Continuous fiber reinforced 3D printing method for reinforced panel

Abstract

The invention discloses a continuous fiber reinforced 3D printing method for a reinforced panel, and belongs to the field of continuous fiber reinforced 3D printing methods. According to the method, by means of a finite element analysis technology, the equivalent principal stress maximum value of each region of the structure is analyzed; printing mode design is carried out on the bottom panel, the intersection area containing the inner ribs and the area with the holes according to the analyzed maximum value of the equivalent principal stress; the straight section area of the reinforcing rib adopts a layer-by-layer printing mode along the length direction of the reinforcing rib; a layer-by-layer staggered printing mode is adopted in the intersecting area of the two outer ribs in the length direction of the two outer ribs; and all the components of the reinforced panel are printed layer by layer from the bottom to the top in the vertical direction according to the designed printing direction, and continuous fiber reinforced 3D printing of the reinforced panel is completed. According to the method, the trend of the fiber is intelligently designed, it is ensured that the fiber is consistent with the structural equivalent principal stress direction, the axial performance of the fiber is utilized to the maximum extent, the matching problem of material anisotropy and structural design intention is solved, and the additive manufacturing efficiency is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of continuous fiber reinforced 3D printing methods, in particular to a continuous fiber reinforced 3D printing method for stiffened panels. BACKGROUND

[0002] Continuous fibers are widely used in industrial engineering due to their excellent specific strength, specific stiffness, designability, and lightweight characteristics. The development of 3D printing technology has changed the production and manufacturing process of continuous fiber composite structures, making free forming of complex structures possible. Stiffened panels have high material utilization efficiency and reasonable load transfer, and are key structures for lightweight implementation in aerospace, ships, vehicles, and other fields. Continuous fiber materials are anisotropic materials with extremely high axial strength and modulus, and their performance is highly dependent on the fiber orientation. Unreasonable paths can severely reduce the performance of the structure. How to solve the problem of the perfect integration of advanced materials, innovative structural design, and flexible additive manufacturing process in the production and design of stiffened panels has great engineering significance.

[0003] In "3D Printing Continuous Fiber Composite Material Process and Structure Optimization Research Progress" by Ye Hongling et al. in Mechanics Progress 2024-54 (2) and "Continuous Carbon Fiber 3D Printing Path Design Research Progress" by Zhang Rongliang et al. in Composite Materials Science and Engineering 2023 (9), the research work on performance analysis, process improvement, and structure optimization of 3D printing continuous fiber composite materials is systematically summarized. Researchers respectively from material performance and structure design, explore the design and manufacturing integrated solution suitable for 3D printing continuous fiber composite materials, realize product innovation design and performance improvement, but the above research focuses on theoretical methods and simple models, and there is no related research on the direction design technology of continuous fiber 3D printing for stiffened panels. SUMMARY

[0004] The technical problem solved by the present application is to provide a continuous fiber reinforced 3D printing method for stiffened panels to solve the problem of the perfect integration of advanced materials, innovative structural design, and flexible additive manufacturing process in the production and design of stiffened panels.

[0005] To solve the above technical problems, the application adopts a technical solution: defining the direction of the stiffened panel and the classification of the stiffener, partitioning each component structure of the stiffened panel according to the geometric shape characteristics of the stiffened panel; with the help of finite element analysis technology, giving the isotropic material properties of the stiffened panel, analyzing the maximum equivalent principal stress of each region of the structure; the bottom panel is designed according to the maximum equivalent principal stress in the transverse and longitudinal directions; the straight section of the stiffener is printed layer by layer along the length direction of the stiffener; the intersection area of the two outer stiffeners is printed layer by layer along the length direction of the two outer stiffeners; the intersection area containing the inner stiffener is designed according to the maximum equivalent principal stress along the length direction of each stiffener; the area with holes is designed according to the maximum equivalent principal stress along the length and width directions of the outer stiffener; each component of the stiffened panel is printed layer by layer from the bottom to the top along the vertical direction according to the designed printing direction, thereby completing the printing method design of the continuous fiber 3D printed stiffened panel, and achieving the purpose of the application.

[0006] The application relates to a continuous fiber reinforced 3D printing method of a stiffened panel. 1) According to the geometric shape characteristics of the stiffened panel, each component structure is partitioned According to the structure characteristics of the stiffened panel, the stiffener and the bottom panel are split into two regions; for the stiffener with complex structure, the stiffener is further split into different regions according to the inner and outer positions, the transverse, longitudinal and inclined directions and the different structures, including the straight section of the stiffener and the intersection section of the stiffener; the intersection section of the stiffener includes the intersection area of two stiffeners and the intersection area containing the inner stiffener; the intersection area of two stiffeners includes the intersection area of two outer stiffeners and the intersection area containing the inner stiffener; 2) With the help of finite element simulation technology, the maximum equivalent principal stress of each region is estimated The stiffened panel adopts an isotropic material model close to the performance of continuous fibers, loads and constraints are applied according to the actual stress working conditions of the stiffened panel, finite element simulation analysis is performed, and the maximum equivalent principal stress in the required direction of each region is obtained; 3) According to the estimated results of the maximum equivalent principal stress of each region, the 3D printing method is designed According to the estimated results of the maximum equivalent principal stress in the required direction of the bottom panel region, the main bearing direction and the secondary bearing direction are determined; the ratio of the maximum equivalent principal stress of the main bearing direction to the secondary bearing direction is calculated and rounded to the nearest integer, and the stress ratio is obtained; the main bearing direction and the secondary bearing direction adopt the staggered printing method, the number of printing layers of the main bearing direction is an integer multiple of the number of printing layers of the secondary bearing direction, and the multiple is the stress ratio; The straight section of the stiffener is printed layer by layer along the length direction of the stiffener; The intersection area of the two outer stiffeners is printed layer by layer along the length direction of the two outer stiffeners; The area containing intersecting internal reinforcements adopts an interlaced printing method; based on the estimated maximum equivalent principal stress, the primary load-bearing direction and secondary load-bearing direction of the area containing intersecting internal reinforcements are determined, and the stress ratio is calculated; when the stress ratio is not less than 2, the ratio of the number of printing layers along the primary load-bearing direction to the secondary load-bearing direction is 3:1; when the stress ratio is less than 2, the layers are interlaced along the primary load-bearing direction and the secondary load-bearing direction. The area where multiple reinforcing bars intersect is printed using an interlaced printing method. Based on the estimated maximum equivalent principal stress, the main load-bearing direction, secondary load-bearing direction, and weak load-bearing direction of the area where multiple reinforcing bars intersect are determined. The number of printing layers in the main load-bearing direction and the secondary load-bearing direction is the same, and the ratio of the number of printing layers in the main load-bearing direction to the number of printing layers in the weak load-bearing direction is 3:1. After printing 3 layers in the main load-bearing direction and the secondary load-bearing direction respectively, one layer is printed in each of the weak load-bearing directions. 4) Complete the 3D printing of the reinforced panel according to the design printing method. According to the printing method designed in step 3), print layer by layer vertically from bottom to top to complete the 3D printing of the stiffened panel.

[0007] Preferably, the reinforcing ribs of the reinforced panel are provided with vertical through holes.

[0008] In a further preferred embodiment, when dividing the various components of the reinforced panel according to its geometric shape characteristics in step 1), a perforated area is separated from the reinforcing rib with the vertical through hole. This area is a square area with the center of the vertical through hole as the center, the side length as 1.5 to 2 times the diameter of the hole, and the cross section as square.

[0009] More preferably, the maximum value of the equivalent principal stress in the required direction of the perforated area is the maximum value of the equivalent principal stress in both the length and width directions of the reinforcing rib.

[0010] More preferably, step 3) further includes designing a 3D printing method based on the estimated maximum value of the equivalent principal stress in the perforated region. Based on the estimated maximum equivalent principal stress in both the length and width directions of the reinforcing rib where the perforated area is located, the primary and secondary load-bearing directions are determined. When the primary load-bearing direction is along the width direction of the reinforcing rib, the perforated area uses a combination of spiral and "U" shaped printing methods, with the inner part being spiral and the outer part being "U". The spiral area accounts for a certain percentage of the total area of ​​the perforated area. When the main load-bearing direction is along the length of the reinforcing rib, the area with holes adopts a printing method that combines the circumferential arc direction and the length direction of the reinforcing rib. When the distance between the printing position and the edge line or central axis parallel to the length direction of the outer rib is not greater than its distance from the edge of the hole, the printing direction is selected as the length direction of the outer rib; otherwise, the printing direction is selected as the circumferential arc direction with the hole center as the center and the distance from the hole center to the printing position as the radius.

[0011] Preferably, in step 3), the required directions of the bottom panel are the transverse direction and the longitudinal direction, and when the maximum equivalent principal stress of the transverse direction and the longitudinal direction is equal, the longitudinal direction is the main load-bearing direction; when the maximum equivalent principal stress of the two directions at the intersection of the two ribs is equal, the main load-bearing direction and the secondary load-bearing direction are not distinguished, and the printing direction is staggered layer by layer along the length direction of the two reinforcing ribs.

[0012] Preferably, in step 3), when the bottom panel is printed layer by layer along the main load-bearing direction and the secondary load-bearing direction at the bottom and the top of the bottom panel, the excess number of layers in the main load-bearing direction is printed at the middle position of the thickness of the bottom panel.

[0013] Preferably, in step 3), at the intersection of the two ribs and the intersection of the multiple ribs, only one reinforcing rib length direction is printed for each layer.

[0014] The present application relates to a continuous fiber reinforced 3D printing method of a ribbed panel, which defines the direction of the ribbed panel and the classification of the reinforcing rib to facilitate the description of the structures of the ribbed panel; according to the geometric shape characteristics of the ribbed panel, the structures of the ribbed panel are distinguished and the printing direction is designed separately; by means of finite element analysis technology, the isotropic material properties of the ribbed panel are given, and the maximum equivalent principal stress of the structure in a specific direction is analyzed; the printing mode of the bottom panel is designed according to the maximum equivalent principal stress of the transverse direction and the longitudinal direction; the printing mode of the straight section of the reinforcing rib is designed to print layer by layer along the length direction of the reinforcing rib; the printing mode of the intersection of the two outer ribs is designed to print layer by layer along the length direction of the two outer ribs; the printing mode of the intersection area containing the inner rib is designed according to the maximum equivalent principal stress along the length direction of each rib; the printing mode of the hole area is designed according to the maximum equivalent principal stress along the length and width directions of the outer rib; the structures of the ribbed panel are printed layer by layer along the vertical direction from the bottom to the top according to the designed printing direction, and the continuous fiber reinforced 3D printing of the ribbed panel is completed. This method can help engineers quickly complete the printing mode design of the continuous fiber 3D printed ribbed panel, intelligently design the fiber direction according to the stress analysis results of the structure, ensure that the fiber direction is consistent with the equivalent principal stress direction of the structure, maximize the use of the axial strength and modulus of the fiber, solve the matching problem of the anisotropy of the material and the design intention of the structure, and improve the efficiency of additive manufacturing. The method of the present application has clear logic, simple operation steps, strong universality and easy engineering implementation. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 It is a schematic diagram of a rectangular straight ribbed panel; Figure 2 It is a schematic diagram of a rectangular inclined ribbed panel; Figure 3 It is a schematic diagram of a square straight ribbed panel; Figure 4 It is a schematic diagram of the intersection of the transverse rib and the longitudinal rib along the longitudinal direction; Figure 5 The schematic diagram is printed along the transverse direction at the intersection of the transverse ribs and the longitudinal ribs.

[0016] Wherein, 1-bottom panel one, 2-outer transverse rib one, 3-inner transverse rib one, 4-inner transverse rib two, 5-outer transverse rib two, 6-outer longitudinal rib one, 7-inner longitudinal rib one, 8-inner longitudinal rib two, 9-outer longitudinal rib two, 10-hole area one, 11-hole area two, 12-hole area three, 13-hole area four, 14-hole area five, 15-hole area six, 16-bottom panel two, 17-outer transverse rib three, 18-inner transverse rib three, 19-outer transverse rib four, 20-outer longitudinal rib three, 21-outer longitudinal rib four, 22-inner diagonal rib one, 23-inner diagonal rib two, 24-hole area seven, 25-hole area eight, 26-hole area nine, 27-hole area ten, 28-bottom panel three, 29-outer transverse rib five, 30-inner transverse rib four, 31-outer transverse rib six, 32-outer longitudinal rib five, 33-inner longitudinal rib three, 34-outer longitudinal rib six. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical method and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described in more detail below in combination with the embodiments of the present application. The described embodiments are part of the embodiments of the present application, rather than all the embodiments. The embodiments described below are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application. The embodiments of the present application will be described in detail below.

[0018] For the convenience of description, the width direction of the reinforced plate is defined as the transverse direction (X direction of the coordinate system in the drawings), the length direction is defined as the longitudinal direction (Y direction of the coordinate system in the drawings), and the thickness direction is defined as the vertical direction (Z direction of the coordinate system in the drawings). According to the different positions of the reinforcing ribs, the reinforcing ribs at the four peripheral boundaries of the reinforced plate are defined as outer ribs, and the internal reinforcing ribs are defined as inner ribs; according to the different directions of the reinforcing ribs, the transverse reinforcing ribs are defined as transverse ribs, the longitudinal reinforcing ribs are defined as longitudinal ribs, and the diagonal reinforcing ribs are defined as diagonal ribs.

[0019] Embodiment 1 The reinforced panel of the embodiment is a rectangular straight rib reinforced panel composed of a 2mm-thick bottom panel 1 and 5mm-thick reinforcing ribs, with a width of 150mm and a length of 300mm. The bottom panel 1 is located below the reinforcing ribs. The reinforcing ribs include four horizontal ribs and four vertical ribs. The four horizontal ribs include an outer horizontal rib 2, an inner horizontal rib 1, an inner horizontal rib 2, and an outer horizontal rib 5. The four vertical ribs include an outer vertical rib 6, an inner vertical rib 1, an inner vertical rib 2, and an outer vertical rib 9. The outer horizontal rib 2, the outer horizontal rib 5, the outer vertical rib 6, and the outer vertical rib 9 have a width of 10mm. The inner horizontal rib 3, the inner horizontal rib 4, the inner vertical rib 7, and the inner vertical rib 8 have a width of 5mm. The outer ribs are provided with vertical through holes with a diameter of 3mm. The outer horizontal rib 2 and the outer horizontal rib 5 are provided with two vertical through holes, and the outer vertical rib 6 and the outer vertical rib 9 are provided with one vertical through hole. As shown in FIG. 6. The printing fiber of the rectangular straight rib reinforced panel is selected from T300 carbon fiber reinforced PA6 resin-based composite material filaments. Figure 1

[0020] When the rectangular straight rib reinforced panel of the embodiment is 3D printed, the specific operation steps are as follows: 1. According to the geometric shape characteristics of the rectangular straight rib reinforced panel, the structures are divided into zones to facilitate the design of the printing method of each structure According to the thickness of the panel of the rectangular straight rib reinforced panel, the bottom panel 1 is split. According to the different positions of the reinforcing ribs, the reinforcing ribs are divided into outer horizontal ribs, outer vertical ribs, inner horizontal ribs, and inner vertical ribs. The intersection and straight section of the reinforcing ribs are designed separately. On the outer rib, with the center of the vertical through hole as the center and 6mm as the side length, the hole area 10, the hole area 11, the hole area 12, the hole area 13, the hole area 14, and the hole area 15 with a square cross section are split on the outer rib, and the printing method is designed separately.

[0021] 2. The rectangular straight rib reinforced panel adopts an isotropic material model for finite element analysis to analyze the maximum equivalent principal stress of each region of the structure According to the structural characteristics of the rectangular straight rib reinforced panel, the finite element analysis technology is used to determine that the maximum equivalent principal stress of the bottom panel 1 in the horizontal and vertical directions, the maximum equivalent principal stress of the straight section of the reinforcing rib along its length, the maximum equivalent principal stress of the intersection of the reinforcing rib along the length of each rib, and the maximum equivalent principal stress of the hole area along the length and width of the outer rib. The maximum equivalent principal stress is the maximum value of the absolute value of the above-mentioned equivalent principal stresses. Only the size of the equivalent principal stress value is compared, and the positive and negative states of the equivalent principal stress are not distinguished.

[0022] ​In the finite element analysis, the finite element model of the rectangular straight ribbed plate is made of aluminum alloy material, the vertical displacement of the bottom panel 1 is constrained at the left and right ends of the bottom, the horizontal and vertical displacements are constrained at the opening of the stiffener, and the concentrated force load is loaded on the two inner longitudinal ribs, wherein the X-direction load FX=750N, the Z-direction load FZ=-750N, as shown in Figure 1 .

[0023] The finite element simulation results are as follows: the maximum value of the horizontal equivalent principal stress of the bottom panel 1 is 42.54MPa, and the maximum value of the longitudinal equivalent principal stress is 76.80MPa; the longitudinal stress value is larger, and the longitudinal direction is the main bearing direction and the horizontal direction is the secondary bearing direction. The maximum value of the equivalent principal stress at the intersection of the outer rib and the inner rib of the stiffener and the intersection of the inner rib and the inner rib along the length direction of the two stiffeners is shown in Table 1, wherein the first stiffener and the second stiffener are only for the convenience of distinguishing and explaining the two stiffeners at the intersection, and have no special meaning. The direction of the main bearing direction is the direction of the larger equivalent principal stress at the intersection of the two stiffeners, and the direction of the secondary bearing direction is the direction of the smaller equivalent principal stress. The maximum value of the equivalent principal stress in the length and width directions of the hole area along the outer rib is shown in Table 2, and the direction of the main bearing direction is the direction of the larger equivalent principal stress, and the direction of the secondary bearing direction is the direction of the smaller equivalent principal stress; the main bearing direction of the hole area 10, the hole area 11, the hole area 14 and the hole area 15 is along the width direction of the outer rib, and the main bearing direction of the hole area 12 and the hole area 13 is along the length direction of the outer rib.

[0024] Table 1 Maximum value of equivalent principal stress at intersection of stiffeners

[0025] Table 2 Maximum value of equivalent principal stress of hole area in length and width directions of outer rib

[0026] 3. According to the maximum value of the equivalent principal stress in the horizontal and longitudinal directions of the bottom panel 1, the 3D printing direction is designed According to the finite element simulation analysis results, the ratio of the maximum value of the longitudinal equivalent principal stress to the maximum value of the horizontal equivalent principal stress of the bottom panel 1 is 1.81, which is rounded to 2. When the bottom panel 1 is 3D printed, the printing direction of each layer is taken as the horizontal or longitudinal direction, the number of layers of the main bearing direction is twice the number of layers of the secondary bearing direction, the horizontal printing and the longitudinal printing are staggered layer by layer at the bottom and the top of the panel, and the excess number of layers in the longitudinal direction is printed in the middle of the panel.

[0027] 4. The length direction of the straight section of the stiffener is taken as the printing direction and printed layer by layer The length direction of the straight section of the stiffener is taken as the printing direction and printed layer by layer.

[0028] 5. According to the maximum value of the equivalent principal stress at the intersection of the reinforcing rib along the length direction of each rib, the 3D printing direction design of the intersection of the reinforcing rib is carried out When the two outer ribs intersect, the intersection along the length direction of the two outer ribs is printed layer by layer in the printing direction.

[0029] According to the finite element simulation analysis results, the ratio of the maximum value of the equivalent principal stress in the main bearing direction to the secondary bearing direction at the intersection of the outer rib and the inner rib, the intersection of the inner rib and the inner rib is calculated. As shown in Table 1.

[0030] The intersection of outer horizontal rib 2 and inner vertical rib 7, outer horizontal rib 2 and inner vertical rib 8, inner horizontal rib 1 and outer vertical rib 9, inner horizontal rib 2 and outer vertical rib 9, outer horizontal rib 5 and inner vertical rib 7, outer horizontal rib 5 and inner vertical rib 8 is the main bearing direction, and the ratio of the maximum value of the equivalent principal stress in the main bearing direction to the secondary bearing direction is not less than 2. After printing 3 layers along the main bearing direction at the above intersection, print 1 layer along the secondary bearing direction. The ratio of the maximum value of the equivalent principal stress in the main bearing direction to the secondary bearing direction at the intersection of the rest of the reinforcing rib is less than 2. The intersection along the main bearing direction and the secondary bearing direction, i.e. the longitudinal direction and the transverse direction, is printed layer by layer in the printing direction. The printing schematic along the longitudinal direction at the intersection is shown in Figure 4 , and the printing schematic along the transverse direction is shown in Figure 5 .

[0031] When printing along the length direction of the intersection of the reinforcing rib, only one reinforcing rib is printed along the length direction of the reinforcing rib.

[0032] 6. According to the maximum value of the equivalent principal stress in the length direction and the width direction of the hole area along the outer rib, the 3D printing direction design of the hole area is carried out According to the finite element simulation analysis results, the hole area 10, the hole area 11, the hole area 14, and the hole area 15 adopt the printing mode of spiral shape and "hui" shape combination, the inside is spiral shape, and the outside is "hui" shape. Among them, the area of the spiral shape area accounts for of the area of the hole area; the printing direction of the hole area 12 and the hole area 13 is the circular arc circumferential direction and the length direction of the outer rib. Take the edge line and the central axis of the hole area parallel to the length direction of the outer rib. When the printing position is not more than the distance from the edge or the central axis, the printing direction is selected as the length direction of the outer rib; otherwise, the printing direction is selected as the circular arc circumferential direction with the hole center as the center and the distance from the hole center to the printing position as the radius.

[0033] 7. When printing each component of the rectangular straight ribbed plate, the printing direction is determined according to the above rules, and the printing is carried out layer by layer along the vertical direction from the bottom to the top Thus, the continuous fiber reinforced 3D printing of the rectangular straight ribbed plate has been completed.

[0034] The continuous fiber 3D printed rectangular straight ribbed panel prepared according to the method of the embodiment has a maximum overall deformation value of 1.03 mm, a maximum fiber direction stress value of 138.12 MPa, and a maximum stress value perpendicular to the fiber direction of 15.73 MPa under the above load and constraint conditions; the structural load is mainly borne by the continuous fiber, the stress value perpendicular to the fiber direction is very small, greatly reducing the risk of structural cracking; the overall deformation and stress value are relatively small, meeting the structural safety requirements.

[0035] The continuous fiber 3D printed rectangular straight ribbed panel prepared according to the traditional one-way layer-by-layer printing method has a maximum overall deformation value of 5.95 mm, a maximum fiber direction stress value of 99.10 MPa, and a maximum stress value perpendicular to the fiber direction of 107.38 MPa under the same load and constraint, and is printed in the horizontal direction. The overall maximum deformation value is 1.24 mm, the maximum fiber direction stress value is 179.21 MPa, and the maximum stress value perpendicular to the fiber direction is 30.96 MPa. Compared with the rectangular straight ribbed panel printed by the method of the embodiment, the overall maximum deformation value is reduced by 17%, the maximum fiber direction stress value is reduced by 23%, and the maximum stress value perpendicular to the fiber direction is reduced by 49%.

[0036] Embodiment 2 The ribbed panel of the embodiment is a rectangular diagonal ribbed panel composed of a 2 mm thick bottom panel 16 and a 5 mm thick reinforcing rib, with a width of 120 mm and a length of 300 mm. The bottom panel 16 is located below the reinforcing rib. The reinforcing rib includes three horizontal ribs, two longitudinal ribs, and two diagonal ribs. The three horizontal ribs include outer horizontal rib three 17, outer horizontal rib four 19, and inner horizontal rib three 18. The two longitudinal ribs include outer horizontal rib three 17 and outer horizontal rib four 19. The two diagonal ribs include inner diagonal rib one 22 and inner diagonal rib two 23. The width of outer horizontal rib three 17, outer horizontal rib four 19, outer longitudinal rib three 20, and outer longitudinal rib four 21 is 10 mm. The width of inner horizontal rib three 18, inner diagonal rib one 22, and inner diagonal rib two 23 is 5 mm. Outer horizontal rib three 17 and outer horizontal rib four 19 are each provided with two vertical through holes with a diameter of 3 mm. As shown in FIG. 2, the rectangular diagonal ribbed panel printing fiber is selected from T300 carbon fiber reinforced PPS resin-based composite material filaments. Figure 2

[0037] When the rectangular diagonal ribbed panel of the embodiment is 3D printed, the specific implementation steps are as follows: 1. According to the geometric shape characteristics of the rectangular diagonal ribbed panel, the structures are divided into zones to facilitate the design of the printing method of each structure ​According to the thickness of the rectangular diagonal rib reinforced plate panel, the bottom panel two 16 is split; according to the position of the reinforcing rib inside and outside, the horizontal and vertical diagonal direction is different, the reinforcing rib is divided into outer horizontal rib, outer vertical rib, inner horizontal rib and inner diagonal rib; The intersection and straight section of the reinforcing rib are designed separately; On the outer rib, with the vertical through hole center as the center, with 4.5mm as the side length, the hole area seven 24, the hole area eight 25, the hole area nine 26 and the hole area ten 27 with square cross section are split on the outer rib, and the printing mode is designed separately.

[0038] 2. Rectangular diagonal rib reinforced plate adopts isotropic material model to carry out finite element analysis, and analyzes the maximum value of equivalent principal stress of each region of the structure According to the characteristics of the partition structure of the rectangular diagonal rib reinforced plate, the finite element analysis technology is adopted to determine that the maximum value of equivalent principal stress of the bottom panel two 16 in horizontal and vertical directions, the maximum value of equivalent principal stress of the straight section of the reinforcing rib along its length direction, the maximum value of equivalent principal stress of the intersection of the reinforcing rib along the length direction of each rib, and the maximum value of equivalent principal stress of the hole area along its length and width of the outer rib. Among them, the maximum value of equivalent principal stress is the maximum value of the absolute value of the above equivalent principal stress, only the size of the equivalent principal stress value is compared, and the positive and negative states of the equivalent principal stress are not distinguished.

[0039] When carrying out finite element analysis, the finite element model of the rectangular diagonal rib reinforced plate adopts aluminum alloy material, the vertical displacement of the bottom left and right ends of the bottom panel two 16 is constrained, the horizontal and vertical displacements of the reinforcing rib opening are constrained, and the rectangular diagonal rib reinforced plate is loaded with concentrated force load, wherein the X direction load FX=500N, the Z direction load FZ=-1000N, as shown in Figure 2 .

[0040] The finite element simulation results are: the maximum value of the lateral equivalent principal stress of the bottom panel two 16 is 65.58 MPa, and the maximum value of the longitudinal equivalent principal stress is 125.75 MPa; the longitudinal stress value is larger, and the longitudinal direction is the main bearing direction and the lateral direction is the secondary bearing direction. At the intersection of the inner lateral rib three 18 and the outer longitudinal rib three 20, the maximum value of the length direction equivalent principal stress of the inner lateral rib three 18 is 4.93 MPa, and the maximum value of the length direction equivalent principal stress of the outer longitudinal rib three 20 is 36.83 MPa, and the longitudinal direction is the main bearing direction; at the intersection of the inner lateral rib three 18 and the outer longitudinal rib four 21, the maximum value of the length direction equivalent principal stress of the inner lateral rib three 18 is 7.43 MPa, and the maximum value of the length direction equivalent principal stress of the outer longitudinal rib four 21 is 39.08 MPa, and the longitudinal direction is the main bearing direction. The maximum value of the equivalent principal stress along the length direction of the intersection of the three reinforcing ribs is shown in Table 3, wherein the first reinforcing rib, the second reinforcing rib and the third reinforcing rib are only for the convenience of distinguishing and explaining the intersection of the three reinforcing ribs, and have no special meaning; according to the maximum value of the equivalent principal stress of the three reinforcing ribs at the intersection of the reinforcing ribs, the direction of the first two high maximum equivalent principal stress is the main bearing direction and the secondary bearing direction, and the remaining equivalent principal stress direction is the weak bearing direction. The maximum value of the equivalent principal stress of the hole area along the length and width directions of the outer rib is shown in Table 4, and the direction of the maximum equivalent principal stress is the main bearing direction, and the direction of the minimum equivalent principal stress is the secondary bearing direction; the main bearing direction of the hole area seven 24, the hole area eight 25, the hole area nine 26 and the hole area ten 27 is along the width direction of the outer rib.

[0041] Table 3 Maximum value of equivalent principal stress along length direction of intersection of three reinforcing ribs

[0042] Table 4 Maximum value of equivalent principal stress of hole area along length and width directions of outer rib

[0043] 3. According to the maximum value of the equivalent principal stress of the bottom panel two 16 in the lateral and longitudinal directions, the 3D printing direction is designed According to the finite element simulation analysis results, the ratio of the maximum value of the longitudinal equivalent principal stress of the bottom panel two 16 to the maximum value of the lateral equivalent principal stress is 1.92, which is rounded to 2. When the bottom panel two 16 is 3D printed, the printing direction of each layer is taken as the lateral direction or the longitudinal direction, the number of layers of the main bearing direction is twice the number of layers of the secondary bearing direction, the lateral printing and the longitudinal printing are staggered layer by layer at the bottom and the top of the panel, and the redundant number of layers is printed in the middle of the panel.

[0044] 4. The length direction of the straight section of the reinforcing rib is taken as the printing direction and printed layer by layer At the straight section where each stiffener in the stiffened plate does not intersect with other stiffeners, the length direction of the stiffener is taken as the printing direction and printed layer by layer.

[0045] 5. Design the 3D printing direction at the intersection of stiffeners based on the maximum equivalent principal stress along the length direction of each stiffener at the intersection of stiffeners. According to the finite element simulation analysis results, at the intersection of the inner transverse rib three 18 and the outer longitudinal rib three 20, the ratio of the maximum equivalent principal stress in the main load-bearing direction to the maximum equivalent principal stress in the secondary load-bearing direction is not less than 2. After printing 3 layers along the main load-bearing direction at the intersection, print 1 layer along the secondary load-bearing direction; at the intersection of the inner transverse rib three 18 and the outer longitudinal rib four 21, the ratio of the maximum equivalent principal stress in the main load-bearing direction to the maximum equivalent principal stress in the secondary load-bearing direction is not less than 2. After printing 3 layers along the main load-bearing direction at the intersection, print 1 layer along the secondary load-bearing direction.

[0046] The intersection area of the three ribs adopts an interleaved printing method. The number of printing layers in the main load-bearing direction and the secondary load-bearing direction is the same, and the ratio of the number of printing layers in the main load-bearing direction and the secondary load-bearing direction to the number of printing layers in the weak load-bearing direction is 3:1. That is, after printing 3 layers layer by layer and alternately in the main load-bearing direction and the secondary load-bearing direction, print 1 layer in the weak load-bearing direction.

[0047] When printing along the length directions of two or three stiffeners at the intersection of stiffeners, only print along the length direction of one stiffener per layer.

[0048] 6. Design the 3D printing direction of the perforated area based on the maximum equivalent principal stress along the length and width directions of the outer rib where the perforated area is located.

[0049] According to the finite element simulation analysis results, the perforated areas seven 24, perforated areas eight 25, perforated areas nine 26, and perforated areas ten 27 adopt a printing method combining spiral and "return" shapes, with a spiral shape inside and a "return" shape outside. Among them, the area of the spiral region accounts for the area of the perforated region .

[0050] 7. When printing each component of the rectangular diagonal rib stiffened plate, the printing direction is determined according to the above rules and printed layer by layer from the bottom to the top vertically. So far, the continuous fiber reinforced 3D printing of the rectangular diagonal rib stiffened plate has been completed.

[0051] For the continuously fiber 3D printed rectangular diagonal rib stiffened plate prepared by the method of this embodiment, under the above load and constraint conditions, the maximum deformation value of the stiffened panel is 1.30 mm, the maximum stress value in the fiber direction is 142.39 MPa, and the maximum stress value perpendicular to the fiber direction is 18.54 MPa; the structural load is mainly borne by the continuous fiber, and the stress value perpendicular to the fiber direction is very small, far reducing the risk of structural cracking; the deformation and stress values of the stiffened panel are both small, meeting the structural safety requirements.

[0052] The continuous fiber 3D printed rectangular diagonal rib stiffened plate prepared according to the traditional one-way layer-by-layer printing mode is difficult to be printed and formed in a diagonal direction. Under the same load and constraint, the overall maximum deformation value is 8.77 mm, the maximum stress value in the fiber direction is 131.74 MPa, and the maximum stress value perpendicular to the fiber direction is 221.63 MPa when printing in the horizontal direction. The overall deformation is too large, and the maximum stress value perpendicular to the fiber direction exceeds the material strength, and the structure cracks. When printing in the vertical direction, the overall maximum deformation value is 1.37 mm, the maximum stress value in the fiber direction is 311.28 MPa, and the maximum stress value perpendicular to the fiber direction is 33.21 MPa. Compared with the above, the overall maximum deformation value of the rectangular diagonal rib stiffened plate printed by the method of the embodiment is reduced by 5%, the maximum stress value in the fiber direction is reduced by 54%, and the maximum stress value perpendicular to the fiber direction is reduced by 44%.

[0053] Embodiment 3 The stiffened panel of the embodiment is a square straight rib stiffened panel composed of a 1.8 mm thick bottom panel three 28 and a 4.8 mm thick stiffener. The width is 120 mm, the length is 120 mm, and the bottom panel three 28 is located below the stiffener. The stiffener includes three horizontal ribs and three vertical ribs. The three horizontal ribs include outer horizontal rib five 29, outer horizontal rib six 31 and inner horizontal rib four 30. The three vertical ribs include outer vertical rib five 32, outer vertical rib six 34 and inner vertical rib three 33. The width of the outer horizontal rib five 29, the outer horizontal rib six 31, the outer vertical rib five 32 and the outer vertical rib six 34 is 6 mm, and the width of the inner horizontal rib four 30 and the inner vertical rib three 33 is 4 mm. As shown in FIG. 4. Figure 3 The printing fiber of the square straight rib stiffened panel is selected from T700 carbon fiber reinforced PA6 resin composite wire.

[0054] When the square straight rib stiffened panel of the embodiment is 3D printed, the specific implementation steps are as follows: 1. According to the geometric shape characteristics of the square straight rib stiffened panel, each component structure is partitioned to facilitate the separate design of the printing mode of each structure According to the thickness of the square straight rib stiffened panel, the bottom panel three 28 is split. According to the different positions of the stiffener inside and outside, the horizontal and vertical directions, the stiffener is divided into outer horizontal rib, outer vertical rib, inner horizontal rib and inner vertical rib. The intersection and straight section of the stiffener are designed separately.

[0055] 2. The square straight rib stiffened panel adopts an isotropic material model for finite element analysis to analyze the maximum equivalent principal stress of each region of the structure According to the characteristics of the square straight stiffener partition structure, the finite element analysis technology is used to determine: the maximum equivalent principal stress of the bottom panel 328 in the transverse and longitudinal directions, the maximum equivalent principal stress of the straight section of the reinforcing rib along the length direction, and the maximum equivalent principal stress of the reinforcing rib intersection along the length direction of each rib. Among them, the maximum equivalent principal stress is the maximum value of the absolute value of each equivalent principal stress. Only the size of the equivalent principal stress value is compared, and the positive and negative states of the equivalent principal stress are not distinguished.

[0056] When performing finite element analysis, the finite element model of the square straight stiffened plate is made of titanium alloy material. One corner of the bottom panel 328 is fixed, and the other three corners are simply supported and constrained. The inner transverse rib and the inner longitudinal rib of the stiffened plate are loaded with Z-direction concentrated force load FZ=-500N, as shown in Figure 3 .

[0057] The finite element simulation results are: the maximum equivalent principal stress of the bottom panel 328 in the transverse direction is 162.18MPa, and the maximum equivalent principal stress in the longitudinal direction is 162.18MPa. The longitudinal direction is the main load-bearing direction, and the transverse direction is the secondary load-bearing direction. The maximum equivalent principal stress of the reinforcing rib at the intersection of the outer rib and the inner rib and the inner rib along the length direction of the two reinforcing ribs is shown in Table 5. Among them, the first reinforcing rib and the second reinforcing rib are only used for convenient distinction and explanation of the two reinforcing ribs at the intersection, and have no special meaning. The direction of the larger maximum equivalent principal stress at the intersection of the two reinforcing ribs is the main load-bearing direction, and the direction of the smaller maximum equivalent principal stress is the secondary load-bearing direction.

[0058] Table 5 Maximum equivalent principal stress at the intersection of the outer rib and the inner rib and the inner rib

[0059] 3. According to the maximum equivalent principal stress in the transverse and longitudinal directions of the bottom panel 328, the 3D printing direction design is performed.

[0060] According to the finite element simulation analysis results, the ratio of the maximum equivalent principal stress in the longitudinal direction to the maximum equivalent principal stress in the transverse direction of the bottom panel 328 is 1, which is rounded to 1. When 3D printing the bottom panel 328, the printing direction of each layer is taken in the transverse or longitudinal direction. The number of layers printed in the longitudinal direction is equal to the number of layers printed in the transverse direction, and the printing in the longitudinal direction and the transverse direction is performed layer by layer.

[0061] 4. The length direction of the straight section of the reinforcing rib is taken as the printing direction layer by layer The length direction of the straight section of the reinforcing rib is taken as the printing direction layer by layer.

[0062] 5. According to the maximum equivalent principal stress along the length direction of the reinforcing rib intersection, the 3D printing direction design of the reinforcing rib intersection is performed When the two outer ribs intersect, the intersection along the length direction of the two outer ribs is the printing direction of layer-by-layer staggered printing.

[0063] According to the finite element simulation analysis results, the ratio of the maximum equivalent principal stress of the main bearing direction to the secondary bearing direction at the intersection of the outer rib and the inner rib, and the intersection of the inner rib and the inner rib is calculated. As shown in Table 5.

[0064] The intersection of the outer transverse rib five 29 and the inner longitudinal rib three 33, and the intersection of the outer transverse rib six 31 and the inner longitudinal rib three 33 is the main bearing direction in the transverse direction; the intersection of the inner transverse rib four 30 and the outer longitudinal rib five 32, and the intersection of the inner transverse rib four 30 and the outer longitudinal rib six 34 is the main bearing direction in the longitudinal direction. The ratio of the maximum equivalent principal stress of the main bearing direction to the secondary bearing direction at the intersection of each reinforcing rib is less than 2, and the intersection along the main bearing direction and the secondary bearing direction, i.e. the longitudinal direction and the transverse direction, is the printing direction of layer-by-layer staggered printing.

[0065] The maximum equivalent principal stress of the intersection of the inner transverse rib four 30 and the inner longitudinal rib three 33 in the two directions is equal, and there is no distinction between the main bearing direction and the secondary bearing direction, and the intersection along the length direction of the two reinforcing ribs, i.e. the longitudinal direction and the transverse direction, is the printing direction of layer-by-layer staggered printing.

[0066] When printing at the intersection of the reinforcing rib along the length direction of the two reinforcing ribs, each layer is printed only along the length direction of one reinforcing rib.

[0067] 6. When printing each component of the square straight rib stiffened plate, the printing direction is determined according to the above rules, and layer-by-layer printing is performed along the vertical direction from the bottom to the top At this point, the continuous fiber 3D printing of the square straight rib stiffened plate has been completed.

[0068] The maximum deformation value of the continuous fiber 3D printed square straight rib stiffened plate prepared according to the method of the embodiment is 1.00 mm, the maximum stress value in the fiber direction is 215.83 MPa, and the maximum stress value perpendicular to the fiber direction is 27.17 MPa under the above load and constraint conditions; the structural load is mainly borne by the continuous fiber, the stress value perpendicular to the fiber direction is very small, and the risk of structure cracking is greatly reduced; the deformation and stress value of the stiffened panel are small, which meets the structural safety requirement.

[0069] The continuous fiber 3D printed square straight rib stiffened plate prepared according to the traditional unidirectional layer-by-layer printing method is printed in the horizontal or vertical direction, and under the same load and constraint, the overall maximum deformation value is 2.36 mm, the maximum stress value in the fiber direction is 304.42 MPa, and the maximum stress value perpendicular to the fiber direction is 115.46 MPa, which exceeds the material strength and causes the structure to crack. Compared with the square straight rib stiffened plate printed by the method of the embodiment, the overall maximum deformation value of the square straight rib stiffened plate printed by the method of the embodiment decreases by 58%, the maximum stress value in the fiber direction decreases by 29%, and the maximum stress value perpendicular to the fiber direction decreases by 76%.

Claims

1. A continuous fiber-reinforced 3D printing method of a reinforced panel, characterized in that, The steps are as follows: 1) According to the geometric characteristics of the reinforced panel, the structures are divided into different regions According to the structural characteristics of the reinforced panel, the reinforcing rib and the bottom panel are divided into two regions; For the reinforcing rib with complex structure, it is further divided into different regions according to its inner and outer positions, horizontal and vertical directions, and different structures, including the reinforcing rib straight section region, the reinforcing rib intersection section region; The reinforcing rib intersection section region includes two rib intersection regions and multiple rib intersection regions, two rib intersection regions include two outer rib intersection regions and inner rib intersection region; 2) Estimate the maximum equivalent principal stress of each region by finite element simulation technology The reinforced panel adopts an isotropic material model with properties close to continuous fibers. According to the actual stress working conditions of the reinforced panel, the load and constraint are applied to carry out finite element simulation analysis, and the maximum equivalent principal stress in the required direction of each region is obtained; 3) According to the estimated results of the maximum equivalent principal stress of each region, the 3D printing method is designed According to the estimated results of the maximum equivalent principal stress in the required direction of the bottom panel region, the main bearing direction and the secondary bearing direction are determined; The ratio of the maximum equivalent principal stress in the main bearing direction to that in the secondary bearing direction is calculated, and the stress ratio is obtained by rounding off; The stress ratio; The main bearing direction and the secondary bearing direction adopt staggered printing method, the number of layers printed in the main bearing direction is an integer multiple of the number of layers printed in the secondary bearing direction, and the multiple is the stress ratio; The reinforcing rib straight section region adopts layer-by-layer printing along the length direction of the reinforcing rib; Two outer rib intersection regions adopt layer-by-layer staggered printing along the length direction of the two outer ribs; The inner rib intersection region adopts staggered printing; According to the estimated results of the maximum equivalent principal stress, the main bearing direction and the secondary bearing direction of the inner rib intersection region are determined, and the stress ratio is calculated; When the stress ratio is not less than 2, the ratio of the number of layers printed along the main bearing direction to that along the secondary bearing direction is 3:1; When the stress ratio is less than 2, layer-by-layer staggered printing is adopted along the main bearing direction and the secondary bearing direction; Multiple rib intersection regions adopt staggered printing; According to the estimated results of the maximum equivalent principal stress, the main bearing direction, the secondary bearing direction and the weak bearing direction of the multiple rib intersection regions are determined; The number of layers printed in the main bearing direction and the secondary bearing direction is the same, and the ratio of the number of layers printed in the weak bearing direction is 3:1; After layer-by-layer staggered printing of 3 layers in the main bearing direction and the secondary bearing direction, one layer is printed in the weak bearing direction; 4) According to the designed printing method, the 3D printing of the reinforced panel is completed According to the printing method designed in step 3), layer-by-layer printing is carried out from the bottom to the top along the vertical direction to complete the 3D printing of the reinforced panel. A vertical through hole is provided on the reinforcing rib of the reinforced panel.

2. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 1, characterized by: When dividing the structures of the reinforced panel according to the geometric characteristics in step 1), a hole region is divided on the reinforcing rib with a vertical through hole, which is a region with a square cross section with the center of the vertical through hole as the center and the side length of 1.5-2 times the diameter of the hole.

3. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 2, characterized in that: The maximum equivalent principal stress in the required direction of the hole region is the maximum equivalent principal stress in the length and width directions of the reinforcing rib.

4. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 3, characterized in that: Step 3 also includes designing the 3D printing method according to the estimated results of the maximum equivalent principal stress of the hole region 5. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 4, characterized in that: ​ Based on the estimated maximum equivalent principal stress in both the length and width directions of the reinforcing rib where the perforated area is located, the primary and secondary load-bearing directions are determined. When the primary load-bearing direction is along the width direction of the reinforcing rib, the perforated area uses a combination of spiral and "U" shaped printing methods, with the inner part being spiral and the outer part being "U". The spiral area accounts for a certain percentage of the total area of ​​the perforated area. When the main load-bearing direction is along the length of the reinforcing rib, the printing method for the area with holes is a combination of the circumferential arc and the length of the reinforcing rib. If the distance between the printing position and the edge line or central axis parallel to the length of the outer rib is not greater than its distance from the edge of the hole, the printing direction is selected as the length of the outer rib; otherwise, the printing direction is selected as the circumferential arc with the hole center as the center and the distance from the hole center to the printing position as the radius.

6. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 1, characterized by: In the step 3), the required directions of the bottom panel are the transverse direction and the longitudinal direction, when the maximum equivalent principal stress of the transverse direction and the longitudinal direction are equal, the longitudinal direction is the main load bearing direction; when the maximum equivalent principal stress of the two directions of the intersection area of the two bars are equal, the main load bearing direction and the secondary load bearing direction are not distinguished, and the printing direction is staggered layer by layer along the length direction of the two reinforcing bars.

7. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 1, characterized by: In the step 3), when the bottom panel is printed layer by layer staggered along the main load bearing direction and the secondary load bearing direction at the bottom and the top of the bottom panel, the redundant layers of the main load bearing direction are printed at the middle position of the thickness of the bottom panel.

8. The continuous fiber-reinforced 3D printing method of a ribbed panel according to claim 1, characterized by: In the step 3), in the intersection area of the two bars and the intersection area of the multiple bars, each layer is printed along the length direction of only one reinforcing bar.

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