Method for forming honeycomb sandwich structure composite material by adopting automatic fiber placement process

Abstract

The invention discloses a method for forming a honeycomb sandwich structure composite material by adopting an automatic fiber placement process, and relates to the field of composite materials. By optimizing the forming technical route of the honeycomb sandwich structure, skin pre-compaction and compaction and honeycomb sandwich curing forming are adopted for step-by-step layer laying forming and control, the shape of the honeycomb sandwich structure is maintained through a mold profile and a process cover plate, it is guaranteed that automatic fiber laying forming of a skin prepreg lamination part is achieved, and meanwhile the production efficiency is improved. The skin prepreg is fully compacted by applying sufficient compression roller forming pressure, and meanwhile, the problem of structural size deviation caused by crushing deformation of the honeycomb sandwich core under relatively high forming pressure is avoided, so that the forming quality of the sandwich structure is fully guaranteed.

Description

Technical Field

[0001] The invention relates to the field of composite materials, and in particular to a method for forming a composite material with a honeycomb sandwich structure by adopting an automatic wire-laying process. Background Art

[0002] Honeycomb sandwich structures can greatly improve the stiffness of material structures, have a significant weight reduction effect on secondary load-bearing structures, and are widely used in aircraft structures. The automatic wire laying process uses program-controlled machinery to achieve the laying of prepreg layers, which can ensure the laying accuracy and laying efficiency of the layers, and ensure the quality of the formed layers through roller pressure. It is the development trend of automated forming of composite materials. However, in the honeycomb sandwich structure, the thickness of the honeycomb core edge gradually decreases and is wrapped by the upper and lower skins. Due to structural changes in the thickness-reduced area, its lateral (W-direction of the honeycomb sandwich) compressive strength will be low. Under the pressure of the automatic wire laying roller, the edge structure of the honeycomb core is prone to collapse, resulting in deviations in the forming size and forming quality of the honeycomb sandwich structure. This also makes it difficult for the honeycomb sandwich structure to be formed by the automatic wire laying process and cannot meet the requirements of stable engineering applications. In addition, due to the limited compressive capacity of the honeycomb core itself, the molding pressure of the honeycomb sandwich structure composite material is generally lower than that of the laminate. For example, the autoclave molding pressure of the honeycomb sandwich structure composite material is generally 0.3MPa, while the autoclave molding pressure of the laminate composite material is generally 0.6MPa. For a specific structure with a thick skin thickness, insufficient molding pressure can easily cause internal molding defects.

[0003] Therefore, it is necessary to optimize and improve the preparation method based on the molding quality problems of honeycomb sandwich structures found in engineering applications, so as to further promote the promotion and application of honeycomb sandwich structure composite materials. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that in the current co-curing molding of honeycomb sandwich structures, it is difficult to carry out corresponding prepreg laying molding through the automatic wire laying process due to the limitation of the compressive resistance of the honeycomb sandwich core; at the same time, the molding pressure of 0.3MPa when the honeycomb sandwich structure is co-cured is smaller than that of 0.6MPa of the conventional laminate, so it is difficult to take into account the molding quality of the skin of the sandwich structure. A method for molding a honeycomb sandwich structure composite material through the automatic wire laying process is proposed, by optimizing the molding technical route of the honeycomb sandwich structure, adopting the pre-compacting and compacting of the skin and the curing molding of the honeycomb sandwich in steps of laying and controlling, and shaping the honeycomb sandwich structure through the mold surface and the process cover plate, so as to ensure the automatic laying molding of the laminated part of the skin prepreg, make the skin prepreg fully dense by applying sufficient pressure of the pressure roller, and avoid the problem of structural dimensional deviation caused by the crushing deformation of the honeycomb sandwich under a large molding pressure, thereby fully ensuring the molding quality of the sandwich structure.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for forming a honeycomb sandwich structure composite material using an automatic wire placement process comprises the following steps:

[0007] 1) Apply a release agent or attach a release cloth to the molding surface of the molding mold of the honeycomb sandwich structure, and adhere an isolation film to the skin laying tooling;

[0008] 2) Using an automatic wire laying machine to automatically lay the skin prepreg laminate on the release agent or release cloth of the forming mold according to the designed wire laying path, and automatically lay the skin prepreg laminate on the isolation film of the skin laying tooling;

[0009] 3) After the skin prepreg laminate is laid, it is vacuum-bag packaged and placed in an autoclave for pre-compaction;

[0010] 4) attaching an adhesive film to the surface of the skin prepreg laminate of the molding mold after the pre-compacting operation;

[0011] 5) After the adhesive film is attached, the honeycomb core machined by the net size machine is placed and fixed on the adhesive film of the forming mold, and the adhesive film is attached to the surface of the honeycomb core;

[0012] 6) Remove the skin prepreg laminate from the skin laying tooling and position and fix it on the surface of the honeycomb sandwich with the adhesive film attached;

[0013] 7) Lay the isolation film on the surface of the skin prepreg laminate fixed in the previous step, and then position and fix the process cover plate on it;

[0014] 8) The whole obtained in the previous step is wrapped with an isolation film, a breathable felt and a vacuum bag in sequence according to the packaging method of autoclave curing and molding, and after the vacuum degree of the vacuum bag packaging system is tested, it is put into the tank for curing and molding;

[0015] 9) After the curing and molding is completed, the product is taken out of the can and demoulded to obtain a honeycomb sandwich structure composite material.

[0016] Preferably, in step 1), the forming mold is a female mold tooling that matches the thickness gradient zone of the honeycomb core of the honeycomb sandwich structure, and the forming mold and the skin laying tooling are made of metal or composite materials.

[0017] Preferably, in step 1), the release agent is one of Chemlease 2721 and meguirs M-0811; and the release cloth is A005 adhesive release cloth.

[0018] Preferably, in step 1), before adhering the isolation film to the skin laying tooling, the surface of the tooling is cleaned.

[0019] Preferably, the prepreg used for the skin prepreg lamination in step 2) is a fiber unidirectional prepreg or a fiber fabric prepreg, wherein the fiber is but not limited to one of carbon fiber, glass fiber, and aramid fiber, and the resin in the prepreg is but not limited to one of epoxy resin, bismaleimide resin, phenolic resin, and polyimide resin.

[0020] Preferably, the pre-compacting conditions in step 3) are: temperature 45° C., pressure 0.6 MPa, and pre-compacting operation time 30-60 min.

[0021] Preferably, the adhesive film in steps 4) and 5) is selected according to the curing temperature, and is selected from one of Henkel's EA9696 of medium temperature curing system, Heilongjiang Petrochemical Research Institute's J-47, and high temperature curing system EA 7000 and J299.

[0022] Preferably, during positioning in step 6), reference line position constraints are used or a laser projector is used to assist positioning.

[0023] Preferably, in step 7), the profile of the process cover plate matches the side of the honeycomb sandwich structure that is not in contact with the profile of the molding mold. The process cover plate is a composite laminate or a rubber laminate reinforced with a composite laminate, preferably a composite laminate prepared by isotropically laying carbon fiber fabric prepreg with a thickness of 2 mm; the process cover plate is positioned by means of positioning pin holes or positioning marks on the molding mold.

[0024] Preferably, the molding pressure in step 8) is 0.3 MPa.

[0025] The advantages of the present invention are as follows:

[0026] 1. The method for preparing a honeycomb sandwich structure of the present invention eliminates the pressure process of the honeycomb core during the automatic wire laying process of the upper skin by laying the upper and lower skins on two independent laying tooling surfaces and then assembling them, thereby realizing the automatic wire laying process of forming a honeycomb sandwich structure composite material.

[0027] 2. The fiber density pre-compaction of the skin prepreg laminate and the co-curing molding of the final honeycomb sandwich structure realize independent control of the molding pressure control. The skin prepreg obtains a sufficient molding pressure of 0.6MPa through hot pre-compaction to fully compact the fibers and remove gas. The conventional 0.3MPa molding pressure is used in the subsequent curing molding of the honeycomb sandwich structure to ensure that the honeycomb core in the sandwich structure does not deform or collapse;

[0028] 3. By using the female mold cavity and the rigid process cover plate at the same time, the molding pressure during the curing molding of the honeycomb sandwich structure only acts on the adhesive bonding of the sandwich structure, avoiding a large lateral crushing force on the edge of the honeycomb sandwich core, thereby further ensuring the dimensional accuracy and molding quality of the honeycomb sandwich structure. Data shows that by using the female mold cavity and the rigid process cover plate shown in this application, the dimensional accuracy of the honeycomb sandwich structure can reach within ±0.5mm, which is a significant improvement over the 1-2mm deviation of the traditional male mold molding dimensional deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the forming mold and skin laying tooling structure used in the embodiment.

[0030] Figure 2 Schematic diagram of mold surface preparation before placement of skin prepreg in the embodiment.

[0031] Figure 3 Schematic diagram of automatic wire placement forming of prepreg stacking on a mold surface in an embodiment.

[0032] Figure 4 Schematic diagram of the prepreg stacking and covering the adhesive film on the molding mold in the embodiment.

[0033] Figure 5 It is a schematic diagram of placing and assembling the honeycomb core on the forming mold in the embodiment.

[0034] Figure 6 Schematic diagram of covering the honeycomb core with adhesive film in the embodiment.

[0035] Figure 7 This is a schematic diagram of transferring the upper skin onto the honeycomb core and positioning and fixing it in an embodiment.

[0036] Figure 8 Schematic diagram of using an isolation film or a release cloth to cover the upper surface of the upper skin prepreg laminate in the embodiment.

[0037] Fig. 9 Schematic diagram of the assembly structure of the process cover plate in the embodiment. DETAILED DESCRIPTION

[0038] In order to make the various technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below with reference to the accompanying drawings.

[0039] This embodiment specifically discloses a method for forming a honeycomb sandwich structure composite material using an automatic wire placement process, which specifically includes the following steps:

[0040] Step 1: This method uses a forming mold of a honeycomb sandwich structure as a female mold tooling that matches the thickness gradient area of ​​the honeycomb sandwich core in the honeycomb sandwich structure, such as Figure 1 As shown in FIG, the tooling materials of the forming mold and the skin laying tooling can be metal, composite materials, etc. Figure 2 As shown, a release agent is applied to the molding surface of the molding mold or a release cloth is attached. The release agent is a conventional commercial release agent, such as Chemlease 2721 and meguirs M-0811. The release cloth is a conventional commercial release cloth, such as A005 adhesive release cloth. Simultaneously, the skin laying tooling on the other side is cleaned and an isolation film is adhered. The isolation film uses Wrightlon5200 or A4000 of airtech.

[0041] Step 2: If Figure 3 As shown, an automatic wire laying machine is used to automatically lay the skin prepreg laminate on the forming mold according to the designed wire laying path, and the skin prepreg laminate is automatically laid on the isolation membrane of the skin laying tooling on the other side according to the designed wire laying path; the prepreg used in the skin prepreg laminate is a conventional aviation prepreg, which is a fiber unidirectional prepreg or a fiber fabric prepreg, wherein the fiber is but not limited to one of carbon fiber, glass fiber, and aramid fiber, and the resin in the prepreg is but not limited to one of epoxy resin, bismaleimide resin, phenolic resin, and polyimide resin. There is no clear limit on the thickness of the skin prepreg laminate, which is generally 0.1-0.3mm.

[0042] Step 3: After the skin prepreg stack is laid, it is vacuum-bag packaged and placed in an autoclave for pre-compaction. The pre-compaction conditions are 45°C and 0.6MPa for 30-60 minutes.

[0043] Step 4: Figure 4 As shown, an adhesive film is attached to the surface of the skin prepreg laminate of the molding mold after the pre-compaction operation; the adhesive film is selected according to the actual process, such as Henkel's EA9696 for the medium temperature curing system, Heilongjiang Petrochemical Research Institute's J-47, and EA 7000 and J299 for the high temperature curing system.

[0044] Step 5: Figure 5 As shown, place the honeycomb sandwich with net size machine on the adhesive film, and then attach the adhesive film to the surface of the fixed honeycomb sandwich (the adhesive film selection is the same as step 4). After the paving is completed, the state is as follows Figure 6 shown.

[0045] Step 6: After the honeycomb core surface is coated with adhesive film, the skin prepreg stack removed from the skin laying tool is positioned and fixed. The reference line position constraint or laser projector auxiliary position positioning can be used, such as Figure 7 shown.

[0046] Step 7: Figure 8As shown, an isolation film is laid on the surface of the skin prepreg laminate, and then the process cover is positioned and fixed thereon. The position of the process cover is determined by the positioning pin holes or positioning lines of the molding mold. The profile of the process cover is matched with the side of the honeycomb sandwich structure that is not in contact with the molding mold profile. The process cover is a composite laminate or a rubber laminate reinforced by a composite laminate, preferably a composite laminate prepared by isotropically laying carbon fiber fabric prepreg with a thickness of 2 mm. The completed state is as follows Fig. 9 shown.

[0047] Step 8: According to the conventional autoclave curing and molding packaging method, the isolation film, breathable felt and vacuum bag are sequentially wrapped, and after the vacuum degree test of the vacuum bag packaging system is completed, the product is put into the can for curing and molding. The molding pressure is preferably 0.3MPa.

[0048] Step 9: After the sandwich structure is cured, the product is taken out of the can and demoulded, and non-destructive testing and dimensional testing are performed to obtain a honeycomb sandwich structure composite material product that meets the requirements of molding quality and dimensional accuracy.

[0049] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions of the technical solutions of the present invention made by ordinary technicians in the field should all be included in the protection scope of the present invention. The protection scope of the present invention shall be based on what is defined in the claims.

Claims

1. A method for forming a honeycomb sandwich structure composite material using an automatic wire placement process, characterized in that: The following steps are involved: 1) Apply a release agent or attach a release cloth to the molding surface of the molding mold of the honeycomb sandwich structure, and adhere an isolation film to the skin laying tooling; 2) Using an automatic wire laying machine to automatically lay the skin prepreg laminate on the release agent or release cloth of the forming mold according to the designed wire laying path, and automatically lay the skin prepreg laminate on the isolation film of the skin laying tooling; 3) After the skin prepreg laminate is laid, it is vacuum-bag packaged and placed in an autoclave for pre-compaction; 4) attaching an adhesive film to the surface of the skin prepreg laminate of the molding mold after the pre-compacting operation; 5) After the adhesive film is attached, the honeycomb core machined by the net size machine is placed and fixed on the adhesive film of the forming mold, and the adhesive film is attached to the surface of the honeycomb core; 6) Remove the skin prepreg laminate from the skin laying tooling and position and fix it on the surface of the honeycomb sandwich with the adhesive film attached; 7) Lay the isolation film on the surface of the skin prepreg laminate fixed in the previous step, and then position and fix the process cover plate on it; 8) The whole obtained in the previous step is wrapped with an isolation film, a breathable felt and a vacuum bag in sequence according to the packaging method of autoclave curing and molding, and after the vacuum degree of the vacuum bag packaging system is tested, it is put into the tank for curing and molding; 9) After the curing and molding is completed, the product is taken out of the can and demoulded to obtain a honeycomb sandwich structure composite material.

2. The method according to claim 1, characterized in that In step 1), the forming mold is a female mold tooling that matches the thickness gradient area of ​​the honeycomb core of the honeycomb sandwich structure, and the materials of the forming mold and the skin laying tooling are metal or composite materials.

3. The method according to claim 1, characterized in that In step 1), the release agent is one of Chemlease 2721 and meguirs M-0811; the release cloth is A005 adhesive release cloth.

4. The method according to claim 1, characterized in that In step 1), before adhering the isolation film to the skin laying tooling, clean the surface of the tooling.

5. The method according to claim 1, characterized in that The prepreg used in the skin prepreg lamination in step 2) is a fiber unidirectional prepreg or a fiber fabric prepreg, wherein the fiber is one of carbon fiber, glass fiber, and aramid fiber, and the resin in the prepreg is one of epoxy resin, bismaleimide resin, phenolic resin, and polyimide resin.

6. The method according to claim 1, characterized in that The pre-compacting conditions in step 3) are: temperature 45° C., pressure 0.6 MPa, and pre-compacting operation time 30-60 min.

7. The method according to claim 1, characterized in that In steps 4) and 5), the adhesive film is selected according to the curing temperature, and one of Henkel's EA9696 of medium temperature curing system, Heilongjiang Petrochemical Research Institute's J-47, and high temperature curing system EA 7000 and J299 is selected.

8. The method according to claim 1, characterized in that During positioning in step 6), reference line position constraints are used or a laser projector is used to assist positioning.

9. The method according to claim 1, characterized in that In step 7), the profile of the process cover plate matches the side of the honeycomb sandwich structure that is not in contact with the profile of the molding mold. The process cover plate is a composite laminate or a rubber laminate reinforced with a composite laminate. The process cover plate is positioned by positioning pin holes or positioning lines of the molding mold.

10. The method according to claim 1, characterized in that In step 8), the molding pressure is 0.3 MPa.

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