Laser peening forming impact load rheological constraint gain method

Abstract

The invention discloses a laser peening forming impact load rheology constraint gain method, which utilizes the rheology effect that a non-Newtonian fluid constraint layer instantaneously generates shear thickening and hardening after being impacted to realize stress peak amplification and action time prolonging of a laser peening forming impact load. The method has the advantages of being easy to deploy and clean, remarkable in impact load amplification efficiency, self-adaptive to laser-induced plasma detonation wave intensity and the like. The restraint layer is formed in the mode that non-Newtonian fluid flows on the to-be-formed surface in a viscous mode and keeps a certain thickness, and strong restraint is achieved on impact loads in the laser peening forming process, so that the impact loads are recoiled to achieve the load amplification effect. The problems that in an existing laser peening forming technology, the impact wave constraint efficiency is insufficient, and the impact load stress peak value and the action time are insufficient are solved. The method provided by the invention is mainly applied to the field of laser peening forming.

Description

Technical Field

[0001] The invention belongs to the technical field of laser shot peening, and in particular relates to a laser shot peening impact load rheological constraint gain method. Background Art

[0002] Laser peening is a process that uses short pulses (pulse width is in the nanosecond or even femtosecond range) and high power density (GW / cm 2 The laser of the magnitude of 1000 nm acts perpendicularly to the surface of a metal workpiece with a constrained layer and an energy absorption layer, inducing a localized plasma detonation wave on the workpiece surface. The outward diffusion of the localized plasma detonation wave is partially restricted by the constrained layer, thus forming a recoil shock wave that strongly acts on the surface of the metal workpiece, causing plastic deformation of the metal surface layer and generating residual compressive stress, thereby enhancing the fatigue resistance of the metal part.

[0003] Laser peening is derived from the principle of laser peening and is a non-contact, non-thermal effect flexible forming method for metal sheets. Laser peening uses laser-induced shock waves to induce bending of metal sheets. This is a purely mechanical process that does not cause thermal damage. In addition, it can improve the fatigue properties of metals by generating beneficial residual compressive stresses and surface work-hardening layers.

[0004] At present, the constraint layers used in laser shot peening are usually glass, flowing water and transparent flexible films. Among them, water is the most widely used due to its low cost, good flexibility and strong adaptability. However, the biggest disadvantage of the water constraint layer is that it is not rigid enough and it is difficult to effectively maintain the intensity and action time of the shock wave. The glass constraint layer is brittle, easy to break, high cost and inconvenient to replace. The flexible film constraint layer is prone to ablation and denaturation during the laser shock process and is not suitable for continuous laser shot peening process. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the existing laser shot peening constrained layer is insufficient in maintaining and amplifying the continuous impact load, and provide a laser shot peening impact load rheological constraint gain method.

[0006] To achieve the above object, the present invention discloses a laser shot peening impact load rheological constraint gain method, which specifically comprises the following steps:

[0007] Step 1: Place the surface to be laser shot peened at an angle of 95 degrees to the horizontal plane, place liquid tank A on the upper edge of the surface to be laser shot peened, immerse the lower edge of the surface to be laser shot peened in liquid tank B, and connect liquid tank A and liquid tank B through pipe C and circulation pump D.

[0008] Step 2: injecting a non-Newtonian fluid into the liquid tank A, so that the non-Newtonian fluid continuously flows from top to bottom along the surface to be laser peened under the action of its own gravity, so that the non-Newtonian fluid covers the surface to be laser peened and maintains a certain thickness;

[0009] Step 3: emitting a pulsed laser to perform point-by-point laser peening on the surface to be laser peened and covered with the non-Newtonian fluid;

[0010] Step 4: The non-Newtonian fluid flowing into the liquid tank B returns to the liquid tank A through the pipeline C under the action of the circulation pump D and then repeats the S2 process for recycling;

[0011] Step 5: After laser peening is completed, rinse the peened surface with a large amount of deionized water to remove residual non-Newtonian fluid.

[0012] Furthermore, in step 2, the non-Newtonian fluid is a colorless, transparent, water-soluble liquid.

[0013] Furthermore, in step 2, the non-Newtonian fluid is a shear thickening liquid.

[0014] Furthermore, in step 3, the pulse laser is a nanosecond pulse laser, and the pulse width of the laser pulse ranges from 20 nanoseconds to 200 nanoseconds.

[0015] Beneficial effects of the present invention:

[0016] 1. The present invention can realize the peak amplification of the impact load stress of laser shot peening based on the shear hardening characteristics of non-Newtonian fluids. When a short-pulse laser induces a plasma detonation wave between the transparent shear-thickening non-Newtonian fluid constraint layer and the surface of the metal sheet, the energy dissipation trend of the shock wave is to propagate and diffuse into the constraint layer and the metal sheet at the same time. Since the rheological characteristics of the shear-thickening non-Newtonian fluid in the constraint layer are: the viscosity of the system increases by an order of magnitude with the increase of shear rate or shear stress, this characteristic causes the area in the shear-thickening non-Newtonian fluid constraint layer that is subjected to the shear stress of the shock wave to instantaneously undergo shear thickening and hardening, and the area is then transformed into an approximately rigid constraint area, so that the stress wave wavefront that propagates and diffuses into the constraint layer is strongly constrained and then recoils into the metal sheet, thereby realizing the peak amplification of the impact load stress of laser shot peening.

[0017] 2. The present invention can extend the action time of the impact load of laser shot peening based on the shear hardening characteristics of non-Newtonian fluid. When a short-pulse laser induces a plasma detonation wave between a transparent shear-thickening non-Newtonian fluid confinement layer and the surface of a metal sheet, the rheological characteristic time from the occurrence of shear thickening hardening to the disappearance of the effect of the shear-thickening non-Newtonian fluid is much longer than the nanosecond level of the laser pulse width. The shear thickening hardening effect of the confinement layer will continuously produce approximately rigid constraints on the laser shot peening shock wave, thereby extending the action time of the impact load of laser shot peening.

[0018] 3. The present invention can realize the laser shot peening forming liquid constraint layer based on the shear hardening characteristics of non-Newtonian fluid, and the liquid constraint layer instantaneously hardens with the appearance of pulse laser induced plasma detonation wave, and recovers the normal fluid form with the disappearance of the pulse laser effect. It is adaptive to the intensity of laser induced plasma detonation wave, easy to deploy and clean, and avoids the shortcomings of solid rigid constraint layer that is fragile, difficult to deploy and difficult to clean, and the shortcomings of water film constraint layer that is insufficient in shock wave constraint efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the rheological constraint gain method for laser shot peening impact load described in the present invention.

[0020] In the figure:

[0021] 1-metal plate to be formed; 2-surface to be shot peened; 3-non-Newtonian fluid confinement layer; 4-pulsed laser beam; 5-non-Newtonian fluid; 6-horizontal plane; 7-pipeline C; 8-circulation pump D; 9-liquid tank A; 10-liquid tank B. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0023] like Figure 1 As shown, the present invention discloses a method for amplifying the impact load of laser shot peening based on the shear hardening characteristics of non-Newtonian fluid, which specifically includes the following steps:

[0024] Step 1: Place the surface to be laser shot peened at an angle of 95 degrees to the horizontal plane, place liquid tank A on the upper edge of the surface to be laser shot peened, immerse the lower edge of the surface to be laser shot peened in liquid tank B, and connect liquid tank A and liquid tank B through pipe C and circulation pump D.

[0025] Step 2: injecting a non-Newtonian fluid into the liquid tank A, so that the non-Newtonian fluid continuously flows from top to bottom along the surface to be laser peened under the action of its own gravity, so that the non-Newtonian fluid covers the surface to be laser peened and maintains a certain thickness;

[0026] Step 3: emitting a pulsed laser to perform point-by-point laser peening on the surface to be laser peened and covered with the non-Newtonian fluid;

[0027] Step 4: The non-Newtonian fluid flowing into the liquid tank B returns to the liquid tank A through the pipeline C under the action of the circulation pump D and then repeats the S2 process for recycling;

[0028] Step 5: After laser peening is completed, rinse the peened surface with a large amount of deionized water to remove residual non-Newtonian fluid. Specific embodiment:

[0030] 1) A TC4 titanium alloy flat plate with a thickness of 0.5 mm was selected as the forming plate, the surface to be laser shot peened was polished with sandpaper, and then the oil stains were cleaned with an alcohol solution.

[0031] 2) Using N,N-dimethylacrylamide aqueous solution as the non-Newtonian fluid constraining layer, adjusting the liquid tank A so that the constraining layer maintains a layer thickness of 3 mm when the surface to be laser peened undergoes a stable viscous flow from top to bottom.

[0032] 3) Use a Q-switched Nd:YAG nanosecond pulse laser to perform shot peening on the surface of the titanium alloy plate to be laser shot peened, wherein the laser parameters are: spot diameter 2 mm, single pulse energy 5.3 J, pulse width 100 ns, and pulse frequency 20 Hz.

[0033] 4) After the laser shot peening is completed, the surface of the formed titanium alloy plate is rinsed with a large amount of deionized water until there is no residual organic matter.

[0034] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A laser shot peening impact load rheological constraint gain method, characterized in that: The following steps are involved: S1: The surface to be shot peened is placed at an angle of 95 degrees to the horizontal plane, a liquid tank A is placed on the upper edge of the surface to be shot peened, and the lower edge of the surface to be shot peened is immersed in liquid tank B, and liquid tank A and liquid tank B are connected by a pipe C and a circulating pump D. S2: injecting a non-Newtonian fluid into the liquid tank A, so that the non-Newtonian fluid continuously flows from top to bottom along the surface to be laser shot peened under the action of its own gravity, so that the non-Newtonian fluid covers the surface to be laser shot peened and maintains a certain thickness; S3: emitting a pulsed laser to perform laser shot peening on the surface to be laser shot peened and covered with the non-Newtonian fluid point by point; S4: The non-Newtonian fluid flowing into the liquid tank B returns to the liquid tank A through the pipe C under the action of the circulation pump D and then repeats the S2 process for recycling; S5: After the laser shot peening is completed, the formed surface is rinsed with a large amount of deionized water to remove the residual non-Newtonian fluid.

2. The laser shot peening impact load rheological constraint gain method according to claim 1, characterized in that: In the step S2, the non-Newtonian fluid is a colorless, transparent, water-soluble liquid.

3. The laser shot peening impact load rheological constraint gain method according to claim 1, characterized in that: In the step S2, the non-Newtonian fluid is a shear thickening liquid.

4. The laser shot peening impact load rheological constraint gain method according to claim 1, characterized in that: In S3, the pulse laser is a nanosecond pulse laser, and the pulse width of the laser pulse ranges from 20 nanoseconds to 200 nanoseconds.

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