Laser cavitation impact forming device

Abstract

The invention provides a laser cavitation impact forming device which comprises a mold, a mold cavity is formed in the top end of the mold, and a focus point is arranged at the top end of the mold cavity; the laser emitting module is used for emitting a laser beam towards a focus point; a first flow channel is formed in the first rectifying cylinder, water flows through the first flow channel, the top end of the first flow channel is a drainage end and is provided with a control valve assembly, and the control valve assembly can open or close the first flow channel; when the control valve assembly closes the first flow channel, pressure waves moving towards the direction close to the mold can be generated in the first flow channel; the device has a forming mode. According to the invention, energy released during collapse of cavitation bubbles can be further increased.

Description

Technical Field

[0001] The invention relates to the technical field of laser forming, in particular to a laser cavitation impact forming device. Background Art

[0002] When the laser beam acts on the liquid medium and its energy reaches the breakdown threshold of the medium, the liquid medium will be broken down and ionized, thereby generating a plasma cavity. The plasma cavity will further absorb the energy of the laser beam, thereby rapidly expanding and evolving into a cavitation bubble. When the cavitation bubble is located near the solid-liquid interface, due to the pressure difference on both sides, the cavitation bubble will produce a "wall-moving" effect and eventually collapse. During the collapse process, the cavitation bubble will release huge energy in the form of shock waves and microjets. When these shock waves and microjets act on the plate, they will have a strong impact on the plate, causing the plate to deform. If a suitable mold is set around the plate, the impact generated by the collapse of the cavitation bubble can be used to press the plate against the mold, thereby realizing the forming of the plate. The greater the energy released by the collapse of the cavitation bubble, the greater the deformation that can be achieved on the plate, and accordingly, the stronger the processing ability of the plate.

[0003] In today's technology, increasing the energy of the laser beam is the main method to increase the energy released when the cavitation bubble collapses. However, due to the power upper limit of the existing laser source, energy conversion efficiency, damage threshold of optical components, transmittance and other conditions, the method of simply increasing the energy released when the cavitation bubble collapses by increasing the laser beam energy has reached its efficiency limit. Therefore, we need to explore new ways to further increase the energy released when the cavitation bubble collapses. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a laser cavitation impact forming device, which can further increase the energy released when the cavitation bubble collapses.

[0005] The present invention adopts the following technical solutions.

[0006] A laser cavitation impact forming device comprises a mold, a top end of the mold is provided with a mold cavity, and a top end of the mold cavity is provided with a focusing point;

[0007] Also included is a laser emitting module, the laser emitting module is used to emit a laser beam toward a focal point;

[0008] It also includes a first rectifying cylinder, wherein a first flow channel is formed in the first rectifying cylinder, water flows through the first flow channel, and the top of the first flow channel is a drainage end and is provided with a control valve assembly, and the control valve assembly can open or close the first flow channel;

[0009] When the control valve assembly closes the first flow channel, it can generate a pressure wave in the first flow channel that moves toward the mold;

[0010] The device has a forming mode. In the forming mode, the laser emission module is started and the control valve assembly closes the first flow channel. When the laser beam emitted by the laser emission module maximizes the volume of the cavitation bubble at the focal point, the peak of the pressure wave generated by the control valve assembly closing the first flow channel and moving toward the mold touches the top bubble wall of the cavitation bubble.

[0011] Furthermore, the device has a pre-processing mode. In the pre-processing mode, the laser emission module is shut down and the control valve assembly repeatedly opens and closes the first flow channel.

[0012] Furthermore, a second straightening cylinder is sleeved on the outer side of the first straightening cylinder, a second flow channel is formed between the first straightening cylinder and the second straightening cylinder, the first flow channel is connected with the bottom end of the second flow channel, a straightening seat is provided at the top end of the second straightening cylinder, an annular straightening cavity is opened in the straightening seat, the straightening cavity is connected with a water inlet joint, and a plurality of diversion holes connected to the second flow channel are evenly distributed at the bottom end of the straightening cavity.

[0013] Furthermore, a conical wall pointing to the edge of the mold cavity is formed at the bottom end of the first rectifier cylinder, and a cavitation gap is formed between the conical wall and the mold.

[0014] Furthermore, the device has a trimming mode. In the trimming mode, the laser emission module is shut down and the control valve assembly continues to open the first flow channel.

[0015] Furthermore, the control valve assembly includes a mounting cylinder, on which a winding and a valve core are provided, the valve core is slidably sleeved with the mounting cylinder, and a permanent magnet coupled with the winding is embedded in the valve core.

[0016] The beneficial effects of the present invention are:

[0017] The present invention has a forming mode. In the forming mode, the laser emission module is started and emits a laser beam toward the focal point. In addition, the control valve assembly closes the first flow channel, and under the action of the water hammer effect, a pressure wave moving toward the direction close to the mold is generated in the first flow channel. The laser beam acts on the water at the focal point, causing it to be broken down and ionized, thereby generating a plasma cavity, which then evolves into a cavitation bubble. The cavitation bubble first expands, and when its volume reaches a maximum, the crest of the pressure wave moving toward the direction close to the mold in the first flow channel just touches the top side bubble wall of the cavitation bubble, thereby increasing the pressure difference between the top side and the bottom side of the cavitation bubble, and causing the cavitation bubble to collapse. During the collapse process, along with the increase in the pressure difference, the shock wave pressure and microjet velocity released by the cavitation bubble are both increased, thereby increasing the total energy released when the cavitation bubble collapses. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is one of the structural schematic diagrams of this embodiment (the first flow channel is in an open state at this time);

[0020] Figure 2 This is the second structural diagram of this embodiment (the first flow channel is in a closed state at this time).

[0021] Description of reference numerals:

[0022] Mold 1, cavity 11, focal point 12,

[0023] Laser emission module 2,

[0024] The first rectifier tube 3, the first flow channel 31, the cavitation gap 32, the tapered wall 301,

[0025] Install the cylinder 41, the winding 42, the valve core 43, the permanent magnet 44,

[0026] The second rectifier tube 5, the second flow channel 51,

[0027] Rectifier seat 6, rectifier cavity 61, diverter hole 62,

[0028] Water inlet connector 7. DETAILED DESCRIPTION

[0029] The drawings are only used for illustrative purposes and should not be construed as limitations of this patent. In order to better illustrate this embodiment, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of the actual product.

[0030] For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings. The technical solution of the present invention is further described below in conjunction with the drawings and embodiments.

[0031] As shown in the accompanying drawings, a laser cavitation impact forming device comprises a mold 1, a mold cavity 11 is formed at the top of the mold 1, and a focusing point 12 is formed at the top of the mold cavity 11;

[0032] It also includes a laser emitting module 2, which is used to emit a laser beam toward a focusing point 12;

[0033] It also includes a first rectifying cylinder 3, in which a first flow channel 31 is formed, water flows through the first flow channel 31, and the top of the first flow channel 31 is a drainage end and is provided with a control valve assembly, which can open or close the first flow channel 31;

[0034] When the control valve assembly closes the first flow channel 31, it can generate a pressure wave in the first flow channel 31 that moves toward the direction close to the mold 1. The direction of water flow in the first flow channel 31 is from bottom to top. When the control valve assembly quickly closes the first flow channel 31, the water flow is forcibly cut off, and its flow velocity changes dramatically. However, due to the inertia of water, it still has a tendency to continue to flow toward the drainage end of the first flow channel 31, thereby generating a water hammer phenomenon. This tendency causes the kinetic energy of the water flow in the first flow channel 31 to be rapidly converted into pressure energy, thereby forming a high-pressure area at the cutoff point. The high-pressure area rapidly expands in the direction close to the mold 1, and its boundary is the crest of the pressure wave.

[0035] The device has a forming mode. In the forming mode, the laser emitting module 2 is started and the control valve assembly closes the first flow channel 31. When the laser beam emitted by the laser emitting module 2 maximizes the volume of the cavitation bubble at the focal point 12, the peak of the pressure wave generated by the control valve assembly closing the first flow channel 31 and moving toward the mold 1 touches the top bubble wall of the cavitation bubble.

[0036] In the forming mode, the laser emission module 2 is started and emits a laser beam toward the focal point 12. In addition, the control valve assembly closes the first flow channel 31, and under the action of the water hammer effect, a pressure wave moving toward the direction close to the mold 1 is generated in the first flow channel 31. The laser beam acts on the water at the focal point 12, causing it to be broken down and ionized, thereby generating a plasma cavity, which then evolves into a cavitation bubble. The cavitation bubble first expands, and when its volume reaches the maximum, the crest of the pressure wave moving toward the direction close to the mold 1 in the first flow channel 31 just touches the top side bubble wall of the cavitation bubble, thereby increasing the pressure difference between the top and bottom sides of the cavitation bubble, and causing the cavitation bubble to collapse. During the collapse process, along with the increase in the pressure difference, the shock wave pressure and microjet velocity released by the cavitation bubble are both increased, thereby increasing the total energy released when the cavitation bubble collapses.

[0037] It should be noted that the maximum volume of cavitation bubbles is directly related to the energy released when the cavitation bubbles collapse. A larger volume of cavitation bubbles means that there are more gas or steam substances inside before they collapse. When the cavitation bubbles collapse, these substances are compressed sharply. Under the same other conditions, according to the law of conservation of energy, the compression process of more substances will release more energy.

[0038] Water pressure affects the maximum volume of cavitation bubbles. In a low water pressure environment, after cavitation bubbles are formed, due to the low external water pressure, the steam or gas pressure inside the cavitation bubbles is relatively dominant, and the cavitation bubbles will expand rapidly, and their volume can grow to a larger value. On the contrary, in a high water pressure environment, the growth of cavitation bubbles will be restricted, and the external water pressure will inhibit the expansion of cavitation bubbles. The volume growth rate of cavitation bubbles will slow down, and the final volume will be relatively small.

[0039] In this embodiment, in order to prevent the pressure wave generated when the control valve assembly closes the first flow channel 31 from affecting the maximum volume of the cavitation bubble, the peak of the pressure wave moving in the direction close to the mold 1 in the first flow channel 31 must contact the top bubble wall of the cavitation bubble when the volume of the cavitation bubble reaches the maximum. To implement the above technical solution, a time difference can be set by the controller between the time point when the laser emitting module 2 emits the laser beam and the time point when the control valve assembly closes the first flow channel 31. The time difference can be determined by fluid mechanics calculation or model simulation.

[0040] Among them, the propagation speed formula of the pressure wave generated by water hammer is:

[0041] a is the pressure wave propagation velocity (m / s), K is the bulk elastic modulus of water, K = 2.06 × 10 9 Pa; ρ is the density of water (kg / m3), ρ = 1000kg / m at room temperature 3 ; E is the elastic modulus (Pa) of the pipe wall material (i.e. the first rectifier tube), for example, for a steel pipe, E=2.06×1011Pa; d is the inner diameter (m) of the pipe (i.e. the first rectifier tube); e is the wall thickness (m) of the pipe (i.e. the first rectifier tube).

[0042] The time it takes for the pressure wave generated by water hammer to reach the focal point is:

[0043] t is the time (s) for the pressure wave to reach the focal point from the starting point; L is the distance (m) for the pressure wave to reach the focal point from the starting point.

[0044] To calculate the time from laser irradiation to the maximum volume of the cavitation bubble, we can use the dynamic equation of the cavitation bubble, such as the Rayleigh-Price equation: R is the radius of the cavitation bubble, is the first-order derivative of the cavitation bubble radius with respect to time, is the second-order derivative of the cavitation bubble radius with respect to time, ρ is the liquid density, ρ0 is the liquid pressure at infinity, and ρ v is the saturated vapor pressure of the liquid, ρ (t)is the externally applied pressure (here it is related to laser irradiation, which causes local pressure changes), and σ is the surface tension of the liquid. When the cavitation bubble volume reaches its maximum, (At this time, the growth rate of the cavitation bubble radius is 0, indicating that the cavitation bubble is about to shrink.) By solving the finite difference method, we can find the solution that satisfies First, the Rayleigh-Price equation is discretized. Let the time step be Δt. At the discrete time point t n =nΔt (n=0,1,2,...), R (t) Represented as R n , Expressed as Expressed as Substituting these discrete expressions into the Rayleigh-Price equation, we obtain the equation for . Given the initial conditions (initial radius R0 and initial velocity of the cavitation bubble at the moment of laser irradiation) The initial speed is related to factors such as laser energy), and then R is calculated step by step by iteration. n Until you find satisfaction (Approximately ) The corresponding t = nΔt is the time from laser irradiation to the time when the cavitation bubble reaches its maximum volume.

[0045] According to the above formula, combined with the actual parameters of the device, the approximate time difference between the time point when the laser emitting module 2 emits the laser beam and the time point when the control valve assembly closes the first flow channel 31 can be calculated. Then, this approximate time difference can be fine-tuned through multiple experiments to obtain an accurate time difference.

[0046] It is understandable that if the propagation speed of the pressure wave generated by the control valve assembly closing the first flow channel 31 is slower than the expansion speed of the cavitation bubble, the time point at which the laser emitting module 2 emits the laser beam can be set after the time point at which the control valve assembly closes the first flow channel 31. On the contrary, if the propagation speed of the pressure wave is faster than the expansion speed of the cavitation bubble, the time point at which the laser beam is emitted should be set before the time point at which the control valve assembly is closed.

[0047] Preferably, the device has a pre-processing mode, in which the laser emission module 2 is turned off and the control valve assembly repeatedly opens and closes the first flow channel 31 .

[0048] It is understandable that the pre-treatment mode occurs before the forming mode. In the pre-treatment mode, the control valve assembly repeatedly opens and closes the first flow channel 31, repeatedly triggers the water hammer effect in the first flow channel 31, and uses the pressure wave with less energy generated by the water hammer effect to repeatedly impact the plate on the mold 1, causing the plate to deform slightly, which is beneficial to avoid excessive deformation of the plate in the subsequent forming mode, and prevent the plate from breaking and stress concentration.

[0049] Preferably, the second rectifier cylinder 5 is sleeved on the outer side of the first rectifier cylinder 3, a second flow channel 51 is formed between the first rectifier cylinder 3 and the second rectifier cylinder 5, the first flow channel 31 is connected to the bottom end of the second flow channel 51, a rectifier seat 6 is provided at the top end of the second rectifier cylinder 5, an annular rectifier cavity 61 is provided in the rectifier seat 6, the rectifier cavity 61 is connected to the water inlet connector 7, and a plurality of diverter holes 62 connected to the second flow channel 51 are evenly distributed at the bottom end of the rectifier cavity 61. It can be understood that the water inlet connector 7 is connected to a water pump through a hose, water is transported into the rectifier cavity 61 through the water pump, and then the water in the rectifier cavity 61 enters the second flow channel 51 through the diverter holes 62.

[0050] Preferably, the bottom end of the first rectifier tube 3 is formed with a conical wall 301 pointing to the edge of the mold cavity 11, and a cavitation gap 32 is formed between the conical wall 301 and the mold 1. It can be understood that the water flow in the second flow channel 51 enters the first flow channel 31 through the cavitation gap 32. In view of the fact that the flow area of ​​the cavitation gap 32 is smaller than the flow area of ​​the second flow channel 51, the flow velocity of the water flow in the cavitation gap 32 is accelerated, and the water pressure decreases accordingly. When the water pressure in the cavitation gap 32 drops below the saturated vapor pressure of the liquid, cavitation occurs and cavitation bubbles are formed. Under the guidance of the conical wall 301, these cavitation bubbles move to the vicinity of the edge of the mold cavity 11, and then collapse, generating shock waves and microjets with less energy. These shock waves and microjets act on the bending part of the plate at the edge of the mold cavity 11, which helps to improve the stress distribution of the part, eliminate the stress concentration phenomenon, and adjust the microstructure of the bending part of the plate, so that the material of the bending part of the plate is more tightly combined.

[0051] The above-mentioned mechanisms for adjusting the microstructure mainly include: energy transfer and lattice vibration, dislocation movement and proliferation, grain boundary migration and recrystallization, and surface plastic deformation and microstructure remodeling.

[0052] When the shock wave and micro jet act on the bending part of the plate, energy is first transferred, causing lattice vibration, which breaks the original equilibrium state of atoms and affects the bonding between atoms.

[0053] Among them, under energy driving, dislocations will move toward the stress concentration area and proliferate, which helps to redistribute the stress state.

[0054] Among them, for polycrystalline materials, the effects of shock waves and microjets can promote the migration of grain boundaries and even induce recrystallization, thereby changing the size distribution of grains and making the materials more tightly bonded.

[0055] In addition, the micro jet will directly cause the surface of the plate bending part to undergo plastic deformation, thereby reshaping the surface microstructure. This surface plastic deformation works together with internal dislocation movement and grain boundary migration to improve the stress distribution and performance of the bending part.

[0056] Preferably, the device has a trimming mode. In the trimming mode, the laser emitting module 2 is shut down, and the control valve assembly continuously opens the first flow channel 31 .

[0057] It is understandable that the trimming mode occurs after the forming mode. In the trimming mode, the control valve assembly continues to open the first flow channel 31, and the water pump causes the water to flow through the second flow channel 51, the cavitation gap 32 and the first flow channel 31 in sequence. When the water flows through the cavitation gap 32, since the flow area of ​​the cavitation gap 32 is smaller than the flow area of ​​the second flow channel 51, the water flow in the cavitation gap 32 undergoes cavitation to form cavitation bubbles. These cavitation bubbles move to the vicinity of the bending part of the sheet at the edge of the mold cavity 11 under the guidance of the conical wall 301, and then collapse. When collapsing, these cavitation bubbles will release shock waves and microjets with less energy, and act on the bending part of the sheet, thereby improving the stress distribution at the bending part of the sheet and improving the structural strength of the bending part of the sheet.

[0058] After the plate is placed on the mold 1, the present embodiment performs the following operations:

[0059] First, the pre-treatment mode is run to slightly deform the sheet. Then, the forming mode is run to use laser beams and pressure waves to cause cavitation bubbles to release high-energy shock waves and microjets, thereby fully forming the sheet. Finally, the trimming mode is run to improve the stress distribution at the bending part of the sheet and enhance the structural strength of the bending part of the sheet.

[0060] Preferably, the control valve assembly includes a mounting cylinder 41, on which a winding 42 and a valve core 43 are provided, the valve core 43 is slidably sleeved with the mounting cylinder 41, and a permanent magnet 44 coupled with the winding 42 is embedded in the valve core 43. It can be understood that by controlling the current direction of the winding 42 so that the winding 42 generates an attractive force or a repulsive force on the permanent magnet 44, the permanent magnet 44 can be driven to move toward or away from the winding 42, thereby causing the valve core 43 to open or close the first flow channel 31.

[0061] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A laser cavitation impact forming device, comprising a mold, wherein a mold cavity is formed at the top of the mold, characterized in that: A focusing point is provided at the top of the mold cavity; Also included is a laser emitting module, the laser emitting module is used to emit a laser beam toward a focal point; It also includes a first rectifying cylinder, wherein a first flow channel is formed in the first rectifying cylinder, water flows through the first flow channel, and the top of the first flow channel is a drainage end and is provided with a control valve assembly, and the control valve assembly can open or close the first flow channel; When the control valve assembly closes the first flow channel, it can generate a pressure wave in the first flow channel that moves toward the mold; The device has a forming mode. In the forming mode, the laser emission module is started and the control valve assembly closes the first flow channel. When the laser beam emitted by the laser emission module maximizes the volume of the cavitation bubble at the focal point, the peak of the pressure wave generated by the control valve assembly closing the first flow channel and moving toward the mold touches the top bubble wall of the cavitation bubble.

2. The laser cavitation impact forming device according to claim 1, characterized in that: The device has a pre-processing mode. In the pre-processing mode, the laser emission module is shut down, and the control valve component repeatedly opens and closes the first flow channel.

3. The laser cavitation impact forming device according to claim 1, characterized in that: A second straightening cylinder is sleeved on the outer side of the first straightening cylinder, a second flow channel is formed between the first and second straightening cylinders, the first flow channel is connected with the bottom end of the second flow channel, a straightening seat is provided at the top end of the second straightening cylinder, an annular straightening cavity is opened in the straightening seat, the straightening cavity is connected with a water inlet joint, and a plurality of diversion holes connected with the second flow channel are evenly distributed at the bottom end of the straightening cavity.

4. The laser cavitation impact forming device according to claim 3, characterized in that: A conical wall pointing to the edge of the mold cavity is formed at the bottom end of the first rectifier cylinder, and a cavitation gap is formed between the conical wall and the mold.

5. The laser cavitation impact forming device according to claim 4, characterized in that: The device has a trimming mode. In the trimming mode, the laser emission module is shut down and the control valve component continues to open the first flow channel.

6. The laser cavitation impact forming device according to claim 1, characterized in that: The control valve assembly comprises a mounting cylinder, on which a winding and a valve core are arranged, the valve core is slidably sleeved with the mounting cylinder, and a permanent magnet coupled with the winding is embedded in the valve core.

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