CN112861252A

CN112861252A - Self-defined lattice standard unit and lattice structure

Info

Publication number: CN112861252A
Application number: CN202011556003.5A
Authority: CN
Inventors: 吉芬; 廖宝华; 柏林; 蒋睿哲; 侯志辉; 许少峰
Original assignee: AVIC Chengdu Aircraft Design and Research Institute
Current assignee: AVIC Chengdu Aircraft Design and Research Institute
Priority date: 2020-12-24
Filing date: 2020-12-24
Publication date: 2021-05-28
Anticipated expiration: 2040-12-24
Also published as: CN112861252B

Abstract

The invention has proposed a self-defining lattice standard cell and lattice structure, self-defining lattice standard cell at first, the geometric definition of this standard cell is to define 8 special nods of the cube with 8 vertexes of the cube, 6 central points of six faces; formed by connection in a specific way. And a sandwich structure formed by self-defined lattice standard units according to a zero-period array at intervals is adopted. The sandwich structure has isotropy, light weight and excellent mechanical property. Meanwhile, by changing the parameters, the structure diversification can be realized, and the structures with different weights and mechanical properties can be obtained so as to meet the design requirements of different structures.

Description

Self-defined lattice standard unit and lattice structure

Technical Field

The invention belongs to the field of structural design, and particularly relates to a user-defined dot matrix standard unit and a dot matrix structure.

Background

The lattice structure is a grid-shaped structure similar to a honeycomb interlayer and is hollow inside, the characteristic is that three-dimensional periodic ordered porous is taken as a characteristic, as shown in figure 1, the lattice structure has excellent strength, rigidity and lighter mass characteristic, the lattice structure is a novel structural form which cannot be realized by the traditional process, and the lattice structure is widely applied to various aspects in the fields of aviation and aerospace along with the rapid development of selective melting additive manufacturing technology in recent years.

All lattice structures are formed by lattice standard cells according to a certain arrangement rule, as shown in fig. 2, the lattice standard cells are basic elements constituting the lattice structure, and the structural form and the arrangement mode of the lattice cells must be defined first for designing and manufacturing the lattice structure.

In the design and manufacture process of the lattice structure, standard cells in a software cell library are generally adopted and stacked in a certain manner to form a lattice structure model, as shown in fig. 3. However, the lattice units are generally complex in shape, variable in cross section and large in data volume, as shown in fig. 4, the data volume of the formed lattice model is far greater than that of a conventional structure digital model, the time for constructing the lattice model is several times longer than that of the general model, the structure stress characteristics brought by different lattice units are different, and the selection of the lattice units is constrained by a software unit library. Occasionally, designers adopt self-designed units to design the lattice structure, but the lattice unit stress characteristics and the model data volume influence cause that a satisfactory effect cannot be achieved.

Although the dot matrix structure is widely applied at home and abroad, software for designing the dot matrix structure is not developed at home at present, a dot matrix unit library of the dot matrix structure is not available, the actual dot matrix structure needs to be applied by means of foreign software, the 3-matic software of Materialise, the added work bench of GE, Netfab issued by Autodesk, 3Dsimd of Ansys and the like, the latest version of CATIA released by a V6 platform also has the dot matrix design capability, the foreign software is expensive in price, has higher requirements on computer configuration, is somewhat immature, and most design units are not introduced. On the premise of a large localization trend, a designer system urgently needs to develop a custom lattice standard unit suitable for structural design, the unit data volume is relatively small, a design model can be quickly formed through conventional software, the unit has good stress characteristics, the requirements of structure strength, rigidity and the like can be met, and the unit is suitable for selective area melting process manufacturing.

Disclosure of Invention

(1) The purpose of the invention is as follows: a novel lattice standard unit is set up in a user-defined mode so as to obtain the model data volume which has excellent stress characteristics, lighter unit body weight and smaller model data volume, and the method is suitable for structural design and modeling of aircrafts and the like.

(2) Technical solution of the invention

The invention provides a self-defined lattice standard unit on one hand, wherein the geometric definition of the standard unit is formed by connecting 8 vertexes of a cube, 6 central points of six faces and 8 special intersection points of the cube by the following method;

a) constructing a cube line frame, and finding out 8 vertexes and 6 central points of six surfaces, wherein the total number of the points is 14;

b) connecting the 6 central points of the six surfaces with four vertexes of the vertical surface (namely the parallel surface) of the surface respectively to obtain 24 straight lines;

c) sequentially connecting 8 non-coplanar vertexes in the cube to obtain 8 straight lines, and sharing 8 special intersection points with the 24 straight lines in the step b);

d) the 8 special intersection points are respectively connected with the central points of three faces closest to the point in the cube to obtain 24 line segments, the 8 special intersection points are respectively connected with the vertex of the cube closest to the point to obtain 8 line segments, and the 8 line segments can effectively increase the boundary area of the unit bodies so that the adjacent unit bodies can be better connected together when the selected area is manufactured in a melting mode; the 32 line segments obtained in total form a line frame structure of the lattice standard cell.

Preferably, 32 line segments in the standard unit body line frame structure are cylinders with the same diameter, and each cylinder is also called a rib small rod to form the custom dot matrix standard micro unit body.

Preferably, 8 small bars of the ribs passing through the top points are trimmed by using six boundary surfaces of the cube respectively, and the ribs converged at the center points of 6 surfaces of the cube are trimmed, so that all the ribs are in the same outline of the cube, and the ends of the ribs are planes and flush with the boundary surfaces of the cube; the resulting standard unit cells are in a regular, monolithic form so that adjacent unit cells can better meet together during selective zone melt fabrication.

Preferably, the diameter of the small bar of the rib is 0.5mm or 0.3 mm.

The invention provides a lattice sandwich structure, and the sandwich layer of the sandwich structure is formed by arranging lattice standard microcell bodies in a periodic array.

Preferably, in the lattice sandwich structure, the lattice standard microcells are arranged in a single-layer array arrangement or a double-layer staggered array arrangement.

Preferably, in the lattice sandwich structure, a lattice standard microcell gradient is added in a specific area to realize the rigidity gradual transition of the solid structure and the sandwich structure.

Preferably, the lattice sandwich structure is integrally formed by 3D printing.

The beneficial technical effects are as follows: by adopting the micro-unit structure provided by the invention, the micro-unit structure has excellent stress characteristic, lighter unit body weight and relatively smaller model data volume, is suitable for structural design and modeling of aircrafts and the like, enables designers to get rid of the limitation of an imported software unit library, can utilize a self-defined lattice standard unit to design a lattice structure through conventional software, reduces the weight of the structure, increases the strength and the rigidity, and realizes data transmission between design and manufacture.

Drawings

Fig. 1, a typical structure diagram of a lattice,

FIG. 2 is a schematic view showing the formation of a lattice structure,

FIG. 3 is a schematic diagram of the lattice structure of different cells,

fig. 4. several lattice elements commonly used in software libraries,

FIG. 5. center points of the cube, cube vertices and faces,

FIG. 6 is a view showing a line connecting a center point of one face of a cube and a vertex of a parallel face thereof,

fig. 7. the vertices of the other four vertical planes are connected in a staggered manner,

fig. 8, the intersection point (the intersection point of the lines of fig. 5 and 6),

FIG. 9. intersection points (all intersection points for each plane in the manner of FIG. 7),

FIG. 10 is a view showing a line connecting the vertex, the center point of the plane and the intersection point,

fig. 11, a standard cell structure diagram,

FIG. 12 is a schematic diagram of the geometric definition and parameters of a standard lattice microcell,

FIG. 13 is a schematic diagram of two typical specifications of standard microcells of a lattice,

FIG. 14. lattice standard microcell arrays form a lattice structure,

FIG. 15 is a schematic view of a lattice sandwich structure formed by lattice standard microcells.

Detailed Description

The invention is described in detail with reference to the accompanying drawings of the specification, firstly, a lattice structure standard unit is defined by user, and the geometric definition of the standard unit defines 8 special intersection points of a cube by 8 vertexes of the cube and 6 central points of six faces; formed by joining in the following manner.

Step 1, constructing a millimeter-scale cube line frame, and finding out 8 vertexes and the central points of six surfaces, wherein the total number of the vertexes and the central points is 14, as shown in fig. 5;

step 2, connecting lines from the central point of one surface to the vertexes of the opposite surface (i.e. parallel surface) of the surface, wherein the total number of lines is 4, as shown in fig. 6, the vertexes of the four surfaces perpendicular to the surface are connected in a staggered manner, and the total number of lines is 4, as shown in fig. 7, and the intersection point of the lines in fig. 5 and 6 is found out, as shown in fig. 8;

step 3, operating each surface according to the step 2, overlapping most of the intersection points, and totally having 8 intersection points, as shown in fig. 9;

step 4, the 8 intersection points shown in fig. 8 are respectively connected with the central point of the nearest one of the two parallel surfaces of the square, 24 lines are used, the 8 intersection points are respectively connected with the vertex of the nearest square, 8 lines are used, and the 8 lines can effectively increase the boundary area of the unit bodies, so that the adjacent unit bodies can be better connected together when the selected area is manufactured by melting; a total of 32 wires make up the geometrically defined bobbin structure of the standard cell body, as shown in fig. 10.

Forming a standard unit body structure by the method, forming mm-level cylinders with the same diameter by using 32 lines, wherein each cylinder is also called a rib small rod; thereby forming the standard microcell body of the custom lattice.

Respectively trimming 8 small bars of the ribs passing through the top points by using six boundary surfaces of the cube, trimming the ribs gathered at the center points of 6 surfaces of the cube, ensuring that all the ribs are in the square outline, and the end heads are planes and are flush with the boundary surfaces of the cube; the resulting standard unit cell is in a regular, monolithic form so that adjacent unit cells can better meet together when the selected area is melt fabricated, as shown in fig. 11.

The constructed isotropic lattice unit is named as a lattice standard micro unit and consists of 32 cylindrical rib small bars with the same diameter, the number, the section shape, the direction and the length of ribs of a unit body in three X \ Y \ Z directions are completely consistent, a fully-enclosed cube with a mm level as a unit can be used for description, and the design elements are cube side length a, and rib small bar diameters d, a and d are parameters, as shown in figure 12. By adjusting the design element parameters, lattice standard microcells with various specifications can be formed. Two lattice standard microcell specifications are commonly used in the design, a is 5mm, the diameter d of the small rib bar is 0.5mm, or a is 3mm, the diameter d of the small rib bar is 0.3mm, as shown in fig. 13.

The lattice standard micro-unit constructed in the above manner has the same projection and characteristics of the physical structure in the three directions of X \ Y \ Z, is an isotropic lattice unit, can be arrayed, and forms a lattice structure suitable for selective area melting process manufacturing, as shown in fig. 14.

The standard cells can construct a lattice sandwich structure formed by the standard cells in a zero-pitch array, as shown in fig. 15. The sandwich structure has isotropy, light weight and excellent mechanical property. Meanwhile, by changing the parameters, the structure diversification can be realized, and the structures with different weights and mechanical properties can be obtained so as to meet the design requirements of different structures.

According to the designed lattice sandwich structure, the standard units can be arranged in a staggered periodic array, and the density gradient of the standard units can be increased in a specific area, so that the rigidity gradual transition of a solid structure and a sandwich structure is realized, and the rigidity mutation of the structure is reduced.

Example 1:

1.1 geometric construction: constructing a lattice standard microcell according to a geometric relationship, and defining the side length a of a design element cube and the diameter d of a rib small rod;

2, process verification: taking a typical lattice standard micro unit with a being 5mm and d being 0.5mm, forming a lattice structure with the same specification and size by an array similar to a lattice unit of a certain software library commonly used in engineering, carrying out a laser selective melting manufacturing test, and verifying process feasibility;

3, in the mechanical property test, a typical lattice standard micro unit with a being 5mm and d being 0.5mm is selected, similar lattice units are formed with a lattice structure with the same specification and size through an array with a certain software library commonly used in engineering, and mechanical property examination and comparison tests such as element-level and typical-level stretching, compression, shearing, bending and the like are carried out to verify the mechanical property;

4 other feature alignment: compared with the similar lattice unit, the lattice unit has lighter structural weight and smaller model data volume.

By adopting the lattice standard unit provided by the invention, through manufacturing of laser selective melting lattice parts and mechanical property tests, the self-constructed lattice standard micro unit is verified to be capable of better forming a lattice structure, through process verification and mechanical property tests, the engineering feasibility is strong, the problem that the micro unit cannot be formed because of being a suspension structure is solved, and the lattice standard unit has good manufacturability, excellent stress characteristic, light structural weight and small model data volume.

Claims

1. A self-defined lattice standard cell is characterized in that the geometric definition of the standard cell is formed by connecting 8 vertexes of a cube, 6 central points of six faces and 8 special intersection points of the cube by the following method;

step S1, constructing a cube line frame, and finding out 8 vertexes and 6 central points of six surfaces, wherein the total number of the points is 14;

step S2, connecting 6 central points of the six surfaces with four vertexes of the facing vertical surface respectively to obtain 24 straight lines;

step S3, sequentially connecting 8 non-coplanar vertexes in the cube to obtain 8 straight lines, wherein the 8 straight lines and the 24 straight lines in the step S2 have 8 special intersection points in total;

step S4, respectively connecting 8 special intersection points to central points of three faces nearest to the point in the cube to obtain 24 line segments, respectively connecting the 8 special intersection points to a vertex of the cube nearest to the point to obtain 8 line segments, wherein the 8 line segments can effectively increase the boundary area of the unit bodies so that adjacent unit bodies can be better connected together when the selected area is manufactured by melting; the 32 line segments obtained in total form a line frame structure of the lattice standard cell.

2. The lattice standard cell of claim 1, wherein 32 line segments in the line frame structure of the lattice standard cell are cylinders with the same diameter, each cylinder is a rib small rod, and a custom lattice standard microcell body is formed.

3. The lattice standard cell of claim 2, wherein the resulting lattice standard microcell body is trimmed by: respectively trimming 8 small rib bars passing through the top points by using six boundary surfaces of the cube, and trimming the small rib bars gathered at the center points of 6 surfaces of the cube to ensure that all ribs are in the same cube outline, and the end heads are planes and flush with the boundary surfaces of the cube; the obtained standard unit body is in a regular and integral form.

4. The lattice standard cell of claim 3, wherein the rib bars have a diameter of 0.5mm or 0.3 mm.

5. A lattice sandwich structure using the lattice standard microcells according to claim 3 as a sandwich layer, wherein the sandwich layer is formed by arranging the lattice standard microcells in a periodic array.

6. The lattice sandwich structure of claim 5, wherein said sandwich structure has lattice standard microcells arranged in a single layer array arrangement or a double layer staggered periodic array arrangement.

7. The lattice sandwich structure of claim 6, wherein said sandwich structure has zero spacing between lattice standard microcells.

8. The lattice sandwich structure of claim 7, wherein in said sandwich structure, lattice standard microcell gradient is added to specific area to realize rigidity gradual transition between solid structure and sandwich structure.

9. The dot matrix sandwich structure according to any one of claims 5 to 8 wherein said sandwich structure is integrally formed by 3D printing.