method to achieve uniform stress distribution;

[0020] Figure 2 Laser shock peening path diagram in the experimental examples: (a) laser moving path in Example 1; (b) laser moving path in Example 2; (c) laser moving path in Example 3;

[0021] Figure 3 Force diagram of laser shock strengthening at the center position under different laser shock paths: (a) Force diagram of laser shock strengthening at the center position of laser shock strengthening in Example 1; (b) Force diagram of laser shock strengthening at the center position of laser shock strengthening in Example 1; (c) Force diagram of laser shock strengthening at the center position of laser shock strengthening in Example 2;

[0022] Figure 4 Comparison table of mechanical properties of laser shock processing under different laser shock paths.

[0023] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the protection scope of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. DETAILED DESCRIPTION

[0024] A laser shock peening method for achieving uniform stress distribution, the method comprising the following steps:

[0025] Step 1, placing the prepared metal sample in the laser processing system;

[0026] Step 2: Set the laser processing parameters, set the impact strengthening path according to the overlap rate, and start processing the metal sample.

[0027] Preferably, the types of metal samples described in step 1 include stainless steel, nickel-based alloys, aluminum alloys, titanium alloys and alloy steels, and the preparation work includes polishing the surface, selecting the impact area, and setting a constraint layer and an absorption layer.

[0028] Preferably, the laser processing system described in step one includes a laser generator, a beam shaping system, a control system, a robot arm control system and an auxiliary device.

[0029] Preferably, in the laser processing system described in step one, the laser is a pulsed laser.

[0030] Preferably, the laser processing parameters described in step 2 are: laser wavelength 193-2940nm, power 10-109W / cm2, pulse width 15fs-1000ns, processing frequency 1Hz-10MHz, overlap rate 30%-70%, impact number 1-10 times, the constraint layer includes water layer, K9 glass, air constraint layer, water film and K9 glass composite layer, and the absorption layer includes aluminum foil, black tape, and carbon powder.

[0031] Preferably, in the laser processing parameters described in step 2, if the number of impact strengthening is not 1, the starting point and the end point are changed between two impact strengthenings.

[0032] Preferably, the impact strengthening path described in step 2 includes multiple cycles of loading, and the overlap rate requirement is met through multiple cycles of loading. Each cycle of loading includes a number of impacts at intervals, and the number of impacts at intervals is determined by the distance the light spot moves each time and the overlap rate.

[0033] Preferably, in the impact strengthening path described in step 2, during each point impact process, the moving distance of the light spot should not be less than the diameter of the light spot. The starting positions of two adjacent columns of light spots should be different, and the moving distance of the light spot is not necessarily the same as the distance between two adjacent columns.

[0034] Preferably, each cyclic loading of the impact strengthening path in step 2 needs to include multiple point-interval impacts, and multiple impact strengthenings are completed to impact harden the surface of the high-temperature alloy in sequence. Multiple cyclic loading is repeated according to the overlap rate requirements, and the starting position of each cyclic loading should be different to ensure that the overlap rate requirements are met.

[0035] The laser shock strengthening method for achieving uniform stress distribution described in the present invention adopts a point-interval shock method to enable the shock wave to effectively propagate in the metal material, so that the shock wave can have an effective impact on the position near the laser action point, thereby increasing the residual stress of the metal material; and through a cyclic loading method, stress concentration and other problems caused by stress accumulation can be avoided, so that the stress distribution is more uniform and the performance of the metal material is improved.

[0036] Embodiment 1:

[0037] Step 1: Take a 20×20×7mm A286 alloy sample, polish its surface to make it smooth, stick black tape on the impact area as an absorption layer, turn on the water flow as a constraint layer, and place it on the sample processing table.

[0038] Step 2, setting laser processing parameters: laser wavelength 1064nm, laser pulse width 15ns, laser energy 6J, spot diameter 3mm, impact number 1 time, laser overlap rate 50%.

[0039] Step 3: The laser shock peening path is to overlap the laser spots in sequence until the surface of the metal material is fully impacted.

[0040] Embodiment 2:

[0041] Step 1: Take a 20×20×7mm A286 alloy sample, polish its surface to make it smooth, stick black tape on the impact area as an absorption layer, turn on the water flow as a constraint layer, and place it on the sample processing table.

[0042] Step 2, setting laser processing parameters: laser wavelength 1064nm, laser pulse width 15ns, laser energy 6J, spot diameter 3mm, impact number 1 time, laser overlap rate 50%.

[0043] Step three, during laser shock strengthening, impact various positions on the surface of the processing area, and then offset a certain distance and use the same method to perform laser shock until the overlap rate requirement is achieved.

[0044] Embodiment three:

[0045] Step 1: Take a 20×20×7mm A286 alloy sample, polish its surface to make it smooth, stick black tape on the impact area as an absorption layer, turn on the water flow as a constraint layer, and place it on the sample processing table.

[0046] Step 2, setting laser processing parameters: laser wavelength 1064nm, laser pulse width 15ns, laser energy 6J, spot diameter 3mm, impact number 1 time, laser overlap rate 50%.

[0047] Step three, during laser shock strengthening, impact various positions on the surface of the processing area, and then offset a certain distance and use the same laser shock method until the overlap rate requirement is achieved, and each time the material surface is laser shocked, the processing method of point-to-point shock is used.

[0048] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A laser shock peening method for achieving uniform stress distribution, the method comprising the following steps: Step 1, placing the prepared metal sample in the laser processing system; Step 2: Set the laser processing parameters, set the impact strengthening path according to the overlap rate, and start processing the metal sample.

2. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: The types of metal samples described in step 1 include stainless steel, nickel-based alloys, aluminum alloys, titanium alloys and alloy steels. The preparation work includes polishing the surface, selecting the impact area, and setting the constraint layer and the absorption layer.

3. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: The laser processing system described in step 1 includes a laser generator, a beam shaping system, a control system, a robot arm control system and an auxiliary device.

4. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: In the laser processing system described in step 1, the laser is a pulsed laser.

5. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: The laser processing parameters described in step 2 are: laser wavelength 193-2940nm, power 10-109W / cm2, pulse width 15fs-1000ns, processing frequency 1Hz-10MHz, overlap rate 30%-70%, impact number 1-10 times, the constraint layer includes water layer, K9 glass, air constraint layer, water film and K9 glass composite layer, and the absorption layer includes aluminum foil, black tape, and carbon powder.

6. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: For the laser processing parameters described in step 2, if the number of impact strengthening is not 1, the starting point and the end point are changed between two impact strengthenings.

7. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: The impact strengthening path described in step 2 includes multiple cycles of loading, and the overlap rate requirement is met through multiple cycles of loading. Each cycle of loading includes a number of impacts at intervals, and the number of impacts at intervals is determined by the distance the light spot moves each time and the overlap rate.

8. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: In the impact strengthening path described in step 2, during each point impact process, the moving distance of the light spot should not be less than the diameter of the light spot. The starting positions of two adjacent columns of light spots should be different, and the moving distance of the light spot is not necessarily the same as the distance between two adjacent columns.

9. The laser shock peening method for achieving uniform stress distribution according to claim 1, characterized in that: The impact strengthening path in step 2 needs to include multiple point-interval impacts in each cyclic loading. Multiple impact strengthening is completed to impact harden the surface of the high-temperature alloy in sequence. Multiple cyclic loading is repeated according to the overlap rate requirements. The starting position of each cyclic loading should be different to ensure that the overlap rate requirements are met.

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