A polygonal stepped opening forming method and forming die for composite material parts

Abstract

The present invention belongs to the technical field of composite material manufacturing and discloses a method and mold for forming a polygonal stepped opening in a composite material part. Preformed core mold sheets are used to layer and occupy positions during the laying process, thereby pre-forming the stepped opening. This method solves the technical problem that existing polygonal stepped openings are difficult to form using CNC machining. It can achieve precise forming of polygonal stepped openings on composite reinforced wall panels, meeting assembly accuracy requirements at the openings, and realizing the integrated forming of the skin layup and the polygonal stepped opening structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material parts / assemblies manufacturing, and specifically relates to a method for forming a polygonal stepped opening of a composite material part and a forming die. Background Art

[0002] With the increasing use of composite materials in the aerospace sector, composite wing stiffeners and beams, the primary load-bearing structures, have become widely used in aircraft. The interior of the wing box serves as an integral fuel tank, increasing fuel storage capacity, increasing flight endurance, and improving flight performance. Access hatches, typically located on the lower wing panel, provide access for box assembly, fuel tank sealing, and maintenance, and are an integral part of the wing stiffener's overall structure.

[0003] In recent years, with the demand for large aircraft, the size of wing panels has increased, the number of inspection cover openings has increased, and the structure has become more and more complex. The polygonal stepped opening on the reinforced panel described in this application is a complex structure cover opening. According to traditional manufacturing methods, in order to ensure the manufacturing accuracy of the assembly at the panel opening, CNC machining is used to form the composite panel after it is cured. However, this processing and forming method can only be used for simple openings. For complex polygonal stepped openings, CNC machining is extremely difficult or even impossible. The solution of this application can achieve precise forming of polygonal stepped openings on composite reinforced panels, meet the assembly accuracy requirements at the openings, and realize the integrated forming of skin layer forming and polygonal stepped opening structure, without the need for CNC machining after the panel is cured. Summary of the Invention

[0004] The present invention addresses the problem that polygonal stepped openings on composite reinforced wall panels are difficult to form using CNC machining, and proposes a method and mold that can simultaneously achieve polygonal stepped opening forming during the composite skin forming process.

[0005] In order to achieve the above-mentioned invention objectives, the technical solutions adopted in this application are as follows:

[0006] A method for forming a polygonal stepped opening of a composite material part comprises the following steps:

[0007] Step 1: Lay several layers of prepreg on the overall surface of the skin, place a preformed core sheet at the corresponding position of the opening, and cut off the prepreg at the position along the edge of the preformed core sheet;

[0008] Step 2: Continue laying the skin prepreg, with the number of layers being the same as in step 1. Cut off the prepreg laid later along the edge of the preformed core mold sheet in step 1, and stack the second preformed core mold sheet on the first preformed core mold sheet. Repeat this step until the polygonal step opening is completed with laying and preforming.

[0009] Step 3: Take out the preformed core mold composed of several preformed core mold sheets from the polygonal step opening of the preformed skin, and replace it with the forming core mold, and use the core mold positioning pins to complete the positioning of the forming core mold through the positioning holes;

[0010] Step 4: Continue laying the remaining layers until all layers of the skin are laid and compacted;

[0011] Step 5: Use a laser projector to determine the position of the elliptical opening above the polygonal step opening, remove the prepreg inside the ellipse, place the annular molding die, and place the breathable core mold in the annular molding die;

[0012] Step 6: Assemble the long skin, place auxiliary materials, make bags and package, and autoclave to obtain a part with a polygonal stepped opening.

[0013] As a further solution of the present invention: the preformed core mold sheet is processed and formed in the shape of a polygonal stepped opening, and its thickness is equivalent to the thickness of several layers laid in step 1.

[0014] As a further solution of the present invention: the thickness of the preformed core mold sheet is generally controlled to be 0.5 mm to 1.0 mm, and according to the theoretical thickness of the prepreg, 3 to 6 layers need to be laid each time.

[0015] A composite material part polygonal stepped opening forming die, used in the above forming method, comprising:

[0016] A preformed core mold, which is composed of a plurality of preformed core mold sheets stacked together;

[0017] A forming core mold, which has the same size and shape as the preforming core mold;

[0018] an annular forming die, which is placed on the forming core die and has an outer contour that matches the elliptical opening;

[0019] The air-permeable core mold is placed in the annular forming mold, and its outer contour is matched with the inner ring of the annular forming mold, and the air-permeable core mold is flush with the upper surface of the annular forming mold.

[0020] As a further solution of the present invention: it also includes an overall surface for skin paving, the preformed core mold or the forming core mold is located on the overall surface for skin paving, the preformed core mold is placed when the polygonal opening is formed, and the forming core mold is placed after paving is completed until solidification is completed.

[0021] As a further solution of the present invention: positioning holes are provided on the overall surface of the skin paving, and the forming core mold is fixed on the overall surface of the skin paving by core mold positioning pins.

[0022] As a further solution of the present invention: the preformed core mold sheet is made of non-metallic polymer material, and its contour tolerance is 0.5-1.0 mm.

[0023] As a further solution of the present invention: the forming core mold is made of a metal material with a thermal expansion coefficient close to that of the composite material, and its thickness is determined according to the step thickness. At the same time, according to the thickness change of the composite material before and after curing, the thickness tolerance of the forming core mold is between 0 and 0.2 mm.

[0024] As a further solution of the present invention: the annular forming mold is formed by curing prepreg and rubber and is machined into an annular structure, the thickness of which is generally consistent with the thickness of the elliptical prepreg above the polygonal step.

[0025] As a further solution of the present invention: the air-permeable core mold is made of honeycomb material, and its thickness is consistent with that of the annular forming mold.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. Use a core mold with a simple structure to achieve integrated molding of the skin and polygonal stepped opening.

[0028] 2. The preforming / forming core mold used in polygonal stepped opening forming has a simple structure, is easy to manufacture, and has readily available materials.

[0029] 3. The polygonal stepped opening formed by this method has high forming precision and meets the assembly precision requirements of the cover. At the same time, it merges the manufacturing processes, improves production efficiency, and achieves the purpose of saving costs in the manufacturing of composite parts.

[0030] The present application is further described below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0032] In the attached figure:

[0033] Figure 1 This is a schematic diagram of the polygonal stepped opening forming die of this application;

[0034] Figure 2 This is a schematic diagram of the polygonal stepped opening preforming die of this application;

[0035] Figure 3 This is a three-dimensional schematic diagram of the polygonal stepped opening of this application;

[0036] Figure 4 These are the bottom and top views of the polygonal stepped opening of this application.

[0037] Explanation of the reference numerals in the figure: 1-paving the overall surface, 2-preforming core mold, 3-preforming core mold sheet, 4-forming core mold, 5-annular forming mold, 6-breathable core mold, 7-positioning hole, 8-core mold positioning pin, 9-polygonal step opening, 10-elliptical opening. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0039] This scheme takes the polygonal stepped opening of the composite material reinforced wall panel structure as an example. Figure 1 As shown, in the first aspect, a composite part step-type opening forming mold is provided, which includes a part paving overall profile 1, a preforming core mold 2, a preforming core mold sheet 3, a forming core mold 4, an annular forming mold 5, a breathable core mold 6, a positioning hole 7, and a core mold positioning pin 8. Positioning holes 7 are provided on the overall profile of the skin paving, and a plurality of preforming core mold sheets 3 or forming core molds 4 are positioned by the core mold positioning pin 8. The preforming core mold 2 is composed of a plurality of preforming core mold sheets 3 that can be separated and combined, and the material is a non-metallic polymer. The thickness of the preforming core mold sheet 3 is determined according to the thickness of the single-layer paving, and the general thickness is controlled at 0.5mm to 1.0mm. The contour tolerance of the preforming core mold sheet 3 is 0.5mm to 1.0mm, and it is used for the preforming of polygonal steps in the skin paving process.

[0040] The pre-forming core mold 2 or the forming core mold 4 is positioned on the integral part-laying surface 1. The pre-forming core mold 2 is placed during the shaping of the polygonal stepped opening 9. The forming core mold 4 is placed after the laying process is complete until curing is complete. The annular forming mold 5 is placed on the forming core mold 4 to form the elliptical opening 10. A breathable core mold 6 is placed on the forming core mold 4, centered between the annular forming mold 5, to prevent bag bridging and maintain thermal uniformity during curing.

[0041] After the polygonal step opening 9 is laid, the forming core 4 replaces the preforming core 2 and is fed into the tank along with the preformed part for curing. The forming core 4 is made of a metal material with a thermal expansion coefficient close to that of the composite material. Its thickness is determined by the step thickness and, based on the thickness change of the material before and after curing, the thickness tolerance of the forming core 4 is between 0 and 0.2 mm.

[0042] The annular forming die 5 is constructed from a composite prepreg and cured silicone rubber, machined into a ring-shaped structure. Its thickness is generally consistent with the thickness of the elliptical prepreg above the polygonal stepped opening 9. It is placed on the forming core die 4 to form the elliptical opening 10. The breathable core die 6, made of honeycomb material of the same thickness or slightly thinner than the annular forming die 5, fills the space between the annular forming die 5 to prevent bag bridging and helps balance thermal uniformity during the curing process in the thick opening area of ​​the panel.

[0043] like Figure 2-4 As shown, in a second aspect, a method for forming a polygonal stepped opening of a composite material part is provided, which comprises the following steps:

[0044] 1. Lay the prepreg layer on the overall skin laying surface 1. After completing 3 to 6 layers of layering according to the theoretical thickness of the material, place a preformed core mold sheet 3 at the corresponding position of the opening, and cut off the prepreg at the position according to the boundary of the preformed core mold sheet 3.

[0045] 2. Continue laying the skin prepreg. After completing 3 to 6 layers based on the theoretical thickness of the material, cut the prepreg laid later along the edge of the first preform core mold sheet 3 and place the second preform core mold sheet 3 into the opening. Repeat the above steps repeatedly until the polygonal step opening 9 is completely laid and preformed.

[0046] 3. Take out the preformed core mold 2 composed of several preformed core mold sheets 3 from the polygonal step opening 9 of the preformed skin, and replace it with the forming core mold 4. Use the core mold positioning pin 8 to complete the positioning of the forming core mold 4 through the positioning hole 7.

[0047] 4. Continue laying the remaining layers until all layers of the skin are laid and compacted. Use a laser projector to determine the location of the elliptical opening 10 above the polygonal step opening 9. Remove the prepreg inside the elliptical opening, insert the annular forming mold 5, and place the breathable core mold 6 inside the annular forming mold 5 to prevent bag bridging and balance thermal uniformity during the curing process.

[0048] 5. Carry out long-line skin assembly, auxiliary material placement, bag packaging and autoclave curing to obtain parts with polygonal stepped openings.

[0049] So far, the purpose of the present invention has been achieved.

[0050] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for forming a polygonal stepped opening of a composite material part, characterized in that: The steps include: Step 1: Lay several layers of prepreg on the overall surface of the skin, place a preformed core sheet at the corresponding position of the opening, and cut off the prepreg at the position along the edge of the preformed core sheet; Step 2: Continue laying the skin prepreg, with the number of layers being the same as in step 1. Cut off the prepreg laid later along the edge of the preformed core mold sheet in step 1, and stack the second preformed core mold sheet on the first preformed core mold sheet. Repeat this step until the polygonal step opening is completed with laying and preforming. Step 3: Take out the preformed core mold composed of several preformed core mold sheets from the polygonal step opening of the preformed skin, and replace it with the forming core mold, and use the core mold positioning pins to complete the positioning of the forming core mold through the positioning holes; Step 4: Continue laying the remaining layers until all layers of the skin are laid and compacted; Step 5: Use a laser projector to determine the position of the elliptical opening above the polygonal step opening, remove the prepreg inside the ellipse, place the annular molding die, and place the breathable core mold in the annular molding die; Step 6: Assemble the long skin, place auxiliary materials, make bags and package, and autoclave to obtain a part with a polygonal stepped opening.

2. A method for forming a polygonal stepped opening of a composite material part according to claim 1, characterized in that: The preformed core mold sheet is processed and formed in the shape of a polygonal stepped opening, and its thickness is equivalent to the thickness of several layers laid in step 1.

3. A method for forming a polygonal stepped opening of a composite material part according to claim 2, characterized in that: The thickness of the preformed core mold sheet is generally controlled to be 0.5 mm to 1.0 mm. According to the theoretical thickness of the prepreg, 3 to 6 layers of lamination need to be completed each time.

4. A polygonal stepped opening forming die for composite parts, used in any forming method according to claim 1-3, characterized in that: include: A preformed core mold, which is composed of a plurality of preformed core mold sheets stacked together; A forming core mold, which has the same size and shape as the preforming core mold; an annular forming die, which is placed on the forming core die and has an outer contour that matches the elliptical opening; The air-permeable core mold is placed in the annular forming mold, and its outer contour is matched with the inner ring of the annular forming mold, and the air-permeable core mold is flush with the upper surface of the annular forming mold.

5. The polygonal stepped opening forming die for composite material parts according to claim 4, characterized in that: It also includes an overall surface for skin paving, and the preformed core mold or the forming core mold is located on the overall surface for skin paving. The preformed core mold is placed when the polygonal opening is formed, and the forming core mold is placed after paving is completed until curing is completed.

6. The polygonal stepped opening forming die for composite material parts according to claim 5, characterized in that: Positioning holes are provided on the overall surface of the skin paving, and the forming core mold is fixed on the overall surface of the skin paving by a core mold positioning pin.

7. A composite material part polygonal stepped opening forming die according to any one of claims 4 to 6, characterized in that: The preformed core mold sheet is made of non-metallic polymer material, and its profile tolerance is 0.5-1.0 mm.

8. A composite material part polygonal stepped opening forming die according to any one of claims 4 to 6, characterized in that: The forming core mold is made of a metal material with a thermal expansion coefficient close to that of the composite material. Its thickness is determined according to the step thickness. At the same time, according to the thickness change of the composite material before and after curing, the thickness tolerance of the forming core mold is between 0 and 0.2 mm.

9. A composite material part polygonal stepped opening forming die according to any one of claims 4 to 6, characterized in that: The annular forming die is formed by curing prepreg and rubber and is machined into an annular structure. The thickness of the annular mold is generally consistent with the thickness of the elliptical prepreg above the polygonal step.

10. A composite material part polygonal stepped opening forming die according to any one of claims 4 to 6, characterized in that: The air-permeable core mold is made of honeycomb material, and its thickness is consistent with that of the annular forming mold.

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