Countersunk screw hole prefabricated structure and preparation method thereof

Abstract

To enhance the connection strength between thin-walled composite shells and other structural components, the present invention proposes a continuous fiber reinforced countersunk screw hole. By preparing a groove mold, a cover mold, and a block mold, the pressure between the molds is applied to the fiber cloth to extrude the shape of the countersunk screw hole. The applied pressure leverages the principle of warp and weft stretchability of the interwoven fiber cloth to achieve the plasticity of the fiber cloth. The extruded shape is then filled with a mesh material to form the shape of a screw head for securing the screw. Finally, a thin fiber cloth is sewn around the mesh to protect its shape.

Description

Technical Field

[0001] The present application relates to the field of composite materials, and in particular to a countersunk screw hole preform structure and a preparation method thereof. Background Art

[0002] In the aerospace field, thin-walled components are widely used due to their lightweight characteristics. In some specific environments, they need to be connected with screws. However, due to the thinness of thin-walled components, the threads produced are too few, the connection with the screws is poor, and they are easy to fall off. In order to strengthen the connection strength between thin-walled components and other components, the load-bearing structure used for the connection needs to be mechanically strengthened.

[0003] The structure of fiber preforms plays a crucial role in determining the strength of thin-walled component joints. The greater the fiber continuity of the preform, the stronger the resulting component. The challenge of cost-effectively and effectively reinforcing the mechanical properties of thin-walled component joints is an urgent one. Summary of the Invention

[0004] In response to the above requirements, this application proposes a countersunk screw hole prefabricated structure and a preparation method thereof, which are characterized by:

[0005] S1, preparation and groove mold, cover mold and block mold;

[0006] S2, preparing a thin-walled shell;

[0007] S3, the thin-walled shell is pressed into the groove mold, and the block mold compacts the thin-walled shell;

[0008] S4, preparing edge fibers;

[0009] S5, the edge of the mesh filling;

[0010] S6. Sew the edge fibers to protect the edges.

[0011] Preferably, there are n groove structures on the groove mold (n is a positive integer), the bottom of the groove structure is a circle 1, the upper edge of the groove of the groove structure is a circle 2, the circumference of circle 2 is greater than the circumference of circle 1, and the centers of circle 2 and circle 1 are in the same axial direction; the side of the groove structure is a slope; the block mold is in the shape of a screw head, and the thickness of one side of the mold is 0.5mm~1mm more than the thickness of one side of the screw head.

[0012] Furthermore, the groove mold has a corresponding cover mold, the cover mold fits the groove mold, and has screw holes to lock the cover mold and the groove mold.

[0013] Preferably, fiber cloths of the same size are cut and layered to form m layers of fiber cloth, where m is a positive integer, to prepare a thin-walled shell.

[0014] Preferably, the thin-walled shell is placed in the groove mold, the block mold is placed on the other side of the groove of the groove mold, the cover mold is covered, and the block mold and the part of the thin-walled shell fiber in contact with the block mold are pressed into the groove of the groove mold.

[0015] Furthermore, the cover plate mold is opened and line marks are drawn along the edge of the block mold.

[0016] Preferably, the fiber cloth is cut into a shape that is a combination of a trapezoid and a rectangle, and the short side of the trapezoid is equal to and connected to a variable length of the rectangle.

[0017] Furthermore, the fibers parallel to the upper and lower sides of the trapezoid and located on the rectangle are removed to release the unidirectional fibers, and the parallel fiber width sufficient for the thickness of the block mold is left on the rectangle to prepare the edge fibers.

[0018] Further, 1-5 pieces of prepared fiber cloth are laminated together, and the trapezoidal portion is simply sutured to lock the 1-5 pieces of prepared fiber cloth.

[0019] Furthermore, 2-8 strands of the fiber bundles released from 1-5 pieces of edge fibers are selected to be bundled into single fibers, and the thin-walled shell is taken out of the mold. The single fibers are used as sutures and sewn in sequence along the marked lines; the sewn fibers are tightened in sequence and folded outwardly of the circumference; the trapezoidal part of the edge fibers remains perpendicular to the thin-walled shell.

[0020] Preferably, the thin-walled shell is placed in the mold, and the block mold is placed as in the previous step; a mesh is added in the gap between the block mold and the thin-walled shell, and the mesh is compacted with a small blunt metal device until the mesh is at the same level as the thin-walled shell.

[0021] Preferably, the edge fiber trapezoidal portion is folded and laid flat on the thin-walled shell; the thin-walled shell is taken out and leaves the groove mold; the sewn-in fibers continue to be used as suture lines to sew the thin-walled shell and the edge fiber trapezoidal portion, and the first suture stitch is at the junction of the thin-walled shell and the protrusion, using a single-strand single-seam suture connection, the suture distance is 1-5mm, and the suture route is in the radial direction with the protrusion cone as the center. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the structural diagram of the groove mold;

[0023] Figure 2 It is the structural diagram of the groove mold and the cover plate mold;

[0024] Figure 3 This is a planed view of the thin-walled shell in the mold;

[0025] Figure 4 This is the structural diagram after the edge fibers are sewn into the groove;

[0026] Figure 5 This is a top view after the groove is filled with mesh. Specific implementation plan

[0027] In order to make the present technology more easily understood, this embodiment is described in detail with reference to the accompanying drawings.

[0028] S1. Preparation and groove mold, cover mold and block mold:

[0029] like Figure 1 、 Figure 2 As shown, the base is a groove mold, the cover is a cover mold, and the rectangular part in the middle of the groove mold is the thin-walled shell placement area. The outer circle of the placement area is a circle of grooves with a groove width of 10mm. The prepared thin-walled shell is 300mm*300mm in length and width and 8mm in thickness. Four identical circular hole grooves are evenly distributed on the thin-walled shell. The bottom of the groove structure is circle 1, and the upper edge of the groove structure is circle 2. The diameter of circle 2 is 28mm, the circumference of circle 1 is 24mm, and the centers of circle 2 and circle 1 are in the same axial direction; the side of the groove structure is a straight slope, and the vertical depth of the groove structure is 6.5mm. The main function of the part outside the rectangle of the groove mold is to ensure that it can fit with the cover mold, and there are corresponding screw holes above and below the groove mold and the cover mold. The shape of the block mold in this embodiment is a regular hexagon, which is the same as the shape of the screw head in the usage scenario. The screw size corresponding to the screw head is M6. The diagonal distance of the block mold is longer than the diagonal distance of the actual screw head used by (√2 / 2+2) / 10mm. The block mold is placed directly above the four grooves of the groove mold and on top of the thin-walled shell. The thickness of the block mold is 6mm.

[0030] S2. Preparation of thin-walled shell:

[0031] The shell of this embodiment has a size of 300mm*300mm. When preparing the shell, 20 pieces of T700-3k carbon fiber cloth with a size of 320mm*320mm need to be cut. The thickness of each piece is 0.3mm. After the 20 pieces of carbon fiber cloth are stacked, the thickness reaches 6mm. The four corners of the stacked carbon fiber cloth are simply pre-stitched and fixed.

[0032] S3. The thin-walled shell is pressed into the groove mold, and the block mold compacts the thin-walled shell:

[0033] Open the groove mold and place the prepared thin-walled shell in it, ensuring that the effective portion of the thin-walled shell is on the square surface of the groove mold, and the remaining portion of the thin-walled shell is suspended above the 10mm groove. Mark the position of the block mold on the cover mold, apply double-sided tape to the four block molds, and stick them on the marked areas of the cover mold. Place the cover mold on the groove mold.

[0034] Slowly apply opposite pressure to the cover mold and the groove mold. This can be done by tightening the screws, which need to be tightened diagonally in turn; or by slowly adding weight to press until the upper and lower molds are sealed. At this time, the cross-section of the thin-walled shell in the mold is as shown in the figure. Figure 3 Open the cover mold, gently remove the fiber cloth around the block mold, and use a marker to draw lines along the block mold.

[0035] S4. Preparation of edge fibers:

[0036] Cut the carbon fiber cloth into a combination of trapezoids and rectangles, with the short side of the trapezoid being equal to and connected to one variable length of the rectangle. Remove the fibers that are parallel to the upper and lower sides of the trapezoid and located on the rectangle, release the unidirectional fibers, and leave enough parallel fiber width on the rectangle to match the thickness of the block mold. Prepare the edge fibers, take two pieces of the above-mentioned edge fibers for simple pre-stitching, select the 4 fiber bundles released by the released edge fibers and bundle them into single fibers, remove the thin-walled shell from the mold, and use the single fibers as suture lines to sew in sequence along the drawn lines. The sewn fibers are tightened in sequence and folded outwards of the circumference. The trapezoidal part of the edge fibers remains perpendicular to the thin-walled shell. At this time, the structural diagram of the groove position of the thin-walled shell is as shown in the figure. Figure 4 As shown, for ease of understanding, a rectangular shape replaces a trapezoidal shape.

[0037] S5. Filling edge of mesh:

[0038] Put the thin-walled shell after S4 treatment into the groove mold again according to its original position, continue to push away the thin-walled shell and the edge fiber position, fill in the mesh, and use a small metal blunt tool to slowly knock the mesh until the groove mold is filled. At the same time, ensure that the mesh surface and the thin-walled shell are in the same horizontal position. The top view is as shown below. Figure 5 As shown, the black part is the mesh, the outer grid part of the mesh is a thin-walled shell, the inner grid part of the mesh is a block mold, and the inner circle of the block mold is a screw hole for subsequent processing. This application is a prefabricated structure and does not involve subsequent processing.

[0039] S6. Sew the edge fibers to protect the edges.

[0040] The trapezoidal portion of the fiber edge is folded and laid flat on the thin-walled shell. The thin-walled shell is removed from the groove mold. The inserted fibers continue to serve as suture lines to sew the thin-walled shell and the trapezoidal portion of the fiber edge. The first stitch is at the junction of the thin-walled shell and the protrusion, using a single-strand hook stitch. The stitching distance is 5mm, and the stitching path is radially centered on the protrusion cone. The stitching continues, and the locations with a stitch density of less than 5mm x 5mm are stitched with a stitch density of 5mm x 5mm, using a single-strand hook stitch. At this point, the thin-walled shell has a concave shape on all eight edges because the fiber length of the protrusion is longer than the length of the flat surface. The thin-walled shell is further trimmed to the required size of 300mm x 300mm.

Claims

1. A method for preparing a countersunk screw hole preform structure, characterized in that The following steps are involved: S1. Prepare a groove mold, a cover plate mold, and a block mold; wherein the groove mold has n groove structures, wherein the groove bottom of the groove structure is a circle 1, the groove upper edge of the groove structure is a circle 2, the circumference of circle 2 is greater than the circumference of circle 1, and the centers of circle 2 and circle 1 are coaxial; and the groove side of the groove structure is a slope; The groove mold has a corresponding cover plate mold, and the cover plate mold is fitted with the groove mold; S2, preparing a thin-walled shell; The method comprises: cutting warp and weft interwoven fiber cloths of the same size, wherein the size of the fiber cloths is larger than the size required for the thin-walled shell; laying m layers of the fiber cloths, where m is a positive integer, and temporarily fixing the laminated fiber cloths to prepare the thin-walled shell; S3. The thin-walled shell is pressed into the groove mold, and the block mold compacts the thin-walled shell; the thin-walled shell is placed in the groove mold, and the thin-walled shell is placed in the block mold on the other side of the groove of the groove mold. The cover mold is covered, and the block mold and the thin-walled shell fiber in contact with the block mold are pressed into the groove of the groove mold; after ensuring that the cover mold and the groove mold are in contact, the cover mold is opened, a boss is pressed out on the thin-walled shell, and a line mark is drawn along the edge of the block mold; S4. Prepare edge fibers; cut a fiber cloth, wherein the fiber cloth is a combination of a trapezoid and a rectangle, and the short side of the trapezoid is equal in length to and connected to one side of the rectangle; remove the fibers parallel to the upper and lower sides of the trapezoid and located on the rectangle, release the unidirectional fibers, and leave a parallel fiber width sufficient for the thickness of the block mold on the rectangle to prepare edge fibers; bond 1-5 pieces of prepared edge fibers together, and simply sew the trapezoidal portion; select 2-8 fiber bundles released from the edge fibers and bundle them into single fibers, remove the thin-walled shell from the mold, and sew the single fibers in sequence along the drawn lines as sutures; tighten the sewn fibers in sequence and fold them outwardly; the trapezoidal portion of the edge fibers remains perpendicular to the thin-walled shell; S5, the mesh tire filling edge; the thin-walled shell is placed in the mold, and the block mold is continued; the mesh tire is added to the gap between the block mold and the thin-walled shell, and the mesh tire is compacted until the mesh tire and the thin-walled shell are at the same level; S6. Suture the edge fibers to protect the edge; the process includes: folding the edge fiber trapezoidal portion and laying it flat on the thin-walled shell; removing the thin-walled shell and leaving the groove mold; using the sewn-in fibers as suture lines to sew the thin-walled shell and the edge fiber trapezoidal portion, with the first stitch being the junction between the thin-walled shell and the protrusion.

2. The method for preparing a countersunk screw hole preform structure according to claim 1, characterized in that: The block mold in step S1 is in the shape of a screw head, and the thickness of one side of the block mold is 0.5 mm to 1 mm greater than the thickness of one side of the screw head.

3. The method for preparing a countersunk screw hole preform structure according to claim 1, characterized in that: In step S1, the cover plate mold and the groove mold have corresponding screw holes to lock the cover plate mold and the groove mold.

4. The method for preparing a countersunk screw hole preform structure according to claim 1, characterized in that: In step S6, single-strand single-seam suture connection is adopted, the suture distance is 1-5 mm, and the suture route is the radial direction with the raised cone as the center.

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