Polyimide fiber composite material forming method and mold
By applying a stepped temperature control and dynamic venting process to a conventional mold, the porosity defect problem in the molding of polyimide fiber composite materials was solved, achieving high density and low cost molding results, which are suitable for high-frequency communication and aerospace fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- UNIV OF ELECTRONICS SCI & TECH OF CHINA
- Filing Date
- 2026-03-26
- Publication Date
- 2026-05-12
AI Technical Summary
High-performance polyimide fiber composites are prone to pore defects during the molding process, and precision venting molds are expensive.
Using a conventional mold structure, combined with programmed step temperature control and dynamic venting process, the pre-degassing stage removes physically adsorbed water and residual solvents, the natural gaps in the mold are used for physical venting at the critical point of resin viscous flow, and the residual gas between layers is forcibly vented during the high-pressure curing stage.
It achieves high-density molding, reduces porosity defects in parts, improves material density and molding quality, and reduces mold costs.
Smart Images
Figure CN122008585A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer composite material processing, specifically to a molding method and matching mold for high-performance polyimide fiber composite materials used in high-frequency communication, aerospace and other fields. Background Technology
[0002] Polyimide fiber composites are the preferred material for high-frequency communications and aerospace applications due to their excellent dielectric properties and heat resistance. Thermosetting polyimides exhibit complex rheological behavior during molding, and the resin readily releases volatile components, leading to porosity defects in the molded parts. However, adding venting channels to the mold often results in excessive resin overflow, forming flash, and the molds themselves are expensive. Therefore, achieving high-density molding within ordinary molds through process control is a pressing technical challenge in the field of polyimide composites.
[0003] The innovations of this invention are: 1. It abandons complex venting pipes and, through precise control of resin rheological behavior, implements multiple dynamic venting processes in the viscous flow range. Utilizing the difference in flowability between gas and resin, the gas is discharged through the mold before the resin cures. 2. A dedicated degassing stage is set before the curing temperature, allowing physically adsorbed water and residual solvents in the prepreg to be fully removed before the resin undergoes a cross-linking reaction, reducing the source of porosity during final molding. 3. The combined effect of a vacuum environment and molding pressure ensures high densification of the fiber and resin. Summary of the Invention
[0004] To address the problems of difficulty in removing volatiles, easy generation of pore defects, and high cost of precision venting molds in the ultra-high temperature molding process of high-performance thermosetting polyimide fiber composite materials, this invention provides a process and matching mold for achieving high-density molding using ordinary molds through programmed step temperature control and dynamic venting.
[0005] A molding die for polyimide fiber composite materials used in the above method, characterized by its structure:
[0006] It includes an upper mold, a lower mold, and an outer frame for positioning; the parting surfaces of the upper and lower molds are kept in their original precision-ground state, without a dedicated venting channel, and the natural gap during mold closing is used as a pressure relief channel.
[0007] A method for molding polyimide fiber composite materials, characterized by utilizing the natural gap of the parting surface of a conventional molding die, and achieving the following steps:
[0008] 1. Pre-degassing stage: A specific degassing temperature is set before the curing temperature, with a temperature range of 250-300℃. Within this temperature range, a vacuum environment of -600 to -900 mbar is used to fully volatilize the physically adsorbed water and residual solvents in the prepreg before the resin undergoes a crosslinking reaction.
[0009] 2. Dynamic venting stage: Heat the resin to the viscous flow temperature range (300-350 ℃), and implement venting measures 5-10 times when the resin enters the critical stage of viscous flow.
[0010] 3. High-pressure curing stage: Under a high temperature environment of 380-410℃, a molding pressure of 3-8 MPa is applied, combined with a vacuum negative pressure environment of -600 to -900 mbar, to force out residual trace gases between layers and complete resin curing.
[0011] In summary, this invention provides a molding method and mold for polyimide fiber composite materials. Its core lies in utilizing a common mold structure combined with programmed step temperature control and dynamic venting process. Without adding precision venting channels, it reduces the gas source through the preheating and degassing stage and implements physical venting by utilizing the natural gap of the mold at the critical point of resin viscous flow. This effectively solves the porosity defects of high-performance polyimide in the molding process above 400 °C, and achieves high density and low-cost molding of composite material parts, which can improve its application performance in high-frequency communication and aerospace fields. Attached Figure Description
[0012] Figure 1 A schematic diagram of the mold designed for Example 1.
[0013] Figure 2 This is a photograph of the polyimide composite material formed in Example 2.
[0014] Figure 3 This is an optical microscope image of the cross-section of the polyimide composite material formed in Example 2.
[0015] Figure 4 This is a scanning electron microscope (SEM) image of the cross-section of the polyimide composite material formed in Example 2. Detailed Implementation
[0016] The present invention will be further described below with reference to specific embodiments.
[0017] Example 1: A molding die for polyimide fiber composite materials
[0018] This embodiment is made of H13 steel. The mold consists of an upper mold, a lower mold, and an outer frame that serves as a guide and limiter. The parting surfaces of the upper and lower molds are precision machined, and the natural gap after mold closing is controlled within 10 μm. This structure does not require additional processing of venting holes or pressure relief grooves; it relies entirely on the dynamic movements during the process to utilize the gaps in the parting surfaces for venting.
[0019] Mold design drawings, such as Figure 1 As shown.
[0020] Example 2: A molding method for polyimide fiber composite materials
[0021] A polyimide fiber composite laminate is formed using the mold described in Example 1. The specific steps are as follows:
[0022] Step 1: Pre-treatment and molding
[0023] First, preheat the mold at 130 ℃ for 30 min, then remove it. Apply a release agent evenly to the surfaces of the upper and lower molds and the outer frame that contact the composite material. Then, dry the release agent by holding it at 240 ℃ for 50 min. Remove the lower mold and assemble it with the outer frame. Place the fiber prepreg, cut to the dimensions of the inner frame and evenly coated with polyimide resin solution on both sides, into the lower mold according to the designed layup sequence, and place the mold in the vacuum chamber of a vacuum hot press.
[0024] Step 2: Preheating and Vacuum Degassing
[0025] After holding at 280 ℃ for 1 h, the vacuum pump is turned on, and the vacuum level in the vacuum chamber is adjusted to -900 mbar. After holding at this temperature for another 1.5 h, the upper mold is then assembled. At this stage, the resin has not yet undergone chemical cross-linking. The vacuum negative pressure is used to accelerate the removal of trace amounts of moisture and solvents from the prepreg, reducing gaseous substances during final curing.
[0026] Step 3: Dynamic Exhaust
[0027] Continue heating to 330℃. When the resin enters the viscous flow critical region, control the press to perform an venting action: that is, after the upper mold is fully closed and under pressure, quickly release the pressure and allow the upper mold to rebound slightly (displacement of 1mm), hold for 10 seconds, and then repressurize. Repeat this action 10 times. In this stage, by utilizing the rheological properties of the resin in the viscous flow state, gas molecules are allowed to be discharged through the natural gaps in the mold after being compressed, while the resin remains inside the mold due to viscosity and surface tension, preventing overflow.
[0028] Step 4: Curing and Cooling for Demolding
[0029] The temperature is raised to 380 °C, a molding pressure of 5 MPa is applied, and the mixture is cured under constant temperature and pressure for 2 hours. Then, the temperature is raised again to 400 °C, and the pressure is maintained at 5 MPa for another 2 hours. Under this high pressure, the remaining micropores are forcibly compressed or dissolved in the matrix, ensuring the material is dense. After curing, the pressure is maintained, and the temperature is lowered to below 100 °C at a rate of 2 °C / min before the mold can be opened and the part removed.
[0030] The final polyimide composite laminate, as shown in the image... Figure 2 As shown.
[0031] Figure 3 This is an optical microscope image of the cross-section of the polyimide composite laminate formed in Example 2. Figure 4 The image shows a scanning electron microscope (SEM) image of the cross-section of the polyimide composite laminate formed in Example 2. As can be seen from the image, the resin and fibers are evenly distributed at different magnifications, the interfacial compatibility is excellent, and there are no serious defects in the resin matrix and at the resin fiber interface.
[0032] As can be seen from the above embodiments, the polyimide composite material molding method and mold provided by the present invention fully realize the high-density molding of polyimide composite materials, improve the product quality of composite material molding, and can be used in high-frequency communication and aerospace fields.
Claims
1. A molding die for polyimide fiber composite materials, characterized in that, include: The lower mold has a first cavity at its top; The upper mold has a second cavity at its bottom; The outer frame is used for positioning and limiting the lower and upper molds; The parting surfaces of the upper and lower molds are kept in their original precision-machined state and no mechanical venting channels are provided. In the mold-closed state, there is a natural gap between the parting surfaces of the upper and lower molds, which is used as a physical pressure relief channel during the molding process.
2. The molding die for polyimide fiber composite materials according to claim 1, characterized in that: The natural gap after the parting surface is closed is controlled within 10 μm.
3. The molding die for polyimide fiber composite materials according to claim 1, characterized in that: The lower and upper molds are made of H13 steel or S136 stainless steel.
4. A method for molding polyimide fiber composite materials, characterized in that, The process, performed using any one of the molds described in claims 1-3, includes the following steps: Step 1, Laying and Molding: Lay the polyimide fiber prepreg in layers inside the cavity and place the mold in a vacuum hot press; Step 2, Preheating and Degassing: Set a degassing temperature zone at 250-300 ℃ before the resin undergoes cross-linking reaction, and use a vacuum negative pressure of -600 to -900 mbar to remove volatile components from the prepreg. Step 3, Dynamic venting: Continue heating to the viscous flow zone of the resin, 300-350 ℃. At the critical stage when the resin enters the viscous flow state, perform 5-10 pressurization and depressurization venting actions to remove residual gas using the natural gap at the parting surface. Step 4, High Temperature and High Pressure Curing: Heat to 380-410 ℃, apply molding pressure of 3-8 MPa, and cure in a vacuum negative pressure environment of -600 to -900 mbar; Step 5, Cooling and Removing Parts: Under pressure, the parts are cooled in a programmed manner and opened after reaching the preset temperature.
5. The method for molding a polyimide fiber composite material according to claim 4, characterized in that: In step 2, the residence time within the degassing temperature range is 1-3 hours.
6. The method for molding a polyimide fiber composite material according to claim 4, characterized in that: In step 3, the specific method of dynamic cyclic action is as follows: after the upper mold is fully closed and subjected to force, the pressure is released to allow the upper mold to rebound with a slight displacement, and after a pause, pressure is applied again, wherein the slight displacement is controlled between 0.5 and 1 mm.
7. The method for molding a polyimide fiber composite material according to claim 4, characterized in that: The molding pressure in step 4 is preferably 5 MPa, and the curing time is 3-6 h.
8. The method for molding a polyimide fiber composite material according to claim 4, characterized in that: In step 5, the cooling rate is controlled below 2 ℃ / min, and the condition for removing the part is to cool down to below 150 ℃.