High-specific-gravity anti-scattering grid 3D printing powder and method

Abstract

The invention relates to the technical field of 3D printing, in particular to 3D printing powder for a high-specific-gravity anti-scattering grid and a method. The WNiCr alloy powder comprises, by mass, 85%-95% of tungsten powder, 2%-9% of Ni, 2%-7% of Cr and inevitable impurities. The method comprises the following steps of: filling the WNiCr alloy powder into selected area laser melting equipment, printing under the protection of inert gas by adopting the process parameters of laser power of 100-200W, scanning speed of 500-1000mm / s and scanning interval of 0.05-0.1 mm to form an anti-scattering grid blank, and performing post-treatment to obtain a final grid. By optimizing the powder components and the printing process, integrated forming of the high-specific-gravity grid with the wall thickness smaller than or equal to 0.1 mm is achieved, and the three-point bending strength and the yield are remarkably improved while the high density is kept.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of 3D printing, in particular to a 3D printing powder of high specific gravity anti-scattering grid and a method thereof. BACKGROUND

[0002] The anti-scattering grid is a key component for radiation shielding and imaging equipment, which is usually made of high specific gravity materials such as tungsten or lead-based materials to effectively absorb and scatter rays. Traditional manufacturing methods mainly include two ways: one is for tungsten material, which is formed into a sheet through powder metallurgy process, then cut through mechanical processing, and finally assembled into a grid structure by artificial grafting; the other is for lead-based material, which is assembled into a grid by alternately arranging lead sheets and aluminum sheets and fixing them through hot pressing.

[0003] However, these traditional methods have significant defects. For tungsten grid, due to the brittleness of tungsten itself, the three-point bending strength of the manufactured grid is low, and in order to improve the strength, the wall thickness needs to be increased, which is difficult to balance the requirements of thin wall and high strength. At the same time, the position precision between the grid walls is high, and the artificial grafting assembly method is extremely dependent on the skills of the operator, resulting in low yield. In addition, the loss rate is high during the mechanical processing of tungsten, and the overall manufacturing cost is high. For lead-based material grid, the lead strips and aluminum strips are prone to shift during hot pressing and fixing, and the tightness between the layers may cause scattering leakage, and lead itself is toxic, causing harm to the environment and human health.

[0004] In recent years, 3D printing technology has been tried to be used to prepare high specific gravity alloy components. For example, the patent with publication number CN109226753A discloses a method for preparing tungsten particle reinforced metal matrix composite based on 3D printing technology, which adjusts the proportion of tungsten reinforcing phase and matrix phase, and uses laser printing to form layer by layer, solving the problems of coarse grains and low density in traditional sintering method. However, this technology mainly focuses on the structure and mechanical properties of macroscopic composite materials, and does not optimize the anti-scattering grid which has a micro-thin wall structure and requires high position precision. In addition, the existing powder and process are difficult to realize one-step forming of the grid thin wall structure, and are prone to problems such as brittle fracture and uneven wall thickness, so the yield and performance cannot meet the actual application requirements. SUMMARY

[0005] To solve the problems in the background art, the present application provides a 3D printing powder of high specific gravity anti-scattering grid, which comprises WNiCr alloy powder, and the WNiCr alloy powder comprises 85%-95% tungsten powder, 2%-9% Ni, 2%-7% Cr and unavoidable impurities, by mass percentage.

[0006] Further, the bulk density of the WNiCr alloy powder is 5.01-5.76 g / cm3, the tap density is 9.14-9.77 g / cm3, and the particle size range is 8-28 μm.

[0007] The application further provides a 3D printing method, comprising the following steps: The WNiCr alloy powder is filled into a selective laser melting device, and a substrate is installed; Under the protection of inert gas, the oxygen content in the printing chamber is controlled to be less than or equal to 200 ppm, and the selective laser melting technology is used for 3D printing to form an anti-scattering grid blank, wherein the printing parameters are as follows: laser scanning power is 100-200 W, scanning speed is 500-1000 mm / s, scanning interval is 0.05-0.1 mm, and the heating temperature of the substrate is 80-200 ℃; The anti-scattering grid blank after printing is post-processed to obtain an anti-scattering grid. The WNiCr alloy powder is the 3D printing powder of the high-specific-gravity anti-scattering grid as described above.

[0008] Further, the post-processing step comprises stress relief annealing, wire cutting separation, cleaning and sand blasting.

[0009] Further, the stress relief annealing step specifically comprises: placing the printed anti-scattering grid in a box-type atmosphere furnace, and performing stress relief annealing treatment at 1000-1100 ℃ for 1-2 h.

[0010] Further, the wire cutting separation step specifically comprises: using a wire cutting device to cut and separate the annealed anti-scattering grid from the substrate. The cleaning step specifically comprises: using an ultrasonic cleaning device to clean the oil stains on the surface of the anti-scattering grid, and air-drying after cleaning.

[0011] Further, in the sand blasting treatment step, corundum sand is used as the sand blasting medium to sand blast the air-dried anti-scattering grid.

[0012] Further, the WNiCr alloy powder is a dried WNiCr alloy powder, the drying temperature is 80-90 ℃, and the drying time is 1-2 hours.

[0013] Further, the substrate material is a tungsten-based high-specific-gravity material.

[0014] Further, in the 3D printing step, the anti-scattering grid is printed using a single-line scanning path.

[0015] Compared with the prior art, the WNiCr alloy powder provided by the application successfully constructs a special material system suitable for 3D printing of high specific gravity anti-scattering grids by controlling the content of tungsten powder to be in a specific range lower than the traditional pure tungsten scheme, i.e. 85% to 95%, and matching with Ni and Cr alloy powder in a corresponding proportion, which successfully solves the technical problem that high specific gravity and thin-wall structure are difficult to be combined, so that the anti-scattering grid printed by using the powder can realize the ultra-thin structure with a wall thickness less than 0.1 mm, and the three-point bending strength of the anti-scattering grid is significantly improved compared with the traditional pure tungsten grid, so that the printed grid structure can realize a more uniform and dense thin-wall form.

[0016] The 3D printing method provided by the application realizes high-strength manufacturing of high specific gravity anti-scattering grids under an ultra-thin wall thickness by synergistically using the WNiCr alloy powder with the specific components and the optimized input printing process, which not only can accurately form a structure with a stable wall thickness less than 0.1 mm, improves the yield of products, but also improves the three-point bending strength compared with the same kind of products manufactured by the traditional process, and realizes the unity of high specific gravity, high strength and high reliability of products. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0018] Figure 1 The anti-scattering grid three-dimensional model diagram provided by the application, wherein (a) is a three-view diagram, (b) is a top view diagram, and (c) is a local detail diagram; Figure 2 The microstructure detection diagram of the anti-scattering grid prepared in Example 1 under a metallographic microscope; Figure 3 The position offset detection result diagram of each wall unit in the anti-scattering grid prepared in Example 1 relative to the horizontal direction; Figure 4 The position offset detection result diagram of each wall unit in the anti-scattering grid prepared in Example 1 relative to the vertical direction; Figure 5 The wall thickness detection result diagram of each wall unit in the anti-scattering grid prepared in Example 1; Figure 6 The schematic diagram of the conventional scanning path (a) used in Comparative Example 3 of the application and the preferred single-line scanning path (b) of the application. DETAILED DESCRIPTION

[0019] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0020] Embodiment 1 The present embodiment provides a WNiCr alloy powder for high specific gravity anti-scattering grid 3D printing and a 3D printing method.

[0021] 1. Preparation of the powder: The WNiCr alloy powder comprises 90% tungsten powder, 5.7% Ni and 4.3% Cr by mass percentage.

[0022] The WNiCr alloy powder is prepared by a gas atomization powdering method.

[0023] The bulk density of the WNiCr alloy powder is 5.41 g / cm3, the tap density is 9.62 g / cm3, and the particle size distribution range is 8-28 μm.

[0024] It should be noted that the preparation of the WNiCr alloy powder is achieved by using the gas atomization powdering technology known in the art. For example, the skilled person can refer to the specific gas atomization process parameters and steps described in the patent with publication number CN109226753A, including but not limited to the process parameters for casting alloy ingots and gas atomization powdering, to prepare the required WNiCr alloy powder. The preparation process is a conventional technical means and does not need to be described in detail.

[0025] 2. 3D printing method of anti-scattering grid: Powder pretreatment: the required amount of WNiCr alloy powder for printing is placed in a vacuum drying oven, dried at 80℃ for 2 hours, and then taken out for standby use.

[0026] Device preparation: the dried powder is filled into the forming cylinder of a selective laser melting (SLM) device, and a substrate made of tungsten-based high specific gravity material is installed.

[0027] 3D printing: the device chamber is filled with inert protective gas argon, the oxygen content in the printing chamber is controlled to be ≤200 ppm, the pre-processed anti-scattering grid three-dimensional model file (8pcs anti-scattering grid) is imported, the printing is started, and the rough casting is obtained after the printing is completed. Among them, for example, Figure 1As shown in (a is a three-view, b is a top view, c is a partial detail view), the length, width and height of the anti-scattering grid three-dimensional model are 30.0mm × 15.0mm × 15.0mm, and the wall thickness is 0.1mm.

[0028] The printing parameters are set as follows: laser scanning power 115 W, scanning speed 800 mm / s, scanning pitch 0.06 mm, and substrate heating temperature 200℃. During the printing process, for the thin-wall structure of the grid, a single-line scanning path is adopted for printing.

[0029] Post-processing: Stress relief annealing: the printed anti-scattering grid blank is placed in a box-type atmosphere furnace, and is kept at 1050℃ for 1 hour to eliminate residual stress.

[0030] Wire cutting separation: the annealed anti-scattering grid is cut from the substrate using a medium-speed wire cutting equipment.

[0031] Cleaning: the surface of the cut anti-scattering grid is cleaned of oil stains using an ultrasonic cleaning device, and is dried.

[0032] Sand blasting: corundum sand is used as the sand blasting medium to perform sand blasting treatment on the dried anti-scattering grid to remove burrs, thereby obtaining the high-specific-gravity anti-scattering grid.

[0033] Test results of Example 1: (1) The Rockwell hardness test sample block printed by the anti-scattering grid process in this embodiment is observed under a metallurgical microscope with a magnification of 200 times, and the microstructure detection diagram is as shown in Figure 2 The detection result shows that the Rockwell hardness (HRC) is 41.8 HRC.

[0034] The results show that the microstructure of the anti-scattering grid is uniform and dense, and has no obvious pores, cracks and other defects, which proves that the microstructure uniformity of the grid material is realized by the 3D printing process, the problems of uneven organization and many defects in the traditional process are solved, and the requirement of the anti-scattering grid on material density is met.

[0035] (2) The wall thickness and position accuracy of the anti-scattering grid after sand blasting in Example 1 are detected, and the detection process is automatic image measurement.

[0036] The detection results are as shown in Figures 3-5 , the offset of each wall unit in the grid relative to the X-wall position (horizontal direction) is Figure 3 , the offset of each wall unit in the grid relative to the Z-wall position (vertical direction) is Figure 4 , and the wall thickness data of each wall unit in the grid is Figure 5 , wherein,Figure 3 , Figure 4 The vertical axis represents the offset (in mm) of each structure within the grid relative to the X and Z walls, while the horizontal axis represents the grid wall number. Figure 5 The vertical axis represents the wall thickness (in mm) of each structure inside the grid, and the horizontal axis represents the grid wall number.

[0037] like Figure 3 and Figure 4 As shown, the offset of each wall unit within the grid relative to the horizontal direction is within ±0.01mm, with no abnormal offset; the offset relative to the vertical direction is also within ±0.01mm, with no interlayer misalignment. This result proves that the 3D printing integrated molding process of this invention can precisely control the horizontal and vertical position accuracy of the wall, eliminate manual assembly errors, meet the μm-level position accuracy requirements of the anti-scattering grid, and effectively solve the defects of poor position accuracy and low yield of traditional processes.

[0038] like Figure 5 As shown, the wall thickness of the anti-scattering grid is mainly concentrated in the range of 0.09–0.10 mm, and the wall thickness fluctuations at different test points and for different samples are small, indicating good uniformity. This result proves that the process of this invention can achieve precise control of thin walls.

[0039] Example 2 The difference between Example 2 and Example 1 is that: The WNiCr alloy powder comprises 85% tungsten powder, 8.6% Ni, and 6.4% Cr by mass percentage.

[0040] The WNiCr alloy powder has a loose packing density of 5.29 g / cm³, a tapped density of 9.04 g / cm³, and a particle size distribution range of 8–28 μm.

[0041] The printing parameters were set as follows: laser scanning power 100 W, scanning speed 800 mm / s, scanning spacing 0.06 mm, and substrate heating temperature 200 ℃.

[0042] The remaining raw material ratios and steps are the same as in Example 1.

[0043] Example 3 The difference between Example 3 and Example 1 is that: The WNiCr alloy powder comprises 95% tungsten powder, 2.9% Ni, and 2.1% Cr by mass percentage.

[0044] The WNiCr alloy powder has a loose packing density of 5.73 g / cm³, a tapped density of 9.74 g / cm³, and a particle size distribution range of 8–28 μm.

[0045] The printing parameters were set as follows: laser scanning power 130 W, scanning speed 800 mm / s, scanning spacing 0.06 mm, and substrate heating temperature 200 ℃.

[0046] The remaining raw material ratios and steps are the same as in Example 1.

[0047] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: The WNiCr alloy powder comprises 80% tungsten powder, 11.4% Ni, and 8.6% Cr by mass percentage. The remaining raw material ratios and steps are the same as in Example 1.

[0048] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that: The WNiCr alloy powder comprises 97% tungsten powder, 1.7% Ni, and 1.3% Cr by mass percentage. The remaining raw material ratios and steps are the same as in Example 1.

[0049] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the single-line scanning method during printing is replaced with a conventional scanning method. The specific differences in scanning methods are as follows: Figure 6 As shown.

[0050] The remaining raw material ratios and steps are the same as in Example 1.

[0051] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that corundum sand was used instead of ceramic sand as the blasting medium.

[0052] The remaining raw material ratios and steps are the same as in Example 1.

[0053] Performance testing 1. The anti-scattering grids obtained in Examples 1-3 and Comparative Examples 1-2 were subjected to wall thickness and three-point bending performance tests. The wall thickness was tested using an automatic image inspection instrument, and the three-point bending strength test was performed on a microcomputer-controlled electronic universal testing machine. The specific process was as follows: the anti-scattering grid sample was placed on two support points, the test span was set to 25 mm, and a load was applied to the downward pressure head at a constant rate of 1 mm / min until the sample broke. The maximum bending force (KN) was recorded. The test results are shown in Table 1.

[0054] Table 1

[0055] As shown in Table 1, a comparison of the data from Examples 1-3 and Comparative Examples 1-2 shows that when the mass percentage of tungsten powder is within the range of 85% to 95% as defined in this invention, the prepared anti-scattering grid maintains an ultra-thin wall thickness while exhibiting a three-point bending strength better than 1.19 KN, achieving a good balance between high specific gravity, thin wall, and high strength.

[0056] Comparative Example 1 had a low mass percentage of tungsten powder in its formula (80%), resulting in an excessively high overall content of the binder phase composed of elements such as Ni and Cr, and a low tungsten content, which significantly reduced the overall strength of the material. Comparative Example 2 had a high mass percentage of tungsten powder in its formula (97%), resulting in an insufficient total amount of binder phase and an excessively high tungsten content. This prevented the material from fully wetting and binding a large number of tungsten particles, leading to increased brittleness. Although the strength was slightly higher, the risk of cracking was significantly increased in subsequent wire cutting, sandblasting, and practical applications, resulting in a low yield.

[0057] 2. The wall thickness of the blank wall of the anti-scattering grid obtained by Example 1 and Comparative Example 3 using different scanning methods was tested, and the test results are shown in Table 2.

[0058] Table 2

[0059] The results in Table 2 show that, compared to Example 1, the conventional multi-line scanning method in Comparative Example 3 results in a significant increase in the thickness of the printed grid wall. This is because the heat-affected zone overlaps between multiple laser scanning lines, increasing the width of the molten pool and thus forming a thicker wall. This excessive wall thickness cannot meet the requirements of the anti-scattering grid for precise imaging and high resolution.

[0060] 3. The wall thickness of the anti-scattering grids obtained before and after sandblasting with different sandblasting media in Example 1 and Comparative Example 4 was tested. The test results are shown in Table 3.

[0061] Table 3

[0062] As shown in Table 3, compared with Comparative Example 4, the results of Example 1 show that corundum sand can reduce grid wall thickness more effectively than ceramic sand. This is because corundum sand has a higher Mohs hardness and more irregular particle shape, resulting in stronger cutting ability and more efficient removal of adhering particles and burrs from the surface of the printed part, thereby achieving a thinner final wall thickness.

[0063] Although this document frequently uses terms such as tungsten powder, WNiCr alloy powder, anti-scattering grid, 3D printing, and wall thickness, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention.

[0064] 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 3D printing powder with a high specific gravity anti-scattering grid, characterized in that: The alloy powder includes WNiCr alloy powder, which, by mass percentage, comprises 85%–95% tungsten powder, 2%–9% Ni, 2%–7% Cr, and unavoidable impurities.

2. The 3D printing powder with high specific gravity anti-scattering grid according to claim 1, characterized in that: The WNiCr alloy powder has a loose packing density of 5.01–5.76 g / cm³, a tapped density of 9.14–9.77 g / cm³, and a particle size range of 8–28 μm.

3. A 3D printing method, characterized in that, Includes the following steps: WNiCr alloy powder is filled into a selective laser melting device, and a substrate is installed. Under inert gas protection, the oxygen content in the printing chamber is controlled to be ≤200 ppm. Selective laser melting technology is used for 3D printing to form an anti-scattering grid blank. The printing parameters are: laser scanning power 100~200W, scanning speed 500~1000mm / s, scanning spacing 0.05~0.1 mm, and substrate heating temperature 80~200℃. Post-processing is performed on the printed anti-scattering grid blank to obtain the anti-scattering grid; The WNiCr alloy powder mentioned therein is the 3D printing powder with high specific gravity anti-scattering grid as described in any one of claims 1 to 2.

4. The 3D printing method according to claim 3, characterized in that: The post-processing steps include stress-relief annealing, wire cutting separation, cleaning, and sandblasting.

5. The 3D printing method according to claim 4, characterized in that: The stress-relief annealing step specifically involves placing the printed anti-scattering grid in a box-type atmosphere furnace and holding it at 1000–1100°C for 1–2 hours to perform stress-relief annealing.

6. The 3D printing method according to claim 4, characterized in that: The wire cutting separation step specifically involves using a wire cutting device to cut and separate the annealed anti-scattering grid from the substrate. The cleaning step specifically involves using ultrasonic cleaning equipment to clean the oil stains on the surface of the anti-scattering grid, and then drying it.

7. The 3D printing method according to claim 4, characterized in that: In the sandblasting process, corundum sand is used as the sandblasting medium to sandblast the dried anti-scattering grid.

8. The 3D printing method according to claim 3, characterized in that: The WNiCr alloy powder is dried WNiCr alloy powder, with a drying temperature of 80-90℃ and a drying time of 1-2 hours.

9. The 3D printing method according to claim 3, characterized in that: The substrate is made of tungsten-based high-density material.

10. The 3D printing method according to claim 3, characterized in that: In the 3D printing step, the anti-scattering grid is printed using a single-line scanning path.

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