CN113386374B - Mold for improving internal quality of liquid molding composite material and control method - Google Patents

Mold for improving internal quality of liquid molding composite material and control method Download PDF

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Publication number
CN113386374B
CN113386374B CN202110531589.8A CN202110531589A CN113386374B CN 113386374 B CN113386374 B CN 113386374B CN 202110531589 A CN202110531589 A CN 202110531589A CN 113386374 B CN113386374 B CN 113386374B
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resin
glue
mold
composite material
injection
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CN113386374A (en
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张代军
雷帅
付善龙
刘燕峰
李军
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AECC Beijing Institute of Aeronautical Materials
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AECC Beijing Institute of Aeronautical Materials
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
    • B29C70/28—Shaping operations therefor
    • B29C70/40—Shaping or impregnating by compression not applied
    • B29C70/42—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles
    • B29C70/46—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using matched moulds, e.g. for deforming sheet moulding compounds [SMC] or prepregs
    • B29C70/48—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using matched moulds, e.g. for deforming sheet moulding compounds [SMC] or prepregs and impregnating the reinforcements in the closed mould, e.g. resin transfer moulding [RTM], e.g. by vacuum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
    • B29C70/28—Shaping operations therefor
    • B29C70/54—Component parts, details or accessories; Auxiliary operations, e.g. feeding or storage of prepregs or SMC after impregnation or during ageing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T50/00—Aeronautics or air transport
    • Y02T50/40—Weight reduction

Abstract

The invention belongs to the field of composite material liquid molding, and relates to a mold for improving the internal quality of a liquid molding composite material and a control method, wherein a glue storage groove is additionally arranged on the inner side of a glue outlet of a liquid molding mold; the invention adopts a reverse pressing method, and applies reverse air pressure from the glue outlet of the glue storage tank in the curing process to make the resin in the glue storage tank flow reversely so as to supplement the reduced resin volume in the die cavity, increase the resin content in the die cavity, and reduce the defects of pores and the like. The liquid molding composite material prepared by the invention has good internal quality and low porosity, has great technical advantages for improving the mechanical properties of composite material plates and workpieces, and has important significance for the application of novel resin-based composite materials for aerospace.

Description

Mold for improving internal quality of liquid molding composite material and control method
Technical Field
The invention belongs to the field of composite material liquid forming, and relates to a mold for improving the internal quality of a liquid forming composite material and a control method.
Background
The composite material has the characteristics of high specific strength, high specific stiffness, fatigue resistance, corrosion resistance and the like, is widely applied to novel civil and military aircrafts, aviation equipment and the like, can greatly reduce the structural quality of an aircraft body, improves the comprehensive performance of the aircraft, and plays an important role in lightening, hiding, improving the performance and miniaturization of the military aircraft.
Based on the reaction characteristics of the advanced composite material and the specific requirement for meeting the internal quality of the advanced composite material component, the internal structure and the mechanical property of the composite material plate and the component which are formed in a liquid state meet the design requirements. The member is not processed any more after being cured and molded, and the surface quality and the appearance size of the member meet the requirement of assembly coordination.
The composite liquid molding process is the most successful composite molding process developed after the autoclave molding process, and is also the most successful non-autoclave low-cost composite molding process. Liquid molding processes used in aircraft construction are mainly Resin Transfer Molding (RTM), resin film melt infusion (RFI) and Vacuum Assisted Resin Infusion (VARI). The principle of the Resin Transfer Molding (RTM) process is that dry fiber or fabric prefabricated parts are placed in a mold in advance, liquid low-viscosity resin with reaction activity flows through and fills the closed mold under the condition of pressure injection or additional vacuum assistance, and gas is exhausted to simultaneously infiltrate and impregnate a dry fiber structure. After the soaking and impregnation are finished, the resin is cured in the mould through a thermal-initiated crosslinking reaction, and finally the molded product is obtained. The RTM process is a forming process which is developed rapidly in recent years and is suitable for producing various, medium-batch and high-quality advanced composite material products.
The mechanical properties of the liquid-state shaped high-performance composite material come from the high volume fraction of the continuous fiber preform. The higher the fiber volume fraction is, the higher the mechanical properties of the liquid molding composite material is, but the greater the process difficulty of liquid molding is. On the other hand, when the RTM process is used to form a liquid molded composite performance panel and part, the resin shrinks in volume when solidifying from a liquid state to a solid state, which reduces the volume of the resin that would otherwise fill the mold cavity, and during curing, voids, delamination and other defects are easily caused in the composite panel or part, which affects the internal quality and performance test of the composite. Therefore, the defects of improving the internal quality, reducing the porosity and the like of the composite material flat plate and the part during liquid molding by adopting effective measures have very important application value and practical significance.
CN108145992A discloses a method for liquid molding of a composite material with an ultra-long open period, which comprises the steps of pre-loading one of the reaction components in a resin system on a fiber preform, then carrying out flow injection molding and mold filling on the resin and the other components under non-reaction conditions, and after ensuring that the mold filling is successful, changing the conditions to initiate the curing reaction of the reaction components. Compared with the characteristics that the mold filling and the curing reaction are synchronously carried out in the in-situ resin transfer molding technology, and the viscosity of the resin is gradually increased along with the time in the mold filling process, the invention is off-position in the process, the mold filling and the curing reaction of the resin are separated, and the two processes are not interfered with each other and not influenced with each other. The invention improves the resin injection molding period from the resin reaction angle, but has complex operation and difficult control of the reaction process.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a specially designed composite material liquid forming die and a control method, the preparation method is novel in thought, unique in design and simple in operation, the internal quality of the liquid forming composite material can be improved, the defects of porosity and the like can be reduced, and the mechanical properties of a composite material plate and a finished piece can be improved.
In order to achieve the aim, the invention provides a mould for improving the internal quality of a liquid forming composite material, which is characterized in that the mould is a composite material flat plate forming mould and is divided into an upper mould, a middle frame and a lower mould, wherein bosses with the same size are respectively designed at the middle parts of the upper mould and the lower mould to be used as mould cavity surfaces, the size of the inner frame of the middle frame is consistent with that of the bosses of the upper mould and the lower mould, the three parts are matched to form a mould cavity, and the thickness of the forming composite material plate is determined by the difference between the thickness of the middle frame and the heights of the bosses of the upper mould and the lower mould of the mould; one side of the middle frame of the mold is provided with a glue injection port, the other side of the middle frame of the mold is provided with a plurality of glue outlets, a groove is additionally arranged on the inner side of the middle glue outlet and serves as a glue storage groove, one end of the glue storage groove is communicated with the glue outlet, and the other end of the glue storage groove is communicated with the inner cavity of the mold.
The glue storage groove is connected with a channel arranged in the die cavity, and the diameter of the channel is consistent with that of other glue outlets.
The volume of the glue storage tank can be designed according to the size of the molded composite material plate and the curing shrinkage rate of the liquid molding resin, and the shrinkage rate of the liquid molding resin is generally about 1% -2%.
A kind of mould and control method for improving the internal quality of liquid molding composite material, characterized by, check the mould and resin injection pipeline temperature and meet the demands, the resin is fully melted in the feeder barrel of the injection machine, presume the injection pressure of the injection machine is 2.0-4.0bar, the injection flow rate is 10-20ml/min, inject the liquid resin into mould cavity and glue storage tank, close the glue outlet valve after all glue outlets go out, the liquid resin has already filled the mould cavity at this moment, and flow into glue storage tank; then gradually pressurizing to 15.0-25.0bar to fully soak the resin in the cavity pre-forming body and fill the glue storage tank, and keeping the time for 30-90 min to finish resin injection; connecting compressed air to a glue outlet in the middle of the mold after the resin injection is finished, starting heating and curing, opening a glue outlet valve in the heating process, applying reverse air pressure inwards from the glue outlet, and controlling the pressurizing pressure to be 1.0-5.0bar through a pressure gauge so that the resin in the glue storage tank flows into the mold cavity of the mold; the resin in the cavity shrinks in the curing process, and the resin in the glue storage tank flows into the cavity to fill the gap generated by the shrinkage of the resin during curing.
The temperature of the mould and the resin injection pipeline reaching the requirement means reaching the optimum injection temperature of the liquid molding resin within +/-10 ℃.
Before adding the resin into the charging barrel of the injection machine, a release agent is required to be uniformly coated inside the charging barrel of the injection machine, the temperature is raised by heating, and after the temperature of the charging barrel is raised to the resin injection temperature, the solid resin is put into the charging barrel for heating and melting.
In the process of injecting the liquid resin into the mold cavity and the glue storage tank, each glue outlet of the mold is connected with a vacuum pipe and connected with a vacuum pump for vacuum pumping, and the liquid resin is guided to flow towards the glue outlet, so that the mold cavity is filled with the resin.
The preparation method of the preform in the mold cavity comprises the steps of paving unidirectional cord fabric and fiber fabric layer by layer according to the layer laying design of the liquid-state molding composite material plate, and compacting and shaping by using an electric iron to form a fiber preform.
The invention has the advantages that:
the invention adopts a molding method that a glue storage tank is added on the inner side of a glue outlet when a composite material liquid molding mold is designed, and reverse pressurization can be carried out when the liquid molding composite material is heated and solidified. The invention has the advantages of no change of the original injection and curing process of the resin, no increase of working procedures, simple operation, good internal quality of the formed composite material plate and the formed part, and obvious reduction of defects such as porosity and the like.
The invention adopts a groove added on the inner side of a glue outlet of a liquid forming die as a glue storage groove, resin is stored when the resin is injected, then reverse air pressure is applied from the glue outlet in the processes of resin temperature rise curing and post-curing, so that the resin in the glue storage groove flows into the die, the volume of the resin in a cavity is supplemented, which is reduced due to curing shrinkage, and the pressurizing pressure is 1.0-5.0bar, thus completing the preparation of the liquid forming composite material;
the method for improving the internal quality of the liquid molding composite material can be applied to the liquid molding resin-based composite materials in various fields such as life, industry, military and the like, and has the advantages of simple implementation process, strong controllability and engineering application feasibility and great application value.
The invention simply and conveniently solves the problem of high internal porosity of the liquid molding composite material and also solves the problem of low mechanical property of the composite material plate.
Drawings
FIG. 1 is a schematic view of a liquid molding die for composite materials
FIG. 2 is a schematic diagram of a middle frame of a composite material liquid forming mold
Reference numerals: 1-upper mould; 2-middle frame; 3-glue injection port; 4-lower mould; 5-glue storage tank; 6-glue outlet
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
The technical features, objects and advantages of the present invention will be more clearly understood and appreciated by the following detailed description of the technical aspects of the present invention, which, however, is not to be taken as limiting the scope of the present invention.
The method comprises the steps of designing and adopting a composite material liquid forming die with a glue storage tank to form composite material plates and workpieces so as to improve the internal quality of the composite material, adopting a liquid forming process to inject liquid resin into a die cavity and the glue storage tank, then adopting a step-by-step reverse pressurization method to prepare the composite material plates and the workpieces in the heating and curing process, and carefully taking off the die after curing is completed so as to finish the preparation of the composite material plates and the workpieces.
As shown in fig. 1 and 2, the mold of the invention is a composite material flat plate forming mold, and is divided into an upper mold 1, a middle frame 2 and a lower mold 4, wherein bosses with the same size are respectively designed at the middle parts of the upper mold 1 and the lower mold 4 to serve as mold cavity surfaces, the size of the inner frame of the middle frame 2 is consistent with that of the bosses of the upper mold and the lower mold, the three parts are matched to form a mold cavity, and the thickness of the formed composite material plate is determined by the difference between the thickness of the middle frame 2 and the height of the bosses of the upper mold and the lower mold of the mold; a glue injection port 3 is arranged on one side of the mold middle frame 2, a plurality of glue outlets 6 are arranged on the other side of the mold middle frame, a groove is additionally arranged on the inner side of one glue outlet in the middle part to serve as a glue storage groove 5, and the position is preferably arranged on the inner side of one glue outlet in the middle part, so that the glue outlets of the composite material flat plate forming mold are designed to be odd numbers, one glue outlet in the middle part and uniformly distributed on two sides; the glue storage tank 5 is arranged in the middle, so that the liquid resin can flow inwards more uniformly when being pressurized reversely; one end of the glue storage groove 5 is communicated with the glue outlet 6, and the other end of the glue storage groove is communicated with the inner cavity of the mold.
The glue storage tank 5 is connected with a channel arranged in the die cavity, and the diameter of the channel is consistent with that of other glue outlets 6. The advantage is on the one hand can guarantee that liquid resin fills the mould die cavity earlier in the injecting glue in-process, flows in storing up gluey groove 5 again, and on the other hand is at reverse pressurized in-process, and the inflow die cavity that stores up gluey 5 interior resin can be even makes the inside quality of fashioned combined material board compacter, and the volume that stores up gluey groove 5 can be according to the solidification shrinkage factor design of shaping combined material plate size and liquid shaping resin.
The control method for improving the internal quality of the liquid molding composite material comprises the following steps:
the method comprises the following steps: firstly, cleaning the molded surface of a die, and uniformly coating a release agent on the molded surface of the die by using cotton yarns; after the release agent is fully dried, the mold middle frame 2 is closed to the mold lower mold 4, then according to the composite material plate or the product laying design, unidirectional cord fabric and fiber fabric are laid layer by layer, and are compacted and shaped by an electric iron to form a fiber preform, and the mold is closed;
step two: placing the mould on a hot press, pressurizing and heating, wherein the pressurizing pressure is 10-15MPa, connecting copper valves to the glue injection port 3 and the glue outlet 6, and connecting the valve of the glue outlet 6 to a vacuum pump for vacuum pumping;
step three: cleaning a high-temperature RTM injection machine, uniformly coating a release agent in the charging barrel, and heating to raise the temperature. After the temperature of the charging barrel rises to the resin injection temperature, putting the solid resin into the charging barrel for heating and melting;
step four: after the resin is completely melted, connecting a charging barrel of an injection machine with vacuum air extraction, discharging air bubbles in the charging barrel and the liquid resin, vacuumizing for more than 40min, connecting a glue injection pipeline between a mould and the injection machine, and preparing for injecting the resin;
step five: checking that the temperature of the mold and a resin injection pipeline meets the requirement, setting the injection pressure of the injection machine to be 2.0-4.0bar and the injection flow rate to be 10-20ml/min after the resin in the charging barrel of the injection machine is fully melted, injecting the liquid resin into the mold cavity and the glue storage tank 5, closing the valve of the glue outlet 6 after all the glue outlets 6 discharge glue, and filling the mold cavity with the liquid resin and flowing into the glue storage tank 5 at the moment; then gradually pressurizing to 15.0-25.0bar to fully soak the resin in the cavity pre-forming body and fill the glue storage tank 5 for 30-90 min to finish resin injection; connecting a glue outlet 6 in the middle of the mold with compressed air after the resin injection is finished, starting heating and curing, opening a valve of the glue outlet 6 in the heating process, applying reverse air pressure inwards from the glue outlet 6, and controlling the pressurizing pressure to be 1.0-5.0bar through a pressure gauge so that the resin in the glue storage tank 5 flows into the mold cavity of the mold; the resin in the cavity shrinks in the curing process, the resin in the glue storage tank 5 flows into the cavity to fill the gap generated by the curing shrinkage of the resin in time, and the generation of the internal pores of the composite material is reduced, so that the internal compactness of the molded composite material is improved, and the internal quality of the molded composite material is improved.
The first embodiment is as follows:
1. preparation of carbon fiber preform
Firstly, selecting a liquid molding composite material die for preparing a composite material plate with the size of 700 x 600 x 2mm, designing the volume of a glue storage tank 5 to be 100 x 50 x 4mm, cleaning the residual resin and sealing materials on the surface of the die, a glue inlet (outlet), a sealing groove and the like, and then uniformly coating a high-temperature release agent on the molded surface of the die. The reinforcement material is fed by hand, the release paper is flatly placed on an operation table, and then the surface density is 222g/m 2 And the carbon fiber unidirectional cord fabric with the thickness of 0.24mm is flatly placed on the demoulding paper, the angle of the cord fabric is corrected by using a set square and a ruler, and 8 layers of cord fabric with the width of 700 x 600mm is cut. And after the release agent is fully dried, paving and pasting 8 layers of cut unidirectional cord fabrics layer by layer, and compacting and shaping by using an electric iron to form a carbon fiber preform.
2. Closing the mold and raising the temperature
After the prefabricated body is paved and pasted, the die is carefully closed, the die is placed on a hot press by a crane to be pressurized, the pressurizing pressure is 14MPa, the die assembly gap is checked by a feeler gauge to be less than or equal to 0.15mm, then a copper valve is connected to the glue injection port 3 and the glue outlet 6, the valve of the glue injection port 3 is closed, the valve of the glue outlet 6 is connected with a vacuum pump to be vacuumized, and the vacuum degree of the die reaches below-0.095 MPa.
Starting the high-temperature hot press and the high-temperature resin injection machine for heating, heating the mould and the injection machine to 275 +/-10 ℃, and keeping the mould vacuumized in the heating process, wherein the vacuum degree is required to be not higher than-0.09 Mpa.
3. Resin injection
After the temperature of a charging barrel of the injection machine reaches 275 +/-10 ℃, 1000g of polyimide resin powder is weighed and poured into the charging barrel for heating and melting, and the mixture is stirred once every 30 min; after the resin is fully melted, connecting a material cylinder of the injection machine with a vacuum pump for vacuumizing, discharging air in the material cylinder and bubbles in the liquid resin, and vacuumizing for 40 min; and connecting a glue injection pipeline between the mould and the injection machine, heating and preparing for resin injection.
After confirming that the vacuum degree and the temperature of the mold meet the requirements, setting the injection pressure of the injection machine to be 4.0bar and the injection flow rate to be 15ml/min, opening a glue outlet 6 valve of the injection machine and a glue inlet valve of the mold, starting automatic injection, closing the glue outlet 6 valve after all glue outlets 6 discharge glue, gradually pressurizing to 20.0bar, and stopping resin injection after keeping for 1 h.
4. Curing and post-treatment
And after the resin injection is finished, closing the valve of the glue injection port 3, connecting compressed air to the valve of the middle glue outlet 6, and then starting heating and curing, wherein the curing process comprises the steps of insulating for 2 hours at 315 ℃ and insulating for 2 hours at 365 ℃. And applying air pressure inwards from the middle glue outlet 6 in the processes of temperature rise and heat preservation, wherein the pressurizing pressure is 3.0bar, and stopping applying reverse air pressure after the heat preservation is finished.
Naturally cooling after curing is finished, removing the pressure of a press when the temperature of the die is reduced to 250 +/-10 ℃, and continuously cooling; when the temperature of the die is reduced to 150 +/-10 ℃, the workpiece is carefully removed, the workpiece is prevented from being damaged, trimmed and deburred, and the preparation of the liquid molding composite material flat plate is completed.
Example two:
1. preparation of carbon fiber preform
Firstly, selecting a liquid molding composite material die for preparing a composite material plate with the size of 700 x 600 x 4mm, designing the size of a glue storage tank 5 to be 100 x 50 x 6mm, cleaning resin and sealing materials remained on the surface of the die, a glue inlet (outlet), a sealing groove and the like, and then uniformly coating a high-temperature release agent on the molded surface of the die. The reinforcement material is fed by hand, the release paper is flatly placed on an operation table, and then the surface density is 222g/m 2 The carbon fiber unidirectional cord fabric with the thickness of 0.24mm is flatly placed on the demoulding paper, the angle of the cord fabric is corrected by using a triangular ruler and a straight ruler, and the cord fabric is arranged according to the specification of [45/0/-45/90 ]] 2s The ply is cut into 16 plies of cord fabric with corresponding angles. And after the release agent is fully dried, paving and pasting the cut 16 layers of unidirectional cord fabrics layer by layer according to the laying sequence, and compacting and shaping by using an electric iron to form the carbon fiber preform.
2. Mold clamping and temperature rising
After the prefabricated body is paved and pasted, the die is carefully closed, the die is placed on a hot press by a crane to be pressurized, the pressurizing pressure is 14MPa, the die closing gap is checked to be less than or equal to 0.15mm by a feeler gauge, then a copper valve is connected to the glue injection port 3 and the glue outlet 6, the valve of the glue injection port 3 is closed, the valve of the glue outlet 6 is connected with a vacuum pump to be vacuumized, and the vacuum degree of the die reaches below-0.095 MPa.
Starting the high-temperature hot press and the high-temperature resin injection machine for heating, heating the mould and the injection machine to 275 +/-10 ℃, and keeping the mould vacuumized in the heating process, wherein the vacuum degree is required to be not higher than-0.09 Mpa.
3. Resin injection
After the temperature of a charging barrel of the injection machine reaches 275 +/-10 ℃, 2000g of polyimide resin powder is weighed and poured into the charging barrel for heating and melting, and the mixture is stirred once every 30 min; connecting the injection machine material cylinder with a vacuum pump for vacuumizing after the resin is fully melted, discharging air in the material cylinder and bubbles in the liquid resin, and vacuumizing for 40 min; and connecting a glue injection pipeline between the mold and the injection machine, heating, and preparing for resin injection.
After confirming that the vacuum degree and the temperature of the mold meet the requirements, setting the injection pressure of the injection machine to be 4.0bar and the injection flow rate to be 15ml/min, opening a glue outlet 6 valve of the injection machine and a glue inlet valve of the mold, starting automatic injection, closing the glue outlet 6 valve after all glue outlets 6 discharge glue, gradually pressurizing to 20.0bar, and stopping resin injection after keeping for 1 h.
4. Curing and post-treatment
And after the resin injection is finished, closing the valve of the glue injection port 3, connecting compressed air to the valve of the middle glue outlet 6, and then starting heating and curing, wherein the curing process comprises the steps of insulating for 2 hours at 315 ℃ and insulating for 2 hours at 365 ℃. And in the processes of temperature rise and heat preservation, air pressure is inwards applied from the middle glue outlet 6, the pressurizing pressure is 2.0bar, and the application of reverse air pressure is stopped after the heat preservation is finished.
Naturally cooling after curing is finished, removing the pressure of a press when the temperature of the die is reduced to 250 +/-10 ℃, and continuously cooling; when the temperature of the die is reduced to 150 +/-10 ℃, the workpiece is carefully removed, the workpiece is prevented from being damaged, trimmed and deburred, and the preparation of the liquid molding composite material flat plate is completed.
Example three:
1. preparation of carbon fiber preform
Firstly, selecting a liquid molding composite material die for preparing a composite material plate with the size of 700 x 600 x 2mm, designing the size of a glue storage tank 5 to be 100 x 50 x 4mm, cleaning the residual resin and sealing materials on the surface of the die, a glue inlet (outlet), a sealing groove and the like, and then uniformly coating a high-temperature release agent on the molded surface of the die. The reinforcement material is fed by hand, the release paper is flatly placed on an operation table, and then the surface density is 222g/m 2 And carbon fiber unidirectional cord fabric with the thickness of 0.24mm is flatly placed on the demoulding paper, the angle of the cord fabric is corrected by using a triangular ruler and a straight ruler, and the cord fabric is arranged according to the angle of [45/-45 ]] 2s 8 layers of cord fabrics with corresponding angles are cut out from the laying layers. And after the release agent is fully dried, paving and pasting 8 layers of cut unidirectional cord fabrics layer by layer according to the laying sequence, and compacting and shaping by using an electric iron to form the carbon fiber preform.
2. Closing the mold and raising the temperature
After the prefabricated body is paved and pasted, the die is carefully closed, the die is placed on a hot press by a crane to be pressurized, the pressurizing pressure is 14MPa, the die closing gap is checked to be less than or equal to 0.15mm by a feeler gauge, then a copper valve is connected to the glue injection port 3 and the glue outlet 6, the valve of the glue injection port 3 is closed, the valve of the glue outlet 6 is connected with a vacuum pump to be vacuumized, and the vacuum degree of the die reaches below-0.095 MPa.
Starting the high-temperature hot press and the high-temperature resin injection machine for heating, heating the mould and the injection machine to 275 +/-10 ℃, and keeping the mould vacuumized in the heating process, wherein the vacuum degree is required to be not higher than-0.09 Mpa.
3. Resin injection
After the temperature of a charging barrel of an injection machine reaches 275 +/-10 ℃, weighing 1000g of polyimide resin powder, pouring the polyimide resin powder into the charging barrel, heating and melting, and stirring once every 30 min; connecting the injection machine material cylinder with a vacuum pump for vacuumizing after the resin is fully melted, discharging air in the material cylinder and bubbles in the liquid resin, and vacuumizing for 40 min; and connecting a glue injection pipeline between the mould and the injection machine, heating and preparing for resin injection.
After confirming that the vacuum degree and the temperature of the mold meet the requirements, setting the injection pressure of the injection machine to be 4.0bar and the injection flow rate to be 15ml/min, opening a glue outlet 6 valve of the injection machine and a glue inlet valve of the mold, starting automatic injection, closing the glue outlet 6 valve after all glue outlets 6 discharge glue, gradually pressurizing to 20.0bar, and stopping resin injection after keeping for 1 h.
4. Curing and post-treatment
And after the resin injection is finished, closing the valve of the glue injection port 3, connecting compressed air to the valve of the middle glue outlet 6, and then starting heating and curing, wherein the curing process comprises the steps of insulating for 2 hours at 315 ℃ and insulating for 2 hours at 365 ℃. And applying air pressure inwards from the middle glue outlet 6 in the processes of temperature rise and heat preservation, wherein the pressurizing pressure is 4.0bar, and stopping applying reverse air pressure after the heat preservation is finished.
Naturally cooling after curing is finished, removing the pressure of a press when the temperature of the die is reduced to 250 +/-10 ℃, and continuously cooling; when the temperature of the die is reduced to 150 +/-10 ℃, the workpiece is carefully removed, the workpiece is prevented from being damaged, trimmed and deburred, and the preparation of the liquid molding composite material flat plate is completed.

Claims (8)

1. A control method for improving the internal quality of a liquid molding composite material is characterized by comprising the steps of firstly checking that the temperature of a mold and a resin injection pipeline meets the requirement, fully melting resin in a charging barrel of an injection machine, setting the injection pressure of the injection machine to be 2.0-4.0bar, setting the injection flow rate to be 10-20ml/min, injecting liquid resin into a mold cavity and a glue storage tank, closing a glue outlet valve after all glue outlets discharge glue, and filling the mold cavity with the liquid resin and flowing into the glue storage tank; then gradually pressurizing to 15.0-25.0bar to fully soak the resin in the cavity pre-forming body and fill the glue storage tank, and keeping the time for 30-90 min to finish resin injection; connecting a middle glue outlet of the mold with compressed air after the resin injection is finished, starting heating and curing, opening a valve of the middle glue outlet in the heating process, applying reverse air pressure inwards from the glue outlet, and controlling the pressurizing pressure to be 1.0-5.0bar through a pressure gauge so that the resin in the glue storage tank flows into the mold cavity of the mold; the resin in the glue storage tank flows into the cavity to fill a gap generated by curing and shrinking of the resin in time;
the die is a liquid forming composite material flat plate forming die and is divided into an upper die, a middle frame and a lower die, wherein bosses with the same size are respectively designed in the middle parts of the upper die and the lower die and are used as die cavity surfaces, the size of the inner frame of the middle frame is consistent with that of the bosses of the upper die and the lower die, the three parts are matched to form a die cavity, and the thickness of the formed composite material plate is determined by the difference between the thickness of the middle frame and the height of the bosses of the upper die and the lower die of the die; one side of the middle frame of the mold is provided with a glue injection port, the other side of the middle frame of the mold is provided with a plurality of glue outlets, a groove is added on the inner side of the middle glue outlet and serves as a glue storage groove, one end of the glue storage groove is communicated with the glue outlet, the other end of the glue storage groove is communicated with the inner cavity of the mold, and reverse air pressure is applied through the glue outlet in the curing process to enable resin in the glue storage groove to flow into the cavity.
2. The method for controlling the internal quality of a liquid molding compound as claimed in claim 1, wherein the glue storage tank is connected with the mold cavity by a channel, and the diameter of the channel is consistent with that of other glue outlets.
3. The method as claimed in claim 1, wherein the volume of the glue storage tank is designed according to the size of the composite material plate and the curing shrinkage of the liquid molding resin, and the shrinkage of the liquid molding resin is about 1% -2%.
4. The method for controlling the internal quality of the liquid molding compound material as claimed in claim 1, wherein the number of the glue outlets of the compound material flat plate molding die is odd, one glue outlet is arranged in the middle, the glue outlets are evenly distributed on two sides, and the glue storage tank is arranged on the inner side of the glue outlet in the middle.
5. The method of claim 1, wherein the mold and resin injection line temperature is within ± 10 ℃ of the optimum injection temperature of the liquid molding resin.
6. The method of claim 1, wherein the step of uniformly coating the inside of the cylinder of the injection machine with the release agent is performed before the resin is added into the cylinder of the injection machine, and then the temperature is raised, and after the temperature of the cylinder is raised to the compound injection temperature, the solid resin is put into the cylinder and heated to melt.
7. The method as claimed in claim 1, wherein during the process of injecting the liquid resin into the mold cavity and the glue storage tank, each glue outlet of the mold is connected to a vacuum tube and connected to a vacuum pump for vacuum pumping, so as to guide the liquid resin to flow to the glue outlet, thereby filling the mold cavity and the glue storage tank with the resin.
8. The method for controlling the internal quality of a liquid molding composite material according to claim 1, wherein the preform in the cavity of the mold is prepared by laying unidirectional cord fabric and fiber fabric layer by layer according to the lay-up design of the liquid molding composite material plate, and compacting and shaping the unidirectional cord fabric and the fiber fabric by an electric iron to form a fiber preform.
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US7943078B2 (en) * 2004-02-17 2011-05-17 Toray Industries, Inc. RTM molding method and device
FR2986179B1 (en) * 2012-01-31 2014-10-10 Techni Modul Engineering DEVICE AND METHOD FOR MANUFACTURING A MOLDED PIECE OF A COMPOSITE MATERIAL
CN111284041A (en) * 2018-12-06 2020-06-16 中国科学院宁波材料技术与工程研究所 Glue injection equipment and process for glue solution circulation
TWI720430B (en) * 2019-02-26 2021-03-01 日月光半導體製造股份有限公司 Packaging mold and packaging method
CN111037951B (en) * 2019-12-30 2022-03-04 中国航空制造技术研究院 Composite material liquid molding injection device and method

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