Low-porosity non-autoclave forming method for composite material structure

Abstract

The invention belongs to the technical field of composite material manufacturing, and relates to a composite material structure low-porosity non-autoclave forming method which comprises the following steps: step 1, preparing a forming mold; 2, auxiliary materials are prepared; step 3, blanking the composite material; step 4, paving a composite material in a non-autoclave; (5) the composite material obtained after laying is completed is packaged; step 6, carrying out vacuum detection on the packaged composite material; step 7, curing the composite material; according to the method, the air guide tows are arranged when the composite material is laid, and auxiliary materials such as the non-adhesive polytetrafluoroethylene cloth and the non-adhesive glass fiber cloth are used when the composite material is compacted and packaged, so that the composite material structure manufactured through non-autoclave molding under the low-pressure condition effectively meets the product porosity requirement.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material manufacturing, and relates to a low-porosity non-autoclave molding method for a composite material structure. Background Art

[0002] Composite materials have been used in aircraft structures since the early 1970s and have rapidly developed into one of the four major structural materials in aviation after aluminum, steel and titanium. The amount of composite materials used has long been an indicator of the advancement of aircraft. Composite materials have the characteristics of simultaneous material manufacturing and structural molding. The properties of the material are imparted to the structure through the manufacturing process, so the molding process of composite components is particularly important. At present, the autoclave molding process is the main method for producing high-quality composite components for aerospace. However, it has problems such as high energy consumption, high equipment manufacturing and operating costs, and high requirements for molding molds.

[0003] Compared with the autoclave molding process, the out of autoclave (OOA) molding process transfers the composite material curing site to an oven or curing furnace that is cheaper and does not require external pressure. It can effectively reduce the manufacturing cost while meeting the use requirements of the manufactured products. Therefore, more and more research is being conducted on the out of autoclave molding process.

[0004] In the non-autoclave molding process, due to the low molding pressure (about 0.1MPa), the porosity of the composite material structure after molding can be as high as 5% to 10%, and these pores will also affect the performance and use effect of the composite material structure. Therefore, it is urgent to improve the non-autoclave molding process technology to produce a composite material structure with a porosity that meets the product performance requirements. Summary of the invention

[0005] Technical problem solved by the invention: The invention aims to solve the problems of high manufacturing cost of the existing autoclave molding process and high porosity of non-autoclave molded composite material structures. A non-autoclave molding method for low-porosity composite material structures is proposed, and the method can be used to manufacture composite material structures with porosity that meets product performance requirements.

[0006] Technical solution of the present invention

[0007] A non-autoclave molding method for a composite material structure with low porosity comprises the following steps:

[0008] Step 1: Preparation of molding mold;

[0009] Step 2: Preparation of auxiliary materials;

[0010] Step 3: Cutting composite materials;

[0011] Step 4: Non-autoclave composite lay-up;

[0012] Step 5: Encapsulate the composite material after stacking;

[0013] Step 6: Perform vacuum testing on the packaged composite material;

[0014] Step 7: Curing the composite material.

[0015] Further, step 1 of preparing the molding mold is as follows: after cleaning the surface of the molding mold, apply a mold release agent, the type of mold release agent is FREKOTE44NC; when a newly made or repaired molding mold is used for the first time, use a brush or soft cloth dipped in the mold release agent, and apply three thin layers of FREKOTE crosswise; when using the mold release agent again on a molding mold that has been used with the mold release agent, do not apply too much mold release agent;

[0016] The specific process of coating the release agent on the surface of the molding mold is as follows: 1) Check the area where the tape is used to isolate the putty strips to prevent the release agent from contaminating the bagging area; 2) On the mold surface, use a brush or soft cloth to dip the release agent and apply a thin cross-coat; 3) After each layer of release agent is applied, dry it at 25°C for 15 minutes; 4) After the release agent is dry, proceed with the composite material laying operation.

[0017] Furthermore, the auxiliary materials in step 2 include isolation film, high temperature resistant tape, non-adhesive polytetrafluoroethylene cloth, non-adhesive glass fiber cloth, vacuum bag, and sealing strip; ensure that the brand and quantity of the above auxiliary materials meet the manufacturing requirements; step 3 composite material unloading specifically includes: after the composite material is thawed in the clean room, unloading is completed according to the composite material structure layer and size, and information marking is done;

[0018] The thawing time of the composite material varies with the total thickness of the composite material. The shortest thawing time (hours) = 1.2 × bundle thickness (mm) × 0.1, and the thawing time is at least 6 hours.

[0019] Further, step 4 of non-autoclave composite material layup specifically includes the following steps:

[0020] Step 4.1 Place the molding mold in a clean room with a temperature of 18°C ​​to 26°C and a relative humidity of 15% to 65%;

[0021] Step 4.2: laying a first layer of composite material on the surface of the forming mold, and using a scraper to comb along the parallel direction of the composite material fibers or the warp direction of the fabric;

[0022] Step 4.3: arranging air-conducting fiber bundles between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material;

[0023] After laying the first layer of composite material on the surface of the forming mold, an air-conducting fiber bundle is arranged between the composite material and the forming mold; then, after laying 1 to 3 layers of composite material, an air-conducting fiber bundle is arranged between two adjacent layers of composite material; and an air-conducting fiber bundle is arranged between the sandwich material and its lower and upper layers of composite material.

[0024] Step 4.4 After the air-conducting fiber bundle is arranged between the first layer of composite material and the forming mold, vacuum compaction is performed; after each subsequent 1 to 3 layers of composite material are laid and the air-conducting fiber bundle is arranged, vacuum compaction is performed; after the lower and upper layers of the sandwich material are laid and the air-conducting fiber bundle is arranged, vacuum compaction is performed.

[0025] Furthermore, when laying composite materials, the laying direction is based on the product design requirements or the coordinate system on the molding die, the fabric laying direction tolerance is ±5°, the process should be strictly controlled according to the linear dimension of ±1°, and the laying boundary position tolerance is: ±3mm; the laying process must strictly prevent the inclusion of foreign matter.

[0026] Furthermore, in step 4.3, the air-conducting fiber bundle is a dry glass fiber material, and the width of each fiber bundle is 5 mm to 10 mm. When arranging the air-conducting fiber bundle between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material, one end of the air-conducting fiber bundle should be placed outside the edge line of the composite material structure product, and the connection length with the composite material should be not less than 20 mm; the length of the air-conducting fiber bundle meets the requirements that the other end can be connected to the adhesive-free glass cloth during subsequent vacuum compaction and can be connected to the breathable felt during packaging; each adjacent two air-conducting fiber bundles in the same layer are arranged along the edge of the composite material at an interval of 250 mm.

[0027] Further, step 4.4 vacuum compaction is as follows: laying glue-free polytetrafluoroethylene cloth on the surface of the last laid composite material, the outer edge size D2 of the glue-free polytetrafluoroethylene cloth is larger than the outer edge size D1 of the composite material layer, and D2-D1≥10mm is satisfied; laying glue-free glass fiber cloth on the surface of the glue-free polytetrafluoroethylene cloth, the outer edge size D3>D2 of the glue-free glass fiber cloth, and satisfying that no bridging occurs during vacuuming; the glass fiber cloth is sealed with high-temperature resistant tape on all sides to ensure that fibers do not fall off; connecting the air-guiding fiber bundles arranged between the composite material and the forming mold, between the composite material and the composite material, and between the composite material and the sandwich material to the glass fiber cloth, placing a vacuum nozzle on the glass fiber cloth, and laying a vacuum bag on the glass fiber cloth; laying a sealing strip around the forming mold outside the composite material to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum compaction, the vacuum degree is not less than 0.09MPa, the time is at least 15min, and then the vacuum nozzle is removed, and the vacuum bag, the glue-free polytetrafluoroethylene cloth, and the glue-free glass fiber cloth are removed.

[0028] Further, step 5: packaging the composite material after the stacking is completed, specifically:

[0029] A non-porous isolation film is laid on the surface of the stacked composite material, and the outer edge dimension D4 of the isolation film is larger than the outer edge dimension D1 of the composite layer, and D4-D1≥10mm is satisfied; a breathable felt is laid on the isolation film, and the breathable felt is connected to the air-guiding fiber bundles arranged between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material; the outer edge dimension D5 of the breathable felt is greater than D4, and it is satisfied that no bridging is generated during vacuuming; a vacuum nozzle is placed on the breathable felt, and a vacuum bag is laid on the breathable felt; a sealing strip is laid around the molding mold outside the composite layer to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum is drawn, and the vacuum degree is ≥0.090MPa.

[0030] Further, in step 6, when the vacuum degree in the vacuum bag reaches 0.09 MPa until the vacuum degree is stable, the vacuum source is disconnected or turned off after 15 minutes, and the vacuum gauge reading drops by no more than 0.017 MPa within 5 minutes;

[0031] In step 7, the encapsulated molding mold is operated into the curing equipment, and the curing parameters are: the vacuum degree in the vacuum bag is not less than -0.090MPa, the room temperature is heated to 82℃±10℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 30min-60min, and the temperature is further heated to 127℃±2℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 120min; the temperature is reduced to below 60℃ at a cooling rate of ≤5℃ / min, and the product is taken out of the curing equipment; during the entire curing cycle, the pressure in the vacuum bag should be maintained at not less than -0.090MPa.

[0032] Furthermore, the method further comprises:

[0033] Step 8: Remove the vacuum nozzle on the breathable felt, remove the vacuum bag, breathable felt and non-porous isolation film; use non-metallic tools to demould and open the mold, and clean the excess materials on the surface of the molding mold;

[0034] Step 9: Check whether the formed composite material has any damage or excess;

[0035] Step 10: If there are delamination defects in the composite material after molding, use high temperature resistant paste glue and repair it according to the following scheme:

[0036] 10.1 Drill a φ2.1mm hole at the upper and lower edges of the defect;

[0037] 10.2 Inject glue into the defect from the lower hole until the glue overflows from the upper hole;

[0038] 10.3 Seal the two holes with tape;

[0039] 10.4 After the injected glue solidifies, remove the tape and grind it smooth.

[0040] Beneficial Effects

[0041] The present invention is a method for non-autoclave molding of composite materials with low porosity. By arranging air guide bundles when laying up composite materials and using auxiliary materials such as adhesive-free polytetrafluoroethylene cloth and adhesive-free glass fiber cloth during compaction and packaging, the composite material structure manufactured by non-autoclave molding under low pressure conditions can effectively meet the product porosity requirements. Using a curing furnace for curing is more effective than the autoclave molding process, which effectively reduces equipment costs and energy and power costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flow chart of the method of the present invention;

[0043] Figure 2 It is a schematic diagram of vacuum compaction of the present invention;

[0044] Among them, 01 molding die, 02 composite material layer, 03 air guide fiber bundle, 04 non-glue polytetrafluoroethylene cloth, 05 non-glue glass fiber cloth, 06 vacuum bag, 07 sealing strip; D1 composite material layer outer edge size, D2 non-glue polytetrafluoroethylene cloth outer edge size, D3 non-glue glass fiber cloth outer edge size;

[0045] Figure 3 This is a schematic diagram of the arrangement of the air-guiding fiber bundle of the present invention;

[0046] Figure 4 This is a schematic diagram of packaging the composite material after stacking according to the present invention;

[0047] Among them, 08 non-porous isolation membrane, 09 breathable felt, D4 isolation membrane outer edge size;

[0048] Figure 5 It is a schematic diagram of curing parameters of the present invention;

[0049] Figure 6 This is a schematic diagram of repairing the formed composite material according to the present invention.

[0050] Among them, 11 is a defect area, 12 is a glue overflow hole, and 13 is a glue injection hole. DETAILED DESCRIPTION

[0051] The features and illustrative embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific settings and methods proposed below, but covers any improvements, replacements and modifications of structures, methods, devices without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention.

[0052] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other, and the embodiments can refer to and quote each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0053] One embodiment of the present invention is: a method for forming a composite material structure with low porosity without autoclave, comprising the following steps:

[0054] Step 1: Preparation of the molding mold; Step 1 Preparation of the molding mold is as follows: After cleaning the surface of the molding mold, apply a release agent, the type of release agent is FREKOTE44NC; when a new or repaired molding mold is used for the first time, use a brush or soft cloth dipped in the release agent, and apply 3 thin layers of FREKOTE crosswise; when using the release agent on a molding mold that has been used with the release agent again, do not apply too much release agent;

[0055] The specific process of coating the release agent on the surface of the molding mold is as follows: 1) Check the area where the tape is used to isolate the putty strips to prevent the release agent from contaminating the bagging area; 2) On the mold surface, use a brush or soft cloth to dip the release agent and apply a thin cross-coat; 3) After each layer of release agent is applied, dry it at 25°C for 15 minutes; 4) After the release agent is dry, proceed with the composite material laying operation.

[0056] Step 2: Preparation of auxiliary materials; auxiliary materials include isolation film, high temperature resistant tape, non-adhesive polytetrafluoroethylene cloth, non-adhesive glass fiber cloth, vacuum bag, sealing strip; ensure that the brand and quantity of the above auxiliary materials meet the manufacturing requirements;

[0057] Step 3: Unloading of composite materials; specifically including: unloading of composite materials according to the structure layer and size of composite materials after thawing in the clean room, and labeling of information;

[0058] The thawing time of the composite material varies with the total thickness of the composite material. The shortest thawing time (hours) = 1.2 × bundle thickness (mm) × 0.1, and the thawing time is at least 6 hours.

[0059] Step 4: Non-autoclave composite layup, specifically including the following steps:

[0060] Step 4.1 Place the molding mold in a clean room with a temperature of 18°C ​​to 26°C and a relative humidity of 15% to 65%;

[0061] Step 4.2: laying a first layer of composite material on the surface of the forming mold, and using a scraper to comb along the parallel direction of the composite material fibers or the warp direction of the fabric;

[0062] Step 4.3: arranging air-conducting fiber bundles between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material;

[0063] After laying the first layer of composite material on the surface of the forming mold, an air-conducting fiber bundle is arranged between the composite material and the forming mold; then, after laying 1 to 3 layers of composite material, an air-conducting fiber bundle is arranged between two adjacent layers of composite material; and an air-conducting fiber bundle is arranged between the sandwich material and its lower and upper layers of composite material.

[0064] In step 4.3, the air-conducting fiber bundle is made of dry glass fiber material, and the width of each fiber bundle is 5mm to 10mm. When arranging the air-conducting fiber bundle between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material, one end of the air-conducting fiber bundle should be placed outside the edge line of the composite material structure product, and the connection length with the composite material should be not less than 20mm; the length of the air-conducting fiber bundle meets the requirements that the other end can be connected to the adhesive-free glass cloth during subsequent vacuum compaction and can be connected to the breathable felt during packaging; each adjacent two air-conducting fiber bundles in the same layer are arranged along the edge of the composite material at an interval of 250mm.

[0065] Step 4.4 After the air-conducting fiber bundle is arranged between the first layer of composite material and the forming mold, vacuum compaction is performed; after each subsequent 1 to 3 layers of composite material are laid and the air-conducting fiber bundle is arranged, vacuum compaction is performed; after the lower and upper layers of the sandwich material are laid and the air-conducting fiber bundle is arranged, vacuum compaction is performed.

[0066] When laying composite materials, the laying direction is based on the product design requirements or the coordinate system on the molding die. The fabric laying direction tolerance is ±5°. The process should be strictly controlled according to the linear dimension of ±1°. The layup boundary position tolerance is: ±3mm. Foreign matter must be strictly prevented from being included during the laying process.

[0067] Step 4.4 vacuum compaction is as follows: lay glue-free polytetrafluoroethylene cloth on the surface of the last laid composite material, the outer edge size D2 of the glue-free polytetrafluoroethylene cloth is larger than the outer edge size D1 of the composite material layer, and D2-D1≥10mm is satisfied; lay glue-free glass fiber cloth on the surface of the glue-free polytetrafluoroethylene cloth, the outer edge size D3>D2 of the glue-free glass fiber cloth, and no bridging is generated during vacuuming; the glass fiber cloth is sealed with high-temperature resistant tape on all sides to ensure that the fibers do not fall off; connect the air-guiding fiber bundles arranged between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material with the glass fiber cloth, place a vacuum nozzle on the glass fiber cloth, and lay a vacuum bag on the glass fiber cloth; lay a sealing strip around the molding mold outside the composite material to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum compaction, the vacuum degree is not less than 0.09MPa, the time is at least 15min, and then the vacuum nozzle is removed, and the vacuum bag, glue-free polytetrafluoroethylene cloth, and glue-free glass fiber cloth are removed.

[0068] Step 5: Encapsulate the composite material after stacking; specifically:

[0069] A non-porous isolation film is laid on the surface of the stacked composite material, and the outer edge dimension D4 of the isolation film is larger than the outer edge dimension D1 of the composite layer, and D4-D1≥10mm is satisfied; a breathable felt is laid on the isolation film, and the breathable felt is connected to the air-guiding fiber bundles arranged between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material; the outer edge dimension D5 of the breathable felt is greater than D4, and it is satisfied that no bridging is generated during vacuuming; a vacuum nozzle is placed on the breathable felt, and a vacuum bag is laid on the breathable felt; a sealing strip is laid around the molding mold outside the composite layer to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum is drawn, and the vacuum degree is ≥0.090MPa.

[0070] Step 6: Perform vacuum testing on the packaged composite material; in step 6, when the vacuum degree in the vacuum bag reaches 0.09MPa until the vacuum degree is stable, the vacuum source is disconnected or turned off after 15 minutes, and the vacuum gauge reading drops by no more than 0.017Mpa within 5 minutes;

[0071] Step 7: Curing the composite material. In step 7, the encapsulated molding mold is operated into the curing equipment. The curing parameters are as follows: the vacuum degree in the vacuum bag is not less than -0.090MPa, the room temperature is heated to 82℃±10℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 30min-60min, and the temperature is further heated to 127℃±2℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 120min; the temperature is reduced to below 60℃ at a cooling rate of ≤5℃ / min, and the mold is taken out of the curing equipment; during the entire curing cycle, the pressure in the vacuum bag should be maintained at not less than -0.090MPa.

[0072] Step 8: Remove the vacuum nozzle on the breathable felt, remove the vacuum bag, breathable felt and non-porous isolation film; use non-metallic tools to demould and open the mold, and clean the excess materials on the surface of the molding mold;

[0073] Step 9: Check whether the formed composite material has any damage or excess;

[0074] Step 10: If there are delamination defects in the composite material after molding, use high temperature resistant paste glue and repair it according to the following scheme:

[0075] 10.1 Drill a φ2.1mm hole at the upper and lower edges of the defect;

[0076] 10.2 Inject glue into the defect from the lower hole until the glue overflows from the upper hole;

[0077] 10.3 Seal the two holes with tape;

[0078] 10.4 After the injected glue solidifies, remove the tape and grind it smooth.

[0079] The second embodiment of the present invention is to provide a low-porosity non-autoclave molding method for a composite material structure, taking the molding of a rear angle material of a cockpit cover frame of a certain type of aircraft as an example, comprising the following steps:

[0080] 01.Prepare the molding die.

[0081] Completed the release agent coating and surface cleaning of the rear angle material forming mold surface of a certain type of aircraft cockpit cover frame.

[0082] Ensure that the tooling has reached room temperature and there is no moisture on the surface. Scrub the tooling work surface with acetone / methyl ethyl ketone to ensure that the tooling surface is clean and grease-free. Use the release agent FREKOTE44NC in a well-ventilated area. This molding mold is a mold that has already used a release agent, so apply a thin layer of release agent.

[0083] The specific coating process is as follows: 1) Check the area where the tape is used to isolate the putty strips to prevent the release agent from contaminating the bagging area; 2) Use a brush or soft cloth to dip the release agent on the mold surface and apply it crosswise and thinly. 3) Dry at 25°C for 15 minutes. 4) After drying, start the composite material laying operation.

[0084] 02.Prepare auxiliary materials.

[0085] Prepare auxiliary materials according to the auxiliary materials required for the rear angle of the cockpit cover frame, including isolation film, high temperature resistant tape, non-adhesive polytetrafluoroethylene cloth, non-adhesive glass fiber cloth, vacuum bag, and sealing strip. Ensure that the brand and quantity of the above auxiliary materials meet the manufacturing requirements.

[0086] 03.Cutting of composite materials.

[0087] After the composite materials used for the rear angle materials of the cockpit cover frame are thawed in the clean room for 6 hours, they are cut according to the layers and sizes, and the information is marked.

[0088] 04. Overlay.

[0089] 04.1 Place the cockpit cover frame rear angle material forming mold in a clean room with a temperature of 18℃~26℃ and a relative humidity of 15%~65%.

[0090] 04.2 Lay the first layer of composite material on the surface of the forming mold, and use a scraper to comb along the parallel direction of the composite material fiber or the warp direction of the fabric. Lay the composite material based on the coordinate system specified on the forming mold. Control the laying to meet the requirements of direction tolerance ±1° and laying boundary tolerance ±3mm. Prevent foreign matter from being mixed during the laying process.

[0091] 04.3 Arrange air-conducting fiber bundles between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material.

[0092] After laying the first layer of composite material on the surface of the forming mold, arrange the air-guiding fiber bundle between the composite material and the forming mold; then, after laying 1 to 3 layers of composite material, arrange the air-guiding fiber bundle between two adjacent layers of composite material; arrange the air-guiding fiber bundle between the sandwich material and its lower and upper layers of composite material. There are 9 layers of rear angle material for the cockpit cover frame. After laying the first layer of prepreg, arrange the air-guiding fiber bundle between the prepreg and the tooling. Then, after laying every 2 layers, arrange the air-guiding fiber bundle between the prepreg.

[0093] The air-guiding fiber bundle is made of dry glass fiber material, and the width of each fiber bundle is 5mm to 10mm. When arranging the air-guiding fiber bundle between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material, one end of the air-guiding fiber bundle should be placed outside the edge line of the composite structure product, and the connection length with the composite material should be not less than 20mm; the length of the air-guiding fiber bundle meets the requirements that the other end can be connected to the adhesive-free glass cloth during subsequent vacuum compaction, and can be connected to the breathable felt during packaging; a group of air-guiding fiber bundles are placed at the V-shaped corners at both ends of the rear angle material of the cockpit cover frame, and are placed at intervals of about 250mm along the length direction of the rear angle material of the cockpit cover frame along the edge of the prepreg. The air-guiding fiber bundles of each layer should be arranged at intervals.

[0094] 04.4 After arranging the air-conducting fiber bundle between the first layer of composite material and the forming mold, vacuum compaction is performed; after laying down 1 to 3 layers of composite material and arranging the air-conducting fiber bundle, vacuum compaction is performed; after laying down the lower and upper layers of the sandwich material and arranging the air-conducting fiber bundle, vacuum compaction is performed. Vacuum compaction is to effectively discharge the air inclusions between the layers when the non-autoclave composite material is laid up, so as to reduce the porosity of the composite material structure after forming.

[0095] Lay glue-free polytetrafluoroethylene cloth on the surface of the last laid composite material, the outer edge size D2 of the glue-free polytetrafluoroethylene cloth is larger than the outer edge size D1 of the composite material layer, and D2-D1≥10mm is satisfied; lay glue-free glass fiber cloth on the surface of the glue-free polytetrafluoroethylene cloth, the outer edge size D3>D2 of the glue-free glass fiber cloth, and satisfy that no bridging occurs during vacuuming; the glass fiber cloth is sealed with high-temperature resistant tape on all sides to ensure that the fibers do not fall off; connect the air-guiding fiber bundles arranged between the composite material and the forming mold, between the composite material and the composite material, and between the composite material and the sandwich material with the glass fiber cloth, place a vacuum nozzle on the glass fiber cloth, and lay a vacuum bag on the glass fiber cloth; lay a sealing strip around the forming mold outside the composite material to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum compaction, the vacuum degree is not less than 0.09MPa, the time is at least 15min, and then the vacuum nozzle is removed, and the vacuum bag, glue-free polytetrafluoroethylene cloth, and glue-free glass fiber cloth are removed.

[0096] 05Package the composite materials after layup.

[0097] A non-porous isolation film is laid on the surface of the stacked composite material, and the outer edge dimension D4 of the isolation film is larger than the outer edge dimension D1 of the composite layer, and D4-D1≥10mm is satisfied; a breathable felt is laid on the isolation film, and the breathable felt is connected to the air-guiding fiber bundles arranged between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material; the outer edge dimension D5 of the breathable felt is greater than D4, and it is satisfied that no bridging is generated during vacuuming; a vacuum nozzle is placed on the breathable felt, and a vacuum bag is laid on the breathable felt; a sealing strip is laid around the molding mold outside the composite layer to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum is drawn, and the vacuum degree is ≥0.090MPa.

[0098] 06. Vacuum detection.

[0099] The vacuum degree in the vacuum bag reaches 0.09MPa until the vacuum degree stabilizes. After 15 minutes, the vacuum source is disconnected or turned off. The vacuum gauge reading should not drop by more than 0.017Mpa within 5 minutes.

[0100] 06. Perform vacuum testing on the packaged composite material.

[0101] When the vacuum degree in the vacuum bag reaches 0.09MPa until the vacuum degree is stable, disconnect or turn off the vacuum source after 15 minutes, and the vacuum gauge reading drops by no more than 0.017Mpa within 5 minutes. Vacuum degree is an important guarantee for the porosity of composite materials formed without autoclaves. Therefore, vacuum testing of packaged composite materials must be carried out before curing.

[0102] 07.Cure the composite material.

[0103] The encapsulated molding mold is moved into the curing equipment with the following curing parameters: the vacuum degree in the vacuum bag is not less than -0.090MPa, the temperature is raised from room temperature to 82℃±10℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 30min-60min, and the temperature is further raised to 127℃±2℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 120min; the temperature is lowered to below 60℃ at a cooling rate of ≤5℃ / min, and the product is taken out of the curing equipment; during the entire curing cycle, the pressure in the vacuum bag should be kept at not less than -0.090MPa.

[0104] 08. Demoulding.

[0105] Remove the vacuum nozzle on the breathable felt, remove the vacuum bag, breathable felt and non-porous isolation film; use non-metallic tools to demould and open the mold, and clean the excess on the surface of the molding mold. Do not damage the product and the molding mold surface.

[0106] 09. Check whether the composite material structure is damaged or has any extra material. Use non-destructive testing to check the internal quality of the composite material structure.

[0107] The porosity test results of the rear angle material of the cockpit cover frame are shown in the following table.

[0108]

[0109] The present invention arranges air guide bundles when the composite materials are stacked, and uses auxiliary materials such as adhesive-free polytetrafluoroethylene cloth and adhesive-free glass fiber cloth during compaction and packaging, so that the composite material structure manufactured by non-autoclave molding under low pressure conditions effectively meets the product porosity requirements. Using a curing furnace for curing is more effective than the autoclave molding process, which effectively reduces equipment costs and energy and power costs.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for forming a composite material structure with low porosity without autoclave, characterized in that: The following steps are involved: Step 1: Preparation of molding mold; Step 2: Preparation of auxiliary materials; Step 3: Cutting composite materials; Step 4: Non-autoclave composite lay-up; Step 5: Encapsulate the composite material after stacking; Step 6: Perform vacuum testing on the packaged composite material; Step 7: Curing the composite material.

2. The low-porosity non-autoclave molding method for composite material structure according to claim 1, characterized in that: Step 1: Preparation of the molding mold: After cleaning the surface of the molding mold, apply a release agent, the type of release agent is FREKOTE44NC; when a new or repaired molding mold is used for the first time, use a brush or soft cloth dipped in the release agent, and apply 3 thin layers of FREKOTE crosswise; when using the release agent on a molding mold that has been used with the release agent again, do not apply too much release agent; The specific process of coating the release agent on the surface of the molding mold is as follows: 1) Check the area where the tape is used to isolate the putty strips to prevent the release agent from contaminating the bagging area; 2) On the mold surface, use a brush or soft cloth to dip the release agent and apply a thin cross-coat; 3) After each layer of release agent is applied, dry it at 25°C for 15 minutes; 4) After the release agent is dry, proceed with the composite material laying operation.

3. The low-porosity non-autoclave molding method for composite material structure according to claim 2, characterized in that: The auxiliary materials in step 2 include isolation film, high temperature resistant tape, non-adhesive polytetrafluoroethylene cloth, non-adhesive glass fiber cloth, vacuum bag, and sealing strip; ensure that the brand and quantity of the above auxiliary materials meet the manufacturing requirements; step 3 composite material unloading specifically includes: after the composite material is thawed in the clean room, unloading is completed according to the composite material structure layer and size, and information marking is done; The thawing time of the composite material varies with the total thickness of the composite material, and the thawing time is at least 6 hours.

4. The low-porosity non-autoclave molding method for composite material structure according to claim 3, characterized in that: Step 4: Non-autoclave composite material layup specifically includes the following steps: Step 4.1 Place the molding mold in a clean room with a temperature of 18°C ​​to 26°C and a relative humidity of 15% to 65%; Step 4.2: laying a first layer of composite material on the surface of the forming mold, and using a scraper to comb along the parallel direction of the composite material fibers or the warp direction of the fabric; Step 4.3: arranging air-conducting fiber bundles between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material; After laying the first layer of composite material on the surface of the forming mold, an air-conducting fiber bundle is arranged between the composite material and the forming mold; then, after laying 1 to 3 layers of composite material, an air-conducting fiber bundle is arranged between two adjacent layers of composite material; and an air-conducting fiber bundle is arranged between the sandwich material and its lower and upper layers of composite material. Step 4.4 After the air-conducting fiber bundle is arranged between the first layer of composite material and the forming mold, vacuum compaction is performed; after each subsequent 1 to 3 layers of composite material are laid and the air-conducting fiber bundle is arranged, vacuum compaction is performed; after the lower and upper layers of the sandwich material are laid and the air-conducting fiber bundle is arranged, vacuum compaction is performed.

5. The low-porosity non-autoclave molding method for composite material structure according to claim 4, characterized in that: When laying composite materials, the laying direction is based on the product design requirements or the coordinate system on the molding die. The tolerance of the fabric laying direction is ±5°. The process should be strictly controlled according to the linear dimension of ±1°. The tolerance of the laying boundary position is: ±3mm. The laying process must strictly prevent the inclusion of foreign matter.

6. The low-porosity non-autoclave molding method for composite material structure according to claim 5, characterized in that: In step 4.3, the air-conducting fiber bundle is made of dry glass fiber material, and the width of each fiber bundle is 5mm to 10mm. When arranging the air-conducting fiber bundle between the composite material and the molding mold, between the composite material and the composite material, and between the composite material and the sandwich material, one end of the air-conducting fiber bundle should be placed outside the edge line of the composite material structure product, and the connection length with the composite material should be not less than 20mm; the length of the air-conducting fiber bundle meets the requirements that the other end can be connected to the adhesive-free glass cloth during subsequent vacuum compaction and can be connected to the breathable felt during packaging; each adjacent two air-conducting fiber bundles in the same layer are arranged along the edge of the composite material at an interval of 250mm.

7. The low-porosity non-autoclave molding method for composite material structure according to claim 6, characterized in that: Step 4.4 vacuum compaction is as follows: lay glue-free polytetrafluoroethylene cloth on the surface of the last laid composite material, the outer edge size D2 of the glue-free polytetrafluoroethylene cloth is larger than the outer edge size D1 of the composite material layer, and D2-D1≥10mm is satisfied; lay glue-free glass fiber cloth on the surface of the glue-free polytetrafluoroethylene cloth, the outer edge size D3>D2 of the glue-free glass fiber cloth, and no bridging is generated during vacuuming; the glass fiber cloth is sealed with high-temperature resistant tape on all sides to ensure that the fibers do not fall off; connect the air-guiding fiber bundles arranged between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material with the glass fiber cloth, place a vacuum nozzle on the glass fiber cloth, and lay a vacuum bag on the glass fiber cloth; lay a sealing strip around the molding mold outside the composite material to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum compaction, the vacuum degree is not less than 0.09MPa, the time is at least 15min, and then the vacuum nozzle is removed, and the vacuum bag, glue-free polytetrafluoroethylene cloth, and glue-free glass fiber cloth are removed.

8. The low-porosity non-autoclave molding method for composite material structure according to claim 7, characterized in that: Step 5: Encapsulate the composite material after stacking, specifically: A non-porous isolation film is laid on the surface of the stacked composite material, and the outer edge dimension D4 of the isolation film is larger than the outer edge dimension D1 of the composite layer, and D4-D1≥10mm is satisfied; a breathable felt is laid on the isolation film, and the breathable felt is connected to the air-guiding fiber bundles arranged between the composite material and the molding mold, between the composite materials and the composite materials, and between the composite materials and the sandwich material; the outer edge dimension D5 of the breathable felt is greater than D4, and it is satisfied that no bridging is generated during vacuuming; a vacuum nozzle is placed on the breathable felt, and a vacuum bag is laid on the breathable felt; a sealing strip is laid around the molding mold outside the composite layer to ensure that the sealing strip is tightly connected to the vacuum bag; vacuum is drawn, and the vacuum degree is ≥0.090MPa.

9. The low-porosity non-autoclave molding method for composite material structure according to claim 8, characterized in that: In step 6, when the vacuum degree in the vacuum bag reaches 0.09 MPa until the vacuum degree stabilizes, the vacuum source is disconnected or turned off after 15 minutes, and the vacuum gauge reading drops by no more than 0.017 MPa within 5 minutes; In step 7, the encapsulated molding mold is operated into the curing equipment, and the curing parameters are: the vacuum degree in the vacuum bag is not less than -0.090MPa, the room temperature is heated to 82℃±10℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 30min-60min, and the temperature is further heated to 127℃±2℃, the heating rate is 0.5~3℃ / min, and the temperature is kept for 120min; the temperature is reduced to below 60℃ at a cooling rate of ≤5℃ / min, and the product is taken out of the curing equipment; during the entire curing cycle, the pressure in the vacuum bag should be maintained at not less than -0.090MPa.

10. The low-porosity non-autoclave molding method for composite material structure according to claim 9, characterized in that: The method further comprises: Step 8: Remove the vacuum nozzle on the breathable felt, remove the vacuum bag, breathable felt and non-porous isolation film; use non-metallic tools to demould and open the mold, and clean the excess materials on the surface of the molding mold; Step 9: Check whether the formed composite material has any damage or excess; Step 10: If there are delamination defects in the composite material after molding, use high temperature resistant paste glue and repair it according to the following scheme: 10.1 Drill a φ2.1mm hole at the upper and lower edges of the defect; 10.2 Inject glue into the defect from the lower hole until the glue overflows from the upper hole; 10.3 Seal the two holes with tape; 10.4 After the injected glue solidifies, remove the tape and grind it smooth.

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