Shell-based lattice structure with mesh simplification features and methods of design and fabrication thereof

Abstract

The application provides a shell-based lattice structure with a mesh simplification feature and a design and preparation method thereof, and belongs to the technical field of precision forming. The design method adopts truncated cubic octahedron (TCO) as a basic unit, the geometric appearance of which is regulated by a shape parameter beta, and then introduces an octagonal prism height h as a design variable, adjusts the h value to control the proportion of the unit cell in the space volume, realizes the decoupling of the volume fraction and the geometric appearance, constructs a shell-based TCO lattice structure through difference set operation of the outer-inner lattice structure, characterizes the gap-solid boundary of the shell-based TCO lattice structure through two groups of triangular facets, and realizes the direct conversion of the lattice structure model and the STL file. The problems of geometric distortion and data redundancy and the like existing in the STL conversion of the three-period minimal surface structure are solved.

Description

Technical Field

[0001] This invention relates to the field of precision molding technology, and in particular to a shell-based lattice structure with simplified grid features, and its design and fabrication method. Background Technology

[0002] Lightweight lattice structures, due to their complex topology and controllable dimensional properties, have become a core solution for the integrated "material-structure-performance" design of advanced equipment. These structures not only exhibit excellent specific strength and stiffness characteristics but also possess outstanding energy absorption, sound absorption, shock resistance, and thermal management capabilities. Currently, lattice structures are widely used in engineering fields such as mechanics, acoustics, electromagnetics, and optics. With breakthroughs in additive manufacturing technology, precision forming processes, such as laser powder bed fusion (LPBF), have provided crucial technological support for the manufacture of lattice structures with complex topological configurations and precise volume fraction control.

[0003] In lattice structures, based on their unit cell characteristics, they can be broadly classified into beam-based, plate-based, and shell-based lattice structures. Different types of lattice structures exhibit different characteristics. Shell-based lattice structures, in particular, have attracted significant attention due to their unique geometry. This structural type possesses a symmetrical structure and the significant characteristic of dividing space into two independent, discontinuous regions. Currently, many researchers have begun to focus on the mechanical properties and energy absorption characteristics of shell-based lattice structures. Experimental characterization and numerical simulation results show that, under equivalent relative density conditions, shell-based lattice structures exhibit significant structural advantages due to their high node connectivity. Their specific strength and specific stiffness not only surpass traditional rod-based structures but also reach performance levels comparable to tension-dominated lattice structures. Furthermore, because shell-based lattice structures only experience minor stress fluctuations after experiencing initial peak stress, their specific energy absorption performance is significantly better than that of rod-based lattice structures. These superior mechanical properties and energy absorption characteristics make shell-based lattice structures more suitable for engineering applications.

[0004] Traditional modeling methods face efficiency bottlenecks when constructing complex shell-based lattice structures. To address this challenge, researchers have proposed an implicit function parameterization modeling theory based on three-period minimal surfaces (TPMS). This method precisely characterizes the solid-void boundary using the implicit equation φ(x,y,z)=C, enabling accurate parameterization of volume fraction and lattice size design. Based on this mathematical framework, typical TPMS configurations such as Primitive, IWP, Neovius, Gyroid, and Diamond can be derived. Among these, the Primitive, Diamond, and Gyroid lattice structures show advantages over traditional body-centered cubic (BCC) lattice structures in terms of compressive modulus, plateau stress, and energy absorption. Furthermore, by coupling compression experiments with simulation, the mechanical properties and energy absorption of several TPMS structures were compared. The test results all indicate that the Primitive TPMS is superior in terms of load-bearing capacity (higher specific stiffness and specific strength) and energy absorption. To broaden its design domain, Jia et al. proposed a design method to modify the shell thickness of the Schwarz Primitive structure to obtain a lightweight structure with excellent mechanical properties. Guo et al. developed three modified P-lattice structures—OP, SP, and BP—by introducing a shape control factor C to reconstruct the implicit function. Among them, the SP structure showed improvements in elastic modulus, compressive strength, and energy absorption compared to OP by 25.84%, 15.63%, and 33.02%, respectively. Furthermore, the mechanical response and energy absorption characteristics of the structure were effectively predicted using a rigid-plastic hardening finite element model.

[0005] However, existing TPMS design models need to be adapted to the additive manufacturing process through geometric format conversion (isosurface → triangular facets → STL file). During the STL conversion process, in order to ensure the continuous surface characteristics of TPMS, high-density triangular facets are required for fitting, which leads to a dramatic increase in the size of the STL file and the generation of facet interference defects, ultimately restricting the engineering application of large-scale shell-based lattice structures. Summary of the Invention

[0006] This invention provides a shell-based lattice structure with grid simplification features, as well as its design and fabrication method, to solve the problems of geometric distortion and data redundancy in STL conversion of three-period minimal surface (TPMS) structures.

[0007] To address the aforementioned technical problems, embodiments of the present invention provide a shell-based lattice structure design method with grid simplification features, the design method comprising at least:

[0008] The truncated cubic octahedron TCO is used as the basic unit. The TCO is a periodic single-cell structure with 48 vertices, 72 edges, and 26 faces. Its geometry is controlled by the shape parameter β.

[0009] By introducing the height h of the octagonal prism as a design variable, the proportion of the unit cell in the spatial volume is controlled by adjusting the h value, thereby achieving decoupling between the volume fraction and the geometric shape.

[0010] A shell-based TCO lattice structure is constructed by difference operations on the outer and inner lattice structures.

[0011] The void-solid boundary of the shell-based TCO lattice structure is characterized by two sets of triangular facets, enabling direct conversion between the lattice structure model and the STL file.

[0012] The aforementioned design methods also include the design of gradient shell-based TCO lattice structures driven by stress fields:

[0013] (1) Perform finite element analysis on the target component under given load and boundary conditions to obtain the normalized stress field or strain energy density field;

[0014] (2) Construct the shell-based volume fraction function ρ of the spatial distribution based on the normalized field. shell (x), and ρ at each TCO unit cell scale shell (x) is decomposed into the volume fraction of the outer surface solid ρ solid1 (x) and the volume fraction of the inner surface solid ρ solid2 (x), and satisfy ρ solid1 (x)+ρ solid2 (x)=1;

[0015] (3) Based on the correspondence between the volume fraction of the TCO unit cell and the shape parameter β and the height h of the octagonal prism, solve the local shape parameter β(x) and the height h(x) of the octagonal prism at each unit cell;

[0016] (4) Under the condition of satisfying the manufacturing constraints of minimum shell thickness and minimum aperture, spatial smoothing is performed on β(x) and h(x) to obtain a continuous gradient parameter field;

[0017] (5) Based on the parameterized algorithm, construct the vertex set and triangular facets of the shell-based TCO unit cell with the outer-inner difference set, and reuse the unit cell in different parameter ranges through templated triangular facet topology to generate an STL file of the shell-based TCO lattice structure with gradient volume fraction.

[0018] In the aforementioned design method, the outer-inner lattice structure difference set construction process is based on the MATLAB parameterization algorithm and includes the following steps: generating the outer-inner surface vertex set, constructing the initial geometry by connecting the vertices, and using triangular facets to repair the junction of the inner and outer surfaces to form a closed shell-based unit cell.

[0019] In the aforementioned design method, the lattice wall thickness is made uniform by adjusting the shape parameter β to change the inner surface morphology.

[0020] In the aforementioned design method, the shape parameter β = a / b, where a is the common side length of the hexagon and the quadrilateral, and b is the common side length of the hexagon and the octagonal prism. By adjusting the shape parameter β, the inner surface morphology is changed, thereby achieving uniformity of the lattice wall thickness.

[0021] In the aforementioned design method, based on the standard TCO shell-based lattice structure NTCO, the side length parameters a and b are controlled by changing the outer surface shape parameter β to construct a small-aperture shell-based TCO lattice structure STCO (β> 1) and a large-aperture shell-based TCO lattice structure BTCO (β< 1).

[0022] This invention also provides a shell-based TCO lattice structure, designed by the above-described design method, wherein the volume fraction ρ of the shell-based TCO lattice structure is... shell Satisfy: ρ shell =ρ solid1 -ρ solid2 , where ρ solid1 and ρ solid2 Let ρ be the volume fraction of the solid TCO lattice structure on the outer and inner surfaces, respectively, and satisfy the constraint condition ρ. solid1 +ρ solid2 =1.

[0023] In the aforementioned shell-based TCO lattice structure, the volume fraction of the lattice structure is the ratio of the effective volume of the unit cell to the corresponding solid material volume. Calculated by subtracting the geometrically adjusted solid TCO lattice structure from the solid TCO lattice structure on the inner surface, the solid TCO unit cell consists of one central node and six octagonal prism pillars. Based on this, its solid volume V is obtained. solid Then, the volume fraction ρ of the solid TCO lattice structure is calculated. solid .

[0024] This invention also provides a method for preparing a shell-based TCO lattice structure, comprising the following steps:

[0025] Using a programming method based on MATLAB, the required lattice structure STL file can be directly generated;

[0026] Ti6Al4V powder was used as the raw material, and laser powder bed melting technology was used for printing.

[0027] After printing, the lattice structure is removed from the substrate using wire cutting technology, without heat treatment.

[0028] In the aforementioned preparation method, the technical parameters for laser powder bed melting are as follows: laser power of 205W, scanning gap of 0.12mm, layer thickness of 30μm, scanning speed of 1200mm / s, and oxygen content controlled at <0.1%.

[0029] This invention addresses the geometric distortion and data redundancy issues in STL conversion of TPMS structures by proposing a parametric design method for shell-based TCO cells based on MATLAB. This method can directly generate shell-based TCO lattice structures with specified volume fractions, sizes, and shapes, significantly reducing the amount of STL file data and eliminating patch interference defects. Furthermore, the above-mentioned solution of this invention also includes at least the following beneficial effects:

[0030] 1. Introduce the height h of the octagonal prism as another joint design variable to control the proportion of the unit cell in the spatial volume by adjusting the value of h while keeping the geometric shape unchanged;

[0031] 2. By adjusting the shape parameter β (side length ratio) to change the inner surface morphology, the lattice wall thickness is made uniform, effectively improving the structural reliability;

[0032] 3. Compared with existing methods that control the P-lattice morphology based on functional functions, this method significantly improves design freedom and adjustment efficiency while ensuring geometric accuracy by directly controlling the shape parameter β.

[0033] 4. The crystal structure can be achieved by adjusting different combinations of volume fractions. The unit cell can be adjusted according to the volume fraction, and the a and b values ​​can be adjusted by adjusting the shape parameter β to adjust the unit cell configuration and achieve the modification of the TCO crystal structure. Attached Figure Description

[0034] Figure 1 These are TCO models with different geometric parameters;

[0035] Figure 2 It is the step in the formation of a shell-based TCO lattice unit cell;

[0036] Figure 3 These are shell-based TCO lattice structures with different shape parameters according to the present invention.

[0037] Figure 4 This is a comparison of important geometric parameters (number of triangular facets, volume, shell thickness distribution, and file size) between shell-based TCO lattice and shell-based TPMS-P structure.

[0038] Figure 5 This is a printout of the desired effect. Detailed Implementation

[0039] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0040] In the following description, certain specific details are set forth for the purpose of illustrating various disclosed embodiments in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments may be practiced without one or more of these specific details. In other instances, well-known apparatuses, structures, and techniques associated with this application may not have been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0041] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0042] In the following description, in order to clearly demonstrate the structure and working method of the present invention, a number of directional terms will be used. However, terms such as "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", and "down" should be understood as convenient terms and not as limiting terms.

[0043] Additive manufacturing 3D models are typically stored in STL file format, and their file size is directly related to the number of triangles. Too many triangles significantly increase the computational load and reduce operational efficiency, becoming a key factor limiting the large-scale application of the model. The main objective of this embodiment is to significantly reduce the data size of the STL file and eliminate triangle interference defects, such as... Figures 1 to 3 As shown, embodiments of the present invention provide a shell-based lattice structure design method with grid simplification features, as detailed below:

[0044] The Archimedean polyhedron of TCO (Truncated Cuboctahedron) exhibits a periodic unit cell structure in its crystallographic properties, with 48 vertices, 72 edges, and 26 faces. Its geometry is jointly controlled by the ratio β (a / b = β) of the cross-sectional side length parameters a and b.

[0045] In this embodiment, to achieve decoupled control of volume fraction and geometric shape and increase design freedom, the octagonal prism height h is introduced as another joint design variable. This allows for control of the proportion of the unit cell within the spatial volume (e.g., 4mm × 4mm × 4mm) by adjusting the h value while maintaining the geometric shape. The evolution of its geometric configuration is as follows: Figure 1 As shown.

[0046] Shell-based TCO lattices are formed through the difference set construction of the outer and inner lattice structures. However, the 3D model used in additive manufacturing processes needs to be saved in STL file format. Therefore, this embodiment characterizes the void-solid boundaries of the shell-based TCO lattice structure using two sets of triangular facets, achieving direct conversion between the lattice structure model and the STL file.

[0047] like Figure 2 As shown (taking shape parameter β = 1 as an example), the parameterization algorithm based on MATLAB includes: (1) generating the vertex set of the outer and inner surfaces; (2) constructing the initial geometry by connecting the vertices; (3) repairing the junction of the inner and outer surfaces with triangular facets to form a closed shell-based unit cell. However, existing methods for constructing the inner surface (high volume fraction unit cell minus low volume fraction isomorphic unit cell) result in a reduction in the wall thickness of the octagonal prism in the connection region ( Figure 2 c), becoming a weak point in the structure. In this embodiment, the inner surface morphology is changed by adjusting the side length ratio β to achieve uniform lattice wall thickness. Figure 2 (ef), effectively improving structural reliability.

[0048] Furthermore, based on the standard TCO shell-based lattice structure (NTCO), by changing the outer surface shape parameter β to control the side length parameters a and b, small-aperture shell-based TCO lattice structures (STCO, β > 1) and large-aperture shell-based TCO lattice structures (BTCO, β < 1) can be constructed. Compared with existing methods that control the P-lattice morphology based on functional functions, this embodiment significantly improves design freedom and adjustment efficiency while ensuring geometric accuracy by directly controlling the shape parameter β. Figure 3 ).

[0049] Based on the above design method, a geometric analysis is performed on the lattice structure of this embodiment:

[0050] The volume fraction of the lattice structure is defined as the ratio of the effective volume of a unit cell to the volume of the corresponding solid material. For the shell-based TCO lattice in this embodiment, its volume fraction can be calculated by subtracting the geometrically adjusted solid TCO lattice structure of the inner surface from the solid TCO lattice structure of the outer surface.

[0051] The solid TCO unit cell consists of one central node and six octagonal prism supports. Based on this, its solid volume (V) solid This can be represented as:

[0052]

[0053]

[0054] In the formula, a is the common side length of the hexagon and quadrilateral, b is the common side length of the hexagon and octagonal prism, h is the height of the octagonal prism, and L is the cell size. Then, the volume fraction (ρ) of the solid TCO lattice structure...solid It can be done through:

[0055]

[0056] Therefore, the volume fraction (ρ) of the shell-based TCO lattice structure shell The following formula is given:

[0057]

[0058] in:

[0059] According to the above formula, when L is a constant, given ρ shell The crystal lattice structure can be adjusted by ρ solid1 and ρ solid2 Different combinations of ρ can be used to achieve this, and ρ can be adjusted via the shape parameter β. solid1 By adjusting the values ​​of a and b, the TCO lattice structure can be modified. To avoid the inner and outer surfaces of the lattice structure intersecting or exceeding the adjustable range, ρ is introduced. solid1 +ρ solid2 =1 is used as a constraint condition.

[0060] In an optional embodiment of the present invention, a method for preparing a shell-based TCO lattice structure is also provided, as follows:

[0061] Using a programming method based on MATLAB, the required lattice structure STL file can be directly generated;

[0062] Using Ti6Al4V powder as raw material, three replicas of each lattice structure were prepared using a laser powder bed melting (LPBF) machine (XDM 250A). The laser power was 205W, the scanning gap was 0.12mm, the layer thickness was 30μm, the scanning speed was 1200mm / s, and the oxygen content was controlled to be <0.1%.

[0063] After fabrication, the lattice structure was removed from the substrate using wire cutting technology, without heat treatment of the lattice structure sample.

[0064] This embodiment also compares the geometric parameters of shell-based TCO lattices and shell-based TPMS-P structures, such as... Figure 4 As shown in (a)-(c), the important geometric parameters (number of triangular facets, volume size, shell thickness distribution, and file size) of the shell-based TCO lattice and the shell-based TPMS-P structure with a volume fraction of 20% are compared under the triangular facet division accuracy that can accurately express the lattice structure morphology.

[0065] The results show that, compared with the shell-based TPMS-P structure, the shell-based TCO lattice has 98% fewer triangular facets (corresponding to a file size of only 1.46 MB), a volume fraction control error of less than 0.01%, and no facet overlap or intersection issues, which can significantly improve computational efficiency.

[0066] Furthermore, Figure 4 The shell thickness visualization results (b)-(d) show that the thickness distribution of the shell-based TCO lattice is highly uniform (0.31–0.34 mm), while the shell-based TPMS-P structure exhibits local thickness abrupt changes (extreme values ​​up to 0.45 mm).

[0067] Example 2

[0068] This embodiment provides a stress field-driven gradient shell-based TCO lattice design method. Based on Embodiment 1, "Unified β and h shell-based TCO lattice + mesh simplification", this embodiment introduces a spatial gradient shell-based TCO lattice design method based on the stress field or energy density field of the target component.

[0069] First, perform finite element analysis (FEA) on the target structure to obtain the normalized stress field σ. norm (x) or strain energy density field W norm (x); Introducing the spatially distributed volume fraction function ρ shell (x), ρ shell (x) refers to the shell-based volume fraction function at spatial location x, representing the local relative density of the shell-based TCO lattice structure at different locations. It is used to implement gradient lattice design, mapping high-stress areas to high ρ. shell Low-stress areas are mapped to low-ρ shell At each unit cell level, solve for the fit ρ. solid1 (x), ρ solid2 (x), thus obtaining local β(x) and h(x); the neighborhood smoothing constraint ensures the continuity of the changes of β(x) and h(x) of adjacent unit cells, avoiding weak points and self-intersection of inner and outer shell surfaces; finally, a gradient shell-based TCO lattice is generated that optimizes mechanical properties and functional distribution on a macroscopic scale, while maintaining the simplified mesh characteristics (low number of triangular facets).

[0070] Example 1 only addresses "single volume fraction + single shell thickness + mesh simplification" without connecting the entire chain of mechanical response → local geometric parameter field (β, h).

[0071] The specific steps of this embodiment are as follows:

[0072] Step S1: Obtaining the macroscopic structure and stress field:

[0073] Determine the external boundary, loads, and constraints of the target component;

[0074] Treating the target component as a solid material (such as an equivalent Ti6Al4V solid), the equivalent stress field σ(x) or the element strain energy density field W(x) is obtained in conventional FEA software; this field is then normalized to obtain σ. norm (x)∈[0,1] or W norm (x)∈[0,1].

[0075] σ(x) refers to the equivalent stress of the solid equivalent structure at position x, in MPa, derived from the finite element analysis results;

[0076] W(x) refers to the strain energy density at position x, which is a physical quantity that reflects the local stress and deformation energy of the structure.

[0077] Step S2: Construction of volume fraction and design variable field:

[0078] Define the volume fraction mapping function:

[0079]

[0080] Where f() is a monotonically increasing function.

[0081] At the scale of each unit cell, the target ρ shell (x) can be decomposed into:

[0082]

[0083] Solving for:

[0084]

[0085] Based on the ρ of each unit cell solid1 (x), ρ solid2 (x), and use the formula for the volume fraction of a unit cell in the TCO entity to find the corresponding a(x), b(x), and h(x), thus obtaining β(x) = a(x) / b(x).

[0086] Step S3: Geometric Manufacturability and Continuity Constraints

[0087] Apply constraints to local β(x) and h(x):

[0088] β min ≤ β(x) ≤ β max h min ≤ h(x) ≤ h max ,

[0089] Ensure the minimum shell thickness during printing is ≥ t min Minimum aperture ≥ d min .

[0090] Smoothing filtering is applied to adjacent unit cells:

[0091]

[0092] The smoothed local shape parameter is represented by the β value obtained after neighborhood weighted averaging. It is used to reduce parameter abrupt changes and ensure geometric continuity and structural safety.

[0093] β(x) is a local shape parameter at spatial location x. β is no longer a constant but a distribution function that varies with location, used to form a gradient shell-based TCO lattice. Through β(x), the aperture, shell thickness, morphology, etc., can be adjusted in different regions.

[0094] h(x), the local octagonal prism height at spatial location x, is also a distribution function used to construct TCO unit cells with different local stiffness / density.

[0095] β min β max The upper and lower limits of the shape parameter β are used to ensure that the geometry does not undergo self-intersection or extreme deformations that are detrimental to manufacturing.

[0096] h min h max The upper and lower limits of the height h of the octagonal prism are designed to ensure the minimum manufacturable size and reasonable structural stability.

[0097] t min Minimum shell thickness, in mm, is the minimum printable thickness allowed by additive manufacturing processes (such as LPBF) and is used to constrain the distance between the inner and outer surfaces.

[0098] d min Minimum aperture, in mm, is used to ensure that pores in the crystal lattice structure are not completely closed or blocked during manufacturing and post-processing.

[0099] The neighborhood set of the i-th cell, i.e., a set of cell indices adjacent to the i-th cell, is used for weighted averaging in the spatial smoothing of β(x) and h(x).

[0100] w ij , in the case of β(x) of unit cell i i ) or h(x i When smoothing, the weight coefficients of the neighboring unit cell j are generally related to the distance or connectivity.

[0101] Ensure that β and h vary gradually rather than abruptly in space to avoid geometric discontinuities or weak necks.

[0102] Step S4: Parametric Modeling and Mesh Simplification

[0103] Based on the existing MATLAB parameterization framework, a local parameter β(x) is used for each unit cell. i h(x) i Construct the outer-inner TCO geometry;

[0104] The approach still employs the concept of "two sets of triangular facets representing the void-solid boundary," but with further refinement:

[0105] Group all unit cells according to their β and h values, and share the same topological connectivity relationship with unit cells that have similar parameters, updating only the vertex coordinates.

[0106] The patch index template is shared during STL generation, thus keeping the STL file size controllable while maintaining the gradient structure.

[0107] Output the overall structure as an STL file.

[0108] Step S5: Additive Manufacturing and Verification

[0109] Using the same Ti6Al4V+LPBF process parameters, the printing and testing of "gradient structure prototypes" can be added to demonstrate: the high-stress area is affected by local ρ shell Increased height and wall thickness delay plastic collapse; low-stress areas are affected by ρ shell The weight reduction is significant; the STL file size is still significantly smaller than that of the TPMS-P gradient structure with an equal volume fraction.

[0110] Based on the stress / energy density field, ρ shell (x) and β(x), h(x) are made into a spatially continuously varying gradient field to achieve integrated design of structural performance, geometric parameters and mesh simplification. This upgrade from geometric modeling tools to performance-driven design methods deeply couples the finite element mechanical field with parametric geometry generation. The solution is how to design shell-based lattices according to target performance while meeting manufacturing constraints and STL simplification.

[0111] Under the same total mass conditions, the gradient shell-based TCO exhibits better peak stress, plateau stress stability, and energy absorption efficiency than the uniform TCO and uniform TPMS-P; the STL file size is still significantly smaller than the implicit TPMS scheme, meaning that while improving performance, it maintains the advantage of mesh simplification.

[0112] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A design method for shell-based lattice structures with grid simplification features, characterized in that, This design methodology includes at least the following: The truncated cubic octahedron TCO is used as the basic unit. The TCO is a periodic single-cell structure with 48 vertices, 72 edges, and 26 faces. Its geometry is controlled by the shape parameter β. By introducing the height h of the octagonal prism as a design variable, the proportion of the unit cell in the spatial volume is controlled by adjusting the value of the height h, thereby achieving decoupling between the volume fraction and the geometric shape. A shell-based TCO lattice structure is constructed by difference operations on the outer and inner lattice structures. The void-solid boundary of the shell-based TCO lattice structure is characterized by two sets of triangular facets, enabling the direct generation of the lattice structure model and STL file; Stress-driven gradient shell-based TCO lattice structure design includes: (1) Perform finite element analysis on the target component under given load and boundary conditions to obtain the normalized stress field or strain energy density field; (2) Construct the spatially distributed shell-based volume fraction function ρ based on the normalized stress field or strain energy density field. shell (x), and the volume fraction ρ at each TCO unit cell scale. shell Decomposed into the volume fraction ρ of the outer surface solid. solid1 With the volume fraction of the inner surface ρ solid2 And satisfy ρ solid1 +ρ solid2 =1; (3) Based on the correspondence between the volume fraction of the TCO unit cell and the shape parameter β and the height h of the octagonal prism, solve the local shape parameter β and the height h of the octagonal prism at each unit cell; (4) Under the condition of satisfying the manufacturing constraints of minimum shell thickness and minimum aperture, the shape parameter β and the height h of the octagonal prism are spatially smoothed to obtain a continuous gradient parameter field. (5) Based on the parameterized algorithm, construct the vertex set and triangular facets of the shell-based TCO unit cell with the outer-inner difference set, and reuse the unit cell in different parameter ranges through templated triangular facet topology to generate an STL file of the shell-based TCO lattice structure with gradient volume fraction.

2. The design method according to claim 1, characterized in that, The outer-inner lattice structure difference set construction process is based on the MATLAB parameterized algorithm and includes the following steps: generating the outer-inner surface vertex set, constructing the initial geometry by connecting the vertices, and using triangular facets to repair the junction of the inner and outer surfaces to form a closed shell-based unit cell.

3. The design method according to claim 1, characterized in that, By adjusting the shape parameter β to change the inner surface morphology, the lattice wall thickness can be made uniform.

4. The design method according to claim 1, characterized in that, The shape parameter β = a / b, where a is the common side length of the hexagon and the quadrilateral, and b is the common side length of the hexagon and the octagonal prism. By adjusting the shape parameter β, the inner surface morphology is changed, thereby achieving uniformity of the lattice wall thickness.

5. The design method according to claim 4, characterized in that, Based on the standard TCO shell-based lattice structure NTCO, by changing the outer surface shape parameter β to control the side length parameters a and b, a small-aperture shell-based TCO lattice structure STCO (β>1) and a large-aperture shell-based TCO lattice structure BTCO (β<1) are constructed.

6. A shell-based TCO lattice structure, characterized in that, The shell-based TCO lattice structure, designed by the design method described in any one of claims 1 to 4, has a volume fraction ρ. shell Satisfy: ρ shell =ρ solid1 -ρ solid2 , where ρ solid1 and ρ solid2 Let ρ be the volume fraction of the solid TCO lattice structure on the outer and inner surfaces, respectively, and satisfy the constraint condition ρ. solid1 +ρ solid2 =1.

7. The shell-based TCO lattice structure according to claim 6, characterized in that, The volume fraction of the lattice structure is the ratio of the effective volume of the unit cell to the volume of the corresponding solid material, calculated by subtracting the solid TCO lattice structure after geometric adjustment of the inner surface from the solid TCO lattice structure of the outer surface.

8. The shell-based TCO lattice structure according to claim 6, characterized in that, The solid TCO unit cell consists of one central node and six octagonal prism supports. Based on this, its solid volume V is obtained. solid Then, the volume fraction ρ of the solid TCO lattice structure is calculated. solid .

9. A method for preparing a shell-based TCO lattice structure based on the design method of claim 1, characterized in that, Includes the following steps: Using a programming method based on MATLAB, the required lattice structure STL file can be directly generated; Ti6Al4V powder was used as the raw material, and laser powder bed melting technology was used for printing. After printing, the lattice structure is removed from the substrate using wire cutting technology.

10. The preparation method according to claim 9, characterized in that, The technical parameters for laser powder bed melting are as follows: laser power of 205W, scanning gap of 0.12mm, layer thickness of 30μm, scanning speed of 1200mm / s, and oxygen content controlled at <0.1%.

Images