A uniform porous structure material of multi-pass scanning additive manufacturing and a preparation method thereof

Abstract

The present application relates to the technical field of metal additive manufacturing, and aims at the problem of uneven pore size distribution and serious fine powder gasification and splashing in the existing additive manufacturing method for preparing porous structure materials, and provides a uniform porous structure material prepared by multi-pass scanning additive manufacturing and a preparation method thereof, which comprises the following steps: S1, an entity model of a space enveloped by the porous material is established, and slicing and layering are performed to obtain a plurality of model slices; S2, metal powder is laid into a powder layer, and then a laser powder bed additive manufacturing equipment is used to perform first-pass preprocessing scanning on the model slices, increase the high laser power, reduce the scanning speed, and perform second-pass forming scanning on the model slices to obtain the uniform porous structure material prepared by multi-pass scanning additive manufacturing.The present application fundamentally solves the problem of mismatch between the Gaussian distribution laser beam and the normal distribution powder particle size, can stably prepare uniform connected pores, and does not need subsequent powder cleaning treatment.

Description

Technical Field

[0001] This invention relates to the field of metal additive manufacturing technology, and more specifically, to a uniform porous structure material manufactured by multi-pass scanning additive manufacturing and its preparation method. Background Technology

[0002] Porous metallic materials, due to their unique porous structure, combine the load-bearing capacity of structural materials with the special functions of functional materials, and are widely used in aerospace, chemical, and medical fields. In the field of high-temperature structural materials, porous metallic materials are often used as evaporative cooling layers. Their core function is to facilitate the transfer of cooling fluid, allowing the cooling fluid to vaporize on the surface of the hot-end structure and carry away heat, thereby achieving effective thermal protection for hot-end structural components in high-temperature environments.

[0003] The dimensional parameters of the porous structure directly determine the sweating capacity of the sweating layer, with the appropriate pore size being particularly crucial: if the pore size is too large, the cooling medium will overflow rapidly, failing to achieve effective thermal protection; if the pore size is too small, it will hinder the flow of the cooling medium, reducing the sweating cooling efficiency. Extensive practical verification has shown that the optimal pore size range for the porous structure in the sweating layer is 30~100μm.

[0004] Currently, the main methods for preparing porous metallic materials include foaming technology, powder metallurgy, and additive manufacturing. Among these, porous structures produced by foaming technology are mostly millimeter-sized spherical pores, and the pores are not interconnected, existing as closed pores, which cannot meet the working fluid transport requirements of the sweating layer. Powder metallurgy, on the other hand, can create open pores at the hundred-micrometer level by controlling the powder particle size, enabling sweating and cooling functions. However, this method is limited by the molding process and is difficult to prepare porous structures with complex shapes. Additive manufacturing, as a novel molding technology proposed in recent years, can achieve precise fabrication of complex structures by layer-by-layer segmentation and molding of the model, providing a new solution for the efficient fabrication of porous metallic structures.

[0005] In existing technologies, there are two main ways to prepare porous metal materials using laser powder bed additive manufacturing: one is to directly form porous structures through model design, but the size of the pores prepared by this method is usually in the millimeter range. In terms of directly forming micron-sized channels, it is greatly limited by the size of the laser spot and the particle size of the powder, and subsequent powder cleaning is required after forming; the other is to prepare porous structures by using a dense structure model and controlling the additive manufacturing process parameters.

[0006] For example, patent CN113020622A provides an integrated design and manufacturing method for controllable porous structures in additive manufacturing, employing a combination of porous and densification processes to achieve the preparation of controllable porous structures. Another example is patent CN117521288A, which provides an additive manufacturing method for porous structures. By fitting the relationship between energy beam power P, scanning speed v, and the porosity and pore size of the metal porous structure, the pore structure and porosity are controlled.

[0007] Existing additive manufacturing of porous metal materials, such as those mentioned above, almost all employ a single-scan strategy, utilizing the partial melting characteristics of powder in a powder bed to prepare porous structures. However, in practical applications, they generally suffer from extremely uneven pore and pore size distributions and severe powder splashing. Summary of the Invention

[0008] The purpose of this invention is to address the problems of extremely uneven pore size distribution and severe fine powder vaporization and splattering in existing additive manufacturing methods for preparing porous materials. It provides a method for preparing a uniform porous material using multi-pass scanning additive manufacturing, fundamentally solving the problem of mismatch between Gaussian distributed laser beams and normally distributed powder particle sizes. This reduces and avoids fine powder splattering, pore blockage, and random pore size inconsistencies, enabling the stable preparation of uniform, interconnected pores without subsequent powder cleaning. It is suitable for various demanding applications such as sweating cooling, filtration separation, and biological scaffolds.

[0009] This invention is achieved through the following technical solution:

[0010] This invention has discovered that existing additive manufacturing methods for porous metal materials suffer from extremely uneven pore and pore size distributions, as well as severe powder spatter. The core reason for this is the physical mismatch between the Gaussian distribution of laser spatial energy and the normal distribution of powder particle size. Therefore, this invention proposes a method for preparing uniform porous materials using multi-channel scanning additive manufacturing, comprising the following steps:

[0011] (1) Model building and hierarchical structure:

[0012] A solid model of the space enclosed by the porous material was created using 3D modeling software, and slicing software was used to slice and layer the material to obtain several model layers. The thickness of the slices was matched with the thickness of the subsequent powder layer.

[0013] (2) Multi-pass scanning additive manufacturing:

[0014] like Figure 1The diagram illustrates the multi-pass scanning additive manufacturing process of this invention. First, a low-power, high-speed scanning strategy is employed to perform the first pre-processing scan on the model layers, achieving initial melting and agglomeration of fine powders and reconstructing the powder bed particle size distribution. Then, the high laser power is increased while the scanning speed is reduced to perform the second forming scan on the model layers. By increasing the energy density, controllable sintering between homogenized coarse powders is achieved, and a uniform porous structure is constructed using the sintering necks formed between powder particles.

[0015] Specifically, metal powder is first laid into a powder layer with a thickness of 20~100μm. Laser powder bed additive manufacturing equipment is used to scan the model layer in two passes with a laser beam with a spot diameter of 50~100μm. A uniform porous structure is prepared by pre-processing, decoupling and homogenizing the powder bed particle size.

[0016] The laser power exhibits a Gaussian distribution at the laser spot, with significantly higher energy at the center than at the edges. This uneven energy distribution during a single scan results in inconsistent powder melting, ultimately leading to inhomogeneity in pore size and diameter. The Gaussian distribution of laser energy (intensity distribution) follows the formula below:

[0017] ;

[0018] In the formula, I(r) is the laser intensity (W / m²) at a distance r from the center of the laser spot. 2 I0 is the maximum light intensity (W / m²) at the center of the laser spot. 2 Let r be the distance (m) from the center of the laser spot to the target point, and ω be the radius (m) of the laser spot. The laser spot diameter D and the radius ω satisfy D=2ω, which matches the spot diameter of 50~100μm in step two of this invention. Therefore, it can be seen that the light intensity at the edge of the spot is usually only about 13.5% of the light intensity at the center.

[0019] During a single-scan heating process, the temperature rise ΔT of a single powder particle is directly proportional to the laser energy it absorbs and inversely proportional to its mass (volume). If we approximate a spherical particle, based on thermodynamic formulas, the particle temperature rise law can be simplified as follows:

[0020] ΔT∝dI(r);

[0021] In the formula, I(r) is the local laser intensity at the location of the particle, and d is the diameter of the powder particle.

[0022] By observing the temperature rise pattern of the particle under heat, it can be found that in a single scan, if the high-intensity laser (I0) at the center of the laser spot happens to irradiate the fine powder particle (d)... min On the surface of the laser beam, the temperature rise ΔT will increase dramatically; however, if the low-intensity laser (0.135I0) at the edge of the laser spot irradiates the coarse powder particles (d... maxOn the surface, the temperature rise is extremely low. Assume d max / d min =4, and in extreme cases, the temperature rise difference between the two can be as high as about 30 times. This leads to a situation where, in a single scan, fine powder is easily overheated and generates a vaporization backlash, causing severe powder splashing. At the same time, a large amount of molten fine powder will seep into the gaps between unmelted powder due to capillary action, causing the channels to be randomly blocked. On the other hand, coarse powder often does not have enough heat and cannot form an effective sintering neck. This contradiction between overheating and splashing of fine powder and insufficient melting of coarse powder is the fundamental technical bottleneck that the existing single-scan process cannot use to prepare uniform micron-sized porous structures, which is the subject of this invention.

[0023] Specifically, the two-pass scanning process is as follows;

[0024] 2.1 First preprocessing scan: Particle size distribution reconstruction preprocessing.

[0025] A low-power, high-scanning-speed weak energy input strategy is used to perform a comprehensive scan of the powder layer.

[0026] In this process, the purpose of the first pre-processing scan is not to form the shape, but to specifically target the smaller fine powder particles in the normal particle size distribution. Based on the characteristic of the low melting threshold of fine powder, the low linear energy density of the first pass is matched so that the fine powder will preferentially produce preliminary melting without vaporization and splashing. Under the action of surface tension, it will adhere to and fuse with the surface of adjacent coarse powder particles, thereby effectively eliminating the fine powder component in the particle size distribution of the powder bed, significantly narrowing the standard deviation of the powder bed particle size, suppressing vaporization and splashing, and realizing the pre-homogenization of powder particle size in the printing area.

[0027] 2.2 Second forming scan, for sintering and forming of homogeneous coarse powder skeleton:

[0028] Based on the first scan, the laser power is increased and the scanning speed is reduced. A weak energy input strategy with medium power and medium-low scanning speed is adopted for scanning. The pretreated powder layer is then scanned a second time to achieve controllable sintering and obtain a uniform porous structure material.

[0029] During this process, the powder bed has removed the free fine powder that is prone to overheating and splashing, transforming it into a homogeneous large particle system. This system is then matched with the higher linear energy density of the second pass. The high-temperature zone at the center of the Gaussian distribution of laser energy can stably and fully act on the homogeneous large particles, causing the particles to melt locally and form a stable sintering neck. Then, by utilizing the three-dimensional mesh gaps of the particle stack, a metal porous structure with uniform and interconnected channels is constructed, exhibiting good connectivity and uniform pore size.

[0030] Furthermore, in step (2), the original metal powder laid into the powder layer is a spherical metal powder with a particle size ≤150μm, and the original particle size distribution satisfies a normal distribution or a bimodal distribution.

[0031] The normal distribution of powder particle size follows the following formula:

[0032] ;

[0033] In the formula, f(d) represents the proportion of powder particles with a diameter of d, d is the particle size of the metal powder (μm), μ is the average particle size of the powder (μm), and σ is the standard deviation of the powder particle size (μm). The particle size of the metal powder used in laser powder bed additive manufacturing exhibits a normal distribution (or bimodal distribution), with an average particle size typically between 30 and 50 μm, but it contains a large amount of fine powder with a particle size less than 20 μm and coarse powder with a particle size greater than 60 μm.

[0034] Preferably, the metal powder is one or more mixed powders of titanium alloy, high-temperature alloy, stainless steel, etc.

[0035] Furthermore, in step (2), the process parameters for the first scan are: laser power 50~100W, scanning speed 1500~3000mm / s, and scanning spacing 80~120μm.

[0036] Furthermore, in step (2), the process parameters for the second scan are: laser power 100~200W, scanning speed 500~1000mm / s, and scanning spacing consistent with the first scan spacing, also maintaining 80~120μm.

[0037] Furthermore, the core of the above two-pass scanning is to achieve precise energy input matching between the Gaussian distribution of laser energy and the normal distribution of powder particle size. The relationship between its energy density and process parameters follows the formula below:

[0038] ;

[0039] Where E is the laser energy density (unit: J / m²) 2 P represents laser power (W), v represents scanning speed (m / s), and s represents scanning spacing (m). Calculations show that the first pass has a low line energy density of 16.6~66.6 J / m, and the second pass has a higher line energy density of 100~400 J / m.

[0040] Secondly, for particles of different sizes in the normal distribution of powder, the corresponding energy density is matched: for fine powder particles (particle size d≤μ-σ), the required melting energy density is lower, corresponding to the low power and high scanning speed parameters of the first scan of 50~100W and 1500~3000mm / s, matching the edge region of the low intensity laser Gaussian distribution, which can achieve full melting of fine powder without splashing; for coarse powder particles (particle size d≥μ+σ), the required sintering energy density is higher, corresponding to the medium power and medium-low scanning speed parameters of 100~200W and 500~1000mm / s of the second scan, matching the central region of the high intensity laser Gaussian distribution, which can achieve full sintering of coarse powder without over-melting; for intermediate particle size particles (μ-σ<d<μ+σ), the energy superposition of the two scans can achieve precise matching, ensuring that all particle sizes of powder can obtain suitable energy input, and finally achieve a uniform porous structure.

[0041] Furthermore, in step (2), the average pore size of the uniform porous structure material is 30~100μm, the pore size fluctuation range is ≤±10μm, the porosity is 20%~60%, and the pores are in a connected state, so there is no need for degreasing and high-pressure cleaning.

[0042] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0043] (1) This invention introduces two-stage energy control logic of pretreatment and sintering. By removing the hidden dangers of fine powder in the normal distribution through the first pass, and then sintering the homogeneous coarse powder in the second pass, the physical contradiction of light field and powder mismatch can be solved in a breakthrough. This fundamentally eliminates the problem of extreme temperature difference caused by the temperature rise law of particles in a single scan, reduces the splashing after fine powder melts and the phenomenon of clogging the powder gap, improves the defect control capability in the additive manufacturing process, and ensures the stability of the molding.

[0044] (2) The present invention adopts a two-stage scanning strategy, which can greatly suppress powder splashing and defect formation, significantly reduce the backflow of fine powder vaporization and splash residue during the printing process, and greatly ensure the molding stability and the purity of the molded parts.

[0045] (3) In the secondary scanning process of the present invention, the first pretreatment can block the pore blockage caused by the melting and filling of fine powder. During the second forming and sintering, the pores are determined only by the spatial topological arrangement of homogeneous coarse particles, and finally a stable and uniform pore preparation is achieved. The pore size fluctuation is reduced to ±10μm, and the pore size uniformity is significantly improved, which is perfectly suited to scenarios with extremely high requirements for pore uniformity, such as sweating layers.

[0046] (4) The present invention can realize the three-dimensional direct molding of interconnected micropores. Since the powder blockage is completely avoided, the open structure is obtained directly after printing. There is no need for the ultrasonic high pressure powder cleaning post-processing step that easily damages the fragile porous skeleton in the traditional process. The preparation process is simplified, the production cost is low, the yield is high, and it is suitable for a variety of fields such as sweating cooling, filtration separation, and biological scaffolds. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the multi-pass scanning additive manufacturing process in this invention;

[0048] Figure 2 This is a diagram of the porous structure of TC4 titanium alloy obtained from two-pass scanning in Example 1;

[0049] Figure 3 This is a two-pass scanning diagram of the porous structure of GH3536 high-temperature alloy in Example 2;

[0050] Figure 4 This is a diagram of the porous structure of 316L stainless steel obtained by two-pass scanning in Example 3;

[0051] Figure 5 This is a single-scan porous structure diagram of TC4 titanium alloy in Comparative Example 1. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0053] Example 1

[0054] This embodiment prepares a uniform porous TC4 titanium alloy material as follows:

[0055] Step 1: Model building and layering.

[0056] A solid model of the sweating cooling component was created using SolidWorks 3D modeling software. The porous region enclosed by the model has dimensions of 50mm×50mm×10mm. The solid model was then layered using slicing software, with a slice thickness of 30μm.

[0057] Step 2: Multi-pass scanning additive manufacturing.

[0058] Spherical TC4 titanium alloy powder with a particle size of 15~53μm and normal distribution was selected and laid into a powder layer with a thickness of 30μm. Laser powder bed additive manufacturing equipment was used, with the laser spot diameter set to 70μm, and two scans were performed.

[0059] First scan: Laser power 70W, scanning speed 2000mm / s, scanning spacing 100μm. This stage performs a full scan of the powder layer, effectively cutting off the fine powder distribution below 20μm, allowing the fine powder to fully melt and fuse with adjacent particles to form large-sized particles, and the splashing phenomenon is basically invisible.

[0060] The second scan: laser power 150W, scanning speed 800mm / s, scanning interval 100μm, to perform a second scan on the homogenized powder bed, so that the powder particles are locally melted and sintered necks are formed to construct a porous structure.

[0061] like Figure 2 The image shown is a diagram of the porous structure of TC4 titanium alloy subjected to two-pass scanning in this embodiment. Based on... Figure 2 Through observation and testing, the TC4 titanium alloy porous structure material has an average pore diameter of 55μm, a pore diameter fluctuation of ±8μm, a porosity of 32%, good pore connectivity, no fine powder splashing traces, and no need for subsequent powder cleaning treatment, which can meet the usage requirements of aviation sweating cooling components.

[0062] Example 2

[0063] This embodiment prepares a uniform porous structure material of GH3536 high-temperature alloy, as detailed below:

[0064] Step 1: Model building and layering.

[0065] A solid model of the high-temperature filter was created using UG 3D modeling software. The porous area measures 80mm × 80mm × 15mm. Layering was performed using slicing software, with a slice thickness of 40μm.

[0066] Step 2: Multi-pass scanning additive manufacturing.

[0067] Spherical GH3536 high-temperature alloy powder with a particle size of 20~63μm and a bimodal distribution was selected and laid into a powder layer with a thickness of 40μm. Laser powder bed additive manufacturing equipment was used, with a laser spot diameter of 60μm, and two scans were performed.

[0068] First scan: laser power 80W, scanning speed 1800mm / s, scanning spacing 110μm, to achieve fine powder melting and fusion.

[0069] The second scan: laser power 160W, scanning speed 700mm / s, scanning spacing 110μm, to achieve porous structure forming.

[0070] like Figure 3 The image shown is a two-pass scanning diagram of the porous structure of the GH3536 high-temperature alloy in this embodiment. Based on... Figure 3Through observation and testing, the GH3536 high-temperature alloy uniform porous structure material has an average pore diameter of 75μm, a pore diameter fluctuation of ±10μm, a porosity of 44%, uniform pore connectivity, excellent high-temperature resistance, no fine powder clogging, no need for powder cleaning, and can be used in high-temperature gas filtration scenarios.

[0071] Example 3

[0072] This embodiment prepares a uniform porous structure material of 316L stainless steel, as detailed below:

[0073] Step 1: Model building and layering.

[0074] A micro-biological scaffold solid model was created using SolidWorks 3D modeling software. The porous region was 10mm×10mm×5mm in size. The slicing software was used to process the layers, and the slice thickness was 20μm.

[0075] Step 2: Multi-pass scanning additive manufacturing.

[0076] Spherical 316L stainless steel powder with a particle size of 10~45μm and normal distribution was selected and laid into a powder layer with a thickness of 20μm. Laser powder bed additive manufacturing equipment was used, with a laser spot diameter of 50μm, and two scans were performed.

[0077] First scan: laser power 60W, scanning speed 2500mm / s, scanning spacing 80μm, to suppress fine powder splashing.

[0078] Second scan: laser power 130W, scanning speed 900mm / s, scanning spacing 80μm, forming a porous structure.

[0079] like Figure 4 The image shown is a diagram of the porous structure of 316L stainless steel subjected to two-pass scanning in this embodiment. Based on... Figure 2 Through observation and testing, the 316L stainless steel uniform porous structure material has an average pore diameter of 50μm, a pore diameter fluctuation of ±8μm, a porosity of 28%, uniform and interconnected pores, a smooth surface, and no fine powder residue, which meets the usage standards for micro biological scaffolds.

[0080] Comparative Example 1

[0081] This comparative example uses a traditional single-scan strategy, maintaining the same materials, model, and slicing parameters as Example 1, as detailed below:

[0082] Step 1: Model building and layering.

[0083] Completely identical to Example 1, with the same solid model and slice thickness.

[0084] Step 2: Single-scan additive manufacturing.

[0085] The same TC4 titanium alloy powder as in Example 1 was selected and laid into a 30μm thick powder layer. The laser spot diameter was 70μm. A single-scan strategy was adopted, with the laser power set to 150W, the scanning speed to 800mm / s, and the scanning interval to 100μm.

[0086] The results showed that the molding process was accompanied by intense, visible sparks and splashes from the vaporization of fine powder, some of the channels were blocked, and some channels were damaged after the powder was removed.

[0087] like Figure 5 The image shown is a single-scan porous structure diagram of TC4 titanium alloy in this comparative example. Based on the... Figure 5 Observation and testing revealed that the average pore size of the single-scan TC4 titanium alloy porous material was 60 μm, with a pore size fluctuation of ±25 μm and a porosity of 28%. Comparative analysis showed that the pore size uniformity of the single-scan TC4 titanium alloy porous material in this comparative example was far lower than that of the uniform porous structure material of TC4 titanium alloy in Example 1. A large number of fine droplets after melting flowed into the gaps between coarse particles, resulting in the formation of closed pores or severely variable pores, which could not meet the application requirements of sweating cooling components, etc.

[0088] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing, characterized in that, Includes the following steps: S1 Model Establishment and Hierarchy: A solid model of the space enclosed by the porous material is established, and then sliced ​​and layered to obtain several model slices. S2 multi-pass scanning additive manufacturing: Metal powder is laid into a powder layer, and then a laser powder bed additive manufacturing equipment is used to perform a first pass of pre-processing scanning on the model layer. Then, the high laser power is increased and the scanning speed is reduced to perform a second pass of forming scanning on the model layer, so as to obtain a uniform porous structure material manufactured by multi-pass scanning additive manufacturing.

2. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 1, characterized in that, In step S2, the relationship between energy density and process parameters in the first pretreatment scan and the second forming scan is as follows: ； In the formula, E is the laser energy density, P is the laser power, v is the scanning speed, and s is the scanning distance.

3. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 2, characterized in that, The energy density of the first pass is 16.6~66.6 J / m, the laser power of the first scan is 50~100 W, the scanning speed is 1500~3000 mm / s, and the scanning spacing is 80~120 μm.

4. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 2, characterized in that, The energy density of the second pass is 100~400J / m, the laser power of the second scan is 100~200W, the scanning speed is 500~1000mm / s, and the scanning spacing is 80~120μm.

5. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 1, characterized in that, In the first preprocessing scan and the second shaping scan, the laser beam spot diameter is 50~100μm.

6. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 1, characterized in that, In step S2, the metal powder is a spherical metal powder with a particle size ≤150μm, and the particle size distribution of the metal powder satisfies a normal distribution or a bimodal distribution.

7. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 6, characterized in that, The metal powder is one or more mixed powders of titanium alloy, high-temperature alloy, and stainless steel.

8. The method for preparing a uniform porous structure material by multi-pass scanning additive manufacturing according to claim 1, characterized in that, In step S2, the thickness of the powder layer is 20~100μm.

9. A uniform porous structure material manufactured by multi-pass scanning additive manufacturing, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The uniform porous structure material manufactured by multi-pass scanning additive manufacturing according to claim 9, characterized in that, The average pore size of the uniform porous structure material is 30~100μm, the pore size fluctuation range is ≤±10μm, and the porosity is 20%~60%.

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