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CN-122008585-A - Polyimide fiber composite material forming method and mold

CN122008585ACN 122008585 ACN122008585 ACN 122008585ACN-122008585-A

Abstract

The invention relates to the technical field of composite material molding, in particular to a polyimide fiber composite material molding method and a polyimide fiber composite material molding die. The die consists of a common upper die, a lower die and an outer frame. The invention has the innovation point that physical exhaust is carried out by utilizing the natural clearance of the parting surface of the die in the critical stage of resin entering into the viscous state through a specific programmed step temperature control and dynamic exhaust process. The method solves the pore defect generated by the difficult discharge of volatile components in the molding process of the high-performance thermosetting polyimide at the temperature of more than 400 ℃. The invention has simple structure and low cost, and is particularly suitable for large-scale production of polyimide fiber composite materials.

Inventors

  • LIANG DIFEI
  • CHEN RUOYU

Assignees

  • 电子科技大学

Dates

Publication Date
20260512
Application Date
20260326

Claims (8)

  1. 1. A polyimide fiber composite forming die, comprising: A lower die, the top of which is provided with a first cavity; an upper die, the bottom of which is provided with a second cavity; the outer frame is used for positioning and limiting the lower die and the upper die; The parting surfaces of the upper die and the lower die keep an original precision machining state, a mechanical exhaust channel is not arranged, a natural gap is arranged between the parting surfaces of the upper die and the lower die in a die clamping state, and the natural gap is used as a physical pressure relief channel in the forming process.
  2. 2. The polyimide fiber composite material molding die of claim 1, wherein the natural clearance after the parting surfaces are clamped is controlled within 10 μm.
  3. 3. The polyimide fiber composite material forming die of claim 1, wherein the lower die and the upper die are made of H13 steel or S136 stainless steel.
  4. 4. A method for molding a polyimide fiber composite material, characterized in that the method is completed by using the mold according to any one of claims 1 to 3, and comprises the following steps: Step 1, paving and die filling, namely paving polyimide fiber prepreg layers in a cavity, and placing the die in a vacuum hot press; Step 2, preheating and degassing, namely setting a degassing temperature zone before the resin undergoes a crosslinking reaction, wherein the temperature is 250-300 ℃, and removing volatile components in the prepreg by utilizing vacuum negative pressure of minus 600 to minus 900 mbar; Step 3, dynamic exhaust, namely continuously heating to 300-350 ℃ in a viscous state interval of the resin, implementing 5-10 times of pressurization and decompression exhaust actions in a critical stage of entering the viscous state of the resin, and exhausting residual gas by utilizing a natural gap of a parting surface; Step 4, high-temperature high-pressure curing, namely heating to 380-410 ℃, applying forming pressure of 3-8 MPa, and curing in a vacuum negative pressure environment of-600 to-900 mbar; And 5, cooling and taking the workpiece, namely performing programmed cooling in a pressure maintaining state, and opening the die after cooling to a preset temperature.
  5. 5. The method of claim 4, wherein the residence time in the degassing temperature range of step 2 is 1-3 h.
  6. 6. The method for forming a polyimide fiber composite material according to claim 4, wherein in the step 3, the dynamic cyclic action is performed in a specific manner that after the upper die is completely closed and stressed, the upper die is released to rebound and slightly displace, and after the upper die stays, the upper die is pressurized again, wherein the slightly displaced amount is controlled to be between 0.5 and 1 mm.
  7. 7. The method of molding a polyimide fiber composite material according to claim 4, wherein the molding pressure in the step 4 is preferably 5 MPa and the curing time is 3 to 6 h.
  8. 8. The method of claim 4, wherein in step5, the cooling rate is controlled to be less than 2 ℃ per minute, and the cooling rate is controlled to be less than 150 ℃ as a pickup judgment condition.

Description

Polyimide fiber composite material forming method and mold Technical Field The invention relates to the field of processing of polymer composite materials, in particular to a forming method and a matched die of a high-performance polyimide fiber composite material used in the fields of high-frequency communication, aerospace and the like. Background Polyimide fiber composite material is the first choice material in the fields of high-frequency communication and aerospace because of its excellent dielectric property and heat resistance. Thermoset polyimides exhibit complex rheological behavior during molding and resins are extremely volatile during molding, resulting in void defects in the article. However, the addition of the vent channels in the mold tends to cause a large overflow of resin to form flash and the mold is expensive. Therefore, how to realize high-density molding in a common mold through process control is a technical challenge to be solved in the field of polyimide composite materials. The invention is innovative in that 1, a complex exhaust pipeline is abandoned, multiple dynamic exhaust actions are implemented in a viscous flow state interval through accurate grasp of the rheological action of the resin, and the gas is exhausted through a die before the resin is solidified by utilizing the flowability difference of the gas and the resin. 2. The special degassing stage is arranged before the curing temperature, so that the physical adsorption water and residual solvent in the prepreg are fully removed before the resin has not undergone the crosslinking reaction, and the pore source in the final molding process is reduced. 3. Through the combined action of the vacuum environment and the molding pressure, the high densification of the fiber and the resin is ensured. Disclosure of Invention Aiming at the problems that the high-performance thermosetting polyimide fiber composite material is difficult to remove volatile matters, easy to generate pore defects, high in cost of a precise exhaust mold and the like in the ultra-high temperature forming process, the invention provides a process for realizing high-density forming by using a common mold through programmed step temperature control and dynamic exhaust and a matched mold. The polyimide fiber composite material forming die used for the method is characterized by comprising the following structure: The die comprises an upper die, a lower die and an outer frame for positioning, wherein the parting surface of the upper die and the parting surface of the lower die keep an original precise grinding state, a special exhaust channel is not arranged, and a natural gap during die assembly is used as a pressure release channel. The molding method of the polyimide fiber composite material is characterized by utilizing the natural clearance of the parting surface of a common molding die and comprises the following steps of: 1. A pre-degassing stage, namely setting a special degassing temperature before the curing temperature, wherein the temperature range is 250-300 ℃. And in the temperature range, the physical adsorption water and residual solvent in the prepreg are fully volatilized before the resin undergoes a crosslinking reaction by utilizing a vacuum environment of-600 to-900 mbar. 2. And in the dynamic exhaust stage, the temperature is raised to a resin viscous state temperature zone (300-350 ℃), and in the critical stage of entering the viscous state of the resin, 5-10 exhaust measures are implemented. 3. And in the high-pressure curing stage, forming pressure of 3-8 MPa is applied under the high-temperature environment of 380-410 ℃ and the vacuum negative pressure environment of-600 to-900 mbar is matched, so that residual trace gas between layers is forcedly discharged, and resin curing is completed. In summary, the invention provides a molding method and a mold for polyimide fiber composite materials, which are characterized in that a common mold structure is utilized to be matched with a programmed step temperature control and dynamic exhaust process, under the premise of not adding a precise exhaust channel, an air source is reduced in a preheating and degassing stage, physical exhaust is implemented by utilizing the natural clearance of the mold at the critical point of a viscous state of resin, the defect of pores in the molding process of high-performance polyimide at the temperature of more than 400 ℃ is effectively overcome, the high densification and low-cost molding of composite material parts are realized, and the application performance of the composite material parts in the fields of high-frequency communication and aerospace can be improved. Drawings Fig. 1 is a schematic diagram of a mold designed in example 1. FIG. 2 is a diagram of a polyimide composite molded in example 2. FIG. 3 is a cross-sectional optical micrograph of a polyimide composite molded in accordance with example 2. FIG. 4 is a cross-sectional Scanning Electron