Cross-scale porous structure and 3D printing forming method and device

Abstract

The invention discloses a cross-scale porous structure and a 3D printing forming method and device, and belongs to the technical field of polymer 3D printing. The method comprises the following steps: heating and melting a polymer wire, injecting gas into a molten polymer so as to form bubbles in the molten polymer, extruding the bubbles in the molten polymer into a vacuum environment along with the molten polymer, and performing 3D printing to form a lattice structure, the macroscopic lattice structure is formed by the bubbles, the macroscopic lattice structure is internally provided with micro-scale holes formed after the bubbles are expanded and cured under the vacuum condition, and the micro-scale holes and the macroscopic lattice structure are combined to form a cross-scale porous structure. Micropores formed by thermal expansion growth of vacuum micropores are combined with macropores of a lattice structure to form a cross-scale effect.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer 3D printing, and in particular to a cross-scale porous structure, a 3D printing forming method and a device. Background Art

[0002] Porous polymer materials and structures have the characteristics of light weight, high specific strength, good thermal insulation and sound absorption, and excellent impact resistance. They are widely used in lightweight components, absorbing materials, thermal insulation materials and other fields to meet the needs of lightweight and multifunctional integration, especially cross-scale porous materials, which combine macro-scale pores with micro-scale pores and use the macro-micro synergistic scale effect to further enhance the load-bearing and function of porous materials. However, traditional porous materials are often prepared by microporous foaming molding technology, which makes it difficult to achieve the free forming of complex porous structures and the precise control of macro-micro pore morphology, limiting the application scope of porous structures.

[0003] 3D printing technology has the ability to form complex structures in an integrated manner, which broadens the freedom of design and manufacturing of porous structures. However, at present, high-performance polymers represented by special engineering plastics such as polyetheretherketone and polyimide are mainly manufactured by 3D printing processes such as material extrusion molding and powder bed melting. Limited by the molding accuracy of such processes, porous structures are mainly composed of macroscopic structural pores, and it is difficult to achieve the preparation of micro-scale pore structures. To achieve the manufacture of micro-scale pores, it mainly relies on high-resolution 3D printing technologies such as digital light processing, photocuring, and ink direct writing. However, such processes mainly use low-viscosity and low-surface tension polymers such as photocurable resins as raw materials. Although they can realize the manufacture of cross-scale porous structures, their mechanical properties are often relatively poor. 3D printing technology for cross-scale porous structures of high-performance polymers is still under development. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems in the prior art and provide a cross-scale porous structure, a 3D printing forming method and a device, which utilizes a vacuum environment to drive bubble growth to achieve the manufacture of a microscopic pore structure, and then integrates the microscopic pore structure into a macroscopic lattice structure to achieve the manufacture of a cross-scale porous structure.

[0005] The present invention provides a cross-scale porous structure 3D printing forming method, which comprises heating and melting a polymer filament, injecting gas into the molten polymer to form bubbles in the molten polymer, and extruding the bubbles in the molten polymer into a vacuum environment to form a lattice structure. The lattice structure has microscale pores formed by the bubbles expanding and solidifying under vacuum conditions. The lattice structure is macroscale pores, and a porous structure having macroscale pores and the microscale pores is a cross-scale porous structure.

[0006] Preferably, the injected gas is injected into the molten polymer in multiple groups of airflows, and the number of the multiple groups of airflows and the gas flow rate are adjusted according to the size of the porosity inside the melt and the distribution of the microscale pores.

[0007] Preferably, the polymer filament is a thermoplastic polymer filament or a composite polymer filament containing chopped or continuous fibers inside.

[0008] Preferably, the polymer filament includes polylactic acid, nylon, polycarbonate, polyurethane, polyetheretherketone or polyimide.

[0009] Preferably, the injected gas is air, nitrogen or helium.

[0010] The present invention also discloses a cross-scale porous structure prepared by the above cross-scale porous structure 3D printing forming method. The cross-scale porous structure includes a skin and a lattice structure located on the skin. The skin is formed by 3D printing under vacuum conditions without injecting gas during 3D printing. The lattice structure includes a plurality of unit cells, and the plurality of unit cells are periodically arranged in an array to form macroscale pores of the cross-scale porous structure, and each unit cell has microscale pores.

[0011] Preferably, the configuration of the unit cell in the lattice structure is one or a combination of more of body-centered cubic, honeycomb, and cross grid.

[0012] The present invention also provides a device adopting the above cross-scale porous structure 3D printing forming method, including a 3D printer. The 3D printer includes a polymer filament feeding unit. The 3D printer is placed in a vacuum chamber. The nozzle of the 3D printer is a bubble injection nozzle, and the bubble injection nozzle includes: A heating and melting head, having a first flow channel and a second flow channel that are connected up and down. The first flow channel is located above the second flow channel, and the inner diameter of the first flow channel is larger than that of the second flow channel. A plurality of air intake channels are connected to the outer periphery of the top of the first flow channel, and the polymer filament enters the heating and melting head from the top of the first flow channel through the feeding unit. A plurality of gas cores, corresponding to the number of the air intake channels one by one. A gas channel is arranged inside the gas core, and a microporous array plate is arranged at the entrance of the gas channel. The gas channel is communicated with the air intake channel. A gas delivery unit, including a gas supply assembly, a gas preheating pipe and a gas diverter that are connected in sequence. A pressure monitoring module and a flow monitoring module are arranged on the connecting pipeline between the gas supply assembly and the gas diverter. The gas diverter has a plurality of gas outlets, and each gas outlet is respectively communicated with the gas channel of the gas core one by one. A temperature control device, arranged outside the heating and melting head for heating the heating and melting head and regulating the temperature inside the heating and melting head.

[0013] Preferably, the temperature control device includes a heating block sleeved on the heating and melting head, as well as heating rods and temperature sensors located on the outer periphery of the heating and melting head. The heating rods and temperature sensors are evenly distributed on the outer periphery of the heating and melting head.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention utilizes the pressure difference enhancement effect in a vacuum environment to overcome the large surface tension of high-performance polymers, realizing the expansion growth of microvoids. At the same time, combined with the vacuum slow heating effect, it provides a longer time for the growth of microvoids, ensuring that the microvoids have a certain size, breaking through the limitation of the forming accuracy of polymer 3D printing methods such as material extrusion forming, and providing a new method for the preparation of high-performance polymer porous structures. The porosity of the cross-scale porous structure prepared by the vacuum microvoid thermal expansion 3D printing method of the present invention is significantly improved, and the retention rates of tensile strength and modulus are high, with high mechanical properties.

[0015] The 3D printing forming method of the cross-scale porous structure proposed by the present invention combines the microvoids formed by vacuum microvoid thermal expansion growth with the macrovoids of the lattice structure to form a cross-scale effect, enabling the porous structure to achieve load-bearing-functional integration. At the same time, due to the characteristics of discrete forming in 3D printing, the distribution, morphology, etc. of macroscale pores and microscale pores can be dynamically adjusted, thereby enabling the controllable manufacturing of the performance of the cross-scale porous structure.

[0016] The cross-scale porous structure of the present invention can regulate crack deflection through the distribution of microscale pores. At the same time, combined with the metamaterial characteristics of the macro lattice structure, it not only has excellent mechanical properties such as impact resistance and shock absorption, but also has functionality in aspects such as heat insulation, sound absorption, and electromagnetic shielding. In addition, the polymers used can be characteristic engineering plastics such as polyether ether ketone and polyimide, which also show excellent performance in terms of high and low temperature resistance and corrosion resistance. Therefore, the prepared cross-scale porous structure has excellent comprehensive performance and has potential application prospects in fields such as aerospace, automotive transportation, and biomedicine. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the vacuum microvoid thermal expansion 3D printing method of the present invention.

[0018] Figure 2 It is a schematic diagram of the bubble injection nozzle device of the present invention.

[0019] Figure 3 It is a schematic diagram of the gas delivery unit device of the present invention.

[0020] Figure 4 It is a schematic diagram of the heating and melting head device of the present invention.

[0021] Figure 5 It is a schematic diagram of the gas core device of the present invention.

[0022] Figure 6 This is a schematic diagram of the temperature control device of the present invention.

[0023] Figure 7 This is a schematic diagram of the cross-scale porous structure of the present invention.

[0024] Figure 8 This is a microstructural diagram of the samples of vacuum 3D printing and atmospheric pressure 3D printing of the present invention.

[0025] Figure 9 This is a mechanical property diagram of the samples of vacuum 3D printing and atmospheric pressure 3D printing of the present invention.

[0026] Explanation of reference numerals: 1. Skin; 2. Lattice structure; 21. Unit cell; 3. Bubble injection nozzle; 4. Feeding unit; 5. Heating and melting head; 51. First flow channel; 52. Second flow channel; 53. Intake channel; 6. Gas core; 61. Gas channel; 62. Microporous array plate; 7. Gas delivery unit; 71. Gas supply component; 72. Gas preheating tube; 73. Gas diverter; 8. Temperature control device; 81. Heating block; 82. Heating rod; 83. Temperature sensor; 9. Melting section; 10. Solidification section; 11. Vacuum chamber; 12. Microscale pores; 13. Polymer filament. Detailed implementation manners

[0027] To make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Apparently, the described embodiments are some but not all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0028] Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present disclosure pertains. The "first", "second" and similar terms used in the present disclosure do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "include" or "comprise" mean that the elements or objects appearing before "include" or "comprise" cover the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. The terms such as "connect" or "be connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationships may also change accordingly.

[0029] The cross-scale porous structure 3D printing and forming method proposed by the present invention places the material extrusion forming 3D printing process in a vacuum environment. When the polymer filament 13 melts, micro-pore bubbles are injected into it. When extruding and depositing, the pressure difference between the micro-pore bubbles and the vacuum environment is used to drive the growth of the bubbles. Combining the vacuum slow heating effect to increase the bubble growth temperature window, the surface tension of the high-viscosity polymer is overcome under the coupling drive of heat and pressure to prepare micro-pores. At the same time, the micro-pore characteristics are integrated into the macroscopic lattice structure to design a cross-scale porous structure, realizing the multi-functional integrated manufacturing of high-performance polymer porous insulation structures. Based on the vacuum micro-pore thermal expansion 3D printing method, the customized preparation of cross-scale porous structures represented by high-performance polymers such as polyether ether ketone and polyimide is realized, achieving the integration of structure and function, and having application potential in the fields of bio-inspired bone, insulation structures, sound insulation structures, etc.

[0030] A cross-scale porous structure 3D printing and forming method provided in this embodiment includes heating and melting the polymer filament 13, injecting gas into the molten polymer to form bubbles in the molten polymer. The bubbles in the molten polymer are extruded with the molten polymer into a vacuum environment to 3D print a lattice structure 2. The lattice structure 2 has micro-scale pores 12 formed after the bubbles expand and solidify under vacuum conditions. The lattice structure 2 is the macro-scale pore, and the porous structure with the macro-scale pore and the micro-scale pores 12 is the cross-scale porous structure. In this embodiment, after the polymer filament 13 is heated and melted, gas is injected into the molten polymer. The injected gas forms bubbles in the molten polymer. The bubbles are extruded into the vacuum environment together with the melt. The vacuum environment can have two effects on the melt. On the one hand, it is the pressure difference enhancement effect. There is a large pressure difference between the gas inside the bubble and the external vacuum environment, which can drive the bubble to expand and grow outward. On the other hand, it is the vacuum slow heating effect. In the vacuum environment, there is no air medium, and the convective heat dissipation of the melt disappears. It can only dissipate heat outward through radiative heat dissipation, and the heat dissipation speed is slow. The solidification rate of the melt slows down, and there is a longer melting section 9 compared to the atmospheric pressure environment, ensuring that the bubbles have a longer expansion and growth time and are shaped in the solidification section 10 to form micro-pores.

[0031] As a preferred embodiment, the gas is injected into the molten polymer in multiple groups of airflows, and the number and gas flow rate of the multiple groups of airflows are adjusted according to the size of the porosity inside the melt and the distribution of the micro-scale pores 12.

[0032] As a preferred embodiment, the polymer filament 13 is a thermoplastic polymer filament or a composite polymer filament containing short-cut or continuous fibers inside. As a preferred embodiment, the polymer filament 13 includes polylactic acid, nylon, polycarbonate, polyurethane, polyether ether ketone or polyimide.

[0033] As a preferred embodiment, the injected gas is air, nitrogen or helium.

[0034] This embodiment also discloses a cross-scale porous structure prepared by the above cross-scale porous structure 3D printing and forming method. The cross-scale porous structure includes a skin 1 and a lattice structure 2 located on the skin 1. In this embodiment, no gas is injected during the 3D printing of the skin 1 in a vacuum environment; the lattice structure 2 includes a plurality of unit cells 21, and the plurality of unit cells 21 are periodically arranged in an array to form the macro-scale pores of the cross-scale porous structure. Each unit cell 21 has micro-scale pores 12. Refer to Figure 7 , the skin 1 of this embodiment adopts a solid structure and no bubbles are injected during 3D printing under vacuum conditions to ensure certain mechanical properties. The lattice structure 2 is formed by periodically arranging unit cells 21 to form the macro-scale pores of the cross-scale porous structure. When printing each unit cell 21, a bubble injection nozzle 3 is used to print with a polymer filament 13 as the raw material in a vacuum environment. Bubbles are injected into the melt during the printing process, and the bubbles are driven to expand and grow under the dual action of enhanced vacuum pressure difference and vacuum slow heating to form micro-scale pores 12 inside the polymer, and finally the preparation of the cross-scale porous structure is completed.

[0035] Refer to Figure 1 , the porosity of the cross-scale porous structure in this embodiment can be changed by adjusting the macro-scale pores and the micro-scale pores 12. The proportion of the macro-scale pores can be changed by adjusting the size, density, etc. of the unit cells 21. The micro-scale pores 12 can be changed by changing parameters such as the number of gas channels 61 and the gas flow rate. The distribution of the pores in the cross-scale porous structure can be uniform or gradient distribution, which is mainly achieved by adjusting the morphology of the macro-scale pores and the micro-scale pores 12 in real time during the 3D printing process.

[0036] As a preferred embodiment, the configuration of the unit cells 21 in the lattice structure 2 is one or a combination of body-centered cubic, honeycomb, and cross grid.

[0037] This embodiment also provides a device using the above cross-scale porous structure 3D printing and forming method, including a 3D printer. The 3D printer includes a feeding unit 4 for the polymer filament 13. The 3D printer is placed in a vacuum chamber 11. The nozzle of the 3D printer in this embodiment is a bubble injection nozzle 3. The bubble injection nozzle 3 includes a heating and melting head 5. The heating and melting head 5 has a first flow channel 51 and a second flow channel 52 that are connected up and down. The first flow channel 51 is located above the second flow channel 52, and the inner diameter of the first flow channel 51 is larger than the inner diameter of the second flow channel 52. A plurality of air intake channels 53 are connected to the outer periphery of the top of the first flow channel 51. The polymer filament 13 enters the heating and melting head 5 from the top of the first flow channel 51 through the feeding unit 4; A plurality of gas cores 6, which are in one-to-one correspondence with the number of the intake channels 53. A gas channel 61 is arranged inside the gas core 6, and a microporous array plate 62 is arranged at the entrance of the gas channel 61. The gas channel 61 is communicated with the intake channel 53; A gas delivery unit 7, which includes a gas supply component 71, a gas preheating pipe 72 and a gas diverter 73 that are connected in sequence. A pressure monitoring module and a flow monitoring module are arranged on the connecting pipeline between the gas supply component 71 and the gas diverter 73. The gas diverter 73 has a plurality of gas outlets, and each gas outlet is respectively communicated with the gas channel 61 of each gas core 6 in one-to-one correspondence; A temperature control device 8, which is arranged outside the heating melt head 5 to heat the heating melt head 5 and regulate the temperature inside the heating melt head 5.

[0038] Refer to Figure 2 , the 3D printer in this embodiment is a material extrusion forming 3D printer. The material extrusion forming 3D printer is placed in a vacuum environment. The polymer wire 13 is fed into the heating melt head 5 through the feeding unit 4 for heating and melting inside. The temperature control device 8 heats and melts the polymer wire 13 in the heating melt head 5. At the same time, the gas delivery unit 7 sends external gas into the heating melt head 5 through pipelines and gas cores 6. To ensure that the gas enters the heating melt head 5 evenly, a plurality of evenly distributed pipelines are used to inject gas into the inside, and each gas core 6 is connected to the heating melt head 5.

[0039] Refer to Figure 3 , the gas delivery unit 7 is composed of a gas supply component 71, a pressure monitoring module, a flow monitoring module, a gas preheating pipe 72 and a gas diverter 73. In this embodiment, the gas supply component 71 supplies gas in the way of a gas syringe, and pushes the gas outwards through a piston push method, and cooperates with the pressure detection module and the flow detection module to realize the stable delivery of gas. The gas preheating pipe 72 heats the gas to prevent the melt from being cooled when the cold gas enters the heating melt head 5. The gas diverter 73 disperses the gas into multiple paths and transports them one by one into different pipelines and gas cores 6.

[0040] Refer to Figure 4 , the melting cavity inside the heating melt head 5 in this embodiment adopts a two-stage structure. The upper part is a large-diameter flow channel, that is, the first flow channel 51, which is used for mixing bubbles with the molten polymer wire 13. The lower part is a small-diameter flow channel, that is, the second flow channel 52. The change in diameter promotes the full flow of the molten polymer wire 13 and the bubbles to achieve uniform mixing.

[0041] Refer to Figure 5 , a gas channel 61 is arranged inside the gas core 6 in this embodiment, and a microporous array plate 62 is arranged at the entrance. There are evenly distributed microporous arrays inside to disperse the gas to form bubbles.

[0042] Reference Figure 6 As shown in Figure 6 , the temperature control device 8 of this embodiment is composed of a heating block 81, a heating rod 82, and a temperature sensor 83. The heating block 81 is wrapped outside the heating melt head 5, and the heating rod 82 and the temperature sensor 83 are evenly distributed to achieve precise temperature control of different regions of the heating melt head 5.

[0043] To verify the printing effect of the above cross-scale porous structure 3D printing forming method of this embodiment, short carbon fiber reinforced polyether ether ketone (SCF / PEEK) filaments are selected in this embodiment to carry out experiments. The results are as Figure 8 shown. Due to the addition of short carbon fibers, the SCF / PEEK filaments have the characteristics of high hardness and high viscosity of the filament melt, and it is difficult to flow and compress during the extrusion process. There are many air pores inside the SCF / PEEK filaments, and the bubble content in the SCF / PEEK filaments reaches about 8%. For the convenience of comparison, the short carbon fiber reinforced polyether ether ketone (SCF / PEEK) filaments are 3D printed in atmospheric pressure and vacuum environments respectively. The results show that the microstructure of the specimens 3D printed in the vacuum environment presents thin-walled porous characteristics, and the porosity reaches more than 20%, which is significantly improved compared with the 2% porosity of the specimens 3D printed in the atmospheric pressure environment. Moreover, the bubble pore size of the specimens 3D printed in the vacuum environment increases from 20μm - 30μm to about 100μm, which proves the feasibility of the principle of driving the expansion and growth of microbubbles by the vacuum environment in this embodiment. And as Figure 9 shown, the tensile strength and modulus retention rates of the specimens 3D printed in the vacuum environment reach more than 70% and more than 67% respectively, and still can maintain good mechanical properties. Therefore, the tensile strength and modulus retention rates of the specimens 3D printed in the vacuum environment of this embodiment are significantly better than those of the specimens 3D printed in the atmospheric pressure environment.

[0044] This embodiment utilizes the pressure difference enhancement and vacuum slow heating effects brought by the vacuum environment, breaks through the high surface tension of the polymer melt under the drive of thermo-mechanical coupling to realize the expansion and growth of bubbles, obtains a micro-porous structure, and integrates it into the macroscopic lattice structure 2 to form a cross-scale porous structure, providing a new method for the preparation of high-performance polymer porous structures. Under the synergistic effect of the macro-micro pore scales, the porous structure-functional integration forming is realized, so that the porous structure has both excellent mechanical properties and special functions.

[0045] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A 3D printing forming method for cross-scale porous structures, characterized in that After heating and melting the polymer filament, gas is injected into the molten polymer to form bubbles in the molten polymer. The bubbles in the molten polymer are extruded with the molten polymer into a vacuum environment for 3D printing into a lattice structure, and the lattice structure has micro-scale pores formed by the expansion and solidification of the bubbles under vacuum conditions.

2. The 3D printing forming method of the cross-scale porous structure according to claim 1, characterized in that The gas injection is divided into multiple groups of airflows injected into the molten polymer, and the number and gas flow rate of the multiple groups of airflows are adjusted according to the size of the porosity inside the melt and the distribution of the micro-scale pores.

3. The 3D printing forming method of the cross-scale porous structure according to claim 1, characterized in that The polymer filament is a thermoplastic polymer filament or a composite thermoplastic polymer filament containing short-cut or continuous fibers inside.

4. The 3D printing forming method of the cross-scale porous structure according to claim 1, wherein The polymer filament includes polylactic acid, nylon, polycarbonate, polyurethane, polyetheretherketone or polyimide.

5. The 3D printing forming method of the cross-scale porous structure according to claim 1, characterized in that, The injected gas is air, nitrogen or helium.

6. The cross-scale porous structure printed by the cross-scale porous structure 3D printing forming method according to any one of claims 1-5, characterized in that, The cross-scale porous structure includes a skin and a lattice structure located on the skin. The skin is formed by 3D printing under vacuum conditions and no gas is injected during 3D printing; the lattice structure includes multiple unit cells, and the multiple unit cells are periodically arranged in an array to form macro-scale pores of the cross-scale porous structure, and each unit cell has micro-scale pores.

7. The cross-scale porous structure according to claim 6, wherein The configuration of the unit cell in the lattice structure is one or a combination of body-centered cubic, honeycomb, and cross-grid.

8. An apparatus for the cross-scale porous structure 3D printing forming method according to claim 1, comprising a 3D printer, the 3D printer including a feeding unit for polymer filaments, characterized in that, The 3D printer is placed inside a vacuum chamber, and the nozzle of the 3D printer is a bubble injection nozzle, and the bubble injection nozzle includes; A heating and melting head, having a first flow channel and a second flow channel that communicate up and down. The first flow channel is located above the second flow channel, and the inner diameter of the first flow channel is larger than that of the second flow channel. A plurality of air intake channels are connected to the outer periphery of the top of the first flow channel, and the polymer filament enters the heating and melting head from the top of the first flow channel through a feeding unit; A plurality of gas cores, corresponding to the number of the air intake channels one by one. A gas channel is arranged inside the gas core, and a microporous array plate is arranged at the entrance of the gas channel, and the gas channel communicates with the air intake channel; A gas delivery unit, including a gas supply component, a gas preheating pipe and a gas splitter that are connected in sequence. A pressure monitoring module and a flow monitoring module are provided on the connecting pipeline between the gas supply component and the gas splitter. The gas splitter has a plurality of gas outlets, and each gas outlet is respectively communicated with the gas channels of each gas core one by one; A temperature control device, arranged outside the heating and melting head for heating the heating and melting head and regulating the temperature inside the heating and melting head.

9. The device according to claim 8, characterized in that The temperature control device includes a heating block sleeved outside the heating and melting head and heating rods and temperature sensors located on the outer periphery of the heating and melting head and the heating block. The heating rods and the temperature sensors are evenly distributed on the outer periphery of the heating and melting head.

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