Preparation and shape control method of three-dimensional braided polygonal core preform

Abstract

The present invention discloses a method for preparing a three-dimensional woven polygonal core preform and controlling its shape. The method adopts an on-machine shape control and off-machine forming method to form the polygonal core preform. The preparation method of the present invention achieves precise control of the aperture size of the polygonal core preform by designing, calculating, and adjusting the weaving parameters of the three-dimensional braided fabric. This solves the problems in the prior art of large deviations between the design parameters and actual production parameters of the three-dimensional woven polygonal core preform, low production efficiency, and difficulty in controlling the fabric structure. It further improves processing efficiency and reduces processing allowances.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-performance fiber weaving, and in particular relates to a method for preparing a three-dimensional woven polygonal core lattice preform and controlling its shape. Background Art

[0002] To meet the material performance requirements of aerospace equipment, the development of composite materials with high specific strength, high specific modulus, and low density has become a key area of ​​research. Polygonal core lattice structures, with their light weight, high porosity, and low density, have become a key component of composite core materials for aviation applications. Currently, widely used polygonal core lattice materials primarily utilize single-layer bonding. This results in weak W-direction inter-wall nodes, forming structural weak links. With the advancement of space exploration, this structure has become unable to meet performance requirements.

[0003] In order to improve the problem of weak W-direction inter-wall connection performance of the existing polygonal core lattice structure, a polygonal core lattice preform with W-direction inter-layer connection is obtained by three-dimensional weaving, such as Figure 1 As shown (the polygonal core cell is hexagonal), the polygonal core cell preform is formed by arranging and connecting identical unit cells in an array, and openings are formed in the unit cells. This structure is used as a reinforcing material to further prepare a polygonal core cell composite material.

[0004] For 3D weaving, the four-step method is the basic method of the overall process of 3D weaving. The four-step 3D weaving is currently a relatively mature one-piece molding process for special-shaped prefabricated bodies. The four-step 3D weaving uses a yarn carrier to carry the yarn, and moves it in the X and Y directions according to the rules on the Cartesian machine. The whole woven prefabricated body is formed by the circular movement of the yarn carrier along the X and Y axes. Figure 2 This is a diagram of the yarn carrier's knitting trajectory. When a certain row of yarn carriers is controlled to move only along a single Y-axis, the preform will split into multiple pieces of fabric. By controlling the spacing and position of the fixed rows, the holes can be opened and closed, ultimately creating a polygonal core preform.

[0005] In the existing technology, although the weaving of polygonal core grid structure fabrics has been achieved, the shape control and weaving parameter control of the woven fabrics in the semi-automatic production mode are generally adopted in actual processing, which has become a key issue affecting the stability of the performance of polygonal core grid fabrics. The existing four-step three-dimensional weaving polygonal core grid technology adopts the core mold forming method (core mold forming method: that is, when a row of cells is completed during the weaving process, a core mold is inserted into the row of cells) to form the polygonal core grid fabric (such as Figure 1 This forming method will produce large fabric deformation under the action of gravity and tension, resulting in tension errors (such as Figure 3 a and Figure 4(As shown). This tension error is affected by the weaving process, operating techniques, and molding technology, making it difficult to predict, control, and correct. Ultimately, it leads to inaccurate molding of the polygonal core structure, severely affecting the performance of the finished material and limiting its use cases.

[0006] For example: The patent with publication number CN115058825A (application number 202210635648.0) discloses a three-dimensional weaving method for a polygonal core grid structure, in which the fiber bundles are interwoven by rotating a planar yarn carrier, so that the fiber bundles form a vertically mounted polygonal core grid structure. CN115976729A (application number 202211730601.9) discloses a large-size polygonal core grid preform and a preparation method using array equipment, involving a four-step three-dimensional weaving process to form a polygonal core grid preform. The above application does not involve the shape control design of the three-dimensional woven polygonal core grid structure, and lacks the structural design and control of the molded polygonal core grid structure, resulting in instability of the processing parameters and ultimately causing structural defects. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a method for preparing a three-dimensional woven polygonal core preform. The method adopts an on-machine shape control and off-machine forming method to form the polygonal core preform.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] A method for preparing a three-dimensional woven polygonal core preform, wherein the polygonal core preform is formed by arranging and connecting identical unit cells in an array, wherein an opening is formed in the unit cell, and the length of the connecting edge of the unit cell is L b , the length of the free edge of the unit cell is L f The method for preparing a three-dimensional woven polygonal core preform comprises the following steps:

[0010] Step 1: Weave a preform using a three-dimensional weaving four-step method, wherein the preform is formed with multiple columns of first fabric opening groups and multiple columns of second fabric opening groups along its width direction, and a column of second fabric opening groups is arranged between every two adjacent first fabric opening groups. The first fabric opening group is a first fabric opening formed on the preform at intervals along the weaving direction, and the second fabric opening group is a second fabric opening formed on the preform at intervals along the weaving direction. The first fabric opening and the second fabric opening are both fabric openings, and the first fabric opening and the second fabric opening are both slits. The lengths of the first fabric opening and the second fabric opening are the same and are both L. The upper part of each first fabric opening is opposite to the lower part of each second fabric opening in the second fabric opening group on both sides thereof, and the relative parts of the preform are upper overlapping parts, and the length of the upper overlapping part is L. fThe lower part of each first fabric opening is opposite to the upper part of each second fabric opening in the second fabric opening group on both sides thereof, and the preform of the opposite part is the lower overlapping part, and the length of the lower overlapping part is L f Each first fabric opening and the non-opposite portion of the second fabric openings in the adjacent second fabric opening groups on both sides are the first non-overlapping portions, and the length of the first non-overlapping portions is L. b =L-2L f Each second fabric opening and its adjacent two sides of the first fabric opening group of the first fabric opening does not correspond to the preformed portion of the second non-overlapping portion, the length of the second non-overlapping portion is L b ;

[0011] The three-dimensional braiding four-step method includes: a first polygonal core lattice bonding edge forming stage, a first polygonal core lattice free edge forming stage, a second polygonal core lattice bonding edge forming stage, and a second polygonal core lattice free edge forming stage. The first polygonal core lattice bonding edge forming stage is used to form the second non-overlapping portion in the preform; the first polygonal core lattice free edge forming stage is used to form the upper overlapping portion in the preform; the second polygonal core lattice bonding edge forming stage is used to form the first non-overlapping portion in the preform; and the second polygonal core lattice free edge forming stage is used to form the lower overlapping portion in the preform.

[0012] When the second polygonal core cell free edge forming stage is completed and the first fabric openings are not sealed, inserting an aperture size control sheet into the unsealed first fabric openings of the row, with the aperture size control sheet being parallel to the length direction of the first fabric openings;

[0013] When the first polygonal core cell free edge forming stage is completed and the second fabric openings are not sealed, inserting an aperture size control sheet into the unsealed second fabric openings of the row, with the aperture size control sheet being parallel to the length direction of the second fabric openings;

[0014] After all the aperture size control sheets are placed into the preform, the length of the relative parts of any two adjacent rows of aperture size control sheets along the weaving direction is L f The length of the edges of the aperture size control sheets in each adjacent row in the same column along the weaving direction is L. b ; The thickness of the aperture size control sheet is less than 2mm;

[0015] Step 2: After the four-step three-dimensional weaving method is completed, the aperture size control sheets are taken out by row, and a core mold is filled into each of the first fabric openings / second fabric openings of the row where the aperture size control sheets are taken out, so that the core mold is filled into the first fabric opening / second fabric opening and the first fabric opening / second fabric opening respectively forms a unit cell opening of the polygonal core lattice preform, thereby obtaining a polygonal core lattice preform.

[0016] In step 2, the core mold is filled into the first fabric opening / the second fabric opening by the opening auxiliary tool.

[0017] In step 1, for the first polygonal core grid edge forming stage, the fixed columns of yarn carriers are numbered as follows: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula:

[0018] (X-1) / (2*n t +2) = integer

[0019] For the first polygonal core grid free edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula:

[0020] (X-1) / (n t +1)=integer

[0021] For the second polygonal core grid edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula:

[0022] (X+n t ) / (2*n t +2) = integer

[0023] For the second polygonal core grid free edge forming stage, the fixed column number of the yarn carrier is the same as that of the first polygonal core grid free edge forming stage;

[0024] Among them, n t It is the number of yarn carrier columns corresponding to a single free edge in the polygonal core preform.

[0025] In step 1, when the honeycomb core opening θ is an acute angle or a right angle, the length of the junction node l in the preparation method of the three-dimensional woven polygonal core preform is b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0026] l b ′=[k b / (k b -1 / 2)]*l b

[0027] l f ′=[k f / (k f +1 / 2)]*l f

[0028] When the honeycomb core opening θ is an obtuse angle or a flat angle, the length of the junction node l in the preparation method of the three-dimensional woven polygonal core preform is b' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0029] l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b

[0030] l f ′=[k f / (k f +1)]*l f

[0031] When the honeycomb core opening θ>180 degrees, the length of the junction node l in the preparation method of the three-dimensional woven polygonal core preform is b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0032] l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b

[0033] l f ′=[k f / (k f +1)-(1 / 2*T b ) / k f ]*l f

[0034] Among them, k b is the number of nodes of the combined edge, k f is the number of nodes on the free edge, l b is the theoretical value of the length of the junction of the polygonal core lattice preform, l f is the theoretical value of the node length of the free edge in the polygonal core preform; T b is the wall thickness of the joining edge.

[0035] The opening auxiliary tool is fixed to the core mold.

[0036] When the opening auxiliary tool is fixed to the core mold, the length direction of the core mold is parallel to the length direction of the opening auxiliary tool.

[0037] The aperture size control sheet is a single piece, and includes: a working part and mounting parts located at both ends of the working part. The working part and the mounting part are connected. The working part is used to be placed in a slit-shaped fabric opening during weaving, and the mounting part is used to fix the aperture size control sheet in the fabric opening after the aperture size control sheet is placed in the fabric opening.

[0038] The length of the working portion along the weaving direction is W1, W1=LB, where B=B1, B2 or B3, and t is the thickness of the working portion;

[0039] When the corner of the edge of the aperture size control sheet is a right angle, B=B1, B1=Q1*t*0.5, where Q1=1.41,

[0040] When the corner of the edge of the aperture size control sheet is chamfered, B=B2, B2=Q2*t*0.5, where Q2 is the sine value of the chamfer taper.

[0041] When the corners of the edge of the aperture size control plate are rounded, B=B3, B3=Q3*(tr), where r is the fillet radius. When the fillet radius r is less than or equal to 0.5t, Q3 is 1.41; when the fillet radius r is greater than 0.5t and less than or equal to t, Q3 is 1; when the fillet radius r is greater than t, Q3 is 0.

[0042] There is a smooth transition between the installation part and the working part.

[0043] In step 1, the length of the mounting portion of the aperture size control sheet along the weaving direction is W2. When W2 is less than W1, W2 is less than or equal to L. b .

[0044] In step 1, when W2 is greater than W1, 6 mm ≤ W2 < 12 mm.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The preparation method of the present invention achieves precise control of the pore size of a polygonal core preform by designing, calculating, and adjusting the braiding parameters of a 3D braided fabric. This method addresses existing issues such as large deviations between design parameters and actual production parameters, low production efficiency, and difficulty controlling the fabric structure. It further improves processing efficiency and reduces machining margins.

[0047] 2. The preparation method of the present invention adopts a two-step molding method, combined with a polygonal core lattice expander design, and adopts precise parameter design and flexible shape variation strategy to effectively improve the structural stability of the polygonal core lattice preform and reduce weaving damage, avoid defects caused by structural variation, further ensure the stability of the preform performance, and enhance the utilization value of the preform.

[0048] 3. Setting the compensation value B according to the edge of the aperture size control piece can further reduce the geometric area deviation rate from the set specifications.

[0049] 4. According to the angle of the honeycomb core opening θ, the length of the flower node of the combined edge and the length of the flower node of the free edge in the polygonal core preform are compensated in size, which can further reduce the geometric area deviation rate from the set specifications.

[0050] 5. The present invention designs an opening auxiliary tool, which can better complete the preparation method of the present invention;

[0051] 6. In order to realize the preparation method of three-dimensional woven polygonal core lattice preform, a three-dimensional woven polygonal core lattice preform forming precision control tooling was designed. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a photo of a polygonal core lattice preform;

[0053] Figure 2 This is the knitting motion trajectory diagram of the yarn carrier in the four-step three-dimensional knitting method;

[0054] Figure 3 The following are photos of polygonal core lattice preforms: a) shows the core mold forming method, and b) shows the preparation method of the three-dimensional woven polygonal core lattice preform of the present invention;

[0055] Figure 4 This is a schematic diagram of the tension error caused by the core mold forming method;

[0056] Figure 5 This is a structural diagram of the preform in step 1 of the method for preparing a three-dimensional braided polygonal core preform in Example 1;

[0057] Figure 6 Schematic diagram of the structure of the polygonal core lattice preform (the opening shape in the unit cell is hexagonal);

[0058] Figure 7 The relationship between the yarn carrier and the formed fabric at each stage;

[0059] Figure 8 Schematic diagram of the structure of the aperture size control piece;

[0060] Figure 9 Schematic diagram of the structure of the aperture size control piece;

[0061] Figure 10 is the honeycomb core opening θ;

[0062] Figure 11 is the honeycomb core opening θ;

[0063] Figure 12Schematic diagram of the structure of the opening auxiliary tool, wherein a is a main view, b is a side view, c is a top view, and d is a three-dimensional view;

[0064] Figure 13 This is a schematic diagram of the structure of the precise shape-control tooling for forming a three-dimensional woven polygonal core preform;

[0065] Figure 14 Schematic diagram of the structure of the precise shape control tooling for forming a three-dimensional woven polygonal core preform, where a is the state when the first fabric of the first row is opened, and b is the state when the second fabric of the first row is opened;

[0066] Figure 15 (a) side view and (b) perspective view of the reference plane frame;

[0067] Figure 16 This is a structural diagram of the length control positioning belt;

[0068] Figure 17 This is a structural diagram of the length control positioning belt;

[0069] Figure 18 This is a structural diagram of the length control positioning belt;

[0070] Figure 19 This is a structural diagram of the aperture size control sheet;

[0071] Figure 20 A structural diagram of an opening auxiliary tool fixed to the core mold;

[0072] Figure 21 This is a schematic diagram of the structure of the precise shape-control tooling for forming a three-dimensional woven polygonal core preform;

[0073] Figure 22 Schematic diagram of the structure of the polygonal core preform;

[0074] Among them, 1: introduction part, 2: hole expansion part, 3: height control frame, 4: reference plane frame, 5: length control positioning belt, 6: first connecting rod, 7: initial position control piece, 8: aperture size control piece, 8-1: installation part, 8-2: working part, 9: core mold, 10: first through hole, 11: second through hole, 12: second connecting rod; DETAILED DESCRIPTION

[0075] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0076] Example 1

[0077] A method for preparing a three-dimensional woven polygonal core preform, such as Figure 6 and Figure 22As shown, the polygonal core lattice preform is formed by arranging and connecting identical unit cells in an array, with openings formed in the unit cells. The shapes of the openings in the unit cells are hexagons, quadrilaterals, circles, octagons, decagons or concave hexagons.

[0078] The length of the bonding edge of the unit cell is L b , the length of the free edge of the unit cell is L f ;

[0079] The method for preparing a three-dimensional woven polygonal core preform comprises the following steps:

[0080] Step 1: Use the three-dimensional weaving four-step method to weave Figure 5 The preform shown in the figure has multiple columns of first fabric opening groups and multiple columns of second fabric opening groups formed along its width direction, a column of second fabric opening groups is provided between every two adjacent first fabric opening groups, the first fabric opening groups are first fabric openings formed on the preform at intervals along the weaving direction, the second fabric opening groups are second fabric openings formed on the preform at intervals along the weaving direction, the first fabric openings and the second fabric openings are both slits, the lengths of the first fabric openings and the second fabric openings are the same and are both L, the upper part of each first fabric opening is opposite to the lower part of each second fabric opening in the second fabric opening groups on both sides thereof, and the relative parts of the preform are upper overlapping parts, and the length of the upper overlapping parts is L f The lower part of each first fabric opening is opposite to the upper part of each second fabric opening in the second fabric opening group on both sides thereof, and the preform of the opposite part is the lower overlapping part, and the length of the lower overlapping part is L f Each first fabric opening and the non-opposite portion of the second fabric openings in the adjacent second fabric opening groups on both sides are the first non-overlapping portions, and the length of the first non-overlapping portions is L. b =L-2L f Each second fabric opening and its adjacent two sides of the first fabric opening group of the first fabric opening does not correspond to the preformed portion of the second non-overlapping portion, the length of the second non-overlapping portion is L b .

[0081] In order to form the gap, the three-dimensional braiding four-step braiding method includes: a first polygonal core lattice bonding edge forming stage, a first polygonal core lattice free edge forming stage, a second polygonal core lattice bonding edge forming stage, and a second polygonal core lattice free edge forming stage, wherein the first fabric opening and the second fabric opening are formed by the first polygonal core lattice bonding edge forming stage, the first polygonal core lattice free edge forming stage, the second polygonal core lattice bonding edge forming stage, and the second polygonal core lattice free edge forming stage;

[0082] The first polygonal core lattice joint edge forming stage is used to form the second non-overlapping portion in the preform; the first polygonal core lattice free edge forming stage is used to form the upper overlapping portion in the preform; the second polygonal core lattice joint edge forming stage is used to form the first non-overlapping portion in the preform; the second polygonal core lattice free edge forming stage is used to form the lower overlapping portion in the preform;

[0083] The relationship between the yarn carrier and the completed preform at each stage is as follows: Figure 7 As shown, Figure 7 The columns marked with a, b and c are the fixed column positions of the yarn carriers.

[0084] For the first polygonal core grid edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula:

[0085] (X-1) / (2*n t +2) = integer

[0086] For the first polygonal core grid free edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula:

[0087] (X-1) / (n t +1)=integer

[0088] For the second polygonal core grid edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula:

[0089] (X+n t ) / (2*n t +2) = integer

[0090] For the second polygonal core grid free edge forming stage, the fixed column number of the yarn carrier is the same as that of the first polygonal core grid free edge forming stage;

[0091] Among them, n t is the number of yarn carrier columns corresponding to a single free edge in the polygonal core preform;

[0092] When the second polygonal core cell free edge forming stage is completed and the first fabric openings are not sealed, inserting an aperture size control sheet into the unsealed first fabric openings of the row, with the aperture size control sheet being parallel to the length direction of the first fabric openings;

[0093] When the first polygonal core cell free edge forming stage is completed and the second fabric openings are not sealed, inserting an aperture size control sheet into the unsealed second fabric openings of the row, with the aperture size control sheet being parallel to the length direction of the second fabric openings;

[0094] The thickness of the aperture size control sheet is less than 2 mm.

[0095] After all the aperture size control sheets are placed into the preform, the length of the relative parts of any two adjacent rows of aperture size control sheets along the weaving direction is L f The length of the edges of the aperture size control sheets in each adjacent row in the same column along the weaving direction is L. b ;

[0096] Step 2: After the three-dimensional knitting four-step method is completed, the aperture size control sheet is removed by row, and the opening auxiliary tool (such as Figure 20 As shown), the opening auxiliary tool fills the core mold into the first fabric opening / the second fabric opening and makes the first fabric opening / the second fabric opening respectively form a single cell opening of the polygonal core lattice preform to obtain the polygonal core lattice preform.

[0097] The opening auxiliary tool and the core mold can be fixed in a variety of ways, such as gluing or magnetic attraction, or they can be integrally formed.

[0098] Preferably, the surface of the pore size control sheet is covered with a release cloth or coated with a release agent to further reduce weaving damage.

[0099] Preferably, the surfaces of the core mold and the opening auxiliary tool are smooth, and more preferably, the surfaces are covered with a release cloth or soaked with a release agent.

[0100] Example 2

[0101] On the basis of Example 1, Figure 8 、 Figure 9 and Figure 19 As shown, the aperture size control sheet is a single piece. The aperture size control sheet cannot be deformed during use, so it needs to have a certain thickness. This means that the variation caused by the thickness of the aperture size control sheet to the polygonal core structure must be considered and compensated:

[0102] The aperture size control sheet 8 includes: a working portion 8-2 and mounting portions 8-1 located at both ends of the working portion. The working portion 8-2 and the mounting portion 8-1 are connected. The working portion 8-2 is used to be placed in the first fabric opening / second fabric opening. The mounting portion 8-1 is used to fix the aperture size control sheet in the first fabric opening / second fabric opening after the aperture size control sheet is placed in the first fabric opening / second fabric opening. The length of the working portion along the weaving direction is W1. The compensation value B is set according to the edge of the aperture size control sheet, W1=LB, where B=B1, B2 or B3; t is the thickness of the working portion;

[0103] When the corner of the edge of the aperture size control sheet is a right angle, B=B1, B1=Q1*t*0.5, where Q1=1.41,

[0104] When the corner of the edge of the aperture size control sheet is chamfered, B=B2, B2=Q2*t*0.5, where Q2 is the sine value of the chamfer taper C (i.e., for a chamfer taper of 60 degrees, Q2 is 2).

[0105] When the corners of the edge of the aperture size control plate are rounded, B=B3, B3=Q3*(tr), where r is the fillet radius. When the fillet radius r is less than or equal to 0.5t, Q3 is 1.41; when the fillet radius r is greater than 0.5t and less than or equal to t, Q3 is 1; when the fillet radius r is greater than t, Q3 is 0.

[0106] Q1, Q2 and Q3 are compensation coefficients.

[0107] The length of the mounting portion along the weaving direction is W2. Figure 8 As shown, when W2 is less than W1, W2 is less than or equal to L b .

[0108] like Figure 9 As shown, when W2 is greater than W1, 6mm≤W2<12mm.

[0109] There is a smooth transition between the installation part and the working part.

[0110] Example 3

[0111] Based on Example 2, dimensional compensation is performed on the rosette lengths of the binding edges and the free edges of the polygonal core preform, based on the angle θ of the honeycomb core opening, to reduce dimensional variation after hole expansion. To ensure that the unit cell opening of the polygonal core preform obtained by the three-dimensional braided polygonal core preform preparation method is as close to the specified specifications as possible, the rosette lengths of the binding edges are increased and the rosette lengths of the free edges are decreased.

[0112] When the honeycomb core opening θ is an acute angle or a right angle (θ is less than or equal to 90 degrees), the change in the length of the polygonal core wall caused by tension can be ignored, and only the difference in the position of the honeycomb core opening is compensated. b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0113] l b ′=[k b / (k b -1 / 2)]*l b

[0114] l f ′=[k f / (k f +1 / 2)]*l f

[0115] When the honeycomb core opening θ is an obtuse or straight angle (90 degrees < θ ≤ 180 degrees), the change in the length of the polygonal core wall caused by tension needs to be considered, and its compensation value is 1 / 2. At the same time, the shortening of the length of the joint edge caused by the thickness of the single cell wall must also be considered. b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0116] l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b

[0117] l f ′=[k f / (k f +1)]*l f

[0118] When the honeycomb core opening θ>180 degrees, the free edge length extension caused by the cell wall thickness must be considered on the basis of the obtuse angle. b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0119] l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b

[0120] l f ′=[k f / (k f +1)-(1 / 2*T b ) / k f ]*l f

[0121] Among them, k b is the number of nodes of the combined edge, k f is the number of nodes on the free edge, lb is the theoretical value of the length of the flower node of the combined edge in the polygonal core lattice preform (i.e., the length of the flower node of the combined edge determined according to the specifications of the polygonal core lattice preform set before weaving), l f T is the theoretical value of the node length of the free edge in the polygonal core lattice preform (i.e., the node length of the free edge determined according to the specifications of the polygonal core lattice preform set before weaving); b is the wall thickness of the joining edge.

[0122] The honeycomb core opening θ of polygonal core preforms with different unit cell shapes is as follows Figure 10 and Figure 11 As shown.

[0123] Example 4

[0124] Based on Example 3, the structural diagram of the opening auxiliary tool is as follows: Figure 12 As shown, it includes: an introduction part 1 and a reaming part 2, the introduction part 1 and the reaming part 2 are connected, the introduction part and the reaming part are arranged along the length direction of the opening auxiliary tool, the rear end of the introduction part is fixed to the front end of the reaming part, the introduction part is a sheet body with a width gradually decreasing from the back to the front, and the edge of the gradually decreasing width is a smooth line (the smooth line is a straight line or an arc), and the thickness of the introduction part is the same as that of the aperture size control sheet;

[0125] After the introduction portion enters the first fabric opening / the second fabric opening, the plane on which the introduction portion is located is parallel to the length direction of the first fabric opening / the second fabric opening; the shape of the rear end surface of the reaming portion is the same as the shape of the unit cell opening of the polygonal core lattice preform, so that after the introduction portion brings the reaming portion into the first fabric opening / the second fabric opening, the shape of the rear end surface of the reaming portion in the first fabric opening / the second fabric opening is the same as the shape of the unit cell opening (the shape of the rear end surface of the reaming portion is the same as the shape of the core mold to which it is fixed);

[0126] The circumference of the rear end surface of the introduction portion is 2L.

[0127] With the center line of the longitudinal direction of the opening auxiliary tool as the axis, all circumferences of the expanded hole portion are the same, namely 2L.

[0128] The lead-in portion is located on the plane where the axis is located.

[0129] When the opening auxiliary tool is fixed to the core mold 9, the length direction of the core mold is parallel to the length direction of the opening auxiliary tool.

[0130] Since the introduction portion is a single piece, the opening auxiliary tool is a smooth transition structure formed by the introduction portion and the rear end surface of the reaming portion. The edges of the introduction portion are chamfered or rounded to ensure smooth entry into the first fabric opening / second fabric opening. The cross-sectional configuration of the opening auxiliary tool should follow the following rules: the cross-section of the introduction portion can be semicircular, semi-elliptical, or diamond-shaped. Different shapes of the introduction portion can be selected for different shapes of unit cell openings. If the unit cell opening is a quadrilateral, the introduction portion is preferably a diamond shape. If the unit cell opening is a hexagon, the introduction portion is preferably a semicircular shape.

[0131] Example 5

[0132] In order to realize the preparation method of three-dimensional braided polygonal core preform, the following design is made: Figures 13 to 18 、 Figure 21 The three-dimensional woven polygonal core lattice preform forming precise shape control tooling shown in the figure includes: a frame, at least one yarn hanging rod (not shown in the figure), multiple mounting parts and multiple aperture size control plates. The yarn hanging rod is fixed on the frame, and each mounting part is used to fix an aperture size control plate on the frame during the weaving process.

[0133] The method for using the precise shape control tooling for forming a three-dimensional woven polygonal core lattice preform includes: hoisting the precise shape control tooling for forming a three-dimensional woven polygonal core lattice preform on a workstation base, performing weaving, inserting an aperture size control sheet into a fabric opening (a first fabric opening / a second fabric opening) of the preform formed by weaving during the weaving process, and securing the aperture size control sheet to a frame. After weaving is completed, the aperture size control sheet is removed.

[0134] Preferably, each mounting member includes two first connecting rods 6 parallel to the yarn hanging rod, and a first through hole for passing the first connecting rod 6 is formed on the frame. The number of first through holes on the frame corresponding to each first connecting rod is two (each first connecting rod has two first through holes at both ends), and a second through hole for passing the first connecting rod is formed on each of the two mounting parts of the aperture size control piece 8. Each second through hole of the aperture size control piece passes through a first connecting rod and each of the two ends of the first connecting rod passes through a first through hole.

[0135] Preferably, the frame includes: a height control frame 3, two reference plane frames 4 and four length control positioning belts 5. The two reference plane frames are arranged in parallel and installed at the bottom of the height control frame. Each reference plane frame is vertically fixed with two parallel length control positioning belts. The two reference plane frames are used to fix the yarn hanging rod (the two ends of the yarn hanging rod are respectively fixed to a reference plane frame), and the length control positioning belt is used to fix the aperture size control piece. The first through hole is located on the length control positioning belt.

[0136] Preferably, the height control frame includes: a planar part and a fixing part, the fixing part is fixed on the upper surface of the planar part, the fixing part is used to be fixed to the work station base and then suspend the three-dimensional woven polygonal core grid preform forming precision control tooling, and the planar part is used to install the reference plane frame.

[0137] Preferably, the two length control positioning belts on each reference plane frame are fixed to the reference plane frame by bolts or slide rails (locking).

[0138] Preferably, the two reference plane frames are fixed on the height control frame by bolts or slide rails (locking).

[0139] Preferably, the length control positioning belts on the two reference plane frames are arranged opposite to each other, and both ends of each first connecting rod are respectively fixed on the two length control positioning belts arranged opposite to each other on the two reference plane frames.

[0140] Preferably, each length control positioning belt has at least one row of first through holes.

[0141] Preferably, when L is less than 6 mm, each length control positioning belt has at least two rows of first through holes, and the multiple rows of first through holes on each length control positioning belt are staggered.

[0142] Preferably, when the first through holes of each length control positioning belt are in a row, the length of each first through hole on the length control positioning belt and the first through hole of the adjacent row directly below it along the weaving direction is L h , L h =1 / 2*(L b +2*L f ), L b is the length of the joint edge of the polygonal core preform, L f is the length of the free edge of the polygonal core preform.

[0143] Preferably, when the first through holes of each length control positioning belt are arranged in multiple columns, the length of each first through hole on the length control positioning belt and the first through hole closest to the adjacent row in a straight line along the weaving direction is L. h (like Figure 18 shown), L h =1 / 2*(L b +2*L f ), L b is the length of the joint edge of the polygonal core preform, L f is the length of the free edge of the polygonal core preform.

[0144] Preferably, it also includes: an initial position control piece 7, which is used to be fixed to two length control positioning belts fixed on the same reference plane frame. The position where the initial position control piece is fixed to the length control positioning belt is a fixed position, and the distance between the two length control positioning belts on the same reference plane frame can be quickly positioned through the fixed position.

[0145] Preferably, the two reference plane frames share the same initial position control plate, or each frame uses its own initial position control plate. When the two reference plane frames share the same initial position control plate, a second connecting rod 12 passes through each of the two fixed positions on the initial position control plate, and the two ends of each second connecting rod are fixed to two opposite length control positioning straps on different reference plane frames.

[0146] “When W2 is less than W1, W2 is less than or equal to L b The arrangement of " can avoid the situation where the aperture size control sheet covers the first through hole 10.

[0147] like Figure 19 As shown, the length of the working portion of the aperture size control piece perpendicular to the weaving direction is L2, L2 is greater than or equal to the depth H of the polygonal core cell preform, and the length of the aperture size control piece perpendicular to the weaving direction is L1.

[0148] The diameter of the first through hole is The diameter of the second through hole 11 is

[0149]

[0150] The number of the second through holes on each mounting portion of the aperture size control sheet is preferably three.

[0151] like Figure 16 and Figure 17 As shown, each length control positioning belt can be directly fixed on the reference plane frame ( Figure 16 ) or fixed on the reference plane frame through other positioning structures ( Figure 17 ).

[0152] Example 6

[0153] Set the specifications of the polygonal core preform: the shape of the opening in the unit cell is hexagonal, and the length of the unit cell's joint edge is L b =9mm, the length of the free edge of the unit cell is L f =9mm; n t The length of the flower node on the joint edge is 1.5mm, and the length of the flower node on the free edge is 1.5mm. The width of the flower node is 1mm. The wall thickness of the joint edge is T b The number of nodes k on the junction edge is 0.2 mm.b is 6, and the number of flower nodes on the free edge is k f A polygonal core cell preform was prepared according to the preparation method of Example 1, wherein the corners of the edges of the aperture size control sheet were right angles, the length of the working portion along the weaving direction was L = 27 mm (i.e., the edges of the aperture size control sheet were not compensated), and the thickness t of the aperture size control sheet was 1 mm;

[0154] The geometric area deviation rate of the unit cell in the polygonal core lattice preform obtained by the preparation method in Example 1 and the set specifications is 7.1%.

[0155] Example 7

[0156] A method for preparing a three-dimensional woven polygonal core lattice preform is basically the same as Example 6, with the only difference being that: the length of the working portion along the weaving direction is W1, W1=LB, B=B1, B1=Q1*t*0.5, where Q1=1.41; and the geometric area deviation rate of the unit cell in the obtained polygonal core lattice preform and the set specifications is 3.2%.

[0157] Example 8

[0158] A method for preparing a three-dimensional woven polygonal core preform is basically the same as Example 7, the only difference being that the length of the flower node of the combined edge in the method for preparing the three-dimensional woven polygonal core preform in Example 7 is used as the theoretical value of the length of the flower node of the combined edge in the polygonal core preform in this embodiment, and the length of the flower node of the free edge in the method for preparing the three-dimensional woven polygonal core preform in Example 7 is used as the theoretical value of the length of the flower node of the free edge in the polygonal core preform in this embodiment. The length of the flower node of the combined edge in the method for preparing the three-dimensional woven polygonal core preform in this embodiment is l b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows:

[0159] l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b

[0160] l f ′=[k f / (k f +1)]*l f

[0161] Among them, k b is the number of nodes of the combined edge, k f is the number of nodes on the free edge, l bis the theoretical value of the length of the junction of the polygonal core lattice preform, l f is the theoretical value of the node length of the free edge in the polygonal core preform; T b is the wall thickness of the joining edge.

[0162] In this embodiment, b ′=1.82mm,l f ′=1.28mm.

[0163] The geometric area deviation rate of the unit cell inside the polygonal core preform obtained in this embodiment and the set specification is 1.8%.

[0164] Comparative Example 1

[0165] The method for preparing a polygonal core lattice preform. The specifications of the polygonal core lattice preform set in this comparative example are the same as those set in Example 6. The only difference is the preparation method. This comparative example directly adopts the core mold forming method (without using an aperture size control sheet).

[0166] The geometric area deviation rate of the unit cell in the polygonal core preform obtained in this embodiment and the set specifications is 16%.

[0167] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional woven polygonal core preform, wherein the polygonal core preform is formed by arranging and connecting identical unit cells in an array, wherein an opening is formed in the unit cell, and the length of the connecting edge of the unit cell is L b , the length of the free edge of the unit cell is L f ; It is characterized in that, The method for preparing a three-dimensional woven polygonal core preform comprises the following steps: Step 1: Weave a preform using a three-dimensional weaving four-step method, wherein the preform is formed with multiple columns of first fabric opening groups and multiple columns of second fabric opening groups along its width direction, and a column of second fabric opening groups is arranged between every two adjacent first fabric opening groups. The first fabric opening group is a first fabric opening formed on the preform at intervals along the weaving direction, and the second fabric opening group is a second fabric opening formed on the preform at intervals along the weaving direction. The first fabric opening and the second fabric opening are both fabric openings, and the first fabric opening and the second fabric opening are both slits. The lengths of the first fabric opening and the second fabric opening are the same and are both L. The upper part of each first fabric opening is opposite to the lower part of each second fabric opening in the second fabric opening group on both sides thereof, and the relative parts of the preform are upper overlapping parts, and the length of the upper overlapping part is L. f The lower part of each first fabric opening is opposite to the upper part of each second fabric opening in the second fabric opening group on both sides thereof, and the preform of the opposite part is the lower overlapping part, and the length of the lower overlapping part is L f Each first fabric opening and the non-opposite portion of the second fabric openings in the adjacent second fabric opening groups on both sides are the first non-overlapping portions, and the length of the first non-overlapping portions is L. b =L-2L f Each second fabric opening and its adjacent two sides of the first fabric opening group of the first fabric opening does not correspond to the preformed portion of the second non-overlapping portion, the length of the second non-overlapping portion is L b ; The three-dimensional braiding four-step method includes: a first polygonal core lattice bonding edge forming stage, a first polygonal core lattice free edge forming stage, a second polygonal core lattice bonding edge forming stage, and a second polygonal core lattice free edge forming stage. The first polygonal core lattice bonding edge forming stage is used to form the second non-overlapping portion in the preform; the first polygonal core lattice free edge forming stage is used to form the upper overlapping portion in the preform; the second polygonal core lattice bonding edge forming stage is used to form the first non-overlapping portion in the preform; and the second polygonal core lattice free edge forming stage is used to form the lower overlapping portion in the preform. When the second polygonal core cell free edge forming stage is completed and the first fabric opening is not sealed, inserting an aperture size control sheet into the unsealed first fabric opening, with the aperture size control sheet being parallel to the length direction of the first fabric opening; When the first polygonal core cell free edge forming stage is completed and the second fabric opening is not sealed, inserting an aperture size control sheet into the unsealed second fabric opening, with the aperture size control sheet being parallel to the length direction of the second fabric opening; After all the aperture size control sheets are placed into the preform, the length of the relative parts of any two adjacent rows of aperture size control sheets along the weaving direction is L f The length of the edges of the aperture size control sheets in each adjacent row in the same column along the weaving direction is L. b ; The thickness of the aperture size control sheet is less than 2mm; Step 2: After the four-step three-dimensional weaving method is completed, the aperture size control sheets are taken out row by row, and a core mold is filled into each of the first fabric openings / second fabric openings from which the aperture size control sheets are taken out, so that the core mold is filled into the first fabric openings / second fabric openings and the first fabric openings / second fabric openings respectively form unit cell openings of the polygonal core lattice preform, thereby obtaining a polygonal core lattice preform.

2. The method for preparing a three-dimensional braided polygonal core preform according to claim 1, characterized in that: In step 2, the core mold is filled into the first fabric opening / the second fabric opening by the opening auxiliary tool.

3. The method for preparing a three-dimensional braided polygonal core preform according to claim 1, characterized in that: In step 1, for the first polygonal core grid edge forming stage, the fixed columns of yarn carriers are numbered as follows: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula: (X-1) / (2*n t +2) = integer For the first polygonal core grid free edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula: (X-1) / (n t +1)=integer For the second polygonal core grid edge forming stage, the fixed columns of yarn carriers are: the first column, the last column, and all columns whose yarn carrier column number X meets the following formula: (X+n t ) / (2*n t +2) = integer For the second polygonal core grid free edge forming stage, the fixed column number of the yarn carrier is the same as that of the first polygonal core grid free edge forming stage; Among them, n t It is the number of yarn carrier columns corresponding to a single free edge in the polygonal core preform.

4. The method for preparing a three-dimensional braided polygonal core preform according to claim 1, characterized in that: In step 1, when the honeycomb core opening θ is an acute angle or a right angle, the length of the junction node l in the preparation method of the three-dimensional woven polygonal core preform is b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f ′ as follows: l b ′=[k b / (k b -1 / 2)]*l b l f ′=[k f / (k f +1 / 2)]*l f When the honeycomb core opening θ is an obtuse angle or a flat angle, the length of the junction node l in the preparation method of the three-dimensional woven polygonal core preform is b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows: l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b l f ′=[k f / (k f +1)]*l f When the honeycomb core opening θ>180 degrees, the length of the junction node l in the preparation method of the three-dimensional woven polygonal core preform is b ' and the length l of the free edge in the method for preparing a three-dimensional braided polygonal core preform f 'as follows: l b ′=[k b / (k b -1)+(1 / 2*T b ) / k b ]*l b l f ′=[k f / (k f +1)-(1 / 2*T b ) / k f ]*l f Among them, k b is the number of nodes of the combined edge, k f is the number of nodes on the free edge, l b is the theoretical value of the length of the junction of the polygonal core lattice preform, l f is the theoretical value of the node length of the free edge in the polygonal core preform; T b is the wall thickness of the joining edge.

5. The method for preparing a three-dimensional braided polygonal core preform according to claim 2, wherein: The opening auxiliary tool is fixed to the core mold.

6. The method for preparing a three-dimensional braided polygonal core preform according to claim 5, characterized in that: When the opening auxiliary tool is fixed to the core mold, the length direction of the core mold is parallel to the length direction of the opening auxiliary tool.

7. The method for preparing a three-dimensional braided polygonal core preform according to claim 1, characterized in that: The aperture size control sheet is a single piece, and includes: a working part and mounting parts located at both ends of the working part. The working part and the mounting part are connected. The working part is used to be placed in a slit-shaped fabric opening during weaving, and the mounting part is used to fix the aperture size control sheet in the fabric opening after the aperture size control sheet is placed in the fabric opening.

8. The method for preparing a three-dimensional braided polygonal core preform according to claim 7, characterized in that: The length of the working portion along the weaving direction is W1, W1=LB, where B=B1, B2 or B3, and t is the thickness of the working portion; When the corner of the edge of the aperture size control sheet is a right angle, B=B1, B1=Q1*t*0.5, where Q1=1.41, When the corner of the edge of the aperture size control sheet is chamfered, B=B2, B2=Q2*t*0.5, where Q2 is the sine value of the chamfer taper. When the corners of the edge of the aperture size control plate are rounded, B=B3, B3=Q3*(tr), where r is the fillet radius. When the fillet radius r is less than or equal to 0.5t, Q3 is 1.41; when the fillet radius r is greater than 0.5t and less than or equal to t, Q3 is 1; when the fillet radius r is greater than t, Q3 is 0.

9. The method for preparing a three-dimensional braided polygonal core preform according to claim 7, characterized in that: There is a smooth transition between the installation part and the working part.

10. The method for preparing a three-dimensional braided polygonal core preform according to claim 7, characterized in that: In step 1, the length of the mounting portion of the aperture size control sheet along the weaving direction is W2. When W2 is less than W1, W2 is less than or equal to L. b ; In step 1, when W2 is greater than W1, 6 mm ≤ W2 < 12 mm.

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