A method for densifying a green body of a ceramic complex component prepared based on an additive manufacturing technology

Abstract

This invention proposes a method for densifying ceramic green bodies of complex components based on additive manufacturing technology, relating to the field of ceramic material preparation technology. The method includes: S1, mixing ceramic powder and a binder, ball milling to obtain printing powder; S2, 3D printing the printing powder to obtain a ceramic green body sample; S3, brushing a polyurethane solution onto the sample surface, drying and curing it, then immersing it in a latex solution, removing it, and immersing it in a solution containing a coagulant, allowing it to solidify and then drying and curing; S4, repeating step S3 at least twice to obtain a latex sleeve, then drying and curing it to obtain a cold isostatic pressing self-sealing sleeve for the ceramic green body; S5, subjecting the ceramic green body to cold isostatic pressing densification treatment to obtain the finished product. The molding method of this invention can achieve near-net-shape forming; the obtained green body has certain initial strength and structural stability, facilitating subsequent densification treatment, and providing a reliable technical basis for the rapid and efficient manufacturing of complex ceramic components.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, and in particular to a method for densifying the green body of complex ceramic components prepared based on additive manufacturing technology. Background Technology

[0002] Ceramic materials, due to their excellent high-temperature strength, corrosion resistance, and wear resistance, have wide applications in aerospace, electronic devices, and biomedicine. Currently, the main forming methods for ceramics include dry pressing, cold isostatic pressing, gel casting, slip casting, and additive manufacturing. In recent years, ceramic additive manufacturing technology (also known as "3D printing technology") has developed rapidly and has become an important means to overcome the limitations of traditional ceramic forming. This technology is based on the discrete-stacking principle, using computer-aided design (CAD) to construct a three-dimensional model and then layering raw materials to form the part. It eliminates the dependence on molds, significantly shortens the processing cycle, and reduces manufacturing costs, making it particularly suitable for the rapid near-net-shape forming of complex ceramic components. Compared with traditional equal-material manufacturing and subtractive manufacturing technologies, additive manufacturing is not limited by molds or processing techniques, solves the problem of difficult structural forming of complex-shaped products, reduces processing steps, shortens the processing cycle, and greatly saves processing costs. Therefore, it is widely used in the manufacturing of polymers, metals, and some ceramic components.

[0003] While 3D printing technology offers significant advantages for manufacturing complex products, complex structures based on 3D printing (such as cantilevered structures, hollow cavities, and thin-walled meshes) face a series of challenges in subsequent densification processes due to a lack of internal support or excessively thin walls. Cold isostatic pressing (CIP), as an effective densification method, uses a liquid (such as water or kerosene) as the pressure transmission medium at room temperature to apply isotropic pressure to the powder material, thereby increasing the density of the green body, reducing internal defects, and improving mechanical properties. However, during CIP, conventional plastic and rubber encapsulation materials cannot effectively contact and encapsulate the green body, leading to deformation or collapse under high pressure. In particular, for complex irregularly shaped ceramic green bodies, a customized encapsulation method is required for CIP. This process is not only complex in terms of production steps, but also requires more time and cost to design and customize the encapsulation material. Therefore, the effectiveness of existing CIP processes for ceramic green bodies, especially irregularly shaped parts, needs improvement.

[0004] Therefore, there is an urgent need to develop a method for densifying the green body of complex ceramic components based on additive manufacturing technology, in order to solve the problem that existing encapsulation materials cannot adapt to complex green body structures and are prone to structural damage, and to further improve the density and mechanical properties of 3D printed ceramic products. Summary of the Invention

[0005] In view of this, the present invention proposes a method for densifying the green body of complex ceramic components based on additive manufacturing technology. The method involves preparing a ceramic green body using additive manufacturing technology and then constructing a composite protective film with a double coating system on the surface of the ceramic green body to achieve cold isostatic pressing densification treatment.

[0006] The technical solution of this invention is implemented as follows:

[0007] This invention provides a method for densifying the green body of complex ceramic components prepared by additive manufacturing technology, comprising the following steps:

[0008] S1. Mix ceramic powder and binder, and ball mill to obtain printing powder;

[0009] S2. The printing powder is 3D printed to obtain a ceramic green sample;

[0010] S3. Apply polyurethane solution to the sample surface, let it dry and cure, then immerse it in latex solution. After taking it out, immerse it in a solution containing coagulant. After the sample surface solidifies and forms, let it dry and cure.

[0011] S4. Repeat the operation of S3 at least twice to obtain a latex sleeve, then dry and cure it to obtain a cold isostatic pressing self-sealing sleeve for ceramic green bodies.

[0012] S5. The ceramic green body treated by S4 is subjected to cold isostatic pressing to increase its density, and the finished product is obtained.

[0013] By employing the aforementioned technical means, and considering the high porosity and easy liquid absorption of ceramic green bodies obtained through additive manufacturing, this invention, to prevent the subsequent coating of natural latex solution from seeping into the interior of the green body, first coats the surface of the green body with an organic mixture containing a non-water-soluble polymer, forming a thin modified protective layer. This protective layer not only effectively blocks the penetration of subsequent coating materials but also provides a good interface foundation for the uniform coating of subsequent film layers. Based on this, a natural latex solution is used as the second film-forming composition, and rapid curing is achieved by immersing it in a coagulant solution (such as calcium chloride solution). Calcium chloride, as a strong electrolyte, dissociates into Ca upon dissolving in water. 2+ and Cl - , where Ca 2+ It can neutralize the negative charges (such as carboxylate –COO–) on the surface of natural latex particles, disrupt their electrostatic stability layer, and promote the rapid aggregation and solidification of latex particles, forming a dense, continuous, and mechanically strong elastic film on the surface of the green body. This double-layer composite protective film can effectively isolate the direct contact between the water medium used in the cold isostatic pressing process and the ceramic green body, preventing the green body from absorbing water and softening or structural damage, thereby ensuring the integrity and forming quality of the green body during high-pressure processing.

[0014] Further, in step S1, the mass content of the binder is 10~20wt% based on the total mass of the printed powder.

[0015] Furthermore, the binder is epoxy resin and / or phenolic resin; the ceramic powder includes at least one of alumina ceramic powder, zirconia ceramic powder, silicon nitride ceramic powder, and silicon carbide ceramic powder.

[0016] Furthermore, the ball milling conditions include: the ball milling medium is SiC microspheres, the mass ratio of the ball milling medium to the mixture is 2:1, the ball milling speed is 200 r / min, and the ball milling time is 12 h.

[0017] Furthermore, in step S2, the 3D printing method includes at least one of selective laser sintering (SLS), inkjet printing (IJP), stereolithography (SLA), digital light processing (DLP), and ink-to-wash (DIW). Different additive manufacturing technologies have different characteristics. IJP, DLP, and SLA offer high printing accuracy but suffer from lower production efficiency, higher costs, and complex curing processes. SLS stands out among numerous additive manufacturing technologies due to its high material utilization, simple process, high production efficiency, and appropriate production accuracy. Its unique forming principle and large-scale forming platform enable the formation of large-sized and structurally complex ceramic composite parts, making it a focus of widespread attention.

[0018] Furthermore, the shape of the ceramic printed green sample includes, but is not limited to, at least one of the following: spherical, ellipsoidal, cubic, cuboid, plate, disc, olive, rod, conical, and irregularly shaped; the irregularly shaped sample includes, but is not limited to, honeycomb type.

[0019] Further, in step S3, the polyurethane solution has a mass content of 43 wt% and a viscosity of 240 Pa·s; the latex solution has a mass content of 60 wt%.

[0020] Furthermore, the solvent of the latex solution includes water, as well as ammonia and / or potassium hydroxide, to adjust and maintain the solution in an alkaline environment, thereby inhibiting the spontaneous aggregation and coagulation of latex particles before contact with the coagulant and ensuring the stability of the coating process.

[0021] Furthermore, the coagulant is selected from at least one of acid coagulants, salt coagulants, and electrolyte coagulants.

[0022] Furthermore, the solution containing the coagulant is selected from a CaCl2 solution with a mass content of 6-10 wt%.

[0023] Furthermore, after brushing on the polyurethane solution, it is dried and cured at 50°C for 5 hours; after immersion in a solution containing a coagulant, it is dried and cured at 50°C for 30 minutes.

[0024] Furthermore, in step S4, the thickness of the latex sheath is 0.5~0.75mm.

[0025] Furthermore, the latex sheath is dried at 50°C for 8 hours.

[0026] The present invention provides a method for densifying the green body of complex ceramic components prepared by additive manufacturing technology, which has the following advantages over the prior art:

[0027] (1) The present invention uses additive manufacturing technology to prepare ceramic green bodies with complex structures. Compared with traditional forming processes, it has higher design freedom and forming flexibility, and can achieve near-net-shape forming. The obtained green bodies have certain initial strength and structural stability, which facilitates subsequent processing and treatment, and provides a reliable technical basis for the rapid and efficient manufacturing of complex structure ceramic components.

[0028] (2) The present invention uses an organic solution containing non-water-soluble polymer as the coating material before cold isostatic pressing, replacing the traditional rubber sleeve, latex sleeve or plastic film packaging method. This not only avoids the structural adaptation problem caused by using solid molds, but also reduces environmental pollution and lowers the cost of subsequent demolding and cleaning processes, thereby effectively reducing the overall production cost.

[0029] (3) The polymer coating material used in this invention, as the encapsulation material for cold isostatic pressing, has the advantages of being environmentally friendly, efficient, and low-cost. It can be directly coated on the surface of ceramic green bodies to form a protective layer, enabling rapid encapsulation of complex-structured green bodies. This coating material is easy to remove, requiring no complex post-processing, significantly shortening the cold isostatic pressing process and improving production efficiency.

[0030] (4) The composite protective film provided by the present invention can form a complete and dense protective layer on the surface of ceramic green body after curing. The green body encapsulated by the protective layer can be directly subjected to cold isostatic pressing. It can still maintain structural integrity under static pressure of up to 200 MPa, effectively transmit liquid pressure, and promote uniform densification of the green body. In addition, the coating can shrink with the green body without peeling off, and has good interface matching and isolation performance, ensuring the safety and reliability of the cold isostatic pressing process. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A process flow diagram of the molding method provided by the present invention;

[0033] Figure 2 This is a static contact angle diagram of the printed preform after coating with the first modified film according to Embodiment 1 of the present invention;

[0034] Figure 3 The image shows a comparison between the ceramic printed blank after cold isostatic pressing and the original blank provided in Embodiment 1 of the present invention. The left image shows the ceramic printed blank after cold isostatic pressing, and the right image shows the original blank.

[0035] Figure 4 This is a demolding diagram of the ceramic printed blank after cold isostatic pressing, as provided in Embodiment 1 of the present invention.

[0036] Figure 5 This is a cold isostatic pressing self-sealing diagram of the ceramic printed blank provided in Embodiment 2 of the present invention;

[0037] Figure 6 The image shows a comparison between the ceramic printed blank after cold isostatic pressing and the original blank provided in Embodiment 2 of the present invention. The left image shows the ceramic printed blank after cold isostatic pressing, and the right image shows the original blank.

[0038] Figure 7 This is a photograph of a ceramic printed blank coated with a protective film after cold isostatic pressing, as provided in Embodiment 3 of the present invention.

[0039] Figure 8 This is a demolding diagram of the ceramic printed blank after cold isostatic pressing, provided in Comparative Example 1 of the present invention.

[0040] Figure 9 The diagram shows the dimensional changes of the ceramic printed blank and the original blank after cold isostatic pressing, as provided in Embodiments 4-6 of the present invention. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] CN 118599371 A discloses a film-forming composition that combines a high molecular weight water-soluble polymer with a low molecular weight polyethylene glycol and a water-soluble organic solvent (such as glycerol). Utilizing the hydrophilic properties of the polymer, water is fixed within the molecular chain structure to form a dense protective film on the surface of the preform. However, this technical solution still has the following significant problems: First, although the film-forming composition can achieve a certain degree of encapsulation and protection of the preform, in actual cold isostatic pressing, the use of oil as the pressure transmission medium introduces a series of engineering and environmental problems. For example, hydraulic oil is expensive, and the equipment must have good oil corrosion resistance; more importantly, the use of oil involves complex waste oil recycling and treatment processes, which may contain additive residues, posing a potential environmental pollution risk and not conforming to the current trend of green manufacturing. Secondly, the film-forming composition is based on a water-soluble polymer system. Although it can provide a certain coating effect in a dry state, it is prone to dissolution, swelling or decreased mechanical strength in humid environments (such as when in contact with aqueous media), which leads to encapsulation failure. This limits its application in cold isostatic pressing processes in aqueous media and also affects the preservation period and stability of the preform before encapsulation.

[0043] Therefore, this invention proposes a cold isostatic pressing self-sealing molding method for additive manufacturing of ceramic green bodies, such as... Figure 1 As shown, this method first uses additive manufacturing technology to prepare ceramic green bodies with complex structures; then, a layer of organic mixed solution composed of non-water-soluble polymers is coated on the surface of the green body to form a thin modified protective layer; on this basis, a film-forming composition of non-water-soluble organic polymers is further coated to construct a composite protective film with a double-layer structure. The green body protected by the coating can be directly subjected to cold isostatic pressing in a hydraulic cylinder containing water. The water is non-toxic, and leaks are easy to clean, which is in line with the trend of green manufacturing. In addition, it can also achieve efficient, uniform, and dense encapsulation of complex structure ceramic green bodies, which is beneficial to the subsequent final sintering process of ceramics.

[0044] The present invention will be further described below with reference to specific embodiments. The scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the materials mainly involved in the following examples are all conventional commercial products or raw materials that can be prepared by existing known chemical methods.

[0045] Example 1

[0046] This embodiment provides a method for densifying the green body of complex ceramic components prepared based on additive manufacturing technology, including the following steps:

[0047] S1. Mix 90 wt% silicon carbide ceramic powder (purity >98%, particle size 35 μm, Shandong Weifang Huarong Ceramic Materials Co., Ltd.) with 10 wt% epoxy resin (E12, binder, particle size 5 μm, Guangzhou Xinxi Metallurgical Chemical Co., Ltd.) to achieve particle size distribution. Then, use mechanical ball milling to mix the powder, using SiC balls with a diameter of 4 mm as the ball milling medium. The ball-to-material mass ratio is 2:1. Place the ball milling jar on a drum ball mill and mill at a speed of 200 r / min for 12 h to obtain uniform printing powder.

[0048] S2. Place the printing powder into a laser selective sintering forming instrument and set the laser parameters as follows: preheating temperature 45℃, laser power P=8 W, scanning rate V=4000 mm / s, scanning distance L=0.1 mm to prepare silicon carbide ceramic printing green body. Record the mass and size of the printing green body, and calculate its theoretical density by combining the mixing density of the printing powder with the mass and volume, and then estimate the relative density of the printing green body.

[0049] S3. After brushing polyurethane solution (Hubei Huitian New Materials Co., Ltd., model Huitian 9422) onto the surface of the green blank, it was cured at 50℃ for 5 hours. The weight change of the sample after curing was recorded. After polyurethane modification, the water contact angle of the sample was approximately 122°. Figure 2 As shown, the liquid (water) forms a highly spherical shape on the solid surface, exhibiting strong hydrophobicity, which prevents other aqueous solutions from entering the blank and thus avoids damage to the blank. The sample is then immersed in a natural latex solution with a solid content of 60 wt%, and then immersed in a CaCl2 solution with a mass fraction of 6%. After the latex on the sample surface solidifies, it is dried at 50°C for 30 min. This step is repeated twice to obtain a latex sleeve with a thickness of 0.5 mm. Finally, it is dried at 50°C for 8 h to obtain a cold isostatic pressing self-sealing sleeve.

[0050] In this embodiment, the silicon carbide ceramic green body covered with a cold isostatic pressing self-sealing sleeve was subjected to cold isostatic pressing treatment and compaction test. Specifically, the coated sample was placed under pressure conditions of 100 MPa and 200 MPa respectively, and pressurized in a cold isostatic pressing equipment (using water as the pressure transmission medium). The pressure holding time was 5 minutes, the pressurization rate was about 0.208 MPa / s, and the depressurization rate was about 6.67 MPa / s.

[0051] Experimental results show that the prepared self-sealing sleeve can effectively withstand high pressure and prevent water from penetrating into the preform. The sample structure remains intact, and the coating layer remains continuous and unbroken after high-pressure treatment. (Samples before and after testing) Figure 3 As shown.

[0052] After processing, remove the sample, such as Figure 4As shown, its mass and dimensions after cold isostatic pressing were recorded, combined with the mixing density of the printing powder (approximately 2.75 g / cm³). 3 The relative density change before and after cold isostatic pressing is calculated using mass and volume.

[0053] The results showed that the relative density of the green body before cold isostatic pressing was 49.8%, and after cold isostatic pressing at 200 MPa, the relative density increased to 66.1%, which significantly reduced the porosity inside the green body. This indicates that the self-sealing sleeve of this application can effectively encapsulate the ceramic green body and promote the densification of the green body during the cold isostatic pressing process.

[0054] Example 2

[0055] The difference from Example 1 is that: a hollow, thin-walled (honeycomb-shaped) irregular part model file for printing ceramic green bodies was designed, with a wall thickness of 1.5 mm, and the ceramic green body was printed using a laser selective sintering instrument. The same protective film as in Example 1 was applied, followed by cold isostatic pressing, as in... Figure 4 , 5 As shown.

[0056] Depend on Figure 5 , 6 It can be seen that the cold isostatic pressing self-sealing protective film prepared by the present invention also has the function of withstanding high pressure and waterproofing irregularly shaped parts.

[0057] Example 3

[0058] The difference from Example 1 is that: a hollow gear-shaped part model file for printing ceramic green bodies was designed, and the ceramic green body was printed using a laser selective sintering instrument. The same protective film as in Example 1 was applied, followed by cold isostatic pressing, such as... Figure 7 As shown.

[0059] Comparative Example 1

[0060] The comparative example uses a rubber sleeve to wrap the ceramic green blank cavity mold and performs the same cold isostatic pressing treatment as in Example 1. The treatment result is as follows: Figure 8 As shown.

[0061] Depend on Figure 8 It can be seen that after cold isostatic pressing, the surface of the billet is damaged. The possible reason is that when the rubber sleeve is used to cover and seal the hole part, air is still left in the center. Under high pressure, the pressure distribution is uneven and the local stress is concentrated, which causes damage to the billet.

[0062] Example 4

[0063] This embodiment provides a method for densifying the green body of complex ceramic components prepared based on additive manufacturing technology, including the following steps:

[0064] S1. Mix 80 wt% silicon nitride ceramic powder (purity >98%, particle size 35 μm) with 20 wt% epoxy resin (E12, binder, particle size 5 μm, Guangzhou Xinxi Metallurgical Chemical Co., Ltd.) to achieve particle size distribution. Then, use mechanical ball milling to mix the powders. Use SiC balls with a diameter of 4 mm as the ball milling medium. The ball-to-material mass ratio is 2:1. Place the ball milling jar on a drum ball mill and mill at a speed of 200 r / min for 12 h to obtain uniform printing powder.

[0065] S2. The printing powder is placed into the HKC500 SLS laser selective sintering forming instrument (Wuhan Huake 3D Technology Co., Ltd.) for forming. This instrument has a forming space of 500 mm × 500 mm × 400 mm (length × width × height) and is equipped with an imported CO2 laser with a maximum laser power of 100 W. The uniformly mixed printing powder is added to the left and right powder feeding cylinders. As the powder spreading rollers move horizontally, they spread the powder in the feeding cylinders onto the forming cylinder. During laser selective sintering to prepare the workpiece, the preheating system raises the powder temperature to the set value. At this time, the CO2 laser emits laser light, which, after passing through X-axis and Y-axis galvanometers, is focused into a laser beam with a spot diameter of 0.3 mm onto the surface of the printing powder. There are two powder cylinders on each side, and the powder spreading rollers are responsible for spreading the ceramic powder in the cylinders evenly within the working area. After the current interface is printed, the worktable will lower a certain height to allow new ceramic powder to be spread, repeating this cycle until the workpiece printing is complete. Based on a computer-generated digital model, a ceramic green body of a specific shape is prepared through a "layered preparation, layer-by-layer superposition" method. The laser parameters were set as follows: preheating temperature 45℃, laser power P=8 W, scanning rate V=4000 mm / s, and scanning spacing L=0.1 mm, in order to prepare alumina ceramic printing green bodies. The mass and size of the printing green bodies were recorded, and the theoretical density was calculated by combining the mixing density of the printing powder with the mass and volume, thereby estimating the relative density of the printing green bodies.

[0066] S3. After brushing a 43wt% polyurethane solution (Huitian 9422) onto the surface of the green compact, cure it at 50℃ for 5 hours, and record the weight change of the sample after curing. (The sample weight is as follows...) Figure 1 As shown; the sample is then immersed in a natural latex solution with a solid content of 60wt%, and after being taken out, it is immersed in a CaCl2 solution with a mass fraction of 6%. After the latex on the surface of the sample solidifies and forms, it is dried at 50℃ for 30min. This step is repeated 3 times to obtain a latex sleeve with a thickness of 0.6mm. Finally, it is dried at 50℃ for 8h to obtain a cold isostatic pressing self-sealing sleeve.

[0067] In this embodiment, the alumina ceramic green body covered with a cold isostatic pressing self-sealing sleeve was subjected to cold isostatic pressing treatment and compaction test. Specifically, the coated sample was placed under pressure conditions of 100 MPa and 200 MPa in a cold isostatic pressing equipment (using water as the pressure transmission medium) for pressurization treatment. The pressure holding time was 5 minutes, the pressurization rate was about 0.208 MPa / s, and the depressurization rate was about 6.67 MPa / s.

[0068] Test results are as follows Figure 9 As shown.

[0069] Example 5

[0070] This embodiment provides a method for densifying the green body of complex ceramic components prepared based on additive manufacturing technology, including the following steps:

[0071] S1. Mix 85wt% silicon nitride ceramic powder (purity >98%, particle size 35um, Nangong Lijia Metal Co., Ltd.) with 15wt% phenolic resin to achieve particle size distribution. Then, use mechanical ball milling to mix the powder, using SiC balls with a diameter of 4 mm as the ball milling medium. The ball-to-material mass ratio is 2:1. Place the ball milling jar on a drum ball mill and mill at a speed of 200 r / min for 12 h to obtain uniform printing powder.

[0072] S2. The printing powder is placed into the HKC500 SLS laser selective sintering forming instrument (Wuhan Huake 3D Technology Co., Ltd.) for forming. This instrument has a forming space of 500 mm × 500 mm × 400 mm (length × width × height) and is equipped with an imported CO2 laser with a maximum laser power of 100 W. The uniformly mixed printing powder is added to the left and right powder feeding cylinders. As the powder spreading rollers move horizontally, they spread the powder in the feeding cylinders onto the forming cylinder. During laser selective sintering to prepare the workpiece, the preheating system raises the powder temperature to the set value. At this time, the CO2 laser emits laser light, which, after passing through X-axis and Y-axis galvanometers, is focused into a laser beam with a spot diameter of 0.3 mm onto the surface of the printing powder. There are two powder cylinders on each side, and the powder spreading rollers are responsible for spreading the ceramic powder in the cylinders evenly within the working area. After the current interface is printed, the worktable will lower a certain height to allow new ceramic powder to be spread, repeating this cycle until the workpiece printing is complete. Based on a computer-generated digital model, a ceramic green body of a specific shape is prepared through a "layered preparation, layer-by-layer superposition" method. The laser parameters were set as follows: preheating temperature 45℃, laser power P=8 W, scanning rate V=4000 mm / s, and scanning spacing L=0.1 mm, in order to prepare alumina ceramic printing green bodies. The mass and size of the printing green bodies were recorded, and the theoretical density was calculated by combining the mixing density of the printing powder with the mass and volume, thereby estimating the relative density of the printing green bodies.

[0073] S3. After brushing a 43wt% polyurethane solution (Huitian 9422) onto the surface of the green compact, cure it at 50℃ for 5 hours, and record the weight change of the sample after curing. (The sample weight is as follows...) Figure 1 As shown; the sample is then immersed in a natural latex solution with a solid content of 60wt%, and after being taken out, it is immersed in a CaCl2 solution with a mass fraction of 8%. After the latex on the surface of the sample solidifies and forms, it is dried at 50℃ for 30min. This step is repeated 3 times to obtain a latex sleeve with a thickness of 0.65mm. Finally, it is dried at 50℃ for 8h to obtain a cold isostatic pressing self-sealing sleeve.

[0074] In this embodiment, the silicon nitride ceramic green body coated with a cold isostatic pressing self-sealing sleeve was subjected to cold isostatic pressing treatment and compaction test. Specifically, the coated sample was placed under pressure conditions of 100 MPa and 200 MPa respectively, and pressurized in a cold isostatic pressing equipment (using water as the pressure transmission medium). The pressure holding time was 5 minutes, the pressurization rate was about 0.208 MPa / s, and the depressurization rate was about 6.67 MPa / s.

[0075] Test results are as follows Figure 9 As shown.

[0076] Example 6

[0077] This embodiment provides a method for densifying the green body of complex ceramic components prepared based on additive manufacturing technology, including the following steps:

[0078] S1. Mix 85 wt% silicon nitride ceramic powder (purity >98%, particle size 35 μm) with 15 wt% epoxy resin (E12, binder, particle size 5 μm) to achieve particle size distribution. Then, use mechanical ball milling to mix the powder, using SiC balls with a diameter of 4 mm as the ball milling medium. The ball-to-powder mass ratio is 2:1. Place the ball milling jar on a drum ball mill and mill at a speed of 200 r / min for 12 h to obtain uniform printing powder.

[0079] S2. The printing powder is placed into the HKC500 SLS laser selective sintering forming instrument (Wuhan Huake 3D Technology Co., Ltd.) for forming. This instrument has a forming space of 500 mm × 500 mm × 400 mm (length × width × height) and is equipped with an imported CO2 laser with a maximum laser power of 100 W. The uniformly mixed printing powder is added to the left and right powder feeding cylinders. As the powder spreading rollers move horizontally, they spread the powder in the feeding cylinders onto the forming cylinder. During laser selective sintering to prepare the workpiece, the preheating system raises the powder temperature to the set value. At this time, the CO2 laser emits laser light, which, after passing through X-axis and Y-axis galvanometers, is focused into a laser beam with a spot diameter of 0.3 mm onto the surface of the printing powder. There are two powder cylinders on each side, and the powder spreading rollers are responsible for spreading the ceramic powder in the cylinders evenly within the working area. After the current interface is printed, the worktable will lower a certain height to allow new ceramic powder to be spread, repeating this cycle until the workpiece printing is complete. Based on a computer-generated digital model, a ceramic green body of a specific shape is prepared through a "layered preparation, layer-by-layer superposition" method. The laser parameters were set as follows: preheating temperature 45℃, laser power P=8 W, scanning rate V=4000 mm / s, and scanning spacing L=0.1 mm, in order to prepare alumina ceramic printing green bodies. The mass and size of the printing green bodies were recorded, and the theoretical density was calculated by combining the mixing density of the printing powder with the mass and volume, thereby estimating the relative density of the printing green bodies.

[0080] S3. After brushing a 43wt% polyurethane solution (Huitian 9422) onto the surface of the green compact, cure it at 50℃ for 5 hours, and record the weight change of the sample after curing. (The sample weight is as follows...) Figure 1 As shown; the sample is then immersed in a natural latex solution with a solid content of 60wt%, and after being taken out, it is immersed in a CaCl2 solution with a mass fraction of 10%. After the latex on the surface of the sample solidifies and forms, it is dried at 50℃ for 30min. This step is repeated 3 times to obtain a latex sleeve with a thickness of 0.75mm. Finally, it is dried at 50℃ for 8h to obtain a cold isostatic pressing self-sealing sleeve.

[0081] In this embodiment, the silicon nitride ceramic green body coated with a cold isostatic pressing self-sealing sleeve was subjected to cold isostatic pressing treatment and compaction test. Specifically, the coated sample was placed under pressure conditions of 100 MPa and 200 MPa respectively, and pressurized in a cold isostatic pressing equipment (using water as the pressure transmission medium). The pressure holding time was 5 minutes, the pressurization rate was about 0.208 MPa / s, and the depressurization rate was about 6.67 MPa / s.

[0082] Test results are as follows Figure 9 As shown.

[0083] Comparative Example 2

[0084] The difference from Example 6 is that a polyurethane solution is simply brushed onto the surface and dried directly until fully cured.

[0085] Comparative Example 3

[0086] The difference from Example 6 is that the polyurethane solution is not brushed on, but only the latex solution is dipped in.

[0087] Comparative Example 4

[0088] The difference from Example 6 is that no coagulant solution is used.

[0089] In Comparative Example 2, the ceramic green body with only a layer of polyurethane solution was coated. After subsequent treatment as in Example 6, no significant dimensional shrinkage was observed, but the desired densification effect was not achieved. In Comparative Example 3, no polyurethane solution was applied; only a latex solution was dipped in the ceramic green body. After subsequent treatment as in Example 6, no significant dimensional shrinkage was observed, but the desired densification effect was not achieved. Furthermore, because the surface of the ceramic green body was not waterproofed, the latex solution penetrated into the sample, and after curing, the latex film on the sample surface could not be separated from the sample. In Comparative Example 4, since no coagulant solution was used, after subsequent treatment as in Example 6, the latex solution on the surface of the ceramic green body cured relatively slowly, requiring approximately 2-3 days, increasing the time cost.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the densification of ceramic green bodies of complex components produced on the basis of additive manufacturing technology, characterized in that The method comprises the following steps: S1, mixing and ball-milling ceramic powder and a binder to obtain a printing powder; S2, 3D printing the printing powder to obtain a ceramic green sample; S3, brushing a non-water-soluble polyurethane solution on the surface of the sample, immersing the sample in a natural latex solution after drying and curing, and then immersing the sample in a solution containing a coagulant, and after the surface of the sample is coagulated and shaped, drying and curing; S4, repeating the operation of S3 at least twice to obtain a latex sheath, and then drying and curing to obtain a cold isostatic pressing self-sealing sheath of the ceramic green body; S5, cold isostatic pressing densification treatment is performed on the ceramic green body, wherein the transmission medium is water, and a finished product is obtained; In step S4, the thickness of the latex sheath is 0.5-0.75 mm; In step S3, the mass content of the non-water-soluble polyurethane solution is 43wt%, and the viscosity is 240Pa·s; the mass content of the natural latex solution is 60wt%; The coagulant is selected from at least one of an acid coagulant and a salt coagulant.

2. The method for green densification of ceramic complex components prepared based on additive manufacturing technology according to claim 1, characterized in that, In step S1, the mass content of the binder is 10-20wt% based on the total mass of the printing powder.

3. The method for green densification of ceramic complex components prepared based on additive manufacturing technology according to claim 2, characterized in that, The binder is epoxy resin and / or phenolic resin; and the ceramic powder comprises at least one of alumina ceramic powder, zirconia ceramic powder, silicon nitride ceramic powder, and silicon carbide ceramic powder.

4. The method for green densification of ceramic complex components prepared based on additive manufacturing technology according to claim 3, characterized in that, The ball-milling comprises that the ball-milling medium is SiC microspheres, the mass ratio of the ball-milling medium to the mixture is 2:1, the ball-milling rotation speed is 200r / min, and the ball-milling time is 12h.

5. The method for green densification of ceramic complex components prepared based on additive manufacturing technology according to claim 1, characterized in that, In step S2, the additive manufacturing technology comprises at least one of laser selective sintering technology, binder jetting molding technology, light curing molding technology, and ink direct writing molding technology.

6. The method for green densification of ceramic complex components prepared based on additive manufacturing technology according to claim 1, characterized in that, The salt coagulant is selected from a CaCl2 solution with a mass content of 6-10wt%.

7. The method for green densification of ceramic complex components prepared based on additive manufacturing technology according to claim 1, characterized in that, The drying temperature of the latex sheath is 50℃, and the time is 8h.

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