Forming process of airplane windshield frame

Abstract

The invention discloses a forming process of an airplane windshield frame. The forming process comprises the steps that the surface of a mold cavity is coated with a release agent, and a mold is put into a drying oven to be preheated before use; the prepreg is laid in the mold, 0 / 90 and + / -45 alternate laying design is adopted in laying design, the prepreg is laid at the near corner of the mold structure in a segmented mode based on the mold structure, the splicing positions of the adjacent laying layers are staggered, and splicing at the fixed position of the corner is avoided; the prepreg comprises a reinforcing material and a resin matrix, the laminating process of the material meets the requirements of users, and the aircraft windshield frame structural member is obtained. Through material selection, layering design optimization and forming process design, the aircraft windshield frame which is light in weight, high in flame retardance, good in size stability and high in precision is obtained, secondary machining is not needed in product forming, the aircraft body assembly requirement is directly met, the manufacturing process can be simplified, and the production cost can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of aviation composite materials, and in particular to a molding process for aircraft windshield frames, and is particularly suitable for structural components of various civil aircraft windshields. Background Art

[0002] Aircraft windshields and frames are key structures in the cockpit and must withstand extreme air pressure, temperature changes, impact loads, and long-term environmental erosion. Currently, aircraft windshield frames are made of metal materials such as aluminum alloys and titanium alloys, or ordinary epoxy resin composites. Metal materials are heavy, increasing aircraft fuel consumption; ordinary epoxy resin composites are insufficiently flame retardant (unable to meet the combustion standards of Appendix F of CCAR 25), and are prone to dimensional deformation at extreme temperatures (-65°C to +77°C). The composite materials currently used for civil aircraft windshield frames have simple layups (mainly single-direction layups or random layups), resulting in significant anisotropy in mechanical properties, and stress concentration and delamination defects are prone to occur at corners. Aircraft windshield frames usually use room temperature curing or low-pressure molding processes, resulting in poor product dimensional accuracy and requiring multiple processing and trimming before they can be used. Traditional aircraft windshield frames are mostly made of metal materials or ordinary composite materials, which have problems such as heavy weight, insufficient flame retardancy, and weak resistance to environmental aging.

[0003] Currently, existing patents CN113500800 A, a composite aircraft window frame HP-RTM mold and molding process, and CN109533272A, a carbon fiber composite aircraft window frame and manufacturing method, both utilize preforms for window frame molding, which are then placed in a mold and cured. This avoids the process limitations of autoclave molding and enables mass production, but the resulting molded products lack mechanical properties. However, with the increasing demand for lightweight, high-safety, and long-life civil aircraft, there is an urgent need to develop composite structural components that combine high strength, high flame retardancy, excellent dimensional stability, and environmental adaptability for use in aircraft windshield frames. Summary of the Invention

[0004] In response to the problems existing in the above-mentioned background technology, the present invention provides a molding process for an aircraft windshield frame based on a high-strength and lightweight composite material. The prepreg is directly laid in the mold cavity, and then the mold is heated and pressurized to achieve prepreg molded integrated molding. In this process, the selection of raw materials, the laying process, etc. are designed and optimized. The resulting composite aircraft windshield frame has the advantages of high strength and high flame retardancy, dimensional stability and environmental adaptability.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A forming process for an aircraft windshield frame comprises the following steps:

[0007] (1) Mold pretreatment: After cleaning the product molding mold, use absorbent gauze to apply a layer of release agent on the cavity surface. Use it at least 30 minutes after applying the release agent. Place the mold in an oven to preheat before use;

[0008] The release agent is 55-NC release agent;

[0009] The mold preheating temperature is 80-100°C and the preheating time is 2-4 hours;

[0010] The shape and structure of the molding die are adapted to the product, and preferably the composite window frame die for aviation designed independently by our company, such as the die disclosed in patent CN 218196370 U;

[0011] (2) Optimization of layer design: prepreg is laid in the mold after preheating in step (1). The layer design adopts 0 / 90 and ±45 alternating layer design, and prepreg is laid in sections near the corners based on the mold structure to improve the multi-directional mechanical properties; and the splicing positions of adjacent layers are staggered to avoid splicing at fixed positions at the corners;

[0012] The number of plies is designed based on the product thickness;

[0013] By adopting the ply design of the present invention, the thickness of the product is controlled by the number of plies, and the mechanical strength of the product is ensured by alternating plies and staggered splicing.

[0014] The prepreg composition includes a reinforcing material and a resin matrix, wherein the resin matrix accounts for 35% to 48% by mass, the reinforcing material is selected from any one of glass fiber, carbon fiber fabric, aramid fiber, and ceramic fiber, and the resin matrix is ​​phenolic resin or epoxy resin;

[0015] (3) Integrated compression molding: Compression molding is performed after the layer design described in step (2), wherein the lamination process meets the user's requirements, and the lamination temperature is controlled to be 125° C. to 160° C., the pressure is 0.5 MPa to 2.0 MPa, and the duration is 2 h to 4 h to obtain an aircraft windshield frame structural component;

[0016] The heating and pressurizing integrated molding method of the present invention has a higher dimensional stability of the product compared with room temperature and low pressure curing.

[0017] (4) Quality control: Use molds with theoretical marking lines to detect line deviations, use ultrasonic testing to detect defects and delamination inside the frame, and verify environmental adaptability;

[0018] The environmental adaptability verification includes: placing the product at -65℃ and +77℃ for 2 hours respectively, and the mold line still meets the requirements after returning to room temperature.

[0019] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a toughening agent, the amount of which is 3% to 5% of the mass of the resin matrix. The toughening agent is used to improve the toughness of the product, and includes a rubber elastomer toughening agent or a nanomaterial toughening agent; preferably, the rubber elastomer toughening agent is a nitrile rubber or a core-shell rubber elastomer toughening agent, and the nanomaterial toughening agent is nano-silica.

[0020] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a flame retardant or a flame retardant and a flame retardant synergist compound system, and the amount of the flame retardant or its compound system is 5% to 15% of the mass of the resin matrix. The flame retardant is selected from any one of phosphorus-based flame retardants and their derivatives, silicon-based flame retardants, nano flame retardants, and bromine-antimony compound flame retardants, and the flame retardant synergist is selected from any one of expandable graphite, aluminum hydroxide, and magnesium hydroxide; preferably, the phosphorus-based flame retardant and its derivatives are selected from any one of ammonium polyphosphate, tricresyl phosphate, and DOPO-based compounds, the silicon-based flame retardant is epoxy polysiloxane or polyhedral oligomeric silsesquioxane, and the nano flame retardant is nano zinc oxide or nano iron oxide.

[0021] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a coupling agent, the amount of which is 0.1% to 0.2% of the mass of the resin matrix, and the coupling agent is selected from any one of a silane coupling agent, a nanocomposite coupling agent, a bio-based coupling agent, and a metal coordination coupling agent; preferably, the silane coupling agent is KH550 or KH560, the nanocomposite coupling agent is a compound of nano-alumina (Al O) and silane, and the bio-based and metal coordination coupling agent is a coordination coupling agent of tannic acid and copper ions.

[0022] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a curing agent, the amount of which is 0% to 15% of the mass of the resin matrix, and the curing agent is selected from any one of phosphoric acid, p-toluenesulfonic acid, phenolsulfonic acid, paraformaldehyde, melamine, and hexamethylenetetramine, or a mixture of more than one.

[0023] Furthermore, the prepreg reinforcement material in step (2) of the present invention is a fiber fabric.

[0024] Furthermore, the joint seams in step (2) of the present invention are butt-jointed, with a butt gap of ≤1.5 mm, and the gaps are filled with pieces of material of the same width.

[0025] Furthermore, in step (2) of the present invention, the mold temperature during laying does not exceed 65°C.

[0026] Furthermore, after the frame is prepared in step (3) of the present invention, it needs to be bonded and sealed to the windshield. Some sealants can be used, specifically polysulfide sealants, polyurethane sealants, silicone-based sealants, etc.

[0027] Furthermore, the present invention also provides a window frame obtained based on the above-mentioned aircraft windshield frame, which includes outer, middle and inner layer frames, and the number of prepreg laying layers of each layer of the frame is set based on the actual performance requirements of the window frame, and the splicing seams of the three layers of frames are staggered with each other.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Lightweight advantage: This is mainly achieved by using high-strength and lightweight composite materials to replace traditional metal materials. Traditional metal frames are heavy, and the use of high-strength and lightweight composite materials can reduce the overall weight of the aircraft. Compared with the use of metal materials, the frames and pads can be reduced by more than 30%, thereby effectively reducing aircraft fuel consumption.

[0030] (2) Flame retardancy and high safety: The vertical combustion standard of Appendix F of CCAR 25 (flame time ≤ 15s) must be met, and the flame retardancy must meet the airworthiness standard to avoid fire risks.

[0031] (3) Dimensional stability: The product has good dimensional stability, does not require secondary processing, and directly matches the fuselage assembly requirements; the product obtained by high-pressure molding is dimensionally stable under extreme temperatures and has a storage life of up to 3 years, which can reduce maintenance costs.

[0032] (4) Molding requirements: No mechanical processing is required to ensure that the product dimensional accuracy meets the technical requirements (thickness deviation ±0.15mm, profile deviation ≤0.5mm).

[0033] (5) The molded products of the present invention do not require secondary processing, which can simplify the manufacturing process and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the prepreg segmented layer design structure in the mold of the present invention, wherein the solid lines represent odd-numbered layers and the dotted lines represent even-numbered layers. DETAILED DESCRIPTION

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] A forming process for an aircraft windshield frame comprises the following steps:

[0037] (1) Mold pretreatment: After cleaning the product molding mold, use absorbent gauze to apply a layer of release agent on the cavity surface. Use it at least 30 minutes after applying the release agent. Place the mold in an oven to preheat before use;

[0038] The release agent is 55-NC release agent;

[0039] The mold preheating temperature is 80-100°C and the preheating time is 2-4 hours;

[0040] The shape and structure of the molding die are adapted to the product, and preferably the composite window frame die for aviation designed independently by our company, such as the die disclosed in patent CN 218196370 U;

[0041] (2) Optimization of layer design: prepreg is laid in the mold after preheating in step (1). The layer design adopts 0 / 90 and ±45 alternating layer design, and prepreg is laid in sections near the corners based on the mold structure to improve the multi-directional mechanical properties; and the splicing positions of adjacent layers are staggered to avoid splicing at corners;

[0042] The number of plies is designed based on the product thickness;

[0043] By adopting the ply design of the present invention, the thickness of the product is controlled by the number of plies, and the mechanical strength of the product is ensured by alternating plies and staggered splicing.

[0044] The prepreg composition includes a reinforcing material and a resin matrix, wherein the resin matrix accounts for 35% to 48% by mass, the reinforcing material is selected from any one of glass fiber, carbon fiber fabric, aramid fiber, and ceramic fiber, and the resin matrix is ​​phenolic resin or epoxy resin;

[0045] (3) Integrated compression molding: Compression molding is performed after the layer design described in step (2), wherein the lamination process meets the user's requirements, and the lamination temperature is controlled to be 125° C. to 160° C., the pressure is 0.5 MPa to 2.0 MPa, and the duration is 2 h to 4 h to obtain an aircraft windshield frame structural component;

[0046] The heating and pressurizing integrated molding method of the present invention has a higher dimensional stability of the product compared with room temperature and low pressure curing.

[0047] (4) Quality control: Use molds with theoretical marking lines to detect line deviations, use ultrasonic testing to detect defects and delamination inside the frame, and verify environmental adaptability;

[0048] The environmental adaptability verification includes: placing the product at -65℃ and +77℃ for 2 hours respectively, and the mold line still meets the requirements after returning to room temperature.

[0049] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a toughening agent, the amount of which is 3% to 5% of the mass of the resin matrix. The toughening agent is used to improve the toughness of the product, and includes a rubber elastomer toughening agent or a nanomaterial toughening agent; preferably, the rubber elastomer toughening agent is a nitrile rubber or a core-shell rubber elastomer toughening agent, and the nanomaterial toughening agent is nano-silica.

[0050] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a flame retardant or a flame retardant and flame retardant synergist compound system, the amount of the flame retardant or its compound system is 5% to 15% of the mass of the resin matrix, the flame retardant is selected from any one of phosphorus-based flame retardants and their derivatives, silicon-based flame retardants, nano flame retardants, and bromine-antimony compound flame retardants, and the flame retardant synergist is selected from any one of expandable graphite, aluminum hydroxide, and magnesium hydroxide; preferably, the phosphorus-based flame retardant and its derivatives are selected from any one of ammonium polyphosphate, tricresyl phosphate, and DOPO-based compounds, the silicon-based flame retardant is epoxy polysiloxane or polyhedral oligomeric silsesquioxane, and the nano flame retardant is nano zinc oxide or nano iron oxide.

[0051] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a coupling agent, the amount of which is 0.1% to 0.2% of the mass of the resin matrix, and the coupling agent is selected from any one of a silane coupling agent, a nanocomposite coupling agent, a bio-based coupling agent, and a metal coordination coupling agent; preferably, the silane coupling agent is KH550 or KH560, the nanocomposite coupling agent is a compound of nano-alumina (Al O) and silane, and the bio-based and metal coordination coupling agent is a coordination coupling agent of tannic acid and copper ions.

[0052] Furthermore, the prepreg resin matrix in step (2) of the present invention also includes a curing agent, the amount of which is 0% to 15% of the mass of the resin matrix, and the curing agent is selected from any one of phosphoric acid, p-toluenesulfonic acid, phenolsulfonic acid, paraformaldehyde, melamine, and hexamethylenetetramine, or a mixture of more than one.

[0053] Furthermore, the prepreg reinforcement material in step (2) of the present invention is E glass fiber fabric.

[0054] Furthermore, the joint seams in step (2) of the present invention are butt-jointed, with a butt gap of ≤1.5 mm, and the gaps are filled with pieces of material of the same width.

[0055] Furthermore, in step (2) of the present invention, the mold temperature during laying does not exceed 65°C.

[0056] Example 1

[0057] A forming process for an aircraft windshield frame comprises the following steps:

[0058] (1) Mold pretreatment: After cleaning the product molding mold, use absorbent gauze to apply a layer of 55-NC release agent on the cavity surface. Use it at least 30 minutes after applying the release agent. Before use, put the mold into the oven for preheating at 90 ° C and for 3 hours.

[0059] The molding die is a composite window frame die for aviation designed by our company, which is the die disclosed in patent CN218196370U.

[0060] (2) Optimization of layer design: prepreg is laid in the mold after preheating in step (1). The layer design adopts 0 / 90 and ±45 alternating layer design, and prepreg is laid in sections near the corners based on the mold structure to improve the multi-directional mechanical properties; and the splicing positions of adjacent layers are staggered to avoid splicing at corners;

[0061] The number of plies is designed based on the product thickness;

[0062] The joints are butt-jointed, with a gap of ≤1.5mm, and gaps are filled with pieces of the same width;

[0063] The mold temperature during laying does not exceed 65°C;

[0064] The prepreg composition includes a reinforcing material and a resin matrix, wherein the resin matrix accounts for 40% by weight, the reinforcing material is selected from glass fiber, and the resin matrix is ​​phenolic resin;

[0065] (3) Integrated compression molding: Compression molding is performed after the layer design described in step (2), wherein the lamination process meets the user's requirements, and the lamination temperature is controlled to be 130°C ± 5°C, the pressure is 1.2MPa ± 0.1MPa, and the duration is 3h ± 1h to obtain an aircraft windshield frame structural component;

[0066] (4) Quality control: Use molds with theoretical marking lines to detect line deviations, use ultrasonic testing to detect defects and delamination inside the frame, and verify environmental adaptability;

[0067] The environmental adaptability verification includes: placing the product at -65℃ and +77℃ for 2 hours respectively, and the mold line still meets the requirements after returning to room temperature.

[0068] Example 2

[0069] A forming process for an aircraft windshield frame comprises the following steps:

[0070] (1) Mold pretreatment: After cleaning the product molding mold, use absorbent gauze to apply a layer of 55-NC release agent on the cavity surface. Use it at least 30 minutes after applying the release agent. Before use, put the mold into the oven for preheating at 90 ° C and for 3 hours.

[0071] The molding die is a composite window frame die for aviation designed by our company, which is the die disclosed in patent CN218196370U.

[0072] (2) Optimization of layer design: prepreg is laid in the mold after preheating in step (1). The layer design adopts 0 / 90 and ±45 alternating layer design, and prepreg is laid in sections near the corners based on the mold structure to improve the multi-directional mechanical properties; and the splicing positions of adjacent layers are staggered to avoid splicing at corners;

[0073] The number of plies is designed based on the product thickness;

[0074] The joints are butt-jointed, with a gap of ≤1.5mm, and gaps are filled with pieces of the same width;

[0075] The mold temperature during laying does not exceed 65°C;

[0076] The prepreg composition includes a reinforcing material and a resin matrix, wherein the resin matrix accounts for 40% by weight, the reinforcing material is selected from glass fiber, and the resin matrix is ​​a phenolic resin; it also includes a toughening agent, a flame retardant, a coupling agent and a curing agent, the toughening agent is a nitrile rubber elastomer toughening agent, the amount of which is 3% by weight of the resin matrix, the flame retardant is a bromine-antimony composite flame retardant, the amount of which is 5% by weight of the resin matrix, the coupling agent is a silane coupling agent KH550, the amount of which is 0.1% by weight of the resin matrix, and the curing agent is phosphoric acid, the amount of which is 5% by weight of the resin matrix;

[0077] (3) Integrated compression molding: Compression molding is performed after the layer design described in step (2), wherein the lamination process meets the user's requirements, and the lamination temperature is controlled to be 130°C ± 5°C, the pressure is 1.2MPa ± 0.1MPa, and the duration is 3h ± 1h to obtain an aircraft windshield frame structural component;

[0078] (4) Quality control: Use molds with theoretical marking lines to detect line deviations, use ultrasonic testing to detect defects and delamination inside the frame, and verify environmental adaptability;

[0079] The environmental adaptability verification includes: placing the product at -65℃ and +77℃ for 2 hours respectively, and the mold line still meets the requirements after returning to room temperature.

[0080] The aircraft windshield frame structural component manufactured by the molding process of the present invention reduces the overall weight of the aircraft by replacing traditional metal materials with high-strength and lightweight composite materials; through the selection of raw material resin matrix, reinforcing fiber and flame retardant, the flame retardant performance of the product meets the airworthiness standard and avoids the risk of fire; the product manufactured by optimizing the prepreg layering process design and the one-piece molding process design has good dimensional stability, does not require secondary processing, and is dimensionally stable under extreme temperatures, and does not require mechanical processing, which can ensure that the product dimensional accuracy meets the technical requirements (thickness deviation ±0.15mm, profile deviation ≤0.5mm).

Claims

1. A forming process for an aircraft windshield frame, characterized in that: The steps include: (1) Mold pretreatment: After cleaning the product molding mold, use absorbent gauze to apply a layer of release agent on the cavity surface. Use it at least 30 minutes after applying the release agent. Place the mold in an oven to preheat before use; The shape and structure of the forming mold are adapted to the product; (2) Optimization of layup design: Lay the prepreg in the mold after preheating in step (1). The layup design adopts 0 / 90 and ±45 alternating layup design. The prepreg is laid in sections near the corners based on the mold structure. The splicing positions of adjacent layups are staggered to avoid splicing at fixed positions at the corners. The prepreg composition includes a reinforcing material and a resin matrix, wherein the resin matrix accounts for 35% to 48% by mass, the reinforcing material is selected from any one of glass fiber, carbon fiber fabric, aramid fiber, and ceramic fiber, and the resin matrix is ​​phenolic resin or epoxy resin; (3) Integrated compression molding: Compression molding is performed after the layer design described in step (2), wherein the lamination process meets the user's requirements, and the lamination temperature is controlled to be 125° C. to 160° C., the pressure is 0.5 MPa to 2.0 MPa, and the duration is 2 h to 4 h to obtain an aircraft windshield frame structural component; (4) Quality control: The mold with theoretical marking lines was used to detect the deviation of the mold line, and the presence of defects and delamination inside the frame was detected by ultrasonic wave, and the environmental adaptability was verified.

2. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The release agent in step (1) is 55-NC release agent; The mold preheating temperature is 80-100° C., and the preheating time is 2-4 hours.

3. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The number of layers in step (2) is designed based on the product thickness; The adjacent plies are butt-jointed, with a butt gap of ≤1.5mm, and gaps are filled with pieces of the same width; The mold temperature does not exceed 65° C. when the prepreg is laid.

4. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The prepreg resin matrix in step (2) also includes a toughening agent, which is a rubber elastomer toughening agent or a nanomaterial toughening agent, and its amount is 3% to 5% of the mass of the resin matrix; the rubber elastomer toughening agent is a nitrile rubber or a core-shell rubber elastomer toughening agent, and the nanomaterial toughening agent is nano-silica.

5. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The prepreg resin matrix in step (2) further includes a flame retardant or a flame retardant and a flame retardant synergist compound system, and the amount of the flame retardant or its compound system is 5% to 15% of the mass of the resin matrix; the flame retardant is selected from any one of phosphorus flame retardants and their derivatives, silicon flame retardants, nano flame retardants, and bromine-antimony compound flame retardants, and the flame retardant synergist is selected from any one of expandable graphite, aluminum hydroxide, and magnesium hydroxide; The phosphorus-based flame retardant and its derivatives are selected from any one of ammonium polyphosphate, tricresyl phosphate, and DOPO-based compounds; The silicon-based flame retardant is epoxy polysiloxane or polyhedral oligomeric silsesquioxane; The nano flame retardant is nano zinc oxide or nano iron oxide.

6. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The prepreg resin matrix in step (2) further includes a coupling agent in an amount of 0.1% to 0.2% of the mass of the resin matrix, wherein the coupling agent is selected from any one of a silane coupling agent, a nanocomposite coupling agent, a bio-based coupling agent, and a metal coordination coupling agent; The silane coupling agent is KH550 or KH560; The nanocomposite coupling agent is a compound of nano-alumina and silane; The bio-based and metal coordination coupling agent is a tannic acid and copper ion coordination coupling agent.

7. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The prepreg resin matrix in step (2) also includes a curing agent, the amount of which is 0% to 15% of the mass of the resin matrix, and the curing agent is selected from any one of phosphoric acid, p-toluenesulfonic acid, phenolsulfonic acid, paraformaldehyde, melamine, and hexamethylenetetramine, or a mixture of more than one.

8. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The prepreg reinforcement material in step (2) is fiber fabric.

9. The forming process of an aircraft windshield frame according to claim 1, characterized in that: The environmental adaptability verification described in step (4) includes: placing the product at -65°C and +77°C for 2 hours respectively, and the mold line still meets the requirements after returning to room temperature.

10. A window frame obtained by using an aircraft windshield frame made by the process according to claims 1 to 9, characterized in that: It includes outer, middle and inner frames, and the number of prepreg laying layers of each frame is set based on the actual performance requirements of the window frame, and the joints of the three frames are staggered with each other.

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