Skin lattice structure and internal support design method for additive manufacturing

Abstract

The present invention relates to the field of lightweight structure technology, and in particular to a skin lattice structure for additive manufacturing and an internal support design method for the structure. The method uses a model that has been designed and assembled according to size as the design basis, and through discretization of the skin, determines the support points, and the internal support obtained satisfies the printing support, ensuring the load transfer between the upper skin and the lattice core layer while minimizing the impact on the mechanical property distribution of the lattice core layer. In addition, since the skin geometry is spatially discretized during the modeling process, the spatial coordinates of the nodes are extracted and can be easily converted into a finite element model for calculation or preparation, which brings convenience to the design and simulation calculation of the product and has very important engineering application value. The skin lattice structure has a skin lattice structure with a reasonable internal support structure, which ensures the load transfer between the upper skin and the lattice core layer, reduces the impact on the mechanical property distribution of the lattice core layer, and does not need to be removed after printing is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of lightweight structures, and in particular to a skin lattice structure for additive manufacturing and an internal support design method for the structure. Background Art

[0002] With the rapid development of engineering technology in various fields in my country, the aerospace and automotive industries are placing higher demands on lightweight, high-performance, and multifunctional structures. Three-dimensional lattice structures, which can adjust the mechanical properties of the lattice structure by adjusting the microstructure geometry, have broad application prospects in the lightweight design of complex structures. In practical engineering applications, a skin lattice structure is often formed by wrapping a lattice core layer over it, providing protection for the lattice core while fully utilizing the excellent performance of the lattice structure.

[0003] Due to its complex geometric structure, the skin-lattice structure is often manufactured using an additive manufacturing process, and the support constraints of the structure need to be considered during the additive manufacturing process. Unlike the support structure of a traditional solid structure, the internal support of the skin-lattice structure is located inside the skin-lattice structure and is connected to the lattice core layer. It cannot be removed after the additive process is completed, and it plays a role in bearing and transferring loads between the skin and core layers. If the structure is unreasonable, it will seriously affect the performance of the skin-lattice structure. In addition, since the skin-lattice structure generally has a more complex geometric configuration, the design and modeling of the support is more difficult. Therefore, how to add suitable rods to the lattice core layer to support the lattice core layer itself and the outer covering skin becomes a key issue in the design process of the skin-lattice structure. At present, there is no method for designing the internal support of the skin-lattice structure specifically for additive manufacturing. Summary of the Invention

[0004] (1) Technical issues to be resolved

[0005] The first object of the present invention is to provide an internal support design method for a skin lattice structure for additive manufacturing, so as to solve the problem of internal support design for a skin lattice structure for additive manufacturing.

[0006] The second object of the present invention is to provide a skin lattice structure with a reasonable internal support structure for additive manufacturing.

[0007] (2) Technical solution

[0008] To achieve the first objective above, in a first aspect, the present invention provides a method for designing an internal support for a skin lattice structure for additive manufacturing, comprising the following steps:

[0009] The upper skin model wrapped on the upper side of the lattice core layer is spatially discretized, and the distance between any two adjacent nodes after discretization is no greater than the minimum span allowed by the additive manufacturing process;

[0010] The centroid of the discrete unit is offset by a preset distance along the negative printing direction to obtain a support reference point of the discrete unit, and the lines connecting the support reference point to each node of the discrete unit are respectively used as axes. A corresponding number of support rods are obtained according to a first preset radius to form a pyramid support of the discrete unit, and the inclination angle of each support rod is not less than the minimum molding angle allowed by the additive manufacturing process used. A connection point is selected on the lattice core layer, and the line connecting the vertex of the pyramid support and the connection point on the lattice core layer is used as the axis. A connecting rod connecting the lattice core layer and the pyramid support is obtained according to a second preset radius, and the inclination angle of the connecting rod is not less than the minimum molding angle allowed by the additive manufacturing process used.

[0011] When a pyramid support is formed at each discrete unit obtained by discretization, and the vertex of each pyramid support is connected to the lattice core layer through a connecting rod, the inner support of the upper skin is obtained.

[0012] Preferably, the preset offset distance of the centroid is less than half the length of a unit cell period of the lattice core layer.

[0013] Preferably, the first preset radius is the same as the radius of the rods of the lattice core layer; and / or

[0014] The second preset radius is the same as the rod radius of the lattice core layer.

[0015] Preferably, within the range between the minimum forming angle allowed by the additive manufacturing process and 90°, the connecting rod is inclined at a larger angle relative to the horizontal plane.

[0016] Preferably, the number of rods connected to the connection points on each lattice core layer does not exceed eight.

[0017] In the second aspect, on the basis of any implementation method in the first aspect, when the unit cell of the lattice core layer close to the lower skin side has a suspended node, the lower skin model is spatially discretized, and the connection point is selected from the nodes after the lower skin is discretized. The line between the suspended node and the connection point on the lower skin is used as the axis, and the suspended point support rod is obtained according to the third preset radius. The inclination angle of the suspended point support rod is not less than the minimum forming angle allowed by the additive manufacturing process adopted, until each suspended node is connected to a suspended point support rod.

[0018] In the second aspect, preferably, within the range between the minimum forming angle allowed by the additive manufacturing process and 90°, the suspension point support rod selects a larger inclination angle relative to the horizontal plane.

[0019] In the second aspect, preferably, the third preset radius is the same as the radius of the rods of the lattice core layer.

[0020] In order to achieve the above-mentioned second purpose, in the third aspect, the present invention also provides a skin lattice structure for additive manufacturing, including an upper skin, a lattice core layer and a lower skin, the lattice core layer is located between the upper skin and the lower skin, and each unit cell of the lattice core layer located in the lower layer has a node connected to the lower skin, so that the lower skin provides the required printing support for the lattice core layer, and an upper skin internal support is provided between the upper skin and the lattice core layer, and the upper skin internal support is obtained by any internal support design method in the first aspect.

[0021] In the fourth aspect, the present invention also provides a skin lattice structure for additive manufacturing, comprising an upper skin, a lattice core layer and a lower skin, the lattice core layer being located between the upper skin and the lower skin, an upper skin internal support being provided between the upper skin and the lattice core layer, and a suspended point support rod being connected to the suspended node between the lattice core layer and the lower skin, and the upper skin internal support and the suspended point support rod being obtained by the internal support design method of any one of the above-mentioned second aspects.

[0022] (3) Beneficial effects

[0023] The above-mentioned technical solution of the present invention has the following advantages: the internal support design method of the skin lattice structure for additive manufacturing provided by the present invention uses a designed and sized assembled model as the design basis, and through discretization of the skin, determines the support points to meet the printing support, thereby ensuring the load transfer between the upper skin and the lattice core layer while minimizing the impact on the distribution of the mechanical properties of the lattice core layer. In addition, since the skin geometry is spatially discretized during the modeling process, the spatial coordinates of the extracted nodes can be easily converted into a finite element model for calculation or preparation, which brings convenience to the design and simulation calculation of the product and has very important engineering application value. In particular, it has advantages when facing skin lattice structures in which the lattice core layer is located in a closed cavity formed by the upper skin and the lower skin and / or has a complex geometric morphology.

[0024] The skin lattice structure has a reasonable internal support structure, which not only meets the printing support, but also fully considers the load-bearing requirements of the internal support, ensuring the load transfer between the upper skin and the lattice core layer while minimizing the impact on the distribution of the mechanical properties of the lattice core layer. It does not need to be removed after printing is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings of the present invention are provided for illustrative purposes only, and the proportions and quantities of the components in the drawings may not necessarily be consistent with the actual product.

[0026] Figure 1 This is a flow chart of an internal support design method for an additively manufactured skin lattice structure in a first embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of a model of a skin lattice part without internal support in an embodiment of the present invention;

[0028] Figure 3 yes Figure 2 Schematic diagram of the middle section of the middle skin lattice part model;

[0029] Figure 4 This is a schematic diagram of a discretized upper skin model of a skin lattice component according to an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of a model of a pyramid support and connecting rod of a discrete unit of an upper skin of a skin lattice part according to an embodiment of the present invention;

[0031] Figure 6 This is a flow chart of an internal support design method for a skin lattice structure for additive manufacturing in a second embodiment of the present invention;

[0032] Figure 7 This is a schematic diagram of a model of the connection between the suspended point support rods of a skin lattice component and the lower skin and the lattice core layer in an embodiment of the present invention;

[0033] Figure 8 It is a schematic diagram of the middle section of a skin lattice part model with added internal support in an embodiment of the present invention.

[0034] In the picture:

[0035] 1: Upper skin;

[0036] 2: lattice core layer;

[0037] 3: lower skin;

[0038] 4: Upper skin inner support;

[0039] 41: pyramid support;

[0040] 411: support rod;

[0041] 42: connecting rod;

[0042] 5: Suspension point support rod. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0044] The terms "first," "second," and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0045] Example 1

[0046] An embodiment of the present invention provides an internal support design method for a skin lattice structure for additive manufacturing, which is mainly aimed at the fact that due to the design of the unit cell structure of the lattice core layer, the lattice core layer cannot meet the printing support requirements for the upper skin when additive manufacturing is adopted.

[0047] See also Figures 1 to 3 As shown, the design of the upper skin 1, the lower skin 2 and the lattice core layer 2 can be designed normally according to the requirements, see Figure 2 and Figure 3 As shown, a pre-designed and dimensioned model is used as the basis for the design. Figure 4 As shown, the upper skin 1 is spatially discretized to obtain the spatial coordinates of each node after discretization (extracting node coordinates). The distance between any two adjacent nodes of the upper skin 1 after discretization is no greater than the minimum span allowed by the additive manufacturing process used. In this embodiment, the upper skin 1 is preferably spatially discretized using quadrilaterals, and the resulting discrete units are quadrilaterals with four nodes.

[0048] See also Figure 5As shown, the centroid of the discrete unit is offset by a preset distance along the negative printing direction (perpendicular to and toward the printing substrate) to obtain the support reference point of the discrete unit, and the lines connecting the support reference point to each node of the discrete unit are used as axes, and four support rods 411 with a circular cross-section are obtained by stretching according to a first preset radius. One end of the four support rods 411 is connected to the four nodes respectively, and the other end is connected to the support reference point to form a pyramid support 41 of the discrete unit (in this embodiment, the pyramid support is a quadrangular pyramid support), and the inclination angle of each support rod 411 of the quadrangular pyramid support is not less than the minimum molding angle allowed by the additive manufacturing process used (it may vary depending on the process, for example, 35°, 40°, etc., but the minimum molding angle is a determined angle after the process is determined). After the support reference point (the vertex of the quadrangular pyramid) is determined, a connection point is selected on the lattice core layer 2. The coordinates of the connection point can be obtained through the model or by spatially discretizing the lattice core layer 2, which is not limited here. The line between the vertex of the pyramid support 41 and the connection point on the selected lattice core layer 2 is used as the axis, and the connecting rod 42 with a circular cross-section connecting the lattice core layer 2 and the pyramid support 41 is stretched according to the second preset radius, wherein the inclination angle of the connecting rod 42 is not less than the minimum forming angle allowed by the additive manufacturing process adopted.

[0049] When each discrete unit obtained by discretization forms a pyramid support 41, and the vertex of each pyramid support 41 is connected to the lattice core layer 2 through a connecting rod 42, the upper skin inner support 4 is obtained. In turn, a skin lattice structure that can meet the manufacturing requirements of the village is obtained.

[0050] The internal support obtained by this design method is not only used to support the upper skin and meet the printing support, but also fully considers the load-bearing requirements of the internal support, ensuring the load transfer between the upper skin and the lattice core layer while minimizing the impact on the distribution of the mechanical properties of the lattice core layer. On the other hand, since the skin geometry is spatially discretized and the spatial coordinates of the nodes are extracted during the modeling process, it can be very conveniently converted into a finite element model for calculation or preparation, which brings great convenience to the design and simulation calculation of the product and has very important engineering application value. In particular, when facing a skin lattice structure in which the lattice core layer is located in a closed cavity formed by the upper skin and the lower skin, or a skin lattice structure with a complex geometric morphology (for example, a large curvature or a variety of different curvatures), the design method of this embodiment is more advantageous.

[0051] In some embodiments, triangles are used to spatially discretize the upper skin, and each discrete unit has three nodes (adjacent discrete units have common nodes). The design method is basically the same as that of using quadrilaterals for spatial discretization, with the difference that the pyramid support obtained by the discrete unit is a triangular pyramid support.

[0052] In other embodiments, polygons such as pentagons and hexagons are used to spatially discretize the upper skin. For some skin shapes, using geometric shapes with too many sides for discretization can easily result in poor packing or severe distortion of some discrete units. In this case, mixed geometric shapes can be used for discretization. That is, one geometric shape (such as a pentagon or hexagon) is used as the primary spatial discretization, and then other geometric shapes, such as triangles or quadrilaterals, are used for discretization in areas where poor packing or severe distortion occur.

[0053] It is worth noting that, regardless of whether a triangle, a quadrilateral, or a mixture of multiple geometric shapes is used for spatial discretization, each discrete unit has a complete pyramid support. Since adjacent discrete units will have a common node, there will be multiple support rods (belonging to different pyramids) at the common node. The number of support rods is the same as the number of discrete units to which the common node belongs. For example, if the common node is a common node of three discrete units, then there will be three support rods at the common node, and these three support rods are part of the pyramid support corresponding to the three discrete units. For another example, if the common node is a common node of four discrete units, then there will be four support rods at the common node, and these four support rods are part of the pyramid support corresponding to the four discrete units.

[0054] In a preferred embodiment, the preset offset distance of the centroid is less than half the period length of the lattice core layer unit cell. While ensuring that the support rod meets the minimum forming angle allowed by the additive manufacturing process adopted, it can ensure that the proportion of the support rod area in the lattice core layer unit cell is as small as possible, thereby further reducing the influence of the support structure on the mechanical properties of the lattice core layer.

[0055] In some embodiments, the centroid's offset distance is equal to the average side length of the discrete unit. The average side length of the discrete unit is further explained by way of example. For example, when the discrete unit is a quadrilateral, the pyramid support of the discrete unit is designed so that the centroid's offset distance is less than half the length of the unit cell period of the lattice core. When the discrete unit is a triangular unit, the pyramid support of the discrete unit is designed so that the centroid's offset distance is equal to one-third of the discrete unit's perimeter and less than half the length of the unit cell period of the lattice core.

[0056] It should be noted that, in general, half of the length of the unit cell period of the lattice core layer is greater than the average side length of the discrete unit.

[0057] The first preset radius and the second preset radius can be designed as needed. In a preferred embodiment, the first preset radius is close to (slightly larger than or slightly smaller than) the radius of the rods of the lattice core layer. More preferably, the first preset radius is the same as (slightly larger than or slightly smaller than) the radius of the rods of the lattice core layer, which can ensure that the rods have sufficient load-bearing performance and better achieve load transfer between the skin and the lattice core layer.

[0058] Likewise, preferably, the second preset radius is close to (slightly larger or smaller than) the radius of the rods in the lattice core layer. More preferably, the second preset radius is the same as the radius of the rods in the lattice core layer. This ensures that the rods have sufficient load-bearing capacity and better achieves load transfer between the skin and the lattice core layer.

[0059] In a preferred embodiment, the inclination angle of the connecting rod is based on the minimum molding angle allowed by the additive manufacturing process used (angle constraint), and within the range between the minimum molding angle allowed by the additive manufacturing process used and 90°, the connecting rod selects a larger inclination angle relative to the horizontal plane, that is, the connecting rod is selected to be closer to the vertical state. For example, when the inclination angle of the connecting rod relative to the horizontal plane can be 60° or 80°, the inclination angle is preferably selected to be 80°. Preferably, the connection point between the connecting rod and the lattice core layer is preferably selected at the unit cell node of the lattice core layer. If there is no requirement for the connecting rod at each node, the connection point between the connecting rod and the lattice core layer is preferably selected at the unit cell node of the lattice core layer that is closest to the connecting rod, that is, the length of the connecting rod is as short as possible (length constraint). Since there are too many rods connected to the same node (including the rods of the unit cell itself), problems such as node breakage are likely to occur. Therefore, it is generally necessary to limit the number of rods connected to the node (node ​​connectivity constraint). Preferably, the number of rods connected to the connection points on each lattice core layer does not exceed eight, for example, six, seven, eight, etc. Among the three constraints (angle constraint, length constraint and node connectivity constraint), in order to ensure that the supporting rods can meet the requirements of the additive manufacturing process, the angle constraint is a hard constraint. In order to ensure the existence of the optimal connection point, the length constraint and the node connectivity constraint can be appropriately relaxed. The specific values ​​of the constraints can be adjusted according to the different processes and design requirements. Under the premise of satisfying the three constraints, the most suitable node in the lattice core layer is selected to connect to the pyramid vertex to complete the modeling of the connecting rod. If there are multiple suitable nodes on the lattice core layer at the same time, any node can be selected as the connection point. Of course, in some less common structures, in order to meet some special requirements, for example, when satisfying angle constraints or satisfying both angle constraints and length constraints, a small number of connecting rod connection points can be selected on the rods of the unit cell, that is, one end of the connecting rod is connected to the vertex of the pyramid, and the other end is connected to the rod of the unit cell.

[0060] Example 2

[0061] An embodiment of the present invention provides an internal support design method for a skin lattice structure for additive manufacturing. The method mainly addresses the problem that due to the design of the unit cell structure of the lattice core layer, the lattice core layer cannot meet the printing support requirements for the upper skin when additive manufacturing is adopted. There is a suspended node between the unit cell of the lattice core layer close to the lower skin and the lower skin, which makes the lower skin unable to meet the printing support requirements of the lattice core layer at the suspended position.

[0062] See also Figures 6 to 8 As shown, the design of the internal support for the upper skin in the second embodiment is basically the same as that in the first embodiment, and the similarities are not repeated here. The difference is that the support design of the suspended nodes of the lattice core layer is also added, which is as follows: the lower skin model is spatially discretized, and the connection points are selected from the nodes after the lower skin 3 is discretized. The line between the suspended node and the connection point on the lower skin 3 is used as the axis, and the suspended point support rod 5 with a circular cross-section is obtained according to the third preset radius, wherein the inclination angle of the suspended point support rod 5 is not less than the minimum forming angle allowed by the additive manufacturing process adopted, until each suspended node is connected with a suspended point support rod 5.

[0063] It should be noted that the geometric shapes used for spatial discretization of the upper skin 1 and the lower skin 3 are not required to be consistent. In this embodiment, the geometric shape used for discretization of the lower skin is not limited. For example, the upper skin 1 uses a quadrilateral for spatial discretization, and the lower skin 3 can use a quadrilateral for spatial discretization, or a triangle for spatial discretization. However, more preferably, the lower skin 3 and the upper skin 1 use the same geometric shape for spatial discretization. For example, the upper skin 1 uses a quadrilateral for spatial discretization, and the lower skin 3 also uses a quadrilateral for spatial discretization.

[0064] In a preferred embodiment, within the range of the minimum molding angle allowed by the additive manufacturing process to 90°, the suspension point support rod 5 is inclined at a larger angle relative to the horizontal plane.

[0065] When designing the suspension point support rod 5, the design constraints are relatively small compared to the connecting rod. Generally, the angle is given priority, that is, the closer the suspension point support rod 5 is to vertical, the better. Secondly, the shorter the length, the better.

[0066] Preferably, the third preset radius is close to the radius of the rods of the lattice core layer, and more preferably, the third preset radius is the same as the radius of the rods of the lattice core layer.

[0067] Example 3

[0068] See also Figure 2 、 Figure 3 and Figure 5As shown, this embodiment provides a skin lattice structure for additive manufacturing, including an upper skin 1, a lattice core layer 2 and a lower skin 3. The upper skin 1 and the lower skin 3 are connected to form a closed cavity between the two. The lattice core layer 2 is located in the closed cavity formed by the upper skin 1 and the lower skin 3. Each unit cell of the lattice core layer 2 located in the lower layer has a node connected to the lower skin 3, so that the lower skin 3 provides the required printing support for the lattice core layer 2. An upper skin internal support 4 is provided between the upper skin 1 and the lattice core layer 2. The upper skin internal support 4 is obtained by any internal support design method in Example 1. Depending on the shape adopted for discreteness, the pyramid support 4 of the discrete unit can be a triangular pyramid support or a quadrangular pyramid support, which will not be repeated here. The skin lattice structure has a reasonable internal support structure, which is not only used to support the upper skin and meet the printing support, but also fully considers the load-bearing requirements of the internal support, ensuring the load transfer between the upper skin and the lattice core layer while minimizing the impact on the distribution of the mechanical properties of the lattice core layer. It does not need to be removed after printing is completed.

[0069] In this embodiment, the support rods and the connecting rods are round rods, which can avoid stress concentration.

[0070] In some other embodiments, the skin lattice structure has a complex geometric morphology, such as a structure with a large curvature or a plurality of different curvatures; it can also be a non-closed structure in the circumferential direction, for example, the upper skin and the lower skin are respectively located on both sides of the lattice core layer, and do not cover the lattice core layer in the circumferential direction.

[0071] Example 4

[0072] See also Figure 2 、 Figure 3 、 Figure 5 、 Figure 7 and Figure 8 As shown, this embodiment provides a skin lattice structure for additive manufacturing, including an upper skin 1, a lattice core layer 2 and a lower skin 3. The upper skin 1 and the lower skin 3 are connected to form a closed cavity between the two. The lattice core layer 2 is located in the closed cavity formed by the upper skin 1 and the lower skin 3. The suspended node between the lattice core layer 2 and the lower skin 3 is connected with a suspended point support rod 5. An upper skin internal support 4 is provided between the upper skin 1 and the lattice core layer 2, wherein the upper skin internal support 4 and the suspended point support rod 5 are obtained by any of the internal support design methods in Example 2. Depending on the shape adopted for discreteness, the pyramid support 4 of the discrete unit can be a triangular pyramid support or a quadrangular pyramid support, which will not be repeated here. The skin lattice structure has a reasonable internal support structure, which is not only used to support the upper skin and the lattice core layer to meet the printing support, but also fully considers the load-bearing requirements of the internal support, ensuring the load transfer between the upper skin and the lattice core layer while minimizing the impact on the distribution of the mechanical properties of the lattice core layer. It does not need to be removed after printing is completed.

[0073] In this embodiment, the support rods, connecting rods and suspension point support rods are all round rods, which can avoid stress concentration.

[0074] In some other embodiments, the skin lattice structure has a complex geometric morphology, such as a structure with a large curvature or a plurality of different curvatures; it can also be a non-closed structure in the circumferential direction, for example, the upper skin and the lower skin are respectively located on both sides of the lattice core layer, and do not cover the lattice core layer in the circumferential direction.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that not every embodiment contains only one independent technical solution. In the absence of a conflict of solutions, the various technical features mentioned in each embodiment can be combined in any manner to form other implementation methods that can be understood by those skilled in the art.

[0076] In addition, without departing from the scope of the present invention, the technical solutions described in the aforementioned embodiments may be modified, or some of the technical features thereof may be replaced by equivalents, without causing the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing internal supports for a skin lattice structure for additive manufacturing, characterized in that: The following steps are involved: The upper skin model wrapped on the upper side of the lattice core layer is spatially discretized, and the distance between any two adjacent nodes after discretization is no greater than the minimum span allowed by the additive manufacturing process; The centroid of the discrete unit is offset by a preset distance along the negative printing direction to obtain a support reference point of the discrete unit, and the lines connecting the support reference point to each node of the discrete unit are respectively used as axes. A corresponding number of support rods are obtained according to a first preset radius to form a pyramid support of the discrete unit, and the inclination angle of each support rod is not less than the minimum molding angle allowed by the additive manufacturing process. A connection point is selected on the lattice core layer, and the line connecting the support reference point and the connection point on the lattice core layer is used as the axis. A connecting rod connecting the lattice core layer and the pyramid support is obtained according to a second preset radius, and the inclination angle of the connecting rod is not less than the minimum molding angle allowed by the additive manufacturing process. When a pyramid support is formed at each discrete unit obtained by discretization, and each support reference point is connected to the lattice core layer through the connecting rod, the upper skin internal support is obtained.

2. The internal support design method according to claim 1, characterized in that: The offset preset distance of the centroid is less than half of the length of the unit cell period of the lattice core layer.

3. The internal support design method according to claim 1, characterized in that: The first preset radius is the same as the rod radius of the lattice core layer; and / or The second preset radius is the same as the rod radius of the lattice core layer.

4. The internal support design method according to claim 1, characterized in that: Within the range between the minimum forming angle allowed by the additive manufacturing process and 90°, the connecting rod selects a larger inclination angle relative to the horizontal plane.

5. The internal support design method according to claim 4, characterized in that: The number of rods connected to each connection point on the lattice core layer does not exceed eight.

6. The internal support design method according to any one of claims 1 to 5, characterized in that: When the unit cell of the lattice core layer close to the lower skin side has a suspended node, the lower skin model is spatially discretized, and a connection point is selected from the nodes after the discretization of the lower skin model. The line between the suspended node and the connection point on the lower skin is used as the axis, and the suspended point support rod is obtained according to the third preset radius. The inclination angle of the suspended point support rod is not less than the minimum forming angle allowed by the additive manufacturing process adopted, until each of the suspended nodes is connected to a suspended point support rod.

7. The internal support design method according to claim 6, characterized in that: In the range between the minimum forming angle allowed by the additive manufacturing process and 90°, the suspension point support rod selects a larger inclination angle relative to the horizontal plane.

8. The internal support design method according to claim 6, characterized in that: The third preset radius is the same as the rod radius of the lattice core layer.

9. A skin lattice structure for additive manufacturing, characterized by: It includes an upper skin, a lattice core layer and a lower skin, the lattice core layer is located between the upper skin and the lower skin, each unit cell of the lattice core layer located in the lower layer has a node connected to the lower skin, so that the lower skin provides the required printing support for the lattice core layer, and an upper skin internal support is provided between the upper skin and the lattice core layer, and the upper skin internal support is obtained by the internal support design method according to any one of claims 1 to 5.

10. A skin lattice structure for additive manufacturing, characterized by: It includes an upper skin, a lattice core layer and a lower skin, the lattice core layer is located between the upper skin and the lower skin, an upper skin internal support is provided between the upper skin and the lattice core layer, a suspended point support rod is connected to the suspended node between the lattice core layer and the lower skin, and the upper skin internal support and the suspended point support rod are obtained by the internal support design method according to any one of claims 6 to 8.

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