A curved sandwich structure path planning method for continuous fiber 3D printing

Abstract

This invention belongs to the field of 3D printing technology and relates to a path planning method for curved sandwich structures in continuous fiber 3D printing. The method includes the following steps: S1, obtaining the boundary contour of the curved model and extracting boundary contour points; S2, determining the boundary offset points and offset angles; S3, generating offset path points point by point based on the boundary offset points, initial position vectors, and offset angles of each boundary contour point, and sequentially connecting the offset path points to obtain the offset path; S4, using the termination position of the above offset path as the initial position of the offset path in the next cycle, returning to step S3 to regenerate the offset path, until the number of cycles equals the preset number, obtaining the core layer path; S5, sequentially connecting the outer skin path, core layer path, and inner skin path to form the planned path. This invention has the manufacturing advantages of uninterrupted and jump-free printing paths, realizing high-quality, high-continuity, and manufacturable automatic path planning for complex curved sandwich structures.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing technology and relates to a path planning method for curved sandwich structures used in continuous fiber 3D printing. Background Technology

[0002] Sandwich structures typically consist of an outer skin, an inner skin, and a core layer. They offer advantages such as light weight, high bending stiffness, strong buckling resistance, and excellent energy absorption capacity, making them widely used in aerospace, automotive, and other fields. Continuous fiber 3D printing technology combines high-performance continuous fiber reinforced composite materials with highly flexible additive manufacturing processes. Through a layer-by-layer stacking process, it reduces mold and assembly steps, thereby enabling the rapid, integrated prototyping of sandwich structures.

[0003] Currently, in sandwich structures printed using continuous fiber 3D printing, the core layer often employs a periodic arrangement of regular units, such as simple geometric units like circles, triangles, squares, and hexagonal honeycombs. The performance of the sandwich structure is controlled by changing these core unit types. Under planar configurations, these regular units can be periodically repeated at fixed dimensions, resulting in 3D printing paths for the generated sandwich structures that exhibit high manufacturability and adaptability.

[0004] However, with the increasing demands for lightweight, high-load-bearing, and complex shape designs in the industrial sector, sandwich structures need to meet the design and manufacturing requirements of curved configurations dominated by aerodynamic shape or other functions. Under curved surface configurations, the aforementioned regular periodic arrangement forms are difficult to adapt to changes in surface geometry, and are prone to problems such as path distortion, local overlap, or forced interruption. This leads to an increase in forming defects in continuous fiber-reinforced composite materials and a decrease in the mechanical properties of 3D printed sandwich structures, thus limiting their engineering applications in complex curved surface high-performance sandwich structures. Summary of the Invention

[0005] The purpose of this invention is to provide a path planning method for curved sandwich structures in continuous fiber 3D printing, so as to solve the technical problems that existing solutions are prone to path distortion, local overlap or forced interruption, and are difficult to apply to complex curved high-performance sandwich structures.

[0006] To achieve the above objectives, the specific technical solution provided by the present invention is as follows: A path planning method for curved sandwich structures in continuous fiber 3D printing includes the following steps: S1. Obtain the boundary contour of the surface model, and extract the boundary contour points on the boundary contour with equal arc length; S2. Based on the boundary contour points, determine the boundary offset point corresponding to each boundary contour point and the offset angle corresponding to each boundary contour point; S3. Set the initial position and obtain the initial position vector based on the initial position; generate offset path points point by point according to the boundary offset points, the initial position vector and the offset angle of each boundary contour point, and connect the offset path points in sequence to obtain the offset path. S4. Take the termination position of the above bias path as the initial position of the bias path in the next cycle, return to step S3 to regenerate the bias path, until the number of cycles equals the preset number, and obtain the core path. S5. Generate outer skin path and inner skin path on both sides of the core layer path according to the boundary contour of the surface model. Connect the outer skin path, core layer path and inner skin path in sequence to form the planned path of the surface model for 3D printing.

[0007] Furthermore, the boundary offset point is determined based on the following formula: ; in, For the first The x-coordinates of the boundary offset points For the first The ordinates of the boundary offset points R This is the boundary offset. s This is the offset direction coefficient, and s ∈{-1,1}, For the first A boundary contour point, For the first The unit normal vector of each boundary contour point.

[0008] Furthermore, the bias path point is determined based on the following formula: ; in, For the first The x-coordinates of the offset path points For the first The ordinates of the offset path points Let be the initial position vector, and , For the first The offset angles corresponding to the boundary contour points, and , Let be the path offset, and satisfy . , The initial phase angle, It is the arc length between two adjacent boundary contour points.

[0009] Furthermore, the determination of the unit normal vector includes the following steps: The tangential direction vectors of each boundary contour point are obtained by difference operation, and then normalized to obtain the corresponding unit tangential vectors. The unit normal vector pointing to the curvature center of the boundary profile is determined based on the unit tangent vector.

[0010] Furthermore, the step of generating outer skin paths and inner skin paths on both sides of the core layer path based on the boundary contour of the surface model includes: generating a skin path on one side based on the boundary contour of the surface model, and then, using the skin path on one side as a reference, generating a skin path on the other side by equidistant offset along the surface normal direction of the core layer path according to the thickness of the core layer path.

[0011] Furthermore, the path planning method for curved sandwich structures used in continuous fiber 3D printing also includes step S6, which follows step S5: Determine whether the radius of curvature of the planned path is greater than or equal to the preset radius of curvature. If yes, use the planned path for 3D printing. If no, return to step S2 and adjust the offset angle of the initial position vector and the boundary contour point.

[0012] Furthermore, the boundary contour is obtained by slicing the surface model into layers.

[0013] Furthermore, in step S3, adjacent offset path points are connected by straight lines.

[0014] The path planning method for curved sandwich structures in continuous fiber 3D printing according to the present invention has the following advantages: The present invention first extracts boundary contour points by equal arc length to ensure that the spatial reference for path generation is uniform and reliable; second, it calculates boundary offset points by normal offset to ensure that the path layout is strictly controlled by the surface geometry boundary; then, it generates an offset path by co-driving the boundary offset points, initial position vector and offset angle to achieve parameterized control of the path shape; finally, it uses the termination position of the offset path in the previous cycle as the initial position of the offset path in the next cycle, generates the core layer path by looping, and constructs skin paths on the outside and inside of the core layer path respectively. The skin path and the core layer path are connected in sequence to form a continuous planning path for 3D printing.

[0015] The present invention utilizes a collaborative approach to generate an offset path based on boundary offset points, initial position vectors, and offset angles, without relying on preset geometric shapes. Compared to existing technologies, it overcomes the design limitations of periodic arrangements of simple geometric units, effectively solving technical problems such as the difficulty in matching regular units with curved surface geometric features, the inability of paths to effectively conform to curved surface contour boundaries, and low path continuity and stability. This reduces defects in continuous fiber forming and improves the mechanical properties of sandwich structures. The invention has good applicability; the generated continuous fiber 3D printing path possesses the manufacturing advantages of being uninterrupted and jump-free, thus achieving high-quality, high-continuity, and manufacturable automatic path planning and manufacturing for complex curved surface sandwich structures. This provides a new solution for the application and promotion of high-performance composite material sandwich structures in the industrial field. Attached Figure Description

[0016] Figure 1 This is a flowchart of the path planning method for the curved sandwich structure of the present invention; Figure 2 This is a schematic diagram of the contour boundary generation path of the present invention; Figure 3 This is a schematic diagram of a single bias path according to the present invention; Figure 4 This is a schematic diagram of the core layer path of the present invention; Figure 5 This is a schematic diagram of the core layer path, outer skin, and inner skin of the present invention; Figure 6 This is a schematic diagram of the planned path of the present invention.

[0017] Figure label: 1. Boundary contour; 2. Offset path; 3. Core layer path; 4. Outer skin path; 5. Inner skin path; 6. Planning path. Detailed Implementation

[0018] The technical solutions of this application will now be described clearly and in detail with reference to the accompanying drawings. In the description of the embodiments of this application, unless otherwise stated, "multiple" refers to two or more. The terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0019] like Figures 1 to 6 As shown, this invention provides a path planning method for curved sandwich structures in continuous fiber 3D printing, comprising the following steps: S1. Obtain the boundary contour 1 of the surface model, and extract the boundary contour points on the boundary contour 1 with equal arc length. S2. Based on the boundary contour points, determine the boundary offset point corresponding to each boundary contour point and the offset angle corresponding to each boundary contour point; S3. Set an initial position and obtain an initial position vector based on the initial position; according to the boundary offset points, the initial position vector, and the offset angles of each boundary contour point, generate offset path points point by point, and connect the offset path points sequentially to obtain the offset path, such as... Figure 2 and Figure 3 As shown; S4. Using the termination position of the above bias path as the initial position of the bias path in the next loop, return to step S3 to regenerate the bias path until the number of loops equals the preset number, thus obtaining core path 3, as shown. Figure 4 As shown; S5. Based on the boundary contour of the surface model, generate outer skin path 4 and inner skin path 5 on both sides of core layer path 3 respectively. Connect outer skin path 4, core layer path 3, and inner skin path 5 in sequence to form the planned path for the surface model used for 3D printing. Figure 5 and Figure 6 As shown.

[0020] In step S1 of the present invention, equal arc length extraction refers to sampling along the contour curve with a fixed arc length step to obtain a set of discrete boundary contour points. This sampling method ensures that the boundary contour points are evenly distributed in geometric space, providing a stable spatial reference for subsequent path generation.

[0021] In step S2 of the present invention, the boundary offset point is a position reference point used to define the path offset boundary; this offset operation ensures that the path generation is always constrained within or outside the contour geometric boundary, thereby ensuring the spatial consistency between the path and the surface shape.

[0022] In step S3 of the present invention, the initial position vector is a two-dimensional vector used to control the initial shape and relative position of the offset path, and the offset angle is an angle parameter that changes dynamically as the boundary contour point number increases; the boundary offset point, the initial position vector, and the offset angle constitute the basis for the generation of the offset path.

[0023] In step S4 of the present invention, the core layer path 3 is a continuous filling path formed by sequentially connecting multiple single-bias paths 2; the preset number of cycles is an integer. ,and The termination position of the offset path point in the previous loop becomes the initial position of the offset path point in the next loop, thus adjusting the initial position of the next loop. This looping mechanism avoids path jumps and breakpoints caused by topology reconstruction in traditional cellular structures, ensuring that the core layer path 3 is continuous and uninterrupted throughout. This application obtains a core layer path 3 with high continuity and adjustable fill density by setting a preset number of iterations.

[0024] In step S5 of this invention, the outer skin path 4 is a closed loop path generated by conforming to the original boundary contour 1, used to bear external loads and provide structural shape constraints; the inner skin path 5 is another closed loop path located inside the core layer path 3 and maintaining an equidistant relationship with the outer skin path 4, used to seal the core layer and collaboratively improve bending stiffness; the two, together with the core layer path 3, constitute a three-layer sandwich path configuration of outer skin-core layer-inner skin; the end point of the outer skin path 4 is connected to the start point of the core layer path 3, and the end point of the core layer path 3 is connected to the start point of the inner skin path 5. This application can generate the inner and outer skin paths 4 by means of contour scaling transformation; this application can also generate the inner and outer skin paths 4 by means of equidistant offset algorithm; further, this application can also generate the inner and outer skin paths 4 by means of parametric envelope fitting. This application obtains a complete single-layer planning path 6 that meets the requirements of continuous fiber 3D printing process based on any of the above methods. A continuous fiber reinforced composite curved sandwich structure has been obtained according to the method of this invention, verifying the feasibility and practicality of this scheme.

[0025] In the path planning method for curved sandwich structures for continuous fiber 3D printing of this invention, firstly, boundary contour points are extracted by equal arc length to ensure that the spatial reference for path generation is uniform and reliable; secondly, boundary offset points are calculated by normal offset to ensure that the path layout is strictly controlled by the curved surface geometric boundary; then, an offset path is generated by the collaborative driving of boundary offset points, initial position vector and offset angle to achieve parameterized control of the path shape; finally, the termination position of the offset path in the previous cycle is used as the initial position of the offset path in the next cycle, and the core layer path 3 is generated by iterative generation, and skin paths are constructed on the outer and inner sides respectively. The skin path and the core layer path 3 are connected in sequence to form a continuous planning path 6 for 3D printing.

[0026] The present invention utilizes a collaborative approach to generate an offset path based on boundary offset points, initial position vectors, and offset angles, without relying on preset geometric shapes. Compared to existing technologies, it overcomes the design limitations of periodic arrangements of simple geometric units, effectively solving technical problems such as the difficulty in matching regular units with curved surface geometric features, the inability of paths to effectively conform to curved surface contour boundaries, and low path continuity and stability. This reduces defects in continuous fiber forming and improves the mechanical properties of sandwich structures. The invention has good applicability; the generated continuous fiber 3D printing path possesses the manufacturing advantages of being uninterrupted and jump-free, thus achieving high-quality, high-continuity, and manufacturable automatic path planning and manufacturing for complex curved surface sandwich structures. This provides a new solution for the application and promotion of high-performance composite material sandwich structures in the industrial field.

[0027] In some embodiments of the present invention, the boundary offset point is determined based on the following formula: ; in, For the first The x-coordinates of the boundary offset points For the first The ordinates of the boundary offset points R This is the boundary offset. s This is the offset direction coefficient, and s ∈{-1,1}, For the first A boundary contour point, For the first The unit normal vector of each boundary contour point. The boundary offset point and the first Each boundary contour point corresponds to one of the points.

[0028] In this embodiment, the boundary offset R is used to characterize the arrangement density of the core layer path 3. As the value of R increases, the path arrangement tends to be sparse; as the value of R decreases, the path arrangement tends to be dense. Offset direction coefficient The generation basis for distinguishing between outer skin path 4 and inner skin path 5—when When the boundary offset point is located on the positive side of the normal of the boundary profile point, it corresponds to the core reference path after the outer skin contracts inward; when At that time, the boundary offset point is located on the side opposite to the normal, corresponding to the core layer reference path after the inner skin expands outward; unit normal vector Ensure the offset is strictly performed along the local geometric normal to avoid path distortion caused by tangential perturbations; boundary contour points As the starting reference for offset calculation, its equal arc length distribution characteristics ensure the spatial uniformity and continuity of the subsequent offset path.

[0029] This embodiment uses boundary offset. With offset direction coefficient The normal offset magnitude and direction of boundary contour points are coordinated and controlled, and the unit normal vector is used as a reference. The offset is ensured to strictly adhere to local geometric features, so that the generated boundary offset points can adapt to the spatial variations of the surface contour. Based on this, boundary contour points extracted with equal arc lengths are combined... This ensures that the entire offset reference curve has good parameter continuity and topological consistency, thereby providing a reliable geometric basis for the regular generation of offset path points in step S3, and ultimately supporting the high-fidelity, low-defect integrated forming of the curved sandwich structure in the continuous fiber 3D printing process.

[0030] In some embodiments of the present invention, the bias path point Determined based on the following formula: ; In the formula, For the first The x-coordinates of the offset path points For the first The ordinates of the offset path points For the first One boundary offset point, Let the initial position vector be... For the first The offset angle corresponding to each boundary offset point. The bias path point, the first The boundary offset point and the first Each boundary contour point corresponds to one of the points.

[0031] In this embodiment, path points with directional consistency and phase continuity are generated at each boundary offset point; spatial orientation mapping of vectors is achieved by using a rotation matrix, so that the offset path naturally conforms to the contour of the curved surface; on this basis, all boundary offset points are sequentially connected to form a single offset path 2, which provides geometrically controllable bottom-layer path units for the multi-loop generation of the core layer path 3 in step S4, thereby solving the dual defects of the curved sandwich structure path in the prior art in terms of geometric adaptability and fiber continuity.

[0032] In some embodiments of the present invention, the initial position vector for: ; In the formula, Let be the path offset, and satisfy . , This is the initial phase angle.

[0033] In this embodiment, the initial position vector is explicitly defined as the path offset. and initial phase angle The polar coordinate form is jointly determined. The path offset determines the core thickness. The thickness of the core layer is twice that of the surface, and its magnitude directly determines the thickness dimension of the core layer structure. Furthermore, by leveraging the adaptive mapping capability of the boundary offset points to the contour geometry in this application, the final generated path is strictly constrained within the surface boundary and possesses curvature continuity and directional gradation for continuous fiber layup processes, thereby effectively solving the problems of fiber breakage and forming defects caused by path distortion in the prior art.

[0034] In some embodiments of the present invention, the first The offset angle corresponding to each boundary offset point for: ; In the formula, d sIt is the arc length between two adjacent boundary contour points.

[0035] In this embodiment, the present application designs the offset angle to be similar to... By establishing a proportional relationship, the initial position vector is rotated at a controllable angle around the corresponding boundary offset point at each point, thereby generating a continuous offset path with Archimedean spiral-like characteristics. Based on this, the normal offset mechanism of the boundary offset point and the equal arc length sampling strategy are combined to ensure that the path maintains geometric continuity under the surface boundary constraints while avoiding local folding or intersection. Finally, without adding jumps or interruptions, a high-quality single-offset path 2 that meets the continuous fiber layup process constraints is output, providing a stable and scalable geometric foundation for the subsequent cyclic generation of the core layer path 3 and the integration of the skin-core-skin three layers.

[0036] In some embodiments of the present invention, the determination of the unit normal vector includes the following steps: (1) Obtain the tangential direction vector of each boundary contour point through difference operation, and normalize it to obtain the corresponding unit tangential vector.

[0037] In this step, the difference operation refers to calculating the coordinate difference between the discrete boundary contour points and their adjacent points to approximately represent the local tangent direction at that point; the tangent direction vector can be the first... Boundary contour points Its previous neighboring point and the next adjacent point The central difference vector formed, i.e. This vector represents the instantaneous motion trend along the contour at that point in a two-dimensional plane.

[0038] Normalization involves dividing the tangential direction vector by its Euclidean magnitude to make its length 1, thereby obtaining a unit tangential vector that retains only directional information. This operation eliminates the differences in vector length caused by uneven sampling density or curvature changes, ensuring that the normal vectors obtained by subsequent rotations are consistent and comparable. In this step, the unit tangent vector is used as the direct input for generating the unit normal vector. Its directional stability directly affects the spatial positioning accuracy of the boundary offset point, and thus affects the geometric fidelity and printing feasibility of the entire offset path.

[0039] (2) Determine the unit normal vector pointing to the curvature center of the boundary profile based on the unit tangent vector.

[0040] In this step, the unit tangent vector can be orthogonally transformed by rotating it by 90 degrees, mapping it to a vector in the vertical direction; this transformation has a deterministic mathematical expression and does not depend on the global coordinate system or local parameterization of the surface.

[0041] The unit normal vector directly participates in the calculation of the boundary offset point defined in this application. Its directional accuracy determines whether the offset path is strictly constrained within the contour geometric boundary, and is the key geometric basis for realizing the adaptive generation of the curved sandwich structure path.

[0042] This embodiment obtains the tangential direction vector through differential operation, eliminates scale interference by normalization, and obtains the unit normal vector pointing uniquely to the curvature center direction of the boundary contour through deterministic rotation, thus achieving robust extraction of the unit normal vector for any shape boundary contour 1. This process does not rely on surface analytical expressions or mesh topology information, but only requires a discrete point set of equal arc length sampling, which is suitable for general boundary data output by modeling software. The obtained unit normal vector provides a geometric reference for the boundary offset point calculation in this application, supports the accurate execution of normal offset in step S2, and thus ensures the overall geometric adaptability and process feasibility of the offset path, core path 3 and skin path in steps S3 to S5.

[0043] In some embodiments of the present invention, the path planning method for curved sandwich structures for continuous fiber 3D printing further includes step S6 following step S5: Determine if the radius of curvature of the planned path 6 is greater than or equal to the preset radius of curvature. If yes, use the planned path 6 for 3D printing; otherwise, return to step S2 to adjust the initial position vector and the offset angle of the boundary contour points. For example, this can be achieved by adjusting the parameters. and Adjustments are made to adjust the offset angles of the initial position vector and boundary contour points, thereby adjusting the radius of curvature of the planned path 6.

[0044] In this embodiment, the planned path 6 is a continuous path formed by sequentially connecting the outer skin path 4, the core layer path 3, and the inner skin path 5. The radius of curvature is the reciprocal of the local geometric curvature of the planned path 6 at any position, used to characterize the degree of path curvature. The preset radius of curvature is the minimum allowable radius of curvature determined according to the constraints of the continuous fiber 3D printing process, and its value depends on the combination of process parameters such as the mechanical properties of the raw material, nozzle diameter, travel speed, fiber placement tension, and forming temperature.

[0045] The curvature at each point along a continuous path can be calculated using the definition of differential geometry, and its reciprocal can be taken as the radius of curvature at the corresponding location. (Preset radius of curvature) Let be a non-negative real threshold, satisfying Furthermore, it is automatically loaded by user input or based on the device's factory calibration parameters during the system initialization phase.

[0046] This embodiment achieves adaptive process verification during path generation by performing a closed-loop comparison between the geometric curvature attributes of the planned path 6 and the minimum radius of curvature required by the continuous fiber 3D printing process, and feeding back to the offset path generation stage when the condition is not met. Through dynamic correction of adjustable parameters such as the initial position vector and offset angle, the generated path automatically avoids high-curvature sections while maintaining overall configuration constraints. This ensures continuous, uniform, and slip-free fiber placement on the curved path without adding additional structural layers or sacrificing the topological integrity of the sandwich structure, effectively suppressing fiber breakage, wrinkling, and delamination defects caused by sharp bends, and improving the forming quality and mechanical property consistency of the curved sandwich structure.

[0047] In some embodiments of the present invention, the surface model is created by modeling software, and the boundary contour 1 is obtained by slicing the surface model into layers.

[0048] In this embodiment, the surface model can be any continuous, smooth, or piecewise continuous free-form surface geometry constructed using computer-aided design software, parametric modeling tools, or a general-purpose 3D modeling platform. The modeling software can be a commercial or open-source 3D modeling tool well-known to those skilled in the art, such as AutoCAD, SolidWorks, Creo, NX, and CATIA, which possesses surface modeling, Boolean operations, thickness offsetting, and model export functions. The established surface model is stored in a standard format for subsequent path planning module reading.

[0049] Boundary contour 1 is the projection of the closed intersection line of the surface model on the plane at a specified height; the intersection line is a two-dimensional planar curve, and its geometric shape strictly inherits the local curvature and orientation characteristics of the original surface at this layer position; layer slicing refers to the equidistant or variable distance scattering of the surface model along a preset direction, and each slice plane intersects with the surface to form one or more continuous closed contour lines.

[0050] This embodiment utilizes modeling software to construct a curved surface model and obtains the boundary contour 1 through layered slicing, achieving a deterministic mapping from three-dimensional digital definition to two-dimensional manufacturing instructions. This method is fully compatible with existing additive manufacturing process chains, requiring no additional reverse modeling or manual outlining, ensuring data traceability and geometric consistency in the path planning process. Simultaneously, layered slicing, as a standardized preprocessing step, allows this method to adapt to arbitrarily complex free-form surfaces, providing reliable data input for high-fidelity, distortion-free placement of continuous fibers in curved sandwich structures.

[0051] In some embodiments of the present invention, in step S3, adjacent offset path points are connected by a straight line.

[0052] In this embodiment, adjacent offset path points are connected by straight lines, which makes it simple and convenient to connect adjacent points without complex calculations and can quickly generate offset paths.

[0053] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A path planning method for curved sandwich structures used in continuous fiber 3D printing, characterized in that, Includes the following steps: S1. Obtain the boundary contour of the surface model, and extract the boundary contour points on the boundary contour with equal arc length; S2. Based on the boundary contour points, determine the boundary offset point corresponding to each boundary contour point and the offset angle corresponding to each boundary contour point; S3. Set the initial position and obtain the initial position vector based on the initial position; generate offset path points point by point according to the boundary offset points, the initial position vector and the offset angle of each boundary contour point, and connect the offset path points in sequence to obtain the offset path. S4. Take the termination position of the above bias path as the initial position of the bias path in the next cycle, return to step S3 to regenerate the bias path, until the number of cycles equals the preset number, and obtain the core path. S5. Generate outer skin path and inner skin path on both sides of the core layer path according to the boundary contour of the surface model. Connect the outer skin path, core layer path and inner skin path in sequence to form the planned path of the surface model for 3D printing.

2. The path planning method for curved sandwich structures for continuous fiber 3D printing according to claim 1, characterized in that, The boundary offset point is determined based on the following formula: ； in, For the first The x-coordinates of the boundary offset points For the first The ordinates of the boundary offset points R This is the boundary offset. s This is the offset direction coefficient, and s ∈{-1,1}, For the first A boundary contour point, For the first The unit normal vector of each boundary contour point.

3. The path planning method for curved sandwich structures for continuous fiber 3D printing according to claim 2, characterized in that, The bias path point is determined based on the following formula: ； in, For the first The x-coordinates of the offset path points For the first The ordinates of the offset path points Let be the initial position vector, and , For the first The offset angles corresponding to the boundary contour points, and , Let be the path offset, and satisfy . , The initial phase angle, It is the arc length between two adjacent boundary contour points.

4. The path planning method for curved sandwich structures used in continuous fiber 3D printing according to claim 2, characterized in that, The determination of the unit normal vector includes the following steps: The tangential direction vectors of each boundary contour point are obtained by difference operation, and then normalized to obtain the corresponding unit tangential vectors. The unit normal vector pointing to the curvature center of the boundary profile is determined based on the unit tangent vector.

5. The path planning method for curved sandwich structures for continuous fiber 3D printing according to claim 1, characterized in that, The method of generating outer skin paths and inner skin paths on both sides of the core layer path according to the boundary contour of the curved surface model includes: generating a skin path on one side according to the boundary contour of the curved surface model, and then using the skin path on one side as a reference, and based on the thickness of the core layer path, generating the skin path on the other side by equidistant offset along the curved surface normal direction of the core layer path.

6. The path planning method for curved sandwich structures for continuous fiber 3D printing according to claim 1, characterized in that, It also includes step S6, which follows step S5: Determine whether the radius of curvature of the planned path is greater than or equal to the preset radius of curvature. If yes, use the planned path for 3D printing. If no, return to step S2 and adjust the offset angle of the initial position vector and the boundary contour point.

7. The path planning method for curved sandwich structures for continuous fiber 3D printing according to claim 1, characterized in that, The boundary contour is obtained by slicing the surface model into layers.

8. The path planning method for curved sandwich structures for continuous fiber 3D printing according to claim 1, characterized in that, In step S3, adjacent offset path points are connected by straight lines.

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