A step-molding method for a high-temperature-resistant polyimide composite member

Abstract

The application discloses a kind of high-temperature-resistant polyimide composite component step-by-step forming method, comprising the following steps: step one: high-temperature-resistant polyimide prepreg is laminated into component shape on hot press forming tool;Step two: auxiliary material is laid on the high-temperature-resistant polyimide prepreg of lamination, sealed using vacuum bag, vacuumizing;Step three: the prepreg packaged in step two is placed in hot press tank, and hot pressing is carried out according to the set hot pressing condition, to obtain a preform;Step four: the preform obtained in step three is placed in mould pressing forming tool, and is placed in hot press, and is solidified according to the set mould pressing condition, to obtain a composite component.By using the two-step forming method of hot press tank water removal + hot press mould pressing, high-temperature-resistant auxiliary material and high-temperature hot press are not needed, the manufacturing cost is reduced, and the risk of pore, delamination and glue deficiency defects in the mould pressing process of product can be effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, and in particular to a stepwise molding method for high-temperature resistant polyimide composite material components. Background Technology

[0002] Polyimide resin maintains high physical and mechanical properties within a temperature range of -269 to 400℃, exhibiting excellent high-temperature resistance, as well as superior weather resistance, electrical insulation, abrasion resistance, and resistance to high-temperature radiation. It has multiple synthesis pathways and can be processed and molded using various methods. Therefore, it is widely used in high-tech fields such as aerospace, electrical engineering, machinery, chemical engineering, microelectronics, instrumentation, petrochemicals, and metrology, and has become an indispensable material in cutting-edge technologies such as rockets and aerospace worldwide. In the preparation of high-temperature resistant polyimide composite components, polyimide resin is mixed with carbon fiber composites. The resulting composite components possess excellent high specific strength, high specific modulus, designability, and fatigue resistance, and have been widely used in aerospace, automotive, and other fields.

[0003] High-temperature resistant polyimide composites require high molding temperatures, and traditional molding processes mainly include two methods: autoclave molding and compression molding. Autoclave molding, due to the high molding temperature of polyimide composites, requires all auxiliary materials to be high-temperature resistant, and the autoclave must be capable of temperatures exceeding 350℃, resulting in high material and process costs. Compression molding, on the other hand, generates significant moisture due to the dehydration and ring-closing reaction of polyimide resin precursors at around 200℃. This moisture is difficult to remove in time during the molding process, leading to internal quality problems such as porosity and delamination after curing. Furthermore, because polyimide resin has many components and complex reactions, with small molecules escaping at each step, timely and complete removal of these small molecules is crucial for ensuring the absence of defects in the molded part. Otherwise, trapped gas will cause porosity defects, affecting the mechanical properties of the composite material. Furthermore, the large amount of water vapor that cannot be discharged may lead to resin loss, resulting in surface quality problems such as insufficient resin on the surface.

[0004] Existing molding methods have high requirements for equipment and materials and are affected by many factors, which can easily lead to a high probability of defects in the molded parts, unstable quality, and low pass rate. Therefore, it is necessary to provide a new molding method for high-temperature resistant polyimide composite material components to reduce the manufacturing cost of composite material components and improve product quality and pass rate. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of high requirements for equipment and materials, many influencing factors, high probability of defects in composite material parts, unstable quality, and low pass rate in the existing technology, and to provide a step-by-step molding method for high-temperature resistant polyimide composite material components, and a preparation method suitable for high-temperature resistant polyimide composite material components.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] A stepwise molding method for high-temperature resistant polyimide composite material components includes the following steps:

[0008] Step 1: Lay out the component shape by stacking the high-temperature polyimide prepreg on a hot press molding fixture;

[0009] Step 2: Lay auxiliary materials on the laid-up high-temperature resistant polyimide prepreg, seal it with a vacuum bag, and then draw a vacuum.

[0010] Step 3: Place the polyimide prepreg that was encapsulated in Step 2 into an autoclave and hot press it according to the set hot pressing conditions to obtain the preform;

[0011] Step 4: Place the preform obtained in Step 3 into a molding fixture, put it into a hot press, and heat and pressurize it according to the set molding conditions to obtain a composite material component.

[0012] Furthermore, in step one, before laying the high-temperature polyimide prepreg, a release material is laid on the forming surface of the hot pressing tooling.

[0013] Furthermore, the forming surface of the hot press forming tool is chrome-plated to prevent the preform from sticking to the hot press forming tool, which is beneficial for the demolding of the preform after hot press forming.

[0014] Furthermore, the auxiliary materials include a first breathable material, a second breathable material, a pressure equalizing plate, a third breathable material, and a sealing strip. The first breathable material, the second breathable material, the pressure equalizing plate, and the second breathable material are arranged sequentially from bottom to top on the laid high-temperature resistant polyimide prepreg, and the sealing strip is arranged at the edge of the polyimide prepreg. The first breathable material is used for air and adhesive permeability. It is laid on the polyimide prepreg to reduce resin loss. The second breathable material is used for air permeability but not adhesive permeability, excluding water vapor generated during hot pressing and preventing resin overflow, thus completely sealing the resin. The sealing strip is set at the edge of the polyimide prepreg and seals the area around the prepreg by bonding it with the second breathable material, preventing resin leakage and ensuring the thickness of the preform. The pressure equalization plate is used to ensure uniform pressure. The pressure equalization plate has holes to ensure that gas can be fully discharged. The third breathable material separates the vacuum bag and the pressure equalization plate. When the vacuum bag is truly evacuated, it forms a gas outflow channel, allowing the gas in the vacuum bag or water vapor generated during hot pressing to flow out to the vacuum port of the vacuum bag, which is beneficial for the discharge of gas and water vapor.

[0015] Furthermore, the edge of the first breathable material is flush with the edge of the laid polyimide prepreg, and the edge of the second breathable material is 5-20 mm longer than the edge of the laid polyimide prepreg. The third breathable material completely covers the laid polyimide prepreg and is 20-100 mm larger on each side than the laid polyimide prepreg.

[0016] Furthermore, a sealing strip is provided at the outlet of the vacuum bag to ensure the airtightness of the vacuum bag.

[0017] Furthermore, in step three, the set hot-pressing conditions include a pressure of 0.2-0.8 MPa and a temperature gradient of: room temperature → 80-100℃ / 1-1.5h → 95℃ / 15~20min → 120-130℃ / 10~30min → 150-170℃ / 30~90min → 200-210℃ / 30~60min. Even further, the pressure is set to 0.4 MPa, and the temperature change is: room temperature → 80℃ / 1h → 95℃ / 15~20min → 130℃ / 15~20min → 160℃ / 50~60min → 200℃ / 50~60min.

[0018] Furthermore, the molding tooling is designed according to different component shapes, including a cavity mold and a punch mold. The preform is placed in the cavity mold, a high-temperature resistant release layer is placed on the surface of the preform, and then the punch mold and the cavity mold are closed.

[0019] Further, in step four, the molding conditions are: room temperature → 210-220℃ / 20-40min → start pressurization, pressure 2.0-2.5MPa → 240-260℃ / 30~90min → 280-290℃ / 20-40min → 300-340℃ / 20~40min → 370-400℃ / 1.5-2.5h. Even further, the molding conditions are: room temperature → 220℃ / 30min → start pressurization, pressure 2.0-2.5MPa → 255℃ / 50~60min → 280℃ / 30min → 300℃ / 2~3min → 320℃ / 10~15min → 340℃ / 4~6min → 370℃ / 120min, hold pressure and cool to 80℃, then release pressure and demold.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The present invention provides a step-by-step molding method for high-temperature resistant polyimide composite material components. Under the premise of ensuring product performance, the two-step molding method of dehydration in an autoclave and molding in a hot press is adopted. This eliminates the need for high-temperature resistant auxiliary materials and high-temperature autoclaves, thereby reducing manufacturing costs and effectively reducing the risk of defects such as porosity, delamination and insufficient glue in the product during the molding process. Attached image description:

[0022] Figure 1 This is a flowchart of the step-by-step molding method for the high-temperature resistant polyimide composite material component of the present invention;

[0023] Figure 2 This is a diagram showing the molding process parameters for Scheme 1 in Example 1;

[0024] Figure 3 This is a diagram showing the process parameters for the autoclave forming in Scheme 2-4 of Example 1;

[0025] Figure 4 This is a diagram showing the molding process parameters for Schemes 2-4 in Example 1;

[0026] Figure 5 This is a schematic diagram of the hot-press assembly of Scheme 2 in Example 1;

[0027] Figure 6 This is a schematic diagram of the hot-press assembly of Scheme 3 in Example 1;

[0028] Figure 7 This is a schematic diagram of the hot-press assembly of Scheme 4 in Example 1;

[0029] Figure 8 This is a schematic diagram of the molding assembly of schemes 2-4 in Example 1;

[0030] Figure 9The components prepared according to Scheme 1 in Example 1: (a) Hot pressing process diagram; (b) Flat plate specimen diagram;

[0031] Figure 10 The components prepared according to Scheme 2 in Example 1: (a) Hot pressing process diagram; (b) Flat plate specimen diagram;

[0032] Figure 11 The components prepared according to Scheme 3 in Example 1: (a) hot pressing process diagram; (b) flat plate specimen diagram;

[0033] Figure 12 The components prepared according to Scheme 4 in Example 1: (a) hot pressing process diagram; (b) flat plate specimen diagram;

[0034] The markings in the diagram are: 1-Hot pressing tooling, 2-Polyimide prepreg, 31-Mold release material, 32-First breathable material, 33-Second breathable material, 34-Equalizing plate, 35-Third breathable material, 36-Sealing strip, 37-Sealing strip, 38-Breathable PTFE cloth, 39-Soft board, 4-Vacuum bag, 51-Die, 52-Piece, 6-Preform, 7-High temperature resistant mold release layer. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0036] Example 1

[0037] A stepwise molding method for high-temperature resistant polyimide composite material components, such as Figure 1 As shown, it includes the following steps:

[0038] Step 1: Lay out the component shape by stacking the high-temperature polyimide prepreg 2 on the hot pressing molding fixture 1;

[0039] The polyimide prepreg 2 is commercially available. Before laying the high-temperature polyimide prepreg 2, a release material 31 is laid on the hot press molding fixture 1. The release material 31 is a high-temperature resistant release cloth, such as PTFE cloth. In some embodiments, the molding surface of the hot press molding fixture 1 is chrome-plated to prevent the preform 6 from sticking to the hot press molding fixture 1, which is beneficial for demolding the preform 6 after molding in the autoclave. In other embodiments, a release agent is used to wipe the hot press molding fixture 1, so that a layer of release agent film is attached to the fixture.

[0040] Step 2: Lay auxiliary materials on the laid-up high-temperature resistant polyimide prepreg 2, seal it with vacuum bag 4, and draw a vacuum.

[0041] The auxiliary materials include a first breathable material 32, a second breathable material 33, a pressure equalizing plate 34, a third breathable material 35, and a sealing strip 36. The first breathable material 32, the second breathable material 33, the pressure equalizing plate 34, and the third breathable material 35 are sequentially arranged from bottom to top on the laid high-temperature resistant polyimide prepreg 2. The sealing strip is placed at the edge of the prepreg 2 and seals the periphery of the polyimide prepreg 2 by bonding it to the second breathable material 33. The first breathable material 32 is used for air and adhesive permeability. The edge of the first breathable material 32 is flush with the edge of the laid polyimide prepreg 2. The first breathable material 32 is laid on the polyimide prepreg 2 to reduce resin loss. In this embodiment, the first breathable material 32 is a porous separator membrane. The porous separator membrane has two layers. Because the pores of the porous separator membrane are relatively large, using two layers reduces the permeability of the porous separator membrane.

[0042] The second breathable material 33 is used to allow air to pass through but not to allow adhesive to pass through. It removes water vapor generated during the hot pressing process and prevents resin from overflowing, completely sealing the resin. The edge of the second breathable material 33 is 5-20 mm longer than the edge of the laid polyimide prepreg 2. In this embodiment, the second breathable material 33 is a spunlace felt, and the second breathable material 33 is used in two layers.

[0043] A sealing strip is placed at the edge of the polyimide prepreg 2 to prevent resin material leakage and ensure the thickness of the preform 6. During the laying process, pressure-sensitive tape is used to seal the gap between the spunlace felt and the sealing strip to prevent relative displacement between the polyimide prepreg 2 and the auxiliary materials during the vacuuming process of the vacuum bag 4. In this embodiment, the sealing strip is made of putty strip, and a sealing strip 37 is provided at the outlet of the vacuum bag 4 to ensure the airtightness of the vacuum bag 4. The sealing strip is also made of putty strip.

[0044] The pressure equalizing plate 34 is used to ensure uniform pressure. The pressure equalizing plate 34 has holes to ensure that gas can be fully expelled. In this embodiment, the pressure equalizing plate 34 is an aluminum plate with the same dimensions as the preform 6 and a thickness of 2mm. The holes are formed on the aluminum plate by drilling.

[0045] The third breathable material 35 is used to separate the vacuum bag 4 and the pressure equalizing plate 34. When the vacuum bag 4 is truly evacuated, it can form a gas outflow channel, allowing the gas in the vacuum bag 4 or the water vapor generated during the hot pressing process to flow out through the gas outflow channel to the vacuum port of the vacuum bag 4, which is beneficial for the discharge of gas and water vapor. The third breathable material 35 is a breathable felt, which is made of two layers, completely covering the laid polyimide prepreg 2, and each side is 20-100mm larger than the laid polyimide prepreg 2.

[0046] Step 3: Place the polyimide prepreg 2, which has been encapsulated in Step 2, into an autoclave and heat press it according to the set heat pressing conditions to obtain the preform 6;

[0047] After hot pressing is completed, the product is cooled by air or water, the vacuum bag 4 and auxiliary materials are removed, and the preform 6 is removed from the hot pressing fixture 1.

[0048] Step 4: Place the preform 6 obtained in Step 3 into a molding fixture, put it into a hot press, and heat and pressurize it according to the set molding conditions to obtain a composite material component.

[0049] The molding fixture is designed according to different component shapes, including a concave mold 51 and a convex mold 52. The preform 6 is placed in the concave mold 51, and a high-temperature resistant release layer 7 is placed on the surface of the preform 6. Then, the convex mold 52 and the concave mold 51 are closed. The molding fixture and the hot pressing fixture 1 are used to form the shape of the component. The hot pressing fixture 1 is a single-sided mold, and the molding fixture is a double-sided mold. In this embodiment, the hot pressing fixture 1 adopts the concave mold 51 in the molding fixture.

[0050] During the subsequent molding process, the pressure is maintained at 2.0-2.5MPa. After molding is completed, the pressure is maintained and the temperature is lowered to 80℃ before releasing the pressure and demolding.

[0051] The polyimide resin used in this embodiment is KH450, and the carbon fiber is T700. The following is a test analysis of the materials:

[0052] (1) DSC test of polyimide resin

[0053] DSC testing was performed on KH450 resin. The results showed that during the heating process, the polyimide resin exhibited an endothermic peak at 158℃ and an exothermic peak at 391℃. The endothermic peak at 158℃ corresponds to the dehydration and ring-closure reaction of the resin precursor, essentially involving the ring-closure and dehydration of the amyl acid oligomer to form the imide oligomer. This reaction begins at 145℃ and completes at 200℃. The endothermic peak at 391℃ corresponds to the exothermic peak of the crosslinking and curing reaction, essentially involving the crosslinking of the imide oligomer to form polyimide. This reaction begins at 320℃ and reaches its maximum rate at 370℃. Simultaneously, a weak exothermic peak formed between 255℃ and 320℃, which is essentially caused by the opening of the double bonds at the end groups of the imide oligomer to form intermediates and initiate pre-crosslinking. Therefore, to ensure complete resin curing, a curing temperature of 370–400℃ was selected as the curing temperature for this resin.

[0054] (2) Polyimide resin flowability test

[0055] To determine the pressure parameters for the T700 / KH450 composite molding process, a rotational rheometer was used to test the viscosity-temperature characteristics of the dehydrated, closed-loop KH450 resin. The temperature-rheological curves showed that the lowest viscosity of the KH450 resin occurred around 250℃. Throughout the process, the resin viscosity remained relatively high, requiring significant pressure to ensure resin compaction. Therefore, KH450 resin is well-suited for compression molding. In the temperature range of 200℃ to 250℃, the resin viscosity decreased rapidly with increasing temperature. This viscosity change is attributed to the increased molecular chain movement and free volume expansion caused by rising temperature, leading to a gradual decrease in viscosity. In the temperature range of 255℃ to 350℃, the resin viscosity initially increased and then decreased with increasing temperature. This viscosity change was caused by the combined effects of multiple factors. Combining the resin's DSC curves and reaction mechanism, in the 255℃ to 280℃ stage, two changes occurred simultaneously: a viscosity increase due to pre-crosslinking and a viscosity decrease due to increased resin molecular chain movement. Pre-crosslinking predominated, causing a rapid increase in viscosity, which reached equilibrium at 280℃. Within the temperature range of 280℃ to 350℃, three viscosity changes occur simultaneously: viscosity decreases due to accelerated resin molecular chain movement, viscosity increases due to pre-crosslinking, and viscosity increases due to crosslinking and curing. In the 280℃ to 320℃ range, the effect of accelerated molecular chain movement outweighs the effect of pre-crosslinking, leading to a viscosity decrease. At 320℃, pre-crosslinking reaches saturation and crosslinking and curing begins. In the 320℃ to 350℃ range, the effect of accelerated molecular chain movement outweighs the effect of crosslinking and curing, leading to a viscosity decrease. At 350℃, equilibrium is reached, maintaining a low viscosity. After 350℃, crosslinking and curing accelerate rapidly. The formation of the crosslinked network structure and the increase in molecular weight significantly restrict molecular chain movement, causing a rapid increase in resin viscosity and a gradual loss of fluidity. Therefore, the processable window for resin is before 350℃; molding and processing resin becomes difficult above 350℃. During composite material molding, to ensure sufficient wetting of the resin matrix and fibers and reduce the generation of internal bubbles during processing, the matrix resin generally needs to be processed at a lower viscosity. Based on the viscosity-temperature curves above, the low viscosity plateau temperature of 255℃ was selected as the pressure temperature for compression molding.

[0056] To test the influence of different polyimide resin molding processes on the internal quality of polyimide composite materials, the composite material component in this embodiment is a flat plate test piece, which is manufactured using a one-step molding process and a two-step molding process. The four process schemes are shown in Table 1.

[0057] Option 1 is a one-step molding process that uses compression molding throughout the entire molding process. The process is as follows: Polyimide prepreg 2 blanks are laid out manually. After laying, compression molding is performed for assembly. After assembly, the amyl acid oligomer undergoes ring-closure dehydration and imide oligomer cross-linking curing on a molding machine. The compression molding process parameters are: room temperature → 80℃ / 1h → 95℃ / 15~20min → 130℃ / 15~20min → 160℃ / 1h → 200℃ / 1h → 220℃ / 30min → start applying pressure of 2.0-2.5MPa → 255℃ / 1h → 280℃ / 30min → 300℃ / 2~3min → 320℃ / 10~15min → 340℃ / 4~6min → 370℃ / 120min → cooling. The molding process parameters are as follows: Figure 2 As shown.

[0058] The two-step molding process refers to the step-by-step molding method for the aforementioned high-temperature resistant polyimide composite material components. The process parameters for autoclave molding are: room temperature → 80℃ / 1h → 95℃ / 15~20min → 130℃ / 15~20min → 160℃ / 1h → 200℃ / 1h. Figure 3 As shown, after the autoclave is formed, it is demolded, then assembled by compression molding, and then... Figure 6 The curing process involves cross-linking and curing the imide oligomers through compression molding. The compression molding process parameters are as follows: heating → 220℃ / 30min → initial pressurization at 2.0-2.5MPa → 255℃ / 1h → 280℃ / 30min → 300℃ / 2~3min → 320℃ / 10~15min → 340℃ / 4~6min → 370℃ / 120min → cooling. The difference between schemes 2, 3, and 4 lies in the pressure during closed-loop dehydration and the assembly method of auxiliary materials. Scheme 2 uses vacuum pressure, meaning only the vacuum bag 4 is evacuated, and the autoclave does not provide positive pressure. The assembly method is assembly method A, where the polyimide prepreg 2 is topped with breathable PTFE cloth 38 and a second breathable material 33, from bottom to top. Figure 5 As shown; the pressure in scheme 3 is vacuum pressure + 0.4MPa pressure. The 0.4MPa pressure is the positive pressure applied by the autoclave, which is the positive pressure generated by N2 being injected into the outside of the vacuum bag 4. The autoclave molding and assembly is assembly method B, and the assembly method is as follows: from bottom to top, the polyimide prepreg 2 consists of breathable PTFE cloth 38, second breathable material 33, and flexible sheet 39, as shown. Figure 6 As shown, the flexible plate 39 has holes; the pressure during closed-loop dehydration in scheme 4 is vacuum pressure + 0.4MPa pressure, and the autoclave molding assembly is assembly method C. The assembly method is as follows: from bottom to top, the polyimide prepreg 2 consists of the first breathable material 32, the second breathable material 33, the pressure equalizing plate 34, and the third breathable material 35, as shown. Figure 7 As shown in the diagram, the molding process is as follows: Figure 8As shown in Table 2, the internal quality of the composite materials after molding according to the four schemes was tested.

[0059] Table 1 Different Molding Process Schemes

[0060]

[0061] Table 2 Internal Quality Inspection Results of Polyimide Composite Materials

[0062]

[0063] As can be seen from Table 2, Scheme 1 directly uses compression molding for assembly. During the closed-loop dehydration process before 200℃, the polyimide prepreg 2 blank is subjected to significant pressure from the mold's own weight, resulting in severe resin overflow during the molding process (e.g., ...). Figure 9 (a) This prevents the effective removal of small molecules from the interior, resulting in the molded test plate lacking a bottom wave and exhibiting poor internal quality (e.g., Figure 9 (b)); In Scheme 2, the polyimide prepreg 2 blank is dehydrated only by vacuum pressure, without external pressure to ensure compaction of the polyimide prepreg 2 blank. When water molecules overflow, they disperse the polyimide prepreg 2 blank, destroying its density (e.g. Figure 10 (a))), resulting in air pockets (e.g.) on the cut surface of the formed laminate. Figure 10 (b) The main difference between Scheme 3 and Scheme 4 lies in their assembly methods. The assembly method in Scheme 3 cannot effectively prevent resin overflow during the closed-loop dehydration process in the autoclave molding, resulting in severe resin overflow (e.g.) Figure 11 (a))), resulting in non-destructive diffuse defects (such as) in the molded flat plate specimen. Figure 11 (b)); Scheme 4 optimizes the assembly method compared to Scheme 3, using a porous isolation membrane instead of breathable PTFE 38 to ensure breathability, and adding a layer of spunlace felt to further ensure breathability without adhesive leakage, and no resin overflow occurs (e.g. Figure 12 (a)) thus ensuring the internal quality of the molded laminate (e.g. Figure 12 (b) Therefore, the molding process of Scheme 4 can effectively ensure the internal quality of the polyimide composite material.

[0064] Example 2

[0065] This embodiment provides a step-by-step molding method for a high-temperature resistant polyimide composite material component. The composite material component has a curved shape, and the step-by-step molding method includes the following steps:

[0066] Step 1: Lay the high-temperature polyimide prepreg 2 onto the hot press molding fixture 1 to form the component shape;

[0067] Step 2: Lay auxiliary materials on the laid-up high-temperature resistant polyimide prepreg 2, seal it with vacuum bag 4, and draw a vacuum.

[0068] The auxiliary materials and assembly method are the same as those in Scheme 4 of Example 1. The first breathable material 32, the second breathable material 33, the pressure equalizing plate 34, and the third breathable material 35 are arranged sequentially from bottom to top on the laid high-temperature resistant polyimide prepreg 2, and the sealing strip is arranged at the edge of the polyimide prepreg 2.

[0069] Step 3: Place the polyimide prepreg 2, which has been encapsulated in Step 2, into an autoclave and heat press it according to the set heat pressing conditions to obtain the preform 6;

[0070] The set hot-pressing conditions have a pressure of 0.2-0.8 MPa and a temperature gradient of: room temperature → 80-100℃ / 1-1.5h → 95℃ / 15~20min → 120-130℃ / 10~30min → 150-170℃ / 30~90min → 200-210℃ / 30~60min; specifically, the pressure is 0.4 MPa and the temperature change is: room temperature → 80℃ / 1h → 95℃ / 15~20min → 130℃ / 15~20min → 160℃ / 50~60min → 200℃ / 50~60min.

[0071] After hot pressing is completed, the product is cooled by air or water, the vacuum bag 4 and auxiliary materials are removed, and the preform 6 is removed from the hot pressing fixture 1.

[0072] Step 4: Place the preform 6 obtained in Step 3 into a molding fixture, put it into a hot press, and heat and pressurize it according to the set molding conditions to obtain a composite material component.

[0073] In step four, the molding conditions are as follows: room temperature → 210-220℃ / 20-40min → start pressurizing, pressure 2.0-2.5MPa → 240-260℃ / 30~90min → 280-290℃ / 20-40min → 300-340℃ / 20~40min → 370-400℃ / 1.5-2.5h. Specifically, the molding conditions are as follows: room temperature → 220℃ / 30min → start pressurizing 2.0-2.5MPa pressure → 255℃ / 50~60min → 280℃ / 30min → 300℃ / 2~3min → 320℃ / 10~15min → 340℃ / 4~6min → 370℃ / 120min. After holding the pressure and cooling to 80℃, release the pressure and demold. During the subsequent molding process, the pressure is maintained at 2.0-2.5MPa. After molding is completed, the pressure is maintained and the temperature is lowered to 80℃ before releasing the pressure and demolding.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A stepwise molding method for high-temperature resistant polyimide composite material components, characterized in that, Includes the following steps: Step 1: Lay the polyimide prepreg (2) on the hot press molding fixture (1) to form the component shape; Step 2: Lay auxiliary materials on the laid polyimide prepreg (2), seal it with a vacuum bag (4), and evacuate the vacuum. The auxiliary materials include a first breathable material (32), a second breathable material (33), a pressure equalizing plate (34), a third breathable material (35), and a sealing strip (36). The first breathable material (32), the second breathable material (33), the pressure equalizing plate (34), and the third breathable material (35) are arranged sequentially from bottom to top on the laid polyimide prepreg (2), and the sealing strip is placed on the polyimide prepreg. (2) The edge of the polyimide prepreg (2) is sealed around by bonding with the second breathable material (33). The pressure equalizing plate (34) is provided with holes. The first breathable material (32) is used for breathable and adhesive-permeable, the second breathable material (33) is used for breathable but not adhesive-permeable, and the third breathable material (35) is used to separate the vacuum bag (4) and the pressure equalizing plate (34). When the vacuum bag (4) is truly vacuumed, a gas outflow channel is formed, and the gas in the vacuum bag (4) or the water vapor generated during the hot pressing process flows out from the gas outflow channel to the vacuum port of the vacuum bag (4). The edge of the first breathable material (32) is flush with the edge of the laid polyimide prepreg (2), the edge of the second breathable material (33) is 5-20 mm longer than the edge of the laid polyimide prepreg (2), and the third breathable material (35) completely covers the laid polyimide prepreg (2) and is 20-100 mm larger on each side than the laid polyimide prepreg (2). Step 3: Place the polyimide prepreg (2) that has been packaged in Step 2 into an autoclave and hot press it according to the set hot pressing conditions to obtain the preform (6); the pressure in the set hot pressing conditions is 0.4MPa, and the temperature changes are room temperature → 80℃ / 1h → 95℃ / 15~20min → 130℃ / 15~20min → 160℃ / 50~60min → 200℃ / 50~60min; Step 4: Place the preform (6) obtained in Step 3 into a molding fixture, put it into a hot press, and heat and pressurize it according to the set molding conditions to obtain a composite material component; the molding conditions are: room temperature → 220℃ / 30min → start pressurizing 2.0-2.5MPa pressure → 255℃ / 50~60min → 280℃ / 30min → 300℃ / 2~3min → 320℃ / 10~15min →340℃ / 4~6min →370℃ / 120min, hold pressure and cool down to 80℃, then release pressure and demold.

2. The step-by-step molding method for high-temperature resistant polyimide composite material components according to claim 1, characterized in that, In step one, before laying the polyimide prepreg (2), a release material (31) is laid on the molding surface of the hot pressing tooling (1).

3. The step-by-step molding method for high-temperature resistant polyimide composite material components according to claim 1, characterized in that, The hot pressing forming tool (1) has a chrome-plated surface.

4. The step-by-step molding method for high-temperature resistant polyimide composite material components according to claim 1, characterized in that, A sealing strip (37) is provided at the outlet of the vacuum bag (4).

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