A density-enhancing additive manufacturing method and product thereof

Abstract

The present invention relates to the field of additive manufacturing technology, and in particular to an additive manufacturing method and product thereof for improving density. The method comprises the following steps: S10, preparation of ceramic paste; S20, three-dimensional model design: designing a three-dimensional model blank of the product through software; S30, additive manufacturing: printing the ceramic paste obtained in S10 into the blank designed in S20 through 3D printing equipment; S40, sintering: sintering the blank obtained in S30 to obtain an additive manufacturing product. By performing special treatments in the three key steps of alumina ceramic paste preparation, blank additive manufacturing, and blank sintering, the interlayer bonding strength of ceramic additively manufactured molded parts is effectively improved, the density of the molded parts is improved, the internal porosity of the molded parts is reduced, and the bulk density of the ceramic additively manufactured molded parts is also increased, thereby improving the comprehensive mechanical properties of the ceramic additively manufactured molded parts.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to an additive manufacturing method for improving density and a product thereof. Background Art

[0002] Additive manufacturing (AM) technology, also known as 3D printing, is a manufacturing method that directly shapes parts from the bottom up by adding materials layer by layer. With its advantages in customization and precision manufacturing, it has played an increasingly important role in the fields of medicine, automobiles, aerospace, etc. in recent years. Similar to traditional processes, both raw materials and finished products in the additive manufacturing process need to undergo relevant characterization tests to meet the corresponding quality standards. Porosity is an important indicator for evaluating the additive manufacturing process. In the additive manufacturing process, the density of the finished product is inversely proportional to the porosity. The more pores a part has, the lower the density and the lower the mechanical strength. It is more likely to be fatigued or cracked under stress. Therefore, the relevant porosity characterization is particularly important.

[0003] Products with different application areas and performance characteristics require precise control of porosity to meet actual application requirements. For example, in fields such as aerospace and electricity, due to the relatively extreme environments, related products are usually required to withstand high fatigue stresses, and the density of some components must reach above 99%, which requires the finished product to have a lower porosity. In the biomedical field, such as artificial bone implants, considering biocompatibility and the complex biological environment, the implant needs to match the surrounding bone tissue with higher porosity. Appropriate porosity can provide suitable space for cell proliferation, reduce stress shielding effects, and promote bone ingrowth and bone integration. Otherwise, problems such as bone resorption and implant loosening are prone to occur. At the same time, the implant must also have good biomechanical properties, but high mechanical properties often conflict with high porosity, which places high demands on the precise control of the implant's porosity.

[0004] The density and related properties of AM finished products are often closely related to the porosity of the paste, making precise control of the porosity of the raw material paste a crucial component of quality control. On the one hand, the porosity of the AM paste affects its flowability, which in turn affects the paste's stability and layup uniformity. On the other hand, the porosity of the AM paste affects the sintering dynamics during the AM process and the surface finish, porosity, and mechanical strength of the final product.

[0005] Generally, low-porosity additive manufacturing pastes produce high-density parts with better surface finish after molding. Studies have shown that in additive manufacturing processes such as powder bed fusion (PBF), due to their rapid solidification rate and high powder porosity, they are prone to various processing defects such as common spherical pores and other cracks and pores within the parts. Some of these defects are difficult to eliminate even after subsequent processes such as heat treatment, which has a serious impact on the mechanical properties of the molded parts.

[0006] In addition, the spheroidization phenomenon, which is common in additive manufacturing processes, can easily make the molding surface very rough and produce a large number of pores between the spheres. Adjusting the porosity of the paste can also help improve this phenomenon and obtain finished products with better density and mechanical properties.

[0007] In summary, understanding and controlling the porosity parameters of additive manufacturing pastes and finished products is crucial for better understanding the entire additive manufacturing process and ensuring efficient production and superior performance of the final product. Therefore, finding additive manufacturing methods that increase density and reduce porosity has become a pressing issue. Summary of the Invention

[0008] In order to solve the porosity problem in additive manufacturing mentioned in the above background, the present invention provides an additive manufacturing method and product with improved density.

[0009] The present invention provides an additive manufacturing method for improving density, comprising the following steps:

[0010] S10, preparation of ceramic paste: The raw materials of the ceramic paste include, by mass percentage: 30-45% of 1000-mesh alumina powder, 10-15% of 500-mesh alumina fiber powder, 5-10% of composite additive, 20-25% of anhydrous ethanol, and 20% of liquid photosensitive resin, wherein the composite additive includes calcium oxide, magnesium oxide, and silicon dioxide;

[0011] S20, 3D model design: Design the 3D model of the product through software;

[0012] S30, additive manufacturing: printing the ceramic paste obtained in S10 into a blank designed in S20 through a 3D printing device;

[0013] S40, sintering: sintering the green body obtained in S30 to obtain an additive manufacturing product.

[0014] Furthermore, the S10 specifically includes the following steps:

[0015] S11. Add the alumina, alumina fiber powder, composite additives, anhydrous ethanol and liquid photosensitive resin into a closed reactor, start stirring for 5 minutes, and adjust the alternating temperature to -30±2℃~60±2℃ while stirring; the purpose of alternating temperature increase and decrease while stirring is to quickly drive out the bubbles in the ceramic paste raw materials and improve the density and uniformity of the ceramic paste.

[0016] S12, stop stirring and let the mixture stand for 10 minutes; after stirring and alternating temperature treatment, the ceramic paste mixture is allowed to stand to allow the ceramic paste in the closed reactor to undergo a natural exhaust process, in preparation for the next stirring and alternating temperature treatment.

[0017] S13. Start stirring for 10 minutes, and adjust the alternating temperature to -30±2°C to 60±2°C while stirring; the purpose of alternating temperature rise and fall while stirring is to quickly expel the bubbles in the ceramic paste raw material again, further improve the density and uniformity of the ceramic paste, avoid the formation of bubbles in the additive manufacturing process, affect the density of the additive manufacturing product, and avoid the production of defective products.

[0018] S14. After adjusting the temperature of the sealed reactor to room temperature, evacuate the sealed reactor for 1 hour until the vacuum degree of the sealed reactor reaches 0.1 MPa; by evacuating the reactor at room temperature, the bubbles in the ceramic paste can be discharged again, thereby further improving the uniformity of the ceramic paste.

[0019] S15, exhausting the closed reactor for 10 minutes to obtain the ceramic paste. Exhausting the air can make the internal and external states of the ceramic paste closer to the production state in the additive manufacturing process, thereby improving the overall uniformity of the ceramic paste.

[0020] Furthermore, the specific operation of adjusting the alternating temperature is: starting from room temperature to 60±2°C at a heating rate of 20°C / min, and then cooling to -30±2°C at a cooling rate of 20°C / min.

[0021] Furthermore, the stirring speed is 60 r / min.

[0022] Stirring, setting alternating temperatures, standing still, and vacuuming can help reduce the air in the alumina ceramic paste, thereby increasing the density of the paste and helping to improve the density of additive manufacturing products.

[0023] Furthermore, the composite auxiliary agent includes, by mass percentage, 40-60% calcium oxide, 20-30% magnesium oxide and 20-30% silicon dioxide.

[0024] Due to the high melting point of alumina, the preparation of alumina ceramics often requires the addition of sintering aids to achieve densification through sintering. This method can usually promote the sintering of alumina ceramics. Liquid-phase sintering of alumina ceramics generates a liquid phase through chemical reactions, promoting diffusion and viscous flow to achieve particle rearrangement and mass transfer processes. The composite additive formed by CaO-MgO-SiO2 can introduce lattice vacancies into alumina, facilitate diffusion, reduce the sintering activation energy, and form a solid solution, thereby having a certain impact on the densification and microstructure of alumina ceramics. The effect is more obvious when introduced in a certain proportion of composite form.

[0025] Furthermore, the S20 specifically includes the following steps:

[0026] S21. Design a three-dimensional solid model;

[0027] S22, STL file data conversion;

[0028] S23, hierarchical slicing and model analysis;

[0029] S24, adding supports and analyzing support forces;

[0030] S25, laser scanning and forming layer by layer to obtain a three-dimensional model of the product;

[0031] S26, processing the blank residual material and the blank surface.

[0032] Furthermore, the 3D printing equipment includes a paste barrel, a movable platform, an ejection cylinder, a laser head, a vibrating scraper and a stable magnetic field. The movable platform is arranged in the paste barrel, the output end of the ejection cylinder is connected to the movable platform, the laser head and the stable magnetic field are arranged above the paste barrel, and the vibrating scraper rotates and scrapes the ceramic paste in the paste barrel under the action of the stable magnetic field. The laser head solidifies the ceramic paste from bottom to top and grows into the blank according to the shape of the three-dimensional model blank of the product.

[0033] During the printing process, the vibrating scraper rotates and scrapes the paste under the action of a stable magnetic field, which can accelerate the removal of bubbles in the paste, thereby reducing the porosity of the printed body and improving the density.

[0034] Furthermore, the S40 is to place the green body obtained in S30 into a sintering furnace, heat it to 1500°C four times and sinter it in a vacuum, keep it warm for 25 hours, and then cool it by gradient to obtain the additive manufacturing product, wherein the total sintering time is 29 hours.

[0035] Furthermore, the step S40 specifically includes the following steps:

[0036] The green body obtained in S41 and S30 is placed in the sintering furnace, and the temperature of the sintering furnace is increased to 200°C at a rate of 1°C / min and sintered for 2 hours. While the temperature is increased, the green body is vacuumed for 1 hour to make the vacuum degree of the sintering furnace 0.1 MPa;

[0037] S42, heating the sintering furnace to 500° C. at a rate of 0.5° C. / min and sintering for 2 h, while vacuuming the furnace for 1 h, until the vacuum degree of the sintering furnace is 0.05 MPa;

[0038] S43, heating the sintering furnace to 1000° C. at a rate of 0.5° C. / min and sintering for 4 h, while vacuuming the furnace for 1 h, until the vacuum degree of the sintering furnace is 0.02 MPa;

[0039] S44, heating the sintering furnace to 1500° C. at a rate of 0.5° C. / min and sintering for 25 h, while vacuuming the furnace for 1 h to a vacuum degree of 0.01 MPa;

[0040] S45, cooling the blank to room temperature at a rate of 1°C / min to obtain the additively manufactured product.

[0041] The pressure provided by vacuum hot pressing promotes the flow of atoms within the particles. Pressure and surface energy act together as driving forces, enhancing diffusion. Because hot pressing can be performed at lower temperatures, grain growth is suppressed, resulting in a dense, uniform product with small grains and high strength.

[0042] The present invention also provides a product produced by the above-mentioned density-enhancing additive manufacturing method.

[0043] Compared with the existing technology, the density-enhancing additive manufacturing method provided by the present invention effectively improves the interlayer bonding strength of ceramic additively manufactured parts, improves the density of the molded parts, reduces the internal porosity of the molded parts, and also improves the bulk density of ceramic additively manufactured parts, thereby improving the comprehensive mechanical properties of ceramic additively manufactured parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0045] Figure 1 A flow chart for preparing ceramic paste provided in an embodiment of the present invention;

[0046] Figure 2 A schematic diagram of the structure of a 3D printing device provided in an embodiment of the present invention;

[0047] Figure 3 A sintering flow chart provided for an embodiment of the present invention;

[0048] Figure 4 This is an electron microscope image of the additive manufacturing product prepared in Example 1 of the present invention, with a scale of 2 μm;

[0049] Figure 5 This is an electron microscope image of the additive manufacturing product prepared in Example 2 of the present invention, with a scale of 2 μm. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0051] Example 1

[0052] A method for increasing density in additive manufacturing, comprising the following steps:

[0053] S10, preparation of ceramic paste: The raw materials of the ceramic paste include, by mass percentage, 40% 1000-mesh alumina, 15% 500-mesh alumina fiber powder, 10% composite additive, 15% anhydrous ethanol, and 20% liquid photosensitive resin, wherein the composite additive includes, by mass percentage, 40% calcium oxide, 30% magnesium oxide, and 30% silicon dioxide;

[0054] The production of ceramic paste specifically includes: Figure 1 The following steps are shown:

[0055] S11, adding alumina, alumina fiber powder, composite additives, anhydrous ethanol and liquid photosensitive resin into a closed reactor, stirring for 5 minutes, while adjusting the alternating temperature to -30±2°C to 60±2°C, to obtain a mixture A;

[0056] S12, stopping stirring of mixture A and allowing mixture A to rest for 10 minutes to obtain mixture B;

[0057] S13, stirring mixture B for 10 minutes, while adjusting the alternating temperature to -30±2°C to 60±2°C, to obtain mixture C;

[0058] S14, adjusting the temperature of the sealed reactor to room temperature, and evacuating the sealed reactor for 1 h until the vacuum degree of the sealed reactor reaches 0.1 MPa to obtain a mixture D;

[0059] S15, venting the closed reactor for 10 minutes to obtain the ceramic paste.

[0060] S20, 3D model design: Design the 3D model of the product through software, which specifically includes the following steps:

[0061] S21. Design a three-dimensional solid model;

[0062] S22, STL file data conversion;

[0063] S23, hierarchical slicing and model analysis;

[0064] S24, adding supports and analyzing support forces;

[0065] S25, laser scanning and forming layer by layer to obtain a three-dimensional model of the product;

[0066] S26, processing the blank residual material and the blank surface.

[0067] S30, additive manufacturing: printing the ceramic paste obtained in S10 into a blank designed in S20 through a 3D printing device;

[0068] in, Figure 2 As shown, the 3D printing device includes a paste barrel 10, a movable platform 11, an ejection cylinder 12, a laser head 13, a vibrating scraper 14 and a stable magnetic field 15. The movable platform 11 is arranged in the paste barrel 10, and the output end of the ejection cylinder 12 is connected to the movable platform 11. The laser head 13 and the stable magnetic field 15 are arranged above the paste barrel 10. The vibrating scraper 14 rotates and scrapes the ceramic paste 16 in the paste barrel 1 under the action of the stable magnetic field 15. The laser head 13 solidifies the ceramic paste 16 from bottom to top according to the shape of the product three-dimensional model blank and grows into a blank 17. As the blank 17 is printed layer by layer, the ejection cylinder 12 drives the movable platform 11 to move down from the paste barrel 10. It can be understood that the laser head 13 is controlled by the laser system. This is a common device and will not be described in detail.

[0069] S40, sintering: sintering the green body obtained in S30 to obtain an additive manufacturing product;

[0070] Sintering specifically includes Figure 3 The following steps are shown:

[0071] S41, placing the green body obtained in S30 into the sintering furnace, heating the furnace to 200° C. at a rate of 1° C. / min and sintering for 2 h, while vacuuming the furnace for 1 h until the vacuum degree of the sintering furnace is 0.1 MPa, to obtain a primary sintered product;

[0072] S42, heating the sintering furnace to 500° C. at a rate of 0.5° C. / min, sintering the primary sintered product for 2 h, and evacuating the furnace for 1 h while heating, so that the vacuum degree of the sintering furnace is 0.05 MPa, to obtain a secondary sintered product;

[0073] S43, heating the sintering furnace to 1000° C. at a rate of 0.5° C. / min and sintering the secondary sintered product for 4 hours, while vacuuming the furnace for 1 hour until the vacuum degree of the sintering furnace is 0.02 MPa, thereby obtaining a tertiary sintered product;

[0074] S44, heating the sintering furnace to 1500° C. at a rate of 0.5° C. / min, sintering the tertiary sintered product for 25 hours, and evacuating the furnace for 1 hour while heating, so that the vacuum degree of the sintering furnace is 0.01 MPa, to obtain a quadruple sintered product;

[0075] S45. Cooling the quadruple sintered product to room temperature at a rate of 1°C / min to obtain the additively manufactured product.

[0076] Example 2

[0077] Different from Example 1, the raw materials of the ceramic paste include: 30% 1000-mesh alumina, 15% 500-mesh alumina fiber powder, 10% composite additive, 25% anhydrous ethanol, and 20% liquid photosensitive resin, wherein the composite additive includes 60% calcium oxide, 20% magnesium oxide, and 20% silicon dioxide by mass percentage; the rest of the preparation process is the same as Example 1.

[0078] Example 3

[0079] Different from Example 1, the raw materials of the ceramic paste include: 45% 1000-mesh alumina, 10% 500-mesh alumina fiber powder, 5% composite additive, 20% anhydrous ethanol, and 20% liquid photosensitive resin, wherein the composite additive includes 50% calcium oxide, 25% magnesium oxide, and 25% silicon dioxide by mass percentage; the rest of the preparation process is the same as Example 1.

[0080] Comparative Example 1

[0081] The difference from Example 1 is that the raw materials of the ceramic paste include: 50% 1000-mesh alumina, 5% 500-mesh alumina fiber powder, 5% composite additive, 20% anhydrous ethanol, and 20% liquid photosensitive resin. The remaining raw materials and preparation process are the same as in Example 1.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that the temperature in step S11 and step S13 is adjusted to 60° C., and the remaining raw materials and preparation process are the same as in Example 1.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that steps S41-45 are not included. Step S40 is to place the green body obtained in S30 into the sintering furnace, heat it to 1500°C and evacuate it to a vacuum degree of 0.01 MPa and sinter it for 33 hours. The remaining raw materials and preparation process are the same as Example 1.

[0086] The additive manufacturing products obtained in Examples 1 and 2 were scanned by electron microscope, and the results were as follows: Figure 4 and Figure 5 As shown in the figure, it can be seen that the additive manufacturing product prepared by the present invention has extremely small shrinkage, high degree of densification, uniform microstructure and excellent comprehensive material performance.

[0087] The additively manufactured products produced in Examples 1-3 and Comparative Examples 1-3 were tested for relative density, hardness, flexural strength, and fracture toughness according to GB4472-1984 Determination of Relative Density of Chemical Products, GB / T230-91 Rockwell Hardness Test Method, GB / T4100-2006 Ceramics Flexural Strength Test Method, and GB / TA23806-2009 Fine Ceramics Fracture Toughness Test Method. The test results are shown in Table 1.

[0088] Table 1 Performance of products prepared by additive manufacturing

[0089] Relative density / % Hardness / Gpa Flexural strength / Mpa <![CDATA[Fracture toughness / Mpa m 1 / 2 > Example 1 100 25 1200 8 Example 2 98 27 1230 10 Example 3 99 26 1180 9 Comparative Example 1 92 20 1080 5.5 Comparative Example 2 89 24 1120 6.8 Comparative Example 3 94 24 1185 7

[0090] As can be seen from Table 1, the products produced by the additive manufacturing method provided by the present invention have a relative density of more than 98. It can be seen that this method can effectively reduce the internal porosity of the additively manufactured products and improve the density of the products. At the same time, the products have excellent mechanical properties and are therefore particularly suitable for the preparation of precision structural parts.

[0091] From the comparison results of Example 1 and Comparative Examples 1-3, it can be seen that the method provided by the technical solution of the present invention effectively improves the interlayer bonding strength of ceramic additively manufactured molded parts by performing special treatments in the three key steps of alumina ceramic paste preparation, green body additive manufacturing and green body sintering, thereby increasing the density of the molded parts and reducing the internal porosity of the molded parts. Therefore, the three key processes are indispensable.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 method for increasing density of additive manufacturing, characterized in that: The following steps are involved: S10, preparation of ceramic paste: The raw materials of the ceramic paste include, by mass percentage: 30-45% of 1000-mesh alumina powder, 10-15% of 500-mesh alumina fiber powder, 5-10% of composite additive, 20-25% of anhydrous ethanol, and 20% of liquid photosensitive resin, wherein the composite additive includes calcium oxide, magnesium oxide, and silicon dioxide; S20, 3D model design: Design the 3D model of the product through software; S30, additive manufacturing: printing the ceramic paste obtained in S10 into a blank designed in S20 through a 3D printing device; S40, sintering: sintering the green body obtained in S30 to obtain an additive manufacturing product; The S10 specifically includes the following steps: S11, adding the alumina, alumina fiber powder, composite additive, anhydrous ethanol and liquid photosensitive resin into a closed reactor, stirring for 5 minutes, and adjusting the alternating temperature to -30±2°C to 60±2°C while stirring; S12, stop stirring and let the mixture stand for 10 minutes; S13, start stirring for 10 minutes, while adjusting the alternating temperature to -30±2℃~60±2℃; S14, after adjusting the temperature of the closed reactor to room temperature, evacuate the closed reactor for 1 h until the vacuum degree of the closed reactor reaches 0.1 MPa; S15, exhausting the closed reactor for 10 minutes to obtain the ceramic paste; The step S40 is to place the green body obtained in step S30 into a sintering furnace, heat it to 1500° C. for four times, sinter it under vacuum, and then cool it in a gradient manner to obtain the additive manufacturing product. The S40 specifically includes the following steps: The green body obtained in S41 and S30 is placed in the sintering furnace, and the temperature of the sintering furnace is increased to 200°C at a rate of 1°C / min and sintered for 2 hours. While the temperature is increased, the green body is vacuumed for 1 hour to make the vacuum degree of the sintering furnace 0.1 MPa; S42, heating the sintering furnace to 500° C. at a rate of 0.5° C. / min and sintering for 2 h, while vacuuming the furnace for 1 h, until the vacuum degree of the sintering furnace is 0.05 MPa; S43, heating the sintering furnace to 1000° C. at a rate of 0.5° C. / min and sintering for 4 h, while vacuuming the furnace for 1 h, until the vacuum degree of the sintering furnace is 0.02 MPa; S44, heating the sintering furnace to 1500° C. at a rate of 0.5° C. / min and sintering for 25 h, while vacuuming the furnace for 1 h to a vacuum degree of 0.01 MPa; S45, cooling the blank to room temperature at a rate of 1°C / min to obtain the additively manufactured product.

2. The method for increasing density of additive manufacturing according to claim 1, wherein: Calculated by mass percentage, the composite auxiliary agent includes 40-60% calcium oxide, 20-30% magnesium oxide and 20-30% silicon dioxide.

3. The additive manufacturing method for increasing density according to claim 1, wherein: The 3D printing equipment includes a paste barrel, a movable platform, an ejection cylinder, a laser head, a vibrating scraper and a stable magnetic field. The movable platform is arranged in the paste barrel, and the output end of the ejection cylinder is connected to the movable platform. The laser head and the stable magnetic field are arranged above the paste barrel. The vibrating scraper rotates and scrapes the ceramic paste in the paste barrel under the action of the stable magnetic field. The laser head solidifies the ceramic paste from bottom to top and grows it into the blank according to the shape of the three-dimensional model blank of the product.

4. A product obtained by the additive manufacturing method for increasing density according to any one of claims 1 to 3.

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