A surface morphology control method based on laser shock wave effect

Abstract

The present application belongs to the technical field of laser manufacturing, and relates to a surface morphology control method based on laser shock wave effect. In laser shock strengthening, different surface relief microstructure phenomena of different morphological characteristics appear on the material surface due to laser energy distribution defects. The method of the present application can realize the acquisition of different surface roughness. A pretest needs to be set, different parameters of porous pipes are used to generate bubbles of different volumes and concentrations in the water constraint layer, the laser energy distribution is guided, and the appropriate parameter range is determined. Further adjustment of laser energy, bubble volume and concentration can finally obtain different surface roughness on the material surface. In the absence of a mold, the present application realizes different surface roughness of the material in a non-contact manner, and has the advantages of high efficiency and wide adaptability.

Description

Technical Field

[0001] This invention belongs to the field of laser manufacturing technology, and specifically relates to a surface morphology control method based on the laser shock wave effect, namely: using the pulsed laser force effect to achieve microscopic morphology control of the material impact region. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Surface micromorphology refers to the microscopic geometric shapes remaining on the surface of a workpiece due to the combined effects of random and uncertain factors during processing. Characterization indicators include surface roughness, surface waviness, form and position errors, and surface profile shape. Surface roughness can be described by surface roughness, which refers to the small spacing and minute peak-valley unevenness of the processed surface. Surface roughness is one of the important parameters in metal processing, specifically referring to the degree of variation in the height and spacing of minute peaks and valleys (Z). Generally, it is classified according to S: S < 1 mm is surface roughness; 1 ≤ S ≤ 10 mm is waviness; and S > 10 mm is profile shape. Surface roughness has different effects on metals under different application conditions: lower surface roughness is more beneficial in terms of the fit properties, wear resistance, fatigue strength, contact stiffness, and vibration of mechanical parts, as well as their service life, reliability, stability, and appearance; a certain surface roughness is required in painting, powder coating, or electroplating to promote the adhesion of decorative paint coatings; and when it is necessary to increase the friction and surface contact area of ​​the workpiece, the surface roughness of the workpiece needs to be appropriately increased.

[0004] For metal workpieces, surface roughness can be achieved through methods such as machining, electrochemical machining, and chemical etching. For example, the vibrations generated by cutting with tools like grinding wheels, drills, and milling cutters produce chatter marks on the workpiece. Surface processing techniques such as shot peening and laser impact create significant plastic deformation on the material surface. However, these machining processes have drawbacks in achieving surface roughness on metals, including high wear and limited applicability. Electrochemical machining and chemical etching can also induce significant morphological changes on the material surface, but these processes are time-consuming and complex when aiming for specific surface roughness conditions. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a surface morphology control method based on the laser shock wave effect. During laser shock blasting using deionized water or K9 glass containing microbubbles as a confinement layer, the microbubbles in the confinement layer influence the formation of surface protrusions with varying morphological characteristics within the laser-shocked area of ​​the material surface. This invention leverages the volume and concentration of bubbles in the water confinement layer to achieve these protruding micro / nano structures on the surface of the structural material, resulting in a certain degree of surface roughness.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a surface morphology control method based on the laser shock wave effect, comprising:

[0008] After cleaning the area of ​​the target material to be processed, an absorption layer is applied.

[0009] A confinement layer is created by dissolving water or glass containing bubbles of a specific size and concentration.

[0010] A laser shock blasting work platform was constructed, with the laser, confinement layer, absorption layer, and target material arranged sequentially from top to bottom.

[0011] Position the laser shock surface treatment device and adjust the laser energy distribution to a flat-top distribution;

[0012] Laser is used to impact the target material, causing the material surface to exhibit a certain degree of roughness.

[0013] This invention proposes a surface morphology control method based on the laser shock wave effect to obtain different surface roughnesses on metal surfaces. Compared with current methods for obtaining surface roughness, this processing method is a non-contact cold processing method, which does not cause ablation or changes in the microstructure of the metal surface. It also has advantages such as high processing efficiency, high material utilization, and the ability to obtain micro-nano morphology of the target micro-region.

[0014] This invention does not limit the specific pretreatment measures for the area to be processed; that is, under the condition that the predetermined processing requirements are met, technicians can also directly perform subsequent processing on the material to be processed. In some embodiments, the cleaning method is ultrasonic cleaning.

[0015] In some embodiments, the absorber layer is made of black paint, graphite, black tape, or metal foil. When a pulsed laser shines on the absorber layer, it ionizes to generate high-temperature, high-pressure plasma, which, under the induction of laser energy, generates a shock wave. This shock wave then acts as a driving force to induce high-strain-rate plastic deformation in the substrate, thus completing the laser impact test.

[0016] In some embodiments, the work platform is used to place and fix the sheet metal, contain a certain volume of liquid, and has the functions of water injection and fixing external equipment.

[0017] It should also be noted that the work platform should be kept dust-free during routine maintenance, and should be cleaned with deionized water before each water injection to reduce the possibility of introducing impurities into the water confinement layer during the laser shock treatment process.

[0018] In some embodiments, the method for setting the water constraint layer includes: adding a water curtain to the working platform, submerging the target material's processing area to a certain depth as a constraint layer. By changing the size and concentration of bubbles in the constraint layer, and through the corresponding changes in the actual energy of the pulsed laser on the material surface, the surface roughness of the material can be controlled.

[0019] Furthermore, the water mentioned in the water constraint layer is deionized water containing a certain volume and concentration of air bubbles and having impurities such as calcium and magnesium ions removed.

[0020] In some embodiments, the volume and concentration of bubbles in the water are controlled by bubbles generated by a porous material. The principle involves pressing a porous tube into a liquid and supplying air under high pressure into the tube. The forced air passes through the porous medium with tiny pores, generating tiny bubbles. The volume of the bubbles generated by this method can be controlled by the porous tube, resulting in bubbles with relatively uniform size and a certain concentration, sufficient to refract or dissipate laser energy.

[0021] In some embodiments, the bubble size is in the range of 60 to 200 μm. Using bubbles of this size allows the laser to be largely dissipated, and the resulting relatively coarse and large microstructures are randomly distributed on the material surface to form a rough surface without obvious pit boundaries.

[0022] In some embodiments, a pre-experiment is used to establish the correspondence between the target surface state and the size and concentration of bubbles in the constraint layer. Specifically, in the pre-experiment, multiple sets of specific laser shock surface treatment processes with different bubble sizes and concentrations are set. The surface morphology of the target material is quantitatively analyzed using testing instruments such as a surface roughness measuring instrument and a laser confocal microscope to determine the bubble size and concentration parameters of the constraint layer that can obtain the target surface state.

[0023] It should be noted that there is an optimal range for the size and concentration of the bubble in the constraint layer to achieve the target surface morphology. Generally speaking, the relationship between bubble size and concentration and the target surface morphology is not monotonically changing. Increasing both bubble size and concentration does not necessarily lead to an increase in the surface roughness of the target. Technicians need to optimize the size and concentration of the bubble in the constraint layer according to the target requirements.

[0024] It should also be noted that, based on the preliminary experiments, it is assumed that the technicians have determined the processing requirements for the surface morphology of the target material to be processed, including but not limited to specific targets for surface morphology indicators such as surface roughness.

[0025] In some embodiments, when precision manufacturing of materials is carried out based on the force effect of pulsed laser, the laser beam is incident perpendicularly on the surface of the target material.

[0026] In some embodiments, laser processing positioning includes, but is not limited to, using a positioner to align the area to be processed on the sheet surface with the laser spot.

[0027] In some embodiments, the power density of the pulsed laser should be greater than 1 GW / cm². 2 Its specific value depends on the pulse width, laser spot diameter, and laser energy.

[0028] It should be noted that technicians are required to determine the laser parameters, such as laser energy, pulse width, and spot size, based on the mechanical properties of the target material to be processed, including its yield strength. Technicians are also required to detect and adjust the laser beam energy distribution to a flat-top distribution, meaning that the laser energy is the same at all points within the laser spot area.

[0029] In some embodiments, the energy distribution within a single beam is achieved by adjusting the voltage. The adjustment method is as follows: a laser beam is emitted onto the surface of a black test paper, and the change in the degree of ablation on the black test paper surface is observed. When the color contrast of the white ablated areas on the black test paper surface is the same, the laser beam energy is considered to be distributed in a flat-top manner.

[0030] It should also be noted that when the spot of the pulsed laser beam passes through the constraint layer, the presence of bubbles in the constraint layer causes the laser energy distributed on the flat top to be randomly distributed in a certain area after dissipation and refraction. Finally, by observing the micro-morphology of the area after the laser impact, the surface relief microstructure of the material surface can be obtained, thereby obtaining different surface roughness.

[0031] In a second aspect, the present invention provides a target material with a certain surface roughness prepared by the above method.

[0032] A third aspect of the present invention provides the application of the above-described method in controlling the surface morphology of a target material.

[0033] Beneficial effects of the present invention

[0034] (1) The method of the present invention is based on the phenomenon that microbubbles in the laser shock confinement layer can form surface relief microstructures with different morphological characteristics in the impact area of ​​the material surface. By adjusting the morphology of microbubbles in the confinement layer, the actual laser energy distribution state received by the material to be processed can be changed, thereby adjusting the surface relief morphology to obtain different surface roughness on the plate surface.

[0035] (2) The method of the present invention is based on the force effect of laser shock to obtain surfaces with different roughness, and there is an absorption layer covering the surface of the sheet material, which will not cause ablation damage and thermal effect to the sheet material.

[0036] (3) The present invention can perform laser shock treatment on any micro-region in the material to obtain different surface roughness, and has the advantages of complex and diverse processing parts and precise control.

[0037] (4) The preparation method of the present invention is simple, practical and easy to promote. Attached Figure Description

[0038] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0039] Figure 1 A diagram of a laser shock blasting device used to control the volume and concentration of bubbles in a water-constrained layer.

[0040] Figure 2 This is a schematic diagram of the microstructure of a laser-shocked surface prepared using a constraint layer of relatively large-scale bubbles of a certain concentration.

[0041] Figure 3 This is a schematic diagram of the microstructure of a laser-shocked surface prepared using a confinement layer of small-scale bubbles with a certain concentration.

[0042] in, Figure 1 The device diagram, from top to bottom, consists of: 1. Laser system; 2. Water confinement layer; 3. Absorption layer; 4. Plate; 5. Bubble generator; 6. Working platform; 7. Workpiece clamping system. Detailed Implementation

[0043] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0044] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0045] Example 1

[0046] This embodiment provides a surface morphology control method based on the laser shock wave effect. The method's apparatus is as follows: Figure 1As shown, from top to bottom, they are: 1. Laser system; 2. Water confinement layer; 3. Absorption layer; 4. Plate; 5. Bubble generator; 6. Working platform; 7. Workpiece clamping system.

[0047] First, a working platform was constructed. A 2mm*10mm*10mm plate sample was made from TC4 titanium alloy and ground and polished to achieve a smooth surface with a surface roughness Ra of 0.006. A 100μm thick black 3M tape was then applied to the plate surface, and the sample was placed and fixed on the horizontal working platform. When applying the tape to the metal surface, the process should be slow to prevent air bubbles from forming.

[0048] After arranging and fixing bubble generators around the perimeter of the board, deionized water is injected into the work platform. The portion of deionized water exceeding the absorption layer serves as a constraint layer, with the distance from the deionized water surface to the absorption layer (i.e., the thickness of the constraint layer) set at 5mm. The bubble generator consists of a porous tube and an air pump; the porous tube has a symmetrical internal and external structure and is made of alumina.

[0049] For parameters such as "effective area of ​​the element", "surface porosity", and "pore size" of porous tubes, the following set of pre-tests is included, but is not limited to. The specific pre-test conditions are described in Table 1, where the air pump applies a pressure of 0.02 MPa.

[0050] Table 1

[0051]

[0052]

[0053] Through the above series of preliminary tests, it was found that the parameters used in the 11th preliminary test can stably form a surface roughness of Ra1.6, and the 11th test will generate bubbles of 80-100μm in size and 1500-2000 per ml in the water-constrained layer.

[0054] In this example, the laser shockwave is induced by an Nd:YAG laser system with a wavelength of 1064 mm, a frequency of 2 Hz, a pulse width of 14 ns, and a laser energy of 8 J. The laser beam emitted by the system is incident perpendicularly on the surface of the material after passing through an optical lens, forming a circular laser beam spot with a diameter of 2 mm on the surface. A positioner is used to align the area of ​​the material to be processed with the laser spot. By adjusting the voltage, a flat-top energy distribution of the single laser beam is achieved.

[0055] After completing the preparation work, the sheet material to be processed was subjected to single-beam laser shock blasting. The microstructure of the sheet surface was observed using a laser confocal microscope, and the surface roughness was measured. A schematic diagram of the morphology is shown below. Figure 2 As shown.

[0056] Comparative Example 1

[0057] This comparative example provides a surface morphology control method based on the laser shock wave effect, differing from the previous embodiment in that the bubble volume and concentration are changed. The method's apparatus is as follows: Figure 1 As shown, from top to bottom, they are: 1. Laser system; 2. Water confinement layer; 3. Absorption layer; 4. Plate; 5. Bubble generator; 6. Working platform; 7. Workpiece clamping system.

[0058] The construction of the work platform is consistent with the previous embodiment. TC4 titanium alloy material is still used to make a 2mm*10mm*10mm plate sample, which is then ground and polished to make the surface smooth with a surface roughness Ra0.006. After slowly applying 100μm thick black 3M tape to the plate surface to prevent air bubbles from forming, it is placed and fixed on the horizontal work platform.

[0059] Bubble generators are arranged and fixed around the perimeter of the board, and then deionized water is injected into the work platform. The portion of deionized water exceeding the absorption layer serves as a constraint layer, with the distance from the deionized water surface to the absorption layer (i.e., the thickness of the constraint layer) set at 5 mm. The bubble generators consist of a porous tube and an air pump; the porous tube is alumina material with a symmetrical internal and external structure. Using the same trial-and-error method as in the previous example, suitable parameters such as pore size and surface porosity are selected to locally create a surface roughness of Ra 0.8 on the material surface. At this point, bubbles of 10–20 μm in size are formed, with a bubble concentration ranging from 6 × 10⁻⁶. 5 ~8×10 5 per ml.

[0060] In this comparative example, the laser shock wave is induced by an Nd:YAG laser system with a wavelength of 1064 mm, a frequency of 2 Hz, a pulse width of 14 ns, and a laser energy of 8 J. The laser beam emitted by the laser system is incident perpendicularly on the surface of the board after passing through an optical lens, forming a circular laser beam spot with a diameter of 2 mm on the surface of the board. The area of ​​the board to be processed is aligned with the laser spot using a locator.

[0061] The laser energy correction method and other preparatory work are the same as in the examples. After completing the preparatory work, the material to be processed is subjected to single-laser-beam laser shock treatment. The surface morphology within the pits on the surface of the material is observed and the surface roughness is measured using a laser confocal device. A schematic diagram of the morphology is shown below. Figure 3 As shown.

[0062] The comparative measurement results show that the bubble size should not be too small. Through multiple comparisons, it was found that the bubble size should be within the range of 60 to 200 μm in order to efficiently obtain different surface roughnesses on the board surface.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A surface morphology control method based on laser shock wave effect, characterized in that, include: After cleaning the area of ​​the target material to be processed, an absorption layer is applied. Water containing dissolved bubbles of a specific size and concentration is used as a confinement layer; A laser shock blasting work platform was constructed, with the laser, confinement layer, absorption layer, and target material arranged sequentially from top to bottom. Position the laser shock surface treatment device and adjust the laser energy distribution to a flat-top distribution; Laser is used to impact the target material, causing the material surface to exhibit a certain degree of roughness. The volume and concentration of bubbles in the water are controlled by bubbles generated by porous materials; The bubble size ranges from 60 to 200 μm; Preliminary experiments were conducted to establish the correspondence between the target surface condition and the size and concentration of bubbles in the constraint layer.

2. The surface morphology control method based on laser shock wave effect as described in claim 1, characterized in that, The cleaning method is ultrasonic cleaning.

3. The surface morphology control method based on laser shock wave effect as described in claim 1, characterized in that, The absorbent layer is made of black paint, graphite, black tape, or metal foil.

4. The surface morphology control method based on laser shock wave effect as described in claim 1, characterized in that, The work platform is used to place and fix the sheet metal, contain a certain amount of liquid, and has the functions of water injection and fixing external equipment.

5. The surface morphology control method based on laser shock wave effect as described in claim 1, characterized in that, The method for setting the water constraint layer includes: adding a water curtain to the working platform so that it submerges the target material to be processed area to a certain depth as a constraint layer.

6. The surface morphology control method based on laser shock wave effect as described in claim 1, characterized in that, The laser beam is incident perpendicularly on the surface of the target material; Alternatively, the power density of the pulsed laser should be greater than 1 GW / cm². 2 ; Alternatively, the energy distribution within a single beam can be achieved by adjusting the voltage.

7. A target material with a certain surface roughness prepared by the method according to any one of claims 1-6.

8. The application of the method according to any one of claims 1-6 in controlling the surface morphology of the target material.

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