Water entry impact test device and equivalent test method for entering of powder with different melting degrees into molten pool

Abstract

The invention belongs to the technical field of laser additive manufacturing direct energy deposition, and particularly relates to a water entry impact test device and an equivalent test method for powder with different melting degrees entering a molten pool, the water entry impact test device comprises a water pool, an iron support, a high-speed camera and a lighting assembly, the water pool is used for simulating the molten pool; the iron stand is arranged on the periphery of the pool, a flow guide block with the adjustable height is arranged on the iron stand, the side face of the flow guide block is coated with a hydrophobic coating, and the hydrophobic coating is used for guiding ice balls to fall into the pool; the high-speed camera is arranged on the periphery of the pool and is used for shooting the water entering process of the ice hockey; the lighting assembly comprises a diffuse reflection plate and a light source which are sequentially arranged on the opposite side of the high-speed camera and used for supplementing light for the high-speed camera. According to the structure, the release stability of the ice hockey can be improved, so that the precision of a water impact test is improved, and the accuracy of a conclusion is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser additive manufacturing direct energy deposition, and particularly relates to a water impact test device and an equivalent test method for powders with different melting degrees entering a molten pool. BACKGROUND

[0002] In recent years, laser directed energy deposition technology in additive manufacturing has attracted extensive attention due to its unique manufacturing and economic advantages in large, integral and complex metal structural components. However, defects such as pores formed during the manufacturing process seriously affect the mechanical properties of the components. In the LDED deposition process, the molten pool has the characteristics of small size, non-transparency and ultra-high temperature. At the same time, the metal powder will appear in three states of unmelted, semi-melted and fully melted due to different laser energy. The current in-situ observation method such as synchrotron radiation has a large deviation from the actual situation in terms of forming size and process parameters, and is not suitable for mechanism research and is difficult to quantitatively study the cavity formation mechanism of powders with different melting degrees. Some researchers have designed an equivalent control test of ice ball entering water, and through the test of laser irradiation of water and water vaporization to form a spoon hole, the spoon hole phenomenon in welding is simulated, but the effectiveness of the equivalent test is not demonstrated by introducing the similarity criterion in fluid mechanics.

[0003] In the LDED deposition process, the metal powder will appear in three states of unmelted, semi-melted and fully melted due to different laser energy. Due to the difficulty in in-situ observation, the phenomenon of bubbles generated by powders with different melting degrees entering the molten pool has not been studied in a targeted manner. Based on this, the ice ball entering water test is designed based on the similarity criterion of fluid mechanics to equivalently study the process of powders with different melting degrees entering the molten pool. SUMMARY

[0004] The purpose of the present application is to provide a water impact test device and an equivalent test method for powders with different melting degrees entering a molten pool to at least partially solve the above technical problems.

[0005] The first aspect of the present application provides a water impact test device, comprising: a water pool for simulating a molten pool; a iron stand arranged at the outer periphery of the water pool, and a height-adjustable flow guide block is arranged on the iron stand, the side surface of the flow guide block is coated with a hydrophobic coating, and the hydrophobic coating is used to guide the ice ball to fall into the water pool; a high-speed camera arranged at the outer periphery of the water pool and used to shoot the water entering process of the ice ball; an illumination assembly, the illumination assembly comprises a diffuse reflection plate and a light source, the diffuse reflection plate and the light source are arranged in sequence at the opposite side of the high-speed camera, and the diffuse reflection plate and the light source are used to supplement light for the high-speed camera.

[0006] The water entry impact test device provided by the application can also have the following additional technical features. In one specific embodiment of the application, the material of the hydrophobic coating comprises a hydrophobic agent and anhydrous ethanol. And / or, the flow guide block is also provided with a vertical positioning hole for placing a scale for assisting the high-speed camera in focusing. The guiding mode of the hydrophobic coating is to use tweezers to hold the ice ball and scratch the side of the flow guide block coated with the hydrophobic coating, so that the ice ball falls.

[0007] In one specific embodiment of the application, the light source is a ring-shaped LED array light source; and / or The high-speed camera has a macro lens, and the frame frequency is adjustable between 2000-10000 fps.

[0008] The second aspect of the application also provides an equivalent test method for powders with different melting degrees entering a molten pool, which is realized by using the water entry impact test device of any one of the above aspects, and comprises the following steps: Based on the similarity criterion number, the characteristic parameters of the ice ball in the equivalent test are determined by comparing the characteristic parameters of the powder. The ice ball is made according to the characteristic parameters of the ice ball, and the test device is set. The ice balls melted to different states are released through the hydrophobic coating of the flow guide block and the water entry process is photographed. Based on the cavity evolution process and the bubble generation condition of the ice balls with different melting degrees when entering the water, the influence of the melting degree of the powder in the LDED deposition process on the formation of pores is characterized.

[0009] In one specific embodiment of the application, the characteristic parameters of the ice ball in the equivalent test are determined based on the Weber number, Reynolds number and Bond number of the unmelted powder, and the characteristic parameters of the ice ball include diameter, water entry speed and material.

[0010] In one specific embodiment of the application, between the steps of determining the characteristic parameters of the ice ball in the equivalent test and making the ice ball, the design rationality of the characteristic parameters of the ice ball is checked.

[0011] In one specific embodiment of the application, making the ice ball according to the characteristic parameters of the ice ball comprises the following steps: Mix the super-hydrophobic coating agent and anhydrous ethanol at a volume ratio of 8:2, and uniformly coat the inner surface of a glass culture dish inclined at an angle of 15°±5°, and then stand still to dry to form a hydrophobic film with uniform thickness; Use a 33G needle to drop the solution onto the hydrophobic treated culture dish, and the droplet spontaneously shrinks into a spherical shape due to the hydrophobic effect. Place the culture dish in a incubator, the incubator is filled with dry ice, the temperature is-40℃, and the freezing time is 7-8min, to obtain an ice ball.

[0012] In one specific embodiment of the present application, the prepared ice balls are respectively placed in a room temperature environment for a predetermined time to melt to different states.

[0013] In one specific embodiment of the present application, the test device is set up according to the characteristic parameters of the ice balls, comprising: The water entry impact test device is taken and the height of the flow guide block is adjusted based on the water entry speed of the ice ball; A ruler is taken and the upper end thereof is placed in the positioning hole of the flow guide block and the lower end thereof is placed in the water pool; The height camera focusing adjustment is completed based on the ruler; The ruler is taken away and the test device setting is completed.

[0014] In one specific embodiment of the present application, the design rationality of the characteristic parameters of the ice balls is checked, comprising: Based on the range of the Froude number and the Weber number of the fully melted powder, the cavity shape thereof is determined and compared with the liquid drop entry into water process in the equivalent test, and the bubble generation condition is consistent, which is reasonable, and if not, it is unreasonable.

[0015] The water entry impact test device provided in the embodiment can clamp the ice ball to the hydrophobic coating of the flow guide block when the water entry impact test is performed, release the ice ball by using the hydrophobicity of the hydrophobic coating, and thus avoid the ice ball sticking to the tweezers and causing failure to release normally. The release stability of the ice ball is improved by the above-mentioned setting, and thus the precision of the water entry impact test is improved and the accuracy of the conclusion is improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0017] Figure 1 FIG. 1 is a structural schematic diagram of the water entry device of the present application; Figure 2 FIG. 2 is a structural schematic diagram of the flow guide block in the present application.

[0018] Figure 3 FIG. 3 is a structural schematic diagram of the flow guide block guiding the ice ball to fall in the present application.

[0019] Explanation of reference signs: High-speed camera 1, water tank 2, computer 3, iron stand 4, light source 5, diffuse reflection plate 6, flow guide block 7, tweezers 8, ice ball 9. DETAILED DESCRIPTION

[0020] Exemplary embodiments of the present application will be described more fully hereinafter with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it is to be understood that the present application can be embodied in various forms without being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the present application to those skilled in the art.

[0021] It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including" and "has" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order in which they are described, unless specifically identified as an order dependent step. It is also to be understood that additional or alternative steps can be employed.

[0022] Although the terms first, second, third, and the like can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first", "second", and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0023] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "over," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure is flipped, an element described as "below other elements or features" or "below other elements or features" would subsequently be oriented as "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or in other directions), and the spatial relative descriptors used in the text will be interpreted accordingly.

[0024] Reference Figures 1-2 The first aspect of the present invention provides a water impact test device, including a water tank 2, an iron stand 4, a high-speed camera 1, and an illumination assembly. The water tank 2 is used to simulate a molten pool. The iron stand 4 is disposed on the outer periphery of the water tank 2 and has a height-adjustable guide block on it. The side of the guide block is coated with a hydrophobic coating, which is used to guide the ice puck into the water tank 2. The high-speed camera 1 is disposed on the outer periphery of the water tank 2 and is used to film the ice puck's entry into the water. The illumination assembly includes a diffuse reflector 6 and a light source 5. The diffuse reflector 6 and the light source 5 are sequentially disposed on the opposite side of the high-speed camera 1 and are used to supplement the lighting of the high-speed camera 1.

[0025] Specifically, the iron stand 4, high-speed camera 1, and lighting components are arranged circumferentially along the pool 2. The high-speed camera 1 and the lighting components are positioned opposite each other, and the iron stand 4 is roughly located on the axis of symmetry between the high-speed camera 1 and the lighting components. The iron stand 4 is equipped with a height-adjustable aluminum guide block. The sides of the guide block are coated with a hydrophobic coating formed by a mixture of hydrophobic agent and ethanol. The hydrophobic coating guides the ice ball placed on it to fall into the water. At the same time, the high-speed camera 1, under the supplementary lighting of the lighting components, captures the cavity evolution of the ice ball at the moment of its entry into the water. The high-speed camera 1 is connected to a computer 3 and transmits the captured images to the computer 3 for analysis and calculation.

[0026] The water impact test device provided in this embodiment has an adjustable height guide block on the iron frame and a hydrophobic coating on the side of the guide block. In this way, when conducting the water impact test, the ice ball can be picked up with tweezers and scraped on the side of the guide block with the hydrophobic coating. The hydrophobicity of the coating is used to release the ice ball, which solves the problem of ice ball sticking. In other words, this embodiment improves the release stability of the ice ball through the above-mentioned settings, thereby improving the accuracy of the water impact test and the accuracy of the conclusion.

[0027] In some embodiments, the hydrophobic coating material includes a hydrophobic agent and anhydrous ethanol.

[0028] In some embodiments, the guide block is also provided with a vertically arranged positioning hole, which is used to place a scale for assisting the high-speed camera 1 in focusing.

[0029] In some embodiments, the light source 5 is a ring-shaped LED array light source 5.

[0030] In some embodiments, the high-speed camera 1 has a macro lens and the frame rate is adjustable between 2000 and 10000 fps.

[0031] A second aspect of the present invention also provides an equivalent test method for powders with different melting degrees entering a molten pool. This method is implemented using the water impact test apparatus described in any one of the above-mentioned methods, and includes the following steps: S10: Based on the similarity criterion number, determine the characteristic parameters of the ice puck in the equivalent test by comparing the characteristic parameters of the powder.

[0032] Specifically, the physical properties of titanium alloy TC11 in the LDED process were compiled using the similarity criteria method of fluid mechanics. The powder particle velocity and particle size were determined from the literature. The surface tension coefficient, liquid density, liquid viscosity and other physical parameters of TC11 were calculated by the material composition through the binary CALPHAD equation. The calculation process was assisted by JMatPro software.

[0033] The process of a partially melted ice ball entering water involves two stages: solid entry and liquid droplet entry. Therefore, parameters such as the ice ball's diameter, entry velocity, and density can be rationally designed based on both the pure solid and pure liquid entry processes. First, the diameter, velocity, and density of the ice ball are determined based on the pure solid entry process (i.e., the unmelted ice ball entering the water). Second, the parameters are verified based on the pure liquid droplet entry process (i.e., the fully melted ice ball entering the water).

[0034] When a solid ice ball enters water, it is subjected to inertial forces, gravity, and surface tension. Key similarity criteria include the Weber number (We), Bond number (Bo), and Reynolds number (Re). In the LDED process, the powder diameter is extremely small, falling within the low Bond number (Bo) range. At this point, the influence of gravity is much smaller than that of inertial forces and surface tension. Therefore, this experiment needs to match the main dimensionless numbers of the LDED process as the Weber number (We, the ratio of inertial force to surface tension) and the Reynolds number (Re, the ratio of inertial force to viscous force). That is, based on the Weber number and Reynolds number, the characteristic parameters of the ice ball in the equivalent experiment are determined. These characteristic parameters include diameter, water entry velocity, and material.

[0035] The Weber number, We, is a dimensionless parameter in fluid mechanics that characterizes the relative magnitudes of inertial forces and surface tensions in a fluid. In flows where inertial forces and surface tensions play a crucial role, to satisfy the dynamic similarity condition, the Weber numbers of the model and the actual fluid must be equal. The calculation formula is as follows: We =(ρv 2 D) / γ, where v, ρ, and γ are the fluid velocity, density, and surface tension coefficient, respectively, and D is the characteristic length. In the ice ball immersion test, D is the equivalent diameter of the ice ball.

[0036] The Reynolds number (Re) is a dimensionless number used to characterize fluid flow. It is a similarity criterion number in fluid mechanics that characterizes the effects of viscosity. The formula for its calculation is: Re =ρvD / μ, where v, ρ, and μ are the fluid velocity, density, and viscosity coefficient, respectively, and D is the characteristic length. In the ice puck immersion test, D is the equivalent diameter of the ice puck.

[0037] The density ratio is the ratio of the density of the sphere to the density of the liquid pool, m. * =ρ s / ρ l ,in ρ s Density of a sphere ρ l The density of the liquid pool and the differences in motion behavior of the spheres with different density ratios during water entry reflect the effect of inertia. The density ratio of the solids during water entry will affect the change in the acceleration of the spheres after entering the water.

[0038] Table 1 Test property parameters

[0039] Table 2. Number of Test Similarity Criteria

[0040] First, the ice ball diameter and water entry velocity were designed based on the similarity number range of the unmelted powder. Considering that ice balls with excessively small diameters are difficult to manufacture, a nominal ice ball diameter of 1.5-2 mm was chosen, and the nominal water entry velocity was determined to be 2 m / s. This experimental design, with a density (We) close to the upper limit of the LDED process, can demonstrate the most intense water entry of the powder during LDED, as well as the most severe bubble generation phenomenon. In addition, the ice ball density also needs to be designed. During LDED, the density ratio is greater than 1. To match this, a saturated copper sulfate solution was chosen to make the ice ball, and deionized water was used as the water tank 2. The density ratio at this point is 1.034, close to the density ratio of 1.107 between the powder and the molten pool during the LDED process.

[0041] Secondly, by comparing the morphology of the water-entry cavity between fully molten powder and fully molten ice balls, the rationality of the characteristic parameters of the ice ball designed based on the solid-to-water-entry process is verified. The morphology of the water-entry cavity depends on the Weber number We and the formula of Froude Fr: We=AFr α , Fr=v 2 / gD ; In the formula, A and α are corresponding empirical parameters. The upper bound is taken when A=48.3 and α=0.247, and the lower bound is taken when A=41.3 and α=0.179. v refers to the velocity of the metal powder entering the molten pool or the velocity of the ice ball entering the water, and g is the acceleration due to gravity, which is taken as 9.8m. 2 / s, where D is the diameter of the metal powder or ice ball. Three different cavity morphologies are exhibited when We is below the lower boundary, between the upper and lower boundaries, and above the upper boundary. When We is below the lower boundary, the cavity is characterized by no bubbles or jets when closed; when We is between the upper and lower boundaries, the cavity is characterized by the generation of bubbles and high-speed thin jets; when We is above the upper boundary, the cavity is characterized by no bubbles but the generation of thick Rayleigh jets. Based on the characteristic parameters of the LDED process, its lower boundary range is calculated to be 230.1-376.4. It can be seen that the We value range in the LDED process is lower than the lower boundary range, resulting in the first type of cavity. Substituting the characteristic parameters of the ice ball designed for the solid-into-water process into the formula, the lower boundary range is calculated to be 103.3-110.4. In the experiment, the We value of the ice ball entering the water is slightly higher than the lower boundary range, but the experimental results verify that the cavity generated after the fully melted ice ball enters the water belongs to the first type of cavity that does not generate bubbles, which is the same type as LDED. This invention focuses on the bubble generation process, thus verifying the rationality of the parameter design.

[0042] S20: Make an ice hockey puck based on its characteristic parameters and set up a test device.

[0043] Specifically, the process of making an ice hockey puck based on its characteristic parameters includes the following steps: The superhydrophobic coating agent was mixed with anhydrous ethanol at a volume ratio of 8:2 and evenly coated on the inner surface of a glass petri dish tilted at 15°±5°. The mixture was then allowed to stand and dry to form a hydrophobic film of uniform thickness. Using a 33G needle, the solution was dropped into a hydrophobic culture dish with a droplet diameter of 1.5-2 mm. Due to the hydrophobic effect, the droplet spontaneously contracted into a spherical shape. The petri dishes were placed in an insulated box filled with dry ice at -40°C for 7-8 minutes to freeze, resulting in ice balls. An acrylic box was placed above the petri dishes, and columnar dry ice was evenly distributed on the acrylic box to ensure uniform temperature distribution.

[0044] S30: Ice balls melted to different states are released through the hydrophobic coating of the guide block, and the water entry process is filmed. Specifically, the fully melted and partially melted states of the ice balls are achieved by placing them at room temperature (23°C) for 5 minutes and 30 seconds and 4 minutes and 30 seconds, respectively. Unmelted and partially melted ice balls are picked up with tweezers and placed at the base of the guide block, then released by horizontal scraping. The release height is consistent, and the water entry speed is 2 m / s ± 0.5 m / s. High-speed camera 1 records the water entry process.

[0045] S40: Characterizes the effect of powder melting degree on pore formation during LDED deposition based on the cavity evolution process and bubble generation of ice balls entering water at different melting degrees.

[0046] This invention provides an experimental method for introducing powders with different melting levels into a molten pool. The method combines the ice ball immersion test and the LDED deposition process under the same dimensionless number, ensuring the similarity of motion and dynamics between the two processes. Experiments revealed that as the melting degree increases, the overall cavity exhibits different morphologies, and the probability of bubble formation gradually decreases. This method reduces the experimental research cost of powder entering the molten pool, and the research results are of great significance for revealing the porosity formation mechanism and internal defect control in LDED.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A water immersion impact test device, characterized in that, include: A water tank is used to simulate a molten pool; An iron frame is set on the outer periphery of the pool, and a height-adjustable guide block is provided on it. The side of the guide block is coated with a hydrophobic coating, which is used to guide the ice puck into the pool. A high-speed camera is positioned around the perimeter of the pool and is used to film the process of the ice puck entering the water. The lighting assembly includes a diffuser and a light source, which are placed sequentially on opposite sides of the high-speed camera and are used to provide supplemental lighting for the high-speed camera.

2. The water impact test apparatus according to claim 1, characterized in that, The hydrophobic coating material includes a hydrophobic agent and anhydrous ethanol; and / or The guide block is also provided with a vertically arranged positioning hole, which is used to place a scale to assist the high-speed camera in focusing; The hydrophobic coating is guided by using tweezers to hold the ice ball and scrape it against the side of the guide block coated with the hydrophobic coating, causing the ice ball to fall.

3. The water impact test apparatus according to claim 1, characterized in that, The light source is a ring-shaped LED array light source; and / or The high-speed camera has a macro lens and its frame rate is adjustable between 2000-10000fps.

4. An equivalent test method for powders with different melting degrees entering a molten pool, characterized in that, The water impact test apparatus described in any one of claims 1-3 is used to achieve this, comprising the following steps: Based on the similarity criterion number, the characteristic parameters of the ice hockey in the equivalent test were determined by comparing the characteristic parameters of the powder. Ice hockeys were manufactured based on their characteristic parameters, and experimental setups were constructed. Ice balls melted to different states are released through the hydrophobic coating of the guide block and the process of entering the water is photographed; The influence of powder melting degree on pore formation during LDED deposition is characterized by the cavity evolution process and bubble generation of ice balls entering water at different melting degrees.

5. The equivalent test method for powders with different melting degrees entering the molten pool according to claim 4, characterized in that, The characteristic parameters of the ice puck in the equivalent test are determined based on the Weber number, Reynolds number, and Bond number of the unmelted powder. The characteristic parameters of the ice puck include diameter, water entry velocity, and material.

6. The equivalent test method for powders with different melting degrees entering the molten pool according to claim 4, characterized in that, Between determining the characteristic parameters of the ice puck in the equivalent test and the steps for making the ice puck, it is also necessary to verify the rationality of the design of the characteristic parameters of the ice puck.

7. The equivalent test method for powders with different melting degrees entering the molten pool according to claim 4, characterized in that, Making an ice hockey puck based on its characteristic parameters involves the following steps: The superhydrophobic coating agent was mixed with anhydrous ethanol at a volume ratio of 8:2 and evenly coated on the inner surface of a glass petri dish tilted at 15°±5°. The mixture was then allowed to stand and dry to form a hydrophobic film of uniform thickness. Using a 33G needle, the solution was dropped into a hydrophobically treated culture dish. The droplet spontaneously shrank into a spherical shape due to the hydrophobic effect. The petri dish was placed in an incubator filled with dry ice and frozen at -40°C for 7-8 minutes to obtain ice balls.

8. The equivalent test method for powders with different melting degrees entering the molten pool according to claim 4, characterized in that, Ice balls in different melting states were obtained by placing the prepared ice balls in a room temperature environment for different times.

9. The equivalent test method for powders with different melting degrees entering the molten pool according to claim 4, characterized in that, The experimental setup, based on the characteristic parameters of ice hockey, includes: Take the water impact test device and adjust the height of the guide block based on the water entry speed of the ice puck; Take a ruler and place its upper end in the positioning hole of the guide block and its lower end in the water tank; Adjust the camera focus based on the scale. Remove the ruler to complete the setup of the experimental apparatus.

10. The equivalent test method for powders with different melting degrees entering the molten pool according to claim 6, characterized in that, Verifying the rationality of the design of the ice hockey's characteristic parameters includes: Based on the range of Froude number and Weber number of the fully melted powder, its cavity morphology is determined and compared with the droplet entry process in the equivalent test. If the bubble generation is consistent, it is reasonable.

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