CN111895015B

CN111895015B - Variant gradient lattice structure based on additive manufacturing

Info

Publication number: CN111895015B
Application number: CN202010637445.6A
Authority: CN
Inventors: 柏龙; 龚程; 陈晓红; 张俊芳; 周晓霞; 孙园喜; 彭艳; 罗均; 蒲华燕; 谢少荣
Original assignee: Chongqing University; University of Shanghai for Science and Technology
Current assignee: Chongqing University; University of Shanghai for Science and Technology
Priority date: 2020-07-03
Filing date: 2020-07-03
Publication date: 2022-07-08
Anticipated expiration: 2040-07-03
Also published as: CN111895015A

Abstract

The invention discloses a variant gradient lattice structure based on additive manufacturing, which comprises a plurality of variant gradient lattice layers which are repeatedly stacked and connected with each other; the variant gradient lattice layer comprises a plurality of variant gradient unit cell columns which are repeatedly arranged and connected with each other; the variant gradient unit cell array comprises a plurality of lattice unit cells which are repeatedly arranged along a single direction and are connected with each other; the lattice unit cell is formed by carrying out size continuation on an original lattice unit cell along one or more directions; the lattice structure of the invention improves the problem of structural mutation at the joint of the existing gradient structure. The high-strength bearing capacity is ensured, and the energy absorption capacity is improved, so that the high-strength bearing capacity shock-resistant cable has better shock resistance.

Description

Variant gradient lattice structure based on additive manufacturing

Technical Field

The invention relates to a lattice structure, in particular to a gradient lattice structure for additive manufacturing and a design method thereof. The structure is stable in connection, has mechanical response different from that of a traditional lattice structure, and has the advantages of high strength, high rigidity and excellent energy absorption capacity.

Background

The lattice structure has the advantages of light weight, high specific strength and high specific rigidity, and plays a significant role in lightweight design in the fields of spaceflight, automobiles and the like. However, the complex internal microstructure of the lattice structure has great challenges for the traditional preparation process, and with the development of the additive manufacturing technology, the application of the complex internal microstructure to the preparation of the lattice structure becomes a trend. The precision and the forming quality of the internal complex microstructure can be guaranteed, and the mechanical property can be effectively guaranteed. In addition, compared with the traditional preparation process, the lattice structure is prepared by adopting the additive manufacturing technology, and the purpose of saving materials is achieved.

In recent years, a gradient lattice structure having a property varying with a regional variation has attracted much attention with its unique advantages, and patent "CN 107498948A" discloses a method of realizing structural graduating by changing the rod diameter of a unit cell, and proves that it has a better impact protection effect. However, because the dimensional differences of different layers of the structure are large, requirements are imposed on manufacturing and processing, and the structure can also be damaged and failed under certain impact, so that the patent "CN 109163212" proposes a gradient lattice structure with a transition layer, but the structure has the common problem of weakening the node connection of the gradient lattice structure, especially at the intersection of rods with different diameters. Under the load, the stress concentration effect of the node is prominent, and the bearing characteristic of the whole structure is greatly influenced.

Disclosure of Invention

The invention aims to provide a novel gradient strategy aiming at the contact weakening problem in the current gradient structure, and the problem of structural mutation at the connection part of the gradient structure is solved. The gradient structure with density and topological structure change is designed, and the high-strength bearing capacity is ensured, and meanwhile, the energy absorption capacity is improved, so that the shock-resistant composite material has a better shock resistance.

The variant gradient lattice structure based on the additive manufacturing comprises a plurality of variant gradient lattice layers which are repeatedly stacked and connected with each other; the variant gradient lattice layer comprises a plurality of variant gradient unit cell columns which are repeatedly arranged and connected with each other; the variant gradient unit cell array comprises a plurality of lattice unit cells which are repeatedly arranged along a single direction and are connected with each other; the lattice unit cell is formed by carrying out size continuation on an original lattice unit cell along one or more directions, wherein the size continuation refers to size extension or size shortening; the sizes of one or more directions of each lattice unit cell in the variant gradient unit cell array are gradually changed, so that a gradient structure is formed; and the rod diameters of all unit cells in the whole lattice structure are the same, so that the problems of node connection mutation and performance weakening at the rod piece connection part of the adjacent unit cells in the lattice structure are avoided.

Further, the original lattice unit cell is a body-centered cubic unit cell; the unit cell configuration of the structural design is not limited to a body-centered cubic structure, and is also suitable for other lattice structure unit cells, and the number of the unit cells and the number of gradient layers of the overall design of the gradient structure are not limited to limited numbers. The adjustment of the size of the single cell structure and the integral number of the gradient lattice structure can be extended to any size and any number of layers.

Further, the variant gradient lattice layer is 7 layers; the variant gradient unit cells are arranged in 7 rows, and the number of lattice unit cells in each variant gradient unit cell row is 7; considering the influence of the number of unit cells on the authenticity of the structure, the number of unit cells of the whole lattice structure is 7 × 7 × 7.

Furthermore, considering the factors of the additive manufacturing process, the rod diameter of the original lattice unit cell is 1mm, and the space size of the original lattice unit cell is 5mm multiplied by 5 mm;

further, the lattice structure is made by using engineering plastic PA2200 as a raw material and adopting a laser sintering process;

further, the laser power of the laser sintering is 30w, the scanning speed is 5m/s, the scanning interval is 60 μm, and the powder deposition thickness is 100 μm.

The invention has the beneficial effects that:

1. the gradient structure is simple in design flow and strong in realizability, is different from the size limitation that the traditional gradient structure is limited in manufacturing and processing, and improves the usability of the gradient structure.

2. The connection of different layers of the gradient structure is more stable, and compared with other gradient structures, the connection part does not have the problem of performance weakening caused by structure mutation.

3. The gradient structure has excellent mechanical property, high bearing characteristic and excellent energy absorption capacity, and can realize the gradient structure design with density and topology complex rule change.

Drawings

The technical scheme of the invention is further explained by combining the drawings and the embodiment as follows:

FIG. 1 is a schematic diagram of the structure of original lattice unit cell (BCC);

FIG. 2 is a schematic diagram of a single cell structure after the single cell is unidirectionally shortened in an original lattice;

FIG. 3 is a schematic diagram of the unit cell structure after the original lattice unit cell is unidirectionally elongated;

FIG. 4 is a schematic structural diagram of a monodirectional graded lattice layer;

FIG. 5 is a schematic diagram of a single layer of a gradient rod diameter BCC structure;

FIG. 6 is a simulated stress-strain curve for several lattice structures;

FIG. 7 is a schematic diagram of the original lattice unit cell after multidirectional expansion;

FIG. 8 is a schematic structural diagram of a multi-variant gradient lattice layer;

FIG. 9 is a schematic three-dimensional structure diagram of a multi-variant radial gradient lattice structure.

Detailed Description

Example one

The embodiment discloses a one-way variant gradient lattice structure, which is characterized in that on the basis of a traditional uniform lattice structure, a single cell is subjected to size prolongation to form a series of new single cells with different topologies and relative densities, the new single cells are periodically arranged to form different layers, and finally the different layers are combined to form a gradient structure with density gradient change characteristics. Because the gradient structure only changes the size of the unit cell, the rod diameter of the gradient structure is not changed, the connection between different layers of the structure is more stable, the problem of connection weakening of the traditional gradient structure is solved, the bearing capacity of the structure is improved, the gradient structure has the special high energy absorption capacity, and reference is provided for designing a protective device with excellent impact resistance.

As shown in fig. 1, a common BCC structure in the lattice structure is selected as an original lattice unit cell, which has an open pore structure, simple topology and excellent carrying capacity; the new variant unit cell structure design is realized by carrying out unidirectional size extension on the BCC structure unit cell, which is shown in the figure 2 and the figure 3; the variant gradient lattice structure comprises seven variant gradient lattice layers which are repeatedly stacked and connected with each other; each layer of variant gradient lattice layer comprises seven variant gradient unit cell columns which are repeatedly arranged and connected with each other; each variant gradient unit cell column comprises seven lattice unit cells which are repeatedly arranged along a single direction and are connected with each other; the lattice unit cell is formed by performing size continuation on an original lattice unit cell (BCC unit cell) along one direction.

Considering additive manufacturing process factors, an original model BCC structure is selected, wherein the rod diameter is 1mm, and the unit cell size is 5 multiplied by 5mm³. The gradient BCC structure obtained by the variant is shown in fig. 4. In order to verify the mechanical formation of the lattice structure of this embodiment, a gradient structure with varying rod diameter, which is commonly used in the conventional gradient structure, is selected as a control, see fig. 5, and the minimum rod diameter of the bottom layer of the lattice structure is 0.5 mm. Considering the influence of the relative density of the lattice structure on the mechanical property of the lattice structure, the two gradient lattice structures follow the principle of unified relative density, namely the relative densities of the structures of the two verification models are the same.

In the embodiment, a laser sintering process belonging to an additive manufacturing technology is adopted to prepare a corresponding sample for analysis and verification, and the engineering plastic PA2200 with high molding quality and excellent performance is selected as a material. In this case, the laser power is 30W, the scanning speed is 5m/s, the scanning distance is 60 μm, the powder deposition thickness is 100 μm, and the processed lattice sample is not subjected to other additional treatment after removing excessive powder.

And (3) testing the sample to obtain the quasi-static compression response of the gradient lattice structure. The compressive stress strain curve is shown in fig. 6. By analyzing the compressive response of the gradient lattice structure, it was found that: the rod deformation mode of the monodirectional variant gradient structure has both bending deformation and tensile deformation. In the stage of small strain, the bending deformation is mainly shown, and the whole body has obvious shear bands and higher modulus and strength. However, in the large strain stage, the structure has the same layer-by-layer crushing failure mode as the rod diameter change gradient structure, and the curve stabilization platform of the variant gradient structure also proves that the structure has an advantage in energy absorption. Therefore, the gradient structure designed by the embodiment has excellent bearing capacity and superior energy absorption capacity, and has a wide application prospect in energy absorption, buffering, impact resistance and other applications.

Example two

Furthermore, by designing the structure in multiple directions, more gradient structures with more complex change rules can be designed, the stability and reliability of node connection are ensured, and the problem of node connection of different layers of the existing gradient structure is solved. In addition, the structure is designed in a multi-directional variant mode by utilizing the high-freedom design advantage of the additive manufacturing technology, and the obtained multi-directional variant radial gradient structure provides a new reference for the bionic design of the bone implant. As shown in fig. 7,8 and 9, the variant gradient lattice structure comprises four variant gradient lattice layers which are repeatedly stacked and connected with each other; each layer of variant gradient lattice layer comprises twenty-four variant gradient unit cell columns which are repeatedly arranged and connected with each other; each variant gradient unit cell array comprises four lattice unit cells which are repeatedly arranged along a single direction and are mutually connected; the lattice unit cell is formed by extending the size of an original lattice unit cell (BCC unit cell) along two directions; as shown in fig. 7, the whole variant gradient unit cell array formed in this embodiment is in a quadrangular frustum structure, twenty-four variant gradient unit cell arrays are repeatedly arranged in a circumferential direction as shown in fig. 8 to form a variant gradient lattice layer in a circular structure, and four variant gradient lattice layers are repeatedly stacked to form a variant gradient lattice structure as shown in fig. 9.

Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.

Claims

1. A variant gradient lattice structure based on additive manufacturing, characterized in that: the lattice structure comprises four variant gradient lattice layers which are repeatedly stacked and connected with each other; each layer of variant gradient lattice layer comprises twenty-four variant gradient unit cell columns which are repeatedly arranged and connected with each other; each variant gradient unit cell array comprises four lattice unit cells which are repeatedly arranged along a single direction and are mutually connected; the lattice unit cell is a variant gradient unit cell array integrally formed by extending the size of a body-centered cubic original lattice unit cell along two directions and has a quadrangular frustum structure, twenty-four variant gradient unit cell arrays are repeatedly arranged along the annular direction to form a variant gradient lattice layer with a circular structure, and the four variant gradient lattice layers are repeatedly stacked to form a variant gradient lattice structure.

2. The variant gradient lattice structure based on additive manufacturing of claim 1, wherein the original lattice unit cell has a rod diameter of 1mm and a spatial dimension of 5mm x 5 mm.

3. The variant gradient lattice structure based on additive manufacturing of claim 2, wherein the lattice structure is made by using engineering plastic PA2200 as a raw material and adopting a laser sintering process.

4. The variant gradient lattice structure based on additive manufacturing of claim 3, wherein the laser power of the laser sintering is 30w, the scanning speed is 5m/s, the scanning pitch is 60 μm, and the powder deposition thickness is 100 μm.