In-situ hybrid composite TPMS structure and design method thereof

Abstract

The application provides an in-situ hybrid composite TPMS structure and a design method thereof, and belongs to the technical field of precision forming. The in-situ hybrid composite TPMS structure comprises: a main body structure formed by fusing a P-type TPMS unit cell and a D-type TPMS unit cell through an implicit function, and the main body structure is a closed entity formed by offsetting the fused TPMS surface along the normal direction by ±C; a transition region for smoothly transitioning the P-type structure and the D-type structure through a Sigmoid function, and the transition region satisfies G 1 Continuity. The problems of obvious performance mutation, damaged geometric integrity, high manufacturing difficulty and cost and the like in the existing TPMS structure are solved.

Description

Technical Field

[0001] This invention relates to the field of precision molding technology, and in particular to an in-situ hybrid composite TPMS structure and its design method. Background Technology

[0002] Porous structures, due to their lightweight, high specific strength, and excellent energy absorption properties, have shown significant application potential in aerospace, automotive, and biomedical fields. Among them, Triply Periodic Minimal Surface (TPMS) structures have become a research hotspot due to their continuous surface topology, high specific surface area, and excellent mechanical properties. However, single types of TPMS structures (such as P-type and D-type) have inherent limitations in mechanical properties: for example, P-type structures exhibit a deformation model dominated by bending under compressive loads, while D-type structures exhibit a deformation model dominated by tension.

[0003] Current research on TPMS structures mainly focuses on the following two directions:

[0004] (1) Single structure optimization: The performance is optimized by adjusting parameters such as the size and relative density of the structural unit. However, due to the geometric characteristics of the structure itself, there is a bottleneck in performance improvement. It is difficult to break through the mechanical limitations of the material itself and cannot simultaneously meet the requirements of high stiffness and high stability.

[0005] (2) Displacement hybrid design: Different TPMS structures are combined in a partitioned or layered manner, and the structural combination is achieved through mechanical connection or simple splicing. However, there are also problems such as obvious geometric discontinuity at the interface, stress concentration, possible introduction of additional defects during manufacturing, and excessive dependence of structural performance on interface quality.

[0006] These existing hybrid technologies have three main limitations: First, they employ a "tailor-made" structural adjustment, sacrificing the geometric integrity of the original structure; second, there are significant performance abrupt changes in the transition region; and finally, the manufacturing process requires additional processing steps or special algorithms, placing excessively high demands on equipment precision. These limitations severely restrict the performance and engineering applicability of hybrid structures. For complex service conditions such as aerospace, automotive protection, and medical implants, there is an urgent need for a porous structure that can simultaneously improve stiffness, stability, and energy absorption efficiency while ensuring geometric integrity and manufacturing feasibility. Summary of the Invention

[0007] This invention provides an in-situ hybrid composite TPMS structure and its design method to solve the problems of obvious performance abrupt changes in the transition region, impaired geometric integrity, and high manufacturing difficulty and cost in existing TPMS structures.

[0008] To address the aforementioned technical problems, embodiments of the present invention provide an in-situ hybrid composite TPMS structure, comprising:

[0009] The main structure is formed by the fusion of P-type TPMS unit cells and D-type TPMS unit cells through implicit functions, and is formed by the normal offset of the fused TPMS surface by ±C, where C is the porosity control parameter. The main structure is a closed solid.

[0010] The transition region achieves a smooth transition between the P-type and D-type structures using the Sigmoid function, and the transition region satisfies G... 1 Continuous, G 1 Continuity is a standard of continuity in geometric modeling and surface design, indicating that adjacent surfaces or curves are not only physically connected at their junctions (G). 0 The curves are continuous and the tangents are in the same direction, thus ensuring that the curvature changes smoothly at the connection point without abrupt changes.

[0011] In the aforementioned composite TPMS structure, the morphology of the unit cell is adjusted by the porosity control parameter C. To ensure the continuity of the structure, the C value range of the P-type TPMS unit cell is -0.6 to 0.6; the C value range of the D-type TPMS unit cell is -0.1 to 0.5; and the C value range of the fused TPMS surface is -0.3 to 0.3.

[0012] In the aforementioned composite TPMS structure, the mathematical expression of the Sigmoid function is:

[0013]

[0014]

[0015]

[0016] P is a P-type implicit TPMS function. D is a D-type implicit TPMS function;

[0017] Let the transition width parameter k>0 and the weight function λ(x)=1 / (1+e^{–k·x}) be used. The implicit function of the composite structure is defined as follows: ;

[0018] By adjusting k to control the transition gradient from P to D, G is guaranteed. 1 Continuity is achieved by eliminating abrupt changes in curvature and ensuring a smooth, continuous structure; k=1 is preferred.

[0019] In the aforementioned composite TPMS structure, the wall thickness t of the main structure ranges from 0.55 to 1.25 mm.

[0020] In the aforementioned composite TPMS structure, the main structure is composed of an n×n×n single-cell array, where n≥4, preferably a 4×4×4 array.

[0021] This invention also provides a design method for an in-situ hybrid composite TPMS structure, comprising the following steps:

[0022] Step 1: Generate P-type and D-type TPMS units

[0023] Based on the preset unit cell size and porosity control parameter C value, P-type and D-type TPMS units are generated respectively;

[0024] Step 2: Sigmoid function transition fusion

[0025] Based on the unit cell generated in step 1, the Sigmoid function is used to achieve a smooth transition between the P-type and D-type structures. The transition gradient is controlled by adjusting the transition width parameter k to form a composite TPMS surface that satisfies G¹ continuity.

[0026] Step 3: Surface offset and wall thickness assignment

[0027] Will The surface is offset by ±C along the normal direction to generate a closed solid structure with a wall thickness of t;

[0028] Step 4: Model Slicing and Process Parameter Optimization

[0029] The solid unit cell array obtained in step 3 is replicated to an n×n×n scale to form macroscopic component geometry.

[0030] In the aforementioned design method, the unit cell morphology described in step 1 is adjusted by the porosity control parameter C. To ensure the continuity of its structure, the C value range for P-type TPMS unit cells is -0.6 to 0.6; the C value range for D-type TPMS unit cells is -0.1 to 0.5. The C value range for the fused TPMS surface is -0.3 to 0.3.

[0031] In the aforementioned design method, the mathematical expression of the Sigmoid function in step 2 is:

[0032]

[0033]

[0034]

[0035] in, P is a P-type implicit TPMS function. D is a D-type implicit TPMS function;

[0036] Let the transition width parameter k>0 and the weight function λ(x)=1 / (1+e^{–k·x}) be used. The implicit function of the composite structure is defined as follows: ;

[0037] By adjusting k to control the transition gradient from P to D, G is guaranteed. 1 Continuity is achieved by eliminating abrupt changes in curvature and ensuring a smooth, continuous structure; k=1 is preferred.

[0038] In the aforementioned design method, the wall thickness t mentioned in step 3 ranges from 0.55 to 1.25 mm.

[0039] In the aforementioned design method, n≥4 in step 4, preferably a 4×4×4 array; the additive manufacturing technology selected is laser powder bed melting (LPBF) technology.

[0040] This invention addresses the technical shortcomings of existing hybrid TPMS structures in terms of interface continuity, geometric integrity, and manufacturing feasibility. It proposes an in-situ hybrid composite TPMS structure and its design method. Based on differential geometry theory and topology optimization, this structure and method achieve seamless connection between P-type and D-type TPMS structures at the mathematical level by establishing a parameterized implicit function fusion model. Specifically, this invention employs the SF splicing method to precisely control the curvature continuity of the transition region. Furthermore, the above-mentioned solution of this invention also includes at least the following beneficial effects:

[0041] 1) Interface continuity: The Sigmoid function is used to achieve a continuous curvature transition between the P-type and D-type structures, avoiding stress concentration and significantly improving fatigue life.

[0042] 2) Geometric integrity: Through topological feature comparison, the original geometric features of P-type and D-type structures are retained at a rate of >95%, and no feature destruction occurs due to "cutting the feet to fit the shoes", ensuring the synergistic optimization of mechanical properties.

[0043] 3) Manufacturing efficiency and cost optimization: Direct modeling through implicit functions without the need for post-processing steps improves forming efficiency and reduces manufacturing costs by more than 30%. Attached Figure Description

[0044] Figure 1 This study demonstrates the morphological changes of P-type and D-type TPMS units under different C values, as well as the morphological differences of composite PD structures.

[0045] Figure 2 The smooth transition between P-type and D-type structures is achieved through the Sigmoid function (k=1), avoiding stress concentration.

[0046] Figure 3The mechanical properties of P-type, D-type, and PD-type structures of 4×4×4 unit cell arrays were compared to demonstrate the superiority of the composite structure. Solid structures were generated by surface offset method to ensure uniform wall thickness. Detailed Implementation

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] See attached document Figure 1 The first row is P-type, the second row is D-type, and the third row is PD structure. The PD structure is reshaped based on the P and D structures, but not any P and D structures can be combined into a continuous PD structure. That is, under the premise of ensuring the continuity and integrity of the structure, the parameter design space of the PD structure is obtained within the design space of P and D. Figure 2 It demonstrates the differences and complementarities in structures, as well as the continuity and integrity that need to be considered in structural hybridization. Figure 2In the diagram, the horizontal axis is used to visually represent the functional relationship between λ and F; the horizontal axis represents the value of F(x,y,z), and the vertical axis represents the value of λ. For the Sigmoid function, when F is negative infinity, λ=0; when F is positive infinity, λ=1; the range here is ±5 to symbolically express this meaning; the width of the transition region (the difference in the connected regions when k=1 is the transition region) is not shown in the diagram. Figure 3 This is to illustrate that at least a 4×4×4 or higher permutation is required to demonstrate the structural advantage. Figure c: Solid structure generated using the surface offset method, ensuring uniform wall thickness. Figure 3 middle (x, y, z) = ±C: The method of surface offset is to offset the median surface (shell structure) at both ends. The inner offset is -C and the outer offset is +C. That is to say, they are offset ±C in two directions to make the structure have a wall thickness t. There is a certain relationship between C and t.

[0052] In this embodiment, an in-situ hybrid composite TPMS structure and its design method are provided to verify its advantages in interface continuity, geometric integrity, and mechanical properties. It is applicable to scenarios such as lightweight components for aerospace, automotive protective structures, and medical implants, including:

[0053] Step 1: Generation of P-type and D-type TPMS single cells

[0054] Parameter settings: The unit cell size is set to 10mm (10mm in the x, y, and z axes); the porosity control parameter C value is selected as -0.6, -0.3, 0, 0.3, 0.6 (covering the range from low to high porosity) (P type); 0.1, 0.2, 0.3, 0.4, 0.5 (D type).

[0055] Unit cell generation: Based on P-type TPMS implicit functions

[0056] P = cos(x) + cos(y) + cos(z) - C = 0, and D-type TPMS implicit function

[0057] D = cos(x)cos(y) + cos(y)cos(z) + cos(z)cos(x) - C = 0. Using software (such as Matlab or SolidWorks), we can generate P-type and D-type unit cells with corresponding C values ​​(e.g., ...). Figure 1 (As shown).

[0058] Step 2: Sigmoid function transition fusion

[0059] Function application: Based on the unit cell generated in step 1, define the weight function for the transition region.

[0060]

[0061]

[0062]

[0063] F(x,y,z) is a function of the x, y, and z coordinates in the TPMS structure, k is the transition width parameter, and e is the base of the natural logarithm. Represents implicit functions for P-type TPMS structures. Implicit functions representing D-type TPMS structures;

[0064] The implicit function of the composite structure is =0

[0065] Both parameters ensure that the transition region satisfies G. 1 Continuous (no abrupt changes in curvature) avoids stress concentration, such as Figure 2 As shown.

[0066] Step 3: Structural Optimization and Materialization

[0067] Surface offset: the result obtained in step 2 =0 surface is offset along the normal by ±C to generate a closed solid structure;

[0068] The wall thickness t is selected from 0.55 to 1.25 mm, covering the commonly used engineering wall thickness range to ensure wall thickness uniformity. Figure 3 As shown.

[0069] Step 4: Additive Manufacturing Implementation

[0070] Array expansion: The solid unit cell obtained in step 3 is copied into a 4×4×4 array with an overall size of 40mm×40mm×40mm, forming a macroscopic component geometric model.

[0071] Process parameter optimization: Laser powder bed melting (LPBF) technology is used for forming, and aluminum alloy powder such as AlSi10Mg is selected. The process parameters are: laser power 175W, scanning speed 1250mm / s, and layer thickness 30μm.

[0072] Post-processing: No additional processing, such as grinding or splicing, is required after forming; the complete component is obtained directly.

[0073] Effect verification:

[0074] 1) Interface continuity: Existing technologies (such as cylindrical embedding schemes) achieve hybridization through mechanical splicing or local interpolation. The curvature change at the interface is too large, resulting in stress concentration. This embodiment uses the Sigmoid function (K=1) to achieve a continuous curvature transition between the P-type and D-type structures, avoiding stress concentration and significantly improving fatigue life.

[0075] 2) Geometric integrity: Existing technologies require sacrificing the original structural features, resulting in an insignificant composite effect. In this embodiment, through topological feature comparison, the original geometric features of the P-type and D-type structures are retained at a rate of >95%, without any “cutting the feet to fit the shoes” type of feature destruction, ensuring the synergistic optimization of mechanical properties.

[0076] 3) Manufacturing efficiency and cost optimization: Existing heterogeneous hybridization technology requires additional pre-processing steps (such as cavity prefabrication), which increases manufacturing costs by more than 30%. This embodiment can directly and quickly model through implicit functions without the need for post-processing, thus improving forming efficiency.

[0077] In another embodiment, an adaptive transition mechanism based on local geometric features is introduced on the basis of the original TPMS hybrid modeling method to improve the geometric continuity and structural stability of the transition region between P-type TPMS and D-type TPMS structures.

[0078] Define the weight function for the transition region:

[0079]

[0080] in:

[0081] λ( ) represents the TPMS structure fusion weights;

[0082] k( ) is the transition width adjustment parameter.

[0083] In the original model, parameter k is a constant used to control the width of the transition region. To further improve the geometric adaptability of the transition region, this implementation extends it to a position function related to local curvature:

[0084]

[0085] in:

[0086] The basic transition width parameter;

[0087] This is the curvature adjustment coefficient;

[0088] The local curvature of the TPMS surface.

[0089] Set a curvature threshold. The value of the curvature threshold is determined based on the curvature range of the TPMS unit cell structure, and can be set to 0.3 to 0.7 times the maximum curvature of the TPMS surface. When the local curvature exceeds the curvature threshold, the parameter... k ( The corresponding decrease makes the transition function change more smoothly, thereby reducing geometrical abrupt changes in high curvature regions; when the local curvature is less than the curvature threshold, the parameter... k ( Maintaining a large value makes the structural transition more compact; the transition weight function is used through an implicit function. With local curvature The joint regulation achieves adaptive fusion of P-type TPMS and D-type TPMS.

[0090] After obtaining the transition weight function, a hybrid TPMS implicit function is constructed through weighted fusion:

[0091]

[0092] When φH ( When )=0, it corresponds to the hybrid TPMS surface.

[0093] Furthermore, by performing a normal offset on the hybrid TPMS surface, a solid porous structure can be generated, whose solid implicit function representation is:

[0094]

[0095] Where t is the structural wall thickness parameter.

[0096] Using the above method, the transition width parameter can be automatically adjusted according to the local curvature in the transition area, making the fusion process between the P-type TPMS and D-type TPMS structures smoother, thereby reducing geometric distortion in the transition area, reducing local weak connections, and improving the surface quality and overall structural stability of the solid structure after offset.

[0097] This embodiment uses the transition weight function through an implicit function. With local curvature The joint regulation achieves adaptive fusion of P-type TPMS and D-type TPMS.

[0098] This embodiment achieves the design and manufacturing of an in-situ hybrid composite TPMS structure through clear parameter settings and operation steps, verifying its advantages in interface continuity, geometric integrity and mechanical properties. Moreover, the manufacturing process does not require additional pretreatment, and the cost is reduced by more than 30% compared with the ex-situ hybrid scheme, making it suitable for engineering applications under complex working conditions.

[0099] 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. An in-situ hybrid composite TPMS structure, characterized in that, include: The main structure is formed by the implicit fusion of P-type TPMS unit cells and D-type TPMS unit cells, and is formed by the offset of the fused TPMS surface along the normal direction by ±C, where C is the porosity control parameter. The main structure is a closed solid. The transition region achieves a smooth transition between the P-type and D-type structures using the Sigmoid function, and the transition region satisfies G... 1 continuous.

2. The structure according to claim 1, characterized in that: The morphology of the unit cell is adjusted by the porosity control parameter C. To ensure the continuity of its structure, the C value range of P-type TPMS unit cell is -0.6 to 0.6; the C value range of D-type TPMS unit cell is -0.1 to 0.5; and the C value range of the fused TPMS surface is -0.3 to 0.

3.

3. The structure according to claim 1, characterized in that: The mathematical expression for the Sigmoid function is: ； ； ； in, P is a P-type implicit TPMS function. D is a D-type implicit TPMS function; Let the transition width parameter k>0 and the weight function λ(x)=1 / (1+e^{–k·x}) be used. The implicit function of the composite structure is defined as follows: ; By adjusting k to control the transition gradient from P to D, G is guaranteed. 1 Continuity is achieved by eliminating abrupt changes in curvature and ensuring a smooth, continuous structure.

4. The structure according to claim 1, characterized in that: The wall thickness t of the main structure ranges from 0.55 to 1.25 mm, and the main structure is composed of an n×n×n single-cell array, where n ≥ 4.

5. The structure according to claim 3, characterized in that: An adaptive transition mechanism based on local geometric features is introduced, and a weight function for the transition region is defined: ； Where: λ( ) represents the TPMS structure fusion weights; k( () is the transition width adjustment parameter; ； in: The basic transition width parameter; This is the curvature adjustment coefficient; The local curvature of the TPMS surface; A curvature threshold is set, and its value is determined based on the curvature range of the TPMS unit cell structure. When the local curvature exceeds the curvature threshold, the parameter k( The corresponding decrease makes the transition function change more smoothly, thereby reducing geometrical abrupt changes in high curvature regions; when the local curvature is less than the curvature threshold, the parameter k( Maintaining a large value makes the structural transition more compact; the transition weight function is used through an implicit function. With local curvature The joint regulation achieves adaptive fusion of P-type TPMS and D-type TPMS.

6. A design method for an in-situ hybrid composite TPMS structure, characterized in that, Includes the following steps: Step 1: Generate P-type and D-type TPMS units: Based on the preset unit cell size and porosity control parameter C value, P-type and D-type TPMS units are generated respectively; Step 2: Sigmoid function transition blending: Based on the unit cell generated in step 1, the Sigmoid function is used to achieve a smooth transition between the P-type and D-type structures. The transition gradient is controlled by adjusting the transition width parameter k to form a composite TPMS surface that satisfies G¹ continuity. Step 3: Surface offset and wall thickness assignment: Will The curved surface is offset by ±C along the normal direction, with a wall thickness of t, to generate a closed solid structure; Step 4: Model slicing and process parameter optimization: The solid unit cell array obtained in step 3 is replicated to an n×n×n scale to form macroscopic component geometry.

7. The method according to claim 6, characterized in that: The C-value range for the composite TPMS surface is -0.3 to 0.

3.

8. The method according to claim 6, characterized in that, The mathematical expression for the Sigmoid function mentioned in step 2 is: ； ； ； in, P is a P-type implicit TPMS function. D is a D-type implicit TPMS function; Let the transition width parameter k>0 and the weight function λ(x)=1 / (1+e^{–k·x}) be used. The implicit function of the composite structure is defined as follows: ; By adjusting k to control the transition gradient from P to D, G is guaranteed. 1 Continuity is achieved by eliminating abrupt changes in curvature and ensuring a smooth, continuous structure.

9. The method according to claim 6, characterized in that: The wall thickness t mentioned in step 3 is in the range of 0.55 to 1.25 mm.

10. The method according to claim 8, characterized in that: An adaptive transition mechanism based on local geometric features is introduced, and a weight function for the transition region is defined: ； Where: λ( ) represents the TPMS structure fusion weights; k( () is the transition width adjustment parameter; ； in: The basic transition width parameter; This is the curvature adjustment coefficient; The local curvature of the TPMS surface; When the local curvature is large, the parameter k( The corresponding decrease makes the transition function change more smoothly, thereby reducing the geometric abrupt changes in high curvature regions; when the local curvature is small, the parameter k( Maintaining a large value makes the structural transition more compact; the transition weight function is used through an implicit function. With local curvature The joint regulation achieves adaptive fusion of P-type TPMS and D-type TPMS.

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