Additive manufacturing method of a biomimetic functionally graded thermal protection structure

Abstract

The application discloses an additive manufacturing method of a bionic functional gradient heat protection structure and belongs to the technical field of additive manufacturing. The method designs a heat protection structure skin structure as a heat insulation layer, a heat absorption layer and a bearing layer, the heat insulation layer is composed of low-thermal-conductivity ablation-resistant heat protection materials, the heat absorption layer is composed of heat insulation honeycomb plates and expanded foam materials, and the bearing layer is composed of a functionally gradient material tree root bionic structure integrally formed through additive manufacturing. The method comprises the following steps: determining the size of a three-dimensional model of a skin and a frame of a heat protection structure workpiece; inputting bearing and heat insulation requirements; topological optimization of a tree root bionic structure; selection of a functionally gradient layer composition gradient; designing a three-dimensional model of a bionic structure; simulation verification of design parameters; slicing of the three-dimensional model and planning of a laser processing path; adding heat absorption foam materials inside the heat insulation honeycomb plates; coating the surface of the heat absorption layer with heat protection materials; and post-processing to obtain a final formed piece. The application realizes the preparation of a bionic functional gradient heat protection structure skin facing the additive manufacturing technology, has excellent heat insulation performance, a lightweight structure, strong designability, high mechanical properties and other characteristics, has wide application potential in the fields of aerospace and national defense and military affairs, and expands the application prospect of additive manufacturing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of additive manufacturing technology, and particularly relates to an additive manufacturing method for realizing the bionic functional characteristics by using bionic structures and functionally graded materials. BACKGROUND

[0002] The flight task of the space-earth round-trip transportation system generally experiences three stages: a launch stage, an on-orbit operation stage and a reentry into the atmosphere and return landing stage. Among them, the reentry into the atmosphere stage is the most complex, which refers to the process that the spacecraft reaches the atmosphere of the celestial body on which it lands along the changed orbit, safely passes through the atmosphere and finally lands safely on the celestial body by using atmospheric deceleration, which is simply referred to as the reentry process. In short, reentry refers to the flight of the spacecraft from outside the atmosphere into the atmosphere again. During the operation process, the temperature difference between the two sides of some components of the spacecraft is as high as 1000 DEG C, and the materials used need to withstand huge thermal expansion stress, and the stress concentration phenomenon is very significant. At this time, the traditional single-phase and homogeneous materials cannot be applied to this service environment. Therefore, the new laser additive manufacturing technology of functionally graded materials gradually replaces the traditional milling and welding technology, which can greatly improve the high-temperature resistance, wear resistance and mechanical properties of the components.

[0003] So far, among the already published patents, although the invention has realized a lightweight metal matrix lattice heat-insulating-bearing structure and its forming, the method does not consider that the residual thermal stress after laser additive manufacturing will cause the combination interface to crack easily due to the large difference in thermophysical properties between the skin and the frame of the metal and ceramic, and even the functionally graded layer with composition transition characteristics is also difficult to meet the requirements of the harsh service environment. SUMMARY

[0004] In view of the above-mentioned deficiencies of the existing device, the present application designs an additive manufacturing method of bionic functionally graded thermal protection structure, wherein the skin of the thermal protection structure is designed by means of various bionic structures such as the shell of the cochlea, the honeycomb, the tree root and the like, and new functionally graded materials, heat-insulating and heat-absorbing materials and the like are used to further improve the heat-insulating and bearing capacity of the sole, which not only has excellent heat-insulating performance, lightweight structure, strong designability and the like, but also the firm tree root structure inhibits the cracks at the interface between the skin and the frame, and meets the harsh service requirements of the spacecraft.

[0005] In order to achieve the above object, the application provides an additive manufacturing method of a bionic functional gradient heat protection structure, which refers to the layered structure of the shell of a snail to design the heat protection structure as a heat insulation layer, a force bearing layer and a framework layer; the main structure of the heat insulation layer is a heat insulation honeycomb board, and an expanded foam material based on phase change heat absorption is added in the interior of the board; the force bearing layer is the core of a heat-force performance transition layer skin structure, mainly composed of a functional gradient layer and a pure metal tree root-like bionic structure, the functional gradient layer is a metal matrix composite material added with ceramic particles, and the ceramic particles are gradually increased along the normal direction from the framework layer to the heat insulation layer; the tree root-like bionic structure is composed of pure metal, and the triangle formed by the main root, the lateral root and the functional gradient layer has structural stability, which enables the framework and the skin to be safely and efficiently connected, and the force bearing layer is printed layer by layer through a laser melting deposition process; the method comprises the following steps:

[0006] 1) Obtain the three-dimensional model size of the heat-resistant bionic skin area of the heat protection structure workpiece, such as the radius and thickness, determine the size of the additive area and perform preliminary pretreatment thereon;

[0007] 2) According to the engineering requirements, determine the heat insulation and insulation capacity required by the functional characteristics of the heat protection structure, which is specifically manifested as the heat flow size that can be borne within a certain time; and determine the bionic structure bearing capacity of the performance constraint condition, which is specifically manifested as the bionic structure not being damaged under the application of a certain normal and torsional load;

[0008] 3) According to the heat insulation and bearing capacity required by the heat protection structure, topological optimization of the honeycomb and tree root structure is performed on the new functional gradient material, so as to achieve reasonable topological design of the two-dimensional planar structure and the three-dimensional entity structure and thus realize good heat-force performance;

[0009] 4) After the bionic structure of the heat protection structure is determined, the composition gradient of the force bearing layer needs to be selected; the composition gradient is that the metal A at the bottom area is gradually changed into the metal A matrix composite material added with b% ceramic particles; the design of the composition gradient needs to determine the content of the ceramic particles at the top along the normal direction, and the gradient size c% of each layer of the layered slice is selected, so as to facilitate the material filling in the printing process;

[0010] 5) Design a three-dimensional model according to the topological optimization parameters and the composition gradient parameters, and perform thermal and mechanical analysis through a finite element software to obtain the temperature field, stress and strain distribution of the bionic functional gradient heat protection structure, if the numerical simulation result can meet the functional characteristic requirements of the heat protection structure, the bionic structure is finalized; if the functional characteristic requirements of the heat protection structure cannot be met, the parameters are reset;

[0011] 6) The digital three-dimensional model of the bionic workpiece to be printed is divided into units and layers, and the processing path of laser additive manufacturing is generated according to the layer-by-layer cycle mode;

[0012] 7) The metal A powder is used as the material of the powder feeding barrel I, and the metal A matrix composite with a% ceramic particle powder is used as the material of the powder feeding barrel II, and different composition gradients are realized by adjusting the rotating speeds of the two powder feeding barrels, and attention should be paid to the position and printing length of the root structure at each layer during coaxial powder feeding printing; the laser parameters, motion parameters and the like in the laser additive manufacturing process are determined according to the composition, heat accumulation and the like;

[0013] 8) The expansion foam material based on phase change heat absorption is added in the heat insulation layer structure after printing is completed;

[0014] 9) The low-thermal-conductivity ablation-resistant heat protection material is coated on the upper part of the heat insulation layer structure after printing is completed, and the final shaped part is obtained through milling and post-processing.

[0015] Further, the additive manufacturing method of the bionic functional gradient heat protection structure is characterized in that the diameter of the trunk part of the root structure is greater than 50 mm, the diameter of the main root is greater than 10 mm, the diameter of the lateral root is greater than 5 mm, and the distribution of the lateral root is at an angle of 30 ° ~ 60 °

[0016] Further, the additive manufacturing method of the bionic functional gradient heat protection structure is characterized in that the metal material is one or a combination of titanium alloy and aluminum alloy, and the ceramic particles are one or a combination of TiC, TiN, TiB and WC.

[0017] Further, the additive manufacturing method of the bionic functional gradient heat protection structure is characterized in that the laser additive process is laser melting deposition, and the process satisfies: laser power 1200 W~1600 W, laser beam spot diameter 3 mm, scanning speed 0.08~0.12 m / s, and scanning interval 1.8 mm.

[0018] Further, the additive manufacturing method of the bionic functional gradient heat protection structure is characterized in that the expansion foam material can be any one or a mixture of any several of rigid polyurethane foam, silicone rubber foam or polystyrene foam.

[0019] Further, the additive manufacturing method of the bionic functional gradient heat protection structure is characterized in that the low-thermal-conductivity ablation-resistant heat protection material can be any one or a mixture of any several of glass fiber reinforced phenolic resin material, phenolic resin impregnated carbon fiber skeleton material or fiber woven body reinforced heat protection material.​

[0020] The application has the advantages and positive effects of:

[0021] The method is based on the superior performance of snail shells, and designs the skin structure as a heat insulation layer, a heat absorption layer and a bearing layer. The optimal topology configuration of the structure is researched based on a material model, the functionally graded material is reasonably designed in two dimensions and three dimensions, and finally a precise optimization design scheme of the structure and performance of each region of the large base is formed. The method realizes the overall structure design through the principle of structural bionics, has excellent heat insulation performance, lightweight structure, strong designability, high mechanical performance and other characteristics, and can be applied to the load-heatproof integrated design of recyclable spacecraft (return capsule, rocket tank structure). BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 is a schematic diagram of the cross-sectional structure of the bionic functionally graded thermal protection structure of the application;

[0023] Fig. 2 is a schematic diagram of the bionic tree root structure of the application;

[0024] Fig. 3 is a flowchart of the preparation of the bionic functionally graded thermal protection structure of the application.

[0025] In the drawings:

[0026] 1-ablation-resistant heat protection material; 2-heat insulation honeycomb plate; 3-expanded foam material; 4-ceramic particle reinforced metal matrix functionally graded material; 5-bionic tree root structure; 6-frame; 51-tree trunk; 52-main root; 53-lateral root. DETAILED DESCRIPTION

[0027] The application will be further described in detail below in combination with the drawings and examples. It can be understood that the specific examples described herein are only used to explain the application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for the convenience of description, not all the structures.

[0028] In the description of the application, unless otherwise explicitly specified and limited, the terms "connected", "connected", "fixed" should be understood broadly, for example, it can be fixedly connected, or detachably connected, or integrated; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0029] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "over" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the first feature is higher in horizontal height than the second feature. The first feature "under", "below" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the first feature is lower in horizontal height than the second feature.

[0030] In the description of the present embodiment, the terms "upper", "lower", "right", "left", and other orientation or position relationships are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0031] The present application will be further described below in conjunction with the drawings and embodiments. Please refer to Figs. 1-3 The present application designs an additive manufacturing method of a bionic functional gradient heat protection structure, forms a heat protection structure skin area structure and performance precise optimization design method based on gradient structure topology optimization design and structure bionics principles, has excellent heat insulation performance, lightweight structure, strong designability, high mechanical properties and other characteristics.

[0032] As Fig. 1 shown, the present application provides an additive manufacturing method of a bionic functional gradient heat protection structure, the shell of a snail has superior heat insulation and overall mechanical properties due to the layered structure, the heat protection structure is designed as a heat insulation layer, a heat absorption layer and a load bearing layer with reference to the structure; the heat insulation layer is composed of a low thermal conductivity ablation-resistant heat protection material (1), the main structure of the heat absorption layer is a heat insulation honeycomb panel (2), and an expanded foam material (3) based on phase change heat absorption is added inside the panel; the load bearing layer is the core of the heat-force performance transition layer skin structure, mainly composed of a functional gradient layer (4) and a metal root-like bionic structure (5), the functional gradient layer is a metal matrix composite material with ceramic particles, and the ceramic particles increase in gradient along the normal direction from the frame layer to the heat insulation layer; the root-like bionic structure is composed of pure metal, the triangle formed by the main root, the lateral root and the functional gradient layer has structural stability, which enables safe and efficient connection of the frame (6) and the skin, the load bearing layer is printed layer by layer through the process of laser melting deposition; the method comprises the following steps:

[0033] 1) Adopting three-dimensional scanner to scan the frame structure of the thermal protection structure, obtaining three-dimensional model data, and then obtaining the CAD model of the heat-resistant bionic skin area of the thermal protection structure workpiece according to the design scheme, so as to accurately extract the three-dimensional model size such as radius and thickness, and determine the size of the additive area; and polishing and decontaminating the surface of the frame structure to facilitate printing the skin on the frame structure;

[0034] 2) According to the engineering requirements, the heat insulation ability of the thermal protection structure functional characteristics requirement is determined, which needs to ensure that the temperature in the frame area is not higher than 25℃ after a certain time of heat flow passing in the sample test process; and the bionic structure bearing capacity of the performance constraint condition is determined, which is specifically manifested as that the bionic structure is not damaged under the application of a certain normal and torsional load;

[0035] 3) According to the heat insulation and bearing capacity required by the thermal protection structure, the topology optimization of the honeycomb and root structure of the new functional gradient material is carried out; the design variable is associated with the material composition, the gradient sensitivity function is combined, the functional gradient material structure variable density topology optimization model is designed with the compliance as the objective function and the volume as the constraint condition, and the honeycomb and root structure design method of the optimal topology configuration in the design domain is sought under the condition of meeting the constraint condition; In the process of topology optimization of the root structure, the diameter of the trunk (51) part needs to be greater than 50mm, the diameter of the main root (52) needs to be greater than 10mm, and the diameter of the lateral root (53) needs to be greater than 5mm, and the distribution of the lateral root is at an angle of 30°-60° with the main root;

[0036] 4) After determining the bionic structure of the thermal protection structure, the composition gradient of the bearing layer needs to be selected; according to the volume fraction change of the metal and ceramic in the gradient material, the function curve of the alloy composition of the gradient material changing with the gradient layer number is fitted. Combined with the minimum thermal stress principle, the optimal gradient material chemical composition distribution function is solved. The composition gradient is that the metal A starts from 100% of the bottom area and gradually changes to the metal A matrix composite material with 50% ceramic particles added; the design of the composition gradient needs to determine the content of the ceramic particles at the top along the normal direction, and the gradient size of each layer of the layered slice is selected as 2%, so as to facilitate the material filling in the printing process;

[0037] 5) According to the topology optimization parameters and the composition gradient parameters, the three-dimensional model is designed, the finite element grid is divided, the initial conditions and boundary conditions are set, and the heat source model is loaded, etc. A laser melting deposition finite element simulation model of the N-layer gradient layer superposition of the new functional gradient material is established, the temperature, stress and strain distribution in the whole deposition area is calculated by using the heat conduction differential equation, if the numerical simulation result can meet the functional characteristic requirements of the thermal protection structure, the bionic structure is finalized; if it cannot meet the functional characteristic requirements of the thermal protection structure, the parameters are reset;

[0038] 6) The digital three-dimensional model of the bionic workpiece to be printed is divided into units and layers, and the processing path of laser additive manufacturing is generated according to the layer-by-layer cycle mode. An iterative algorithm is used to calculate the spreading deposition amount in real time and transfer data to the next step of spreading deposition amount calculation process, so as to ensure that the height of each deposition layer remains consistent;

[0039] 7) The metal A powder is used as the material of the powder feeding barrel I, and the metal A matrix composite with a% ceramic particle powder is used as the material of the powder feeding barrel II. By adjusting the rotating speed of the two powder feeding barrels, different composition gradients are realized. During the coaxial powder feeding printing process, attention should be paid to the position and printing length of the tree root structure at each layer. The process meets the following conditions: laser power 1200W-1600W, laser wavelength 1065nm, laser beam spot diameter 3mm, scanning speed 0.08-0.12m / s, scanning interval 1.8mm, and laser parameters and motion parameters in the laser additive manufacturing process are adjusted according to composition, heat accumulation and other factors. The metal material is one or a combination of titanium alloy and aluminum alloy, and the ceramic particles are one or a combination of TiC, TiN, TiB and WC;

[0040] 8) After the printing is completed, expandable foam materials based on phase change heat absorption are added inside the heat insulation layer structure. Any one or mixture of any several of hard polyurethane foam, silicone rubber foam or polystyrene foam can be used;

[0041] 9) After the printing is completed, low thermal conductivity ablation-resistant heat protection materials are coated on the upper part of the heat insulation layer structure. Any one or mixture of any several of glass fiber reinforced phenolic resin materials, phenolic resin impregnated carbon fiber skeleton materials or fiber woven body reinforced heat protection materials can be used. Finally, the shaped part is obtained through milling and post-processing.

Claims

1. An additive manufacturing method for a biomimetic functionally graded thermal protection structure, characterized in that: The scaly-foot snail's shell possesses superior thermal insulation and overall mechanical properties due to its layered structure. Based on the biomimetic layered characteristics of the scaly-foot snail's shell, the thermal protection structure is designed as an insulation layer, a heat-absorbing layer, and a load-bearing layer. The main structure of the heat-absorbing layer is an insulation honeycomb panel, filled with an expanding foam material based on phase change heat absorption. A low thermal conductivity, ablation-resistant thermal protection material is coated on the upper surface of the heat-absorbing layer to form the insulation layer. The load-bearing layer is the core of the thermo-mechanical performance transition layer skin structure, mainly composed of a functionally graded layer and a metal root-like biomimetic structure. The functionally graded layer is... A metal matrix composite material with added ceramic particles, wherein the ceramic particles in the load-bearing layer grow in a gradient from the frame layer to the insulation layer along the normal direction; the root-like biomimetic structure is made of pure metal, and the structure includes a trunk, main root, and lateral roots. The root-like biomimetic structure is grown on the frame surface through laser additive manufacturing to form a metallurgical bond. The triangle formed by the main root, lateral roots, and functionally graded layer has structural stability. The root-like biomimetic structure formed by the trunk, main root, and lateral roots and the functionally graded layer connect the frame and the heat-absorbing layer; the method includes the following steps: 1) Obtain the three-dimensional model dimensions of the radius and thickness of the heat-resistant biomimetic skin region of the thermal protection structure workpiece, determine the size of the additive region, and perform preprocessing on it; 2) Based on the engineering requirements, determine the heat insulation capacity required for the functional characteristics of the thermal protection structure, specifically the amount of heat flow it can withstand within a certain time period; and determine the load-bearing capacity requirements of the biomimetic structure based on the performance constraints, specifically the ability of the biomimetic structure to remain intact under certain normal and torsional loads. 3) Based on the required heat insulation and load-bearing capacity of the thermal protection structure, the topology of honeycomb and tree root structures is optimized to achieve a reasonable topology design in two-dimensional planar structures and three-dimensional solid structures, thereby achieving good thermal-mechanical performance; 4) After determining the biomimetic structure of the thermal protection structure, the composition gradient of the load-bearing layer is selected. The composition gradient is that it gradually changes from 100% metal A in the bottom region to metal A matrix composite material with added b% ceramic particles. The design of the composition gradient needs to determine the ceramic particle content at the top along the normal direction, and set the change ratio of ceramic particle content for each layer of the layered slice, that is, the ceramic particle content between adjacent layers increases by c% layer by layer, so as to facilitate the material filling in the printing process. 5) Design a three-dimensional numerical model based on the topology optimization parameters and composition gradient parameters, and perform thermal and mechanical analysis using finite element software to obtain the temperature field, stress, and strain distribution of the biomimetic functional gradient thermal protection structure. If the numerical simulation results meet the functional characteristics requirements of the thermal protection structure, the biomimetic structure is finalized; if they do not meet the functional characteristics requirements of the thermal protection structure, the parameters are reset. 6) Divide the digital 3D model of the bionic workpiece to be printed into units and layers, and generate the processing path of laser additive manufacturing according to the layer-by-layer loop. 7) Using metal A powder as the material of powder feeding hopper I and metal A matrix composite material with added a% ceramic particles as the material of powder feeding hopper II, printing with different composition gradients can be achieved by adjusting the rotation speed of the two powder feeding hoppers. During coaxial powder feeding printing, pay attention to the position and printing length of the root structure in each layer; determine the laser parameters and motion parameters in the laser additive manufacturing process based on the composition and heat accumulation factors. 8) Fill the inside of the printed heat-absorbing layer insulation honeycomb panel with expanding foam material based on phase change heat absorption; 9) A heat insulation layer is formed by coating a low thermal conductivity ablation-resistant heat protection material on the upper part of the heat absorption layer structure. The low thermal conductivity ablation-resistant heat protection material is made of carbon fiber skeleton material impregnated with phenolic resin, and the final part is obtained by milling and post-processing.

2. The additive manufacturing method for a biomimetic functionally graded thermal protection structure as described in claim 1, characterized in that, The diameter of the trunk portion of the root structure is greater than 50 mm, the diameter of the main root is greater than 10 mm, the diameter of the lateral roots is greater than 5 mm, and the distribution of the lateral roots is at an angle of 30° to 60° with the main root.

3. The additive manufacturing method for a biomimetic functionally graded thermal protection structure as described in claim 1, characterized in that, The metallic material is one or a combination of titanium alloy and aluminum alloy, and the ceramic particles are one or a combination of TiC, TiN, TiB, and WC.

4. The additive manufacturing method for a biomimetic functionally graded thermal protection structure as described in claim 1, characterized in that, In step 7), the laser additive manufacturing process is specifically laser melting deposition, and the process meets the following requirements: laser power 1200W~1600W, laser beam spot diameter 3mm, scanning speed 0.08~0.12m / s, and scanning spacing 1.8mm.

5. The additive manufacturing method for a biomimetic functionally graded thermal protection structure as described in claim 1, characterized in that, The expanded foam material is any one or a mixture of any of rigid polyurethane foam, silicone rubber foam, and polystyrene foam.

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