Laser Peeling Method

Abstract

This invention provides a laser peening method that can be performed in the atmosphere and allows for easy peening with reduced constraints. [Solution] The laser peening method according to the embodiment comprises a coating step of applying a liquid resin to a metal material, a curing step of curing the resin, and a peening step of irradiating the surface of the metal material with a pulsed laser that penetrates the resin, which has a refractive index higher than that of the atmosphere.

Description

Technical Field

[0001] The embodiment relates to a laser peening method.

Background Art

[0002] The laser peening method modifies the metal surface with a shock wave of a laser on an object such as metal.

[0003] However, since laser peening is performed underwater, there are restrictions on the environment for peening.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the embodiment is to provide a laser peening method that can be performed in the atmosphere, relaxes the above restrictions, and enables easy peening.

Means for Solving the Problems

[0006] The laser peening method according to the embodiment includes an application step of applying a liquid resin to a metal material, a curing step of curing the resin, and a peening step of irradiating a pulsed laser onto the surface of the metal material through the resin having a refractive index higher than that of the atmosphere.

Brief Description of the Drawings

[0007] [Figure 1]This figure shows the steps of the laser peening method according to the embodiment. [Figure 2] This diagram shows the process of peening a metal material. [Figure 3] These are sample diagrams from the examples and comparative examples, showing the state of the samples before laser peening. [Figure 4] These are sample diagrams from the examples and comparative examples, showing the state of the samples after laser peening. [Figure 5] This figure shows the Pickers hardness of the samples in the examples and comparative examples. [Modes for carrying out the invention]

[0008] Figure 1 is a diagram showing the steps of the laser peening method according to the embodiment. As shown in Figure 1, the laser peening method according to the embodiment comprises a coating step S1, a curing step S2, and a peening step S3. The steps will be described below.

[0009] <Coating process S1> In coating step S1, a liquid resin is applied to the metal material. Furthermore, in coating step S1, the resin only needs to be applied to the surface of the metal material in the area where peening is required.

[0010] The metal material is an iron material such as stainless steel, an aluminum material, a magnesium material, a titanium material, a copper material, a gold material, or an alloy thereof. The metal material to be peened is a flat metal surface or a metal surface in a narrow area. The metal material may also be a welded metal surface. Welded areas are often narrow. In the laser peening method according to this embodiment, peening can be easily performed by applying resin to these surfaces.

[0011] The resin is permeable and has a refractive index higher than that of air. Furthermore, the resin is preferably in gel form. Making the resin gel-like helps to suppress dripping when applying it to metal materials.

[0012] Furthermore, the resin is preferably a thermosetting resin or a photocurable resin. Examples of thermosetting resins include urea resin, melamine resin, phenolic resin, urea resin, epoxy resin, unsaturated polyester resin, alkyd resin, silicone resin, polyurethane resin, and thermosetting polyimide resin. Examples of photocurable resins include acrylate resin, epoxy resin, urethane acrylate resin, and polyester acrylate resin.

[0013] When using thermosetting resins, curing agents, initiators, catalysts, etc., are added. When using photocurable resins, photopolymerization initiators, fillers, non-external radiation absorbers, etc., are added.

[0014] The thickness of the resin can be several tens of micrometers, and may be 1 micrometer or more, or 10 micrometers or more.

[0015] <Curing process S2> In curing step S2, the resin is cured. For thermosetting resins, the resin is heated and polymerized to cure it. The temperature, holding time, and heating time for curing the resin can be those of known origin. For photocurable resins, the resin is irradiated with ultraviolet light to polymerize and cure it. The ultraviolet irradiation for curing the resin can be those of known origin. By curing the resin, it can adhere to the metal material and prevent the resin from peeling off the metal surface. Furthermore, curing the resin allows peening even if the metal material is not level. Alternatively, the resin may be cured simply by drying.

[0016] <Peening process S3> In the peening process S3, a pulsed laser is irradiated onto the surface of the metal material, penetrating the resin. The pulsed laser outputs light at a constant repetition frequency. Examples of pulsed lasers include YAG lasers, CO2 lasers, excimer lasers, fiber lasers, alexandrite lasers, and green lasers. In the peening process S3, it is preferable to use a laser with a small pulse width and high peak power. Furthermore, it is preferable that the pulsed laser has a wavelength that penetrates the resin and is absorbed by the metal plate.

[0017] Figure 2 shows a state of performing peening on the metal material 10. In the peening process S3, as shown in Figure 2, an impact wave of the pulsed laser 31 is applied from the laser device 30 to modify the surface of the metal material 10. The surface is modified by the plasma generated at that time. Specifically, when the pulsed laser 31 is irradiated on the surface of the metal material 10, the metal of the irradiated portion is instantaneously turned into plasma. And since the cured resin is in close contact with the metal material 10, the expansion of the plasma is suppressed by the above-mentioned resin, and an impact wave is applied to the surface of the metal material 10 to modify the metal surface. By performing peening, the fatigue strength and durability of the surface of the metal material 10 are improved.

[0018] When the pulsed laser 31 is irradiated on the surface of the metal material 10, the metal surface of the portion where the resin 20 is applied and cured is peened, but the metal surface of the portion where the resin is not applied and cured is not peened because the expansion of the plasma cannot be suppressed.

[0019] As shown in Figure 2, when the peening process S3 is performed, the cured resin 20 is peeled off from the metal material 10 by the reaction force of the plasma, and the resin can be easily removed. In other words, it can be confirmed that the surface of the metal material 10 is peened by the peeling of the cured resin 20 from the metal material. When it is desired to peen the surface of the peened metal material 10 again, the coating process, the curing process, and the peening process may be performed again.

[0020] As described above, the laser peening method according to the embodiment applies the resin 20 to the surface of the metal material 10 of the portion that requires peening, and then cures the resin 20. Then, the pulsed laser 31 is irradiated on the surface of the metal material 10 through the cured resin 20 to perform peening.

[0021] Conventional methods involve peening underwater, which requires immersing even metal parts that don't require peening. This necessitates large-scale peening equipment and increased equipment costs. Furthermore, conventional methods are unsuitable or difficult to use with water, such as on steel towers and bridges. Additionally, performing laser peening in air instead of underwater requires the introduction of expensive lasers, and even then, the peening time increases. Thus, conventional methods had many limitations.

[0022] Therefore, according to the laser peening method of the embodiment, since resin can be applied to the portion of the metal material 10 that requires peening and then peening can be performed, the peening equipment can be made smaller and equipment costs can be reduced. Furthermore, according to the laser peening method of the embodiment, plasma expansion is suppressed by the resin 20, and peening can be performed, so it can be carried out in the atmosphere. Moreover, according to the laser peening method of the embodiment, since it can be carried out in the atmosphere, even in cases where water cannot be used or is difficult to use, such as on steel towers and bridges, peening can be easily performed by using the resin 20. Furthermore, according to the laser peening method of the embodiment, the introduction of an expensive laser is unnecessary, and the increase in peening time can be suppressed. Thus, according to the laser peening method of the embodiment, the above constraints are alleviated and peening can be easily performed.

[0023] Since the resin 20 is a liquid, it penetrates into narrow and uneven areas of the metal material 10, making peening possible even in those narrow areas.

[0024] Furthermore, according to the laser peening method of the embodiment, the surface of the metal material 10 in the area where the resin 20 is applied is peened, so by adjusting the application range of the resin 20, the surface of the metal material 10 can be selectively peened.

[0025] Furthermore, according to the laser peening method of this embodiment, the peening force can be controlled by controlling the adhesive force between the metal material 10 and the resin 20. The adhesive force can be controlled by adjusting the type of resin 20 to be cured and the curing conditions, or by adjusting the surface roughness of the metal material 10.

[0026] Furthermore, according to the laser peening method of the embodiment, the stress distribution of the metal material 10 can be controlled by controlling the amount of absorption by the metal material 10. The amount of absorption can be controlled by adjusting the laser output.

[0027] The refractive index of water is approximately 1.33, while the refractive index of epoxy resin, for example, is 1.55 to 1.61, meaning the refractive index of resin 20 is higher than that of water. Therefore, the laser peening method according to the embodiment can perform peening with a smaller pulse energy than that used in water.

[0028] Specifically, while the pulse energy used in laser peening performed underwater is typically several joules to several hundred joules, the laser peening method according to this embodiment allows for peening with a smaller pulse energy. For example, the pulse energy is preferably 1 joule or less, more preferably 500 mJ or less, more preferably 100 mJ or less, 10 mJ or less, or 5 mJ or less. The peak power of the pulsed laser is preferably 1 MW or more. This allows for energy saving and reduces production costs. Furthermore, if the pulse energy is the same as in the conventional method, it is possible to achieve higher speeds than before. [Examples]

[0029] The laser peening method according to the embodiment will be described in detail below with reference to examples. However, the laser peening method according to the embodiment is not limited to this embodiment.

[0030] (Example 1) As part of the coating process, a photocurable epoxy resin was applied to the metal material. SUS304 was used as the metal material.

[0031] As a curing step, the epoxy resin was cured by irradiating it with ultraviolet light.

[0032] As part of the peening process, a pulsed laser was irradiated onto the surface of SUS304 through the resin. A fiber laser was used as the laser device. The pulse conditions at that time were as follows:

[0033] Pulse conditions Wavelength: 1064nm Output: 200W Repeat frequency: 50kHz Spot size: 170 μm Pulse width: 270ns Pulse energy: 4 mJ Peak power: 55MW

[0034] Under the above conditions, a peening process was performed, specifically laser peening.

[0035] (Comparative Example 1) In Comparative Example 1, the coating and curing processes were omitted. Other conditions were the same as in Example 1. Specifically, in Comparative Example 1, laser peening was performed by directly irradiating the surface of SUS304 with a pulsed laser in the atmosphere.

[0036] (Comparative Example 2) In Comparative Example 2, the coating and curing processes were omitted. Furthermore, laser peening was performed underwater in Comparative Example 2. All other conditions were the same as in Example 1.

[0037] Figure 3 shows sample images of the examples and comparative examples, illustrating the state of the samples before laser peening. Figure 4 shows sample images of the examples and comparative examples, illustrating the state of the samples after laser peening. Figure 5 shows the Pickers hardness of the samples in the examples and comparative examples. In Figure 5, the values ​​enclosed by the dotted line represent the Pickers hardness before peening, and the values ​​enclosed by the solid line represent the Pickers hardness after peening.

[0038] The samples of Example 1, Comparative Example 1, and Comparative Example 2 obtained in this manner before laser peening are shown in Figure 3. The samples of Example 1, Comparative Example 1, and Comparative Example 2 obtained in this manner after laser peening are shown in Figure 4.

[0039] As shown in Figure 4, the surface of the SUS304 in Example 1 was modified by irradiation with a pulsed laser. Furthermore, as shown in Figure 5, the Pickers hardness of the SUS304 in Example 1 after peening was nearly doubled compared to before peening, showing a significant improvement. Therefore, a high peening effect was obtained in Example 1.

[0040] On the other hand, the surfaces of the SUS304 in Comparative Example 1 and Comparative Example 2 appear to have been modified by irradiation with a pulsed laser, as shown in Figure 4. However, as shown in Figure 5, the Pickers hardness of the SUS304 in Comparative Example 1 after peening is the same as before peening. Therefore, no peening effect was obtained in Comparative Example 1. Also, as shown in Figure 5, the Pickers hardness of the SUS304 in Comparative Example 2 after peening is slightly improved compared to before peening. Therefore, the peening effect obtained in Comparative Example 2 is small.

[0041] As described above, in Example 1, the process could be carried out in the atmosphere, and peening could be easily performed with reduced constraints.

[0042] Furthermore, the surface of the SUS304 coated with resin has turned black. This indicates that the resin has carbonized, or that the SUS304 has oxidized and undergone surface modification, resulting in blackening, and signifies that the peening process is complete. Therefore, the completion of peening can be determined by the color of the surface. Also, as shown in Figure 4, when peening is complete, the hardened resin peels off from the SUS304. Therefore, the completion of peening can also be confirmed by the peeling off of the resin.

[0043] Based on the above, according to the embodiment, it is possible to carry out the procedure in the atmosphere, and peening can be easily performed with reduced constraints. Furthermore, laser peening can be performed in various situations desired by the user.

[0044] Although several embodiments have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

[0045] The present invention includes the following embodiments.

[0046] (Note 1) A coating process in which liquid resin is applied to a metal material, A curing step for curing the aforementioned resin, A peening process in which a pulsed laser is irradiated onto the surface of the metal material through the resin, which has a refractive index higher than that of the atmosphere, A laser peening method equipped with [specific features / features].

[0047] (Note 2) The laser peening method described in Appendix 1, wherein the resin is in the form of a gel.

[0048] (Note 3) The laser peening method according to Appendix 1 or 2, wherein the resin is a thermosetting resin.

[0049] (Note 4) The laser peening method according to Appendix 1 or 2, wherein the resin is a photocurable resin.

[0050] (Note 5) The pulse energy of the pulsed laser in the peening process is 1 J or less. The laser peening method according to any one of the appendices 1 to 4, wherein the peak power of the pulsed laser is 1 MW or more.

[0051] (Note 6) The laser peening method according to any one of Appendix 1 to 5, wherein the pulsed laser has a wavelength that penetrates the resin and is absorbed by the metal material.

[0052] (Note 7) The laser peening method according to any one of the appendices 1 to 6, wherein the metal material is a flat metal surface or a welded metal surface. [Explanation of symbols]

[0053] 10 Metal materials, 20 resins, 30 laser devices, 31 pulsed lasers, S1 coating process, S2 curing process, S3 peening process

Claims

1. A coating process in which liquid resin is applied to a metal material, A curing step for curing the aforementioned resin, A peening process in which a pulsed laser is irradiated onto the surface of the metal material through the resin, which has a refractive index higher than that of the atmosphere, A laser peening method equipped with [specific features / features].

2. The laser peening method according to claim 1, wherein the resin is in the form of a gel.

3. The laser peening method according to claim 1, wherein the resin is a thermosetting resin.

4. The laser peening method according to claim 1, wherein the resin is a photocurable resin.

5. The pulse energy of the pulsed laser in the peening process is 1 J or less. The laser peening method according to claim 1, wherein the peak power of the pulsed laser is 1 MW or more.

6. The laser peening method according to claim 1, wherein the pulsed laser has a wavelength that penetrates the resin and is absorbed by the metal material.

7. The laser peening method according to claim 1, wherein the metal material is a flat metal surface or a welded metal surface.

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