A forming method for the tail cone of a polyimide composite material

Abstract

The present invention discloses a forming method for a polyimide composite material tail cone cover in the technical field of composite products, comprising the following steps: Step 1) Design a mold. Design the mold according to the molding process. The mold includes an outer mold unit for laying as a female mold, and an inner mold unit for molding as a male mold is arranged inside the outer mold unit. The outer mold unit and the inner mold unit are arranged in a mold frame, and a bottom plate and a top plate are respectively arranged at the bottom and the top of the mold frame. A mold cavity is formed among the mold frame, the bottom plate and the top plate. The outer mold unit includes a plurality of laying surface inserts, and the inner mold unit includes a plurality of molding surface inserts; Step 2) Prepare prepreg, Step 3) Cut prepreg, Step 4) Prepare the mold, Step 5) Lay prepreg, Step 6) Pre-remove solvent, Step 7) Cold press and pre-press, Step 8) Cure, Step 9) Demold. The present invention solves the problem of the forming quality inside the tail cone cover and meets the use requirements of the aircraft.

Description

Technical Field

[0001] The present invention relates to the technical field of composite products, and particularly relates to a forming method for a composite aircraft tail fairing. Background Art

[0002] The aircraft tail fairing is located at the tail of the fuselage and is generally composed of high-temperature resistant material parts to ensure the smooth discharge of the high-temperature gas ejected from the engine during the working state of the aircraft. In addition to the function of streamline rectification, it also has the function of ejecting the tail nozzle airflow to increase the thrust. Due to being in the high-temperature area and at the tail, the tail fairing is usually prone to damage. For some aircraft, due to the particularity of their fuselage structure, the tail fairing is located in the wing-body fusion area and needs to have the maneuverability and stealth performance of the aircraft. At present, the tail fairing structures of aircraft at home and abroad are all metal structures, and most of them are aluminum alloy thin-wall riveted structures. Considering the weight reduction requirements of the aircraft, using advanced composite materials in aerospace structures can reduce the weight by more than 20% - 30%, which is an effect that cannot be achieved by other advanced technologies. At the same time, in order to adapt to the high-temperature use environment of the tail fairing, ordinary epoxy or bismaleimide resin-based composite materials cannot meet the high-temperature use conditions of the tail fairing. Polyimide resin has excellent heat resistance, thermal oxidation resistance, mechanical properties, dielectric properties and good solvent resistance, and has gradually become the main matrix resin for high-temperature resistant composite materials. Therefore, polyimide resin-based composite materials are selected to prepare the aircraft tail fairing. Due to its high molding temperature, molding pressure and the operability of prepreg raw materials, etc., the molding process of polyimide composite materials is difficult, the manufacturing cost is high and there are generally over-standard defects. Thus, it can be seen that the heat resistance, molding process and high molding quality of polyimide resin-based composite materials are mutually restrictive contradictions. Summary of the Invention

[0003] Aiming at the deficiencies existing in the prior art, the present invention provides a forming method for a polyimide composite aircraft tail fairing, which solves the problem of the internal molding quality of the tail fairing and meets the use requirements of the aircraft.

[0004] The object of the present invention is achieved as follows: A forming method for a polyimide composite aircraft tail fairing, the tail fairing includes a bottom edge, a first side edge and a second side edge are respectively provided on both sides of the bottom edge, and a third side edge is provided on the tail side of the bottom edge. The first side edge, the second side edge and the third side edge are all arc-shaped structures protruding inwards. The angles between the first side edge, the third side edge and the bottom edge are obtuse angles, and the angle between the second side edge and the bottom edge is an acute angle. The forming method includes the following steps:

[0005] Step 1) Design the mold. Design the mold according to the molding process. The mold includes an outer mold unit for laying the female mold, and an inner mold unit for male mold pressing is arranged inside the outer mold unit. The outer mold unit and the inner mold unit are arranged in a mold frame. A bottom plate and a top plate are respectively arranged at the bottom and top of the mold frame. A mold cavity is formed among the mold frame, the bottom plate and the top plate. The outer mold unit includes a plurality of laying surface inserts, and the inner mold unit includes a plurality of molding surface inserts.

[0006] Step 2) Production of prepreg. The reinforcing fiber is carbon fiber fabric, the resin is polyimide resin solution, and the solution solvent is DMAC. The specific production process is as follows: Weigh the resin solution according to the area of the dry cloth, and use a fine brush to evenly apply the resin solution on the carbon fiber fabric. After coating, put it into an oven for baking to volatilize most of the solvent, so that the final prepreg has lay-up tackiness.

[0007] Step 3) Cutting of prepreg. Cut the baked prepreg, use an automatic cutting machine for cutting. After the cutting of the material piece is completed, use a vacuum packaging machine to package it and put it into a cold storage for storage. Take out the material piece before use.

[0008] Step 4) Mold preparation. Clean the mold, then put the mold into an oven for baking. After baking, apply a high-temperature release agent, and then assemble the mold for standby.

[0009] Step 5) Laying of prepreg. Lay the prepreg on the surface of the outer mold unit and the surface of the bottom plate. The prepreg is laid in a butting form, and the laying process is carried out in cooperation with vacuum pumping.

[0010] Step 6) Pre-removal of solvent. Make a vacuum bag. The auxiliary material uses a medium-temperature system material. Lay a perforated separator film, a breather felt, a vacuum bag film, and putty strips on the prepreg surface in sequence from the inside to the outside, and then put it into an oven to remove the solvent.

[0011] Step 7) Cold pressing and pre-pressing. Put the molding surface inserts in sequence, and apply pressure with a press to carry out cold pressing and pre-closing of the mold.

[0012] Step 8) Curing. Use a vacuum press, evacuate the whole process, and carry out alternating operations of heating, heat preservation, and pressurization according to the preset parameters.

[0013] Step 9) Demolding. Remove the top plate, the inner mold unit, and the bottom plate in sequence, take out the outer mold unit, and remove the tail cover from the outer mold unit to complete the demolding.

[0014] As a preferred technical solution of the forming method of a polyimide composite tail cover described in the present invention, in step 1), the outer mold unit includes three laying surface inserts corresponding to the first side, the second side, and the third side. The inner mold unit includes a first molding surface insert, a second molding surface insert, a third molding surface insert, a fourth molding surface insert, a first driving insert, and a second driving insert.

[0015] The molded side of the first molded surface insert acts on the first side edge and the bottom edge of the tail cone cover, and the driving side of the first molded surface insert is wedge-fitted with the driving side of the first driving insert;

[0016] The molded side of the second molded surface insert acts on the second side edge and the bottom edge of the tail cone cover, and the driving side of the second molded surface insert is wedge-fitted with the driving side of the first driving insert;

[0017] The molded side of the third molded surface insert acts on the second side edge and the bottom edge of the tail cone cover, and the driving side of the third molded surface insert is wedge-fitted with the driving side of the second driving insert;

[0018] The molded side of the fourth molded surface insert acts on the first side edge and the bottom edge of the tail cone cover, and the driving side of the fourth molded surface insert is wedge-fitted with the driving side of the second driving insert;

[0019] The rear sides of the third molded surface insert, the fourth molded surface insert, and the second driving insert act on the third side edge of the tail cone cover;

[0020] The inner end faces of the first driving insert and the second driving insert are wedge-fitted;

[0021] The top plate drives the first driving insert to move downward, the first driving insert drives the second driving insert to move downward, and together with the second driving insert, they jointly push the first molded surface insert, the second molded surface insert, the third molded surface insert, and the fourth molded surface insert to move to both sides, thereby applying corresponding pressures to each part of the tail cone cover.

[0022] As a preferred technical solution of the molding method of the polyimide composite material tail cone cover of the present invention, in step 2), the reinforcing fiber is a T700 grade carbon fiber fabric, the fiber surface density is 200 ± 10 g, the resin is a polyimide resin solution with a solid content of 30 - 40%, and the solution solvent is DMAC. The specific production process is as follows: prepare a prepreg according to a resin content of 40 ± 5%. Weigh a certain weight of the resin solution according to the area of the dry cloth, and use a fine brush to evenly apply the resin solution on the carbon fiber fabric. The resin should be applied in small amounts quickly, and the resin should not be poured on the fabric in large amounts for brushing. After the prepreg is brushed, it needs to be baked in an oven at 100 °C for 30 min to volatilize most of the solvent, so that the final prepreg has lay-up tackiness.

[0023] As a preferred technical solution of the molding method of the polyimide composite material tail cone cover of the present invention, in step 4), the mold is placed in an oven and baked to 150 ± 5 °C, kept warm for 10 ± 1 min, and then coated with a high-temperature release agent multiple times, with an interval of more than 15 min each time.

[0024] As a preferred technical solution of the forming method of the polyimide composite material tail cone cover described in the present invention, the prepreg laying in step 5) specifically includes: The prepreg is laid in a butting form, and lapping is strictly prohibited. After the first layer is laid, it is pre-evacuated for more than 15 minutes, and then evacuated and compacted for more than 15 minutes every two layers.

[0025] As a preferred technical solution of the forming method of the polyimide composite material tail cone cover described in the present invention, the oven parameters in step 6) are: first at 200 ± 10 °C for 2 ± 0.1 h, then at 240 ± 10 °C for 2 ± 0.1 h.

[0026] As a preferred technical solution of the forming method of the polyimide composite material tail cone cover described in the present invention, during the pre-clamping in step 7), observe the die clamping gap of the mold and conduct inspections. It is required that the die clamping gap does not exceed the set value. If the die clamping gap exceeds, it is necessary to check whether there is any abnormality in the assembly of the core block, re-assemble and then clamp the mold again until the die clamping gap meets the requirements. After pre-clamping, use bolts to tighten the connecting bolts of the top plate and the mold frame again, and release the pressure of the press.

[0027] As a preferred technical solution of the forming method of the polyimide composite material tail cone cover described in the present invention, step 8) specifically includes: The mold is placed in the center of the vacuum press. Start the vacuum press so that the upper surface of the vacuum press fits with the mold without applying pressure. Start vacuum pumping, heat up to 240 °C and keep it warm for 2 h, heat up to 330 °C and apply a pressure of 10 MPa, with a pressure application time of 10 minutes. After pressure application, the temperature is raised to 340 °C. After pressure application is completed, the temperature is raised to 370 °C and kept warm for 2 h. After heating up to 380 °C and keeping it warm for 2 h, turn off the heating and break the vacuum, cool down to below 150 °C and release the pressure. The operating temperature is based on the thermocouple connected to the mold. There are temperature measurement holes on the mold, and the heating and cooling rate is 1 °C / min.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses a vacuum molding process to manufacture typical structural parts of polyimide composite material tail cone covers, meeting the weight reduction requirements of the aircraft, and can effectively solve the molding quality inside the product; reduce the internal delamination defects and porosity of the product, improve the qualified rate and economic benefits of the product, and the forming method is simple and highly feasible. Using a special mold can ensure the strength of each part of the integrally molded tail cone cover. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0030] Figure 1Stereoscopic structure view of the tail cover obtained by the present invention.

[0031] Figure 2 Side view of the tail cover obtained by the present invention Figure 1 .

[0032] Figure 3 Side view of the tail cover obtained by the present invention Figure 2 .

[0033] Figure 4 Side view of the tail cover obtained by the present invention Figure 3 .

[0034] Figure 5 Schematic diagram of the three-dimensional structure of the mold in the present invention.

[0035] Figure 6 Schematic diagram of the internal structure of the mold in the present invention.

[0036] Figure 7 Top view of the interior of the mold in the present invention.

[0037] Figure 8 Is along Figure 7 A - A cross-sectional view in.

[0038] Figure 9 Is along Figure 7 B - B cross-sectional view in.

[0039] Figure 10 Is along Figure 7 C - C cross-sectional view in.

[0040] Among them, 100 is the tail cover, 101 is the bottom edge, 102 is the first side edge, 103 is the second side edge, 104 is the third side edge, 200 is the mold, 201 is the bottom plate, 202 is the mold frame, 203 is the top plate, 204 is the outer mold unit, 204a is the first laying surface insert, 204b is the second laying surface insert, 204c is the third laying surface insert, 205 is the inner mold unit, 205a is the first molding surface insert, 205b is the second molding surface insert, 205c is the third molding surface insert, 205d is the fourth molding surface insert, 205e is the first driving insert, and 205f is the second driving insert. Specific embodiments

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] A molding method for a polyimide composite tail cover, asFigures 1-4 As shown in the figure, the tail cover 100 includes a bottom edge 101. On both sides of the bottom edge 101, there are respectively a first side edge 102 and a second side edge 103. On the tail side of the bottom edge 101, there is a third side edge 104. The first side edge 102, the second side edge 103, and the third side edge 104 are all arc-shaped structures protruding inward. The angles between the first side edge 102, the third side edge 104 and the bottom edge 101 are obtuse angles, and the angle between the second side edge 103 and the bottom edge 101 is an acute angle. The forming method includes the following steps:

[0043] Step 1) Design the mold 200. Design the mold 200 according to the molding process, such as Figures 2-10 As shown in the figure, the mold 200 includes an outer mold unit 204 for laying the female mold. Inside the outer mold unit 204, there is an inner mold unit 205 for male mold pressing. The outer mold unit 204 and the inner mold unit 205 are arranged inside the mold frame 202. The inner surface of the mold frame 202 is a setting plane. The bottom and top of the mold frame 202 are respectively provided with a bottom plate 201 and a top plate 203. A mold cavity is formed between the mold frame 202, the bottom plate 201, and the top plate 203. The outer mold unit 204 includes a plurality of laying surface inserts, and the inner mold unit 205 includes a plurality of pressing surface inserts;

[0044] The outer mold unit 204 includes a first laying surface insert 204a, a second laying surface insert 204b, and a third laying surface insert 204c corresponding to the first side edge 102, the second side edge 103, and the third side edge 104. The inner side surfaces of the first laying surface insert 204a, the second laying surface insert 204b, and the third laying surface insert 204c are respectively used as the laying surfaces of the first side edge 102, the second side edge 103, and the third side edge 104. The bottom plate 201 is provided with a laying surface for the bottom edge 101;

[0045] The inner mold unit 205 includes a first pressing surface insert 205a, a second pressing surface insert 205b, a third pressing surface insert 205c, a fourth pressing surface insert 205d, a first driving insert 205e, and a second driving insert 205f. The first pressing surface insert 205a and the fourth pressing surface insert 205d cooperate with the first laying surface insert 204a and the third laying surface insert 204c, and the second pressing surface insert 205b and the third pressing surface insert 205c cooperate with the second laying surface insert 204b and the third laying surface insert 204c;

[0046] The pressing side surface of the first pressing surface insert 205a acts on the first side edge 102 and the bottom edge 101 of the tail cover 100. The driving side surface of the first pressing surface insert 205a is wedge-shaped and fitted with the driving side surface of the first driving insert 205e;

[0047] The molded side of the second molded surface insert 205b acts on the second side 103 and the bottom side 101 of the tail cone 100, and the driving side of the second molded surface insert 205b is wedge-fitted with the driving side of the first driving insert 205e;

[0048] The molded side of the third molded surface insert 205c acts on the second side 103 and the bottom side 101 of the tail cone 100, and the driving side of the third molded surface insert 205c is wedge-fitted with the driving side of the second driving insert 205f;

[0049] The molded side of the fourth molded surface insert 205d acts on the first side 102 and the bottom side 101 of the tail cone 100, and the driving side of the fourth molded surface insert 205d is wedge-fitted with the driving side of the second driving insert 205f;

[0050] The rear sides of the third molded surface insert 205c, the fourth molded surface insert 205d, and the second driving insert 205f act on the third side 104 of the tail cone 100;

[0051] The inner end faces of the first driving insert 205e and the second driving insert 205f are wedge-fitted;

[0052] The top plate 203 drives the first driving insert 205e to move downward, the first driving insert 205e drives the second driving insert 205f to move downward, and together with the second driving insert 205f, they jointly push the first molded surface insert 205a, the second molded surface insert 205b, the third molded surface insert 205c, and the fourth molded surface insert 205d to move to both sides, thereby applying corresponding pressures to various parts of the tail cone 100.

[0053] Step 2) Preparation of prepreg. The reinforcing fiber is T700 grade carbon fiber fabric with a fiber areal density of 200 ± 10 g, the resin is a polyimide resin solution with a solid content of 30 - 40%, and the solution solvent is DMAC. The specific production process is as follows: Prepare the prepreg according to a resin content of 40 ± 5%. Weigh a certain weight of the resin solution according to the area of the dry cloth, and use a fine brush to evenly apply the resin solution on the carbon fiber fabric. When brushing the resin, apply it in small amounts quickly and do not pour a large amount of resin on the fabric for brushing. After the prepreg is brushed, it needs to be baked in an oven at 100 °C for 30 min to volatilize most of the solvent, so that the final prepreg has lay-up tackiness;

[0054] Step 3) Cutting of prepreg. The baked prepreg is cut, and an automatic cutting machine is used for cutting. After the material pieces are cut, they are packaged with a vacuum packaging machine and stored in a cold storage. The material pieces are taken out before use;

[0055] Step 4) Preparation of mold 200: Clean the mold 200, then place the mold 200 in an oven for baking until it reaches 150 ± 5 °C and keep it warm for 10 ± 1 min. After baking, apply a high-temperature release agent three times, with an interval of more than 15 min each time;

[0056] Step 5) Laying of prepreg: Lay the prepreg on the surface of the outer mold unit 204 and the surface of the bottom plate 201. The prepreg is laid in a butt joint form, and lapping is strictly prohibited. After the first layer is laid, pre-evacuate for more than 15 min, and then evacuate and compact for more than 15 min every two layers;

[0057] Step 6) Pre-removal of solvent: Make a vacuum bag. The auxiliary materials use medium-temperature system materials, which are, from the inside out, perforated separator film → breather felt → vacuum bag film → putty strip. The vacuum nozzles are placed on the bottom plate 201, with a total of two nozzles. Put it into the oven to remove the solvent, and perform two evacuations throughout the process. The oven parameters are 200 °C for 2 h + 240 °C for 2 h. It is required that the mold 200 is connected with a thermocouple, and the temperature measured by the thermocouple shall prevail. This part of the process measures can remove more than 95% of the solvent contained in the product;

[0058] Step 7) Cold pressing and pre-pressing: Place the die assembly core blocks in sequence, apply a pressure of 10 MPa on the press for cold pressing and pre-closing the mold. Observe the mold closing gap of the mold 200 and use a feeler gauge for inspection. It is required that the mold closing gap shall not exceed 0.05 mm; if the mold closing gap exceeds, it is necessary to check whether there is any abnormality in the assembly of the core block, re-assemble and close the mold again until the mold closing gap meets the requirements; after pre-closing the mold, use bolts to tighten the connecting bolts of the top plate 203 and the mold frame 202 again, release the pressure of the press, and proceed with the curing procedure;

[0059] Step 8) Curing: The curing requires the use of a vacuum press, evacuating throughout the process to reduce the porosity of the product. The mold 200 is placed in the center of the press. Close the tank door and start the press to make the upper table surface of the press fit with the mold 200 (without applying pressure). Start evacuating, heat up to 240 °C and keep it warm for 2 h, heat up to 330 °C and apply a pressure of 10 MPa (the pressurizing time is about 10 min, and the temperature for applying the pressure is about 340 °C). After pressurizing, heat up to 370 °C and keep it warm for 2 h, heat up to 380 °C and keep it warm for 2 h, then turn off the heating and break the vacuum. Release the pressure after cooling to below 150 °C. The operating temperature is based on the temperature measured by the thermocouple connected to the mold 200. There are temperature measurement holes on the mold 200, and the heating and cooling rate is controlled at 1 °C / min;

[0060] Step 9) Demolding. The demolding sequence is to remove the 4 bolts connecting the top plate 203 and the mold frame 202, use the jacking screw holes on the top plate 203 to jack out the top plate 203 and the first driving insert 205e together, and sequentially remove the second driving insert 205f, the first molded surface insert 205a, the second molded surface insert 205b, the fourth molded surface insert 205d, and the third molded surface insert 205c in order. The second driving insert 205f is lifted out by using a bolt. For the second molded surface insert 205b, the fourth molded surface insert 205d, and the third molded surface insert 205c, see the Figure 7 arrow direction. Remove the 4 bolts connecting the mold frame 202 and the bottom plate 201, use the jacking screw holes on the bottom plate 201 to jack out the mold frame 202 and the mold 200 for demolding. Remove the 6 bolts connecting the third laying surface insert 204c, the second laying surface insert 204b, the first laying surface insert 204a, and the bottom plate 201, and take out the second laying surface insert 204b, the first laying surface insert 204a, and the third laying surface insert 204c from around the part, so as to take out the test piece and complete the demolding.

[0061] It should be noted that the difficulty in changing the metal tail cover 100 to be made of composite materials lies in:

[0062] Since the structure of the common tail cover 100 is relatively complex, including a bottom edge 101, a first side edge 102 and a second side edge 103 are respectively provided on both sides of the bottom edge 101, a third side edge 104 is provided on the tail side of the bottom edge 101, and the first side edge 102, the second side edge 103, and the third side edge 104 are all arc-shaped structures protruding inward. The included angles between the first side edge 102, the third side edge 104 and the bottom edge 101 are obtuse angles, and the included angle between the second side edge 103 and the bottom edge 101 is an acute angle;

[0063] The forming process methods of polyimide composite materials include vacuum bag autoclave forming process, high-temperature RTM process and compression molding process. Due to the poor processability of auxiliary materials such as high-temperature vacuum bags and sealing rubber strips in the vacuum bag autoclave process, it is easy to leak vacuum during the high-temperature curing process of the product and it is difficult to effectively compact, resulting in poor internal quality of the product; in the high-temperature RTM process and compression molding process, it is difficult to effectively remove the bubbles generated during the curing process of the product, resulting in a high porosity of the product; aiming at the disadvantages of the above forming processes, the present invention uses a vacuum compression molding process to manufacture typical structural parts of the polyimide tail cover 100 to solve the forming quality problem inside the product and meet the use requirements of the aircraft.

[0064] The core inventive point is: if ensuring that the first side edge 102, the second side edge 103, the third side edge 104 and the bottom edge 101 are simultaneously compression molded, they can be simultaneously stressed during the compression molding process, and it is also convenient to demold after curing without affecting the surface of the tail cover 100.

[0065] The present invention adopts an inner die unit 205 with a specific structure and an outer die unit 204 to cooperate with a die frame 202, a top plate 203, and a bottom plate 201 to achieve the above requirements. The molding process is as follows: control the top plate 203 to press down. The top plate 203 and the first driving insert 205e are structured. The fitting relationship between the first driving insert 205e and the second driving insert 205f causes the two to press down simultaneously. The wedge-shaped fitting relationship of the molding sides on both sides of the first driving insert 205e and the second driving insert 205f drives the first molding surface insert 205a, the second molding surface insert 205b, the third molding surface insert 205c, and the fourth molding surface insert 205d to move to both sides, pressing the first side 102, the second side 103, and the third side 104 tightly, and finally feeding them into the press to achieve integral molding. In addition, the demolding of this structure is also relatively convenient.

[0066] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A forming method of a polyimide composite material tail cone cover, the tail cone cover (100) includes a bottom edge (101), a first side edge (102) and a second side edge (103) are respectively arranged on both sides of the bottom edge (101), a third side edge (104) is arranged on the tail side of the bottom edge (101), the first side edge (102), the second side edge (103) and the third side edge (104) are all arc-shaped structures protruding inwards, the included angles between the first side edge (102), the third side edge (104) and the bottom edge (101) are obtuse angles, and the included angle between the second side edge (103) and the bottom edge (101) is an acute angle, characterized in that, The forming method includes the following steps: Step 1) Design a mold (200). Design the mold (200) according to the molding process. The mold (200) includes an outer mold unit (204) for laying the female mold. An inner mold unit (205) for male mold pressing is provided inside the outer mold unit (204). The outer mold unit (204) and the inner mold unit (205) are arranged inside a mold frame (202). A bottom plate (201) and a top plate (203) are respectively provided at the bottom and top of the mold frame (202). A mold cavity is formed among the mold frame (202), the bottom plate (201), and the top plate (203). The outer mold unit (204) includes a plurality of laying surface inserts, and the inner mold unit (205) includes a plurality of pressing surface inserts. The outer mold unit (204) includes three laying surface inserts corresponding to the first side (102), the second side (103), and the third side (104). The inner mold unit (205) includes a first pressing surface insert (205a), a second pressing surface insert (205b), a third pressing surface insert (205c), a fourth pressing surface insert (205d), a first driving insert (205e), and a second driving insert (205f); The pressing side of the first pressing surface insert (205a) acts on the first side (102) and the bottom side (101) of the tail cover (100). The driving side of the first pressing surface insert (205a) is wedge-fitted with the driving side of the first driving insert (205e); The pressing side of the second pressing surface insert (205b) acts on the second side (103) and the bottom side (101) of the tail cover (100). The driving side of the second pressing surface insert (205b) is wedge-fitted with the driving side of the first driving insert (205e); The pressing side of the third pressing surface insert (205c) acts on the second side (103) and the bottom side (101) of the tail cover (100). The driving side of the third pressing surface insert (205c) is wedge-fitted with the driving side of the second driving insert (205f); The pressing side of the fourth pressing surface insert (205d) acts on the first side (102) and the bottom side (101) of the tail cover (100). The driving side of the fourth pressing surface insert (205d) is wedge-fitted with the driving side of the second driving insert (205f); The rear sides of the third pressing surface insert (205c), the fourth pressing surface insert (205d), and the second driving insert (205f) act on the third side (104) of the tail cover (100); The inner end faces of the first driving insert (205e) and the second driving insert (205f) are wedge-fitted; The top plate (203) drives the first driving insert (205e) to move downward, the first driving insert (205e) drives the second driving insert (205f) to move downward, and together with the second driving insert (205f), they jointly push the first die pressing surface insert (205a), the second die pressing surface insert (205b), the third die pressing surface insert (205c), and the fourth die pressing surface insert (205d) to move toward both sides, thereby applying corresponding pressures to various parts of the tail cover (100); Step 2) Production of prepreg. The reinforcing fiber is carbon fiber fabric, the resin is polyimide resin solution, and the solution solvent is DMAC. The specific production process is as follows: Weigh the resin solution according to the area of the dry cloth, use a fine brush to evenly apply the resin solution on the carbon fiber fabric, and after coating, put it into an oven for baking to volatilize most of the solvent, so that the final prepreg has lay-up tackiness; Step 3) Cutting of prepreg. The baked prepreg is cut. Use an automatic cutting machine for cutting. After the sheet is cut, use a vacuum packaging machine to package it and store it in a cold storage. Take out the sheet before use; Step 4) Preparation of the mold (200). Clean the mold (200), then put the mold (200) into an oven for baking. After baking, apply a high-temperature release agent, and then assemble the mold (200) for standby; Step 5) Laying of prepreg. Lay the prepreg on the surface of the outer mold unit (204) and the surface of the bottom plate (201). The prepreg is laid in a butted form, and the laying process is carried out in cooperation with vacuum pumping; Step 6) Removal of solvent. Make a vacuum bag. The auxiliary materials are medium-temperature system materials. From the inside to the outside, place a perforated separator film, a breather felt, a vacuum bag film, and putty strips on the surface of the prepreg in sequence, and then put it into an oven to remove the solvent; Step 7) Cold pressing and pre-pressing. Put the die pressing surface inserts in sequence, and apply pressure with a press for cold pressing and pre-closing the mold; Step 8) Curing. Use a vacuum press, evacuate the air throughout the process, and perform alternating operations of heating, heat preservation, and pressurization according to the preset parameters; Step 9) Demolding. Remove the top plate (203), the inner mold unit (205), and the bottom plate (201) in sequence, take out the outer mold unit (204), and remove the tail cover (100) from the outer mold unit (204) to complete demolding.

2. The forming method of a polyimide composite material tail cone according to claim 1, characterized in that In step 2), the reinforcing fiber is T700 grade carbon fiber fabric, the fiber surface density is 200±10 g, the resin is polyimide resin solution with a solid content of 30 - 40%, and the solution solvent is DMAC. The specific production process is as follows: Produce the prepreg according to a resin content of 40±5%. Weigh a certain weight of resin solution according to the area of the dry cloth, use a fine brush to evenly apply the resin solution on the carbon fiber fabric. When brushing the resin, do it in small amounts and quickly, and do not pour a large amount of resin on the fabric for brushing. After the prepreg is brushed, it needs to be put into an oven and baked at 100℃ for 30 min to volatilize most of the solvent, so that the final prepreg has lay-up tackiness.

3. A forming method of a polyimide composite material tail cone cover according to claim 1, characterized in that In step 4), the mold (200) is put into an oven and baked to 150±5℃, kept warm for 10±1 min, and then apply a high-temperature release agent multiple times, with an interval of more than 15 min each time.

4. The forming method of a polyimide composite material tail cone according to claim 1, characterized in that, Step 5) The prepreg laying specifically includes: The prepreg is laid in a butting form, and lapping is strictly prohibited. After the first layer is laid, it is pre-evacuated for more than 15 minutes, and then evacuated and compacted for more than 15 minutes every 2 layers hereafter.

5. A method for forming a polyimide composite material tail cone, according to claim 1, characterized in that, In Step 6), the oven parameters are: first at 200 ± 10 °C for 2 ± 0.1 h, then at 240 ± 10 °C for 2 ± 0.1 h.

6. The forming method of a polyimide composite material tail cone according to claim 1, characterized in that, In Step 7), when pre-closing the mold, observe the closing gap of the mold (200) and conduct an inspection. It is required that the closing gap does not exceed the set value. If the closing gap exceeds, it is necessary to check whether there is any abnormality in the assembly of the inserts, reassemble and close the mold again until the closing gap meets the requirements. After pre-closing the mold, use bolts to tighten the connection bolts of the top plate (203) and the mold frame (202) again, and release the pressure of the press.

7. A forming method of a polyimide composite tail cone, according to claim 1, characterized in that, Step 8) specifically includes: The mold (200) is placed in the center of the vacuum press. Start the vacuum press to make the upper table surface of the vacuum press fit with the mold (200) without applying pressure. Start vacuum pumping, heat up to 240 °C and keep it warm for 2 h, heat up to 330 °C and apply a pressure of 10 MPa, the pressurizing time is 10 min. After pressurizing, heat up to 340 °C. After pressurizing is completed, heat up to 370 °C and keep it warm for 2 h, heat up to 380 °C and keep it warm for 2 h, then turn off the heating and break the vacuum, cool down to below 150 °C and release the pressure. The operating temperature is based on the thermocouple connected to the mold (200). There are temperature measurement holes on the mold (200), and the heating and cooling rate is 1 °C / min.

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