Carbon fiber prepreg filling twist bar forming tool and process method

Abstract

The present application relates to a kind of carbon fiber prepreg filling twist bar forming tool and process method, belong to civil aviation composite structure forming processing field.The main body of tool is frame structure, upper end is platform, and inside and outside forming die are fixed on the platform to form inner cavity for shaping, which is consistent with the shape of twist bar bevel, compaction cover plate is placed on the top of inner cavity for compaction;When forming, multiple cylindrical twist bars are used to fill and form three times compaction processing mode one by one.The present application avoids the stacking and subsidence caused by the conventional method forming twist bar extrusion composite structure sidewall after heat curing, reduces unqualified products, saves new cycle period and cost by using this forming tool and using this process method for processing and forming.

Description

Technical Field

[0001] This invention belongs to the field of molding and processing of composite material structural parts for civil aviation, and relates to a tooling and process for molding carbon fiber prepreg filled twist strips. Background Technology

[0002] Composite materials, as advanced materials in aerospace manufacturing, are a crucial pillar of scientific and technological development and national economic construction. Advanced composite materials, as a class of lightweight, efficient, energy-saving, and environmentally friendly new materials, hold an extremely important position in the field of advanced materials. Since their emergence in the 1960s, advanced composite materials have consistently been a key material for research and development in countries worldwide, playing a vital role, especially in the aerospace field. The amount of advanced composite materials used has become an important indicator of the sophistication of aerospace structures. Large aircraft such as the Boeing 787 and Airbus A350 use over 50% advanced composite materials, while the use in domestically produced large aircraft has increased from 2% in the ARJ to 11.5% in the C919, and further to 50% in the CR929, demonstrating its promising future and development trend.

[0003] China's composite material molding and manufacturing started later than that of foreign countries, and there is a lack of accumulated design and manufacturing experience, incomplete product performance data, and insufficient manufacturing precision. At present, the aerospace industry is in a stage of high performance, multi-functionality and cutting-edge development of composite materials, and is rapidly penetrating and expanding into the civilian field. The industry has entered a new stage where application expansion drives continuous cost reduction.

[0004] Due to the special nature of composite structural components, almost all composite structural components have connection gaps during the manufacturing process, which need to be filled by composite twist strips. Traditional twist strip forming methods and processes are outdated. During the forming process, the twist strips squeeze the web and edge of the composite material, resulting in defects such as delamination and sinking in the internal structure of the composite parts after curing. Summary of the Invention

[0005] To improve the internal defects caused by the quality of twist strips in the manufacturing process of composite material structural parts for civil aircraft, this invention provides a tooling and process method for forming carbon fiber prepreg-filled twist strips. By using a set of composite material twist strip forming tooling and corresponding twist strip forming process method, this invention overcomes the internal defects of such parts and eliminates unqualified products from visual inspection and destructive testing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A molding fixture for carbon fiber prepreg filled twist strips is provided for the molding process of carbon fiber prepreg twist strips. The molding fixture includes a main frame 1, an outer molding mold 2, an inner molding mold 3, a compaction cover plate 4, and a hook 7.

[0008] The main frame 1 is a frame structure with a solid platform on the upper surface. The platform's dimensions and shape are designed according to the shape of the composite material twist strip 6, minimizing tooling weight while accommodating platform operation. A 10mm margin is left between the platform edge and the edge connecting to the lower frame. The middle of the upper platform of the main frame 1 serves as the forming work area, with several bolt holes for fixing the outer forming mold 2 and the inner forming mold 3. The distance from the platform edge to the edges of the two forming molds is greater than 200mm for bonding sealing strips. Hooks 7 are provided at all four corners of the main frame 1 for tooling transportation and installation.

[0009] The outer forming mold 2 and the inner forming mold 3 together form the twist strip forming mold. The inner side of the outer forming mold 2 and the outer side of the inner forming mold 3 serve as forming surfaces. The two surfaces are opposite each other to form a cavity with a triangular cross-section. The two surfaces are consistent with the hypotenuse of the composite material twist strip 6. The cavity formed by the two is consistent with the shape of the composite material twist strip 6. The R-angle of the cavity is used to form the composite material twist strip 6. The flatness of the cavity is 0.02mm. The two forming molds are respectively fixedly installed on the forming working area of ​​the main frame 1 platform. After fixed installation, the lower sides of the two surfaces are tightly fitted without gaps, with a tolerance of no more than 0.1mm. The upper end face of the two forming molds is recessed on the side near the cavity. The shape of the recess is consistent with the shape of the compaction cover plate 4, and the connection position of the two forming molds with the main frame 1 avoids the recessed area.

[0010] The compaction cover plate 4 has a segmented structure. After being assembled, it is consistent with the recessed shape formed by the two molding molds. Its bottom surface and two sides are in contact with the recessed shape of the two molding molds. The compaction cover plate 4 is made of carbon fiber material that is consistent with the composite material twist strip 6.

[0011] Furthermore, the platform is designed with a hexagonal structure with a thickness of 20mm, following the shape of the composite material twist strip 6.

[0012] Furthermore, the outer molding mold 2 and the inner molding mold 3 are either integral or segmented, with a segment gap of no more than 0.1 mm.

[0013] Furthermore, the outer forming mold 2 and the inner forming mold 3 are manufactured using 7050 aerospace aluminum alloy.

[0014] Furthermore, the lower end faces of the outer molding mold 2 and the inner molding mold 3 are provided with weight-reducing grooves.

[0015] The present invention also provides a method for forming carbon fiber prepreg filled twist strips, based on the above-mentioned forming tooling, and the forming method includes the following steps:

[0016] Step 1, Raw material preparation: Use carbon fiber unidirectional tape to cut and make two unidirectional tapes with a width of 2mm, six unidirectional tapes with a width of 6mm and two unidirectional tapes with a width of 20mm. The length is the actual length plus 50mm, and the length direction is 0° fiber direction.

[0017] Step 2: Manually roll 6mm and 20mm wide unidirectional tapes into 8 cylindrical twist strips. After forming, mark the center line of the cylinder length according to the center line on the backing.

[0018] Step 3: Remove the inner molding mold 3 and fix the outer molding mold 2 to the main frame 1. Using the lines on the outer molding mold 2 as a reference, lay two layers of 2mm wide unidirectional carbon fiber tape, with a layup tolerance of 0-0.75mm. After laying, install the inner molding mold 3.

[0019] Step 4: First, place three pre-formed 6mm cylindrical twist strips into the cavity between the outer forming mold 2 and the inner forming mold 3, with one strip at the bottom and two at the top, and the three strips closely attached to form an inverted triangle shape in cross-section, and compact them. Then, place two pre-formed 20mm cylindrical twist strips side by side into the cavity and compact them. The compaction requirements are as follows: Use a sealing strip to assist in compaction: Cover the entire stacked twist strip cylinder with a layer of non-porous release film, and lay a sealing strip along the cavity. The sealing strip should fill the entire cavity, and the sealing strip should be flush with or higher than the upper surface of the cavity. Lay a layer of non-porous release film on top of the sealing strip and compact it.

[0020] Step 5: Finally, place the three pre-formed 6mm cylindrical twist strips into the cavity. One strip is placed between two 20mm cylindrical twist strips, and the other two are placed on the outside of the two 20mm cylindrical twist strips and compacted. Place the compaction cover plate 4 above all the compacted cylindrical twist strips, i.e., in the recessed area above the cavity. Adhere the sealing strip along the outer 100mm area of ​​the outer forming mold 2 and the inner forming mold 3. Remove the backing of the sealing strip to expose the adhesive surface, and seal it with an aviation sealing bag and sealing tape. Perform vacuum compaction and extrusion to form composite material twist strips 6. During the compaction process, the vacuum pressure should be at least -0.06MPa, and the compaction time should be no less than 30 minutes.

[0021] Furthermore, when filling the cylindrical twist strip, the filling is carried out from the middle to both ends, aligning the pin in the center of the twist strip tooling with the center line on the twist strip, and cutting off the cylinder that exceeds the length of the forming tooling.

[0022] The beneficial effects of this invention are as follows: By using this molding tooling and this process method for processing and molding, this invention avoids the delamination and sinking caused by the extrusion of the sidewalls of composite material structural parts by the twist strips formed by conventional methods after thermosetting, thereby reducing defective products and saving new production cycle and cost. Attached Figure Description

[0023] Figure 1 An isometric view of the entire figure;

[0024] Figure 2The diagram shows the structure of the outer molding mold, where (a) is an overall schematic diagram and (b) is an enlarged sectional view (AA).

[0025] Figure 3 This is a schematic diagram of the compaction cover plate structure, where (a) is an overall schematic diagram and (b) is an enlarged BB sectional view;

[0026] Figure 4 This is a schematic diagram of composite material twisted strip filling molding, where (a) is a schematic diagram of the overall structure and (b) is an enlarged cross-sectional view.

[0027] In the diagram: 1. Main frame; 2. Outer molding mold; 3. Inner molding mold; 4. Compactor cover plate; 5. Socket head bolt; 6. Composite material tweezers; 7. Lifting hook. Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments derived by those skilled in the art based on the embodiments of the present invention through modifications or adjustments are within the protection scope of the present invention.

[0029] A molding fixture for carbon fiber prepreg filled twist strips is provided for the molding process of carbon fiber prepreg twist strips. The molding fixture includes: a main frame 1, an outer molding mold 2, an inner molding mold 3, a compaction cover plate 4, hexagon socket head cap bolts 5, and a hook 7, as shown below. Figure 1 As shown.

[0030] The main frame 1 is a frame structure with a solid platform on the upper surface. The platform's dimensions and shape are hexagonal, designed according to the shape of the composite material twist strip 6. The platform thickness is 20mm to minimize tooling weight while accommodating platform operation. A 10mm margin is left between the platform edge and the edge connecting to the lower frame. The middle of the platform serves as the forming work area, with 36 bolt holes of 8mm diameter for fixing the outer forming mold 2 and the inner forming mold 3 using hexagonal socket head cap screws 5. The distance from the platform edge to the edges of the two forming molds is greater than 200mm for bonding sealing strips. The platform surface of the main frame 1 has reference lines for installation positioning. Hooks 7 are provided at all four corners of the main frame 1 for tooling transportation and installation.

[0031] like Figure 2As shown, the outer forming mold 2 and the inner forming mold 3 are both integral forming molds, manufactured using 7050 aviation aluminum alloy. Together, they form the twist strip forming mold. The inner side of the outer forming mold 2 and the outer side of the inner forming mold 3 serve as forming surfaces. The two surfaces are opposite each other to form a cavity with a triangular cross-section. The two surfaces are consistent with the hypotenuse of the composite material twist strip 6. The cavity formed by the two is consistent with the shape of the composite material twist strip 6. The R-angle of the cavity is used to form the composite material twist strip 6. The flatness of the cavity is 0.02mm. The upper end face of the two forming molds is recessed by 3mm on the side near the cavity. The shape of the recess is consistent with the shape of the compaction cover plate 4. The two forming molds have 36 bolt through holes in the non-recessed area that match the platform of the main frame 1. The maximum thickness of the two forming molds is 15mm and the width is 60mm. The lower end face is provided with a weight reduction groove. The two forming molds are fixedly installed at the bolt holes in the forming working area of ​​the platform of the main frame 1. After fixed installation, the lower sides of the two surfaces fit tightly without gaps, with a tolerance of no more than 0.1mm.

[0032] In other embodiments, the two molding dies are segmented, with a segment gap of no more than 0.1 mm.

[0033] like Figure 3 As shown, the compaction cover plate 4 has a 5-segment structure. After assembly, it conforms to the recessed shape formed by the two molding molds. Its bottom surface and two sides fit snugly against the recessed areas of the two molding molds. The compaction cover plate 4 is made of carbon fiber material consistent with the composite material twist strip 6. The compaction cover plate 4 has a thickness of 3mm and a flatness of no more than 0.5mm. The outer sides of the 5 segments are sequentially marked with numbers 1 to 5, as shown below. Figure 3 As shown.

[0034] The forming tooling is made of Q235 steel, with weight reduced as much as possible without affecting rigidity. The working surface roughness of the forming tooling is Ra1.6, and the non-working surface roughness is Ra3.2. Sharp angles on the non-working surfaces are rounded, and the tooling surface is free of manufacturing defects such as sand holes, with a surface tolerance of 0.2. The tooling number, tooling weight, serial number, and other information are marked on the non-working surface (side) of the forming tooling.

[0035] The present invention also provides a method for forming carbon fiber prepreg filled twist strips, based on the above-mentioned forming tooling, and the forming method includes the following steps:

[0036] Step 1, Raw material preparation: Using carbon fiber unidirectional tape, cut two unidirectional tapes with a width of 2mm, six unidirectional tapes with a width of 6mm, and two unidirectional tapes with a width of 20mm. The length is the actual length plus 50mm, for a total of 10 unidirectional tapes with a cumulative width of 80mm and the length direction is 0° fiber direction.

[0037] Step 2: By hand, roll 6mm and 20mm wide unidirectional tapes into 8 cylindrical twist strips. After forming, mark the center line of the cylinder length according to the center line on the backing.

[0038] Step 3: Clean the platform of the main frame 1 with solvent and dry it. Remove the inner molding mold 3 and fix the outer molding mold 2 to the main frame 1. Using the scribed lines of the molding fixture as a reference, lay two layers of 2mm wide unidirectional carbon fiber tape, with an overlap tolerance of 0-0.75mm. After laying, install the inner molding mold 3, as follows... Figure 4 As shown.

[0039] Step 4: First, place three pre-formed 6mm cylindrical twist strips into the cavity between the outer forming mold 2 and the inner forming mold 3, with one strip at the bottom and two at the top, and the three strips closely attached to form an inverted triangle shape in cross-section, and compact them. Then, place two pre-formed 20mm cylindrical twist strips side by side into the cavity and compact them with rollers. The compaction requirements are as follows: Use a sealing strip to assist in compaction: Cover the entire stacked twist strip cylinder with a layer of non-porous release film, and lay a sealing strip along the cavity. The sealing strip should fill the entire cavity, and the sealing strip should be flush with or higher than the upper surface of the cavity. Lay a layer of non-porous release film on top of the sealing strip and compact it.

[0040] Step 5: Finally, place the three pre-formed 6mm cylindrical twist strips into the cavity. One strip is placed between two 20mm cylindrical twist strips, and the other two are placed on the outside of the two 20mm cylindrical twist strips respectively. Compact them with rollers. Above all the compacted cylindrical twist strips, i.e., in the recessed area above the cavity, place the compaction cover plate 4 in order from 1 to 5. Adhere the sealing strip along the outer 100mm area of ​​the outer forming mold 2 and the inner forming mold 3. Remove the backing of the sealing strip to expose the adhesive surface. Seal it with an aviation sealing bag and sealing tape. Perform vacuum compaction and extrusion into triangular composite material twist strips 6. The vacuum during compaction should be at least -0.06MPa, and the compaction time should be no less than 30 minutes.

[0041] When filling the cylindrical tumbler strip, the filling is carried out from the middle to both ends. The internal hex bolt 5 at the center of the forming tool is aligned with the center line on the cylindrical tumbler strip, and the cylinder that exceeds the length of the forming tool is cut off.

[0042] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for forming carbon fiber prepreg-filled twisted strips, characterized in that, This is achieved using a carbon fiber prepreg filling twist strip forming tool, which includes a main frame (1), an outer forming mold (2), an inner forming mold (3), and a compaction cover plate (4). The main frame (1) is a frame structure with a solid platform on the upper end. The platform size and shape are designed according to the shape of the composite material twist strip (6). The middle part of the upper platform of the main frame (1) serves as the forming work area, which is used to fix the outer forming mold (2) and the inner forming mold (3). The distance from the edge of the platform to the edge of the two forming molds is greater than 200mm, which is used to bond the sealing strip. The outer molding mold (2) and the inner molding mold (3) together form the twist strip molding mold. The inner side of the outer molding mold (2) and the outer side of the inner molding mold (3) serve as the molding surface. The two surfaces are opposite to each other to form a cavity with a triangular cross section. The cavity is consistent with the shape of the composite twist strip (6). The two molding molds are fixedly installed on the molding work area of ​​the main frame (1) platform. After the fixed installation, the lower side of the two surfaces fits tightly without gaps. The upper end face of the two molding molds is recessed on the side near the cavity. The shape of the recess is consistent with the shape of the compaction cover plate (4). The compacted cover plate (4) is a segmented structure. After being assembled, it is consistent with the recessed shape formed by the two molding molds. Its bottom surface and two sides are in contact with the recessed shape of the two molding molds. The molding process includes the following steps: Step 1: Use carbon fiber unidirectional tape to cut and make two unidirectional tapes with a width of 2mm, six unidirectional tapes with a width of 6mm and two unidirectional tapes with a width of 20mm. The length is the actual length plus 50mm, and the length direction is 0° fiber direction. Step 2: Roll the unidirectional tapes with widths of 6mm and 20mm into 8 cylindrical twist strips respectively; Step 3: Remove the inner molding mold (3) and fix the outer molding mold (2) to the main frame (1); lay two layers of 2mm wide carbon fiber unidirectional tape; after laying, install the inner molding mold (3). Step 4: First, place three pre-formed 6mm cylindrical twist strips into the cavity between the outer forming mold (2) and the inner forming mold (3), with one strip at the bottom and two at the top, and the three strips closely attached to form an inverted triangle shape in cross section, and compact them; then place two pre-formed 20mm cylindrical twist strips side by side into the cavity and compact them; the two compaction requirements are as follows: use a sealing strip to assist in compaction: cover the entire stacked twist strip cylinder with a layer of non-porous release film, and lay a sealing strip along the cavity. The sealing strip should fill the entire cavity, and the sealing strip should be flush with or higher than the upper surface of the cavity. Lay a layer of non-porous release film on top of the sealing strip for compaction; Step 5: Finally, place the three pre-formed 6mm cylindrical twist strips into the cavity. One strip is placed between two 20mm cylindrical twist strips, and the other two are placed on the outside of the two 20mm cylindrical twist strips respectively, and compact them. Place a compaction cover plate (4) above all the compacted cylindrical twist strips, i.e., in the depression above the cavity. Paste the sealing strip along the outer 100mm area of ​​the outer molding mold (2) and the inner molding mold (3), and seal it with an aviation sealing bag and sealing tape. Perform vacuum compaction and extrusion into composite material twist strips (6). The vacuum during compaction is at least -0.06 MPa, and the compaction time is not less than 30 minutes.

2. The method for forming carbon fiber prepreg filled twisted strips according to claim 1, characterized in that, The main frame (1) is equipped with hooks (7) at all four corners for tooling transportation and installation.

3. The method for forming carbon fiber prepreg filled twisted strips according to claim 1, characterized in that, The compacted cover plate (4) is made of carbon fiber material consistent with the composite twist strip (6).

4. The method for forming carbon fiber prepreg filled twisted strips according to claim 1, characterized in that, The lower end faces of the outer molding mold (2) and the inner molding mold (3) are provided with weight reduction grooves.

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